RESUMO
Silicon nanoparticles (SiNPs) with a median size of 51 nm are prepared by the sand mill from waste silicon, and then carbon-interweaved SiNPs/graphite anode materials are designed. Because of the size of SiNPs is restricted below a critical fracture size of 150 nm as well as the rational decoration of carbon and graphite, fracture of SiNPs, and volume deformation of active materials are highly alleviated, leading to low impedance, enhanced electrochemical reaction kinetics, and good electronic connection between active materials and current collector. Furthermore, delithiation reversibility of the formed crystalline Li15Si4 alloy is enhanced. As a result, the anode with 10.5 wt % content of Si (including SiOx) delivers a properly high initial reversible capacity of 505 mA h g-1, high cycling stability with capacity retentions of 86.3%, and 91.5% at 0.1 and 1 A g-1 after 500 cycles, respectively. After cycling at a series of higher current densities, the reversible capacity recovers to the original level completely (100% recovery) when the current density is set back to the original value, exhibiting outstanding rate performance. The results indicate that the silicon-carbon anode can achieve high cycling performances with enhanced delithiation reversibility of the formed crystalline Li15Si4 alloy by restricting size of SiNPs and decoration of carbon materials, which are discussed systematically. The SiNPs are recycled from waste Si, and synthetic strategy of anode materials is very facile, cost-effective, and nontoxic, which has potential for industrial production.
RESUMO
Residual Si was produced on a furnace wall when upgraded metallurgical grade Si was refined by electron beam melting. It was then recycled to prepare Si-SiOx nanoparticles with an average size of 100â¯nm by planetary ball milling. The obtained Si-SiOx nanoparticles mainly consist of amorphous Si, crystalline Si and amorphous SiOx, which was confirmed by XRD, FTIR, XPS and TEM. SiOx is mainly composed of SiO2 and SiO1.35. Distilled water used as a grinding aid not only enhances milling efficiency, but also plays a key role in obtaining SiOx. During refining of upgraded metallurgical grade Si, the deposition pattern of residual Si on furnace wall agrees with model of three-dimension growth. Growth of Si-SiOx nanoparticles is the mutual effect of distilled water and ball milling. Si-SiOx nanoparticles were doped into phenolic resin pyrolysis carbon as anode materials for lithium ion batteries, and 10% doping was observed to improve the specific capacity. After 500 cycles, specific capacity of delithiation remained around 550â¯mAâ¯h/g. It suggests the residual Si is a value-added by-product, and it can be recycled as anode materials for lithium ion batteries.
