Separator and secondary battery

Abstract

The present application relates to the technical field of lithium-ion batteries, and particularly relates to a separator and a secondary battery. The separator provided in the present application comprises a base film and a coating which is provided on at least one surface of the base film, wherein the coating comprises a ceramic layer and an adhesive layer, and the ceramic layer comprises ceramic particles, a binder and a functional material; the porosity of the coating of the separator is 35-65%; and the surface density of the coating is 0.5-14 g / m2. The separator in the present application has good thermal stability, and the degrees of thermal shrinkage in an MD and a TD under a high-temperature condition are relatively small. The separator has good liquid absorption and retention capabilities for electrolytic solutions, and has good wettability, so that rapid passing and homogeneous transmission of lithium ions during a reaction can be ensured. Moreover, the separator can also reduce the risks of capacity reduction and local overcharging, thereby playing the role of protecting secondary batteries. By using the separator in the present application, an improvement in the power density, energy density and safety of secondary batteries is facilitated.

Description

Separator and secondary battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 2023107666417, filed with the State Intellectual Property Office of China on June 26, 2023, entitled “A Diaphragm and Secondary Battery,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the field of secondary battery technology, in particular to a separator and a secondary battery. Background Art

[0004] With the development and progress of social technology, lithium-ion batteries, as a high-efficiency energy storage technology, have been widely used in consumer electronics, electric vehicles and large-scale energy storage equipment. At the same time, the requirements for lithium-ion batteries in all aspects are becoming higher and higher.

[0005] As one of the four main materials in lithium-ion batteries, lithium-ion battery separators play a vital role. Traditional polypropylene and polyethylene separators can no longer meet the high power density, high energy density, high safety, and fast charging requirements of lithium-ion batteries. There is an urgent need to modify these basic separators. Furthermore, polyolefin-based separators have poor thermal stability under high temperature conditions and are prone to shrinkage, which can easily cause short circuits during battery operation, leading to a series of safety issues.

[0006] At present, the development of new coatings mainly focuses on ceramics, which are widely used in lithium-ion battery separator layers due to their good heat resistance. However, their ability to absorb and retain liquid needs to be further improved.

[0007] In view of this, this application is hereby filed.

[0008] Summary of the Invention

[0009] The present application provides a diaphragm, comprising a base film and a coating provided on at least one surface of the base film, wherein the coating comprises a ceramic layer, and the ceramic layer comprises ceramic particles, a binder, and a functional material;

[0010] The porosity of the coating of the diaphragm is 35-65%;

[0011] The surface density of the coating is 0.5 to 14 g / m 2 .

[0012] The present application provides a diaphragm, comprising a base membrane and a coating provided on at least one surface of the base membrane, wherein the coating comprises a ceramic layer and a glue layer, wherein the ceramic layer comprises ceramic particles, a binder, and a functional material; the porosity of the diaphragm coating is 35-65%; the surface density of the coating is 0.5-14 g / m 2 .

[0013] Optionally, the porosity of the coating is 50-60%, and the surface density of the coating is 1.5-6.5 g / m 2 .

[0014] Optionally, the functional material includes at least one material selected from the following:

[0015] Kapok, wood, sponge, coral, metal organic framework material, covalent organic framework material or carbon material formed from at least one of the foregoing functional materials.

[0016] Optionally, the functional material is a porous material, comprising micropores, mesopores and macropores. Optionally, in the functional material, the ratio of the pore volume of the micropores, the pore volume of the mesopores and the pore volume of the macropores is (0.01-0.4):(0.01-0.7):(0.01-0.6).

[0017] Optionally, in the functional material, the pore volume of micropores is 20-40% of the total pore volume.

[0018] Optionally, the ceramic particles include at least one of aluminum oxide, boehmite, silicon oxide, zirconium oxide, magnesium oxide and titanium oxide.

[0019] Optionally, in the ceramic layer, the mass ratio of the ceramic particles, the functional material and the binder is (0.01-0.5):(0.01-0.4):(0.01-0.15).

[0020] In the ceramic layer, the mass ratio of the ceramic particles to the functional material is 1:0.75-3.

[0021] Optionally, the adhesive layer includes polyvinylidene fluoride.

[0022] Optionally, the thickness of the ceramic layer is 3-6 μm.

[0023] Optionally, the thickness of the adhesive layer is 3 to 7 μm.

[0024] Optionally, the coating layer of the diaphragm includes an auxiliary agent, wherein the auxiliary agent includes a dispersant and / or a wetting agent.

[0025] Optionally, the coating of the diaphragm includes an auxiliary agent, wherein the auxiliary agent includes a dispersant and a wetting agent. The auxiliary agent includes a dispersant and a wetting agent.

