USOO9105402B2

(12) United States Patent (10) Patent No.: US 9,105,402 B2 Sassin et al. (45) Date of Patent: *Aug. 11, 2015

(54) COMPOSITE ELECTRODESTRUCTURE HOLM 4/1393 (2010.01) HOLM 4/583 (2010.01) (71) Applicants: Megan B. Sassin, Alexandria, VA (US); HOIM IO/O525 (2010.01) Jeffrey W. Long, Alexandria, VA (US); (52) U.S. C. Debra R. Rollison, Arlington, VA (US) CPC ...... H0IG 9/042 (2013.01); H0IG 9/048 (2013.01); H0IG 9/145 (2013.01); H0IM (72) Inventors: Megan B. Sassin, Alexandria, VA (US); 4/133 (2013.01); H0IM 4/1393 (2013.01); Jeffrey W. Long, Alexandria, VA (US); H0IM 4/583 (2013.01); HOIM 10/0525 Debra R. Rollison, Arlington, VA (US) (2013.01); Y02E 60/122 (2013.01) (58) Field of Classification Search (73) Assignee: The United States of America, as None represented by the Secretary of the See application file for complete search history. Navy, Washington, DC (US) (56) References Cited (*) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S. PATENT DOCUMENTS U.S.C. 154(b) by 0 days. 2002/014 1964 A1* 10, 2002 Patterson et al...... 424/78.1 This patent is Subject to a terminal dis 2007/0048614 A1* 3/2007 Long et al...... 429,245 claimer. 2008/0248192 A1* 10/2008 Long et al...... 427/80 2009/0185327 A1* 7/2009 Seymour ...... 361,500 (21) Appl. No.: 14/572,365 * cited by examiner (22) Filed: Dec. 16, 2014 Primary Examiner — Barbara Gilliam Assistant Examiner — Adam A Arciero (65) Prior Publication Data (74) Attorney, Agent, or Firm — US Naval Research US 2015/O103471 A1 Apr. 16, 2015 Laboratory; Stephen T. Hunnius Related U.S. Application Data (57) ABSTRACT A method of storing charge comprising the steps of providing (62) Division of application No. 12/644,604, filed on Dec. a capacitor comprising an anode, a cathode, and an electro 22, 2009, now Pat. No. 9,058,931. lyte, wherein the electrolyte comprises a nonaqueous liquid (60) Provisional application No. 61/143,903, filed on Jan. of sufficient dielectric constant to dissociate salts soluble in 12, 2009. the nonaqueous liquid, a composite comprising a prefabri cated porous carbon electrode structure or a carbon foam (51) Int. C. Substrate that is a prefabricated paper structure and a coating HOIG 9/042 (2006.01) deposited by infiltrating the structure with oxide via HOIG 9/048 (2006.01) self-limiting electroless deposition on the Surface. HOIG 9/45 (2006.01) HOLM 4/33 (2010.01) 10 Claims, 6 Drawing Sheets

::::::::::::::::::::::::::::8 f : M . . 3', U.S. Patent Aug. 11, 2015 Sheet 1 of 6 US 9,105,402 B2

::::::::::::::::::::::::::::::ge {3 - 3 - 3 3 ct: Figure 1 U.S. Patent Aug. 11, 2015 Sheet 2 of 6 US 9,105,402 B2

Figure 2 U.S. Patent Aug. 11, 2015 Sheet 3 of 6 US 9,105,402 B2

8000 '''''''''''''''' B are carbon so e o e o a 40 h. Fe Ox-Carbon 6000

e 4000 O | 2000 e

e.i

Energy, keV

Figure 3 U.S. Patent Aug. 11, 2015 Sheet 4 of 6 US 9,105,402 B2

7.5e-3 ...... - Bare Carbon \ -o- 20 h FeCDX 6.0e-3 -O- 40 h. FeOX o - 5 4.5e-3

E 3.0e-3 O D GD5 1.5e-3 n 0.0 O 5 10 5 20 25 30 Pore Width (nm)

