Coating-transfer separator, and preparation method therefor and use thereof

Abstract

A coating-transfer separator, and a preparation method therefor and a use thereof. The coating-transfer separator comprises a substrate and a composite coating provided on at least one side of the substrate; the composite coating comprises a first coating and a second coating provided on the surface of the first coating; and when pressed, the composite coating can be transferred to a surface of a positive electrode sheet. The dry bonding force between the first coating and the substrate is F1, and the dry bonding force between the second coating and the positive electrode sheet is F2, wherein F1 and F2 satisfy the relation: F2 / F1≥1.0. The coating-transfer separator has good bonding force; in addition, the second oil-based coating comprised therein can be completely transferred to the surface of the positive electrode sheet, and can be completely retained on the surface of the positive electrode sheet when wetted by an electrolyte, thereby mitigating the risk of short circuits of secondary batteries.

Description

Coating transfer separator and preparation method and application thereof

[0001] Cross-reference to related applications

[0002] The present application claims priority to the Chinese patent application No. CN202411285986.1, filed on September 13, 2024, and entitled "Coating transfer separator and preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application belongs to the technical field of separator materials, and specifically relates to a coating transfer separator and a preparation method and application thereof. BACKGROUND

[0004] With the rapid development of secondary battery technology, the safety characteristics of secondary batteries are increasingly valued, and short circuit of the battery is one of the important reasons for battery failure, fire and even explosion. As one of the important components of secondary batteries, the separator not only prevents the direct contact of the positive and negative plates inside the battery, thereby avoiding the occurrence of short circuit phenomenon, but also allows ions to move between the positive and negative electrodes to realize the charging and discharging process of the battery. At the same time, the material, porosity and thermal stability of the separator have a direct impact on the electrochemical performance and safety of the secondary battery.

[0005] At present, the main raw material of the base film in the separator is polyethylene or polypropylene. The thermal deformation temperature of the above polyolefin material is low, and when the temperature is too high, the base film is easy to shrink, which eventually causes the thermal shrinkage of the separator to be serious, inducing the short circuit of the positive and negative electrodes in the secondary battery, and further causing the thermal runaway phenomenon of the secondary battery. In order to solve the above problems, researchers usually coat a layer of high-temperature resistant coating material on the surface of the separator, which can improve the thermal shrinkage performance of the separator, and at the same time can improve the puncture strength of the separator to prevent lithium dendrite from being pierced, thereby improving the safety of the secondary battery. However, although the above coating separator disclosed in the prior art can reduce the short circuit risk of the secondary battery to a certain extent, the coating is mostly water-based. Since the separator itself has lipophilicity, water-based coating may cause the uniformity and adhesion of the product to decrease, thereby affecting the quality of the water-based coating and the performance of the battery. In addition, the water-based coating is easy to fall off under the wetting of the electrolyte, so the short circuit risk of the secondary battery cannot be avoided.

[0006] Therefore, in the art, there is an urgent need to develop a separator material to solve the above technical problems.

[0007] SUMMARY

[0008] Therefore, the present application aims to provide a coating transfer separator, a preparation method and application thereof. The coating transfer separator provided by the present application not only has good adhesion, but also the second oil-based coating can be completely transferred to the surface of the positive electrode sheet and can remain intact on the surface of the positive electrode sheet after being soaked in electrolyte, thereby improving the short circuit risk of the secondary battery.

[0009] In a first aspect, the present application provides a coating transfer separator, comprising a substrate and a composite coating arranged on at least one side of the substrate, wherein the composite coating comprises a first coating and a second coating arranged on the surface of the first coating, and the composite coating can be transferred to the surface of the positive electrode sheet after pressing treatment.

[0010] The dry adhesion between the first coating and the substrate is F1, and the dry adhesion between the second coating and the positive electrode sheet is F2, and the relationship between F1 and F2 satisfies F2 / F1≥1.0, for example, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, etc.

[0011] It should be particularly noted that the dry adhesion refers to the adhesion obtained in a dry state, i.e., without using liquid medium. The test conditions of the dry adhesion include testing according to the GB / T363363-2018 standard. In addition, the first coating is arranged on the surface of at least one side of the substrate, and the second coating is arranged on the surface of the first coating away from the substrate.

