Tris(4-fluorophenyl) Phosphine and Tris(2,2,2-trifluoroethyl) Phosphite as Flame-Retarding Additives in Li-Ion Batteries

Tris(4-fluorophenyl) phosphine (TFPP) and tris(2,2,2trifluoroethyl) phosphite (TTFP) were used as flame-retarding additives in Li-ion battery electrolytes. The cell performance of the TFPP- and TTFP-containing electrolytes was examined by cyclic voltammetry, differential scanning calorimetry, electrochemical impedance spectroscopy and scanning electron microscopy. The flammability of the electrolytes was also examined by measuring the self-extinguishing time of the electrolytes. The results showed that the TTFP additive suppressed the flammability of the electrolyte, improved the thermal stability of the battery and its electrochemical cell performance. On the other hand, the TFPP additive only improved the thermal stability of the electrolyte at the expense of a slight decrease in electrochemical cell performance. The results show that TTFP is a better flameretarding additive in the electrolyte of Li-ion batteries than TFPP.