Bromine Assisted MnO2 Dissolution Chemistry: Toward a Hybrid Flow Battery with Energy Density of over 300 Wh L−1

Abstract

AbstractMn2+/Mn3+ redox pair has been considered as a promising cathode for high energy density batteries, due to its attractive features of high redox potential, solubility and outstanding kinetics. However, the disproportionation side reaction of Mn3+, which results in accumulation of “dead” MnO2 limits its reversibility and further energy density. Herein, a novel catholyte based on mixture of Mn2+ and Br− was proposed for flow batteries with high energy density and long cycle life. In the design, the “dead” MnO2 can be fully discharged via Br− by a chemical‐electrochemical reaction. Coupled with Cd/Cd2+ as anode, the assembled Bromine‐Manganese flow battery (BMFB) demonstrates a high energy efficiency of 76 % at 80 mA cm−2 with energy density of 360 Wh L−1. The battery assembled with silicotungstic acid as anode could continuously run for over 2000 cycles at 80 mA cm−2. With high power density, energy density and durability, the BMFB shows great potential for large‐scale energy storage.