Hydrogels are usually recognized as soft and weak materials, the poor mechanical properties of which greatly limit their applications as structural elements. Designing of hydrogels with high strength and high modulus has both fundamental and practical significances. Herein we report a series of tough, stiff, and transparent hydrogels facilely prepared by copolymerization of 1-vinylimidazole and methacrylic acid in dimethyl sulfoxide followed by solvent exchange to water. The equilibrated hydrogels with water content of 50–60 wt % possessed excellent mechanical properties, with tensile breaking stress, breaking strain, Young’s modulus, and tearing fracture energy of 1.3–5.4 MPa, 40–330%, 20–170 MPa, and 600–4500 J/m2, respectively. These tough hydrogels were also stable over a wide pH range (2 ≤ pH ≤ 10), resulting from the formation of dense and robust hydrogen bonds between imidazole and carboxylic acid groups. Moreover, the water content and mechanical properties of one gel can be adjusted over a wide range by controlling the dissociation and re-formation of hydrogen bonds during the solvent exchange and heating process; the treated hydrogel with specific characters was stable in water at room temperature. This is because the density of hydrogen bonds can be modulated at high temperature yet immediately fixed at room temperature due to the high stiffness and glassy state of the hydrogel. This strategy to prepare tough and stiff hydrogels should be applicable to other systems as structural materials with promising applications in diverse fields.

notorious Zn dendrites and hazardous side reactions ascribing to the interactions between Zn 2+ and the functional groups in hydrogel. [8][9][10][11][12][13][14] Nevertheless, battery electrolytes with conventional hydrogels will be ineluctably freezing at subzero temperatures due to the relatively high freezing point of water. This can dramatically deteriorate the polymer gel mechanical property and ionic conductivities, [15,16] resulting in inferior cycling stability or even occurring short circuit. [17] In addition, the mechanical property of the hydrogel electrolyte should also be elaborately designed, to simultaneously satisfy the flexibility of wearable batteries and withstand the acting force during daily operation.Generally, hydrogel freezing is mainly on account of the strong HB formation between water molecules on polymer chains. [18,19] To date, two main strategies including the organic additives [20][21][22][23][24][25] and high concentration salts [26][27][28][29][30] are demonstrated on breaking the HB of water to achieve batteries with low temperature performance. The organic additives can form new HB with water molecules for achieving ultralow freezing point, and regulate the Zn 2+ solvation structure by coordinating with Zn 2+ for dendrite and side reaction suppression. [20,21,23] However, the radii of the Zn 2+ solvation structure are increased during the coordination, which significantly decrease the ionic conductivity of the batteries especially at subzero temperatures. [31] For high-concentration salts, they own much higher ionic conductivity than organic molecules, [26][27][28][29]32] but are expensive and undergo poor electrolyte wettability and severe salt precipitation at low temperature. [33][34][35] Critically, the mechanical durability of the hydrogel will be deteriorated by the high concentration salts when cooperated in batteries. Apart from the abovementioned strategies, grafting alcohol molecules to the polymer chains can also dedicate to the hydrogel antifreezing, whereas the fabrication process is tedious and complicated comparatively. [36,37] Therefore, exploring a new salt with low concentration to confer the hydrogel electrolyte with adjustable mechanical property and high ionic conductivities at subzero temperatures is of great importance.The Hofmeister effect is one of the ubiquitous phenomenon in nature, including two distinct solvation behaviors for hydrogels regarded as the "salting out" effect of the kosmotropes and "salting in" effect of the chaotropes. [38][39][40][41][42] Current literatures have employed inorganic salts to tailor the mechanical property The new-generation flexible aqueous zinc-ion batteries require enhanced mechanical properties and ionic conductivities at low temperature for practical applications. This fundamentally means that it is desired that the hydrogel electrolyte possesses antifreezing merits to resist flexibility loss and performance decrease at subzero temperatures. Herein, a highly flexible polysaccharide hydrogel is realized in situ and ...

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Aqueous Zn‐ion batteries own great potential on next generation wearable batteries due to the high safety and low cost. However, the uncontrollable dendrites growth and the negligible subzero temperature performance impede the batteries practical applications. Herein, it is demonstrated that dimethyl sulfoxide (DMSO) is an effective additive in ZnSO4 electrolyte for side reactions and dendrites suppression by regulating the Zn‐ion solvation structure and inducing the Zn2+ to form the more electrochemical stable (002) basal plane, via the higher absorption energy of DMSO with Zn2+ and (002) plane. Moreover, the stable reconstructed hydrogen bonds between DMSO and H2O dramatically lower the freezing point of the electrolyte, which significantly increases the ionic conductivity and cycling performance of the aqueous batteries at subzero temperatures. As a consequence, the symmetrical Zn/Zn cell can be kept stable for more than 2100 h at 20 °C and 1200 h at −20 °C without dendrite and by‐products formation. The Zn/MnO2 batteries can perform steadily for more than 3000 cycles at 20 °C and 300 cycles at −20 °C. This work provides a facile and feasible strategy on designing high performance and dendrite free aqueous Zn‐ion batteries for various temperatures.