Diaphragm and preparation method thereof, battery monomer and energy storage device

Abstract

The invention relates to the technical field of new energy, in particular to a diaphragm and a preparation method thereof, a battery monomer and an energy storage device. The diaphragm comprises a base film, a first adhesive layer and a second adhesive layer, wherein each of the first adhesive layer and the second adhesive layer comprises a first adhesive and a second adhesive; a) the mass ratio of the second adhesive in the total amount of the adhesive of the first adhesive layer is greater than the mass ratio of the second adhesive in the total amount of the adhesive of the second adhesive layer; b) one side, deviating from the first surface, of the first adhesive layer is provided with a plurality of first recesses of which the inner walls are provided with pores; and c) the surface density of the first adhesive layer is greater than that of the second adhesive layer. The invention focuses on improving the bonding capacity of the diaphragm and the adhesive layer on one side of the positive pole piece, and aims at constructing an integrated structure of the diaphragm and the positive pole piece. When applied to a winding battery cell, the composite material can improve the wrinkle phenomenon of the inner layer of the winding cell after the battery is charged and discharged, and can improve the risk of micro-short circuit or short circuit of the battery cell caused by dendritic crystals formed by lithium precipitation.

Description

Separator and its preparation method, battery cell and energy storage device Technical Field

[0001] This application relates to the field of new energy technology, and in particular to separators and their preparation methods, battery cells and energy storage devices. Background Technology

[0002] Currently, battery cores suffer from wrinkling issues. For example, square aluminum-cased batteries exhibit wrinkling in the inner layer of the core, particularly at the square corners. Lithium deposition and dendrite formation at these wrinkles pose a risk of micro-short circuits or short circuits within the cell; therefore, it is necessary to reduce core wrinkling.

[0003] Traditional methods for reducing core wrinkles primarily involve controlling deformation during the winding process or adjusting the formation process. These methods include reducing tension and tension fluctuations, using circular winding needle structures or semi-automatic winding inserts, reducing baking time to minimize diaphragm thermal shrinkage, reducing impact through multiple liquid injections, and employing negative pressure fixtures for formation. However, among these methods, tension control is relatively poor, and other methods have limited effectiveness in improving wrinkles generated after winding and formation. Summary of the Invention

[0004] Based on this, the first aspect of this application provides a diaphragm, the technical solution of which is as follows:

[0005] A diaphragm includes a base membrane, a first adhesive layer, and a second adhesive layer. The base membrane has opposing first and second surfaces. The first adhesive layer is located on the first surface, and the second adhesive layer is located on the second surface. Both the first and second adhesive layers include a first adhesive and a second adhesive.

[0006] Wherein, the first adhesive and the second adhesive satisfy: a) the particle size D50 of the first adhesive is greater than the particle size D50 of the second adhesive; b) after being soaked in the electrolyte, the adhesive force of the first adhesive is less than the adhesive force of the second adhesive;

[0007] The first adhesive layer and the second adhesive layer satisfy the following conditions: a) the mass percentage of the second adhesive in the total amount of adhesive in the first adhesive layer is greater than the mass percentage of the second adhesive in the total amount of adhesive in the second adhesive layer; b) the first adhesive layer has a plurality of first recesses with pores on the side opposite to the first surface; c) the areal density of the first adhesive layer is greater than the areal density of the second adhesive layer.

[0008] The second aspect of this application provides a method for preparing the above-mentioned diaphragm, the technical solution of which is as follows:

[0009] A method for preparing a diaphragm includes the following steps:

[0010] A base film is provided, the base film having opposing first and second surfaces;

[0011] A first slurry is coated on the first surface to form a first adhesive layer, and a second slurry is coated on the second surface to form a second adhesive layer; wherein, both the first slurry and the second slurry include the first adhesive and the second adhesive, the mass percentage of the second adhesive in the total amount of adhesive in the first slurry is greater than the mass percentage of the second adhesive in the total amount of adhesive in the second slurry, the coating surface density of the first slurry is greater than the coating surface density of the second slurry, and the first adhesive layer forms a plurality of first depressions with pores on the side away from the first surface.

