Battery separator and lithium battery prepared from same

Abstract

A battery separator. The battery separator comprises: a porous base material and a bonding layer, which is formed on one side of the porous base material, wherein the bonding layer comprises a polymer material having bonding performance, and has a coating coefficient C. The coating coefficient C is equal to the ratio of the bonding strength A of the bonding layer to an air permeability increase value P of the unit coating thickness and satisfies the relational expression C=A / P, wherein the ratio range of the coating coefficient C is 0.3<C<1, with the unit of the bonding strength A of the bonding layer being N / m, and the unit of the air permeability increase value P of the unit coating thickness of the bonding layer being s / 100cc / μm.

Description

Battery separator and lithium battery prepared therefrom Technical Field

[0001] The present application relates to the technical field of secondary battery materials, and in particular to a lithium-ion battery diaphragm and a lithium battery prepared therefrom. Background Art

[0002] Lithium-ion batteries are secondary batteries that not only convert electrical energy into chemical energy for storage, but also convert chemical energy back into electrical energy to power electrical appliances. Their high energy density and long cycle life have led to their widespread use. Since the 21st century, with the rise of laptops, smartphones, and electric vehicles, the use of lithium-ion batteries has become even more widespread.

[0003] As a key component of lithium-ion batteries, separators are primarily required to have high ionic conductivity and low electronic conductivity. Currently, commonly used lithium battery separators are porous materials made from polyolefins through uniaxial or biaxial stretching. These materials offer excellent ionic conductivity, superior mechanical properties, and electrolyte resistance.

[0004] Due to the low melting point of polyolefins, their heat resistance is poor, and a ceramic coating is generally applied to improve their heat resistance. However, while ceramic coatings can improve the heat shrinkage resistance of separators, the adhesion between the ceramic coating and the separator is poor, resulting in the ceramic coating easily peeling off from the separator. Therefore, improving the coating's adhesion strength is a key issue that needs to be addressed.

[0005] Summary of the Invention

[0006] Therefore, the main purpose of this application is to provide a battery separator and a lithium battery prepared therefrom to further optimize the above-mentioned problems.

[0007] In order to solve the above technical problems, the purpose of the present application is to provide a battery separator, comprising: a porous substrate or a composite material consisting of a porous substrate and a heat-resistant layer located on the porous substrate; and an adhesive layer formed on the porous substrate or the composite material, wherein the adhesive layer contains a polymer material with adhesive properties, and the adhesive layer has a coating coefficient C, the coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the air permeability increase value P per unit coating thickness, satisfying the relationship C=A / P, and the ratio range of the coating coefficient C is 0.3<C<1, wherein the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the air permeability increase value P per unit coating thickness of the adhesive layer is s / 100cc / μm.

[0008] In the battery separator as described above, the adhesive layer comprises an adhesive polymer material or a mixture of an adhesive polymer material and a filler, and the filler comprises an organic or inorganic high-temperature resistant material.

[0009] In the battery separator as described above, the adhesive polymer material includes polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, methyl methacrylate homopolymer, methyl methacrylate copolymer or a mixture thereof.

[0010] As described above, the battery separator, wherein the molar ratio of the vinylidene fluoride monomer in the polyvinylidene fluoride copolymer is higher than 50%, and the other comonomers can be one or more selected from hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate and vinyl acetate.

[0011] In the battery separator as described above, the adhesive layer may be located on one side of the porous substrate, on both sides of the porous substrate, on one side of the composite material, or on both sides of the composite material.

[0012] In the battery separator as described above, the heat-resistant layer comprises a ceramic material, a heat-resistant polymer material, or a mixture of a ceramic material and a heat-resistant polymer material.

[0013] Another object of the present application is to provide a battery separator, characterized in that it includes: a porous substrate; and an adhesive layer formed on one side of the porous substrate, wherein the adhesive layer contains a polymer material with adhesive properties, the polymer material includes polyvinylidene fluoride (PVDF), and the adhesive layer has a coating coefficient C, which is equal to the ratio of the adhesive strength A of the adhesive layer to the air permeability increase value P per unit coating thickness, satisfying the relationship C=A / P, and the ratio range of the coating coefficient C is 0.4<C<0.9, wherein the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the air permeability increase value P per unit coating thickness of the adhesive layer is s / 100cc / μm.

[0014] The battery separator as described above, wherein the raw material crystallinity of the polyvinylidene fluoride copolymer is between 10% and 50%.

[0015] In the battery separator as described above, the adhesive layer is coated with water-based polyvinylidene fluoride, and the proportion of the α phase in the crystal region of the water-based polyvinylidene fluoride is greater than 30% and less than 70%.

[0016] In the battery separator as described above, the adhesive layer is coated with oily polyvinylidene fluoride, and the proportion of the α phase in the crystal region of the oily polyvinylidene fluoride in the adhesive layer is less than 20%.

[0017] Another object of the present application is to provide a lithium battery, characterized in that it includes: a positive electrode, a negative electrode and a battery separator as described above, wherein the battery separator is located between the positive electrode and the negative electrode.

