Lithium-ion battery anode material series five - preparation method of graphite anode material

If a lithium-ion battery company is compared to a chef, the negative electrode material is a hard vegetable. How to make this hard vegetable well is the main responsibility of the engineers of the majority of lithium battery companies, and the quality of the hard vegetable itself needs to be considered. The ability of the vegetable masters is now, and these vegetable masters are the negative material manufacturers. As the last article in the series of basic knowledge of negative electrodes, I will go back to the source and conduct a preliminary exploration of the production process of negative electrode materials, hoping to popularize basic knowledge for the majority of lithium battery colleagues.

1. The production process of artificial graphite

People often think that the manufacture of negative electrode materials is very simple, just throw the raw materials into the sintering furnace and raise the temperature for sintering, but this understanding is very superficial. The preparation of artificial graphite needs to go through four major processes of "crushing, granulation, graphitization, and screening" and many small processes. The two links of granulation and graphitization have high technical barriers, which are not simple. A simple sintering will do. Let's start with the raw materials of artificial graphite:

The aggregates of artificial graphite are divided into three categories: coal series, petroleum series and coal and petroleum mixed series. Among them, coal-based needle coke, petroleum-based needle coke and petroleum coke are the most widely used. As far as the current market is concerned, needle coke is used as raw material for high-end negative electrodes, and cheap petroleum coke is used as raw material for medium and low-end negative electrodes. The binder acts to bind the different particles together.

The first is the pretreatment process. According to the needs of the product, the graphite raw materials and asphalt are mixed in different proportions, and then the jet mill is carried out. The ground raw materials enter the granulation process. The granulation process is divided into pyrolysis and ball milling. Screening process , the size, distribution and morphology of the granulation will directly affect the performance of the negative electrode material, which has been covered in the previous topic and will not be described in detail here; the pyrolysis process is a process of gradient heating and stirring, which can be To the intermediate product, the ball-milling screening process is a mechanical ball-milling process. Large particles are ground into smaller ones. At this time, the product enters the graphitization process, and is sintered to different temperatures as required to obtain products with different degrees of graphitization. Finally, ball milling is performed. There are many small processes in the middle of screening, and each manufacturer is different, so I will not repeat them here.

Graphitization is a high temperature heat treatment in which the product to be prepared is placed in a protective medium in a graphitization furnace and heated to a high temperature, so that the hexagonal carbon atom plane grid is transformed from the disordered overlapping of the two-dimensional space to the ordered overlapping of the three-dimensional space, and has a graphite structure. In the process, as the sintering temperature increases, the defects of the graphite structure become less and less, and the degree of graphitization becomes higher and higher, but in the actual production process, the temperature distribution is often uneven, which requires thinking on the equipment. The method makes the temperature distribution more uniform, makes the heating of the whole material more uniform, and improves the purity of the product.

2. The production process of natural graphite

The steps are also the four main processes of crushing, granulation, graphitization, and screening. Due to the defects of natural graphite, steps such as spheroidization, magnetic removal, and surface coating must also be performed, which is also to improve the physical properties of natural graphite. and electrochemical performance.
With the development of technology, the production of artificial graphite with natural graphite as raw material is also being carried out at the same time. After all, my country has a vast territory and abundant natural graphite reserves. However, there are still major problems at present, and the process route and related technologies are still developing. among.

3. Production process of mesocarbon microspheres (MCMB)

When the pitch compounds are heat treated, thermal polycondensation occurs to form anisotropic mesophase spheres.

It is a spherical particle that can be tightly packed to form a high-density electrode; has a low surface area, which reduces side reactions during charge and discharge; the internal crystal structure is radially arranged, which means that there are many exposed surfaces on its surface The edge of the graphite crystal, which enables it to be charged and discharged at a high current density, has been widely used in power and fast-charging lithium-ion batteries.

4. Other graphite materials production process

Soft carbon: commonly known as easily graphitized carbon material, it is an amorphous carbon material that can be graphitized below 2000 °C, with low crystallinity, large interlayer spacing, high irreversible capacity for the first discharge, and no obvious voltage plateau. It can pass petroleum coke and needle coke. sintered;

Hard carbon: commonly known as difficult-to-graphitize carbon material, it is difficult to graphitize at temperatures above 3000 °C. Generally, resin carbon materials, acetylene black and other substances have suitable interlayer spacing, no obvious expansion during charging and discharging, and have good charging and discharging performance. , has been widely used in Japan.

With the progress of negative electrode production technology, some manufacturers can coat the surface of artificial graphite with soft carbon or hard carbon material, which not only ensures the high capacity of artificial graphite for charge and discharge, but also enables the material itself to have high-rate charge and discharge capacity. and good high and low temperature performance, but the cost will be correspondingly higher.

Summary: This article briefly introduces the production steps and processes of artificial graphite, natural graphite, and mesocarbon microspheres. Each enterprise has its own unique technology and production process. Performance anode materials will also be gradually developed and mass-produced, and the entire lithium-ion battery industry will also progress accordingly. So far, the series of anode materials ends here. I hope that the majority of lithium battery colleagues can give valuable opinions to promote the common development of the industry.