Separator, preparation method, and use thereof

Abstract

A separator, a preparation method, and a use thereof. The separator comprises a base membrane and a non-fluorine adhesive coating provided on at least one surface of the base membrane. The material of the non-fluorine adhesive coating comprises polymer microspheres; the polymer microspheres comprise first polymer microspheres and second polymer microspheres; and the arrangement density ρ1 per unit area of the first polymer microspheres and the arrangement density ρ2 per unit area of the second polymer microspheres satisfy the following formula: formula (I). The separator has high dry and wet adhesive forces, can improve the cycle stability of a battery, uses an environmentally-friendly material, and is low in cost.

Description

A diaphragm, its preparation method and its application Technical Field

[0001] This application relates to the field of lithium-ion battery technology, such as a separator, a preparation method thereof, and its application. Background Technology

[0002] The separator in a lithium-ion battery is a thin film used to separate the positive and negative electrodes during electrolysis, preventing direct reaction and energy loss in the electrolytic cell. As one of the key internal components of a lithium-ion battery, the performance of the separator directly affects the performance of the battery. Therefore, developing high-performance separators is one of the effective means to improve the performance of lithium-ion batteries. Typically, to obtain a high-performance separator, it is modified by coating, such as by adding an adhesive coating to the surface of the base film. This improves various aspects of the separator's performance, thereby increasing the energy density and cycle performance of the lithium-ion battery.

[0003] Currently, the adhesive-type separator products used in lithium-ion battery cell assembly processes such as plywood stacking and thermal bonding primarily use fluorine-containing materials for their adhesive coatings, which is not environmentally friendly. Secondly, while fluorine-containing materials can ensure high dry-state adhesion to meet customer assembly and production yield improvement requirements, their wet-state adhesion is almost zero after being immersed in electrolyte, which is not conducive to improving the cycle performance of the battery cells and meeting high energy density design requirements.

[0004] Therefore, developing an adhesive material that can effectively improve the adhesion performance of the diaphragm and ensure high adhesion in both dry and wet states is an urgent problem to be solved in this field.

[0005] Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] This application provides a separator, a preparation method thereof, and its application. The separator has high dry and wet adhesion, improving the cycle stability of the battery.

[0008] In a first aspect, this application provides a diaphragm, the diaphragm comprising a base membrane and a non-fluorinated adhesive coating disposed on at least one surface of the base membrane; the non-fluorinated adhesive coating is made of non-fluorinated polymer microspheres, the non-fluorinated polymer microspheres comprising first polymer microspheres and second polymer microspheres, wherein the unit area packing density ρ1 of the first polymer microspheres and the unit area packing density ρ2 of the second polymer microspheres satisfy the following formula:

[0009] In this application, the non-fluorinated adhesive coating is configured such that by controlling the unit area arrangement density ρl of the first polymer microspheres and the unit area arrangement density ρ2 of the second polymer microspheres to satisfy a specific ratio, the diaphragm including the non-fluorinated adhesive coating has good adhesion. It can achieve both high dry and wet adhesion while using a smaller amount of non-fluorinated adhesive coating material, effectively avoiding the adverse effects of polymer material swelling, achieving good cycle performance, and avoiding the use of fluorinated materials, thus being environmentally friendly.

[0010] Secondly, this application provides a method for preparing the diaphragm according to the first aspect, the method comprising the following steps:

[0011] A non-fluorinated adhesive resin slurry is coated on at least one surface of a base membrane and dried to obtain the diaphragm; the preparation method of the non-fluorinated adhesive resin slurry includes: mixing a material of the non-fluorinated adhesive coating and a solvent to obtain the non-fluorinated adhesive resin slurry; the mass percentage of the solvent in the non-fluorinated adhesive resin slurry is 80wt% to 96wt%; the material of the non-fluorinated adhesive coating includes non-fluorinated polymer microspheres.

[0012] Thirdly, this application provides a lithium-ion battery, the lithium-ion battery comprising a separator obtained according to the method for preparing the separator according to the first aspect or the method for preparing the separator according to the second aspect.

[0013] In this application, the lithium-ion battery including the separator has better cycle stability and higher energy density, and can be used in EV, 3C and other application fields.

