Talking about the compaction density of the four major cathode materials

Talking about the compaction density of the four major cathode materials

It is well known that compaction density is generally affected by true density and material morphology.

True density

The compaction density of the material is mainly affected by the true density. The true densities of different materials are: lithium cobaltate: 5.1, lithium manganate: 4.2, lithium iron phosphate 3.6, the ternary materials are different in composition, the true density is Change, the general type 111, taking the US 3M BC-618 as an example, is about 4.8, so according to the true density from large to small, the order of the four materials is as follows: lithium cobaltate> ternary> lithium manganate > Lithium iron phosphate, which is also in line with the current trend of compaction density. It can be seen that true density is the most influential factor affecting the compaction of a material.

Morphological structure

The smoothness of the surface of the material, the size of the internal voids of the secondary particles, and the degree of regularity of the material are all factors that affect the compaction density of the material. The current lithium cobaltate is a primary particle, which does not have the internal gap of the secondary particle. Influence, our company's lithium manganate and ternary materials have also been made into primary particles of lithium cobalt oxide (lithium manganate can become a single crystal, ternary materials are controversial), also increased the compaction density to lithium manganate (2.9-3.2), ternary (3.7-3.9), as for lithium iron phosphate, (more special, will be explained in the rate performance section) due to the nanocrystallization of the material, which limits the further improvement of compaction, the particle size distribution is compared Complex factors, reasonable particle size distribution can properly improve compaction, which can generally be adjusted according to their own products.

Rate performance

The rate performance is electrochemical, independent of the objective compaction density of the material, but it is necessary to elaborate on the application of the battery. Purely from the rate performance of the material itself (excluding the influence of the particle size) lithium manganate > lithium cobalt oxide > ternary material > lithium iron phosphate. In order to ensure the rate performance of the material, the current industrialized products are adjusted in the process to ensure the rate performance, so the current range of D50 is also proportional to the rate of magnification, the better the rate, the general The larger the particle size can be achieved, because the large particle size can ensure a higher compaction density of the material (although the ratio is not strictly), of course, the special field of high-rate products is an exception.

Therefore, we can reasonably believe that the rate performance limits the improvement of compaction density to some extent.

The above is the description of the compaction density. For some customers' questions about the current compaction of the granular product and its rate performance, the following is explained:

(Supplement: Our way to improve compaction: make the product into a primary particle of lithium cobalt oxide)

The compaction density of single crystal primary particles is higher than that of secondary particles, which is undoubted, but the new problem is that it may affect the rate performance, because the rate performance is highly correlated with the transport rate of lithium ions inside the particles. Generally, the smaller the particle size, the faster the transfer rate (this is also the main reason why lithium iron phosphate must be nanosized), and the small particles of ordinary secondary particles are all nanometer or less, so even if the particle size of the secondary particles is D50 More than ten or even tens of micrometers, the rate performance is still good, but another advantage of the single crystal primary particles is that the freely grown crystal surface is very smooth, and the contact with the conductive agent is very close, in addition, the free growth at high temperatures There are few lattice defects in the crystal, which makes the ion transport more smooth. In addition, we make the particle size small (less than the secondary agglomerated particles) also contribute to the improvement of the rate performance. As for the specific performance, many customers have done specific tests and do not explain too much.

This article is taken from: Battery Forum (http://club.battery.com.cn) For details, please refer to: http://club.battery.com.cn/thread-117847-1-1.html

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