Due to the low diffusion coefficient of lithium ions, lithium iron phosphate has poor conductivity. The current practice is to make its particles small, or even make them into nanoscale, and shorten the migration path of Li+ and electrons to increase its charge and discharge speed ( Theoretically, the migration time is inversely proportional to the square of the migration path). But this brings a series of problems to battery processing. Let’s take a look at how to solve the coating uniformity problem of lithium iron phosphate battery management system?
Uneven coating of lithium iron phosphate batteries not only leads to poor battery consistency, but also concerns issues such as design and use safety. Therefore, the control of coating uniformity in the manufacturing process of lithium iron phosphate batteries is very strict. It is well known that the smaller the particle size of the material, the more difficult it is to apply it evenly. The key point is to improve the material, such as increasing the conductivity, increasing the size of the particles, and making the particles spherical, etc., which may have limited effects in a short period of time. Based on the existing materials, from the perspective of battery processing, the ways to improve can be tried from the following items.
1. Lithium iron phosphate battery adopts “linear” conductive agent
The so-called “linear” and “granular” conductive agents are vivid expressions, which may not be described academically. The lithium iron phosphate battery management system uses “linear” conductive agents, currently mainly VGCF (carbon fiber) and CNTs (carbon nanotubes), metal nanowires, etc. Their diameters are several nanometers to tens of nanometers, and their lengths are more than tens of microns or even several centimeters, while the size of the commonly used “granular” conductive agents is generally tens of nanometers, and the size of battery materials is several microns. The pole piece composed of “granular” conductive agent and active material is similar to the contact between points, and each point only contacts with the surrounding points; in the pole piece composed of “linear” conductive agent and active material, it is In the contact between point and line, line and line, each point can be in contact with multiple lines at the same time, and each line can also be in contact with multiple lines at the same time, with more nodes in contact, the conductive channel will be smoother, and the conductivity will be improved. The use of a variety of conductive agents in different forms can achieve better conductive effects.
2. Lithium iron phosphate battery improves dispersion effect
If the dispersion effect is good, the probability of particle contact and agglomeration will be greatly reduced, and the stability of the slurry will be greatly improved. The dispersion effect can be improved to a certain extent through the improvement of formula and batching process, and the aforementioned ultrasonic dispersion is also an effective method.
3. Improved slurry transfer process for lithium iron phosphate batteries
When storing the slurry of lithium iron phosphate battery, it may be considered to increase the stirring speed to avoid the viscosity of the slurry; for the use of turnover barrels to transfer the slurry, the time from discharge to coating should be shortened as much as possible, and pipeline transportation should be used if possible to improve the slurry viscosity.
4. Lithium iron phosphate battery adopts extrusion coating (spray coating)
Extrusion coating can improve the surface texture and uneven thickness of scraper coating, but the price of lithium iron phosphate battery equipment is relatively high, and the stability of the slurry is required to be high.