[0014] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0015] Compared with related technologies, the beneficial effects of this application are as follows:

[0016] The separator provided in this application includes a non-fluorinated adhesive coating. The non-fluorinated adhesive coating is made of two non-fluorinated polymer microspheres with different unit area densities. The unit area densities of the two different non-fluorinated polymer microspheres are controlled to meet a specific ratio, which can provide good adhesion. This allows the separator to have high dry and wet adhesion while using a smaller amount of non-fluorinated adhesive coating material. This can effectively avoid the adverse effects of polymer material swelling, achieve good battery cycle performance, and avoid the use of fluorinated materials, making it environmentally friendly.

[0017] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0018] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0019] Figure 1 is a scanning electron microscope image of the non-fluorine adhesive coating in the diaphragm provided in Example 1 of this application, magnified 2000 times.

[0020] Figure 2 is a scanning electron microscope image of the non-fluorine adhesive coating in the diaphragm provided in Example 1 of this application, magnified 10,000 times. Detailed Implementation

[0021] The technical solution of this application will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this application and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments of this application, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] This application provides a diaphragm, the diaphragm comprising a base membrane and a non-fluorinated adhesive coating disposed on at least one surface of the base membrane; the non-fluorinated adhesive coating is made of non-fluorinated polymer microspheres, the non-fluorinated polymer microspheres comprising a first polymer microsphere and a second polymer microsphere, wherein the unit area packing density ρ1 of the first polymer microsphere and the unit area packing density ρ2 of the second polymer microsphere satisfy the following formula:

[0023] In this application, the unit area arrangement density ρ of the non-fluorinated polymer microspheres in the non-fluorinated adhesive coating can be calculated by the mass ratio of the non-fluorinated polymer microspheres in the non-fluorinated adhesive coating and the coating surface density; for example, the unit area arrangement density ρ1 of the first polymer microspheres = (the surface density of the non-fluorinated adhesive coating × the mass ratio of the first polymer microspheres in the non-fluorinated adhesive coating) / the average particle size of the first polymer microspheres, and the unit area arrangement density ρ2 of the second polymer microspheres = (the surface density of the non-fluorinated adhesive coating × the mass ratio of the second polymer microspheres in the non-fluorinated adhesive coating) / the average particle size of the second polymer microspheres.

[0024] In this application, the non-fluorinated adhesive coating is configured such that by controlling the unit area arrangement density ρl of the first polymer microspheres and the unit area arrangement density ρ2 of the second polymer microspheres to satisfy a specific ratio, the diaphragm including the non-fluorinated adhesive coating has good adhesion. It can achieve both high dry and wet adhesion while using a smaller amount of non-fluorinated adhesive coating material, effectively avoiding the adverse effects of polymer material swelling, achieving good cycle performance, and avoiding the use of fluorinated materials, thus being environmentally friendly.

[0025] When the If the value does not meet the above range, the use of the two different polymer microspheres is inappropriate and will seriously reduce the coating adhesion and battery cycle performance.

[0026] In this application, the described The value is 1.4 to 2.5, for example, it can be a range of 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.1, 2.2, 2.3, 2.4, 2.5 or any two of them.

[0027] It should be noted that the term "surface" refers to the two surfaces with the largest area that are arranged opposite each other in the film or layer, and the term "at least one side surface" refers to at least one of the two surfaces.

[0028] The areal density of the coating can be obtained by testing using industry-standard methods, such as the weighing method.

[0029] The average particle size can be obtained by testing using industry-standard methods in this field. For example, the average particle size can be the particle size corresponding to the cumulative particle size distribution percentage of the sample reaching 50%, i.e., D50. The average particle size can also be obtained by observing the average particle size of a coating surface over a certain area (e.g., 10cm × 10cm) using SEM and ImageJ image processing tools.

[0030] In this application, "non-fluorine" means that the adhesive coating does not contain fluorinated polymers, such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-tetrafluoroethylene copolymer (PVDF-TFE), copolymers of VDF (vinylidene fluoride) with trifluoroethylene, trifluorochloroethylene, fluoroethylene, or trichloroethylene.

[0031] In this application, "dry bonding" refers to bonding performance in a solid state (without solvent); "wet bonding" refers to bonding performance after being impregnated with a solvent. In this application, "solvent" refers to electrolyte.

[0032] In some embodiments, the average particle size of the first polymer microsphere is smaller than the average particle size of the second polymer microsphere.

