Nickel oxide (NiO) nanoparticles are distributed uniformly in the vertically aligned carbon nanotube arrays (VACNTs) with millimeter thickness by an effective supercritical carbon dioxide-assisted method. The as-prepared VACNT/NiO hybrid structures are used as electrodes without binders and conducting additives for supercapacitor applications. Due to the synergetic effects of NiO and VACNTs with nanoporous structures and parallel 1D conductive paths for electrons, the supercapacitors exhibit a high capacitance of 1088.44 F g⁻¹. Furthermore, an asymmetric supercapacitor is assembled using the as-synthesized VACNTs/NiO hybrids as the positive electrode and the VACNTs as the negative electrode. Remarkably, the energy density of the asymmetric supercapacitor is as high as 90.9 Wh kg⁻¹ at 3.2 kW kg⁻¹ and the maximum power density reaches 25.6 kW kg⁻¹ at 24.9 Wh kg⁻¹, which are superior to those of the NiO or VACNTs-based asymmetric supercapacitors. More importantly, the asymmetric supercapacitors exhibit capacitance retention of 87.1% after 2000 cycles at 5 A g⁻¹. The work provides a novel approach in decorating highly dense and long VACNTs with active materials, which are promising electrodes for supercapacitors with ultrahigh power density and energy density.

A copper-stabilized sulfur-microporous carbon (MC-Cu-S) composite is synthesized by uniformly dispersing 10% highly electronically conductive Cu nanoparticles into microporous carbon (MC), followed by wet-impregnating S. In the MC-Cu-S composite, the MC host that physically confines S/polysulfides provides free space to accommodate volumetric expansion of S during lithiation, while the Cu nanoparticles that are anchored in the MC further chemically interact with S/polysulfides through bonding between Cu and S/polysulfides. The Cu loading allows the S content to increase from 30 to 50% in the carbon-S cathode material without scarifying the electrochemical performance in a low-cost carbonate electrolyte. At a current density of 100 mA g^-1, the MC-Cu-S cathode shows that Coulumbic efficiency is close to 100% and capacity maintains more than 600 mAh g^-1 with progressive cycling up to more than 500 cycles. In addition, the Cu nano-inclusins also enhance the electronic conductivity of the MC-Cu-S composite, remarkably increasing the rate capabilities. Even the current density increases 10.0 A g^-1, the MC-Cu-S cathode can still deliver a capacity of 200 mAh g^-1. This strategy of stabilization of S with small amount of metal nanoparticles anchored in MC provides an effective approach to improve the cycling stability, Coulumbic efficiency, and S loading for Li–S batteries.