Tandem structure of porous silicon film on single-walled carbon nanotube macrofilms for lithium-ion battery applications.

Development of materials and structures leading to high energy and power density lithium-ion batteries is a major challenge to the power needs of the electronic and automobile industries. Silicon is an attractive anode material being closely scrutinized for use in lithium-ion batteries but suffers from a poor cyclability and early capacity fading. In this work, we present a tandem structure of porous silicon film on single-walled carbon nanotube (SWNT) film to significantly improve the cycling stability of silicon as lithium-ion battery anode material. With this new structure configuration of the silicon films, a reversible specific capacity of 2221 mAh/g was retained after 40 charge-discharge cycles at 0.1 C rate, which is 3.6 times that of silicon film on a regular copper substrate and more than 11 times that of the SWNT film. The facile method is efficient and effective in improving specific capacity and stability of silicon anode lithium-ion batteries and will provide a powerful means for the development of lithium-ion batteries.

In-situ formation of sandwiched structures of nanotube/CuxOy/Cu composites for lithium battery applications.

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.

Effect of temperature on the capacitance of carbon nanotube supercapacitors.

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.

Anthocyanin-sensitized solar cells using carbon nanotube films as counter electrodes.

Carbon nanotube (CNT) films have been used as counter electrodes in natural dye-sensitized (anthocyanin-sensitized) solar cells to improve the cell performance. Compared with conventional cells using natural dye electrolytes and platinum as the counter electrodes, cells with a single-walled nanotube (SWNT) film counter electrode show comparable conversion efficiency, which is attributed to the increase in short circuit current density due to the high conductivity of the SWNT film.

Direct growth of aligned multiwalled carbon nanotubes on treated stainless steel substrates.

Growth of aligned carbon nanotubes (CNTs) on electrically conductive substrates is promising for many applications; however, the lack of complete understanding of the substrate effects on CNT growth poses a lot of technical challenges. Here, we report the direct growth of aligned multiwalled nanotubes (MWNTs) on chemically treated stainless steel (Type 304) using a chemical vapor deposition (CVD) process. A detailed X-ray photoelectron spectroscopy (XPS) analysis has been carried out for the various treated samples in order to better understand the correlation between the surface properties of the substrates and the MWNT growth. The XPS studies revealed that the CNTs prefer to grow on the enriched surface of iron oxides obtained by the chemical treatment rather than on the passive chromium oxide films present on the surface of the as-received stainless steel substrates. The density and alignment of the MWNTs could therefore be controlled by tuning the ratio of the iron oxides to chromium oxides through the chemical treatment on the stainless steel surfaces. On the basis of this method, selective growth of CNT patterns on stainless steel has also been demonstrated.