A diaphragm and a method for manufacturing and using the same

Abstract

The application discloses a diaphragm and a preparation method and application thereof, and belongs to the technical field of diaphragms. The diaphragm comprises a base film and a ceramic coating; the ceramic coating contains first ceramic particles and second ceramic particles; along the thickness direction of the diaphragm, the ceramic coating comprises three regions connected in sequence; in the first region, the number ratio of the first ceramic particles to the second ceramic particles contained in 100 mu m 2 of the area is 1:25 to 1:50; in the third region, the number ratio of the first ceramic particles to the second ceramic particles contained in 100 mu m 2 of the area is 1:25 to 1:50; and in the second region, the number ratio of the first ceramic particles to the second ceramic particles contained in 100 mu m 2 of the area is 1:5 to 1:20. The diaphragm has good air permeability, electrolyte wettability and peeling strength, can relieve the wettability speed of water-soluble slurry to the ceramic coating, and improves the bonding effect of the ceramic coating and the base film after secondary processing.

Description

Technical Field

[0001] This invention relates to the field of diaphragm technology, and more specifically, to a diaphragm, its preparation method, and its application. Background Technology

[0002] When a water-soluble slurry is used to perform a secondary coating on the diaphragm, the ceramic coating that the diaphragm originally has will undergo secondary dissolution or swelling of the water-soluble binder contained within it after being impregnated by the water-soluble slurry. During the subsequent drying process, this part of the binder will float to the surface, resulting in a reduction of the binder contained in the diaphragm. This leads to a decrease in the peel force between the diaphragm and the base film, making it easy for problems such as coating powdering and peeling off, and an increase in product defect rate to occur.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a diaphragm, its preparation method, and its application, so as to solve or improve the above-mentioned technical problems.

[0005] This invention can be implemented as follows: In a first aspect, the present invention provides a diaphragm, the diaphragm comprising a base membrane and a ceramic coating disposed on at least one surface of the base membrane; The ceramic coating contains first ceramic particles and second ceramic particles, the average particle size of the first ceramic particles being larger than the average particle size of the second ceramic particles; along the thickness direction of the diaphragm, the ceramic coating includes a first region, a second region, and a third region; The first region extends from the side of the ceramic coating away from the base film towards the base film, covering an area of ​​10% to 30% of the total thickness of the ceramic coating; along the thickness direction of the separator, within the first region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:25 to 1:50; The third region extends from the interface between the ceramic coating and the base film, away from the base film, to a depth of 10% to 30% of the total thickness of the ceramic coating; along the thickness direction of the separator, within the third region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:25 to 1:50; The second region is located between the first and third regions; along the thickness direction of the membrane, in the second region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:5 to 1:20.

[0006] In an optional embodiment, the first ceramic particle has at least one of the following characteristics: Feature 1: The average particle size D1 of the first ceramic particles is 0.5μm~1μm; Feature 2: The aspect ratio of the first ceramic particles is 1:1 to 1.3:1; And / or, the average particle size D2 of the second ceramic particles is 0.05 μm to 0.2 μm.

[0007] In an optional embodiment, the ceramic coating also has at least one of the following characteristics: Feature 3: On the surface of the first region away from the base film, at least 90% of the ceramic particles contained in any 25μm×25μm area have a particle size range of (D1+D2) / 2 to D1. Feature 4: On the surface of the third region at the junction with the base film, at least 90% of the ceramic particles contained in any 25μm×25μm area have a particle size range of (D1+D2) / 2 to D1. Feature 5: The total thickness of the ceramic coating is 1.5μm~5μm; Feature 6: The 0s contact angle between the ceramic coating and the secondary slurry used for coating the surface of the first region is 30°~50°; preferably, the decrease in the contact angle of the ceramic coating to the secondary slurry within time t is θ=-at+b; where a is the decrease rate, a takes the value of 1° / s~2° / s, and b is the 0s contact angle, b takes the value of 35°~50°; Feature 7: The air permeability increase of the ceramic coating is 4cc / sec to 25cc / sec; Feature 8: The electrolytic wettability of the ceramic coating is 60 mm / min to 80 mm / min; Feature 9: The peel strength of the ceramic coating is 160 N / m to 200 N / mm.

[0008] In a second aspect, the present invention provides a method for preparing a diaphragm as described in any of the foregoing embodiments, comprising the following steps: coating a slurry containing first ceramic particles and second ceramic particles onto at least one side surface of a base membrane, and drying.

[0009] In an optional embodiment, the mass ratio of the first ceramic particles to the second ceramic particles in the slurry is 1:1 to 1:3.

[0010] In an optional embodiment, the preparation of the slurry includes: mixing a mixed ceramic, a binder, a dispersant, and a wetting agent with water; wherein the mass ratio of the mixed ceramic, the binder, the dispersant, and the wetting agent is 100:(2~4):(0.5~1):(0.1~0.5); the mixed ceramic is composed of first ceramic particles and second ceramic particles.

