What are the factors that affect the compaction density of lithium batteries?

In addition to the intrinsic properties of the active substances in lithium ion batteries, the microstructure of the electrodes has a great influence on the energy density and electrochemical properties of batteries. Of the uncrushed electrodes, only 50 % of the space is occupied by active substances, which improves the compaction density and can effectively increase the volumetric energy density and the weight energy density of the electrode.

At present, there are four main factors that affect the compaction density of positive polar tablets:(1) the true density of the material; (2) Material morphology; (3) Particle size distribution of materials; (4) Polarization process; By optimizing these factors, we can increase the energy density by increasing the compaction density.

(1) True density of material

The true density of currently commercialized cathode materials: lithium cobalt acid & GT; ternary material & GT; Lithium manganate & GT; Lithium iron phosphate, which is consistent with the compaction density law, the effect of the true density of the material on the compaction density can not be changed.

At present, the difference between lithium cobalt acid compaction density and true density is less than 1.0 g · cm-3. If the ternary material also reaches this value, the compaction density can reach 3.8 g · cm-3. At present, the method of increasing compaction density mainly starts from three aspects: material morphology, material particle size distribution, and polar plate technology.

(2) Material morphology

The current commercial lithium cobalt acid is a primary particle, a single crystal is large, and a ternary material is a secondary aggregate of a small single crystal. As shown in the figure, a single particle of a few hundred nanometers is reunited into a secondary sphere of a ternary material. There are many voids; After preparing the electrode, there will also be a large number of gaps between the ball and the ball. The above reasons further reduce the compaction density of the ternary material.

If the morphology of the ternary material is prepared into a large single crystal similar to that of lithium cobalt acid, its compaction density (3.8 g · cm-3 or more) can be effectively increased, but the current process is not yet mature. Product capacity and initial release efficiency are lower than conventional products.

(3) Particle size distribution of materials

The reason why the particle size distribution of the ternary material affects its compaction density is related to the spherical morphology of the ternary material. When the equal diameter sphere accumulates, there will be a large number of gaps between the sphere and the sphere, if there is no suitable small particle size to fill these voids., The packing density is very low, so the appropriate particle size distribution can increase the compaction density of the material.

Optimizing the particle size distribution of a ternary material can increase its compaction density. D50 close to the material, if there are differences in D10, D90, Dmin, and Dmax, it will also cause different compaction density. The narrow distribution of granularity or the wide distribution of granularity will reduce the compaction density of the material. For the impact of granularity distribution, some battery manufacturers will request manufacturers of positive materials. Some battery manufacturers achieve the purpose of increasing compaction density by mixing products with different grain distributions.

(4) Polarization process

The surface density of the electrode, the amount of binders and conductive agents will affect the compaction density. The true density of the conductive agents and binders is very low, and the more the amount of addition, the lower the compaction density of the electrode.

Therefore, the electrode is made using a good conductive agent to reduce the amount of conductive agent; In addition, the plasma adjustment process is highly dispersed, so that the conductivity and binder evenly dispersed can also increase the compaction density.

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