Light‐Induced Charge Separation in Mixed Electronic/Ionic Semiconductor Driving Lithium‐Ion Transfer for Photo‐Rechargeable Electrode

Abstract Li‐ion batteries need to be regularly recharged, requiring chargers and connection to the grid to reverse the lithium‐ion transfer. Autonomous power sources independent of the electrical infrastructure are desired. A strategy to develop continuously functioning Li‐ion batteries is focused on a new architecture of electrodes which are capable of both harvesting light energy and storing it. One possible way to achieve this lies in a study aimed at evaluating whether lithium ions can display mobility inside a crystal structure upon light absorption, as in analogy to the dissociation process of excitons. Herein, it is demonstrated that by using LixTiO2 nanoparticles, bandgap excitation can induce a quantitative Li‐ion deinsertion reaction by the free holes generated. The half‐electrochemical cells containing these mesoporous lithiated TiO2 can be fully oxidized in only 1 h of light exposure. It displays close to 3 V open‐circuit potential under light and electrical load, and, provides a constant output power under fluctuating light conditions. Such an approach has the potential, when integrated into a fully regenerative device containing a suitable counter electrode, to generate energy during both day and night, thus having the potential to close the gap between electrochemical energy storage batteries and energy conversion photovoltaics.