[0026] Optionally, the mass ratio of the dispersant to the wetting agent is 0.5:(0.01-0.1).

[0027] The present application also provides a method for preparing a diaphragm, comprising:

[0028] Preparation of functional materials;

[0029] Ceramic particles, functional materials, adhesives, additives and solvents are made into slurry, and then the slurry is coated on the base film to obtain a ceramic layer.

[0030] The present application also provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and the separator as described above.

[0031] The present application also provides an electrical device including the secondary battery described above. DETAILED DESCRIPTION

[0032] The technical solutions of this application will be described clearly and completely below in conjunction with specific embodiments. However, those skilled in the art will understand that the embodiments described below are only part of the embodiments of this application, not all of them, and are only used to illustrate this application and should not be considered to limit the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of this application.

[0033] The following is a detailed description of a separator and a secondary battery according to an embodiment of the present application.

[0034] The first purpose of the present application is to provide a diaphragm with excellent thermal stability, good liquid absorption and liquid retention capabilities for electrolyte, and excellent wettability for electrolyte; and conducive to homogeneous transmission of electrolyte.

[0035] A second object of the present application is to provide a secondary battery having high power density, high energy density and high safety.

[0036] In order to achieve the above-mentioned purpose of this application, the following technical solutions are adopted:

[0037] In some embodiments of the present application, a diaphragm is provided, comprising a base film and a coating disposed on at least one surface of the base film, the coating comprising a ceramic layer, the ceramic layer comprising ceramic particles, a binder, and a functional material;

[0038] The porosity of the coating of the diaphragm is 35-65%;

[0039] The surface density of the coating is 0.5 to 14 g / m 2 .

[0040] In some embodiments of the present application, a diaphragm is provided, comprising a base film and a coating disposed on at least one surface of the base film, wherein the coating comprises a ceramic layer, and the ceramic layer comprises ceramic particles, a binder, and a functional material;

[0041] The porosity of the coating of the diaphragm is 35-65%;

[0042] The surface density of the coating is 0.5 to 14 g / m 2 .

[0043] In some embodiments of the present application, a diaphragm is provided, comprising a base film and a coating disposed on at least one surface of the base film, wherein the coating comprises a ceramic layer and a glue layer, wherein the ceramic layer comprises ceramic particles, a binder, and a functional material; the porosity of the diaphragm coating is 35-65%; the surface density of the coating is 4-15 g / m 2 .

[0044] It can be understood that, in the present application, the coating layer may be a ceramic layer, or may be composed of a ceramic layer and a glue layer.

[0045] The diaphragm of the present application, through the combination of functional materials and ceramics, can reduce the degree of thermal shrinkage of the diaphragm in the MD and TD directions under high temperature conditions and improve the thermal stability of the diaphragm. The diaphragm coating is provided with a ceramic layer and a glue layer, and the functional material is added to the ceramic layer. The porosity of the prepared diaphragm coating is 35-65% and the surface density of the coating is 4-15g / m 2 , promoting the improvement of the separator's ability to absorb and retain electrolyte, greatly improving the separator's wettability to the electrolyte. At the same time, the functional material has abundant pores, large pore volume, good pore size distribution and pore structure, which can prevent the growth of lithium dendrites that may lead to puncture of the separator, and has high safety performance.

[0046] It is understandable that the addition of functional materials can change the porosity and surface density of the coating, and the reduction of the volume proportion of micropores and the increase of the volume proportion of mesopores and macropores can improve the wetting of the electrolyte and increase the liquid absorption rate of the diaphragm.

[0047] The diaphragm of the present application can also reduce the risk of capacity reduction and local overcharging, thereby protecting the secondary battery; and the functional materials are rich in resources, low in price, and green and environmentally friendly, which is conducive to reducing the cost of the diaphragm.

[0048] In some embodiments of the present application, the porosity of the coating is 35-65%. For example, the porosity can be 35%, 40%, 45%, 50%, 55%, 60%, or 65%, or a range consisting of any two thereof. For example, the porosity of the coating is controlled within the range of 40-60%, 45-60%, or 50-60%, etc., which promotes the improvement of the electrolyte absorption and retention ability of the separator, thereby greatly improving the wettability of the separator to the electrolyte.

[0049] In some embodiments of the present application, the surface density of the coating is 4 to 15 g / m 2 .

[0050] In some embodiments of the present application, the surface density of the coating is 0.5 to 14 g / m 2 , the surface density can be 0.5g / m 2 , 1g / m 2 、 2g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , 10g / m 2 , 11g / m 2 , 12g / m 2 , 13g / m 2 , 14g / m 2 Or a range consisting of any two of them. For example, 1.5 to 6.5 g / m 2 etc.

