Surface-modified silicon-carbon composite material and preparation method and application thereof

Abstract

The invention discloses a surface-modified silicon-carbon composite material and a preparation method and application thereof. The preparation method comprises the following steps: purifying commercial coarse silicon, enabling the purified commercial coarse silicon to react with magnesium to obtain a magnesium-silicon alloy, carrying out thermal decomposition of the magnesium-silicon alloy to obtain nano-silicon, carrying out in-situ carbon coating to obtain a silicon-carbon nano-material, and compounding the nano-silicon carbon with fluoride through ball milling to obtain a silicon-based composite material. Compared with the prior art, the method provided by the invention is low in energy consumption, low in cost, short in period and beneficial to large-scale production. According to themethod, the volume change of silicon in the lithiation/delithiation process can be buffered, and the contact between silicon particles and the electrolyte can be prevented, so that the silicon is prevented from being corroded by the electrolyte, and the diffusion of lithium ions from the liquid electrolyte to the silicon particles is not influenced. The prepared surface fluoride modified silicon-carbon composite material is high in capacity, is high in initial coulombic efficiency, and is excellent in cycle performance.

Description

technical field [0001] The invention relates to the technical field of energy storage batteries, in particular to a surface-modified silicon-carbon composite material and a preparation method and application thereof. Background technique [0002] Lithium-ion batteries are now widely used in mobile electronic devices, such as smartphones, laptops, etc., and have huge markets in grid energy storage, electric vehicles. However, with the large-scale use of lithium-ion batteries in electric vehicles, traditional graphite-based anodes cannot meet the increasing requirements of high energy density for power batteries. Compared with graphite-based negative electrodes, the theoretical capacity of silicon-based negative electrodes reaches 4200mAh / g, which has important application prospects. [0003] However, in the process of forming the lithium-silicon alloy, the volume expansion is as high as 300%, which seriously affects the cycle life of the material. At present, measures to im...

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Problems solved by technology

Although nanonization and compounding can improve the cycle performance of silicon-based negative electrodes, it is still a big challenge to realize the simple and large-scale preparation of nano-silicon-based materials.

In addition, unlike graphite anodes, it is difficult for silicon-based anodes to form a stable SEI film. The residual HF in the electrolyte also has a corrosive effect on silicon, so it is necessary to protect the surface of silicon to form an artificial SEI film. In addition, the electrical conductivity of silicon Low, need to introduce conductive agent

[0004] Currently, additives are used in the electrolyte to form the SEI film. Too many additives will affect the performance of the battery, and too few additives will be gradually consumed during use.

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