Preparation of thin-film electrolyte from chitosan-containing ionic liquid for application to electric double-layer capacitors.

A novel thin-film electrolyte (TFE) based on chitosan (CS) with 1‑ethyl‑3‑methylimidazolium tetrafluoroborate (EMImBF4) was prepared by a new procedure for use as a solid electrolyte in electric double-layer capacitors (EDLCs). In this system, EMImBF4 plays important roles as both a dissolving solution and a charge carrier for EDLC application. By analyzing and characterizing the obtained products, the CS-TFEs showed a surface without CS/EMImBF4 phase separation and with high thermal stability and good tensile properties. The electrochemical properties were measured as the charge-discharge performance, the discharge capacitance, and alternating-current impedance. A test cell with CS-TFE with a calculated dry thin-film content of 80 wt% EMImBF4 showed a comparable IR drop and higher discharge capacitance than a liquid-phase EMImBF4 system and also showed low electrode/electrolyte interfacial resistance. Consequently, this novel CS-TFE is suitable for high-performance EDLCs and improves the safety of such devices.