[0018] The present application improves the bonding performance between the diaphragm and the electrode by introducing adhesive polymer materials into the diaphragm coating. In addition, the introduction of heat-resistant polymer materials such as aramid into the diaphragm coating can increase the rupture temperature of the diaphragm. Furthermore, ceramics are introduced into the diaphragm coating to improve the heat shrinkage resistance of the diaphragm. Through the above-mentioned improvement measures, the problem of the current ceramic coating being easily peeled off from the diaphragm due to insufficient bonding strength can be effectively solved. In addition, the present application expresses the bonding performance and air permeability of the coating by designing the coating coefficient C value, and limits it to a certain preferred range, so that it is very convenient to evaluate and ensure whether the bonding performance and air permeability of the diaphragm meet the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic diagram of the cross-sectional structure of a battery separator according to an embodiment of the present application.

[0020] FIG2 is a schematic diagram of the cross-sectional structure of a battery separator according to another embodiment of the present application.

[0021] FIG3 is a schematic diagram of the cross-sectional structure of a battery separator according to another embodiment of the present application.

[0022] FIG4 is a schematic diagram of the cross-sectional structure of a battery separator according to another embodiment of the present application.

[0023] FIG5 is a flow chart of a method for preparing a battery separator according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] The following descriptions of the various embodiments refer to the accompanying drawings to illustrate specific embodiments that may be implemented in this application. Directional terms used in this application, such as "upper," "lower," "front," "back," "left," "right," "inner," "outer," and "side," refer only to the directions in the accompanying drawings. Therefore, the directional terms used are for the purpose of illustrating and understanding this application and are not intended to limit this application.

[0025] The accompanying drawings and descriptions are to be considered illustrative in nature and not restrictive. In the drawings, structurally similar elements are denoted by the same reference numerals. Furthermore, for ease of understanding and description, the dimensions and thicknesses of each component shown in the drawings are arbitrarily illustrated, but the present application is not limited thereto.

[0026] In the drawings, the thickness of layers, films, regions, etc. are exaggerated for clarity. In the drawings, the thickness of some layers and regions are exaggerated for understanding and ease of description. It will be understood that when a component such as a layer, film, region, or substrate is referred to as being "on" another component, the component can be directly on the other component or intervening components may also be present.

[0027] In addition, in the specification, unless explicitly described to the contrary, the word "comprising" will be understood to mean including the components described, but not excluding any other components. In addition, in the specification, "on..." means being above or below the target component, and does not mean necessarily being on the top based on the direction of gravity.

[0028] In order to further illustrate the technical means and effects adopted by this application to achieve the predetermined purpose of the invention, the following, in combination with the accompanying drawings and specific embodiments, describes in detail the specific implementation method, structure, characteristics and effects of a battery separator and a proton exchange membrane sheet prepared therefrom proposed in this application.

[0029] One embodiment of the present invention, referring to Figure 1 , includes a battery separator 1 comprising a porous substrate 11, a heat-resistant layer 13 disposed on one side of the porous substrate 11, wherein the porous substrate 11 and the heat-resistant layer 13 together form a composite material; and an adhesive layer 12 formed on the composite material. Alternatively, as shown in Figure 3 , the heat-resistant layer 13 may be omitted, leaving only the porous substrate 11, with the adhesive layer 12 formed directly on one side of the porous substrate 11. Regardless of whether the bonding layer 12 is formed on the porous substrate 11 or the composite material, the bonding layer 12 comprises an aggregate layer formed by a polymer material 121 having bonding properties, and the bonding layer 12 has a coating coefficient C, which is equal to the ratio of the bonding strength A of the bonding layer 12 to the air permeability increase value P per unit coating thickness, satisfying the relationship C=A / P, and the ratio range of the coating coefficient C is 0.3<C<1, wherein the unit of the bonding strength A of the bonding layer 12 is N / m, and the unit of the air permeability increase value P per unit coating thickness of the bonding layer 12 is s / 100cc / μm.

[0030] In this embodiment, the porous substrate 11 refers to a material having voids or pores within the substrate. It can be a porous sheet formed from fibrous materials such as non-woven fabrics or paper-like sheets; or a composite porous sheet obtained by laminating one or more other porous layers on these microporous membranes or porous sheets. The porous substrate can also be a polyolefin material with a porous structure obtained by unidirectional or multidirectional stretching, dry or wet methods, or a porous material obtained by methods such as non-solvent-induced phase separation, heat-induced phase separation, and steam-induced phase separation. The polyolefin material generally refers to polyethylene or polypropylene. The porous substrate 11 can also be prepared by methods such as electrospinning. The substrate material can be one or more fibers of materials such as polyethylene terephthalate, nylon, aramid, polysulfone, polyetheretherketone, and polyimide. The thickness of the porous substrate 11 is generally between 3 and 30 μm, and the air permeability of the porous substrate 11 is between 30 and 500 s / 100 ml.

[0031] In this embodiment, the adhesive layer 12 can be provided on both sides of the composite material, and its surface density on each side of the composite material is 0.1-6.0 g / m 2 The adhesive layer 12 may be disposed on only one side of the composite material or on one or both sides of the porous substrate 11. In this embodiment, the adhesive layer 12 comprises a polymer material 121 having adhesive properties, such as a collection of polyvinylidene fluoride (PVDF) particles or acrylic particles. However, the adhesive layer 121 is not limited to a granular form and may also be in a fibrous, mesh, or cross-linked form.

