Photo-electrochemical enhanced mechanism enables a fast-charging and high-energy aqueous Al/MnO₂ battery

Rechargeable aqueous batteries, such as metal aluminum ion batteries (AAIBs), are highly desirable for large-scale energy storage owing to their low cost, long-term stability and high safety. As a promising positive electrode material for AAIBs, manganese oxide (n-type semiconductor) presents high operating voltage, good reversibility, and high energy density, while slow kinetics and undesired soluble Mn²⁺ are major issues for limiting their applications. Here, we demonstrate a highly reversible photo-electrochemical coupling system, where the induced photoelectrons enable for rapid kinetics, fast charging, and enhanced rate performance. The cell under illuminated allows MnO₂ for delivering a massively promoted discharge capacity 531 mA h g ^{− 1} (with a specific current of 0.1 A g ^{− 1}) along with a high increment of 41.3%, competitive with the record values achieved in the documented AAIBs. Additionally, the generated soluble Mn²⁺ in discharging process could be oxidized to Mn⁴⁺ due to exist of photochemical oxidation behavior, thus further enhancing the charge storage ability. The mechanism of the photo-electrochemical coupling system has been fully understood, which provides a design path for other energy storage systems.