Bromine Assisted MnO Dissolution Chemistry: Toward a Hybrid Flow Battery with Energy Density of over 300 Wh L.

Mn /Mn 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 Mn , which results in accumulation of "dead" MnO limits its reversibility and further energy density. Herein, a novel catholyte based on mixture of Mn and Br was proposed for flow batteries with high energy density and long cycle life. In the design, the "dead" MnO can be fully discharged via Br by a chemical-electrochemical reaction. Coupled with Cd/Cd as anode, the assembled Bromine-Manganese flow battery (BMFB) demonstrates a high energy efficiency of 76 % at 80 mA cm with energy density of 360 Wh L . The battery assembled with silicotungstic acid as anode could continuously run for over 2000 cycles at 80 mA cm . With high power density, energy density and durability, the BMFB shows great potential for large-scale energy storage.