Battery separator and preparation method therefor, and lithium-ion battery

Abstract

The battery separator comprises a base film (11), a heat-resistant ceramic coating (12), a porous oily coating (13) and an interval coating layer (14). The heat-resistant ceramic coating (12) is arranged on one surface of the base film (11); the porous oily coating (13) is arranged on the surface of the heat-resistant ceramic coating (12) facing away from the base film (11), and the components of the porous oily coating comprise polymer particles and a first organic binder; the interval coating layer (14) is arranged on the surface of the base film (11) facing away from the heat-resistant ceramic coating (12) and comprises a plurality of oily coating units (141) arranged at intervals, a blank unit (142) with an extension direction inclined in the length direction of the base film (11) is formed between adjacent oily coating units (141), and the components of the oily coating units (141) comprise an inorganic filler and a second organic binder. By arranging the interval coating layer (14) and designing the extension direction of the blank unit (142) between adjacent oily coating units (141) to be inclined in the length direction of the base film, the risk of interfacial lithium plating can be favorably reduced, appearance defects such as streaks or ribs during winding in the separator processing are diminished, and the product yield is improved.

Description

A battery separator, its preparation method, and a lithium-ion battery Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a battery separator, a method for preparing the same, and a lithium-ion battery. Background Technology

[0002] With the increasing scarcity of fossil fuels and the rise of the new energy industry, lithium-ion batteries, with their advantages of high energy density, good rate performance, low self-discharge rate, no memory effect, and environmental friendliness, are widely used as energy sources for energy storage, power, and consumer products. Lithium-ion batteries mainly consist of five components: the positive electrode, the negative electrode, the separator, the electrolyte, and battery packaging materials. The separator, located between the positive and negative electrodes, primarily functions to separate them, preventing short circuits caused by contact between the electrodes. It also allows electrolyte ions to pass through. Therefore, the performance of the separator directly affects the performance of the lithium-ion battery.

[0003] To improve separator performance, the mainstream solution in the market is to coat the separator surface with a modified coating. Existing technology involves setting multiple strip-shaped modified coatings spaced apart along the width of the separator base layer. Adjacent strip-shaped modified coatings form gaps along the length of the separator base layer, creating a buffer space between the positive and negative electrodes to relieve stress on the corners caused by the expansion of the positive and negative electrode sheets during charging and discharging. However, after this separator is rolled into a battery cell, lithium plating at the interface can easily occur due to electrolyte diffusion and bridging at the middle of the gaps. Furthermore, during separator winding, appearance abnormalities such as winding streaks or bursting are prone to appear, affecting product yield. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a battery separator, a method for preparing the same, and a lithium-ion battery.

[0005] A first aspect of this application provides a battery separator, comprising:

[0006] Base film;

[0007] A heat-resistant ceramic coating is disposed on one surface of the base film;

[0008] A porous oily coating is disposed on the surface of the heat-resistant ceramic coating away from the base film; the components of the porous oily coating include polymer particles and a first organic binder;

[0009] An intermittent coating layer is disposed on the surface of the base film away from the heat-resistant ceramic coating; the intermittent coating layer includes a plurality of oil-based coating units spaced apart, with blank units formed between adjacent oil-based coating units, and the extension direction M of the blank units being inclined to the length direction P of the base film; the components of the oil-based coating units include inorganic fillers and a second organic binder.

[0010] According to the battery separator of the present application embodiment, it has at least the following beneficial effects: the battery separator can be used in lithium-ion batteries, and further in wound lithium-ion batteries. A heat-resistant ceramic coating is provided on one surface of the base film to improve the heat resistance of the separator. A porous oily coating comprising polymer particles and a first organic binder is further provided on the surface of the heat-resistant ceramic coating facing away from the base film, which can improve the adhesion between the separator and the electrode, improve the cycle performance of the battery, and prevent insufficient adhesion leading to OH lithium deposition. Simultaneously, its porous structure provides electrolyte storage space, preventing the electrolyte from being completely squeezed out during the later stages of cycling, thus preventing corner lithium deposition. Furthermore, the heat-resistant ceramic coating on the base film facing away from the base film... The surface is configured with a spacer coating layer consisting of several oil-based coating units spaced apart. On one hand, each oil-based coating unit has an adhesive function, ensuring the adhesion between the separator and the electrode. On the other hand, the blank units between adjacent oil-based coating units can provide more electrolyte storage space, while reducing ion transport resistance and improving battery performance. Furthermore, the extension direction M of the blank units between adjacent oil-based coating units is inclined to the length direction P of the base film. This helps to promote the diffusion of electrolyte from the beginning and end to the middle after the cell is wound, reducing the risk of lithium plating due to electrolyte breakage in the middle. It can also reduce appearance abnormalities such as streaks or cracks during separator processing and improve product yield.

[0011] In this case, the extension direction M of the blank unit on the spacer coating layer is inclined to the length direction P of the base film. That is, the angle between the extension direction M of the blank unit and the length direction P of the base film is greater than 0° and less than 90°. The blank unit and the base film are in a state that is neither perpendicular nor parallel.

[0012] In some embodiments of this application, the angle between the extension direction M and the length direction P is 30° to 60°. Further, the angle between the extension direction M of the blank unit and the length direction P of the base film can be controlled between 42° and 48°. If the angle is too large, the processing of the printing roller becomes more difficult and costly, and if the shearing is perpendicular to the blade during processing, it will lead to severe wear on the printing roller. Conversely, if the angle is too small, after the battery separator is used to assemble the battery, electrolyte breakage is likely to occur during electrolyte transport. Therefore, by controlling the angle between the extension direction M of the blank unit and the length direction P of the base film within the above range, it is possible to effectively ensure that the electrolyte diffuses from the beginning and end towards the middle, preventing lithium plating due to electrolyte breakage in the middle. It also effectively reduces or even avoids appearance abnormalities such as streaks or cracks during winding, improving product yield, facilitating processing, and reducing printing roller wear.

[0013] In some embodiments of this application, adjacent oil-coated units and blank units satisfy the following ratio: W1 / W2 = 0.5 to 3, where W1 is the width of the oil-coated unit along the extension direction M, and W2 is the width of the blank unit along the extension direction M. Further, adjacent oil-coated units and blank units can be controlled to satisfy: W1 / W2 = 1 to 2. If the width ratio of the oil-coated unit to the blank unit is too small, the adhesion of the spacer coating layer to the electrode sheet is low, which will deteriorate the cycling interface.

[0014] The width W1 of each oil-coated unit can be the same or different, or some oil-coated units can have the same width W1; the component configuration of each oil-coated unit can also be the same or different, or partially the same. The width W2 of each blank unit can be the same or different, or partially the same. To improve the uniformity of the structure, the oil-coated units can be evenly distributed on the surface of the base film.

[0015] Studies have shown that aqueous coatings formed by using water as a diluent to prepare the coating slurry have poor adhesion. At the OH positions (where the separator extends beyond the negative electrode in the width direction and where the negative electrode extends beyond the positive electrode in the width direction), poor adhesion can easily lead to lithium plating due to OH defects. Therefore, this application's battery separator features a porous oily coating on the surface away from the base film on the heat-resistant ceramic coating. Specifically, the coating preparation process uses an organic solvent as a diluent to prepare the coating slurry. The resulting porous oily coating has higher adhesion compared to aqueous coatings, ensuring a good overall interface between the coating and the electrode, and reducing the risk of lithium plating due to poor adhesion at the OH positions.

