High-temperature-operating (over 140 °C) Li-ion supercapacitor via water-locking bimodal cross-linked hydrogel

The utilization of quasi-solid conducting medium possessing superior interfacial properties represents a significant approach in tackling the issue of leakage and stability in supercapacitors. However, preserving the conductivity of ions like Li+ and enabling their adaptability to high-temperature environments pose significant challenges to the improvement of water-locking capacity. Herein, a bimodal cross-linked hydrogel with a mesoporous structure has been developed based on the polyacrylamide-lithium chloride (PAM-LiCl) hydrogel system using polyethylene glycol (PEG). This hydrogel not only exhibits a high water-binding capacity but also facilitates the migration of Li-ions. Using activated carbon as the electrode material, the assembled quasi-solid state supercapacitor devices achieve a single electrode specific capacitance of 32.6 F/g at 0.1 A/g and an energy density of 1.77 W h/kg by varying the ratio of acrylamide and polyethylene glycol (AM/PEG). The findings of this study demonstrate that utilizing a bimodal cross-linked hydrogel can enable the operation of a supercapacitor at high temperatures above 140 °C. •To tackle the poor mechanical strength in hydrogels.•Overcoming the limitation of a narrow operating temperature range in hydrogels.•The super water-locking capability guaranteeing ascendant charge transmission.