INTERCALATION OF IONICALLY CONDUCTIVE POLYMERS INTO LITHIUM HECTORITE
A Thesis
Submitted to the Graduate Faculty
in Partial fulfillment of the Requirements
for the Degree of Master of Science
Department of Chemistry
Faculty of Science
University of Prince Edward Island
Iskandar Saada
Charlottetown, Prince Edward Island
March 2012
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REMOVED Acknowledgements
I would like to thank Dr. Rabin Bissessur for welcoming me into his lab as an undergraduate student (Chem. 482), and later as a graduate student in materials research. I would also like to thank Dr. Jason Pearson for welcoming me into his lab as a student research assistant during the summer of 2009, and serving as a committee member during my graduate studies.
I would like to thank Dr. Douglas Dahn for his contributions as a committee member and providing his laboratory in the physics department. All of the AC Impedance Spectroscopy data was completed in Dr. Dahn’s lab. A special thank you to Matthieu Hughes and Vicki Trenton for operating the instrumentation, and calculating the ionic conductivity of the materials.
Thank you to Dawna Lund for her expertise in the department instrumentation, and guidance in the laboratory safety measures. Thank you to the department of chemistry at the
University of Prince Edward Island for making my undergraduate and graduate experience memorable.
This project would not have been as easy without the support of my brother (Robbie
Saada) and father (Norman Saada). I would also like to thank all of my friends and colleagues for their daily support, and entertainment. Abstract
Renewable energy sources such as wind and solar have become appealing sources of energy with low environmental impact. However, the challenge with using these energy sources is their intermittent and unpredictable power generation. In order to overcome this challenge, energy storage mechanisms such as lithium-ion batteries are dependable systems for such applications. The purpose of this project is intended to synthesize environmentally benign and
safe materials which can be used as electrolytes in lithium-ion batteries.
The ionically conductive polymers POEGO, POMOE, and MEEP were successfully
intercalated into the two-dimensional layered structure Lithium Hectorite. The goal of the project was to synthesize a series of nanocomposites with increasing polymer molar ratios to Lithium
Hectorite, and investigate the thermal and ionic conductivity properties of the synthesized nanocomposites.
A second series of nanocomposites using the same polymer molar ratio to Lithium
Hectorite were synthesized after the polymers were complexed with lithium triflate. The salt- complexed nanocomposites were compared to the pristine nanocomposites based on thermal
stability, polymer flexibility, as well as their ionic conductivity.
The synthesized polymers, nanocomposites, and salt-complexed materials,, were
characterized using powder X-ray diffraction, attenuated total reflectance spectroscopy,
thermogravimetric analysis, and differential scanning calorimetry. Ionic conductivity data was
investigated using AC impedance spectroscopy. List of Abbreviations
XRD - X-ray diffraction
TGA - Thermogravimetric analysis
DSC - Differential scanning calorimetry
ATR - Attenuated total reflectance
POEGO - Poly[oligo(ethylene glycol)-oxalate]
POMOE - Poly[oxymethylene-(oxyethylene)]
MEEP - Poly[bis-(methoxyethoxyethoxy)phosphazene]
PEG - Poly(ethylene glycol)
PEO - Poly(ethylene oxide)
SPE - Solid polymer electrolyte
Li-POEGO - UCF 3 SO 3 ( P O E G O )i6
Li-POMOE - UCF 3SO 3 (P O M O E ) 25
Li-MEEP - LiCF 3S 0 3 (M E E P ) 4
Li-Hectorite - Lithium Hectorite Table of Contents List of Figures...... x List of Tables...... xii List of Abbreviations ...... vi Acknowledgements ...... iv Abstract...... v Chapter 1: Introduction ...... 1 1.1 Background ...... 1 1.2 Battery Types...... 5 1.2.1 Primary Cells (Batteries)...... 5 1.2.2 Secondary Cell (Batteries) ...... 5
1.3 The Lithium-Ion Battery ...... 6
1.3.1 Anode ...... 8 1.3.2 Cathode ...... 11 1.3.3 Electrolyte...... 15 1.3.3.1 Liquid Organic Electrolytes...... 16 1.3.3.2 Polymer Electrolytes...... 18 1.3.3.2.1 Solid Polymer Electrolytes ...... 19 1.3.3.2.2 Gel Polymer Electrolytes...... 20 1.3.3.2.3 Composite Polymer Electrolytes...... 21 1.4 Intercalation Chemistry ...... 21 1.5 Hectorite...... 24
1. 6 Polymers...... 28 1.6.1 POEGO/POMOE ...... 28 1.6.2 Polyphosphazenes ...... 29 1.7 Research Goals ...... 32 Chapter 2: Instrumentation ...... 34 2.1 Powder X-ray Diffraction (p-XRD) ...... 34 2.2 Thermogravimetric Analysis (TGA)...... 35 2.3 Differential Scanning Calorimetry (DSC) ...... 36 2.4 Attenuated Total Reflectance (ATR) ...... 37 2.5 AC Impedance Spectroscopy (IS) ...... 37 Chapter 3: Experimental and Characterization ...... 39 3.1 Reagents and Solvents ...... 39 3.2 Synthesis of Poly[oligo(ethylene glycol)-oxalate] (POEGO)...... 39
3.2.1 Synthesis of P 0 EG0 /LiCF3 S0 3 Complex...... 39 3.3 Synthesis of Poly[oxymethylene-(oxyethylene)] (POMOE) ...... 40
3.3.1 Synthesis of POMOE/UCF 3 SO3 Complex...... 41 3.4 Synthesis of Poly[bis-(methoxyethoxyethoxy)phosphazene] (MEEP) ...... 41
3.4.1 Synthesis of MEEP/LiCF 3 S0 3 Complex...... 42 3.5 Purification, Lithiation, and Intercalation of Hectorite ...... 42 3.5.1 Purification of Sodium-Hectorite ...... 42 3.5.2 Lithiation of Sodium Hectorite ...... 43 3.5.3 Preparation of Nanocomposites ...... 43 3.6 Characterization of Starting Materials ...... 44 3.6.1 POEGO Characterization ...... 44 3.6.2 POMOE Characterization ...... 46 3.6.3 MEEP Characterization ...... 48 3.6.4 Lithium Hectorite Characterization ...... 50 Chapter 4: POEGO/Lithium Hectorite Results and Discussion ...... 55 4.1 Powder X-ray Diffraction ...... 55 4.2 Thermogravimetric Analysis...... 58 4.3 Differential Scanning Calorimetry ...... 61 4.4 Attenuated Total Reflectance ...... 63 4.5 AC Impedance Spectroscopy...... 65
4.6 POEGO/Lithium Hectorite Conclusion...... 6 8 Chapter 5: POMOE/Lithium Hectorite Results and Discussion ...... 70 5.1 Powder X-ray Diffraction ...... 70 5.2 Thermogravimetric Analysis...... 73 5.3 Differential Scanning Calorimetry ...... 76 5.4 Attenuated Total Reflectance ...... 78 5.5 AC Impedance Spectroscopy ...... 81 5.6 POMOE/Lithium Hectorite Conclusion ...... 84
Chapter 6 : MEEP/Lithium Hectorite Results and Discussion ...... 8 6
6 .1 Powder X-ray Diffraction ...... 8 6 6.2 Thermogravimetric Analysis ...... 89 6.3 Differential Scanning Calorimetry ...... 92 6.4 Attenuated Total Reflectance ...... 93
viii 6.5 AC Impedance Spectroscopy ...... 95
6 . 6 MEEP/Lithium Hectorite Conclusion ...... 98 Chapter 7: Summary ...... 99 7.1 POEGO :Li-Hectorite Nanocomposites ...... 99 7.2 POMOE :Li-Hectorite Nanocomposites ...... 99 7.3 MEEP:Li-Hectorite Nanocomposites ...... 100 Appendix ...... 101 List of Figures Figure 1-1: Applications for Lithium-Ion Batteries ...... 1 Figure 1-2: Electrochemical Cell...... 2 Figure 1-3: Volumetric and Gravimetric Energy Densities of Battery Technologies ...... 6 Figure 1-4: Working Principle of Lithium-Ion batteries (Discharge) ...... 8 Figure 1-5: Crystal Structures of (a) LiCoC >2 (layered structure), (b) LiMn 2 0 4 (spinel structure), and (c) LiFePC >4 (olivine structure) ...... 12 Figure 1-6: Capacity range of various cathode materials ...... 14 Figure 1-7: Schematic of Segmental Motion...... 18 Figure 1-8: Schematic of Interlayer Spacing in Two-Dimensional Layered Structures ...... 23 Figure 1-9: Structure of Hectorite ...... 25 Figure 1-10: Cation Exchange, Exfoliation and Intercalation into Hectorite ...... 27 Figure 1-11: a) Structure of POEGO b) Structure of POMOE ...... 29 Figure 1-13: Structure of MEEP ...... 31 Figure 3-14: Synthesis of POEGO ...... 39 Figure 3-15: Synthesis of POMOE ...... 40 Figure 3-16: Synthesis of MEEP ...... 42 Figure 3-17: *H NMR of POEGO ...... 45 Figure 3-18: 13C NMR of POEGO...... 45 Figure 3-19: ‘H NMR of POMOE...... 47 Figure 3-20: 13C NMR of POMOE...... 47 Figure 3-21: 31P NMR of MEEP...... 49 Figure 3-22: Lithium Hectorite heated to 650 °C ...... 51 Figure 3-23: Control experiment with water and lithium hectorite ...... 52 Figure 3-24: Thermogram of Lithium Hectorite...... 53 Figure 3-25: Infrared Spectrum of Lithium Hectorite ...... 54 Figure 4-26: XRD of a) Li-Hectorite:H 2 0 and b) POEGO:Li-Hectorite Nanocomposite (1:1)... 55 Figure 4-27: Schematic of POEGO layers in Lithium Hectorite (1:1) ...... 57 Figure 4-28: TGA thermograms a) Li-POEGO:Li-Hectorite (1:1) b) POEGO:Li-Hectorite (1:1) c) Li-POEGO d) POEGO ...... 59 Figure 4-29: DSC data for a) POEGO:Li-Hectorite (1:1) b) Li-POEGO:Li-Hectorite (1:1) c) Li- POEGO d) POEGO ...... 62 Figure 4-30: IR Spectra of a) POEGO b) Li-POEGO c) POEGO:Li-Hectorite(l :1) d) Li- POEGO :Li-Hectorite (1:1)...... 64 Figure 4-31: Nyquistplot of Li-POEGO:Li-Hectorite (1:1) at 300K ...... 6 6 Figure 4-32: Conductivity of Li-POEGO and Li-POEGO:Li-Hectorite Nanocomposites 67 Figure 5-33: a) Li-Hectorite:H2 0 and b) POMOE:Li-Hectorite Nanocomposite (1:1) ...... 70 Figure 5-34: Schematic of POMOE layers in Lithium Hectorite (1:1) ...... 72 Figure 5-35: TGA thermograms a) POMOE:Li-Hectorite (1:1) b) Li-POMOE:Li-Hectorite (1:1) c) Li-POMOE d) POMOE ...... :...... 73 Figure 5-36: DSC data for a) POMOE: Li-Hectorite (1:1) b) Li-POMOE:Li-Hectorite (1:1) c) POMOE d) Li-POMOE ...... 77 Figure 5-37: IR Spectra for a) POMOE b) Li-POMOE c) POMOE:Li-Hectorite (1:1) d) Li- POMOE:Li-Hectorite (1:1)...... 79 Figure 5-38: Nyquist plot of Li-POMOE:Li-Hectorite (1:1) at 300K...... 81 Figure 5-39: Conductivity of Li-POMOE:Li-Hectorite Nanocomposites ...... 82
x Figure 6-40: a) Li-HectoriteiFhO and b) MEEP:Li-Hectorite (1:1) Nanocomposite ...... 8 6 Figure 6-41: Schematic arrangement of MEEP in Lithium Hectorite (1:1) ...... 8 8 Figure 6-42: TGA thermograms a) Li-MEEP:Li-Hectorite (1:1) b) MEEP:Li-Hectorite (1:1) c) MEEP d) Li-MEEP ...... 89 Figure 6-43: DSC data for a) MEEP: Li-Hectorite (1:1) b) Li-MEEP:Li-Hectorite (1:1) c) MEEP d) Li-MEEP ...... 92 Figure 6-44: IR Spectra of a) MEEP b) Li-MEEP: Li-Hectorite (1:1) c) Li-MEEP d) Li- MEEP: Li-Hectorite (1:1)...... 94 Figure 6-45: Nyquist plot of Li-MEEP at 300K ...... 96 Figure 6-46: Conductivity plot of Li-MEEP ...... 97 Figure A-47: TGA of 1:1 POEGO:Li-Hectorite nanocomposite for stoichiometry ...... 101 Figure A-48: *H NMR of MEEP ...... 104 Figure A-49: 13C NMR of MEEP...... 104 Figure A-50: XRD data for a) POMOE b) POEGO c) MEEP ...... 105 Figure A-51 :XRD data for a) POEGO:Li-Hectorite (2:1) b) POEGO:Li-Hectorite (1/2:1) c) POEGO:Li-Hectorite (4:1) Nanocomposites ...... 105 Figure A-52:TGA data for a) POEGO:Li-Hectorite (1/2:1) b) POEGO:Li-Hectorite (2:1) c) POEGO:Li-Hectorite (4:1) Nanocomposites ...... 106 Figure A-53: DSC data for a) POEGO:Li-Hectorite (1/2:1) b) POEGO:Li-Hectorite (2:1) c) POEGO.Li-Hectorite (4:1) Nanocomposites ...... 106 Figure A-54: AC Impedance Spectroscopy raw data ...... 107 Figure A-55: AC Impedance Spectroscopy raw data ...... 107 Figure A-56: XRD data for a) POMOE:Li-Hectorite (1/4:1) b) POMOE:Li-Hectorite (1/2:1) c) POMOE: Li-Hectorite (2:1) d) POMOE:Li-Hectorite (4:1) Nanocomposites ...... 108 Figure A-57: TGA data for a) POMOE:Li-Hectorite (1/4:1) b) POMOE:Li-Hectorite (1/2:1) c) POMOE:Li-Hectorite (2:1) d) POMOE:Li-Hectorite (4:1) Nanocomposites ...... 108 Figure A-58: DSC data for a) POMOE:Li-Hectorite (1/4:1) b) POMOE:Li-Hectorite (1/2:1) c) POMOE:Li-Hectorite (2:1) d) POMOE: Li-Hectorite (4:1) Nanocomposites ...... 109 Figure A-59: AC Impedance Spectroscopy raw data ...... 109 Figure A-60: AC Impedance Spectroscopy raw data ...... 110 Figure A-61: AC Impedance Spectroscopy raw data ...... 110 Figure A-62: AC Impedance Spectroscopy raw data ...... I ll Figure A-63: XRD data for a) MEEP:Li-Hectorite (1/2:1) b) MEEP:Li-Hectorite (2:1) c) MEEP: Li-Hectorite (4:1) Nanocomposites ...... 111 Figure A-64: TGA data for a) MEEP:Li-Hectorite (1/2:1) b) MEEP:Li-Hectorite (2:1) c) MEEP:Li-Hectorite (4:1) Nanocomposites...... 112 Figure A-65: DSC data for a) MEEP:Li-Hectorite (1/2:1) b) MEEP:Li-Hectorite (2:1) c) MEEP: Li-Hectorite (4:1) Nanocomposites ...... 112 List of Tables
Table 3-1: Properties of POEGO...... 46 Table 3-2: Properties of POMOE...... 48 Table 3-3: Properties of MEEP...... 50 Table 3-4: IR vibrations of Lithium Hectorite ...... 54 Table 4-5: Summary of XRD data ...... 56 Table 4-6: Summary of TGA data ...... 60 Table 4-7: Stoichiometry of POEGO:Li-Hectorite Nanocomposites ...... 61 Table 4-8: Summary of DSC data ...... 63 Table 4-9: Summary of IR data ...... 65 Table 4-10: Ionic conductivity of Li-POEGO and Li-POEGO:Li-Hectorite Nanocomposites.... 6 8 Table 5-11: Summary of XRD data ...... 71 Table 5-12: Summary or TGA data ...... 75 Table 5-13: Stoichiometry of POMOE:Li-Hectorite Nanocomposites ...... 76 Table 5-14: Summary of DSC data ...... 78 Table 5-15: Summary of IR data ...... 80 Table 5-16: Ionic conductivity of Li-POMOE:Li-Hectorite Nanocomposites ...... 83 Table 6-17: Summary of XRD data ...... 87 Table 6-18: Summary of TGA data ...... 90 Table 6-19: Stoichiometry of MEEP:Li-Hectorite Nanocomposites ...... 91 Table 6-20: Summary of DSC data ...... 93 Table 6-21: Summary of IR data ...... 95 Table A-22: TGA Stoichiometry sample calculation ...... 101 Table A-23: Calculation of Ionic Conductivity ...... 102 Chapter 1: Introduction
1.1 Background
Energy production from renewable sources is attracting academic and industry attention worldwide. Policy makers are looking to deviate away from the use of conventional fossil fuels such as petroleum, coal, and natural gas sources by focusing on renewable energy sources.
Renewable energy sources such as solar, wind, and hydrogen are all proving to be potential large scale candidates (eg. electric grid, electric vehicles) with minimal safety or catastrophic concerns.
However, these intermittent energy sources require a safe and convenient storage system for the energy harnessed during their operation. One solution that could solve this energy storage dilemma is the use of lithium-ion batteries. ’ 1 Lithium-ion 0 batteries are rechargeable batteries that have dominated the small scale applications market (eg. mobile phones and laptops) over the past two decades. However, in order to apply lithium-ion battery technology as a large scale storage system, the capacity and energy density must be further improved. Implementing such a technology on a large scale requires years of research to fully ensure the batteries operate safely under dynamic conditions (temperature, pressure, etc.), prolonged use time, and of course to be economically feasible . 3 , 4
Figure 1-1: Applications for Lithium-Ion Batteriess (Reprinted with permission from John
Wiley and Sons)
1 The concept of using batteries as an energy storage mechanism has existed for centuries.
Early examples of the technology were demonstrated with the voltaic/galvanic cell during the late 1700s. The original cells were made out of a relatively simple design which consisted of two metals immersed in a solution of the metal separated by a salt bridge, as depicted in Figure 1-2.
s
This electrochemical design converted chemical energy to electrical energy . 6
V
Salt Bridge
Electrode ectrode
Salt Solution Salt Solution
Anode Oxidation Reaction Cathode Reduction Reaction
Figure 1-2: Electrochemical Cell
Since the discovery of the electrochemical cell, batteries have been improved
dramatically from their material composition to the final product dimensions. Even though the
material composition and design used in batteries have been improved significantly since the
original battery concept was proposed, the basic components have not changed. The three basic
components of a battery are the anode, electrolyte, and cathode. Current research is being
conducted to improve all three components in order to maximize their capacity. This is achieved
by investigating the properties of the materials at the nanoscale level ( 1 - 1 0 0 nm), and
determining their potential use as battery materials. ■
Battery materials research in academic and industrial labs belongs to a discipline referred
to as materials science. Materials science, at the atomic or molecular scale, is the study of the relationship between a material’s structure and its macroscopic properties. In recent years, nanotechnology has become a prominent field of study in material science. Research in nanotechnology has focused on a variety of applications ranging from biomedical drug delivery
systems7 to smart polymers8, and electronics . 9 , 10 The basis of the research and development in nanotechnology has focused on investigating the characteristics of materials at the nanoscale and
implementing scientific methods to utilize their modified properties in certain applications. More
specifically, the discovery of new polymers, new ceramics, metal alloys, and nanocomposite
materials are all prime examples. 10
Nanocomposites are multiphase materials that are the result of blending a bulk matrix and
a nanostructured material with dimensions less than lOOnm. They are commonly used in
products such as plastics, ceramics, and metals by combining varying compositions of two or
more materials. Since the pristine or raw materials chemistry and structure differ from one
another, their nanocomposites’ properties will also differ from the starting materials. The final
nanocomposites’ characteristics, such as thermal, mechanical, electrical, and optical properties
are highly dependent on the composition of the pristine materials. A particular type of
nanocomposite material that has attracted attention is the polymer-clay nanocomposite (PCN).
