阅读说明：本技术 复合陶瓷隔膜及其制备方法以及锂离子电池 (Composite ceramic diaphragm, preparation method thereof and lithium ion battery ) 是由 周忠年 吕豪杰 齐士博 于 2021-03-11 设计创作，主要内容包括：本申请涉及锂电池领域,涉及一种复合陶瓷隔膜及其制备方法以及锂离子电池。该复合陶瓷隔膜包括基膜、第一陶瓷涂层以及第二陶瓷涂层；第一陶瓷涂层形成在基膜上,第二陶瓷涂层形成在第一陶瓷涂层上；第一陶瓷涂层的致密度大于第二陶瓷涂层的致密度。通过设置第一陶瓷涂层和第二陶瓷涂层,能够在基膜上形成两种不同致密度的陶瓷涂层,使两种不同致密度的陶瓷涂层形成优势互补的结构,从而使两种不同致密度的陶瓷涂层的优势协同发挥。致密度较高的第一陶瓷涂层直接接触基膜,能够保障电池的安全；致密度较低的第二陶瓷涂层设置在第一陶瓷涂层上,用于与电池负极直接接触,能够实现吸液保液及抑制负极副反应产物堵孔的趋势。(The application relates to the field of lithium batteries, and relates to a composite ceramic diaphragm, a preparation method thereof and a lithium ion battery. The composite ceramic diaphragm comprises a base film, a first ceramic coating and a second ceramic coating; a first ceramic coating layer formed on the base film, and a second ceramic coating layer formed on the first ceramic coating layer; the density of the first ceramic coating is greater than that of the second ceramic coating. Through the arrangement of the first ceramic coating and the second ceramic coating, two ceramic coatings with different densities can be formed on the base film, so that the two ceramic coatings with different densities form a structure with complementary advantages, and the advantages of the two ceramic coatings with different densities are cooperatively exerted. The first ceramic coating with higher density directly contacts the base film, so that the safety of the battery can be guaranteed; the second ceramic coating with lower density is arranged on the first ceramic coating and is used for being in direct contact with the battery cathode, so that liquid absorption and retention can be realized, and the tendency of blocking holes by side reaction products of the cathode can be inhibited.)

1. A composite ceramic diaphragm, comprising:

a base film, a first ceramic coating and a second ceramic coating; the first ceramic coating layer is formed on the base film, and the second ceramic coating layer is formed on the first ceramic coating layer;

the density of the first ceramic coating is greater than the density of the second ceramic coating.

2. The composite ceramic membrane of claim 1, wherein:

the first ceramic coating comprises nano-scale ceramic particles;

the second ceramic coating comprises micron-sized ceramic particles.

3. The composite ceramic membrane of claim 1, wherein:

the average particle size of the ceramic particles in the first ceramic coating is less than 200 nm;

the ceramic particles in the second ceramic coating have an average particle size greater than 1 μm.

4. The composite ceramic membrane of claim 3, wherein:

the average grain diameter of the ceramic grains in the first ceramic coating is within the range of 50 nm-200 nm;

the average particle size of the ceramic particles in the second ceramic coating is in the range of 1 μm to 4 μm.

5. The composite ceramic membrane according to any one of claims 1 to 4, wherein:

the thickness of the first ceramic coating is within the range of 1-3 mu m; further optionally, the first ceramic coating has a thickness in a range of 1 μm to 2 μm;

the thickness of the second ceramic coating is within the range of 1-3 mu m; further optionally, the thickness of the second ceramic coating is 2-3 μm;

the total thickness of the first ceramic coating and the second ceramic coating is less than or equal to 4 μm.

6. The composite ceramic membrane of claim 1, wherein:

the ceramic particles in the first ceramic coating comprise at least one of nano-alumina particles, nano-ceramic fibers or nano-barium sulfate particles;

the ceramic particles in the second ceramic coating are micron alumina particles.

7. The composite ceramic membrane of claim 1, wherein:

the thickness of the base film is 7-20 μm;

optionally, the material of the base film is a polyolefin polymer material.

