A Renewable Light-Promoted Flexible Li-CO₂ Battery with Ultrahigh Energy Efficiency of 97.9

Directly converting and storing abundant solar energy in next-generation energy storage devices is of central importance to build a sustainable society. Herein, a new prototype of a light-promoted rechargeable and flexible Li-CO₂ battery with a TiO₂ /carbon cloth (CC) cathode is reported for the direct utilization of solar energy to promote the kinetics of the carbon dioxide reduction reaction and carbon dioxide evolution reaction (CO₂ ER). Under illumination, photoelectrons are generated in the conduction band of TiO₂ /CC, followed by the enhancing diffusion of electrons and lithium ions during the discharge process. The photoelectrons on the cathode surface can regulate the morphology of the discharge product Li₂ CO₃ , contributing to boosting the kinetics of the subsequent CO₂ ER process. In the reverse charge process, photogenerated holes can favor the decomposition of Li₂ CO₃ , leading to a negative charge potential of 2.88 V without increased polarization over ≈60 h of cycling. Owing to an ultralow overpotential of 0.06 V between the discharge and charge process, an ultrahigh energy efficiency of 97.9% is attained under illumination. The introduction of a light-promoted flexible Li-CO₂ battery can pave the way toward developing the use of solar energy to address the charging overpotential of conventional Li-CO₂ batteries.