Battery separator, method for manufacturing the same, and secondary battery

Abstract

The application discloses a battery diaphragm, a preparation method thereof and a secondary battery, and relates to the technical field of secondary batteries.The battery diaphragm provided by the application has a base material and a regular point pattern, the point pattern has a hollow region, and the diaphragm can better balance the adhesion of the pole piece, the air permeability and the performance of the internal resistance of the battery.In a further preferred scheme, the point pattern on the surface of the base material has a height difference, and the polymer particles are regularly distributed, so that the electrolyte wettability is better, the particles in a single pattern are more uniformly stacked, the impedance performance is slightly improved, and the uniformity of the diaphragm performance is better ensured.

Description

Technical Field

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

[0002] Currently, the commonly used coating methods for lithium battery separators in industry are spin coating and gravure coating. Spin coating suffers from problems such as uneven spray dot size and height, and difficulty in controlling coverage, making it difficult to guarantee stable electrode adhesion and electrolyte wettability. Furthermore, because it is a non-contact coating method, it generates a large amount of dust during spraying, which is harmful to health and the environment. Gravure coating, on the other hand, has difficulty controlling coverage, and the coating coverage is often above 70%, which not only consumes a large amount of slurry, increasing costs in industrial production, but also makes it difficult to guarantee suitable air permeability and ionic conductivity of the separator.

[0003] Therefore, there is an urgent need to improve the membrane structure in order to enhance the wettability of the electrolyte and improve the battery impedance performance.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a battery separator, its preparation method, and a secondary battery, which aims to improve the wettability of the electrolyte and improve impedance performance.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a battery separator, comprising a substrate and a plurality of dot-shaped patterns regularly distributed on at least one side surface of the substrate, wherein the dot-shaped patterns have hollow areas, and the ratio of the maximum height H of the dot-shaped patterns to the minimum height h satisfies: 0.1 < h / H < 1.

[0007] In an optional implementation, the ratio of the maximum height H to the minimum height h of the dot pattern satisfies: 0.3 ≤ h / H ≤ 0.8; And / or, the maximum height H of the dot pattern ranges from 4.6 μm to 9 μm; And / or, the number of dot patterns on a unit area substrate is 150-650 per cm. 2 .

[0008] In an optional embodiment, the dot pattern is circular, with the outermost radius R of the dot pattern being 100μm-250μm. A circular hollow area is provided near the center, and the radius r of the circular hollow area satisfies: 0.75R≥r≥0.25R.

[0009] In an optional embodiment, the dot pattern has N ring structures with the same center, N≥2, and the height difference ΔH1 between the highest and lowest points in adjacent ring structures is 1μm-4μm, preferably 2μm-3μm; Preferably, the height of the ring structure gradually increases from the center to the edge of the dot pattern; Preferably, N takes the value of 2-6, and more preferably 2-3.

[0010] In an optional implementation, in a single dot pattern, the total width of the ring structures whose bulge height is 20%-50% of the height of the highest ring structure accounts for 20%-50% of the total outer diameter of the dot pattern.

[0011] Secondly, the present invention provides a method for preparing a battery separator according to any of the foregoing embodiments, comprising: Provide base materials; The paste is transferred to one side of the substrate using a printing roller that meets the requirements of the dot pattern structure, and then dried to obtain a battery separator with a substrate and a dot pattern.

[0012] In an optional embodiment, the slurry used to form the dot pattern comprises, by weight percentage: 12.0-13.5 wt% polymer, 0.5-1.2 wt% binder, 0.5-1.2 wt% dispersant, and the remainder being solvent.

[0013] In an optional embodiment, the solid content of the slurry is 3-15.0 wt%; And / or, the polymer is selected from at least one of polyvinylidene fluoride copolymers, polyvinylidene fluoride homopolymers, acrylate polymers, methacrylate polymers, polyimides, and polyethylene waxes; preferably, the polymer has a crystallinity of 10-25%; And / or, the adhesive comprises copolymers, homopolymers or modified versions of at least one of acrylic acid, acrylates, acrylonitrile, and styrene; And / or, the dispersant is selected from at least one of sodium polyacrylate, polyether siloxane, polyether-modified siloxane, and sodium dodecylbenzenesulfonate.

[0014] In an optional embodiment, the printing roller has an annular pattern, and the annulus has a gradient structure; And / or, control the wrap angle between the substrate and the back roller to be 30-120°. The back roller is a roller used to support the substrate and cooperate with the printing roller or the slurry extrusion die to perform dot coating. Preferably, control the wrap angle between the substrate and the back roller to be 60-90°. And / or, control the drying temperature to 60℃-80℃.

[0015] Thirdly, the present invention provides a secondary battery, comprising the battery separator of any of the foregoing embodiments or the battery separator prepared by any of the foregoing embodiments.

[0016] The present invention has the following beneficial effects: The battery separator provided by the present invention has a substrate and a regular dot pattern, and the dot pattern has hollow areas, which can better balance the performance of separator electrode adhesion, air permeability and battery internal resistance. In a further preferred embodiment, the dot pattern on the substrate surface has a height difference and the polymer particles are regularly distributed, which makes the electrolyte wettability better, and at the same time makes the particle accumulation in a single pattern more uniform, slightly improving the impedance performance and better ensuring the uniformity of separator performance. Attached Figure Description

[0017] 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.

[0018] Figure 1 This is a schematic diagram of a battery separator provided in one embodiment of the present invention; Figure 2 A schematic diagram of a battery separator provided in another embodiment of the present invention; Figure 3 for Figure 2 A schematic diagram of a single dot pattern; Figure 4 for Figure 2 A cross-sectional schematic diagram of a dotted pattern; Figure 5 This is a schematic diagram of the coating equipment. Figure 6 This is a schematic diagram of the coating roller structure; Figure 7 A schematic diagram defining the wrap angle.