[0011] In an optional embodiment, the solid content of the slurry is 30% to 35%.

[0012] In an optional embodiment, the coating thickness of the slurry is 1.5 μm to 5 μm; And / or, the thickness of the base film is 5μm~25μm.

[0013] In an optional embodiment, the coating is performed using a microgravure coating method; the coating speed of microgravure coating is 80m / min to 200m / min.

[0014] In an optional embodiment, after coating, a first stage of drying is performed at 50°C to 60°C, followed by a second stage of drying at 60°C to 80°C.

[0015] Thirdly, the present invention provides a battery comprising a separator according to any of the foregoing embodiments.

[0016] The beneficial effects of this invention include: The diaphragm provided by this invention, by containing different proportions of first and second ceramic particles in different regions, can effectively slow down the wetting speed of water-soluble secondary slurry on the ceramic coating and improve the adhesion performance between the coating and the base film after secondary processing. Specifically, the different proportions of ceramic particles of varying sizes in the first region reduce the porosity and increase the density of the first region, which helps to prevent the water-based solvent from wetting the ceramic coating during secondary coating, avoiding a decrease in the adhesion of the ceramic coating after secondary coating due to wetting, thus hindering subsequent slitting processing. The different proportions of ceramic particles of varying sizes in the second region increase the gaps between ceramic particles, resulting in more porosity in the second region, which in turn improves the air permeability of the ceramic coating and the wetting ability of the electrolyte. The different proportions of ceramic particles of varying sizes in the third region increase the contact area between the third region and the base film, thereby improving the adhesion performance between the ceramic coating and the base film.

[0017] The aforementioned diaphragm exhibits good air permeability, electrolyte wettability, and peel strength, and can alleviate the wetting speed of water-soluble slurry on the ceramic coating, thereby improving the adhesion between the ceramic coating and the base film after secondary processing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1This is a schematic diagram showing the distribution of ceramic particles of different sizes within a 25μm×25μm region on the outer surface of a ceramic coating, where D1 represents the first ceramic particle and D2 represents the second ceramic particle. Figure 2 This is a schematic diagram showing the distribution of ceramic particles of different sizes in a certain region of the ceramic coating cross-section along the thickness direction of the diaphragm, where H1 represents the first region, H2 represents the second region, and H3 represents the third region. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The diaphragm, its preparation method, and its application provided by the present invention will be described in detail below.

[0022] The present invention provides a diaphragm comprising a base membrane and a ceramic coating disposed on at least one surface of the base membrane.

[0023] The ceramic coating contains first ceramic particles and second ceramic particles (such as...) Figure 1 As shown in the figure, the average particle size of the first ceramic particle is greater than that of the second ceramic particle.

[0024] In some optional embodiments, the average particle size D1 of the first ceramic particles can be 0.5 μm to 1 μm, such as 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, or other values ​​in the range of 0.5 μm to 1 μm.

[0025] The aspect ratio of the first ceramic particle can be from 1:1 to 1.3:1, such as 1:1, 1.1:1, 1.2:1, or 1.3:1, or other values ​​within the range of 1:1 to 1.3:1. That is, the first ceramic particle can be spherical or near-spherical. In some preferred embodiments, the first ceramic particle is near-spherical.

[0026] In this article, "aspect ratio" refers to the ratio of the longest axis (major axis) of the first ceramic particle on the same projection plane to the average minor axis (minor axis) perpendicular to that direction. Within the aforementioned aspect ratio range of 1:1 to 1.3:1, the larger the aspect ratio, the better the first ceramic particle can provide support within the ceramic coating, resulting in larger gaps between particles and a lower packing density, which facilitates the filling of smaller second ceramic particles.

[0027] In some optional embodiments, the average particle size D2 of the second ceramic particles can be 0.05 μm to 0.2 μm, such as 0.05 μm, 0.1 μm, 0.15 μm, or 0.2 μm, or other values ​​within the range of 0.05 μm to 0.2 μm. This invention does not limit the aspect ratio of the second ceramic particles, but preferably the second ceramic particles are spherical.

[0028] In this invention, such as Figure 2 As shown, along the thickness direction of the diaphragm, the ceramic coating includes a first region, a second region, and a third region.

[0029] The first region is a region extending from the side of the ceramic coating away from the base film towards the base film, accounting for 10% to 30% of the total thickness of the ceramic coating; the third region is a region extending from the interface between the ceramic coating and the base film away from the base film, accounting for 10% to 30% of the total thickness of the ceramic coating; and the second region is the region located between the first region and the third region.

[0030] In some alternative embodiments, along the thickness direction of the diaphragm, in the first region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles within the area is 1:25 to 1:50, such as 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50, or other values ​​within the range of 1:25 to 1:50. Further, along the thickness direction of the diaphragm, in the first region, per 100 μm... 2 The ratio of the number of first ceramic particles to the number of second ceramic particles within the area is 1:28 to 1:45. The number of smaller-diameter ceramic particles (second ceramic particles) is significantly greater than the number of larger-diameter ceramic particles (first ceramic particles), which can reduce the voids in the first region, increase the density of the first region, and thus help to shield the ceramic coating from the wetting of moisture or water-soluble secondary slurry.

