Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 122, Issue 18, Pages 9811-9824Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.8b02056
Keywords
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Funding
- U.S. Department of Energy's Vehicle Technologies Program (DOE-VTP)
- Applied Battery Research (ABR) for Transportation Program
- Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]
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The use of high-voltage, high-capacity positive electrodes in lithium ion batteries presents a challenge, given their tendency to degrade organic electrolytes. To prevent this damage, electrolyte additives modifying the cathode surface are required. Tris(trimethylsilyl) phosphite (TMSPi) is one such electrolyte additive. However, the mechanism for its protective action (similar to other phosphite, borate, and boroxane compounds) remains not completely understood. In LiPF6 containing carbonate electrolytes, TMSPi undergoes reactions yielding numerous products. Here we demonstrate that one of these products, PF2OSiMe3, is responsible for mitigation of the impedance rise that occurs in aged cells during charge/discharge cycling. This same agent can also be responsible for reducing parasitic oxidation currents and transition metal loss during prolonged cell cycling. Mechanistic underpinnings of this protective action are examined using computational methods. Our study suggests that this beneficial action originates mainly through inhibition of catalytic centers for electrolyte oxidation that are present on the cathode surface, by forming capping ligands on the transition metal ions that block solvent access to such centers.
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