Polyolefin-based separators have a low melting point (150℃ and below). When the battery temperature rises abnormally, they are prone to shrinkage and melting, which can easily cause short circuits between the positive and negative electrodes, and even lead to safety accidents such as explosions. To solve this industry pain point, coated composite separators have emerged. As the two core technologies among them, CCS ceramic coating and PCS polymer coating have built a solid performance line of defense for lithium batteries from the two dimensions of high-temperature safety protection and structural bonding stability, respectively.
This article will deeply analyze the core functions, technological iteration, material characteristics and performance advantages and disadvantages of CCS and PCS coatings, clearly define their functional positioning, and provide accurate reference for the selection and process optimization of lithium battery separator coatings.
1. CCS Ceramic Coating: High-Temperature Safety “Shield” for Lithium Batteries
CCS ceramic coating is the core solution to solve the high-temperature thermal shrinkage of polyolefin separators and avoid internal short circuits. By coating inorganic particles on the surface of the separator substrate, it fundamentally improves the safety characteristics of the battery under extreme conditions with its excellent heat resistance. A high-quality CCS ceramic coating must have three core performances: heat resistance, oxidation resistance and puncture resistance, without affecting the wettability of the electrolyte to the separator.
After technological iteration, CCS ceramic coating has developed three generations of products. Each generation of technology has its own focus on material selection, coating parameters and performance, with distinct advantages and disadvantages:
1st Generation CCS: α-Al₂O₃ as the Core, a Cost-Effective Choice
Alumina (Al₂O₃) is used as the main inorganic coating material, and a one-time gravure coating process is adopted, with the single-sided coating thickness controlled at 2~4μm.
Core Advantages: Excellent electrolyte wettability, low material procurement cost, suitable for the basic safety needs of large-scale mass production;
Obvious Shortcomings: Al₂O₃ has high hardness, which causes serious wear on the gravure roll during the coating process, easily affecting the coating appearance and thickness uniformity; the coating adhesion is poor, and powder shedding is prone to occur when the thickness is too large, and water-based slurry cannot be coated on its surface for the second time.
2nd Generation CCS: Boehmite as the Main Material, Process Compatibility Upgrade
Boehmite is selected as the core coating material, the single-sided coating thickness is expanded to 1.5~6μm, and the compatibility of the coating process is greatly improved.
Core Advantages: The hardness of boehmite is much lower than that of Al₂O₃, which can effectively reduce the wear on the gravure roll and improve the service life of the equipment; the coating adhesion is stronger, the coating structure is tighter, and the appearance and thickness uniformity are significantly optimized;
Obvious Shortcomings: The electrolyte wettability is slightly lower than that of the Al₂O₃ coating, and the cost of boehmite material is higher, which increases the mass production cost to a certain extent.
3rd Generation CCS: Submicron Al₂O₃ + Heat-Resistant Polymer, High Energy Density Adaptation
A composite system of submicron Al₂O₃ and heat-resistant polymer is adopted, and the single-sided coating thickness can be flexibly adjusted between 0.5~6μm, achieving a breakthrough in coating thinning.
Core Advantages: The coating thickness can be made thinner, which can effectively improve the energy density of lithium batteries; other core performances (heat resistance, puncture resistance, adhesion) are the same as those of the 2nd generation CCS, with balanced comprehensive performance;
Obvious Shortcomings: The composite system has stricter requirements on process control, greatly increasing the threshold for the precision of coating equipment and testing instruments, and further increasing the process and equipment costs.
2. PCS Polymer Coating: Structural Stability “Adhesive” for Lithium Batteries
If CCS is the “safety shield” of lithium batteries, then PCS (Polymer Coated Separator) is the “strong adhesive” for the internal structure of the battery. Its core function is not to improve thermal stability, but to enhance the adhesion between the positive and negative electrode sheets and the separator, and at the same time effectively prevent the battery from deforming during cyclic charging and discharging, improve the overall hardness of the cell, and ensure the structural stability of the battery during long-term cycling.
1. Material Composition of Mainstream Mass-Produced PCS Slurry
In large-scale production, the core component matching of water-based PCS slurry has formed a mature system: PVDF is used as the core polymer particle, water-based thickeners (BI-4/CMC-Na) are used to adjust the slurry viscosity, and polyacrylate emulsion (FA-3) is used as the binder to ensure the bonding strength between the coating and the separator and electrode sheets.
2. Core Performance Value of PCS Coating
The existence of PCS coating can not only ensure the structural stability of the battery, but also slightly improve the cell capacity without affecting the core electrochemical performance:
The improvement of interface adhesion effectively reduces the polarization phenomenon caused by electrochemical reactions inside the battery, thereby realizing a slight increase in cell capacity;
PVDF particles are distributed in the coating in an island shape, which is easy to be swollen by the electrolyte. After swelling, PVDF can maintain good lithium ion transport characteristics by virtue of its special chemical properties and morphology, without affecting the exertion of the battery’s dynamic performance;
Experimental verification shows that the addition of PCS coating will not have a negative impact on the internal resistance and initial Coulombic efficiency of the cell, achieving the dual goals of “structural stability” and “no performance loss”.
3. CCS & PCS: Dual Cores of Separator Coatings with Complementary Functions
As the two core technologies of separator coatings, CCS and PCS have different positioning and complementary functions. They protect the performance and stability of lithium batteries from different dimensions. There is no substitution relationship between them, but they can be combined and used according to the needs of battery application scenarios:
Core Positioning of CCS: Solve the high-temperature thermal shrinkage pain point of polyolefin separators, improve the safety boundary of the battery, cope with extreme working conditions such as high temperature and thermal charging, and is the basic coating for lithium battery safety protection;
Core Positioning of PCS: Optimize the internal interface combination of the battery, improve the structural strength of the cell, prevent deformation and interface peeling during cycling, and is an auxiliary coating to ensure the long-term cycle stability of lithium batteries.
For power batteries and energy storage batteries with strict safety requirements, CCS coating is a mandatory configuration, and the corresponding generation of CCS technology can be selected according to energy density and cost budget; for high-end consumer electronics batteries with high requirements for cycle life and structural stability, PCS coating can be matched on the basis of CCS coating to achieve dual protection of safety and stability.
For more in-depth research on CCS and PCS separator coatings, material matching and process optimization, you can refer to the research published by the Journal of Power Sources. Our previous articles on ceramic separator materials and processes and PVDF hierarchical porous membranes further elaborate on the development of battery separator technologies. For detailed industry standards and coating process specifications, refer to the report released by the Institute of Electrical and Electronics Engineers (IEEE).