[0016] The porous oily coating comprises polymer particles and a first organic binder; furthermore, the mass ratio of polymer particles to the first organic binder can be controlled between 1:1.5 and 2.5, for example, the mass ratio of polymer particles to the first organic binder can be 1:2, 1:1.5 or 3:7.

[0017] In some embodiments of this application, in the porous oily coating, the particle size distribution width of the polymer particles satisfies: 0 < (D90-D10) / D50 ≤ 3, preferably 1 to 3; and the difference (Tf-Tg) between the flow temperature Tf and the glass transition temperature Tg of the polymer particles is 10℃ to 50℃. Specifically, if (D90-D10) / D50 is too large for the polymer particles, it indicates that the particle size distribution is too wide and the particle size is dispersed, which will cause large fluctuations in the coating thickness, significantly affecting the subsequent cell manufacturing process and easily causing electrode misalignment during cell winding. Conversely, if the Tf-Tg of the polymer particles is too small, the polymer microsphere structure is prone to collapse, failing to provide support and effectively improving the corner effect. A porous oily coating is constructed by combining the above-mentioned large polymer particles with the first organic binder. The polymer particles have a certain degree of compressibility and support, which can provide more space for electrolyte storage, alleviate the problem of lithium plating at corners caused by electrolyte squeezing due to electrode expansion, and reduce the risk of electrode breakage due to excessive internal stress caused by electrode expansion.

[0018] Furthermore, the particle size distribution width of the polymer particles used can be controlled to satisfy (D90-D10) / D50=2~2.5, and the polymer particles satisfy Tf-Tg is 20℃~50℃.

[0019] Furthermore, when the polymer particle size satisfies (D90-D10) / D50 = 1 to 3, the D50 particle size can be controlled to be 5 μm to 15 μm; further, when the polymer particle size satisfies (D90-D10) / D50 = 2 to 2.5, the D50 particle size can be controlled to be 7 μm to 10 μm. D50 cannot be too large or too small. If D50 is too large, the overall thickness of the porous oily coating is large, and after compression, electrolyte breakage at the cell corners can easily occur, leading to lithium plating. If D50 is too small, the overall compressible space of the coating is small, and it cannot effectively improve lithium plating.

[0020] In some embodiments of the invention, the molecular weight of the first organic binder is 30W to 100W, and the first organic binder has a characteristic peak at a diffraction angle 2θ between 10° and 40°. The first organic binder has a characteristic peak at a diffraction angle 2θ between 10° and 40°, exhibits good crystallinity (approximately 15% to 35%), ensuring minimal swelling in the electrolyte. The molecular weight of the organic binder is between 30W and 100W, and its Young's modulus is between 500MPa and 2000MPa, resulting in good adhesion to the electrode and ensuring a good cycling interface.

[0021] Furthermore, the molecular weight of the first organic binder can be 60W to 80W, and its Young's modulus can be between 600MPa and 1500MPa; or the molecular weight of the first organic binder can be 30W to 80W, 30W to 70W, 45W to 75W, or 50W to 70W. The first organic binder has characteristic peaks in the diffraction angle 2θ between 15° and 30°, or in the diffraction angle 2θ between 20° and 25°.

[0022] In some embodiments of this application, the polymer particles are selected from at least one of polyamide, polyacrylonitrile, polyethylene oxide, polyurethane, polyphenylene ether, and acrylate copolymers;

[0023] And / or, the first organic binder is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, hexafluoropropylene, and trifluoroethylene.

[0024] In some embodiments of this application, the thickness of the porous oily coating is 0.5 μm to 5 μm. Further, the thickness of the porous oily coating may be 0.5 μm to 3 μm, 1 μm to 4 μm, 1 μm to 2 μm, 1.5 μm to 3 μm, 2 μm to 4 μm, or 3 μm to 5 μm.

[0025] In some embodiments of this application, the heat-resistant ceramic coating comprises inorganic ceramic materials and heat-resistant adhesive; the particle size distribution width of the inorganic ceramic materials satisfies (D90-D10) / D50 = 0.5~2, and the glass transition temperature of the heat-resistant adhesive is greater than or equal to 180°C. Specifically, for the inorganic ceramic materials, if (D90-D10) / D50 is too large, it indicates that the particle size distribution width is too wide, with too many large and small particle sizes, which will result in insufficient compaction of the coating, poor thermal shock resistance, reduced porosity, and increased lithium-ion transport resistance. For the heat-resistant adhesive, if its glass transition temperature is too low, the coating's heat resistance is poor.

[0026] Furthermore, the components of the heat-resistant ceramic coating may include 95wt% to 98wt% inorganic ceramic materials and 2wt% to 5wt% heat-resistant adhesive.

[0027] Furthermore, the particle size distribution width of the controllable inorganic ceramic material satisfies: (D90-D10) / D50=1~1.5, and the glass transition temperature of the heat-resistant adhesive is greater than or equal to 200℃.

[0028] Furthermore, when the inorganic ceramic material satisfies (D90-D10) / D50 = 0.5 to 2, the D50 particle size can be controlled to be 100nm to 500nm; when the inorganic ceramic material satisfies (D90-D10) / D50 = 1 to 1.5, the D50 particle size can be controlled to be 200nm to 400nm.

[0029] Furthermore, the specific surface area of ​​the inorganic ceramic material can be controlled to be 10m². 2 / g~50m 2 / g.

[0030] In some embodiments of this application, the inorganic ceramic material is selected from at least one of silicon dioxide, alumina, silicon oxide, calcium oxide, magnesium oxide, ZnO, TiO2, boehmite, and ceramic fiber; and / or, the heat-resistant adhesive is selected from at least one of polyacrylic acid and styrene-butadiene rubber.

[0031] In some embodiments of this application, the heat-resistant ceramic coating is a water-based heat-resistant ceramic coating, and water is used as a diluent to prepare the coating slurry during the coating preparation process.

[0032] In some embodiments of this application, the thickness of the heat-resistant ceramic coating is 0.5 μm to 3 μm. Further, the thickness of the heat-resistant ceramic can be controlled to be 0.5 μm to 1 μm, 1 μm to 2.5 μm, 1 μm to 2 μm, 1.5 μm to 3 μm, 1.5 μm to 2.5 μm, or 2 μm to 3 μm.

[0033] An interstitial coating layer is set on the surface of the base film away from the heat-resistant ceramic coating. The interstitial coating layer is constructed using an oil-based coating unit. An organic solvent is used as a diluent during the coating slurry preparation process. The resulting interstitial coating layer is an oil-based coating. Compared with water-based coatings, it can also improve adhesion, ensure a good overall interface between the coating and the electrode, and reduce the risk of lithium plating.

[0034] The spaced-apart coating layer comprises several spaced-apart oily coating units, each constructed from a component including inorganic fillers and a second organic binder, specifically a porous oily coating unit. Because water-based coatings have low adhesion, each coating typically requires individual application during preparation, resulting in high costs. In this application, both the porous oily coating and the spaced-apart coating layer are porous oily layers, allowing for simultaneous application of both coatings, thus reducing costs. Furthermore, the oily coating unit may comprise 5 wt%–15 wt% inorganic fillers and 85 wt%–95 wt% a second organic binder.

[0035] In some embodiments of this application, in the spacer coating layer, the second organic binder has a molecular weight of 30W to 100W, and the second organic binder has characteristic peaks with a diffraction angle 2θ between 10° and 40°. The above-mentioned second organic binder has good crystallinity and adhesion, which can reduce the amount of sol in the electrolyte and ensure a good circulation interface between the coating and the electrode.

