Interface modifications by tris(2,2,2-trifluoroethyl) borate for improving the high-voltage performance of LiNi_1/3Co_1/3Mn_1/3O₂ cathode

Tris(2, 2, 2-trifluoroethyl) borate (TTFEB) is evaluated as an effective electrolyte additive for LiNi_1/3Co_1/3Mn_1/3O₂ cathode. Galvanostatic charge/discharge tests indicate that the cycling performance and rate capability of LiNi_1/3Co_1/3Mn_1/3O₂ cathode are enhanced dramatically with the presence of 0.5 wt% TTFEB in electrolyte, which delivers a high initial discharge capacity of 185.3 mAh g^-1 at 0.5 C with high capacity retention of 89.5% after 100 cycles. Moreover, superior discharge capacity of 135.1 mAh g^-1 is displayed at high rate of 4 C, while only 73.7 mAh g^-1 is delivered for the cell without TTFEB. The effects of TTFEB on the LiNi_1/3Co_1/3Mn_1/3O₂ cathode surface are further investigated by EIS, SEM, XRD and XPS. It is found that the enhanced electrochemical performance can mainly be attributed to the alleviation of electrolyte decomposition and prevention of LiNi_1/3Co_1/3Mn_1/3O₂ cathode structural deterioration at the high voltage, which is benefited by the formation of the thin and uniform film with lower interfacial impedance on cathode surface with the presence of TTFEB.