Interfacial Mechanics of Carbon

Heterogeneous nanostructures may offer better or new properties that are not originally present in constituting components by judiciously combining two or more different materials. For example, silicon coating on carbon nanotubes (CNTs) improves the thermal stability of carbon nanotubes by acting as a protective fi lm, [ 1 ] and silicon-coated CNT composites have been proposed as promising lithium ion battery electrodes. [ 2–5 ] Silicon has a theoretical charge capacity of ≈ 4200 mA h g − 1 as the anode for lithium ion batteries. However, the major problems preventing its practical use are pulverization due to huge volume changes (nearly 400%) during Li + insertion/extraction [ 6 ] and the low electrical conductivity due to the semiconductor nature of silicon. CNTs, because of their outstanding electrical properties apart from their high chemical stability, high aspect ratio, strong mechanical strength, electrical conductivity, and high activated surface area, are attractive electrode materials in energy storage devices, such as electrochemical capacitors, fuel cells, and lithium batteries. [ 7–9 ] Heterogeneous structures of amorphous silicon coated CNTs (CNT@ α -Si) separate lithium ion storage and electron transport pathways. The α -Si layer acts as the lithium ion storage medium, while the CNT core provides a mechanical support for α -Si and a continuous electron transport pathway. Thus, this core/shell structure may combine advantages of both CNTs and nanostructured α -silicon, while eliminating the weakness for each other. Experiments using silicon-coated carbon fi bers have shown early promise of this strategy for improving the performance of lithium ion batteries. [ 10 ]