[0012] A third aspect of this application provides a battery cell, the battery cell including a wound body, the wound body being wound along a virtual axis by a laminate, the laminate including a positive electrode, a negative electrode and a spacer film located between the positive electrode and the negative electrode, the spacer film being as described above, and a first adhesive layer being bonded to the positive electrode and a second adhesive layer being bonded to the negative electrode.

[0013] A fourth aspect of this application provides an energy storage device comprising a battery cell as described above, the battery cell being used to store electrical energy.

[0014] Compared with traditional solutions, this application has the following advantages:

[0015] This application analyzes the causes of wrinkling problems after the winding and formation of the battery cell, and believes that the wrinkling problem is mainly related to the expansion and contraction of the negative electrode material after charging and discharging. After the expansion and contraction of the negative electrode material, the inner layer of the core cannot release stress, resulting in stress concentration and deformation, thus producing wrinkles. Therefore, the applicant developed the idea of ​​improving the wrinkling problem by configuring the bonding ability between the separator and the positive and negative electrode sheets. Based on this, this application focuses on improving the bonding ability between the separator and the adhesive layer on the positive electrode sheet, and strives to construct an integrated structure of the separator and the positive electrode sheet. Specifically, this application sets a first adhesive layer and a second adhesive layer with different areal densities on both sides of the base film. On this basis, both the first adhesive layer and the second adhesive layer include first adhesive and second adhesive with different particle size Dv50 and different wet adhesion strength, but the second adhesive accounts for a larger proportion in the first adhesive layer, ensuring that after immersion in electrolyte, the separator can bond with the positive and negative electrode sheets, and the adhesion strength is tilted towards the positive electrode side. Meanwhile, the first adhesive layer has several first recesses with pores on the inner wall on the side opposite to the first surface. After being pressed with the positive electrode sheet, these first recesses can provide a vacuum adsorption structure, enhancing the adhesion with the positive electrode sheet. In summary, the separator of this application, when applied to wound cells, can improve the wrinkling phenomenon of the inner layer of the wound core after battery charging and discharging, and can mitigate the risk of lithium dendrite formation causing micro-short circuits or short circuits in the cell. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 is a SEM image of the first adhesive layer in Example 1;

[0018] Figure 2 is a microscopic image of the surface of the first adhesive layer in Example 2;

[0019] Figure 3 is a microscopic image of the surface of the first adhesive layer in Example 3;

[0020] Figure 4 is a microscopic image of the surface of the first adhesive layer in Example 4. Detailed Implementation

[0021] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0023] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0024] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0025] In this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0026] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0027] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0028] In this application, numerical intervals (i.e. numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the above-mentioned numerical intervals are considered continuous, and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints.

[0029] Regarding the wrinkling problem that occurs after winding and forming of battery cells, this application analyzes its causes and believes that the wrinkling problem is mainly related to the expansion and contraction of the negative electrode material after charging and discharging. After the expansion and contraction of the negative electrode material, the inner layer of the core cannot release stress, leading to stress concentration and deformation, resulting in wrinkles. Therefore, the applicant developed the idea of ​​improving the wrinkling problem by configuring the bonding ability of the separator with the positive and negative electrode sheets. This forms the technical solution of this application.

[0030] The first aspect of this application provides a diaphragm. In one embodiment, the diaphragm includes a base film, a first adhesive layer, and a second adhesive layer. The base film has opposing first and second surfaces. The first adhesive layer is located on the first surface, and the second adhesive layer is located on the second surface. Both the first and second adhesive layers include a first adhesive and a second adhesive.

[0031] Wherein, the first adhesive and the second adhesive satisfy: a) the particle size Dv50 of the first adhesive is greater than the particle size Dv50 of the second adhesive; b) after being soaked in the electrolyte, the adhesive force of the first adhesive is less than the adhesive force of the second adhesive.

[0032] The first adhesive layer and the second adhesive layer satisfy the following conditions: a) the mass percentage of the second adhesive in the total amount of adhesive in the first adhesive layer is greater than the mass percentage of the second adhesive in the total amount of adhesive in the second adhesive layer; b) the first adhesive layer has a plurality of first recesses with pores on the side opposite to the first surface; c) the areal density of the first adhesive layer is greater than the areal density of the second adhesive layer.