[0051] Without being bound by theory, the surface density of the coating is controlled within the scope of the present application, which promotes the improvement of the diaphragm's ability to absorb and retain electrolyte liquid, and greatly improves the wettability of the diaphragm to the electrolyte. In some embodiments of the present application, the functional material includes at least one of kapok, wood, sponge, coral, metal organic framework material, covalent organic framework material or a carbon material formed by at least one of the aforementioned functional materials. In the functional materials of the present application, for example, kapok, wood, sponge, and coral can be cut into pieces, put into a grinder for crushing, ground, washed and dried to obtain functional materials. Metal organic framework materials and covalent organic framework materials can be synthesized and prepared by chemical methods. In addition, in order to obtain functional materials with suitable pore structures, at least one of the above functional materials can be calcined to obtain carbon materials.

[0052] In some embodiments of the present application, in the functional material, the ratio of the pore volume of micropores, the pore volume of mesopores, and the pore volume of macropores is (0.01-0.4):(0.01-0.7):(0.01-0.6).

[0053] Optionally, in the functional material, the ratio of the pore volume of micropores, the pore volume of mesopores and the pore volume of macropores is (0.1-0.3):(0.1-0.5):(0.1-0.5).

[0054] Optionally, in the functional material, the ratio of the pore volume of micropores, the pore volume of mesopores and the pore volume of macropores is (0.2-0.4):(0.3-0.4):(0.3-0.4).

[0055] Optionally, in the functional material, the pore volume of the micropores is 20-40% of the total pore volume, calculated based on the total pore volume, for example, 20%, 30%, 40%, etc., or a range consisting of any two thereof.

[0056] The functional material of the present application includes micropores, mesopores and macropores at the same time. The total pore volume can be understood as the sum of the volumes of micropores, mesopores and macropores. By regulating the pore volume of micropores, mesopores and macropores in the functional material, the pore volume of the three is appropriately proportioned, which can enable the functional material to exhibit a good pore size distribution, porosity and pore structure, thereby facilitating the improvement of the wettability of the diaphragm to the electrolyte; and reducing the problem of heterogeneous transmission of the electrolyte during transmission. It is understandable that the reduction in the proportion of micropores and the increase in the proportion of mesopores and macropores can further improve the wetting of the electrolyte and increase the liquid absorption rate of the diaphragm. In some embodiments of the present application, in the ceramic layer, the mass ratio of ceramic particles, functional materials and binders is (0.01 to 0.5): (0.01 to 0.4): (0.01 to 0.15).

[0057] In some embodiments of the present application, in the ceramic layer, the mass ratio of ceramic particles to functional materials is 1:0.75 to 3, such as 1:0.75, 1:1, 1:1.25, 1:1.5, 1:1.75, 1:2, 1:2.5, 1:2.75, 1:3, etc., or any combination thereof.

[0058] By controlling the mass ratio of ceramic particles, functional materials and binder within the scope of the present application, the present invention is conducive to coordinating the pore structure of the base film and the ceramic layer, promoting the diaphragm to have good liquid absorption and liquid retention capabilities for the electrolyte, and greatly improving the wettability of the diaphragm to the electrolyte;

[0059] In some embodiments of the present application, the adhesive layer includes polyvinylidene fluoride.

[0060] In some embodiments of the present application, the separator includes a base film, a ceramic layer, and an adhesive layer in sequential contact; the ceramic layer and adhesive layer are disposed on one side of the base film, or the ceramic layer and adhesive layer are disposed on both sides of the base film; that is, the separator has a three-layer structure or a five-layer structure. The adhesive layer can promote close adhesion between the separator and the positive or negative electrode sheet, which helps reduce the risk of separation between the separator and the positive or negative electrode sheet during long-cycle charge and discharge, thereby reducing the battery's cycling capacity.

[0061] In some embodiments of the present application, the ceramic particles include at least one of aluminum oxide, boehmite, silicon oxide, zirconium oxide, magnesium oxide, and titanium oxide. Adding the aforementioned ceramic particles to the separator of the present application can effectively improve the thermal shrinkage of the separator and enhance its thermal stability.

[0062] In some embodiments of the present application, the ceramic layer has a thickness of 3 to 6 μm. Typically, but not limiting, the thickness of the ceramic layer is 3 μm, 4 μm, 5 μm, 6 μm, or any combination thereof. Controlling the thickness of the ceramic layer within the range of the present application facilitates coordination of the pore structure of the ceramic layer and the base membrane, ensuring the air permeability of the separator.