[0019] Key component symbols: 100 - Battery separator; 110 - Substrate; 120 - Dot pattern; 121 - First ring structure; 122 - Second ring structure; 123 - Third ring structure; 001 - Hollowed-out area; 101-Printing roller; 1011-Roller body; 1012-Protrusion; 200-Material box; 310-Feeding roller; 320-Transfer roller; 330-Back roller; 340-Discharge roller; 350-Scraper. 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] Regular dot matrix coating is a non-full-coverage contact coating method. It involves applying the paste in regular dots onto the diaphragm using regularly etched protrusions on a printing roller, which can solve the problem of difficult coverage control. However, existing solutions use a regularly distributed dot-shaped coating layer on the substrate. Although this slightly improves adhesion and air permeability, the irregular distribution of particles in the dot-shaped areas (e.g., the particles in the center are too densely packed) is not conducive to ion permeation, resulting in poor impedance and wetting performance.

[0022] like Figure 1 As shown, an embodiment of the present invention provides a battery separator 100, including a substrate 110 and a plurality of dot patterns 120 coated on at least one side surface of the substrate 110. The dot patterns 120 are regularly distributed, and the distribution of the dot patterns 120 is not limited to a matrix.

[0023] Combination Figure 1 , Figure 2 , Figure 3 and Figure 4 The dot pattern 120 has a hollow area 001, which can be located at the center, but is not limited to this. The ratio of the maximum height H to the minimum height h of the dot pattern 120 satisfies: 0.1 < h / H < 1, that is, the surface of the dot pattern 120 is an irregular plane with a specific height difference. The value of h / H can be 0.11, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 0.95, etc., preferably 0.3 ≤ h / H ≤ 0.8. By adjusting the value of h / H, it is beneficial to improve the stress concentration in the thickness direction of the coated separator during battery assembly or battery charge-discharge cycles, improve the adhesion of the coated separator, and thus reduce the internal resistance of the battery. If the h / H value is too low, for example below 0.3, the difference between the lowest and highest points of the dot pattern is large. The lowest point of the dot pattern has almost no effect on electrode adhesion, and there is a risk of deterioration of adhesion durability under heating or humidification, resulting in local delamination of the separator and electrode. If the h / H value is too high, for example above 0.8, the difference between the lowest and highest points of the dot pattern is small. After assembling the battery, there is too little space left between the separator and electrode, which will greatly reduce the amount of electrolyte retained and affect the battery's internal resistance performance.

[0024] In some embodiments, the maximum height H of the dot pattern ranges from 4.6 μm to 9 μm, such as 4.6 μm, 4.8 μm, 5.0 μm, 5.2 μm, 5.5 μm, 6.0 μm, 6.3 μm, 6.5 μm, 7 μm, 7.2 μm, 7.3 μm, 8 μm, 8.2 μm, 8.5 μm, 9 μm, etc. The diameter of the dot pattern 120 is 100 μm to 500 μm, such as 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, etc. The dot pattern can be circular, elliptical, quadrilateral, pentagonal, etc. Controlling the height and size of the dot pattern within the above range helps to provide more electrolyte wetting channels while ensuring adhesion, resulting in lower battery internal resistance. The height, radius, and other dimensions of the dotted patterns mentioned in this application can be obtained by scanning multiple (e.g., 5) independent regions at an appropriate magnification using a confocal microscope (model OLYMPUSOLS5100) and taking the average size of the multiple dotted patterns within each region. Alternatively, other commonly used testing methods in the field can be employed, such as measuring the height after taking SEM images of the diaphragm cross-section.

[0025] In some embodiments, the dot pattern 120 is circular, and the outermost radius R of the dot pattern 120 is 100μm-250μm, such as 100μm, 130μm, 150μm, 180μm, 200μm, 230μm, 250μm, etc. A circular hollow area is provided near the center, and the radius r of the circular hollow area satisfies: 0.75R ≥ r ≥ 0.25R, specifically 0.25R, 0.30R, 0.35R, 0.40R, 0.45R, 0.50R, 0.55R, 0.60R, 0.65R, 0.70R, 0.75R, etc. Adjusting the values ​​of R and r helps control the coverage area of ​​the dot pattern 120 on the substrate surface, thereby further improving the adhesion performance between the battery separator and the electrode, while also ensuring better air permeability.

[0026] In some embodiments, the dot pattern 120 has N annular structures with the same center, where N≥2. The following example illustrates a circular dot pattern, with its center as the center of the circle. The width of each annular structure is 25μm-375μm, such as 25μm, 50μm, 100μm, 150μm, 200μm, 225μm, 250μm, 300μm, 350μm, 375μm, etc., preferably 40μm-225μm. Controlling the width of each annular structure within the above range helps to ultimately form a dot pattern with a suitable gradient height, coordinating the area of ​​the ineffective bonding region in a single dot pattern with the liquid-retaining region after electrode bonding, thereby reducing the impact on the battery's internal resistance performance. The height difference ΔH1 between the highest and lowest points in adjacent annular structures is 1μm-4μm, such as 1μm, 2μm, 3μm, 4μm, etc., preferably 2μm-3μm. Controlling the height difference between the highest and lowest points in adjacent annular structures within the same dot pattern 120 within a certain range is beneficial for the regular distribution of particles within the dot pattern, resulting in better electrolyte wettability and more uniform particle accumulation, thus slightly improving impedance performance.

[0027] To reduce production costs (the cost of printing roller design, the cost of matching and debugging equipment and paste formula) and improve production continuity, it is preferable to control the number of annular structures to 2-6, that is, the value of N is 2-6, and more preferably 2-3.

