Solar‐Light‐Assisted Lithium‐Ion Storage Using Solar‐Light Absorbing Material

This study directly irradiates solar light on an electrode and evaluates the effect of solar‐light irradiation on lithium‐ion storage in tungsten oxide which has dual properties of solar‐light absorption and lithium‐ion storage. WO 3 can be excited by solar‐light irradiation and then generates photoelectrons that can affect the electrochemical properties of WO 3 during lithiation and delithiation. The specific capacitance of WO 3 for lithium‐ion storage increases approximately 150% under solar‐light irradiation, which is attributed to the photoelectrons by increasing the conductivity of the WO 3 electrode and decreasing the surface energy for intercalating the lithium ions. The advantage of light irradiation is maximized under continuous light irradiation during lithiation and delithiation rather than intermittent irradiation. Delithiation showed a more significant improvement under light irradiation than lithiation due to the agreement of the direction of electron and photoelectron flows caused by the band bending of WO 3 semiconductors (enabling easier deintercalation of lithium ions). Both the generated photoelectrons and intrinsic properties (such as band bending of the WO 3 ) affect the lithium‐ion storage ability of WO 3 under light irradiation.