[0036] In some embodiments of this application, the particle size distribution width of the inorganic filler in the spacer coating layer satisfies: (D90-D10) / D50 = 1~3. The D50 particle size of the inorganic filler can be controlled to be 500nm~1000nm. By controlling the particle size distribution width of the inorganic filler within this range, the particle size is relatively uniform, which improves the uniformity of the coating structure.

[0037] In some embodiments of this application, the inorganic filler is selected from at least one of silica, alumina, silicon dioxide, calcium oxide, magnesium oxide, ZnO, TiO2, boehmite, and ceramic fiber;

[0038] And / or, the second organic binder is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, hexafluoropropylene, and trifluoroethylene.

[0039] In some embodiments of this application, the thickness of the spacer coating is 0.5 μm to 1.5 μm. Further, the thickness of the spacer coating can be controlled to be 0.5 μm to 1 μm, 0.8 μm to 1.6 μm, or 1 μm to 1.5 μm.

[0040] In some embodiments of this application, the base film is selected from one or more composite films selected from PE film, PP film, PET film, and PI film.

[0041] In some embodiments of this application, the thickness of the base film is 1 μm to 20 μm. Further, the thickness of the base film may be 3.0 μm to 15.0 μm, 5 μm to 12 μm, 6 μm to 10 μm, 4 μm to 8 μm, or 5 μm to 17 μm.

[0042] In some embodiments of this application, the areal density of the base film can be controlled at 1.0 g / m³. 2 ~12.0g / m 2 The porosity of the base membrane can be controlled to be greater than or equal to 30%; the tortuosity of the base membrane can be controlled to be less than or equal to 5.

[0043] A second aspect of this application provides a method for preparing any of the aforementioned battery separators, comprising the following steps:

[0044] A heat-resistant ceramic coating is applied to one surface of the base film;

[0045] A first oily slurry is prepared by mixing a component comprising polymer particles and a first organic binder with a first organic solvent, and a second oily slurry is prepared by mixing a component comprising inorganic fillers and a second organic binder with a second organic solvent.

[0046] The first oily slurry is coated on the surface of the base film away from the heat-resistant ceramic layer; at the same time, the second oily slurry is coated on the surface of the base film away from the heat-resistant ceramic coating at intervals, and the extension direction of the blank area between adjacent coating areas is inclined to the length direction of the base film. After drying, a battery separator is obtained.

[0047] In the above preparation method, the first and second oily slurries are coated on both sides of the composite membrane material, consisting of a base film and a heat-resistant ceramic coating, in a single, one-time process. This simplifies the preparation process and reduces production costs. Corresponding to the structural design of the battery separator, it thus achieves the aforementioned beneficial effects of a battery separator.

[0048] In some embodiments of this application, forming a heat-resistant ceramic coating on one surface of a base film includes: preparing a heat-resistant ceramic slurry by mixing a component comprising inorganic ceramic material and heat-resistant adhesive with solvent water, then applying the heat-resistant ceramic slurry to one surface of the base film using a micro-gravure roller, and forming a heat-resistant ceramic layer after drying.

[0049] In some embodiments of this application, the heat-resistant ceramic slurry further includes additives, which include at least one of dispersants and wetting agents. For example, the additives may be one or more of phosphate esters, acetylenic diols, polycarboxylic acid polymers, polysiloxanes, arylphenyl polyoxyethylene ethers, and polyethers.

[0050] In some embodiments of this application, the coating of the first oily slurry can be specifically achieved by using a micro-gravure roller to coat the first oily slurry onto the surface of the base film away from the heat-resistant ceramic layer.

[0051] In some embodiments of this application, the second oily slurry can be applied by using a gapped anilox roller to apply the second oily slurry intermittently to the surface of the base film away from the wear-resistant ceramic coating. The gapped anilox roller has spaced coating areas for applying the slurry, with recessed blank areas between adjacent coating areas. The extension direction of the recessed blank areas is at an angle of 30° to 60° to the rotation direction of the gapped anilox roller. Further, the ratio of the width of the coating area on the gapped anilox roller along the extension direction perpendicular to the recessed blank area to the width of the recessed blank area along its extension direction perpendicular to its extension direction is 0.5 to 3.0.

[0052] A third aspect of this application provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode, wherein the separator is any of the aforementioned battery separators.

[0053] In some embodiments of this application, the porous oily coating on the battery separator is disposed toward the positive electrode, and the spacer coating is disposed toward the negative electrode.

[0054] In some embodiments of this application, the porous oily coating on the battery separator is disposed toward the negative electrode, and the spacer coating is disposed toward the positive electrode.

[0055] In some embodiments of this application, the lithium-ion battery is a wound lithium-ion battery. Attached Figure Description

[0056] The present application will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0057] Figure 1 is a schematic diagram of the structure of the battery separator in Example 1;

[0058] Figure 2 is a schematic diagram of the surface structure of the spacer coating layer in the battery separator of Example 1. Detailed Implementation

[0059] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0060] Example 1

[0061] This embodiment proposes a battery separator, the structure of which is shown in Figure 1, including a base film 11, a heat-resistant ceramic coating 12, a porous oily coating 13, and a spacer coating layer 14.

[0062] The heat-resistant ceramic coating 12 is disposed on one surface of the base film 11. In this embodiment, the base film 11 is a PE film, and the heat-resistant ceramic coating 12 is an aqueous coating; by mass percentage, its components include 94% inorganic ceramic material, 5% heat-resistant adhesive, and 1% acetylenic diol as an additive; the inorganic ceramic material is specifically boehmite with a particle size distribution width (D90-D10) / D50 of 1.33 and a D50 of 0.3 μm, and the heat-resistant adhesive is modified styrene-butadiene rubber (manufacturer: Kraton, USA, product model: MD6951) with a glass transition temperature of 210℃.

[0063] A porous oily coating 13 is disposed on the surface of the heat-resistant ceramic coating 12 away from the base film 11. The components of the porous oily coating 13 include polymer particles and a first organic binder. In this embodiment, the polymer particles are acrylate copolymer particles (manufacturer: Shenzhen Deli New Material Technology Co., Ltd., product model: CFL) with a particle size distribution width (D90-D10) / D50 of 1.5, D50 of 5 μm, and a flow temperature Tf and glass transition temperature Tg difference (Tf-Tg) of 25 °C. The first organic binder is polyvinylidene fluoride (manufacturer: Dongyangguang Group, product model: 601A) with a molecular weight of 70W and characteristic peaks between diffraction angles 2θ and 20° and 25°. The mass ratio of polymer particles to the first organic binder is 3:7.

