Novel diaphragm of secondary battery and preparation method of novel diaphragm

Abstract

The invention relates to a secondary battery, in particular to a novel diaphragm of a lithium battery and a preparation method of the novel diaphragm, novel secondary batteries with different effects are formed by combining organic salt with different materials, and different purposes of high conductivity, flame retardance and the like can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to a new type of separator for secondary batteries, in particular lithium batteries, and a method for preparing the same. BACKGROUND

[0002] In recent years, the global energy structure is accelerating the transformation to clean, and as the core energy storage carrier, the market size of lithium-ion batteries continues to expand with the popularization of new energy vehicles, the large-scale application of new energy storage systems, and the iteration of consumer electronics technology. According to industry research data, the global lithium-ion battery market size has exceeded 70 billion US dollars in 2023, and is expected to continue to expand at a compound annual growth rate of more than 25% in the next five years, reaching a market size of 278 billion US dollars by 2029.

[0003] However, safety accidents caused by thermal runaway of lithium batteries have become a key bottleneck restricting the sustainable development of the industry. As the core safety barrier of the battery system, the thermodynamic stability of the separator directly determines the failure threshold of the battery under extreme working conditions. Although the current mainstream polyolefin (PE / PP) based separator has excellent processing adaptability, its intrinsic thermal performance has major safety hazards: the softening point of the material is in the critical interval of 130℃ (PE) and 160℃ (PP), and it shows more than 20% irreversible in-plane shrinkage under thermal shock exceeding its softening point temperature. This thermal deformation will directly trigger heterogeneous contact short circuit of the electrode, and then activate the chain thermal runaway reaction. The current technical route in the industry mainly uses ceramic coating process for heat-resistant modification. Although this scheme can improve the intrinsic heat resistance of the separator, its protection mechanism has a fundamental defect: when the battery is subjected to abuse conditions such as mechanical puncture, overcharge / overdischarge, or external thermal shock, the coating structure cannot effectively block the thermal runaway process, nor can it inhibit the secondary damage effect caused by heat spread. SUMMARY

[0004] Therefore, one of the purposes of the present application is to: in view of the difficulties that the existing separator cannot effectively block the thermal runaway process, and is more difficult to inhibit the heat spread, a multifunctional flame-retardant heat-resistant coating is constructed on the surface of the traditional separator to significantly improve the thermal safety performance of the battery.

[0005] To achieve the above purpose, the following technical solutions are adopted in the present application: A new type of separator, comprising a base film and a coating layer; the coating layer is located on at least one side surface of the base film; the base film comprises a polymer base film; and the coating layer comprises at least one organic salt, the organic salt comprises melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and the new type of separator has a combustion time of less than 10 seconds measured by the flame retardant method. The coating layer is obtained by coating a coating slurry on at least one side surface of the base film and then drying.

[0006] Preferably, the coating further comprises a binder; the mass of the binder is 0.5% to 15% of the mass of the organic salt.

[0007] Preferably, the binder comprises polyvinyl alcohol, polyacrylic acid and its modified materials, polymethacrylate and its modified materials, styrene butadiene rubber, polyacrylamide and its modified materials, polyvinyl acetate, natural latex, chloroprene latex, nitrile latex, or any combination thereof.

[0008] Preferably, the base film is in a single-layer form, a double-layer form, or a multi-layer form, and when the base film is in a double-layer form or a multi-layer form, the material thereof comprises the same or different materials, and the porosity of the base film is 30% to 70%.

[0009] Preferably, the average particle size of the organic salt is 0.1 μm to 20 μm; or 0.1 μm to 15 μm; or 0.1 μm to 10 μm; and the particle size distribution D99≤ 15 μm.

[0010] Preferably, the thickness of the novel separator is 3 μm to 42 μm; and / or, the thickness of the base film is 2 μm to 40 μm; and / or, the thickness of the coating is 0.5 μm to 9 μm, and the areal density of the coating is 0.4 g / m 2 to 5 g / m 2 .

[0011] The present application also provides another novel separator, comprising a base film and a coating; the coating is located on at least one side surface of the base film; the base film comprises a polymer base film; and the coating at least comprises an organic salt, the organic salt comprises melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and the leakage rate of the novel separator is less than 5%, and the agglomeration rate is less than 10%. The coating is obtained by coating a coating slurry on at least one side surface of the base film, and then drying.

[0012] Preferably, the coating further comprises a binder; the mass of the binder is 0.5% to 15% of the mass of the organic salt.

[0013] Preferably, the binder comprises polyvinyl alcohol, polyacrylic acid and its modified materials, polymethacrylate and its modified materials, styrene butadiene rubber, polyacrylamide and its modified materials, polyvinyl acetate, natural latex, chloroprene latex, nitrile latex, or any combination thereof.