[0033] In some embodiments, the average particle size of the first polymer microspheres is 0.3 μm to 0.7 μm, for example, it can be a range of 0.3 μm, 0.32 μm, 0.34 μm, 0.36 μm, 0.38 μm, 0.4 μm, 0.42 μm, 0.44 μm, 0.46 μm, 0.48 μm, 0.5 μm, 0.52 μm, 0.54 μm, 0.56 μm, 0.58 μm, 0.6 μm, 0.62 μm, 0.64 μm, 0.66 μm, 0.68 μm, 0.7 μm, or any combination thereof.

[0034] In this application, the average particle size of the first polymer microspheres is within the above-mentioned range, which can control the overall areal density of the coating and is beneficial to improving the wet adhesion of the coating after it is wetted by the electrode liquid.

[0035] In some embodiments, the average particle size of the second polymer microspheres is 0.7 μm to 1.1 μm, for example, it can be a range of 0.7 μm, 0.71 μm, 0.72 μm, 0.74 μm, 0.76 μm, 0.78 μm, 0.8 μm, 0.82 μm, 0.84 μm, 0.86 μm, 0.88 μm, 0.9 μm, 0.92 μm, 0.94 μm, 0.96 μm, 0.98 μm, 1 μm, 1.02 μm, 1.04 μm, 1.06 μm, 1.08 μm, 1.1 μm, or any combination thereof.

[0036] In this application, the average particle size of the second polymer microspheres is within the above-mentioned range. The microspheres will not be embedded in the pits and pores of the substrate layer, thus affecting the adhesion performance between the microspheres and the electrode sheet. Furthermore, after hot pressing with the electrode sheet, the interface contact area is larger, which is beneficial for providing greater dry adhesion force.

[0037] In some embodiments, the ratio of the average particle size of the first polymer microsphere to the average particle size of the second polymer microsphere is 0.4 to 0.7, for example, it can be a range of 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7 or any combination thereof.

[0038] In this application, the ratio of the average particle size of the first polymer microsphere to the average particle size of the second polymer microsphere is within the above-mentioned range, which is beneficial to further improve the cycle performance.

[0039] In some embodiments, the mass ratio of the first polymer microsphere to the second polymer microsphere is (0.6 to 1.5):1, wherein the specific values ​​in (0.6 to 1.5) can be, for example, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or any combination thereof.

[0040] In this application, the mass ratio of the first polymer microsphere and the second polymer microsphere is within the above-mentioned range, which can better ensure the dry and wet bonding performance and reduce the swelling of the diaphragm in the electrolyte, while taking into account the good coating pore structure, further improving the surface resistance and enhancing the cell cycle performance.

[0041] In some embodiments, the glass transition temperature of the second polymer microsphere is 30°C to 50°C, for example, it can be a range of 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C or any combination thereof.

[0042] In some embodiments, the absolute value of the difference between the glass transition temperature of the second polymer microsphere and the glass transition temperature of the first polymer microsphere is 20°C to 40°C, for example, it can be a range of 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, 32°C, 34°C, 36°C, 38°C, 40°C or any combination thereof.

[0043] In this application, the glass transition temperature (Tg) of the first polymer microsphere and the second polymer microsphere is controlled within a specific range, and their Tg satisfies the above-mentioned relationship, so that the coating can better balance dry and wet adhesion performance and electrochemical performance.

[0044] In some embodiments, the glass transition temperature (Tg) of the first polymer microsphere is higher than that of the second polymer microsphere, thereby forming a polymer with a smaller particle size and a higher glass transition temperature, while the polymer with a larger particle size has a relatively lower glass transition temperature, which is more conducive to achieving both dry and wet bonding performance.

[0045] In some embodiments, the first polymer microspheres comprise polymethyl methacrylate microspheres, and the second polymer microspheres comprise polymethyl methacrylate microspheres.

[0046] In some embodiments, the areal density of the non-fluorinated adhesive coating is 0.15 g / m³. 2 ~0.3g / m 2For example, it can be 0.15g / m 2 0.16g / m 2 0.17g / m 2 0.18g / m 2 0.19g / m 2 0.2g / m 2 0.21g / m 2 0.22g / m 2 0.23g / m 2 0.24g / m 2 0.25g / m 2 0.26g / m 2 0.27g / m 2 0.28g / m 2 0.29g / m 2 0.3g / m 2 Or a range consisting of any two of them.

[0047] In this application, the areal density of the non-fluorinated adhesive coating is within the above-mentioned range, which can ensure that the membrane quality (e.g., air permeability, porosity, etc.) does not change significantly while further improving the electrochemical performance.

