Composite coating for battery diaphragm as well as preparation method and application of composite coating

Abstract

The invention provides a composite coating for a battery diaphragm as well as a preparation method and application thereof, and relates to the technical field of secondary batteries. Specifically, the composite coating for the battery diaphragm comprises a heat-resistant polymer, a modified ceramic material, a binding material and a flame-retardant material, wherein the modified ceramic material comprises a ceramic material of which the surface is grafted with an MOFs (Metal-Organic Frameworks) material, and the ceramic material comprises porous ceramic particles and ceramic nanowires. By designing and providing the coating, the liquid absorption and liquid retention performance of the battery diaphragm are remarkably improved, the liquid injection time of the battery can be greatly shortened, the manufacturing efficiency is improved, and the cycle life of a battery cell is prolonged; meanwhile, the diaphragm disclosed by the invention is excellent in flame retardance and heat resistance, can effectively improve the safety performance of the battery, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and more particularly, to a composite coating for battery separators, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the rapid development of the new energy field, lithium-ion batteries have stood out with their excellent performance and are widely used in electric vehicles, portable electronic devices, energy storage systems, etc. Compared with traditional secondary batteries, lithium-ion batteries have the advantages of high energy density, high working voltage, long cycle life, etc.; and the separator, as one of the four main materials of lithium-ion batteries, can isolate the positive and negative electrodes to avoid short circuits, and the micro-nano size pore structure provides an effective channel for lithium ions, enabling lithium ions to deintercalate and move back and forth between the positive and negative electrodes. At the same time, its pore structure also provides a liquid storage space for the electrolyte. With the future development of lithium batteries mainly in the four directions of long life, fast charging, high safety, and low cost, faster wetting, higher safety, etc. are also required for the separator.

[0003] Traditional lithium-ion battery separators usually include a base film and a functional coating loaded on the base film. Among them, the base film generally uses PE or PP materials, which have strong non-polarity and poor affinity for electrolytes. Usually, a ceramic material coating is applied to provide the heat resistance and wettability of the separator. However, traditional ceramic materials have a small specific surface area. After the electrode assembly is wound or hot-pressed, the electrode sheet fits tightly with the ceramic coating, resulting in a poor actual liquid retention effect of the separator. In the central area of the electrode sheet after long-term cycling of the battery cell, due to the weak liquid supply ability, the phenomenon of liquid deficiency occurs, resulting in an increase in the interfacial impedance of ion transport, uneven current density, and obvious temperature rise, further leading to local lithium plating in the battery cell, and ultimately affecting the service life and safety of the battery.

[0004] In addition, during the manufacturing process of the battery cell, there is an electrolyte injection process, that is, injecting the electrolyte into the battery cell; the electrolyte injection process usually has defects such as a long injection time, a large number of injection cycles, and electrolyte overflow phenomena, resulting in a decrease in the production efficiency and performance of the battery. At the same time, current commercial separators lack flame retardant functions and cannot inhibit or weaken the combustion of the electrolyte inside the battery when the battery undergoes thermal runaway to avoid battery fire and explosion.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a composite coating for battery separators, which is used to solve the defect of poor liquid supply ability of battery separators due to material and property factors such as slow liquid absorption speed or poor liquid retention ability, and also solve the defects of low efficiency of the electrolyte injection process, electrolyte overflow, and liquid deficiency of the separator, as well as the defects of insufficient heat resistance or flame retardancy of the separator.

[0007] The second object of the present invention is to provide a battery separator with good liquid absorption and retention capabilities and safety performance.

[0008] The third object of the present invention is to provide a method for preparing the battery separator, which meets the requirements of mass production and is simple and easy to implement.

[0009] The fourth object of the present invention is to provide a secondary battery.

[0010] The fifth object of the present invention is to provide an electrical device.

[0011] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0012] A composite coating for a battery separator, comprising a heat-resistant polymer, a modified ceramic material, a binder material, and a flame retardant material;

[0013] Wherein, the modified ceramic material comprises a ceramic material grafted with MOFs material on the surface, and the ceramic material comprises porous ceramic particles and ceramic nanowires.

[0014] A battery separator, comprising the composite coating for a battery separator.

[0015] A method for preparing the battery separator, comprising the following steps:

[0016] Fully mix a heat-resistant polymer, a modified ceramic material, a binder material, a flame retardant material, and a polar solvent in sequence to obtain a composite coating slurry;

[0017] Coat the composite coating slurry on at least one side surface of a base film, and obtain the battery separator after curing.