[0028] In some embodiments, such as Figure 3 As shown, the dot pattern design includes three ring structures. A first ring structure 121, a second ring structure 122, and a third ring structure 123 are respectively arranged in the direction from the center to the outermost edge. The average height of the protrusions of the first ring structure 121, the second ring structure 122, and the third ring structure 123 is independently 1μm-8μm (e.g., 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, etc.), and the height difference between adjacent ring structures is 2μm-3μm, e.g., 2.0μm, 2.3μm, 2.5μm, 2.8μm, 3.0μm, etc.

[0029] In some embodiments, the height of the annular structure gradually increases from the center to the edge of the dot pattern 120, i.e., the annular structure is higher on the outside and lower on the inside. Specifically, the height of the annular structure can be designed such that the average height of the adjacent annular structures changes from the outer edge of the protrusion to the center by 0.5~2.5μm. That is, the average height of the protrusions of the first annular structure 121, the second annular structure 122, and the third annular structure 123 increases sequentially, and the height between any adjacent annular structures changes with a certain gradient. The inventors have found that the regular dot-coated separator with a gradient height has better electrolyte wettability than the coated separator with a disordered coating height distribution, resulting in lower internal resistance after assembly into a battery. The formulation (e.g., component compatibility, solid content) and process (e.g., printing roller design, substrate and back roller wrap angle, drying speed) work together to allow the dot-coated slurry to spread and adhere better on the substrate surface, achieving controllable planar morphology and height.

[0030] To further improve the adhesion and air permeability between the battery separator and the electrode, the number of dot patterns on the substrate per unit area is controlled at 150-650 per cm. 2 For example, it can be 150 pieces / cm 2 200 pieces / cm 2 250 pieces / cm 2 300 pieces / cm 2 350 pieces / cm 2 400 pieces / cm 2 450 pieces / cm 2 500 pieces / cm 2 550 pieces / cm 2 600 pieces / cm 2 650 pieces / cm 2 Etc. To further improve the overall performance of the battery separator, the preferred dot pattern density is 520-630 dots / cm². 2 This is because the dot pattern is regularly distributed. If the number of dot patterns per unit area is too low, its adhesion is often poor. When used in batteries, it is easy to delaminate, which can lead to safety issues. On the other hand, if there are too many dot patterns per unit area, the processing is more difficult, and the dots are prone to overlap and adhesion. At the same time, the membrane has poor air permeability, and the liquid retention space is limited after bonding with the electrode, which often results in poor overall performance.

[0031] Furthermore, to achieve more uniform adhesion and impedance performance, in a single dot pattern 120, the total width of the rings with a protrusion height of 20%-50% of the height of the highest ring structure accounts for 20%-50% of the total outer diameter of the dot pattern 120, preferably 30-40%. The inventors discovered through extensive experimental research that the proportion of ring widths with a protrusion height of 20-50% in a single dot pattern 120 is one of the key factors affecting the adhesion and breathability of the dot pattern. When the proportion of rings with a height of 20-50% of the highest ring structure exceeds 50%, the height distribution of each ring in the cross-section of the ring pattern is too concentrated, resulting in excessively high breathability. When the proportion of rings with a height of 20-50% of the highest ring structure is less than 20%, the pattern cross-section is relatively steep, with most particles clustered in a small area, resulting in less effective component contacting the electrode and thus excessively low adhesion.

[0032] In some embodiments, the slurry used to form the dot pattern 120, by weight percentage, comprises: 12.0-13.5 wt% polymer, 0.5-1.2 wt% binder, 0.5-1.2 wt% dispersant, and the remainder being solvent. Specifically, the mass fraction of the polymer can be 12.0 wt%, 12.3 wt%, 12.5 wt%, 12.8 wt%, 13.0 wt%, 13.3 wt%, 13.5 wt%, etc.; the mass fraction of the binder can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, etc.; and the mass fraction of the dispersant can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, etc. The solid content of the slurry (i.e., the content excluding solvent) is 3-15.0 wt%, such as 3 wt%, 5 wt%, 8 wt%, 10 wt%, 13 wt%, 15 wt%, etc.

[0033] In some embodiments, the polymer may include any one or more selected from polyvinylidene fluoride copolymers, polyvinylidene fluoride homopolymers, acrylate polymers, methacrylate polymers, polyimides, or polyethylene waxes, and the polymer has a crystallinity of 10-25%. The polyvinylidene fluoride copolymer may, for example, be a polyvinylidene fluoride-hexafluoropropylene copolymer, a polyvinylidene fluoride-tetrafluoroethylene copolymer, a polyvinylidene fluoride-acrylic acid copolymer, etc. The adhesive may include copolymers, homopolymers, or modified versions of at least one of acrylic acid, acrylates, acrylonitrile, and styrene. The dispersant may include at least one selected from sodium polyacrylate, polyether siloxane, polyether-modified siloxane, and sodium dodecylbenzenesulfonate. The solvent may include water. This invention employs a dotted pattern with a specific morphology, combined with a polymer crystallinity preferably within the range of 10-25%, resulting in a coating with a suitable softening and bonding temperature and good adhesion during battery assembly. Simultaneously, the appropriate polymer crystallinity ensures orderly molecular chain arrangement and reserves sufficient amorphous regions, allowing the electrolyte to easily penetrate the dotted coating. Furthermore, the non-fully covered dotted coating forms numerous "microchannels" on the substrate surface for electrolyte passage. During electrolyte injection, capillary action further enhances the wetting and retention of the electrolyte within the battery separator, significantly reducing "dead zones" within the separator without electrolyte wetting, thereby resulting in superior internal resistance performance of the battery. Understandably, the polymer crystallinity mentioned in this invention can be tested using differential scanning calorimetry (DSC), by dividing the measured melting enthalpy by the theoretical enthalpy by 100%. For example, this invention uses 104.7 J / g as the theoretical enthalpy of polyvinylidene fluoride copolymer and polyvinylidene fluoride homopolymer for calculation. Of course, other commonly used testing methods in the field, such as X-ray diffraction, can also be used for testing, and this invention is not limited thereto.