[0032] The polymer material 121 having adhesive properties can refer to a polyvinylidene fluoride or polyacrylate polymer material, wherein the polyacrylate resin is a copolymer of materials such as methyl methacrylate (PMMA), acrylic acid, methacrylic acid, ethyl methacrylate, styrene, butyl methacrylate, methacrylamide, isobutylene, and acrylonitrile, or can be a polymerization of multiple monomers such as methacrylate, acrylic acid, acrylate, styrene, ethylene glycol, and acrylonitrile. The resin may also be obtained after a cross-linking reaction, and the resin may also be a material with a core-shell structure, that is, the core layer and the shell layer are made of different materials. Therefore, in some embodiments, the adhesive layer 12 includes an adhesive polymer material, and the adhesive polymer material includes a polyvinylidene fluoride homopolymer, a polyvinylidene fluoride copolymer, a methyl methacrylate homopolymer, a methyl methacrylate copolymer, or a mixture thereof.

[0033] In this embodiment, the polyvinylidene fluoride (PVDF) resin is a fluorine-containing polymer material with vinylidene fluoride monomer as the main component. It can be a homopolymer of polyvinylidene fluoride or a copolymer of polyvinylidene fluoride, such as a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trifluoroethylene, a mixture of polyvinylidene fluoride and an acrylic polymer, and a polyvinylidene fluoride copolymer, wherein the comonomer can be selected from monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate, and vinyl acetate.

[0034] In some embodiments, the bonding layer 12 includes an adhesive polymer material or a mixture of an adhesive polymer material and a filler, and the filler includes an organic or inorganic high-temperature resistant material, wherein the inorganic high-temperature resistant material includes ceramic materials such as alumina, boehmite, barium sulfate, magnesium hydroxide, barium titanate, and the like, and the organic high-temperature resistant material includes polyimide microspheres, cross-linked polyacrylic acid, cross-linked acrylate, cross-linked polymethacrylate (ester), cross-linked polystyrene, cross-linked polysiloxane, polysulfone, polyacrylonitrile, etc.

[0035] In this embodiment, the permeability increase P per unit coating thickness of the adhesive layer 12, i.e., the ratio of the difference between the permeability of the adhesive layer 12 and the permeability of the porous substrate 11 to the thickness of the adhesive layer, is approximately 0-50 s / 100 cc / μm, more preferably 0-30 s / 100 cc / μm, and even more preferably 0-15 s / 100 cc / μm. "Permeability per unit coating thickness" refers to the difference between the permeability of the adhesive layer 12 and the permeability of the porous substrate 11 divided by the thickness of the adhesive layer 12. The unit of permeability is "s / 100 cc," and the unit of thickness of the adhesive layer 12 is "μm." In this embodiment, the adhesive layer 12 comprises a polymer resin material or a mixture of a polymer resin and a ceramic material, and the surface smoothness of the adhesive layer 12 is 1.30 or less.

[0036] In some embodiments, compared with water-based adhesive coatings, oil-based adhesive coatings often have better bonding strength due to their higher coverage area, but poorer air permeability. The better the bonding strength, the tighter the bond between the diaphragm and the electrode, which can greatly improve the volume energy density of the diaphragm. Since gas is produced during the charge and discharge cycle, and the presence of gas between the diaphragm and the electrode will cause the ion conductivity to deteriorate, the battery cycle life will also be shortened. Due to the presence of the adhesive layer, this problem can be avoided. However, the presence of the adhesive layer will lead to a decrease in air permeability and reduce the ion conductivity, so it is necessary to control the bonding strength and air permeability of the diaphragm at the same time to optimize its overall performance. Therefore, the coating coefficient C of the above-mentioned adhesive layer 12 has a ratio range of 0.3<C<1. Such parameter restrictions will enable the battery diaphragm 1 of the present application to achieve the optimal design of bonding strength and air permeability.

[0037] In this embodiment, the coating coefficient C ratio of the adhesive layer 12 is approximately in the range of 0.3<C<1, but is not limited thereto. In some embodiments, the coating coefficient C ratio may also preferably be in the range of 0.5<C<1, 0.3<C<0.8 or 0.4<C<0.9. For example, a battery separator in another embodiment of the present application has a structure similar to that of Figure 3, which includes: a porous substrate and an adhesive layer located on one side of the porous substrate, wherein the adhesive layer includes a polymer material with adhesive properties, the polymer material includes polyvinylidene fluoride (PVDF), and the adhesive layer has a coating coefficient C, which is equal to the ratio of the adhesive strength A of the adhesive layer to the air permeability increase value P per unit coating thickness, satisfying the relationship C=A / P, and the ratio range of the coating coefficient C is 0.4<C<0.9, wherein the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the air permeability increase value P per unit coating thickness of the adhesive layer is s / 100cc / μm.

[0038] The molar ratio of the PVDF monomer in the above-mentioned polyvinylidene fluoride (PVDF) copolymer is higher than 50%. For the above-mentioned PVDF copolymer, the raw material crystallinity is in the range of 10%-50%. For the water-based PVDF coated diaphragm, the proportion of the α phase in the crystalline region of the PVDF in its PVDF coating is greater than 30% and less than 70%. For the oily PVDF coated diaphragm, the proportion of the α phase in the crystalline region of the PVDF in its PVDF coating is less than 20%. In this way, the design of the molar ratio, the design of the raw material crystallinity range and the design of the proportion of the α phase in the crystalline region will have a practical impact on the ratio of the coating coefficient C, thereby limiting the ratio range of the coating coefficient C to 0.4<C<0.9.

