Preparation and electrochemical properties of novel silicon-carbon composite anode materials with a core-shell structure

Multi-component porous Si-SiOx (pSi) consisting of Si, SiO and SiO2 was formed by the pretreatment of SiO at 950 degrees C for 3 h in an inert atmosphere (He) using a disproportionation reaction. Hybrids of pSi and carbon nanofibers (pSi-CNFs) with a core-shell structure were prepared by catalytic chemical vapor deposition (CVD) using Fe-Ni species as the catalyst and a mixture of CO/H-2/C2H4 (volumetric ratio 3:1:1) as the reactant for 0.5, 1 and 2 h, and were characterized by SEM, TEM, EDS, XRD, Raman spectroscopy and XPS. Results indicate that the pSi-CNF particle sizes are 5-20 mu m with the diameters of the CNFs being 5-40 nm. The CNFs are uniformly coated on the surface of the pSi to form a core-shell structure. Electrochemical performance testing shows that the reversible capacity of the pSi-CNF (0.5 h) remains at 1 411 mAh.g(-1) and the capacity retention is 74% after 100 cycles at a current density of 0.2 A.g(-1). The reversible capacity remains at 735 mAh.g(-1) at a current density of 1 A g(-1) after 300 cycles with a capacity retention of 86%. In the pSi, Si and SiO provide the electrochemical reversible capacity. The core-shell structure with the CNF coating effectively improves the conductivity of the composites, and also inhibits the volume expansion of silicon to maintain the integrity of the core shell structure.