<p>Aqueous batteries offer inherent safety and low cost, but the inherently fixed physicochemical functionality and poor interfacial compatibility of existing binders limit their ability to boost positive electrode performance. Here we present a hydroxyl-chemistry regulation strategy that transforms cellulose, an abundant biopolymer on Earth, into a high-affinity, interfacially compatible binder that stabilizes high-capacity, shuttling-prone positive electrodes. By selectively opening the rigid cellulose ring structure within its molecular chains, we enhance dipole polarity, chain flexibility, and intermolecular hydrogen-bond density, thereby increasing functional-group accessibility and interfacial adhesion. These molecular-level modifications drive the formation of a dense nanofibrous network that conformally encapsulates active particles and anchors polyiodides, accelerating redox kinetics and reinforcing electrode stability. Iodine positive electrode incorporating the engineered binder deliver a reversible capacity of 150.9 mAh g⁻¹ at 20 A g⁻¹, with pouch cells retaining 98.07% capacity after 3000 h at 0.2 A g⁻¹. The binder also enables layer-by-layer fabrication of high mass loading electrodes, and benefits other dissolution-prone positive electrodes such as V₂O₅. Overall, this work establishes a general and sustainable route for the molecular engineering of biopolymer binders, expanding their role in the design of advanced aqueous batteries.</p>