Dot-array coated battery separator and preparation method therefor, and secondary battery

Abstract

A dot-array coated battery separator, comprising a separator substrate and a polymer coating applied to the surface of at least one side of the separator substrate. The polymer coating comprises a plurality of crater-like dot-shaped coatings, each dot-shaped coating forming a frustoconical protruding structure having a raised periphery and a central depression. The dot-shaped coatings are arranged on the surface of the separator substrate to form a dot array. The crater structure of the dot-shaped coatings on the dot-array coated battery separator effectively reduces polymer accumulation at the coating points, and correspondingly lessens the impact of hot pressing on separator performance. As a result, the battery separator has good ion permeability, wettability, and gas permeability while satisfying bonding-strength requirements with the battery electrodes, thereby achieving a good performance balance. Further provided are a preparation method for the dot-array coated battery separator and a secondary battery comprising the dot-array coated battery separator.

Description

A dot-matrix array coated battery separator, its preparation method, and a secondary battery Technical Field

[0001] This invention belongs to the field of battery separator technology, and specifically relates to a dot-array coated battery separator and its preparation method, as well as a secondary battery using the dot-array coated battery separator. Background Technology

[0002] In the battery separator manufacturing process, the separator coating plays a crucial role in improving battery performance and enhancing battery safety. Applying a functional separator coating to the surface of the battery separator substrate can enhance the separator's thermal stability, mechanical strength, puncture resistance, and ion conductivity, effectively improving the overall performance of the battery separator.

[0003] Currently, polymer coatings on substrate surfaces are mainly prepared using techniques such as roller coating, spraying, and spot coating. Among these, spraying and spot coating, compared to traditional roller coating, produce coatings that do not completely cover the substrate, thus having less impact on separator performance. They also support higher production speeds, higher coating efficiency, and produce coatings with higher ion conductivity. However, spraying, by atomizing the slurry, results in lower slurry utilization and increases costs. In contrast, spot coating effectively improves slurry utilization, avoids the environmental pollution problems caused by spraying atomization, and allows for more precise control of coating thickness and distribution, enabling precise coating of specific areas on the substrate. This contributes to a more uniform coating, thereby improving the overall performance of the battery. It also effectively reduces coating material waste, which is especially important when using high-cost, high-performance polymer materials as coatings. Furthermore, spot coating has lower requirements for the working environment and exhibits better stability and applicability. Therefore, spot coating technology plays an increasingly important role in battery separator coating preparation processes.

[0004] In the prior art, regarding the preparation of diaphragm coatings by dot coating, Chinese patent document CN114039170A discloses a dot coating process for PVDF coating, which uses a dot coating gravure roller to dot coat at least one side of the base film to obtain a uniformly distributed dot PVDF coating; Chinese patent document CN114142175A discloses a rate-type diaphragm, which includes a base film and an adhesive layer and a ceramic layer sequentially disposed on the surface of the base film, wherein the adhesive layer is formed by dot coating of adhesive slurry onto a wet-process base film to form unconnected adhesive dots.

[0005] While coating the surface of a battery separator with a polymer coating can improve the adhesion between the separator and the battery electrodes, the accumulated polymer increases the battery's internal resistance and reduces its charge / discharge rate. Balancing these performance characteristics is a crucial challenge for battery separator coatings. Existing dot-coating techniques for preparing separator coatings, because the coating is not fully covered, can improve adhesion and reduce the impact of the polymer coating on battery charge / discharge performance to some extent, but there is still room for improvement. How to fabricate higher-performance polymer-coated battery separators using a dot-coating process, further improving the balance between coating adhesion strength and separator ion permeability, wettability, and air permeability, is a technical problem that needs to be solved. Summary of the Invention

[0006] This invention addresses the technical problem of how to better balance the adhesion between the separator coating and the battery electrode and the charge and discharge performance of the battery under the existing dot coating process. It provides a dot array coated battery separator, its preparation method and a secondary battery, which can further improve the balance between the coating adhesion strength and the separator ion permeability, wettability and air permeability, thereby improving the performance of the battery separator.

[0007] To address the aforementioned technical problems, the present invention provides a dot-array coated battery separator, comprising a separator substrate and a polymer coating coated on at least one surface of the separator substrate, wherein: the polymer coating comprises a plurality of dot-shaped coatings, the dot-shaped coatings being arranged on the surface of the separator substrate to form a dot-shaped array; the dot-shaped coatings are crater-shaped, that is, forming a frustum-shaped protrusion structure with peripheral protrusions and a central depression, and are formed by the accumulation of polymer particles.