[0014] Preferably, the base film is in a single-layer form, a double-layer form, or a multi-layer form, and when the base film is in a double-layer form or a multi-layer form, the material thereof comprises the same or different materials, and the porosity of the base film is 30% to 70%.

[0015] Preferably, the average particle size of the organic salt is 0.1 μm to 20 μm; or 0.1 μm to 15 μm; or 0.1 μm to 10 μm; and the particle size distribution D99≤ 15 μm.

[0016] Preferably, the thickness of the novel separator is 3 μm to 42 μm; and / or, the thickness of the base film is 2 μm to 40 μm; and / or, the thickness of the coating layer is 0.5 μm to 9 μm, and the areal density of the coating layer is 0.4 g / m 2 to 5 g / m 2 .

[0017] The present application also provides a method for manufacturing a novel separator, comprising the following steps: a coating slurry preparation step of adding a solid material and a binder into a dispersion medium to form a coating slurry, wherein the solid material comprises an organic salt, and the organic salt comprises melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and a coating step of coating the coating slurry on at least one side surface of a base film to form a novel separator.

[0018] Preferably, the solid content of the coating slurry is 5% to 50%; and / or, the viscosity of the coating slurry is 10 cp to 1000 cp. Preferably, the viscosity of the coating slurry is 10 cp to 80 cp. And / or, the D50 of the coating slurry is 0.1 to 10 μm; and / or, the D99 of the coating slurry is 1 to 10 μm.

[0019] Preferably, the coating slurry preparation step further comprises: a first step of adding the solid material and a dispersant into the dispersion medium to form a first slurry; and a second step of adding the binder and a wetting agent into the first slurry to form the coating slurry.

[0020] Preferably, the dispersant is at least one of polymethacrylate, polyacrylamide, polyacrylate, polyacrylic acid and its salts, triethylhexylphosphoric acid, sodium dodecyl sulfate, fatty acid polyethylene glycol ester, sodium hexametaphosphate, and methylamyl alcohol.

[0021] Preferably, the wetting agent comprises at least one of ethanol, propylene glycol, glycerol, polyoxyethylene alkyl phenol ether, polyoxyethylene fatty alcohol ether, fatty acid ester sulfate, and vinyl triethoxy silane.

[0022] Preferably, after the coating step, the method further comprises the following steps: a drying step of drying the novel separator to form a dried novel separator. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1This is a surface SEM image of a certain region in the novel diaphragm prepared in Example 3; Figure 2 The image shows a surface SEM image of the particle agglomeration region in the novel diaphragm prepared in Example 4. Figure 3 The image shows a surface SEM image of the region where micelles appear in the novel diaphragm prepared in Example 5. Figure 4 A surface SEM image of a certain region in the diaphragm prepared in Comparative Example 3; Figure 5 A surface SEM image of a certain region in the diaphragm prepared in Comparative Example 4; Figure 6 The surface SEM image of a certain area of ​​the novel diaphragm prepared in Example 3 after heat shrinkage at 180°C is shown. Figure 7 This is a flowchart of the preparation method in the first embodiment; Figure 8 This is a flowchart of the preparation method in the second embodiment. Detailed Implementation

[0024] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] According to one objective of the present invention, a novel separator is provided, comprising a base membrane and a coating; the coating is located on at least one surface of the base membrane; the base membrane comprises a polymer base membrane; and the coating comprises at least one organic salt, the organic salt comprising melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and the novel separator has a burning time of less than 10 seconds as measured by a flame retardant method. The coating is obtained by applying a coating slurry to at least one surface of the base membrane and then drying it.

[0028] In a preferred embodiment, the coating further includes an adhesive; the adhesive is present in an amount of 0.5% to 15% of the organic salt by mass.

[0029] In a preferred embodiment, the adhesive includes polyvinyl alcohol, polyacrylic acid and its modified forms, polymethacrylate and its modified forms, styrene-butadiene rubber, polyacrylamide and its modified forms, polyvinyl acetate, natural latex, chloroprene latex, nitrile latex, or any combination thereof.

[0030] In a preferred embodiment, the base film is in the form of a single layer, a double layer, or a multilayer, and when the base film is in the form of a double layer or a multilayer, its material includes the same or different materials, and the porosity of the base film is 30% to 70%.

[0031] In a preferred embodiment, the average particle size of the organic salt is 0.1 μm to 20 μm; or 0.1 μm to 15 μm; or 0.1 μm to 10 μm; and the particle size distribution D99 ≤ 15 μm.

[0032] In a preferred embodiment, the thickness of the novel separator is 3 μm to 42 μm; and / or, the thickness of the base film is 2 μm to 40 μm; and / or, the thickness of the coating is 0.5 μm to 9 μm, and the areal density of the coating is 0.4 g / m³. 2 Up to 5g / m 2 .