[0018] A secondary battery, comprising the battery separator.

[0019] An electrical device, comprising the secondary battery.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The present invention provides a high-infiltration and high-safety coating and a battery separator loaded with this coating. The coating can be arranged on one side or both sides; the coating can greatly shorten the liquid injection time of the electrolyte, improve the manufacturing efficiency of the battery cell, and at the same time solve the problem of liquid overflow during liquid injection; at the same time, based on the excellent liquid retention performance of the coating, it can replenish the liquid for the battery cell of the secondary battery loaded with this coating at the end stage of the cycle, and improve the rapid decline of the life of the separator due to liquid deficiency.

[0022] (2) The present invention provides a separator with good heat resistance and flame retardancy. By introducing a heat-resistant polymer and a flame retardant material into the separator coating, on the one hand, the initial temperature of thermal runaway of the battery cell is improved, and on the other hand, when the battery is subjected to external force impact, extrusion, overcharging or overheating, it can prevent the further combustion of the electrolyte, inhibit the thermal spread, and improve the battery safety. Detailed Embodiments

[0023] The technical solutions of the present invention will be clearly and completely described below in conjunction with the detailed embodiments. However, those skilled in the art will understand that the following described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments, and are only used to illustrate the present invention, and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] The first aspect of the present invention is to provide a composite coating for a battery separator. Specifically, the composite coating for a battery separator includes a heat-resistant polymer, a modified ceramic material, a binder material, and a flame retardant material; wherein, the modified ceramic material includes a ceramic material grafted with MOFs material on the surface, and the ceramic material includes porous ceramic particles and ceramic nanowires.

[0025] As a preferred embodiment, the heat-resistant polymer includes at least one of aramid, polyamide, polyimide, polyether ether ketone, or polybenzimidazole.

[0026] As a preferred embodiment, the binder material includes at least one of polyacrylate compounds, polyacrylic acid compounds, polyurethane compounds, polyolefin compounds, polyvinylidene fluoride, or polyacrylonitrile.

[0027] As a more preferred embodiment, the polyacrylate compounds include, but are not limited to, polymethyl methacrylate, polyacrylate methyl, polyethyl methacrylate, or polyacrylate ethyl, etc., the polyacrylic acid compounds include, but are not limited to, polyacrylic acid, the polyurethane compounds include, but are not limited to, polyurethane, polyamino acetate, polyurethane acrylate, polyurethane benzoate, polyurethane phenylacetate, etc., and the polyolefin compounds include, but are not limited to, polyethylene microspheres or polypropylene microspheres, etc.

[0028] As a preferred embodiment, the flame retardant material includes at least one of decabromodiphenylethane, decabromodiphenyl ether, brominated polystyrene, or tetrabromobisphenol A.

[0029] As a preferred embodiment, the ceramic material includes at least one of alumina, boehmite, barium sulfate, aluminum sulfate, titanium dioxide, aluminum nitride, magnesium nitride, magnesium hydroxide, aluminum hydroxide, molybdenum disulfide, or barium titanate; it should be noted that the types of raw materials that can be selected for the ceramic material are listed here, and in the present invention, the porous ceramic particles and the ceramic nanowires are still defined, which is a morphological limitation for the ceramic material; it can be understood that whether it is the porous ceramic particles or the ceramic nanowires, any selection or combination can be made among the material types such as alumina, boehmite, barium sulfate, etc.

[0030] In the present invention, by compounding two ceramic materials with different structures, the structural parameters of the porous particles and nanowires are planned based on the ceramic raw material end of the initial raw materials, and then a composite ceramic material with a high specific surface area is obtained, laying a morphological foundation for subsequent modification to obtain the modified ceramic material. As a preferred embodiment, for the porous ceramic particles: the particle size is 200 nm to 1100 nm, and the pore size is 18 nm to 54 nm. It should be noted that the pore size here covers the size of any holes on the surface or inside of the porous ceramic particles. As a preferred embodiment, for the ceramic nanowires: the wire diameter is 30 nm to 75 nm, and the aspect ratio of the wire is 30 to 80.

[0031] Furthermore, in the present invention, a specific modification process is carried out on the ceramic material. Combining with the specific modification steps provided in the present invention, first, the surface of the ceramic material is modified by a linker to endow grafting sites on the ceramic surface, and then a metal-organic framework material (MOFs) is used for grafting. Through coordination bonds and hydrogen bond interactions, the MOFs material is grafted onto the surface-modified ceramic material, and then the modified ceramic material is obtained.

