In situ ambient pressure X-ray photoelectron spectroscopy studies of lithium-oxygen redox reactions

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 (UHV) and at 500 mtorr of oxygen pressure using ambient pressure X-ray photoelectron spectroscopy (APXPS). 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 (∼240 mV) than the charge overpotentials of conventional Li-O 2 cells with aprotic electrolytes (∼1000 mV). 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.