Microphase-Separated Hydrogel Electrolytes with Selective Ion Transportation Pathways for Flexible Zinc-Ion Batteries

Flexible aqueous zinc-ion batteries (ZIBs) are promising candidates for next-generation wearable electronics and soft robotics, yet their development is hindered by the non-selective ion transport of conventional hydrogel electrolytes, which induces concentration polarization, uneven Zn²⁺ flux, and dendrite formation, ultimately causing battery failure. Here, a microphase-separated single-zinc-ion conducting hydrogel electrolyte (SIHE) constructed via polymer chain disentanglement within a polyanionic zinc-alginate (ZA) matrix is reported. Due to the pronounced steric disparity between Zn²⁺ and the alginate chains, ZA holds intrinsic potential for ion-selective transport. However, spontaneous chain entanglement within the alginate network under the applied electric field severely impedes the formation of continuous ion transport pathways, limiting Zn²⁺ conduction. By incorporating Nafion, well-defined hydrophilic/hydrophobic domains are induced that simultaneously relax the entangled polymer network and establish continuous Zn²⁺-conducting pathways. This microstructural engineering enables a high Zn²⁺ transference number of 0.967 and ionic conductivity of 25.5 mS cm^-1, resolving the long-standing trade-off between ion selectivity and transport kinetics. The zinc-alginate/Nafion (ZA/N) electrolyte enables dendrite-free cycling for over 4600 h. The ZA/N-based flexible ZIB retains 90% capacity after 5000 cycles at 10 A g^-1. This work presents a general strategy to engineer high-performance SIHEs for safe and durable flexible zinc-ion batteries.