Boosting Electrolytic MnO₂–Zn Batteries by a Bromine Mediator

Abstract

An aqueous electrolytic MnO 2 −Zn battery with eyecatching 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.

Issues and Opportunities Facing Aqueous Mn2+/MnO2‐based Batteries

“…This strategy could lead to complete MnO 2 dissolution and the recovery of the exfoliated MnO 2 . Also, similar strategy was reported to be employed in Zn−MnO 2 /Br 2 batteries (sulfated‐based) [30] …”

“…Also, similar strategy was reported to be employed in ZnÀ MnO 2 /Br 2 batteries (sulfated-based). [30]…”

Unleashing energy storage ability of aqueous battery electrolytes

“…Lu et al introduced an iodide [99]. Likewise, Chen et al [100] employed Br 3 − /Br − mediator to improve the dissolution of the over deposited MnO 2 and enhance the reversibility of the cathodic reaction. The acidic electrolyte facilitates the Mn 2+ /Mn 4+ conversion but brings a high risk of Zn corrosion.…”

Rechargeable Manganese Dioxide−Zinc Batteries: A Review Focusing on Challenges and Optimization Strategies under Alkaline and Mild Acidic Electrolyte Media

“…Zheng et al constructed a new type MnO 2 /Br 2 À Zn battery, whereas, bromine mediator was used in order to enhance the electrochemical performances of MnO 2 positive electrode. [117] The proposed MnO 2 /Br 2 À Zn battery is operated through synergistic reactions between the MnO 2 / Mn 2 + and Br 3 À /Br À chemistries at positive electrode and the Zn/ Zn 2 + reactions at negative electrode. The composite electrolyte comprises 1 M ZnSO 4 , 1 M MnSO 4 and 0.2 M H 2 SO 4 along with 0.05 M ZnBr 2 and 0.2 M Br 2 as the mediators.…”