These nanocomposites are based on varying compositions of polymers and clays. They have
attracted attention due to the synergetic effects both materials have on one another, which
ultimately yield enhanced properties. Polymer-clay nanocomposites (PCNs) were originally
demonstrated by the Toyota R&D group in 1985. ’11 12 The group discovered PCNs by randomly
and homogenously dispersing clay in nylon- 6 . Once the material was molded, it had superior
mechanical, thermal, and barrier properties compared to the pristine polymer. This enhancement
in the physical properties of the materials was due to the enhanced interaction between the clays
3 and the polymer matrix . 13 Therefore, since the discovery of PCNs by the Toyota group, there has been a considerable amount of interest in applying these enhanced materials in other potential applications.
There are three well-established techniques for synthesizing polymer-clay nanocomposites, these techniques are referred to as in-situ polymerization, melt processing, and
solution induced intercalation. In-situ polymerization is the polymerization of a monomer within a structured material (eg. layered silicate), the monomer is inserted into the swollen form of the
structured material followed by polymerization that is initiated by heat, radiation, a suitable
initiator, or by an organic initiator. Melt processing involves annealing a mixture of polymer and
structured material at a temperature above the softening point of the polymer. Finally, the
method used throughout this research is solution induced intercalation. Intercalation, in simple
terms, is the insertion of a guest into a host. Therefore in solution induced intercalation, the
methodology is based on a solvent system where the polymer and structured material are
separately suspended in a solution (eg. water). Once both materials are suspended, they are
mixed together and the polymer chains intercalate and displace the solvent within the layers of
the material. Upon solvent removal, the polymer is intercalated into the structured material,
resulting in a nanocomposites material . 1 4 ' 17 The focus of this thesis is directed towards a
literature review on battery materials, the components of the lithium-ion battery, and the
synthesis and characterization of polymer-clay nanocomposites as potential electrolytes in
lithium-ion polymer batteries.
4 1.2 Battery Types
1.2.1 Primary Cells (Batteries)
Non-rechargeable batteries are referred to as primary batteries due to their irreversible reaction chemistry. These types of batteries typically range from moderate to high energy density and are relatively inexpensive. However, unless they are desired for one time use applications, they have drawbacks such as short shelf-life, are non-rechargeable and have long-term environmental impacts. During discharge, hydrogen atoms accumulate in the cathode when aqueous electrolytes are used, thus reducing the capacity of the battery. Furthermore, the materials used in primary battery materials are toxic, and any potential leaks could lead to toxic materials coming in contact with the equipment or even the individual operating them.
Examples of non-rechargeable batteries are Zinc-Carbon, Alkaline (some being rechargeable), and lithium metal batteries . 1 8 , 19
1.2.2 Secondary Cell (Batteries)
Rechargeable batteries are referred to as secondary batteries because they operate based on reversible electrochemical reactions, which render them rechargeable. These rechargeable cells are utilized in vehicle batteries, power tools, medical equipment, and other daily applications. The common types of secondary batteries on the market are lead-acid, nickel- cadmium, nickel-zinc, nickel metal hydride, and lithium-ion batteries. These types of secondary cells are desired over primary cells due to their rechargeable characteristics, long shelf-life, and lower environmental impact.
Since 1985, the development of secondary batteries, such as lithium-ion batteries, has been a successful and prominent field of research. This is due to the realization that certain intercalation compounds can undergo many charge/discharge cycles without a significant loss in capacity. These findings have since sparked over two decades of research and development in lithium-ion batteries, which has made a significant impact in the field of nanotechnology. The following section will outline the components of a lithium-ion battery, currently used materials, and potential future materials. 19
1.3 The Lithium-Ion Battery
400
Li metal (unsafe) 300 Li ion
Ni-MH Ni-MH 0 50 100 150 200 250 Energy Density (W h Kg ') Figure 1-3: Volumetric and Gravimetric Energy Densities of Battery Technologies20 Lithium-ion batteries (LIBs) are a new technology compared to traditional secondary batteries based on nickel and lead. LIBs have a higher operating voltage, high volumetric and gravimetric energy densities, low self discharge potential, and no memory effect. The motivation for using lithium in secondary batteries stems from its high specific capacity (3862 mAh g'1), which provides longer electric charge per gram. Lithium is the lightest metal with the highest energy density with respect to its mass, high specific capacity, and high electrochemical reduction potential . 1 8 , 21 Even though lithium is an ideal metal for use in secondary batteries, it was faced with challenges when it was first brought to market. One of these challenges being 6 that lithium metal became highly reactive upon cycling, leading the battery to short circuit and rendering it unsafe for consumer electronics. Since lithium metal was deemed unsafe for consumer products, the use of lithium-ion intercalation into carbonaceous materials was later implemented. Since then, lithium-ion batteries have become the preferred high energy density power source used in consumer products. Their properties make them an ideal energy storage source in handheld devices, hybrid/electric vehicles, and potentially electric grid storage applications . 2 2 *2 4 A lithium-ion cell is composed of three components, namely the anode (negative), cathode (positive), and electrolyte/separator mixed with a salt that provides free lithium-ions. The anode is typically a material intercalated with lithium ions; the cathode is a metal oxide, while the electrolyte is an electrically insulating/ionically conductive material complexed with lithium salt. In a typical discharge cycle, electrons migrate from the anode through the circuit towards the cathode. This results in a state where the cathode exhibits a negative charge. The negative state in the cathode is balanced with the free lithium ions that readily have the energy potential to travel via the electrolyte and towards the cathode. This cycle is reversed during the charge period of a lithium-ion battery. The scheme for a typical lithium-ion battery discharge cycle is shown in Figure 1-4 . 2 1 >2 2 ’ 25 7 ► e" Device •+ Li+ Li+ Li+ Li Li Li Li+ Li+ Li+ Anode Electrolyte Cathode LixC6 LiyCo02 Figure 1-4: Working Principle of Lithium-Ion batteries (Discharge) Lithium-ion batteries were first introduced into consumer products by Sony in the early 1990s.19 In the past two decades researchers have focused on improving the lithium-ion battery components by synthesizing new materials with high capacity, low cost, and most importantly enhanced safety. In the following sections, a summary is given on the components found in lithium-ion batteries. 1.3.1 Anode Discharge LixC6 xLi +xe'+ 6 C Charge The anode is the site of oxidation in the battery. During operation, electrons flow from the anode towards the circuit due to their electrical potential. In lithium-ion batteries, the anode functions as the source of both electrons and lithium-ions. The properties desired for a working anode are : 2 4 1) High specific capacity 2) Stability upon charge/discharge cycles 8 3) Low self-discharge potential 4) Safety and low cost Research on anode materials can be categorized into three groups referred to as insertion-type, alloying-type materials, and more recently conversion-type. Insertion-types refer to the traditionally used materials such as carbon and titanium dioxide, alloying-type are based on silicon, tin and germanium, and finally conversion-type which consist of metal oxides (C 0 3 O4 , Fe2 0 3, CuO ) . 2 5 Insertion-type anodes are based on the conventional intercalation reaction of lithium into the layers of a system such as graphite. Graphite-based anodes have proven their superior capability in lithium-ion batteries due to their stability, high cycling performance, and low cost. However, lithium-ion batteries are becoming highly desired for large scale energy storage applications such as hybrid/electric vehicles and electric grid storage. These technologies require anode materials that have high cycling capabilities and capacities. Therefore it is anticipated that the next generation of anode materials will outperform the widely used graphite anode . 2 5 Even though researchers are investigating all three types of anode materials, perhaps the most promising candidate in the literature has been silicon-based anode materials. Silicon anodes can be alloyed with lithium to form a LixSi alloy upon lithiation. Silicon has a theoretical capacity that is an order of magnitude greater than graphite (4212 mAh g‘- vs. 372 mAh g'1) indicating the battery will last longer, have low self-discharge potential, and does not suffer from solvent co-intercalation. 2 4 However, silicon-based anodes have been noted to expand by 90% in volume upon lithium intercalation (versus 1 0 % in graphite), resulting in tremendous mechanical stress, and ultimate cracking of the electrode. Currently researchers are determined on overcoming these challenges by focusing on the nanoscale morphologies of 9 silicon/tin/germanium, such as nano wires, nanopores, nanoparticles etc. The motivation behind investigating the nanoscale morphologies allows researchers to improve the mechanical stability of materials by minimizing the total volumetric expansion via creating pores or voids that accommodate material expansion. If electrode cracking can be avoided, then stable cell cycling can be obtained with little capacity loss upon lithium intercalation. This indicates that irreversible capacity loss is proportional to lithium intercalation, and if the stability is improved, then anode materials with higher capacities than graphite may be developed . 2 4 This has proven to be successful for tin-based electrode materials, which have recently been introduced to the 'y’7 market. The final group is a new type of anode candidates referred to as conversion-type anode materials. Conversion-type anodes utilize 3-D transition metal oxides such as C 0 3 O4 , CuO, and Fe2 C>3 . In 2000, a publication by Tarascon et al. on reversible conversion reactions sparked interest on the mechanism of lithium storage using cobalt-based oxides. Although little is currently known about conversion-type reactions with metal oxides as anode materials, it is believed that Li 2 0 is formed. Due to this 2:1 ratio of lithium ions per oxygen atom, these materials possess superior theoretical capacity (896 mAh g'1) compared to traditional carbonaceous anode materials (372 mAh g'1). However, synthetic procedures and sufficient cycling capabilities remain a challenge for conversion-type anode materials. It was not until 2008 that Wu and co-workers reported the first successful growth of mesoporous C 0 3 O4 nanowire arrays. Therefore there remains a substantial amount of research to improve conversion-type anode materials. ’ 10 1.3.2 Cathode , Discharge LiixCo02 + xLi +xe' ^ LiCo02 1 x z Charge The cathode is the site of reduction in a battery. During the discharge cycle, electrons end up in the cathode leaving it in a negative state. In order to balance the negatively charged cathode, positively charged lithium-ions migrate from the anode through the ionically conductive electrolyte, and end up in the cathode. Materials research on cathodes for rechargeable lithium- ion batteries has been a major focus for academics and industry in the past three decades. As outlined by Whittingham et al.31 the following properties are desired for a material to be utilized as a cathode material in lithium batteries: 1) A reducible/oxidizable ion, for example a transition metal 2) React with lithium reversibly, where the host structure is not changed upon intercalation/de-intercalation of lithium 3) React with lithium with high free energy of reaction 4) Fast reaction with lithium 5) Electrically conductive 6 ) Stable upon cycling 7) Low cost 8 ) Environmentally benign Studies reported in the literature categorize materials research on cathodes into two categories. The first category consists of layered compounds where the structure consists of transition metal cations that occupy alternate layers, with lithium ions intercalated into the empty layers. Examples of these layered compounds are LiCo 0 2 , LiFePC>4 , and LiMSi 0 4 . The second category 11 of cathode materials consists of layered structures such as vanadium oxides and manganese oxides, where the layers are separated by a void called an interlayer spacing or d-spacing . 2 5 Figure 1-5: Crystal Structures of (a) LiCoC >2 (layered structure), (b) LiMn 2 0 4 (spinel structure), and (c) LiFeP 0 4 (olivine structure)32 (Reprinted with permission from Elsevier) Intercalation chemistry was first demonstrated in battery cells using dichalcogenides O | materials such as TiS 2 and M 0 S2 in the 1970s, Following the introduction of intercalation using dichalcogenides, materials such as vanadium and manganese oxides were utilized. However, it was not until the 1980s that lithium cathode materials based on IJC 0 O2 were discovered by Goodenough et. al. at Oxford University . 3 4 , 3 5 This discovery was a major breakthrough in high energy density battery materials, which was later commercialized by Sony. Since the commercialization of the first LiCo 0 2 battery in the early 1990s, the volumetric energy density has been enhanced from 250 to 400 W h/1, which illustrates the significant improvements that have been made to lithium-ion batteries over the past two decades .31 Although LiCo0 2 has dominated the market since its discovery, researchers have continued to search for materials that are less toxic and associated with a lower cost compared to cobalt-based cathodes. Much of the success has been achieved using other layered lithium metal oxides such as manganese and nickel-based materials. These materials have proven to be effective cathode materials with varying compositions, such as LiCoi/ 3 Nii/3 Mni/ 3 C>2 . 12 Polyoxyanion compounds such as LiFePC >4 are another group of cathode materials that have attracted a considerable amount of attention from academic and industrial laboratories. The motivation for using these materials as cathodes in lithium-ion batteries stems from their enhanced safety, abundance, low cost and high cycling capability with minimal degradation. Lithium iron phosphate (LiFePdt), discovered in 1997, has an ordered-olivine structure where phosphorus atoms occupy the tetrahedral sites, while iron/lithium atoms occupy the octahedral, as shown in Figure 1-5. The theoretical capacity of lithium iron phosphate is 170 mAh g'1, although experimentally this has been difficult to achieve. Therefore the majority of research efforts have focused on overcoming the low electronic conductivity lithium iron phosphate iio exhibits. The most successful outcome was demonstrated by Armand et al. when it was reported that a carbon coating can almost achieve the theoretical capacity of lithium iron phosphate. Another new class of polyoxyanion cathode materials that has attracted attention is based on orthosilicates, LiMSiC >4 (where M=Mn, Fe, and Co). These materials exhibit high lattice stabilization due to the strong Si-0 bonds, similar to that of the phosphate bonds in LiFeP 0 4 . Although the most studied system is Li 2 FeSi0 4 , these materials have one key feature in common, which is high theoretical capacity. The reason for these materials’ high theoretical capacity is because it is expected that two lithium-ions can be exchanged for two electrons. Theoretical capacities of 300 mAh g' 1 have been obtained for Li 2 MnSi 0 4 , although experimentally this has been difficult to achieve. Current research is focusing on improving the synthetic methods, characterization, and potentially coating the materials as conducted for LiFePC^ in order to achieve higher experimental capacities. 13 Although metal oxides and phosphate metal oxides have been commercialized, there remains an interest in discovering cathode materials with superior theoretical capacities than the currently commercially available materials. Lithium-sulfur and lithium-air batteries have been interesting candidates due to their substantially enhanced capacity and energy density that could potentially render them useful for large-scale energy storage applications. Theoretical capacities have approached 1675 mAh g'1, assuming complete reaction, which is nearly seven times higher than conventional cathode materials. However, in order to use these types of technologies, they would require compatible anode materials with superior capacities over what is currently available. Another important distinction between sulfur-based cells and the conventional transition metal-based cathodes is their reversible chemical reaction. In the conventional transition metal-based cathodes the reaction with alkali metals is an intercalation reaction, but in sulfur-based reactions, it is referred to as an integration reaction. It is referred to as an integration reaction because the reduction of sulfur involves a reversible chemical reaction with lithium, which forms another material. The other cathode material of interest based on integration chemistry reactions is lithium-air cells. Lithium-air cells are based on redox reactions between oxygen and lithium. However, like lithium-sulfur cells, there remain challenges with respect to the reversibility and understanding the mechanism of the materials with lithium . 