Chain-Length-Selective Adsorption Governs Diffusion-Limited Dendrite Growth Mode in Battery Electrodes

Abstract

Growth of classical dendrites in metal anodes represents a far-from-equilibrium, diffusion-limited crystallization process that critically impacts the safety and performance of energy storage systems. Zn-a promising aqueous anode material-exhibits two distinct modes: continuous growth (CG), where a few crystallographically guided dendrites propagate rapidly, and independent nucleation (IN), where numerous smaller, randomly oriented dendrites form with slower propagation. Here we show that ethylene glycol-derived additives, HO-(CH2CH2O)n-H, can reliably shift growth from CG to IN. Using operando tools including optical visualization, electrochemical impedance spectroscopy, and quartz crystal microbalance, we resolve the kinetic and interfacial origins of this transition. The effect is highly chain-length dependent: PEG-400 (n ≈ 9) achieves the most efficient CG→IN shift with a threshold of 0.001 wt.% (10 ppm), while shorter or longer chains require ~1 wt.%, and no transition occurs for n <= 3 at all. Experimental measurements and quantum-chemical analysis reveals that the transition arises from two coupled processes: adsorption of PEG molecules at the electrode surface, and coordination with Zn adatoms and Zn 2+ cations, which destabilize continuous growth pathways and favor repeated independent nucleation. Importantly, the shift from CG to IN reduces dendrite propagation velocity by a factor of 6. These findings establish molecular-level design rules for engineering task-specific organic molecules to control far-from-equilibrium crystallization, with direct implications for high-power batteries and electrochemical synthesis.