Study On Effect Of Fluoroethylene Carbonate On The Performance Of Lithium-ion Battery

Electrolyte additives used in Li-ion batteries has been concerned gradually due to its advantages of little consumption and much efficacy, etc, much research focused on additives for electrolyte used in Li-ion battery in recent years. Use of electrolyte additives is one of the most economic and effective methods for the improvement of Li-ion battery performance. Usually, the amount of an additive in the electrolyte is no more than 5% either by weight or by volume while its presence significantly improves the performance of Li-ion batteries. The development of lithium-ion battery and its additive were reviewed. According to their functions, the additives can be divided into these categories: SEI forming improver additives, overcharge protection additives, improve low-temperature performance additives, thermal stability of improvement additives, and so on.In this paper, we use 1mol·L-1 LiPF6/EC+DEC+EMC (1:1:1 by volume) as basic electrolyte, adding 5% (v/v) Fluoroethylene carbonate (FEC) into it as additive. The effects of FEC on electrode/electrolyte interface and the performance of lithium-ion battery were researched by CV, SEM, FTIR, DSC, charge-discharge of constant current, cycle performance test of batteries, and so on. The results showed that it almost had no effect on the physical indicators of electrolyte and LiCoO2 materials by adding of 5% (v/v) of FEC. It can restrain the decomposition of the solvent in the electrolyte and cause the formation of an excellent performance solid electrolyte interface (SEI) film on the surface of electrode which can reduce the impedance of the battery. As a result, the battery got excellent cycle performance: the capacity retain percentage of the battery reaches up to 88.68% after 300 cycles. In addition, it turns out that the FEC is able to improve the low temperature performance of the battery. Also, we put forward one decomposition mechanism according to the component analysis of SEI film and the molecular structure of ethylene carbonate (EC), vinylene carbonate (VC) and fluoroethylene carbonate (FEC), the decomposition of FEC.At last, we researched the influence on the performance of the battery in the event that two different additives are used together, the result showed that it can improve the cyclic performance of batteries obviously by using FEC and VC together, it can improve the high-temperature performance of batteries by using FEC and LiBF4 together. The FEC is applicable to be additive of the electrolyte for commercial secondary Li-ion batteries.