A high-voltage rechargeable alkaline Zn–MnO4− battery with enhanced stability achieved by highly reversible MnO4−/MnO42− redox pair

Development of rechargeable alkaline Zn–Mn batteries has been facing big challenges for low working voltage and poor cycling stability, although they have advantages of low cost, high safety, and simple maintenance. For the first time, this work demonstrates a record high voltage (1.78 V) for rechargeable alkaline Zn–MnO 4 − battery achieved by a high reversible redox pair of MnO 4 − /MnO 4 2− , which shows excellent cycling stability up to 1,500 cycles at a high current density of 20 mA cm −2 without obvious capacity attenuation. The MnO 4 − /MnO 4 2− redox reaction investigated by ex-situ  scanning electron microscope as well as ultraviolet and visible absorption spectrum indicates high reversibility of the MnO 4 − /MnO 4 2− redox couple after the activation during the first discharge process. Furthermore, benefiting from the liquid-phase reaction nature of MnO 4 − /MnO 4 2− , a flow battery is further prototyped to show highly stable cycles with 95.8% of discharge capacity retention for 600 cycles at the current density of 40 mA cm −2 .