Composite separator and preparation method therefor, and battery

Abstract

A composite separator. The composite separator comprises a base membrane (10), a composite coating (20) provided on one side of the base membrane (10), a heat-resistant layer (30) provided on the side of the base membrane (10) facing away from the composite coating (20), and an adhesive layer (40) provided on the side of the heat-resistant layer (30) facing away from the base membrane (10), wherein the material of the composite coating (20) comprises a first heat-resistant material and a first separator adhesive material. By forming the composite coating (20) and the heat-resistant layer (30) having a continuous phase on the surface of the base membrane (10), the rupture temperature of the separator can be increased, thereby lowering the risk of a short circuit caused by contact between positive and negative electrodes due to the rupture of the separator, and facilitating the control over thermal runaway of a battery.

Description

Composite diaphragm, preparation method thereof and battery

[0001] Cross-reference to related applications

[0002] The present application claims priority from the Chinese patent application No. 202410474457X filed on April 19, 2024, and entitled "Composite diaphragm, preparation method thereof and battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to the field of batteries, and in particular to a composite diaphragm, a preparation method thereof and a battery. BACKGROUND

[0004] With the continuous expansion of the battery market, the cost of battery prices continues to fall, forcing enterprises to continuously innovate to reduce manufacturing costs; the safety of battery capacity continues to increase, and the consequences of battery thermal runaway are more serious, and the market's requirements for battery safety are becoming higher and higher.

[0005] In terms of improving battery thermal runaway, the diaphragm needs to have a lower thermal shrinkage rate and a higher film breaking temperature, and the existing diaphragm heat-resistant coating is mainly ceramic. Although ceramic materials are heat-resistant, the non-continuous phase heat-resistant layer formed by coating the powder particles on the surface of the diaphragm cannot improve the film breaking temperature of the diaphragm. When the battery experiences thermal runaway, as the battery deforms under heat, the diaphragm is prone to rupture, which increases the short-circuit area between the positive and negative electrodes, which is not conducive to the control of thermal runaway.

[0006] SUMMARY

[0007] The present disclosure provides a composite diaphragm, comprising a base film, a composite coating layer arranged on one side of the base film, a heat-resistant layer arranged on the side of the base film away from the composite coating layer, and an adhesive layer arranged on the side of the heat-resistant layer away from the base film.

[0008] In some embodiments, the material of the composite coating layer comprises a first heat-resistant material and a first diaphragm adhesive material.

[0009] In some embodiments, the mass ratio of the first heat-resistant material to the first diaphragm adhesive material is 1:(1-10).

[0010] In some embodiments, the composite coating layer has a first micropore, and the pore size of the first micropore is 50-600 nm.

[0011] In some embodiments, the base film has a first thickness H1, the composite coating layer has a second thickness H2, the heat-resistant layer has a third thickness H3, and the adhesive layer has a fourth thickness H4, which satisfy H1>H2+H3+H4 and H3 / H2<3.

[0012] In some embodiments, the first thickness H1 ranges from 3 to 20 um.

[0013] In some embodiments, the second thickness H2 ranges from 0.5 to 4 um.

[0014] In some embodiments, the third thickness H3 ranges from 1.2 to 4.5 um.

[0015] In some embodiments, the fourth thickness H4 ranges from 0.5 to 10 um.

[0016] In some embodiments, the composite coating has a second thickness H2, the adhesive layer has a fourth thickness H4, and the adhesive layer has a coverage F on the heat-resistant layer, which satisfies: F = (0.5-1) x H2 / H4* %.

[0017] In some embodiments, the adhesive layer has a coverage F on the heat-resistant layer, and the coverage F ranges from 5 to 90 %.

[0018] In some embodiments, the base film has a second micropore, and the porosity of the base film ranges from 25 to 70 %.

[0019] In some embodiments, the base film has a second micropore, and the ratio of the maximum pore size of the second micropore to the average pore size of the second micropore ranges from 1.3 to 3.5.

[0020] In some embodiments, the material of the base film is selected from polyethylene or polypropylene.

[0021] In some embodiments, the first heat-resistant material is selected from at least one of nylon 66, aramid 1313, and aramid 1414.

