Principle and Process of Lithium-Ion Battery Kneading

The kneading process is a critical step in lithium-ion battery electrode manufacturing, responsible for uniformly mixing active materials, conductive agents, binders, and solvents to form a homogeneous slurry. This slurry, when coated onto current collectors (copper for anodes, aluminum for cathodes), determines the electrode’s electrochemical performance, including capacity, conductivity, and cycle life.

The principle of kneading relies on mechanical shear and dispersion forces to break up agglomerates of active materials (such as LiCoO₂ for cathodes or graphite for anodes) and distribute conductive agents (like carbon black or graphene) evenly throughout the mixture. The binder, often polyvinylidene fluoride (PVDF) for cathodes or carboxymethyl cellulose (CMC) for anodes, acts as a glue to hold particles together and ensure adhesion to the current collector. Solvents (e.g., N-methyl-2-pyrrolidone for PVDF) adjust the slurry’s viscosity, facilitating smooth coating.

The process typically involves three stages. First, premixing: active materials and conductive agents are dry-blended to initially disperse large agglomerates. Second, kneading proper: solvents and binders are added gradually while the mixture is stirred at high speeds (500–2000 rpm) using planetary mixers or double-screw extruders. This stage applies intense shear, breaking down remaining agglomerates and forming a uniform slurry. Third, dilution and degassing: the slurry is thinned to the desired viscosity with additional solvent, and vacuum degassing removes trapped air bubbles that could cause coating defects.

Key parameters include temperature (controlled to prevent solvent evaporation), mixing time (30–120 minutes, depending on material complexity), and viscosity (monitored via rotational viscometers). Proper kneading ensures that each particle is surrounded by conductive agents and binders, maximizing electron and ion transport during battery operation. Poorly kneaded slurries lead to uneven electrode thickness, reduced conductivity, and capacity loss, highlighting the process’s role in battery performance.

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