Electrode slurry preparation is one of the most critical yet underestimated steps in lithium-ion and sodium-ion battery manufacturing. Problems such as particle sedimentation, agglomeration, poor dispersion uniformity, and unstable viscosity often originate at the slurry stage, but their consequences propagate downstream into coating defects, capacity inconsistency, and yield loss.
This article systematically explains why slurry sedimentation and agglomeration occur, how key process parameters such as mixing speed and vacuum level influence slurry quality, and how to select a suitable vacuum mixer from an engineering perspective. The content is written for battery manufacturers, R&D centers, and pilot-line engineers seeking stable, scalable, and reproducible slurry preparation.
Electrode slurries consist of high-density solid materials (active materials, conductive additives) dispersed in relatively low-density liquid phases (NMP or water-based solvents). Typical cathode and anode powders-such as NCM, LFP, graphite, silicon–graphite composites, or hard carbon-have densities several times higher than the solvent system.
If the shear force generated during mixing is insufficient, gravitational forces dominate over suspension forces, causing heavier particles to gradually settle. This phenomenon becomes more severe under the following conditions:
Sedimentation leads to vertical composition gradients in the slurry. The bottom layer becomes over-concentrated with solids, while the upper layer becomes binder- and solvent-rich. Once such gradients form, they are difficult to eliminate and directly affect coating thickness uniformity, electrode density, and electrochemical consistency.
Agglomeration originates from the high surface energy of fine powders. Nano- or micron-scale particles tend to cluster together to minimize total surface energy. In battery slurries, this natural tendency is amplified by process-related factors.
Common causes include:
Once agglomerates form, they behave as large pseudo-particles that are resistant to dispersion. These hard clusters often survive the entire mixing process and later appear as pinholes, streaks, or localized resistance anomalies in coated electrodes.
Air introduced during powder addition or high-speed atmospheric mixing becomes trapped inside particle clusters. These air pockets prevent solvent penetration and block effective wetting of internal particle surfaces.
Without degassing, trapped air stabilizes agglomerates and worsens sedimentation behavior. This is why slurries mixed under atmospheric conditions often show acceptable appearance initially but degrade rapidly during storage or transfer.
Mixing speed directly determines the magnitude of shear stress applied to particle clusters. As rotational speed increases:
However, increasing speed alone has limitations. Excessive speed under atmospheric conditions can introduce new air, raise slurry temperature, and accelerate binder degradation. Therefore, mixing speed must be optimized rather than maximized.
Vacuum fundamentally changes slurry behavior. Under reduced pressure, entrapped air expands and escapes from the slurry, allowing solvent to penetrate particle clusters more effectively.
At high vacuum levels (typically −0.08 to −0.095 MPa):
This results in finer dispersion, lower apparent viscosity fluctuation, and improved long-term slurry stability.
Engineering data consistently show that:
In practice, vacuum acts as a multiplier for shear effectiveness, enabling high-quality dispersion without excessive mechanical stress.
Traditional planetary or paddle mixers operating at atmospheric pressure are limited by:
These limitations become critical when scaling from laboratory formulations to pilot and mass production.
A vacuum mixer designed for battery electrode slurries should meet the following engineering requirements:
| Equipment Feature | Engineering Advantage | Practical Application |
|---|---|---|
| High-stability vacuum system | Efficient removal of entrapped air and dissolved gases | Prevents agglomeration and viscosity fluctuation |
| Variable speed control | Enables staged mixing from wetting to dispersion | Improves reproducibility across batches |
| High torque output | Handles high-viscosity and high-solid slurries | Suitable for high-energy-density formulations |
| Uniform mixing geometry | Eliminates dead zones and local concentration gradients | Ensures coating consistency |
| Temperature control (optional) | Prevents binder degradation and solvent loss | Critical for long mixing cycles |
Vacuum mixers are widely used in:
In production environments, vacuum mixers enable process standardization, which is essential for yield control, scale-up, and quality assurance.
Sedimentation and agglomeration in electrode slurries are not random defects but predictable physical phenomena driven by density differences, surface energy, and air entrapment.
From an engineering perspective:
By understanding these mechanisms and selecting appropriate equipment, battery manufacturers can achieve stable, reproducible, and scalable slurry preparation-laying a solid foundation for high-quality electrode production.
About TOB NEW ENERGY
TOB NEW ENERGY is a one-stop solution provider for battery laboratory lines, pilot lines, and mass production lines. With deep expertise in electrode slurry preparation, mixing process design, and customized battery equipment, TOB supports global battery manufacturers, research institutes, and universities in building stable, scalable, and reproducible electrode manufacturing systems.
Learn more about TOB NEW ENERGY’s battery equipment and engineering solutions
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