THE STUDY OF ELECTROLYTE-SOLUTIONS BASED ON ETHYLENE AND DIETHYL CARBONATES FOR RECHARGEABLE LI BATTERIES .2. GRAPHITE-ELECTRODES

The electrochemical behavior of Li-graphite intercalation anodes in et hylene and diethyl carbonates (EC-DEC) solutions was studied using sur face sensitive Fourier transform infrared spectroscopy (FTIR) and impe dance spectroscopy in conjunction with standard electrochemical techni ques. Three different solvent combinations, four different salts: LiBF 4, LiPF6, LiClO4, and LiAsF6, and the influence of the presence of CO2 were investigated. Graphite electrodes could be cycled hundreds of ti mes obtaining a reasonable reversible capacity. The best electrolyte w as found to be LiAsF6 and the presence of CO2 in solutions considerabl y increased the reversible capacity upon cycling. This improved perfor mance is due to precipitation of the ethylene carbonate reduction prod uct, (CH2OCO2Li)(2), which is an excellent passivating agent, on the e lectrode surface. Aging processes of these surface films and their inf luence on the electrode properties are discussed.