[0039] Referring to FIG. 1 , in this embodiment, the heat-resistant layer 13 comprises a ceramic material, a heat-resistant polymer material, or a mixture of ceramic and heat-resistant polymer materials, wherein the ceramic material is selected from at least one of metal hydroxides, metal oxides, and metal-containing salts, and the ceramic material includes, but is not limited to, particles of inorganic materials such as alumina, boehmite, magnesium hydroxide, barium titanate, and barium sulfate. The heat-resistant polymer material includes, but is not limited to, meta-aramid, para-aramid, polyimide (including homophenyl polyimide, soluble polyimide, polyetherimide, and polyamide-imide), polyethersulfone, polyetheretherketone, and polyethylene glycol dicarboxylate, and the like. The polymer material has a glass transition temperature of above 200° C. and a thermal decomposition temperature of above 400° C. The heat-resistant polymer material can be in the form of particles, fibers, a mesh, or cross-linked polymer microspheres.

[0040] In this embodiment, only one heat-resistant layer 13 is located on a single side of the porous substrate 11. However, this is not limited to the above. As shown in FIG2 , the heat-resistant layer 13 may also be located on both sides of the porous substrate 11, wherein the heat-resistant layer 13 comprises an aramid polymer and an inorganic filler, and the adhesive layer 12 comprises polyvinylidene fluoride (PVDF) microparticles and / or acrylic microparticles formed from a polymer material 121 having adhesive properties. In some embodiments, as shown in FIG3 , in addition to the polymer material 121 having adhesive properties, the adhesive layer 12 also comprises ceramic material particles 122. Therefore, the adhesive layer 12 is a particle assembly layer formed by the aggregate of the polymer material 121 microparticles and the ceramic material particles 122. In other embodiments, referring to FIG. 4 , a polymer material 121 may be continuously coated on the adhesive layer 12 on one side of the porous substrate 11 described in FIG. 3 , so that the polymer material 121 can cover the ceramic material particles 122 , thereby improving the adhesion and increasing the thickness of the entire adhesive layer 12 .

[0041] In some embodiments, a lithium battery according to an embodiment of the present application is characterized in that it comprises: a positive electrode, a negative electrode and a battery separator 1 as described above, wherein the battery separator 1 is located between the positive electrode and the negative electrode, and obtains an electromotive force by the insertion and extraction of lithium ions. The positive electrode contains substances such as a positive electrode active material, a conductive agent, an adhesive, and a current collector. The conductive agent can include materials such as acetylene black, Ketjen black, and graphite powder. The negative electrode contains a material that can receive lithium ions, such as a carbon material, silicon, aluminum, and an alloy with lithium. The electrolyte is a solution obtained by dissolving a lithium salt in a non-aqueous solvent, wherein the lithium salt can be materials such as LiPF6, LiBF4, LiClO4, LiTFSI, and LiFSI. As non-aqueous solvents, for example, there can be mentioned cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and its fluorinated derivatives; cyclic esters such as γ-butyrolactone and γ-valerolactone, etc., which can be used alone or in combination. As external packaging materials, there can be mentioned metal shells, aluminum laminated film packaging, etc. The shapes of batteries include square, cylindrical, button-shaped, etc., and the battery separator 1 of the present invention is suitable for any shape. From the viewpoint of ion permeability, the air permeability value of the battery separator 1 of the present application is preferably within 300s / 100ml, the thickness of the battery separator 1 is preferably within 30μm, and the resistance of the battery separator 1 is preferably 0.5-10ohm.cm 2 The puncture strength of the battery separator 1 is preferably in the range of 10-1200 gf, preferably in the range of 200-800 gf.

[0042] The method for manufacturing a non-aqueous secondary battery separator is a method for manufacturing a non-aqueous secondary battery separator having an aggregate containing microparticles, a filler, and a heat-resistant polymer coating in the aforementioned amount on one or both sides of a porous substrate, wherein the coating process includes an aqueous coating process and an oily coating process, wherein the aqueous coating process includes: (1) using a wetting agent, a dispersant, a thickener, a filler, a polymer material with adhesive properties, an adhesive, etc., adding them in a certain order and mixing and stirring to obtain a uniform slurry. (2) using a wire rod coating, a roller coating method, etc. to coat the slurry on the separator. (3) entering an oven and drying to obtain an aqueous slurry coating layer. The oily coating process includes: (1) dissolving a polymer material or a heat-resistant polymer material in an appropriate solvent to obtain a uniform solution, or mixing the solution with ceramic particles, heat-resistant polymer particles, heat-resistant polymer fibers, etc. to obtain a uniform dispersion. (2) Apply the solution or dispersion onto the base film and create pores using a method such as non-solvent-induced phase separation, or directly place the film in an oven to create pores by steam-induced phase separation. (3) Rinse with water to remove the solvent. (4) Place the film in an oven for drying.

[0043] In some embodiments, a filler comprising adhesive polymer particles and at least one of an organic compound and an inorganic compound is dispersed, suspended, or emulsified in a solvent in a solid state to produce an aqueous dispersion. This dispersion can be either an emulsion or a suspension. During the preparation of the coated membrane, the water in the aqueous slurry must be evaporated to produce a dry coating. For oil-based coatings, the membrane also requires drying to remove the solvent, as water must be used to wash it off.