[0022] In some embodiments, the first diaphragm glue material is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, and hexafluoropropylene copolymer.

[0023] In some embodiments, the material of the heat-resistant layer is selected from at least one of nylon 66, aramid 1313, and aramid 1414.

[0024] In some embodiments, the material of the adhesive layer is selected from at least one of polyvinylidene fluoride, polymethyl methacrylate, and polyacrylic acid.

[0025] The second aspect of the present disclosure provides a preparation method of a composite diaphragm, comprising:

[0026] providing a base film;

[0027] mixing a first heat-resistant material, a first diaphragm glue material, and a first solvent to obtain a first coating;

[0028] The first coating is applied to one side of the base film by oil coating to obtain a composite coating layer;

[0029] The second heat-resistant material and the second solvent are mixed to obtain a second coating;

[0030] The second coating is applied to the side of the base film away from the composite coating layer by oil coating to obtain a heat-resistant layer;

[0031] The second separator adhesive material is applied to the side of the heat-resistant layer away from the base film by water coating to obtain a bonding layer.

[0032] In some embodiments, the mass ratio of the first heat-resistant material and the first separator adhesive material is 1:(1-10).

[0033] The third aspect of the present disclosure provides a battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a composite separator, wherein the composite separator comprises the composite separator as described above;

[0034] The composite separator comprises a base film, a composite coating layer arranged on one side of the base film, a heat-resistant layer arranged on the side of the base film away from the composite coating layer, and a bonding layer arranged on the side of the heat-resistant layer away from the base film;

[0035] The composite coating layer is attached to the positive electrode sheet;

[0036] The bonding layer is attached to the negative electrode sheet. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only represent the embodiments of the present disclosure by way of example, and the true proportions of the embodiments cannot be directly corresponded to the proportions in the drawings. Meanwhile, the following drawings only show some of the embodiments of the present disclosure, and therefore should not be regarded as a limitation on the scope.

[0038] FIG. 1 is a structural schematic diagram of a composite separator provided by the present disclosure.

[0039] Reference signs:

[0040] 10, base film; 20, composite coating layer; 30, heat-resistant layer; 40, bonding layer. DETAILED DESCRIPTION

[0041] The advantages of the embodiments in the specification will be illustrated in the following description of the embodiments, some of which are obvious from the specification or can be obtained by some of the embodiments of the present disclosure.

[0042] The technical solutions of the present disclosure will be further illustrated below in combination with the accompanying drawings and some embodiments.

[0043] In order to make the purposes, technical solutions and advantages of the present disclosure clearer, the present disclosure will be further described in detail below in combination with the accompanying drawings and embodiments. It should be understood that the embodiments described herein are only used to explain the present disclosure and not used to limit the present disclosure. In addition, the technical features involved in the various embodiments of the present disclosure described below can be combined with each other as long as they do not conflict with each other. Without departing from the principles of the embodiments of the present disclosure, a number of improvements and refinements can also be made, which are also considered within the protection scope of the embodiments of the present disclosure. In this specification, the numerical range shown using “~” represents a range including the minimum value and the maximum value respectively recorded before and after “~” as the minimum value and the maximum value.

[0044] The first aspect of the present disclosure provides a composite separator, which will be described in detail below in combination with specific embodiments.

[0045] A composite separator includes a base film 10, a composite coating layer 20 arranged on one side of the base film 10, a heat-resistant layer 30 arranged on the side of the base film 10 away from the composite coating layer 20, and a bonding layer 40 arranged on the side of the heat-resistant layer 30 away from the base film 10; wherein the material of the composite coating layer 20 includes a first heat-resistant material and a first separator adhesive material.

[0046] It can be understood that by forming the composite coating layer 20 and the heat-resistant layer 30 with a continuous phase on the surface of the base film 10, the present disclosure can improve the film breaking temperature of the composite separator, reduce the risk of short circuit caused by the contact between the positive and negative electrodes due to the rupture of the composite separator, and facilitate the control of battery thermal runaway.

[0047] In some embodiments, the mass ratio of the first heat-resistant material and the first separator adhesive material is 1:(1-10). Specifically, the mass ratio of the first heat-resistant material and the first separator adhesive material is any one of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or a range consisting of any two thereof.

