Water-Induced Surface Reconstruction of CoO on the (111) Plane for High-Efficiency Li-O Batteries in a Hybrid Electrolyte.

The crystal plane effect of cobalt oxide has attracted much attention in Li-O batteries (LOBs) and other electrocatalytic fields. However, boosting the catalytic activity of a specific plane still faces significant challenges. Herein, a strategy of adding water into the electrolyte is developed to construct a LiOH-based Li-O battery system using the (111) plane-exposed CoO as a cathode catalyst. The electrochemical performance shows that on the (111) plane, in the presence of water, the overpotential is largely reduced from 1.5 to 1.0 V and the cycling performance is enhanced. It is confirmed that during the discharge process, water reacts to form LiOH and induce the phase transformation of CoO to amorphous CoO(OH). At the recharge stage, LiOH is first decomposed and then CoO(OH) is reduced to CoO. Compared with pristine (111), the newly formed CoO surface exhibits more active sites, which accelerates the following oxygen reduction and oxygen evolution processes. This work not only reveals the reaction mechanism of water-induced reaction on the (111) plane of CoO but also provides a new perspective for further design of hybrid Li-O batteries with a low polarization and a longer cycle life.