(a) SWCNTs as Anodes for LIBs
Since the electronic properties of semiconducting and metallic CNTs differ dramatically, it is expected that the electrochemical properties may differ, including the Li storage properties. In LIB devices, electronic conductivity of the anode materials is important especially in granular media in order to bring the electronic carrier as rapidly as possible from the current collector to the electrolyte. Kawasaki et al. obtained two kinds of SWCNTs by attempting several methods, and confirmed that the reversible Li ion storage capacity of metallic SWCNTs is about 5 times greater than that of semiconducting ones, through electrochemical charge-discharge measurements. Some theoretical works have been published regarding the preferential interaction of lithium ions with SWCNTs of different chiralities. Udomvech et al. concluded that chirality plays a crucial role in Li-tube interactions, and may therefore possibly affect the application of CNTs in LIBs(3).
(b) MWCNT as Anode for LIBs
MWCNTs, with concentric graphene layers spaced 0.34 nm apart, display diameters from 10 to 20 nm and lengths of hundreds of microns SWCNTs can be described conveniently by chirality vectors. In contrast, the prediction of electronic properties of MWCNTs, which contain multiple layers of graphene sheets that may have different chiralities, is more complicated. However, due to the multiple rolled layers, MWCNTs are able to insert Li ions in a way similar to graphite, making them a promising candidate as an anode material for LIBs.