[0033] This invention provides another novel separator, comprising a base membrane and a coating; the coating is located on at least one surface of the base membrane; the base membrane comprises a polymer base membrane; and the coating comprises at least one organic salt, the organic salt comprising melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and the novel separator has a coating omission rate of less than 5% and an agglomeration rate of less than 10%. The coating is obtained by applying a coating slurry to at least one surface of the base membrane and then drying it.

[0034] In a preferred embodiment, the coating further includes an adhesive; the adhesive is present in an amount of 0.5% to 15% of the organic salt by mass.

[0035] In a preferred embodiment, the binder comprises polyvinyl alcohol, polyacrylic and its modified materials, polymethacrylate and its modified materials, styrene butadiene rubber, polyacrylamide and its modified materials, polyvinyl acetate, natural latex, chloroprene latex, nitrile latex, or any combination thereof.

[0036] In a preferred embodiment, the base film is in a single layer, double layer or multi-layer form, and when the base film is in a double layer or multi-layer form, the material thereof comprises the same or different materials, and the porosity of the base film is 30% to 70%.

[0037] In a preferred embodiment, the average particle size of the organic salt is 0.1 μm to 20 μm; or 0.1 μm to 15 μm; or 0.1 μm to 10 μm; and the particle size distribution D99≤ 15 μm.

[0038] In a preferred embodiment, the thickness of the novel separator is 3 μm to 42 μm; and / or, the thickness of the base film is 2 μm to 40 μm; and / or, the thickness of the coating layer is 0.5 μm to 9 μm, and the areal density of the coating layer is 0.4 g / m 2 to 5 g / m 2 .

[0039] The present application also provides a manufacturing method of a novel separator, comprising: a coating slurry preparation step of adding a solid material and a binder in a dispersion medium to form a coating slurry, wherein the solid material comprises an organic salt, and the organic salt comprises melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and a coating step of coating the coating slurry on at least one side surface of a base film to form a novel separator.

[0040] In a preferred embodiment, the solid content of the coating slurry is 5% to 50%; and / or, the viscosity of the coating slurry is 10 cp to 1000 cp. Preferably, the viscosity of the coating slurry is 10 cp to 80 cp. And / or, the D50 of the coating slurry is 0.1 to 10 μm; and / or, the D99 of the coating slurry is 1 to 10 μm.

[0041] In a preferred embodiment, the coating slurry preparation step further comprises: a first step of adding the solid material and a dispersant in a dispersion medium to form a first slurry; and a second step of adding the binder and a wetting agent in the first slurry to form a coating slurry.

[0042] In a preferred embodiment, the dispersing agent is at least one of polymethacrylate, polyacrylamide, polyacrylate, polyacrylic acid and its salts, triethylhexylphosphoric acid, sodium dodecyl sulfate, fatty acid polyglycol ester, sodium hexametaphosphate, and methylamyl alcohol.

[0043] In a preferred embodiment, the wetting agent includes at least one of ethanol, propylene glycol, glycerol, polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, fatty acid ester sulfate, and vinyl triethoxy silane.

[0044] In a preferred embodiment, after the coating step, a drying step is further included, in which the novel diaphragm is dried to form a dried novel diaphragm.

[0045] The present application is further described in detail by the following examples, but is not intended to limit the scope of protection of the present application, and the implementation method thereof is described with reference to the Figure 7 and / or Figure 8 the flow chart.

[0046] The materials used in the examples and comparative examples are as follows: The base film was selected from porous polyethylene (PE) produced by Shanghai Enjie, with model number ND9 (Examples 1-10, Examples 12-20, and Comparative Examples 1-8) and model number HSE (Example 11); MCA, with CAS number 37640-57-6, was purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.; MPP, with CAS number 15541-60-3, was purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.; polymethacrylate was purchased from Jinzhou Shengda Chemical Co., Ltd.; polyacrylamide, with CAS number 25085-02-3, was purchased from Jiangsu Puleisi Biological Technology Co., Ltd.; methylamyl alcohol, with CAS number 42072-39-9, was purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.; and vinyl triethoxy silane, with CAS number 78-08-0, was purchased from Jiangsu Bosite Chemical Technology Co., Ltd.

[0047] Example 1 This example provides a novel diaphragm, which includes a base film and a coating layer coated on both sides of the base film.

[0048] The base film is a 9 μm-thick porous polyethylene (PE), and the thickness of the coating layer on both sides of the base film is 2 μm. The total thickness of the novel diaphragm is 13 μm.

[0049] The preparation raw materials of the coating include 100 parts of MCA particles (average particle size of 1 μm), 1 part of polymethacrylate as a binder, 0.5 part of polyacrylamide and 0.5 part of methyl amyl alcohol as a dispersant, and 0.1 part of vinyl triethoxysilane as a wetting agent, by mass fraction.