[0034] In this application, the substrate 110 can be a polymer microporous membrane (e.g., a base membrane made of polyolefin, polyamide, polyester, fluoropolymer, etc.) or a coated separator with a functional layer on at least one surface of the polymer microporous membrane (e.g., a polymer functional layer, an organic-inorganic composite material layer, etc. coated on the surface of the base membrane). This application does not impose any special limitations on the molding process of the substrate (e.g., dry process, wet process, extrusion, coating, etc.). Conventional separator substrates that can be used in secondary batteries are all applicable to this application.

[0035] In one embodiment, the base membrane includes a polyethylene (PE) base membrane, a polypropylene (PP) base membrane, or a polyolefin composite membrane. A polyolefin composite membrane refers to a multilayer composite porous membrane formed by stacking polypropylene (PP) and polyethylene (PE) in any order, such as a PP-PE-PP three-layer composite porous membrane, a PP-PE two-layer composite porous membrane, or a PP-PP-PE-PP four-layer composite porous membrane.

[0036] In one embodiment, the thickness of the base film is 2-25 μm, for example, it can be 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm, 22 μm or 25 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific values ​​included in the range, but it can be selected as 3-20 μm.

[0037] This application does not particularly limit the average pore size and porosity of the base film, but from the viewpoint of mechanical strength, ion permeability and electrochemical safety, a porosity between 30% and 65% is preferred, for example, it can be a range of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or any two of these; the average pore size is preferably in the range of 20-100 nm, for example, it can be a range of 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm or any two of these.

[0038] This invention also provides a method for preparing a battery separator, comprising the following steps: S1, providing slurry According to the composition of the slurry, the polymer, binder, dispersant, and solvent are mixed. The slurry composition meets the following requirements: polymer 12.0-13.5 wt%, binder 0.5-1.2 wt%, dispersant 0.5-1.2 wt%, and the remainder is solvent. Refer to the above text for the specific types of polymer, binder, dispersant, and solvent.

[0039] S2. Select printing rollers A printing roller that meets the structural requirements of dot pattern 120 is selected, and the specific pattern is transferred to the surface of the substrate to form a dot pattern.

[0040] S3, Coating The paste is transferred to the substrate surface via transfer rollers and printing rollers.

[0041] The specific working principle is as follows: like Figure 5As shown, in one embodiment, the coating equipment may include a material cassette 200, transfer rollers (feeding roller 310 and intermediate roller 320), a printing roller 101, and a back roller 330. The feeding roller 310 is rotatably disposed in the material cassette 200 and is used to obtain slurry from the material cassette 200. The intermediate roller 320 is rotatably disposed on one side of the feeding roller 310 and contacts the feeding roller 310. The printing roller 101 is disposed on the side of the intermediate roller 320 opposite to the feeding roller 310 and contacts the intermediate roller 320. During operation, the intermediate roller 320 can transport the slurry on the feeding roller 310 to the printing roller 101. In this embodiment, the back roller 330 is disposed on the side of the printing roller 101 opposite to the intermediate roller 320, and a gap for the substrate to pass through may be configured between the back roller 330 and the printing roller 101. When the substrate passes through the gap between the back roller 330 and the printing roller 101, the printing roller 101 applies a certain pressure to the substrate and coats the slurry onto it. The back roller 330 provides support for the substrate. A doctor blade 350 is also provided on one side of the transfer roller 320 to ensure that the slurry on the transfer roller 320 is evenly coated onto the printing roller 101. In addition, the coating equipment also includes a unwinding roller 340, which can be used to carry the roll of substrate to be coated, thereby unwinding the substrate.

[0042] like Figure 6As shown, the printing roller 101 may include a roller body 1011. A plurality of protrusions 1012 are provided on the circumferential side of the roller body 1011. The plurality of protrusions 1012 may be arrayed on the surface of the roller body 1011 and cover the entire surface of the roller body 1011. It is understood that, as a roller that directly contacts the substrate, those skilled in the art can perform paste printing by engraving regular recesses or protrusions on the roller surface. Specifically, different printing rollers can be selected according to the size of the dotted pattern, the size of the cutouts, etc. For example, the size of the recesses or protrusions on the printing roller can be designed within a deviation range of ±50μm based on the size of the coated pattern. In one embodiment of this application, the regular protrusions (i.e., protrusions 1012) engraved on the selected printing roller are hollow cylinders. Their projection on the unfolded plane of the roller surface can be circular, square, or similar. Specifically, the projection of the hollow cylinder can be designed as a circular ring, and the height of the highest and lowest points of the pattern can be controlled. The regular protrusion can be designed with a gradient from its outer edge to its center. Specifically, the gradient design means that the height of the regular protrusion gradually increases or decreases from its inner root near the central axis of the roller towards its radially outer top away from the central axis of the roller. The gradient design can be a stepped design, a slope design, etc., that is, to achieve a regularly distributed circular coating pattern with a height gradient, the internal structure of a single protrusion of the printing roller exhibits a certain regular height change (e.g., unidirectional change or first increasing and then decreasing along a certain direction), while the design between different protrusions remains consistent. Specifically, the regular protrusions engraved on the selected printing roller are circular hollow cylinders with an outer ring radius D and an inner ring radius d. When the paste formula specified in this application is used, the printed dot pattern 120 with a hollow area can satisfy the inner ring radius r = d ± 0.1D. That is, when the paste formula and pattern are the same (e.g., both are circular and have the same number of rings), if the inner diameter of the hollow area of ​​the target pattern is within the range of d ± 0.1D, it is not necessary to change the printing roller; the dimensions of the dot pattern can be adjusted by changing the process parameters.

