This work reports the nanocomposites of graphitic nanofibers (GNFs) and carbon nanotubes (CNTs) as the electrode material for supercapacitors. The hybrid CNTs/GNFs was prepared via a synthesis route that involved catalytic chemical vapor deposition (CVD) method. The structure and morphology of CNTs/GNFs can be precisely controlled by adjusting the flow rates of reactant gases. The nest shape entanglement of CNTs and GNFs which could not only have high conductivity to facilitate ion transmission, but could also increase surface area for more electrolyte ions access. When assembled in a symmetric two-electrode system, the CNTs/GNFs-based supercapacitor showed a very good cycling stability of 96% after 10 000 charge/discharge cycles. Moreover, CNTs/GNFs-based symmetric device can deliver a maximum specific energy of 72.2 Wh kg⁻¹ at a power density of 686.0 W kg⁻¹. The high performance of the hybrid performance can be attributed to the wheat like GNFs which provide sufficient accessible sites for charge storage, and the CNTs skeleton which provide channels for charge transport.

Lithium-ion batteries (LIBs) are considered new generation of large-scale energy-storage devices. However, LIBs suffer from a lack of desirable anode materials with excellent specific capacity and cycling stability. In this work, we design a novel hierarchical structure constructed by encapsulating cobalt sulfide nanowires within nitrogen-doped porous branched carbon nanotubes (NBNTs) for LIBs. The unique hierarchical Co₉S₈@NBNT electrode displayed a reversible specific capacity of 1310 mAh g⁻¹ at a current density of 0.1 A g⁻¹, and was able to maintain a stable reversible discharge capacity of 1109 mAh g⁻¹ at a current density of 0.5 A g⁻¹ with coulombic efficiency reaching almost 100% for 200 cycles. The excellent rate and cycling capabilities can be ascribed to the hierarchical porosity of the one-dimensional Co₉S₈@NBNT internetworks, the incorporation of nitrogen doping, and the carbon nanotube confinement of the active cobalt sulfide nanowires offering a proximate electron pathway for the isolated nanoparticles and shielding of the cobalt sulfide nanowires from pulverization over long cycling periods.

3D hierarchical nanocomposites always lead to excellent electrochemical properties. In this research, we have successfully designed and synthesized a hierarchical three-dimensional cobalt sulfide encapsulated carbon nanotube/carbon nanofiber (Co₉S₈@CNT/CNF) composite, resulting in a high-performance supercapacitor with an unrivalled capacitance of ≈1580 F g⁻¹ at a current density of 1 A g⁻¹. An asymmetric supercapacitor (ASC) based on these 3D hierarchical Co₉S₈@CNT/CNF composites exhibits a maximum energy density of 58 W h kg⁻¹ at a power density of 1000 W kg⁻¹ and maintains it at 38 W h kg⁻¹ at a higher power density of 16.7 kW kg⁻¹. Even after 10 000 charge/discharge cycles, the ASC still retains 93% of the initial capacitance at a current density of 5 A g⁻¹. A large number of aligned CNF nanochannels combined with the synergistic effects of cobalt sulfide nanowires encapsulated in CNTs obviously accelerates the ion transfer speed and shortens the ion transfer distance, thereby boosting both power density and energy density.

We describe the single-step synthesis of carbon nanospheres hanging on carbon nanotubes (CNs/CNTs), using a simple chemical vapor deposition method. The structure of CNs/CNTs could be easily controlled. In the CN/CNT composites the CNTs have a diameter of ca. 200 nm and were cladded by carbon spheres. The TEM image displays homogeneous dispersion of the carbon spheres on the walls of CNTs which have a length of ca. 5 μm. The shape of the obtained composites is like grapes hanging in the branches which not only possess high electric conductivity for charge transport but also possess specific surface areas for accessing electrolyte ions. When using an ionic liquid electrolyte, CN/CNT-based electric double layer (EDL) supercapacitors can deliver a high specific energy of 61.2 W h kg⁻¹ at a power density of 563.4 W kg⁻¹. The EDL capacitor demonstrates excellent cycling performance with 92.7% capacitance retention after 10 000 cycles at a current density of 10 A g⁻¹. The key to high performance lies in the hanging CNs for ion accumulation and the CNT backbone providing path channels for ion faster diffusion, thereby boosting both power density and energy density.

An N-doped 3D ordered mesoporous graphite nanofiber (3D OMGNF-N) with an N-doping level of up to 16.5 at% for high-performance supercapacitors is designed and synthesized. OMGNF-N shows a conductive 3D open-structured matrix, large surface area, hierarchical porous structure, and great number of electrochemically active sites by N-doping. The supercapacitors (SCs) based on OMGNF-N show a remarkably excellent electrochemical behavior with a high specific capacitance of 460, 420, and 345 F g⁻¹, respectively, in KOH, H₂SO₄, and KCl electrolytes when measured in a three-electrode configuration. In practical devices, the material can achieve a remarkably high capacitance of 426 F g⁻¹, good cycling stability with 92% capacitance retention after 50 000 cycles. Moreover, the OMGNF-N based SCs show a remarkably excellent electrochemical behavior with good rate capability and low internal resistance, thereby leading to both high power density and relatively high energy density.