A high-voltage quasi-solid-state flexible supercapacitor with a wide operational temperature range based on a low-cost water-in-salt hydrogel electrolyte

Recently, water-in-salt electrolytes have provided a huge boost to the realization of high energy density for water-based supercapacitors by broadening the electrochemical stability window. However, the high cost and low conductivity of high concentration LiTFSI greatly restrict the possibility of practical application. Herein, we adopt a new strategy to develop a low-cost and quasi-solid-state polyelectrolyte hydrogel accommodating a superhigh concentration of CH3COOK through in situ polymerization, avoiding the problem that many conventional polymers cannot accommodate ultra-high ion concentration. The polyelectrolyte hydrogel with 24 M CH3COOK exhibits a conductivity of up to 35.8 mS cm(-1) and a stretchability of 950%. With advanced N-doped graphene hydrogel electrodes, the assembled supercapacitor yields a voltage window of 2.1 V with an energy density of 33.0 W h kg(-1) and superior cyclability with 88.2% capacitance retention at 4 A g(-1) after 6000 cycles comparable to those supercapacitors using high-cost LiTFSI salts. Besides, the supercapacitor with excellent temperature stability in the range of -20 to 70 degrees C can light an LED for more than one minute. The assembled flexible device with the PAAK/CMC-24 M gel film sandwiched in between demonstrates excellent bendability from 0 degrees to 180 degrees and shows great potential for flexible/wearable electronic devices. Our feasible approach provides a new route for assembling quasi-solid-state flexible high-energy storage devices with water-in-salt electrolytes.

Automated summary

By developing a low-cost polyelectrolyte hydrogel with ultra-high ion concentration, the research team has significantly improved the energy density and practicality of water-based supercapacitors. The flexible device shows great potential for flexible and wearable electronic devices.