[0064] A spacer coating layer 14 is disposed on the base film 11 away from the surface of the heat-resistant ceramic coating 12. The spacer coating layer 14 includes a plurality of oily coating units 141 spaced apart, and blank units 142 are formed between adjacent oily coating units 141. The extension direction M of the blank units 142 is inclined to the length direction P of the base film 11, as shown in Figure 2. The components of the oily coating unit 141 include inorganic fillers and a second organic binder. In this embodiment, the inorganic filler is alumina (manufacturer: Zhejiang Jidun New Material Technology Co., Ltd., product model: AP55) with a particle size distribution width satisfying (D90-D10) / D50 = 1~3, specifically, D10 = 0.2um, D50 = 0.5um, and D90 = 1.2um; the second organic binder is polyvinylidene fluoride (manufacturer: Dongyangguang Group, product model: 601A) with a molecular weight of 70W and characteristic peaks between 20° and 25° of diffraction angle 2θ; according to the mass percentage, the composition of the oily coating unit 141 includes 20% inorganic filler and 80% second binder. In this embodiment, the angle between the extension direction M of the blank unit 142 and the length direction P of the base film 11 is 45°. The oil coating unit 141 is uniformly distributed on the surface of the base film 11, and the adjacent oil coating unit 141 and the blank unit 142 satisfy: W1 / W2 = 1.5, where W1 is the width of the oil coating unit 141 along the extension direction M perpendicular to the blank unit 142, and W2 is the width of the blank unit 142 along its extension direction M perpendicular to its extension direction.

[0065] The method for preparing the battery separator includes the following steps:

[0066] S1. Take 94% of boehmite, an inorganic ceramic material with a particle size distribution width (D90-D10) / D50 of 1.33 and a D50 of 0.3μm, 5% of styrene-butadiene rubber with a glass transition temperature of 210℃ and 1% alkynyl glycol as an additive, according to the mass percentage. Disperse them evenly in deionized water and mix them evenly to obtain a heat-resistant ceramic slurry.

[0067] S2. A layer of heat-resistant ceramic slurry is coated on one surface of the PE base film using a 180LPI micro-gravure roller, and after drying, a heat-resistant ceramic coating with a thickness of 1μm is obtained.

[0068] S3. Large-diameter polymer acrylate copolymer particles with a particle size distribution width (D90-D10) / D50 of 1.5, D50 of 5 μm, and a flow temperature Tf and glass transition temperature Tg difference of 25 °C are dispersed in the organic solvent N-methylpyrrolidone to prepare a dispersion with a solid content of 10%. Polyvinylidene fluoride (PVDF), a first organic binder with a molecular weight of 70W and characteristic peaks in the diffraction angle 2θ between 20° and 25°, is dissolved in the organic solvent N-methylpyrrolidone to obtain a binder solution with a solid content of 10%. Then, the dispersion and binder solution are mixed and stirred evenly at a mass ratio of acrylate copolymer particles to PVDF of 3:7 to obtain a first oily slurry.

[0069] S4. According to the mass percentage, take 80% of the second organic binder polyvinylidene fluoride with a molecular weight of 70W and a characteristic peak before the diffraction angle 2θ is 20° to 25° and 20% of the inorganic filler alumina. Dissolve the polyvinylidene fluoride in N-methylpyrrolidone and disperse the alumina in N-methylpyrrolidone. Mix and stir evenly to obtain the second oily slurry.

[0070] S5. Using a conventional 180LPI microgravure roller, the first oily slurry obtained in step S3 is coated onto the surface of the heat-resistant ceramic coating obtained in step S2, away from the PE base film. Simultaneously, using a 180LPI intermittent anilox roller, the second oily slurry obtained in step S4 is coated onto the surface of the PE base film, away from the heat-resistant ceramic coating. The coating of the first and second oily slurries is completed in one step. The 180LPI intermittent anilox roller has spaced coating areas for coating the slurry, with adjacent coating areas... There are recessed blank areas between the material areas. The extension direction of the recessed blank areas is 45° with the rotation direction of the gap anilox roller. The ratio of the width W1' of the coating area along the extension direction perpendicular to the recessed blank area to the width W2' of the recessed blank area along the extension direction perpendicular to its extension direction is W1' / W2' = 1.5. After drying, a porous oily coating with a thickness of 4μm is formed on the surface of the heat-resistant ceramic layer. A spacer coating layer with a thickness of 1μm is formed on the PE base film away from the surface of the heat-resistant ceramic layer to obtain the product battery separator.

[0071] Example 2

[0072] This embodiment proposes a battery separator, which differs from the battery separator of Example 1 in that: the inorganic ceramic material of the heat-resistant ceramic coating in this embodiment is replaced by boehmite (manufacturer: Zhejiang Jidun New Material Technology Co., Ltd., product model: BP10) with a particle size distribution width (D90-D10) / D50 of 2.0 and a D50 of 0.3 μm, instead of boehmite in Example 1. The other components, their formulation, structure and preparation methods are basically the same as those in Example 1.

[0073] Example 3

[0074] This embodiment proposes a battery separator, which differs from the battery separator of Example 1 in that: the inorganic ceramic material of the heat-resistant ceramic coating in this embodiment is replaced by boehmite (manufacturer: Zhejiang Jidun New Material Technology Co., Ltd., with particle size distribution width (D90-D10) / D50 of 0.67 and D50 of 0.3 μm, which is a product with particle size distribution adjusted by screening based on commercial BP10) instead of boehmite in Example 1. The other components, their formulation, structure and preparation methods are basically the same as those in Example 1.

[0075] Example 4

[0076] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: the heat-resistant adhesive component of the heat-resistant ceramic coating in this embodiment uses PAA (manufacturer Gao Rui) with a glass transition temperature Tg of 180℃ instead of styrene-butadiene rubber in Embodiment 1, while the formulation, structure and preparation method of other components are the same as those in Embodiment 1.

[0077] Example 5

[0078] This embodiment proposes a battery separator, which differs from the battery separator of Example 1 in that: the polymer particles of the porous oily coating component in this embodiment are acrylate copolymer particles (manufacturer: Shenzhen Deli New Material Technology Co., Ltd., model: CFL, product before spray drying and grading) with a particle size distribution width (D90-D10) / D50 of 3, D50 of 5 μm, and a Tf-Tg of 25 °C, instead of the acrylate copolymer particles in Example 1. The formulation, structure, and preparation method of other components are basically the same as those in Example 1.

[0079] Example 6

[0080] This embodiment proposes a battery separator, which differs from the battery separator of Example 1 in that: the polymer particles of the porous oily coating component in this embodiment are acrylate copolymer particles (manufacturer: Shenzhen Deli New Material Technology Co., Ltd., model: CFL, spray-dried and graded product) with a particle size distribution width (D90-D10) / D50 of 1.04, a D50 of 4.8 μm, and a Tf-Tg of 25 °C, instead of the acrylate copolymer particles in Example 1. The formulation, structure, and preparation method of other components are basically the same as those in Example 1.

[0081] Example 7

[0082] This embodiment proposes a battery separator, which differs from the battery separator of Example 1 in that: the polymer particles of the porous oily coating component in this embodiment are acrylate copolymer particles (manufacturer: Shenzhen Deli New Material Technology Co., Ltd., trade name: CFL) with a particle size distribution width (D90-D10) / D50 of 1.5, a D50 of 5 μm, and a Tf-Tg of 10 °C, instead of the acrylate copolymer particles in Example 1. The formulation, structure, and preparation method of other components are the same as those in Example 1.

[0083] Example 8

[0084] This embodiment proposes a battery separator, which differs from the battery separator of Example 1 in that: the first organic binder of the porous oily coating in this embodiment is polyvinylidene fluoride (manufacturer: Sinochem Lantian Group Co., Ltd.) with a molecular weight of 30W and a characteristic peak between 30° and 40° diffraction angle 2θ, instead of polyvinylidene fluoride in Example 1. The formulation, structure and preparation method of other components are the same as those in Example 1.

