Abstract: A conventional electrolyte for a secondary cell having a carbonaceous anode is comprised of an alkali metal salt dissolved in an organic electrolyte solvent. Intercalation and de-intercalation during repeated discharge/charge cycles of the secondary cell using a conventional electrolyte solvent causes continual exposure of bare surfaces of the carbonaceous material to the electrolyte, resulting in continual consumption of electrolyte in the formation of new passivation films on the bared or partially covered surfaces, adversely affecting the performance and capacity of the cell. In accordance with the present invention, the organic electrolyte solvent comprises chloroethylene carbonate, propylene carbonate and ethylene carbonate. The chloroethylene carbonate is capable of forming a very stable passivation film on the anode. The performance and capacity of the secondary cell is improved substantially by the addition of the halogenated organic solvent.

Abstract: A conventional electrolyte for a secondary cell having a carbonaceous anode is comprised of an alkali metal salt dissolved in an organic electrolyte solvent. Intercalation and de-intercalation during repeated discharge/charge cycles of the secondary cell using a conventional electrolyte solvent causes continual exposure of bare surfaces of the carbonaceous material to the electrolyte, resulting in continual consumption of electrolyte in the formation of new passivation films on the bared or partially covered surfaces, adversely affecting the performance and capacity of the cell. In accordance with the present invention, at least a portion of the organic electrolyte solvent is replaced with a chloroethylene carbonate solvent capable of forming a very stable passivation film. The performance and capacity of the secondary cell is improved substantially by the addition of the halogenated organic solvent to propylene carbonate.