[0048] It can be understood that by controlling the mass ratio of the first heat-resistant material and the first separator adhesive material to be 1:(1-10), the present disclosure can form a composite coating layer 20 with a continuous phase on the surface of the base film 10, and the composite coating layer 20 has good heat resistance and bonding performance matching the positive electrode plate.

[0049] In some embodiments, the composite coating 20 has first micropores with a pore size of 50-600 nm. Specifically, the first micropores have a pore size of any one of or a range consisting of any two of 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm.

[0050] It can be understood that the present disclosure forms the continuous-phase composite coating 20 on the surface of the base film 10, and controls the pore size of the first micropores in the composite coating 20 to be 50-600 nm, so that the composite coating 20 has good ion permeability, and ensures the ion conductivity of the battery.

[0051] In some embodiments, the base film 10 has a first thickness H1, the composite coating 20 has a second thickness H2, the heat-resistant layer 30 has a third thickness H3, and the adhesive layer 40 has a fourth thickness H4, which satisfy H1>H2+H3+H4, and H3 / H2<3.

[0052] It can be understood that when the total thickness of the composite coating 20, the heat-resistant layer 30, and the adhesive layer 40 exceeds the thickness of the base film 10, the flexibility of the prepared composite separator is poor, and the coating is easy to fall off; it can be understood that the heat-resistant coating is easy to absorb water, and when the thickness of the heat-resistant coating on both sides of the base film 10 is greatly different, the separator is easy to curl, which causes the separator to fail to effectively wrap the pole piece, and there is a risk of short circuit.

[0053] In some embodiments, the first thickness H1 is in a range of 3-20 um. Specifically, the first thickness H1 is any one of or a range consisting of any two of 3 um, 5 um, 10 um, 15 um, 20 um.

[0054] It can be understood that when the first thickness H1 is too thick, that is, the thickness of the base film 10 is too thick, the heat resistance of the prepared composite separator is affected, and when the first thickness H1 is too thin, that is, the thickness of the base film 10 is too thin, the resistance to foreign object puncture of the prepared composite separator is affected, and the present disclosure controls the first thickness H1 in a range of 3-20 um, so that the composite separator has good heat resistance and resistance to foreign object puncture.

[0055] In some embodiments, the second thickness H2 is in a range of 0.5-4 um. Specifically, the second thickness H2 is any one of or a range consisting of any two of 0.5 um, 1 um, 1.5 um, 2 um, 2.5 um, 3 um, 3.5 um, 4 um.

[0056] It can be understood that when the second thickness H2 is too thick, that is, the composite coating 20 is too thick, the ion permeability of the prepared composite diaphragm is affected, and when the second thickness H2 is too thin, that is, the composite coating 20 is too thin, the heat resistance of the prepared composite diaphragm is affected, and the present disclosure controls the range of the second thickness H2 to be 0.5-4 um, so that the composite coating 20 has good heat resistance and ion permeability.

[0057] In some embodiments, the third thickness H3 is in the range of 1.2-4.5 um. Specifically, the third thickness H3 is any one of 1.2 um, 1.5 um, 2 um, 2.5 um, 3 um, 3.5 um, 4 um, 4.5 um or a range consisting of any two of them.

[0058] It can be understood that when the third thickness H3 is too thick, that is, the heat-resistant layer 30 is too thick, the ion permeability of the prepared composite diaphragm is affected, and when the third thickness H3 is too thin, that is, the heat-resistant layer 30 is too thin, the heat resistance of the prepared composite diaphragm is affected, and the present disclosure controls the range of the third thickness H3 to be 1.2-4.5 um, so that the heat-resistant layer 30 has good heat resistance and ion permeability.

[0059] In some embodiments, the fourth thickness H4 is in the range of 0.5-10 um. Specifically, the fourth thickness H4 is any one of 0.5 um, 1 um, 2 um, 3 um, 4 um, 5 um, 6 um, 7 um, 8 um, 9 um, 10 um or a range consisting of any two of them.