[0085] Example 9

[0086] This embodiment proposes a battery separator, which differs from the battery separator of Example 1 in that: the first organic binder of the porous oily coating in this embodiment is polyvinylidene fluoride (manufacturer: Sinochem Lantian Group Co., Ltd., product model: 2703) with a molecular weight of 80W and a characteristic peak between 10° and 15° diffraction angle 2θ, instead of polyvinylidene fluoride in Example 1. The formulation, structure and preparation method of other components are the same as those in Example 1.

[0087] Example 10

[0088] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the width ratio W1 / W2 of adjacent oil-coated units and blank units on the spacer coating layer is 0.5, unlike W1 / W2 = 1.5 in Embodiment 1; other structures are the same as in Embodiment 1. Accordingly, in the battery separator preparation process of this embodiment, the width ratio W1' / W2' of the coated area and the recessed blank area on the gapped anilox roller used in the preparation of the spacer coating layer is 0.5, unlike W1' / W2' = 1.5 in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0089] Example 11

[0090] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the width ratio W1 / W2 of adjacent oil-coated units and blank units on the spacer coating layer is 3, unlike W1 / W2 = 1.5 in Embodiment 1; other structures are the same as in Embodiment 1. Accordingly, in the battery separator preparation process of this embodiment, the width ratio W1' / W2' of the coated area and the recessed blank area on the gap anilox roller used in the preparation of the spacer coating layer is 3, unlike W1' / W2' = 1.5 in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0091] Example 12

[0092] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the angle between the extension direction M of the blank unit on the spacer coating layer and the length direction P of the base film is 30°, unlike the 45° in Embodiment 1; other structures are the same as in Embodiment 1. Correspondingly, in the battery separator preparation process of this embodiment, the extension direction of the recessed blank area on the gap anilox roller used in the preparation of the spacer coating layer is 30° to the rotation direction of the gap anilox roller, unlike the 45° in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0093] Example 13

[0094] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the angle between the extension direction M of the blank unit on the spacer coating layer and the length direction P of the base film is 60°, unlike the 45° in Embodiment 1; other structures are the same as in Embodiment 1. Correspondingly, in the battery separator preparation process of this embodiment, the extension direction of the recessed blank area on the gap anilox roller used in the preparation of the spacer coating layer is 60° to the rotation direction of the gap anilox roller, unlike the 45° in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0095] Example 14

[0096] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the width ratio W1 / W2 of adjacent oil-coated units and blank units on the spacer coating layer is 1, unlike W1 / W2 = 1.5 in Embodiment 1; other structures are the same as in Embodiment 1. Accordingly, in the battery separator preparation process of this embodiment, the width ratio W1' / W2' of the coated area and the recessed blank area on the gap anilox roller used in the preparation of the spacer coating layer is 1, unlike W1' / W2' = 1.5 in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0097] Example 15

[0098] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the width ratio W1 / W2 of adjacent oil-coated units and blank units on the spacer coating layer is 2, unlike W1 / W2 = 1.5 in Embodiment 1; other structures are the same as in Embodiment 1. Accordingly, in the battery separator preparation process of this embodiment, the width ratio W1' / W2' of the coated area and the recessed blank area on the gap anilox roller used in the preparation of the spacer coating layer is 2, unlike W1' / W2' = 1.5 in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0099] Example 16

[0100] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the angle between the extension direction M of the blank unit on the spacer coating layer and the length direction P of the base film is 42°, unlike the 45° in Embodiment 1; other structures are the same as in Embodiment 1. Correspondingly, in the battery separator preparation process of this embodiment, the extension direction of the recessed blank area on the gap anilox roller used in the preparation of the spacer coating layer is 42° with the rotation direction of the gap anilox roller, unlike the 45° in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0101] Example 17

[0102] This embodiment proposes a battery separator, which differs from the battery separator of Embodiment 1 in that: in this embodiment, the angle between the extension direction M of the blank unit on the spacer coating layer and the length direction P of the base film is 48°, unlike the 45° in Embodiment 1; other structures are the same as in Embodiment 1. Correspondingly, in the battery separator preparation process of this embodiment, the extension direction of the recessed blank area on the gap anilox roller used in the preparation of the spacer coating layer is 48° with the rotation direction of the gap anilox roller, unlike the 45° in Embodiment 1; other preparation operations are the same as in Embodiment 1.

[0103] Comparative Example 1

[0104] This comparative example proposes a battery separator, which differs from the battery separator of Example 1 in that: the porous oily coating in Example 1 is replaced with a porous watery coating; the other structures are the same as in Example 1. Accordingly, in the preparation process of the battery separator in this comparative example, in step S3, an equal amount of water is used instead of the organic solvent N-methylpyrrolidone used in step S3 of Example 1 to prepare an aqueous slurry, and in step S5, the aqueous slurry is used instead of the first oily slurry in Example 1 to prepare a porous watery coating on the surface of the heat-resistant ceramic coating away from the PE base film. Since the adhesion of the aqueous slurry is weak, the coating of the porous watery coating and the coating of the spacer coating cannot be carried out simultaneously, but are prepared separately and sequentially. Specifically, the aqueous slurry is first coated on the surface of the heat-resistant ceramic coating away from the PE base film, and after drying, a porous watery coating is obtained. Then, a second oily slurry is coated on the side of the PE base film away from the heat-resistant ceramic coating, and after drying, a spacer coating is obtained. Thus, the preparation of each layer on the base film involves three coatings. The other component formulation and preparation procedures are the same as in Example 1.

[0105] Comparative Example 2

[0106] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the angle between the extension direction M of the blank unit on the spacer coating layer and the length direction P of the base film is 0°, unlike the 45° angle in Example 1; other structures are the same as in Example 1. Correspondingly, in the preparation process of the battery separator in this comparative example, the extension direction of the recessed blank area on the spacer coating roller is 0° to the rotation direction of the spacer coating roller, unlike the 45° angle in Example 1; other preparation operations are the same as in Example 1.

[0107] Comparative Example 3

[0108] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the angle between the extension direction M of the blank unit on the spacer coating layer and the length direction P of the base film is 90°, unlike the 45° angle in Example 1; other structures are the same as in Example 1. Correspondingly, in the preparation process of the battery separator in this comparative example, the extension direction of the recessed blank area on the spacer coating roller is 90° to the rotation direction of the spacer coating roller, unlike the 45° angle in Example 1; other preparation operations are the same as in Example 1.

[0109] Comparative Example 4

[0110] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that: a fully coated oily layer is used in this comparative example instead of the spacer coating layer in Example 1, and the composition and thickness of the oily coating layer in this comparative example are the same as the oily coating unit of the spacer coating layer in Example 1, while other structures are the same as in Example 1. Accordingly, in the preparation process of the battery separator in this comparative example, the spacer coating layer is prepared using a 180LPI microgravure roller instead of the 180LPI gap anilox roller in Example 1, and the oily coating layer is prepared on the surface of the PE base film away from the heat-resistant ceramic layer; other preparation operations are the same as in Example 1.

[0111] Comparative Example 5

[0112] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the first organic binder of the porous oily coating in this comparative example is polyvinylidene fluoride (manufacturer: Sinochem Lantian Group Co., Ltd.) with a molecular weight of 20W and a characteristic peak between 0° and 10° diffraction angle 2θ, instead of the polyvinylidene fluoride in Example 1. The formulation, structure and preparation method of other components are the same as those in Example 1.