[0063] In some embodiments of the present application, the thickness of the adhesive layer is 3 to 7 μm. Typical, but non-limiting, examples include a thickness of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or a range consisting of any two thereof. The thickness of the adhesive layer directly affects the bonding strength between the separator and the positive or negative electrode sheet, which in turn affects battery performance, particularly the battery's ability to cycle charge and discharge over long periods of time. Controlling the adhesive layer thickness within the range of the present application ensures bonding between the positive and negative electrode sheets and the separator while minimizing the impact on the separator's air permeability and heat resistance.

[0064] In some specific embodiments of the present application, the pore volume of micropores accounts for 20% to 50% of the total pore volume of the functional material; the pore volume of mesopores accounts for 15% to 40% of the total pore volume of the functional material; and the pore volume of macropores accounts for 15% to 40% of the total pore volume of the functional material.

[0065] In some specific embodiments of the present application, the pore volume of micropores accounts for 20% to 40% of the total pore volume of the functional material; the pore volume of mesopores accounts for 30% to 40% of the total pore volume of the functional material; and the pore volume of macropores accounts for 30% to 40% of the total pore volume of the functional material. In some specific embodiments of the present application, in the structural material of the functional material, the pore diameter of the micropores is less than 2 nm, the pore diameter of the mesopores is 2 to 50 nm, and the pore diameter of the macropores is greater than 50 nm.

[0066] In some embodiments of the present application, the membrane coating includes an additive, which includes a dispersant and / or a wetting agent. The additive can disperse and wet the ceramic layer material during the preparation of the ceramic layer, ensuring that the ceramic particles, functional materials, and binder in the ceramic layer are fully wetted and uniformly dispersed.

[0067] In some embodiments of the present application, the membrane coating layer includes an auxiliary agent, and the auxiliary agent includes a dispersant and a wetting agent.

[0068] In some specific embodiments of the present application, the contact angle of the separator is less than 11°. Typically, but not limiting, the contact angle of the separator can be 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1°, or a range consisting of any two thereof. A contact angle of the separator within the range of the present application is conducive to sufficient infiltration of the electrolyte into the separator, thereby improving the overall performance of the separator.

[0069] In some specific embodiments of the present application, the liquid absorption rate of the membrane is 175% to 215%. Typically, but not limited to, it can be 175%, 180%, 185%, 190%, 195%, 200%, 205%, 210%, 215%, or any two thereof.

[0070] In some specific embodiments of the present application, the separator has a heat shrinkage in the MD direction of 0.95% to 1.7% at 130° C. for 0.5 h, typically but not limited to 0.95%, 1.0%, 1.15%, 1.25%, 1.35%, 1.45%, 1.55%, 1.65%, 1.7%, or any combination thereof.

[0071] In some specific embodiments of the present application, the separator has a heat shrinkage in the TD direction of 1.05% to 1.85% at 130° C. for 0.5 h, typically, but not limited to, 1.05%, 1.15%, 1.25%, 1.35%, 1.45%, 1.55%, 1.65%, 1.75%, 1.85%, or any combination thereof.

[0072] In some specific embodiments of the present application, the dispersant includes at least one of esters such as polyoxyethylene dioleate, polyethylene glycol monostearate, triethylhexyl phosphate, sodium lauryl sulfate, methyl amyl alcohol, cellulose derivatives, polyacrylamide, guar gum and fatty acid polyethylene glycol esters.

[0073] In some specific embodiments of the present application, the wetting agent includes at least one of alkyl sulfates, sulfonates, fatty acids, fatty acid ester sulfates, carboxylic acid soaps, phosphates, polyoxyethylene alkylphenol ethers, and polyoxyethylene fatty alcohol ethers.

[0074] In some embodiments of the present application, the mass ratio of the dispersant to the wetting agent is 0.5:(0.01-0.1). Typically, but not limiting, for example, the mass ratio of the dispersant to the wetting agent is 0.5:0.01, 0.5:0.02, 0.5:0.03, 0.5:0.04, 0.5:0.05, 0.5:0.06, 0.5:0.07, 0.5:0.08, 0.5:0.09, 0.5:0.1, or a range consisting of any two thereof. Controlling the mass ratio of the dispersant to the wetting agent within the range of the present application is conducive to obtaining a ceramic layer with uniform texture, thereby obtaining a uniform and stable diaphragm.

[0075] In some embodiments of the present application, the mass ratio of ceramic particles, functional materials, adhesives and additives is (0.01~0.5): (0.01~0.4): (0.01~0.15): (0.001~0.05); preferably, the mass ratio of ceramic particles, functional materials, adhesives and additives is (0.2~0.5): (0.1~0.4): (0.05~0.15): (0.01~0.05).

[0076] The diaphragm of the present application has a ceramic layer arranged on the surface of the base membrane. The ceramic layer uses ceramic particles and functional materials as the main components, and adopts suitable binders, dispersants and wetting agents to improve the dispersibility and wettability of the base membrane, so that the prepared diaphragm has excellent performance.

