Regulating the solvation structure of Zn²⁺ via glycine enables a long-cycling neutral zinc-ferricyanide flow battery

Zinc-based flow batteries hold potential promise for extensive energy storage on a large scale owing to their high energy density and low cost. However, their widespread implementation is impeded by challenges associated with zinc (Zn) dendrites and side reactions like the hydrogen evolution reaction on the anode. Theoretical calculations have confirmed that glycine (Gly) has the ability to coordinate with Zn²⁺, displacing H₂O molecules in the solvation shell, thereby restoring the solvation structure of Zn²⁺ and promoting the release of reactive Zn²⁺ during plating/stripping processes. As a result, the incorporation of Gly into the anolyte of a neutral zinc-ferricyanide (Zn/Fe) flow battery (ZIFB) effectively inhibits the formation of Zn dendrites and impedes side reactions, leading to highly reversible and stable Zn plating/stripping reactions. A Zn||Zn symmetric flow battery utilizing Gly in the anolyte demonstrated extended cycling durability, lasting over 550 h at a current density of 30 mA cm^-2, in contrast to the failure of a Gly-free anolyte system after 150 h. Notably, this approach facilitates a neutral ZIFB achieving an impressive energy efficiency exceeding 70 %, even at a high current density of 70 mA cm^-2, with a cycle lifespan exceeding 800 h (33 days) at a current density of 30 mA cm^-2. Conversely, the neutral ZIFB lacking Gly showed a significantly shorter cycle life of only 260 h under identical operational conditions (30 mA cm^-2). Due to the economic benefits of Gly and the proposed user-friendly route, this strategy demonstrates great potential for promoting the widespread adoption of zinc-based flow batteries with improved performance for practical use.