[0043] It is understood that the height of the protrusions on the printing roller that transfers the paste changes in the opposite direction to the height of the dot pattern coating. That is, when the required coating height is higher on the outside and lower on the inside, the height of the protrusions should be designed to be higher on the inside and lower on the outside. In some embodiments, a printing roller with a protrusion height gradient design of ±5μm of the gradient change parameter of the required pattern is selected.

[0044] In some embodiments, the wrap angle between the substrate and the back roller is controlled to be 30~120°, such as 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 120°, etc., preferably 60~90°. The back roller is a roller used to support the substrate and cooperate with the printing roller or the paste extrusion die to perform dotted coating. The "wrap angle" refers to the central angle angle corresponding to the arc segment where the substrate and the back roller actually contact and bend, such as... Figure 7 Specifically, the wrap angle can be adjusted by adjusting the relative positions of the rollers around the substrate. For example, the wrap angle can be adjusted by adjusting the relative positions of the traction rollers at the rear ends of the feed roller 340 and the back roller 330. Alternatively, the wrap angle can be adjusted by adding or removing traction rollers before and after the back roller. This invention is not limited to these methods.

[0045] After coating, the membrane is dried and wound up to obtain a battery separator 100 with a substrate 110 and a dot pattern 120. The drying temperature is controlled at 60℃-80℃, such as 60℃, 70℃, 80℃, etc. This application controls the drying temperature and wrap angle within a certain range, which can synergistically control morphological parameters such as the height difference between the maximum and minimum heights of the dot pattern and the height difference between adjacent replacement clusters. For example, if the drying temperature is too high, the dot slurry may form before it has had time to fully spread on the membrane surface. It is understood that if either of these factors is outside the range defined in this application, the distribution and size of the dot pattern cannot be controlled within an optimal range, thus affecting the performance of the separator.

[0046] It should be noted that the regular dot-matrix coating method used in this embodiment of the invention is a non-full-coverage contact coating method, which can effectively control the coverage of the diaphragm coating and prevent the generation of atomized dust, reducing hazards during operation. Simultaneously, the regular dot matrix arrangement improves the utilization rate of the slurry and the effectiveness of the coating dots. Through the regularly arranged coating dots, suitable air permeability and ionic conductivity can be ensured, preventing the coating from clogging the substrate pores, while also improving the adhesion between the diaphragm and the electrode, giving the diaphragm superior performance.

[0047] This invention provides a secondary battery, including the battery separator 100 provided in this embodiment, and may also include a positive electrode, a negative electrode, an electrolyte, etc. The secondary battery can be a lithium battery, but is not limited thereto.

[0048] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0049] Some of the raw material components in the examples and comparative examples are as follows: First polymer: Polyvinylidene fluoride hexafluoropropylene copolymer, crystallinity 18%; Second polymer: Polyvinylidene fluoride hexafluoropropylene copolymer, crystallinity 42%; Adhesive: Polyacrylate, grade GR-406, manufactured by Hunan Gaorui Power Materials Co., Ltd. Dispersant: Polyether siloxane, brand name QS-446, manufactured by Jiangxi Tiansheng New Materials Co., Ltd. Substrate: Polyethylene microporous membrane, 7μm thick, grade SW507E, air permeability 103s, manufactured by Shenzhen Xingyuan Material Technology Co., Ltd.

[0050] Example 1 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.33R (51 / 153 = 0.33R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 47 μm and 55 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase in a gradient. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0051] That is, the maximum height H of the dot pattern is 5.4 μm, the minimum height h is 2.6 μm, and h / H = 0.48. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.8 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 31% of the total outer diameter of the dot pattern.

[0052] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry According to the composition of the slurry, the first polymer, binder, dispersant and solvent are mixed, with a solid content of 15%. The slurry composition satisfies: polymer 13.5wt%, binder 0.75wt%, dispersant 0.75wt%, and the remainder is solvent, which is deionized water.

[0053] (2) Select printing rollers The selected printing roller is engraved with regular protrusions. The pattern of the regular protrusions on the unfolded surface of the printing roller is a ring. The outer diameter of the ring is 300±10μm, and the ring has a gradient design. Other specific parameters are as described above in this embodiment.

[0054] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 60°C. A dotted coating is applied to the surface of another substrate using the same process.

[0055] Example 2 This embodiment provides a battery separator, such as Figures 1-3 As shown, the substrate includes a substrate 110 and multiple dot patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot patterns is 156 μm (2R = 312 μm). A circular hollow area is provided near the center, and the radius r of the circular hollow area satisfies: r = 0.26R (40 / 156 = 0.26R). The dot patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 55 μm and 61 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase gradually. The number of dot patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0056] That is, the maximum height H of the dot pattern is 4.8 μm, the minimum height h is 1.3 μm, and h / H = 0.27. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 3.5 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 35% of the total outer diameter of the dot pattern.

[0057] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0058] (2) Select printing rollers The printing roller is consistent with that in Example 1.

[0059] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 120°, and the drying temperature is 60°C. A dotted coating is applied to the surface of another substrate using the same process.

[0060] Example 3 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 150.5 μm (2R = 301 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.37R (55 / 150 = 0.37R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 41 μm and 54 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase gradually. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0061] That is, the maximum height H of the dot pattern is 5.6 μm, the minimum height h is 2.8 μm, and h / H = 0.51. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.7 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 27% of the total outer diameter of the dot pattern.

