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

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 Zn²⁺ 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 ZnSO₄, ZnCl₂, 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 Zn²⁺ solvation without significantly affecting mass transport. Collectively, these findings provide a rational basis for electrolyte design in AZMBs.