Figure 4 U.S. Patent Aug. 11, 2015 Sheet 5 of 6 US 9,105,402 B2

150 Bare Carb. On Fe Ox-Carbon 100 'o 50 d

O O

s -50

- 1 OO

- 150 -0.8 -0.6 -0.4 -0.2 O.O 0.2 Potential (V vs. Ag|AgCl)

Figure 5 U.S. Patent Aug. 11, 2015 Sheet 6 of 6 US 9,105,402 B2

0.06

0.04

0.02

0.00

-0.02 i 0.04 -0.06

-0.08

-0. 10 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Potential (V vs. Li)

Figure 6 US 9,105,402 B2 1. 2 COMPOSITE ELECTRODESTRUCTURE ing of the pores of the after incorporation of the FeCx coatings, but with retention of a through-connected This application claims priority to U.S. patent application pore structure. Ser. No. 61/143,903 filed Jan. 12, 2009 and U.S. patent appli FIG.5 illustrates specific capacitance versus potential for a cation Ser. No. 12/644,604 filed on Dec. 22, 2009, the entirety bare carbon nanofoam and a FeCX-coated carbon nanofoam of each are herein incorporated by reference. in aqueous 2.5 M LiSO at a Voltammetric scan rate of 5 Multifunctional electrode structures comprising nanoscale mV/s. coatings of electroactive iron oxide (FeCox) on pre-formed, FIG. 6 is a cyclic voltammogram for an FeCX-carbon nano ultraporous, electrically conductive carbon nanoarchitectures foam electrode that is cycled in a nonaqueous Li-ion electro 10 lyte (1 M LiPF in ethylene carbonate:diethylcarbonate), (e.g., nanofoams and ) are synthesized for use in scanning at 0.1 mV/s. high-performance electrochemical capacitors and batteries. The electrochemical performance of conventional forms of Conformal FeCX coatings are produced by reacting an Fe ironoxide is not yet competitive with current commercialized containing oxidant, such as KFeC), under self-limiting electrode materials, but significant improvements in charge deposition conditions in aqueous media with the interior and 15 storage capacity can be achieved when the FeCX is synthe exterior surfaces of the carbon nanoarchitecture. The redox sized in high-Surface-area, nanoscale forms. reactions at the resulting nanoscale FeCX coating signifi The electrochemical properties of nanoscale iron oxides cantly increase the energy-storage capacity of the FeCX-car may be further enhanced by distributing them on high-Sur bon nanoarchitecture hybrid electrodes, while the supporting face-area, electrically conductive carbon Substrates. carbon nanoarchitecture establishes long-range electron con For example, “co-precipitated FeCX-carbon materials via duction to the electroactive FeCX domains. sol-gel reaction from Fe precursors can be prepared in the Mixed ion/electron-conducting transition metal oxides presence of carbon black powder, and demonstrated high dominate the landscape of active materials for electrical specific capacitance, 510 Fg', normalized to the Fe0x con energy storage in secondary (i.e., rechargeable) batteries, tent, but only at low oxide weight loadings. Note that in this Such as Li-ion batteries, and are also being Successfully 25 protocol, the particulate carbon (the high electronic conduc adapted for use in electrochemical capacitors, also known as tor) is coated by a vastly poorer electronic conductor (FeCX). “supercapacitors' or “ultracapacitors'. Oxides of , In order to process this into a device-ready , manganese, and mixed oxides thereof, are the most electrode structure, additional conductive powder (usually common materials used in Li-ion battery cathodes, while carbon black powder) as well as a polymer binder must be 30 blended with the nanocomposite to form a usably conductive hydrous ruthenium oxides are state-of-the-art electrode mate mixture. rials for electrochemical capacitors (ECs). Although these It is suggested that the performance limitations of iron classes of metal oxides are well-established for electrochemi oxides for electrochemical capacitors and batteries can be cal energy-storage applications, the development of new addressed with a hybrid electrode design, in which discrete active materials continues, with an emphasis on achieving 35 nanoscale coatings or deposits of Fe0X are incorporated onto/ enhanced stability, charge-storage capacity, and/or high-volt into ultraporous, high-surface-area carbon structures, e.g., age operation. The costs, monetary and strategic, and the aerogels, nanofoams, templated mesoporous/macroporous environmental impact of state-of-the-art battery/EC oxides carbon, assemblies, as illustrated in FIG. 1. based on nickel, cobalt, and ruthenium oxides are also driving In Such a configuration, long-range electronic conduction the search for alternative materials. 