[0062] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0063] (2) Select printing rollers The printing roller is consistent with that in Example 1.

[0064] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 65°, and the drying temperature is 75°C. A dotted coating is applied to the surface of another substrate using the same process.

[0065] Example 4 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 158 μm (2R = 316 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.23R (37 / 158 = 0.23R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 57 μm and 64 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase gradually. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0066] That is, the maximum height H of the dot pattern is 4.3 μm, the minimum height h is 1.9 μm, and h / H = 0.44. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.4 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 36% of the total outer diameter of the dot pattern.

[0067] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0068] (2) Select printing rollers The printing roller is consistent with that in Example 1.

[0069] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound up to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 180°, and the drying temperature is 68°C.

[0070] Example 5 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.38R (58 / 153 = 0.38R). The dot-shaped patterns have a ring structure with the same center, and the ring width of the ring structure is 95 μm. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0071] In other words, the maximum height H and minimum height h of the dot pattern are both approximately 3.7 μm. Within a single dot pattern, the total width of the annular structures whose raised height is 20%-50% of the total height accounts for 0% of the total outer diameter of the dot pattern.

[0072] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0073] (2) Select printing rollers The selected printing roller is engraved with regular circular protrusions, and only one ring is set. The outer diameter of the ring is 300±10μm. Other specific parameters are as described above in this embodiment.

[0074] (3) Coating The slurry is transferred to a substrate via a transfer roller and a printing roller, then dried and wound to obtain a battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 68°C. A dotted coating is applied to the surface of another substrate using the same process.

[0075] Example 6 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.1R (15 / 153 = 0.1R). The dot-shaped patterns have four ring structures with the same center. The ring widths of the ring structures are 52 μm, 43 μm, 38 μm, and 31 μm, respectively. The height of the ring structures increases gradually from the center to the edge of the dot-shaped patterns, at 1.7 μm, 2.8 μm, 4.1 μm, and 5.3 μm, respectively. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0076] That is, the maximum height H of the dot pattern is 5.3 μm, the minimum height h is 1.7 μm, and h / H = 0.32. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 1.2 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 23% of the total outer diameter of the dot pattern.

[0077] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0078] (2) Select printing rollers The selected printing roller is engraved with regular circular protrusions, and is set to 4 concentric rings with an outer diameter of 450±10μm. Other specific parameters are as described above in this embodiment.

[0079] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 68°C. A dotted coating is applied to the surface of another substrate using the same process.

[0080] Example 7 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.15R (2³ / 15³ = 0.15R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 50 μm and 80 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase gradually. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0081] That is, the maximum height H of the dot pattern is 4.6 μm, the minimum height h is 2.3 μm, and h / H = 0.5. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.3 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 33% of the total outer diameter of the dot pattern.

[0082] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0083] (2) Select printing rollers The regular raised patterns engraved on the printing roller are designed into a circular pattern, and the circular pattern has a gradient design. For specific parameters, please refer to the above description of this embodiment.

[0084] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 68°C. A dotted coating is applied to the surface of another substrate using the same process.

[0085] Example 8 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.78R (119 / 153 = 0.78R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 30 μm and 4 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase gradually. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0086] That is, the maximum height H of the dot pattern is 5.2 μm, the minimum height h is 2.4 μm, and h / H = 0.46. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.8 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 20% of the total outer diameter of the dot pattern.

[0087] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0088] (2) Select printing rollers The regular raised patterns engraved on the printing roller are designed into a circular pattern, and the circular pattern has a gradient design. For specific parameters, please refer to the above description of this embodiment.

[0089] (2) Provide slurry Same as Example 1.

[0090] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 68°C. A dotted coating is applied to the surface of another substrate using the same process.

[0091] Example 9 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.34R (52 / 153 = 0.34R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 22 μm and 79 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase in a gradient. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0092] That is, the maximum height H of the dot pattern is 4.8 μm, the minimum height h is 2.1 μm, and h / H = 0.44. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.7 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 14% of the total outer diameter of the dot pattern.

[0093] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry According to the composition of the slurry, the first polymer, binder, dispersant and solvent are mixed, with a solid content of 22%. The slurry composition satisfies the following: first polymer 19.8 wt%, binder 1.1 wt%, dispersant 1.1 wt%, and the remainder is solvent, which is deionized water.

[0094] (2) Select printing rollers The printing roller is consistent with that in Example 1.

[0095] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 70°, and the drying temperature is 65°C. A dotted coating is applied to the surface of another substrate using the same process.

[0096] Example 10 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.37R (57 / 153 = 0.37R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 82 μm and 14 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase in a gradient. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0097] That is, the maximum height H of the dot pattern is 5.8 μm, the minimum height h is 2.8 μm, and h / H = 0.48. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 3.0 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 54% of the total outer diameter of the dot pattern.

[0098] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry According to the composition of the slurry, the first polymer, binder, dispersant and solvent are mixed, with a solid content of 8%. The slurry composition satisfies: first polymer 7.2wt%, binder 0.4wt%, dispersant 0.4wt%, and the remainder is solvent, which is deionized water.

[0099] (2) Select printing rollers The printing roller is consistent with that in Example 1.

[0100] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 100°, and the drying temperature is 75°C. A dotted coating is applied to the surface of another substrate using the same process.

[0101] Example 11 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.33R (51 / 153 = 0.33R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 40 μm and 62 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase in a gradient. The number of dot-shaped patterns on the substrate per unit area is 100 per cm². 2 .

[0102] That is, the maximum height H of the dot pattern is 5.4 μm, the minimum height h is 2.6 μm, and h / H = 0.48. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.8 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 31% of the total outer diameter of the dot pattern.

