Scalable synthesis of porous graphite/silicon@pitch carbon nanocomposites derived from wastes of silica fume for high-performance lithium storage

Abstract

A novel porous pitch-pyrolyzed carbon-coated spent graphite/silicon (SG/Si@C) nanocomposite was fabricated by a scalable and cost-effective method, including the processes of mechanical ball-milling and spray-drying, followed by simultaneous magnesiothermic reduction and carbonization processes. Spent graphite and silica fume were employed as the sources of carbon and silicon, respectively. Another carbon source was directly deposited on the surface of the spent graphite/silicon particles by means of the carbonization of mesophase pitch. In this ingenious structure of composites, nano-Si particles are uniformly distributed and anchored on the surface of graphite via pitch-pyrolyzed carbon. The graphite in the composites provides sufficient electrical conductivity and mechanical strength for SG/Si@C nanocomposites, and the amorphous carbon coating layer pyrolyzed by mesophase pitch is beneficial for relieving the volume expansion of Si particles, stabilizing SEI passivation layers and inhibiting the pulverization of Si nanoparticles during the lithiation/delithiation process. Benefiting from this innovative approach and rational structural design, an as-prepared SG/Si@C nanocomposite electrode delivers a high initial reversible specific capacity of 903.69 mA h g⁻¹ with an initial Coulombic efficiency of 82.34%, and the reversible capacity was maintained at 799.37 mA h g⁻¹ over 500 cycles at a current density of 200 mA g⁻¹. On account of these aspects, the proposed rational design of pitch-pyrolyzed carbon coating for macro-scale SG/Si structures, as well as low-cost raw materials, is practical for implementation in commercial applications.