Addition of silver hexafluorophosphate to propylene carbonate (PC)-based electrolyte may suppress the cointercalation and decomposition of PC in mesocarbon microbeads (MCMB). During the first charge/discharge cycle, silver ions are reduced at a potential (2.15 V vs. Li/Li+) higher than that of the PC cointercalation potential (0.75 V vs. Li/Li+) to form a protective film on the MCMB surface, thereby obstructing PC cointercalation. Results show an increasing trend for both reversible capacity and cycle life performance with increasing AgPF6. A satisfactory reversible capacity may be obtained when the silver addition is greater than 5 wt %. (C) 2004 The Electrochemical Society.