[0032] As a preferred embodiment, the modified ceramic material includes the following components: the ceramic material, the MOFs material, and alginate; that is, alginate is used as the linker between the ceramic material and the MOFs material.

[0033] As a more preferred embodiment, the mass ratio of the ceramic material to the alginate is (180 - 750):1, including but not limited to any one or any ratio range formed by any two of 180:1, 210:1, 240:1, 270:1, 300:1, 330:1, 360:1, 390:1, 420:1, 450:1, 480:1, 510:1, 540:1, 570:1, 600:1, 630:1, 660:1, 690:1, 720:1, 750:1.

[0034] As a more preferred embodiment, the mass ratio of the ceramic material to the MOFs material is (10.8 - 62.6):1, including but not limited to any one or any ratio range formed by any two of 10.8:1, 21.2:1, 31.6:1, 42:1, 52.4:1, 62.6:1.

[0035] As a preferred embodiment, the MOFs material includes at least one of ZIF-8 (formed by zinc ions and 2-methylimidazole ligands), ZIF-67 (formed by cobalt ions and 2-methylimidazolate ligands), MOF-74 (formed by magnesium ions and 2,5-dihydroxyterephthalic acid ligands), Uio-66 (formed by zirconium ions and terephthalic acid ligands), or Uio-88 (formed by zirconium ions and 1,4-carboxybenzene ligands).

[0036] As a preferred embodiment, the particle size of the MOFs material is 100nm - 400nm, including but not limited to any one or any numerical range formed by any two of 100, 120, 150, 180, 200, 250, 280, 300, 325, 350, 375, 400 (nm).

[0037] In the modified ceramic material used in the present invention, compared with the conventional ceramic material, on the one hand, the specific surface area is increased by using porous particulate ceramic material to increase the electrolyte storage space; on the other hand, two types of ceramic materials, namely porous particles and linear ones, are compounded to play a role in electrolyte drainage, forming "line-line" and "point-line" type lap joints to improve the electrolyte wetting speed; on the other hand, through the introduction of MOFs modification, since the MOFs material has the advantages of large specific surface area, high porosity, and low density, the overall weight of the separator coating can be reduced, and the electrolyte absorption rate and liquid retention capacity of the separator can be improved; thus, a separator coating material with remarkable and excellent liquid retention performance is obtained.

[0038] As a preferred embodiment, the composite coating for the battery separator comprises the following components by weight parts: 150 - 500 parts of heat-resistant polymer, 80 - 150 parts of modified ceramic material, 800 - 2000 parts of binder, and 5 - 18 parts of flame retardant; in some alternative embodiments, the weight parts of the components of the composite coating for the battery separator include but are not limited to: heat-resistant polymer 150, 160, 180, 200, 250, 300, 350, 400, 425, 450, 475, 500; modified ceramic material 80, 90, 100, 110, 120, 130, 140, 150; binder 800, 900, 1000, 1200, 1400, 1500, 1600, 1800, 2000; flame retardant 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18; the weight parts of each component can adopt any point value listed above, or a numerical range formed by any two point values.

[0039] As a preferred embodiment, the mass ratio of the porous ceramic particles to the ceramic nanowires is (1.8 - 3.5):1, including but not limited to any one of 1.8:1, 1.9:1, 2:1, 2.2:1, 2.4:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1 or a ratio range formed by any two of them.

[0040] The second aspect of the present invention lies in providing a battery separator. Specifically, the battery separator comprises the composite coating for the battery separator as described in the first aspect.

[0041] As a preferred embodiment, the battery separator comprises a base film and the composite coating for the battery separator loaded on at least one side of the base film. It can be understood that those skilled in the art can choose to coat and fix the composite coating for the battery separator on one side or both sides of the base film, and independently select the thickness of the base film and the coating thickness in the two cases respectively to obtain the battery separator with high wettability and high safety.

[0042] As a more preferred embodiment, the base film comprises one of PE, PP, and a combination of PE and PP; the thickness of the base film is 3μm - 25μm, including but not limited to any one of 3, 5, 8, 10, 12, 15, 18, 20, 22, 24, 25 (μm) or a numerical range formed by any two of them.