[0077] In some embodiments of the present application, the adhesive includes at least one of polymethyl methacrylate (PMMA), polyimide (PI), polyacrylonitrile (PAN), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF) oily adhesive and water-dispersed emulsion of polytetrafluoroethylene (PTFE).

[0078] In some embodiments of the present application, the material of the base film includes at least one of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polyimide (PI), aramid, polyethylene terephthalate (PET) and polyacrylonitrile (PAN).

[0079] In some embodiments of the present application, the thickness of the base film is 5 to 20 μm; typically but not limitatively, for example, the thickness of the base film is 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm or a range consisting of any two thereof.

[0080] In some embodiments of the present application, a method for preparing a diaphragm is also provided, comprising the following steps:

[0081] Preparation of functional materials;

[0082] Ceramic particles, functional materials, adhesives, additives and solvents are made into slurry, and then the slurry is coated on the base film to obtain a ceramic layer.

[0083] Optionally, a glue layer is applied to the surface of the ceramic layer.

[0084] In some embodiments of the present application, the following steps are included:

[0085] Preparation of functional materials: First, wash the functional material with ultrapure water three times and then with washing alcohol three times, place it in a 60-80°C oven and bake it for 12-24 hours, then put the baked functional material into a grinder and grind it, first coarse grinding and then fine grinding. The coarse grinding pressure is 0.3-0.5MPa, the coarse grinding speed is 400-1800r / min, and the coarse grinding time is 5-20min; the fine grinding pressure is 0.05-0.2MPa, the fine grinding speed is 2000-6000r / min, and the fine grinding time is 10-60min. After the above steps, the ratio of the pore volume of micropores, the pore volume of mesopores and the pore volume of macropores of the functional material of this application is (0.01-0.4): (0.01-0.7): (0.01-0.6).

[0086] Ceramic particles, functional materials, adhesives, additives and solvents are made into slurry, which is then coated on a base film to obtain a ceramic layer, and then polyvinylidene fluoride is sprayed onto the surface of the ceramic layer.

[0087] In some specific embodiments of the present application, the solvent includes an aqueous solvent and / or an oily solvent; preferably, the solvent includes at least one of water, ethanol, glycerol, acetone, and NMP. More preferably, the viscosity of the slurry is 120 to 240 mPa·s.

[0088] In some embodiments of the present application, the slurry is coated on one side, and the polyvinylidene fluoride is coated on one side; or, the slurry is coated on both sides, and the polyvinylidene fluoride is coated on both sides.

[0089] In some embodiments of the present application, the slurry coating method includes roller coating.

[0090] In some embodiments of the present application, the polyvinylidene fluoride coating method includes spray coating.

[0091] In some embodiments of the present application, a secondary battery is further provided, comprising a positive electrode sheet, a negative electrode sheet and the above-mentioned separator.

[0092] The secondary battery of the present application, by adopting the above-mentioned separator, is conducive to improving the power density, energy density and safety of the secondary battery.

[0093] In some specific embodiments of the present application, the secondary battery includes a positive electrode sheet comprising a ternary positive electrode active material. Preferably, the ternary positive electrode active material comprises lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide; more preferably, the lithium nickel cobalt manganese oxide comprises at least one of the following: lithium nickel cobalt manganese oxide 111 series, lithium nickel cobalt manganese oxide 333 series, lithium nickel cobalt manganese oxide 523 series, lithium nickel cobalt manganese oxide 622 series, and lithium nickel cobalt manganese oxide 811 series; and the negative electrode sheet includes a negative electrode active material, preferably, the negative electrode active material comprises graphite.

[0094] In some embodiments of the present application, a method for preparing a lithium-ion battery is further provided, comprising the following steps:

[0095] The positive electrode sheet, negative electrode sheet and separator are wound and hot pressed to form a battery cell, and then go through Hi-pot testing, welding, top sealing, vacuum baking, liquid injection, packaging, formation and capacity separation processes to prepare a lithium-ion battery.

[0096] The beneficial effects of this application are:

[0097] (1) The diaphragm of the present application can reduce the degree of thermal shrinkage in the MD and TD directions under high temperature conditions through the combination of functional materials and ceramic particles, thereby improving the thermal stability of the diaphragm.

[0098] (2) The diaphragm of the present application is provided with a ceramic layer and a glue layer through a diaphragm coating, and functional materials are added to the ceramic layer. The porosity of the prepared diaphragm coating is 35-65% and the surface density of the coating is 4-15 g / m 2 , which promotes the improvement of the membrane's ability to absorb and retain electrolyte, and greatly improves the membrane's wettability to the electrolyte.

