Biopolymer-based gel electrolytes with an ionic liquid for high-voltage electrochemical capacitors

Abstract

This paper reports on the preparation, characterization, and electrochemical performance of the novel, nonaqueous biopolymer-based gel electrolytes with an ionic liquid for high-voltage electrochemical capacitors. The quasi solid-state electrolytes contain a biopolymer matrix, made of cellulose or chitin, and ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4), which acts as a plasticizer and an ionic conductor. The gel biopolymer electrolytes were prepared by a novel, but simple method. It was based on the casting solution technique with an intermediate step of hydrogel production, followed by the exchanging of aqueous phase by IL plasticizer. Contrary to well-known hydrogel electrolytes, the biopolymer-based gels with IL could safely operate to high voltages, up to 3.0 V according to our experiments. The wide electrochemical stability allowed to extend the maximum energy density of gel electrolyte-based supercapacitors. Moreover, the investigated systems displayed a high performance in terms of specific capacitance, energy-power densities, and cyclability. There are compared to the reference cell with liquid electrolyte in terms of electrochemical characteristic, showing the specific capacitance values up to 140–145 F g−1, with excellent capacitance retention (ca. 90 %) after 10,000 galvanostatic charge and discharge cycles. Taking into account all the above-mentioned features, the prepared gel biopolymer electrolytes appear to be promising eco-friendly materials for high-performance supercapacitors.