Boosting Electrolytic MnO₂–Zn Batteries by a Bromine Mediator

An aqueous electrolytic MnO 2 –Zn battery with eye-catching Mn 2+ /MnO 2 cathode chemistry has been attracting immense interest for next-generation energy storage devices due to its irreplaceable advantages. However, the limited MnO 2 conductivity restricts its long service life at high areal capacities. Here, we report a high-performance electrolytic MnO 2 –Zn battery via a bromine redox mediator, to enhance its electrochemical performance. The MnO 2 /Br 2 –Zn battery displays a high discharge voltage of 1.98 V with a capacity of ∼5.8 mAh cm –2 . It also shows an excellent rate performance of 20 C with a long-term stability of over 600 cycles. Furthermore, the scaled-up MnO 2 /Br 2 –Zn battery with a capacity of ∼950 mAh exhibits a stable 100 cycles with a practical cell energy density of ∼32.4 Wh kg –1 and an attractively low energy cost of below 15 US$ kWh –1 . The design approach can be generalized to other electrodes and battery systems, thus opening up new possibilities for large-scale energy storage.