Electrochemical and infrared studies of the reduction of organic carbonates

The reduction potentials of five organic carbonates commonly employed in lithium battery electrolytes, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and vinylene carbonate (VC) were determined by cyclic voltammetry using inert (Au or glassy carbon) electrodes in tetrahydrofuran/LiClO4 supporting electrolyte. The reduction potentials for all five organic carbonates were above 1 V (vs. Li/Li+). PC reduction was observed to have a significant kinetic hindrance. The measured reduction potentials for EC, DEC, and PC were consistent with thermodynamic values calculated using density functional theory (DFT) assuming one-electron reduction to the radical anion. The experimental values for VC and DMC were, however, much more positive than the calculated values, which we attribute to different reaction pathways. The role of VC as an additive in a PC-based electrolyte was investigated using conventional constant-current cycling combined with ex situ infrared spectroscopy and in situ atomic force microscopy (AFM). We confirmed stable cycling of a commercial li-ion battery carbon anode in a PC-based electrolyte with 5 mol % VC added. The preferential reduction of VC and the solid electrolyte interphase layer formation therefrom appears to inhibit PC cointercalation and subsequent graphite exfoliation. (C) 2001 The Electrochemical Society.