# Synthesis of C/SiC Mixtures for Composite Anodes of Lithium-Ion Power Sources
## 3 Results  
### Samples Characterization  
C/SiC mixtures: Figure 2 shows a SEM-image of a C/SiC mixture and maps of elemental distribution after carbothermal synthesis and treatment in HF solution. The resulting mixture is represented by particles with a size of about 20-40 microns (graphite) and smaller fibers (SiC). According to X-ray microanalysis, the content of the elements was (wt%) silicon 47.5-51.3; carbon 47.7-51.7; oxygen--up to 1.6. The presence of oxygen could be due to both the insufficient treatment time of the mixture in the HF solution and the subsequent oxidation of the silicon or SiC presented in the mixture. According to ICP analysis, the resulting mixture contained 48.8-49.4 wt% silicon (the rest was carbon) and no more than 0.4 ppm of such impurities as Fe, Al, Ti and Ca. If we do not take into account the presence of oxygen, the ratio of components corresponds to a mixture of (wt%): 70.5 SiC-29.5C. SiC: Figure 3 shows a SEM-image of a typical SiC agglomerate obtained after annealing of residual carbon from a C/SiC mixture. Its total size is about 50-60 \(\upmu\)m. It consists of fibers with a diameter of 0.1 to 2 \(\upmu\)m. The obtained morphology is similar to the previously obtained samples of ultrafine SiC [40] since the reagents and the synthesis procedure were reproduced almost completely. The distribution of elements in the resulting SiC are also shown. Uniform distribution of silicon, carbon and oxygen is observed for this sample. According to X-ray microanalysis, the average content of elements at different points of the sample was (wt%): 68-69 silicon, 29-30 carbon, up to 1.6 oxygen. This ratio is close to the SiC stoichiometric composition. Figure 2: SEM-images and elements distribution in a C/SiC mixture after carbothermal synthesis and treatment in HF solution. Figure 4 shows the X-ray diffraction patterns and Raman spectra for C/SiC and SiC samples. For the C/SiC sample there are peaks of residual SiO\({}_{2}\) (21-22\({}^{\circ}\)), carbon (26-27\({}^{\circ}\)), as well as peaks indicating presence of two carbide modifications (\(\alpha\)-SiC, \(\beta\)-SiC) in sample (35-36\({}^{\circ}\), 41.5\({}^{\circ}\), 44.5\({}^{\circ}\), 55\({}^{\circ}\) and 60\({}^{\circ}\)). For the SiC sample, there are no peaks of C and SiO\({}_{2}\); only additional signals of the \(\beta\)-SiC phase appear at 64.5\({}^{\circ}\). A similar picture is also observed in Raman spectra, in which responses of \(\alpha\)-SiC and \(\beta\)-SiC carbide modifications at 770-793 cm\({}^{-1}\) were fixed. In this case, for the SiC sample, there is also a response at 502 cm\({}^{-1}\) that can correspond to both residual silicon and the \(\beta\)-SiC modification [43]. Moreover, there are lines near 1370, 1510 and 1585 cm\({}^{-1}\) on both spectra, which indicate the C-C bonds. In this work, the structure of the used graphite powder was not studied in detail. However, based on the absence of pronounced peaks and intensity ratio of carbon lines, one can only note the presence of different carbon structures [44; 45; 46; 47]. For the SiC sample, the intensities of these lines are less pronounced. Electrodeposited Si: Figure 5 shows a SEM-image of silicon deposits obtained by electrolysis of the (wt%) 98 KCl-2K\({}_{2}\)SiF\({}_{6}\) melt at a temperature of 780 \({}^{\circ}\)C and a cathode current density of 25 mA cm\({}^{-2}\). A detailed procedure and parameters for silicon synthesis were provided earlier [42]. The resulting silicon deposits are arbitrarily shaped fibers with a diameter in the range of 0.45-0.55 \(\upmu\)m and a length of up to 20-25 \(\upmu\)m. According to X-ray microanalysis data, the oxygen content in the obtained silicon was from 1.2 to 1.5 wt% and other impurities did not exceed 0.18 ppm (mainly iron and nickel). Figure 6 shows the X-ray diffraction pattern and the Raman spectra of silicon deposit. As can be seen, the sample is represented by polycrystalline silicon with SiO\({}_{2}\) impurities.