As the last article in the series of industrialized manufacturing and mass production of lithium-ion battery materials, this paper mainly introduces the related synthesis methods and related technical methods of cathode materials. Compared with the other three main materials, the industrial production steps of cathode materials are more and more synthetic. The route is also relatively complicated, and the control of temperature, environment and impurity content is also strict. The cathode materials mainly include lithium cobaltate, lithium manganate, lithium iron phosphate, ternary materials, etc., due to the current high energy density of the power battery on the market. The positive electrode materials are all ternary materials with different ratios. Therefore, this paper starts with the ternary materials and begins to introduce the industrial production methods of materials.
The origin of ternary materials:
The ternary materials can be considered as the first doping research in the 1990s, such as the doping of LiCoO2 and LiNiO2, and the study of doping Co in LiNiO2 to form LiNi1-xCoxO2 series cathode materials in the late 1990s. Researchers have conducted studies on the doping of Mg, Al and Mn in LiNi1-xCoxO2. French Saft-LiNi1-x-yCoxAlyO2 and LiNi1-x-yCoxMgyO2, but the early Li(Ni, Co, Mn)O2 did not clarify the reaction mechanism and adopt the appropriate preparation method. At the beginning of the 21st century, Japan Ohzuku and Canada JR Dahn, utilized A series of Li(Ni,Co,Mn)O2 compounds were prepared by hydroxide coprecipitation. Among them, nickel is the main electrochemically active element, and manganese guarantees the structural stability and thermal stability of the material. Cobalt plays an irreplaceable role in reducing the electrochemical polarization and improving the rate characteristics of the material. Ternary materials have high specific capacity, good cycle performance, stable structure, reliable safety and moderate cost. In the basic research of the laboratory, no obvious shortcomings of the material were found.
It can also be seen from the development roadmap of the positive electrode material that the development of the ternary material plays an important role in improving the energy density of the entire power battery.
Synthesis method of ternary materials:
First, the thermal stability of different materials is released. It can be seen from the figure that as the nickel content increases, the thermal stability of the entire positive electrode material decreases, and it is necessary to find a balance point in performance and safety, and not blindly improve Use energy density to apply unsafe materials.
The previous figures simply show the process flow of the ternary material and the intermediate control points. Of course, the precursor of a good ternary material is also very important. The synthesis process of the pre-precursor will be briefly introduced below.
Firstly, a certain concentration of the metal ion mixed solution is arranged according to the stoichiometric ratio, and a certain concentration of the ammonia-alkali mixed solution is disposed as a precipitating agent and a complexing agent, and the reaction vessel is continuously subjected to nitrogen gas to carry out the reaction, and the pH value of the solution is adjusted. The composite precipitate is produced, and the precursor is directly obtained after being filtered, washed, and vacuum dried. It involves the selection of precipitants, the use of complexing agents, the choice of feeding mode, the control of the reaction atmosphere, and the like.
Lithium source selection:
Industrial production generally selects lithium hydroxide and lithium carbonate, but lithium hydroxide contains crystal water, and the mixing effect is not good, so lithium carbonate is used more. The most common lithium-containing minerals are spodumene and brine.
The above diagram briefly describes the flow of the two methods. After the preparation of lithium carbonate, a series of tests are required before use.
Mixing equipment: The precursor and the lithium salt are mixed, and there are dry and wet methods, and dry mixing is more used.
Calcination equipment: divided into roller kiln and pusher kiln, the performance is still different.
As a relatively important process in the preparation of ternary materials - calcination, its temperature, time and atmosphere control are among the most important parameters. The calcination temperature is high, the calcination time can be shortened appropriately, the nickel content is high, and the calcination temperature is also appropriately reduced. The materials prepared under the conditions are also different in electrochemical performance.
Crushing equipment: According to the size of the material produced, it needs to be crushed and ground.
Grading, screening, packaging: The products produced need to be packaged according to the size of the particle size. The screening equipment is as follows:
Iron removal: This process runs through the preparation process of the entire ternary material. From the screening, sintering, sieving, etc. of raw materials, iron removal is required for each step. The equipment generally has electromagnetic iron removal equipment and pipe iron removal equipment.
Performance testing: including the physical and physical properties of the material, has been specifically introduced before, and will not be detailed here.
summary:
This paper mainly introduces the industrial production methods and equipment of ternary materials. At this point, the basic performance introduction, detection methods and synthesis methods of the four main materials are all reported in the paragraph. For lithium-ion batteries, it is necessary to cooperate with the four main materials to achieve a balance of the system and to exert the performance of the material itself. This requires working hard at each link to get the bottom out, and finally to achieve good performance. Lithium-ion batteries, of course, this also requires the efforts of the plaid colleagues.
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