[0099] (3) The diaphragm of the present application provides an excellent environment for the homogeneous transmission of the electrolyte by adding functional materials in the coating, which can ensure the rapid passage and homogeneous transmission of lithium ions during the reaction process.

[0100] The present application is further described in detail below through specific embodiments.

[0101] Example 1:

[0102] The preparation of the positive electrode sheet includes the following steps:

[0103] The ternary materials nickel cobalt manganese oxide (NCM811), polyvinylidene fluoride and conductive carbon black are added to N-methylpyrrolidone solvent in a mass ratio of 94:3:3, stirred evenly and coated on aluminum foil. The positive electrode sheet is prepared through drying, cold pressing and slitting processes.

[0104] The preparation of the negative electrode sheet includes the following steps:

[0105] Graphite, conductive carbon black, and negative electrode binder (carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA)) were added to deionized water in a mass ratio of 95:2.5:2.5, stirred, and evenly coated on copper foil. The negative electrode sheet was prepared through drying, cold pressing, and slitting processes.

[0106] The preparation of the electrolyte comprises the following steps:

[0107] Lithium hexafluorophosphate is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate to prepare an electrolyte, wherein the mass ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1.2:1.9:0.9; the mass percentage of lithium hexafluorophosphate in the electrolyte is 12.8%.

[0108] The preparation of the diaphragm includes the following steps:

[0109] The coral was washed three times with ultrapure water and then three times with detergent alcohol. It was then baked in a 60°C oven for 24 hours. The baked coral was then ground in a grinder, first coarsely and then finely. The coarse grinding process was performed at a pressure of 0.3 MPa, a rotation speed of 800 r / min, and a time of 8 minutes. The fine grinding process was then repeated at a pressure of 0.1 MPa, a rotation speed of 4000 r / min, and a time of 15 minutes. This yielded a coral functional material with a micropore:mesopore:macroporous ratio of 0.5:0.3:0.2. A 12μm PP film was then used as the base film. A coating slurry was prepared by combining boehmite powder, coral (micropore:mesopore:macroporous ratio = 0.5:0.3:0.2), and PVDF in a mass ratio of 0.2:0.2:0.15. This slurry was then applied to the PP base film, achieving a single-sided coating thickness of 3μm.

[0110] Example 2

[0111] The preparation method of Example 2 refers to that of Example 1, except that the ceramic layer is coated on both sides.

[0112] Examples 3 to 8

[0113] The preparation methods of Examples 3 to 8 refer to Example 1, except that the mass ratios of boehmite:coral:PVDF are different, as shown in Table 1.

[0114] Examples 9 to 11

[0115] The preparation methods of Examples 9 to 11 refer to Example 3, except that PVDF is sprayed into the ceramic layer after the ceramic layer is obtained. The thickness of the PVDF adhesive layer is shown in Table 1.

[0116] Examples 12-13

[0117] The preparation methods of Examples 12 to 13 refer to those of Example 3, with the difference being the thickness of the ceramic layer, as detailed in Table 1.

[0118] Examples 14-15:

[0119] The preparation methods of Examples 14 to 15 refer to Example 3, except that the types of ceramic particles are different, see Table 1 for details.

[0120] Examples 16-17:

[0121] Examples 16-17: The preparation method is similar to that of Example 3, except that the types of functional materials are different, see Table 1 for details.

[0122] Examples 18-19:

[0123] The preparation methods of Examples 18 to 19 refer to Example 3, except that the types of binders in the ceramic layer are different, see Table 1 for details.

[0124] Example 20:

[0125] The preparation method of Example 20 refers to that of Example 3, except that the time for fine grinding of the coral is 45 minutes.

[0126] Example 21:

[0127] The preparation method of Example 21 refers to that of Example 10, except that the coral is finely ground for 20 minutes.

[0128] Example 22:

[0129] The preparation method of Example 22 refers to Example 20, except that the coating of the diaphragm includes an additive, and a polyoxyethylene dioleate dispersant and a polyoxyethylene alkylphenol ether wetting agent are added to the slurry, and the ratio of the polyoxyethylene dioleate dispersant to the polyoxyethylene alkylphenol ether wetting agent is 0.5:0.08.

[0130] Examples 23-24:

[0131] The preparation methods of Examples 23 to 24 refer to Example 22, except that the ratios of the polyoxyethylene dioleate dispersant to the polyoxyethylene alkylphenol ether wetting agent are different, see Table 1 for details.

[0132] Example 25:

[0133] The preparation method of Example 25 refers to that of Example 23, except that the types of auxiliary agents are different, as shown in Table 1.