[0033] This application focuses on improving the adhesion between the separator and the adhesive layer on one side of the positive electrode sheet, aiming to construct an integrated structure of the separator and the positive electrode sheet. Specifically, this application sets a first adhesive layer and a second adhesive layer with different areal densities on both sides of the base film. Both the first and second adhesive layers include first and second adhesives with different particle sizes (Dv50) and different wet adhesion strengths, but the second adhesive accounts for a larger proportion in the first adhesive layer. This ensures that after immersion in the electrolyte, the separator can adhere to both the positive and negative electrode sheets, with the adhesion strength tilting towards the positive electrode side. Simultaneously, the first adhesive layer has several first depressions with pores on the inner wall on the side facing away from the first surface. After pressing with the positive electrode sheet, these first depressions provide a vacuum adsorption structure, enhancing the adhesion to the positive electrode sheet. In summary, the separator of this application, when applied to wound battery cells, can improve the wrinkling phenomenon of the inner layer of the wound core after battery charging and discharging, and can mitigate the risk of lithium dendrite formation leading to micro-short circuits or short circuits in the battery cell. The areal density of the adhesive layer refers to the mass of solid adhesive per unit area of ​​the adhesive layer.

[0034] In one embodiment, the mass ratio of the first adhesive to the second adhesive in the first adhesive layer is (80~90):(10~20). In another embodiment, the mass ratio of the first adhesive to the second adhesive in the second adhesive layer is (92~99):(1~8).

[0035] In this embodiment, a plurality of first recesses can be formed by extrusion after the diaphragm and the electrode are hot-pressed, and then adsorbed onto the electrode through vacuum adsorption, thereby improving the adhesion to the electrode. In one embodiment, the depth of at least one first recess is 1 μm to 10 μm. For example, the depth is 1 μm, 2 μm, 5 μm, 8 μm, or 10 μm. Wherein, "at least one" refers to a portion of the first recesses, which can be all of the first recesses. The depths of each first recess are independent of each other. In one embodiment, the equivalent diameter of the first recess is between 50 μm and 400 μm, for example, the equivalent diameter is 50 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, or 500 μm; in one embodiment, the distribution density of the first recesses is 2 recesses / mm². 2 ~8 pieces / mm 2 For example, the distribution density is 2 per mm. 2 3 / mm 2 4 pieces / mm 2 5 pieces / mm 2 6 pieces / mm 2 7 pieces / mm 2 8 pieces / mm 2 .

[0036] In one embodiment, the raw materials for preparing the first adhesive layer include a first pore-forming agent for forming pores on the inner wall of the first recess to prevent pore blockage. The first pore-forming agent includes at least one of polymethyl methacrylate (PMMA) microspheres and ammonium carbonate.

[0037] In one embodiment, the second adhesive layer has a plurality of second recesses with pores on the side opposite to the second surface, satisfying the following: a) the average depth of the second recess is less than that of the first recess; b) the equivalent diameter of the second recess is less than that of the first recess; and c) the distribution density of the second recess is less than that of the first recess.

[0038] In one embodiment, the raw materials for preparing the second adhesive layer include a second pore-forming agent for forming pores on the inner wall of the second recess to prevent pore blockage. The second pore-forming agent includes at least one of PMMA microspheres and ammonium carbonate.

[0039] In one embodiment, the areal density ratio of the first adhesive layer to the areal density of the second adhesive layer is (2~9):1. In another embodiment, the areal density of the first adhesive layer is 4.2 g / m³. 2 ~4.725g / m 2 In one embodiment, the areal density of the second adhesive layer is 1.575 g / m³. 2 ~2.1g / m 2 .

[0040] In one embodiment, the first adhesive comprises polyvinylidene fluoride (PVDF).

[0041] In one embodiment, the second adhesive comprises at least one selected from polyacrylic acid (PAA), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), acrylonitrile copolymer, and polyvinyl alcohol (PVA). When the second adhesive comprises acrylonitrile copolymer, it can be LA132.

[0042] In one embodiment, the particle size Dv50 of the first adhesive is 10 μm to 50 μm. The aforementioned particle size of the first adhesive facilitates the formation of depressions on the adhesive layer surface.

[0043] In one embodiment, the particle size Dv50 of the second adhesive is 0.1 μm to 2 μm.