[0113] Comparative Example 6

[0114] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the polymer particles of the porous oily coating component in this comparative example are acrylate copolymer particles (manufacturer: Shenzhen Deli New Material Technology Co., Ltd.) with a particle size distribution width (D90-D10) / D50 of 3.27, a D50 of 5.5 μm, and a Tf-Tg of 25 °C, instead of the acrylate copolymer particles in Example 1. The formulation, structure, and preparation method of other components are basically the same as those in Example 1.

[0115] Comparative Example 7

[0116] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the polymer particles of the porous oily coating component in this comparative example are acrylate copolymer particles (manufacturer: Shenzhen Deli New Material Technology Co., Ltd.) with a particle size distribution width (D90-D10) / D50 of 0.83, a D50 of 6 μm, and a Tf-Tg of 25 °C, instead of the acrylate copolymer particles in Example 1. The formulation, structure, and preparation method of other components are basically the same as those in Example 1.

[0117] Comparative Example 8

[0118] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the polymer particles of the porous oily coating component in this comparative example are acrylate copolymer particles (manufacturer: Shenzhen Deli New Material Technology Co., Ltd.) with a particle size distribution width (D90-D10) / D50 of 1.5, a D50 of 5 μm, and a Tf-Tg of 5 °C, instead of the acrylate copolymer particles in Example 1. The formulation, structure, and preparation method of other components are basically the same as those in Example 1.

[0119] Comparative Example 9

[0120] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the heat-resistant ceramic coating component of this comparative example battery separator uses PAA (manufacturer: Gaorui) with a glass transition temperature Tg of 150℃ instead of styrene-butadiene rubber in Example 1. The formulation, structure and preparation method of other components are the same as those of Example 1.

[0121] Comparative Example 10

[0122] This comparative example presents a battery separator that differs from the battery separator of Example 1 in that the inorganic ceramic material used in the heat-resistant ceramic coating of this comparative example is boehmite with a particle size distribution width (D90-D10) / D50 of 3.0 and a D50 of 0.3 μm, instead of the boehmite in Example 1. The other components, their formulation, structure, and preparation methods are basically the same as those in Example 1.

[0123] The specific selection of some layer components and structural settings of the battery separators in the above embodiments and comparative examples are shown in Table 1 below. The total coating thickness on each battery separator and the number of coating processes on the base film are shown in Table 2. The total coating thickness was directly measured using a Mahr thickness gauge. The total coating thickness was obtained by applying the coating based on the designed thickness; therefore, the actual measured thickness may fluctuate, resulting in differences. Furthermore, the porous oil-based coating contains large-diameter polymer particles, which are not uniformly spherical. The particle size distribution width also affects the total coating thickness, hence the differences in total coating thickness.

[0124] The battery separators of the above embodiments and comparative examples can be further applied to the preparation of lithium-ion batteries. Specific preparation methods include:

[0125] S1. Preparation of the positive electrode sheet: Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) are mixed in a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry is uniformly coated onto one surface of an 8 μm thick aluminum foil. The aluminum foil is dried at 125°C for 1 hour to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. After cold pressing, cutting, and slitting, the sheet is dried under vacuum at 125°C for 2 hours to obtain a positive electrode with dimensions of 65 mm × 860 mm.

[0126] S2. Preparation of the negative electrode sheet: Graphite (negative electrode active material), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (sodium carboxymethyl cellulose) were mixed at a mass ratio of 98:1:1. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry with a solid content of 60 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil. The copper foil was dried at 120°C to obtain a negative electrode with a single-sided coating of the negative electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a negative electrode with a double-sided coating of the negative electrode material layer. After cold pressing, cutting, and slitting, the negative electrode was dried under vacuum at 120°C for 2 hours to obtain a negative electrode with dimensions of 69 mm × 868 mm.

[0127] S3. Electrolyte preparation: In an argon-atmospheric glove box with a water content of <10ppm, ethyl oxalate (EC), propylene carbonate (PC), and diformimide (DMC) are mixed in a mass ratio of 3:2:4 to obtain an organic solvent. Then, lithium hexafluorophosphate is added to the organic solvent to obtain the electrolyte. The concentration of the lithium salt is 1 mol / L.

[0128] S4. Assembly of Lithium-ion Batteries: The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, the lithium-ion battery is obtained.

[0129] The battery separators from Examples 1-17 and Comparative Examples 1-10 were further assembled into lithium-ion batteries using the above methods. The battery performance was then further tested, with specific test items and methods as follows:

[0130] 1. Adhesion between the battery separator and the electrodes (including positive and negative electrodes)

[0131] The test method is as follows: after hot pressing the diaphragm and the corresponding electrode at 93℃ and 3MPa for 5 minutes, the force required for the two to separate is tested.

[0132] 2. Battery separator thermal shrinkage rate test: Cut the separator into 30*70mm pieces, bake them in an oven at 130℃ for 0.5h, remove them and let them cool to room temperature. Measure the size A*Bmm after baking and calculate the corresponding shrinkage rate. MD and TD represent the longitudinal and transverse shrinkage rates, respectively.

[0133] 3. Gap value test: The Gap value is the difference in thickness of the battery separator before and after hot pressing. The test method is as follows: first measure the thickness D1 of the 8-layer battery separator, then measure the thickness D2 of the 8-layer battery separator after hot pressing at 85℃ and 1Mpa for 1 hour. The Gap value is equal to D1-D2.

[0134] 4. Thickness after hot pressing: Thickness after hot pressing refers to the thickness of the coating after hot pressing. This thickness is a calculated value, which is equal to the total thickness minus the change in thickness of the coating after hot pressing. The Gap value is the thickness of 8 layers. Therefore, the thickness of a single layer needs to be divided by 8. Thus, the thickness after hot pressing = total coating thickness - Gap value / 8.

[0135] 5. Cyclic Interface Test: Place the lithium-ion battery in a 25℃ environment and let it stand for 30 minutes. Then charge it at a constant current of 3.5C to 4.50V, and then charge it at a constant voltage of 4.50V to 0.05C. Let it stand for 5 minutes, and then discharge it at a constant current of 0.7C to 3.0V. This constitutes one cycle (cls). After 300cls, disassemble the cell interface and observe the lithium plating on the negative electrode. OH indicates a specific location of lithium in the cell. In the cell, the separator width > the negative electrode width > the positive electrode width; the location exceeding this width is the OH position. Lithium plating generally occurs on the negative electrode because the negative electrode potential is low, potentially below 0V, making it prone to plating. Mainly, lithium plating refers to plating on the cell plane, i.e., lithium plating on the entire surface of the negative electrode. The criteria for judging the degree of lithium plating are: the appearance of silvery-white lithium elemental is considered severe; for purple or black spots, the size matters; less than 1 / 10 of the cell height is considered slight, otherwise it is severe.

[0136] 6. High-temperature external short test: Place the battery cell in an oven at a specific temperature (57°C), short-circuit the two poles with a resistor of a specific size (60mΩ), and observe whether it catches fire, explodes, or produces gas. If it does not catch fire, explode, or produce gas, it is considered PASS.

[0137] The performance of the battery separators and corresponding assembled lithium-ion batteries of each embodiment and comparative example was tested using the above methods, and the results are shown in Table 2.

