Polymer Chain Length Governs Ion Transport and Interfacial Dynamics in Aqueous Zinc-Metal Batteries

Abstract

Polymers are emerging as powerful modulators of both bulk electrolyte structure and interfacial chemistry at zinc-metal anodes, enabling substantial improvements in battery performance. Among their structural parameters, polymer chain length, spanning tens to thousands of repeating units, critically governs both ion migration networks in the bulk electrolyte and adsorption dynamics at zinc-metal anodes, thereby determining electrochemical behavior. Despite its importance, the mechanistic role of chain length remains poorly understood. Here, we synthesize a series of poly(N-vinylpyrrolidone) (PNVP) with systematically varied chain lengths to investigate their effects on Zn2+ transport, interfacial adsorption, and battery performance. Medium-chain PNVP optimally balances bulk network formation and interfacial regulation, simultaneously establishing efficient Zn2+ migration pathways and an in situ dense, ion-channel-rich interfacial adsorption layer, enabling stable cycling for over 3600 h. In contrast, short-chain PNVP yields weak ion networks and poor adsorption, restricting lifespan to 1100 h, while long-chain PNVP suffers from excessive entanglement and a thick interfacial layer, limiting lifespan to 1700 h. These findings reveal a chain-length-dependent mechanism that couples bulk ion transport with interfacial regulation, offering molecular-level guidance for the rational design of high-performance aqueous zinc-metal batteries.