Regarding the analysis of the requirements of lithium-ion batteries for cathode materials, do you know what are there?

With the development of global diversification, our lives are constantly changing, including the various Electronic products we come into contact with, so you must not know some of the components of these products, such as lithium-ion battery cathode materials. The important components of lithium ion batteries include positive electrode, negative electrode, electrolyte, separator, etc. The storage and release of lithium ion energy are realized in the form of redox reaction of electrode materials, and the positive electrode active material is the most critical core material of lithium ion batteries.

With the development of global diversification, our lives are constantly changing, including the various electronic products we come into contact with, so you must not know some of the components of these products, such as lithium-ion battery cathode materials. The important components of lithium ion batteries include positive electrode, negative electrode, electrolyte, separator, etc. The storage and release of lithium ion energy are realized in the form of redox reaction of electrode materials, and the positive electrode active material is the most critical core material of lithium ion batteries.

After nearly 30 years of rapid development, cathode materials include lithium cobalt oxide, lithium manganate, nickel nickel cobalt oxide (LiNi1-xCoxO2, also known as NC), lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, etc. . Industrialization, and has been expanded to be used in many fields. With the demand for high-energy density cathode materials for new energy vehicles, lithium nickel cobalt manganese oxide ternary materials have become the most important cathode materials and account for the largest proportion of cathode materials.

1. The main element content of the positive electrode material: the positive electrode material in the lithium ion battery is an oxide containing lithium. Generally, the higher the lithium content, the higher the capacity. For example, the Li content of lithium manganate is only 4.2%, while the content of lithium cobaltate and lithium nickelate is about 7.1%, and the content of lithium-rich manganese alkali is about 10%. If the material composition is fixed, the content of the main elements should be given in the form of the actual test average plus tolerance to achieve the corresponding electrochemical activity and maintain stability between batches. The cathode materials in lithium-ion batteries are all lithium-containing oxides. Generally, the higher the lithium content, the higher the capacity.

2. The crystal structure of the cathode material: The crystal structure of the cathode material of the lithium ion battery is mainly divided into three categories: α-NaFeO2 layered, olivine type and spinel type. In the cathode material, the pure phase of LiCoO2 is easier to prepare, and the product has a layered structure of α-NaFeO2, which corresponds to the card 50-0653# issued by the United States Joint Committee on Powder Diffraction Standards. The pure phase of LiMn2O4 is relatively easy to obtain, and the product has spinel. Cubic structure, corresponding to JCPDS5-0782# card; LiFePO4 must be prepared in an inert atmosphere, because its Fe is +2, and the product has an olivine structure, corresponding to JCPDS83-2092# card.

Regarding the analysis of the requirements of lithium-ion batteries for cathode materials, do you know what are there?

3. Particle size distribution of the positive electrode material: The particle size of the positive electrode material will directly affect the preparation of battery slurry and pole shoes. Generally, the slurry of large particle size materials has low viscosity and good fluidity, and can use less solvent and higher solid content. The particle size of the positive electrode material is usually measured by a laser particle size analyzer, and the equivalent diameter D50 of the maximum particle size when the cumulative distribution in the particle size distribution curve is 50% is taken as the average particle size. The particle size and distribution of the cathode material are closely related to the precursor, sintering and crushing process. Generally, it should show a normal distribution. Lithium cobaltate is generally prepared from cobalt tetroxide and lithium carbonate, and its sintering performance is very good. It can grow by controlling key factors (such as Li/Co, sintering temperature and heating rate), so the demand for raw materials is low.

4. The density of the cathode material: The volumetric energy density of a lithium-ion battery depends to a large extent on the density of the active material. The density of the positive electrode material is closely related to the atomic weight of the elements contained therein, crystal arrangement, crystallinity, sphericity, particle size and distribution, density, etc., and is affected by the preparation process. The density of the positive electrode material is divided into loose bulk density, tap density, powder compaction density, pole shoe compaction density, theoretical density and so on.

5. The specific surface area of ​​the positive electrode material: When the specific surface area of ​​the positive electrode is larger, the rate characteristics of the battery are better, but it is usually easier to react with the electrolyte, which makes the cycle and storage worse. The specific surface area of ​​the positive electrode material is closely related to the particle size and distribution, surface porosity and surface coating. In the lithium cobalt oxide system, the rate-type product with small particles corresponds to the largest specific surface area. Due to the poor conductivity of lithium iron phosphate, the particles are designed in the form of nano-aggregates, and the surface is covered with amorphous carbon, thereby obtaining the highest specific surface area among all positive electrode materials.

6. The moisture content of the positive electrode material: the moisture content of the positive electrode material is closely related to its specific surface area, particle size and distribution, surface porosity and surface coating. Moisture content has a great influence on battery beating. Generally, the positive electrode slurry mainly uses polyvinylidene fluoride (PVDF) as a binder, and uses N-methylpyrrolidone (NMP) as a solvent. In this organic system, PVDF with a large molecular weight is not completely dissolved, but exists in the form of a sol. When the moisture and residual alkali content of the positive electrode material is high, the organosol system will be destroyed, PVDF and NMP will be separated, the viscosity of the slurry will increase sharply, and even jelly will appear.

In the process of research and design, there must be problems of this kind or that kind, which requires our scientific research workers to constantly sum up experience in the design process, so as to promote the continuous innovation of products.

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