The coating process consists of three parts: the slurry feeding system, the coating system, and the electrode drying system. These three systems work in tandem, and each needs to maintain stability to ensure electrode consistency. This article will discuss the impact of coating on the performance consistency of lithium batteries.
The slurry feeding system transfers the mixed slurry to a storage tank, then to a transition tank via a diaphragm pump. A screw pump then steadily pumps the slurry through a filter and iron removal device before delivering it to the coating equipment for coating. Several key points to consider in an automatic slurry feeding system include: preventing slurry stratification in the storage tank, maintaining the slurry level in the transition tank, ensuring the stability of the screw pump, and promptly cleaning any blockages in the filter tank. The following diagram illustrates a type of automatic feeding system; see the references for details.
The main coating methods for lithium battery slurries include comma-type doctor blade coating, transfer coating, and slot extrusion coating. Each method has its own characteristics: doctor blade coating is primarily used in laboratory conditions, transfer coating is mainly used in the production of 3C batteries, and slot extrusion coating is mainly used in power batteries. The parameters characterizing electrode stability are mainly electrode areal density, electrode thickness, and adhesion. In the coating system, factors affecting electrode consistency include the manufacturing precision of the coating head, the stability of the slurry delivery by the screw pump, the stability of the compressed gas, speed stability, and the control of dynamic tension.
scraper type
Transfer
Slit extrusion
The electrode drying system mainly consists of several ovens with different temperature distributions, designed to dry the electrodes. A key consideration in this system is the temperature setting. Excessive temperature during coating can cause electrode cracking, while insufficient temperature will prevent complete drying, both leading to inconsistent polarization in the battery. Additionally, it's crucial to prevent the binder from floating to the surface.
Common problems encountered in the coating process include thick beginnings and thin ends, thick edges on both sides, dark spots, rough surfaces, and exposed foil. The thickness at the beginning and end can be adjusted by changing the opening and closing time of the coating valve or intermittent valve. Thick edges can be improved by adjusting the slurry properties, coating gap, and slurry flow rate. Rough, uneven surfaces with streaks can be improved by stabilizing the foil, reducing the speed, and adjusting the air knife angle.
