Abstract: 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 cycle 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 fluorinated 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.