Structure characterization and electrochemical properties of new lithium salt LiODFB for electrolyte of lithium ion batteries

Abstract

Lithium difluoro(axalato)borate (LiODFB) was synthesized in dimethyl carbonate (DMC) solvent and purified by the method of solventing-out crystallization. The structure characterization of the purified LiODFB was performed by Fourier transform infrared (FTIR) spectrometry and nuclear magnetic resonance (NMR) spectrometry. The electrochemical properties of the cells using 1 mol/L LiPF₆ and 1 mol/L LiODFB in ethylene carbonate (EC)/DMC were investigated, respectively. The results indicate that LiODFB can be reduced at about 1.5 V and form a robust protective solid electrolyte interface (SEI) film on the graphite surface in the first cycle. The graphite/LiNi_1/3Mn_1/3Co_1/3O₂ cells with LiODFB-based electrolyte have very good capacity retention at 55 °C, and show very good rate capability at 0.5C and 1C charge/discharge rate. Therefore, as a new salt, LiODFB is a most promising alternative lithium salt to replace LiPF₆ for lithium ion battery electrolytes in the future.

Keywords

lithium ion battery / electrolyte / lithium difluoro(axalato)borate / synthesis / electrochemical properties

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