[0031] Along the thickness direction of the diaphragm, in the second region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles within the area is 1:5 to 1:20, such as 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, or 1:20, or other values ​​within the range of 1:5 to 1:20. Further, along the thickness direction of the diaphragm, in the second region, per 100 μm... 2The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:12 to 1:20. Compared with the first and third regions, the second region has a higher proportion of large-diameter ceramic particles (first ceramic particles), which can reduce the packing density of the second region and give the second region a higher porosity, thereby helping the product to have good air permeability.

[0032] Along the thickness direction of the diaphragm, in the third region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles within the area is 1:25 to 1:50, such as 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50, or other values ​​within the range of 1:25 to 1:50. Further, along the thickness direction of the diaphragm, in the third region, per 100 μm... 2 The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:30 to 1:48. In the third region, the number of small-diameter ceramic particles (second ceramic particles) is significantly greater than the number of large-diameter ceramic particles (first ceramic particles), which is beneficial to increasing the contact area between the third region and the base film, thereby improving the adhesion performance of the ceramic coating to the base film.

[0033] In some alternative embodiments, on the surface of the first region away from the base film (referred to herein as the "ceramic coating outer surface"), at least 90% of the ceramic particles contained within any 25 μm × 25 μm area have a particle size ranging from (D1 + D2) / 2 to D1. Further, on the surface of the first region away from the base film, at least 90% of the ceramic particles contained within any 25 μm × 25 μm area have a particle size ranging from 0.35 μm to 0.65 μm.

[0034] If at least 90% of the ceramic particles on the surface of the first region have a particle size range of less than (D1+D2) / 2, it indicates that the surface of the first region contains too many small-diameter ceramic particles. This will make the surface of the first region too dense, which will not only prevent the aqueous solvent from wetting the surface, but also affect the wetting of the electrolyte, thereby affecting the subsequent battery rate and cycle performance. If at least 90% of the ceramic particles have a particle size range greater than D1, it indicates that the surface of the first region contains too many large-diameter ceramic particles. This will accelerate the wetting of the ceramic coating by the aqueous solvent, resulting in a significant decrease in the adhesion of the ceramic coating after secondary coating.

[0035] In some optional embodiments, in any 25 μm × 25 μm area of ​​the surface at the interface between the third region and the base film (referred to herein as the "inner surface of the ceramic coating"), at least 90% of the ceramic particles contain a particle size ranging from (D1+D2) / 2 to D1. Further, in any 25 μm × 25 μm area of ​​the surface at the interface between the third region and the base film, at least 90% of the ceramic particles contain a particle size ranging from 0.32 μm to 0.62 μm.

[0036] If at least 90% of the ceramic particles on the surface of the third region have a particle size range smaller than (D1+D2) / 2, it indicates that the surface of the third region contains too many small-diameter ceramic particles, which can easily clog the membrane pores and worsen the air permeability. If at least 90% of the ceramic particles have a particle size range larger than D1, it indicates that the surface of the third region contains too many large-diameter ceramic particles, which will reduce the contact area between the third region and the base membrane, thereby leading to poor adhesion between the entire ceramic coating and the base membrane and reduced peel strength.

[0037] In some alternative embodiments, the total thickness of the ceramic coating is 1.5 μm to 5 μm, such as 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, or other values ​​within the range of 1.5 μm to 5 μm.

[0038] In some alternative embodiments, the 0s contact angle between the ceramic coating and the secondary slurry used for coating the surface of the first region is 30° to 50°. In some more typical embodiments, the 0s contact angle between the ceramic coating and the secondary slurry used for coating the surface of the first region is 35° to 47.5°.

[0039] In some alternative embodiments, the 2s contact angle between the ceramic coating and the secondary slurry used for coating the surface of the first region is 30° to 45°.

[0040] Ceramic coatings with the aforementioned contact angle range allow for a slower wetting rate of subsequent secondary slurries, which improves processing controllability. If the contact angle is too small, wetting will be too rapid, causing the binder inside the ceramic coating to dissolve or swell; conversely, if the contact angle is too small, the secondary slurry will fail to wet the ceramic coating, hindering secondary coating.

[0041] In some alternative embodiments, the contact angle of the ceramic coating to the secondary slurry decreases by θ = -at + b over time t; where a is the decreasing rate, and a takes the value of 1° / s to 2° / s, and b is the contact angle at 0s, and b takes the value of 35° to 50°.

[0042] In some alternative embodiments, the air permeability increment of the ceramic coating is 4 cc / sec to 25 cc / sec. In some more typical embodiments, the air permeability increment of the ceramic coating is 6 cc / sec to 21 cc / sec.

