This article describes the stirring process in the lithium-ion battery manufacturing process, from the aspects of stirring purpose, principle, equipment and effect measurement.
1. Purpose of mixing
The purpose of stirring is to mix the various components in the slurry (mainly including active substances, conductive agents, adhesives, etc.) according to standard proportions, and prepare a slurry to facilitate uniform coating and ensure the consistency of the pole pieces. For the production of lithium battery cells for sale, mixing is the first process. The quality of mixing will directly affect the superiority rate of subsequent processes, the efficiency and the performance of the finished battery cells. Therefore, the quality control of this process is particularly important.
2. Stirring principle
Through the mutual rotation of the stirring blade and the revolution frame, the solid-liquid suspension of the liquid is generated and maintained under the condition of mechanical stirring, and the mass transfer between the liquid-solid phase is enhanced. Solid-liquid stirring is usually divided into the following parts:
(1) Suspension of solid particles. (2) Resuspension of settled particles. (3) Infiltration of suspended particles into liquid. (4) The force disperses the particle agglomerates or controls the particle size. (5) Mass transfer between liquid and solid.
3. Mixing equipment
The quality of the stirring effect depends largely on the quality of the stirring equipment, and the agitator is one of the key components of the stirring equipment. At present, the commonly used mixers are as follows: toothed disc mixers, suction mixers, and paddle mixers.
4. Measurement of stirring effect
There are several ways to detect the uniform stirring of a solid-liquid suspension system:
(1) Viscosity method. Sample from different positions of the system, measure the viscosity of the slurry with a viscometer. The smaller the deviation, the more uniform the mixing. (2) Particle size method. Sample from different positions of the system, observe the slurry with a particle size scraper. The closer the particle size is to the size of the raw material powder, the more uniform the mixing is. The samples are taken from different positions of the system, and the particle size of the slurry is observed with a laser diffraction particle size tester. The more normal the particle size distribution, the smaller the large particles, and the more uniform the mixing. (3) Specific gravity method. Take samples from different positions of the system, measure the density of the slurry, the smaller the deviation, the more uniform the mixing.
(1) Solid content method (macro). Sample from different positions of the system, after baking at appropriate temperature and time, measure the weight of solid content, the smaller the deviation, the more uniform the mixing. (2) SEM/EPMA (microscopic). Different from the system sampling at the position, coating on the substrate, drying, and observing the distribution of particles or elements in the membrane after the slurry is dried with SEM (electron microscope)/EPMA (electron probe). (The solids in the system are usually conductor materials), since the viscosity of the slurry is greatly affected by the temperature and increases with the decrease of the temperature, a constant temperature water bath is usually used to measure the viscosity.