[0048] In some embodiments, the thickness of the non-fluorinated adhesive coating is 0.3 μm to 1.1 μm, for example, it can be a range of 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.1 μm, or any combination thereof.

[0049] In this application, the thickness of the non-fluorine adhesive coating is within the above-mentioned range, ensuring bonding strength while further improving the energy density of the battery.

[0050] This application also provides a method for preparing the diaphragm according to the first aspect, the method comprising the following steps:

[0051] A non-fluorinated adhesive resin slurry is coated on at least one surface of a base membrane and dried to obtain the diaphragm; the preparation method of the non-fluorinated adhesive resin slurry includes: mixing a material of the non-fluorinated adhesive coating and a solvent to obtain the non-fluorinated adhesive resin slurry; the mass percentage of the solvent in the non-fluorinated adhesive resin slurry is 80wt% to 96wt%, for example, it can be 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, 96wt%, or any combination thereof; the material of the non-fluorinated adhesive coating includes non-fluorinated polymer microspheres.

[0052] In some embodiments, the material of the non-fluorinated adhesive coating further includes an adhesive, the adhesive having a mass percentage of 0.05 wt% to 4 wt% relative to the non-fluorinated polymer microspheres, for example, a range of 0.05 wt%, 0.06 wt%, 0.08 wt%, 0.1 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, or any combination thereof.

[0053] In some embodiments, the material of the non-fluorinated adhesive coating further includes an additive, the additive having a mass percentage of 0.01wt% to 0.1wt% relative to the non-fluorinated polymer microspheres, for example, 0.01wt%, 0.02wt%, 0.04wt%, 0.06wt%, 0.08wt%, 0.1wt%, etc.

[0054] In some embodiments, the adjuvant includes a wetting agent and / or a dispersant.

[0055] In some embodiments, the drying temperature is 60°C to 80°C, for example, it can be a range of 60°C, 65°C, 70°C, 75°C, 80°C or any combination thereof.

[0056] In this application, the drying temperature is within the above-mentioned range, which can soften the coating surface but prevent the overall structure from collapsing, thus ensuring good adhesion between the coating particles and the substrate, preventing them from falling off or shedding powder.

[0057] In some embodiments, the coating method includes roller coating; for example, a micro gravure roller may be used for coating.

[0058] This application provides a lithium-ion battery, the lithium-ion battery comprising a separator obtained according to the method for preparing the separator according to the first aspect or the method for preparing the separator according to the second aspect.

[0059] In this application, the diaphragm can be used in applications such as EVs and 3C products.

[0060] The technical solutions provided in this application will be clearly and completely described below with reference to the accompanying drawings, embodiments, and comparative examples. Obviously, the specific embodiments described are only a part of the embodiments of this application, and not all of the embodiments.

[0061] Example 1

[0062] 1. This embodiment provides a diaphragm, comprising a base membrane (a polyethylene base membrane with a thickness of 7 μm) and a non-fluorinated adhesive coating disposed on one surface of the base membrane; the areal density of the non-fluorinated adhesive coating is 0.2 g / m³.2 The thickness is 0.6μm.

[0063] The non-fluorinated adhesive coating material includes polymethyl methacrylate microspheres (PMMA microspheres); the PMMA microspheres include a first PMMA microsphere (Tg 55°C, selected from Zeon 2570, Japan) and a second PMMA microsphere (Tg 30°C, selected from Indira Gandhi FS505A) with a mass ratio of 0.82:1.

[0064] The average particle size (D1) of the first PMMA microspheres is 0.5 μm, and the average particle size (D2) of the second PMMA microspheres is 0.9 μm; the ratio of D1 to D2 is 0.56; the ratio of the unit area arrangement density of the first PMMA microspheres to that of the second PMMA microspheres in the non-fluorinated adhesive coating is... The value is 1.5.

[0065] This embodiment provides a method for preparing the diaphragm, specifically including the following steps:

[0066] Polymethyl methacrylate microspheres, adhesive (Zhuhai Chenyu CYJ-5088A, 2 wt% of the total mass of PMMA microspheres), wetting agent (polyether-modified polysiloxane, Maiturui's wetting and leveling agent MT-845L, 0.05 wt% of the total mass of PMMA microspheres) were mixed evenly with water to obtain a non-fluorinated adhesive resin slurry (the solvent in the non-fluorinated adhesive resin slurry was 90 wt%). The non-fluorinated adhesive resin slurry was coated onto one surface of the base film using a micro gravure roller and dried at 70°C to obtain the separator.

