• Hydrogel electrolytes effectively address limitations of aqueous electrolytes in zinc-ion batteries, including dendrite growth, side reactions, and cathode dissolution.
• Functional designs of hydrogel electrolytes enable operation under harsh conditions: extreme temperatures, mechanical deformations, and physical damages.
• The review systematically covers fundamentals, species, and mechanisms of hydrogel electrolytes, along with their compatibility with Zn anodes and cathodes.
• Future perspectives highlight remaining challenges and opportunities for practical application of hydrogel electrolyte-based rechargeable zinc-ion batteries.