Z-Scheme g-C3N4/TiO2 heterojunction for a high energy density photo-assisted Li–O2 battery†

A lithium–oxygen battery based on the formation of lithium oxide (Li₂O) can theoretically achieve a high energy density through a four-electron reaction. This is more challenging to accomplish than the one- and two-electron reactions that produce lithium superoxide (LiO₂) and lithium peroxide (Li₂O₂), respectively. A stable cathode with a sufficient supply of electrons and Li cations to form Li₂O must be developed to achieve a four-electron reaction for a lithium–oxygen battery. Herein, by utilizing a composite 3D-printed cathode composed of a g-C₃N₄/TiO₂ (gCNTO) heterostructure nanoparticle with high porosity and high conductivity, we were able to provide ample space and numerous active/catalytic sites during the reaction process. Our findings indicate that Li₂O is the product of the photo-assisted lithium–oxygen battery. Under illumination, the battery can be rechargeable for over 1000 hours at 0.05 mA cm⁻² with a small polarization gap. The photocathode delivers an ultra-high discharge capacity of 29.7 mA h cm⁻² at 0.5 mA cm⁻², resulting in a specific energy of approximately 515.12 W h kg⁻¹_cell. The performance is superior to the battery with Li₂O₂ as a discharge product in the dark. This study paves the way for the rapid development of high-energy-density photo-assisted Li–O₂ batteries.