[0067] The morphology of the non-fluorinated adhesive coating of the diaphragm obtained in Example 1 was characterized by scanning electron microscopy, and the results are shown in Figures 1 and 2. Figure 1 is a scanning electron microscopy image of the non-fluorinated adhesive coating magnified 2000 times, and Figure 2 is a scanning electron microscopy image of the non-fluorinated adhesive coating magnified 10000 times. As can be seen from Figures 1 and 2, two types of microspheres with different particle sizes are uniformly distributed on the surface of the non-fluorinated adhesive coating.

[0068] 2. Preparation of the positive electrode sheet

[0069] Lithium cobalt oxide, Super P and PVDF were mixed in a mass ratio of 85:10:5 and added to NMP to prepare a positive electrode slurry;

[0070] The positive electrode slurry is coated on both sides of the aluminum foil. After drying and rolling, positive electrode active material layers are formed on both sides of the aluminum foil to obtain the positive electrode sheet.

[0071] 3. Preparation of negative electrode sheet

[0072] Graphite, Super P and PVDF were mixed in a mass ratio of 85:10:5 and added to deionized water to prepare a negative electrode slurry;

[0073] The negative electrode slurry is coated on both sides of the copper foil. After drying and rolling, negative electrode active material layers are formed on both sides of the copper foil to obtain the negative electrode sheet.

[0074] 4. Battery manufacturing

[0075] The positive electrode, separator, and negative electrode are stacked in sequence, and then the resulting laminate is hot-pressed so that one side of the separator is bonded to the positive electrode and the other side is bonded to the negative electrode, thus producing a stacked battery cell. The battery cell is then encapsulated with an aluminum-plastic film, and then subjected to processes such as liquid injection and formation to produce a lithium-ion battery.

[0076] The electrolyte used has the following composition: the organic solvent is DMC, EMC, EC, DEC and PC in a volume ratio of 15:35:35:10:5 (i.e. DMC:EMC:EC:DEC:PC=15:35:35:10:5(vol)), and the mass content of LiPF6 in the electrolyte is 11%.

[0077] Example 2

[0078] This embodiment provides a diaphragm, comprising a base membrane (a polyethylene base membrane with a thickness of 7 μm) and a non-fluorinated adhesive coating disposed on one surface of the base membrane; the areal density of the non-fluorinated adhesive coating is 0.15 g / m³. 2 The thickness is 0.8μm.

[0079] The non-fluorinated adhesive coating material includes polymethyl methacrylate microspheres (PMMA microspheres); the PMMA microspheres include a first PMMA microsphere (Tg of 25°C) and a second PMMA microsphere (Tg of 50°C) in a mass ratio of 1:1.

[0080] The average particle size (D1) of the first PMMA microspheres is 0.44 μm, and the average particle size (D2) of the second PMMA microspheres is 1.1 μm, with a D1 to D2 ratio of 0.4; in the non-fluorinated adhesive coating, The value is 2.5.

[0081] This embodiment provides a method for preparing the diaphragm, specifically including the following steps:

[0082] Polymethyl methacrylate microspheres, adhesive (Zeon BM900B, 1 wt% of the total mass of PMMA microspheres), wetting agent (TEGO245, 0.08 wt% of the total mass of PMMA microspheres) and water were mixed evenly to obtain a non-fluorinated adhesive resin slurry (the solvent in the non-fluorinated adhesive resin slurry was 85 wt%). The non-fluorinated adhesive resin slurry was coated onto one surface of a base film using a micro gravure roller and dried at 70°C to obtain the separator.

[0083] Example 3

[0084] This embodiment provides a diaphragm, comprising a base membrane (a polyethylene base membrane with a thickness of 7 μm) and a non-fluorinated adhesive coating disposed on one surface of the base membrane; the areal density of the non-fluorinated adhesive coating is 0.3 g / m³. 2 The thickness is 0.5μm.

[0085] The non-fluorinated adhesive coating material includes polymethyl methacrylate microspheres (PMMA microspheres); the PMMA microspheres include a first PMMA microsphere (Tg of 15°C) and a second PMMA microsphere (Tg of 45°C) with a mass ratio of 1.3:1.

[0086] The average particle size (D1) of the first PMMA microspheres is 0.5 μm, and the average particle size (D2) of the second PMMA microspheres is 0.75 μm, with a D1 to D2 ratio of 0.67; in the non-fluorinated adhesive coating, The value is 2.

