A High-Energy Aqueous Manganese–Metal Hydride Hybrid Battery

Aqueous rechargeable batteries show great application prospects in large-scale energy storage because of their reliable safety and low cost. However, a key challenge in developing this battery system lies in its low energy density. Herein, a high-energy manganese–metal hydride (Mn–MH) hybrid battery is reported in which a Mn-based cathode operated by the Mn²⁺/MnO₂ deposition–dissolution reactions, a hydrogen-storage alloy anode that absorbs and desorbs hydrogen in an alkaline solution, and a proton-exchange membrane separator are employed. Given the benefit derived from the high solubility and high specific capacity of the Lewis acidic MnCl₂ in the cathode and the low electrode potential of the MH anode, this aqueous Mn–MH hybrid battery exhibits impressive electrochemical properties with admirable discharge voltage plateaus up to 2.2 V, a competitive energy density of about 240 Wh kg⁻¹ (based on the total mass of the 5.5 m MnCl₂ solution and the hydrogen storage alloy electrode system), good cycling stability over 130 cycles, and a desirable rate capability. This work demonstrates a new strategy for achieving high-performance and low-cost aqueous rechargeable batteries.