Effects of aromatic esters as propylene carbonate-based electrolyte additives in lithium-ion batteries

The role of aromatic esters as additives in propylene carbonate (PC) based electrolytes used in lithium-ion batteries has been investigated. The addition of aromatic esters into the 1.0 M LiPF6-PC:DEC (3:2 in volume) suppresses the co-intercalation of PC and solvated Li+ ions and inhibits the further decomposition of electrolytes during the first lithium intercalation process. A graphitic anode (MCMB-2528, mesocarbon microbeads) in a PC-based electrolyte with the aromatic esters exhibits a high reversible capacity. Scanning electron microscopy and the first discharge curve results show that the aromatic esters decompose and form a proper solid electrolyte interphase (SEI) film on the MCMB surface to not only prevent exfoliation of the graphite electrode but also stabilize the electrolyte. Both cyclic voltammogram and the lowest unoccupied molecular orbital energy level show that the aromatic esters have higher reduction potentials than that of the electrolyte solvents. An increase in reverse capacity may be achieved by increasing the addition. However, when the addition exceeds a certain critical value, the SEI film inhibits the intercalation of lithium ions and lowers the capacity. Furthermore, the percentage of the aromatic esters in electrolytes directly influences the low-temperature performance and the rate capability of the cells. An optimal result may be obtained when the addition is approximately 2-4%. (c) 2005 The Electrochemical Society.