[0087] This embodiment provides a method for preparing the diaphragm, specifically including the following steps:

[0088] Polymethyl methacrylate microspheres, an adhesive (Zeon BM900B from Japan, with a mass of 2.05 wt% of the total mass of PMMA microspheres) were mixed with water to obtain a non-fluorinated adhesive resin slurry (the solvent in the non-fluorinated adhesive resin slurry had a mass of 90 wt%). The non-fluorinated adhesive resin slurry was coated onto one surface of a base film using a micro-gravure roller and dried at 70°C to obtain the diaphragm.

[0089] Examples 4-8, Comparative Examples 1-3

[0090] Examples 4-8 and Comparative Examples 1-3 each provide a diaphragm, which differs from Example 1 only in that the thickness, areal density, particle size (D1), Tg of the first PMMA microspheres, particle size (D2), Tg of the second PMMA microspheres, mass ratio (m1 / m2) of the first PMMA microspheres and the ratio (ρ1 / ρ2) of the unit area arrangement density of the first PMMA microspheres and the second PMMA microspheres are different; the specific formulation is shown in Table 1; the type and thickness of the substrate and the preparation method of the diaphragm (including the type and amount of adhesive and the type and amount of additives) are the same as those in Example 1.

[0091] Table 1

[0092] Performance testing

[0093] (1) The test procedure for the dry adhesion between the diaphragm and the electrode sheet (including the dry adhesion between the diaphragm and the positive electrode sheet, and the dry adhesion between the diaphragm and the negative electrode sheet) is as follows:

[0094] The diaphragm was cut into test strips with a width of 25 mm and a length of 60 mm, and the electrode sheet was cut into test strips with a width of 25 mm and a length of 40 mm. The cut diaphragm test strips and electrode sheet test strips were bonded together and sandwiched between two strips of white paper (the size of the white paper strips was larger than the size of the diaphragm test strips). The strips were then subjected to pressure (hot pressing) at 80℃ and 6.5 MPa for 20 seconds, and then allowed to cool naturally at room temperature. The hot-pressed diaphragm strips were then subjected to a 180° peel test using a tensile testing machine at a test speed of 300 mm / min and a gauge length of 100 mm. After the test, the test results (i.e., the dry adhesion force between the diaphragm and the electrode sheet) were recorded.

[0095] (2) Wet adhesion between the diaphragm and the electrode sheet (including wet adhesion between the diaphragm and the positive electrode sheet, and wet adhesion between the diaphragm and the negative electrode sheet): The diaphragm is cut into test strips with a width of 25 mm and a length of 60 mm, and the electrode sheet is cut into test strips with a width of 25 mm and a length of 40 mm; the cut diaphragm test strips and electrode sheet test strips are attached together and sandwiched between two strips of white paper (the size of the white paper strips is larger than the size of the diaphragm test strips), and pressure is applied at 80℃ and 6.5 MPa for 20 s (hot pressing), and then cooled naturally at room temperature. The hot-pressed diaphragm test strips are immersed in electrolyte solvent at room temperature for 24 h, and after removal, the electrolyte on the surface of the diaphragm is removed. A 180° peel test is performed using a tensile tester at a test speed of 300 mm / min and a gauge length of 100 mm; after the test is completed, the test results are recorded to test the wet adhesion of the diaphragm.

[0096] (3) Surface resistance

[0097] Four diaphragm samples with a diameter of 45 mm were cut from a flat surface. The samples were immersed in the electrolyte and sealed for 30 minutes. About 15 ml of 1 mol / L fresh electrolyte was poured into the sheet resistance testing fixture. The 1st, 2nd, 3rd and 4th diaphragms were placed in the fixture for testing. A linear fit was performed with the number of diaphragm layers as the x-axis and the diaphragm resistance as the y-axis. The slope and goodness of fit of the line were calculated. When the goodness of fit was greater than 0.999, the slope was the sheet resistance of the diaphragm.

[0098] The electrolyte composition is as follows: the organic solvent is DMC, EMC, EC, DEC, and PC in a volume ratio of 15:35:35:10:5 (i.e., DMC:EMC:EC:DEC:PC=15:35:35:10:5(vol)), and the mass content of LiPF6 in the electrolyte is 11%.

