## 3 Results and Discussion  
The X-ray diffraction patterns of as milled Si powder at various milling times are shown in Figure 1a. The diffraction peaks of all the powders are matching with JCPDS (Joint Committee on Powder Diffraction Standards) Card file 27-1402. Comparing to the starting silicon powders, the milled Si powder diffraction peak intensities are obviously decreased and broadened with respect to milling time, which indicates the pulverization of the Si powder and decrease of the Si crystal size during the mechanical milling. The change in Si crystal size was saturated by 8 h milling, which was the first step for the nano-crystalline Si/C composite powders. The Si powders were followed by the mixing with carbon solution and heat treatment at 900 \({}^{\circ}\)C for 1 h in Ar ambient (carbonization process). Through the carbonization, the Si/C composite powder was produced and additionally milled at different milling times and their diffraction patterns are shown in Figure 1b. The Si peak intensities were slightly increased, compared with 8 h-milled Si powder (the first step), which was due to partial recovery of the Si crystallinity. No graphite carbon peaks were observed, which was presumed to be amorphous phase carbon. However, the additional milling drastically deceased intensities of the Si diffraction peaks with severe background broadening. Since such X-ray diffraction results are correlated with a marked reduction in the crystal size and loss of crystallinity, it was believed that Si powders were reduced, and their crystallinity ceaselessly collapsed. In even 8 h-milling, no peaks such as Fe, SiC and SiO\({}_{2}\) were detected, which indicated the contamination driven by the mechanical milling was not serious. The normalized Si (111) peak intensity changes in the Si and Si/C composite powders were studied with respect to milling time, as shown in Figure 1c. A rapid decline in the Si peak intensity ratio was observed within the first 8 h of the high-energy mechanical milling; further milling up to 8 h showed less influence on the intensity ratio. The linear extrapolation of the Si powder with respect to milling time appeared to be almost flat without any significant reduction in the intensity ratio, as shown in Figure 1c, indicating that 8 h is the critical milling time for effective pulverization of the Si powders. However, a ceaseless decrease in intensity ratio of the Si/C powder (carbonized and additionally milled) was observed, indicating that further fragmentation of Si crystals occurred in the type of the Si/C powder. Thus, the extended milling (i.e., 8 h) for the Si/C was believed to be effective to obtain the Si/C nanocomposite. The starting silicon powder was composed of unevenly distributed irregular particles with size ranging 50-100 \(\upmu\)m (Figure 2a). In the case of 8 h milled silicon, the powder size was significantly decreased, and distributed in the range of 100-500 nm (Figure 2b), which was estimated from the particle size distribution analysis (Table 1). The Si/C composite powder size increased after the carbonization at 900 \({}^{\circ}\)C, and agglomerated powders were observed (Figure 2c). The Si powders were connected during the carbonization and resulted in the agglomeration. However, as shown in Figure 2c, the Si powders were connected during the carbonization and resulted in the agglomeration. However, as shown in Figure 2c, the Si powders were connected during the carbonization and resulted in the agglomeration. The Si powders were connected during the carbonization and resulted in the agglomeration. However, as shown in Figure 2c, the Si powders were connected during the carbonization and resulted in the agglomeration. However, as shown in Figure 2c, the Si powders were connected during the carbonization and resulted in the agglomeration. However, as shown in Figure 2c, the Si powders were connected during the carbonization and resulted in the agglomeration.