Si@Si3N4@C composite with egg-like structure as high-performance anode material for lithium ion batteries

Si-based anode materials in lithium-ion batteries (LIB) suffer huge volume changes during the charge–discharge cycling. Employing buffer materials to restrain the volume effect is important for these alloy-mechanism materials. In this work, we present a composite with an egg-like structure (denoted as [email protected]3N4@C) prepared by a two-step gas–solid reaction. The nanosized Si core exhibits high capacity. The highly strong and tough Si3N4 intermediate layer acts as a structural buffer, and the Li+ conductive layer accommodates volume variations and facilitates ion transport. The highly graphitized carbon shell enhances the integral conductivity. Consequently, the proposed composite can deliver a high first discharge capacity of 3093.8 mAh g−1 with an initial coulombic efficiency (ICE) of 91.51%. More than 80% capacity retention (vs. 2nd discharge) is observed after 200 cycles; when discharged at 10 A g−1, a capacity of 881 mAh g−1 is still displayed. The influence of the Si3N4 intermediate layer on Li+ diffusion is studied first, and the overall lithium-ion solid diffusion coefficient (DLi+) of the egg-like structure composite is found to be 8.111 × 10−11 cm2 s−1, which is approximately 300 times higher than that of Si, indicating a significant increase in Li+ diffusion. The probable reason is discussed and presented.