Date: 2026-06-11 hits: 101
The separator in a lithium-ion battery acts as an insulating barrier between the positive and negative electrodes, and its performance directly affects the battery's safety, cycle life, and energy density. Polyolefin-based films (PE/PP) inherently suffer from poor temperature resistance and weak electrolyte wettability; therefore, surface coating modification has become a mainstream technology. Coating with materials such as ceramics and PVDF can significantly improve thermal stability, electrolyte absorption and retention capacity, and electrode adhesion. Currently, roller coating and spray coating are two common methods in separator coating processes, each with its own applicable scenarios.
I. Introduction to Roller Coating
Roller coating is one of the most mature and widely used processes in separator coating, especially gravure roller coating or micro-gravure roller coating. Its working principle is as follows: the coating roller (gravure roller) rotates to carry slurry from the slurry tank. A doctor blade precisely measures the amount of slurry in the groove, and then pressure transfers the slurry to the surface of the separator base film. It then enters a drying section to remove the solvent, forming a uniform coating.
Based on the transfer method, it can be divided into transfer roller coating and direct roller coating. Common slurries include ceramic particles + binder (PVDF or water-based systems) and organic PVDF slurries. Coating thickness is typically controlled between 1-5µm, allowing for single-sided or double-sided coating. The equipment structure is relatively simple, with high production speed, suitable for large-scale continuous production.
1. Advantages of Roll Coating:
High precision and uniformity: The groove design allows for precise control of the coating amount, resulting in strong coating thickness consistency, suitable for ceramic coatings with precision requirements.
Mature and stable: Process parameters are easily adjustable, the equipment is mature, and the yield is high, suitable for high-viscosity slurries and thick coatings.
Efficiency and cost advantages: Continuous roll-to-roll production results in high slurry utilization, suitable for mass production of inorganic coatings such as ceramics, and is currently the main choice for mainstream manufacturers (such as Enjie and Xingyuan).
Strong adaptability: Coating characteristics can be flexibly controlled by adjusting the roller groove depth, doctor blade pressure, and rotation speed.
2. Disadvantages of Roller Coating:
Roller Surface Wear: The high hardness of ceramic particles easily wears down the gravure rollers over long-term operation, leading to a gradual thinning of the coating. Regular roller replacement is necessary, increasing maintenance costs.
Limited Flexibility in Thickness Adjustment: Changing rollers to different texture depths is cumbersome and unsuitable for frequent product specification changes.
Potential Defects: High-pressure transfer may produce streaks or bubbles. Poor slurry dispersion can result in uneven coating or pore blockage, affecting air permeability.
Exposed Operation: Partial exposure of the slurry to air can affect the stability of sensitive slurries.
II. Introduction to Spray Coating Methods
Spray coating is a process where slurry is atomized through nozzles and evenly sprayed onto the diaphragm surface. This includes conventional spray coating and electrospinning spray coating. Under pressure or electrostatic action, the slurry forms tiny droplets or fibers that deposit directly onto the moving base membrane, followed by drying and curing. Electrospinning is a high-end method that uses a high-voltage electric field to pull the polymer solution into nanofibers, forming a high-porosity coating.
Spray coating is particularly suitable for PVDF organic coatings or scenarios requiring porous fiber structures. The coating can be made very thin (even submicron level) and can achieve complex functional layers.
1. Advantages of Spray Coating:
High Flexibility and Adaptability: Suitable for complex shapes or thin-layer coating, with minimal damage to the base film, easily achieving gradient coatings or multi-layer composites.
Unique Coating Structure: Electrospinning forms a nanofiber network with a large specific surface area and high porosity, facilitating ion transport and electrolyte wetting, thus improving rate performance.
High Speed: Some spray coating equipment has high production efficiency, suitable for small-batch, multi-variety production.
Low Damage: No direct mechanical pressure, reducing the risk of base film deformation.
2. Disadvantages of Spray Coating:
Uniformity Challenges: The atomization process is susceptible to airflow and nozzle clogging, potentially resulting in spots or thickness deviations, requiring a precise control system and subsequent corrections.
Low Slurry Utilization: There is splashing and overspraying, leading to significant waste, especially with oily slurries, requiring careful safety and recycling.
Equipment Complexity: Electrospinning has high requirements for voltage and environmental humidity, making equipment maintenance difficult and increasing the cost of large-scale production. Production Efficiency and Stability: Traditional spray coating sometimes results in lower uniformity than roller coating, making consistency control difficult in high-speed continuous production and potentially requiring additional drying or compaction processes.
III. Summary:
Roller coating, characterized by high precision, large-scale production, and low cost, is the mainstream process for ceramic-coated separators, suitable for power batteries that prioritize thermal stability and uniformity. Spray coating, on the other hand, offers advantages in flexibility, porous structures, and thin-layer functionalization, making it suitable for high-end PVDF coatings or novel functional separators. Optimization of the coating process directly affects separator permeability, internal resistance, and thermal shrinkage rate, ultimately determining the battery's safety margin. In the future, thinner, more uniform, and intelligent coating technologies will be a key focus for the industry.
