Twin problems of interfacial carbonate formation in nonaqueous Li-O ₂ batteries

Abstract

We use XPS and isotope labeling coupled with differential electrochemical mass spectrometry (DEMS) to show that small amounts of carbonates formed during discharge and charge of Li-O 2 cells in ether electrolytes originate from reaction of Li 2O 2 (or LiO 2) both with the electrolyte and with the C cathode. Reaction with the cathode forms approximately a monolayer of Li 2CO 3 at the C-Li 2O 2 interface, while reaction with the electrolyte forms approximately a monolayer of carbonate at the Li 2O 2-electrolyte interface during charge. A simple electrochemical model suggests that the carbonate at the electrolyte-Li 2O 2 interface is responsible for the large potential increase during charging (and hence indirectly for the poor rechargeability). A theoretical charge-transport model suggests that the carbonate layer at the C-Li 2O 2 interface causes a 10-100 fold decrease in the exchange current density. These twin "interfacial carbonate problems" are likely general and will ultimately have to be overcome to produce a highly rechargeable Li-air battery. © 2012 American Chemical Society.