Analysis of common problems of lithium iron phosphate material in battery processing

The first problem is material dispersion

Pulping is one of the most critical processes in the battery production process. Its core task is to evenly mix active substances, conductive agents, adhesives and other materials, so that the material performance can be better played. To mix well, you must be able to disperse. When the particle size decreases, the corresponding specific surface area increases, the surface energy increases, and the tendency of polymerization between particles increases. The greater the energy required to overcome surface energy dispersion. Now mechanical stirring is widely used. The energy distribution of mechanical stirring is uneven. Only in a certain area, the shear strength is large enough and the energy is high enough, can the polymerized particles be separated. To improve the dispersion capacity, one is to optimize the structure of the mixing equipment, and increase the space proportion of the effective dispersion area without changing the maximum shear speed; One is to increase the mixing power (increase the mixing speed) and shear speed, and the corresponding effective dispersion space will also increase. The former belongs to the problem of equipment. How much room for improvement is? The coating line will not comment. In the latter case, the lifting space is limited, because if the shear speed is raised to a certain limit, the material will be damaged and the particles will be damaged. The more effective method is to use ultrasonic dispersion technology. Only the price of ultrasonic equipment is relatively high. The price of one we contacted earlier is comparable to that of imported Japanese mechanical mixers. The ultrasonic dispersion process is characterized by short time, low overall energy consumption, good slurry dispersion effect, effective delay in the polymerization of material particles, and greatly improved stability. In addition, the dispersion effect can be improved by using dispersants.

Coating uniformity

If the coating is uneven, not only the battery consistency is poor, but also the design, use safety and other issues. Therefore, the uniformity of coating is strictly controlled during battery production. The smaller the material particles, the more difficult it is to make uniform coating. As far as the mechanism is concerned, I haven't seen any explanation. The coating line is considered to be caused by the non-newtonian fluid characteristics of the electrode slurry. Electrode slurry shall be a thixotropic fluid in non Newtonian fluid, which is characterized by being viscous or even solid at rest, but becoming thinner and easier to flow after stirring. In the submicroscopic state, the binder is a linear or network structure. When it is stirred, these structures are destroyed, and the fluidity is good. When it is still, they are formed again, and the fluidity becomes poor. Lithium iron phosphate particles are small. With the same quality, the number of particles increases. To connect them to form an effective conductive network, the amount of conductive agent required also increases. With small particles and increased conductive agent dosage, the required binder dosage also increases. When it is still, it is easier to form a network structure, and its fluidity is worse than that of conventional materials.

During the process from the slurry taken out of the mixer to the coating, many manufacturers still use turnover barrels to transfer the slurry. During the process, the slurry is not stirred or the mixing intensity is low, and the liquidity of the slurry changes, becoming sticky gradually, so that it looks like jelly. Poor fluidity leads to poor uniformity of coating, which is manifested by increased density tolerance of the pole surface and poor surface morphology.

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