8. The method for preparing the composite ceramic separator according to any one of claims 1 to 7, comprising:

forming first ceramic slurry on the surface of the base film, and drying to obtain a first ceramic coating;

then forming a second ceramic slurry on the first ceramic coating, and drying to obtain a second ceramic coating;

wherein an average particle size of the ceramic particles in the first ceramic slurry is larger than an average particle size of the ceramic particles in the second ceramic slurry.

9. The method of manufacturing a composite ceramic membrane according to claim 8, comprising:

the first ceramic slurry comprises nano-scale ceramic particles;

the second ceramic slurry includes micron-sized ceramic particles.

10. A lithium ion battery, comprising: the composite ceramic separator according to any one of claims 1 to 7.

Technical Field

The application relates to the field of lithium batteries, in particular to a composite ceramic diaphragm, a preparation method thereof and a lithium ion battery.

Background

The diaphragm is used as a key material in the lithium ion battery, and has obvious influence on the safety and the electrical property of the battery. The diaphragm plays a role in separating the positive electrode from the negative electrode and preventing short circuit, and for a multiplying power type battery, when high power is adopted for charging and discharging, heat is easily generated inside the battery, so that the temperature of the battery is rapidly increased in a short time, and at the moment, the high-temperature-resistant contractive capacity of the diaphragm is a challenge.

At present, the conventional solution is to coat a ceramic layer on the surface of the separator, and the denser the ceramic particles, the stronger the heat resistance. However, as the density of the ceramic particles increases, the overall effect of the ceramic particles on the passage of ions is inhibited, thereby affecting the rate performance of the battery. And the lithium also has certain influence on the cycle performance of the battery, because the lithium is easy to generate a series of nano-scale side reaction products at the negative electrode at the later stage of the battery cycle, and the nano-scale side reaction products are easy to block the gaps on the surface of the ceramic diaphragm. On the contrary, if the ceramic layer particles are large, gaps among the stacked particles are large, so that the adsorption and liquid retention of electrolyte are facilitated, the ion permeability of the diaphragm is good, the hole plugging tendency of the battery in the later cycle period can be reduced, and the relatively loose ceramic layer formed by large-particle ceramic is easy to reduce the heat resistance of the diaphragm, so that the safety of the battery is influenced.

Disclosure of Invention

The embodiment of the application aims to provide a composite ceramic diaphragm, a preparation method thereof and a lithium ion battery, and aims to ensure the safety of the battery and inhibit the pore blocking tendency of a negative electrode side reaction product.

In a first aspect, the present application provides a composite ceramic diaphragm comprising:

a base film, a first ceramic coating and a second ceramic coating; a first ceramic coating layer formed on the base film, and a second ceramic coating layer formed on the first ceramic coating layer;

the density of the first ceramic coating is greater than that of the second ceramic coating.

The density of the first ceramic coating is set to be larger than that of the second ceramic coating, so that two ceramic coatings with different densities can be formed on the base film, the two ceramic coatings with different densities form a structure with complementary advantages, and the advantages of the two ceramic coatings with different densities can be brought into play synergistically. The first ceramic coating with higher density directly contacts the base film, so that the safety of the battery can be guaranteed; the second ceramic coating with lower density is arranged on the first ceramic coating and is used for being in direct contact with the battery cathode, so that liquid absorption and retention can be realized, and the tendency of blocking holes by side reaction products of the cathode can be inhibited.

In other embodiments of the present application, the first ceramic coating includes nano-scale ceramic particles therein;

the second ceramic coating includes micron-sized ceramic particles therein.

In other embodiments of the present application, the ceramic particles in the first ceramic coating have an average particle size of less than 200 nm;

the ceramic particles in the second ceramic coating have an average particle size greater than 1 μm.

In other embodiments of the present application, the ceramic particles in the first ceramic coating have an average particle size in a range of 50nm to 200 nm;

the average particle size of the ceramic particles in the second ceramic coating is in the range of 1 μm to 4 μm.

