battery slurry mixer
Lithium battery cell slurry mixing is the mixing and dispersion process in the entire production process of lithium-ion batteries. The quality of the product impact degree of more than 30% is an essential part of the production process.
In the electrode manufacturing of lithium-ion batteries, the positive electrode slurry consists of a binder, conductive agent, cathode material, etc.; the negative electrode slurry consists of a binder, graphite carbon powder, etc. Preparing positive and negative pastes includes a series of processes such as mixing, dissolving, and dispersing between liquid and liquid, liquid and solid materials. The process is accompanied by changes in temperature, viscosity, and environment. In the positive and negative electrode slurry, the dispersion and uniformity of the granular active material directly affect the movement of lithium ions between the two electrodes of the battery, so the mixing and distribution of the slurry of each electrode material are crucial in the production of lithium-ion batteries.
The traditional slurry process is.
preparation of materials.
1. Solution preparation.
a) The mixing ratio and weighing of PVDF (or CMC) and solvent NMP (or deionized water).
b) Stirring time, stirring frequency, and the number of solution times (and the key's surface temperature).
c) Inspection of the solution after preparation: viscosity (test)\ dissolution degree (visual inspection) and shelving time;
d) Negative: SBR+CMC solution, stirring time, and frequency.
2. Active substance:
a) Weighing and mixing to monitor whether the mixing ratio and quantity are correct.
b) Ball milling: the ball milling time of positive and negative electrodes; the ratio of agate beads to mixed material in the ball milling barrel; the percentage of large and small balls in the agate balls.
c) Baking: setting baking temperature and time; testing temperature after cooling after baking is completed.
d) Mixing and stirring of active substance and solution: stirring method, stirring time, and frequency.
e) Sieving: passing 100 mesh (or 150 mesh) molecular sieve.
f) Testing, inspection.
The following tests are performed on the slurry and mixer: solid content, viscosity, mixer fineness, vibration density, and slurry density.
Mainstream process of lithium battery core slurry
Ultra-fine dispersion in the traditional process is because: through the conventional mixing and stirring equipment, only the solution can be broken up and uniform distribution of large powder clusters; however, the powder form is stored in the key in the form of micro-fine powder clusters, only to meet the macro-dispersion processing requirements.
After macroscopic mixing and dispersion, the slurry can be further broken up and homogenized by the mechanical solid cutting force of the ultra-fine dispersion and homogenization equipment so that the microscopic ultra-fine dispersion and homogenization can be achieved, which can significantly improve the comprehensive performance of the slurry.
The preparation of the existing lithium-ion battery slurry is done in the dispersion equipment. Although the technology has become increasingly mature in the production of small cells, the production process of lithium-ion batteries, cell consistency control is still a technical difficulty in the production of lithium-ion batteries, especially for large-capacity, high-power power-type lithium-ion batteries. In addition, with the continuous progress of lithium-ion battery materials, the particle size of raw materials is getting smaller and smaller, which not only improves the performance of lithium-ion batteries but also makes it very easy to form secondary agglomerates, thus increasing the difficulty of the mixing and dispersion process. In the process of lithium-ion battery production, the control of the battery electrode structure is the key; However, many lithium-ion manufacturers have not paid attention to this; the self-discharge rate, cyclability, capacity, and consistency of the batteries produced using electrode sheets of different structures are different.
Control of the microstructure inside its electrode sheet is the critical technology for lithium-ion battery production. Therefore, in preparing electrode sheets, the mixing and dispersion quality of lithium-ion battery slurry must be controlled to improve the uniform consistency and dispersion stability.
The mixing and dispersion process of lithium-ion battery slurry can be divided into macroscopic mixing and microscopic dispersion processes, which will always accompany the whole process of lithium-ion battery slurry preparation. And according to the impeller shear-circulation characteristics of the traditional method, the role of the impeller can be divided into two categories; the first is the light effect on the vicinity of the impeller; the second is the circulation effect through the flow of the impeller pump out. The further dispersing action of the slurry mainly relies on the shearing action of the impeller, and the impeller's flow rate determines the impeller's ability to disperse. In the area far from the end of the impeller, there will always be a layer of slurry that is always stagnant; this area is often called the "dead zone" the more significant the working area of the dispersion equipment, and the higher the viscosity of the slurry, the more prominent the problem of "dead zone," even if they use of Even if different impellers and structures are used, the dead zone is still challenging to avoid. Therefore, in the lithium-ion battery slurry preparation process, the resulting slurry products will have a series of problems such as uneven mixing and dispersion, inconsistent contact between powder particles and binder, easy delamination, and hard precipitation. The rheology of the slurry is very complex. A slurry may behave as Newtonian fluid or pseudoplastic fluid at low concentration, as Bingham fluid after flocculation at higher concentration, and as swelling plastic fluid at higher concentration.
For the same - kind of slurry, in the shear rate is not too high and does not appear to swell the flow phenomenon, a shear rate may be transformed into rushing plastic fluid. Some non-Newtonian fluids at low shear rates and high shear rates may show the image of a Newtonian fluid, which may be because at low shear rates, the irregular thermal motion of molecules dominates, reflecting the shear rate of which the material rearrangement so that the apparent viscosity changes, when the shear rate increases to a specific limit, the shear orientation reached the optimal degree, and thus the apparent viscosity does not change with the shear rate. As mentioned earlier, the rheological properties of many non-Newtonian bodies are influenced by structural changes in the system.
In ultra-sheer dispersion equipment, the energy acting on the liquid is generally quite concentrated, which allows the liquid to receive a high energy density. The type and intensity of the introduced energy must be sufficient to effectively and uniformly disperse the dispersed phase particles. The essence of uniform dispersion is to make the material in the dispersed phase (solid particles, liquid droplets, etc.) by the hydrodynamic shear and pressure effect of breaking and distribution.
Liquid material dispersion system in the solid dispersed phase particles or droplets broken dispersion is the direct cause of shear and pressure joint action. The specific hydrodynamic effects of shear and anxiety are caused by three main effects: the laminar effect, turbulence effect, and cavitation effect. The role of the laminar impact is to drive the shear and elongation of the solid dispersed phase particles or droplets; the part of the turbulent effect is to cause the random deformation of the solid dispersed phase particles or droplets under the action of pressure fluctuations, while the role of the cavity effect is to drive the formation of tiny bubbles to break instantaneously to generate shock waves and cause violent stirring.
To sum up, the dispersion mechanism of the material in the super-shear dispersion equipment is relatively complex, mainly with the shear effect playing a leading role and other roles as a supplement. The slurry material is repeatedly compressed under the action of a high-frequency pressure wave. At the same time, it is strongly affected by the shearing force and gyratory shearing force in the narrow gap of the ultra-sheer dispersion equipment.
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