Binder Interactions in the Electrodes of the Lithium-Ion Batteries Gao Liu
Binder Interactions in the Electrodes of the Lithium-ion Batteries
Gao Liu, Honghe Zheng, Xiangyun Song, Paul Ridgeway, Suhan Kim, Andrew Minor, Yonghong Deng, and Vince Battaglia
Lawrence Berkeley National Laboratory
TFUG Conference, San Jose, CA
February 17th, 2009 Outline
• A introduction to Lithium-ion battery. •Energy vs. Power. •Cost. •Structure. •Cathode and anode performance. •Cell performance improvement.
• Cathode electrode optimization. •Three components cathode – a polymer composite. •Acetylene black and polymer binder as conductive glue. •The mathematic modeling of the electrode electronic conductivity – the nano-scale interaction between PVDF and particles. •The cell performance governed by the interaction. Relative Performance of Various Electrochemical Energy-Storage Devices 1000 6 IC Engine 4 Fuel Cells EV – Electric Vehicle 100 h EV goal 2 HEV – Hybrid-Electric Li-ion Vehicle 100 PHEV goal PHEV– Plug-in Hybrid- 6 Ni-MH 4 Electric Vehicle Lead-Acid HEV goal 2 10 h 10 6 Capacitors 4 Specific Energy (Wh/kg) Specific Energy 1 h 0.1 h 36 s Range 2 3.6 s 1 0 1 2 3 4 10 10 10 10 10 Specific Power (W/kg) Acceleration Source: Product data sheets
• Goals developed in cooperation with DOE and United States Advanced Battery Consortium (USABC) under the FreedomCAR partnership • USABC is a cooperative of major automotive manufactures
• Li-ion batteries have higher performance compared to Nickel-metal hydrides batteries. However, research is needed to simultaneously address the life, cost, and abuse tolerance issues Cost of Consumer Electronics Batteries
1,800 $/kWh Cost Trend in Japan – Small Rechargeable 1,600 Cells Averaged Across Sizes 1,400
1,200
1,000
800
$/kWh NiMH 600 NiCd 400 Li-ion
200
0 J M S J M S J M S J M S J M S J M S J M S J M S 1999 2000 2001 2002 2003 2004 2005 2006 Source: U.S. DOE Source: TIAX, based on METI data
Performance and cost drivers for Li-ion cells However, numerous problems remain before use in vehicles Conductive additives new material development, Innovation can occur via Innovation canoccur or bybetter engineering Binder Li + e +e − - +C Anode: 6 Lithium-ion battery →LiC 6 Modern Li-ionBattery Li
+ Separator LiCoO e − Cathode: 2 →Li + +e - +CoO e − 2 LiPF Electrolyte carbonate carbonate/diethyl 6 in Ethylene A commercial Lithium-ion Rechargeable 26650 Cell
Open from the anode side Anode crimped closed
Cathode side of the jelly roll Open up the jelly roll SEM Images of Cathode and Anode Surfaces
Cathode
Anode Cycling of a Graphite-LiCoO2 Cell
Electrolyte oxidation
Cobalt oxide + - 140 mAh/g LiCoO2→Li +e +CoO2
Electrolyte:
LiPF6 in Ethylene carbonate/diethyl carbonate Solvent reduction- Passive film formation Voltage (V) vs. Li Voltage
+ - Li +e +C6→LiC6 Graphite 372 mAh/g
x in Li C or y in Li CoO x 6 1-0.6y 2 Lithium deposition Energy Density Increase of Consumer Electronic Li-ion Batteries
Theoretical Energy Density
Source: TIAX, LLC Complete Cathode Electrodes
Materials Electrode
LiNi0.80Co0.15Al0.05O2
Ave. diam.: 10 μm Surface area: 0.78 m2/g
Scale bar: 10 μm
Acetylene black (AB)
Ave. diam.: 50 nm Surface area: 60.4 m2/g
Scale bar: 100 nm Scale bar: 10 μm PVDF Polymer Binder Molecular weight: 760,000 Laminates without Active Material The Electronic Conductivity of AB/PVDF films
from 4-point probe measurements
LiNi0.80Co0.15Al0.05O2/Graphite Cells AB:PVDF (AB+PVDF)% in the cathode electrode
Most conductive 0.8:1 3.6%; 9%; 18%; 27% Least conductive 0.2:1 1.2%; 2.4%; 4.8%; 9.6%; 24%
0.4:1 2.8%; 11.2%; 21% 0.6:1 3.2%; 12.8%; 24% The Modeling Results of Active material/AB/PVDF ρ keff = Ɛ *k0(AB/PVDF) TEM Images of the Morphology of AB/PVDF Conductive Matrix
AB:PVDF = 0.2:1 (w/w) 0.5:1 0.8:1 1:1
200 nm 140 nm 140 nm 200 nm
Scale bar Three Different States of Polymer When in Contact with Particles
Immobilized polymer*
1-100 nm Free polymer Immobilized polymer
Bound polymer Bound polymer^ Micron to nano size particle
Bound polymer layer and immobilized polymer layer form Fixed Layer on the surface of particles.
