Tailoring Zn-ion Solvation Structures for Enhanced Durability and Efficiency in Zinc–Bromine Flow Batteries

Aqueous zinc-bromine flow batteries (ZBFBs) are among the most appealing technologies for large-scale stationary energy storage due to their scalability, cost-effectiveness, safety and sustainability. However, their long-term durability is challenged by issues like the hydrogen evolution reaction (HER) and dendritic zinc electroplating. Herein, we address these challenges by reshaping the Zn²⁺ ion solvation structures in zinc bromide (ZnBr₂) aqueous electrolytes using a robust hydrogen bond acceptor as a cosolvent additive. Our findings highlight the critical role of interactions within the first and second Zn²⁺ solvation shells in determining electrochemical performance. By selectively incorporating a low volume percentage of organic additive into the second coordination shell of Zn²⁺, we achieve effective proton capture, electrolyte pH stabilization during the Zn⁰ electroplating, and mitigation of ion transport resistance. This approach prevents the formation of a passivation interphase layer on the electrode surface, which typically occurs with higher additive concentrations, leading to increased interphase resistance and cell polarization. This work opens a new avenue in modulating Zn²⁺ reactivity and stability through precise solvation structure design, enabling efficient and reversible Zn^0/2+ plating/stripping in aqueous electrolytes with suppressed H₂ evolution. These findings pave the way for the development of commercially viable, high-performance ZBFBs for energy storage applications.