Sodium alginate-based high conductive, ultra-stretchable hydrogel fibers for electrolytes of flexible solid-state supercapacitors.

The flexibility and safety of energy storage systems are crucial, and hydrogels as one of the most promising candidates for solid-state electrolytes. We present a conductive hydrogel based on sodium alginate that exhibits ultra-stretchable (4200 %) and high conductivity (16.3 S m). The mechanical properties of the conductive hydrogel are achieved by optimizing the topology of the sodium alginate and harnessing the synergistic effect of non-covalent interaction among different components. And a conductive structure within hydrogels was successfully established through the synergistic combination of ion and metal nanoparticles. The flexible supercapacitor (FSC) with conductive hydrogel as solid electrolytes demonstrated an area-specific capacitance of up to 274.28 mF cm at a current density of 1 mA cm. And the energy density of the FSC is as high as 187 μWh cm at a power density of 1.2 mW cm. The voltage range of the FSC is also extended to 1.4 V. The FSC also exhibited exceptional flexibility and stability, including insensitivity to bending angles and remarkable cycle durability (82.4 % after 10,000 cycles). The study presents a novel design for the development of solid-state electrolytes, with the aim of creating a new generation of FSC that exhibit superior safety and high energy density.