Hydrophobic Association Enabled Salt‐Concentrated all‐Cellulose Hydrogel Electrolytes for High‐Temperature Zinc‐Ion Hybrid Supercapacitors

Hydrogel electrolytes have great potential in electrochemical energy storage devices due to their high flexibility, conductivity, and safety. However, at high temperatures, the mechanical stability and ionic conductivity of hydrogel electrolytes are compromised due to water evaporation and unstabilization of polymer matrix. Herein, we propose a salt-concentrated hydrogel electrolyte with its matrix showing hydrophobic association effect upon heating for achieving high-temperature adaptability. The cotton cellulose supports a stable homogeneous polymer-salt phase in the hydrogel electrolytes. The methylcellulose works through temperature-dependent hydrophobic interactions, maintaining the stability of the salt-concentrated hydrogel over a wide temperature range. An all-biobased hydrogel with both mechanical and conductive stability is realized at high temperatures (more than 60 °C). We have demonstrated a zinc-ion hybrid supercapacitor with a high specific capacity of 250.3 mAh g^-1 at 120 °C and 85.4% retention for 10,000 cycles at 60 °C. This work is expected to provide a general strategy to achieve high-temperature hydrogel electrolyte.