In other embodiments of the present application, the thickness of the first ceramic coating is in a range of 1 μm to 3 μm; further optionally, the first ceramic coating has a thickness in the range of 1 μm to 2 μm;

the thickness of the second ceramic coating is within the range of 1-3 mu m; further optionally, the thickness of the second ceramic coating is 2-3 μm;

the total thickness of the first ceramic coating and the second ceramic coating is less than or equal to 4 μm.

In other embodiments of the present application, the ceramic particles in the first ceramic coating include at least one of nano alumina particles, nano ceramic fibers, or nano barium sulfate particles;

the ceramic particles in the second ceramic coating are micron alumina particles.

In other embodiments of the present application, the thickness of the base film is 7 to 20 μm.

In other embodiments of the present application, the material of the base film is a polyolefin polymer material.

In a second aspect, the present application provides a method of preparing a composite ceramic separator, comprising:

forming first ceramic slurry on the surface of the base film, and drying to obtain a first ceramic coating;

then forming second ceramic slurry on the first ceramic coating, and drying to obtain a second ceramic coating;

wherein the average particle size of the ceramic particles in the first ceramic slurry is larger than the average particle size of the ceramic particles in the second ceramic slurry.

In other embodiments of the present application, the first ceramic slurry includes nano-scale ceramic particles;

the second ceramic slurry includes micron-sized ceramic particles.

In a third aspect, the present application provides a lithium ion battery comprising: any of the preceding embodiments provide a composite ceramic diaphragm.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.

Fig. 1 is a schematic structural view of a composite ceramic diaphragm provided in an embodiment of the present application;

FIG. 2 is a schematic view of a coating system for a composite ceramic separator according to an embodiment of the present disclosure;

FIG. 3 shows EIS test results of batteries fabricated with the composite ceramic separators provided in examples 1 to 3 of the present application;

FIG. 4 shows the results of rate capability tests of batteries fabricated with the composite ceramic separators provided in examples 1 to 3 of the present application;

FIG. 5 shows the results of cycle performance (25 ℃) measurements of batteries fabricated with the composite ceramic separators provided in examples 1 to 3 of the present application;

FIG. 6 shows the results of testing the cycle performance (45 ℃) of batteries manufactured by the composite ceramic separators provided in examples 1 to 3 of the present application.

Icon: 110-a base film; 120-a first ceramic coating; 130-a second ceramic coating; 1-unwinding roller; 2-a first drive roll; 3-coating roller No. one; 4-a second driving roller; 5-front section oven; 6-a third driving roller; 7-coating roll II; 8-a fourth driving roller; 9-a rear section oven; 10-a fifth driving roller; 11-a wind-up roll; 12-diaphragm.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments.

Some embodiments of the present application provide a composite ceramic membrane comprising: a base film, a first ceramic coating, and a second ceramic coating.

Further, a first ceramic coating layer is formed on the base film, and a second ceramic coating layer is formed on the first ceramic coating layer.

Further, the density of the first ceramic coating is greater than that of the second ceramic coating. In other words, the second ceramic coating has larger voids than the first ceramic coating.

The density of the first ceramic coating is set to be larger than that of the second ceramic coating, so that two ceramic coatings with different densities can be formed on the base film, the two ceramic coatings with different densities form a structure with complementary advantages, and the advantages of the two ceramic coatings with different densities can be brought into play synergistically. The first ceramic coating with higher density directly contacts the base film, so that the safety of the battery can be guaranteed; the second ceramic coating with lower density is arranged on the first ceramic coating and is used for being in direct contact with the battery cathode, so that liquid absorption and retention can be realized, and the tendency of blocking holes by side reaction products of the cathode can be inhibited.

In some embodiments, the composite ceramic membrane is formed into a three-layer structure, and two ceramic coatings are arranged on the surface of the base membrane. Referring to FIG. 1, in the illustrated embodiment, a composite ceramic diaphragm structure is illustratively shown. The surface of the base film 110 is provided with a first ceramic coating layer 120; a second ceramic coating 130 is disposed on the first ceramic coating 120. The whole composite ceramic diaphragm forms a three-layer structure.

The first ceramic coating layer may be formed on the entire surface of one side of the base film or may be formed in a partial region according to actual needs. Likewise, the same may be true of the second ceramic coating.

