What effect does the positive electrode material of lithium-ion battery have?

The positive electrode materials are mostly micron or nano-sized particles, which are very easy to absorb moisture in the air, especially the ternary material with high Ni content. In the preparation of the positive electrode slurry, if the positive electrode material has high moisture content, the NMP absorbs water during the slurry agitation process, which causes the PVDF solubility to decrease, resulting in the slurry gel being frozen and affecting the processing performance. After the battery is fabricated, its capacity, internal resistance, circulation and rate will be affected. Therefore, the moisture of the positive electrode material is the same as the metal foreign matter.

The higher the automation of the production line equipment, the shorter the exposure time of the powder in the air and the less water is introduced. Promote material suppliers to improve the degree of equipment automation, such as achieving full pipeline transportation, monitoring pipeline dew point, installing robots to achieve automatic loading, and cutting materials to contribute to the prevention of moisture introduction. However, some material suppliers are limited by the design of the plant or the cost pressure. The degree of automation of the equipment is not high. When the number of breakpoints in the manufacturing process is large, the exposure time of the powder should be strictly controlled. The powder in the transfer process is preferably filled with a cylinder filled with nitrogen. The temperature and humidity of the production workshop is also a key control indicator. In theory, the lower the dew point, the more favorable it is. Most material suppliers will focus on moisture control after the sintering process. They believe that the sintering temperature of about 1000 degrees can remove most of the moisture in the powder. As long as the moisture introduction after the sintering process to the packaging stage is strictly controlled, the material can be basically guaranteed. The water does not exceed the standard. Of course, this does not mean that there is no need to control the moisture before the sintering process, because if the moisture is introduced too much in the previous process, the sintering efficiency and the microscopic morphology of the material are affected. In addition, the way of packaging is also very important, most of the material suppliers use aluminum plastic bag vacuum packaging, so far this way is still the most economical and effective.

Of course, the material design is different, and the water absorption will be greatly different. For example, the difference in coating material and the difference in specific surface area will affect the water absorption. Although some material suppliers prevent the introduction of moisture during the manufacturing process, the material itself has the property of being easily absorbed, and the moisture is extremely difficult to be baked after the pole piece is formed, which causes trouble for the battery manufacturer. Therefore, the development of new materials should take into account the problem of water absorption and the development of more universal materials, which is of great benefit to both the supply and demand sides.

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