Nanostructured Metal Carbides for Aprotic Li–O₂ Batteries: New Insights into Interfacial Reactions and Cathode Stability

The development of nonaqueous Li–oxygen batteries, which relies on the reversible reaction of Li + O₂ to give lithium peroxide (Li₂O₂), is challenged by several factors, not the least being the high charging voltage that results when carbon is typically employed as the cathode host. We report here on the remarkably low 3.2 V potential for Li₂O₂ oxidation on a passivated nanostructured metallic carbide (Mo₂C), carbon-free cathode host. Online mass spectrometry coupled with X-ray photoelectron spectroscopy unequivocally demonstrates that lithium peroxide is simultaneously oxidized together with the Li_<i>x</i>MoO₃-passivated conductive interface formed on the carbide, owing to their close redox potentials. The process rejuvenates the surface on each cycle upon electrochemical charge by releasing Li_<i>x</i>MoO₃ into the electrolyte, explaining the low charging potential