A nonflammable diethyl ethylphosphonate-based electrolyte improved by synergistic effect of lithium difluoro(oxalato)borate and fluoroethylene carbonate

Abstract

The vital physical and chemical properties of the lithium conducting salt, solvent/co-solvent and functional additive determine the overall properties and performance of the resulting electrolyte formulation. Explorations on right combinations of the carefully selected electrolyte components are expected to further balance the electrochemical and safety performances of chosen electrolyte formulations in given cell chemistries. In this study, a new nonaqueous aprotic electrolyte is designed by using lithium difluoro(oxalato)borate (LiODFB) as conducting salt, diethyl ethylphosphonate (DEEP) as solvent, and fluoroethylene carbonate (FEC) as co-solvent to achieve a nonflammable electrolyte formulation with competent electrochemical performance. The LiODFB and FEC are believed to take part in complex interfacial interactions with a synergistic effect. LiNi0.8Co0.1Mn0.1O2 (NCM811)‖Li cells using the optimized electrolyte formulation of 1.3 M LiODFB/DEEP 30% FEC exhibits a stable long-term cycling performance at 1.0 C with a reversible average specific discharge capacity of 169.5 mAh g−1 during 100 cycles, which is comparable to cells using commercial electrolytes. Furthermore, the 1.3 M LiODFB/DEEP 30% FEC electrolyte shows good thermal stability and effectively reduces the heat generation during thermal decomposition of NCM811 cathode. The results provide a good reference for the design of next generation of safe, nonflammable electrolytes for lithium-based battery application.