Silicon/carbon composite material and preparation method thereof

Abstract

The invention relates to a silicon / carbon composite material and a preparation method thereof, and belongs to the technical field of electrode materials. In the process, the silicon / carbon composite material is obtained by performing metal thermal reduction of a low temperature binary molten salt system on the silica / carbon precursor, and drying the processed precursor after pickling and removal of impurities. The silicon / carbon composite material has a shape similar to that of the precursor and has a hollow structure inside. Compared with the prior art, the invention has the advantages that the molten salt system is used as the reaction system, and aluminum powder, magnesium powder or zinc powder is used as the reducing agent to make the reactant contact more uniform, the reaction temperature lower and the reaction yield higher, and to remain the appearance of the obtained product intact; the prepared silicon / carbon composite material exhibits excellent electrochemical performance asa negative electrode material for lithium ion batteries; the preparation method is simple in process, green and environmentally friendly, and convenient for large-scale production; the raw materials are rich in content in nature and can be expanded to prepare a wide variety of nanoparticles, which has wide application value.

Description

technical field [0001] The invention belongs to the technical field of lithium-ion battery electrode materials, and in particular relates to a silicon / carbon composite material and a preparation method thereof. Background technique [0002] With the rapid development of portable devices and electric vehicles, there is an increasingly urgent demand for lithium-ion secondary batteries with high specific capacity, long cycle life, and high energy density in the world. Electrode material is one of the most critical components. In terms of negative electrode materials, graphite-based carbon negative electrode materials are mainly used, but their capacity is low (372mAh / g), and because their lithium intercalation potential is close to that of metal lithium, "lithium separation" is prone to occur during fast charging, leading to safety issues. . Among other non-carbon anode materials, silicon has attracted extensive attention from researchers for its highest theoretical capacity ...

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Problems solved by technology

The third is to construct the silicon anode material into a three-dimensional porous and hollow structure: especially to construct a three-dimensional porous and hollow structure to ensure the rapid transport of lithium ions in the electrolyte and electrodes, and it is also beneficial to speed up the electrochemical reaction and reduce the storage capacity. The volume expansion of the material when lithium is used, thereby improving its electrochemical performance: However, the disadvantage of this method is that the reaction temperature for preparing porous silicon is high, and the original material itself is required to be porous, which limits its large-scale preparation and wide application.

[0004] In the literature (1) Journal of Materials Chemistry, 2012, 22:5454-5459, Liu et al. used LiCl / KCl or NaCl / MgCl 2 system, with nano-SiO 2 Powder, SBA-15, etc. are used as raw materials to prepare nano-silicon grains. Due to the high reaction temperature (550°C), the prepared silicon particles are relatively large, and the original shape of the reaction precursor cannot be maintained.

The traditional direct solid-phase metallothermal reduction method usually needs to reduce the silicon sample first, and then carry out the carbon compounding, and the temperature is mostly above 650°C, the reaction heat is relatively large, and silicon carbide may be formed, resulting in poor lithium battery performance of the material. Difference

single AlCl 3 system, when the temperature exceeds 200°C, a higher vapor pressure will be generated, and the chloride salt will be easily volatilized and lost. The reaction needs to be carried out in a very airtight container, and the reaction yield is low, and it will also cause the collapse of the template morphology.

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