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.