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

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.