Fluoroethylene carbonate as the additive of lithium difluoro(oxalate)borate–sulfolane electrolytes to improve the electrochemical performance of LiNi0.5Mn1.5O4 cathode

Spinel LiNi0.5Mn1.5O4(LNMO) cathode with high voltage plateau at around 4.7 V (vs. Li/Li+) has attracted great attention. While the unsatisfactory electrochemical performance at high voltage hinders its practical application in next generation lithium ion batteries. Based on our previous research, FEC as electrolyte additive significantly improves the electrochemical performance of high voltage LNMO cell. The LNMO/Li cell with 4 wt% FEC shows the best rate capability, 76% capacity retention even at 5C. And the high temperature cycling performance of LNMO/G full cell with FEC is improved. The result from Raman indicates that FEC can transform the association structure of AGGs in the electrolytes to the salvation structure of SSIPs which increases the conductivity of electrolyte. EIS, SEM, TEM, XPS and FTIR analyses indicate that a more stable CEI film has been formed on the cathode surface with appropriate FEC as additive, which can promote the transport of lithium ions and inhibit the dissolution of transition metal elements.