Stretchable electronic devices, such as p-n diodes, [1] photovoltaic devices, [2,3] transistors, [4,5] and functional electronic eyes, [6] have been fabricated using buckled single-crystal (e.g., Si, GaAs) thin films supported by elastomeric substrates. Recently, carbon nanotube (CNT)-based highly conducting elastic composites [7,8] and stretchable graphene films [9] have been reported, which are suitable as interconnects in stretchable electronic devices. As an indispensable component of stretchable electronics, a stretchable power-source device should be able to accommodate large strains while retaining intact function. Of various power-source devices, supercapacitors have attracted great interest in recent years due to their high power and energy densities compared with lithium-ion batteries and conventional dielectric capacitors, respectively. The most active research in supercapacitors is the development of new electrode materials. Recently, CNTs have been studied as good candidates for electrode materials [10][11][12][13][14][15][16] because of several advantages, including a high surface area, nanoscale dimensions, and excellent electrical conductivity.Here, we report stretchable supercapacitors based on periodically sinusoidal single-walled carbon nanotube (SWNT) macrofilms (a 2D network of randomly oriented SWNTs). The stretchable supercapacitors comprise two sinusoidal SWNT macrofilms as stretchable electrodes, an organic electrolyte, and a polymeric separator. Electrochemical tests were performed and the fabricated stretchable supercapacitors are found to possess energy and power densities comparable with those of supercapacitors using pristine SWNT macrofilms as electrodes. Remarkably, the electrochemical performance of the stretchable supercapacitors remains unchanged even under 30% applied tensile strain.The preparation of the periodically sinusoidal SWNT macrofilms is of primary importance for stretchable supercapacitors. The synthesis of high-quality, purified, and functionalized SWNT macrofilms is, thus, an important preprocess, which has been presented elsewhere.[17] The purified SWNT macrofilm was then shaped to a sinusoidal form by following the steps shown in Figure 1a. The procedure introduced here (step i in Fig. 1a) involves the uniaxial prestretching (e pre ) of an elastomeric substrate of a poly(dimethylsiloxane) (PDMS) slab (e pre ¼ DL/L for length changed from L to L þ DL), followed by a chemical surface treatment to form a hydrophilic surface (see Experimental Section). The exposure of UV light introduces atomic oxygen, an activated species that reacts with PDMS and, thus, changes the Figure 1. Fabrication steps of a buckled SWNT macrofilm on an elastomeric PDMS substrate. a) Illustration of the fabrication flow comprising surface treatment, transfer, and relaxation of the prestrained PDMS substrate. b) Optical microscopy image of a 50-nm-thick, buckled SWNT macrofilm on a PDMS substrate with 30% prestrain, where the well-defined periodic buckling structure is shown. c) SEM image of ...

The effect of temperature on the kinetics and the diffusion mechanism of the ions in a supercapacitor assembled with single-walled carbon nanotube (SWNT) film electrodes and an organic electrolyte were thoroughly investigated. An improved room temperature performance of the supercapacitor was observed due to the combined effects of an increase in the conductivity of the SWNT films and surface modifications on the SWNT films by repeatedly heating and cooling the supercapacitor between the temperatures of 25 and 100 degrees C. Modified Randles equivalent circuit was employed to carry out an extensive analysis of the Nyquist spectra measured at different temperatures between 25 and 100 degrees C in order to understand the fundamentals of the capacitive and resistive variations in the supercapacitor. The experimental results and their thorough analysis will have significant impact not only on the fundamental understanding of the temperature-dependent electrode/electrolyte interfacial properties but also on supercapacitor design with appropriate electrode materials for numerous industrial and consumer applications. The supercapacitor with SWNT film electrodes was capable of withstanding current densities as high as 100 A/g, yielding eminent specific power density values of about 55 kW/kg. Ultralong galvanostatic charge-discharge cycling over 200 000 cycles with a constant current density of 20 A/g at 25 and 100 degrees C, respectively, showed excellent stability in capacitance with more than 80% efficiency. The usage of such a supercapacitor potentially enables far-reaching advances in backup energy storage and high pulse power applications.

Carbon nanotubes (CNTs) are considered to be excellent candidates for high performance electrode materials in Li ion batteries. The nanometer‐sized pore structures of CNTs can provide the hosting sites for storing large numbers of Li ions. A short diffusion distance for the Li ions may bring about a high discharge rate. The long‐cycle performance of aligned multiwalled carbon nanotubes (MWNTs) directly synthesized on stainless‐steel foil as an anode material in lithium battery is demonstrated. An increase in the specific capacity with an increase in the cycle number is observed. Starting at a value of 132 mA hg−1 in the first cycle at a current rate of 1 C, the specific capacity increased about 250% to a value of 460 mA hg−1 after 1 200 cycles. This is an unusual but a welcoming behavior for battery applications. It is found that the morphology of the MWNTs with structural and surface defects and the stainless‐steel substrate play an important role in enhancing the capacity during the cycling process.

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Development of materials and structures leading to lithium ion batteries with high energy and power density is a major requirement for catering to the power needs of present day electronic industry. Here, we report an in situ formation of a sandwiched structure involving single-walled carbon nanotube film, copper oxide, and copper during the direct synthesis of nanotube macrofilms over copper foils and their electrochemical performance in lithium ion batteries. The sandwiched structure showed a remarkably high reversible capacity of 220 mAh/g at a high cycling current of 18.6 A/g (50 C), leading to a significantly improved electrochemical performance which is extremely high compared to pure carbon nanotube and any other carbon based materials.