Improved interfacial properties of LiNi0.8Co0.15Al0.05O2 cathode by tris(trimethylsilyl) borate as an electrolyte additive to inhibit HF formation

Abstract

Tris(trimethylsilyl)borate (TMSB) is selected as an electrolyte additive in Li/LiNi0.8Co0.15Al0.05O2 cell due to its low oxidation potential. Its positive effect on improving the performances of the cells is analyzed by nuclear magnetic resonance, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma. The results show that the oxidative decomposition products of TMSB are involved in the formation of cathode electrolyte interface film. The trimethylsilyl group can react with HF to form trimethylsilyl fluoride and dimethyldifluorosilane, which reduces transition metal leaching through HF on LiNi0.8Co0.15Al0.05O2 (NCA) cathode. Meanwhile, a thinner interfacial film with a lower LiF content is formed, which contributes to the structural stability of NCA and inhibits the decomposition of the electrolyte. As a result, the NCA cathode in the electrolyte containing 1% TMSB shows higher cycling stability and rate performance, and has a lower impedance. Even at 1 C after 200 cycles, it still provides capacity retention with 86.0% compared to 67.2% for the cathode in baseline electrolyte. This work could provide an idea for the use of silicon-boron compounds as electrolyte additive to improve the electrochemical performances of ternary cathodes.