Editor's Note
When preparing the slurry for lithium batteries, there are two critical aspects to consider. First, ensuring that the primary materials are uniformly dispersed throughout the mixture. Second, preventing secondary agglomeration caused by interactions between different raw materials. This is essential because the quality of the final electrode depends heavily on the consistency and homogeneity of the slurry.
The thickness of a lithium battery electrode typically ranges from 40 to 200 micrometers, and this can vary depending on the battery type—such as high-energy or high-power batteries. For optimal electrochemical performance, the electrode must maintain consistent thickness, have a smooth surface, and be free of defects. The coating process is highly dependent on the quality of the slurry, which is determined during the preparation stage. A well-prepared slurry should have stable viscosity, small particle size, no visible granularity after drying, and no bubbles or foreign particles.
Therefore, during the slurry preparation process, it is crucial to both disperse the materials effectively and prevent them from re-agglomerating. This ensures that the final electrode performs consistently and reliably over its lifetime.
Lithium battery electrodes come in two types: positive and negative. The materials used in each—such as active materials, conductive agents, binders, and solvents—can differ based on the battery system. Mixing such a complex multiphase system into a uniform slurry requires both technical expertise and a solid theoretical foundation.
Smaller particle sizes can make dispersion more challenging, especially for materials like carbon black, which tend to form large agglomerates during mixing. These agglomerates not only reduce conductivity but can also negatively affect the battery’s energy density. Carbon black is widely used in various industries, including plastics and polymers, so many studies have focused on improving its dispersion in different applications.
According to current research, there are several methods to break up these agglomerates. One common approach involves applying mechanical forces at different intensities. When the force is low, the material flows and forms agglomerates of varying sizes. As the force increases, smaller particles begin to separate from larger ones, creating secondary particles. At higher levels of mechanical energy, sudden particle rupture may occur, though this is less common due to the energy required.
During the slurry preparation process, the interaction between materials can take on three distinct states. Initially, carbon black exists in a structured form, with relatively uniform distribution. As mechanical agitation continues, the conductive agent begins to disperse and coat the surface of the active material, leading to better conductivity and performance.
The transition from individual particles to a homogeneous mixture is a key step in the process. This can be divided into three stages: solid powder state (I), mixed wetting state (II), and finally, a suspension state (III). Each stage has unique characteristics and challenges, and controlling them is vital for achieving a high-quality slurry.
The dry mixing stage involves factors such as the energy input of the equipment, the mechanical force applied, and the particle size of the active material. Additionally, environmental humidity plays a significant role in how materials agglomerate.
In the wetting stage, the first addition of solvent to the solid powder determines the degree of wetting, which is influenced by the powder's saturation level and adhesion properties. During this phase, both dispersion and agglomeration continue, gradually changing the mixture’s state. Once the gel point or full saturation is reached, further mechanical force is minimized, reducing particle interactions and allowing for dilution to the desired solids content.
In the suspension stage, hydrodynamic forces and shear stress become important. The mixer applies shearing forces that help keep the particles in a stable, well-dispersed state.
Different processing controls apply varying levels of force to the raw materials, which directly affects the uniformity of particle dispersion. This is particularly important for conductive agents like carbon black, as their dispersion significantly impacts the electrode’s electron conductivity, battery capacity, and current density. Understanding the material mixing state during slurry preparation is therefore crucial for producing high-performance lithium batteries.
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