Preparation method of silicon-carbon composite material

Abstract

The invention relates to a preparation method of a silicon-carbon composite material. The preparation method comprises the following steps of: S1, preparing a carbon-coated nano silicon-based oxide, namely separately weighing silicon particles and a carbon source aqueous solution and uniformly mixing the two in a silicon-carbon molar ratio of (5-15) to 1 to form a suspension; transferring the suspension to a container, cooling the container to room temperature and taking the container out after a hydrothermal reaction at a first predetermined temperature for a first predetermined time, and washing and drying the suspension in vacuum to obtain the carbon-coated nano silicon-based oxide; and S2, preparing the silicon-carbon composite material, namely grinding and mixing the carbon-coated nano silicon-based oxide obtained in the S1 with metal magnesium powder in a mass ratio of 1 to (0.6-1.6) to form a mixture, and then mixing the mixture in an inorganic salt; filling the container with the mixed mixture and the inorganic container, putting the container in inert gas, raising the temperature to a second predetermined temperature at a predetermined temperature raising rate, keeping the second predetermined temperature for a second predetermined time, cooling the mixture, cleaning impurities, and then drying the mixture in vacuum to obtain the silicon-carbon composite material.

Description

[0001] 【Technical field】 [0002] The invention relates to the technical field of negative electrode materials for lithium batteries, in particular to a method for preparing a silicon-carbon composite material. [0003] 【Background technique】 [0004] At present, lithium batteries have been widely used in 3C digital, electric vehicle power storage systems and other aspects. Electric energy storage systems require lithium batteries to have higher energy density and better cycle life, while requiring low cost and good safety. However, the theoretical mass specific capacity of the graphite-based anode material of the traditional lithium battery is only 372mAh / g, resulting in a low gravimetric energy density of the battery, which is difficult to meet the current requirements. Non-carbon anode materials are mainly metal or alloy materials with high lithium storage performance. Among them, silicon has become a research hotspot because of its large lithium-intercalation specific cap...

AI Technical Summary

Problems solved by technology

However, the lithium storage principle of metal or alloy materials represented by silicon is the alloying process, which will be accompanied by a large volume change effect during the lithium intercalation process, and the large mechanical force generated by it will make the silicon active. The material is pulverized, and after many cycles, the battery electrode active material and the current collector fall off, causing the weakening of electrical contact; and the volume change effect makes it difficult for silicon to form a stable electrolyte interface film (SEI film) in conventional electrolytes , the new SEI film on the newly exposed silicon interface will consume a lot of lithium ions and electrolyte after each intercalation and desorption of lithium, resulting in a decrease in charge and discharge efficiency, and a rapid decline in overall capacity and cycle performance.

The conventional methods for preparing silicon materials, such as metallothermic reduction of silica, use glucose, graphite, graphene and other carbon sources to coat the prepared nano-silicon particles, and use chemical vapor deposition and other multi-step framework structures of carbon / Silicon materials, etc., from the perspective of the material itself, are faced with problems such as nanoparticle agglomeration, uneven distribution, and volume expansion effects that are difficult to completely solve, resulting in poor actual cycle performance of lithium batteries.

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