The stable interfacial chemistry of LiCoO2 (LCO) is the cornerstone for its high-voltage operation. However, interfacial side reactions, originating from the Co/O catalytic sites, lead to ethylene carbonate (EC) oxidation, lithium hexafluorophosphate (LiPF6) hydrolysis, and LCO surface degradation. Herein, we propose that the formation of functional phosphate derivatives (FPD) in the electrolyte, which are generated from the reaction between tris(trimethylsilyl) phosphate (TMSP) and PF6 - anions, can achieve targeted regulation of the polyphosphates cathode-electrolyte interphase (CEI). During cycling, the FPD spontaneously forms covalent interactions with surface Co/O sites, triggering in situ polymerization that constructs a robust and full-coverage CEI on LCO. The resulting CEI is enriched with polyphosphates and LiF/Li2O, which ensures high thermodynamic stability and fast Li+ transport kinetics simultaneously. Consequently, the LCO with optimized electrolyte (1.0 M LiPF6 in fluoroethylene carbonate (FEC)-based solvents with 2.0 wt.% TMSP) demonstrates exceptional cell performance with a high capacity retention of 81.0% after 3000 cycles within 3.0-4.6 V (vs. Li/Li+), 81.6% after 2000 cycles within 3.0-4.65 V, and shows the feasibility in the LCO||graphite pouch cell with a retention of 80.0% after 500 cycles. This work provides a new insight into the uniform CEI construction for high-voltage LCO cathodes through functional electrolyte engineering.
Ren et al. (2026) studied this question.