3 3 ,4 0 i CO ? (LijMnOjr LiMnOj .LiCoO; Layered Spinel Olivine Figure 1-6: Capacity range of various cathode materials 41 14 The second category of layered cathode materials includes materials such as vanadium oxide, and manganese oxide. Although these materials have typically been studied and employed as cathode materials in commercial primary batteries, their application in secondary cells is also being pursued by researchers. Vanadium oxides (V 2 O5 ) in particular, have multiple valence states of vanadium and rich structural chemistry which enables versatile redox-dependant properties. Their theoretical capacities are higher than lithium cobalt oxides; however, their main drawback is they become amorphous upon cycling. Therefore some groups are focusing on the introduction of a secondary metal cation to stabilize their framework, which can be done by varying the composition of transition metals such as silver, copper, iron, cobalt, and nickel with vanadium oxides. This ultimately yields materials such as copper, iron, or cobalt-based vanadium oxides, which have better cycling capability and lower cost than silver-based composites.42 1.3.3 Electrolyte The final component in lithium-ion batteries is the electrolyte. The electrolyte in a lithium-ion battery acts as both an ionic conductor and electrical insulator. Since the electrolyte is the medium for lithium-ion transport from the anode to the cathode during the discharge process, the ionic conductivity is a vital property of the electrolyte. High electrical insulation is also necessary to prevent the battery from short circuiting during the operation of the battery. In order to explore new electrolyte materials, there are a number of properties that are desired for operational standards. The properties desired are listed below :4 3 ,4 4 1) Lithium ion conductivity > 10 "4 S/cm 2) Electrical conductivity < 10 ' 10 S/cm 3) Chemical stability upon cycling between -20 °C and 60 °C 15 4) Mechanical, electrochemical, and thermal stability between -20 °C and 60 °C 5) Non-flammable, low toxicity, and low cost material Even though the general properties have been outlined, some variables are subject to change depending on the application that the battery is required for. For example, batteries used in electric vehicle applications are required to withstand higher temperature tolerance and vigorous operational conditions than batteries utilized in handheld devices. Furthermore, research on electrolyte materials is diverse and can be broadly categorized into liquid organic electrolytes, ionic liquids, inorganic liquid electrolytes, polymer electrolytes, and hybrid electrolyte system. Although liquid organic electrolytes are widely used in commercial products due to their low cost and compatibility with most electrode materials, other types of electrolytes such as polymer electrolytes are competing with liquid organic electrolytes due to their enhanced safety. Commercial use of other electrolyte candidates such as inorganic liquid electrolytes, ionic liquids, and hybrid electrolyte systems is difficult to predict for future use in lithium-ion batteries due to the costs associated with their manufacturing. Therefore the discussion below is focused on liquid organic electrolyte and polymer electrolyte materials . 4 3 1.3.3.1 Liquid Organic Electrolytes The use of liquid organic electrolytes in commercial batteries is favored because of the low cost, high ionic conductivity, and compatibility with most anode and cathode materials currently utilized. These materials are typically carbonate blends of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC) mixed with lithium salts such as LiPF 6 . 43 Although these materials provide high ionic conductivity, they lack safety due to the fact that they are in the liquid state. Since they are in the liquid state, they will ultimately leak out of the 16 cell if they are not contained properly. Therefore important precautions are required in order to enhance the safety of these electrolyte materials, which also increase the cost of the cell. Since liquid organic electrolytes have been well established in lithium-ion batteries, there is less work being done on improving their potential relative to cathode and anode materials. However, some researchers are aiming at improving the separators used in lithium-ion batteries, which provides thermal, mechanical, and electrochemical stability between the cathode and anode. The function of a separator is to prevent physical contact between the cathode and anode while still facilitating lithium-ion flow. Although the separator does not participate in any chemical reactions within the battery cell, it does contribute to battery performance. Typically, separators are required to be chemically stable, exhibit certain dimensions, high porosity and permeability, and possess high mechanical durability and thermal stability. Therefore the research currently being conducted is focused on improving separators via surface modifications, polymer coating methods, and impregnating the membrane with gel polymer electrolytes. After all, the separator accounts for approximately 2 0 percent of the cell costs and contributes significantly to the energy density, cycle life, and safety of a battery . 45 In order to overcome the challenges associated with liquid organic (non-aqueous) electrolytes, academic and industrial labs have focused on finding alternate methods to improve the electrolyte component. This effort has primarily focused on shifting to polymer-based electrolytes, which ultimately lead to a solid-state battery system. Solid-state batteries entail reduced manufacturing costs due to the elimination of bulky cells and safety mechanisms required in lithium-ion batteries that utilize liquid organic electrolytes. Therefore the next three sections outline the common types of polymer electrolytes being investigated. 17 1.3.3.2 Polymer Electrolytes The use of polymer-based electrolytes is a fairly new type of technology compared to the conventional liquid organic electrolytes that are composed of carbonate blends mixed with lithium salts. The motivation behind using polymers and polymer blends is because a solid-state battery will be safe, allow for flexible cell designs, and decreased cell cost. However, the shift to a solid-state battery has possessed a number of challenges; the biggest challenge being that polymer-based electrolytes exhibit lower ionic conductivity than carbonate blends with salts. This is simply due to the fact that lithium ions travel more conveniently through a liquid medium than a solid or viscous medium. Therefore researchers are currently focused on discovering alternate routes to improve the ionic conductivity properties of polymer electrolyte materials . 4 6 The movement of lithium ions in polymer electrolytes is refered to as segmental motion. Segmental motion in polymers is believed to occur due to the electron-rich functionalities in the polymer chain. Although polymers can be found with both amorphous and crystalline characteristics, it is believed that the less crystalline a polymer is (ie. amorphous), the higher the ionic conductivity of the material will be due to the enhanced flexibility of the polymer chain. The mechanism of segmental motion is displayed in Figure 1-7 . 4 7 , 4 8 o o Figure 1-7: Schematic of Segmental Motion 18 The flexibility of polymers can be monitored using instrumentation such as differential scanning calorimetry, which determines the thermal transitions of a polymer. Typical thermal transitions of a polymer are crystallization temperature (Tc), melting temperature (Tm), and glass transition temperatures (Tg) At temperatures below the glass transition temperature of a polymer, the polymer becomes hard, brittle, and less flexible. Therefore depending on the application the lithium-ion battery will be utilized in, the glass transition temperature of the polymer is expected to be lower than the optimal working temperatures. In general, a polymer with low glass transition temperature is desired for lithium-ion batteries, since application temperatures may vary. However, polymers with lower glass transition temperatures exhibit low dimensional stability due to their highly flexible polymer chains and require methods to improve their dimensional stability. Research on improving the dimensional stability and ionic conductivity of polymers can be categorized into three types of polymer electrolytes namely solid polymer electrolytes, gel polymer electrolytes, and nanocomposite polymer electrolytes . 4 6 1.3.3.2.1 Solid Polymer Electrolytes In the early 1970s, researchers focused on synthesizing polymer-based electrolyte materials with high ionic conductivity, mechanical stability, and electrochemical stability. Wright et al.49 were the first to report that poly (ethylene oxide) (PEO) would form a crystalline polymer-salt complex. However, it was not until 1978, that Armand et al46 reported that solvent- free polymer salt-complexes may be applicable as solid polymer electrolytes in batteries. Since the discovery, the ultimate goal has been to improve the properties of solid polymer electrolytes and achieve the ionic conductivity of liquid organic/aqueous electrolytes at room temperatures. Solid polymer electrolytes are a polymer matrix complexed with an alkali metal salt, such as LiX (Where X= T, Cl", Br", CICV). Poly (ethylene oxide) and Poly (propylene oxide) were interesting 19 polymers to study due to their electrochemical stability, and dissolving capability of lithium salts. Their compatibility with lithium salts is due to the oxyethylene polar groups. However, the drawback with PEO is that it becomes crystalline below 70 °C, which decreases its ionic conductivity at ambient temperatures. In order to overcome this challenge, there have been modified forms of PEO synthesized with grafted polymers, block copolymers, and cross-linked polymer networks. Although these experiments have resulted in low degrees of crystallinity and glass transition temperatures, their ionic conductivities remain < 1C 4 S cm' 1 . 4 6 1.3.3.2.2 Gel Polymer Electrolytes First demonstrated by Fenullade and Perche in 1975, Gel Polymer Electrolytes (GPEs) are obtained by mixing a polymer and alkali metal salt dissolved in large amounts of an organic solvent (the plasticizer ) . 4 6 Preparation of GPEs involves heating a mixture of the polymer and plasticizer above the glass-transition temperature of the polymer. The heating process is followed by casting the viscous solution onto a glass plate . 5 0 The goal behind synthesizing GPEs is to obtain a mechanically stable electrolyte with high ionic conductivity. This can be achieved with the addition of polymers such as poly(propylene oxide), poly(ethylene imine), and poly(vinylidene carbonate) to yield dimensionally stable GPEs with enhanced ionic conductivities under ambient temperatures (< 10 ' 3 S cm'1). Although the advantages of GPEs are obvious, there were reports that stated the polymer corrosively reacts with the metal electrode . 5 0 This was later overcome by using lithium intercalated carbon compounds rather than lithium metal anodes 4 6 Another drawback facing GPEs is the decreased mechanical strength once excessive amounts of plasticizer are added. This challenge can be resolved via implementing methods such as high-energy radiation, but this method is associated with higher cell costs. 20 1.3.3.2.3 Composite Polymer Electrolytes Composite Polymer Electrolytes (CPEs) are polymer electrolytes mixed with ceramic filler. Originally demonstrated by Weston and Steel in 1982, CPEs are prepared by the addition of varying micro/nano-sized inorganic (ceramic) or organic fillers into the SPE . 51 The advantages associated with using ceramic fillers in SPEs are the enhanced ionic conductivity and improved interfacial properties with the lithium electrode. These enhanced properties are due to the increased amorphous characteristics of the polymer chain, which aids in ionic conductivity based on the theory of segmental motion. The ceramic filler types are classified into two categories: active and passive. The active fillers participate in the ionic conduction and include materials such as Li 2 N, and IJAI 2 O3 , while passive filler, such as Si0 2 and A 12 C>3 , do not participate in ionic conductivity. CPEs properties have been shown to be highly dependent on the particle size and characteristics of the filler used. Researchers working on CPEs have predominantly focused on improving poly(ethylene oxide) properties at ambient temperatures, since PEO possesses crystalline characteristics and low ionic conductivity at ambient temperatures. Regardless, there remains an ample amount of research in order to determine the ideal CPE that exhibits competitive ionic conductivity and low cost . 2 3 , 4 6 , 52 1.4 Intercalation Chemistry The term intercalation was coined from the latin verb intercalare, which assigns the insertion of an additional day in special years to synchronize the calendar with the solar year. In chemistry, intercalation is defined as the insertion of a guest species into a host lattice that yields a non-stoichiometric product. Intercalation chemistry was originally demonstrated by Schaffhautl in 1841, who observed the swelling of graphite in a solution of sulfuric acid. However, it was not until the introduction of X-ray diffraction techniques in the 1920s that research using 21 intercalation chemistry became more prominent. Since then, the investigation of layered compounds such as graphite and clay minerals using intercalation chemistry has been an ongoing field of research in the search for new materials . 1 0 ,5 3 An intercalation reaction is typically a reversible type of solid or liquid state process that introduces a guest species into a host without any major structural changes done to the host. The reaction is typically carried out using a two-dimensional layered host, however, intercalation of guests into one and three dimensional hosts can also be carried out. Compared to the three- dimensional frameworks and one-dimensional chain structures, a two-dimensional lattice possesses vacancies between the layers that accommodate larger atoms, molecules, and polymers. In order to yield an intercalation compound, the host lattice is required to possess the following properties: 5 4 1) Covalently bonded network of atoms, which remains unchanged upon intercalation 2) Highly oxidized metal centre 3) Unoccupied lattice sites to accommodate the diffusion of the guest The advantage of intercalating atoms, molecules, or polymers into two-dimensional layered hosts is due to the synergetic effects both starting materials have on one another. The space in two- dimensional layered structures is referred to as the interlayer space, which is held together by weak electrostatic interactions, as illustrated in Figure 1-8. Upon intercalation, this interlayer spacing is filled with the guest and yields a material with properties that are different from the pristine starting materials, these are typically enhanced physical properties. In the case of ionically conductive polymers, the polymer matrix provides the medium for ion mobility, while the two-dimensional layered host provides the thermal and dimensional stability for the polymer. 55 22 Figure 1-8: Schematic of Interlayer Spacing in Two-Dimensional Layered Structures Although the concept of intercalation has been in the literature for over a century, it was not until the 1970s that intercalation chemistry was utilized in rechargeable batteries. Intercalation chemistry was first demonstrated for use in potential battery materials when Armand et al?1 attempted to incorporate oxides such as Cr 0 3 into layered graphite; however, further investigation indicated that no intercalation had taken place. Subsequent research at Stanford illustrated the intercalation of electron-donating molecules and ions into layered dichalcogenides, particularly tantalum disulfide. Exxon then decided to pursue this research, which ultimately lead to the development of titanium disulfide cathodes in the late 1970s.31 The discovery of titanium disulfide cathodes sparked a considerable amount of interest by academics and industry to further pursue intercalation compounds and produce battery materials with higher capacities than the nickel and lead-based technologies. Therefore, researchers focused for decades on using intercalation compounds such as LiCoCh, which later became the commercialized lithium-ion battery cathode in the early 1990s. Even though intercalation chemistry has become the standard technique for rechargeable lithium-ion batteries, recent research has been focused on finding alternate methods to the 23 conventional intercalation chemistry techniques. Perhaps the most promising method currently being pursued in the literature is conversion-type reactions. Initially, conversion-type reactions displayed irreversible characteristics at room temperature, but excellent reversibility at higher temperatures. However, recent studies have indicated that binary M-X compounds (where M=Ti, Cr, Co, Ni and X= O, N, F,S, P) can be reversible at room temperature, and potentially have a 77 future in the lithium-ion battery industry. 1.5 Hectorite In 1850, H.S. Thompson recognized the cation exchange capabilities in certain soils, and this discovery lead to over a century of research on clay materials dedicated towards understanding the synthetic methods, intercalation chemistry, and properties of clays. The clays were initially interesting because of their swelling behavior in water, which attracted the attention of scientists who wanted to study their properties upon guest insertion. This breakthrough led researchers to introduce a large number of organic molecules, polymers and biochemicals into the interlayer space of the clay minerals . 10 24 Td-Si04 Oh-Li, Al, Mg Td-Si0 4 Exchangeable cations (Li+, Na+) nH 2 0 Figure 1-9: Structure of Hectorite56 Hectorite (Nao.4 Mg2 .7 Li0 .3 Si4 0 io(OH)2) is a phyllosilicate that belongs to the family of smectite clays. 5 7 Smectites have been commonly known for their use in industrial applications and research in fields such as the pharmaceutical , 5 8 cosmetic, 5 9 and automobile industry , 6 0 as well as potential solid electrolytes in battery technology . 6 1 ’6 2 ,6 3 The research and applications of clays in these fields have primarily focused on layered silicates such as montmorillonite, saponite, and hectorite. Hectorite has a two-dimensional layered structure that is composed of a central octahedral (Oh) sheet of magnesia, and small amounts of lithium and alumina. This Oh sheet is infused between two tetrahedral (Td) silica sheets, where the oxygen atoms of the Td sheets and Oh sheet are shared. In the central Oh sheet, occasional isomorphous substitution occurs in the lattice where Li+ displace Mg2+, which causes an overall net negative charge. This overall 25 negative charge is balanced with exchangeable Na+ and Li+ in the interlayer. The tetrahedral sheets (T structure. The layer thickness is typically lnm ( 1 0 A) with lateral dimensions that span from 300 A to several microns, depending on the silicate. These layers form stacks with relatively weak electrostatic interaction between the negatively charged layers and the cations in the interlayer space, an interlayer space or gallery is shown in Figure 1-8. This interlayer space (ie. d-spacing) allows for the intercalation of molecules or polymers within the layers. Hectorite is appealing as a layered host due to its high thermal stability, high surface area, exfoliation/restacking ability, and high cation exchange capacity . 6 4 Although hectorite is a naturally abundant mineral, naturally occurring minerals suffer several drawbacks due to the presence of impurities and random mineralogical composition. Therefore, synthetic methods such as hydrothermal techniques are typically employed for the synthesis of hectorite . 6 5 Synthetic sodium hectorite has a high abundance of sodium and lithium cations that balance the negatively charged layers. Therefore their cation exchange properties can be exploited to exchange the naturally lying sodium ions with lithium ions . 6 6 The advantage of using the lithiated form of hectorite is dependent on the application the material is required for. In this case, lithium-ion polymer batteries require a high abundance of lithium ions within the structure, and the overall synthesized nanocomposite. Therefore intercalation into the lithiated form of hectorite is desired over sodium hectorite. Intercalation into sodium hectorite has been reported using PEO , 61 polylactide , 6 7 and pyridine derivatives . 