ELECTROLYTE COMPRISING FLUORO-ETHYLENE CARBONATE AND PROPYLENE CARBONATE, FOR ALKALI METAL-ION SECONDARY BATTERY

摘要

The invention disclosed is an alkali metal-ion secondary cell having a carbonaceous anode and an electrolyte, comprising an alkali metal salt dissolved in an organic electrolyte solvent. Intercalation and de-intercalation during repeated charge/discharge 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. An improvement on the conventional electrolyte involves the addition of chlorinated organic solvent to the conventional electrolyte and results in a more stable passivation film, much less consumption of electrolyte and better performance and cell capacity. In accordance with the present invention, the chlorinated organic solvent, chloroethylene carbonate, is replaced with a fluorinated organic solvent, fluoro-ethylene carbonate, capable of forming a very stable passivation film which is insoluble in the electrolyte. The cell efficiency of the secondary cell is improved substantially and high capacity retained by the replacement of the chlorinated organic solvent with fluorinated organic solvent.