Evidence for epoxide formation from the electrochemical reduction of ethylene carbonate

It is now generally agreed that the electrochemical reduction of ethylene c arbonate (EC) plays an important role in the formation of an effective soli d electrolyte interface layer on the carbon anode in lithium-ion cells. How ever, neither the composition of this layer nor the reaction pathways invol ved in its formation have been clearly established. We report reflectance i nfrared spectra from a glassy carbon electrode surface after EC/tetrahydrof uran electrolyte reduction that is unlike any other we have seen in the lit erature. The spectrum has its strong absorption peak at 838 cm(-1), and thi s feature is clearly shown not to be from the monoethylcarbonate lithium sa lt. Ethylene oxide is suggested as a possible, but not exclusive, reduction product. The suggested reaction pathway is an electrochemical-chemical seq uence, electrochemical reduction of water to form hydroxide, and hydroxide addition to form ethylene oxide and lithium bicarbonate. (C) 2001 The Elect rochemical Society.