[0060] It can be understood that when the fourth thickness H4 is too thick, that is, the thickness of the bonding layer 40 is too thick, the ion permeability of the prepared composite diaphragm is affected, and when the fourth thickness H4 is too thin, that is, the thickness of the bonding layer 40 is too thin, the adhesion performance of the prepared composite diaphragm to the negative electrode sheet is affected, and the present disclosure controls the range of the fourth thickness H4 to be 0.5-10 um, so that the bonding layer 40 has good adhesion performance.

[0061] In some embodiments, the composite coating 20 has a second thickness H2, the bonding layer 40 has a fourth thickness H4, and the bonding layer 40 has a coverage F on the heat-resistant layer 30, which satisfies: F=(0.5-1) x H2 / H4*%. For the same material, the greater the thickness, the greater the mass, and the greater the mass, the higher the coverage of the material.

[0062] It can be understood that the coverage of the bonding layer 40 on the heat-resistant layer 30 is low, and the adhesion between the diaphragm and the negative electrode sheet is weak; the coverage of the bonding layer 40 on the heat-resistant layer 30 is high, and the heat-resistant layer 30 is easily blocked.

[0063] In some embodiments, a test method for coverage is provided, comprising:

[0064] The surface coating of the composite separator is tested using a microscope instrument, in which the profile of the gel particles protruding from the surface of the coating is focused clearly by adjusting the focal length, and the color and area of the gel particles are counted using microscope software, and the ratio of the area of the gel particles to the total area of the coating is the coverage.

[0065] In some embodiments, the adhesive layer 40 has a coverage F on the heat-resistant layer 30, and the coverage F ranges from 5% to 90%. Specifically, the coverage F of the adhesive layer 40 on the heat-resistant layer 30 is any one or a range consisting of any two of 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%.

[0066] In some embodiments, the base film 10 has second micropores, and the porosity of the base film 10 ranges from 25% to 70%. Specifically, the porosity of the base film 10 is any one or a range consisting of any two of 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70%.

[0067] It can be understood that when the coating liquid for oily coating is used to form a coating on the surface of the base film 10, the solvent will penetrate into the pores on the surface of the base film 10, causing the pores to be blocked. By controlling the porosity of the base film 10 to range from 25% to 70%, the present disclosure can reduce the influence of the blocking effect caused by the penetration of the solvent into the pores on the electrical performance when the oily coating method is used.

[0068] In some embodiments, the base film 10 has second micropores, and the ratio of the maximum pore diameter of the second micropores to the average pore diameter of the second micropores ranges from 1.3 to 3.5. Specifically, the ratio of the maximum pore diameter of the second micropores to the average pore diameter of the second micropores is any one or a range consisting of any two of 1.3, 1.5, 2, 2.5, 3, and 3.5.

[0069] It can be understood that by selecting the pore diameter of the base film 10 to satisfy the ratio of the maximum pore diameter to the average pore diameter ranging from 1.3 to 3.5, the influence of the blocking effect caused by the penetration of the solvent into the pores on the electrical performance is smaller when the oily coating method is used.

[0070] In some embodiments, the material of the base film 10 is selected from polyethylene (PE) or polypropylene (PP).

[0071] In some embodiments, the first heat-resistant material is selected from at least one of nylon 66 (polyhexamethylene adipamide), aramid 1313 (poly-m-phenylene isophthalamide), and aramid 1414 (poly-p-phenylene terephthalamide).

[0072] In some embodiments, the first separator glue material is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride and hexafluoropropylene copolymer.

[0073] In some embodiments, the material of the heat-resistant layer 30 is selected from at least one of nylon 66, aramid 1313, aramid 1414.

[0074] In some embodiments, the material of the adhesive layer 40 is selected from at least one of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyacrylic acid (PAA).

[0075] The second aspect of the present disclosure provides a preparation method of a composite separator, comprising:

[0076] providing a base film 10;

[0077] mixing a first heat-resistant material, a first separator glue material and a first solvent to obtain a first coating;

[0078] applying the first coating to one side of the base film 10 by means of oil coating to obtain a composite coating layer 20;

[0079] mixing a second heat-resistant material and a second solvent to obtain a second coating;

[0080] applying the second coating to the side of the base film 10 away from the composite coating layer 20 by means of oil coating to obtain a heat-resistant layer 30;

[0081] applying the second separator glue material to the side of the heat-resistant layer 30 away from the base film 10 by means of water-based coating to obtain an adhesive layer 40.