40 is facilitated through the carbon backbone and solid-state Iron oxides are a class of materials that are potentially transport distances for ions through the FeCX phase are mini advantageous for energy-storage applications due to their low mized by maintaining a nanoscopic carbon FeCX electro cost and low toxicity. Although iron oxides have not been as lyte interface. extensively studied for batteries and ECs as other metal We recently demonstrated an example of such a hybrid oxides, recent work has demonstrated that certain forms of 45 metal-oxide-carbon nanoarchitecture, using an electroless nanoscale iron oxides can be used as both the active cathode deposition process based on the decomposition of aqueous and anode material for Li-ion batteries, and also as an anode permanganate, to incorporate conformal 10- to 20-nm-thick material for aqueous asymmetric ECs. MnO coatings that extend throughout the macroscopic (~170-um) thickness of carbon-paper-supported nanofoam BRIEF DESCRIPTION OF THE FIGURES 50 structures. Our preliminary electrochemical experiments in mild aqueous electrolytes demonstrated that the pseudoca FIG. 1 is a schematic of a hybrid electrode structure com pacitance of the nanoscopic MnO, coating at least doubles the prising a highly porous carbon in which the specific capacitance of carbon nanofoams, while the Volumet walls are coated with nanoscopic FeCX deposits. Note the ric capacitance is increased by more than a factor of 4. distinction in the typical electrical conductivities (O) of the 55 Extremely high footprint-normalized capacitances, >2.1 F carbon and FeCX components. cm', are also achieved with such MnO-carbon structures, a FIG. 2 includes scanning electron micrographs of a bare consequence of the three-dimensional design of the carbon carbon nanofoam and a FeCX-coated carbon nanofoam. The nanofoam Substrate Supporting the electroactive MnO, coat top images are of the exterior of the nanofoams and the ing. bottom images are of the interior of the nanofoams. 60 Herein, an electroless deposition process is described in FIG. 3 shows energy dispersive spectroscopy of a cross which we use the redox reaction of potassium ferrate section of an FeCX-coated carbon nanofoam, demonstrating (KFeC), a strong oxidizer, with ultraporous carbon Sub the presence of iron oxide following the electroless deposi strates to generate nanoscale conformal FeCX coatings on and tion procedure. The cross-section was created using a freeze throughout the carbon nanoarchitecture. fracture method. 65 In the present case, the use of pre-formed carbon nanoar FIG. 4 is a pore-size distribution plot derived from nitro chitectures with macroscopic dimensions presents new chal gen-sorption porosimetry measurements, showing a narrow lenges for achieving homogeneous FeCX deposition through US 9,105,402 B2 3 4 out the electrode structure, while preserving the native pore the exposed walls of the carbon substrate until those walls are structure of the carbontemplate. A high-quality porestructure coated and passivated with nanoscale FeCX deposits, and in the active electrode is vital for high-rate operation batteries autocatalytic decomposition of the ferrate ion in Solution or at and ECs because it facilitates electrolyte infiltration and ion the exterior of the carbon substrate is minimized. transport to the internal charge-storing electrode/electrolyte As shown in FIG. 2, under strongly alkaline deposition interfaces. conditions, this electroless deposition process results in con We have previously demonstrated that by using self-limit formal FeCX deposits that permeate the macroscopic thick ing deposition methods, ranging from the electrodeposition ness of the carbon nanofoam Substrate. Using this method, a of arylamine-based redox polymer coatings to the aforemen weight gain of at least 30% is attained for a 20-h deposition. tioned electroless deposition of nanoscale MnO, one is able 10 to incorporate homogeneous, conformal, nanoscale coatings The SEM analysis further confirmed that the porous texture of of electroactive moieties onto carbon nanoarchitectures, the initial carbon nanofoam is largely retained following while preserving a through-connected pore structure