[0134] Comparative Examples 1-2

[0135] The preparation methods of Comparative Examples 1 to 2 refer to Example 1, except that in Comparative Example 1, boehmite:coral:PVDF=0.6:0.2:0.15, and in Comparative Example 2, boehmite:coral:PVDF=0.2:0.005:0.15.

[0136] Comparative Example 3

[0137] The preparation method of Comparative Example 3 refers to that of Example 1, except that the ratio of boehmite to PVDF is 0.2:0.15, and there is no coral.

[0138] Comparative Example 4

[0139] Comparative Example 4 refers to Example 1, except that the diaphragm is not provided with a coating.

[0140] The detailed parameters of each embodiment and comparative example are shown in Table 1.

[0141] Table 1

[0142] The basic physical properties of the diaphragms prepared in the examples and comparative examples were tested, and the results are shown in Table 2.

[0143] Among them, the surface density measurement method: weighing method, parallel samples ≥ 10; cut the diaphragm into 50mm×50mm, weigh the weight of the base film, the weight after ceramic coating, and the weight after adhesive coating to calculate the coating weight per unit area.

[0144] The density of the base film used in the examples and comparative examples of the present application is: the median value is 5.8 g / m 2 .

[0145] In the double-sided coating, the coating density refers to the density of the double-sided coating.

[0146] Porosity test method: weighing calculation method, 1-(area density / thickness / skeleton density).

[0147] Thickness test method: Mahr thickness gauge test, parallel samples N = 20.

[0148] Air permeability test method: Gurley tester, parallel samples N≥3.

[0149] Thermal shrinkage test method: Cut the diaphragm into 100mm×50mm and bake it in a forced air oven at a certain temperature. Then measure the length after baking. The number of samples N≥3.

[0150] Contact Angle Test Method: Refer to GB / T 30447-2013, Contact Angle Measurement Method for Nanofilms. Sample Size: ≥2cm*8cm. Test Method: Measure the contact angle of the electrolyte on the separator surface. Test Settings: Total time: 10.0s, start and pause: 0.0s, pipette tip size: 300μL, drop volume: 2.0μL. Record the contact angle of the electrolyte droplet on the separator surface after 10s. ≥3 replicates.

[0151] Liquid absorption rate test method: Use a balance to weigh the mass of the cut fixed-size diaphragm before absorbing the electrolyte as m1, then immerse the diaphragm in the electrolyte, take it out and weigh it after it is completely soaked and record it as m2. Liquid absorption rate = (m2-m1) / m1*100%, parallel samples N≥3.

[0152] Table 2

[0153] As can be seen from Table 2, by comparing Examples 1 to 19 with Comparative Example 3, the thermal shrinkage of the separator of the present application in the MD and TD directions is greatly improved under high temperature conditions. The improvement in thermal stability is due to the ceramic particles and functional materials used being highly heat-resistant materials with excellent thermal stability. In addition, the liquid absorption rate of Examples 1 to 19 is significantly greater than that of the separator of Comparative Example 3. This is mainly due to the addition of functional materials, which provide an excellent environment for electrolyte absorption, improve the liquid absorption and retention capacity of the separator, and further improve the wettability of the separator.

[0154] By comparing Examples 10, 20 and 21, it can be seen that when the pore volume of micropores, the pore volume of mesopores and the pore volume of macropores in the functional material are within the scope of the present application, the better the wettability of the prepared diaphragm to the electrolyte, the higher the liquid absorption rate. It is worth noting that the applicant has found that the reduction of the proportion of micropores and the increase of the proportion of mesopores and macropores can further improve the infiltration of the electrolyte and improve the liquid absorption rate of the diaphragm. As in Examples 10, 20 and 21, by adjusting the grinding time, the relative value of the micropores is changed. The longer the grinding time, the less the total pore volume of the micropores. This is because grinding for a certain period of time leads to particle breakage, agglomeration and reorganization. In this process, the total volume of mesopores and macropores will increase, thereby resulting in a reduction in the proportion of micropore volume, and further improving the liquid absorption and retention capacity of the diaphragm and the wettability of the diaphragm.

[0155] The electrochemical performance of the embodiments and comparative examples was tested, and the results are shown in Table 3.

[0156] Among them, the cycle performance test: the lithium-ion battery is charged and discharged at a rate of 1C at 25°C for 1000 cycles in sequence. The battery capacity at the cycle test rate of 1C is compared with the battery capacity before the cycle, and the capacity retention rate after the cycle is calculated.

[0157] Battery gravimetric energy density: Test and calculate the gravimetric energy density of battery cells in Wh / kg.

[0158] Short-circuit safety performance test: After the battery is fully charged to 4.4V at constant current and constant voltage, it is short-circuited with an external circuit with an internal resistance of <5mΩ for 10 minutes.