[0008] Preferably, with the surface of the diaphragm substrate as the reference height 0, the height H of the outer protrusion top is 2-7 μm, and the height h of the central depression bottom is 0-3 μm; within the same dotted coating, H > h, and the height difference h′ = Hh < 5 μm.

[0009] More preferably, in the dotted coating, h > 0, meaning the dotted coating is not a completely hollow structure, and the surface of the separator substrate in the central depression of the crater is not completely exposed, but at least partially covered with polymer. Conversely, if h = 0, meaning the central depression of the dotted coating is not coated with polymer, the surface of the separator substrate is exposed here, and the entire dotted coating has a hollow "crater" structure. However, in this case, since the exposed separator substrate is not covered with polymer, the battery separator is prone to stress difference with the surrounding polymer-covered areas during drying, causing damage to the separator substrate surface. Therefore, it is not recommended to completely expose the substrate surface in the central depression. Since a small h′ will result in an indistinct "crater" structure, h′ > 0.5 μm is preferred.

[0010] In a preferred embodiment of any of the dot-matrix array coated battery separators of the present invention, the longest diameter d1 of the bottom of the dot-matrix coating is 250-600 μm, and the longest diameter d2 of the bottom of the central depression is 100-500 μm; d1 > d2 is maintained in the same dot-matrix coating, and the width d3 of the peripheral protrusion is 1 / 2(d1-d2).

[0011] In a preferred embodiment of any of the dot-matrix array coated battery separators of the present invention, the distance D between adjacent dots in the dot-matrix array is 400 to 1000 μm.

[0012] As a preferred embodiment of any of the dot-matrix coated battery separators of the present invention, the polymer includes at least one of polyvinylidene fluoride homopolymer (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polyvinylidene fluoride-methyl methacrylate copolymer (PVDF-PMMA), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-acrylic acid copolymer, polymethyl methacrylate (PMMA), polyethylene (PE), and acrylate polymers.

[0013] The present invention also provides a method for preparing a dot-array coated battery separator as described in the first aspect above, comprising at least the following steps:

[0014] (1) Coating equipment preparation: The coating equipment includes a first coating roller and a second coating roller; the first coating roller is a roller coating a gravure roller; the second coating roller is a rubber roller with dotted protrusions on its surface. The shape, size and spacing of the dotted protrusions are determined according to the preset coating coverage and the shape and size of the "volcano" dotted coating.

[0015] (2) Polymer slurry grinding: The polymer slurry is ground to reduce the particle size of the polymer particles in the polymer slurry;

[0016] (3) Coating material transfer: The polymer slurry used as coating material is fed into the first coating roller, and the coating material is transferred to the second coating roller by rotating the first coating roller; the pressure and speed are controlled, and the second coating roller is rotated to transfer the coating material onto the diaphragm substrate;

[0017] (4) Separator drying: After the coating material is transferred onto the separator substrate, it is dried to obtain a battery separator with a coating.

[0018] Throughout the coating process, airflow and humidity stability should be maintained.

[0019] Preferably, in step (2), the solid content of the polymer slurry is 10-30%; the particle size of the polymer particles in the ground polymer slurry is: D10≤3μm, 3μm<D50≤6μm, D90≤12μm; and the primary particle size is 80-300nm.

[0020] In a preferred embodiment of any embodiment of the method for preparing the dot-matrix array coated battery separator of the present invention, in step (3), by controlling the liquid loading of the first coating roller and the coverage of the second coating roller, the liquid content can be adjusted from 0.1 to 1.8 g / m³. 2 Adjust the coating surface density per unit area of ​​the diaphragm substrate within the specified range.

[0021] The present invention also provides a secondary battery comprising a dot-array coated battery separator provided in the first aspect of the present invention, or comprising a battery separator product prepared by the dot-array coated battery separator preparation method provided in the second aspect of the present invention.

[0022] The above-described technical solution of this invention creatively designs a dotted coating with a "crater" structure as the monomer, and forms an array of "crater" dotted coatings on the surface of the diaphragm substrate through a dot-coating process. Its beneficial effects are as follows:

[0023] During the assembly of battery cells, the battery separator needs to be hot-pressed, and the polymer coated on its surface will also deform under hot pressing, which will negatively affect the performance of the battery separator. However, compared with the general dot coating of the prior art, the dot coating with the "crater" structure has unfilled polymer space inside the "crater" structure. After hot pressing, the thickness and area of ​​the coating points of the "crater" structure are smaller than those of the non-"crater" structure. The impact of hot pressing on the performance of the battery separator is reduced accordingly. This allows the battery separator to meet the bonding strength requirements with the battery electrode while also having good ion permeability, wettability and air permeability, achieving a better performance balance.

