Exploring high-voltage fluorinated carbonate electrolytes for LiNi0.5Mn1.5O4 cathode in Li-ion batteries

Ethyl-(2,2,2-trifluoroethyl) carbonate (ETFEC) is investigated as a solvent component in high-voltage electrolytes for LiNi 0.5 Mn 1.5 O 4 (LNMO). Our results show that the self-discharge behavior and the high temperature cycle performance can be significantly improved by the addition of 10% ETFEC into the normal carbonate electrolytes, e.g., the capacity retention improved from 65.3% to 77.1% after 200 cycles at 60 °C. The main reason can be ascribed to the high stability of ETFEC which prevents large oxidation of the electrolyte on the cathode surface . In addition, we also explore the feasibility of electrolytes using single fluoriated-solvents with and without additives. Our results show that the cycle performance of LNMO material can be greatly improved in 1 M LiPF 6  + pure ETFEC-solvent system with 2 wt% ethylene carbonate (EC) or ethylene sulfate (DTD). The capacity retention of the LNMO materials is 93% after 300 cycles, even better than that of carbonate-based electrolytes. It is shown that the additives are oxidized on the surface of LNMO particles and contribute to the formation of cathode/electrolyte interphase (CEI) films. This composite CEI film plays a crucial role in suppressing the serious decomposition of the electrolyte at high voltage.