Organic electrolyte and lithium cell using it

An organic electrolytic solution includes a lithium salt and an organic solvent containing a phosphonate compound, and a lithium battery utilizes the organic electrolytic solution. When using the organic electrolyte containing the phosphonate compound to manufacture a lithium secondary battery, the lithium secondary battery has improved stability to reduction-induced decomposition, reduced first cycle irreversible capacity, and improved charging/discharging efficiency and lifespan. In addition, the lithium secondary battery does not swell beyond a predetermined thickness range after formation and standard charging at room temperature and has improved reliability. Even when the lithium secondary battery swells seriously at a high temperature, its capacity is high enough for practical applications. The capacity of the lithium secondary battery may substantially be recovered after being left at a high temperature.