Compacting surface charge layers for efficient charge transfer toward stable Zn anodes

Abstract

The dynamic reconstruction of electric double layers (EDLs) holds the key to stabilizing aqueous Zn metal batteries. However, the charge compatibility within EDLs is destroyed by the spatiotemporal discord between electron transfer and ion diffusion, which promotes dendrite generation. Herein, an electron transfer-mediated EDL compression mechanism is proposed using metformin hydrochloride (MF·HCl) as an additive, achieving synchronous regulation of interfacial charge/ion dynamics. The protonation-enabled cationic nature of MF²⁺ orchestrates a multifaceted modulation of the electrode–electrolyte interface: it redistributes interfacial electrons to neutralize localized electric fields, supplements surface charge to compress the Debye shield length for shortening Zn²⁺ diffusion paths, and inhibits water decomposition through constructing the hydrogen bond confinement effect. These synergistic effects collectively enable homogeneous Zn deposition and exceptional electrochemical performance. The distinctively designed EDL enables unprecedented cycling stability, achieving over 650 hours of operation at 20 mA cm⁻² with a cumulative capacity of 6500 mA h cm⁻². The full cells paired with NaV₃O₈·1.5H₂O (NVO) sustain a remarkable capacity reversibility of 83% at a low N : P ratio (3 : 1). This work provides profound insights into charge modification within the EDL, pioneering new pathways for optimizing charge transport, ion distribution, and deposition kinetics in electrochemical systems.