Effects of hydrogen gas injection on the properties of SiO x nanoparticles synthesized by using an evaporation and condensation process

Abstract

SiOx nanoparticles were synthesized by using an evaporation and condensation process involving induction melting of silicon (Si) chunks followed by the injection of a H2/Ar mixed gas into the melt. In particular, this research studied the effects of hydrogen gas on the nanoparticles’ microstructural and electrochemical properties, etc. During the microstructural analysis, regardless of H2 content, all the nanoparticles were observed to have random shapes; their average particle sizes were 30 ∼ 35 nm. However, a crystalline Si phase, even though it was a small amount, was formed when H2/Ar gas was injected. From the X-ray photoelectron spectroscopy (XPS) analysis, the amount of the SiO2 phase in SiOx decreased when the H2/Ar gas ratio was higher than 1.0 vol.%. Injected hydrogen produced a Si-H network in SiOx, and the Si-H concentration was independent of the amount of injected gas. Consequently, due to hydrogen incorporation, not only was a crystalline Si phase formed, but also the amount of the SiO2 phase decreased. In addition, Si-H bonds were formed in the nanoparticles. The crystalline Si phase and the relatively small amount of the SiO2 phase resulted in an enhancement of the Li-ion capacity when those nanoparticles were applied as an anode material for a Li-ion battery. Furthermore, cycle performance was improved even when hydrogen was incorporated. For the sample synthesized with 5.0-vol.% H2/Ar gas, the discharge capacity and the columbic efficiency at the 21st cycle were 889.1 mAhg−1 and 95.0%, respectively.