Formation and quantitative analysis of internal structure of Si nanoparticles developed via bead-milling

Amorphous silicon nanomaterial is isotropic on the macroscale and can effectively inhibit the expansion/contraction during lithiation/delithiation processes, which remarkably improves the cycle performance of Li-ion batteries. Bead-milling is a simple, cost-effective, and scalable method for manufacturing amorphous and/or crystalline silicon nanoparticles. In this work, the internal structure of Si nanoparticles prepared by bead-milling was found to consist of amorphous and nanocrystalline silicon as well as amorphous silicon oxide. X-ray diffraction patterns and Raman spectra are used to calculate the average crystallite size and estimate the degree of crystallization and amorphization of silicon. The quantitative analysis of amorphous silicon oxide is carried out through x-ray photoelectron spectroscopy characterization and oxygen content measuring. It was found that the average particle size (D50) and the crystallite size were reduced to 91 and 3.7 nm, respectively, from 4.06 μm and 50.6 nm before bead-milling, and the degree of amorphization and oxygen content increased to 85.7% and 7.38%, respectively, from 37.5% and 0.12% before bead-milling. It is demonstrated that the longer the milling time, the smaller the sizes of particles and crystals and the higher the ratio of the amorphous phase. However, it inversely causes side-effects such as the increase in oxidization of Si nanoparticles and the increase in content of ZrO2 impurity.