[0043] As a further preferred embodiment, the porosity of the base film is 25% - 70%, the pore size range of the base film is 17nm - 150nm, and the air permeability of the base film is 30 - 300 (s / 100cc).

[0044] As a preferred embodiment, the thickness of the composite coating for the battery separator is 1 μm to 4 μm, including but not limited to any value or any numerical range composed of any two of 1, 1.5, 2, 2.5, 3, 3.5, 4 (μm); it can be understood that when the two sides of the base film are respectively coated with coatings, the coatings on both sides are independently selected within the above thickness range.

[0045] As a preferred embodiment, the surface density of the composite coating for the battery separator is 0.5 to 1.2 (g / m 2 / μm), and the air permeability increase of the coating is 10 to 50 (s / 100cc / μm).

[0046] As a preferred embodiment, the total thickness of the battery separator is 4 μm to 33 μm.

[0047] The third aspect of the present invention lies in providing a preparation method of the battery separator as described in the second aspect, which mainly includes the following steps: fully mixing a heat-resistant polymer, a modified ceramic material, a binder material, a flame retardant material and a polar solvent to obtain a composite coating slurry; coating the composite coating slurry on the surface of a base film to obtain the battery separator.

[0048] As a preferred embodiment, the polar solvent includes at least one of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0049] As a preferred embodiment, the solid content of the composite coating slurry is 2.5% to 10%, and the viscosity of the composite coating slurry is 30 cp to 80 cp; in a further preferred embodiment, the solid content of the composite coating slurry is 5.5% ± 3%.

[0050] In the present invention, through the selection of the components of the composite coating slurry and the polar solvent, it can be seen that the coating adopted in the present invention is an oil-based coating process. Compared with the water-based coating, the coating of the present invention has good initial tack and strong adaptability to the base film.

[0051] As a preferred embodiment, the preparation method of the battery separator specifically includes the following steps: S1. First, add the heat-resistant polymer to a part of the polar solvent and stir to fully dissolve the heat-resistant polymer; S2. Then add the modified ceramic material, the binder material and the remaining polar solvent, and continue to stir to fully dissolve the components; S3. Finally, add the flame retardant material, fully mix and obtain the composite coating slurry; S4. Coat the composite coating slurry on the surface of the base film to obtain the battery separator.

[0052] As a preferred embodiment, the coating on the surface of the base film includes the following steps: unreeling the base film to obtain the flatly placed base film; performing a coating operation with a gravure roll, controlling the usage amount of the composite coating slurry through the number of lines on the roll surface and the depth of the groove, and then scraping off the excess slurry with a doctor blade; transferring the coated film to a coagulation bath for phase transition forming of the coating, and performing water washing and drying after complete forming to obtain the battery separator.

[0053] As a preferred embodiment, the preparation method of the modified ceramic material includes the following steps: preparing an aqueous dispersion containing ceramic material, MOFs material and alginate, and obtaining the modified ceramic material after sufficient mixing, solid-liquid separation, washing and drying.

[0054] As a more preferred embodiment, for any sufficient mixing involved in the present invention, methods such as oscillation, stirring, shaker, centrifugation, ultrasound, heating, etc. can be selected to assist, which helps to accelerate dispersion and obtain a relatively uniform dispersion system.

[0055] As a more preferred embodiment, the alginate includes at least one of calcium alginate, sodium alginate, potassium alginate or magnesium alginate.

[0056] As a more preferred embodiment, the preparation method of the modified ceramic material includes the following steps: preparing a first dispersion containing ceramic material, preparing a second dispersion containing MOFs material, and preparing a third dispersion containing alginate; fully mixing the first dispersion, the second dispersion and the third dispersion, and obtaining the modified ceramic material after centrifugation, washing and drying.

[0057] In a further preferred embodiment, taking the concentration of the alginate in the third dispersion as x and the particle size of the MOFs material as y, the range of the product value of x and y is 0.06 - 0.18, where x is dimensionless and the unit of y is nm. It should be noted that when x is measured by mass percentage concentration, x should take the value including the percentage; for example, when the concentration of the alginate is 0.06 wt.%, the x value substituted into the calculation is 0.0006.

[0058] In the present invention, through the comprehensive measurement of particle size and concentration, it is found that: when the particle size of MOFs is smaller and the specific surface area is larger, the required concentration of the alginate as a binder is higher. The above specific numerical limitations help to achieve the sufficient connection of the alginate to the ceramic material and the sufficient grafting of the MOFs material.