[0043] In some alternative embodiments, the electrowetting rate of the ceramic coating is 60 mm / min to 80 mm / min. In some more typical embodiments, the electrowetting rate of the ceramic coating is 64 mm / min to 79 mm / min.

[0044] In some alternative embodiments, the peel strength of the ceramic coating is 160 N / m to 200 N / mm.

[0045] Continuing from the above, the diaphragm provided by this invention contains a specific ceramic coating that effectively slows down the wetting speed of the water-soluble secondary slurry on the ceramic coating, improving the adhesion between the ceramic coating and the base membrane after secondary processing. Specifically, in the first region of the ceramic coating, the increased content of small-diameter ceramic particles reduces the porosity within the first region, increasing its density and preventing the water-based solvent from wetting the ceramic coating during secondary coating. This avoids a decrease in the adhesion of the ceramic coating after secondary coating due to wetting, which would be detrimental to subsequent slitting processes. In the second region of the ceramic coating, the increased content of large-diameter ceramic particles increases the gaps between ceramic particles, resulting in more porosity in the second region and thus improving the air permeability of the ceramic coating and the wetting ability of the electrolyte. In the third region of the ceramic coating, the high content of small-diameter ceramic particles increases the contact area between the third region and the base membrane, thereby improving the adhesion between the ceramic coating and the base membrane. Furthermore, the aspect ratio of the large-diameter ceramic particles in the ceramic coating of this invention facilitates structural interlocking within the ceramic coating, enhancing the peel strength of the diaphragm.

[0046] Accordingly, the present invention also provides a method for preparing the above-mentioned diaphragm, comprising the following steps: coating a slurry containing first ceramic particles and second ceramic particles onto at least one side surface of a base membrane, and drying.

[0047] In some alternative embodiments, the mass ratio of the first ceramic particles and the second ceramic particles in the slurry can be from 1:1 to 1:3, such as 1:1, 1:1.5, 1:2, 1:2.5 or 1:3, or other values ​​within the range of 1:1 to 1:3.

[0048] Malvern particle size analyzer tests show that as the mass proportion of small-diameter ceramic particles increases, the particle size distribution changes from a unimodal distribution to a bimodal distribution, with the bimodal distribution structure being preferred. This structure increases the proportion of small-diameter ceramic particles within the system, and the size difference between small and large particles is relatively large, which is beneficial for small-diameter ceramic particles to fill the gaps between large-diameter ceramic particles and to achieve multidirectional migration of small-diameter ceramic particles during the drying process.

[0049] In some optional embodiments, the preparation of the slurry may include mixing a mixed ceramic, a binder, a dispersant, and a wetting agent with water. The mixed ceramic consists of first ceramic particles and second ceramic particles. The mass ratio of the mixed ceramic, binder, dispersant, and wetting agent may be 100:(2~4):(0.5~1):(0.1~0.5).

[0050] For example, the mass ratio of the mixed ceramic to the binder can be 100:2, 100:2.5, 100:3, 100:3.5 or 100:4, or other values ​​within the range of 100:(2~4).

[0051] For example, the mass ratio of the mixed ceramic to the dispersant can be 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9 or 100:1, or other values ​​within the range of 100:(0.5~1).

[0052] For example, the mass ratio of the mixed ceramic to the wetting agent can be 100:0.1, 100:0.2, 100:0.3, 100:0.4 or 100:0.5, or other values ​​within the range of 100:(0.1~0.5).

[0053] The binders, dispersants and wetting agents mentioned above can be substances commonly used in the art, and no further limitations are imposed here.

[0054] In some alternative embodiments, the solid content of the slurry can be 30% to 35%, such as 30%, 31%, 32%, 33%, 34% or 35%, or other values ​​within the range of 30% to 35%.

[0055] In some optional embodiments, the coating thickness of the slurry can be 1.5μm to 5μm, such as 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, or other values ​​within the range of 1.5μm to 5μm.

[0056] In some optional embodiments, the thickness of the base film can be 5μm to 25μm, such as 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm or 25μm, or other values ​​within the range of 5μm to 25μm.

[0057] In some alternative embodiments, the coating can be performed using a microgravure coating method. The coating speed of microgravure coating can be 80 m / min to 200 m / min, such as 80 m / min, 100 m / min, 120 m / min, 150 m / min, 180 m / min or 200 m / min, or other values ​​within the range of 80 m / min to 200 m / min.

[0058] The aforementioned coating speed provides sufficient time for the second ceramic particles to float and sink. A slow coating speed results in an excessive amount of second ceramic particles floating and sinking, leading to an overabundance of particles in both the first and third regions. Excessive floating of small-diameter ceramic particles causes the outer surface of the ceramic coating to become too dense, hindering wetting by aqueous solvents and affecting electrolyte wetting, thus impacting subsequent battery rate and cycle performance. Excessive sinking of small-diameter ceramic particles can clog membrane pores, worsening permeability. Conversely, a fast coating speed results in insufficient floating and sinking of the second ceramic particles, leading to an insufficient amount in both the first and third regions. Insufficient floating of small-diameter ceramic particles can cause the outer surface of the ceramic coating to become easily wetted, reducing adhesion after secondary coating and hindering subsequent slitting. Insufficient sinking of small-diameter ceramic particles results in a small contact area between the third region and the base film, leading to poor adhesion between the ceramic coating and the base film.

