Thinner-than-paper and broad-temperature-adaptive zinc-iodine batteries enabled by nanophase separated deep-eutectic hydrogel electrolytes.

Abstract

Hydrogel electrolyte based secondary batteries are promising for wearable electronics, yet face challenges including limited mechanical resilience, and narrow temperature range. Herein, we report a robust deep-eutectic hydrogel electrolyte fabricated via synergistic interplay of dual nanophase separation, hydrated eutectic solvation, and hydrogen-bond networks. The interwoven nanophase separation architecture, integrating hydrophilic polyvinyl alcohol phases and hydrophobic polyacrylonitrile phases, realizes high fracture-strength (4.1 MPa) and toughness (13.66 MJ m^-3). Meanwhile, deep-eutectic chemistry modulates Zn²⁺ solvation structures and leverages cyano-coordination channels of polyacrylonitrile to achieve high Zn²⁺ ionic conductivity (28.2 mS cm^-1) and transference number (0.65) at 20 °C. Concurrently, abundant hydrogen bonds induced by multiple donor sites of hydrophilic phases, urethane, and Zn(ClO₄)₂ immobilize active H₂O to ensure broad-temperature durability. This tripartite synergy directs planar Zn deposition along (002) planes and suppresses dendrite growth, enabling Zn||I₂ batteries with a thinner-than-paper thickness (42 μm) and high flexibility. The assembled Zn||I₂ batteries demonstrate high specific energy (108.99 Wh kg^-1) and cycling stability (over 36,000 cycles under -40 to 80 °C). In this work, the convergence of molecule design, phase modulation, and process engineering establishes a feasible methodological framework for developing advanced flexible batteries that integrate high energy density and harsh environment tolerance.