[0024] In addition, the central recessed bottom position of the dot-shaped coating "crater" in the embodiments of the present invention can be hollowed out or not. The non-hollowed-out structure is easier to implement in terms of process and has a lower cost than the hollowed-out structure. When the hollowed-out structure is used, since the hollowed-out separator substrate is exposed without polymer coverage, it is easy to generate a stress difference with the surrounding polymer-covered areas when drying the battery separator, which can damage the membrane surface of the separator substrate.

[0025] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] The following figures are provided to further illustrate the invention and form part of the specification. They are used together with the detailed embodiments to explain the invention, but do not constitute a limitation thereof. They include:

[0027] Figure 1 is a schematic diagram of the dotted coating arrangement forming a dotted array in a dotted array coated battery separator provided by an embodiment of the present invention;

[0028] Figure 2 is a top view of the "crater" structure of the dotted coating provided in an embodiment of the present invention;

[0029] Figure 3 is a cross-sectional view along the AA direction of the "crater" structure shown in Figure 2;

[0030] Figure 4 is a scanning electron microscope image of the cross-section of the dotted array coated battery separator provided in the embodiment of the present invention (accelerating voltage 1.0kV, working distance 4.2mm, SE2 detector, magnification 200).

[0031] Figure 5 is a scanning electron microscope image of the cross-section of the outer protrusion of the dotted coating provided in the embodiment of the present invention (accelerating voltage 1.0kV, working distance 4.2mm, SE2 detector, magnification 5000).

[0032] Figure 6 is a scanning electron microscope image of the cross-section of the central depression of the dotted coating provided in the embodiment of the present invention (accelerating voltage 1.0kV, working distance 4.2mm, SE2 detector, magnification 5000).

[0033] Figure 7 is a flowchart of the steps of the method for preparing a dotted array coated battery separator provided in an embodiment of the present invention.

[0034] [Explanation of Key Component Symbols]

[0035] 1-Separator substrate; 2-Dotted coating; 21-Outer periphery protrusion; 22-Central depression. Detailed Implementation

[0036] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0037] To address the existing technical problems, as shown in Figures 1 to 3, a first aspect of the present invention provides a dot-array coated battery separator, comprising a separator substrate 1 and a polymer coating coated on at least one surface of the separator substrate 1; the polymer coating includes a plurality of dot-matrix coatings 2, which are arranged in a dot-matrix array on the surface of the separator substrate 1. The dot-matrix coatings have a "crater" structure, that is, they form frustum-shaped protrusions with peripheral protrusions 21 and central depressions 22, which are formed by the accumulation of polymer particles. In the scanning electron microscope image of the cross-section of the dot-array coated battery separator in Figure 4, the dashed line outlines a "crater"-shaped "protrusion-depression-protrusion" structure of a dot-matrix coating.

[0038] A preferred embodiment of the dot-array coated battery separator of the present invention is as follows:

[0039] With the surface of the diaphragm substrate 1 as the reference height 0, as shown in Figure 3, the top height of the protrusion 21 on the periphery of the dotted coating 2 is H, and the bottom height of the central depression 22 is h; H is limited to 2 to 7 μm, specifically 2, 3, 4...6 and 7 μm, as shown in Figure 5, which is 4.945 μm, which is an H value measured by scanning electron microscopy; h is limited to 0 to 3 μm, specifically 0, 1, 2 and 3 μm, as shown in Figure 6, which is 1.251 μm, which is an h value measured by scanning electron microscopy.

[0040] When h = 0, the dotted coating 1 is a hollow structure, with no polymer coating at the central depression 22, and the surface of the membrane substrate 1 is directly exposed. Given that the non-hollowed-out "crater" structure has more advantages than the hollow structure, h > 0 is usually chosen to make the dotted coating 1 form a non-hollowed-out "crater" structure as much as possible. Within the same dotted coating, the height H of the corresponding protrusions and depressions should be greater than h. To maintain a clear "crater" structure and avoid the central depression being too deep, it is advisable to limit it to 0.5 μm < h′ < 5 μm.

