Hexamethylphosphoramide (HMPA) was investigated as a flame retarding additive for lithium-ion batteries. The flammability, electrochemical stability, conductivity, and cycling performance of electrolytes containing HMPA were studied. The addition of HMPA to electrolytes comprising solutions of LiPF6 in organic carbonates provided a significant reduction in the flammability of the electrolyte. However, the HMPA caused a slight decrease in the conductivity and electrochemical stability window of the electrolyte. Cycling performance of coin cells containing HMPA modified electrolytes was diminished.