6 8 Layered structures can be characterized using analytical instruments such as powder x- ray diffraction, thermogravimetric analysis, and transmission electron microscopy. Chemically, hectorite and other clays have a high abundance of water adsorbed and bound to the surface; 26 however, water content can be minimized in the structure upon heating to high temperatures. In order to use intercalation chemistry techniques with hectorite, exfoliation in water is utilized. This methodology exfoliates the negatively charged layers and randomly disperses them until a polymer or molecule is introduced. Once a polymer or molecule is introduced into the hectorite suspension, the interlayer restacks with the guest intercalated between the layers (Figure 1-10). The intercalation of the guest into the clay layers is an entropy driven process, which ultimately displaces the majority of the water molecules adsorbed or bound onto the surface of the clay. This is confirmed by conducting control experiments with hectorite suspended in water only. The schematic for the exfoliation and intercalation of a polymer into hectorite is displayed in Figure 1- 10. Na+ Lih Na+ Na+ LiC1 + H 90 Exfoliation Li+PolymerUH Na+ Li+ Na-Hectorite Li--Hectorite L i+ Figure 1-10: Cation Exchange, Exfoliation and Intercalation into Hectorite The future of clay materials is not only promising because of their physical properties, but also as a potential source of lithium. Alkali metals such as lithium are used in applications such as ceramics, glass, lubricants, and batteries. Therefore the demand for lithium from sources other than brines, seawater, and oil residues is rising. Hectorite clay represents the third largest source of lithium in the world, however due to economical reasons extraction from brines is preferred Over hectorite . 6 9 Current research is focused on improving the costs associated with the extraction process of lithium from clays, which could ultimately yield an abundance of lithium 7A reserves in the future. 27 1.6 Polymers Poly (ethylene oxide) (PEO) and poly (ethylene glycol) (PEG) represent a class of 71 77 polyether compounds used in medicinal applications, polymer lubricants, and as potential solid polymer electrolytes.73, 7 4 When polyether compounds are complexed with lithium salts such as lithium triflate (LiS 0 3 CF3 ) they possess ionic conductivities that have potential application as electrolytes in lithium-ion batteries. However, at room temperatures polyethers exhibit crystalline characteristics which yield lower ionic conductivities than conventional liquid organic electrolytes. 7 5 Researchers have overcome this drawback by synthesizing derivatives with low crystallinity at room temperatres, or utilizing other completely amorphous polymers *JIQ with low glass transition temperatures, such as polyphosphazenes. ' Unfortunately these polymer derivatives and polyphosphazenes possess a lack of dimensional stability due to their low glass transition temperatures. Therefore, we exploit intercalation chemistry techniques, and intercalate the polymers into physically stable layered structures, such as lithium hectorite, to enhance their dimensional stability. 1.6.1 POEGO/POMOE As mentioned above, PEG tends to crystallize at ambient temperatures, which results in poor ionic conductivity. Therefore PEG-based polymer derivatives such as poly[oligo(ethylene glycol)-oxalate], (POEGO) and poly[oxymethylene-(oxyethylene)], (POMOE) have been synthesized. 7 6 ,7 7 POEGO and POMOE are polymers that possess ionic conductivity when complexed with lithium salts, are electrical insulators, and exhibit electrochemical stability. Their structures have electron donor coordination sites, which provide sufficient mobility for lithium ions when the polymers are complexed with lithium salts such as lithium triflate. Lithium triflate (LiS0 3 CF3) provides a sufficient amount of free Li+ that migrate throughout the polymer 28 based on the theory of segmental motion. In fact, ionic conductivities of 5.9 x 10 ' 5 S cm' 1 (POEGO), and 5.0 x 10 ' 5 S cm' 1 (POMOE) at 25 °C have been achieved. 7 7 ,7 6 This is due to the polymers’ low glass transition temperatures (high flexibility) and low crystallinity at ambient temperatures. O (b) (a) O n o Figure 1-11: a) Structure of POEGO b) Structure of POMOE The drawback of POEGO and POMOE, like most solid polymer electrolytes based on PEG, is low dimensional stability at room temperature. Once they are assembled into a cell, they ultimately leak causing the battery to short circuit. In order to overcome this drawback, intercalation into a two-dimensional layered structure is employed. The intercalation of POEGO o 1 and POMOE has been investigated into layered structures such as molybdenum disulfide, tin (II) disulfide, 87 graphite oxide, 8^ and natural hectorite. Throughout 84 this research, we have investigate the intercalation of POEGO and POMOE into lithium hectorite, and characterize the thermal and ionic conductivity properties of the nanocomposites. 1.6.2 Polyphosphazenes oc The synthesis of soluble polyphosphazenes was first reported in 1965 by Allcock et al. Polyphosphazenes are amorphous polymers that possess a backbone of alternating phosphorus and nitrogen atoms with two side groups that may be organic, inorganic, or organometallic. Due to the large number of pendant R groups that may be added to polyphosphazenes, their properties can be altered dramatically. Depending on the R groups attached to the polymer backbone, their 29 thermal, biodegradable, hydrophobicity, and ionic conductivity properties can be modified. Their dynamic properties make them applicable in research fields ranging from biomedical to solid polymer electrolytes. 8 6 ,8 5 In 1984 Blonsky et al.49 discovered that salt complexed polyphosphazenes with pendant polyether side chains possess ionic conductivity that surpasses electrolyte materials based on PEO. This sparked a considerable amount of interest in the application of polyphosphazenes as SPEs. It was later determined that their organic polyether side chains provide the coordination sites for lithium ions and facilitate mobility of the ions throughout the polymer. 87 Cl Cl R R=Functional group 250 °C, 4 hrs. + 2NaH + 2NaCl THF Cl R c r N | Cl Cl Figure 1-12: Synthesis of Polyphosphazenes The synthesis of polyphosphazenes can be classified into three methods, namely polymerization-substitution route, catalysis-solution polymerization, and thermal ring-opening polymerization. The thermal ring-opening polymerization method is chosen as the preferred synthetic route due to its simplicity and enhanced separation from cross-linked products. The ring-opening polymerization mechanism involved in polyphosphazenes is still open to debate since some researchers believe that radical ring-opening polymerization is involved, while others believe that it is an anion ring-opening polymerization mechanism. Regardless, most researchers commonly use this method to synthesize polyphosphazenes. 30 Figure 1-13: Structure of MEEP Since the discovery of poly[bis-(methoxyethoxyethoxy)phosphazene] (MEEP) (Figure 1- 13) there have been many polymers synthesized using the phosphazene backbone with different • > 7Q Oft • alkyl ether and alkoxy side groups, yielding flexible ionically conductive polymers. ’ MEEP is an amorphous polymer at room temperature with a low glass transition temperature (Tg, -84 °C), which dictates its high macromolecular flexibility. Along with its macromolecular flexibility, it has been found that MEEP serves as an excellent solid solvent for lithium salts, such as lithium triflate. The conductivity of salt complexed MEEP at room temperatures has been reported to be 2-3 orders of magnitude higher than similar PEO salt complexes.49, 89, 9 0 However polyphosphazenes, more specifically MEEP, are like PEG-based polymers in that they leak once assembled in a cell due to their low dimensional stability, which prevents them from directly being utilized as SPEs. Therefore researchers have explored different routes to improve the dimensional stability of MEEP. These include polymer blends with PEO , 91 induced cross-linking via 6 0 Co-gamma irradiation , 8 9 and polyphosphazene-silicate networks , 9 2 all with varying degrees of success. Other groups have merely used MEEP as an additive to propylene carbonate liquid electrolytes, which yields electrolytes with 90% lower flammability than the pristine propylene carbonate electrolyte. Researchers have also demonstrated enhanced dimensional stability of MEEP by synthesizing intercalated nanocomposites using two-dimensional layered structures .78,84,94,95 Due to the weak electrostatic interaction in the interlayer of the two-dimensional layered structures, the layers are easily exfoliated and ionically conductive polymer can be inserted between the sheets using intercalation techniques. This yields nanocomposite materials with ionically conductive properties, along with enhanced mechanical and thermal durability provided by the layered structure. Intercalation of MEEP has been investigated using layered structures such as graphite oxide, 7 8 molybdenum disulfide , 9 4 sodium montmorillonite , 9 5 and sodium hectorite , 8 4 and typically yields ionically conductive nanocomposite materials with enhanced physical properties. Therefore, we investigate the effect varying molar ratios of MEEP have on lithium hectorite, and monitor the physical (thermal) and ionic conductivity properties of the nanocomposites upon intercalation. 1.7 Research Goals The ultimate goal of this research project was to intercalate ionically conductive polymers POEGO, POMOE, and MEEP into lithium hectorite and determine the thermal, crystalline, and ionic conductivity properties of the synthesized nanocomposites. The final goal was broken down into tasks such as the lithiation of sodium hectorite, synthesis of the polymers, and the development of a systematic approach to synthesize the nanocomposites. Once the nanocomposites were synthesized, the characterization process was carried out using instrumentation such as powder X-ray diffraction (p-XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and attenuated total reflectance (ATR) spectroscopy. The experimental process involved exploring the cation exchange and intercalation properties of hectorite in order to develop a systematic approach for intercalating ionically conductive polymers into lithium hectorite. A large portion of the experimental research focused on determining the most viable method for exchanging sodium ions with lithium ions. Once this 32 method was established, nanocomposites of varying polymer molar ratios to lithium hectorite molar ratios were synthesized and characterized. Another goal was to complex the polymers with lithium triflate (LiSOaCFa) to determine their ionic resistance using AC impedance spectroscopy. From this technique, the ionic conductivity of the nanocomposites and the salt-complexed polymers could be determined. Once all the polymers and nanocomposites were synthesized, the final goal was to compare the nanocomposite properties to the pristine materials and report the thermal properties, crystalline characteristics, bond vibrations, and ionic conductivity differences between the salt- complexed materials and non-salt complexed materials. 33 Chapter 2: Instrumentation 2.1 Powder X-ray Diffraction (p-XRD) is an analytical technique used to determine the crystalline properties of a material (e.g. minerals, inorganic compounds). The instrument consists of three main components, the X-ray tube, sample holder and X-ray detector. During operation, X-rays are generated in the tube and are directed towards the sample, where the X-rays are then diffracted off the sample into a detector which produces a characteristic XRD spectrum of the sample. Since crystalline materials produce a unique set of diffraction peaks, the XRD spectra are useful in determining basal spacing (d-spacing), structural elucidation, and crystallite size of the bulk sample . 9 6 , 9 7 , 9 8 The working principle of the instrument is based on constructive interference of monochromatic X-rays and the crystalline characteristics of the sample which satisfy Bragg’s law (rik-2d sin0). In Bragg’s law n is an integer, X is the source wavelength (A), d is the interlayer spacing, while 0 is the angle between the incident ray and scattering plane. Bragg’s law relates the wavelength of the X-ray radiation to the diffraction angle and the d-spacing in a crystalline sample. Throughout the data collection the sample rotates at an angle 0, while the X- ray detector rotates at an angle of 20. The sample and detector rotate until the constructive interference of the X-rays and the crystalline material satisfy Bragg’s law. Once this X-ray signal is diffracted, the detector converts the signal based on the X-ray intensity counts and sends the data to the computer . 9 6 , 9 7 , 9 8 Using the XRD difffactograms, the average crystallite size was calculated for the raw materials and the synthesized nanocomposites. Most solids, such as hectorite, are composed of a large number of crystals found throughout the structure. Therefore an approximate value for the crystallites that make up the materials can be determined using the Schrrer equation 34 (D=(KX(57.3))/ (P1/2 cos0), where D is the average diameter of the crystallites (A), K is 0.9, X is 1.542 A, 57.3 is a conversion factor from radians to degrees, pi /2 is the peak width at half height in 20, and 0 is the peak position or 20/2. The Schrrer equation relates the crystallites found in a solid to the width of the peak in the diffraction pattern obtained from p-XRD." The samples were tested using a Bruker AXS D 8 Advance diffractometer. The monochromator is made of graphite. Cu (ka) radiation (A.=l .542 A) was utilized and the data was collected at room temperature on glass substrates. 2.2 Thermogravimetric Analysis (TGA) is a thermal analysis technique used to determine the thermal properties and stoichiometries of materials. The instrument works by monitoring the weight changes of a sample as a function of temperature, and produces curves of percent weight versus temperature. TGA can be used to analyze the composition of materials, degradation characteristics, and any absorbed contents (eg. volatiles, water) in the material. The instrument consists of a high precision balance with a wire to hang the sample, a platinum pan loaded with sample (>lmg), thermocouple, and electrically heated furnace. Once the sample pan is loaded, it is lifted by the wire connected to the high precision balance. The furnace is then electronically lifted to enclose the sample. The atmosphere in the furnace can be purged with an inert gas or compressed air, depending on the type of analysis desired. During operation, the furnace heats the sample to temperatures up to 1000 °C, which is monitored using the sensitive thermocouple. The heating procedure removes volatile compounds, and later decomposes the material depending on its composition. The polymers and nanocomposites were analyzed using a TA Q500 with a heating rate of 10 °C/minute. Samples were loaded onto platinum pans and analyzed under dry compressed air. All of the samples were freeze dried prior to TGA analysis to minimize• * moisture • content. 98 35 The TGA thermograms were used to calculate the approximate stoichiometry in a material analyzed. If the final residue that remain in the sample upon heating are known, then the stoichiometry of the material can be calculated by taking the weight of the residue and dividing it by the original mass. Therefore upon heating the nanocomposites to 650 °C, there are three decomposition steps observed in the thermograms. The first weight loss step is water, while the second step is ascribed to externally lying polymer, and the final step is the decomposition of intercalated polymer. This is displayed as (H 2 0 )a (POEGOExt)b (POEGOin)c (Li-Hectorite) throughout the thesis, where a is the ratio of water present, b is the externally lying polymer ratio, and c is the intercalated polymer ratio. Since the final phase of the nanocomposites is known to be the stable Li-Hectorite residue, the molar mass of the layered structure is used, along with each decomposition step in the thermograms to calculate the stoichometry of the nanocomposites. A sample calculation is provided in the appendix, A-47. 2.3 Differential Scanning Calorimetry (DSC) is a thermal analysis technique used to determine thermal transitions in materials (eg. polymers, nanocomposites, etc.) such as enthalpy change, and phase transitions such as melting temperature (Tm), crystallization temperature (Tc), and glass transition temperature (Tg). The apparatus consists of two electrically heated furnaces, a sample pan and a reference pan, and a computer. The working principle of the technique is based on the furnaces heating both the sample pan and the reference pan at the same temperature. Since heat is applied to the sample pan, the material being analyzed will exhibit physical transformations, which ultimately decreases (or increases) the heat flow to the sample in order to maintain both pans at the same temperature. This change in heat flow allows the instrument to measure the amount of heat flow delivered during the phase transitions and records it. The QO computer then produces a heat flow as a function of temperature curve. 36 The samples were analyzed with a TA Q100 heat/cool/heat cycles using aluminum pans under nitrogen at a rate of 50 mL/min. Samples were tested at a heating and cooling rate of 5 °C/min. 2.4 Attenuated Total Reflectance (ATR) is a surface technique used for infrared spectroscopy that simplifies the process of obtaining infrared data from solids and liquids. The fundamental principle which ATR is based on is referred to as total internal reflection. Total internal reflection is an optical phenomenon that occurs in a medium when light hits a boundary at an angle larger than the medium’s critical angle. The critical angle is the angle of incidence at which total internal reflection occurs. This phenomenon occurs in the crystal used in the instrument (eg. diamond, silicon, germanium), which has a high refractive index, and allows light to travel as a wave beyond the surface of the crystal and into the surface sample. This wave protrudes up to 5 microns into the sample, where the sample absorbs infrared energy and returns as an altered beam of infrared wave to the crystal. The wave is then reflected from the crystal as an altered (attenuated) beam directed towards the detector in the IR spectrometer which generates an infrared spectrum. The infrared spectra were obtained using a Bruker Alpha A-T with 0.9 resolution, and all samples were tested using 128 scans . 1 0 0 ,9 8 2.5 AC Impedance Spectroscopy (IS) was used to determine the ionic resistance of the nanocomposites and polymers once Complexed with lithium triflate salt (LiSC^CFs ) . 