Recently, a team led by Dr. Xianfeng Li and Dr. Wenjing Lu, researchers at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has made significant progress in the research of electrodes for bromine-based flow batteries. By exploiting a reversible solid-state bromine complexation effect on the electrode surface, the team has simultaneously improved the electrode's solid bromine capacity and catalytic activity, reduced the self-discharge rate of bromine-based flow batteries, and enhanced the battery's power density and cycle life. Their findings have been published in Energy & Environmental Science.
Bromine-based flow batteries offer advantages such as high energy density and low cost, making them promising for applications in distributed energy storage. However, the relatively low reactivity of bromine and the self-discharge issue caused by bromine diffusion severely impact the power density and cycle life of bromine-based flow batteries.
To address these challenges, the research team proposed a strategy to introduce solid-state bromine complexing agents onto the electrode surface. Based on a strong reversible solid-state complexation effect, this strategy can suppress battery self-discharge while enhancing the reactivity of bromine. The study found that compared to liquid complexing agents in traditional electrolytes, the solid-state complexing agents on the electrode have a stronger complexation effect on bromine. They securely capture and immobilize soluble bromine in the electrode, effectively preventing bromine diffusion from the electrode surface into the bulk electrolyte, thus inhibiting the battery's self-discharge reaction. The team tested this electrode in a zinc-bromine flow battery and observed a significant improvement in capacity retention, from 39.15% to 82.93%, after charging to 40mAh/cm2 and resting for 24 hours.
Furthermore, unlike liquid complexing agents in traditional electrolytes, the solid-state bromine complexation effect on the electrode surface does not affect the electrochemical activity of bromine couples. Zinc-bromine flow batteries assembled with this electrode can stably cycle 580 times at a high current density of 180mAh/cm2, with an average coulombic efficiency of 99.30%.
This work provides a new approach for developing electrode materials for bromine-based flow batteries with high power density, high capacity retention, and long cycle life.
Related paper: https://doi.org/10.1039/D4EE00580E