[0059] In some alternative embodiments, after coating, a first stage of drying is performed at 50°C to 60°C (e.g., 50°C, 55°C, or 60°C), followed by a second stage of drying at 60°C to 80°C (e.g., 60°C, 70°C, or 80°C).

[0060] For example, the drying is carried out by the drying method. The drying length in the oven is L. The drying temperature corresponding to the first L / 4 length is 50℃~60℃, and the drying temperature corresponding to the last 3L / 4 length is 60℃~80℃.

[0061] The first stage of drying described above is the pre-drying stage. This stage mainly involves the second ceramic particles settling downwards due to their own gravity. That is, under the influence of gravity, some of the second ceramic particles in the slurry are deposited into the lower region (third region) of the ceramic coating through the gaps between the larger-diameter first ceramic particles. Subsequently, through the second stage of drying, the moisture in the slurry evaporates more quickly, causing some of the smaller-diameter second ceramic particles to migrate upwards to the upper region (first region) of the ceramic coating. This results in the formation of first, second, and third regions of ceramic coating with different distributions and proportions of ceramic particles.

[0062] In addition, the present invention also provides a battery comprising the above-mentioned separator, which can have better rate performance and cycle performance, etc.

[0063] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0064] Example 1 This embodiment provides a membrane, the preparation method of which includes: S1: Ceramic blend.

[0065] First ceramic particles and second ceramic particles were mechanically mixed at a mass ratio of 1:2 using a dispersing plate to obtain a mixed ceramic. The first ceramic particles were alumina with an average particle size D1 of 0.8 μm and an aspect ratio of 1.2:1; the second ceramic particles were alumina with an average particle size D2 of 0.1 μm. The particle size distribution of the mixed ceramic was measured using a Malvern 3000 micrometer, and the resulting particle size distribution curve showed a bimodal distribution.

[0066] S2: Slurry preparation.

[0067] 100g of mixed ceramics was added to 188.96g of deionized water containing 0.7g of dispersant (sodium polyacrylate) and mechanically stirred for 30min. Then, 3g of binder (polyacrylamide aqueous solution with a solid content of 25%) was added and stirred for another 30min. Finally, 0.3g of wetting agent (sodium dodecyl sulfate) was added and stirred to obtain a slurry with a solid content of approximately 34.13%.

[0068] S3: Diaphragm coating.

[0069] The above slurry was coated onto the surface of a PE diaphragm with a thickness of 7 μm at a coating speed of 130 m / min using a micro-gravure coating method, resulting in a coating thickness of 2 μm. Subsequently, the diaphragm was dried in a 20 m long oven. The first 5 meters of the oven were dried at 55 °C, and the remaining 15 meters were dried at 75 °C to obtain the diaphragm.

[0070] Example 2 The difference between this embodiment and Embodiment 1 is that in S1, the mass ratio of the first ceramic particles to the second ceramic particles is 1:1. The distribution peak shape of the mixed ceramic is unimodal.

[0071] Example 3 The difference between this embodiment and Embodiment 1 is that in S1, the mass ratio of the first ceramic particle to the second ceramic particle is 1:3.

[0072] Example 4 The difference between this embodiment and Embodiment 1 is that the average particle size D1 of the first ceramic particles is 0.5 μm; and the average particle size D2 of the second ceramic particles is 0.05 μm.

[0073] Example 5 The difference between this embodiment and Embodiment 1 is that the average particle size D1 of the first ceramic particles is 1 μm; and the average particle size D2 of the second ceramic particles is 0.2 μm.

[0074] Example 6 The difference between this embodiment and Embodiment 1 is that in S1, the aspect ratio of the first ceramic particle is 1.3:1.

[0075] Example 7 The difference between this embodiment and Embodiment 1 is that in S1, the aspect ratio of the first ceramic particle is 1.1:1.

[0076] Example 8 The difference between this embodiment and embodiment 1 is that in S3, the first stage of drying is carried out at 60°C within the first 5 meters of the oven; and the second stage of drying is carried out at 80°C within the last 15 meters of the oven.

[0077] Example 9 The difference between this embodiment and embodiment 1 is that in S3, the first stage of drying is carried out at 50°C within the first 5 meters of the oven; and the second stage of drying is carried out at 60°C within the last 15 meters of the oven.

[0078] Example 10 The difference between this embodiment and embodiment 8 is that in S3, the coating speed is 200m / min.

[0079] Example 11 The difference between this embodiment and embodiment 8 is that in S3, the coating speed is 80m / min.

[0080] Example 12 The difference between this embodiment and embodiment 8 is that in S2, the mass ratio of the mixed ceramic, binder, dispersant, and wetting agent is 100:2:0.5:0.1; the solid content of the slurry is 30%. The amount of mixed ceramic used is the same as in embodiment 1.