[0012] Beneficial effects: The coating transfer separator provided by the present application has good adhesion, and further regulates the dry adhesion between the first coating and the substrate and the dry adhesion between the second coating and the positive electrode sheet, so that the adhesion of the second coating is improved, and the adhesion of the first coating is reduced, so that the composite coating can be completely transferred to the surface of the positive electrode sheet after heat pressing treatment, and the second coating can remain intact on the surface of the positive electrode sheet after being soaked in electrolyte. Therefore, even if the separator shrinks at high temperature, the secondary battery will not short circuit due to direct contact between the positive and negative electrodes, thereby improving the safety performance of the secondary battery. Compared with the water-based coating separator disclosed in the prior art, the second oil-based coating provided by the present application has higher adhesion and is not easy to fall off after being soaked in electrolyte, so it can be well attached to the surface of the positive electrode sheet. In addition, the composite coating provided by the present application has high ionic conductivity, which can reduce the electrolyte injection amount, thereby reducing the fire risk of the secondary battery.

[0013] In an alternative embodiment, the relationship between F1 and F2 satisfies: 1.4≤F2 / F1≤8.0, for example, it can be 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 7.8, etc.

[0014] Beneficial effects: By regulating the relationship between F1 and F2, the composite coating can be transferred to the surface of the positive electrode sheet after hot pressing, and after the composite coating is transferred to the surface of the positive electrode sheet, the composite coating can still remain on the surface of the positive electrode sheet even in the case of serious shrinkage of the separator at high temperature, thereby preventing the direct contact and short circuit of the positive and negative electrodes, and improving the safety performance of the secondary battery.

[0015] In an alternative embodiment, the value of F1 ranges from 10 N / m to 30 N / m, preferably from 15 N / m to 25 N / m, for example, it can be 10 N / m, 12 N / m, 15 N / m, 18 N / m, 20 N / m, 22 N / m, 25 N / m, 28 N / m, 30 N / m, etc.

[0016] In an alternative embodiment, the value of F2 ranges from 30 N / m to 80 N / m, preferably from 35 N / m to 70 N / m, for example, it can be 30 N / m, 32 N / m, 35 N / m, 38 N / m, 40 N / m, 42 N / m, 45 N / m, 48 N / m, 50 N / m, 52 N / m, 55 N / m, 58 N / m, 60 N / m, 62 N / m, 65 N / m, 68 N / m, 70 N / m, 72 N / m, 75 N / m, 78 N / m, 80 N / m, etc.

[0017] In an alternative embodiment, the thickness of the substrate is H1, the thickness of the first coating is H2, and the thickness of the second coating is H3, and the relationship between H1, H2 and H3 satisfies: 0.7≤H1 / (H2+H3)≤10, preferably 1≤H1 / (H2+H3)≤8, for example, it can be 0.7, 0.8, 1, 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, etc.

[0018] Beneficial effects: By regulating the relationship between H1, H2 and H3, the thermal shrinkage rate of the coating transfer separator at high temperature is small, thereby further improving the safety performance of the secondary battery.

[0019] In an alternative embodiment, the value of H1 ranges from 5 μm to 20 μm, preferably from 5 μm to 16 μm, for example, it can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, 18 μm, 20 μm, etc.

[0020] In an alternative embodiment, the H2 is in the range of 1 μm to 4 μm, preferably in the range of 1 μm to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, etc.

[0021] In an alternative embodiment, the H3 is in the range of 1 μm to 3 μm, preferably in the range of 1 μm to 2 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc.

[0022] In an alternative embodiment, the material in the first coating layer comprises a semi-solid material, an ion-conductive material, and a heat-resistant material.

[0023] In an alternative embodiment, the mass ratio of the semi-solid material, the ion-conductive material, and the heat-resistant material is (2-5):(90-95):(2-5), for example, 2:90:2, 2:91:2, 2:92:3, 3:93:3, 4:94:5, 5:94:5, 2:95:3, 3:94:4, 5:95:5, etc.

[0024] In an alternative embodiment, the semi-solid material comprises at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium oxide, or lithium lanthanum zirconium titanium oxide.

[0025] In an alternative embodiment, the average particle size of the semi-solid material is in the range of 0.5 μm to 1.0 μm, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, etc.

[0026] In an alternative embodiment, the ion conductivity of the semi-solid material is in the range of 10 -3 S / cm to 10 -4 S / cm, for example, 10 -3 S / cm, 9x10 -4 S / cm, 8x10 -4 S / cm, 7x10 -4 S / cm, 6x10 -4 S / cm, 5x10 -4 S / cm, 4x10 -4 S / cm, 3x10 -4 S / cm, 2x10 -4 S / cm, 1x10 -4 S / cm, etc.

