A two-pronged electrolyte engineering strategy was employed to construct a water-poor electrical double layer and modulate vertically oriented Zn (100) plating for enhancing the reversibility of Zn plating/stripping toward highly stable Zn metal batteries.

Abstract

Controlling the growth orientation of zinc (Zn) is an effective method of stabilizing Zn anodes. Although Zn (100) exhibits faster Zn electroplating/stripping kinetics than Zn (002), its high chemical reactivity results in susceptibility to water-induced side reactions. Herein, a two-pronged electrolyte engineering strategy is proposed to enhance the reversibility of Zn anodes, that is, modulating vertically oriented Zn (100) plating while simultaneously constructing a water-poor electrical double layer (EDL). Mechanistic studies revealed that the difluoro(oxalato)borate (DFOB⁻) anions of sodium-difluoro(oxalato)borate (NaDFOB) function as a Zn²⁺ trapping agent at the inner Helmholtz layer, displacing active water molecules and inducing the preferential deposition of Zn on the Zn (100) crystal facets, thus effectively inhibiting both side reactions and dendrite growth. Consequently, a symmetrical cell with the ZnSO₄/NaDFOB electrolyte exhibited a long lifetime of over 950 h under severe conditions of 10 mA cm⁻² and 5 mAh cm⁻². Furthermore, a practical Zn||NH₄V₄O₁₀ pouch cell could achieves a high capacity of 156 mAh at industrial-level mass loading of 16.6 mg cm⁻². This work provides insights for achieving stable Zn anodes via electrolyte engineering-triggered crystallographic orientation and EDL regulation.