In other alternative embodiments of the present application, the first ceramic coating layer of the composite ceramic diaphragm may be optionally provided as multiple layers, for example, two layers, and the density of the two layers is different but greater than that of the second ceramic coating layer.

In other alternative embodiments of the present application, the second ceramic coating layer of the composite ceramic diaphragm may also be optionally disposed in multiple layers, for example, two layers, and the density of the two layers is different but smaller than that of the first ceramic coating layer.

In other alternative embodiments of the present application, a coating layer may be selectively formed on the other side surface of the base film according to actual requirements.

Further, the first ceramic coating comprises nano-scale ceramic particles; the second ceramic coating includes micron-sized ceramic particles therein.

The first ceramic coating is arranged to include nano-scale ceramic particles, and the second ceramic coating includes micro-scale ceramic particles, so that two layers of ceramic coatings with different densities can be formed on the base film. Furthermore, the density of the first ceramic coating formed by the nano-scale ceramic particles is higher, and the high-temperature-resistant shrinkage performance of the base film is greatly improved. Therefore, when the composite diaphragm is applied to a lithium ion battery, and when the composite diaphragm is charged and discharged with higher power and the temperature of the battery is rapidly increased in a short time due to heat generation inside the battery, the excellent high-temperature-resistant contractibility of the diaphragm greatly improves the use safety and the electrical property of the battery. Furthermore, the second ceramic coating formed by the micron-sized ceramic particles has lower density, so that the formed coating has higher porosity, and gaps among the stacked particles are larger, thereby providing more channels for ions to pass through. When the composite diaphragm is applied to a lithium ion battery, the composite diaphragm is favorable for the adsorption and liquid retention of electrolyte, the ion permeability of the diaphragm is good, and the hole plugging tendency of the battery in the later cycle period can be reduced.

The nanoscale means 10 to 500 nm. The micron-sized means 1 μm to 10 μm.

In some embodiments, the ceramic particles in the first ceramic coating are all nano-scale ceramic particles, and the ceramic particles in the second ceramic coating are all micro-scale ceramic particles.

In some embodiments of the present application, at least 20% or more of the ceramic particles in the first ceramic coating are nano-scale ceramic particles, and at least 20% or more of the ceramic particles in the second ceramic coating are micro-scale ceramic particles.

Further, the ceramic particles in the first ceramic coating each have an average particle size of less than 200 nm.

Further optionally, the nano-scale ceramic particles in the first ceramic coating have an average particle size in a range of 50nm to 200 nm. Further optionally, the nano-scale ceramic particles have an average particle size of 60nm to 180 nm; further optionally, the nano-scale ceramic particles have an average particle size of 100nm to 150 nm.

Illustratively, the nanoscale ceramic particles in the first ceramic coating described above have an average particle size of 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, or 190 nm.

By setting the average particle size of the nano ceramic particles in the first ceramic coating within the above range, a ceramic coating with higher density cannot be obtained to ensure the safety of the battery, and agglomeration is not easy to occur.

Further, the average particle size of the ceramic particles in the second ceramic coating is greater than 1 μm.

Further optionally, the average particle size of the ceramic particles in the second ceramic coating is in the range of 1 μm to 4 μm. Further optionally, the average particle size of the ceramic particles in the second ceramic coating is in the range of 1.5 μm to 3.5 μm.

Illustratively, the average particle size of the ceramic particles in the second ceramic coating described above is 1.1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2.1 μm, 2.3 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, or 3.4 μm.

By setting the average particle size of the ceramic particles in the second ceramic coating within the above range, not only can larger gaps be obtained and more channels for ions to pass through be provided, but also a structure with complementary advantages can be formed with the first ceramic coating, so that the advantages of two ceramic coatings with different densities can be exerted synergistically.

Further, the first ceramic coating has a thickness in a range of 1 μm to 3 μm. Further, the thickness of the first ceramic coating is in the range of 1.1 μm to 2.9 μm. Further, the first ceramic coating has a thickness in a range of 1 μm to 2 μm.

