Developing flexible and lightweight energy storage systems for miniaturized electronic equipment and high volumetric performance is arousing increasing interest.
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.
A compressible single-walled carbon nanotube (SWNT) sponge was developed by a superfast flame burning method in less than 20[Formula: see text]s by moving polyurethane (PU) sponge template coated with SWNTs through an ethanol flame. By adjusting the geometries of the templates, the arbitrary shapes of the SWNT sponges composed of a unique network structure could be prepared as required. The SWNT sponges possessing good hydrophobicity and outstanding organic solvent adsorption capacity could adsorb various organic solvents and oils with high adsorption rate and good adsorption–volatilization and adsorption–combustion recycling performance. The SWNT sponges present good elasticity and compression stability even after a compressive strain of 80% and the 1000th loading/unloading cycle due to the stable skeleton structures. The SWNT sponges as flexible electrodes could also achieve high-specific capacitance of 126.8[Formula: see text]F[Formula: see text]g[Formula: see text] at 1[Formula: see text]A[Formula: see text]g[Formula: see text] and 95% capacitance retention after 10 000 charge/discharge cycles. Owing to the availability of the flame, easy decomposition of the PU sponge and flame resistance of SWNTs, this facile flame burning method was demonstrated to be a practical approach to prepare the SWNT sponges on a large scale with controllable shape and density, moderate organic liquid adsorption capability, good elasticity and decent electromechanical properties.
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