[0082] Specifically, the preparation method of the composite separator can be realized by the following steps:

[0083] S1: providing a base film 10;

[0084] S2: mixing a first heat-resistant material, a first separator glue material and a first solvent to obtain a first coating;

[0085] S3: applying the first coating to one side of the base film 10 by means of oil coating with a gravure roll to obtain a composite coating layer 20 after first drying treatment;

[0086] S4: mixing a second heat-resistant material and a second solvent to obtain a second coating;

[0087] S5: applying the second coating to the side of the base film 10 away from the composite coating layer 20 by means of oil coating with a gravure roll to obtain a heat-resistant layer 30 after second drying treatment;

[0088] S5: coating the second separator adhesive material on the side of the heat-resistant layer 30 away from the base film 10 by means of water-based coating with a gravure roll to obtain the adhesive layer 40 after a third drying treatment.

[0089] It can be understood that the present disclosure forms the composite coating layer 20 on the side of the base film 10 by means of oil-based coating, and there is no powder material on the surface of the coating layer, and there is no problem of powder falling during the contact between the coating layer and the composite roller in the thermal compounding process; the composite coating layer 20 and the heat-resistant layer 30 having a continuous phase are formed on the side of the base film 10 by means of oil-based coating, which can improve the film breaking temperature of the separator and reduce the risk of short circuit caused by the contact between the positive and negative electrodes due to the rupture of the separator; the adhesive layer 40 is coated on the side of the heat-resistant layer 30 away from the base film 10 by means of water-based coating, so that the composite separator and the negative electrode plate can meet the compounding requirements during the thermal compounding process.

[0090] Specifically, the preparation method of the composite separator can also be realized by the following steps:

[0091] S11: providing a base film 10;

[0092] S22: mixing the first heat-resistant material, the first separator adhesive material and the first solvent to obtain a first coating material; mixing the second heat-resistant material and the second solvent to obtain a second coating material;

[0093] S33: coating the first coating material on one side of the base film 10 by means of oil-based coating with a gravure roll at the same time as coating the second coating material on the other side of the base film 10 by means of oil-based coating with a gravure roll, the one side of the base film 10 being arranged opposite to the other side of the base film 10, and forming a composite coating layer 20 on the one side of the base film 10 and a heat-resistant layer 30 on the other side of the base film 10 after drying treatment;

[0094] S44: coating the second separator adhesive material on the side of the heat-resistant layer 30 away from the base film 10 by means of water-based coating with a gravure roll to obtain the adhesive layer 40 after a third drying treatment.

[0095] It can be understood that coating the first coating material and the second coating material on the surface of the base film 10 at the same time and drying the first coating material and the second coating material at the same time can reduce the coating cost.

[0096] In some embodiments, the first solvent is selected from N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), ethanol, acetone.

[0097] In some embodiments, the temperature of the first drying treatment is 50-80℃, and the time of the first drying treatment is 5-60s. Specifically, the temperature of the first drying treatment can be any one or a range formed by any two of 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, and 80℃; the time of the first drying treatment can be any one or a range formed by any two of 5s, 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, and 60s.

[0098] In some embodiments, the second solvent is selected from N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), ethanol, and acetone.

[0099] In some embodiments, the temperature of the second drying treatment is 50-80℃, and the time of the second drying treatment is 5-60s. Specifically, the temperature of the second drying treatment can be any one or a range formed by any two of 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, and 80℃; the time of the second drying treatment can be any one or a range formed by any two of 5s, 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, and 60s.

[0100] In some embodiments, the temperature of the third drying treatment is 65-85℃, and the time of the third drying treatment is 10-120s. Specifically, the temperature of the third drying treatment can be any one or a range formed by any two of 65℃, 70℃, 75℃, 80℃, and 85℃; the time of the second drying treatment can be any one or a range formed by any two of 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, and 120s.