[0059] In a further preferred embodiment, the concentration of the first dispersion is 30 wt.% to 36 wt.%, the concentration of the second dispersion is 0.23 wt.% to 0.58 wt.%, and the concentration of the third dispersion is 0.04 wt.% to 0.08 wt.%.

[0060] In a further preferred embodiment, by volume, the dosage ratio of the first dispersion, the second dispersion, and the third dispersion is 1:(2.5 - 4.8):(1.2 - 2.0).

[0061] The fourth aspect of the present invention is to provide a secondary battery. Specifically, it includes the battery separator as described in the second aspect.

[0062] It can be understood that the secondary battery should include a positive electrode, a negative electrode, an electrolyte, and other necessary or non-necessary functional elements or packaging components, etc. Those skilled in the art can make any selection and combination thereof; when the battery separator described in the present invention is included in the secondary battery, regardless of whether other separator functional components are also used in the secondary battery, it can be regarded as an embodiment of the present invention.

[0063] In addition, the secondary battery including the battery separator in the present invention should include winding and laminating, etc. in the battery manufacturing process; the battery types it applies to include but are not limited to lithium iron phosphate, ternary, etc. The actual application is not limited to lithium batteries, and it can also be sodium batteries, potassium batteries, etc.

[0064] The fifth aspect of the present invention is to provide an electrical device. Specifically, it includes the secondary battery as described in the fourth aspect.

[0065] It can be understood that the electrical device can be any device or apparatus that relies on electrical energy to work or operate, including but not limited to new energy vehicles, building electrical equipment, industrial electrical appliances, household and agricultural electrical appliances, etc.; when including the secondary battery, any electrical device equipped with the secondary battery can belong to an embodiment of the present invention.

[0066] Example 1

[0067] S1. Prepare an aqueous solution of sodium alginate with a concentration (C A ) of 0.06 wt.%, defined as solution A; prepare an aqueous dispersion of ZIF-8 (average particle diameter of 250 nm) with a concentration (C B ) of 0.45 wt.%, defined as solution B; then prepare an aqueous dispersion of ceramics with a concentration (C C) is 32 wt.%, defined as Solution C; wherein, the ceramic uses alumina porous particles (average particle size is 600 nm, average pore size is 30 nm, porosity is 43%) and alumina nanowires (average diameter is 45 nm, aspect ratio is 50), and the porous particles and nanowires are compounded according to a mass ratio of 2:1.

[0068] Mix the uniformly dispersed Solution A, Solution B, and Solution C according to a volume ratio of 1:3.6:1.6, stir at 1000 rpm for 2 h at room temperature, and then centrifuge and wash to obtain the high specific surface area composite modified ceramic powder of this example.

[0069] S2. Prepare raw materials according to a mass ratio of heat-resistant polymer: modified ceramic: bonding material: flame retardant of 3:1:14:0.12. Among them, the heat-resistant polymer uses polyimide, the bonding material selects PMMA, and the flame retardant selects brominated polystyrene.

[0070] Add the above-prepared raw materials to the NMP solvent, and control the solid content of the mixed solution to be 5.5% ± 0.1% to obtain the coating slurry of this example.

[0071] S3. Prepare a base film (Sinoma SNS07, thickness is 7 μm); unwind the film and coat the above coating slurry with a gravure roll, and coat only on one side of the base film; after scraping off the excess slurry, form it by phase inversion in a coagulation bath, and after complete forming, wash with water and dry in sequence to obtain the battery separator of this example.

[0072] Example 2

[0073] It is basically the same as Example 1, except that: replace Solution B in Step S1 with: prepare an aqueous dispersion of Uio-66 (average particle diameter is 350 nm) and Uio-88 (average particle diameter is 350 nm), and the mass ratio of Uio-66 to Uio-88 is 1:1, and the total concentration of the dispersion (C B ) is 0.55 wt.%;

[0074] Correspondingly, Solution A, Solution B, and Solution C are mixed according to a volume ratio of 1:4.0:1.8.

[0075] Example 3

[0076] It is basically the same as Example 1, except that: replace the ceramic raw material of Solution C in Step S1 with: titanium dioxide porous particles and titanium dioxide nanowires, and the specifications of the particles and nanowires are still the same as those in Example 1.

[0077] Example 4

[0078] Basically the same as Example 1, except that: the ceramic raw material of Solution C in Step S1 is replaced with: barium sulfate porous particles, magnesium nitride nanowires and magnesium hydroxide nanowires (the mass ratio of the two nanowires is 1:1), and the specifications of the particles and nanowires remain the same as those in Example 1.