[0138] Table 1

[0139] Table 2

[0140] According to Tables 1 and 2, a comparison of the various embodiments (especially Embodiment 1) and Comparative Example 1 shows that the porous aqueous coating (different from the porous oil coating in Embodiment 1) on the heat-resistant ceramic coating surface of the battery separator in Comparative Example 1 has very poor adhesion, resulting in severe lithium plating at the OH (Over Hang) position of the negative electrode interface during cycling. In contrast, the embodiments use a porous oil coating with strong adhesion, which effectively reduces the risk of lithium plating due to poor adhesion at the OH position. Furthermore, in the coating preparation process of the battery separator in Comparative Example 1, due to the poor adhesion of the aqueous slurry, each coating needs to be applied individually. In contrast, the porous oil coating used in the embodiments has strong adhesion of the corresponding oil slurry, allowing for simultaneous coating on both sides, thereby reducing the number of coating operations and lowering production costs.

[0141] Comparing Examples 1, 12, 13, 16, 17 and Comparative Examples 2 and 3, in Comparative Example 2, the angle between the extension direction M of the blank cells on the spacer coating layer and the length direction P of the base film is 0°. When applied to a lithium-ion battery, the electrolyte cannot quickly diffuse from the beginning and end to the middle during battery cycling, resulting in electrolyte bridging in the middle and severe lithium deposition at the main interface. Furthermore, there are many abnormal appearance phenomena such as streaks or bursting during the winding process of the battery separator. In Comparative Example 3, the angle between the extension direction M of the blank cells on the spacer coating layer and the length direction P of the base film is 90°, resulting in good lithium-ion battery performance. However, the coating doctor blade and printing roller suffer severe wear during the battery separator preparation process, leading to high production costs. In Examples 1, 12, 13, 16, and 17, the extension direction M of the blank cells on the spacer coating of the battery separator is inclined to the length direction P of the base film. This facilitates the diffusion of the electrolyte from the beginning and end towards the middle, reducing the risk of lithium plating in the middle due to electrolyte bridging. It also reduces appearance abnormalities such as streaks or cracks during separator winding, improving product yield. Specifically, in Example 12, the angle (30°) between the extension direction M of the blank cells and the length direction P of the base film is small, making it easier for the electrolyte to diffuse from the beginning and end to the middle, resulting in a good interface. In Example 13, the angle (60°) between the extension direction M of the blank cells and the length direction P of the base film is large, making it relatively difficult for the electrolyte to diffuse from the beginning and end to the middle, resulting in slight lithium plating at the interface. Therefore, considering the processing difficulty and wear of the printing roller, the separator winding yield, and the prevention of interface lithium plating, the angle between the extension direction M of the blank cells on the spacer coating of the battery separator and the length direction P of the base film can be controlled between 30° and 60°.

[0142] Comparing Examples 1, 10, 11, 14, and 15, compared to Example 1, in Example 10, the ratio (W1 / W2) of the width of the oil-coated unit to the width of the blank unit in the spacer coating layer of the battery separator is reduced, the spacing between adjacent oil-coated units is increased, the adhesion of the coating to the anode (i.e., the negative electrode) is reduced, and slight lithium plating occurs at the OH position of the negative electrode interface. Compared to Example 1, in Example 11, the ratio (W1 / W2) of the width of the oil-coated unit to the width of the blank unit in the spacer coating layer of the battery separator is increased, the spacing between adjacent oil-coated units is reduced, the relative resistance to lithium-ion transport is increased, and slight lithium plating occurs at the cell corners during cycling. Therefore, considering the combined effects of the adhesion between the separator and the electrode and the lithium-ion transport resistance on lithium plating, the ratio (W1 / W2) of the width of the oil-coated unit to the width of the blank unit in the spacer coating layer can be controlled within the range of 0.5 to 3.0.

[0143] Comparing the various embodiments (especially Embodiment 1) and Comparative Example 4, the battery separator of Comparative Example 4 uses a fully coated oily coating layer instead of the interstitial coating layer of the battery separator of Embodiment 1. This results in high ion transport resistance, rapid capacity decay during battery cycling, and relatively severe lithium plating in the later stages of the main body. In the battery separator of Embodiment 1, several oily coating units are arranged at intervals to form an interstitial coating layer. The interstitial arrangement of adjacent oily coating units can effectively reduce ion transport resistance, alleviate cycle capacity decay, and improve interface lithium plating.

[0144] Comparing Examples 1, 8, 9 and Comparative Example 5, the first organic binder in the porous oily coating of the battery separator in Comparative Example 5 has a very small molecular weight, high crystallinity, and is hard, resulting in very weak adhesion. Therefore, severe lithium deposition at the negative electrode interface and large volume expansion occur during battery cycling. Compared to Comparative Example 5, the first organic binder in the porous oily coating of the battery separator in Example 8 has a larger molecular weight, lower crystallinity, and stronger adhesion, significantly improving lithium deposition and volume expansion at the negative electrode interface during battery cycling. Example 1 shows a significant improvement over Comparative Example 5. In Example 9, the first organic binder in the porous oily coating of the battery separator has a further increased molecular weight and further decreased crystallinity, resulting in strong adhesion, which affects electrolyte diffusion and causes slight black spots at the main interface. In addition, if the molecular weight of the first organic binder is too large, the porosity is poor, the permeability is slightly high, and the lithium-ion transport resistance is high, which may also cause black spots on the main interface. In summary, the molecular weight of the first organic binder in the porous oily coating can be controlled between 30W and 100W or between 30W and 80W; the first organic binder has characteristic peaks between diffraction angles of 10° and 40°.

[0145] Compared with Examples 1, 5, and 6 and Comparative Examples 6 and 7, the porous oily coating of the battery separator in Comparative Example 6 has a larger particle size distribution width (D90-D10) / D50 of polymer particles, which is 3.27. The polymer particles are very dispersed, with a large number of large and small particles. The thickness of the prepared battery separator is uneven and fluctuates greatly. During battery assembly, electrode misalignment is likely to occur, the cell yield is reduced, and the adhesion is decreased. Lithium plating is likely to occur at the OH position of the negative electrode interface. In addition, there are many large particles. After hot pressing, the cell has the risk of being too thick. In Example 5, the particle size distribution width (D90-D10) / D50 of the polymer particles decreased to 3.0, the polymer particle size was slightly dispersed, the amount of large and small particles was relatively reduced, the thickness fluctuation was improved, the adhesion between the porous oily coating and the cathode (i.e., the positive electrode) was significantly enhanced, the interface in the cycle test was good, and the amount of large particles was relatively reduced. The thickness after hot pressing was reduced, but there was still a slight risk of being too thick. In Example 1, the particle size distribution width (D90-D10) / D50 of the polymer particles in the battery separator decreased to 1.5, the battery separator thickness fluctuation was small, the adhesion between the porous oily coating and the positive electrode was strong, the thickness after hot pressing was small, and the product performance was excellent. In Example 6, the particle size distribution width of the polymer particles was further reduced to 1.04, the particle size was relatively concentrated, and compared with Example 1, the coating Gap value was slightly smaller, the thickness after hot pressing was slightly thicker, and there was a slight risk of being too heavy, but the interface of the negative electrode was good in the cycle test. In contrast, the polymer particle size distribution width (D90-D10) / D50 in the porous oil coating of the battery separator in Comparative Example 7 is smaller and the particle size is more concentrated, but the raw material cost is too high. Therefore, considering production cost, stability, cell thickness, and lithium deposition at the interface during cycling, the polymer particle size distribution width (D90-D10) / D50 in the porous oil coating can be controlled within the range of 1 to 3.

