Methods for Successful Cycling of Alloy Negative Electrodes in Li-ion ion Cells Mark Obrovac, Leif Christensen, Larry Krause, Dinh Ba Le, Jagat Singh, Kevin Eberman, Lowell Jensen, Li Liu, Jehwon Choi, Vincent Chevrier, Jamie Gardner 3M Company, EMMD 2011-10-10 1/30
Outline Benefits of Si 3M Material Design Implementation in Cells 2/30
Anode Energy Density Comparison at 100% Vol. Expansion Li molar volume is 9 cc/mol for most alloys 100% volume expansion or less is desired Energy density at a given volume expansion is nearly insensitive to alloy composition Si is by far the most inexpensive Li-host on a $/Ah basis Incorporating alloys in current cell designs yields 20% increase in energy M.N. Obrovac, Leif Christensen, Dinh Ba Le and J.R. Dahn, J. Electrochem. Soc. 154 (2007) A849 Only stating mah/g can be (very) misleading Si does not give 10x capacity in practical cells 3/30
3M alloy Materials Design Micron sized particles Maximize packing density and energy density Drop-in technology Low surface area Minimize irreversible capacity and parasitic reactions Maximize i thermal stability Properties optimized for real-world applications 4/30
3M alloy Materials Design Nanostructured Active / Inactive nanostructure Active Si remains amorphous crystalline Li 15 Si 4 3M alloy (L-20772) Pure Si good 5/30 bad
L-20772 Voltage Curve Stable voltage curve 6/30 Absence of crystallization plateaus
Coin Cell Tests of L-20772 Alloy Coating formulation (wt%) L-20772 LiPAA Coulombic Efficiency ~ 99.7% 92 8 Minimal i Fade High Coulombic Efficiency High Electrical Conductivity 7/30
L-20772 comparison to SiO 3M L-20772 SiO 1 st lithiation capacity 982 mah/g 1520 mah/g 1 st delithiation capacity (@ 0.9V) 835 mah/g ~940 mah/g Irreversible Capacity 15 % 38% Density 41g/cc 4.1 ~2.5 25g/cc Reversible Volumetric Capacity (after expansion) FMC Lithium, 26 th International Battery Seminar & Exhibit, 2009 3M Alloy: 8/30 1608 mah/cc ~1324 mah/cc Lower irreversible capacity Higher volumetric capacity 3M material can lead to greater capacity in practical cell
Implementation in Cells 9/30
Key Factors Influencing Cycle Life Alloy Level Composition Microstructure Electrode Level Graphite Conductive Carbon Binder Dispersion Quality Cell Level Matching Cathode Electrolyte Alloy active/inactive Alloy Graphite Conductive C Binder 10/30
Key Factors Influencing Cycle Life Graphite Dispersion Composite electrode formulation example: Weight % L-20772 60.0 CPG-8 28.0 Super P 2.0 LiPAA 10.00 11/30
Key Factors Influencing Cycle Life Graphite Dispersion 3M Alloy + Graphite A 3M Alloy + Graphite B 800 Capacity (ma Ahr/gm) 600 400 200 3M Alloy + Graphite A 3M Alloy + Graphite B 0 0 10 20 30 40 50 Cycle # Smaller graphite (A) leads to a better dispersion and cycling 12/30
Use of LiPAA Binder with Alloy 1000 800 TY (mah/g) CAPACI 600 400 Li-PAA CMC PVDF 300 C/Ar PVDF 120 C/vac 200 0 10 20 30 40 50 60 70 80 90 100 CYCLE NUMBER Carboxylic acid groups in CMC form strong bonds with metal surfaces* PAA has many more acid groups on chain than CMC, resulting in significantly better performance *N. S. Hochgatterer, M. R. Schweiger, S. Koller, P. R. Raimann, T. Wöhrle, C. Wurm, and M. Winter, Electrochemical and Solid-State Letters, 11 A76-A80 (2008). 13/30
Lithium Polyacrylate (LiPAA) Binder Preparation Using LiPAA greatly improves cycle-life US 2008/0187838 LiPAA made by neutralizing PAA solution with LiOH (ph ~8.5) 0 % Residu ual Moisture -2 Moisture uptake manageable with -4 standard vacuum -6 drying -8 LiOH addition to PAA solution LiPAA Binder Content 5 wt% 10 wt% 20 wt% Samples Vacuum dried for 12 hrs at 120 C LiPAA is industry compatible 14/30
Key Factors Influencing Cycle Life - Electrolyte Alloy/graphite composite cycling in 18650 (50% FEC doesn t cycle) Flooded coincells require 10% FEC System dependent optimal FEC range 15/30
3M Alloy Partner Cycling Data 18650 using 60:28:2:10 of L-20772:CPG8:SuperP:LiPAA NCA 81% @ 400 cycles, C/5 3.0 4.3V cutoff 78% @ 400 cycles, C/2 16/30 18650 showing 78% retention at 400 cycles
Production Industry scalable synthesis method Production scale up in progress 17/30
Conclusion Evaluation of alloy materials should be based on volumetric considerations True alloy-based anode performance depends on many factors Binder Electrolyte Graphite/Alloy dispersion Cathode matching 3M Si alloys are ready for commercialization Proven performance Proven large scale synthesis method 18/30