Vapor-phase fluorination to regulating oxygen content of silicon anode materials

SiO_x is a high-potential candidate material for silicon (Si) derived anodes, owing to its high specific capacity and commendable cycling performance. However, the irreversible formation of phases during lithiation results in low Initial Coulombic Efficiency (ICE). In this work, the Si/C composite (Si@FC) with a fluorine (F) -doped bilayer structure is synthesized via "Vapor-Phase Fluorination" using Polytetrafluoroethylene (PTFE) as a source of fluorine and carbon. The hydrogen fluoride gas generated from the high-temperature pyrolysis of PTFE effectively etches away the oxygen-containing coating on the surface of the Si particles. By optimizing the oxygen content in Si oxide, the issue of low ICE associated with Si oxide can be effectively addressed. Consequently, the Si@FC anode achieves an ICE of 46.70 %, representing a 20 % improvement over that of raw Si. Furthermore, a composite material designated as Si@FC@G, which comprises 10 wt% Si@FC and 90 wt% graphite matrix is prepared through ball milling. After 200 cycles at 0.2 A g^-1, Si@FC@G maintains a reversible capacity of 409 mAh g^-1, demonstrating a high capacity retention of 91.32 %. The exceptional performance of these composite materials arises from the precise regulation of oxygen content, the distinctive double-layer structure, and the incorporation of F atoms. Additionally, interactions between Li⁺ on the surface of SiO_x and F groups facilitate the formation of a solid electrolyte interphase enriched with LiF. This innovative design effectively addresses the fundamental issue related to low ICE in SiO_x while providing a viable strategy for the large-scale development of high-stability Si-based anodes.