Abstract:

The effect of lithium difluoro(oxalato)borate, which was added to the propylene carbonate (PC)+ethylene carbonate (EC)+methyl ethyl carbonate (EMC) (mass ratio 1:1:3) mixed solvent as a lithiumsalt, on the cyclic performance of LiFePO4/graphite batteries at high temperature (60 ℃) was investigated. Linear sweep voltammetry(LSV) was used to examine the electrochemical stability of the lithium difluoro(oxalato)borate-based electrolyte. Inductively coupled plasma (ICP) and energy dispersive spectroscopy (EDS) were used to analyze the stability of the LiFePO4 cathode in the LiODFB-based electrolyte at high temperature. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) were used to analyze the thermal stability of the solid electrolyte interphase (SEI) film formed on the graphite anode. Results showed that the LiODFB-based electrolyte could restrain iron dissolution from LiFePO4 and prevent the reduction of dissolved iron ions'reducing at the anode's surface which decreased the impedance effectively. On the other hand, the SEI film formed on the graphite surface in the LiODFB-based electrolyte had better thermal stability. The cyclic performance of the LiFePO4/graphite battery at high temperatures improved dramatically.

Key words: Electrolyte, Lithiumdifluoro(oxalato)borate, LiFePO₄/graphite cell, High-temperature performance, SEI film