[0081] Example 13 The difference between this embodiment and embodiment 8 is that in S2, the mass ratio of the mixed ceramic, binder, dispersant, and wetting agent is 100:4:1:0.5; and the solid content of the slurry is 35%. The amount of mixed ceramic used is the same as in embodiment 1.

[0082] Comparative Example 1 The difference between this comparative example and Example 1 is that the drying process was carried out at a temperature of 75°C throughout the oven.

[0083] Comparative Example 2 The difference between this comparative example and Example 1 is that the drying process was carried out at a temperature of 55°C throughout the oven.

[0084] Comparative Example 3 The difference between this comparative example and Example 1 is that in S1, the mass ratio of the first ceramic particles to the second ceramic particles is 2:1. The distribution peak shape of the mixed ceramic is unimodal.

[0085] Comparative Example 4 The difference between this comparative example and Example 1 is that in S1, the mass ratio of the first ceramic particles to the second ceramic particles is 1:4. The distribution peak shape of the mixed ceramic is unimodal.

[0086] Comparative Example 5 The difference between this comparative example and Example 1 is that in S1, the average particle size D1 of the first ceramic particles is 1.3 μm, and the average particle size D2 of the second ceramic particles is 0.02 μm. The distribution peak shape of the mixed ceramic is unimodal.

[0087] Comparative Example 6 The difference between this comparative example and Example 1 is that in S1, the average particle size D1 of the first ceramic particle is 0.4 μm, and the average particle size D2 of the second ceramic particle is 0.3 μm.

[0088] Comparative Example 7 The difference between this comparative example and Example 1 is that in S1, the aspect ratio of the first ceramic particle is 1.4:1.

[0089] Comparative Example 8 The difference between this comparative example and Example 1 is that in S3, the coating speed is 60 m / min.

[0090] Comparative Example 9 The difference between this comparative example and Example 1 is that in S3, the coating speed is 220 m / min.

[0091] Test case The membranes prepared in Examples 1-13 and Comparative Examples 1-9 were subjected to performance tests. The test methods and test results are as follows, and the test results are shown in Tables 1 and 2.

[0092] (1) SEM images were taken of the surface of the first region of the diaphragm away from the base film (outer surface of the ceramic coating). ImageJ software was used to statistically analyze the particle size of the exposed ceramic within any 25μm×25μm area. Excel software was used to obtain the D. 90 The particle size (denoted as outer surface D)V90 ).

[0093] SEM images were taken of the interface surface (inner surface of the ceramic coating) between the third region and the base membrane in the diaphragm. ImageJ software was used to statistically analyze the particle size of the exposed ceramic within any 25μm × 25μm area. Excel software was used to obtain the D... 90 The particle size (denoted as inner surface D) V90 ).

[0094] The first region is a region extending from the side of the ceramic coating away from the base film towards the base film, accounting for 10% to 30% of the total thickness of the ceramic coating; the third region is a region extending from the interface between the ceramic coating and the base film away from the base film, accounting for 10% to 30% of the total thickness of the ceramic coating; and the second region is the region located between the first region and the third region.

[0095] (2) Along the thickness direction of the diaphragm, SEM images were taken of the cross-section of the diaphragm, and the 100μm area in each region was statistically analyzed using a Nano Measurer. 2 The number of first ceramic particles and second ceramic particles contained in the area is determined, and the ratio of the number of first ceramic particles to the number of second ceramic particles is calculated (that is, the ratio of the number of large-diameter ceramic particles to the number of small-diameter ceramic particles).

[0096] (3) Contact angle: The contact angle measuring instrument SDC-200S purchased from Guangdong Dongguan Shengding Precision Instrument Co., Ltd. was used for testing.

[0097] (4) Diaphragm permeability: The diaphragm permeability value was tested using the Xiong Gu Wang Yan Shi 0518-P air permeability meter, which is the time required for 100cc of air to pass through, to evaluate the diaphragm permeability performance.

[0098] (5) Electrolyte wettability: Take 20 μL of a mixed electrolyte with a solvent composition of ethylene carbonate (EC): diethyl carbonate (DEC): methyl ethyl carbonate (EMC) = 1:1:1 (volume ratio) and containing 1 mol / L LiPF6 and drop it onto a 0.5 cm wide diaphragm. Measure the corresponding wetting distance within 1 min.

[0099] (6) Peel strength: A layer of double-sided tape is pasted on the steel plate, the diaphragm is placed flat and lightly pressed on the double-sided tape, and then a layer of test tape is pasted on the surface of the first area of ​​the diaphragm. The pressure roller (2000g) is held and rolled back and forth on the test tape three times. One end of the tape is torn to the middle of the sample, and the tensile testing machine is used to peel it 180 degrees at a peeling speed of 50mm / min and a peeling test time of 1min. The test tensile strength value is divided by the width of the corresponding tape to obtain the final peel force N / m.

