Tris(2,2,2-trifluoroethyl) Phosphate as a Cosolvent for a Nonflammable Electrolyte in Lithium-Ion Batteries

Tris(2,2,2-trifluoroethyl) phosphate, as a flame-retarding cosolvent, is initially mixed with γ-butyrolactone for the first time to formulate a nonflammable electrolyte, in which lithium difluoro(oxalato)borate is added as a film-forming additive. This electrolyte possesses a higher safety level and better wettability compared with a commercial electrolyte. The conductivity of this electrolyte is 7.40 mS cm–1 at room temperature. This high-safety electrolyte helps graphite/LiNi0.5Co0.2Mn0.3O2 full cells to obtain good electrochemical performance. The capacity retention after 200 cycles at room temperature (1C) is 90.8% and the capacity retention of 100 cycles at 60 °C (1C) is up to 86.7%, which are better than those of the commercial electrolyte. To further analyze the relationships between compositions of electrolytes and the electrochemical performance of the full cells, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements are performed.