1 0 1 ' 1 03 The general approach when using AC impedance spectroscopy is to apply an electrical source (voltage) to the electrodes of a cell and a observe the response (current). The response is recorded using a frequency response analyzer, which measures the real and imaginary parts of the impedance at a specific frequency. Using the real and imaginary parts of the impedance, a Nyquist plot is constructed, which allows for the selection of the resistance (R) in a material. In 37 order to obtain accurate resistance values for the entire set of temperatures (280-310 K), a complex non-linear least-square fit is made to an equivalent circuit model using the program LEVMW (Levenberg-Marquardt).103,104The program gives the R value, which can then be used with the sample dimensions to calculate the resistivity of a sample. Since resistivity is inversely proportional to conductivity, the ionic conductivity of the sample can then be determined. (Table A-23 has the equations used) The samples were tested using rectangular glass substrates with two rectangular stainless steel electrodes on the opposite ends of the glass substrate. In order to remove moisture, the samples were placed in a vacuum chamber for at least 24 h at room temperature prior to data collection. The temperature of the samples was controlled using a Cryodyne 350CP refrigerator, electrical heater, and a Lakeshore 321 temperature controller. The data collection was performed using a Solartron 1250 frequency response analyzer and a home-built accessory circuit for high- impedance samples. The instrument is setup in the UPEI physics department, where it was operated, and the conductivity measurements were done by undergraduate students Vicki Trenton and Matthieu Hughes. 38 Chapter 3: Experimental and Characterization 3.1 Reagents and Solvents Poly(ethylene glycol) (MW 380-420), benzene (99%), oxalic acid dihydrate, dichloromethane, calcium hydride, potassium hydroxide, phosphonitrilic chloride trimer 99.9% ([PNCl2 ]3 ), anhydrous THF, di(ethylene glycol) methyl ether (MEEOH) were purchased from Sigma-Aldrich. 3.2 Synthesis of Poly[oligo(ethylene glycol)-oxalate] (POEGO) 77 POEGO was synthesized as described in the literature. Poly(ethylene glycol) 400 (16.0 mL, 4.50 x 10' 2 mol) was mixed with 100 mL of benzene in a 250 mL round bottom flask. Once the PEG was mixed well, one equivalent of oxalic acid dihydrate (5.00 g, 5.55 x 10 ' 2 mol) was added. The reaction was refluxed in air for two days with magnetic stirring. When the reaction was complete, benzene was removed under reduced pressure. The remaining product was dried in a vacuum oven at 120 °C for two days, yielding a viscous pale yellow polymer. O OH 1) Refluxed^ + HO 2) Dried @ 120 °C H O Figure 3-14: Synthesis of POEGO 3.2.1 Synthesis of POEGO/UCF3 SO3 Complex 77 The (POEGO)i6 LiCF3 S0 3 ratio was chosen based on previously reported literature. In a nitrogen glove box, lithium triflate was weighed and added to an appropriate amount of dry POEGO in a vial. The vial was capped and transported to a vacuum oven and heated at 90 °C for 24 hours. After heating, the product was stirred with a spatula and left to mix under mechanical stirring for an additional 2 hours. The salt-complexed POEGO was then subsequently used in intercalation experiments. Throughout this thesis the salt-complexed POEGO is referred to as Li- POEGO. 3.3 Synthesis of Poly [oxymethylene-(oxyethylene)] (POMOE) POMOE was synthesized as prepared in the literature . 7 6 KOH (50.0 g, 0.891 mol) was finely ground and transferred into a three neck round bottom flask. Dichloromethane (200 mL, 3.13 mol) was refluxed over CaH 2 for one day to remove any moisture, and then distilled under nitrogen into the three neck round bottom flask. This was followed by the addition of (50.0 mL, 1.40 x 10'1 mol) polyethylene glycol (MW 400) via dropping funnel, the PEG was previously dried over molecular sieves (4A) at 400 °C for four hours. A mechanical stir bar was inserted and the reaction mixed for two days. After two days, the dichloromethane was removed under reduced pressure, followed by the addition of water to dissolve any remaining KOH. In order to remove the remaining KOH and low molecular weight polymers, the clear liquid was placed in dialysis tubes (MW cut-off 3500) for one week, where the water was exchanged twice a day. 2KOH + 2 R.T. in N h 2o 2 + 2 n KC1 Figure 3-15: Synthesis of POMOE 40 3.3.1 Synthesis of P0M0E/LiCF3 S 0 3 Complex The synthesized POMOE was complexed with lithium triflate based on previously reported literature, (POMOE ) 2 5 IJCF3 SO3 . 7 6 POMOE and lithium triflate were separately dissolved in deionized water and left to mix for one day. The following day, the salt was added to the polymer and the mixture was left to stir for 16 hours. The remaining water was removed by freeze-drying, and the salt complexed polymer was used in subsequent intercalation reactions. Throughout the thesis, the salt-complexed POMOE is referred to as Li-POMOE. 3.4 Synthesis of Poly [bis-(methoxyethoxyethoxy)phosphazene] (MEEP) Poly [bis(-methoxyethoxyethoxy)phosphazene] (MEEP) was synthesized as prepared in the literature .4 9 Hexachlorophosphazene [PNCl 2 ] 3 (4.00 g, 1.15 x 10' 2 mol) was charged into a pyrex tube and sealed under vacuum. The pyrex tube was placed in an oven at 250 °C for four hours to perform ring opening polymerization of the trimer. After heating, the clear material was cooled to room temperature and transferred to a sublimator in a nitrogen dry-box. The excess phosphonitrillic chloride trimer was removed via sublimation, under vaccuum at 40 °C. The poly(dichlorophsphazene) was transferred to a Schlenk flask and dissolved in anhydrous THF (7.40 x 10 ' 3 g polymer/mL THF). In a separate Schlenk flask an alkoxide solution was prepared in the dry-box, where two equivalents of NaH with respect to poly(dichlorophsphazene) were dissolved in anhydrous THF (2.10 x 10‘2 g polymer/mL THF) and refluxed for one hour. At the one hour mark, dry 2-(2- methoxy ethoxy) ethanol (1 mL) was syringed into the NaH mixture and refluxed for 3 hours. Once the alkoxide solution changed from a white suspension to a pale yellow solution, it was syringed into the poly(dichlorophsophazene) suspended in THF. The reaction was left under mechanical stirring for 24 hours under nitrogen. Volatile materials were then removed under 41 reduced pressure, leaving cross-linked [PNCl 2 ]n and linear [PNChJn in the product. Cross-linked [PNCl2]n was removed via vacuum filtration, and the linear [PNCl 2 ]n was purified via dialysis. The final material was then freeze-dried, yielding a viscous honey-like material. Cl " 1 O' T f THF Cl + 2 NaCl ,0. 2HO ' ' 0 ' 2NaH THF Figure 3-16: Synthesis of MEEP 3.4.1 Synthesis of MEEP/LiCFjSOa Complex The chosen molar ratio was (MEEP ) 4 LiCF3 S0 3 , based on previously reported literature . 9 2 The MEEP-salt complex was prepared by mixing both MEEP and LiCF 3 SC>3 in deionized water. The mixture was allowed to stir overnight and the water was removed by freeze-drying. Throughout the thesis, the salt-complexed MEEP is referred to as Li-MEEP. 3.5 Purification, Lithiation, and Intercalation of Hectorite 3.5.1 Purification of Sodium-Hectorite Sodium hectorite (SHCa-1) was purchased from Source Clays Repository as a fine powder. Since the fine powder has calcium carbonate and other impurities a purification process was performed as described in the literature . 8 4 The purification of hectorite was conducted by suspending 20.0 grams of hectorite in 850 mL of water contained in a 1000 mL Erlenmeyer flask. The suspension was left to stir for one day, then left to settle for three days to allow impurities to settle to the bottom of the flask. This sedimentation process was repeated three times, until no impurities could be detected visually or via XRD. 42 3.5.2 Lithiation of Sodium Hectorite Once the purification process was complete, a cation exchange process was employed using previously reported methodology in order to exchange the sodium ions with lithium ions . 6 6 The cation exchange process began with the addition of LiCl solution (0.750 M) to the purified sodium-hectorite. This mixture was left to stir for one day and then centrifuged. The supernatant was discarded and the process was repeated twice. Once the final LiCl exchange was complete, the white translucent-gel was washed and centrifuged three times with deionized water. The resulting gel mixture was then dried in an oven at 100 °C for a minimum of three days. The solid clay was then rinsed with methanol, three times to remove any excess LiCl and NaCl. Finally, the lithium hectorite (Li-Hectorite) was dried in the oven at 70 °C for at least one day to remove residual methanol. The lithiation process was carried out twice to ensure that maximum sodium ions have been displaced with lithium ions. Elemental analysis was utilized to monitor the sodium and lithium ion content at Guelph Chemical Laboratories Ltd, Ontario. The data indicated lithium ion content enhancement and sodium ion reduction from Lio.sNao.g Sii (sodium hectorite) to Li3 Nao.4 Si] (lithium hectorite). 3.5.3 Preparation of Nanocomposites A general procedure was employed for the exfoliation of hectorite and intercalation of polymers into lithium hectorite. Lithium hectorite (0.100 g, 2.60 x 10 -4 mol) was added to 20 mL of deionized water, and left to stir until fully suspended, which typically takes 30 minutes. In the meantime, polymer with molar ratios of (0.25 for POMOE only), 0.5, 1, 2, and 4 with respect to lithium hectorite was allowed to dissolve in 5 mL of deionized water. A Pasteur pipette was used to transfer the polymer to the lithium hectorite. The progress of the reactions was monitored via XRD, and the final products were isolated via freeze-drying and stored in a vacuum desiccator. 43 • Throughout the thesis, the non-salt complexed nanocomposites are referred to as Polymer: Li- Hectorite, while the salt-complexed nanocomposites are referred to as Li-Polymer:Li-Hectorite. 3.6 Characterization of Starting Materials 3.6.1 POEGO Characterization The synthesis of POEGO was outlined in the experimental section using previously reported literature . 7 7 A thorough characterization of the synthesized polymer was conducted using nuclear magnetic resonance, thermogravimetric analysis, powder X-ray diffraction, differential scanning calorimetry, and attenuated total reflectance spectroscopy in order to ensure the polymer was successfully synthesized. Nuclear Magnetic Resonance (NMR) was conducted using a Bruker 300 Spectrometer, 300 MHz for 'H, 75 MHz for 1 3 C, and 121 MHz for 3 1 P. The reference solvent used was deuterated chloroform (CDCI 3), while the reference for the 31P NMR was H 3PO 4 . The polymer was characterized using NMR to determine whether the chemical shifts 1 1 agreed with previously reported literature. The H and C NMR spectra are displayed in Figures 3-17 and 3-18, respectively, outlining the chemical shifts of the hydrogen and carbon elements present in the polymer. 44 1 2 3 5 E S -COCOOCH2CH2(OCH2CH2)n-20- — j — I— — r ~ —i— T I — I— —I— I i 5 . 6 5 .2 5.0 4.8 4 . 4 4.2 4.0 3 .8 3.6 3 .4 3.2 3.0 ppm V ¥ Y Figure 3-17: NMR spectrum of POEGO 2 3 4 Ss3 1 1 2 3 4 4 -COCOOCH2CH2(OCH2CH2)n-20- A Jlii 75 70 65 60 55 ppm Figure 3-18:13C NMR spectrum of POEGO 45 The data is in agreement with the literature, and we can conclude that the polymer was successfully synthesized. Table 3-1 illustrates the properties of the POEGO synthesized 77 compared to literature values. Table 3-1: Properties of POEGO Analytical Method Experimental Literature 7 7 , 8 4 *H NMR Chemical Shift (ppm) 4.43 4.43 3.77 3.79 3.64 3.65 UC NMR Chemical Shift (ppm) 157.5 157.4 70.34 70.35 6 8 . 0 1 68.17 65.68 65.69 DSC Tg -53 °C -55 °C TGA Thermal Decomposition 170 °C 171 °C 3.6.2 POMOE Characterization The synthesis of POMOE is described thoroughly in the experimental section, and is based on previously reported literature . 7 6 In order to ensure that POMOE was successfully synthesized, it was characterized via powder X-ray diffraction, thermogravimetric analysis, differencial scanning calorimetry, and attenuated total reflectance spectroscopy. Furthermore, 'H and 13C NMR were used to ensure , the chemical shifts of the POMOE synthesized were in agreement with literature, Figures 3-19 and 3-20 illustrate the NMR spectra obtained. 46 g«' o8 ppm 8 I* Figure 3-19: 1H NMR spectrum of POMOE 1 2 3 3 3 3 3 -OCH2 OCH2CH2(OCH2CH2 )n. 2OCH2 CH2- i wn*n'>tnni' • M lp Figure 3-20:13C NMR spectrum of POMOE 47 From the thorough characterization of the synthesized polymer and agreement with previously reported literature, we can conclude that the polymer was successfully synthesized. Table 3-2 illustrates the properties of the synthesized POMOE compared to literature values. Table 3-2: Properties of POMOE Analytical Method Experimental Literature76' ‘H NMR Chemical Shift (ppm) 4.74 4.71 3.63 3.60 13C NMR Chemical Shift (ppm) 95.7 95.0 70.7 70.1 66.9 66.3 DSC Tg -60 °C - 6 6 °C TGAThermal Decomposition 186°C 216°C 3.6.3 MEEP Characterization The synthesis of MEEP was presented in the experimental section and followed previously reported literature . 4 9 The characterization of the pristine polymer was conducted via powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and attenuated total reflectance spectroscopy. NMR was used to ensure the chemical shifts of the synthesized polymer were in agreement with literature values, and the data confirms the successful synthesis of MEEP. The properties of MEEP are presented in Table 3-3 and compared to literature values. 48 100 50 0 -5 0 -1 0 0 -1 5 0 -2 0 0 ppm Figure 3-21: 31P NMR spectrum of MEEP 49 Table 3-3: Properties of MEEP Analytical Method Experimental Literature 8 4 ’ 8 6 31P NMR Chemical Shift (ppm) -7.3 -7.7 'H NMR Chemical Shift (ppm) 4.1 4.1 3.6 3.7 3.5 3.5 3.3 3.3 13C NMR Chemical Shift (ppm) 72.3 71.6 70.8 70.3 70.6 70.1 65.4 65.8 59.2 58.6 DSC Tg -73 °C -83 °C TGAThermal Decomposition 240 °C 181 °C 3.6.4 Lithium Hectorite Characterization Lithium hectroite was characterized to determine its crystalline characteristics (eg. basal spacing), thermal properties, and vibrational characteristics. Upon the purification and lithiation process of hectorite, the properties of the flaky material were characterized using powder X-ray diffraction, thermogravimetric analysis, and attenuated total reflectance spectroscopy. The XRD diffractogram of dry lithium hectorite shown in Figure 3-22 clearly illustrates the layered chracteristics of lithium hectorite, with an interlayer spacing of 9.5 A. 50 600 - 500 - O 300 o T~r T t- r ■t—r 2 10 20 30 40 50 S 2-Theta - Scale Figure 3-22: Lithium Hectorite heated to 650 °C A control experiment was carried out using deionized water prior to the intercalation of polymers into lithium hectorite. The control experiment was conducted using the same procedure as the synthesis of the nanocomposites, except without the addition of polymer. This experiment yields an XRD diffractogram with an interlayer spacing of 12.1 A, an increase of 2.6 A compared to dry lithium hectorite. Given that water has an average cross-sectional dimension of approximately 2.8 A, this increase indicates that water readily exfoliates the layers of hectorite, and is subsequently intercalated within the layers. 51 5000 *£ 3000 *• 102 20 30 40 50 a 2-Theta - Scale Figure 3-23: Control experiment with water and lithium hectorite Thermogravimetric analysis of pristine lithium hectorite was carried out to determine the thermal properties of the layered structure. From the TGA thermogram (Figure 3-24), it can be deduced that lithium hectorite is stable beyond 650 °C, suggesting that lithium hectorite has high thermal stability. 52 102 1.5 100 - 1.0 98 c E 96 g. £ b 0.5 D) g> i i 94 92 0.0 90 88 — i— - 0 .5 100 200 300 40 0 50 0 6 0 0 7 00 Temperature (°C) Universal V4.7A TA Instruments Figure 3-24: Thermogram of Lithium Hectorite Attenuated total reflectance spectroscopy was utilized to monitor the infrared vibrations of lithium hectorite. The IR spectrum of the layered structure prior to intercalation illustrates the tetrahedral Si-0 stretch/bend, and H-O-H vibrations in the structure. The. peaks and their assignments are presented in Table 3-4 and are in agreement with literature values.56,106 53 Transmittance (%'S Hectorite Lithium of vibrations IR 3-4: Table 3626 1) (cm Peak 655 700 947 1628 8030 32003800 3400 3800 Figure 3-25: Infrared Spectrum of Lithium Hectorite Lithium of Spectrum Infrared 3-25: Figure 002800 3000 2600 Wavenumber (cm'1) Wavenumber 54 Assignment HOH Stretch HOH HOH Bend HOH OH Bend OH Bend Si-0 Stretch Si-0 000 0 20 1800 1800 1200 1000 800 400 Chapter 4: POEGO/Lithium Hectorite Results and Discussion 4.1 Powder X-ray Diffraction Powder X-ray diffraction was used to confirm whether POEGO was successfully intercalated into lithium hectorite (Li-Hectorite). The XRD data was used to compare the basal spacing (ie. d-spacing) of the intercalated polymer nanocomposites to the pristine Li-Hectorite, and determine if varying the polymer molar ratios has an effect on the basal spacing of the layered structure. Figure 4-26 compares the POEGO:Li-Hectorite nanocomposite (1:1) to the control and illustrates the increased basal spacing of the layered structure. 2 10 20 3040 50 & 2-Theta - Scale Figure 4-26: XRD of a) Li-Hectorite:H2O and b) POEGO:Li-Hectorite Nanocomposite (1:1) Throughout the course of the research, the polymeric molar ratio was systematically increased with respect to Li-Hectorite (0.5, 1, 2, and 4), and the basal spacing of the resulting 55 nanocomposites was determined by using p-XRD. The net interlayer expansion is obtained by taking the difference between the basal spacing of the nanocomposites and the dry Li-Hectorite, heated to 650 °C (d-spacing = 9.5 A). For example, a 1:1 POEGO:Li-Hectorite nanocomposite has a basal spacing of 18.9 A, which implies a net interlayer expansion of 9.4 A. The XRD data of the nanocomposites is summarized in Table 4-5. Table 4-5: Summary of XRD data Average POEGO: Li-Hectorite Basal spacing Net expansion Material Crystallite Size (Mol) (A) (A) (A) POEGO 0.5:1 17.4 7.9 88 1:1 18.9 9.4 88 2:1 22.0 12.5 67 ------4:1 — ------Na-Hectorite — 10.0 140 Dry Li- 9.50 182 — Hectorite As illustrated in 4-5, upon increasing the POEGO molar ratio with respect to Li-Hectorite, the amount of the intercalated POEGO increases. This enhancement in basal spacing is observed when the molar ratio of POEGO with respect to Li-Hectorite increases from 0.5 to 2. Increasing the molar ratio to 4, results in an amorphous material as shown by XRD, also suggesting the characteristics of an exfoliated nanocomposite. From the X-ray diffractograms, the average crystallite size of the nanocomposites was determined by using the Scherrer formula and the 56 results are presented in Table 4-5." According to the overall trend, the average crystallite size appears to decrease upon increasing the amount of POEGO, indicating that the amorphous polymer significantly contributes to the reduction of the crystallite size of the nanocomposite. Lithium Hectorite 18.9 A Lithium Hectorite Figure 4-27: Schematic of POEGO layers in Lithium Hectorite (1:1) The cross-sectional dimension of POEGO from the top carbonyl oxygen to the bottom carbonyl oxygen was calculated using Spartan ’08, which indicates that the largest possible dimension, assuming the polymer is linear, is approximately 3.5 A .102 This suggests a bilayer arrangement of POEGO in the 1:1 nanocomposite, which has a net interlayer expansion of 9.4 A. Although a bilayer arrangement is assigned to the 1:1 nanocomposite, it is important to note the polymer is likely not oriented in a linear fashion within the layers of hectorite, and could be randomly oriented between the layersdue to its flexible polymer chain. A schematic diagram showing the bilayer arrangement of POEGO in Li-Hectorite (1:1) is illustrated in Figure 4-27, even though the polymer could be oriented differently from what is depicted. The amount of POEGO packed in a crystallographic unit cell was determined using the basal plane area per formula unit of Hectorite (16 A), and the area of a POEGO monomer. 