[0044] In one embodiment, a first ceramic layer is further included between the first adhesive layer and the base film, or the first adhesive layer comprises first ceramic powder. In another embodiment, a second ceramic layer is further included between the second adhesive layer and the base film, or the second adhesive layer comprises second ceramic powder.

[0045] In one embodiment, the thickness of the first adhesive layer is 1 μm to 5 μm. The thickness of the second adhesive layer is 0.2 μm to 0.5 μm. The thickness of the base film is 5 μm to 10 μm. The base film is made of polypropylene (PP).

[0046] Traditional adhesive-coated separators, when forming adhesive layers on both sides of the base membrane, mainly consider cost control and whether the adhesion between the adhesive layer and the electrodes on both sides meets the usage requirements. However, this application, by reconfiguring the adhesion between the adhesive layers on both sides of the separator and the positive and negative electrodes, can achieve the desired adhesion while tilting the adhesion towards the positive electrode side, thereby controlling costs and improving the wrinkling problem of wound cells.

[0047] A second aspect of this application provides a method for preparing the above-mentioned diaphragm. In one embodiment, the method for preparing the diaphragm includes the following steps:

[0048] A base film is provided, the base film having opposing first and second surfaces;

[0049] A first slurry is coated on the first surface to form a first adhesive layer, and a second slurry is coated on the second surface to form a second adhesive layer; wherein, both the first slurry and the second slurry include the first adhesive and the second adhesive, the mass percentage of the second adhesive in the total amount of adhesive in the first slurry is greater than the mass percentage of the second adhesive in the total amount of adhesive in the second slurry, the coating surface density of the first slurry is greater than the coating surface density of the second slurry, and the first adhesive layer forms a plurality of first depressions with pores on the side away from the first surface.

[0050] In one embodiment, the first slurry includes a first adhesive, a second adhesive, and a solvent. In one embodiment, a first ceramic layer is formed on the first surface before the first slurry is applied to the first surface, and the first slurry is applied to the first ceramic layer. In one embodiment, the first slurry includes a first adhesive, a second adhesive, first ceramic powder, and a solvent. In one embodiment, the first slurry includes a first pore-forming agent to form a first recess with porous inner walls. The solvent includes water.

[0051] In one embodiment, the second slurry includes a first adhesive, a second adhesive, and a solvent. In one embodiment, a second ceramic layer is formed on the second surface before the second slurry is applied to the second surface, and the second slurry is then applied to the second ceramic layer. In one embodiment, the second slurry includes a first adhesive, a second adhesive, second ceramic powder, and a solvent. In one embodiment, the second slurry includes a second pore-forming agent to form a second recess with porous inner walls. The solvent includes water.

[0052] Understandably, the first and second slurries can be coated simultaneously on both sides of the base film, or they can be coated separately. The first and second adhesive layers can be dried and cured simultaneously, or they can be dried and cured separately.

[0053] The areal density of the slurry refers to the mass of solid adhesive per unit area. In this application, the areal density of the slurry is the same as the areal density of the adhesive layer.

[0054] The coating method can be rotary spraying, and the pump speed on both sides can be controlled to create different surface densities.

[0055] The first depression can be formed by adjusting the pump speed and the conveyor belt speed.

[0056] The formation of several first recesses with pores on the inner wall of the first adhesive layer on the side opposite to the first surface can be achieved by either method one or method two.

[0057] Method 1: Forming a plurality of first depressions with pores on the inner wall of the first adhesive layer on the side opposite to the first surface, including the following steps:

[0058] The first slurry contains a first pore-forming agent.

[0059] Method 2: Forming a plurality of first depressions with pores on the inner wall of the first adhesive layer on the side opposite to the first surface, including the following steps:

[0060] A portion of the first slurry is coated to form a first sub-coating, wherein a portion of the first slurry includes a first adhesive;

[0061] The remaining portion of the first slurry is coated over the first sub-coating to form a second sub-coating, wherein the remaining portion of the first slurry includes a second adhesive and a first pore-forming agent.

