In Young Jang

The Reinforcing Effect of Combined Carbon Nanotubes and Acetylene Blacks on the Positive Electrode of Lithium-Ion Batteries

Here, we demonstrate the preparation of high-performance positive electrodes for lithium-ion batteries by adding small amounts of both carbon nanotubes and acetylene blacks to LiCoO2-based active materials. The merits of using carbon nanotubes together with acetylene blacks as cathode fillers include not only the enhancement of the electrical and the thermal properties of the electrode but also the enhancement of the density of the electrode and the shortening of the electrolyte absorption time. We envisage that the use of carbon nanotubes as multifunctional fillers will increase in both cathode and anode materials for lithium-ion secondary batteries. Since the development of lithium-ion batteries in 1990, they have had an enormous influence on our lives. 2] At present, portable electronic devices and hybrid vehicles have evergrowing requirements for safe and high-performance lithiumion batteries. Therefore, new types of the nanostructure electrode materials or fillers including carbon nanotubes have been examined to improve the electrochemical performance of lithium-ion batteries (e.g. , large capacity, high rate capability and long life cycle), as well as for developing new end-use products (e.g. , cosmetics). In commercial lithium-ion batteries, up to 100 tons per year of highly pure crystalline carbon nanotubes are incorporated as effective fillers in anode materials, in which the resilience and the electrical properties of carbon nanotubes are believed to play an important role in extending the life cycle of the batteries. Similarly, several studies have examined the capability of carbon nanotubes to enhance the electrical conductivity of cathode materials in relation to that of conventionally used carbon blacks as lithium metal oxides, which have low electrical conductivity, experience structural deterioration or capacity degradation during charging and discharging cycles. However, there appears to be a critical question regarding the complete replacement of acetylene blacks by carbon nanotubes in cathodes owing to the capability of acetylene blacks to store a significant amount of electrolyte in their primary structure in addition to enhancing the conductivity. Also, previous studies have emphasized the electrical conductivity of the cathode as the only advantage of the incorporated carbon nanotubes, even though homogeneously distributed carbon nanotubes appear to give rise to additional functions. In this study, we examine the advantages of adding a hybridtype filler, consisting of acetylene blacks and high-purity crystalline thick multiwalled carbon nanotubes, to a LiCoO2-based cathode as compared to a cathode with added acetylene blacks or carbon nanotubes, from the viewpoint of their electrical and thermal properties and electrolyte adsorption capabilities as well as their electrochemical performance. Consequently, we demonstrate that optimally combined carbon nanotubes within a cathode act as electrical, thermal and structure-linking segments and provide suitably created pores, thereby decreasing the electrolyte absorption time. The prepared electrode consisted of three different morphological components: micrometer-sized LiCoO2 particles, long carbon nanotubes and nanometer-sized acetylene blacks. The technical reason for selecting LiCoO2 (Figure 1 c) as an active

Carbon-supported Pt–Ru nanoparticles prepared in glyoxylate-reduction system promoting precursor–support interaction

A high dispersion of carbon-supported Pt–Ru alloy nanoparticles have been prepared in an alkaline aqueous solution by using glyoxylate as a reducing agent. The glyoxylate monoanion is converted to oxalate dianion with the reduction of metal precursor ions. The surface-potential analysis of unsupported Pt–Ru black in the presence of all the anion species coexistent in the preparation system suggests a possibility of oxalate dianion as the most effective particle stabilizer. In the glyoxylate-reduction system, a precursor–support interaction is significantly promoted to affect the formation and stabilization of nanoparticles. The glyoxylate reduction at 20-wt% metal loading has provided a higher Pt(0)/Ru concentration ratio in the near-surface region than that of 60-wt% catalyst. The structural and morphological features and advantageous surface composition of the 20-wt% catalyst contribute to the high mass activity for methanol oxidation in the anode overpotential range of typical direct methanol fuel cells.

Freestanding, bendable thin film for supercapacitors using DNA-dispersed double walled carbon nanotubes

Freestanding, thin, and bendable electrodes for supercapacitors are fabricated by filtering DNA-dispersed double walled carbon nanotubes (DWNTs) into a thin film and thermally treating the film in argon. We found that DNA has the ability to disperse the strongly bundled DWNTs and is converted to phosphorus-enriched carbons, which give rise to strong redox peaks at around 0.4 V. The combination of the large capacitance from the DNA-derived carbons and the high electrical conductivity of carbon nanotubes allow DWNT/DNA films to be used as a potential electrode material for supercapacitors.

An environmentally friendly dispersion method for cup-stacked carbon nanotubes in a water system

A dry process using VUV light was confirmed as a novel technique to attach functional groups onto cup-stacked carbon nanotubes and to develop their isolation in a water system without the use of dispersing agents.