Scientists develop a manganese-based hybrid single flow battery with high energy density

A research group led by Prof. Li Xianfeng from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has developed a bromine-assisted-MnO₂-based hybrid single flow battery that exhibits advantages of high energy density and reversibility.

This study was published in Angewandte Chemie International Edition on Oct. 26.

The Mn²⁺/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 energy density.

In this study, the researchers provided a new concept to solve the issue of "dead" MnO₂ by introducing Br^-/Br₂into Mn²⁺/MnO₂ catholyte in a highly acidic environment.

Br^- was first oxidized to Br₂ during charge, and then Mn²⁺ was oxidized to Mn³⁺, which could be partially disproportionated to form MnO₂ simultaneously. During discharge, Mn³⁺ and part of MnO₂ were reduced to Mn²⁺ first and Br₂ was reduced to Br^-. Then the produced Br^- could react with "dead" MnO₂ to Br₂, participating in discharge, completing the reduction process, and avoiding the accumulation of "dead" MnO₂.

Furthermore, the researchers assembled a bromine-manganese flow battery (BMFB) coupling with Cd/Cd²⁺ as the anode. The battery exhibited high energy density of 360 Wh L^-1 and stable running for over 500 cycles at a current density of 80 mA cm^-2.

"The battery assembled with silicotungstic acid as anode could continuously run for over 2000 cycles at 80 mA cm^-2, which further confirmed the reliability and universality of the catholyte," said Prof. Li. "We believe the BMFB has great potential for large-scale energy storage."