Lawrence Berkeley National Laboratory

A homologous series of propylene carbonate (PC) analog solvents with increasing length of linear alkyl substitutes were synthesized and used as co-solvents with PC for graphite-based lithium-ion half cells. A graphite anode reaches a capacity of around 310 mAh/g in PC and its analog co-solvents, with 99.95 percent Coulombic efficiency, similar to the values obtained with ethylene carbonate-based electrolytes. Solvent interaction with the graphite anode and subsequent decomposition determines the graphite anode performance. Gaseous products from cyclic carbonates with short alkyl chains cause exfoliation of the graphite anode; solvents with longer alkyl chains are able to prevent graphite exfoliation when used as co-solvents with PC. The PC co-solvents compete for solvation of the Li ion with the PC solvent, delaying PC co-intercalation. Reduction products of PC on a graphite surface via a single-electron path form a stable Solid Electrolyte Interphase (SEI), which allows the reversible cycling of graphite. © 2013 The Electrochemical Society.