[0050] The preparation method of the novel separator includes: S1: According to the use amount of the above preparation raw materials, 100 parts of MCA particles, 1 part of a dispersant (0.5 parts of polyacrylamide and 0.5 parts of methyl amyl alcohol) are added to 300 parts of deionized water, and mechanical stirring is carried out at a speed of 2000 rpm for 1 h to obtain a first slurry, i.e. a stable dispersion liquid; the first slurry is uniformly dispersed in a ball mill tank by ball milling at a speed of 700 rpm for 1 h to obtain a first slurry after ball milling.

[0051] S2: The first slurry after ball milling is filtered, 1 part of polymethacrylate (i.e. a binder) and 0.1 part of vinyl triethoxysilane are added to the filtered first slurry, and mechanical stirring is carried out at a speed of 500 rpm for 1 h to obtain a coating slurry.

[0052] S3: The coating slurry is uniformly coated on both sides of the base film on a coating machine, and dried at 60℃ for 5 min to obtain a novel separator with a coating layer on both sides of the base film. The solid content of the coating slurry is 25.4%; the slurry viscosity of the coating slurry is 18 cP.

[0053] Example 2 The difference between this example and Example 1 is that the amount of the binder is 3 parts. The solid content of the coating slurry is 25.8%; the slurry viscosity of the coating slurry is 25 cP.

[0054] Example 3 The difference between this example and Example 1 is that the amount of the binder is 5 parts. The solid content of the coating slurry is 26.1%; the slurry viscosity of the coating slurry is 35 cP.

[0055] Example 4 The difference between this example and Example 1 is that the amount of the binder is 10 parts. The solid content of the coating slurry is 27.0%; the slurry viscosity of the coating slurry is 185 cP.

[0056] Example 5 The difference between this example and Example 1 is that the amount of the binder is 15 parts. The solid content of the coating slurry is 27.9%; the slurry viscosity of the coating slurry is 18 cP.

[0057] Example 6 The difference between this embodiment and embodiment 3 is that a coating layer of 2 μm is arranged on one side surface of the base film. The solid content of the coating slurry is 26.1%, and the slurry viscosity of the coating slurry is 35 cP.

[0058] Embodiment 7 The difference between this embodiment and embodiment 6 is that the thickness of the coating layer is 3 μm.

[0059] Embodiment 8 The difference between this embodiment and embodiment 6 is that the thickness of the coating layer is 5 μm.

[0060] Embodiment 9 The difference between this embodiment and embodiment 3 is that the average particle size of MCA is selected as 0.3 μm. The slurry viscosity of the coating slurry is 40 cP.

[0061] Embodiment 10 The difference between this embodiment and embodiment 3 is that the average particle size of MCA is selected as 0.5 μm. The slurry viscosity of the coating slurry is 30 cP.

[0062] Embodiment 11 The difference between this embodiment and embodiment 3 is that the thickness of the base film is 5 μm.

[0063] Embodiment 12 The difference between this embodiment and embodiment 3 is that the thickness of the coating layer on both side surfaces of the base film is 3 μm. The slurry viscosity of the coating slurry is 40 cP.

[0064] Embodiment 13 The difference between this embodiment and embodiment 3 is that MCA is replaced by MPP. The slurry viscosity of the coating slurry is 40 cP.

[0065] Embodiment 14 The difference between this embodiment and embodiment 3 is that the solid content is adjusted to 21%, and the slurry viscosity of the coating slurry is 18 cP.

[0066] Embodiment 15 The difference between this embodiment and embodiment 2 is that the solid content is adjusted to 22.2%, and the slurry viscosity of the coating slurry is 25 cP.

[0067] Embodiment 16 The difference between this embodiment and embodiment 3 is that the solid content is adjusted to 23.3%, and the slurry viscosity of the coating slurry is 35 cP.

[0068] Embodiment 17 The difference between this embodiment and embodiment 3 is that the solid content is adjusted to 25.5%, and the slurry viscosity of the coating slurry is 45 cP.

[0069] Example 18 The difference between this example and Example 3 is that the solid content is adjusted to 28%, and the coating slurry viscosity is 85 cP.

[0070] Example 19 The difference between this example and Example 3 is that the solid content is adjusted to 23.1%, and the coating slurry viscosity is 40 cP.

[0071] Example 20 The difference between this example and Example 3 is that the average particle size of MCA is selected as D50 of 5 μm and D99 of 13.7 μm, the coating thickness is 4 μm, and the solid content of the coating slurry is 23.3%; the coating slurry viscosity is 95 cP.

[0072] Comparative Example 1 The difference between this comparative example and Example 3 is that the solid particles in the coating are replaced by the same size Al203. The slurry viscosity of the coating slurry is 18 cP.

