Abstract

The lack of fundamental understanding of the oxygen reduction and oxygen evolution in nonaqueous electrolytes significantly hinders the development of rechargeable lithium-air batteries. Here we employ a solid-state Li 4+x Ti 5O 12/LiPON/Li xV 2O 5 cell and examine in situ the chemistry of Li-O 2 reaction products on Li xV 2O 5 as a function of applied voltage under ultra high vacuum and at 500 mtorr of oxygen pressure using ambient pressure X-ray photoelectron spectroscopy. Under UHV, lithium intercalated into Li xV 2O 5 while molecular oxygen was reduced to form lithium peroxide on Li XV 2O 5 in the presence of oxygen upon discharge. Interestingly, the oxidation of Li 2O 2 began at much lower overpotentials than the charge overpotentials of conventional Li-O 2 cells with aprotic electrolytes. Our study provides the first evidence of reversible lithium peroxide formation and decomposition in situ on an oxide surface using a solid-state cell, and new insights into the reaction mechanism of Li-O 2 chemistry.