A key to achieving this capacity comes by utilizing water based binders such as lithium substituted polyacrylic acid (LiPAA).(4) Binders, like LiPAA, interact with the hydroxyl groups on the surface Si allowing for better distribution throughout the electrode.(5) Although these binders show improvements in electrochemical performance, water-based slurries bring about a unique set of processing challenges not found with its n-methyl-2-pyrrolidone (NMP) counterpart. A commonly overlooked issue is continued oxidation of Si upon exposure to water.(6) Not only does this affect the electrochemical performance, but prolonged exposure can lead to excessive hazardous H2gas production.
In this study, we look at the reaction of Si and with water, monitoring gas production in a unique pressure vessel mimicking industrial mixing techniques used in large scale slurry production. Si is examined for changes using Si NMR, powder XRD, TEM, FTIR, and XPS. In addition to the chemical characterization of Si, industrial relevant large format (5.5cmX 8.6cm) pouch cells are assembled utilizing a LiNi0.5Mn0.3Co0.2O2cathode against 15% Si-graphite composite anodes. Both Water and NMP based anodes are compared at several secondary drying temperatures. Uniform drying of these anodes adds an additionally layer of difficulty as water is easily bound to the surface of Si.(7) Despite these complications, Si-graphite full cells prepared with water based slurries still outperform full cells with anodes prepared using NMP based slurries, with full cell capacities ~1.5 times better after 100 cycles.
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2. R. Petibon, V. L. Chevrier, C. P. Aiken, D. S. Hall, S. R. Hyatt, R. Shunmugasundaram and J. R. Dahn, J. Electrochem. Soc., 163, A1146 (2016).
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5. Z. J. Han, K. Yamagiwa, N. Yabuuchi, J. Y. Son, Y. T. Cui, H. Oji, A. Kogure, T. Harada, S. Ishikawa, Y. Aoki and S. Komaba, Physical Chemistry Chemical Physics, 17, 3783 (2015).
6. A. Touidjine, M. Morcrette, M. Courty, C. Davoisne, M. Lejeune, N. Mariage, W. Porcher and D. Larcher, J. Electrochem. Soc., 162, A1466 (2015).
7. S. Yoshida, Y. Masuo, D. Shibata, M. Haruta, T. Doi and M. Inaba, J. Electrochem. Soc., 164, A6084 (2017).
This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office(VTO) (Deputy Director: David Howell) Applied Battery Research subprogram (Program Manager: Peter Faguy).