Photo‐energy Conversion and Storage in an Aprotic Li‐O2 Battery

Abstract A photo‐involved Li‐O 2 battery with carbon nitride (C 3 N 4 ) is presented as a bifunctional photocatalyst to accelerate both oxygen reduction and evolution reactions. With illumination in a discharge process, photoelectrons generated in the conduction band (CB) of C 3 N 4 are donated to O 2 for O 2 − , which undergoes a second electron reduction to O 2 2− and gives the final product of Li 2 O 2 ; in a reverse process, holes left behind in the valence band (VB) of C 3 N 4 plus an applied lower voltage than the equilibrium drive the Li 2 O 2 oxidation. The discharge voltage is significantly increased to 3.22 V, surpassing the thermodynamic limit of 2.96 V, and the charge voltage is reduced to 3.38 V. This leads to a record‐high round‐trip efficiency of 95.3 % and energy density increase of 23.0 % compared to that in the dark.