# Synthesis of C/SiC Mixtures for Composite Anodes of Lithium-Ion Power Sources
## 3 Results
### Electrochemical Performance of the Composite Anodes
This situation can be caused by gradual activation of the anode material accompanied by partial destruction of SiC and the formation of Li-C and Li-Si compounds [28; 29] via the reactions:  
\[\mathrm{SiC}+x\mathrm{Li}^{+}+x^{e-}\rightarrow\mathrm{Li}_{\mathrm{S}}\mathrm{ Si}_{\mathrm{y}}C+(1-y)\mathrm{Si}\;(y<1) \tag{2}\]  
\[\mathrm{Si}+z\mathrm{Li}^{+}+ze^{-}\leftrightarrow\mathrm{Li}_{\mathrm{z}} \mathrm{Si} \tag{3}\]  
Figure 7: Cycling of C/SiC electrode: (**a**) potential change during lithiation (dashed line) and delithiation (solid line); (**b**) discharge capacity and Coulombic efficiency; (**c**) CVs at different scan rates and \(\log(I)\)–\(\log(\
u)\) dependencies; (**d**) EIS data with equivalent circuit diagram. As a result, a gradual conversion of SiC to Si and C occurs [28; 29]. In turn, reactions (1) and (2) also explain the reason for the onset of lithium discharge on anodes with SiC at a potential 0.22 V more positive than the lithium potential (see Figure 7b). With an increase in the charge current to C, the discharge capacity decreased, while its value was stable during 100 cycle and the Coulombic efficiency was more than 99.2%. Relatively low capacity can be explained by the presence of voids (see Figure 3) and a lack of the electrical contact between stiff SiC wires. Si/C/SiC anode: Figure 9 shows the changes of the Si/SiC/C electrode potential during lithiation and delithiation as well as changes in its discharge capacity and Coulombic efficiency during cycling. A voltage plateau below 0.1 V (Figure 9a) indicates lithiation of graphite and silicon; delithiation occurs at 0.15-0.4 V. Similar results were obtained for lithiation of the silicon anode [52]. In the first cycle at a current of C/20, the discharge capacity was 225 mAh g\({}^{-1}\) and the initial Coulombic efficiency was 54%. Coulombic efficiency gradually increased during further cycling at a current of 0.5C and remained above 98% after 20 cycles (Figure 9b). The discharge capacity gradually increased up to 525 mAh g\({}^{-1}\) after 40 cycles. The higher capacity value can be explained by the silicon lithiation in the anode material and the additional increase during cycling can be explained by the gradual activation of the electrode, as in the case of the SiC anode (see Figure 8a). The subsequent decrease in the discharge capacity to 400 mAh g\({}^{-1}\) by the 100 th cycle may be due to the contact loss of part of the anode material with the substrate due to the local expansion and cracking of silicon. Figure 9c shows the CVs obtained at different scan rates for the Si/SiC/C electrode. There are clear redox peaks indicating the charge and discharge of the sample. In this case the calculated value of \(b\) was 0.63 (see Figure 9c). This indicates that the operation of the Si/C/SiC electrode mainly proceeds under lithium diffusion conditions. A distinctive feature of the obtained CVs is also the fact that the charge and discharge currents of the anode sample are observed in a wider potential range (0.8-0.1 and 0.1-1.4 V respectively), which is due to the higher bonding energy of lithium with silicon and a larger number of compounds in the Li-Si system [52; 53; 54]. Figure 9d shows the electrochemical impedance spectrum of the Si/C/SiC sample after the forming cycle. One can note the relatively high resistance R1 (7.7 \(\Omega\)), which can result in a significant change in the parameters of two series-connected RC chains (R2, C2, R3 and W1) [49; 50]. The decrease in R1 will be the subject of our further research.