Lithium Nitrate As Regenerable SEI Stabilizing Agent for Rechargeable Li/O2 Batteries

A major unsolved problem with rechargeable Li/O-2 batteries is the identification of electrolyte compositions that allow efficient and stable cycling of both Li metal and O-2 electrodes simultaneously. Previously, lithium nitrate (LiNO3) was employed in a rechargeable Li/O-2 battery to stabilize the solid electrolyte interphase on Li metal in an electrolyte based on N,N-dimethylacetamide (DMA), a solvent with favorable properties vis-a-vis the O-2 electrode. We show that LiNO3 is regenerated following reaction with Li metal in the presence of dissolved O-2, which may account for the surprising long-term cycling previously demonstrated in DMA. According to this new concept, nitrate anions incorporated into the electrolyte react with Li metal to form soluble nitrite anions and a passivating layer of Li2O on the Li electrode surface. The soluble nitrite anions subsequently react with dissolved O-2 through a combined electrochemical and chemical process that results in regeneration of nitrate. Discovery of this regenerative principle provides a strategy for using other solvents that have favorable characteristics in the O-2 electrode but are highly unstable toward Li metal without the use of a ceramic Li-ion-conducting membrane.