Polyaniline nanoflowers grown on vibration-isolator-mimetic polyurethane nanofibers for flexible supercapacitors with prolonged cycle life
The brittle nature and poor cycling stability of polyaniline hinder its practical applications as a freestanding electrode for supercapacitors. It is expected that the stress induced by the repeated volume change of polyaniline during cycling is alleviated using polyurethane nanofibers as the polyaniline support mimicking mechanical vibration isolators. A flexible electrode for supercapacitors with remarkable cycling stability is developed by using carbon nanotube-reinforced electrospun polyurethane as a cushiony support for the deposition of polyaniline. The in situ polymerization of aniline is controlled such that flower-like polyaniline is grown on individual polyurethane nanofibers resulting in a porous membrane with high surface area and adjustable mass loading of polyaniline by repeating the coating process. In contrast to the continuous degradation of pure polyaniline electrodeposited on carbon cloth, the current design exhibits an excellent capacitance retention of 93% after 10000 cycles of charge–discharge. Moreover, after an initial increase of ∼13% and ∼18% in power density and energy density during the transient phase of cycling, very slight variations in parameters are observed, which could be attributed to the regulation of ion diffusion to the active sites of electrode materials. The cushiony effect of polyurethane and the strong affinity between grown polyaniline and polyurethane nanofibers as well as buffer spaces between nanofibers, which accommodate the volume expansion of polyaniline nanoflowers, all lead to the structural stability of polyaniline during cycling. The facile strategy to attain a stable and flexible polymer electrode could open up new opportunities for flexible and wearable pseudocapacitors.