To improve the energy density of supercapacitors, a new type of electrode material with high electrochemical activity and favorable morphology is extremely desired.

Developing flexible and lightweight energy storage systems for miniaturized electronic equipment and high volumetric performance is arousing increasing interest.

Homogeneous ZnCo2O4 nanoflowers have been synthesized on a 3D layered structure of carbon nanotubes/nitrogen-doped graphene (NGN/CNTs) film by a hydrothermal process and subsequent calcination method.

To increase the volumetric and gravimetric capacitances of supercapacitors, a new class of electrode materials with high electrochemical activity and favorable structures is extremely desired. In this work, a hollow novel nitrogen-doped 3D elastic single-walled carbon nanotube sponge (NSCS) which is ultra lightweight with the lowest density of 0.8 mg cm, and has a high open surface structure for electrolyte accessibility and excellent compressible properties as the electrode scaffold has been successfully fabricated by the pyrolysis method which could produce the carbon nanotube sponge easily on a large scale without high-cost and time-consuming processes. Moreover, a NiCoO nanosheet supported on the NSCS has been successfully fabricated. The highest volumetric and gravimetric capacitance of this electrode is 790 F cm at 1.43 g cm and 1618 F g at 0.54 g cm with excellent cycling stability. The density of NiCoO/NSCS electrode was adjusted by mechanical compression and the most favorable density of the film for both high volumetric and gravimetric capacitances obtained was 1.21 g cm. The thick NiCoO/NSCS film of 72 μm has been fabricated at this favorable density, presenting both high volumetric and gravimetric capacitances of 597 F cm and 1074 F g at 1 A g, respectively, indicating that the structure of the NSCS is extremely feasible for obtaining a thick film electrode with excellent volumetric and gravimetric capacitances. Furthermore, an asymmetric supercapacitor of NiCoO/NSCS//NGN/CNTs was fabricated, exhibiting a high gravimetric energy density of 47.65 W h kg at 536 W kg and a volumetric energy density of 33.44 W h L at 376.16 W L.

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