[0103] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0104] (2) Select printing rollers The regular raised patterns engraved on the printing roller are designed into a circular pattern, and the circular pattern has a gradient design. For specific parameters, please refer to the above description of this embodiment.

[0105] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 68°C. A dotted coating is applied to the surface of another substrate using the same process.

[0106] Example 12 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.33R (51 / 153 = 0.33R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 47 μm and 55 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase in a gradient. The number of dot-shaped patterns per unit area of ​​the substrate is 800 per cm². 2 .

[0107] That is, the maximum height H of the dot pattern is 5.4 μm, the minimum height h is 2.6 μm, and h / H = 0.48. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.8 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 31% of the total outer diameter of the dot pattern.

[0108] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0109] (1) Select printing rollers The regular raised patterns engraved on the printing roller are designed into a circular pattern, and the circular pattern has a gradient design. For specific parameters, please refer to the above description of this embodiment.

[0110] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 68°C. A dotted coating is applied to the surface of another substrate using the same process.

[0111] Example 13 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 149 μm (2R = 295 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.42R (62 / 147.5 = 0.42R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 40 μm and 46 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase in a gradient. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm².2 .

[0112] That is, the maximum height H of the dot pattern is 3 μm, the minimum height h is 2.6 μm, and h / H = 0.86. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 0.4 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 0% of the total outer diameter of the dot pattern.

[0113] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Same as Example 1.

[0114] (2) Select printing rollers The printing roller is consistent with that in Example 1.

[0115] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 10°, and the drying temperature is 82°C. A dotted coating is applied to the surface of another substrate using the same process.

[0116] Example 14 This embodiment provides a battery separator, including a substrate 110 and a plurality of dot-shaped patterns 120 coated on two surfaces of the substrate 110. The outermost radius R of the dot-shaped patterns is 153 μm (2R = 306 μm), and a circular hollow area is provided near the center. The radius r of the circular hollow area satisfies: r = 0.33R (51 / 153 = 0.33R). The dot-shaped patterns have two ring structures with the same center, namely a first ring structure 121 and a second ring structure 122. The ring widths of the two ring structures are 47 μm and 55 μm, respectively, and the heights of the first ring structure 121 and the second ring structure 122 increase in a gradient. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 .

[0117] That is, the maximum height H of the dot pattern is 5.4 μm, the minimum height h is 2.6 μm, and h / H = 0.48. The height difference ΔH1 between the highest and lowest points in adjacent ring structures is 2.8 μm. In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the total height accounts for 31% of the total outer diameter of the dot pattern.

[0118] This embodiment also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry The only difference is that the first polymer in the slurry is replaced with the second polymer, while the other components and their amounts remain the same as in Example 1.

[0119] (2) Select printing rollers Same as Example 1.

[0120] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (with a gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 60°C. A dotted coating is applied to the surface of another substrate using the same process.

[0121] Comparative Example 1 This comparative example provides a battery separator with irregular dot coating, including a substrate and dot patterns coated on two surfaces of the substrate. The dot patterns are irregular, and the number of dots of varying sizes per unit area exceeds 1000. The size of the annular patterns is also irregular, with a maximum height H of 9.4 μm.

[0122] This comparative example also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide slurry Consistent with Example 1.

[0123] (2) Coating The slurry was applied to the substrate surface using a rotary spraying method with a rotor speed of 6100 rpm and a slurry flow rate of 1500 mL / min, forming an irregular polymer dot-like coating. Other conditions were the same as in Example 1. The coating was then dried and wound up to obtain the battery separator. The wrap angle between the substrate and the back roller was controlled at 120°, and the drying temperature was 68°C. The dot-like coating was applied to another substrate surface using the same process.

[0124] Comparative Example 2 This comparative example provides a battery separator, comprising a substrate and a plurality of dot-shaped patterns coated on two surfaces of the substrate. The outermost radius R of the dot-shaped patterns is 153 μm (2R is 306 μm), and it is a solid dot non-ring structure. The number of dot-shaped patterns per unit area of ​​the substrate is 550 per cm². 2 The maximum height H of the dot pattern is 3.3 μm.

[0125] This comparative example also provides a method for preparing a battery separator, the steps of which are as follows: (1) Provide printing rollers The regular raised bumps engraved on the printing roller are designed into a dotted raised pattern, with the outer edge diameter of the bumps being 300±10μm.

[0126] (2) Provide slurry Consistent with Example 1.

[0127] (3) Coating The slurry is transferred to the substrate via a transfer roller and a printing roller (without gradient), then dried and wound to obtain the battery separator. The wrap angle between the substrate and the back roller is controlled at 90°, and the drying temperature is 68°C. A dotted coating is applied to the surface of another substrate using the same process.

[0128] The performance of the battery separators prepared in the test examples and comparative examples is shown in Table 1.

[0129] Performance testing methods: Air permeability increment: The air permeability values ​​of the diaphragm and the substrate are tested according to GB / T36363-2018, and the difference between the two air permeability values ​​is the air permeability increment described in this application.

[0130] Adhesion strength: Take three positions along the TD direction of the battery separator and cut them into three 210mm×25mm strips. The long side of the strip is along the MD direction and the short side is along the TD direction. Cut the negative electrode (graphite negative electrode) into three 60mm×25mm negative electrode strips. Place the side of the strip with the polymer dotted coating opposite the negative electrode strip and hot press them together at 60℃, 1000kgf, and 120s. Use a tensile tester (Shenzhen Tesmet Instrument Equipment Co., Ltd. EM6.202) to test the peel strength between the battery separator and the negative electrode strips at a width of 25mm, a displacement of 50mm, and a tensile speed of 200m / min. Take the average peel strength as the electrode adhesion strength.

