Fabrication Of Silicon Anode Via Magnesiothermic Reduction And Controllable Synthesis Of Nanostructured Hematite

Silicon has been considered as a promising candidate for high-performance anode material in lithium ion battery due to its high capacity, low cost and low toxicity. But the poor capacity retention has impeded its deployment. This problem is mainly caused by poor conductivity and large volume change during insertion and extraction process of lithium ion. This research aims to prepare different nanostructured silicon anode materials and improve their electrochemistry properties.Magnesiothermic reduction is a potential method to prepare nanostructured silicon materials. The mechanism of the reaction has been discussed in detail.The diffusion rate of magnesium vapor is the key factor to obtain pure nano silicion. By tuning reaction time, reactant ratio and reaction vessel, this study determined the optimal reaction parameters and processes.The influence of nanostructure and carbon content on the electrochemistry performance of silicon anode materials has been studied. Template-assisted method has been employed to prepare silicon spheres and rings. Using silica spheres and a-Fe2O3rings as the templates, silicon spheres and hollow rings were obtained respectively via magnesiothermic reduction method. Carbon coated silicon spheres and rings were prepared by chemical vapor deposition. After50cycles at a current density of100mA/g, the spheres with carbon content of24%retain the capacity of711mAh/g while the rings keep the capacity of973mAh/g.This work studies controllable synthesis of hollow nanostructures of a-Fe2O3by a facile hydrothermal route. A diversity of nanostructures including nanotubes, nanobeads, nanorings, nanoplates, and nanospindles were obtained via finely tuning the phosphate ions concentration and reaction time. All these hollow α-Fe2O3nanostructures experienced an evolution process including nucleation, aggregation, re-crystallization and dissolution. Using different a-Fe2O3structures as templates, various Fe3O4/C were synthesized with reserved morphologies, which exhibit morphology-dependent magnetic properties.