# Scalable Fabrication of Si-Graphene Composite as Anode for Li-ion Batteries
## 3 Results and Discussions  
Figure 1 illustrates the schematic diagram of synthesizing Si-graphene nanocomposite in aqueous solutions by utilizing SDBS surfactant. During the sonication, SDBS surfactant was first dissolved in DI water. When graphene nanosheets were added and ultrasonication was applied, the carbon chain of SDBS was attracted to the surface of the graphene sheets by van der Waals forces and \(\pi\)-\(\pi\) interactions. After Si nanoparticles were dispersed in the fluid, the Si nanoparticles yielded a positive zeta potential that tend to attract negatively charged particles. That being, the Si nanoparticles would be electrostatically attracted to the negatively charged SDBS surfactant particles which were attached to graphene sheets. Therefore, the insoluble graphene nanosheets and the Si nanoparticles were uniformly dispersed in water by simply adding the SDBS surfactant. The morphology of the as-received Si nanoparticles, graphene nanosheets, and the fabricated Si-graphene composite was characterized by scanning electron microscopy (SEM), as shown in Figure 2. The average diameter of the spherical Si nanoparticles was confirmed to range from 50-70 nm. Figure 2b shows that the lateral dimension of the graphene nanosheets varies from 50 to 150 nm, indicating the relatively low quality of the material. However, the thickness of the graphene sheets is about a few nanometers, which is beneficial for applications that require high specific surface area and electrical conductivity. Figure 2c,d are the SEM images of the fabricated Si-graphene composite. The Si nanoparticles were successfully attached to the graphene nanosheets by utilizing SDBS surfactant in the aqueous media. The red arrows in Figure 2d highlight the graphene nanosheets, and it is confirmed that the uniform dispersion of Si nanoparticles and graphene nanosheets was obtained. The tight connections between Si nanoparticles and graphene nanosheets indicate that it is efficient to utilize SDBS surfactant to provide sufficient electrostatic interactions. It is anticipated that the enhanced electrochemical performance of the Si-graphene electrode is attributed to the structural flexibility of graphene that accommodates the volume expansion of Si nanoparticles. EDS mapping (see Figure 3) was performed to verify the composition of the fabricated Si-graphene compound. The results confirm that the Si nanoparticles and the graphene nanosheets were uniformly distributed by the use of SDBS surfactant, which contains sulfur (S) and oxygen (O) elements. It is concluded to be an efficient and facile way of utilizing surfactant to homogeneously disperse Si nanoparticles and graphene nanosheets through electrostatic interactions. The crystalline structures of Si nanoparticle and the fabricated Si-graphene nanocomposite were characterized by XRD using a Cobalt source (\(\lambda\) = 0.1789 nm) (see Figure 4a). The XRD spectrum shows characteristic peaks of Si nanoparticle at 33.2\({}^{\circ}\), 55.5\({}^{\circ}\), 66.2\({}^{\circ}\), and  
Figure 3: (**a**) SEM image of Si-graphene; EDS mapping of Si-graphene (**b**), element C (**c**), element Si (**d**), element O (**e**), and element S (**f**). Figure 2: SEM images of (**a**) Si nanoparticle; (**b**) graphene; (**c,d**) Si-graphene (the red arrows highlight the graphene nanosheets). 82.4\({}^{\circ}\), referring to the (111), (220), (311), and (400) planes of cubic Si that matches PDF 27-1402. The broad and weak peak at 30\({}^{\circ}\) is the reflection of the graphene. The broad diffraction peak indicates that the graphene sheets in the stack direction are not well ordered, meaning the graphene sheets were well dispersed with Si nanoparticles. Figure 4b shows the Raman spectra of Si, graphene and Si-graphene composite. The characteristic peak around 520 cm\({}^{-1}\) indicates Si nanoparticle, and the other two peaks at around 1335 cm\({}^{-1}\) and 1575 cm\({}^{-1}\) are the D and G peaks of graphene, corresponding to the vibration of sp\({}^{3}\) defects-induced and sp\({}^{2}\) bonded carbon atoms.