Research Progress on Polyaniline-Ionic liquids for Long Cycle-Stable Supercapacitors with High Capacitance

Ionic liquids have been used either as polymerization medium or as electrolytes for polyaniline (PANI) electrodes to produce long cycle-stable supercapacitors with high capacitance. As a polymerization medium, ionic liquids play the role of a soft template agent and induce the formation of nanostructured PANI morphology. Nanorod, nanowire, or spherical PANI morphology has been obtained in ionic liquids instead of agglomerated particles resulted in the conventional media. The well-defined one-dimensional PANI morphology ensures a short charge transfer distance in the PANI materials and low contact resistance between PANI and electrolyte interfaces. The efficiency of ionic liquids as a soft template agent is related to their structure as well as to their proportion in the reaction medium. As electrolytes, “neat” ionic liquids provide low but stable specific capacitance of PANI over more than hundreds of cycles. Binary mixtures of ionic liquids and solvents (e.g. acetonitrile, water) have increased both the specific capacitance and the capacitance retention of PANI compared with the performances resulting in the conventional aqueous acid electrolytes. Using ionic liquids to carry out both the synthesis and the electrochemical characterization of PANI is an effective approach to improve PANI cycle life. The key parameter is to choose the convenient ionic liquids. This review covers the most significant studies conducted on PANI/ionic liquids for supercapacitor applications.