Composition-dependent electrochemical performance of pitch-derived Si/C composite anodes from recycled silicon

Silicon (Si) is considered one of the most promising anode materials for next-generation lithium-ion batteries (LIBs) due to its exceptionally high theoretical capacity; however, its practical application is severely limited by large volume expansion, unstable interfacial reactions, and poor intrinsic conductivity. In this study, pitch-coated Si/C composite anodes were developed using recycled waste Si, and the effect of Si/C composition on structural and electrochemical properties was systematically investigated. By employing petroleum pitch as a carbon precursor, a conformal carbon matrix was formed around Si particles, providing enhanced electrical connectivity, effective buffering of volume expansion, and improved interfacial stability. A key finding of this work is that the Si-to-carbon ratio critically governs the trade-off between capacity and stability. As the carbon content increased, the initial capacity decreased, whereas the initial Coulombic efficiency and cycling stability were significantly improved. Notably, the Si/C (35:65) electrode exhibited the optimal balance between reversible capacity and cycling performance. These results demonstrate that pitch-derived carbon not only stabilizes the electrode structure but also regulates interfacial reactions, highlighting compositional optimization of recycled Si-based composites as a practical and scalable strategy for high-performance LIB anodes.