# Synthesis of C/SiC Mixtures for Composite Anodes of Lithium-Ion Power Sources
## 3 Results
### Electrochemical Performance of the Composite Anodes  
C/SiC composite anode: Figure 7 shows the change in the C/SiC composite anode potential during lithiation/delithiation, as well as changes in the discharge capacity and Coulombic efficiency of the sample during cycling. When the C/SiC composite anode sample was initially charged with a current of 0.1 C (first cycle) its charging capacity was 658 and discharge capacity was 322 mAh g\({}^{-1}\) (Coulombic efficiency is 49%). Such capacity loss is usually attributed to a solid-electrolyte interface (SEI) layer formation. All subsequent cycling was carried out at a current of 0.5 C. In the second cycle, the discharge capacity was 308 mAh g\({}^{-1}\) (Coulombic efficiency is 92%), and after the 100 th cycle the discharge capacity was 328 mAh g\({}^{-1}\) (see Figure 7c). During cycling, the Coulombic efficiency of the C/SiC anode reached 99% and remained at this level even after capacity began to fade. Figure 5: SEM-image and the elements distribution in a Si sample 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\({}^{-2}\). Figure 6: X-ray diffraction pattern (**a**) and the Raman spectra (**b**) of silicon deposit. Figure 7: _Cont._Figure 7c shows current-voltage dependences (CVs) characterizing the kinetics of charge and discharge of a C/SiC composite anode material. It can be noted that the beginning of the charge occurs at an electrode potential negatively than 0.22 V relative to the potential of the lithium electrode. This behavior may be due to the interaction of lithium ions with the electrode material, which is accompanied by the chemical formation of compounds. In this case the presence of several peaks in the cathode region of the CVs indicates the occurrence of several lithiation reactions. At a potential of about 0.05 V a lithium reduction wave is formed. During discharge in the anodic region of the CVs in the potential range from 0.05 to 0.5 V there are corresponding discharge (oxidation) peaks of lithium. Moreover, the shift in the peak potentials of the lithium reduction and oxidation indicates that the processes is not electrochemically reversible. Obviously, the irreversibility may be due to the interaction of lithium with the anode material. Since the LIBs capacity includes the contribution of both diffusion and capacitance reactions the expression [48] is valid for the usual lithiation/delithiation process:  
\[\log(I)=\log(a)+b\log(\
u) \tag{1}\]  
where \(I\)--peak current, A; \(\
u\)--potential sweep rate, V s\({}^{-1}\); \(a\) and \(b\)--constants. In our case, the calculated \(b\) value was of 0.73 (see Figure 7c), which indicates the pseudocapacitive behavior of the C/SiC anode material [48]. This may be associated with a slow chemical reaction of silicon carbide with lithium. Figure 7d shows the electrochemical impedance spectra (frequency range from 100,000 to 1 Hz) of the sample after the forming cycle. The EIS contains two arcs corresponding to the processes of charge transfer through the electrolyte layer and between the electrode and electrolyte [49; 50; 51]. The obtained data can be described by a typical for LIBs equivalent circuit. It has two RC circuits connected in series and a resistance (Figure 7e). Parameters changes in this scheme during cycling have not yet been studied. SiC anode: The cycling results of the SiC electrode are shown in Figure 8. When the SiC electrode sample was initially charged at a current of C/20 (first cycle) its charge capacity was only 78 and the discharge capacity was of 42 mAh g\({}^{-1}\) (Coulombic efficiency is 54%). During further cycling, the capacity gradually increased. After the 60 cycles at C/20, capacity increased up to 180 mAh g\({}^{-1}\).