Powder dropping refers to the phenomenon of powder falling off at the cutting edge of prepared pole or pole. The loss of electrode powder will lead to the increase of short circuit rate in the subsequent battery process or the electrochemical performance of the prepared battery is poor. So why ternary materials than lithium cobalt oxide electrode pieces easy to drop powder?
The reasons for pole piece powder drop are:
1. Too little binder or the relative molecular weight of binder used is too small:
The surface density of the electrode sheet, the amount of binder and conductive agent will affect the compaction density. It can be seen from the table that the true density of conductive agent and binder is very low, and the more the amount is added, the lower the compaction density of pole sheet will be.
2. The mixing time of slurry is not enough or the design of mixing container is unreasonable, resulting in uneven mixing of binder, conductive agent and active substance;
3. Slurry moisture exceeds the standard;
4. When coating, the temperature is too low or the time is too short, resulting in the pole piece is not dried;
5. Uneven coating thickness;
6. The pole piece baking temperature is too high, so that the bonding agent structure damage;
7. The water content of the pole piece exceeds the standard before rolling;
8. The pressure of the pole piece is too large when the roller presses, and the pole piece is overpressed: when the roller presses, the feeding mode of the pole piece is wrong or the roller press is deformed, so that the pole piece is subjected to uneven force.
No matter what material, the above several reasons will cause the pole piece to drop powder.
The electrode plate of ternary material is more prone to powder loss than lithium cobalate electrode plate, which may be caused by the following reasons:
1. The conductivity and morphology of ternary materials are different from lithium cobalt acid. When mixing slurry, the conductive agent and binder need to be added slightly more than lithium cobalt acid.
2. The binding force between the single crystal particles forming the secondary sphere of ternary material is not so strong. If the polar chip overpressures, it is easy to destroy the morphology of the secondary sphere, so that the single crystal particles are separated from the sphere and the polar chip drops the powder.
3 terpolymer material than lithium cobalt acid easy water absorption, if the environmental humidity control is not strict, it is easy to cause the problem caused by excessive moisture powder.