Illustratively, the thickness of the first ceramic coating described above is 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, or 2.8 μm.

Through setting up the thickness of foretell first ceramic coating in foretell within range, can effectively improve the heat resistance of base film, guarantee battery safety, make the whole thickness of whole composite ceramic diaphragm be unlikely to too thick moreover within this range, guarantee battery electrical property.

Further optionally, the second ceramic coating has a thickness in a range of 1 μm to 3 μm. The thickness of the second ceramic coating is 1.1-3 μm. Further optionally, the second ceramic coating has a thickness of 2 μm to 3 μm. Further optionally, the second ceramic coating has a thickness of 2 μm to 2.9 μm.

Illustratively, the thickness of the second ceramic coating described above is 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, or 2.9 μm.

The thickness of the second ceramic coating is set in the range, so that the liquid absorption and retention can be guaranteed, the hole blocking tendency of a negative electrode side reaction product can be inhibited, the second ceramic coating is cooperated and complemented with the first ceramic coating, the whole thickness of the whole composite ceramic diaphragm is not too thick, and the electrical property of the battery is guaranteed.

Further, the total thickness of the first ceramic coating and the second ceramic coating is less than or equal to 4 μm. Further optionally, the total thickness of the first ceramic coating and the second ceramic coating is between 3.1 μm and 3.9 μm. Further optionally, the total thickness of the first ceramic coating and the second ceramic coating is between 3.2 μm and 3.8 μm.

Illustratively, the total thickness of the first ceramic coating and the second ceramic coating is 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, or 3.8 μm.

By setting the thickness of the entire composite ceramic separator within the above range, the electrical performance of the battery can be ensured.

Further, the ceramic particles in the first ceramic coating include at least one of nano alumina particles, nano ceramic fibers, or nano barium sulfate particles.

The nano alumina particles, the nano ceramic fibers or the nano barium sulfate particles can be manufactured into stable nano-scale particle sizes, the density requirement of the first ceramic coating is met, the heat resistance of the base film is guaranteed to be improved, and the safety of the battery is guaranteed.

Further, the ceramic particles in the second ceramic coating are micron alumina particles.

The alumina particles can more easily obtain micron-sized particle sizes, meet the density requirement of the second ceramic layer, ensure that more channels for ions to pass through are provided, and realize the liquid absorption and retention and inhibit the tendency of pore blocking of the side reaction product of the negative electrode. The barium sulfate is powdery in normal state and is difficult to prepare micron-sized particles, so that the requirement on the density in the second ceramic coating cannot be met; ceramic fibers also have similar drawbacks.

Further, the thickness of the base film is 7-20 μm; further optionally, the thickness of the base film is 8-19 μm; further optionally, the thickness of the base film is 9-18 μm.

Illustratively, the thickness of the above-described base film is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or 18 μm.

Further, the material of the base film is selected from polyolefin, non-woven fabric and polyimide polymer material.

Embodiments of the present application provide a composite ceramic separator that can be used to prepare the composite ceramic separator provided in any of the preceding embodiments.

In some embodiments, the composite ceramic separator described above is prepared by:

and step S1, forming first ceramic slurry on the surface of the base film, and drying to obtain a first ceramic coating.

Further, the first ceramic slurry includes nano-scale ceramic particles.

Further, in some embodiments of the present application, the step of preparing the first ceramic slurry includes:

mixing the nano-scale ceramic particles, a stabilizer, a dispersant, a bonding agent and a wetting agent to prepare first ceramic slurry.

Further alternatively, the above-mentioned stabilizer is prepared as a solution and then mixed with other reagents. Optionally, the stabilizer is sodium carboxymethylcellulose, and further optionally, the sodium carboxymethylcellulose is mixed with deionized water and stirred uniformly.

In some embodiments, when the sodium hydroxymethyl cellulose is mixed with deionized water, 2.0-3.0 parts by weight of sodium hydroxymethyl cellulose; 0.01 to 0.05 portion of deionized water.

Further, the stirring time is 0.5 h-1.5 h; furthermore, the stirring speed is 50 r/min-70 r/min.

