Asymmetric Hydrogel Electrolyte Featuring a Customized Anode and Cathode Interfacial Chemistry for Advanced Zn–I₂ Batteries

An integrated asymmetric hydrogel electrolyte with a tailored composition and chemical structure on the cathode/anode–electrolyte interface is designed to boost the cost-effective, high-energy Zn–I2 battery. Such a configuration concurrently addresses the parasitic reactions on the Zn anode side and the polyiodide shuttle issue afflicting the cathode. Specifically, the Zn2+-cross-linked sodium alginate and carrageenan dual network (Carra-Zn-Alg) is adopted to guide the Zn2+ transport, achieving a dendrite-free morphology on the Zn surface and ensuring long-term stability. For the cathode side, the poly(vinyl alcohol)-strengthened poly(3,4-ethylenedioxythiophene)polystyrenesulfonate hydrogel (PVA–PEDOT) with high conductivity is employed to trap polyiodide and accelerate electron transfer for mitigating the shuttle effect and facilitating I2/I– redox kinetics. Attributing to the asymmetrical architecture with a customized interfacial chemistry, the optimized Zn–I2 cell exhibits a superior Coulombic efficiency of 99.84% with a negligible capacity degradation at 0.1 A g–1 and an enhanced stability of 10 000 cycles at 5 A g–1. The proposed asymmetric hydrogel provides a promising route to simultaneously resolve the distinct challenges encountered by the cathode and anode interfaces in rechargeable batteries.