[0041] In the actual coating process, the height H of the outer protrusions at different positions of the same dot coating may vary, and H may also be inconsistent in different dot coatings. We should try to ensure the consistency of the top height of the outer protrusions in each dot coating and limit the height difference ΔH to within 50% of the minimum value of H in the battery separator dot coating.

[0042] In this embodiment of the invention, as shown in Figures 2 and 3, the outer contour of the dot-shaped coating 2 is basically a frustum-shaped protrusion. However, due to limitations in processing precision, the actual bottom surface of the dot-shaped coating 2 in contact with the diaphragm substrate 1 is approximately circular. The degree of approximation to a circle is represented by the circularity e.

[0043] In this embodiment of the invention, the roundness e of the approximately circular bottom surface of the dotted coating 2 is limited to the range of 0.9 to 1.

[0044] In embodiments of the present invention, the bottom contour of the central recess 22 of the dotted coating 2 is also approximately circular, and its circularity e is limited to the range of 0.8 to 1.

[0045] As shown in Figures 2 and 3, the longest diameter d1 at the bottom of the dotted coating 2 is limited to 250–600 μm, specifically 250, 300, 350…550 and 600 μm; the longest diameter d2 at the bottom of the central depression 22 is limited to 100–500 μm, specifically 100, 150, 200…450 and 500 μm; within the same dotted coating, d1 > d2, and the width d3 of the outer protrusion 21 is 1 / 2(d1-d2), with d3 ranging from 50 to 150 μm, specifically 50, 60, 70, 80, 90, 100, 110, 120, 130, 140 and 150 μm.

[0046] In the actual coating process, similar to H and h, the width d3 of the outer protrusion 21 in different dot coatings may vary. In order to ensure the consistency of the width of the outer protrusion in each dot coating as much as possible, the width difference Δd3 is limited to within 50% of d3.

[0047] In the dot array formed by the dot coatings 2 arranged on the surface of the diaphragm substrate 1, as shown in Figure 3, the spacing D (including the MD and TD directions) between adjacent dot coatings 2 is limited to 400-1000 μm. The dot of the dot coating 2 is the intersection of the longest and shortest diameters at the bottom of the dot coating 2.

[0048] Also due to limitations in processing precision, the D values ​​of the dot coatings 2 at different locations in the dot array may be inconsistent. In this embodiment of the invention, to ensure the consistency of the D values ​​as much as possible, the spacing difference ΔD is limited to within 20% of the minimum D value in the dot array.

[0049] The coating polymer material includes at least one of polyvinylidene fluoride homopolymer (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polyvinylidene fluoride-methyl methacrylate copolymer (PVDF-PMMA), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-acrylic acid copolymer, polymethyl methacrylate (PMMA), polyethylene (PE), and acrylate polymers.

[0050] The membrane substrate can be an uncoated base membrane or a base membrane coated with an inorganic coating. There are no specific requirements, and the choice can be made according to actual needs.

[0051] The membrane substrate can be selected from one or more of the following: polyethylene membrane, polypropylene membrane, polyimide membrane, polyvinylidene fluoride membrane, polyvinylidene fluoride-hexafluoropropylene membrane, polyamide membrane, and polyethylene terephthalate membrane; there are no specific requirements for the thickness and porosity of the membrane substrate, and it can be selected according to actual needs.

[0052] In a second aspect, as shown in FIG7, an embodiment provides a method for preparing a dot-array coated battery separator according to the first aspect of the present invention, comprising the following steps:

[0053] S1. Coating equipment preparation: The coating equipment includes a first coating roller and a second coating roller; the first coating roller is a roller coating a gravure roller; the second coating roller is a rubber roller with dotted protrusions on its surface. The shape, size and spacing of the dotted protrusions are determined according to the preset coating coverage and the shape, size and spacing of the "volcano" dotted coating; the interior of the dotted protrusions has a circular concave structure.

[0054] S2. Polymer slurry grinding: The polymer slurry is ground more than once to reduce the particle size of the polymer particles in the polymer slurry;

[0055] S3. Coating material transfer: The polymer slurry, which serves as the coating material, is fed onto the first coating roller, and the coating material is transferred to the second coating roller by rotating the first coating roller; the pressure and rotation speed are controlled, and the second coating roller is rotated to transfer the coating material onto the diaphragm substrate;

[0056] S4. Separator drying: After the coating material is transferred onto the separator substrate, it is dried to obtain a battery separator with a coating.

[0057] Throughout the coating process, airflow and humidity stability should be maintained.

