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

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 degrees 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.

Automated summary

The introduction of water-in-salt (WIS) electrolyte into hydrogels improves the electrochemical stability of aqueous supercapacitors, and the addition of an organic co-solvent helps to overcome salt precipitation issues and extend temperature adaptability. The in situ cross-linking approach to obtain DWIS chitosan hydrogel electrolyte shows great potential in the application of high-performance solid-state energy storage devices.