High-performance hydrogel electrolytes play a crucial role in flexible supercapacitors (SCs). However, the unsatisfactory mechanical properties of widely used polyvinyl alcohol-based electrolytes greatly limit their use in the flexible SCs. Here, a novel LiSO-containing agarose/polyacrylamide double-network (Li-AG/PAM DN) hydrogel electrolyte was synthesized by a heating-cooling and subsequent radiation-induced polymerization and cross-linking process. The Li-AG/PAM DN hydrogel electrolyte possesses extremely excellent mechanical properties with a compression strength of 150 MPa, a fracture compression strain of above 99.9%, a tensile strength of 1103 kPa, and an elongation at break of 2780%, greatly superior to those have been reported. It also achieves a high ionic conductivity of 41 mS cm originating from its interconnected three-dimensional porous network structure that provides a three-dimensional channel for ionic migration. Compared to the SC applying LiSO aqueous solution electrolyte, the corresponding flexible Li-AG/PAM DN hydrogel electrolyte-SC presents lower charge-transfer resistance, better ionic diffusion, being closer to ideal capacitive behaviors, superior rate capability, and better cycling stability, owing to the improved ionic transport in the Li-AG/PAM DN hydrogel electrolyte and electrode interfaces. Moreover, after testing with overcharge, short circuit, and high temperature, the capacitance of the Li-AG/PAM DN hydrogel electrolyte-SC can still be well maintained. Furthermore, the electrochemical properties of the Li-AG/PAM DN hydrogel electrolyte-SC remain almost intact under different compression strains/bending angles and even after 1000 compression/bending cycles. It is expected that the Li-AG/PAM DN hydrogel electrolyte may have broad applications in modern flexible and wearable electronics.

Polymeric ionic liquids (PILs) not only have the unique properties of ionic liquid, but also possess diverse mechanical properties of polymers. Due to their safety and conductivity, PILs-based gel polymer electrolytes (GPEs) are the promising candidates for the design of the devices. Here, we reported a facile approach to synthesize novel star-shaped GPE (named PIL-POSS-Li GPE) based on 1-vinyl-3-butylimidazolium hexafluorophosphate ionic liquid, octavinyl polyhedral oligomeric silsesquioxane (POSS) and LiPF 6 solution in one step via gamma-ray radiation. Compared with PIL-Li GPE without POSS, the incorporation of POSS into the PIL-Li GPE can improve properties of PIL-POSS-Li GPE due to the formation of a star-shaped structure, and the as-prepared PIL-POSS-Li GPE showed excellent compressive strength of 1617 kPa, high fracture compression stain of 79% and high ionic conductivity of 3.88 mS cm -1 at 25°C. What is more, the PIL-POSS-Li supercapacitor (SC) showed better electrochemical performance than PIL-Li SC.

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