Dual-function ethyl 4,4,4-trifluorobutyrate additive for high-performance Ni-rich cathodes and stable graphite anodes

Abstract

An ethyl 4,4,4-trifluorobutyrate (ETFB) additive, with ester and partially fluorinated alkyl moieties, is employed to stabilize the interface structure of Ni-rich layered LiNi0.7Co0.15Mn0.15O2 (NCM) cathodes and graphite anodes. The analysis of the surface chemistry of the electrodes shows that ETFB serves as a bifunctional additive for constructing protective layers on both electrodes in a full cell. Cycling tests reveal that the addition of 1% ETFB leads to excellent capacity retention (84.8%) for the NCM/graphite full cell, which also delivers a superior discharge capacity of 167 mAh g−1 and a high Coulombic efficiency of over 99.8% after 300 cycles at 45 °C. The ETFB-derived protective layer effectively reduces intergranular cracking in secondary NCM cathode particles upon repeated charge-discharge cycling and limits the dissolution of transition metal ions from the cathode at high temperatures. In addition, after ETFB reduction, the graphite anode develops a thermally stable interface structure, which suppresses the self-discharge of graphite coupled with the NCM cathode at 60 °C.