[0073] Comparative Example 2 The difference between this comparative example and Comparative Example 3 is that the solid particles in the coating are replaced by the same size boehmite. The slurry viscosity of the coating slurry is 20 cP.

[0074] Comparative Example 3 The difference between this example and Example 3 is that the solid content is adjusted to 5%, and the coating slurry viscosity is 8 cP.

[0075] Comparative Example 4 The difference between this example and Example 3 is that the solid content is adjusted to 10%, and the coating slurry viscosity is 12 cP.

[0076] Comparative Example 5 The difference between this comparative example and Example 3 is that the MCA raw material is not sufficiently ball-milled and dispersed, and the particles are severely agglomerated, with D50 of 20 μm and D99 > 50 μm. When the solid content is only 15% during preparation of the slurry, the viscosity is as high as 700 cP, and the slurry has extremely poor flowability, so uniform coating cannot be performed, and therefore subsequent performance testing is not performed.

[0077] Comparative Example 6 The difference between this comparative example and Example 3 is that the average particle size of the MCA used is too small, with D50 of 0.1 μm. When the dispersant amount is increased to 3 parts during preparation of the slurry, even when the solid content is 20%, the slurry is paste-like, with a viscosity of more than 1000 cP, and normal coating cannot be completed, so subsequent performance testing is not performed.

[0078] Comparative Example 7 The difference between this example and Example 3 is that the solid content is adjusted to 25.5%, and the coating slurry viscosity is 380 cP.

[0079] Comparative Example 8 The difference between this example and Example 3 is that the average particle size of MCA is selected as D50 of 10 pm, and D99 of 40 pm, the coating thickness of both sides of the base film is 7 pm, and the solid content of the coating slurry is 23.3%; the coating slurry viscosity is 320 cP.

[0080] The scanning electron microscope test is then performed on the example and the comparative example The present application uses a scanning electron microscope (SEM) to observe the microstructure of the sample, and simultaneously uses an energy dispersive spectrometer (EDS) for element analysis.

[0081] The organic salt D50 and D99 in the example and the comparative example are recorded in Table 1 below.

[0082] Table 1

[0083] The performance test method of the new diaphragm refers to: Heat shrinkage resistance: The new diaphragm is cut into multiple 120 mm x 100 mm (length x width) sizes in the longitudinal (MD) and transverse (TD) directions, an A4 paper is covered on the surface of the new diaphragm, and is placed in an oven at 130°C, 150°C, and 180°C respectively for 1 hour. The size of the direction after heat shrinkage is measured, and the shrinkage ratio is calculated. The heat shrinkage rate of the new diaphragm in Table 2 is based on the average value obtained in each direction after three measurements in the MD and TD directions.

[0084] Peeling strength: The peeling strength between the coating and the base film is tested on a universal tensile tester. The new diaphragm is cut into a sample strip of 150 mm x 30 mm (length x width) by a sampler, and is adhered to the double-sided tape of the test plate. A transparent tape of 200 mm x 20 mm (length x width) is then adhered above the sample strip, and then a cylindrical roller is used to naturally press the diaphragm in the same direction. When the new diaphragm is single-side coated, the corresponding base film faces downward, and the coating faces upward. One end of the transparent tape is peeled off from the coating surface of the new diaphragm, until the length of the transparent tape adhered to the coating surface of the new diaphragm is 80 mm. The free end of the transparent tape is folded, and the free end of the transparent tape and the test plate are clamped on the upper and lower clamps respectively. The continuous peeling is performed by the tensile tester at a stretching speed of 50 mm / min in the same environment until the coating and the base film are completely separated, and the peeling strength of the coating of the new diaphragm is directly read and recorded.

[0085] Air permeability: Refer to the standard GBT36363-2018; thickness is measured using a Marl film thickness gauge.

[0086] Flame retardancy test: The new diaphragm was cut into multiple 127mm × 12.7mm (length × width) specimens along the longitudinal (MD) and transverse (TD) directions, and the experiment was conducted in a non-ventilated test chamber. The upper end of the specimen was clamped with a fixture on a support, keeping the longitudinal axis of the specimen perpendicular. The lower end of the specimen was 9.5mm ± 2mm from the nozzle of the Bunsen burner. The Bunsen burner was lit and adjusted to produce a blue flame 19mm ± 5mm high. The Bunsen burner flame was placed at the lower end of the specimen and ignited for 10 seconds. Then the flame was removed, and the burning time of the specimen was recorded (no burning was recorded as 0 seconds). At the same time, the above specimens were tested according to the standard GBT40302-2021 to obtain the burning time T. Both flame retardancy tests were repeated three times for each group of specimens, and the average value was taken.