[0079] Example 5

[0080] Basically the same as Example 1, except that: the specifications of the ceramic particles in Step S1 are replaced with: the average particle size is 1000 nm, the average pore size is 50 nm, and the porosity is 46%; the specifications of the ceramic nanowires are replaced with: the average diameter is 70 nm, and the aspect ratio is 80.

[0081] Example 6

[0082] Basically the same as Example 1, except that: the specifications of the ceramic particles in Step S1 are replaced with: the average particle size is 200 nm, the average pore size is 20 nm, and the porosity is 40%; the specifications of the ceramic nanowires are replaced with: the average diameter is 30 nm, and the aspect ratio is 30.

[0083] Example 7

[0084] Basically the same as Example 1, except that: in Step S1, the porous particles and nanowires are compounded according to a mass ratio of 3:1.

[0085] Example 8

[0086] Basically the same as Example 1, except that: in Step S2, the raw materials are prepared according to the mass ratio of heat-resistant polymer: modified ceramic: binder: flame retardant of 1.5:1:8:0.05.

[0087] Example 9

[0088] Basically the same as Example 1, except that: in Step S2, the raw materials are prepared according to the mass ratio of heat-resistant polymer: modified ceramic: binder: flame retardant of 5:1:20:0.18.

[0089] Example 10

[0090] Basically the same as Example 1, except that: in Step S2, the following raw material selection is replaced with: the heat-resistant polymer is aramid, the adhesive material is polyvinylidene fluoride, and the flame retardant is decabromodiphenylethane.

[0091] Example 11

[0092] Basically the same as Example 1, except that: in Step S3, the coating process is carried out on both sides of the base film.

[0093] Comparative Example 1

[0094] It is basically the same as Example 1, except that: in Solution C of Step S1, the ceramic only uses alumina porous particles and does not use alumina nanowires.

[0095] Comparative Example 2

[0096] It is basically the same as Example 1, except that: in Solution C of Step S1, the ceramic only uses alumina nanowires and does not use alumina porous particles.

[0097] Comparative Example 3

[0098] It is basically the same as Example 1, except that: Step S1 is cancelled, and in Step S2, the modified ceramic is replaced with the ceramic raw material used in Solution C of Step S1.

[0099] Comparative Example 4

[0100] It is basically the same as Example 1, except that: Step S1 is cancelled, and Step S2 also does not contain a ceramic component; the raw materials are prepared according to the mass ratio of heat-resistant polymer: binder: flame retardant of 3:14:0.12.

[0101] Comparative Example 5

[0102] It is basically the same as Example 1, except that: the addition of the flame retardant is cancelled in Step S2.

[0103] Comparative Example 6

[0104] It is basically the same as Example 1, except that: the addition of the heat-resistant polymer is cancelled in Step S2.

[0105] Test Example

[0106] (1) The battery diaphragms prepared in the above examples and comparative examples were tested; specifically, the test methods are as shown in (1) to (5) below, and the test results are shown in Table 1 below.

[0107] (1) Thermal shrinkage: First, measure the dimensions of each battery diaphragm sample in the MD (longitudinal) and TD (transverse) directions, denoted as L1 and H1 respectively; then bake the diaphragm at a certain temperature for 1 h, and measure the dimensions in the MD and TD directions again, denoted as L2 and H2 respectively; the baking temperatures are 150 / 180 (°C); calculate the MD thermal shrinkage rate = (L1 - L2) / L1 × 100%, and the TD thermal shrinkage rate = (H1 - H2) / H1 × 100%; record the thermal shrinkage rates of MD and TD respectively and record them in Table 1.

[0108] (2) Limiting oxygen index: Test according to the national standard GB / T 2406.

[0109] (3) Heat nail piercing area: Using a hot nail piercing test system with the equipment model AF-S100, heat the hot needle to 250 °C, and let the hot needle descend uniformly at a speed of 10 mm / s to pierce the separator, penetrating 0.1 mm into the separator; then raise the hot needle and calculate the area of the pierced area.

[0110] (4) Contact angle: Using the equipment LSA100, drop 5 μL of electrolyte (Golden Bull A60) onto the separator, and take the reading at 10 s to obtain the contact angle.