* Dannenberg, E. M., Polymer, 14, 309 (1973) ^Westlinning, H and Butecnuth, G., Makromol. Chem., 47, 215 (1961) Cathode Material vs. Acetylene Black Particles
Fixed layers
Active Material Acetylene Black
Fixed layer of binder on acetylene black material surface. Single AB particle size: 40 nm. Fixed layer of binder on active material surface. Free binder Active material size: 10 μm Matrix Conductivity of the Electrode Reflects the Competition for Binder between AB and Active Materials AB/PVDF e-
from AB/PVDF films
AB/PVDF/Active material - e k0 = f(AB/PVDF)
ρ keff = Ɛ *k0(AB/PVDF’)
PVDF’ =PVDF - cathode particle immobilized PVDF A Model and Experimental Comparison of the Conductivities Active Material/AB/PVDF Complete Cells
LiNi0.80Co0.15Al0.05O2/Graphite Cells AB:PVDF = 0.8:1 (Most Conductive)
HPPC Test EIS at 40% DOD
(AB+PVDF)
Decrease cell resistance 32 Hz
5012 Hz LiNi0.80Co0.15Al0.05O2/Graphite Cells AB:PVDF = 0.2:1 (Least Conductive)
HPPC Test EIS at 40% DOD
170 1.2% (AB+PVDF) (AB+PVDF)
c 2.4% A ) 2 4.8%
•cm 130 9.6% Ω 24% 200 Hz 794 Hz 90 1259 Hz Increase cell resistance 316 Hz 1585 Hz 50 Discharge ASI (
10 0% 20% 40% 60% 80% 100% Depth of Discharge LiNi0.80Co0.15Al0.05O2/Graphite Cells AB:PVDF = 0.4:1
HPPC Test EIS at 40% DOD
2.8% (AB+PVDF) (AB+PVDF)
c 170 11.2% ) ) 2 21%
•cm 130
Ω 1580 Hz Increase cell resistance 90 200 Hz 2510 Hz 50 Discharge ASI ( ASI Discharge
10 0% 20% 40% 60% 80% 100% Depth of Discharge LiNi0.80Co0.15Al0.05O2/Graphite Cells
AB:PVDF = 0.6:1
HPPC Test EIS at 40% DOD
(AB+PVDF)
63 Hz
Stable resistance 3980 Hz The Distribution of Binder, AB, and Active Material at Different Combinations
AB:PVDF = 0.8:1 AB:PVDF = 0.2:1 Active Low Material High Low High Content:
Electronic Conductivity: Small Change Small Change Interfacial impedance of the electrodes: The Interfacial Impedances of All Compositions
HEV region Energy density is less important.
AB:PVDF P-HEV/EV region Energy density is important. Conclusions
•The amount of binder plays critical role in the composite electrode beyond providing mechanical integrity.
•The binder to conductive carbon ratio dictates the electronic conductivity of the laminate. The addition of active material alters the ratio through competition for the binder.
•The electronic conductivity of a laminate appears to be reflected in the charge transfer capability of the laminate.
•High acetylene black content, such as AB:PVDF > 0.8:1, tends to produce electrodes with lower electronic conductivity and higher charge transfer at high active material loadings.
•Low acetylene black content, such as AB:PVDF < 0.4:1, tends to produce electrodes with higher electronic conductivities at high active material loadings. Acknowledgments
•Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U.S. Department of Energy. Contract # DE-AC03-76SF00098.
•Electron microscopy performed at the National Center for Electron Microscopy, Lawrence Berkeley Lab, U.S. Department of Energy. Contract # DE-AC02-05CH11231.
•Toda American for the NCA Material. •Denka Japan for the acetylene black conductive additive. Thank you for your attention! End