in the FeCox deposition, FIG. 2. Retention of the nanofoam’s high resulting hybrid electrode. quality pore structure results in better electrochemical perfor We now use a self-limiting deposition approach to the 15 mance under high-rate charge-discharge operation. electroless deposition of nanoscale FeCx such that the Energy-dispersive spectroscopy was used to confirm the KFeC) precursor only reacts with the surface of the carbon presence of Fe0X deposits on the walls of the interior of the nanoarchitecture until the surface is passivated to further nanofoam, as shown in FIG. 3. reaction with the precursor by the formation of a nanoscale We note that using aqueous KFeO to oxidize graphite FeCx coating. Careful control of the solution pH also mini powders in an effort to improve the electrochemical proper mizes extraneous reactions of the K-FeC) precursor. ties of the graphite for Li-ion batteries has been reported, but The result is a homogenous, nanoscale coating of a disor in that case the resulting iron oxide coatings were deliberately dered iron oxide that permeates the pre-formed carbon removed by treatment with dilute acid prior to electrochemi nanoarchitecture electrode. The disordered, as-deposited cal evaluation of the resulting material. The improved perfor FeCX coating can be subsequently converted by thermal pro 25 mance of the ferrate-treated graphite was attributed to oxida cessing to various nanocrystalline forms (e.g., Fe-O, alpha tion of the graphite Surface, which increased the inherent Fe2O, or gamma-Fe2O), each of which should exhibit dis Li-ion-intercalation capacity of the graphite. For the inven tinct electrochemical properties for various battery and EC tion described herein, the incorporated FeCx coating itself applications. serves as the active charge-storage phase, while the Support We present electrochemical data that demonstrate that the 30 ing carbon nanoarchitecture simply, but critically serves as FeCX redox reactions significantly increase the charge-stor the 3-D current collector. age capacity of the resulting hybrid electrode structure rela Electrochemical Characterization of Hybrid Structures in tive to the native carbon nanoarchitecture, and do so at the Aqueous Electrolytes. high charge-discharge rates that are relevant for next-genera The FeCX-nanofoam electrodes were wetted for electro tion, high-performance batteries and electrochemical capaci 35 chemical analysis with 2.5 M LiSO using vacuum infiltra tOrS. tion. The electrodes were characterized in a conventional Carbon nanofoam papers were either purchased from a 3-electrode electrochemical cell using techniques such as commercial source (MarkeTech, Int.) or prepared in-house cyclic Voltammetry, impedance spectroscopy, and galvano using methods disclosed. Potassium ferrate (KFeC)) was static charge-discharge measurements. either purchased or synthesized in-house using published 40 Table 1 presents the specific, geometric, and Volumetric methods. capacitance values calculated from the Voltammetric data Electroless deposition of FeCX on carbon nanofoams. We (range: 200 to -700 mV versus Ag/AgCl) measured at a scan used a strategy to synthesize FeCX-carbon nanoarchitecture rate of 5 mV s'. hybrids, based on the decomposition of ferrate salts, in this The specific capacitance versus potential for a bare carbon case K-FeC), from aqueous solutions, where the carbon 45 nanofoam and an FeCX-coated carbon nanofoam demon nanoarchitecture Surface serves as a sacrificial reductant that strates the improved capacitive properties of the coated nano converts the aqueous ferrate to surface-sited insoluble FeCox. foam, FIG. 4. In a typical synthesis, carbon nanofoam Substrates, 50- to The capacitance values, specific and Volumetric, for all 170-um-thick, were first wetted in an aqueous solution of FeCox-nanofoam samples are at least 2-fold higher than the controlled pH by vacuum infiltration. The samples were then 50 bare carbon nanofoam. The estimated FeCX-specific capaci soaked in aqueous solutions of KFeC), typically 10 to 50 tance attributable to the FeCX component, at a mass loading mM, of controlled pH, typically pH>14, for a period of time of 30%, is also presented. ranging from 30 min to 24 h. The FeCX-nanofoam papers were rinsed thoroughly with ultrapure water and subse TABLE 1 quently dried at ~50° C. under N for 8 h and then under 55 