Aqueous Lithium–Iodine Solar Flow Battery for the Simultaneous Conversion and Storage of Solar Energy

Integrating both photoelectric-conversion and energy-storage functions into one device allows for the more efficient solar energy usage. Here we demonstrate the concept of an aqueous lithium–iodine (Li–I) solar flow battery (SFB) by incorporation of a built-in dye-sensitized TiO2 photoelectrode in a Li–I redox flow battery via linkage of an I3–/I– based catholyte, for the simultaneous conversion and storage of solar energy. During the photoassisted charging process, I– ions are photoelectrochemically oxidized to I3–, harvesting solar energy and storing it as chemical energy. The Li–I SFB can be charged at a voltage of 2.90 V under 1 sun AM 1.5 illumination, which is lower than its discharging voltage of 3.30 V. The charging voltage reduction translates to energy savings of close to 20% compared to conventional Li–I batteries. This concept also serves as a guiding design that can be extended to other metal-redox flow battery systems.