Analysis of the Lithium Storage Mechanism in the SiO<sub><i>x</i></sub>/C Composite Based on the Performance Variation Applied to a Lithium-Ion Battery
Duxin Zhang, Meilin Fan, Shifeng Tan, Hongfei Pan, Wenmao Tu, Haining Zhang, Yadong Wang
Abstract
The SiO x /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 SiO 0.71 C 1.95 N 0.47 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 29 Si nuclear magnetic resonance (NMR) demonstrate the existence of SiO 4 and SiO 3 C 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 (Li 2 SiO 4 ). 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 (Li 2 SiO 3 and Li 2 Si 2 O 5 ) 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.