In order to improve the ability of overcharge protection, 4BA was added as a novel electropolymerizable additive to the electrolyte of lithium-ion batteries. Proved by overcharge of batteries, cyclic voltammetry, infrared spectra, AC impedance tests, and discharge capacity measurements in this research, the overcharge protection ability of this novel additive was confirmed. When the external potential was 4.4 V, 4BA (5% by mass) in the system of electrolyte 1 mol•L－1 LiPF6/ EC＋DEC＋DMC (1/1/1, m/m/m) started to electrochemically polymerize and produced a layer of polymer film, which increased the internal resistance and prevented the voltage from dramatically rising up. Therefore, the lithium-ion batteries can be much safer. During the normal charge-discharge processes of the battery system, the addition of the proper weight percentage of 4BA does not have negative effect on the capacity of lithium-ion batteries, and the mechanism of overcharge protection is an interdiction mechanism.

Key words: lithium-ion battery, overcharge protection, additive, 4-bromoanisole