In-situ hybrid armor layer enabled by additive-anion synergy for dendrite-free and stable Zn anode

Zinc acetate electrolyte-based aqueous zinc-ion energy storage devices (AZDs) offer advantages such as low cost and a mild electrolyte environment. However, their development is hindered by issues of the Zn anode like dendrite growth and serious by-product passivation layer formation. Herein, we find that the N-Methyl-2-pyrrolidinone (NMP) and acetate anions can trigger synergistic effects in zinc acetate electrolytes, which transform the pristine passivation layer on Zn anode surface into an electrochemically favorable hybrid armor layer. The hybrid armor layer (consisting of a zincophilic ZnO nanorod array and an additional organic–inorganic surface layer) is distinct from the irregular solid-electrolyte interphase layer formed in conventional ZnSO₄ electrolytes with NMP functionalization. The armor layer leads to uniform Zn flux, high anti-corrosion capabilities, reduced side reactions, and dendrite-free growth of the Zn anode. As a result, the corresponding Zn//Zn symmetric cell achieves over 1900 h of stable operation, 31.9 times longer than pure zinc acetate electrolyte. The cycling stability is much higher than in previous studies using NMP additives. The corresponding Zn ion hybrid supercapacitor also exhibits excellent cyclability (over 20,000 cycles). This study represents the first trial of an additive-anion synergistic strategy for enhancing Zn anode cycling stability, which opens novel avenues to develop advanced AZDs.