The team has successfully developed a novel bromine based two electron transfer reaction system, achieving concept validation and system scaling up of long-life zinc bromine flow batteries. The relevant results were published in the academic journal Nature Energy.

Bromine based flow batteries rely on the redox reaction between bromide ions (Br -) and bromine elements (Br2), and have the advantages of wide resource sources, high electrode potential, and high solubility. However, the large amount of Br2 generated during the charging process can cause severe corrosion to battery materials, significantly reducing the battery's cycle life and placing higher demands on the corrosion resistance of battery materials, further pushing up battery costs. Although traditional bromine chelating agents can alleviate corrosion problems to some extent, the phase separation structure formed by them often leads to poor system uniformity and increases system complexity.
To solve this problem, the team has developed a novel bromine double electron transfer reaction pathway. By introducing amine compounds with electron withdrawing groups as bromine scavengers in bromine electrolytes, they found that the Br produced in electrochemical reactions can be converted into brominated amine compounds, effectively reducing the concentration of Br in the solution. Unlike traditional single electron transfer methods (Br to Br0), this reaction achieves double electron transfer from Br to Br (brominated amine compounds), significantly improving the energy density of the battery. At the same time, the ultra-low Br concentration significantly reduces the corrosiveness of the electrolyte and improves the battery life.
The research team further applied this new reaction to zinc bromide flow batteries. Experiments have shown that using inexpensive and poorly corrosion-resistant SPEEK (sulfonated polyether ether ketone) membranes, batteries can still achieve long-term stable operation. In the system test amplified to the 5kW level, the battery can operate stably for over 700 cycles at 40mA cm-2, with a total lifespan of over 1400 hours and an energy efficiency of over 78%. Due to the extremely low concentration of Br, there was no corrosion observed in the key materials of the battery, such as the current collector, electrode, and separator, before and after cycling, further verifying the non corrosiveness of the electrolyte.
This work provides a new approach for the design of long-life bromine based flow batteries and lays the foundation for further application and promotion of zinc bromine flow batteries.