A high-energy aqueous aluminum-manganese battery

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 MnO2 cathode, which can be greatly optimized by a divalence manganese ions (Mn2+) electrolyte pre-addition strategy. The battery exhibits a remarkable energy density of 620 Wh kg−1 (based on the Birnessite MnO2 material) and a capacity retention above 320 mAh g−1 for over 65 cycles, much superior to that with no Mn2+ pre-addition. The electrochemical reactions of the battery are scrutinized by a series of analysis techniques, indicating that the Birnessite MnO2 pristine cathode is first reduced as Mn2+ to dissolve in the electrolyte upon discharge, and AlxMn(1−x)O2 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.