Abstract: Thermally stable electrolytes for Li-ion batteries obtained with the use of Lewis base additives to the electrolytes are disclosed. The Lewis bases stabilize electrolytes composed of solutions of LiPF6 in organic carbonates against decomposition at temperatures as high as 85° C. Additives suitable for stabilizing LiPF6-containing electrolytes include amines, for example, triethylenediamine (TEDA) and 2,2′-bipyridine (BIPY), phosphines, for example, triphenylphosphine (TPP) and tributylphosphine (TBP), and nitrogen-phosphorus bonded compounds such as hexamethoxycyclotriphosphazene ([N═P(OCH3)2]3) (HMOPA), hexamethyl phosphoramide (HMPA), and N-phenyl-P,P,P-trimethylphosphorimidate (PhTMI). These additives are also capable of stabilizing electrolytes in solvents other than carbonates including ethers, esters and sulfones.