[0027] In an alternative embodiment, the ion-conductive material comprises molybdenum disulfide and / or a metal organic framework compound.

[0028] In an alternative embodiment, the metal organic framework compound illustratively comprises at least one of a Zn-based metal organic framework (MOF), a Ni-based MOF, a Fe-based MOF, or a Co-based MOF.

[0029] In an alternative embodiment, the ion conductivity of the ion conducting material is 10 -3 S / cm to 10 -4 S / cm, for example, can be 10 -3 S / cm, 9 x 10 -4 S / cm, 8 x 10 -4 S / cm, 7 x 10 -4 S / cm, 6 x 10 -4 S / cm, 5 x 10 -4 S / cm, 4 x 10 -4 S / cm, 3 x 10 -4 S / cm, 2 x 10 -4 S / cm, 1 x 10 -4 S / cm, etc.

[0030] In an alternative embodiment, the heat resistant material comprises a silicide.

[0031] In an alternative embodiment, the silicide comprises at least one of molybdenum silicide, titanium silicide, or nickel silicide.

[0032] In an alternative embodiment, the average particle size of the heat resistant material is 0.5 μm to 1.8 μm, for example, can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, etc.

[0033] In an alternative embodiment, the material of the first coating further comprises a first binder material, which illustratively comprises at least one of a polyacrylic binder, a polyacrylonitrile binder, or a polyacrylamide binder.

[0034] In an alternative embodiment, the material of the second coating comprises an oil-based polymer.

[0035] In an alternative embodiment, the oil-based polymer comprises polyolefin microspheres and / or hydrogenated nitrile butadiene rubber.

[0036] In an alternative embodiment, the material of the substrate is a high temperature resistant substrate material, for example, can be at least one of aramid or polyimide.

[0037] In a second aspect, the present application provides a method for preparing the coating transfer separator according to the first aspect, the method comprising the following steps:

[0038] mixing the material of the first coating layer and the first solvent to prepare a first coating layer slurry; coating the first coating layer slurry on at least one side of the substrate once, and obtaining the first coating layer after drying;

[0039] mixing the material of the second coating layer and the second solvent to prepare a second coating layer slurry; coating the second coating layer slurry on the surface of the first coating layer twice, and obtaining the coating transfer separator after drying.

[0040] In an optional embodiment, the first solvent comprises water.

[0041] In an optional embodiment, the coating mode of the first coating layer comprises gravure transfer coating.

[0042] In an optional embodiment, the areal density of the first coating layer is 2.8 g / m 2 ~ 5.6 g / m 2 , for example, it can be 2.8 g / m 2 , 3 g / m 2 , 3.2 g / m 2 , 3.5 g / m 2 , 3.8 g / m 2 , 4 g / m 2 , 4.2 g / m 2 , 4.5 g / m 2 , 4.8 g / m 2 , 5 g / m 2 , 5.2 g / m 2 , 5.4 g / m 2 , 5.6 g / m 2 , etc.

[0043] In an optional embodiment, the second solvent comprises at least one of N-methyl pyrrolidone or N,N-dimethylacetamide.

[0044] In an optional embodiment, the coating mode of the second coating layer comprises at least one of roll coating or spraying.

[0045] In an optional embodiment, the areal density of the second coating layer is 0.3 g / m 2 ~ 0.5 g / m 2 , for example, it can be 3 g / m 2 , 3.2 g / m 2 , 3.5 g / m 2 , 3.8 g / m 2 , 4 g / m 2 , 4.2 g / m 2 , 4.5 g / m 2 , 4.8 g / m2 5g / m 2 etc.

[0046] In a third aspect, the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the separator comprises the coating transfer separator according to the first aspect.

[0047] In a fourth aspect, the present application provides a method for preparing the secondary battery according to the third aspect, comprising the following steps:

[0048] The positive electrode sheet, the negative electrode sheet, and the coating transfer separator are compounded and subjected to a hot-pressing treatment, the compound coating is in-situ transferred to the surface of the positive electrode sheet by the pressure during the hot-pressing treatment, and the secondary battery is obtained after injecting the electrolyte.

[0049] In an optional embodiment, the compounding process comprises a hot-compound lamination process.

