LAUSR

Biodegradable hydrogel electrolytes due to environmental benignity and avoiding leakage are particularly attractive in the fabrication of all-solid-state supercapacitors. Introduction of "water-in-salt" (WIS) electrolytes into hydrogels will further broaden the electrochemical stability window of aqueous supercapacitors significantly. Meanwhile, the addition of organic co-solvent can effectively overcome the inevitable salt precipitation and extend the temperature adaptability. Herein, we demonstrate a novel in situ cross-linking approach without any extra binder to obtain a "dimethyl sulfoxide/water-in-salt"-based (DWIS) chitosan hydrogel electrolyte. Interestingly, the addition of 4-7 molL-1 of LiTFSI salts not only conforms to the criterion of WIS, but also promotes the successful gelation through the supramolecular complexation between Li+-solvated complexes and chitosan chains. Then a hydrogel-based all-solid-state supercapacitor has been fabricated using the DWIS chitosan hydrogel as the electrolyte and separator while the nitrogen-doped graphene hydrogel as the electrode. The optimized supercapacitor with a wide operating voltage of 2.1 V yields a high specific capacitance of 107.6 Fg-1 at 1A g-1, remarkable capacitance retention of 80.1% after 5000 cycles, superior energy density of 62.9 Whkg-1 at a power density of 1025.5 Wkg-1 and excellent temperature stability in the range of -20 to 70 °C. These findings suggest that the as prepared hydrogel electrolyte holds great potential in the practical application of high-performance solid-state energy storage devices.