Commonly Used Coating Materials for Lithium Battery Separators & Advantages of Boehmite
Commonly used coating materials include inorganic (represented by alumina and boehmite) and organic (represented by PVDF and aramid). At present, the coating materials industry presents two major trends:
Inorganic materials have high puncture strength + lower single-sided cost, and the addition ratio is stable at 90%.
Performance: Inorganic material coating has better air permeability, tensile and puncture strength, which can make up for the disadvantages of insufficient lightness and insufficient adhesion;
Cost: The single-sided consumption of organic materials is about 50% of inorganic materials, and the single-sided cost of organic materials is expected to be more than 2.5 times that of inorganic materials.
Better safety + economy, boehmite replaces alumina in part of the market.
Boehmite has lower water absorption and magnetic substances, which can more effectively ensure the safety of battery separators.
The specific gravity of boehmite is low, and the dosage can be reduced by 25% under the same coating area; the hardness is low, the service life of the coating roller is prolonged by 3-4 times, and the comprehensive economy is better. At present, boehmite accounts for 40-50% of inorganic materials, and it is expected that the proportion will reach 70% in 5 years.
Product advantages:
The boehmite products produced by AVANT have reached a high level in particle size distribution, purity, and magnetic substance control, and can produce boehmite products with the smallest particle size of 0.2-0.3 um.
The higher the difficulty.
From the product point of view: At present, inorganic materials have good coating flatness, air permeability, tensile and puncture strength;
The organic material coating is light and thin, which can better comply with the trend of increasing the energy density of the battery, and due to the adhesiveness of PVDF, it can improve the hardness of the battery core and reduce the deformation.
1) From the range of areal density: boehmite (±2) < PVDF (±3), indicating that its flatness is better, the areal density is more uniform, and the consistency is good;
(2) From the perspective of air permeability: for the base film of 7 and 9 μm, although the thickness of the boehmite coating is 3 μm and the thickness of the PVDF layer is only 2 μm, the air permeability of boehmite is still better than that of PVDF, indicating that its unit gas passes through The shorter the time of the separator, the smaller the internal resistance, which is conducive to the passage of lithium ions and ensures the rate of lithium ion batteries.
(3) From the perspective of tensile strength and puncture strength: due to the different thicknesses of boehmite and PVDF coatings, they cannot be directly compared. Selecting the same base film and coating thickness for comparison, the tensile strength and puncture strength of the boehmite diaphragm are better than those of the mixed-coated diaphragm, indicating that the mixed-coated diaphragm is dragged by PVDF, and it can be seen that the tensile strength and puncture strength of the ceramic diaphragm are superior in PVDF.
In addition to the use of boehmite for separator coating, the pole piece coating market is also gradually emerging. Coating in the pole piece of the lithium battery can avoid the burr generated during the slitting process of the positive electrode material from piercing the separator, improve the safety performance of the lithium battery, improve the battery production process, and increase the energy density.
