PURPOSE: To remove water and impurity in electrolyte and increase performance of a battery by heating under a reduced pressure when supporting electrolyte is dissolved in nonaqueous organic solvent.

CONSTITUTION: Propylene carbonate (PC) is purified under a reduced pressure of 1mmHg at 75°C with distilling equipment. 1,2-dimethoxyethane (DME) is purified in an atmosphere or argon under normal pressure at 83°C by distillation. LiClO4 obtained by drying under a reduced pressure at 100∼200°C is dissolved in the above PC. During dissolving, PC is heated at 100∼200°C under reduced pressure for about 30min. Then a specified amount of the above DME is added to the above solution and mixed so that the ratio of PC:DME is 2:1 and concentration of LiClO4 is 1mol/l. A lithium battery using this electrolyte shows excellent discharge performance and high rare pulse performance compared with a conventional battery.