[0087] Particle size testing: The particle size of the fully dispersed powder or the prepared coating slurry is tested using a Malvern MS3000 laser particle size analyzer.

[0088] Reunion rate Definition: In a dried coating, "macrophages" are the percentage of area occupied by "macrophages" formed by the aggregation of multiple primary particles through van der Waals forces and other forces, with a size greater than twice the D99 value of a single primary particle. These "macrophages" are a direct manifestation of poor dispersion, which will damage the uniformity of the coating and become a performance bottleneck.

[0089] Calculation method: The surface morphology of the dried novel diaphragm coating sample was observed using a field emission scanning electron microscope (FE-SEM) at magnifications ranging from 1000 to 5000. Five fields of view (each with an area of ​​not less than 100 μm) were randomly selected. 2 Using image analysis software (such as Image-Pro Plus), threshold segmentation was performed to identify and count the total area of ​​particle aggregates (i.e., "molecular aggregates") with a size greater than 2 × D99 (raw material). The aggregation rate was calculated using the formula: Aggregation rate (%) = (∑molecular aggregate area / total observed area) × 100%, with the final aggregation rate being the highest value under different magnifications.

[0090] Missing coating rate Definition: This refers to the percentage of the base film exposed on the surface of a novel diaphragm after coating and drying, due to poor slurry wettability, the presence of large agglomerates, or improper processing, and not effectively covered by the coating. Missing points directly expose the thermally unstable polymer base film, becoming a weak point for thermal runaway.

[0091] Calculation method: Using the scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) surface scanning function, the characteristic elements (such as nitrogen element N in organic salt, or cyanuric acid radical in MCA) of the coating are analyzed under 1000-5000 times. The area with the characteristic element signal intensity lower than 3 times the standard deviation of the background value is defined as the "leakage coating area". Randomly select 5 macroscopic fields (the area of each field is not less than 1 mm 2 ), and calculate the area ratio of the leakage coating area: Leakage coating rate (%) = (∑leakage coating area / total observation area) x 100%, and the final leakage coating rate is the highest value under different magnifications.

[0092] The test results of the foregoing test method are arranged into Table 2 and Table 3, as shown below.

[0093] Table 2

[0094] Table 3

[0095] From Comparative Examples 1-8, it can be seen that as the binder content and coating thickness increase, the heat resistance and peel strength of the new type of separator show a positive correlation trend. Mechanism analysis shows that: (1) increasing the binder content can enhance the chemical bonding effect with MCA particles, forming a more compact composite structure; (2) increasing the coating thickness can increase the effective binding sites per unit area, and through synergistic effect, it can inhibit the thermal shrinkage of the base film, and the double-sided coating process has better mechanical distribution characteristics than the single-sided thick coating. However, it should be noted that when the binder content is less than 2 parts (such as Example 1), the interfacial bonding force is insufficient, resulting in a significant decrease in peel strength and powder shedding phenomenon; on the contrary, when the binder content reaches 10 parts (such as Example 4), a small amount of MCA particles agglomerate (as shown in Figure 2 ), and excessive addition of binder (Example 5) will form colloidal aggregates (as shown in Figure 3 ), causing coating defects. Under the appropriate binder content, the coating has a flat and dense structure (as shown in Figure 1 ), which can effectively prevent mechanical damage to the new type of separator by lithium dendrites or other foreign matter; at high temperature (180°C), it ensures the integrity of the new type of separator (as shown in Figure 6 ), avoiding short circuit caused by direct contact between the positive and negative electrodes. In addition, if the slurry solid content is low (5%, Figure 4 ; 10%, Figure 5 ) during coating, it will cause the new type of separator to be leaky, resulting in a decrease in heat resistance and flame retardancy.

[0096] When the new type of separator coating thickness is controlled at 4 pm and the total thickness is close to 13 pm, the thermal shrinkage of most examples can be stably controlled below 5% after 1 h of heat treatment at 180 DEG C, while maintaining excellent anti-powdering performance, significantly improving the thermal safety characteristics of the new type of separator. Compared with Comparative Examples 1 to 4, the new type of separator samples of Inventive Examples 1 to 13 are all not burned, having good flame retardant characteristics. This flame retardant characteristic effectively improves the safety performance of the battery: when the battery encounters abuse conditions such as mechanical puncture, overcharge / overdischarge or external heat shock, the new type of separator system constructed by the application, which has intrinsic flame retardant mechanism and high temperature size retention ability, can effectively block the heat runaway process and inhibit the secondary damage effect caused by heat spread, which has great strategic value for realizing the safety leap of new energy industry.

[0097] Particle size and thermal shrinkage: Examples 9 and 10 (small particle size) exhibit better thermal shrinkage resistance because small particles can form a more dense and strongly bonded coating.