[0044] The purpose of this application and the solution of its technical problems are achieved by adopting the following technical solutions.

[0045] The present application provides a battery separator preparation and processing method 2, please refer to Figures 1 and 5 simultaneously, which includes: step S1: providing a porous substrate; step S2: coating a heat-resistant layer on one side of the porous substrate; and step S3: coating an adhesive layer on the heat-resistant layer, wherein the adhesive layer comprises an aggregate layer formed by assembling a polymer material having adhesive properties, and the adhesive layer has a coating coefficient C, which is equal to the ratio of the adhesive strength A of the adhesive layer to the increased permeability value P per unit coating thickness, satisfying the relationship C = A / P, and the ratio range of the coating coefficient C is 0.3 < C < 1, wherein the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the increased permeability value P per unit coating thickness of the adhesive layer is s / 100cc / μm. It can be understood that the battery separator structure obtained by this battery separator preparation and processing method 2 includes a porous substrate, a heat-resistant layer formed on the porous substrate, and an adhesive layer formed on the heat-resistant layer. However, the present invention is not limited thereto. When the customer does not need a heat-resistant layer, step S2 may be omitted and step S3 may be performed directly. In this case, the obtained battery separator structure includes a porous substrate and an adhesive layer formed on the porous substrate.

[0046] In the invention, some parameters are designed to conduct experiments, and the experimental process and results are summarized as follows.

[0047] Determination method 1: Test method for diaphragm thickness

[0048] For uniform coating testing, the thickness measurement equipment is a Mahr Millimar thickness tester with a 12mm diameter test head and a measuring load of 0.75N. Samples measuring 100mm x 100mm should be flat and uniform, free of defects such as scrap, pinholes, warping, oil stains, and scratches. Before measuring, check that the instrument reading is zero. This should be confirmed before and after each test. During thickness measurement, the probe should be lowered gently to avoid specimen deformation, and the center of the 100mm x 100mm area should be determined.

[0049] Determination method 2: Air permeability test method

[0050] The test equipment is a Wangyan-type permeability tester. A battery separator is fixed in place and a 0.05 MPa air pressure is applied to one side of the separator. Due to the micropores in the separator, this pressure gradually decreases. When 100 mL of air completely passes through the separator, the pressure equals atmospheric pressure. The time it takes for 100 mL of air to pass through the separator at 0.05 MPa is recorded in seconds per 100 cc. A shorter pressure drop time indicates better separator permeability, and vice versa.

[0051] Determination method 3: Test method for electrode adhesion

[0052] The diaphragm and electrode were stacked together and hot-pressed at 3.5 tons and 90°C for 60 seconds. The diaphragm was cut into 25mm x 200mm strips and then subjected to a universal tensile testing machine for adhesion strength.

[0053] Test method 4: Capacity retention rate test method

[0054] The battery is based on a conventional 3Ah soft-pack battery, with an NCM523 positive electrode and a graphite negative electrode. Cyclic performance testing at 25°C: 500 charge-discharge cycles were performed at 1C. Capacity retention is the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle.

[0055] The bonding mechanism of the adhesive layer in the separator in this application is as follows: Polyvinylidene fluoride (PVDF) and acrylic polymer particles generate adhesive forces under heat and pressure, bonding them to the electrode. This adhesive layer can improve the following battery cell performance: (1) It makes the battery cell harder and easier to insert into the shell. (2) It extends the cycle life of the battery cell. (3) PVDF has good liquid absorption and retention capabilities.

[0056] Test method 5: Crystallinity test method:

[0057] The infrared spectrometer of PVDF / PVDF-HFP was used to measure the infrared spectrum of PVDF / PVDF-HFP. 750-775cm -1 The peak integration yielded A1, and 825-852 cm -1 The peak of A2 is integrated. F(α) is equal to 1.26A1 / (1.26A1+A2).

[0058] Test method 6: Test method for α phase in crystal phase:

[0059] The crystallinity of PVDF / PVDF-HFP was measured using a TA Differential Scanning Calorimeter (DSC-Q2000). The temperature was first increased from room temperature to 300°C, eliminating the thermal history, at a rate of 5°C / min. The percent crystallinity (Xc) of all samples was calculated using the following formula:

[0060] ΔH f is the melting heat of the crystalline part, ΔH f 0 Heat of fusion for 100% crystallization, ΔH for PVDF f 0 104.7 J·g -1 .

[0061] Example 1:

[0062] (1) Preparation of slurry: PVDF powder and binder were added to a certain amount of water to prepare a slurry with a solid content of 10% according to the solid dry weight ratio of PVDF-HFP (the copolymerization ratio of VDF and HFP was 95:5, Kynar powerflex LBG PWD from Arkema) and binder (LA133 from Sichuan Meishan Yindi Le Company) of 9:1.