57 Assuming the polymer is linear, the dimensions determined are 3.5 A and 28 A, indicating a projected area of 98 A for a bilayer of POEGO. Therefore the ratio of Hectorite/POEGO is 0.32 in a single unit cell for a single layer of POEGO. A sample calculation is provided in the appendix, Table A-24. 4.2 Thermogravimetric Analysis Thermogravimetric analysis was utilized to investigate the thermal stability of the pristine materials, nanocomposites, and to calculate the stoichiometry of the synthesized nanocomposites. The thermal stability of the synthesized nanocomposites was compared to the thermal stability of the pristine polymer and the lithium salt complexed polymer using the TGA thermograms. Figure 4-28 illustrates the thermal decomposition data of the pristine POEGO, POEGO:Li- Hectorite nanocomposite (1:1), Li-POEGO, and Li-POEGO:Li-Hectorite nanocomposite (1:1). 58 100 80- 60- O) 1 40- 2 0 - 0 100 200 300 500 600400 Temperature (°C) Universal V4.7A TA Instruments Figure 4-28: TGA thermograms a) Li-POEGO:Li-Hectorite (1:1) b) POEGO:Li-Hectorite (1:1) c) Li-POEGO d) POEGO The thermograms of the nanocomposites (Figure 4-28 (a) and (b)) conducted in air, display three distinguishable weight loss steps. The first step corresponds to the removal of the co-intercalated water and typically occurs around 100 °C, while the second decomposition step is ascribed to the loss of externally bound polymer. The third and final step is the decomposition of the intercalated POEGO in the layers of hectorite, and occurs after the pristine POEGO thermogram (Figure 4-28 (d)) had fully decomposed. 59 Table 4-6: Summary of TGA data Polymer POEGO: Li-Hectorite (Mol) Ta(°C) Tb (°C) ATc(°C) POEGO N/A 170 N/A N/A 0.5:1 182 402 232 1:1 182 408 238 2:1 186 420 250 4:1 180 423 253 a=Onset decomposition temperature of externally lying polymer b=Onset decomposition temperature of intercalated polymer c=Difference in decomposition temperature of intercalated polymer and pristine polymer As shown in Figure 4-28 and summarized in Table 4-6, the 1:1 POEGO:Li-Hectorite nanocomposite (thermogram (b)) displays an enhancement in the onset decomposition temperature of the intercalated polymer when compared to the pristine POEGO (thermogram (d)). For pristine POEGO (thermogram (d)), full decomposition of the polymer is observed at approximately 400 °C. On the other hand, the decomposition of the intercalated POEGO begins at 408 °C in the 1:1 nanocomposite, thus indicating a thermal enhancement of 238 °C compared to the onset decomposition temperature of pristine POEGO (170 °C). When the TGA of the Li-POEGO:Li-Hectorite nanocomposite (1:1) (thermogram (a)) is compared to the Li-POEGO (thermogram (c)), it is found that the decomposition in Li-POEGO is slightly compromised due to the decomposition of the lithium triflate salt near 400 °C. The lithium triflate salt (LiCFsSOs) decomposes over the same region as the intercalated polymer (observed in thermogram (b)). Therefore due to this decomposition overlap near the 400 °C region, the thermograms of the salt-complexed nanocomposites were not used for the stoichometry calculations. Furthermore, the stoichiometry of the POEGO :Li-hectorite 60 nanocomposites was determined from their corresponding thermograms, and the results are summarized in Table 4-7. Table 4-7: Stoichiometry of POEGO:Li-Hectorite Nanocomposites POEGO: Li-Hectorite (Mol) Stoichiometry 0.5:1 (H20)o.78 (POEGOExt)o.39 (POEGOin)0.040 (Li-Hectorite) 1:1 (H20)3.7 (POEGO exOi.i (POEGO i„)o.ii (Li-Hectorite) 2:1 (H20)2.7 (POEGOexOi.9 (POEGOin)o.2 0 (Li-Hectorite) 4:1 (H20)5.o (POEGOExt)4.o (POEGOin)o.43 (Li-Hectorite) From the data presented in Table 4-7, higher amounts of intercalated POEGO are observed with increasing molar ratios of POEGO to the Li-Hectorite, which is in agreement with the increased basal spacing observed in the XRD data, and the theoretical calculation of intercalated POEGO into a single crystallographic unit cell of Hectorite determined in section 4.1. At the same time, with increasing polymer ratios a significant amount of externally lying polymer is observed, which is displayed as POEGOExt in the stoichiometry data. 4.3 Differential Scanning Calorimetry Differential scanning calorimetry was used to monitor the glass transition temperature (Tg) of the polymer upon intercalation into Li-Hectorite. The Tg was determined for the pristine POEGO, POEGO:Li-Hectorite nanocomposites, Li-POEGO, and Li-POEGO:Li-Hectorite nanocomposites. 61 -0.05- -59.14°C -40.28”C i 05 LL ra -0 25- 1® -53.20°C -0.45 -95 -45 Exo Up Temperature (°C) Universal V4.7ATA Instruments Figure 4-29: DSC data for a) POEGO:Li-Hectorite (1:1) b) Li-POEGO:Li-Hectorite (1:1) c) Li-POEGO d) POEGO The pristine polymer exhibits a glass transition temperature at -53 °C and is in very good agreement with the literature (-55 °C).77 However, it is interesting to observe that the glass transition temperature of the polymer does not shift upon intercalation and slightly decreases when the polymer molar ratio is increased. This indicates that the nancomposites are still flexible to very low temperatures and theoretically intercalation should not affect the ionic conductivity of the material based on the theory of segmental motion.47 This is in contrast to what has been previously reported in the literature where intercalation of polymers into layered structures leads to an increase in the glass transition temperature of the polymers, due to the rigid nature of the 62 nanocomposites.78 The Tg data for the non salt-complexed POEGO nanocomposites is presented in Table 4-8. Table 4-8: Summary of DSC data Polymer POEGO: Li-Hectorite (Mol) Glass Transition Temperature (Tg) POEGO N/A -53 Li-POEGO N/A -57 0.5:1 -55 1:1 -59 2:1 -62 4:1 -62 While the POEGO:Li-Hectorite nanocomposites do not show a shift in glass transition temperatures, the salt-complexed nanocomposite (Figure 4-29 (b)) behave differently. The Tg observed in (Figure 4-29 (b)) shows a significant shift in its Tg to -40 °C, indicating a 13 °C increase in glass transition temperature. The increase in Tg of the salt-complexed nanocomposites is most likely due to the crystalline nature of the lithium triflate salt. Although this glass transition temperature had increased, it is well below the optimal operation temperatures for a lithium-ion battery. 4.4 Attenuated Total Reflectance Attenuated total reflectance spectroscopy was used to monitor the vibrations of pristine POEGO, POEGO.Li-Hectorite nanocomposites, Li-POEGO, and Li-POEGO:Li-Hectorite nanocomposites. The IR spectra are presented in Figure 4-30. 63 Transmittance (%) 4-30 (a) and (c). Upon intercalation, the position of the carbonyl vibrations in the polymer polymer the in vibrations carbonyl the of position the intercalation, Upon (c). and (a) 4-30 remain unchanged (1744 cm'1), however, the ester C-0 vibrations shift to lower wavenumbers wavenumbers lower to shift vibrations C-0 ester the however, cm'1), (1744 unchanged remain that the lithium triflate presence has little effect on the vibrations of the materials. This further This materials. the of vibrations the on effect little has presence triflate lithium the that indicates which (d)), 4-30 (Figure nanocomposites salt-complexed and (b)) 4-30 (Figure POEGO salt-complexed the enhanced for observed is indicate trend shifts similar A These Li-Hectorite. with polymer cm'1). the of 988 interaction to cm'1 1094 and cm'1 1057 to cm'1 1180 (from Figure 4-30: IR Spectra of a) POEGO b) Li-POEGO c)POEGO:Li-Hectorite(l:l) Li-POEGO b) POEGO a) of Spectra IR 4-30: Figure The IR spectra of pristine POEGO and POEGO :Li-Hectorite (1:1) are displayed in Figure in displayed are (1:1) POEGO and :Li-Hectorite POEGO pristine of spectra IR The d) Li-POEGO:Li-Hectorite (1:1) Li-POEGO:Li-Hectorite d) O 2400 iO0 Wavenumber (cm’1) Wavenumber 64 1800 solidifies the theory that the lithium salt is merely acting as a free lithium-ion source, and not compromising the vibrations in the nanocomposites, the IR data is summarized in Table 4-9. Table 4-9: Summary of IR data Major Vibrations (cm1) POEGO Li-POEGO POEGO:Li- Li-POEGO: Li- Hectorite (1:1) Hectorite (1:1) Li-Hectorite HOH stretch N/AN/A 3689 3689 Hydroxyl 3470 3431 3411 3406 Spa C-H stretch 2868 2875 2872 2878 C=0 Carboxylic acid 1719 — 1719 1719 C=0 Ester 1744 1740 1740 — Li-Hectorite HOH bend N/A N/A 1635 1653 C-0 ester/ether/alcohol 1180/1094 1082/1029 1057/988 1061/980 c f 3 N/A 1249 N/A 1253 C-F deformation N/A 638 N/A 638 S0 3 Asymmetric bend N/A 573 N/A 573 SO3 Symmetric bend N/A 518 N/A 518 --Peak not found in spectrum 4.5 AC Impedance Spectroscopy AC impedance spectroscopy was used to determine the resistance of the Li-POEGO, and Li-POEGO:Li-Hectorite nanocomposites. As shown in the Nyquist plot in Figure 4-31, the impedance data of Li-POEGO :Li-Hectorite (1:1) illustrates a typical curve observed for an ionic conductor, where the touchdown point in the curve before shooting up corresponds to the resistance (R) of the sample. The value of R along with the dimensions of the sample glass 65 substrate was used to calculate the ionic conductivity of the sample. In order to obtain more accurate values of R from the data obtained, a complex non-linear least-square fit was made to an equivalent circuit model using the program LEVMW . 103 A three-component equivalent circuit in series consisting of a resistor (R), a constant-phase element (CPE), and a capacitor (C) was used and is displayed in Figure 4-31. 3.00E+06 2.50E+06 o - 2.00E+06 CPE N 1.50E+06 1.00E+06 5.00E+05 0.00E+00 0.00E+00 5.00E+05 1.00E+06 1.50E+062.00E+06 2.50E+06 3.00E+06 Re Z (O) Figure 4-31: Nyquist plot of Li-POEGO:Li-Hectorite (1:1) at 300K The ionic conductivity shown in Figure 4-32 compares Li-POEGO to different ratios of Li- POEGO: Li-Hectorite nanocomposites. A trend in the ionic conductivity is observed when the molar ratio of Li-POEGO increases with respect to Li-Hectorite. 66 1.00E-05 1.00E-06 • Li-POEGO ■ Li-POEGO:Li-Hectorite (1:1) 1.00E-07 > Li-POEGO:Li-Hectorite (4:1) 1.00E-08 i------1------r 275 280 285 290 295 300 305 310 315 Temperature (K) Figure 4-32: Conductivity of Li-POEGO and Li-POEGO:Li-Hectorite Nanocomposites An enhancement in ionic conductivity is notable in the 4:1 nanocomposite, where the ionic conductivity is on the same magnitude as Li-POEGO. Although the error bar is 9.5 times greater in the 4:1 than in the 1:1 nanocomposite, it is necessary to account for this error which is due to difficulty in measuring the dimensions of the polymeric film. The ionic conductivity for all the Li-POEGO:Li-Hectorite nanocomposites is displayed in Table 4-10. 67 Table 4-10: Ionic conductivity of Li-POEGO and Li-POEGO:Li-Hectorite Nanocomposites Li-POEGO: Li-Hectorite (Mol) Conductivity (O'1, cm 1) at 300K 1 : 1 (3.2310.09) x 10 2 : 1 (2.9311.18) x 10 4:1 (1.5111.19) xlO Li-POEGO (2.3110.52) xlO The trend in the ionic conductivity of the Li-POEGO:Li-Hectorite nanocomposites indicates that with increasing polymer molar ratio to Li-Hectorite, the ionic conductivity of Li-POEGO can be achieved. Although there appears to be a decrease in the ionic conductivity when the polymer ratio is increased from 2 to 4, this is likely due to measuring a polymeric film using mechanical instruments. A dial caliper and a micrometer are used to determine the area of the polymer film, however, determining the polymer area requires an accurate measurement of the polymer film thickness using a micrometer. Since the polymer film is non-uniform at higher polymeric ratios, it is likely that there is error associated with the measurement. Therefore, this error is accounted for in the standard deviation presented in Table 4-10. 4.6 POEGO/Lithium Hectorite Conclusion Varying amounts of POEGO have been successfully intercalated into Li-Hectorite as evidenced by p-XRD. The nanocomposites have also been characterized by TGA, DSC, ATR, and AC impedance spectroscopy. TGA data confirm that an increase in the molar ratio of POEGO (0.5, 1, 2, 4) to the layered host, results in a larger amount of the intercalated polymer. 68 The amount of intercalated POEGO was further confirmed using theoretical calculation of the area of the polymer and the basal plane area per formula unit of Hectorite. TGA data also indicate that the thermal stability of the POEGO:Li-Hectorite (1:1) nanocomposites are enhanced by approximately 238 °C when compared to pristine POEGO. Further characterization using AC impedance spectroscopy confirms that the Li-POEGO:Li-Hectorite nanocomposites are ionically conductive. DSC confirms the glass transition temperature of the nanocomposites remains relatively the same upon intercalation, indicating the polymer chains are still flexible at low temperatures, which are well below lithium-ion cell operation temperatures. ATR spectroscopy confirmed the polymer chains remain relatively flexible upon intercalation and do not affect the rigidity of the nanocomposites. In conclusion, the data obtained for the nanocomposites indicates that the materials are promising as electrolytes in lithium-ion polymer cells. 69 Chapter 5: POMOE/Lithium Hectorite Results and Discussion 5.1 Powder X-ray Diffraction Powder X-ray diffraction was used to determine the crystallinity of the nanocomposites by monitoring the basal spacing (d-spacing) of lithium hectorite (Li-Hectorite) upon the intercalation of POMOE. The XRD data was used to confirm if varying the molar ratio of POMOE has an effect on the basal spacing of the Li-Hectorite, and whether intercalation was successful. Figure 5-33 illustrates the increased basal spacing of the POMOE:Li-Hectorite nanocomposite ( 1 :1 ) compared to the control. 10 20 30 40 50 61 2-Theta - Scale Figure 5-33: XRD of a) Li-Hectorite:H20 and b) POMOE:Li-Hectorite Nanocomposite (1:1) The molar ratio of POMOE with respect to the Li-Hectorite was systematically increased from 0.25 to 4. The net layer expansion was calculated by determining the difference between 70 the basal spacing of the synthesized nanocomposites and the basal spacing of the dry Li- Hectorite heated to 650 °C (d-spacing=9.5 A). For example, a 1:1 POMOE:Li-Hectorite nanocomposite has a basal spacing of 18.4 A, which implies a net interlayer expansion of 8.9 A. The XRD data of the nanocomposites is summarized in Table 5-11. Table 5-11: Summary of XRD data Average POMOE: Li-Hectorite Basal spacing Net expansion Material Crystallite Size (Mol) (A) (A) (A) POMOE 0.25:1 18.2 8.7 1 1 0 0.5:1 18.3 8 . 8 106 1 : 1 18.4 8.9 103 2 : 1 18.5 9.0 97 4:1 18.5 9.0 92 Na-Hectorite --- 1 0 . 0 --- 140 Dry Li- 182 --- 9.50 Hectorite As shown in Table 5-11, increasing the molar ratio of the polymer to the layered host appeared to have no effect on the interlayer expansion of the layered structure. This could be due to the POMOE highly orienting itself in multiple layers in a stacked manner within the layered matrix, while the excess polymer remains outside the layers. From the XRD difffactograms of the nanocomposites, the average crystallite size was also determined using the Scherrer formula." The crystallite size appeared to decrease upon increasing the POMOE molar ratios to 71 the Li-Hectorite, indicating that the amorphous polymer reduces the crystallite size with higher polymer ratios. Lithium Hectorite 18.4 A Lithium Hectorite Figure 5-34: Schematic of POMOE layers in Lithium Hectorite (1:1) The cross-sectional dimensions of POMOE were calculated using molecular modeling (5 (Spartan ’08)102, and the largest possible dimension measured, assuming the polymer is linear, was found to be approximately 3.1 A. This indicates that for a 1 : 1 nanocomposite, the intercalated polymer is in a bilayer arrangement, which correlates well with the observed net interlayer expansion of 8.9 A. Furthermore, it is important to note that the polymer is assumed to intercalate linearly between the layers. However, due to the polymer flexibility it is possible that the polymer orientation within the layers is quite random. A schematic diagram showing the bilayer arrangement of POMOE in the layered structure is illustrated in Figure 5-34, assuming the polymer is oriented in a linear fashion within the layers. The amount of POMOE packed in a crystallographic unit cell was determined using the basal plane area per formula unit of Hectorite (16 A), and the area of a POMOE monomer. Assuming the polymer is linear, the dimensions determined are 3.1 A and 35 A, indicating a projected area of 108 A for a bilayer of POMOE. Therefore the ratio of Hectorite/POMOE is 72 0.29 in a single unit cell for a single layer of POMOE. A sample calculation is provided in the appendix, Table A-24. 5.2 Thermogravimetric Analysis Thermogravimetric analysis was used to investigate the thermal stability of the pristine POMOE, nanocomposites, and the salt-complexed materials in air. The thermograms were also used to calculate the stoichiometry of the nanocomposites. Figure 5-35 illustrates the thermograms of the pristine POMOE, POMOE:Li-Hectorite nanocomposite (1:1), Li-POMOE, and Li-POMOE:Li-Hectorite nanocomposite (1:1). 100 80- 60- O) I 40- 20 - 0 100 200 300 400500 600 Temperature (°C) Universal V4.7A TA Instruments Figure 5-35: TGA thermograms a) POMOE:Li-Hectorite (1:1) b) Li-POMOE:Li-Hectorite (1:1) c) Li-POMOE d) POMOE 73 As shown in Figure 5-35, the synthesized nanocomposites (Figure 5-35 (a) and (b)) show three weight loss steps. The first weight loss step at approximately 100 °C is minimal and represents the loss of water, while the second decomposition is ascribed to externally lying POMOE. The third and final step represents intercalated POMOE, which occurs after the decomposition of POMOE (which has fully decomposed at 300 °C). The final decomposition step is not as distinct as the second step in the TGA thermograms due to the gradual decomposition of the intercalated POMOE rather than the defined weight loss step observed in externally lying polymer. The TGA thermogram of the Li-POMOE:Li-Hectorite nanocomposite (1:1) (Figure 5-35 (b)) was compared to the Li-POMOE thermogram (Figure 5-35 (c)), and it was observed that the decomposition pattern near 415 °C of both thermograms is similar due to the decomposition of lithium triflate salt. The lithium triflate salt decomposes over the same region as the intercalated polymer found in (Figures 5-35 (a)). Therefore due to this decomposition overlap near the 415 °C region, the onset decomposition temperatures of the externally lying/intercalated polymer, and stoichometry calculations were determined using the non-salt complexed materials. The thermal data for the POMOE nanocomposites are displayed in Table 5-12. 