High Energy Efficiency and Stability for Photoassisted Aqueous Lithium–Iodine Redox Batteries

We demonstrated photoassisted lithium–iodine (Li–I<sub>2</sub>) redox cells integrated with a hematite photoelectrode that are applicable to energy storage systems (ESSs). The hematite photoelectrode presents low cost, light absorption in the visible light region, and inertness to aqueous electrolytes, which allow for stable production of photocurrent under illumination. In the aqueous Li–I<sub>2</sub> redox cells, the harnessing of photoenergy generates photocarriers that promote the I<sup>–</sup> oxidation process without electrolysis of the aqueous solution. The energy efficiency for the photoassisted charge process is ∼95.4%, which is ∼20% higher than that in the absence of illumination at a current rate of 0.075 mA cm<sup>–2</sup>. The hematite is profoundly stable in aqueous I<sup>–</sup>/I<sub>3</sub><sup>–</sup> catholyte and exhibits over 600 h of cycling without noticeable performance decay and photocorrosion. This achievement highlights photoinduced ESSs with improved energy efficiency.