Stabilizing the LiCoO2 Interface at High Voltage with an Electrolyte Additive 2,4,6-Tris(4-fluorophenyl)boroxin

To achieve higher energy density, LiCoO2 (LCO) is being developed for high-voltage operation at raised charge cutoff voltages up to 4.6 V vs Li/Li+, which however is beyond the electrochemical stability window of carbonate-based electrolytes. In this work, a novel electrolyte additive 2,4,6-tris(4-fluorophenyl)boroxin (TFPB) is proposed for enhancing the interfacial stability of LCO. Thanks to the TFPB additive, the LCO cathode exhibits substantially improved capacity retention of 84.6% after 200 cycles at 1C at a high charge cutoff of 4.6 V, surpassing the 63.2% attained in the baseline electrolyte. The improved performance could be rationalized by the fact that TFPB additive is preferentially oxidized to build a uniform and protective B–O bond-containing cathode–electrolyte interphase, contributing to the reduced parasitic side reactions, inhibited surface structural transformation, and better-maintained interfacial lithium-ion diffusion kinetics.