Improved redox-active ionic liquid-based ionogel electrolyte by introducing carbon nanotubes for application in all-solid-state supercapacitors

Abstract

More attention has been focused on the design of all-solid-state supercapacitors (ASSCs) due to that this kind of supercapacitors can avoid some problems such as electrolyte leakage occurring in liquid electrolyte-based supercapacitors. However, ASSCs present lower specific energy, which is generally in great relation with the very low ionic conductivity of utilized electrolyte. To achieve high-specific-energy ASSCs with superior performance, a redox-active ionic liquid-based ionogel electrolyte (IGE) consisting of 1-butyl-3-methylimidazolium iodide (BMIMI) IL, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and carbon nanotubes (CNTs) was prepared by a solution-casting method. By optimizing BMIMI/PVDF-HFP and CNTs/PVDF-HFP mass ratios, the obtained PVDF-HFP/BMIMI/CNTs IGE presents the maximum ionic conductivity as high as 17.6 mS cm−1. A sandwiched ASSC constructed by two identical activated carbon electrodes and an as-prepared PVDF-HFP/BMIMI/CNTs IGE possesses a high specific energy of 50.1 Wh kg−1 as a result of the extra pseudocapacitance contribution from the redox-reactions related to I-based ions happening at the interface between electrolyte and electrode and the increased ionic conductivity of IGE for the existence of CNTs network into the IGE providing fast ion transfer channel. The self-discharge behavior of this device is effectively weakened due to the addition of CNTs. Furthermore, the promising cyclic stability is achieved.