High-efficiency low-temperature molten-salt preparation method of nano Si

Abstract

The invention discloses a high-efficiency low-temperature molten-salt preparation method of nano Si, and belongs to the technical field of inorganic material synthesis. The method comprises the following specific steps: using a Si source (SiO2 or silicate) and coarse particle Mg powder or Al powder as reaction raw materials, using a quaternary chloride salt with a specific molar ratio of KCl to CaCl2 to NaCl to AlCl3 as a low-temperature molten salt, putting the reaction raw materials and the low-temperature molten salt into a ball milling tank, performing ball milling for 3-5 h, performing heat treatment in an oven at 150-180 DEG C for 8-12 h, putting the ball milling tank in 0 DEG C ice water, performing cooling, repeating the above ball milling and heat treatment processes, washing theobtained product by using hydrochloric acid, performing centrifugal separation, performing treatment by using hydrofluoric acid, and performing vacuum drying to obtain the nano Si powder. The preparation method provided by the invention has higher efficiency (a Si yield can reach 88.1-95.6%), a simple preparation process, lower costs, simple and easy equipment, and environmental friendliness, andcan be directly used for industrialized production.

Description

technical field [0001] The invention belongs to the technical field of inorganic material synthesis, and in particular relates to a synthesis method of nanometer materials, in particular to a method for preparing high-efficiency low-temperature molten salt of high-purity nanometer Si powder. technical background [0002] As a lithium-ion battery anode material, the theoretical specific capacity of Si material is as high as 3500mAh g -1 , much larger than the specific capacity of the current commercial graphite anode material (372mAh g -1 ), and Si is abundant in the earth's crust and is cheap. Therefore, using Si material as the negative electrode material of lithium-ion batteries has aroused great research interest of scientists from all over the world. [0003] However, the volume expansion of Si negative electrode material is serious during the discharge process. In the state of fully intercalated lithium, the volume expansion of Si is as high as 300%. The severe volume ...

AI Technical Summary

Problems solved by technology

This preparation method partially overcomes the shortcomings of the above-mentioned magnestic reduction method or aluminothermic reduction method, but the shortcomings of this method itself are also obvious: in AlCl 3 In the molten salt, the Si formed during the reduction reaction is preferentially in the SiO 2 Or heterogeneous nucleation on the surface of a silicate solid. As the Si crystal nucleus grows, the generated nano-Si gradually covers SiO 2 Or the surface of silicate particles, hindering Mg powder or Al powder and SiO 2 or further reaction of silicate particles, resulting in a lower yield of final Si, especially with coarse-grained SiO 2 or silicate as raw material; secondly, when the reaction temperature is 200°C, the yield of Si obtained by this preparation method is only about 40%. In order to obtain a higher yield, the reaction temperature must be further increased to about 250°C. Therefore, the The actual reaction temperature used in the preparation method is significantly higher than that of AlCl 3 The boiling point (183°C), resulting in AlCl 3 The volatilization is serious, which aggravates the corrosion of heating equipment and pollutes the production environment. At the same time, it increases the amount of AlCl in the reaction process. 3 The amount of molten salt causes an increase in material cost; in addition, in this AlCl 3 In the molten salt method, if Mg powder or Al powder with a coarser particle size is used, their reactivity is low, and they interact with SiO 2 Or the contact area of ​​silicate particles is small, resulting in a low yield of Si. If nano-Mg powder or Al powder is used, it is beneficial to improve the Si yield, but the reactivity of nano-Mg powder or Al powder is extremely high, which is difficult for transportation, Storage and production pose safety risks, and also increase the complexity of the production process and production costs

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