[0063] (2) Coating step: Using a roller coating process, the PVDF slurry configured above is coated on a diaphragm (a diaphragm with a thickness of 9 μm produced by Shanghai Enjie Company), and the thickness of the coating is controlled to be 2 microns to obtain a PVDF coating film. Through testing, it was found that the crystallinity of PVDF-HFP is 45%, the proportion of α phase in the crystalline phase of PVDF-HFP is 55%, the bonding strength between the diaphragm and the positive electrode sheet is about 6.1 N / m, the permeability increase per unit coating thickness is about 10.2 s / 100 ml, and the C value is 0.6. The capacity retention rate of the battery prepared using the diaphragm at 500 cycles is 85%. Through testing, it was found that the bonding strength between the diaphragm and the positive electrode sheet is about 8.2 N / m, the permeability increase per unit coating thickness is about 11.9 s / 100 ml, and the C value is 0.69. The capacity retention rate of the battery prepared using the diaphragm at 500 cycles is 88%.

[0064] Example 2:

[0065] (1) Preparation of slurry: PVDF-HFP (the copolymerization ratio of VDF to HFP is 95:5, Kynar powerflex LBG PWD from Arkema) is fully dissolved in DMAc solvent to form a solution with a concentration of 8%.

[0066] (2) Coating step: Using a roller coating process, the PVDF-HFP solution prepared above was coated on a diaphragm (a diaphragm with a thickness of 9 μm produced by Shanghai Enjie Company). Pores were formed by a non-solvent induced phase separation method to obtain an oily PVDF-HFP coated diaphragm. The thickness of the coating was controlled to be 2 μm to obtain a PVDF-HFP coated membrane. Tests showed that the crystallinity of PVDF-HFP was 25%, of which the proportion of α phase in the crystalline phase accounted for 8%. The bonding strength between the diaphragm and the positive electrode sheet was about 20.5 N / m, the permeability increase per unit coating thickness was about 25.8 s / 100 ml, and the C value was 0.79. The capacity retention rate of the battery prepared using this diaphragm was 90% at 500 cycles.

[0067] Example 3:

[0068] PVDF was replaced with PMMA (from Japan's Zeon Co., Ltd.), with all other properties remaining the same as in Example 1. Testing revealed that the membrane's bonding strength to the positive electrode sheet was approximately 12.1 N / m, the air permeability increase per unit coating thickness was approximately 12.5 s / 100 ml, and the C value was 0.97. The battery prepared using this membrane exhibited a capacity retention rate of 93% after 500 cycles.

[0069] Example 4:

[0070] (1) Preparation of mixed slurry: A slurry with a solid content of 20% was prepared according to the dry weight ratio of alumina: PVDF-HFP: binder = 100:40:10.

[0071] (2) Using a roller coating process, the above-configured alumina and PVDF-HFP mixed slurry was coated on a diaphragm (a diaphragm with a thickness of 9 μm produced by Shanghai Enjie Company), and the coating thickness was controlled to be 2 μm to obtain a ceramic and PVDF-HFP mixed coating film.

[0072] Testing revealed that the PVDF-HFP has a crystallinity of 45%, with the α phase accounting for 55%. The separator exhibits a bond strength of approximately 7.2 N / m to the positive electrode sheet, an increase in air permeability per unit coating thickness of approximately 12.3 s / 100 ml, and a C value of 0.59. Batteries fabricated using this separator exhibited a capacity retention rate of 85% after 500 cycles.

[0073] Example 5:

[0074] (1) Slurry preparation: A ceramic slurry with a solid content of about 30% was prepared by mixing alumina (Shandong Guoci, SAO-035EQ) and a binder (Japan Zeon BM-900B) in a ratio of 100:5.

[0075] (2) Using a roller coating process, the above-configured alumina slurry was coated on a diaphragm (a diaphragm with a thickness of 9 μm produced by Shanghai Enjie Company), and the thickness of the coating was controlled to be 1 μm to obtain a ceramic coating film.

[0076] (3) According to the solid dry weight ratio of PVDF-HFP to binder of 9:1, PVDF-HFP powder (monomers are VDF and HFP, where the copolymerization ratio of VDF to HFP is 95:5) and binder (Sichuan Meishan Yindile Company, LA133) were added to a certain amount of water to prepare a 10% solid content slurry.

[0077] (4) Coating step: Using a roller coating process, the PVDF-HFP slurry prepared above was coated on the ceramic coating film obtained in step (2), and the coating thickness was controlled to be 1 micron to obtain a PVDF-HFP coating film. Testing found that the crystallinity of PVDF-HFP was 45%, and the proportion of α phase in the crystalline phase was 55%. The bonding strength between the separator and the positive electrode sheet was approximately 6.4 N / m, the permeability increase per unit coating thickness was approximately 11.4 s / 100 ml, and the C value was 0.56. The battery prepared using this separator had a capacity retention rate of 83% after 500 cycles.

[0078] Example 6:

[0079] [Corrected 24 / 10 / 2024 according to Rule 91] The same method as Example 5 was used, except that the aluminum oxide was replaced with magnesium hydroxide. Testing revealed that the crystallinity of the PVDF-HFP was 45%, with the α phase accounting for 55%. The adhesion strength of the separator to the positive electrode sheet was approximately 6.5 N / m, the increased air permeability per unit coating thickness was approximately 11.8 s / 100 ml, and the C value was 0.55. The battery prepared using this separator exhibited a capacity retention of 82% after 500 cycles.

