Effect of Water and HF on the Distribution of Discharge Products at Li–O2 Battery Cathode

Li–air battery has attracted much attention because of its very high theoretical energy density, but its actual performance is still very low. Most important reasons are the slow kinetics and low reversibility of electrodeposition/dissolution of Li–O2 species at the cathode. Thus, much effort has been devoted to understand the mechanisms of these processes but low reproducibility makes the full understanding of the mechanism difficult. Here we demonstrate that low reproducibility is caused by impurities in solution by showing how HF and H2O, major impurities, affect the potential dependent product distribution during discharge at Li–O2 cathode. HF causes significant mass increase as a result of the deposition of fluorine-containing species and H2O converts Li2O2 to proton containing side products such as H2O2, LiHO2, and LiOH and induces the solvent, DMSO, decomposition. These results demonstrate the importance of the impurity control in the operation of Li–air battery.