A High‐Energy Aqueous Aluminum‐Manganese Battery

Abstract Rechargeable aluminum‐ion batteries have drawn considerable attention as a new energy storage system, but their applications are still significantly impeded by critical issues such as low energy density and the lack of excellent electrolytes. Herein, a high‐energy aluminum‐manganese battery is fabricated by using a Birnessite MnO 2 cathode, which can be greatly optimized by a divalence manganese ions (Mn 2+ ) electrolyte pre‐addition strategy. The battery exhibits a remarkable energy density of 620 Wh kg −1 (based on the Birnessite MnO 2 material) and a capacity retention above 320 mAh g −1 for over 65 cycles, much superior to that with no Mn 2+ pre‐addition. The electrochemical reactions of the battery are scrutinized by a series of analysis techniques, indicating that the Birnessite MnO 2 pristine cathode is first reduced as Mn 2+ to dissolve in the electrolyte upon discharge, and Al x Mn (1− x ) O 2 is then generated upon charge, serving as a reversible cathode active material in following cycles. This work provides new opportunities for the development of high‐performance and low‐cost aqueous aluminum‐ion batteries for prospective applications.