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