新型锂盐LiBC2O4F2在EC＋DMC溶剂中的电化学行为

采用差热-热重(TG-DTA)、恒电流充放电和交流阻抗(EIS)分析了二氟草酸硼酸锂(LiODFB)的热稳定性,研究了LiODFB/碳酸乙烯酯(EC)+碳酸二甲酯(DMC)电解液的电化学性能及界而特征.实验结果表明,LiODFB不仅具有更高的热稳定性,而且在EC+DMC溶剂中具有较好的电化学性能.与使用LiPF6/EC+DMC的电解液相比,锂离子电池应用LiODFB基电解液在55℃的高温具有更好的容量保持能力;以0.5C、1C(1C=250 mA·g-1)倍率循环放电,两种电池间的倍率性能差别较小;LiODFB能够在1.5 V(vs Li/Li+)左右在石墨电极表面还原形成一个优异稳定的保护性固体电解质相界面膜(SEI膜);交流阻抗表明,使用LiODFB基电解液的锂离子电池仅具有稍微增加的界面阻抗.因此LiODFB是一种非常有希望替代LiPF6用作锂离子电池的新盐.

Electrochemical Behaviors of New Lithium Salt LiBC2O4F2 in EC+DMC Solvents

The thermal stability of lithium difluoro(axalato)borate (LiODFB)was analyzed by thermal gravimetric-differential thermal analysis (TG-DTA).The electrochemical performance and interfacial characteristics of the LiODFB/ethylene carbonate(EC)+dimethyl carbonate(DMC)electrolyte were studied by constant current charge-discharge and electrochemical impedance spectroscopy(EIS).Results show that LiODFB has higher thermal stability and that the lithium-ion cells using LiODFB salt in EC+DMC solvents exhibit excellent electrochemical performances.Compared with the LiPF6/EC+DMC electrolyte,the lithium-ion cells using LiODFB-based electrolyte have very good capacity retention at 55℃.At 0.5C and 1C(1C=250 mA·g-1)discharge rates,the difference between the rate capability of the two cells is tiny.LiODFB iS reduced at about 1.5 V(vs Li/Li+) and forms a robust protective solid electrolyte interphase (SEI)film on the graphite surface.EIS tests show that these lithium-ion batteries which use the LiODFB-based electrolyte have a slightly higher interfacial impedance.Therefore,as a new salt,LiODFB is a promising alternative lithium salt for the replacement of LiPF6 in lithium ion battery electrolytes.