Thin carbon nanotube coiled around thick branched carbon nanotube composite electrodes for high-performance and flexible supercapacitors

High performance and flexible supercapacitors are strongly desired in miniaturized, smart energy-storage devices. Here, a hierarchical three-dimensional carbon nanostructure based on thin carbon nanotube (TCNT) coiled around thick branched carbon nanotube (BCNT) composites (TCNT/BCNT) is constructed to improve the accessibility of ions in the electrodes of electrochemical energy storage devices. The coiled TCNTs could increase the surface area for ion storage and accumulating charge, while the branches of the BCNTs provide ion and electron path channels for efficient charge transport. When assembled into an electric double layer (EDL) capacitor using an ionic liquid electrolyte, the composite exhibits the maximum energy density of 73.2 W h kg(-1) at a power density of 523.0 W kg(-1) and retains 27.9 W h kg(-1) at a higher power density of 9.87 kW kg(-1). Moreover, TCNT/BCNT-based flexible supercapacitors exhibit exceptional cycling performance and remarkable flexibility over 10 000 cycles under bending. The excellent electrochemical performance shows the great application potential of TCNT/BCNT in wearable and portable electronics.