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.