Irradiation Spillover Effect in Photo‐Assisted Ion Batteries: Overcoming Size Limits for Solar Utilization

Abstract Photo‐assisted ion batteries demonstrate remarkable potential for portable and decentralized solar energy utilization, due to their profound capacity enhancement under irradiation accompanied by promoted discharge voltages. However, ion batteries in practice are highly compact with limited surface area for irradiation. Overcoming the size limit for irradiation is a challenge. Herein, an irradiation spillover effect in photo‐assisted ion batteries is demonstrated, that is the impact of irradiation on the battery is not restrained within the irradiated area but can spillover the whole electrode. This phenomenon is a consequence of the light‐induced potential difference between irradiated and unirradiated regions, leading to selective ion insertion. Irradiated regions favored H⁺ insertion due to light‐induced proton‐coupled electron transfer, while unirradiated regions preferred Zn²⁺ insertion. Consequently, the capacity enhancement remains unaffected by halving the irradiated area. This study overcomes the irradiation size limit for photo‐assisted ion batteries and encourages highly integrated photo‐assisted ion batteries for practice application.