[0098] Core flame retardant performance: all examples (1-13) achieve the extreme flame retardant effect of "0 second" burning. In contrast, Comparative Examples 1 and 2 (inorganic flame retardant) and Comparative Examples 3 and 4 (too low solid content) have significantly decreased flame retardant performance. This fully proves the necessity of organic salt (MCA / MPP) as the main flame retardant component and the high-quality coating obtained by optimizing the slurry.

[0099] Mechanical performance: peel strength increases with increasing binder content (Examples 1-5). Air permeability and puncture strength are related to coating thickness, composition and density.

[0100] Processing boundary: Comparative Examples 5 and 6 cannot be coated, again proving from the opposite side that controlling the particle size of organic salt in the range of 0.3 pm to 10 pm is crucial for realizing processability.

[0101] Comparative Examples 1-2: prove the uniqueness of the flame retardant mechanism, and inorganic materials cannot achieve rapid gas phase flame retardation.

[0102] Comparative Examples 3-4: prove the importance of the solid content window, and too low solid content will result in a non-dense coating (leakage rate increases dramatically) and performance collapse.

[0103] Comparative Examples 5-6: prove the boundary of the raw material particle size window, and too small or too large will result in unprocessable or performance degradation.

[0104] Comparative Example 7: proves the decisive role of the dispersion process. Even if the formula and solid content are the same, poor dispersion (slurry D99 up to 28.2 pm, agglomeration rate 15%) results in a comprehensive deterioration of all performance. It proves the non-obviousness of the process required to achieve low agglomeration rate.

[0105] Example 20 and Comparative Example 8 are single-sided coated due to the large particle size.

[0106] The aforementioned process (processability) affects the performance of the new type of separator (including flame retardancy) in terms of solid content, viscosity, particle size, and dispersibility. The solid content directly affects the production efficiency and drying energy consumption. In the dispersion system of the present application, a stable and coatable slurry can be prepared within this solid content range. Too low solid content leads to low coating efficiency and high drying load; while too high solid content (such as > 50%) easily exceeds the carrying capacity of the dispersion system, resulting in uncontrolled viscosity and particle settling, which cannot guarantee long-term storage and coating stability.

[0107] 10cp to 80cp, this viscosity range is a "golden window" verified by a large number of experiments, which is suitable for conventional coating process. If the viscosity is lower than this range, the slurry is easy to flow, and it is difficult to control the coating thickness and area density; if the viscosity is higher than this range, it proves that the particle dispersion is not good, there is serious agglomeration, and the slurry cohesion is too strong, which cannot be smoothly flattened and coated. In addition, viscosity and particle agglomeration are the two aspects of the dispersion effect of the slurry, and good dispersion will reduce the particle size of the slurry and thus reduce the viscosity.

[0108] Successful dispersion not only means that the initial viscosity is qualified, but also means that the slurry has good storage stability and shear thinning characteristics. That is, the slurry can remain uniform and not stratified when at rest, the viscosity rapidly decreases under the shearing force of coating to facilitate flow and spreading, and the structure quickly recovers after coating to prevent sagging. The present application achieves this goal through a specific dispersion process (including but not limited to high-speed shearing and ball milling).

[0109] Finally, all the controls of particle size and slurry serve one goal: to build a flame-retardant functional layer with optimal microstructure on the new type of separator.

[0110] The relationship is as follows: Structure determines performance: a well-dispersed coating layer has its organic salt particles uniformly "isolated" and firmly fixed on the surface of the base film by the binder and dispersant. This structure brings two core advantages: maximize reaction efficiency: when heat is conducted to the coating layer, each organic salt particle can act as an independent "micro-reactor" without being disturbed by adjacent agglomerates, with the maximum specific surface area in contact with the heat source, thereby achieving "fast, synchronous, and full-effect" decomposition. This ensures that in the extremely short time when thermal runaway occurs, the maximum amount of non-flammable gas (such as N2, NH3) is released, rapidly diluting oxygen and isolating combustible materials, achieving "zero burning time".

[0111] Maintain structural integrity: evenly dispersed particles in the fixed under the binder, even after decomposition, its residue can maintain the skeleton structure of the coating, to avoid the coating powder off, so that the battery still can provide a certain physical isolation and protection under extreme conditions. Therefore, the present application by precise control of the particle size and its distribution of organic salt, and match to be able to realize the specific slurry viscosity and solid content range of high efficiency dispersion process, successfully the inherent processing difficulties of organic salt into the performance advantages of the product. This not only solves the technical bottleneck of the application of organic salt in the diaphragm coating, but also makes its flame retardant efficiency fully play unprecedentedly, and finally gives the battery excellent safety performance under the condition of heat abuse.

