Slowing Down Zinc Electrodeposition Kinetics Can Maximize and Compromise Anode Stability: How Slow Is Too Slow?

Abstract

ABSTRACT Aqueous zinc metal batteries (AZMBs) are promising for next‐generation grid storage due to their low cost and intrinsic safety. However, their deployment is limited by poor zinc plating/stripping reversibility at the anode, driven by hydrogen evolution, corrosion, and dendrite formation. Solvation modulation of Zn 2+ using high‐donor‐number additives is widely reported to enhance performance by imposing sluggish charge‐transfer and desolvation kinetics, often reflected in a reduced zinc electrodeposition exchange current ( i 0,Dep ). Yet beyond a critical concentration, additive‐induced over‐suppression of deposition kinetics leads to pronounced anode instability, the mechanistic origin of which remains unresolved. Here, we establish a framework defining an optimal kinetic window for additive concentration. Using ZnSO 4 , ZnCl 2 , and Zn(OTf) 2 electrolytes with systematically tuned solvation environments, we demonstrate that enhanced stability emerges from a synergistic interplay among electrodeposition, nucleation‐growth dynamics, and corrosion kinetics. Within this optimal regime, uniform restructured (002)‐oriented zinc deposition suppresses hydrogen evolution, improving reversibility and cyclability. Beyond this threshold, further reduction of i 0,Dep shifts the system toward mass‐transport induced corrosion‐dominated behavior, eliminating the restructuring advantage and accelerating hydrogen evolution. This framework is generalizable across additives that primarily alter Zn 2+ solvation without significantly affecting mass transport. Collectively, these findings provide a rational basis for electrolyte design in AZMBs.