Shedding light on the light-driven lithium ion de-insertion reaction: towards the design of a photo-rechargeable battery

Abstract

Li-ion batteries need to be charged by being plugged into the grid, limiting their autonomy. Charging a battery consists of applying an external load to reverse the spontaneous electrochemical reactions during discharge. A strategy to improve their autonomy is to design nanostructured electrodes whose composition and architecture allow for these reactions to be driven by light. Classical electrochemical experiments (in the dark and under light) demonstrate that light promotes the de-insertion reaction of 3D Li_xTiO₂ mesoporous thin films due to the participation of photogenerated holes (h⁺). These holes allow the oxidation of Ti³⁺ into Ti⁴⁺, simultaneously giving rise to Li-ion extraction. Galvanostatic experiments performed on Li-rich TiO₂ mesoporous films show that competition between ion insertion and de-insertion occurs, leading to electrodes with potentially infinite capacity. This work constitutes a proof of concept that low potential Li-ion batteries (TiO₂//Li⁰) can solely be recharged by exposure to light.