Lewis-acidic coordination in cellulose biopolymer binders for high-rate, shuttle-free aqueous zinc-iodine batteries

Natural biopolymers such as cellulose, which are rich in hydroxyl groups, have been widely explored as ion-regulators for stabilizing dissolution-prone cathodes such as iodine. However, their application in aqueous zinc-iodine batteries is limited by the weak and reversible nature of polyiodide-hydroxyl interactions, as well as detrimental water-induced swelling. Here we demonstrate that surface engineering transforms nanocellulose from a Lewis-basic scaffold into a Lewis-acidic, zirconium-coordinated network (ZNF), fundamentally reshaping the electrode-electrolyte interfaces. Unlike conventional binders, ZNF provides abundant electron-deficient Zr⁴⁺ centers that immobilize polyiodides through strong coordination while catalytically accelerating redox kinetics. This dual-functional binder forms a conformal, swelling-resistant network that preserves electrode integrity over 18,000 cycles, achieving 89.6% capacity retention at 5 A g^-1. Our findings demonstrate that regulating the Lewis acidity of sustainable biopolymers can overcome the intrinsic trade-off between hydrophilicity and stability, offering a promising paradigm for the design of high-performance aqueous batteries.