Silicon-carbon composite material and preparation method thereof

Abstract

The invention discloses a silicon-carbon composite material which is a composite material similar to a dragon fruit structure. The silicon-carbon composite material comprises a base core, a silicon-carbon composite housing and a coating layer. The silicon-carbon composite housing is formed by uniformly dispersing a plurality of nano silicon particles in conductive carbon. The nano silicon particles are formed by pyrolysis of a silicon source. The conductive carbon is formed by pyrolysis of an organic carbon source. The coating layer is a carbon coating layer. At least one carbon coating layeris provided. The thickness of a single carbon coating layer is 0.2 to 3[mu]m. Compared with the prior art, a silicon-carbon composite material precursor is formed by using vapor phase synchronous deposition, and carbon coating is performed to form the silicon-carbon composite material similar to the dragon fruit structure. The silicon-carbon composite material has a high first effect, low expansion and long circulation, slows down the silicon material grain growth during the heat treatment process, avoids the powdering of the material during the cycle, alleviates the volume expansion effect ofthe silicon-based material, and is improved in the cycle performance, the electrical conductivity and the rate performance.

Description

technical field [0001] The invention relates to the technical field of new energy materials, in particular to a silicon-carbon composite material and a preparation method thereof. Background technique [0002] Secondary batteries have been widely used in portable electronic products. With the miniaturization of portable electronic products and the increasing demand for secondary batteries in aviation, military and automotive industries, the capacity and energy density of batteries need to be greatly improved. At present, commercial anode materials are mainly graphite materials, but due to their low theoretical capacity (372mAh / g), they cannot meet the market demand. In recent years, people have focused their attention on new high specific capacity negative electrode materials: lithium storage metals and their oxides (such as Sn, Si) and lithium transition metal phosphides. One of the potential alternative graphite materials, but the Si base has a huge volume effect during t...

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Problems solved by technology

[0003] In the prior art, the Chinese patent CN105552323A discloses a silicon / silicon oxycarbide / carbon negative electrode material and its preparation method and application. Ultra-small silicon oxygen carbon nanoparticles are uniformly dispersed in a carbon matrix as a buffer matrix, while silicon nanoparticles are It is evenly embedded in the carbon / silicon carbon buffer matrix. Although the negative electrode active material has high capacity and good cycle performance, its initial efficiency is low, which limits its application in lithium-ion batteries.

Chinese patent CN104103821B discloses a method for preparing a silicon-carbon negative electrode material, which uses a metal catalyst to first decompose the silicon source to obtain a precursor Si-SiO x , and then compound the Si-SiOx prepared by the reaction with the carboxylated carbon matrix in the dynamic rotary deposition chamber through the carrier gas to obtain the precursor of the silicon-carbon negative electrode material, and finally obtain the silicon-carbon negative electrode material through carbon coating. The method can prepare high-capacity nano-silicon, but the nano-silicon cannot be evenly distributed on the surface of the carbon matrix, and there are hidden dangers such as unsatisfactory cycle performance and high volume expansion.

[0004] In view of this, it is necessary to develop a silicon-carbon composite material and its preparation method to overcome the huge volume effect, easy cracking and pulverization, and loss of contact with the current collector in the prior art Si-based materials during charging and discharging. , resulting in a sharp decline in cycle performance, and the large volume effect and low conductivity of silicon-based negative electrode active materials lead to technical problems such as poor cycle performance and poor rate performance.

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