Chitin and cellulose as constituents of efficient, sustainable, and flexible zinc-ion hybrid supercapacitors

A zinc-ion hybrid supercapacitor (ZIHS) is a prospective energy storage device featuring cost-effectiveness, operational safety, environmental friendliness, high-power performance, and satisfied energy density. The sustainability of this ZIHS technology is even improved by introducing biopolymer constituents into the cell construction. Herein, efficient, sustainable, and flexible ZIHSs employing polysaccharide (chitin- or cellulose-based) components are developed. Using green ionic liquid solvents, biopolymer-bound, activated carbon-based cathode materials and hydrogel biopolymer electrolytes containing conductive zinc salts are obtained. According to systematical characterization results, the prepared materials possess favorable functional properties. Biopolymer binders provide homogeneity and integrity within the electrode network and high adhesion to the surface of the current collector. Depending on the type of zinc salt, hydrogel biopolymer electrolytes display high ionic conductivity (up to 46 mS cm−1), expanded electrochemical stability window (up to ca. 2.8 V), and zinc dendrites growth suppression. Biopolymer components assembled with zinc foil electrodes operate efficiently in both coin and pouch ZIHS cell configurations, providing satisfactory energy (45–50 Wh kg−1) and high power (10–20 kW kg−1) density combined with excellent cycle stability. Moreover, these ZIHS pouch-type devices exhibit superior durability and flexibility, withstanding mechanical stress up to 150° bending states with at least 90% of capacitance retention. It suggests a prospect for their application in wearable electronics.