Tris(2,2,2-trifluoroethyl) phosphite (TTFP) as a flame-retardant co-solvent to improve the safety and electrochemical performances of lithium-ion batteries

Abstract

Although many researchers continue to pursue improved battery capacity, battery safety remains a major concern. The main cause of battery fires is the flammability of the currently available commercial organic liquid electrolytes, which are mainly composed of 1 M lithium hexafluorophosphate (LiPF₆) and EC-containing carbonate solvents. Herein, a flame-retardant co-solvent tris(2,2,2-trifluoroethyl) phosphite (TTFP) was applied to improve the flame retardancy of a battery. It could improve the battery's discharging capacities at both 4.2 V and high cut-off voltage (4.5 V). Specifically, at a common voltage of 4.2 V, the cells’ 100th discharge capacity without TTFP was 130 mA h g⁻¹ by 0.2C with a capacity retention (CR) of 69%. In comparison, under the same conditions, the capacity of the 10% TTFP-containing cell was 162.3 mA h g⁻¹ with a CR of 73.9%. This increase in the electrochemical properties of the cell is clearly due to the addition of TTFP. When charging and discharging at 2.75–4.5 V, the capacity of the battery with STD after 100 cycles at 0.2C was 118.7 mA h g⁻¹, and the corresponding CR was 60.93%. Meanwhile, the discharged capacity of the battery containing 10% TTFP was 150.0 mA h g⁻¹ with a corresponding CR of 65.39%. Through combustion test with and without the TTFP electrolyte, it can be concluded that the TTFP-containing electrolyte is difficult to ignite. This result indicates that TTFP can efficiently enhance the safety performance of the battery. Thus, the incorporation of TTFP can be beneficial to improve the flame retardancy of the electrolyte. Moreover, TTFP does not affect the electrochemical stability of batteries. Thus, the present work may provide a good direction for the next generation of high-performance and high-safety lithium-ion batteries.