Chelation-regulated release of alloying species stabilizes electrochemical interfaces on metal anodes in batteries

Functional additives are widely used in electrochemical systems to guide metal deposition and suppress unfavorable porous growth modes. A key strategy involves adding secondary metal cations with higher redox potentials, which spontaneously undergo ion exchange and deposit as an interfacial alloying layer to promote uniform growth during battery recharge. However, we discover that in the absence of kinetic control, this electroless deposition of the alloying layer unexpectedly induces dendritic growth due to local ion depletion, especially when additive concentrations are low. Contrary to conventional wisdom, free additive cations can therefore destabilize-rather than stabilize-metal anode interfaces. To overcome this, we introduce a chelation-based approach that regulates the release of additive cations and smooths interfacial deposition. Using Cu²⁺ additives and EDTA chelators in aqueous Zn batteries as a model system, we demonstrate that chelation enables controlled Cu²⁺ release, forming uniform interfacial layers and remarkably improving cycling stability. The chelation-regulated system achieves >99% Zn reversibility and 2-3× longer cycle life under practical current densities and capacities (i.e., 1 mAh cm^-2 at 10 mA cm^-2, and 10 mAh cm^-2 at 10 mA cm^-2), while unregulated systems fail rapidly. Extension of the controlled release framework to systems beyond the Cu²⁺-EDTA pair is also demonstrated. This work highlights the importance of molecular-level control over additive reactivity and offers a generalizable strategy for stabilizing metal anodes in energy-dense batteries.