Elucidating Synergistic Mechanisms of Anion–Cation Electrolyte Additive for Ultra–Stable Zinc Metal Anodes

Abstract

Uncontrollable dendrite formation and rampant parasitic reactions in Zinc (Zn) metal anodes obstruct the practical application of aqueous Zn–metal batteries (AZMBs). Herein, we demonstrate a synergistic cation–anion regulation strategy to stabilize Zn metal anodes using NaI as a proof–of–concept additive for the ZnSO4 electrolyte system. By combining rigorous physicochemical, computational and electrochemical analyses, it is found that the I– anions can reshape the solvation sheath of Zn(H2O)62+, break the association of H2O and specifically absorb on the Zn surface, promoting Zn2+ transfer kinetics, guiding homogenous Zn deposition and constraining parasitic reactions. Meanwhile, the Na+ cations ions absorb on irregular Zn tips as an electrostatic shielding to prevent dendrite growth. As a result, at the optimal additive concentration of 0.2 M, the Zn symmetric cells can deliver an astonishing 8632 h cyclability at 1 mA cm–2/1 mAh cm–2, exceeding by 83–fold that using BE electrolyte. Furthermore, the additive supports highly reversible Zn stripping/plating at –10 °C, enables Zn||NaV3O8·1.5 H2O to attain significantly upgraded rate and cycling performances, and most importantly and uniquely, unlocks the high–capacity I–/I3– redox couple for long–cycling Zn||I batteries. This work provides a novel strategy to stabilize Zn metal anodes towards dendrite–free AZMBs.