[0112] The above description is only the preferred embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A novel diaphragm, characterized in that, Including base film and coating; The coating is located on at least one side surface of the base film; the base film comprises a polymer base film; and The coating comprises at least one organic salt, said organic salt comprising melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and The novel diaphragm has a combustion time of less than 10 seconds as measured by the flame retardant method.

2. The novel diaphragm according to claim 1, characterized in that, The coating also includes an adhesive; the adhesive is present in an amount of 0.5% to 15% of the organic salt by mass.

3. The novel diaphragm according to claim 1, characterized in that, The adhesive includes polyvinyl alcohol, polyacrylic acid and its modified materials, polymethyl methacrylate and its modified materials, styrene-butadiene rubber, polyacrylamide and its modified materials, polyvinyl acetate, natural latex, chloroprene latex, nitrile latex, or any combination thereof.

4. The novel diaphragm according to claim 1, characterized in that, The base membrane is in the form of a single layer, a double layer, or a multilayer. When the base membrane is in the form of a double layer or a multilayer, its material includes the same or different materials, and the porosity of the base membrane is 30% to 70%.

5. The novel diaphragm according to claim 1, characterized in that, The organic salt has an average particle size of 0.1 μm to 20 μm, and a particle size distribution D99 ≤ 15 μm.

6. The novel diaphragm according to claim 1, characterized in that, The novel diaphragm has a thickness of 3 μm to 42 μm; and / or, the base film has a thickness of 2 μm to 40 μm; and / or, the coating has a thickness of 0.5 μm to 9 μm, and the areal density of the coating is 0.4 g / m³. 2 Up to 5 g / m 2 .

7. A novel diaphragm, characterized in that, Including base film and coating; The coating is located on at least one side surface of the base film; the base film comprises a polymer base film; and The coating comprises at least one organic salt, said organic salt comprising melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and The novel diaphragm has a coating leakage rate of less than 5% and an agglomeration rate of less than 10%.

8. The novel diaphragm according to claim 7, characterized in that, The coating also includes an adhesive; the adhesive is present in an amount of 0.5% to 15% of the organic salt by mass.

9. The novel diaphragm according to claim 8, characterized in that, The adhesive includes polyvinyl alcohol, polyacrylic acid and its modified materials, polymethyl methacrylate and its modified materials, styrene-butadiene rubber, polyacrylamide and its modified materials, polyvinyl acetate, natural latex, chloroprene latex, nitrile latex, or any combination thereof.

10. The novel diaphragm according to claim 7, characterized in that, The base membrane is in the form of a single layer, a double layer, or a multilayer. When the base membrane is in the form of a double layer or a multilayer, its material includes the same or different materials, and the porosity of the base membrane is 30% to 70%.

11. The novel diaphragm according to claim 7, characterized in that, The organic salt has an average particle size of 0.1 μm to 20 μm, and a particle size distribution D99 ≤ 15 μm.

12. The novel diaphragm according to claim 7, characterized in that, The novel diaphragm has a thickness of 3 μm to 42 μm; and / or, the base film has a thickness of 2 μm to 40 μm; and / or, the coating has a thickness of 0.5 μm to 9 μm, and the areal density of the coating is 0.4 g / m³. 2 Up to 5 g / m 2 .

13. A method for manufacturing a novel diaphragm, comprising the following steps: Coating slurry preparation steps: Solid materials and binders are added to a dispersion medium to form a coating slurry, wherein the solid materials include organic salts, and the organic salts include melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and Coating step: Coating slurry is applied to at least one side of the base membrane to form a novel diaphragm.

14. The method for preparing the novel diaphragm according to claim 13, characterized in that, The coating slurry has a solids content of 5% to 50%; and / or, the coating slurry viscosity is 10cp to 1000cp; and / or, the coating slurry D50 is 0.1 to 10μm; and / or, the coating slurry D99 is 1 to 10μm.

15. The method for preparing the novel diaphragm according to claim 13, characterized in that, The coating slurry preparation steps further include: First step: Add the solid material and dispersant to the dispersion medium to form a first slurry; and The second step: add the binder and wetting agent to the first slurry to form a coating slurry.

16. The method for preparing the novel diaphragm according to claim 15, characterized in that, The dispersant is at least one of polymethacrylate, polyacrylamide, polyacrylate, polyacrylic acid and its salts, triethylhexylphosphate, sodium dodecyl sulfate, fatty acid polyethylene glycol ester, sodium hexametaphosphate and methylpentanol.

17. The method for preparing the novel diaphragm according to claim 15, characterized in that, The wetting agent includes at least one of ethanol, propylene glycol, glycerin, polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, fatty acid ester sulfate, and vinyltriethoxysilane.

18. The method for preparing the novel diaphragm according to claim 13, characterized in that, Following the coating step, the following steps are further included: Drying step: The novel diaphragm is dried to form a dried novel diaphragm.

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