[0050] In an optional embodiment, the hot-compound lamination process comprises the following steps: firstly, the coating transfer separator and the negative electrode sheet are subjected to a hot-roller lamination and bonding, and then the negative electrode sheet is coated with the sandwich structure of the upper and lower two layers of the coating transfer separator after being cut; and secondly, the material of the sandwich structure of the negative electrode sheet coated with the upper and lower two layers of the coating transfer separator is laminated with the positive electrode to form an electrode group.

[0051] In an optional embodiment, the temperature of the hot-roller lamination and bonding is 70-120°C, for example, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, etc.; the pressure is 0.3-0.55Mpa, for example, 0.3Mpa, 0.35Mpa, 0.4Mpa, 0.45Mpa, 0.5Mpa, 0.55Mpa, etc.; and the efficiency is 30-90%, for example, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.

[0052] In an optional embodiment, the cutting temperature is 170-290°C, for example, 170°C, 190°C, 200°C, 220°C, 250°C, 280°C, 290°C, etc.

[0053] In an optional embodiment, the temperature of the hot-pressing treatment is 90-105°C, for example, 90°C, 92°C, 95°C, 98°C, 100°C, 105°C, etc.; and the time is 60s. DETAILED DESCRIPTION

[0054] Embodiments of the present application are described below in the detailed description and illustrated in the accompanying drawings by using examples. Identical or similar elements or elements having identical or similar functions are denoted throughout the drawings by the same reference numerals, and a description of the same will not be repeated. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0055] The following disclosure provides many different embodiments, or examples, for implementing different structures of the present application. For the purpose of simplicity, the elements and settings of the specific examples in the following are described. Of course, they are only examples and are not intended to limit the present application. In addition, reference numerals and / or letters can be repeated in different examples in the present application. Such repetition is for the purpose of simplification and clarity, and does not indicate a relationship between the various embodiments and / or settings being discussed. In addition, the present application provides examples of various specific processes and materials, but those of ordinary skill in the art can realize the applicability of other processes and / or the use of other materials.

[0056] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0057] The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0058] Example 1

[0059] The present embodiment provides a coating transfer separator, which comprises an aramid substrate and a composite coating arranged on both sides of the aramid substrate, the composite coating comprising a first coating and a second coating arranged on the surface of the first coating, and the composite coating can be transferred to the surface of the positive electrode sheet after heat pressing treatment.

[0060] In the present embodiment, the dry adhesion between the first coating and the aramid substrate is F1, the value of F1 is 20 N / m; the dry adhesion between the second coating and the positive electrode sheet is F2, the value of F2 is 55 N / m; the relationship between F1 and F2 satisfies F2 / F1 = 2.75. The thickness of the aramid substrate is H1, the value of H1 is 12 μm; the thickness of the first coating is H2, the value of H2 is 2 μm; the thickness of the second coating is H3, the value of H3 is 2 μm; the relationship between H1, H2 and H3 satisfies H1 / (H2+H3) = 3.

[0061] The present embodiment also provides a preparation method of the coating transfer separator, which comprises the following steps:

[0062] Titanium aluminum lithium phosphate (average particle size 0.7 μm, ionic conductivity 1.3 x 10 -4 S / cm), molybdenum disulfide (ionic conductivity 1.1 x 10-4 S / cm) and flaky molybdenum silicide (average particle size 1.1 μm) are mixed with a polyacrylic binder material and water to prepare a first coating slurry; the first coating slurry is coated on both sides of the aramid substrate using gravure transfer coating, with a surface density of 4.2 g / m 2 , to obtain the first coating after drying;

[0063] Polyolefin microspheres with a weight average molecular weight of 50W are mixed with N-methyl pyrrolidone solvent to prepare a second coating slurry; the second coating slurry is twice roll-coated on the surface of the first coating, with a surface density of 0.4 g / m 2 , to obtain the coating transfer separator after drying.

[0064] Example 2

[0065] The present embodiment provides a coating transfer separator, which comprises an aramid substrate and a composite coating arranged on both sides of the aramid substrate, the composite coating comprising a first coating and a second coating arranged on the surface of the first coating, and the composite coating being capable of being transferred to the surface of a positive electrode sheet after heat pressing treatment.

[0066] The dry adhesion between the first coating and the aramid substrate is F1, the value of F1 being 15 N / m; the dry adhesion between the second coating and the positive electrode sheet is F2, the value of F2 being 35 N / m; the relationship between F1 and F2 satisfies F2 / F1 = 2.3. The thickness of the aramid substrate is H1, the value of H1 being 16 μm; the thickness of the first coating is H2, the value of H2 being 3 μm; the thickness of the second coating is H3, the value of H3 being 1 μm; the relationship between H1, H2 and H3 satisfies H1 / (H2+H3) = 4.