[0111] (5) Electrolyte wetting area: Also using the equipment LSA100, drop 10 μL of electrolyte (Golden Bull A60) onto the separator, and after 30 s, read the electrolyte wetting area after calculation by the equipment.

[0112] Table 1

[0113]

[0114] (2) Prepare the battery separators obtained in the above-mentioned examples and comparative examples, and obtain lithium-ion batteries corresponding to the examples and comparative examples. The specific method is as follows:

[0115] 1) Preparation of the positive electrode sheet: Prepare a slurry by using lithium iron phosphate, carbon black, PVDF binder, polyether dispersant and NMP solvent, coat the slurry on the carbon-coated aluminum foil and dry it to obtain the positive electrode sheet. Among them, the mass ratio of lithium iron phosphate, carbon black, PVDF binder and dispersant is 96.8%: 1.25%: 1.85%: 0.1%.

[0116] 2) Preparation of the negative electrode sheet: Prepare a slurry by using artificial graphite, carbon black conductive agent, CMC thickener, SBR binder and water, coat the slurry on the copper foil and dry it to obtain the negative electrode sheet. Among them, the mass ratio of artificial graphite, carbon black, CMC thickener, SBR binder is 96.2%: 1.0%: 1.1%: 1.7%.

[0117] 3) Preparation of the electrode assembly: Shape the positive and negative electrode sheets and the separator by winding to obtain the electrode assembly; if the separator has only a single-sided coating, the coating faces the positive electrode during winding; if both sides have coatings, there is no distinction between the positive and negative electrodes; after winding, perform hot pressing to obtain an electrode assembly with a certain hardness.

[0118] 4) Encapsulation, baking, and electrolyte injection: Adopt a square shell form to encapsulate each electrode assembly, put the encapsulated battery cell into an oven, bake it at 95 °C ± 5 °C for 12 h, and then inject the electrolyte; the electrolyte used is Shinzo LF-136 (the solvent contains EC, EMC, DMC, and the lithium salt is LiPF6).

[0119] 5) Pre-charging and formation: The battery after injection is left at high temperature for 24 hours, and then left at room temperature for 24 hours; after the standing period, the battery cell is pre-charged, formed and capacity divided to obtain the test lithium iron phosphate batteries corresponding to each embodiment and comparative example.

[0120] The lithium iron phosphate battery prepared as above was subjected to the following tests; specifically, the test methods are shown in (1) to (6) below, and the test results are shown in Table 2 below.

[0121] (1) Injection time: The total time taken for each lithium-ion battery from the start of injection to the end of injection in step 4) (which can also be understood as the time until the high-temperature standing in step 5) is recorded.

[0122] (2) Weight of free electrolyte after full charge and disassembly: For the battery cell charged to 100% SOC, the interface is disassembled and the weight of the free electrolyte is weighed.

[0123] (3) Cycle retention rate: The capacity retention rate of lithium-ion batteries after 1500 cycles at different temperatures was tested.

[0124] (4) Hot box: Tested in accordance with the national standard GB 38031-2020.

[0125] (5) Acupuncture: Tested in accordance with the national standard GB 38031-2020.

[0126] (6) Heat spread: Tested in accordance with the national standard GB 38031-2020.

[0127] Table 2

[0128]

[0129] Through comparative analysis of the embodiments and comparative examples in Tables 1 and 2, the high-wetting and high-safety diaphragm proposed in the present invention can meet the heat shrinkage of <5% at 180°C, the limiting oxygen index can reach 25.1%, and the hot nail puncture area is small (only 1.2mm 2) It exhibits excellent heat resistance and low flammability. And within the same time, the electrolyte contact angle of the separator in the example is small, and the wetting area is large, indicating good wettability and strong liquid absorption and retention ability. From the battery test performance of the corresponding ones prepared, the battery prepared by the highly wettable and highly safe separator of the present invention can significantly shorten the liquid injection time and improve the manufacturing efficiency of the battery core. After full charge, there is less free electrolyte, indicating strong liquid retention ability, replenishing the electrolyte for the battery core in the later stage of cycling, and enhancing the long life of the battery core. It can also be seen from the cycling data that the capacity retention rate of the example is the best at 1500 cls at 25 °C and 45 °C, can pass the 240 °C extreme heat box test and the needle penetration test, and the battery core does not undergo thermal runaway at normal temperature and 60 °C; in contrast, in the comparative example, the liquid injection time is longer, there is more free electrolyte after full charge and disassembly, and both the wettability and heat resistance become worse, thereby affecting the battery cycling performance and safety performance. And in Comparative Examples 5 and 6, the lack of heat-resistant or flame-retardant materials significantly affects the heat resistance of the separator, and the safety performance of the battery core is the worst.

