Benzoic Anhydride as a Bifunctional Electrolyte Additive for Hydrogen Fluoride Capture and Robust Film Construction over High‐Voltage Li‐Ion Batteries

High-voltage LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)-based Li-ion batteries (LIBs) with enhanced performance can be achieved by properly tailoring the electrolyte systems. Benzoic anhydride (BA) is proposed here as a promising bifunctional electrolyte additive that can not only construct a robust cathode-electrolyte interface (CEI) film on the electrode surface but also capture HF/H 2 O in the electrolyte effectively. Compared to the cell without the BA additive, the capacity of Li/NCM811 half-cell with 1.0 wt% BA is increased from 128.5 to 149.6 mAh g -1 after 200 cycles at 1 C between 3.0 and 4.3 V. Even at a higher cut-off voltage of 4.5 V, the BA-containing Li/NCM811 half-cell delivers a capacity retention of 69 % after 200 cycles, much higher than that of the half-cell without the additive (56 %). Both theoretical calculation and experimental results verify that the BA additive can be preferentially oxidized to form stable interface film with high conductivity that protects the NCM811 cathode and suppresses the decomposition of the electrolyte.