[0099] (4) Cycle life

[0100] According to the reference standard GB / T 23366-2009, the cycle life is the ratio of the discharge capacity after 500 cycles to the discharge capacity of the first cycle multiplied by 100%.

[0101] The specific test results are shown in Table 2.

[0102] Table 2

[0103] As shown in Table 2, the separator provided in this application includes a non-fluorinated adhesive coating. The non-fluorinated adhesive coating is made of two non-fluorinated polymer microspheres with different unit area densities. The unit area densities of the two polymer microspheres are controlled to meet a specific ratio, which is beneficial to improve the dry and wet adhesion between the separator and the electrode, thereby achieving good battery cycle performance. Moreover, the material usage is small, avoiding the impact of polymer swelling on the material, and eliminating the need for fluorinated polymers, making it environmentally friendly.

[0104] As can be seen from Comparative Examples 1 to 3, the unit area arrangement density of the two polymer microspheres in the separator provided in this application does not satisfy a specific ratio relationship, resulting in poor dry and wet adhesion performance of the separator and short cycle life of the battery.

[0105] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A diaphragm comprising a base membrane and a non-fluorinated adhesive coating disposed on at least one surface of the base membrane; The non-fluorinated adhesive coating material includes non-fluorinated polymer microspheres, which comprise a first polymer microsphere and a second polymer microsphere. The unit area packing density ρ1 of the first polymer microsphere and the unit area packing density ρ2 of the second polymer microsphere satisfy the following formula:

2. The diaphragm according to claim 1, wherein, The average particle size of the first polymer microsphere is smaller than that of the second polymer microsphere.

3. The diaphragm according to claim 1 or 2, wherein, The average particle size of the first polymer microspheres is 0.3 μm to 0.7 μm.

4. The diaphragm according to any one of claims 1-3, wherein, The average particle size of the second polymer microspheres is 0.7 μm to 1.1 μm.

5. The diaphragm according to any one of claims 1-4, wherein, The ratio of the average particle size of the first polymer microsphere to the average particle size of the second polymer microsphere is 0.4 to 0.

7.

6. The diaphragm according to any one of claims 1 to 5, wherein, The mass ratio of the first polymer microsphere to the second polymer microsphere is (0.6–1.5):

1.

7. The diaphragm according to any one of claims 1 to 6, wherein, The glass transition temperature of the second polymer microsphere is 30℃~50℃.

8. The diaphragm according to any one of claims 1 to 7, wherein, The absolute value of the difference between the glass transition temperature of the second polymer microsphere and the glass transition temperature of the first polymer microsphere is 20℃~40℃.

9. The diaphragm according to any one of claims 1 to 8, wherein, The first polymer microsphere comprises polymethyl methacrylate microspheres, and the second polymer microsphere comprises polymethyl methacrylate microspheres.

10. The diaphragm according to any one of claims 1 to 9, wherein, The areal density of the non-fluorinated adhesive coating is 0.15 g / m³. 2 ~0.3g / m 2 .

11. The diaphragm according to any one of claims 1 to 10, wherein the thickness of the non-fluorinated adhesive coating is 0.3 μm to 1.1 μm.

12. A method for preparing a diaphragm according to any one of claims 1 to 11, comprising the following steps: A non-fluorinated adhesive resin slurry is coated on at least one surface of the base membrane and dried to obtain the diaphragm. The method for preparing the non-fluorinated adhesive resin slurry includes: mixing the non-fluorinated adhesive coating material and the solvent. The solvent is combined to obtain the non-fluorinated adhesive resin slurry; the solvent content in the non-fluorinated adhesive resin slurry is 80wt% to 96wt%; the material of the non-fluorinated adhesive coating includes non-fluorinated polymer microspheres.

13. The method for preparing the diaphragm according to claim 12, wherein, The non-fluorinated adhesive coating also includes an adhesive, the adhesive comprising 0.05 wt% to 4 wt% of the non-fluorinated polymer microspheres by mass.

14. The method for preparing the diaphragm according to claim 12 or 13, wherein, The material of the non-fluorinated adhesive coating also includes additives, the additives accounting for 0.01 wt% to 0.1 wt% of the mass of the non-fluorinated polymer microspheres; Optionally, the additives include wetting agents and / or dispersants; Optionally, the drying temperature is 60°C to 80°C.

15. A lithium-ion battery, wherein, The lithium-ion battery includes a separator according to any one of claims 1 to 11 or a separator prepared by any one of claims 12 to 14.

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