Water-Induced Surface Reconstruction of Co 3 O 4 on the (111) Plane for High-Efficiency Li-O 2 Batteries in a Hybrid Electrolyte.

The crystal plane effect of cobalt oxide has attracted much attention in Li-O 2 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 2 battery system using the (111) plane-exposed Co 3 O 4 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 Co 3 O 4 to amorphous CoO x (OH) y . At the recharge stage, LiOH is first decomposed and then CoO x (OH) y is reduced to Co 3 O 4 . Compared with pristine (111), the newly formed Co 3 O 4 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 Co 3 O 4 but also provides a new perspective for further design of hybrid Li-O 2 batteries with a low polarization and a longer cycle life.