Further, in some embodiments, nano-scale ceramic particles and a dispersant are added to the prepared stabilizer solution and uniformly dispersed. Further optionally, the dispersing speed is 1000 r/min-2000 r/min, and the dispersing time is 0.1 h-1 h.

Furthermore, the average particle size of the nano-scale ceramic particles is less than 200 nm.

Further optionally, the nano-scale ceramic particles have an average particle size in a range of 50nm to 200 nm. Further optionally, the nano-scale ceramic particles have an average particle size of 60nm to 180 nm; further optionally, the nano-scale ceramic particles have an average particle size of 100nm to 150 nm.

Illustratively, the nano-sized ceramic particles described above have an average particle size of 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, or 190 nm.

Further, the nano-scale ceramic particles are at least one selected from nano-alumina particles, nano-ceramic fibers or nano-barium sulfate particles.

Further, the dispersant is selected from polyether modified organic silicon solvent. Mixing the nano-alumina ceramic particles with a dispersant, and then uniformly dispersing. Optionally, the dispersion speed is selected to be 1000 r/min-2000 r/min, and the dispersion time is selected to be 0.1 h-1 h.

Further, a binder is added to the dispersant solution. Alternatively, the adhesive is selected from acrylates.

Further, a wetting agent was added to the above dispersion liquid, and dispersion was performed.

Further optionally, the dispersing speed is 100 r/min-150 r/min, and further optionally, the dispersing time is 0.1 h-1 h.

Further, the coating comprises, by mass, 1.0-2.0 parts of nano-scale ceramic particles, 0.01-0.05 part of a stabilizer, 0.01-0.05 part of a dispersant, 0.1-0.5 part of an adhesive and 0.1-1 part of a wetting agent.

Further, the thickness of the first ceramic coating layer is in the range of 1 μm to 3 μm.

Further optionally, the thickness of the first ceramic coating is in a range of 1.1 μm to 2.9 μm.

Illustratively, the thickness of the first ceramic coating described above is 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, or 2.8 μm.

And step S2, forming second ceramic slurry on the first ceramic coating, and drying to obtain a second ceramic coating.

Further, the preparation steps of the second ceramic slurry are the same as the preparation steps of the first ceramic slurry, except that: the selection of the ceramic particles in the second ceramic slurry, the particle size of the ceramic particles, and the thickness of the first ceramic coating are different.

Further, in some embodiments of the present application, the ceramic particles in the second ceramic slurry are selected from alumina.

The alumina ceramic is easier to be made into micron-sized particles, so that the alumina ceramic is added into the second ceramic slurry to be made into a micron-sized second ceramic coating.

Further, the average particle size of the ceramic particles in the second ceramic slurry is greater than 1 μm. Further alternatively, the average particle diameter of the ceramic particles in the second ceramic slurry is in the range of 1 μm to 4 μm. Further alternatively, the average particle size of the ceramic particles in the second ceramic slurry is in a range of 1.5 μm to 3.5 μm.

Illustratively, the average particle size of the ceramic particles in the above-described second ceramic slurry is 1.1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2.1 μm, 2.3 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, or 3.4 μm.

Further, the thickness of the second ceramic coating is 1-3 μm. Further optionally, the second ceramic coating has a thickness of 1.1 μm to 1.9 μm. Further optionally, the second ceramic coating has a thickness of 2 μm to 3 μm.

Illustratively, the thickness of the second ceramic coating described above is 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, or 2.9 μm.

Further, in some embodiments of the present application, a total thickness of the first ceramic coating and the second ceramic coating is less than or equal to 4 μm.

Further optionally, the total thickness of the first ceramic coating and the second ceramic coating is 3 μm to 4 μm. Further optionally, the total thickness of the first ceramic coating and the second ceramic coating is between 3.1 μm and 3.9 μm. Further optionally, the total thickness of the first ceramic coating and the second ceramic coating is between 3.2 μm and 3.8 μm.

Illustratively, the total thickness of the first ceramic coating and the second ceramic coating is 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, or 3.8 μm.

And step S3, drying the composite diaphragm coated with the first ceramic coating and the second ceramic coating.