[0067] The present embodiment also provides a preparation method of the above coating transfer separator, which comprises the following steps:

[0068] Titanium aluminum lithium phosphate (average particle size 0.6 μm, ionic conductivity 1.3 x 10 -4 S / cm), molybdenum disulfide (ionic conductivity 1.1 x 10 -4 S / cm) and flaky molybdenum silicide (average particle size 0.9 μm) are mixed with a polyacrylic binder material and water to prepare a first coating slurry; the first coating slurry is coated on both sides of the aramid substrate using gravure transfer coating, with a surface density of 3.5 g / m 2 , to obtain the first coating after drying;

[0069] The polyolefin microspheres with a weight average molecular weight of 35W are mixed with N-methyl pyrrolidone solvent to prepare a second coating slurry; the second coating slurry is secondarily roll-coated on the surface of the first coating, and the surface density of the coating is 0.35 g / m 2 After drying, the coating transfer separator is obtained.

[0070] Example 3

[0071] The present embodiment provides a coating transfer separator, which comprises an aramid substrate and a composite coating arranged on both sides of the aramid substrate, the composite coating comprising a first coating and a second coating arranged on the surface of the first coating, and the composite coating can be transferred to the surface of the positive electrode sheet after heat pressing treatment.

[0072] The dry adhesion between the first coating and the aramid substrate is F1, and the value of F1 is 25 N / m; the dry adhesion between the second coating and the positive electrode sheet is F2, and the value of F2 is 70 N / m; the relationship between F1 and F2 satisfies F2 / F1 = 2.8. The thickness of the aramid substrate is H1, and the value of H1 is 7 μm; the thickness of the first coating is H2, and the value of H2 is 1 μm; the thickness of the second coating is H3, and the value of H3 is 2 μm; the relationship between H1, H2 and H3 satisfies H1 / (H2+H3) = 2.3.

[0073] The present embodiment also provides a preparation method of the above-mentioned coating transfer separator, which comprises the following steps:

[0074] Titanium aluminum lithium phosphate (average particle size 0.8 μm, ionic conductivity 1.3 x 10 -4 S / cm), molybdenum disulfide (ionic conductivity 1.1 x 10 -4 S / cm) and sheet molybdenum silicide (average particle size 1.2 μm) are mixed with polyacrylic acid binder material and water to prepare a first coating slurry; the first coating slurry is transferred and coated on both sides of the aramid substrate by gravure transfer, and the surface density of the coating is 4.9 g / m 2 After drying, the first coating is obtained.

[0075] The polyolefin microspheres with a weight average molecular weight of 35W are mixed with N-methyl pyrrolidone solvent to prepare a second coating slurry; the second coating slurry is secondarily roll-coated on the surface of the first coating, and the surface density of the coating is 0.35 g / m 2 After drying, the coating transfer separator is obtained.

[0076] Example 4

[0077] The embodiment provides a coating transfer diaphragm, the coating transfer diaphragm comprising an aramid base material and a composite coating arranged on both sides of the aramid base material, the composite coating comprising a first coating and a second coating arranged on the surface of the first coating, and the composite coating being capable of being transferred to the surface of a positive plate after heat pressing treatment.

[0078] The dry adhesion between the first coating and the aramid base material is F1, the value of F1 being 10 N / m; the dry adhesion between the second coating and the positive plate is F2, the value of F2 being 30 N / m; the relationship between F1 and F2 satisfies F2 / F1=3. The thickness of the aramid base material is H1, the value of H1 being 5 microns; the thickness of the first coating is H2, the value of H2 being 1 micron; the thickness of the second coating is H3, the value of H3 being 1 micron; the relationship between H1, H2 and H3 satisfies H1 / (H2+H3)=2.5.

