Significance of Electrolyte Additive Molecule Structure in Constructing Robust Interphases on High-Voltage Cathodes

Electrolyte additives have been successfully applied for the performance amelioration of lithium-ion batteries, especially under high voltage, which are based on the protective interphases on anode and cathode. Many additives have been proposed but less knowledge is available on the relationship between additive molecule structure and the interphase stability. In this work, we uncover the significance of the additive molecule structure in constructing a stable and robust interphase by comparing the effects of two similar additives, trimethyl borate (TMB) and tripropyl borate (TPB), on the performance of a layered lithium-rich oxide cathode (LRO) under a high voltage (4.8 V). Electrochemical measurements combined with physical characterizations and theoretical calculations demonstrate that TMB and TPB exhibit similar oxidative activity and both can build protective cathode interphases on LRO but they yield different cyclic stability improvement for LRO. The B-containing species derived from the TMB oxidation are more stable, yielding a more robust interphase than those from the TPB oxidation. This established relationship paves a road to design electrolyte additives more efficiently for high-voltage batteries.