Further, the drying is carried out at 70-90 ℃. Further optionally, the drying is performed at 72-89 ℃. Further optionally, the drying is performed at 75-85 ℃.

Illustratively, the drying temperature is 73 ℃, 76 ℃, 78 ℃, 79 ℃, 80 ℃, 82 ℃ or 84 ℃.

In some embodiments of the present application, the composite ceramic separator described above is prepared using the coating system shown in figure 2 of the specification. Referring to fig. 2, the separator 12 is unwound by the unwinding roller 1 and wound by the winding roller 11. After the unwinding roller 1 unwinds, the first driving roller 2 is used for conveying the diaphragm 12. When the separator 12 reaches the coating roller No. one 3, a first ceramic slurry is first coated on the separator 12 (in this case, an uncoated base film); the second driving roller 4 continues to transmit the diaphragm 12, the diaphragm 12 reaches the front section drying oven 5, after drying treatment, the third driving roller 6 continues to transmit the diaphragm 12 and reaches the second coating roller 7, the second coating roller 7 coats second ceramic slurry on the first ceramic coating, after coating is completed, the fourth driving roller 8 continues to transmit the diaphragm 12, the diaphragm reaches the rear section drying oven 9, after drying treatment, the fifth driving roller 10 continues to transmit the diaphragm 12 and reaches the wind-up roller 11 for winding. At the moment, the composite ceramic diaphragm coated with two layers of different densities is coiled by the coiling roller 11.

The features and properties of the present application are described in further detail below with reference to examples:

example 1

Providing a composite ceramic separator, prepared by:

(1) preparing first ceramic slurry:

step 1: 2.3kg of deionized water and 0.02kg of sodium carboxymethylcellulose stabilizer are uniformly mixed, the stirring speed is 60r/min, and the stirring time is 1 h;

step 2: adding 1.5kg of nano-grade alumina ceramic particles (with the average particle size of 100nm) and 0.03kg of polyether modified organic silicon solvent dispersant, wherein the dispersion speed is 1500r/min, and the dispersion time is 0.5 h;

and 3, step 3: adding 0.2kg of acrylate adhesive, wherein the dispersion speed is 500r/min, and the dispersion time is 0.5 h;

and 4, step 4: adding 0.5g of wetting agent, dispersing at the speed of 200r/min for 0.5h to prepare first ceramic slurry.

(2) Preparing a second ceramic slurry:

the second ceramic slurry was prepared in substantially the same manner as the first ceramic slurry except that the nano-alumina of the above-mentioned step 2 was replaced with micro-alumina (average particle size 2 μm).

(3) And forming: (Combined FIG. 2)

Step 1: unreeling a 10 mu m polyolefin polymer base film, and firstly coating the first ceramic slurry prepared in the step (1) on the polyolefin base film by a first coating roller 3 by adopting a micro-gravure transfer forming method to form the thickness of 1 mu m;

step 2: the formed film enters a front-section drying oven to be dried, the temperature of the drying oven is controlled at 60 ℃, and a first drying film containing a first ceramic coating is obtained after the formed film is taken out of the drying oven;

and 3, step 3: the first drying film is taken out of the oven and then is continuously taken, second ceramic slurry is coated on the first ceramic coating through a second coating roller 7, and the thickness of the second ceramic coating is controlled to be 3 mu m, so that a second drying film containing the second ceramic coating is obtained;

and 4, step 4: and (4) feeding the second dried film into a rear-section oven to finish drying, controlling the temperature of the oven at 80 ℃, and finishing winding of the finished diaphragm after the second dried film is discharged from the rear-section oven.

Example 2

A composite ceramic separator was provided, substantially the same as the procedure of example 1, except that:

the coating thickness of the first ceramic coating is 2 μm; the second ceramic coating was applied to a thickness of 2 μm.

Example 3

A composite ceramic separator was provided, substantially the same as the procedure of example 1, except that:

the coating thickness of the first ceramic coating is 3 μm; the second ceramic coating was applied at a thickness of 1 μm.

