二氟二草酸硼酸锂对LiFePO_4/石墨电池高温性能的影响

Effect of Lithium Difluoro(oxalato)borate on the High-Temperature Performance of LiFePO_4/Graphite Batteries

研究了二氟二草酸硼酸锂(LiODFB)作为锂盐加入到碳酸丙烯酯(PC)+碳酸乙烯酯(EC)+碳酸甲乙酯(EMC)(质量比为1∶1∶3)混合溶剂中对LiFePO4/石墨电池高温(60℃)循环性能的影响.用线性扫描伏安法(LSV)测试了电解液的电化学窗口.通过等离子发射光谱(ICP)和能量散射光谱(EDS)对LiFePO4材料高温条件下在不同电解液中的稳定性进行了研究;并用扫描电镜(SEM)和电化学交流阻抗谱(EIS)分析了石墨负极表面的固体电解液相界面(SEI)膜的热稳定性.结果表明:一方面LiODFB基电解液能抑制LiFePO4材料在高温条件下Fe(II)的溶解,防止溶解的Fe(II)在石墨上还原,有效地降低电池阻抗;另一方面,在LiODFB基电解液中形成的石墨负极表面SEI膜具有更好的热稳定性,能显著提高LiFePO4/石墨电池的高温循环性能.

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 lithium salt, 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.