Sodium alginate-incorporated double-network polymer hydrogel electrolyte with synergistic self-healing and low-temperature resistant properties for energy storage devices

DN polymer hydrogel electrolyte is prepared via free-radical copolymerization. • Boronic ester and hydrogen bonds in DN enable excellent self-healing properties. • LiCl and iL hybrid electrolyte imparts good low-temperature resistance (−30 °C). • The electrolyte shows good self-healing and low-temperature ionic conductivity. • The assembled supercapacitor shows self-healing and low-temperature resistance. The practical application of flexible energy storage devices is constrained by their susceptibility to mechanical damage and performance degradation under low-temperature environment. The hydrogel electrolytes with integrated self-healing and low-temperature-resistant properties offers a viable solution to the challenges. This study developed a novel double-network (DN) polymer hydrogel electrolyte (B-(PVHA/SA)/LiCl-iL) with hydrogen bonds and dynamic borate ester bonds, using copolymer of 1-vinylimidazole and N-(hydroxymethyl) acrylamide (PVHA) as the matrix, sodium alginate (SA) as the reinforcing phase, borax (B) as a crosslinker and lithium chloride (LiCl) and 1-ethyl-3-methylimidazolium acetate ionic liquid (iL) as a hybrid electrolyte. The DN structure endows the hydrogel electrolyte with excellent thermal, mechanical and self-healing properties. Furthermore, LiCl and iL as a hybrid electrolyte endows the hydrogel electrolyte with remarkable low-temperature resistance. The optimal B-(PVHA/SA)/LiCl-iL hydrogel electrolyte shows a three-dimensional porous structure, with an ionic conductivity of 9.12 × 10 −2  S/cm. After being severed, it can recover its original structure within 20 min, and this healing process can be repeated for up to 15 cycles. The hydrogel electrolyte exhibits outstanding low-temperature resistance and its ionic conductivity at −30 °C remains at 62.3% of its value at room temperature. The supercapacitor assembled with the hydrogel electrolyte demonstrates a capacitance retention of 80.6% after five cut-healing cycles, and retains 52.1% of its initial capacitance at −30 °C. This work provides a feasible strategy for designing multifunctional hydrogel electrolytes, offering promising potential for flexible energy storage and electronics devices operating in environments with temperature fluctuations and mechanical stress.