Example 4

A composite ceramic separator was provided, substantially the same as the procedure of example 1, except that:

the average particle size of the ceramic particles in the first ceramic coating is 50 nm; the average particle size of the ceramic particles in the second ceramic coating is 1 μm.

Example 5

A composite ceramic separator was provided, substantially the same as the procedure of example 1, except that:

the average particle size of the ceramic particles in the first ceramic coating is 200 nm; the average particle size of the ceramic particles in the second ceramic coating was 4 μm.

Comparative example 1

A composite ceramic diaphragm is provided. Substantially the same procedure as in example 1 was followed, except that only the first ceramic coating was prepared and had a thickness of 4 μm.

Comparative example 2

A composite ceramic diaphragm is provided. Substantially the same procedure as in example 1, except that only the second ceramic coating was prepared, and had a thickness of 4 μm.

Comparative example 3

A composite ceramic diaphragm is provided. The same as the base film, the first ceramic slurry and the second ceramic slurry in example 1, except that the first ceramic slurry and the second ceramic slurry were mixed and coated in one layer having a thickness of 4 μm.

Examples of the experiments

The physical properties of the composite ceramic diaphragms provided in examples 1 to 5 and comparative examples 1 to 3 were examined. The detection results are shown in table 1:

TABLE 1

As can be seen from the test results in table 1, the composite ceramic separators obtained in examples 1 to 5 were excellent in all of puncture strength, air permeability, tensile strength, heat shrinkability, and moisture content. Particularly, the membrane has obvious ion permeability (air permeability value is lower than 270) and temperature resistance stability (heat shrinkage value at 130 ℃ is less than or equal to 1.5). The ion permeability is improved, the problem of diaphragm hole blocking for inhibiting long-term circulation of the battery cell can be improved to a certain extent, and the service life of the battery is prolonged; in addition, the high-temperature shrinkage rate of the diaphragm is reduced, the high-temperature heat-resistant stability of the battery core is effectively improved, and the high-temperature heat-resistant diaphragm has a certain help effect on preventing thermal runaway of the battery.

While the composite ceramic separator of comparative example 1, which is provided with only the nano-scale ceramic coating, has improved the puncture strength of the separator, the gas permeation value (up to 284) thereof becomes large, and the gas-permeable ion permeability becomes poor, which may result in deterioration of the cycle performance of the battery. The composite ceramic separator in comparative example 2, in which only the micro-sized ceramic coating layer is provided, has a reduced air permeability value and improved air permeability, but has deteriorated thermal shrinkage, particularly high-temperature thermal shrinkage (up to 2.0), resulting in deteriorated safety of the battery. In comparative example 3, the micro-and nano-sized ceramic particles were mixed and coated as one layer, resulting in an increase in the permeability (up to 291), a low ion permeability, and easy pore blocking, resulting in deterioration of cycle performance of the battery.

Experimental example 2

The composite ceramic diaphragm provided in the embodiment 1-3 is made into a lithium ion battery, and the battery specification is a ternary soft packaging lamination with the capacity of 6.8 Ah.

Detecting EIS and rate performance of the battery:

the detection result is shown in the attached figures 3-6 of the specification.

As can be seen from the attached figures 3-6 in the specification, the lithium ion batteries manufactured by the composite ceramic diaphragms provided by the embodiments 1-3 have excellent electrical properties.

Wherein fig. 3 shows a battery EIS; fig. 4 shows the rate capability. As can be seen from fig. 3 and 4, EIS results show that the impedance of the battery corresponding to example 1 is relatively small, the capacities of the batteries corresponding to the three schemes of examples 1-3 are kept similar when the current is less than 3C during rate discharge, and after the discharge rate is greater than 3C, example 1 performs relatively well in terms of battery rate performance.

Fig. 5 and 6 show the battery cycle performance. As can be seen from fig. 5 and 6, the cycle life of examples 1 and 2 is superior to that of example 3 in terms of cycle performance because the ion-passing capacity of the entire separator tends to decrease as the thickness of the nano-sized ceramic particles increases, and the probability of the side reaction products blocking the ceramic pores on the surface of the separator increases as the cycle progresses.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.