vacuum overnight. Capacitance values for a bare carbon nanofoam and a Although this protocol is attractive and straightforward, FeCx-coated carbon nanofoam. careful control of the ferrate reduction/decomposition reac Specific Fe0x-Specific Geometric Volumetric tion is required to achieve nanoscale FeCX deposits at the Capacitance Capacitance Capacitance Capacitance carbon Surfaces throughout the carbon nanoarchitecture as 60 (F/gtota) (FigFeo) (F/cm) (F/cm) well as to inhibit the formation of thick FeCx coatings on the Carbon 29 NA O.15 21 exterior boundary of the carbon electrode. Preliminary results nanofoam Suggest that Solution pH is a critical factor in determining the FeCox-carbon 84 315 O.85 121 quality of the FeCX deposition, where the best results are nanofoam achieved in strongly alkaline solutions, e.g., 9 M KOH, in 65 which the K-FeO precursor is the most stable. Under such The electroless deposition described herein is a cost-effec conditions, the K-FeC) reacts in a self-limiting fashion with tive and scaleable approach for synthesizing FeCX-carbon US 9,105,402 B2 5 6 hybrid nanoarchitectures with electrochemical charge-stor porous electrode structure of greater than about 5um age characteristics that are Superior to unmodified carbon with an aqueous KFeC), solution such that the iron Substrates. based oxidant reacts with the surface of the oxidizable Our work demonstrates that by controlling solution pH electrode structure to ensure self-limiting deposition of (typically using strongly alkaline Solutions) during the depo 5 the iron oxide as an ultrathin coating of less than about sition process, homogenous, nanoscale FeCX deposits are 50 nm distributed commensurately over the internal and achieved throughout macroscopically thick, pre-formed car external Surfaces throughout the entirety of the macro bon electrode substrates. The benefits of homogenous FeCX Scopically thick monolithic porous electrode structure deposition are evident when such structures are electrochemi and inherent conductive electrode scaffold; cally analyzed. 10 wherein the coating has a thickness of less than about 50 For example, FeCx-carbon hybrids exhibit higher overall nm, wherein the prefabricated porous carbon electrode specific and geometric capacitance. structure or carbon foam substrate that is a prefabricated Uniform deposition within the interior of the carbon paper is used directly as an electrode without requiring nanoarchitecture also results in greater enhancement when additional conductive additives or binders to be pro the Volumetric capacitance is considered, as the addition of 15 cessed into a device-Suitable electrode; and a current the FeCx component contributes additional capacitance with collector in electrical contact with the composite; and out increasing the bulk volume of the electrode structure. charging the capacitor. For example, with a carbon nanofoam coated under 2. The method of claim 1, wherein a mass loading of iron strongly alkaline conditions the specific capacitance is oxide of about 30% is achieved and the specific capacitance is increased by a factor of at least3, while the volumetric capaci increased by a factor of about 3. tance is increased by a factor of at least 7. 3. The method of claim 1, wherein the structure is a carbon The FeCox-carbon hybrid nanoarchitectures produced by . this electroless deposition method also exhibit enhanced 4. The method of claim 1, wherein the structure is selected charge-storage capacity when electrochemically cycled in from the group consisting of carbon nanofoam, Xerogel, tem nonaqueous electrolytes that are commonly used in Li-ion 25 plated mesoporous carbon, templated macroporous carbon, batteries, as shown in FIG. 6. Preliminary experiments indi and carbon nanotube/nanofiber assemblies. cate that the Li-ion capacity of the FeCX coating in Such 5. The method of claim 1, wherein the coating has a thick structures is >200 mAh/g. ness of about 10 nm. Even greater enhancements can be predicted in electro 6. A method of storing charge comprising the steps of: chemical performance for these hybrids with further optimi 30 providing a capacitor comprising an anode, a cathode, and Zation of the electroless deposition conditions and also by an electrolyte, wherein the electrolyte comprises a liquid varying the carbon template pore structure, particularly tar selected from