[0062] A third aspect of this application provides a battery cell, the battery cell including a wound body, the wound body being wound along a virtual axis by a laminate, the laminate including a positive electrode, a negative electrode and a spacer film located between the positive electrode and the negative electrode, the spacer film being as described above, and a first adhesive layer being bonded to the positive electrode and a second adhesive layer being bonded to the negative electrode.

[0063] This application provides a fourth aspect of an energy storage device, which includes the battery cells described above, wherein the battery cells are used to store electrical energy. The energy storage device can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system. The aforementioned energy storage device possesses excellent long-term energy storage capabilities. It can support continuous operation for 4 hours, 8 hours, or even longer, effectively addressing long-term, high-load power consumption scenarios, achieving stable and reliable long-term energy storage support, providing users with sustained power security, and meeting the stringent requirements of high-capacity energy storage devices for structural stability and electrical connection durability.

[0064] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available. Unless otherwise specified, the instruments used are all commercially available. Unless otherwise specified, the processes involved are conventionally selected by those skilled in the art.

[0065] Example 1

[0066] This embodiment provides a diaphragm and its preparation method, the steps of which are as follows:

[0067] A first slurry was prepared by mixing PVDF, PAA, ceramic powder, PMMA microspheres, and water. A second slurry was prepared by mixing PAA, PVDF, ceramic powder, PMMA microspheres, and water, wherein the particle size Dv50 of PVDF was 20 μm and the particle size Dv50 of PAA was 1 μm. The mass ratio of PVDF to PAA in the first and second slurries is shown in Table 1.

[0068] Using a 7μm thick PP film as the base film, a first slurry is coated on the first surface. The pump speed and conveyor belt speed are adjusted, and the film is dried to obtain a first adhesive layer with a thickness of 2μm and first depressions with pores on the inner wall. The areal density of the first slurry is shown in Table 1. A second slurry is coated on the second surface and dried to obtain a second adhesive layer with a thickness of 0.5μm. The areal density of the second slurry is shown in Table 1.

[0069] Examples 2 to 4

[0070] The above embodiments provide a diaphragm and its preparation method, which are basically the same as the method in Embodiment 1. The main differences are shown in Table 1.

[0071] Comparative Examples 1 to 3

[0072] The above comparative example provides a diaphragm and its preparation method, which is basically the same as the method in Example 1, with the main differences shown in Table 1. In Comparative Example 2, PVDF is replaced with an equal mass of PAA. In Comparative Example 2, PAA is replaced with an equal mass of PVDF.

[0073] Performance testing

[0074] Surface morphology of the first adhesive layer: Figure 1 shows the SEM image of the first adhesive layer in Example 1, and Figures 2 to 4 show the surface microscopic images of the first adhesive layers in Examples 2 to 4. Figure 2 shows the first adhesive layer of Example 2, Figure 3 shows the first adhesive layer of Example 3, and Figure 4 shows the first adhesive layer of Example 4. It can be seen that the surface of the first adhesive layer in the above examples all has a first depression with pores on its inner wall. The equivalent diameter of the depression is between 50 μm and 400 μm, and the distribution density is 2 depressions / mm². 2 ~8 pieces / mm 2 .

[0075] Preparation of positive electrode sheet: Lithium nickel cobalt manganese oxide NCM811, Super P, and PVDF are mixed in N-methylpyrrolidone at a mass ratio of 96.5:2:1.5. After stirring evenly, the mixture is coated on a 12μm thick aluminum foil. After drying, rolling and slitting, the positive electrode sheet is obtained.

[0076] Preparation of negative electrode sheet: Graphite, Super P, CMC and SBR are mixed in deionized water at a mass ratio of 95:1.5:1.5:2. After stirring evenly, the mixture is coated on an 8μm thick copper foil. After drying, rolling and slitting, the negative electrode sheet is obtained.

[0077] Using a knife, cut the separator, positive electrode, and negative electrode into 3cm strips along the width of the core. Stack these strips in two configurations: separator-positive electrode-separator-positive electrode-separator and separator-negative electrode-separator-negative electrode-separator. Hot-press (5t, 90℃, 60s) to obtain two laminates. Immerse the laminates in the electrolyte for 24 hours. The electrolyte includes solvent (ethylene carbonate EC, methyl ethyl carbonate EMC, diethyl carbonate DEC, volume ratio 1:1:1), lithium salt (1.0 mol / L lithium hexafluorophosphate LiPF6), and additive (1.5 wt% vinylene carbonate VC). After removal, test the peel strength of the two laminates according to standard GB / T 2792-1999. The peel strength with the positive electrode is the wet adhesive strength of the first adhesive layer, and the peel strength with the negative electrode is the wet adhesive strength of the second adhesive layer. The results are shown in Table 1.

