Chitosan-based gel electrolyte containing an ionic liquid for high-performance nonaqueous supercapacitors

Nonaqueous gel electrolytes based on chitosan and 1-ethyl-3-methylimidazolim tetrafluoroborate (Chi/EMImBF4) are prepared for electric double-layer capacitors (EDLCs). The transparent colorless gel sheet has the high levels of mechanical strength and ionic liquid retention required in EDLC cells. Charge–discharge measurements revealed that a model EDLC cell with a chitosan gel exhibits high discharge capacitance although a gel-state electrolyte was used, indicating that the high affinity of chitosan for the activated carbon electrode decreases the electrode–electrolyte interfacial resistance. A test cell with Chi/EMImBF4 maintained a Coulombic efficiency of more than 99.9% during 5000 cycles.