the group consisting of an aqueous, basic geting larger pore sizes (100-200 nm) and higher overall (pH>8) electrolyte, and wherein the anode, the cathode, porosity, which should result in higher mass loadings of or both comprise: a composite comprising a prefabri FeCox. In one embodiment, the attainable mass loading is 30% 35 cated porous carbon electrode structure or a carbon foam for a 20-h deposition. Substrate that is a prefabricated paper structure compris The above description is that of a preferred embodiment of ing a surface and pores wherein the pores have an aver the invention. Various modifications and variations are pos age diameter that ranges from about 2 nm to about 1 um; sible in light of the above teachings. It is therefore to be and a coating deposited by infiltrating the structure with understood that, within the scope of the appended claims, the 40 iron oxide via self-limiting electroless deposition on the invention may be practiced otherwise than as specifically surface; wherein the coating does not completely fill the described. Any reference to claim elements in the singular, pores; wherein the coating comprising iron oxide covers e.g. using the articles “a” “an,” “the or “said is not con the interior and exterior surfaces of the porous carbon Strued as limiting the element to the singular. electrode structure and is continuous over the Surface What is claimed is: 45 and is deposited in a homogenous form and is evenly 1. A method of storing charge comprising the steps of: distributed throughout the thickness of the carbon foam providing a capacitor comprising an anode, a cathode, and Substrate that is a prefabricated paper, an electrolyte, wherein the electrolyte comprises a non wherein the modifying coating of iron oxide is achieved by aqueous liquid to dissociate salts soluble in the nonaque infiltrating the prefabricated porous carbon electrode ous liquid, and wherein the anode, the cathode, or both 50 structure that is a macroscopically thick monolithic comprise: a composite comprising a prefabricated porous electrode structure of greater than about 5um porous carbon electrode structure or a carbon foam Sub with an aqueous KFeO Solution Such that the iron strate that is a prefabricated paper structure comprising based oxidant reacts with the surface of the oxidizable a surface and pores wherein the pores have an average electrode structure to ensure self-limiting deposition of diameter that ranges from about 2 nm to about 1 um; and 55 the iron oxide as an ultrathin coating of less than about a coating deposited by infiltrating the structure with iron 50 nm distributed commensurately over the internal and oxide via self-limiting electroless deposition on the Sur external Surfaces throughout the entirety of the macro face; wherein the coating does not completely fill the Scopically thick monolithic porous electrode structure pores; wherein the coating comprising iron oxide covers and inherent conductive electrode scaffold; the interior and exterior surfaces of the porous carbon 60 wherein the coating has a thickness of less than about 50 electrode structure and is continuous over the Surface nm, wherein the prefabricated porous carbon electrode and is deposited in a homogenous form and is evenly structure or carbon foam substrate that is a prefabricated distributed throughout the thickness of the carbon foam paper is used directly as an electrode without requiring Substrate that is a prefabricated paper; additional conductive additives or binders to be pro wherein the modifying coating of iron oxide is achieved by 65 cessed into a device-Suitable electrode; and a current infiltrating the prefabricated porous carbon electrode collector in electrical contact with the composite; and structure that is a macroscopically thick monolithic charging the capacitor. US 9,105,402 B2 7 7. The method of claim 6, wherein a mass loading of iron oxide of about 30% is achieved and the specific capacitance is increased by a factor of about 3. 8. The method of claim 6, wherein the structure is a carbon aerogel. 5 9. The method of claim 6, wherein the structure is selected from the group consisting of carbon nanofoam, Xerogel, tem plated mesoporous carbon, templated macroporous carbon, and carbon nanotube/nanofiber assemblies. 10. The method of claim 6, wherein the coating has a 10 thickness of about 10 nm.

k k k k k