Single-Ion Conducting Double-Network Hydrogel Electrolytes for Long Cycling Zinc-Ion Batteries

As one of the promising alternatives of lithium-ion batteries, zinc-ion batteries (ZIBs) have received growing interest from researchers due to their good safety, eco-friendliness, and low cost. Nevertheless, aqueous ZIBs are still a step away from practical applications due to the nonuniform deposition of Zn and parasitic side reactions, which cause capacity fading and even short circuit. To tackle these problems, here we introduce a single-Zn-ion conducting hydrogel electrolyte (SIHE), P(ICZn-AAm), synthesized with iota carrageenan (IC) and acrylamide (AAm). The SIHE manifests single Zn²⁺ conductivity via the abundant sulfates fixed on the IC polymer backbone, delivering a high Zn²⁺ transference number of 0.93. It also exhibits outstanding ionic conductivity of 2.15 × 10^-3 S cm^-1 at room temperature. The enhanced compatibility at the electrode-electrolyte interface was verified by the stable Zn striping/plating performance along with a homogenous and smooth Zn deposition layer. It is also found that the passivation of the Zn anode can be effectively prohibited due to the lack of free anions in the electrolyte. The practical performance of the SIHE is further investigated with Zn-V₂O₅ batteries, which showed a stable capacity of 271.6 mA h g^-1 over 150 cycles at 2 C and 127.5 mA h g^-1 over 500 cycles at 5 C.