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.