Silicon-carbon composite negative electrode material with high-density structure and preparation method of silicon-carbon composite negative electrode material

Abstract

The invention provides a silicon-carbon composite negative electrode material with a high-density structure and a preparation method thereof.The silicon-carbon composite negative electrode material comprises a silicon / graphite composite inner core, the silicon / graphite composite inner core comprises multiple layers of flake graphite and nanometer silicon, the flake graphite is arranged in an oriented mode, and the nanometer silicon is located between the flake graphite to form a sandwich structure; gaps among particles in the silicon / graphite composite core are filled with a carbon material; and the silicon / graphite composite core is coated with a carbon layer. The preparation method comprises the following steps: dispersing nano silicon and flake graphite or a composition of flake graphite and other carbon materials in a solvent, carrying out ultrasonic treatment, adding a binder, and uniformly mixing; coating a polymer substrate with the obtained silicon / graphite slurry, and drying to obtain a lamellar material; performing hot pressing after stacking; roasting is performed; crushing and shaping; carrying out carbon coating treatment; depolymerizing and sieving; the material has high density and high strength, and solves the problems of poor circulation and limited increase of volume energy density when a silicon-carbon negative electrode is applied to a battery.

Description

technical field [0001] The invention belongs to the technical field of negative electrode materials for lithium ion batteries, and in particular relates to a silicon-carbon composite negative electrode material with a high-density structure and a preparation method thereof. Background technique [0002] In order to meet the market's demand for portable digital product batteries, and the Ministry of Industry and Information Technology's requirement that the energy density of a pure electric vehicle battery unit reach 300Wh / kg, the development of a new generation of high-capacity negative electrode materials has become the development direction. As a traditional anode material, the capacity of graphite is difficult to meet the requirements, while silicon-based anodes will become the trend of mass production in the future due to their high capacity, but their poor conductivity and large volume expansion directly lead to the problems of low first efficiency and poor cycle perform...

AI Technical Summary

Problems solved by technology

Although this type of product has improved battery energy density compared with pure graphite negative electrodes, its cycle performance and compaction density are still inferior to graphite negative electrodes. The key lies in the dispersion of silicon and graphite and the interface impedance between silicon and graphite. Difficult to solve

Nano-silicon has a large specific surface area, is easy to agglomerate, and is difficult to disperse uniformly with graphite. The resulting silicon enrichment causes excessive local expansion; porosity, resulting in poor densification and structural stability of the material

At the same time, more coating agents are required to repair the pores on the surface of the material, which leads to a decrease in the capacity and compaction density of the material, which in turn affects the energy density of the battery. The capacity advantage of silicon-based materials is difficult to reflect

[0004] Patent CN107785560A discloses a method for preparing silicon-carbon anode materials by kneading and pressing. This method can better improve the particle core strength, but the direct granulation of nano-silicon and graphite through spray drying cannot avoid the formation of flake graphite filling. Pores, resulting in low charge and discharge stability of the material

[0005] In the patent CN112310363A, the amorphous carbon is dispersed in the gaps of the graphite skeleton to control the internal pore size of the material to no more than 50nm, which improves the structural stability of the composite material to a certain extent, but from the perspective of structural design, it does not solve the problem of disorder. The pores formed by graphite flakes during granulation, and the non-dense morphology of the particle surface affect the processing performance of the material

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