[0079] The embodiment also provides a preparation method of the coating transfer diaphragm, the preparation method comprising the following steps:

[0080] Lithium lanthanum zirconium oxide (average particle size 0.5 microns, ionic conductivity 1*10 -4 S / cm), molybdenum disulfide (ionic conductivity 1*10 -4 S / cm) and cubic nickel silicide (average particle size 0.5 microns) are mixed with a polyacrylic acid binder material and water to prepare a first coating slurry; the first coating slurry is coated on both sides of the aramid base material by gravure transfer coating, the face density of the coating being 3.0 g / m 2 , and the first coating is obtained after drying;

[0081] Hydrogenated butyl nitrile rubber with a weight average molecular weight of 20W is mixed with an N-methyl pyrrolidone solvent to prepare a second coating slurry; the second coating slurry is secondarily roll-coated on the surface of the first coating, the face density of the coating being 0.3 g / m 2 , and the coating transfer diaphragm is obtained after drying.

[0082] Embodiment 5

[0083] The embodiment provides a coating transfer diaphragm, the coating transfer diaphragm comprising an aramid base material and a composite coating arranged on both sides of the aramid base material, the composite coating comprising a first coating and a second coating arranged on the surface of the first coating, and the composite coating being capable of being transferred to the surface of a positive plate after heat pressing treatment.

[0084] The dry adhesion between the first coating layer and the aramid substrate is F1, and the value of F1 is 30 N / m; the dry adhesion between the second coating layer and the positive plate is F2, and the value of F2 is 80 N / m; the relationship between F1 and F2 satisfies F2 / F1 = 2.67. The thickness of the aramid substrate is H1, and the value of H1 is 20 μm; the thickness of the first coating layer is H2, and the value of H2 is 4 μm; the thickness of the second coating layer is H3, and the value of H3 is 3 μm; the relationship between H1, H2 and H3 satisfies H1 / (H2+H3) = 2.86.

[0085] The present embodiment also provides a preparation method of the coating transfer separator membrane, and the preparation method comprises the following steps:

[0086] Lithium lanthanum zirconium oxide (average particle size 1.0 μm, ionic conductivity 1×10 -3 S / cm), molybdenum disulfide (ionic conductivity 1×10 -3 S / cm) and cubic nickel silicide (average particle size 1.8 μm) are mixed with a polyacrylic acid binder material and water to prepare a first coating layer slurry; the first coating layer slurry is coated on both sides of the aramid substrate by gravure transfer coating, and the surface density of the coating is 5.6 g / m 2 After drying, the first coating layer is obtained;

[0087] Hydrogenated nitrile rubber with a weight average molecular weight of 60W is mixed with an N-methyl pyrrolidone solvent to prepare a second coating layer slurry; the second coating layer slurry is roll-coated on the surface of the first coating layer, and the surface density of the coating is 0.5 g / m 2 After drying, the coating transfer separator membrane is obtained.

[0088] Example 6

[0089] The difference between the present embodiment and example 1 is that the dry adhesion between the first coating layer and the aramid substrate is F1, and the value of F1 is 20 N / m; the dry adhesion between the second coating layer and the positive plate is F2, and the value of F2 is 30 N / m; the relationship between F1 and F2 satisfies F2 / F1 = 1.5, and the others are the same as example 1.

[0090] Example 7

[0091] The difference between the present embodiment and example 1 is that the dry adhesion between the first coating layer and the aramid substrate is F1, and the value of F1 is 10 N / m; the dry adhesion between the second coating layer and the positive plate is F2, and the value of F2 is 100 N / m; the relationship between F1 and F2 satisfies F2 / F1 = 10.0, and the others are the same as example 1.

[0092] Example 8

[0093] The difference between this embodiment and embodiment 1 is that H1 is 10 μm, H2 is 10 μm, H3 is 10 μm, the relationship between H1, H2 and H3 satisfies H1 / (H2+H3) = 0.5, and the others are the same as embodiment 1.

[0094] Example 9

[0095] The difference between this embodiment and embodiment 1 is that H1 is 15 μm, H2 is 0.5 μm, H3 is 0.5 μm, the relationship between H1, H2 and H3 satisfies H1 / (H2+H3) = 15, and the others are the same as embodiment 1.

[0096] Example 10

[0097] The difference between this embodiment and embodiment 1 is that the first coating layer does not add molybdenum silicide, and the others are the same as embodiment 1.

[0098] Example 11

[0099] The difference between this embodiment and embodiment 1 is that the second coating layer replaces the polyolefin microspheres with equal mass of polyacrylic acid, and the others are the same as embodiment 1.

[0100] Comparative Example 1

[0101] The difference between this comparative example and embodiment 1 is that the coating transfer separator does not have a first coating layer, and the others are the same as embodiment 1.

