Deciphering the Enigma of LiCO Oxidation Using a Solid-State Li-Air Battery Configuration.

LiCO is a ubiquitous byproduct in Li-air (O) batteries, and its accumulation on the cathode could be detrimental to the devices. As a result, much efforts have been devoted to investigating its formation and decomposition, in particular, upon cycling of Li-O batteries. At high voltages, LiCO is expected to decompose into CO and O. However, as recognized from the work of many authors, only CO, and no O, has been identified, and the underlying mechanism remains uncertain so far. Herein, a solid-state Li-O battery (Li|LiLaZrTaO|Au) has been designed to interrogate the LiCO oxidation without interferences from the decomposition of other battery components (organic electrolyte, binder, and carbon cathode) widely applied in conventional Li-O batteries. It is revealed that LiCO can indeed be oxidized to CO and O in a more stable solid-state Li-O battery configuration, highlighting the feasibility of reversible operation of Li-O batteries with ambient air as the feeding gas.