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Electrode drop refers to the phenomenon that the prepared electrode or electrode has a powder falling off at the edge of the slit. The powder drop of the electrode is likely to cause an increase in the short circuit rate of the subsequent battery process, or the electrochemical performance of the prepared battery is poor. So why is the Nickel Cobalt Manganese material easier to drop than the lithium cobalt oxide electrode?
The reasons for the loss of the electrode are:
Too little binder or the relative molecular mass of the binder used is too small;
The areal density of the electrode, the amount of binder and the amount of conductive agent will affect the compaction density. It can be seen from the table that the true density of the conductive agent and the binder is very low, and the more the amount of addition, the lower the compact density of the electrode.
True density (g.cm-3)
True density of common conductive agents and binders
The slurry mixing time is insufficient or the design of the stirring vessel is unreasonable, resulting in uneven mixing of the bonding agent, the conductive agent, and the active material;
The slurry moisture exceeds the standard;
The temperature at the time of coating is too low or the time is too short, resulting in the electrode not being dried;
Coating thickness is not uniform;
The baking temperature of the electrode is too high to break the structure of the bonding agent;
The water content of the electrode exceeds the standard before rolling;
When the electrode is pressed, the pressure is too large, and the electrode is over-pressed;
When the roller is pressed, the electrode is not conveyed or the roller press is deformed, so that the electrode is unevenly stressed.
Regardless of the material, the above reasons will cause the electrodes to fall off.
The electrode of the NCM material is more prone to powder drop than the lithium cobaltate electrode, and the analysis may be caused by the following reasons:
The conductivity and morphology of the NCM material are different from those of lithium cobaltate. The conductive agent and the binder to be added during the slurry adjustment are also slightly more than the lithium cobalt oxide. The conductive agent and the binder are not uniformly stirred, which is easy to cause the NCM material electrode. Piece of powder off.
The bonding force between the single crystal particles forming the secondary sphere of the NCM material is not so strong. If the electrode is over-pressed, it is easy to break the morphology of the secondary sphere, and the single crystal particles are detached from the sphere to cause the electrode to fall off.
NCM materials are more absorbent than lithium cobalt oxide. If the environmental humidity is not strictly controlled, it is easy to cause the problem of falling powder caused by excessive moisture.
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