What are the preparation methods of negative electrode materials for Silicon-carbon composite lithium batteries?

Silicon carbon composite has become a hot spot in the field of negative electrode materials for lithium-ion batteries because of its excellent cyclic properties and high capacity properties. It is expected to replace graphite as a new generation of negative electrode materials for lithium-ion batteries. Silicon-carbon composite methods and the selection of carbon materials have an important influence on the morphology and electrochemical properties of composite materials.

At present, carbon as a matrix in silicon-carbon composite negative materials can be divided into graphite carbon, amorphous carbon, intermediate phase carbon micro-spheres, carbon fiber, carbon nanotubes, graphene and so on. The following is a brief introduction of Silicon carbon composite negative electrode materials.

Silicon carbon binary composite

1, silicon-graphite composite material

Graphite is the most widely used negative electrode material in lithium-ion batteries. It has a good voltage platform and is cheap. The lamellar structure can effectively buffer the internal stress generated during the process of charge and discharge. How to optimize the electrochemical properties of silicon-graphite composites has always been the focus of research.

The main preparation methods of silicon-graphite composites are Sol gel method and mechanical ball grinding method.

1) The Sol gel method uses Si5H10 as the precursor of Silicon to be mixed with porous natural graphite. After heat treatment, silicon-graphite composites are obtained.

The advantage of this method is that the composite has good cyclic stability.

2) The mechanical ball grinding method is to embed poly(styrene-divinyl benzene) micro spheres into silicon-graphite composites and prepare silicon-graphite composites through high-energy ball grinding.

The advantages of this method are: reducing material volume expansion and improving the circulation performance of electrode materials.

2, Silicon-amorphous carbon composite material

Unstereotyped carbon is a kind of amorphous carbon material, which is usually obtained from the low temperature cracking of polymer materials. Most of them have a high reversible specific capacity and have good compatibility with electrolytes. Using amorphous carbon as matrix not only plays a good volume buffer role, but also improves the conductivity of the material.

The main methods for preparing silicon-amorphous carbon composites are pyrolysis and high-energy ball grinding.

1) Pyrolysis is the preparation of silicon-carbon composites by pyrolysis of phenolic resins. The study shows that the reversible specific capacity of the composite material after 10 cycles is 640 ~ 1029 mA/g.

The advantage of this method is that the Covalent bond formed between the phenolic resin and Silicon enhances the binding force between the silica, improves the structural stability of the material and reduces the first irreversible specific capacity.

2) The high-energy ball grinding method uses Silicon monoxide and sucrose as raw materials to prepare silicon-carbon composites through high-energy ball grinding and subsequent pyrolysis in situ, in which the nanosilicate particles(<UNK> 50 nm) are evenly dispersed in the amorphous carbon matrix.

3, silicon-nano carbon composite material

Silico-nano carbon composites are mainly divided into silicon-carbon nanotubes and silicon-graphene.

1) Silicon carbon nanotube composites

The preparation methods of silicon-carbon nanotube composites include chemical vapor deposition, high-energy ball grinding and pulsed laser deposition. Carbon nanotubes are nanotubes that are curled by single-layer or multi-layer graphite sheets. The distance between the layer and the layer is about 0.34 nm, and the larger layer spacing is more conducive to the embedding and extraction of lithium ions. Due to the limited length of the carbon tube, the depth of deem bedding of lithium ions is small, the path is relatively short, and the electrode is less polarized by charging and discharging under large currents. In addition, its structure is stable and its conductivity is good, so carbon nanotubes have received extensive attention.

The chemical vapor deposition method uses C8H10, Fe(C5H5) 2 as a carbon source and catalyst to first prepare a longitudinal ordered carbon nanotube array, and then SiH4 as a Silicon source to deposit nanoparticles on the surface of carbon nanotubes. The silicon-carbon nanotube composite material was obtained.

Syntheses of silicon-carbon nanotube composites

This method has the advantage of good cyclic stability. The disadvantage is that the yield is low, the production cost is high, and the preparation process is difficult to control accurately, and it is not suitable for large-scale production.

2) Silicon graphene composites

Graphene has superior conductive, thermal, and mechanical properties, and has a high specific surface area. These factors are all conducive to the improvement of electrochemical properties, so it is expected to be used as a matrix to prepare silicon-carbon composites.

The preparation method of silicon-graphene composite material is to prepare silicon-graphene composite material by placing Silicon source and graphite oxide in water after ultrasonic mixing and freezing drying to obtain frozen dry powder, placing it in a non-oxidizing atmosphere for reduction reaction.

The advantage of this method is that there is no template, the degree of practicality is high, and the resulting silicon-graphene composites combine the advantages of graphene matrix composites and porous materials. The problems of low specific capacity, poor cycle performance, poor ratio and low Coulomb efficiency of Silicon based materials as negative electrode materials for lithium ion batteries were improved.

Silicon carbon composite materials

At present, the researchers have made great progress in improving the electrochemical properties of electrode materials through the combination of Silicon, carbon and various metals or metal oxides. Silico-carbon composite materials mainly include Si 1.81 Co 0.6 Mn 0.6 Al 0.3 composite materials, SixCo 0.6 B 0.6 Al 0.2 composite materials, Si/MgO / C composite materials, etc..

Silicon, carbon and various metals or metal oxides can effectively improve the reversible capacity and cycling performance of the material. At the present stage, the research is limited to simple mechanical ball grinding and other methods to prepare, and there is still a lot of research space in this area.

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