Mechanically Robust\nand Highly Conductive Poly(ionic\nliquid)/Polyacrylamide Double-Network Hydrogel Electrolytes for Flexible\nSymmetric Supercapacitors with a Wide Operating Voltage Range

Abstract

Flexible electronic devices, such as supercapacitors\n(SCs), place\nhigh demands on the mechanical properties, ionic conductivity, and\nelectrochemical stability of electrolytes. Hydrogels, which combine\nflexibility and the advantages of both solid and liquid electrolytes,\nwill meet the demand. Here, we report the synthesis of novel poly(ionic\nliquid)/polyacrylamide double-network (DN) (PIL/PAM DN) hydrogel electrolytes\ncontaining different metal salts via a two-step γ-radiation\nmethod. The resultant Li₂SO₄-1.0/PIL/PAM DN\nhydrogel electrolyte possesses excellent mechanical properties (tensile\nstrength of 3.64 MPa, elongation at break of 446%) and high ionic\nconductivity (24.1 mS·cm^–1). The corresponding\nflexible SC based on the Li₂SO₄-1.0/PIL/PAM\nDN hydrogel electrolyte (SC-Li₂SO₄) presents\nimproved ion diffusion, ideal electrochemical double-layer capacitor\nbehavior, good rate capability, and excellent cyclic stability. Moreover,\nsymmetric SC-Li₂SO₄ achieves a wide operating\nvoltage range of up to 1.5 V, with a maximum energy density of 26.0\nW h·kg^–1 and a capacitance retention of 94.1%\nafter 10,000 galvanostatic charge–discharge cycles, owing to\nthe deactivation of free water molecules by the synergistic effect\nof PIL, PAM, and SO₄^2–. Above all, the\ncapacitance of SC-Li₂SO₄ is well-maintained\nafter overcharge, overdischarge, short circuit, extreme temperature,\ncompression, and bending tests, indicating its high security and flexibility.\nThis work reveals the enormous application potential of PIL-based\nconductive hydrogel electrolytes for flexible electronic devices.