Abstract:

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 lithiumion battery electrolytes.

Key words: Lithium-ion battery, Electrolyte, Lithiumdifluoro(axalato)borate, Electrochemical
performance, Interfacial property