Biomass‐Derived Ion‐Selective Binder Modulates Zn 2+ Solvation Enabling High‐Capacity Cathodes in Aqueous Zinc Batteries

The electrochemical performance of aqueous zinc batteries (AZBs) critically relies on advanced binders to regulate the solvation structure of hydrated Zn²⁺ and accelerate the redox kinetics at the cathode interface. However, conventional hydrophobic polyvinylidene fluoride (PVDF) binders fail to achieve this goal due to their weak interactions with H₂O and Zn²⁺. Here, we present a bioinspired sulfate-rich polysaccharide binder network derived from marine ι-carrageenan (CAG), which mimics biological ion channels to enable selective ion coordination and dynamic hydration regulation. By establishing dual ion-selective coordination sites, the zincophilic ─OSO₃ ^- and hydrophilic ─OH groups of CAG form Zn²⁺─OSO₃ ^- and H₂O─OH interactions, effectively disrupting the primary solvation shell of Zn²⁺─H₂O and accelerating Zn²⁺ desolvation kinetics, thereby enabling adaptive ion transport across the cathode interface. Consequently, Zn||CAG@Mn_0.15V₂O₅·nH₂O batteries deliver an ultrahigh capacity of 421 mAh g^-1 at 0.6 A g^-1, which is 76% higher than PVDF-based counterparts (239 mAh g^-1). This water-processable binder demonstrates universal applicability across various cathode materials (e.g., MnO₂, V₂O₅, and organics), providing a green, scalable solution for high-performance AZBs. This study establishes a biomimetic binder design paradigm, where sulfate-hydroxyl dual coordination emulates biological ion transport, enabling precise regulation of Zn²⁺ solvation and interfacial chemistry.