Functional-Group-Engineered Cellulose Separators for Aqueous Zinc-Ion Batteries: Structural Design and Interfacial...

Aqueous zinc-ion batteries have broad application prospects in large-scale energy storage owing to their high safety, low cost, and environmental compatibility. However, Zn metal anodes still suffer from dendrite growth, hydrogen evolution, corrosion, and interfacial side reactions, which severely limit cycling stability. As a key component connecting the electrolyte and electrode interfaces, the separator has gradually evolved from a conventional physical barrier into a functional layer for regulating Zn²⁺ transport, water state, and interfacial reactions. Cellulose separators have attracted extensive attention in aqueous zinc-ion batteries because of their abundant resources, renewability, good hydrophilicity, tunable pore structure, and facile chemical modification. This review focuses on functional-group-engineered cellulose separators, highlighting the structural features, advantages, and potential limitations of hydroxyl-rich, carboxylated, sulfonated, and amino-functionalized cellulose separators. The interfacial regulation mechanisms involving Zn²⁺ coordination and flux homogenization, anion exclusion and selective transport, water-activity regulation, and side-reaction suppression are further discussed. Finally, future directions, including precise functional-group design, fast ion-channel construction, green scalable fabrication, and standardized device-level evaluation, are proposed to provide guidance for the design of highly stable separators for aqueous zinc-ion batteries.