to be faced. Therefore, it's necessary to develop a new nonliquid electrolyte with comprehensive performance for fulfilling various energy devices.Hydrogel electrolyte with hydrated salt crystal may be a new candidate to solve the above requirements by the introduction of new phase. The hydrated salt crystals, as one kind of industrial liquid-solid phase change materials, can be immobilized into hydrogel by the facile dissolution-crystallization transition. The demonstrated polymer gel electrolyte with NaAc·3H 2 O crystal as aligned porous template was designed by the in situ supersaturated crystallization of NaAc. [16,17] The introduction of inorganic crystal into polymer hydrogel can form the inorganic-organic composite with enhanced mechanical strength due to hydrogen bond or other synergistic effects. [18,19] The bound hydrated salt can suppress the electrochemical activity of water and broaden operating voltage of aqueous electrolyte [20] due to the strong interaction with water molecules, similar to the solvation sheath in "waterin-salt" electrolyte. [21][22][23] The high-concentrated salts within crystal-type gel can also efficiently reduce the freezing point and increase the boiling point of aqueous solutions. [24] At last, the hydrated salt crystal can endow gel electrolytes with thermalresistant performance through liquid-solid phase transition accompanied by endothermic and exothermic phenomena. [25,26] All in all, the crystal-type composite gel electrolyte can realize the comprehensive performance, including ultrahigh toughness, high operating voltage, extreme temperature tolerance, and good interfacial compatibility by a facile dissolution-crystallization transition approach.In this work, the pioneering crystal-type composite gel with excellent performance was prepared using a facile method that employed the crystallization of NaAc. There are only three main components in the precursor solution (Figure 1a,b): distilled water, abundant soluble salt, and a certain amount of monomer (or macromolecule). First, a high concentration of the salt solution was prepared by dissolving excessive soluble salt in the distilled water at high temperature. Then, the hydrogel was formed by UV irradiation for monomer solution (Figure 1c). Finally, the supersaturated salt within hydrogel was initiated to crystallize by placing a small crystal particle as seed on the surface of the hydrogel, and soon the crystal-type composite gel with extensive soluble salt crystals was obtained (Figure 1d). Typically, the crystal-type composite gel containing 15 wt% acrylamide (AAm) monomer and a certain quality of