[0080] Example 7:

[0081] Except for replacing aluminum oxide with barium titanate, the remainder of the test was identical to Example 6. Testing revealed that the crystallinity of the PVDF-HFP was 45%, with the α phase accounting for 55%. The adhesion strength of the separator to the positive electrode sheet was approximately 6.3 N / m, the increased air permeability per unit coating thickness was approximately 11.5 s / 100 ml, and the C value was 0.55. The battery prepared using this separator exhibited a capacity retention of 82% after 500 cycles.

[0082] Example 8:

[0083] (1) Slurry Preparation: Aramid was dissolved in DMAc solvent to prepare an aramid solution with a certain solid content. Barium sulfate was dispersed in DMAc to prepare a dispersion with a certain solid content. A mixed dispersion of aramid (Teijin Co., Ltd., meta-1313 aramid) and barium sulfate was prepared with a solid content ratio of 4:6 to prepare a total solid content of 20% aramid and barium sulfate.

[0084] (2) The mixed slurry prepared above was coated on a diaphragm (a diaphragm with a thickness of 9 μm produced by Shanghai Enjie Company) using a roller coating process, and pores were formed by a coagulation bath method, and the thickness of the coating was controlled to be 1 μm, thereby obtaining a mixed porous coating membrane of aramid and barium sulfate.

[0085] (3) According to the solid dry weight ratio of PVDF-HFP to binder of 9:1, PVDF-HFP powder (monomers are VDF and HFP, where the copolymerization ratio of VDF to HFP is 95:5) and binder (Sichuan Meishan Yindile Company, LA133) were added to a certain amount of water to prepare a 10% solid content slurry.

[0086] (4) Coating step: Using a roller coating process, the PVDF-HFP slurry prepared above was coated on the ceramic coating film obtained in step 2, with the coating thickness controlled to be 1 μm, to obtain a PVDF-HFP coating film. Testing revealed that the crystallinity of the PVDF-HFP was 25%, with the α-phase accounting for 8% of the crystalline phase. The bonding strength between the separator and the positive electrode sheet was approximately 6.5 N / m, the permeability increase per unit coating thickness was approximately 11.2 s / 100 ml, and the C value was 0.58. The battery prepared using this separator exhibited a capacity retention rate of 84% after 500 cycles.

[0087] Comparative Example 1:

[0088] The process was identical to Example 1, except that PVDF was replaced with polystyrene microparticles (laboratory-made, with a D50 particle size of approximately 0.8 μm). Testing revealed that the separator exhibited a bonding strength of approximately 2.1 N / m to the positive electrode sheet, an increase in air permeability per unit coating thickness of approximately 10.3 s / 100 ml, and a C value of 0.2. A battery fabricated using this separator exhibited a capacity retention of 60% after 500 cycles.

[0089] Comparative Example 2:

[0090] The same procedures as in Example 1 were used, except that PVDF was replaced with a copolymerized PVDF-HFP (sourced from Zhejiang Zhonghua Lantian, with a 45% VDF content) with a high HFP content. Testing revealed that the crystallinity of PVDF-HFP was 33%, with the α-phase accounting for 25% of the crystalline phase. The separator exhibited a bonding strength of approximately 2.8 N / m to the positive electrode sheet, an increase in air permeability per unit coating thickness of approximately 11.2 s / 100 ml, and a C value of 0.25. The battery prepared using this separator exhibited a capacity retention rate of 65% after 500 cycles.

[0091] Comparative Example 3:

[0092] The same procedures as in Example 2 were employed, except that the PVDF-HFP in Comparative Example 2 was replaced with homopolymer PVDF (from Zhejiang Zhonghua Lantian, with a 100% VDF ratio). Testing revealed that the homopolymer PVDF had a crystallinity of 65%, with the α-phase ratio in the crystalline phase accounting for 76%. The separator exhibited an adhesion strength of approximately 2.5 N / m to the positive electrode sheet, an increase in air permeability per unit coating thickness of approximately 10.2 s / 100 ml, and a C value of 0.245. The battery fabricated using this separator exhibited a capacity retention of 63% after 500 cycles.

[0093] Comparative Example 4:

[0094] The same procedures as in Example 6 were used, except that PVDF was replaced with polystyrene microparticles (laboratory-made, with a D50 particle size of approximately 0.8 μm). Testing revealed that the membrane exhibited a bonding strength of approximately 1.2 N / m to the positive electrode sheet, an increase in air permeability per unit coating thickness of approximately 10.4 s / 100 ml, and a C value of 0.12. The battery fabricated using this membrane exhibited a capacity retention of 51% after 500 cycles.

[0095] Comparative Example 5:

[0096] The same procedures as in Example 9 were employed, except that the PVDF was replaced with polystyrene microparticles (laboratory-made, with a D50 particle size of approximately 0.8 μm). Testing revealed that the membrane exhibited a bonding strength of approximately 1.5 N / m to the positive electrode sheet, an increase in air permeability per unit coating thickness of approximately 11.5 s / 100 ml, and a C value of 0.13. The battery fabricated using this membrane exhibited a capacity retention rate of 52% after 500 cycles.

[0097] Comparative Example 6:

[0098] The separator was the base film in Example 1 (a separator with a thickness of 9 μm produced by Shanghai Enjie Co., Ltd.). The capacity retention rate of the battery prepared using this separator was 45% after 500 cycles.

[0099] Comparative Example 7:

[0100] The separator is the same as steps (1) and (2) in Example 6, but does not include steps (3) and (4). The battery prepared using this separator has a capacity retention rate of 46% at 500 cycles.