74 Table 5-12: Summary or TGA data Polymer POMOE: Li-Hectorite (Mol) Ta(°C) Tb(°C) ATc(°C) POMOE N/A 186 N/A N/A 0.25:1 255 325 139 0.5:1 230 320 134 1 : 1 185 320 134 2 : 1 175 318 132 4:1 171 300 114 a=Onset decomposition temperature of the externally lying POMOE b=Onset decomposition temperature of intercalated POMOE c=Difference in decomposition temperature of intercalated polymer and pristine polymer At low POMOE molar ratios (0.25, 0.50) the onset decomposition temperature of the nanocomposite was enhanced by 69 °C and 44 °C, respectively. Therefore at the 0.25 POMOE ratio, it is possible that POMOE was mostly intercalated between the layers and less likely to be externally lying, indicating maximum percentage of intercalated POMOE versus externally lying POMOE at this low ratio. The TGA data of the POMOE:Li-Hectorite nanocomposites reveals an important trend for polymer ratios above 0.5. As shown in Table 5-12, a thermal enhancement of 134 °C is observed for the intercalated POMOE. However, this thermal enhancement was similar for the entire polymer ratios used, indicating that increasing the amount of the polymer with respect to the Li-Hectorite does not necessarily affect the thermal stability of the nanocomposites. This data trend correlates well with the basal spacing of the nanocomposites as obtained from the XRD diffractograms. The XRD data is the same for all the polymeric ratios used, as shown in Table 5- 75 11, further indicating that a maximum amount of POMOE is intercalated into the layers of Li- Hectorite. This ultimately indicates similar thermal stability for the nanocomposites. The thermograms obtained from thermogravimetric analysis were used to calculate the stoichiometry of three decomposition steps mentioned above. Therefore we can calculate the approximate amount of water, externally lying polymer, and intercalated polymer within the layered host from the TGA thermograms. The data is summarized in Table 5-13. Table 5-13: Stoichiometry of POMOE:Li-Hectorite Nanocomposites POMOE:Li-Hectorite (Mol) Stoichiometry 0.25:1 (H20)o.65 (POMOEexOo.16 (POMOEm)o.ii (Li-Hectorite) 0.5:1 (H20 )i.2 (POMOEExt)o.27 (POMOEin)o. 14 (Li-Hectorite) 1:1 (H20)2.5 (POMOE exOo.95 (POMOEin)o.is (Li-Hectorite) 2:1 (H20)7.7 (POMOEExt)2.3 (POMOEin)o.25 (Li-Hectorite) 4:1 (H20 )2.2 (POMOEexOs.i (POMOE,n)o.20 (Li-Hectorite) The stoichiometry calculations are in good agreement with the XRD data, and the theoretical calculation of intercalated POMOE into a single crystallographic unit cell of Hectorite determined in section 5.1. This data further indicates that a maximum amount of POMOE is intercalated into Li-Hectorite. 5.3 Differential Scanning Calorimetry Differential scanning calorimetry was utilized to measure the glass transition temperature (Tg) of the pristine POMOE, pristine POMOE:Li-Hectorite nanocomposites, and the salt complexed materials. From the Tg shifts, the polymer flexibility was determined after the polymer was complexed with lithium triflate and upon intercalation into the layered host. Figure 76 5-36 illustrates the Tg observed for the pristine POMOE, pristine POMOE:Li-Hectorite nanocomposite (1:1), Li-POMOE, and Li-POMOE:Li-Hectorite nanocomposite (1:1). o.o -57.67°C O) 5 og LL. a>CO X -0.5 -100 -50 Exo Up Temperature (°C) Universal V4.7A TA Instruments Figure 5-36: DSC data for a) POMOE: Li-Hectorite (1:1) b) Li-POMOE:Li-Hectorite (1:1) c) POMOE d) Li-POMOE The pristine polymer exhibits a glass transition temperature at -60 °C and is in agreement with the literature ( - 6 6 °C) . 76 Prior to lithium salt addition, the glass transition temperature of the synthesized nanocomposite (Figure 5-36 (a)) is similar to that of pristine POMOE (Figure 5-36 ((c)), which indicates that the polymer remains flexible at relatively low temperatures. Therefore the nancomposites are still flexible and theoretically should not affect the ionic conductivity of 77 the material based on the theory of segmental motion .47 The glass transition temperature for the non salt-complexed nanocomposites is presented in Table 5-14. Table 5-14: Summary of DSC data Material POMOE: Li-Hectorite (Mol) Glass Transition Temperature (Tg) POMOE N/A -60 Li-POMOE N/A -56 0.25:1 0.5:1 -59 1 : 1 -57 2 : 1 -63 4:1 -63 Upon lithium triflate addition to the polymer and intercalation into Li-Hectorite (Figure 5-36 ((b)), a 10 °C increase in the Tg is observed. The increase in Tg indicates an increase in rigidity of the nanocomposites due to the crystalline nature of lithium triflate. Although the glass transition temperature has increased compared to the polymer, it remains well below the operational temperatures of lithium-ion cells. 5.4 Attenuated Total Reflectance Attenuated total reflectance spectroscopy was used to monitor the vibrations of pristine POMOE, Li-POMOE and the synthesized nanocomposites. The IR data is displayed in Figure 5- 37 and also summarized in Table 5-15. 78 Transmittance (%) wavelengths. Upon intercalation, the major shifts observed in the pristine POMOE (Figure 5-37 (Figure POMOE pristine the in observed shifts major the intercalation, Upon wavelengths. most likely due to O-H vibration from the Li-Hectorite framework. A similar trend was observed observed was trend similar A framework. Li-Hectorite the from vibration O-H to due likely most vibrations C-O-C the were (c)) 5-37 (Figure nanocomposites (1:1) POMOE:Li-Hectorite and (a)) lower to higher from shifts vibrational distinct the are spectra IR the in observed trends The in the salt-complexed materials Li-POMOE (Figure 5-37 (b)) and Li-POMOE:Li-Hectorite (1:1) Li-POMOE:Li-Hectorite and (b)) 5-37 (Figure Li-POMOE materials salt-complexed the in interaction between the polymer and the layered host. The appearance of a peak at 1600 cm 1600 at peak a of appearance The host. layered the and polymer the between interaction hf fo 19 cm 1095 from shift Figure 5-37: IR Spectra of a) POMOE b) Li-POMOE c) POMOE:Li-Hectorite (1:1) c)POMOE:Li-Hectorite Li-POMOE b) POMOE a) of Spectra IR 5-37: Figure 1 ' o 00c', n 13 cm 1030 and cm'1, 1060 to 002600 3000 d) Li-POMOE: Li-Hectorite (1:1) Li-POMOE: Li-Hectorite d) Wavenumber (cm'1) Wavenumber 79 1 ' to 984 cm'1. This indicates an enhanced enhanced an indicates This cm'1. 984 to 1600 1200 un un 2 1 ' is 400 nanocomposites (Figure 5-37 (d)), where the C-O-C vibrations also shifted to lower vibration upon intercalation. Table 5-15: Summary of IR data Major Vibrations (cm 1) POMOE Li-POMOE POMOE:Li- Li-POMOE:Li- Hectorite (1:1) Hectorite (1:1) Li-Hectorite HOH stretch N/A N/A 3685 3685 Hydroxyl 3467 3464 3447 3475 Sp'3 C-H stretch 2866 2868 2875 2875 Li-Hectorite HOH bend N/A N/A 1600 1646 OCH2 symmetric bend 1459 1457 1465 1457 CH2 symmetric bend 1349 1349 1351 1350 C-0 ester/ether/alcohol 1292/1248 — 1297/1249 — C-O-C stretch 1095/1030 1093/1030 1060/984 1061/984 CH2 rocking 945 946 984 984 CH2 rocking 848 845 845 846 c f 3 N/A 1253 N/A 1254 C-F deformation N/A 638 N/A 638 SO3 Asymmetric bend N/A 572 N/A 573 SO3 Symmetric bend N/A 518 N/A 518 —Peak overlap with lithium triflate CF3 stretch 80 5.5 AC Impedance Spectroscopy AC impedance spectroscopy was used to determine the resistance of the Li-POMOE, and Li-POMOE:Li-Hectorite nanocomposites. As shown in Figure 5-38, the Nyquist plot displays the impedance spectroscopy data of Li-POMOE:Li-Hectorite (1:1) and illustrates a typical curve observed for an ionic conductor, where the touchdown point of the curve before shooting up corresponds to the resistance (R) of the sample. A three-component equivalent circuit was used to achieve consistent resistance (R) values for the samples, and the data was fit into an equivalent circuit model using the program LEVMW. The circuit components are a resistor (R), constant- phase element (CPE), and a capacitor (C). The ionic conductivity is calculated based on the lowest R value obtained from the LEVMW model, and the dimensions of the sample. 3.50E+07 3.00E+07 o - -O 2.50E+07 CPE 2.00E+07 N ' 1.50E+07 1.00E+07 5.00E+06 0.00E+00 0.00E+00 1.00E+07 2.00E+07 3.00E+07 4.00E+07 5.00E+07 6.00E+07 7.00E+07 ReZ Figure 5-38: Nyquist plot of Li-POMOE:Li-Hectorite (1:1) at 300K 81 Variable ionic conductivity data of the synthesized Li-POMOE:Li-Hectorite nanocomposites with increasing molar ratios of Li-POMOE to Li-Hectorite are presented in Figure 5-39. When the molar ratio of Li-POMOE with respect to Li-Hectorite is increased, the ionic conductivity of the salt-complexed nanocomposites increased. The reason for this is due to the externally lying salt-complexed POMOE, which could still contribute to the ionic conductivity. Another reason for observing increased ionic conductivity could be due to the Li-Hectorite clay. Lithium ions were introduced into Li-Hectorite prior to intercalation, therefore these ions could be contributing to the enhanced ionic conductivity throughout the nanocomposite. However, this was not confirmed qualitatively. 1.00E-04 Hi < £ (/)u 1.00E-05 +■>>• ■Li-POMOE:Li-Hectorite > (1:1) U 3 • Li-POMOE:Li-Hectorite * o (8:1) oC 1.00E-06 u 1.00E-07 275 295 305 315285 Temperature (K) Figure 5-39: Conductivity of Li-POMOE:Li-Hectorite Nanocomposites 82 The ionic conductivity trend of the Li-POMOE:Li-Hectorite nanocomposites illustrates the enhanced ionic conductivity of the nanocomposites upon increasing molar ratios of Li- POMOE to Li-Hectorite. According to the data, the highest polymeric ratio of Li-POMOE to Li- 7(\ Hectorite (8:1) can retain the ionic conductivity of the polymer as observed in the literature. Although at such a high polymer ratio, the raw data (Figure A-62) displays two semicircles, this possibly indicates that there are two conduction paths at high POMOE ratios and diluted Li- Hectorite, one contributing from the nanocomposite and the other due to the externally lying polymer. The ionic conductivity data for varying molar ratios of Li-POMOE to Li-Hectorite is summarized in Table 5-16. Table 5-16: Ionic conductivity of Li-POMOE:Li-Hectorite Nanocomposites Li-POMOE:Li-Hectorite (Mol) Conductivity (O'1, cm 1) at 300K 0.25:1 --- 0.5:1 (1.18±0.29) x 10 1 : 1 (1.92±0.20) x 10 2 : 1 (6.1510.63) x 10 4:1 (4.9410.71) x 10 8 : 1 (4.7011.90) x 10 Li-POMOE/b 5.00 x 1 O' 5 The trend in the ionic conductivity of the Li-POMOE:Li-Hectorite nanocomposites increased upon increasing polymer to Li-Hectorite ratios. Ultimately the nanocomposite at high polymer ratio (8:1) achieved the same magnitude as Li-POMOE. Although there is an apparent increase 83 in the overall trend of the ionic conductivity, there is a dip in the ionic conductivity between molar ratios 2 and 4, this error is due to the difficulty in measuring a polymeric film using mechanical instruments. A dial caliper and a micrometer are used to determine the area of the polymer film, however, determining the polymer area requires an accurate measurement of the polymer film thickness using a micrometer. Since the polymer film is non-uniform at higher polymeric ratios, it is likely that there is error associated with the measurement. Therefore, this error is accounted for in the standard deviation presented in Table 5-10. 5.6 POMOE/Lithium Hectorite Conclusion The intercalation of varying molar ratios of POMOE into Li-Hectorite has been successfully carried out and characterized via TGA, DSC, ATR, XRD, and AC impedance spectroscopy. XRD data confirms the successful intercalation of POMOE into Li-Hectorite, while TGA shows an enhancement in the thermal stability of the materials. The TGA data illustrate that with increasing molar ratios of POMOE (0.25, 0.5, 1, 2, and 4), the amount of POMOE intercalated within the layers remains relatively the same. The amount of intercalated POMOE was further confirmed using theoretical calculation of the area of the polymer and the basal plane area per formula unit of Hectorite. Furthermore, at lower polymer ratios, such as 0.25, the polymer appears to be mostly intercalated and exhibits high thermal stability (approximately 250 °C). AC impedance spectroscopy confirms that the Li-POMOE:Li-Hectorite nanocomposites are ionically conductive. It was determined that at high Li-POMOE:Li-Hectorite ratio (8:1), the ionic conductivity obtained was nearly (4.70±1.90)xl0's S/cm. The ionic conductivity achieved by the nanocomposites is very close to the Li-POMOE prior to intercalation. DSC confirms the glass transition temperature of the nanocomposites remains well below operational temperatures of lithium-ion cells, while ATR spectroscopy confirms the polymer is still flexible upon intercalation. In conclusion, the data obtained for the nanocomposites indicate the ionic conductivity of the nanocomposites can indeed reach the ionic conductivity of the polymer, while enhancing the physical (thermal) properties of the polymer. 85 Chapter 6: MEEP/Lithium Hectorite Results and Discussion 6.1 Powder X-ray Diffraction Powder X-ray diffraction was utilized to monitor whether intercalation of MEEP into lithium hectorite (Li-Hectorite) was complete, and if varying the molar ratio of MEEP to Li- Hectorite affected the polymer loading into the layered structure. 2 10 20 30 40 SO a 2-Theta - Scale Figure 6-40: XRD of a) Li-Hectorite:H20 and b) MEEP:Li-Hectorite (1:1) Nanocomposite The difffactograms of Li-Hectorite:H2 0 and MEEP.Li-Hectorite (1:1) are displayed in Figure 6-40 to illustrate the enhancement in basal spacing(ie. d-spacing) of the layered host upon the intercalation of MEEP. The net interlayer expansion is obtained by subtracting the basal spacing of dry Li-Hectorite heated to 650 °C (d spacing = 9.5 A) from the basal spacing of the synthesized nanocomposite. For example, MEEP:Li-Hectorite (1:1) has a basal spacing of 21.7 86 A, which corresponds to an interlayer expansion of 1 2 . 2 A. The XRD data for all nanocomposites are summarized in Table 6-17. Table 6-17: Summary of XRD data Average MEEP: Li-Hectorite Basal spacing Net Expansion Material Crystallite (Mol) (A) (A) Size (A) MEEP 0.5:1 18.9 9.40 73 1 : 1 21.7 1 2 . 2 74 2 : 1 36.4 26.9 126 4:1 41.5 32.0 135 Na-Hectorite --- 1 0 . 0 --- 140 Dry Li- 182 --- 9.50 Hectorite The synthesized nanocomposites are crystalline as indicated by p-XRD, and when the molar ratio of MEEP increases with respect to the Li-Hectorite, a significant increase in the basal spacing is observed. From the XRD difffactograms of the nanocomposites, the average crystallite size was determined using the Scherrer formula." The crystallite size trend appeared to increase upon increasing the MEEP molar ratio to Li-Hectorite, this is possible due to the significant enhancement in basal spacing upon polymer loading into the layered structure. 87 Lithium Hectorite Lithium Hectorite Figure 6-41: Schematic arrangement of MEEP in Lithium Hectorite (1:1) The dimensions of MEEP were estimated using Spartan ’08, 1 theC\0 average dimension was determined for the largest possible distance between the ether oxygens on the R groups in MEEP, and was found to be approximately 7.9 A for one unit of MEEP. This indicates that a single layer of MEEP is inserted between the Li-Hectorite sheets for the MEEP:Li-Hectorite (1:1) nanocomposite, which had a net layer expansion of 1 2 . 2 A. The difference of 4.3 A between the observed basal spacing of the 1:1 nanocomposite and the calculated dimensions of MEEP could be due to the manner in which MEEP orients itself within the layers. MEEP is a highly flexible polymer and may not necessarily be oriented within the layers as depicted in Figure 6-41, and a helical conformation may also be possible. The amount of MEEP packed in a crystallographic unit cell was determined using the basal plane area per formula unit of Hectorite (16 A), and the area of a MEEP monomer. Assuming the polymer is linear, the dimensions determined are 7.9 A and 1 0 A, indicating a projected area of 79 A for a single layer of MEEP. Therefore the ratio of Hectorite/MEEP is 0.20 in a single unit cell for a single layer of MEEP. A sample calculation is provided in the appendix, Table A-24. 88 6.2 Thermogravimetric Analysis Thermogravimetric analysis was used to compare the thermal stability of MEEP, MEEP:Li-Heetorite, Li-MEEP, and Li-MEEP:Li-Hectorite. The objectives were to determine whether the salt-complexed materials have different thermal stability than their corresponding non salt-complexed counterparts, and to monitor the thermal stability of the nanocomposites upon varying the amount of the polymer used. The MEEP:Li-Hectorite thermograms were also used to calculate the stoichiometry of the synthesized nanocomposites. 100 80- 60- O) I 40- 2 0 - 0 200 600400 Temperature (°C) Universal V4.7A TA Instruments Figure 6-42: TGA thermograms a) Li-MEEP:Li-Hectorite (1:1) b) MEEP:Li-Hectorite (1:1) c) MEEP d) Li-MEEP 89 The thermogram of pristine MEEP (Figure 6-42 (c)) shows that it undergoes a major decomposition between 230-350 °C, followed by an onward gradual weight loss. Once MEEP was complexed with lithium salt, its decomposition is slightly compromised due to the presence of the salt which appeared to decrease the polymer onset decomposition temperature by approximately 30 °C; thereafter complete decomposition of the lithium triflate salt is observed at 420 °C (Figure 6-42 (d)). Upon polymer intercalation, the nancomposites thermograms appeared to have three weight loss steps, where the thermogram of MEEP:Li-Hectorite (1:1) (Figure 6-42 (b)) illustrates a small loss of water near 100 °C, followed by the decomposition at 178 °C corresponding to the presence of externally lying polymer. The final decomposition is the gradual decomposition of the intercalated MEEP occurring at 305 °C. This is quite similar to what was observed in the thermal behavior of Li-MEEP :Li-Hectorite (Figure 6-42 (a)), except for the decomposition of the salt which occurs at around 420 °C. The TGA data is summarized in Table 6-18. Table 6-18: Summary of TGA data Polymer MEEP:Li-Hectorite (Mol) T a (°C) Tb (°C) ATc(°C) MEEP N/A 240 N/A N/A Li-MEEP N/A 204 N/A N/A 0.5:1 205 312 72 1 : 1 178 305 65 2 : 1 176 315 75 4:1 170 324 84 a=Onset decomposition temperature of externally lying MEEP b=Onset decomposition temperature of intercalated MEEP c=Difference in decomposition temperature of the intercalated MEEP and pristine MEEP 90 As shown in Table 6-18, the onset decomposition temperature of the externally lying MEEP (Ta) for the synthesized MEEP:Li-Hectorite nanocomposites was lower than that of the bulk polymer, which occurs at 240 °C. However, with increasing MEEP molar ratios, the onset decomposition temperature of the intercalated MEEP (Tb) is significantly higher than that of the pristine MEEP, indicating an enhancement in the thermal stability of the intercalated polymer in the nanocomposites. Since the synthesized nanocomposites displayed three decomposition steps, the stoichiometry was calculated in order to compare the spread between externally lying and intercalated polymer. It is important to note that the stoichiometry was calculated for the MEEP:Li-Hectorite nanocomposites, and not the Li-MEEP nanocomposites due to the presence of lithium salt in the thermograms. The stoichiometry data of the synthesized nanocomposites are presented in Table 6-19. Table 6-19: Stoichiometry of MEEP:Li-Hectorite Nanocomposites MEEP: Li-Hectorite (Mol) Stoichiometry 0.5:1 (H2O)0.6i ( M E E P Ext)o.i7 (M E E P in )o.o23(Li-Hectorite) LI (H20 )o.42 (MEEPexOo.44 (M EEPin)o.o73(Li-Hectorite) 2 : 1 (H20 )o.48 (MEEPExt)o.7i(MEEPin)o.i2(Li-Hectorite) 4:1 (H20)o.34 (MEEPexOo.84 (M E E P in )o .i4 (Li-Hectorite) As shown in Table 6-19, when the molar ratio of MEEP increases with respect to the layered host, the amount of the externally lying and intercalated polymer increase, and this observation is consistent with the XRD data (Table 6-17), where the basal spacing of the intercalated nanocomposites increase upon increasing the amount of MEEP. In fact, the 4:1 nanocomposite 91 has nearly 200% more of the intercalated MEEP compared to the 1:1 MEEP:Li-Hectorite nanocomposite. The theoretical calculation of intercalated MEEP into a single crystallographic unit cell of Hectorite was determined in section 6.1 and is roughly in agreement with the amount of polymer intercalated into the lattice. 