[0078] The positive electrode, separator, negative electrode, separator, positive electrode, separator, and negative electrode are stacked and hot-pressed (5t, 90℃, 60s) to obtain a laminate. This laminate is then wound according to the size requirements of a square aluminum-cased battery to form a wound cell. The wound cell is then inserted into a pre-stamped square aluminum casing and injected with electrolyte. The electrolyte includes a solvent (ethylene carbonate EC, ethyl methyl carbonate EMC, diethyl carbonate DEC, volume ratio 1:1:1), a lithium salt (1.0 mol / L lithium hexafluorophosphate LiPF6), and an additive (1.5 wt% vinylene carbonate VC). After electrolyte injection, the cell is allowed to stand for 24 hours to ensure complete electrolyte wetting.

[0079] After electrolyte filling, the battery was placed in a constant temperature environment at 45°C and charged to 3.0V using a constant current of 0.05C, then charged to 3.65V using a constant current of 0.1C, and finally charged under constant voltage until the current dropped to 0.05C. It was then placed in a constant temperature environment at 25°C for cycle testing. The test steps are as follows:

[0080] 1. Let stand: Let stand for 5 minutes.

[0081] 2. Charging: Charge at a constant current of 1.0C to 4.2V, then switch to constant voltage charging at 4.2V until the current drops to 0.05C.

[0082] 3. Let stand: Let stand for 5 minutes.

[0083] 4. Discharge: Discharge to 2.8V with a constant current of 1.0C.

[0084] 5. Repeat steps 1 to 4 above for 500 cycles.

[0085] The battery cells were disassembled, and CT scans were used to examine the cross-section of the core. Protrusions were identified as cell wrinkles, and the proportion of wrinkled areas to the total area was calculated. The results are shown in Table 1.

[0086] Table 1

[0087]

[0088] It is evident that by adjusting the mass ratio of large PVDF particles to small PAA particles, forming the first depression, and controlling the areal density of the adhesive coating on both sides of the base film, the proportion of cell wrinkles can be reduced. In Comparative Example 1, the areal density on both sides of the base film is the same, and the improvement effect on wrinkles is not significant. In Comparative Examples 2 and 3, using large PVDF particles alone or small PAA particles alone results in fewer first depressions, and the overall improvement effect on wrinkles is not significant.

[0089] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A diaphragm, characterized in that, The device includes a base film, a first adhesive layer, and a second adhesive layer. The base film has a first surface and a second surface opposite to each other. The first adhesive layer is located on the first surface, and the second adhesive layer is located on the second surface. Both the first and second adhesive layers include a first adhesive and a second adhesive. The first and second adhesives satisfy the following conditions: a) the particle size Dv50 of the first adhesive is greater than the particle size Dv50 of the second adhesive; b) after immersion in an electrolyte, the adhesive force of the first adhesive is less than the adhesive force of the second adhesive. The first and second adhesive layers satisfy the following conditions: a) the mass percentage of the second adhesive in the total amount of adhesive in the first adhesive layer is greater than the mass percentage of the second adhesive in the total amount of adhesive in the second adhesive layer; b) the first adhesive layer has a plurality of first recesses with pores on the inner wall on the side opposite to the first surface; c) the areal density of the first adhesive layer is greater than the areal density of the second adhesive layer.

2. The diaphragm according to claim 1, characterized in that, It includes at least one of the following features: (1) in the first adhesive layer, the mass ratio of the first adhesive to the second adhesive is (80~90):(10~20); (2) in the second adhesive layer, the mass ratio of the first adhesive to the second adhesive is (92~99):(1~8).

3. The diaphragm according to claim 1, characterized in that, The first depression satisfies at least one of the following conditions: (1) the depth of at least one of the first depressions is 1 μm to 10 μm; (2) the equivalent diameter of the first depression is between 50 μm and 400 μm; (3) the distribution density of the first depression is 2 depressions / mm. 2 ~8 pieces / mm 2 .