[0159] Table 3

[0160] As shown in Table 3, when comparing Examples 1-19 with Comparative Example 3, the batteries of Examples 1-19 not only have high gravimetric energy density and high capacity retention, but also exhibit no short circuits during cell testing. In contrast, the battery of Comparative Example 3 has lower gravimetric energy density and capacity retention, and is more prone to short circuits, which can easily lead to thermal runaway and pose a safety hazard. The introduction of functional materials ensures homogeneous electrolyte transport, achieving high battery safety performance and high capacity retention.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application. Industrial Applicability

[0162] The diaphragm provided in the present application comprises a base film and a coating provided on at least one surface of the base film, wherein the coating comprises a ceramic layer and a glue layer, wherein the ceramic layer comprises ceramic particles, a binder and a functional material; the porosity of the diaphragm coating is 35-65%; the surface density of the coating is 4-15 g / m 2 The separator of the present application has excellent thermal stability, with minimal thermal shrinkage in the MD and TD directions under high temperature conditions. It has good electrolyte absorption and retention capabilities, as well as excellent wettability, ensuring rapid passage and homogeneous transmission of lithium ions during the reaction. Furthermore, the separator can reduce the risk of capacity reduction and local overcharging, thereby protecting secondary batteries and possessing excellent industrial applicability.

Claims

1. A diaphragm, comprising a base film and a coating disposed on at least one surface of the base film, wherein the coating comprises a ceramic layer, and the ceramic layer comprises ceramic particles, a binder and a functional material; The porosity of the coating of the diaphragm is 35-65%; The surface density of the coating is 0.5 to 14 g / m 2 .

2. A diaphragm, comprising a base film and a coating disposed on at least one surface of the base film, the coating comprising a ceramic layer and a glue layer, the ceramic layer comprising ceramic particles, a binder and a functional material; The porosity of the coating of the diaphragm is 35-65%; The surface density of the coating is 0.5 to 14 g / m 2 .

3. The diaphragm according to claim 1 or 2, wherein: The porosity of the coating is 50-60%, and the surface density of the coating is 1.5-6.5 g / m 2 .

4. The diaphragm according to claim 1 or 2, wherein: The functional material comprises at least one material selected from the following: Kapok, wood, sponge, coral, metal organic framework material, covalent organic framework material or a carbon material formed by at least one of the foregoing functional materials.

5. The diaphragm according to claim 1 or 2, wherein: The functional material is a porous material, and the porous material includes micropores, mesopores and macropores.

6. The diaphragm according to claim 1 or 2, wherein: In the functional material, the ratio of the pore volume of micropores, the pore volume of mesopores and the pore volume of macropores is (0.01-0.4):(0.01-0.7):(0.01-0.6).

7. The diaphragm according to claim 1 or 2, wherein: In the functional material, the pore volume of micropores accounts for 20-40% of the total pore volume.

8. The diaphragm according to claim 1 or 2, wherein: The ceramic particles include at least one of aluminum oxide, boehmite, silicon oxide, zirconium oxide, magnesium oxide, and titanium oxide.

9. The diaphragm according to claim 1 or 2, wherein: In the ceramic layer, the mass ratio of the ceramic particles, the functional material and the binder is (0.01-0.5): (0.01-0.4): (0.01-0.15).

10. The diaphragm according to claim 1 or 2, wherein: In the ceramic layer, the mass ratio of the ceramic particles to the functional material is 1:0.75-3.

11. The diaphragm according to claim 2, wherein: The adhesive layer includes polyvinylidene fluoride.

12. The diaphragm according to claim 1 or 2, wherein: The thickness of the ceramic layer is 3-6 μm.

13. The diaphragm according to claim 2, wherein: The thickness of the adhesive layer is 3-7 μm.

14. The diaphragm according to claim 1 or 2, wherein: The coating of the separator includes an auxiliary agent, and the auxiliary agent includes a dispersant and / or a wetting agent.

15. The diaphragm according to claim 1 or 2, wherein: The coating of the diaphragm includes an auxiliary agent, and the auxiliary agent includes a dispersant and a wetting agent. The mass ratio of the dispersant to the wetting agent is 0.5:(0.01-0.1).

16. A method for preparing a diaphragm, comprising: Preparation of functional materials; Ceramic particles, functional materials, adhesives, additives and solvents are made into slurry, and then the slurry is coated on a base film to obtain a ceramic layer.

17. The method according to claim 16, wherein: A glue layer is applied to the surface of the ceramic layer.

18. A secondary battery, wherein: The invention comprises a positive electrode sheet, a negative electrode sheet and a separator according to any one of claims 1 to 15.

19. An electrical device comprising the secondary battery according to claim 18.

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