6.3 Differential Scanning Calorimetry Differential scanning calorimetry was utilized to monitor the glass transition temperature (Tg) of pristine MEEP, Li-MEEP and their corresponding synthesized nanocomposites. - 0.1 o> -71.35X § LL ©TO X -28.45'C - 0.6 -95 -45 Exo Up Temperature (°C) Universal V4.7A TA Instruments Figure 6-43: DSC data for a) MEEP: Li-Hectorite (1:1) b) Li-MEEP:Li-Hectorite (1:1) c) MEEP d) Li-MEEP 92 The DSC of pure MEEP indicates a Tg of -71 °C, which correlates well with previously reported literature (-83 °C ) . 8 8 Upon complexing MEEP with lithium triflate (LiCF 3 SC>3 ), the glass transition temperature (Tg) significantly increases to -28 °C due to the crystalline nature of lithium triflate. However, upon intercalation of pristine MEEP or Li-MEEP into Li-Hectorite, a Tg is not observed for any of the polymeric ratios used. Due to the lack of glass transition temperature in both Li-MEEP:Li-Hectorite and MEEP:Li-Hectorite nanocomposites, it is believed that either the oxygen atoms of the polymer are potentially interacting with the tetrahedral coordinated silicon atoms in the hectorite sheets and restricting chain mobility or the polymer is no longer flexible when it is intercalated in the layers of hectorite. The glass transition temperatures are displayed in Table 6-20. Table 6-20: Summary of DSC data Material MEEP: Li-Hectorite (Mol) Glass Transition Temperature (Tg) MEEP N/A -71 Li-MEEP N/A -28 0.5:1 — 1 : 1 -- 2 : 1 -- 4:1 -- 6.4 Attenuated Total Reflectance ATR spectroscopy was utilized to monitor the bond vibrations of MEEP, MEEP:Li- Hectorite, Li-MEEP, and Li-MEEP:Li-Hectorite. More specifically, it was important to determine whether intercalating MEEP or Li-MEEP into Li-Hectorite hinders the flexibility of the polymer, and ultimately its ionic conductivity. 93 Transmittance (%) vibration of the polymer shifts to 1251 cm'1, and ultimately to 1257 cm 1257 to ultimately and cm'1, 1251 to shifts polymer the of vibration h icesd iiiy fte oye sd can. hrfr te R aa uprs h lc of lack the supports data IR the Therefore chains. side polymer the of rigidity increased the P-O- The backbone. polymer of the rigidity increased the of indicative is bond P=N the of vibrational energy in increase successive This (d)). 6-44 (Figure nanocomposites MEEP: Li-Hectorite irto lo hfs rm99 cm 959 from shifts also vibration C 1243cm Figure 6-44: IR Spectra of a) MEEP b) Li-MEEP: Li-Hectorite (1:1) c) Li-MEEP c) (1:1) Li-Hectorite Li-MEEP: b) MEEP a) of Spectra IR 6-44: Figure rmte R aa i i osre htte = vbain ntepr plmr cus at occurs polymer pure the in vibration P=N the that observed is it data, IR the From 1 ' in Figure 6-44 (a). Upon complexation with lithium triflate (Figure 6-44 (b)), the P=N the (b)), 6-44 (Figure triflate lithium with complexation Upon (a). 6-44 Figure in 3000 d) Li-MEEP:Li-Hectorite (1:1) Li-MEEP:Li-Hectorite d) 1 ' n EPt 92 cm 972 to MEEP in 2000 Wavenumber (cm'1) Wavenumber 94 1 ' upon intercalation, which indicates indicates which intercalation, upon 1 " in the synthesized Li- synthesized the in 1000 000 flexibility that was observed in the DSC results upon polymer intercalation. The various bond QQ vibrations from the IR data are summarized in Table 6-21. Table 6-21: Summary of IR data Major Vibrations MEEP MEEPrLi- Li-MEEP Li-MEEP :Li- (cm 1) Hectorite(l:l) Hectorite(l:l) Li-Hectorite HOH N/A 3686 N/A 3624 stretch Sp3 C-H stretch/bend 2877/1457 2883/1457 2896/1457 2887/1457 P=N 1243 1242 1251 1257 P-O-C 959 967 980 972 C-O-C ether 1199-1043 1 2 0 1 1170-1036 1189 PNP skeletal 849/803/753 848/801/757 855/766 798/768 c f 3 N/A N/A 1249 1253 C-F deformation N/A N/A 638 638 S0 3 asymmetric bend N/A N/A 573 573 SO3 symmetric bend N/A N/A 518 518 6.5 AC Impedance Spectroscopy AC impedance measurements were conducted on Li-MEEP, and Li-MEEP:Li-Hectorite nanocomposites. Since the DSC and IR data indicated that polymer chain flexibility was restricted in the nanocomposites, it was necessary to investigate the ionic conductivity properties 95 of Li-MEEP prior to intercalation and post intercalation. The room temperature ionic conductivity of Li-MEEP was determined to be (1.29±0.04) x 10‘5 S/cm. However, upon intercalation of Li-MEEP into the Li-Hectorite layers, the resistance observed was high and beyond our detection limits. These observations further indicate that there is an interaction occurring between the polymer and the layered structure that is ultimately inhibiting the synthesized nanocomposites from conducting lithium ions. The Nyquist plot is displayed in Figure 6-45, and demonstrates the ionic characteristics of Li-MEEP. 3.50E+07 3.00E+07 2.50E+07 £T 2.00E+07 N E T 1.50E+07 1.00E+07 -0O- 5.00E+06 0.00E+00 O.OOE+OO 2.00E+07 4.00E+07 6.00E+07 8.00E+07 1.00E+08 1.20E+08 1.40E+08 Re Z (Q) Figure 6-45: Nyquist plot of Li-MEEP at 300K As shown in the Nyquist plot, Figure 6-45, Li-MEEP demonstrates a typical curve observed for an ionic conductor, where the touchdown point before shooting up corresponds to the resistance 96 (R) of the sample at a particular temperature. The value of R and the dimensions of the sample are used to calculate the ionic conductivity of the sample, shown in Figure 6-46. In order to obtain more accurate values of R for the ionic conductivity calculation, a complex non-linear 1 ft’? least-square fit was made to an equivalent circuit model using the program LEVMW. A three- component equivalent circuit consisting of a resistor (R), a constant-phase element (CPE), and a capacitor (C) was used and is displayed in Figure 6-45. Using the resistance value and the dimensions of the polymeric film, the ionic conductivity of Li-MEEP was calculated and a plot is displayed in Figure 6-46. 0.0001 Hi < UE IE-05 I/) >« > •4-> M U 3 "O IE-06 c o u IE-07 9 20270280 290260 300250 310 320 Temperature (K) Figure 6-46: Conductivity plot of Li-MEEP 97 6.6 MEEP/Lithium Hectorite Conclusion A series of MEEP molar ratios have been successfully intercalated into Li-Hectorite and the nanocomposites were characterized via TGA, DSC, ATR, p-XRD, and AC impedance spectroscopy. P-XRD data confirm successful intercalation of MEEP into the layered silicate, while TGA was utilized to investigate the thermal stability and stoichiometry of the nanocomposites. The TGA data confirm that increasing molar ratios of MEEP (0.5, 1, 2, 4) result in a larger amount of the polymer within the layers. In fact, the 4:1 MEEP:Li-Hectorite nanocomposite has approximately 200% more of the intercalated MEEP versus the 1:1 MEEP:Li-Hectorite nanocomposite. The amount of intercalated MEEP was further confirmed using theoretical calculation of the area of the polymer and the basal plane area per formula unit of Hectorite. TGA data also indicates an enhancement in thermal stability of the intercalated polymer versus the pristine polymer, for all molar ratios. For instance, the 1:1 MEEP:Li- Hectorite nanocomposite begins thermal decomposition of the intercalated polymer at 305 °C, while the pristine polymer begins to decompose at 240 °C. The room temperature ionic conductivity of Li-MEEP was determined to be (1.29±0.04) x 10'5 S/cm, although once Li- MEEP was intercalated into the Li-Hectorite, it displayed high ionic resistance with no measurable ionic conductivity. This is further supported with DSC data, where there was no measurable glass transition temperature in any of the synthesized nanocomposites. ATR spectroscopy also reaffirmed polymer backbone rigidity upon lithium salt complexation and intercalation into Li-Hectorite. 98 Chapter 7: Summary In summary, a series of polymer (POEGO, POMOE, and MEEP) molar ratios were intercalated into the layers of Li-Hectorite. The varying polymer molar ratios allowed us to monitor the effect polymer loading has on the layered structure, and the ionic conductivity of the nanocomposites. The ultimate goal was to report whether the synthesized nanocomposites would be rendered useful as solid polymer electrolyte in lithium-ion polymer batteries. Further work on the nanocomposites should involve an improved methodology for making polymeric films on the substrates for AC Impedance Spectroscopy. 7.1 POEGO:Li-Hectorite Nanocomposites > The successful intercalation of varying POEGO molar ratios into Li-Hectorite was reported and an increased amount of POEGO was observed within the layers of Li-Hectorite upon increasing polymer molar ratios. The thermal stability of the intercalated polymer was enhanced compared to the pristine polymer, along with the ionic conductivity once the polymer was complexed with lithium triflate. Future work on these nanocomposites should involve the construction of varying ratios of Li-POEGO:Li-Hectorite nanocomposites and test their potential as solid polymer electrolytes in a lithium-ion polymer cell. 7.2 POMOE:Li-Hectorite Nanocomposites A series of POMOE molar ratios to Li-Hectorite nanocomposites were successfully synthesized and investigated for their potential as solid polymer electrolytes. Upon reviewing the data, it was apparent that a maximum amount of POMOE may be intercalated into the layers of hectorite, while the rest of the polymer remained externally lying in the nanocomposites. Furthermore, once lithium triflate salt was complexed with the POMOE and intercalated into Li- 99 Hectorite, there was a direct relationship between the polymer ratio and the ionic conductivity. This relationship indicated higher ionic conductivity of the nanocomposites with increasing polymer molar ratios. Therefore future work should involve determining the viability of Li- POMOE:Li-Hectorite nanocomposites as solid polymer electrolytes in lithium-ion polymer cells. 7.3 MEEP:Li-Hectorite Nanocomposites A series of MEEP molar ratios were successfully intercalated into Li-Hectorite. The polymer loading increased with increasing MEEP molar ratios. Upon complexing the polymer with lithium salt, the ionic conductivity was determined and was found to be within the ideal range required for solid polymer electrolytes. However, once the polymer was intercalated into the layered structure, it did not possess any ionic characteristics and ultimately ionic conductivity was not detected. Further investigation using DSC and ATR illustrated that the MEEP:Li- Hectorite nanocomposites do not possess any glass transition temperatures, indicating an increase in the polymer rigidity once it was intercalated. Therefore, if future work was to be conducted on this system, it could involve higher ratios of salt-complexed MEEP to Li-Hectorite beyond 4:1. Since the salt-complexed MEEP itself displayed ionic characteristics, it is possible to observe ionic conductivity with higher Li-MEEP molar ratios to Li-Hectorite, although ionic conductivity was undetected in all of the molar ratios (0.5, 1, 2, 4). Otherwise, this material may not suffice as a solid polymer electrolyte in lithium-ion polymer cells. 100 Appendix Sample: IS 1-33A Re-Li-Hect P0G0E1-1Hir File: IS 1-33A Re-Li-Hect P0EG01-1 ratio Hi... Size: 18.5950 mg TGA Operator IS Method: Hi-Res - Dynamic Run Date: 09-Aug-2010 17:56 Comment: 1:1 in Air HiRES Instrument TGA Q500 V6.7 Build 203 100 93.45% -20 80- -15 cn 60- 1 -10 Deriv. Deriv. Weight (%/min) 42.51% 40- 37.64% 0 100 200 300 400 500 600 Temperature (°C) Universal V4.7A TA Instruments Figure A-47: TGA of 1:1 POEGO:Li-Hectorite nanocomposite for stoichiometry Table A-22: TGA Stoichiometry sample calculation Known->Li-Hectorite = 383.25 (g/mol) = 37.64% sample residue Step 1 ->42.50% = (Intercalated polymer)x Li-Hectorite = ? 383.25 (g/moD x 42.50% = 432.73 g/mol 37.64% (Intercalated polymer)x + 383.25 (g/mol) = 432.73 (g/mol), Where Intercalated polymer = molar mass of POEGO = 453.47 (g/mol) Therefore, x= 432.73 (g/mol) - 383.25 (g/mol) = 0.109 = (polymer)int (Intercalated polymer) Step 2->93.46% = (Intercalated polymer)x (External polymer)y Li-Hectorite = ? 432.73 (g/mol) x 93.46% = 951.61 g/mol 101 42.50% (External polymer)y + 432.73 (g/mol) = 951.61 (g/mol), Where External polymer = molar mass of polymer Therefore. v= 951.61 (g/mol) - 432.73 (e/moll = 1.14 = (polymer)Ext (External polymer) Step 3-> 100% = (H20)z (Intercalated polymer)x (External polymer)y Li-Hectorite = ? 951.61 (g/mol) x 100% = 1018.2 g/mol 93.46% (H20)z = 1018.2 (g/mol) - 951.61 (g/mol), Where H2 O = molar mass of water Therefore, z= 1018.2 (g/mol) - 951.61 ('g/mol) =3.70 = (H2 O) (H20) TGA stoichiometry for POEGO:Li-Hectorite (1:1) = ( ^ 0 )3 .7 0 (POEGOexOi.m (POEGOinOo.ii Li- Hectorite Table A-23: Calculation of Ionic Conductivity Resistivity(p)= Resistance (TO x Width (ml x Thickness (ml Length ( m) Conductivity (0) = J. Resistivity (p) 102 Table A-24: Polymer packed in Hectorite crystallographic unit cell i) Basal plane area per formula unit of Hectorite =a x b= 16 A Z where a (5.25 A) and b (9.18) are the dimensions of Hectorite unit cell, Z (3) is the number of formula units in crystallographic unit cell (where one formula unit = Nao.4Mg2.7Lio.3Si40io(OH)2) ii) Area of a single layer of polymer = c x d 2 or 1 Where c (width of polymer in A) and d (length of the polymer in A, assuming it is linear), 2 or 1 depends on whether the polymer is assumed to be in a bilayer or single layer arrangement in the layered structure iii) Ratio of Hectorite to polymer = Basal plane area per formula unit of Hectorite (i) Area of a single layer of polymer (ii) POEGO Area of a single layer of POMOE = 3.5 A x 28 A = 49 A 2 Ratio of Hectorite to POEGO = 16 A = 0.33 A 49 A POMOE Area of a single layer of POMOE = 3.1 A x 35 A = 54 A 2 Ratio of Hectorite to POMOE = 16 A = 0.30 A 54 A MEEP Area of a single layer of MEEP = 7 A x 10 A = 35 A 1 Ratio of Hectorite to MEEP = 16 A - 0.23 A 70 A 103 c/d b e 2!(| uiiii n b b ww B \l \l r — 1— T —!— T- T 8 4 .2 4 .0 3.8 3 .2 3.0 2.8 ppm ?r m m Figure A-48: ’H NMR spectrum of MEEP a c/d b e K KB 72 71 70 69 68 67 6 6 65 64 63 62 61 60 5958 57 56 ppm73 Figure A-49: 13C NMR spectrum of MEEP 104 500 400 c Li 200 100 0 2 10 20 30 40 SO 9 2-Theta - Scale Figure A-50: XRD data for a) POMOE b) POEGO c) MEEP 1 I 1 1 *‘ i |-r ..i- r-t-i > 1 i | * i 1 i I * ~1 1 1 j 1 1 1 1 I 1 1 1 1 I 1 1 1 1 * 1 1 > |' » r 1 -i r—r r-| 2 10 20 30 40 SO 9 ^.Thflta - RtpIp Figure A-51:XRD data for a) POEGO:Li-Hectorite (2:1) b) POEGO:Li-Hectorite (1/2:1) c) POEGO: Li-Hectorite (4:1) Nanocomposites 105 100 182.40°C 80- 60- JZ cp I 40- 2 0 - 100 200 300 400 500 600 700 Temperature (°C) Universal V4.7A TA Instruments Figure A-52:TGA data for a) POEGOrLi-Hectorite (1/2:1) b) POEGO:Li-Hectorite (2:1) c) POEGO:Li-Hectorite (4:1) Nanocomposites -0.05 0 3 5 | -0.25- ll. 0)<0 X -0.45 -95 -45 ExoUp Temperature (°C) Universal V4.7ATA Instruments Figure A-53: DSC data for a) POEGO:Li-Hectorite (1/2:1) b) POEGO:Li-Hectorite (2:1) c) POEGO:Li-Hectorite (4:1) Nanocomposites 106 -imz(o) -ImZ(Q) 4.00E+08 3.00E+08 3.50E+08 2.50E+08 0.00E+00 4.00E+07 8.00E+07 5.00E+07 2.00E+08 0.00E+00 2.00E+07 6.00E+07 1.80E+08 2.00E+08 1.20E+08 1.60E+08 1.00E+08 1.50E+08 1.00E+08 1.40E+08 0.00E+00 .0+0 .0+7 .0+8 1.50E+08 1.00E+08 5.00E+07 0.00E+00 v r ------IS2-57B Cast Film - Li POEGO:Li-Hectorite (2:1) Li POEGO:Li-Hectorite - Film Cast IS2-57B rv Figure A-54: AC Impedance Spectroscopy raw data raw Spectroscopy Impedance AC A-54: Figure Figure A-55: AC Impedance Spectroscopy raw data raw Spectroscopy Impedance AC A-55: Figure IS2-57C Cast Film - Li POEGO:Li-Hectorite (4:1) Li- Film POEGO:Li-Hectorite IS2-57CCast a # -+kA Y js ' + • ^ * A X * V mm A X ® + X— m .0+8 .0+830E0 4.00E+08 3.00E+08 2.00E+08 1.00E+08 ..... i ■ ..... r f k .. X ...... a L J . . . + 3 + m A NX A ------Re Z (Cl)Re t I Re ZRe (O) - A 107 ■ f X ® A ■ V \ A' A .... A ■ 1 — A A Aa A A gA A A A A ------— ± 2.D0E+08 X .... ▲ A X - at re tu ra e p m e T r ure tu era p m e T 0 K 300 ■ K 310 ♦ • 260 K 260 • A X X X ■ 300 K 300 ■ K 310 ♦ • 260 K 260 • A X 270 K 270 X X 270 K 270 K 280 K 290 290 K 290 8 K 280 (a) (b) (c) (d) 2-Thet3 - 3csl6 Figure A-56: XRD data for a) POMOE:Li-Hectorite (1/4:1) b) POMOE:Li-Hectorite (1/2:1) c) POMOE:Li-Hectorite (2:1) d) POMOE:Li-Hectorite (4:1) Nanocomposites 100 V ------—A—'—-Kj30-36"0 " ------J '4\_265.09"C 175.62°C I \' V 80- JZg> 60- I 40- 318.66®C 20 100 200 300 400 500 600 700 Temperature (°C) Universal V4.7A TA Instruments Figure A-57: TGA data for a) POMOE:Li-Hectorite (1/4:1) b) POMOE:Li-Hectorite (1/2:1) c) POMOE:Li-Hectorite (2:1) d) POMOE:Li-Hectorite (4:1) Nanocomposites 108 0.0 CD § I LL -0.5 -95 -50 exo up Temperature (°C) • Universal V4.7A TA Instruments Figure A-58: DSC data for a) POMOE:Li-Hectorite (1/4:1) b) POMOE:Li-Hectorite (1/2:1) c) POMOE:Li-Hectorite (2:1) d) POMOE:Li-Hectorite (4:1) Nanocomposites IS2-77A Cast Film - Li-POMOE:Li-Hectorite (1/2:1) 2.00E+09 + • 1.80E+09 X X • X X 1.60E+09 X XX Temperature 1.40E+09 • • ♦ 310 K 1.20E+09 X • ■ 300 K ▲ 1.00E+09 ▲ 290 K a ▲ ▲ * . . ▲ ▲ ▲ N 8.00E+08 X 280 K 1 ► E , A ► X 270 K l 6.00E+08 > • 260 K 4.00E+08 + 240K 2.00E+08 - 220 K 0.00E+00 0.00E+00 5.00E+08 1.00E+09 1.50E+09 2.00E+09 2.50E+09 Re Z (O) Figure A-59: AC Impedance Spectroscopy raw data 109 Figure A-60: AC Impedance Spectroscopy raw data raw Spectroscopy Impedance AC A-60: Figure -Im Z (ft) 4.00E+07 0.00E+00 8.00E+07 2.00E+08 2.00E+07 6.00E+07 1.20E+08 1.80E+08 1.00E+08 1.40E+08 1.60E+08 IM G I 1 4.00E+06 1.80E+07 2.00E+07 0.00E+00 8.00E+06 1.00E+07 1.20E+07 1.40E+07 1.60E+07 2.00E+06 6.00E+06 .0+050E0 1.00E+08 5.00E+07 0.00E+00 % .0+0 .0+720E0 3.00E+07 2.00E+07 1.00E+07 1.00E+00 -K . M * , M • T m X x IS2-77C Cast Film - U-POMOE:Li-Hectorite (2:1) U-POMOE:Li-Hectorite - Film Cast IS2-77C Figure A-61: AC Impedance Spectroscopy raw data raw Spectroscopy Impedance AC A-61: Figure IS2-77G Cast Film - Li-POMOE:Li-Hectorite (4:1) Li-POMOE:Li-Hectorite - Film Cast IS2-77G x , j ♦ ♦ ------m " ■ ♦ F a .... ^ .... A * i A 1 T j A A ReZ (ft) ------X Re Z Re ■ / 110 ■ (Cl) ------♦ A ♦ 1.50E+08 4.00E+07 2.00E+08 r ure tu era p m e T at re tu ra e p m e T -220K A 290 K 290 A K 300 ■ K 310 ♦ 4- K 260 • K 270 X K 280 X - 240 K 240 - 250 k 250 = 220 K 220 = K 260 • K 290 A K 300 ■ K 310 ♦ X 270 K 270 X K 280 X 20 250K + 240K K 0 4 -2 IS2-77E Cast Film run2- Li-POMOE:Li-Hectorite (8:1) 5.00E+06 X A 4.50E+06 X Temperature 4.00E+06 Ml X X A ♦ 310 K 3.50E+06 ► A ■ 300 K A ■--* 3.00E+06 v A A 290 K c i f A ~ X 280 K N 2.50E+06 E JT X 270 K T 2.00E+06 X , ■ • 260 K 1.50E+06 k ■ ■■ + 250K - 240 K 1.00E+06 — 220 K 5.00E+05 r ^ v / i ■ ▼ A O.OOE+OO O.OOE+OO 2.00E+06 4.00E+06 6.00E+06 8.00E+06 1.00E+07 Re Z (O) Figure A-62: AC Impedance Spectroscopy raw data 2000 ■E3 oo c 1000 0 2 10 20 X 40 9 s ■ Scdle Figure A-63: XRD data for a) MEEP:Li-Hectorite (1/2:1) b) MEEPrLi-Hectorite (2:1) c) MEEP: Li-Hectorite (4:1) Nanocomposites 111 100 312.70°C 80- o> I 315.51 *C 60- 200 400 600 Temperature (°C) Universal V4.7A TA Instruments Figure A-64: TGA data for a) MEEP:Li-Hectorite (1/2:1) b) MEEP:Li-Hectorite (2:1) c) MEEP:Li-Hectorite (4:1) Nanocomposites 0.0 o> I § 0.2 - - u. a)CO I (b) " -95 -46 ExoUp Temperature (°C) Universai V4.7A TA Instruments Figure A-65: DSC data for a) MEEP:Li-Hectorite (1/2:1) b) MEEP:Li-Hectorite (2:1) c) MEEP:Li-Hectorite (4:1) Nanocomposites 112 References (1) Panero, S., Settimi, L., Croce, F.; Scrosati, B. 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