Suppression of an alkyl dicarbonate formation in Li-ion cells

Two methods were developed to suppress the formation of alkyl dicarbonate in Li-ion cells. One is the addition of vinylene carbonate (VC), which is vulnerable to nucleophilic attack, into the electrolyte to trap alkoxide anions that promote an alkyl dicarbonate formation. The addition of VC into the electrolyte of practical graphite/LiCoO2 prismatic cells effectively suppressed an alkyl dicarbonate formation and gave better cycle and power performance. The other method is a surface treatment of graphite to reduce the concentration of phenolic groups that were directly bonded to the graphite edge plane. The mild burn-off treatment successfully decreased the oxygen concentration on graphite surface and effectively suppressed an alkyl dicarbonate formation in the electrolyte. However, the irreversible capacity increased significantly, which was considered to be due to a change in the surface morphology of graphite by the burn-off treatment. (c) 2005 The Electrochemical Society.