A kind of carbon cage type silicon-graphite composite material and preparation method thereof

Abstract

The invention discloses a carbon cage type silicon-graphite composite material and a preparation method thereof. The graphite is intercalated and oxidized; the treated graphite and nano-scale silicon powder are stirred and dispersed in the presence of a dispersant to obtain a silicon-graphite composite material. Suspension of graphite composite material; adding sucrose and acid to the suspension to hydrolyze the sucrose under acid catalysis, and then drying; calcining and carbonizing the dried product under an inert atmosphere, and coating the silicon-graphite composite material without Shape the carbon layer to obtain a carbon-cage silicon-graphite composite material. The carbon cage silicon-graphite composite material prepared by this method has high specific capacity and good cycle stability. Using surface treatment technology, the combination of graphite and silicon is realized, and the volume of silicon is adjusted by a simple carbon coating method. The expansion problem is effectively controlled, and the disadvantage of low specific capacity of traditional commercial graphite electrode materials is improved.

Description

technical field [0001] The invention belongs to the field of composite materials, and in particular relates to a carbon cage silicon-graphite composite material and a preparation method thereof. Background technique [0002] my country is the country with the most abundant graphite reserves in the world, and it is also the largest producer and exporter, occupying an important position in the world graphite industry. Graphite material has good electrical conductivity, high thermal and chemical stability. But the specific capacity of graphite is only 372mA h g -1 . Moreover, the potential of the graphite negative electrode material is low, which is easy to cause lithium precipitation; poor compatibility with the electrolyte; the ion migration rate is slow, so the charge and discharge rate is low; layered graphite will generate about 10% in the process of lithium ion insertion and deintercalation. The deformation will affect the cycle life of the battery. The voltage platfo...

AI Technical Summary

Problems solved by technology

But silicon-based materials have always had a serious problem: the volume expansion effect

During the charging and discharging process of the battery, with the intercalation and extraction of lithium ions, the volume expansion effect of silicon reaches 297%, and the volume expansion causes the destruction of the material structure and mechanical pulverization, resulting in the separation between the electrode materials and the electrode materials and the current collector. Loss of electrical contact, resulting in rapid capacity decay and deterioration of cycle performance

Due to the severe volume effect, the SEI film on the silicon surface collapses and forms reciprocally, continuously consuming lithium ions, increasing the irreversible capacity of the electrode, and further affecting the cycle performance

[0004] Most researchers use different processes to solve the volume expansion problem of silicon by carbon coating, and synthesize carbon-coated silicon materials with different structures through a series of processes. Although the volume expansion problem of silicon has been effectively solved, However, the process steps are too complex for commercial application, and enter the bottleneck due to insufficient electrode loading and limited energy density.

[0005] The main problem of silicon-graphite composites is that the interface between graphite and silicon is not firmly bonded, and it is difficult to give full play to the synergistic lithium storage effect.

The limited surface area of ​​graphite also leads to limited loading of silicon on graphite, and the prepared electrode material cannot achieve the ideal specific capacity.

Moreover, graphite is easily deformed during cycling under the condition of low load and high energy density, which affects the cycle performance of electrode materials.

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