Bromine-based flow batteries (Br-FBs) are promising for stationary energy storage due to their advantages of high energy density and low cost. However, the sluggish reaction kinetics of the Br₂/Br⁻ redox couple results in low power density and the bromine diffusion/migration causes severe self-discharge of the batteries, affecting their overall performance.

Recently, a research team led by Prof. LI Xianfeng and Dr. LU Wenjing from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) developed novel electrodes for Br-FBs, achieving ultralow self-discharge, high power density and long cycle life.

This work was published in Energy & Environmental Science on April 1.

Illustration of the Ti₃C₂T_x-CTAB decorated electrode with high catalytic activity and excellent bromine retention capacity for a Br-FB with ultralow self-discharge and long lifespan (Image by TANG Luyin)

"We proposed a strategy of introducing a strong and reversible solid bromine complexation effect to the electrode surface, enhancing the activity of Br₂/Br⁻ reactions and inhibiting battery self-discharge simultaneously," said Prof. LI. Compared with the traditional liquid bromine complexes in the electrolyte, the formation of solid bromine complexes on the electrode exhibited a stronger bromine complexing effect, entrapping/retaining bromine species in the electrode more effectively. The zinc-bromine flow battery based on the developed electrode showed a significant increase in capacity retention from 39.15% to 82.93% after being charged to 40 mAh cm⁻² and resting for 24 h. Moreover, the solid bromine complexation effect on the electrode did not affect the electrochemical activity of the Br₂/Br⁻ couple. As a result, this battery could work stably for 580 cycles at a high current density of 180 mA cm⁻² with an average coulombic efficiency of 99.30%.

This work offers a new insight into developing electrodes for Br-FBs with high power density, high capacity retention and long life.

The above work was supported by the National Key R&D Program of China, National Natural Science Foundation of China, Dalian Science and Technology Innovation Fund, International Partnership Program of Chinese Academy of Sciences, and Youth Innovation Promotion Association CAS. (Text by TANG Luyin)