Analysis of the Lithium Storage Mechanism in the SiOx/C Composite Based on the Performance Variation Applied to a Lithium-Ion Battery

The SiOx/C composite, as a form of silicon-based materials, has been considered as an attractive alternative anode for next-generation lithium-ion batteries. The porous SiO0.71C1.95N0.47 anode material exhibiting robust Si–O skeletons wrapped by carbon layers is successfully prepared and delivers an initial capacity of over 1700 mAh g–1 with an initial coulombic efficiency of 69.4% and favorable cycle life. Both Si (2p) X-ray photoelectron spectroscopy (XPS) and 29Si nuclear magnetic resonance (NMR) demonstrate the existence of SiO4 and SiO3C units as main lithium storage sites in the original state. The XPS curve moved toward the direction of the binding energy decreasing with NMR spectra shifting to a high field after the first lithiation process. The massive capacity loss during the first discharge and charge cycle results from the formation of irreversible Li silicate (Li2SiO4). The fluctuation of the charge and discharge capacity, including a persistent decline during the first 30 cycles and a continuous elevation in the following 400 cycles, could be attributed to the participated degree of reversible Li silicate (Li2SiO3 and Li2Si2O5) in the delithiation process. The Si–O skeletons are gradually corroded and ultimately destroyed in the final 400 cycles, leading to the sharp drop of the cycling performance of the half-cell.