Performances of Li/LixCoO2 cells in LiAlCl4 · 3SO2 electrolyte

A nonaqueous inorganic electrolyte, LiAlCl4·3SO2, was employed in an Li/LixCoO2 rechargeable battery. In this medium, the LixCoO2 cathodes reversibly intercalate and de-intercalate Li+ ions at 3.90 and 3.92 V (versus Li/Li+), respectively. Because of the high electrolyte conductivity (about 0.1 S cm−1 at 0–25 °C), the cell could be operated at a relatively high charge/discharge rate (C/1 rate) even at subambient temperature. Anode degradation could be alleviated by adding small amounts of LiPF6 to the electrolyte. Cl2 evolution at the end of the charging period (>4.07 V) was the major side reaction involved in the present cell system which has detrimental effects on the coulombic efficiency of the cells and on the cathodic reversibility. The observed cathode degradation seems to be caused by a Cl2 attack on the cathode material. The Cl2 generation was less significant at lower temperatures, such that a higher coulombic efficiency and better capacity retention could be achieved at lower temperatures even though the discharge voltages were slightly lower due to higher cell polarization.