[0100] The peel strength of the sample with the secondary coating was tested in the manner described in (6) above, except that the test sample was replaced with a sample with the secondary coating.

[0101] Peel strength reduction rate = [(peel strength - peel strength including secondary coating) / peel strength] × 100%.

[0102] Table 1 Test Results

[0103] Table 2 Test Results

[0104] As can be seen from Tables 1 and 2, all of Examples 1 to 13 can obtain diaphragms with better overall performance.

[0105] In Examples 1-3, by adjusting the mixing ratio of the first and second ceramic particles, as the proportion of small-diameter alumina (the second ceramic particle) increases, the volume distribution of the mixed ceramic formed by it and the first ceramic particle changes from a unimodal distribution to a bimodal distribution, with a significant difference in the number of the two particle sizes. This results in a difference in the number of small-diameter particles sinking due to gravity and floating due to solvent evaporation during the drying process in S3. The more small-diameter ceramic particles in the mixed ceramic, the more they sink and float, thus increasing the number of small-diameter ceramic particles on the outer and inner surfaces of the ceramic coating. When the number of small-diameter ceramic particles on the outer surface of the ceramic coating increases, it is more conducive to forming a dense coating, which helps to prevent the water-based solvent from wetting the ceramic coating during the second coating, avoiding a decrease in the adhesion of the ceramic coating after the second coating due to wetting, which would be detrimental to subsequent slitting processing. The number of small-diameter ceramic particles on the inner surface of the ceramic coating affects the contact area between the ceramic coating and the base film. When the number of small-diameter ceramic particles increases, the peel force between the ceramic coating and the base film is better.

[0106] In Comparative Example 3, the excessive proportion of large-diameter ceramic particles led to an increase in the number of large-diameter ceramic particles on the outer surface of the ceramic coating. This accelerated the wetting of the ceramic coating by the water-based solvent, resulting in a significant decrease in the adhesion of the ceramic coating after secondary coating. At the same time, there were also too many large-diameter ceramic particles on the inner surface of the ceramic coating, which reduced the effective contact area between the ceramic diaphragm and the base film, resulting in a lower peel strength between the ceramic coating and the base film.

[0107] In Comparative Example 4, the excessive proportion of small-diameter ceramic particles resulted in too many small-diameter ceramic particles floating and sinking. Among them, the floating small-diameter ceramic particles caused the outer surface of the ceramic coating to be too dense, which not only prevented the aqueous solvent from wetting the ceramic, but also affected the wetting of the electrolyte, thereby affecting the subsequent battery rate and cycle performance.

[0108] Comparing Examples 1, 4-5, and Comparative Example 6, it can be seen that, under the same mass, changing the particle size of the ceramic particles results in different quantities of ceramic particles with different sizes. Larger particle sizes result in fewer ceramic particles, while smaller particle sizes result in more ceramic particles, which is equivalent to adjusting the blending ratio by adjusting the particle size.

[0109] In addition, Comparative Example 5 uses two ceramics with greater size differences, which contain too many small-diameter ceramic particles, resulting in a large number of small-diameter ceramic particles accumulating on the outer and inner surfaces of the ceramic coating, producing a result similar to that of Comparative Example 4.

[0110] In Examples 6 and 7, by adjusting the aspect ratio of the large-diameter ceramic particles based on Example 1, a simple mechanical interlocking structure can be constructed by controlling the number of large-diameter particles in the second region to be close, thereby enhancing the peel strength of the ceramic coating. In Comparative Example 7, the aspect ratio is too high, which increases the migration distance on the basis of forming the interlocking structure, resulting in an increase in the number of small-diameter particles in the second region and reducing the peel strength of the ceramic coating.

[0111] Comparing Examples 1, 8, and 9 with Comparative Examples 1 and 2 reveals that the oven temperature range has a certain impact on the particle size distribution of the coating. Using a lower initial drying temperature allows time for the small-diameter ceramic particles inside the ceramic coating to settle. Increasing the drying temperature at the later stage increases the evaporation rate of the aqueous solvent, causing the small-diameter ceramic particles to float due to capillary action. This results in differences in the number of large and small-diameter ceramic particles in the first, second, and third regions of the ceramic coating. In the first region, a reasonable increase in the number of small-diameter ceramic particles improves the density of the outer surface of the ceramic coating, reduces the wetting of the ceramic coating by the aqueous solvent, and slows down the wetting rate, thus helping the ceramic coating maintain good adhesion after secondary coating. However, if there are too many small-diameter ceramic particles in this region, it will affect the electrolyte wetting performance. In the second region, a reasonable decrease in the number of small-diameter ceramic particles allows for a relatively high porosity, which is beneficial for improving air permeability. In the third region, a reasonable increase in the number of small-diameter ceramic particles can improve the density of the inner surface of the ceramic coating, increase the contact area between the ceramic coating and the base film, and improve the peel strength between the ceramic coating and the base film; however, if there are too many small-diameter ceramic particles in this region, they can easily clog the membrane pores and deteriorate the air permeability.

