Chemical “Pickling” of Phosphite Additives Mitigates Impedance Rise in Li Ion Batteries
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 of such electrolyte additives. However, the mechanism for its protective action (similarly 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 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.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1460835
- Journal Information:
- Journal of Physical Chemistry. C, Vol. 122, Issue 18; ISSN 1932-7447
- Publisher:
- American Chemical Society
- Country of Publication:
- United States
- Language:
- English
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