Carbon Materials for Electrochemical Energy Storage Devices: Studies of Structure by X-ray Diffraction

This paper focuses on discussing X-ray diffraction patterns of carbon materials that are promising for use as components of electrodes in electrochemical energy storage devices such as supercapacitors, lithium-ion and post-lithium-ion batteries: graphites, graphenes, carbon nanofibers, nanotubes, and carbon blacks. Based on the X-ray diffraction patterns, the following characteristics of carbons were calculated: interplanar distance, crystallite sizes, the number of aromatic layers and carbon atoms in crystallites, the content of the amorphous phase, and the crystallographic density. In the studied graphites, the content of the amorphous phase varies in the range 0.5–10%, and the interplanar distance is 3.35 Å. The content of the amorphous phase in carbon nanofibers is 10–15%, and the interplanar distance is 3.40 Å. For the carbon nanotubes studied, the interplanar distance is 3.45–3.48 Å, and the content of the amorphous phase is 40–60%. The interplanar distance in carbon blacks varies in the range of 3.5–3.7 Å, and the content of the amorphous phase reaches 70%. The structure of all the studied carbon materials contains highly crystalline and low crystalline phases, as well as an amorphous phase. In the X-ray diffraction patterns of nanofibers, nanotubes, and carbon blacks, a shift and broadening of the (002) reflections is observed compared to graphite. This shift indicates an increase in the defectiveness of the crystal lattice. The calculated crystallographic density of the studied samples of allotropic forms of carbon is 2.28 g/cm3 for graphites, 2.22 g/cm3 for carbon nanofibers, 2.19–2.20 g/cm3 for carbon nanotubes, and 1.96–2.20 g/cm3 for carbon black. Thus, it can be concluded that the smallest amount of amorphous phase is observed in graphites and the largest, in carbon blacks. Graphites have the smallest interplanar distance and carbon blacks, the largest one.