Supercritical CO₂ fluid assisted synthesis of Si-Fe-Fe₃O₄-C composites and lithium storage performance

Silicon-carbon anode is an important issue for the development of lithium-ion battery materials. Aiming at the problems of uneven combination and poor interfacial contact of silicon-carbon anode prepared by traditional ball milling, this paper proposes a new strategy to synthesize Si-Fe-Fe₃O₄-C composite by ball milling in supercritical carbon dioxide (scCO₂) fluid medium. It is found that during the process of ball milling mixture of nano-silicon and mesophase carbon microspheres (MCMB) in the scCO₂ medium, CO₂ and Fe reacts firstly to form a uniformly dispersed Si-FeCO₃-C precursor, and then in situ high temperature decomposition of FeCO₃ solid phase results in final Si-Fe-Fe₃O₄-C product. Under the infiltration of scCO₂ fluid, MCMB microspheres exfoliate into graphite flakes, and achieve ideal combination with nano-silicon and Fe-Fe₃O₄. The introduction of Fe-Fe₃O₄ in the composite has significantly improved the lithium storage capacity, cycle stability and rate performance of silicon-carbon anode, the synthesized Si-Fe-Fe₃O₄-C composite material maintains a reversible capacity of 1065 mA·h·g⁻¹ after 100 cycles at 0.2 A·g⁻¹. The method shows the merits of facile operation procedure, easy industrial production and potential commercial application basing on the supercritical fluid permeability and strong diffusion ability.