Gel electrolytes are of great importance for supercapacitors (SCs) operating at high temperatures. However,
it is a fundamental challenge for SCs using aqueous gel electrolytes at elevated temperatures to ensure
good work durability due to the evaporation of water. Here we report a “water-in-salt” gel electrolyte
that exhibits superior water-retention and even water-absorption capability. What is noteworthy is that
a quasi-solid-state SC utilizing the gel electrolyte is able to work and exhibit long cycling life across
a wide temperature range from room temperature up to 120 C in an extremely dry atmosphere,
representing the best record among the previously reported aqueous gel-based SCs, as far as we know.
This strategy may provide a new way to develop reliable aqueous gel electrolytes for SCs operating at
high temperatures.