In Situ Formation of “Dimethyl Sulfoxide/Water‐in‐Salt”‐Based Chitosan Hydrogel Electrolyte for Advanced All‐Solid‐State Supercapacitors

Abstract Biodegradable hydrogel electrolytes are particularly attractive in the fabrication of all‐solid‐state supercapacitors due to environmental benignity and avoiding of leakage. The introduction of “water‐in‐salt” (WIS) electrolytes into hydrogels will further broaden the electrochemical stability window of aqueous supercapacitors significantly. Meanwhile, the addition of an organic co‐solvent can effectively overcome the inevitable salt precipitation and extend the temperature adaptability. Herein, an in situ cross‐linking approach was demonstrated without any extra binder to obtain a “dimethyl sulfoxide/water‐in‐salt”‐based (DWIS) chitosan hydrogel electrolyte. Interestingly, the addition of 4–7 mol L −1 of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salts not only conforms to the criterion of WIS, but also promoted the successful gelation through the supramolecular complexation between Li + ‐solvated complexes and chitosan chains. A hydrogel‐based all‐solid‐state supercapacitor was fabricated using the DWIS chitosan hydrogel as the electrolyte and separator while nitrogen‐doped graphene hydrogel (NG) was used as the electrode. The optimized supercapacitor with a wide operating voltage of 2.1 V showed a high specific capacitance of 107.6 F g −1 at 1 A g −1 , remarkable capacitance retention of 80.1 % after 5000 cycles, a superior energy density of 62.9 Wh kg −1 at a power density of 1025.5 W kg −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.