Author ：Iflowpower – Portable Power Station Supplier
Silicon-carbon composite materials have become a hot spot in the field of lithium-ion battery negative materials in the field of lithium-ion battery, which is expected to be a new generation of lithium-ion battery negative electrode materials in the field of negative electrode materials in lithium-ion batteries. Silicon-carbon composite methods and carbon materials have an important effect on the morphology of composite materials and electrochemical properties. At present, carbon-carbon-carbon composite negative electrode materials can be divided into graphite carbon, amorphous carbon, intermediate phase carbon microspheres, carbon fibers, carbon nanotubes, graphene, etc.
The following small series is a brief introduction to the silicon-carbon composite negative material. I. Silicon-carbon binary composite 1, silicon-graphite composite graphite is currently the most widely used lithium-ion battery negative electrode material, has a good voltage platform and low price, and the layer-like structure can effectively generate during charge.
Internal stress. How to make silicon-graphite composite electrochemical properties to optimize the focus of research. Silicon-graphite composite material main preparation method with sol gel method and mechanical ball mill.
1) The sol gel method is a precursor using Si5h10 as a precursor with a porous natural graphite, and a silicon-graphite composite material is obtained after heat treatment. The method has the advantage that the prepared composite material has good circulating stability. 2) Mechanical ball mill is to embed the poly (styrene-dilyne) microspheres into the silicon-graphite composite, by high energy ball milling silicon-graphite composite material.
The method has the advantage of reducing the volume expansion of the material to improve the circulating performance of the electrode material. 2, silicon-amorphous carbon composite material amorphous carbon is a carbon material of an amorphous structure, which is usually obtained by low temperature cracking from a polymer material. Most of the highly reversible comparison capacity is better than the electrolyte compatibility.
Using amorphous carbon as a substrate not only serves a good volume buffer, but also improves the conductivity of the material. Silicon-amorphous carbon composite material main preparation method has pyrolysis and high energy ball mill. 1) The pyrolysis is to prepare silicon-carbon composite materials by pyrolysis phenolic resin.
Studies have shown that the composite material is 640 ~ 1029mA / g after 10 cycles of the composite. The method has the advantage that the covalent bond formed between the phenolic resin and the silicon enhances the bonding force between silicon carbon, which can improve the stability of the material structure and reduce the first irreversible specific capacity. 2) High-energy ball mill is based on silica and sucrose, produce silicon-carbon composite materials by high energy ball milling and subsequent pyrolysis, wherein nano-silica particles (<50 nm) are uniformly dispersed in an amorphous carbon matrix.
3, silicon-nanocarbon composite silicon-nanocarbon composite material is mainly divided into silicon-carbon nanotubes and silicon-graphene. 1) Silicon-carbon nanotube composite silicon-carbon nanotube composite material has a chemical vapor deposition method, high energy ball mill and pulsed laser deposition method. The carbon nanotube is a nanotube made from a single layer or a plurality of graphite sheets, and the distance between the layers and the layers is about 0.
34 nm, and the larger layer spacing is more advantageous for lithium ions. Embedding and extraction. Due to the limited length of the carbon tube, the depth depth of the lithium ion is small, the path is relatively short, the degree of charge and discharge of the electrode under large current is small.
In addition, its structure is stable, good conductivity, so carbon nanotubes have been widely concerned. The chemical vapor deposition method is C8H10, Fe (C5H5) 2 as a carbon source and a catalyst, first preparing a longitudinal ordered carbon nanotube array, and then deposited from nanotube from the surface of the silicon nanotube in a silicon nanotube to obtain silicon- Carbon nanotube composite material. Silicon-carbon nanotube composite synthetic diagram This method is that the cycle stability is good.
The disadvantage is that the yield is low, the production cost is high and the preparation process is difficult to accurately control, and it is not suitable for large-scale production. 2) Silicon-graphene composite graphene has superior conductive, thermally conductive and mechanical properties, and has a high specific surface area, which facilitates the improvement of electrochemical properties, and thus is expected to be prepared as a substrate. The silicon-graphene composite preparation method is to place the silicon source and the graphite ink to ultrasonically mix well after mixing the silicon and dry freeze-drying powder, reacting it under a non-oxidizing atmosphere, reacting silicon - graphite Ethylene composite material.
The method has the advantage of no need for template, high degree of practicalization, and the obtained silicon-graphene composite material sets the advantages of graphene composites and porous materials, and improves the amount of silicon-based material as a lithium ion battery negative material. , Poor cycle performance and magnification performance, low efficiency. Silicon-graphene composite SEM picture (right) two, silicon-carbon polymer composites, researchers have improved electrochemical properties of electrode materials by silicon, carbon and various metallic or metal oxides, have achieved great progress.
Silicon-carbon polymer composites mainly include Si1.81CO0.6Mn0.
6Al0.3 composite, Sixco0.6B0.
6Al0.2 composite, Si / MgO / C composite materials, etc. Silicon, carbon and various metal or metal oxides can effectively improve the reversible capacity and cycle performance of the material.
At this stage, research is limited to simple mechanical ball mills, and there is still a large research space in this respect.
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