| Among all natural silicide discovered in history,only CaSi2 has a layered lattice structure in its lattice.This property made CaSi2 a dominating precursor in producing layered Si structure by topochemical exfoliation method.Now,melting Ca and Si in stoichio-metry ratio and solid phase epitaxy method are two primary methods to produce CaSi2.The former method can avoid high amount Si impurity in CaSi2 while the latter method has low efficiency and cost a lot.In this thesis,we focuses on the preparation of high purity and low cost CaSi2 in large scale and related scientific problems and key technologies.The main results are as follows:(1)The CaSi2 with high purity was successfully prepared by using ball milling sea sand or silicon micro powder as precursor and calcium metal granules as reducing agent with the present of KClO4.The morphology and combination of obtained CaSi2 was characterized by X-ray diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy,scanning electron microscope and etc,by which confirmed the formation of CaSi2 with high purity,loosely stacked morphology and highly hydroxide surface.Combined experiment results with thermodynamic calculation of system,the formation mechanism of CaSi2 was discussed.(2)Siloxene was obtained by etching commercial CaSi2 or CaSi2 produce by our method as precursor.The morphology and structure of obtained siloxene was characterized by X-ray diffraction,Raman spectroscopy and scanning electron microscope.As prepared CaSi2 and siloxene was used as the anode active material for Li ion battery.Found that CaSi2 is not suitable to be used in Li ion battery with the capacity only remain 20 mA·hvg-1 after 10 cycles.While siloxene had an enhanced performance with first discharge capacity 1965.8 mA·h·g-1 and even after 200 cycles it could still maintain 200 mA·h·g-1.Because of higher oxidation degree of siloxene made from CaSi2 which produced by combustion calciothermic method,its performance was degraded. |
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