According to the characteristics of stirring process in the production of polymer lithium ion battery, the process of stirring production is described, and the particularity of stirring dispersion is explained by stirring theory. It is put forward that the production of lithium ion battery by using a new planetary double high speed dispersion mixer is feasible in theory and practice. A new type mixer has been successfully developed and applied to the production of battery.
The design and application characteristics of a new type of planetary double high speed dispersing mixer are described in this page.
1. 1 main material of polymer lithium ion battery
For lithium batteries, the typical battery system is composed of carbon material negative electrode, lithium transition metal oxide positive electrode and organic electrolyte. The development and application of these three materials have been extensively studied by research institutes and battery manufacturers around the world. For example, the basic materials of each part of the polymer lithium battery are composed of: negative electrode: graphite, carbon black, PVDF, DBP, acetone; Positive electrode: lithium cobalt acid, carbon black, PVDF, DBP, acetone; Electrolytes: silica, PVDF, DBP, acetone
1.2 material pre-treatment.
In order to ensure the uniformity of the mixture and particle size of each component, the materials of different components need to be pre-treated.
Negative electrode: 1. Grind, dry and premix graphite and carbon black to make anode powder. 2. PVDF was mixed with acetone and stirred to preform adhesive.
Positive electrode: 1. Grind potassium cobaltite and carbon black, dry premixed and make cathode powder. 2. PVDF was mixed with acetone and stirred to preform adhesive.
Electrolytes: 1. After being ground and dried, silica is packed in an airtight container as an electrolyte powder. 2. PVDF was mixed with acetone and stirred to preform adhesive.
Fluid properties and agitation requirements
Viscosity is a property of fluids. It reflects the ratio relationship between shear stress and shear velocity gradient during fluid movement. Therefore, the viscosity has a great influence on the flow state of the fluid, and it must also have a great influence on the stirring process. Just like the fluid flowing in the pipeline, there are three states of laminar flow, transition flow and turbulence in the stirring tank, and one of the main parameters determining the flow pattern is viscosity. The main component of polymer lithium ion battery slurry is the mixture of macromolecule acetone solution and powder, the viscosity is around 8, 000~10, 000cp, is a high viscosity fluid for stirring, it is a non-newtonian fluid, the viscosity will also change during the stirring process, so the requirements for agitator is higher than the low viscosity Newtonian fluid. At the same time, because the preparation of the yin-yang slurry is mainly to add powder to distribute it evenly, which makes the general stirring method and agitator is difficult to do this work.
Planetary mixer with high speed dispersing disc
In essence, the stirring process is a process of momentum transfer in the flow field, and the agitator is a device to input mechanical energy to the stirring medium by making it obtain the appropriate flow field. Therefore, the research workers of agitation attach great importance to the choice of agitation mode, the agitator and the amount of energy to provide the agitator with the flow field, and make the fluid produce the appropriate circulating flow rate, turbulence degree or shear speed in the flow field, so as to finally obtain the uniform product with excellent effect. Polymer lithium ion battery slurry mixing is a mixture of solid powder and polymer solution, belong to solid ∋ liquid mixing. Solid ∋ liquid mixing problem, especially the viscous fluid is much more complex than that of homogeneous liquid mixing. The physical properties of the two phases are different, and the general density is quite different. The essence of uniform dispersion is to make the powder evenly suspended in the liquid. Generally speaking, solid substances have the problem of settling in liquid. Many previous experiments have proved that there is a minimum stirring speed of solid suspension in the solid suspension process, which is called the critical stirring speed of solid suspension. Stir the critical speed and the density difference between the solid ∋ liquid, liquid density, concentration of solid phase, liquid phase viscosity, particle size and other physical conditions, are also associated with the geometric relationships between a mixing tank, mixer [. PLI cell size of the final product requirements, to the highest degree that is homogeneous in suspension grade suspension. This makes we should choose the right means of mixing (or components) and the stirring speed and blender to meet this requirement. The prime problem of the high viscosity liquid mixing is to solve the problem of fluid flow and circulation. In this case, not by increasing the stirring speed to increase the circulation flow, because of discharge volume for high viscosity mixer is small, high speed will also formed in high slime channel flow, and is still the fluid surrounding the dead zone, the important way is to try to make the blade to promote a wider range of liquid. Regular use of agitator of the big diameter, blade width, but it has some problems during mixing. PLI battery slurry due to adding powder particles is very fine, powder will be reunited after powder entry into it and not easy to disperse, must add high-speed dispersion impeller, mandatory scattered shear. Simple large diameter, wide blade blender can't install dispersion impeller. On the other hand, the agitator power consumption is very big, There are still some dead zones, so we developed and designed planetary agitators.