Photo-energy Conversion and Storage in an Aprotic Li-O Battery.

A photo-involved Li-O battery with carbon nitride (C N ) 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 N are donated to O for O , which undergoes a second electron reduction to O and gives the final product of Li O ; in a reverse process, holes left behind in the valence band (VB) of C N plus an applied lower voltage than the equilibrium drive the Li O 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.