A Long-Life Zinc-Bromine Single-Flow Battery Utilizing Trimethylsulfoxonium Bromide as Complexing Agent

Aqueous zinc-bromine single-flow batteries (ZBSFBs) are highly promising for distributed energy storage systems due to their safety, low cost, and relatively high energy density. However, the limited operational lifespan of ZBSFBs poses a significant barrier to their large-scale commercial viability. Here, trimethylsulfoxonium bromide (TMSO), a nonquaternary ammonium salt, is introduced as a bromine complexing agent to extend the cycle life of ZBSFBs by reducing the imbalance of active substances. Benefiting from the strong interaction between TMSO and H₂O, the hydrogen evolution reaction is notably suppressed compared with the traditional N-ethyl-N-methyl-pyrrolidinium bromide (MEP) complexing agent, resulting in reduced bromine accumulation at the cathode. The resultant solid polybromide-TMSO complex, featuring rapid electrochemical redox reaction of Br₂/Br^-, further contributes to reduce the residual bromine. Consequently, the ZBSFB with TMSO demonstrates a longer lifespan of 1500 cycles with a higher average energy efficiency (EE) of ≈81.6% than that with MEP (less than 300 cycles with an average EE of ≈80.2%). This research explores a sulfonium complexing agent and provides a feasible strategy to effectively extend the cycle life of ZBSFBs.