4. The diaphragm according to claim 1, characterized in that, The raw materials for preparing the first adhesive layer include a first pore-forming agent, which is used to form pores on the inner wall of the first depression; the first pore-forming agent includes at least one of PMMA microspheres and ammonium carbonate.

5. The diaphragm according to claim 1, characterized in that, The ratio of the areal density of the first adhesive layer to the areal density of the second adhesive layer is (2~9):

1.

6. The diaphragm according to claim 5, characterized in that, Includes at least one of the following features: (1) the areal density of the first adhesive layer is 4.2 g / m³. 2 ~4.725g / m 2 (2) The areal density of the second adhesive layer is 1.575 g / m³. 2 ~2.1g / m 2 .

7. The diaphragm according to claim 1, characterized in that, It includes at least one of the following features: (1) the first adhesive includes polyvinylidene fluoride; (2) the second adhesive includes at least one of polyacrylic acid, styrene-butadiene rubber, sodium carboxymethyl cellulose, epoxy resin and polyvinyl alcohol; (3) the particle size Dv50 of the first adhesive is 10 μm to 50 μm; (4) the particle size Dv50 of the second adhesive is 0.1 μm to 2 μm.

8. The diaphragm according to any one of claims 1 to 7, characterized in that, The second adhesive layer includes at least one of the following features: (1) a first ceramic layer is further included between the first adhesive layer and the base film, or the first adhesive layer includes first ceramic powder; (2) the second adhesive layer has a plurality of second recesses with pores on the side opposite to the second surface, satisfying: a) the average depth of the second recess is less than the first recess; b) the equivalent diameter of the second recess is less than the first recess; c) the distribution density of the second recess is less than the first recess; (3) the raw material for preparing the second adhesive layer includes a second pore-forming agent for forming pores on the inner wall of the second recess; the second pore-forming agent includes at least one of PMMA microspheres and ammonium carbonate; (4) a second ceramic layer is further included between the second adhesive layer and the base film, or the second adhesive layer includes second ceramic powder.

9. The diaphragm according to any one of claims 1 to 7, characterized in that, It includes at least one of the following features: (1) the thickness of the first adhesive layer is 1 μm to 5 μm; (2) the thickness of the second adhesive layer is 0.2 μm to 0.5 μm; (3) the thickness of the base film is 5 μm to 10 μm.

10. A method for preparing a diaphragm according to any one of claims 1 to 9, characterized in that, Includes the following steps: A base film is provided, the base film having opposing first and second surfaces; a first slurry is coated on the first surface to form a first adhesive layer, and a second slurry is coated on the second surface to form a second adhesive layer; wherein the first slurry and the second slurry both include the first adhesive and the second adhesive, the mass percentage of the second adhesive in the total amount of adhesive in the first slurry is greater than the mass percentage of the second adhesive in the total amount of adhesive in the second slurry, the coating surface density of the first slurry is greater than the coating surface density of the second slurry, and the first adhesive layer forms a plurality of first recesses with pores on the side opposite to the first surface.

11. The method for preparing the diaphragm according to claim 10, characterized in that, To form a plurality of first recesses with pores on the inner wall of the first adhesive layer on the side opposite to the first surface, the method includes at least one of the following steps: (1) including a first pore-forming agent in the first slurry; (2) coating a portion of the first slurry to form a first sub-coating, wherein a portion of the first slurry includes a first adhesive; coating the remaining portion of the first slurry on the first sub-coating to form a second sub-coating, wherein the remaining portion of the first slurry includes a second adhesive and a first pore-forming agent.

12. A single battery cell, characterized in that, The invention includes a wound body formed by winding a laminated body along a virtual axis, the laminated body including a positive electrode, a negative electrode, and a spacer membrane located between the positive electrode and the negative electrode, the spacer membrane being as described in any one of claims 1 to 9, and a first adhesive layer being bonded to the positive electrode and a second adhesive layer being bonded to the negative electrode.

13. An energy storage device, characterized in that, The energy storage device includes a battery cell as described in claim 12, the battery cell being used to store electrical energy.

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