[0058] A preferred embodiment of the method for preparing the dot-array coated battery separator of the present invention is as follows:

[0059] In step S1, the preset coating coverage is 15-60%, the dot-like protrusions are circular in shape, the diameter of the dot-like protrusions is 250-600 μm, and the spacing between the dots is 400-1000 μm. The circular recessed structure has a depth of 0-1 mm and a diameter of 200-600 μm.

[0060] In step S2, the solid content of the polymer slurry is 10-30%; after grinding, the polymer particles contained in the slurry have the following particle sizes: D10≤3μm, 3μm<D50≤6μm, D90≤12μm; the primary particle size is 80-300nm. The grinding can be done once, twice, three times, four times or more. The more grinding times, the deeper the central depression of the "volcano" in the dotted coating, i.e., the larger the value of h′.

[0061] In step S3, the liquid loading of the first coating roller is controlled to be between 0.1 and 1.8 g / m³. 2 The coating surface density per unit area of ​​the diaphragm substrate can be adjusted within a certain range; the thickness and distribution of the coating are ensured by precisely controlling the pressure and speed of the second coating roller.

[0062] In step S4, the process of transferring the coating material onto the separator substrate is heat-free and consistent with roller coating and spray coating. Afterwards, the battery separator can be obtained by drying in an oven. The drying temperature and time are precisely controlled to ensure the adhesion and uniformity of the polymer coating.

[0063] In a third aspect, the present invention provides a secondary battery comprising a dot-array coated battery separator provided in the first aspect of the present invention, or a battery separator product prepared by the preparation method provided in the second aspect of the present invention.

[0064] The following specific examples include Examples 1-8 and Comparative Examples 1-2. Unless otherwise specified, the raw materials, reagents, and methods used in the examples are all conventional in the art. All parts mentioned below are by mass, with pure water as the mass standard. Detailed parameter settings for the above examples are shown in the table below:

[0065] Table 1: Parameter Table for Examples and Comparative Examples

[0066] Continued from Table 1-1:

[0067] Continued from Table 1-2:

[0068] The following are test methods for the technical characteristics of the dot-array coated battery separators provided in the foregoing embodiments and comparative examples of the present invention:

[0069] 1. Coverage testing can be performed using any of the following methods:

[0070] Method 1: Measure the longest diameter d1 and the dot spacing D of the dotted coating under a magnifying glass, and calculate the coverage C using the following formula:

[0071] Method 2: Cut a 5×5cm diaphragm, stain it with a blue staining solution, and use ImageJ to automatically calculate the coverage.

[0072] 2. Follower loss rate test, the steps include:

[0073] (1) The color fastness to rubbing was tested using a rubbing fastness tester. The size of the lens paper was 5×5cm and the size of the sample diaphragm was 3×22cm.

[0074] (2) Weigh the cut sample diaphragm and record the weight M1;

[0075] (3) Place the lens cleaning paper on the rubbing head and clamp it with the clamp, making sure that the clamp is clamped in the recessed position of the rubbing head;

[0076] (4) Place the sample diaphragm on the sample clamp and hold it in place. When clamping, pull the sample diaphragm tightly to prevent wrinkles from forming during the test and affecting the experimental results.

[0077] (5) Press the relevant number of bits button to set the required number of tests. The standard setting is 5 tests / min.

[0078] (6) Open the safety cover and remove the sample diaphragm. Weigh and record the weight M2 on the electronic balance. The powder loss value M = (M1-M2) and the powder loss rate = M / M1 × 100%.

[0079] 3. Electrode bonding strength (positive / negative electrode) test, the steps include:

[0080] (1) Cut the battery separator to be tested into a sample separator with a size of 2.5×13cm; cut two rectangular pieces of paper with a weight of 80g from the printing paper, and fold the rectangular pieces of paper along the short side; cut out an electrode with a size of 2.5×6cm (select the positive electrode or the negative electrode according to the test requirements).

[0081] (2) Prepare stacked samples:

[0082] When the separator of the battery under test is coated on one side, stack one folded rectangular paper piece ×1, one electrode piece ×1, one sample separator ×1 and one folded rectangular paper piece ×1 in sequence from top to bottom to make a stacked sample.

[0083] When the battery separator to be tested is double-sided coated, 1 folded rectangular paper piece, 1 electrode, 1 sample separator, 1 PET film and 1 folded rectangular paper piece are stacked from top to bottom to make a stacked sample. The PET film used has the following specifications: 10-20g single-sided release, 36μm×1040mm×100m.

