Approaching the theoretical capacity of TiO₂ anode in a photo-rechargeable lithium-ion battery

New generation of lithium-ion batteries (LIBs) integrating solar energy conversion and storage is emerging, as they could solve the fluctuation problem in the utilization of solar energy. Photo-rechargeable lithium-ion batteries (PR-LIBs) are ideal devices for such target, in which solar energy is converted into electricity and stored in LIB. In order to achieve the high performance of PR-LIB, it is crucial to develop dual-function electrode materials that can synergistically capture solar energy and store lithium. Herein, we present photo-rechargeable lithium-ion batteries using defective black TiO₂ as photoanode prepared by lithium reduction. The photoanode exhibits excellent photo response in full solar spectrum with a capacity enhancement of 46.4% under illumination, corresponding to the energy conversion efficiency of 4.4% at the current density of 1 A·g⁻¹. When illumination is applied at 20 mA·g⁻¹, the battery capacity increases from ~ 230 in dark to ~ 349 mAh·g⁻¹ at the first cycle, and then stabilizes at 310 mAh·g⁻¹, approaching the theoretical value of 335 mAh·g⁻¹ of TiO₂ electrode material. This finding provides thoughts for breaking the capacity limitations in TiO₂ and paves the way for powering LIBs by solar illumination.