[0101] Table 1: Structure and physical properties of the diaphragms in the examples and comparative examples

[0102] The above experimental results are sorted out as shown in Table 1. From the comparison between the examples and the comparative examples, it can be found that the use of PVDF, PMMA and other materials coated on the surface of the diaphragm can ensure the relatively good bonding strength of the diaphragm, thereby improving the cycle life (capacity retention rate) of the lithium battery. For oily coatings, such as Example 3, the bonding performance of the diaphragm is even better. This case uses the coating coefficient C value to express the ratio of bonding performance to air permeability increase value, and limits it to a certain range, so as to fully ensure the bonding performance and air permeability of the diaphragm. When the diaphragm does not have an adhesive layer, after 500 cycles of charge and discharge, the capacity retention rate is less than 80%, the capacity retention rate is small, and the cycle life is short. When the coating coefficient C value is in the range of 0.3 to 1, the capacity retention rate is greater than 80%, and it has a longer cycle life.

[0103] In summary, in order to improve the adhesion and air permeability of current battery separators, the present invention proposes a method of introducing polymer particles into the separator coating to improve the adhesion between the separator and the pole piece. In addition, heat-resistant polymer materials such as aramid are introduced into the separator coating to increase the membrane rupture temperature of the separator. Furthermore, ceramics are introduced into the separator coating to improve the heat shrinkage resistance of the separator. Through the above-mentioned improvement means, not only can the problem of peeling off from the separator due to insufficient adhesion strength of the current ceramic coating be effectively solved, but also the air permeability of the separator can be guaranteed. In addition, the present application expresses the adhesion and air permeability of the coating by designing the coating coefficient C value, and limits it to a certain preferred range, so that it is very convenient to evaluate and ensure whether the adhesion and air permeability of the separator meet the requirements.

[0104] Phrases such as "in some embodiments" and "in various embodiments" are used repeatedly. These phrases generally do not refer to the same embodiment; however, they may refer to the same embodiment. The words "including," "having," and "comprising" are synonymous unless the context indicates otherwise.

[0105] The above description is merely an embodiment of the present application and does not constitute any form of limitation to the present application. Although the present application has been disclosed as above with specific embodiments, it is not intended to limit the present application. Any technician familiar with this profession can make slight changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present application. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application are still within the scope of the technical solution of the present application.

Claims

1. A battery separator, characterized in that: include: A porous substrate or a composite material consisting of a porous substrate and a heat-resistant layer on the porous substrate; as well as An adhesive layer is formed on the porous substrate or the composite material, wherein the adhesive layer comprises a polymer material with adhesive properties, and the adhesive layer has a coating coefficient C, the coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the air permeability increase value P per unit coating thickness, and satisfies the relationship C=A / P, and the ratio range of the coating coefficient C is 0.3<C<1, wherein the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the air permeability increase value P per unit coating thickness of the adhesive layer is s / 100cc / μm.

2. The battery separator according to claim 1, characterized in that: The adhesive layer includes an adhesive polymer material or a mixture of an adhesive polymer material and a filler, and the filler includes an organic or inorganic high temperature resistant material.

3. The battery separator according to claim 2, characterized in that: The adhesive polymer material includes polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, methyl methacrylate homopolymer, methyl methacrylate copolymer or a mixture thereof.

4. The battery separator according to claim 3, characterized in that: The molar ratio of the vinylidene fluoride monomer in the polyvinylidene fluoride copolymer is higher than 50%, and other copolymer monomers can be one or more selected from hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate and vinyl acetate.

5. The battery separator according to claim 1, characterized in that: The adhesive layer may be located on a single side of the porous substrate, on both sides of the porous substrate, on a single side of the composite material, or on both sides of the composite material.

6. The battery separator according to claim 1, characterized in that: The heat-resistant layer includes ceramic material, heat-resistant polymer material or a mixture of ceramic material and heat-resistant polymer material.

7. A battery separator, characterized in that: include: a porous substrate; as well as An adhesive layer is formed on one side of the porous substrate, wherein the adhesive layer comprises a polymer material having adhesive properties, the polymer material comprises polyvinylidene fluoride (PVDF), the adhesive layer has a coating coefficient C, the coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the air permeability increase value P per unit coating thickness, satisfies the relationship C=A / P, and the ratio range of the coating coefficient C is 0.4<C<0.9, wherein the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the air permeability increase value P per unit coating thickness of the adhesive layer is s / 100cc / μm.

8. The battery separator according to claim 7, characterized in that: The raw material crystallinity of the polyvinylidene fluoride copolymer is between 10% and 50%.

9. The battery separator according to claim 7, characterized in that: When the adhesive layer is coated with water-based polyvinylidene fluoride, the proportion of the α phase in the crystal region of the water-based polyvinylidene fluoride is greater than 30% and less than 70%.

10. The battery separator according to claim 7, characterized in that: When the adhesive layer is coated with oily polyvinylidene fluoride, the proportion of the α phase in the crystal region of the oily polyvinylidene fluoride is less than 20%.

11. A lithium battery, characterized in that: include: A positive electrode, a negative electrode and a battery separator according to any one of claims 1 to 10, wherein the battery separator is located between the positive electrode and the negative electrode.

Images