[0084] When stacking, the coating layer of the sample diaphragm to be measured for bonding strength is brought into contact with the electrode.

[0085] (3) Use a hot press (any type, such as QMESYS QM940AS) to make the laminated sample into a hot press sample; set the hot press parameters as follows: temperature 70℃, pressure 0.8T, time 1S; after the set temperature is reached and the temperature is stable for 10 minutes, put the laminated sample into the hot press for hot pressing.

[0086] (4) Peel off the part 5mm from the end of the hot-pressed sample by hand, and then use a tensile testing machine (any type, such as the high-speed rail tensile testing machine AI-3000-SU) to test the tensile force; fix the hot-pressed sample on the lower clamp of the tensile testing machine, clamp the hot-pressed sample in the order of clamping the lower clamp (with steel plate as an auxiliary) first, and then clamping the upper clamp, keeping the sample flat without wrinkles, vertical and not skewed; the distance between the clamps is (65±5)mm, and the test speed is (300±10)mm / min.

[0087] There are no particular limitations on the positive and negative electrodes used in this test method, and they can be obtained by bonding the electrode active material to at least one surface of the electrode current collector using methods generally known in the art. Non-limiting examples of positive electrode active materials include conventional positive electrode active materials that can be used as the positive electrode in conventional electrochemical devices. In particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides containing combinations thereof are preferred. Non-limiting examples of negative electrode active materials include conventional negative electrode active materials that can be used as the negative electrode in conventional electrochemical devices. In particular, lithium intercalation materials, such as lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, graphite, or other carbonaceous materials, are preferred. Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or combinations thereof. Non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, or copper alloys, or combinations thereof.

[0088] The dotted array coated battery separators in the embodiments and comparative examples of the present invention were tested using the above test methods. The test results are shown in the table below:

[0089] Table 2: Results of Physical Property Tests

[0090] As can be seen from the test results above, compared with the comparative example, the dotted array coated battery separator provided in this embodiment of the invention not only meets the bonding strength requirements with the battery electrode, but also has good ion permeability, wettability and air permeability.

[0091] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0092] In the description of this invention, it should be noted that the terms "peripheral," "central," "top," "bottom," and "horizontal," etc., indicating orientation or positional relationships, are only for the convenience of describing this invention and do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first" and "first" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0093] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A dot array coated battery separator, comprising a separator substrate and a polymer coating applied on at least one surface of the separator substrate, characterized in that: The polymer coating comprises a plurality of dot coatings, and the dot coatings are arranged on the surface of the separator substrate to form a dot array, wherein: The dot coating has a "crater" structure, that is, a frustum-shaped convex structure with a peripheral convex and a central concave, which is formed by stacking polymer particles.

2. The dotted array coated battery separator according to claim 1, characterized in that, Based on the surface of the separator substrate, the height H of the top of the peripheral convex is 2-7 μm, and the height h of the bottom of the central concave is 0-3 μm; in the same dot coating, H>h is maintained, and the height difference h' = H - h < 5 μm.

3. The dotted array coated battery separator according to claim 2, characterized in that, In the dot coating, h>0, and at least part of the surface of the separator substrate in the central concave is covered with polymer.

4. The dotted array coated battery separator according to claim 1, characterized in that, The longest diameter d1 of the bottom of the dot coating is 250-600 μm, and the longest diameter d2 of the bottom of the central concave is 100-500 μm; in the same dot coating, d1>d2 is maintained, and the width d3 of the peripheral convex is 1 / 2(d1 - d2).

5. The dotted array coated battery separator according to any one of claims 1 to 4, characterized in that, In the dot array, the center-to-center distance D between adjacent dot coatings is 400-1000 μm.

6. The dotted array coated battery separator according to claim 1, characterized in that, [[ID= 7. A method for preparing a dot-array coated battery separator according to any one of claims 1 to 6, characterized in that, ​ ​ ​ ​ ​ ​ 8. The method for preparing a dotted array coated battery separator according to claim 7, characterized in that, ​ 9. The method for preparing a dotted array coated battery separator according to any one of claims 7 to 8, characterized in that, In the coating material transfer step, the liquid loading of the first coating roller and the coverage of the second coating roller are controlled to be between 0.1 and 1.8 g / m³. 2 Adjust the coating surface density per unit area of ​​the diaphragm substrate within the specified range.

10. A secondary battery, characterized in that, ​

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