Abstract
Carbon nanotubes are frequently selected for supercapacitors because of their major intrinsic properties of mechanical and chemical stability, in addition to their excellent electrical conductivity. However, electrodes using carbon nanotubes suffer from severe performance degradation by the phenomenon of re-stacking during fabrication, which hinders ion accessibility. In this study, short single-wall carbon nanotubes were further shortened by sonication-induced cutting to increase the proportion of edge sites. This longitudinally short structure preferentially exposes the active edge sites, leading to high capacitance during operation. Supercapacitors assembled using the shorter-cut nanotubes exhibit a 7-fold higher capacitance than those with pristine single-wall nanotubes while preserving other intrinsic properties of carbon nanotubes, including excellent cycle performance and rate capability. The unique structure suggests a design approach for achieving a high specific capacitance with those low-dimensional carbon materials that suffer from re-stacking during device fabrication.
Highlights
As the demands for renewable energy sources have grown in environmentally friendly industries, high-performance energy storage systems are required for applications ranging from mobile electronic instruments to electric vehicles and buildings
Carbon nanotubes are frequently selected for supercapacitors because of their major intrinsic properties of mechanical and chemical stability, in addition to their excellent electrical conductivity
The electrochemical performance of SCs is primarily affected by the active surface area of the electrode materials, since the specific capacitance is proportional to the number of ions interacting with the electrochemical surface area [5]
Summary
As the demands for renewable energy sources have grown in environmentally friendly industries, high-performance energy storage systems are required for applications ranging from mobile electronic instruments to electric vehicles and buildings. SCs store and release electrical energy based on the electrical double layers formed by electrostatic interactions between ions in the electrolyte and the electrodes [3] This charge storage mechanism creates electrochemical energy without chemical/mechanical stress on the electrode materials, and introduces advantages such as high rate capabilities and long-term cycle stabilities [4]. Nanostructuring the electrode material to increase the number of active sites has been widely adopted to create high-performance electrodes for SCs. Recently, metal oxide- [6,7,8] and conductive polymer-based [9,10] materials for pseudocapacitors (which have a different mechanism from EDLCs, using a surface redox reaction) have been developed to resolve the insufficient capacitance issues [1] of carbon-based SCs. long-term stability issues are still a concern in pseudocapacitors since the redox reactions on the surface during ion storage induce a constraining stress in the electrodes by volume expansion [8,10]. The as-prepared c-SWNT electrode exhibits a 7-fold higher specific capacitance than SWNT electrodes and excellent rate capabilities with 100% capacity retention after 2500 cycles at 5 A g−1
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