[0130] Although the present invention has been illustrated and described with reference to specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A composite coating for a battery separator, characterized in that, The composite coating for the battery separator comprises a heat-resistant polymer, a modified ceramic material, a binder material and a flame retardant material; Among them, the modified ceramic material comprises a ceramic material grafted with MOFs material on the surface, and the ceramic material comprises porous ceramic particles and ceramic nanowires.

2. The composite coating for battery separator according to claim 1, wherein It satisfies at least one of the following characteristics (a) to (e): (a) The heat-resistant polymer comprises at least one of aramid, polyamide, polyimide, polyether ether ketone or polybenzimidazole; (b) The binder material comprises at least one of polyacrylate compounds, polyacrylic acid compounds, polyurethane compounds, polyolefin compounds, polyvinylidene fluoride or polyacrylonitrile; (c) The flame retardant material comprises at least one of decabromodiphenylethane, decabromodiphenyl ether, brominated polystyrene or tetrabromobisphenol A; (d) The ceramic material comprises at least one of alumina, boehmite, barium sulfate, aluminum sulfate, titanium dioxide, aluminum nitride, magnesium nitride, magnesium hydroxide, aluminum hydroxide, molybdenum disulfide or barium titanate; (e) The MOFs material comprises at least one of ZIF-8, ZIF-67, MOF-74, Uio-66 or Uio-88.

3. The composite coating for battery separator according to claim 1, characterized in that, For the porous ceramic particles, the particle size is 200 nm to 1100 nm, and the pore size is 18 nm to 54 nm; And / or, for the ceramic nanowires, the diameter is 30 nm to 75 nm, and the aspect ratio is 30 to 80; And / or, the particle size of the MOFs material is 100 nm to 400 nm.

4. The composite coating for battery separator according to claim 1, wherein, The composite coating for the battery separator comprises the following components by weight: 150 to 500 parts of heat-resistant polymer, 80 to 150 parts of modified ceramic material, 800 to 2000 parts of binder material, 5 to 18 parts of flame retardant material; Preferably, the mass ratio of the porous ceramic particles to the ceramic nanowires is (1.8 to 3.5):

1.

5. A battery separator, characterized in that, The battery separator comprises the composite coating for the battery separator according to any one of claims 1 to 4; Preferably, the battery separator comprises a base film and the composite coating for the battery separator loaded on at least one side of the base film; More preferably, the thickness of the base film is 3 μm to 25 μm, and the thickness of the composite coating is 1 μm to 4 μm.

6. The method for preparing a battery separator according to claim 5, characterized in that, Comprises the following steps: Fully mix the heat-resistant polymer, the modified ceramic material, the binder material, the flame retardant material and the polar solvent in sequence to obtain a composite coating slurry; Coat the composite coating slurry on the surface of at least one side of the base film, and obtain the battery separator after curing.

7. The preparation method according to claim 6, characterized in that The preparation method of the modified ceramic material comprises the following steps: Prepare an aqueous dispersion containing ceramic material, MOFs material and alginate, and obtain the modified ceramic material after sufficient mixing, solid-liquid separation, washing and drying; Preferably, the alginate comprises at least one of calcium alginate, sodium alginate, potassium alginate or magnesium alginate.

8. The preparation method according to claim 7, characterized in that, The preparation method of the modified ceramic material comprises the following steps: Prepare a first dispersion containing the ceramic material, a second dispersion containing the MOFs material, and a third dispersion containing the alginate; fully mix the first dispersion, the second dispersion, and the third dispersion, and obtain the modified ceramic material after centrifugation, washing, and drying; Preferably, the concentration of the first dispersion is 30 wt.% to 36 wt.%, the concentration of the second dispersion is 0.23 wt.% to 0.58 wt.%, and the concentration of the third dispersion is 0.04 wt.% to 0.08 wt.%; Preferably, taking the concentration of the alginate in the third dispersion as x and the particle size of the MOFs material as y, the product of x and y is 0.06 to 0.18; wherein, x is dimensionless and y is in nm.

9. A secondary battery, characterized in that, It includes the battery separator as described in claim 5.

10. An electrical device, characterized in that, It includes the secondary battery as described in claim 9.

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