The Lithium-ion Battery Overcharge Protection Additive Research

2-Chloroanisole was investigated as a safety electrolyte additive for lithium-ion batteries.The electrochemical behavior of electrolyte containing 2-chloroanisole was examined by cyclic voltammetry and charge-discharge experiments.It was found that this molecule can be polymerized at 4.67V(vs.Li/Li⁺).The electrolyte with 2-chloroanisole exhibited good compatibility with graphite anode and LiFePO₄ cathode. The graphite/LiFePO₄ cells with 2-chloroanisole additive could endure 0.5C/5h and 1C/3h overcharge.At same time,The capacity holding ratio of graphite /LiFePO₄ cell with 2-chloroanisole additive reached 81.4% after 338 cycles under room temperature,and 79.9%after 200 cycles under 60℃at 1C rate.The cycle performance of batteries with 2-chloroanisole additive can be improved by adding 1%VC.The overcharge protection and electrochemical property of lithium ion battery was investigated by microelectrode voltammetry, potentiodynamic polarization experiment charge-discharge cycling and SEM measurement,when functional additives with different overcharge protection mechanisms such as biphenyl(BP) and 3-Chloroanisole(3CA) were co-used in the electrolyte.The results shows that the polymerize potential of electrolyte with mixed additives was moved forward from 4.7V to 4.6V,as the content of 3-chloroanisole increased.When overcharged,3-chloroanisole molecules were oxidized in the form of redox shuttle reaction at the positive electrode,but biphenyl molecules was polymerized forming a compact film at the surface of electrode.The film formed at the surface of electrode can effectively prevent the insertion and extraction of Li⁺.In this way,the safety performance of lithium battery can be improved by the co-use of the two additives with different overcharge protection mechanisms.In order to study the effect of partly and slightly overcharge problem to the performance of li-ion batteries,a good redox shuttle additive 2,5-Di -fluoro-1,4-dimethoxybenzene(F₂DMB) was selected,which co-used with biphenyl and investigated by cyclic voltammetry,charge-discharge cycling and overcharge test.We discovered that F₂DMB can take a good protection to LiFePO₄ batteries under 146 cycle time at 4.3V,and didn't influence the normal performance of batteries.