[0102] Comparative Example 2

[0103] The difference between this comparative example and embodiment 1 is that the coating transfer separator does not have a second coating layer, and the others are the same as embodiment 1.

[0104] Comparative Example 3

[0105] The difference between this comparative example and embodiment 1 is that the dry adhesion between the first coating layer and the aramid substrate is F1, the value of F1 is 20 N / m; the dry adhesion between the second coating layer and the positive electrode sheet is F2, the value of F2 is 10 N / m; the relationship between F1 and F2 satisfies F2 / F1 = 0.5, and the others are the same as embodiment 1.

[0106] Test conditions

[0107] The coating transfer separators provided by embodiment 1 and the prior art were assembled into lithium ion batteries and tested for performance, and the test method was as follows:

[0108] The coating transfer separator provided by the prior art and the coating transfer separator of Example 1 were transferred to the negative electrode sheet by hot-rolling to form a continuous coating transfer separator-negative electrode sheet-coating transfer separator sandwich structure composite sheet, and the continuous composite sheet was cut into independent composite units by a hot cutter, wherein the composite temperature was 95°C, the composite pressure was 45 MPa, the composite efficiency was 60%, and the hot cutter temperature was 230°C. Finally, the composite units and the positive electrode sheet were stacked into a cell group, and the cell group was subjected to hot-pressing treatment at 100°C. The cell group was disassembled after the hot-pressing treatment to observe the transfer of the composite coating to the surface of the positive electrode sheet. One cell group was immersed in electrolyte for 24 hours, and the cell group was disassembled to observe the transfer of the coating to the surface of the positive electrode sheet. The water-based gel layer separator with the same structure in the prior art was used as a comparison to verify the test results, as shown in Table 1.

[0109] Table 1

[0110] As can be seen from Table 1, the coating of the water-based coating transfer separator used in the prior art and the oil-based coating transfer separator provided by the present application can be completely transferred to the surface of the positive electrode sheet after hot-pressing treatment. However, only the second coating of the oil-based coating transfer separator provided by the present application can be completely retained on the surface of the positive electrode sheet after the cell group is immersed in electrolyte for 24 hours, and no water-based separator coating can be observed on the surface of the positive electrode sheet. This further indicates that the wet adhesion effect of the oil-based coating transfer separator provided by the present application is better than that of the water-based coating separator, and meets the transfer requirements.

[0111] The lithium ion battery obtained after hot-pressing treatment was placed in an oven for high-temperature baking test. The battery was first tested for short circuit after baking, and then disassembled to observe the shrinkage of the separator. The water-based coating transfer separator battery was used as a comparison to verify the test results, as shown in Table 2.

[0112] Table 2

[0113] As can be seen from Table 2, after baking at 150°C, 180°C and 200°C for 1 hour, the water-based coating transfer separator used in the prior art has a serious thermal shrinkage phenomenon, while the oil-based coating transfer separator provided by the present application only has a slight shrinkage. Moreover, the coating of the oil-based transfer separator can still be completely retained on the surface of the positive electrode sheet after being wetted by the electrolyte, so the lithium ion battery does not have a short circuit. This further indicates that the oil-based coating transfer separator provided by the present application has better safety characteristics than the water-based coating transfer separator.

[0114] Although embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made thereto without departing from the principles and spirit of the present application, and the scope of the present application is defined by the claims and their equivalents. Industrial applicability

[0115] The coating transfer separator provided by the application has good adhesion, and further regulates the dry adhesion between the first coating and the substrate and the dry adhesion between the second coating and the positive electrode sheet, so that the adhesion of the second coating is improved, and the adhesion of the first coating is reduced, so that after heat pressing treatment, the composite coating can be completely transferred to the surface of the positive electrode sheet, and after soaking in electrolyte, the second coating can still be completely retained on the surface of the positive electrode sheet. Therefore, even if the separator shrinks at high temperature, the secondary battery will not short circuit due to the direct contact between the positive and negative electrodes, thereby improving the safety performance of the secondary battery.

Claims

1. A coating transfer septum characterized in that, The coating transfer separator film comprises a substrate and a composite coating arranged on at least one side of the substrate, the composite coating comprises a first coating and a second coating arranged on the surface of the first coating, and the composite coating can be transferred to the surface of the positive electrode sheet after a pressing process; The dry adhesion between the first coating and the substrate is F1, the dry adhesion between the second coating and the positive electrode sheet is F2, and the relationship between F1 and F2 satisfies F2 / F1≥1.

