Polysaccharide-Based Gel Electrolytes Containing Hydrophobic Ionic Liquids for Electric Double-Layer Capacitors

Abstract

Non-aqueous gel electrolytes based on polysaccharides (alginate or chitosan) with hydrophobic 1-ethyl-3-methylimidazolim tetrafluoroborate (EMImBF4) were prepared for electric double layer capacitors (EDLCs). The transparent colorless gel sheets have high mechanical strength and high retentivity of EMImBF4 enough to construct EDLC cells. According to charge/discharge measurements, the model EDLC cells with alginate- and chitosan-based gels show high discharge capacitance in spite of using a gel-state electrolyte, implying that high affinity of alginate for an activated carbon electrode leads to a decrease in the electrode/electrolyte interfacial resistance. A test cell with Alg/EMImBF4 maintains its coulombic efficiency over 99.8 % during 5,000 cycles.