[0112] Comparative examples 10, 11, 8, and 9 show that coating speed is a significant factor affecting the distribution of small particle sizes in this invention. A moderate coating speed allows sufficient migration time for the small particles, resulting in good breathability and reduced wetting of the ceramic coating by the water-soluble slurry. When the coating speed is too high, the small particles do not have enough time to migrate, leading to deterioration of peel strength, particularly hindering the adhesion between the ceramic coating and the base film after secondary processing. Conversely, a slow coating speed results in insufficient migration time, causing the small particles in the first and third regions to enlarge, potentially clogging the membrane pores and worsening breathability.

[0113] In summary, the diaphragm provided by the present invention has good air permeability, electrolyte wettability and peel strength, and can alleviate the wetting speed of water-soluble slurry on ceramic coating, thereby improving the adhesion between ceramic coating and base film after secondary processing.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that, The diaphragm includes a base membrane and a ceramic coating disposed on at least one surface of the base membrane; The ceramic coating contains first ceramic particles and second ceramic particles, wherein the average particle size of the first ceramic particles is larger than the average particle size of the second ceramic particles; along the thickness direction of the diaphragm, the ceramic coating includes a first region, a second region, and a third region; The first region is a region extending from the side of the ceramic coating away from the base film towards the base film, covering an area of ​​10% to 30% of the total thickness of the ceramic coating; along the thickness direction of the separator, in the first region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:25 to 1:50; The third region extends from the interface between the ceramic coating and the base film, away from the base film, to a depth of 10% to 30% of the total thickness of the ceramic coating; along the thickness direction of the diaphragm, within the third region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:25 to 1:50; The second region is the area located between the first region and the third region; along the thickness direction of the membrane, in the second region, every 100 μm 2 The ratio of the number of first ceramic particles to the number of second ceramic particles contained in the area is 1:5 to 1:

20.

2. The diaphragm according to claim 1, characterized in that, The first ceramic particle has at least one of the following characteristics: Feature 1: The average particle size D1 of the first ceramic particles is 0.5 μm to 1 μm; Feature 2: The aspect ratio of the first ceramic particles is 1:1 to 1.3:1; And / or, the average particle size D2 of the second ceramic particles is 0.05 μm to 0.2 μm.

3. The diaphragm according to claim 1 or 2, characterized in that, The ceramic coating also has at least one of the following characteristics: Feature 3: In the first region, on the surface away from the base film, at least 90% of the ceramic particles contained in any 25μm×25μm area have a particle size range of (D1+D2) / 2 to D1. Feature 4: On the surface of the third region at the junction with the base film, at least 90% of the ceramic particles contained in any 25μm×25μm area have a particle size range of (D1+D2) / 2 to D1. Feature 5: The total thickness of the ceramic coating is 1.5μm~5μm; Feature 6: The 0s contact angle between the ceramic coating and the secondary slurry used for coating the surface of the first region is 30°~50°; preferably, the decrease in the contact angle of the ceramic coating to the secondary slurry within time t is θ=-at+b; where a is the decrease rate, a takes the value of 1° / s~2° / s, and b is the 0s contact angle, b takes the value of 35°~50°; Feature 7: The air permeability increase of the ceramic coating is 4cc / sec to 25cc / sec; Feature 8: The electrolytic wettability of the ceramic coating is 60 mm / min to 80 mm / min; Feature 9: The peel strength of the ceramic coating is 160 N / m to 200 N / mm.

4. A method for preparing a diaphragm as described in any one of claims 1 to 3, characterized in that, The process includes the following steps: coating a slurry containing the first ceramic particles and the second ceramic particles onto at least one side of the base film and drying it.

5. The preparation method according to claim 4, characterized in that, In the slurry, the mass ratio of the first ceramic particles to the second ceramic particles is 1:1 to 1:

3.

6. The preparation method according to claim 5, characterized in that, The preparation of the slurry includes: mixing a mixed ceramic, a binder, a dispersant, and a wetting agent with water; wherein the mass ratio of the mixed ceramic, the binder, the dispersant, and the wetting agent is 100:(2~4):(0.5~1):(0.1~0.5); the mixed ceramic is composed of the first ceramic particles and the second ceramic particles; Preferably, the solid content of the slurry is 30% to 35%.

7. The preparation method according to claim 5, characterized in that, The coating thickness of the slurry is 1.5μm~5μm; And / or, the thickness of the base film is 5μm~25μm.

8. The preparation method according to claim 4, characterized in that, The coating is performed using a microgravure coating method; the coating speed of microgravure coating is 80m / min~200m / min.

9. The preparation method according to any one of claims 4 to 8, characterized in that, After coating, the first stage of drying is carried out at 50℃~60℃, and the second stage of drying is carried out at 60℃~80℃.

10. A battery, characterized in that, Includes the diaphragm as described in any one of claims 1 to 3.

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