Twin problems of interfacial carbonate formation in nonaqueous Li-O₂ batteries

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-O₂ cells in ether electrolytes originate from reaction of Li₂O₂ (or LiO₂) both with the electrolyte and with the C cathode. Reaction with the cathode forms approximately a monolayer of Li₂CO₃ at the C-Li₂O₂ interface, while reaction with the electrolyte forms approximately a monolayer of carbonate at the Li₂O₂-electrolyte interface during charge. A simple electrochemical model suggests that the carbonate at the electrolyte-Li₂O₂ 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-Li₂O₂ 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.