[0131] Battery internal resistance: The separators of the examples and comparative examples were prepared into batteries according to the following method. The batteries were tested using a Chenhua 660E electrochemical workstation, and the corresponding battery internal resistance (mΩ) was obtained by EIS AC impedance testing. The specific battery assembly method was as follows: 1) The positive electrode active material NCM811, conductive agent SP, and binder PVDF were mixed in a mass ratio of 94:3:3 with solvent NMP to form a positive electrode slurry. This slurry was coated onto a 10μm aluminum foil current collector; then dried in an oven at 95℃, and rolled on a roller press for later use. 2) The active material artificial graphite, conductive agent acetylene black, and binder CMC / SBR (mass ratio 1:1) were mixed in water at a mass ratio of 90:5:5 to form a negative electrode slurry. This slurry was coated onto a 10μm thick copper foil current collector, dried in an oven at 85℃, and rolled on a roller press for later use. 3) In a dry room with a dew point <-40℃, the separators of the examples and comparative examples were stacked and packaged between the positive and negative electrode sheets, and then packaged according to 2.5g / m 2 The electrolyte (Xinzhoubang, LBC3008A) was injected in a certain proportion to obtain the battery.

[0132] Table 1 Performance test results of the battery separators prepared in the examples and comparative examples

[0133] Comparing Examples 1-14 and Comparative Examples 1-2, it can be seen that the present invention, by setting a regular dot pattern with hollowed-out areas, can better balance the performance of separator electrode adhesion, air permeability and battery internal resistance.

[0134] Comparing Examples 1 and 2-14, it can be seen that Example 1 has the best overall performance. Examples 2-3, compared to Example 1, mainly changed the wrap angle, the height difference of the dots, and the ratio; Examples 4 and 13, compared to Example 1, mainly changed the wrap angle; Examples 5-6, compared to Example 1, mainly changed the number of rings; Examples 7-8, compared to Example 1, mainly changed the radius of the hollowed-out area, showing cases where the radius was too small and too large, respectively; Examples 9-10, compared to Example 1, mainly changed the ring width ratio at a specific height, showing cases where it was too small and too large, respectively; Examples 11-12, compared to Example 1, mainly changed the number of dotted patterns per unit area, showing cases where it was too few and too many, respectively; Example 14, compared to Example 1, mainly changed the choice of polymer.

[0135] 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 battery separator, characterized in that, It includes a substrate and a plurality of dot-shaped patterns regularly distributed on at least one side surface of the substrate. The dot-shaped patterns have hollow areas, and the ratio of the maximum height H to the minimum height h of the dot-shaped patterns satisfies: 0.1 < h / H < 1.

2. The battery separator according to claim 1, characterized in that, The ratio of the maximum height H to the minimum height h of the dot pattern satisfies: 0.3 ≤ h / H ≤ 0.8; And / or, the maximum height H of the dot pattern has a height range of 4.6 μm to 9 μm; And / or, the number of the dot pattern on the substrate per unit area is 150-650 per cm. 2 .

3. The battery separator according to claim 2, characterized in that, The dot pattern is circular, and the outermost radius R of the dot pattern is 100μm-250μm. A circular hollow area is provided near the center, and the radius r of the circular hollow area satisfies: 0.75R≥r≥0.25R.

4. The battery separator according to claim 1, characterized in that, The dot pattern has N ring structures with the same center, N≥2, and the height difference ΔH1 between the highest and lowest points in adjacent ring structures is 1μm-4μm, preferably 2μm-3μm; Preferably, the height of the annular structure gradually increases from the center to the edge of the dotted pattern; Preferably, N takes the value of 2 to 6.

5. The battery separator according to claim 4, characterized in that, In a single dot pattern, the total width of the ring structures whose convex height is 20%-50% of the height of the highest ring structure accounts for 20%-50% of the total outer diameter of the dot pattern.

6. A method for preparing the battery separator according to any one of claims 1-5, characterized in that, include: Provide base materials; The paste is transferred to at least one side of the substrate using a printing roller that meets the requirements of the dot pattern structure, and then dried to obtain a battery separator having a substrate and a dot pattern.

7. The preparation method according to claim 6, characterized in that, The slurry used to form the dot pattern comprises, by weight percentage: 12.0-13.5 wt% polymer, 0.5-1.2 wt% binder, 0.5-1.2 wt% dispersant, and the remainder being solvent.

8. The preparation method according to claim 7, characterized in that, The solid content of the slurry is 3-15.0 wt%; And / or, the polymer is selected from at least one of polyvinylidene fluoride copolymers, polyvinylidene fluoride homopolymers, acrylate polymers, methacrylate polymers, polyimides, and polyethylene waxes; preferably, the polymer has a crystallinity of 10-25%; And / or, the adhesive comprises copolymers, homopolymers or modified versions of at least one of acrylic acid, acrylates, acrylonitrile, and styrene; And / or, the dispersant is selected from at least one of sodium polyacrylate, polyether siloxane, polyether-modified siloxane, and sodium dodecylbenzenesulfonate.

9. The preparation method according to any one of claims 6-8, characterized in that, The printing roller has a circular pattern, and the circular pattern has a gradient structure; And / or, control the wrap angle between the substrate and the back roller to be 30-120°, wherein the back roller is used to support the substrate and cooperate with the printing roller to perform dot-coating, and preferably control the wrap angle between the substrate and the back roller to be 60-90°; And / or, control the drying temperature to 60℃-80℃.

10. A secondary battery, characterized in that, The battery separator includes any one of claims 1-7 or the battery separator prepared by any one of claims 8-9.

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