Milked-Extracted Macromolecules Constructing Bio-Interphase to Realise Dendrite-Free Aqueous Zinc Metal Batteries With Long Cycle Life

Abstract

Dairy-derived biomacromolecules offer a sustainable and bio-functional platform for interfacial engineering in aqueous zinc-ion batteries (AZIBs). Herein, we present a comparative study using three milk-based substances—casein (CA), whey protein (WP) and enzymatically hydrolysed whey protein peptides (WPPs)—to construct artificial solid electrolyte interphase (SEI) coatings on Zn metal anodes. These protein-based films, rich in functional groups such as ─COOH, ─NH₂ and ─SH, chelate with Zn²⁺ and form conformal, ion-conductive protection layers that mitigate side reactions and dendrite growth. Among them, the WPP-derived SEI exhibits superior interfacial compatibility and molecular mobility, promoting homogeneous Zn deposition and significantly enhanced cycling stability. Zn||Zn symmetric cells with the WPP coating achieved an ultralong lifespan exceeding 3000 h, markedly outperforming WP- and casein-based counterparts. Furthermore, Zn||V₂O₅ full batteries employing WPP-coated Zn anodes delivered a high capacity and extended cyclability. This study not only highlights the interfacial regulation mechanisms of dairy-derived biomolecules but also offers a green and cost-effective strategy for developing high-performance aqueous zinc-ion batteries.