[0101] In some embodiments, the mass ratio of the first heat-resistant material and the first separator glue material is 1:(1-10). Specifically, the mass ratio of the first heat-resistant material and the first separator glue material is any one or a range formed by any two of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10.

[0102] The third aspect of the present disclosure provides a battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a composite separator, wherein the composite separator comprises the composite separator as described above; the composite separator comprises a base film 10, a composite coating layer 20 arranged on one side of the base film 10, a heat-resistant layer 30 arranged on the side of the base film 10 away from the composite coating layer 20, and an adhesive layer 40 arranged on the side of the heat-resistant layer 30 away from the base film 10; the composite coating layer 20 is attached to the positive electrode sheet; and the adhesive layer 40 is attached to the negative electrode sheet.

[0103] It can be understood that the composite coating 20 is used to realize the bonding of the composite separator and the positive electrode tab, the bonding layer 40 is used to realize the bonding of the composite separator and the negative electrode tab, and the battery prepared by using the composite separator provided by the present disclosure is beneficial to the control of the thermal runaway of the battery.

[0104] Example 1

[0105] The base film 10 has a thickness of 15 um, a porosity of 50%, and a ratio of the maximum pore size to the average pore size of 2.

[0106] The first coating is prepared by mixing nylon 66, polyvinylidene fluoride and N,N-dimethylacetamide, wherein the mass ratio of nylon 66 to polyvinylidene fluoride is 1:1; the first coating is coated on one side of the base film 10 by means of oil coating with a gravure roll, and the composite coating 20 is obtained after the first drying treatment, the temperature of the first drying treatment is 65°C, and the time of the first drying treatment is 30s.

[0107] The second coating is prepared by mixing nylon 66 and N,N-dimethylacetamide; the second coating is coated on the side of the base film 10 away from the composite coating 20 by means of oil coating with a gravure roll, and the heat-resistant layer 30 is obtained after the second drying treatment, the temperature of the second drying treatment is 65°C, and the time of the second drying treatment is 30s.

[0108] The third coating is prepared by coating polyvinylidene fluoride on the side of the heat-resistant layer 30 away from the base film 10 by means of water-based coating with a gravure roll, and the bonding layer 40 is obtained after the third drying treatment, the temperature of the third drying treatment is 75°C, and the time of the third drying treatment is 60s.

[0109] Examples 2-7

[0110] The preparation methods of examples 2-7 are the same as those of example 1, except that the structural parameters and material parameters are adjusted.

[0111] Comparative example 1

[0112] The battery separator of Shanghai Enjie Company is selected,

[0113] The base film has a thickness of 15 um, a porosity of 50%, and a ratio of the maximum pore size to the average pore size of 2;

[0114] The first coating is located on one side of the base film, has a thickness of 3 um, and is made of mixed coating of aluminum oxide and large particle PMMA, which plays a role of heat resistance and bonding, and the film breaking temperature is 164°C;

[0115] The second coating is located on the side of the base film away from the first coating, has a thickness of 1 um, and is made of PVDF.

[0116] Comparative example 2

[0117] Comparative Example 2 has the same preparation method as Example 1, except that the thicknesses of the base film, the composite coating layer, the heat-resistant layer, and the adhesive layer do not satisfy H1 > H2 + H3 + H4 and H3 / H2 < 3.

[0118] Comparative Examples 3-4

[0119] Comparative Examples 3-4 have the same preparation method as Example 1, except that the thicknesses of the base film, the composite coating layer, the heat-resistant layer, and the adhesive layer do not satisfy H1 > H2 + H3 + H4 and H3 / H2 < 3; and do not satisfy F = (0.5-1) x H2 / H4*%, and F ranges from 5-90%.

[0120] The following describes battery assembly by taking a lithium battery as an example.

[0121] (1) Preparation of the positive electrode sheet: A slurry is prepared using lithium iron phosphate or ternary nickel-cobalt-manganese material, the slurry is coated on a carbon-coated aluminum foil to obtain a positive electrode sheet after processing, the proportion of the coating layer in the positive electrode sheet is 96.5%, and the rest is adhesive, conductive agent, etc.

