Honeycombed NiCo2O4 nanosheets grown on the sponge of a carbon nanotube/graphene prepared by the flame burning method with an advanced performance as a supercapacitor

Abstract

To obtain high performance supercapacitors suitable for tiny, compact and portable electronic devices, a new type of electrode with high energy density, high speed performance and long cycling-stability is essential. In practical applications, both volumetric capacitance and gravimetric capacitance should be regarded as equally important parameters. Due to their high open surface structures, high compressibility and high conductivity, low-density three-dimensional (3D) carbon scaffolds hold great promise for excellent electrochemical performance, high diffusion rates and low ion transport resistance. Here, a new 3D elastic sponge composed of single-walled carbon nanotubes/graphene (SWNT-rGO-S) was successfully prepared by a superfast and facile flame burning method in an open environment within 20 s. Moreover, the hierarchical NiCo2O4 nanosheets were deposited on the SWNT-rGO-S scaffold through the hydrothermal method and the annealing treatment. Due to the 3D open pore and compositional features, the compressed NiCo2O4/SWNT-rGO-S electrode exhibits a high gravimetric capacitance of 2050 F g−1 and a volumetric capacitance of 1200 F cm−3, together with a high cycling stability with 115.3% capacitance retention after 6800 cycles at the current density of 20 A g−1 and a high rate performance of 73.2% capacitance retention with the current density being increased from 2 to 80 A g−1. Additionally, a high performance asymmetric supercapacitor was fabricated by using NiCo2O4/SWNT-rGO-S as the positive electrode and activated polyaniline derived carbon (APDC) as the negative electrode, presenting high gravimetric and volumetric energy densities of 53.5 Wh kg−1 and 26.9 Wh L−1, respectively, and exhibiting a very high 83.5% capacitance retention after 10,000 cycles.