0.

2. The coating transfer septum of claim 1, wherein, The relationship between F1 and F2 satisfies 1.4≤F2 / F1≤8.0; Preferably, the value range of F1 is 10N / m-30N / m, preferably 15N / m-25N / m; Preferably, the value range of F2 is 30N / m-80N / m, preferably 35N / m-70N / m.

3. The coating transfer septum of claim 1 or 2, wherein, The thickness of the substrate is H1, the thickness of the first coating is H2, and the thickness of the second coating is H3, and the relationship between H1, H2 and H3 satisfies 0.7≤H1 / (H2+H3)≤10, preferably 1≤H1 / (H2+H3)≤8; Preferably, the value range of H1 is 5μm-20μm, preferably 5μm-16μm; Preferably, the value range of H2 is 1μm-4μm, preferably 1μm-3μm; Preferably, the value range of H3 is 1μm-3μm, preferably 1μm-2μm.

4. The coating transfer septum of any one of claims 1-3, wherein, The material in the first coating comprises a semi-solid material, an ion-conducting material and a heat-resistant material; Preferably, the mass ratio of the semi-solid material, the ion-conducting material and the heat-resistant material is (2-5):(90-95):(2-5); Preferably, the semi-solid material comprises at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide or lithium lanthanum zirconium titanium oxide; Preferably, the average particle size of the semi-solid material is 0.5μm-1.0μm; Preferably, the ionic conductivity of the semi-solid material is 10 -3 S / cm ~ 10 -4 S / cm; Preferably, the ion-conducting material comprises molybdenum disulfide and / or metal organic framework compounds; Preferably, the ionic conductivity of the ionically conductive material is 10 -3 S / cm to 10 -4 S / cm; Preferably, the heat-resistant material comprises a silicide; Preferably, the silicide comprises at least one of molybdenum silicide, titanium silicide or nickel silicide; Preferably, the average particle size of the heat-resistant material is 0.5μm-1.8μm; Preferably, the material of the first coating further comprises a first binder material.

5. The coating transfer septum of any one of claims 1-4, wherein, The material of the second coating comprises an oil-based polymer; Preferably, the oil-based polymer comprises polyolefin microspheres and / or hydrogenated nitrile rubber.

6. A method of making a coating transfer separator according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: Mixing the material of the first coating and a first solvent to prepare a first coating slurry; coating the first coating slurry on at least one side of the substrate once, and drying to obtain the first coating; Mixing the material of the second coating and a second solvent to prepare a second coating slurry; coating the second coating slurry on the surface of the first coating twice, and drying to obtain the coating transfer separator film.

7. The method of claim 6, wherein, The first solvent comprises water; Preferably, the mode of the first coating comprises gravure transfer coating; Preferably, the areal density of the primary coating is 2.8 g / m 2 ~ 5.6 g / m 2 ; Preferably, the second solvent comprises at least one of N-methyl pyrrolidone or N,N-dimethylacetamide; Preferably, the secondary coating method comprises at least one of roll coating or spray coating; Preferably, the areal density of the secondary coating is 0.3 g / m 2 ~ 0.5 g / m 2 .

8. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the separator comprises the coating transfer separator according to any one of claims 1-5.

9. A method of manufacturing the secondary battery according to claim 8, characterized by, The method comprises the following steps: The positive electrode sheet, the negative electrode sheet, and the coating transfer separator are compounded and subjected to hot pressing treatment, the coating is in-situ transferred to the surface of the positive electrode sheet by the pressure in the hot pressing treatment process, and the secondary battery is obtained after electrolyte injection.

10. The method of claim 9, wherein, The compounding process comprises a hot compounding lamination process; Preferably, the hot compounding lamination process comprises the following steps: firstly, the coating transfer separator and the negative electrode sheet are subjected to hot roller pressing and bonding; secondly, the sandwich structure of the negative electrode sheet coated with the upper and lower two layers of coating transfer separators is formed after slitting; and thirdly, the material of the sandwich structure of the negative electrode sheet coated with the upper and lower two layers of coating transfer separators is laminated with the positive electrode sheet to form a pole group. Preferably, the temperature of the hot roller pressing and bonding is 70-120°C, the pressure is 0.3-0.55 Mpa, and the efficiency is 30-90%. Preferably, the temperature of the slitting is 170-290°C. Preferably, the temperature of the hot pressing treatment is 90-105°C, and the time is 60 s.

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