Chemical Synthesis Of Nano-silicon Materials And Their Lithium Ion Batteries Property

Nano-silicon material is one of the most candidate anode material of lithium ion batteries (LIBs) owning to its high lithium ion storage performance. Thus, it is become a more important to prepare nano-silicon by an efficial way. In this paper, we try our best to design of new reaction system, develop new chemical reaction route for nano-silicon preparation. Using the low cost silicate materials, silicon oxidation or the raw silicon in industry as the silicon source precursors, based on the reaction system of molten salt assisten, hydrothermal reaction or the demagnesiation route in air oxidation process to synthesize the nano-silicon. In addition, combining the process analysis to explore the the reaction mechanism. As anodes for lithium ion batteries, the electrochemical performance of the as-prepared silicon nanomaterials are also examined and analyzed. Further, we hope to provide a large-scale and rapid synthesis route for high-quality nano-silicon electrode materials. The specific content is as follows:1. We report an extensible synthesis method for scalable fabrication of uniform vesica-like hollow nano-silicon from fumed SiO2in molten salt magnesiothermic reduction process, with an Mg-NaCl-KCl inorganic melt liquid system. The fabrication of hollow inside of the nano-vesica structure is confirmed through a mechanism analogous to the Kirkendall effect. Get rid of the restrictions of the pseudomorphic transformation process in traditional magnesium thermal reduction reaction. The conversion yield of nano-silicon is higher as80%. The as prepared nano-silicon without further modification exhibit high electrochemical storage capacity, high-rate capability and long cycling properties (～712mAh g-1at0.36A g-1over200cycles).2. We present a new synthetic approach for direct synthesis of honeycomb porous nano-silicon via low temperature reaction at200℃by using sodium metasilicate nonahydrate (Na2SiO3·9H2O) as Si precursors and Mg as reductant agent. Such reaction temperature is only approximately tenth of that applied in the earlier carbothermic reduction silica and third of magnesiothermic reduction silica process. The as-prepared nano-silicon feature a satisfactory electrochemical storage properties after graphene coating, which shown a capacity of about576mAh g-1at3.6A g-1after300cycles. Moreover, this chemical reaction process can be regarded as a general low temperature synthesis method for different kinds of silicide based material such as SiC and MgSiN2. Reviewers to evaluate the work as:"The results are of great significance and importance for the researchers in the field of new energy","I consider this as an incremental progress in the field".3. Porous nano-silicon materials were hydrothermally synthesized based on the reduction of silica by magnesium metal in autoclave at<200℃. The related reaction in the process can be expressed as follows:SiO2+Mg+H2Oâ†'Mg(OH)2+H2+Si, The mechanism of the hydrothermal reduction reaction process showed that the hydrogen ion concentration affect the initial reaction temperature, reaction process of authigenic heat and active hydrogen intermediates prompted the reaction occurs at lower temperatures. The silicon source precursors can be silica sol, aqueous silicate such as water glass, amorphous hydrated silicon dioxide solid such as silica gel and silica minerals such as diatomaceous earth. For the further large-scale preparation of nano-silicon provides the basis. The as-prepared nano-silicon anode delivers a high reversible specific capacity of2650mA h g-1at0.36A g-1and cycling stability about950mA h g-1at3.6A g-1after400cycles.4. We have developed an air-oxidation demagnesiation from Mg2Si to obtain nanoporous Si from the raw silicon in industrial as precursors. Each experiment can produce10g nanoporous silicon powder, and the yield is about90%. Since Mg2Si was prepared from200meshes commercial Si, comparing with previous work, the route is relatively simple and suitable for the large scale production of Si nanomaterials. As anode for rechargeable lithium ion battery, the as-prepared nanoporous Si delivers the reversible capacity of1000mAh g-1at36A g-1and～1200mAh g-1at1.8A g-1over400cycles.