[0122] (2) Preparation of the negative electrode sheet: A slurry is prepared using artificial graphite, the slurry is coated on a copper foil to obtain a negative electrode sheet after processing, the proportion of the coating layer in the negative electrode sheet is 95.5%, and the rest is adhesive, conductive agent, etc.

[0123] (3) Preparation of the electrode group: The composite separator and the negative electrode sheet are bonded in the form of hot roll hot pressing by using a hot compounding process, and the hot roll temperature is 70-100°C; the unit formed after hot pressing is cut into a single piece using a hot cutter to form a sandwich structure of separator-negative electrode-separator; the sandwich structure and the positive electrode sheet are stacked in the form of a stack to form an electrode group, and the preparation of the electrode group is completed by hot pressing at 85-95°C using a flat plate hot press.

[0124] (4) Packaging and liquid injection: The prepared electrode group is packaged in a square shell form, and then electrolyte is injected.

[0125] (5) Pre-charging and formation: The battery is prepared by pre-charging and formation of the battery cell.

[0126] Structural parameters and performance tests:

[0127] (1) Breakage temperature test: The breakage temperature is tested by using the TMA method.

[0128] (2) Thickness test: The thickness is tested by using a Malvern thickness tester.

[0129] (3) Pore size test: The base film pore size is tested by using a PMI instrument.

[0130] (4) Test of the bonding force between the composite separator and the positive electrode tab: using a flat plate hot press equipment, under the test conditions of temperature 90℃, pressure 2MPa, time 120s, test the bonding force between the composite separator and the positive electrode tab.

[0131] (5) Test of the bonding force between the composite separator and the negative electrode tab: using the form of folding the separator, under the test conditions of temperature 90℃, surface pressure 1Mpa, time 60s, test the bonding force between the composite separator and the negative electrode tab.

[0132] (6) Test of the short circuit rate after the heat pressing of the electrode group: under the condition of test voltage 50v, test the short circuit rate after the heat pressing of the electrode group.

[0133] (7) Battery thermal runaway test: GB38031-2020 Safety requirements for power storage batteries for electric vehicles, appendix C, C5.3.3. Needle trigger thermal runaway method.

[0134] Table 1 is the parameter setting of examples 1-7 and comparative examples 1-4.

[0135] Table 1 is the parameter setting of examples 1-7 and comparative examples 1-4.

[0136] Table 2 is the test results of examples 1-7 and comparative examples 1-4.

[0137] Table 2 is the test results of examples 1-7 and comparative examples 1-4.

[0138] Result analysis:

[0139] From the test results of examples 1-7 and comparative examples 1-4, in comparative example 1, the separator coating layer uses existing ceramic heat-resistant material, the film breaking temperature is 164℃, which does not meet the requirement of ≥5min according to the national standard thermal runaway test method; in the present disclosure, the continuous phase composite coating layer 20 and heat-resistant layer 30 are formed on the surface of the base film 10, the composite separator of the present disclosure breaks the film, the film breaking temperature is generally above 200℃, the thermal runaway time is >5min, and the trend of obvious battery safety improvement effect is presented with the increase of the film breaking temperature.

[0140] For comparative example 3, by controlling the coverage rate F of the adhesive layer 40 to the heat-resistant layer 30, meeting: F=(0.5-1)×H2 / H4*%, the coverage rate is <5%, the bonding force between the separator and the negative electrode tab is weak, and larger heat pressing parameters are needed to match, corresponding to the risk of damage in the heat pressing of the separator, and the increase of the short circuit rate.

[0141] For Comparative Example 2 and Comparative Example 4, although the film breaking temperature is generally above 200°C, the thermal runaway time is >5 min, but because the total thickness of the composite coating 20, the heat-resistant layer 30 and the adhesive layer 40 and other coatings exceeds the thickness of the base film 10, the flexibility of the composite diaphragm prepared is poor, and the coating is easy to fall off; and the difference in the thickness of the heat-resistant coating on both sides of the base film 10 is large, and the diaphragm is easy to curl, which causes the diaphragm to fail to effectively cover the pole piece, and there is a risk of short circuit. Industrial applicability

[0142] In summary, the present disclosure provides a composite diaphragm and a preparation method thereof and a battery. By forming a composite coating and a heat-resistant layer with a continuous phase on the surface of the base film, the film breaking temperature of the diaphragm can be improved, the risk of short circuit caused by the contact of the positive and negative electrodes due to the rupture of the diaphragm can be reduced, and the control of the thermal runaway of the battery is beneficial.

