A lithium battery includes an electrolyte comprised of a non-aqueous solvent, and a salt mixture. The salt mixture includes an alkali metal electrolyte salt and an additive salt having an anion of a mixed anhydride of oxalic acid and boric acid. Specific additive salts include lithium bis(oxalato) borate and lithium oxalyldifluoroborate. Particular electrolyte salts comprise LiPF6 and LiBF4. The additive salt is present in an amount of 0.1–60 mole percent of the total of the additive salt and electrolyte salt content of the electrolyte. Also disclosed is a method for enhancing the performance characteristics of a lithium battery through the use of the electrolyte composition. Also disclosed is the compound lithium oxalyldifluoroborate.