Abstract: A non-aqueous electrolyte usable in rechargeable lithium-ion batteries including a solution of LiPF6/carbonate based electrolytes with low concentrations of LiFOP such that the thermal stability is increased compared to a standard lithium battery. A method of making lithium tetrafluorophospahte (LiF4C2O4, LiFOP) including, reacting PF5 with lithium oxalate, recrystallizing DMC/dichloromethane from a 1:1 mixture of to separate LiF4OP from LiPF6 to form a lithium salt. An electric current producing rechargeable Li-ion cell. The rechargeable lithium ion cell includes an anode, a cathode, and a non-aqueous electrolyte comprising a solution of a lithium salt in a non-aqueous organic solvent containing lithium tetrafluorooxalatophosphate (LiPF4(C2O4), LiF4OP).