In the electrode manufacturing of lithium-ion batteries, the positive electrode slurry is composed of binders, conductive agents, positive electrode materials, etc.; the negative electrode slurry is composed of binders, graphite carbon powder, etc. The preparation of positive and negative electrode slurries includes a series of processes such as mutual mixing, dissolution, and dispersion of liquids and liquids, liquids and solid materials, and this process is accompanied by changes in temperature, viscosity, environment, etc. In the positive and negative electrode slurries, the dispersion and uniformity of the granular active materials directly affect the movement of lithium ions between the two electrodes of the battery. Therefore, the mixing and dispersion of the slurry of each electrode material is crucial in the production of lithium-ion batteries. , The quality of slurry dispersion directly affects the quality of subsequent lithium-ion battery production and the performance of its products.

　　Ultra-fine dispersion is carried out based on traditional technology. This is because: through traditional mixing and stirring equipment, only large powder groups in the solution can be broken up and evenly distributed; however, the powder form exists in the form of fine powder groups. In the solution, it only meets the processing requirements of macroscopic dispersion. The slurry after macroscopic stirring and dispersion can further disperse and homogenize the fine powder or solid particle agglomerates in the solution under the strong mechanical cutting force of the ultra-fine dispersion and homogenization equipment to obtain sufficiently fine solids. The particles are evenly distributed in the solution to achieve microscopic ultra-fine dispersion and homogeneity, which can significantly improve the comprehensive performance of the slurry.

　　The current traditional slurry process is:

　　(1) Ingredients:

　　1. Solution preparation:

　　a) Mixing ratio and weighing of PVDF (or CMC) and solvent NMP (or deionized water);

　　b) Stirring time, stirring frequency and times of the solution (and solution surface temperature);

　　c) After the solution is prepared, inspect the solution: viscosity (test), degree of dissolution (visual inspection) and storage time;

　　d) Negative electrode: SBR+CMC solution, stirring time and frequency.

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　　2. Active substances:

　　a) Monitor whether the mixing ratio and quantity are correct when weighing and mixing;

　　b) Ball milling: ball milling time of positive and negative electrodes; ratio of agate beads to mixed material in ball mill barrel; ratio of large balls to small balls in agate balls;

　　c) Baking: Setting of baking temperature and time; test the temperature after cooling after baking is completed.

　　d) Mixing and stirring of active substances and solutions: stirring method, stirring time and frequency.

　　e) Sieve: pass through 100 mesh (or 150 mesh) molecular sieve.

　　f) Testing and inspection:

　　Conduct the following tests on slurries and mixtures: solid content, viscosity, mixture fineness, tap density, and slurry density.

　　In addition to clarifying the traditional manufacturing process, it is also necessary to understand the basic principles of lithium battery slurry.

　　colloid theory

　　The main effect that causes the agglomeration of colloidal particles comes from the van der Waals force between particles. If you want to increase the stability of colloidal particles, there are two ways. One is to increase the electrostatic repulsion between colloidal particles, and the other is to create steric positions between powders. Block the agglomeration of powder in these two ways.

　　The simplest colloidal system consists of a dispersed phase and a phase dispersion medium, where the scale of the dispersed phase ranges from 10-9 to 10-6m. Substances in colloids must have a certain degree of dispersion ability to exist in the system. A variety of different colloidal forms can be produced depending on the solvent and dispersed phase. For example, mist is an aerosol in which droplets are dispersed in gas, and toothpaste is a sol in which solid polymer particles are dispersed in liquid.

　　The applications of colloids abound in life, and the physical properties of colloids vary depending on the dispersed phase and dispersion medium. Observing colloids from a microscopic perspective, the colloidal particles are not in a constant state, but move randomly within the medium. This is what we call Brownian motion. Above absolute zero, colloidal particles will undergo Brownian motion due to thermal motion. This is the dynamic characteristic of microscopic colloids. The collision of colloidal particles due to Brownian motion is an opportunity for aggregation. Colloidal particles are in a thermodynamically unstable state, so the interaction force between particles is one of the key factors in dispersion.

　　electric double layer theory

　　The electric double layer theory can be used to explain the distribution of charged ions in colloids and the potential problems generated on the surface of particles. In the 19th century, Helmholtz proposed the parallel capacitor model to describe the electric double layer structure. He simply assumed that the particles are negatively charged and the surface is like an electrode in a capacitor. The positively charged counterions in the solution are attracted to the particle surface due to the attraction of different charges. However, this theory ignores the diffusion behavior of charged ions due to thermal motion.

　　Therefore, in the early 20th century, Gouy and Chapman proposed the diffusion double layer model. Counter ions in the solution will be adsorbed on the surface of charged particles due to electrostatic interaction, and at the same time diffuse around the particles due to the influence of thermal motion. Therefore, the distribution concentration of counterions in the solution will decrease as the distance from the particle surface increases. In 1924, Stern combined the two models of parallel capacitor and diffused electric double layer to describe the electric double layer structure. Stern believes that counterions will form a tight adsorption layer on the surface of the particle, also known as the Sternlayer. As the distance from the particle surface increases, the potential of the particle will decrease linearly. At the same time, there is also a diffusion layer outside the Sternlayer, and the particles are in the diffusion layer. The potential decreases exponentially with distance.

　　The zeta potential is closely related to the dispersion stability of the colloid. When the zeta potential is larger, the more electrostatic charges are on the surface of the colloidal particles. When the zeta potential of the particles in the aqueous solution reaches more than ±25~30mV, the colloid has sufficient Electrostatic repulsion overcomes the van der Waals forces between particles to maintain colloidal stability.

　　From 1940 to 1948, Deryagin, Landau, Verwey, and Overbeek established relevant theories on energy changes when colloidal particles approach each other and their impact on colloid stability, referred to as DLVO theory. Its theory mainly describes the relationship between the distance between colloidal particles and energy changes. This interaction energy is the result of the addition of the overlapping charge repulsion energy of the colloidal double electric layer and the van der Waals force.

　　The figure below is a schematic diagram of DLVO, indicating that there are attraction and repulsion forces between colloidal particles. The magnitude of these two forces determines the stability of the colloidal solution. The attraction between particles is the main effect, and the particles will agglomerate; while the repulsion force In a state where the attraction force is greater than the attraction force, particle aggregation can be avoided and the stability of the colloid can be maintained.

　　According to the DLVO curve, when the distance between particles becomes shorter and shorter, the particles will first generate attraction. If the particles continue to approach each other, a repulsive force will be generated between the particles. If the particles cross the repulsive energy barrier, there will be Quickly produces reunions. Therefore, in order to improve the dispersion stability of particles in the colloid, the repulsive force between particles must be increased to avoid agglomeration between particles.

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