Amorphous SiO2 coating layers with thicknesses of ca. 2, 7, 10, and 15 nm are introduced into bulk@nanowire core@shell Si particles via direct thermal oxidation at 650–850 °C. Of the coated samples, Si with a coating thickness of ca. 7 nm has the best electrochemical performance. This sample shows an initial discharge capacity of 2279 mA h g−1 with a Coulombic efficiency of 92% and displays 83% capacity retention after 50 cycles at 0.2C rate.