锂离子电池用LiPF_6/PC+FEC电解液的低温性能

Low temperature performances of LiPF_6/PC+FEC electrolyte for Li-ion battery

研究氟代碳酸乙烯酯(fluoroethylene carbonate,FEC)添加剂对锂离子电池用碳酸丙烯酯(PC)基电解液低温放电性能和常温循环性能的影响,并通过电化学阻抗谱(EIS)、X线光电子能谱(XPS)以及气质联用谱(GC-MS)等对FEC在PC基电解液中的作用机理进行探讨。研究结果表明:往PC电解液中添加质量分数为5%的FEC可以在石墨电极表面形成完整且致密的SEI膜,从而有效阻止PC在负极石墨的共嵌入;电池在低温-20℃及-40℃下0.5C放电容量分别可达到室温容量的98%及87%;FEC形成的SEI膜有效降低了锂离子电池的低温电荷转移阻抗,是提高电池低温性能的主要因素之一;FEC在正极钴酸锂材料表面形成了导电性能优异的SEI膜层,改善了锂离子电池的低温性能和常温循环性能。

The influence of FEC additive on the cycle performance and low temperature discharge capacity of lithium battery with PC based electrolyte was studied. Electrochemical impedance spectroscopy（EIS）, X-ray photoelectron spectroscopy（XPS） and gas chromatography-mass spectrometry（GC-MS） were used to study the mechanism of FEC in lithium battery. The results show that a smooth and compact SEI film which can restrain the intercalation of PC into graphite electrode is formed when 5% FEC is added in PC based electrolyte, and the capacity retention ratio is 98% and 87% respectively when it is discharged at-20 ℃ and-40 ℃.The low charge transfer impedance of SEI film formed by FEC is the main reason. SEI film with high conductivity is formed on the surface of lithium cobalt oxide cathode, which can improve the low temperature performances and cycling life at normal temperature of the Li-ion battery.