Evidence for Epoxide Formation from the Electrochemical Reduction of Ethylene Carbonate

It is now generally agreed that the electrochemical reduction of ethylene carbonate (EC) plays an important role in the formation of an effective solid electrolyte interface layer on the carbon anode in lithium-ion cells. However, neither the composition of this layer nor the reaction pathways involved in its formation have been clearly established. We report reflectance infrared spectra from a glassy carbon electrode surface after EC/tetrahydrofuran electrolyte reduction that is unlike any other we have seen in the literature. The spectrum has its strong absorption peak at 838 cm −1 , and this feature is clearly shown not to be from the monoethylcarbonate lithium salt. Ethylene oxide is suggested as a possible, but not exclusive, reduction product. The suggested reaction pathway is an electrochemical-chemical sequence, electrochemical reduction of water to form hydroxide, and hydroxide addition to form ethylene oxide and lithium bicarbonate.