In Situ Synthesis of Graphene-Coated Silicon Monoxide Anodes from Coal-Derived Humic Acid for High-Performance Lithium-Ion Batteries

Silicon monoxide (SiO) is attaining extensive interest amongst silicon-based materials due to its high capacity and long cycle life; however, its low intrinsic electrical conductivity and poor coulombic efficiency strictly limit its commercial applications. Here low-cost coal-derived humic acid is used as a feedstock to synthesize in situ graphene-coated disproportionated SiO (D-SiO@G) anode with a facile method. HR-TEM and XRD confirm the well-coated graphene layers on a SiO surface. Scanning transmission X-ray microscopy and X-ray absorption near-edge structure spectra analysis indicate that the graphene coating effectively hinders the side-reactions between the electrolyte and SiO particles. As a result, the D-SiO@G anode presents an initial discharge capacity of 1937.6 mAh g⁻¹ at 0.1 A g⁻¹ and an initial coulombic efficiency of 78.2%. High reversible capacity (1023 mAh g⁻¹ at 2.0 A g⁻¹), excellent cycling performance (72.4% capacity retention after 500 cycles at 2.0 A g⁻¹), and rate capability (774 mAh g⁻¹ at 5 A g⁻¹) results are substantial. Full coin cells assembled with LiFePO₄ electrodes and D-SiO@G electrodes display impressive rate performance. These results indicate promising potential for practical use in high-performance lithium-ion batteries.