A Bioinspired Gradient Hydrogel Electrolyte Network with Optimized Interfacial Chemistry toward Robust Aqueous Zinc-Ion Batteries

Hydrogel electrolytes are regarded as a promising option for high-performance aqueous zinc-ion batteries (ZIBs), but they frequently fail to balance the reaction kinetics and Zn²⁺ deposition stability. Inspired by articular cartilage, here we develop a gradient-networked hydrogel electrolyte comprising poly(vinyl alcohol) (PVA), cellulose nanofiber (CNF), and graphene oxide (GO) for ZIBs. The low-network-density PVA/CNF (PC) hydrogel layer (cathode side) with extensive channels and a higher water content ensures the rapid transport of ions, while the interfacial hydrogel layer in contact with the Zn anode exhibits a high-density PVA/CNF/GO (PCG) network with enriched carboxyl and hydroxyl groups, which facilitates the desolvation of Zn²⁺, decreases the activity of water, and homogenizes the Zn²⁺ flux. Moreover, the polar oxygen-containing groups in GO endow it with dielectric and electronegative properties, collectively enhancing the Zn²⁺ transference numbers and ionic conductivity of the hydrogel electrolyte. Benefiting from such a gradient-networked structure and modulated interfacial chemistry, the hydrogel electrolyte can effectively stabilize Zn anodes while simultaneously accelerating reaction kinetics. Consequently, the hydrogel electrolyte enables Zn-symmetric cells to exhibit excellent stability over a duration exceeding 2200 h at 1 mA cm^-2, and Zn-MnO₂ full cells demonstrate enhanced rate capability and safety under various external damages. Overall, this work provides a reliable nature-inspired design strategy of hydrogel electrolytes toward high-performing ZIBs.