[0146] Comparing Examples 1 and 7 with Comparative Example 8, the flow temperature (Tf) and glass transition temperature (Tg) of the polymer particles in the porous oily coating of the battery separator in Comparative Example 8 are relatively close, with a difference (Tf-Tg) of 5°C. The polymer particles are too soft to provide support and cannot effectively improve lithium plating at the corners, resulting in severe lithium plating at the battery corners. In Example 7, the Tf-Tg of the polymer particles increases to 10°C, increasing hardness and providing some support, thus improving lithium plating at the battery corners, with only slight lithium plating remaining. In Example 1, the Tf-Tg of the polymer particles increases to 25°C, indicating high hardness and effective support, resulting in a good interface during battery cycling. Therefore, the Tf-Tg of the polymer particles can be controlled above 10°C.

[0147] Comparing Examples 1 and 4 with Comparative Example 9, the heat-resistant adhesive in the heat-resistant ceramic coating of the battery separator in Comparative Example 9 has an excessively low glass transition temperature (Tg), resulting in weak coating heat resistance, a large thermal shrinkage rate of the separator, poor high-temperature performance of the battery, and a 0% pass rate in the high-temperature external short-circuit test. In Examples 1 and 4, the increased Tg of the heat-resistant adhesive improves the heat resistance of the coating, thereby enhancing the high-temperature performance of the battery. Therefore, the glass transition temperature (Tg) of the heat-resistant adhesive in the heat-resistant ceramic coating can be controlled to be greater than or equal to 180°C.

[0148] Comparing Examples 1-3 and Comparative Example 10, the particle size distribution width (D90-D10) / D50 of the inorganic ceramic material in the heat-resistant ceramic coating of the battery separator in Comparative Example 10 was too large. The particle size distribution was too wide, resulting in loose packing of the inorganic ceramic material in the coating, a high thermal shrinkage rate of the separator, poor high-temperature resistance of the battery, and a 0% pass rate in the high-temperature external short-circuit test. In Example 2, the particle size distribution width (D90-D10) / D50 of the inorganic ceramic material was reduced to 2.0, increasing the packing density of the inorganic ceramic material in the coating, reducing the thermal shrinkage rate of the separator, improving the high-temperature resistance of the battery, and increasing the pass rate in the high-temperature external short-circuit test. In Example 1, the particle size distribution width (D90-D10) / D50 of the inorganic ceramic material was reduced to 1.33, resulting in tight packing of the inorganic ceramic material in the coating, a low thermal shrinkage rate of the separator, good heat resistance of the battery, and a 100% pass rate in the high-temperature external short-circuit test. In Example 3, the particle size distribution width (D90-D10) / D50 of the inorganic ceramic filler was further reduced to 0.67. The material particle size was highly concentrated, the coating was densely packed, the membrane thermal shrinkage rate was low, and the battery had good high-temperature resistance. However, the inorganic ceramic material with this particle size distribution width was expensive. Therefore, considering both production cost and product thermal stability, the particle size distribution width (D90-D10) / D50 of the inorganic ceramic filler can be roughly controlled between 0.5 and 2.

[0149] The embodiments described above are merely examples of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.

Claims

1. A battery separator, comprising: a base film; a heat-resistant ceramic coating layer disposed on a surface of the base film; a porous oil coating layer disposed on a surface of the heat-resistant ceramic coating layer facing away from the base film; components of the porous oil coating layer comprising polymer particles and a first organic binder; and a spacer coating layer disposed on a surface of the base film facing away from the heat-resistant ceramic coating layer, the spacer coating layer comprising a plurality of oil coating units arranged at intervals, adjacent oil coating units forming a blank unit therebetween, an extension direction M of the blank unit being inclined to a length direction P of the base film, components of the oil coating unit comprising inorganic fillers and a second organic binder. an angle between the extension direction M and the length direction P is 30°-60°; and / or, adjacent oil coating units and the blank unit satisfy: W1 / W2=0.5-3, wherein W1 is a width of the oil coating unit along a direction perpendicular to the extension direction M, and W2 is a width of the blank unit along a direction perpendicular to the extension direction M. the angle between the extension direction M and the length direction P is 42°-48°. adjacent oil coating units and the blank unit satisfy: W1 / W2=1-2. in the porous oil coating layer, a particle size distribution width of the polymer particles satisfies: 0<(D90-D10) / D50≤3; and a difference between a flow temperature Tf and a glass transition temperature Tg of the polymer particles is 10℃-50℃; and / or, a molecular weight of the first organic binder is 30W-100W, and the first organic binder has a characteristic peak at a diffraction angle 2θ of 10°-40°. a particle size distribution width of the polymer particles satisfies: 1<(D90-D10) / D50≤3. a particle size distribution width of the polymer particles satisfies: 2<(D90-D10) / D50≤2.5; and a difference between a flow temperature Tf and a glass transition temperature Tg of the polymer particles is 20℃-50℃. a D50 particle size of the polymer particles is 5um-15um. the polymer particles are selected from at least one of polyamide, polyacrylonitrile, polyethylene oxide, polyurethane, polyphenylene ether, and acrylate copolymer; and / or, the first organic binder is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, hexafluoropropylene, and trifluoroethylene. components of the heat-resistant ceramic coating layer comprise inorganic ceramic material and heat-resistant glue; a particle size distribution width of the inorganic ceramic material satisfies: (D90-D10) / D50=0.5-2, and a glass transition temperature of the heat-resistant glue is greater than or equal to 180℃. the inorganic ceramic material is selected from at least one of silicon dioxide, aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, ZnO, TiO2, boehmite, and ceramic fiber; and / or, the heat-resistant glue is selected from at least one of polyacrylic and styrene-butadiene rubber. a molecular weight of the second organic binder in the spacer coating layer is 30W-100W, and the second organic binder has a characteristic peak at a diffraction angle 2θ of 10°- 40°. ​ ​ ​ ​ ​ 2. The battery separator of claim 1, wherein, ​ ​ 3. The battery separator of claim 2, wherein, ​ 4. The battery separator of claim 2, wherein, ​ 5. The battery separator of claim 1, wherein, ​ ​ 6. The battery separator of claim 5 wherein, ​ 7. The battery separator of claim 6 wherein, ​ 8. The battery separator of claim 6 wherein, ​ 9. The battery separator of claim 5 wherein, ​ ​ 10. The battery separator of claim 1, wherein, ​ 11. The battery separator of claim 10, wherein, ​ ​ 12. The battery separator of any one of claims 1 to 11, wherein, ​ 13. The battery separator of claim 12, wherein, The inorganic filler is selected from at least one of silicon dioxide, aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, ZnO, TiO2, boehmite, and ceramic fiber; And / or, the second organic binder is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, hexafluoropropylene, and trifluoroethylene.

14. A method for preparing the battery separator according to any one of claims 1 to 13, comprising the following steps: applying a heat-resistant ceramic coating on one surface of the base film; preparing a first oil-based slurry by mixing a component comprising polymer particles and a first organic binder with a first organic solvent, and preparing a second oil-based slurry by mixing a component comprising an inorganic filler and a second organic binder with a second organic solvent; applying the first oil-based slurry on the surface of the base film away from the heat-resistant ceramic layer, and simultaneously applying the second oil-based slurry on the surface of the base film away from the heat-resistant ceramic coating in an interval manner, and making the extension direction of the blank area between adjacent application areas inclined to the length direction of the base film, and drying to obtain the battery separator.

15. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator sandwiched between the positive electrode sheet and the negative electrode sheet, wherein the separator is the battery separator according to any one of claims 1 to 13.

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