Claims

1. A composite separator, characterized by, The composite diaphragm comprises a base film, a composite coating layer arranged on one side of the base film, a heat-resistant layer arranged on the side of the base film away from the composite coating layer, and a bonding layer arranged on the side of the heat-resistant layer away from the base film. The material of the composite coating layer comprises a first heat-resistant material and a first diaphragm adhesive material.

2. The composite separator of claim 1, wherein The mass ratio of the first heat-resistant material to the first diaphragm adhesive material is 1:(1-10).

3. The composite separator according to claim 1 or 2, characterized in that, The composite coating layer has first micropores, and the pore size of the first micropores ranges from 50 nm to 600 nm.

4. The composite separator of claim 1, wherein The base film has a first thickness H1, the composite coating layer has a second thickness H2, the heat-resistant layer has a third thickness H3, and the bonding layer has a fourth thickness H4, and the following conditions are met: H1>H2+H3+H4, and H3 / H2<3.

5. The composite separator of claim 4, wherein, The first thickness H1 ranges from 3 um to 20 um; and / or, The second thickness H2 ranges from 0.5 um to 4 um; and / or, The third thickness H3 ranges from 1.2 um to 4.5 um; and / or, The fourth thickness H4 ranges from 0.5 um to 10 um.

6. The composite separator of claim 1, wherein The composite coating layer has a second thickness H2, the bonding layer has a fourth thickness H4, and the bonding layer has a coverage F on the heat-resistant layer, and the following condition is met: F=(0.5-1)×H2 / H4*%.

7. The composite separator of claim 6, wherein The bonding layer has a coverage F on the heat-resistant layer, and the coverage F ranges from 5% to 90%.

8. The composite separator of claim 1, wherein The base film has second micropores, and the porosity of the base film ranges from 25% to 70%.

9. The composite separator according to claim 1 or 8, wherein The base film has second micropores, and the ratio of the maximum pore size of the second micropores to the average pore size of the second micropores ranges from 1.3 to 3.

5.

10. The composite diaphragm according to claim 1, wherein The material of the base film is selected from polyethylene or polypropylene; and / or The first heat-resistant material is selected from at least one of nylon 66, aramid 1313, and aramid 1414; and / or The first diaphragm adhesive material is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, and hexafluoropropylene copolymer; and / or The material of the heat-resistant layer is selected from at least one of nylon 66, aramid 1313, and aramid 1414; and / or The material of the bonding layer is selected from at least one of polyvinylidene fluoride, polymethyl methacrylate, and polyacrylic acid.

11. A method of preparing a composite separator, characterized by, The method comprises: providing a base film; mixing a first heat-resistant material, a first diaphragm adhesive material, and a first solvent to obtain a first coating; applying the first coating on one side of the base film by oil coating to obtain a composite coating layer; mixing a second heat-resistant material and a second solvent to obtain a second coating; applying the second coating on the side of the base film away from the composite coating layer by oil coating to obtain a heat-resistant layer; applying a second diaphragm adhesive material on the side of the heat-resistant layer away from the base film by water coating to obtain a bonding layer.

12. The method of claim 11, wherein the composite separator is prepared by a method comprising: The mass ratio of the first heat-resistant material to the first diaphragm adhesive material is 1:(1-10).

13. A battery, characterized by The composite diaphragm comprises a base film, a composite coating layer arranged on one side of the base film, a heat-resistant layer arranged on the side of the base film away from the composite coating layer, and a bonding layer arranged on the side of the heat-resistant layer away from the base film. The composite diaphragm comprises a base film, a composite coating layer arranged on one side of the base film, a heat-resistant layer arranged on the side of the base film away from the composite coating layer, and a bonding layer arranged on the side of the heat-resistant layer away from the base film; The composite coating layer is attached to the positive electrode tab; The bonding layer is attached to the negative electrode tab.

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