Separator, preparation method therefor, and use thereof

Abstract

A separator (3), a preparation method therefor, and a use thereof. The separator (3) comprises a base film (31), and an adhesive layer (32) present on the surface of at least one side of the base film (31). The adhesive layer (32) comprises an organic matrix material, the organic matrix material containing polar groups; and the molar content of the polar groups in the organic matrix material is greater than or equal to 3%.

Description

A diaphragm and its preparation method and application TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a diaphragm and its preparation method and application. BACKGROUND

[0002] A battery is a common electrochemical energy storage device, which is widely used in 3C digital electronic products, smart wearable devices and other electronic products. Generally, a battery includes a diaphragm and electrode sheets (positive electrode sheet and negative electrode sheet), and the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet to avoid short circuit caused by contact between the positive electrode sheet and the negative electrode sheet. Among them, ensuring the adhesion between the diaphragm and the electrode sheet and improving the structural stability of the battery cell formed by the positive electrode sheet, the diaphragm and the negative electrode sheet are of great significance to the performance of the battery cycle stability.

[0003] However, in the related art, the adhesion between the diaphragm and the electrode sheet is poor, which is usually manifested as poor dry-state adhesion and poor wet-state adhesion after electrolyte immersion. Specifically, the dry-state adhesion between the diaphragm and the electrode sheet is poor, which is not conducive to the adhesion and assembly between the electrode sheet and the diaphragm during the preparation of the battery, affecting the production efficiency and yield of the battery. Although coating the surface of the base film of the diaphragm with an adhesive resin can improve the dry-state adhesion between the diaphragm and the electrode sheet to some extent, the improvement effect is still limited, and there is electrolyte in the battery. After the electrolyte is immersed, the interfacial adhesion between the polymer (such as the above-mentioned adhesive resin) in the diaphragm and the electrode sheet decreases or even disappears (i.e. the wet-state adhesion between the diaphragm and the electrode sheet after the electrolyte is immersed is basically zero), which is not conducive to the performance of the battery cycle stability (for example, after long-term cycle charging, the interface between the diaphragm and the electrode sheet is prone to dislocation, which causes the shuttling of active ions (such as lithium ions) to be blocked, thereby affecting the cycle stability and capacity retention rate of the battery after cycling, etc.).

[0004] Therefore, how to improve the adhesion between the diaphragm and the electrode sheet in the battery, especially to improve the dry-state adhesion and the wet-state adhesion after the electrolyte is immersed, is still a technical problem to be solved by those skilled in the art.

[0005] SUMMARY

[0006] The present application provides a diaphragm and its preparation method and application, which can improve the adhesion between the diaphragm and the electrode sheet, especially to improve the dry-state adhesion and the wet-state adhesion after the electrolyte is immersed, and effectively overcome the defects existing in the prior art.

[0007] According to an aspect of the present application, there is provided a separator including a base film, and an adhesive layer present on at least one side surface of the base film; the adhesive layer includes an organic matrix material, the organic matrix material containing a polar group; the molar content of the polar group in the organic matrix material is greater than or equal to 3%.

[0008] According to an embodiment of the present application, the molar content of the polar group in the organic matrix material is 3% to 40%.

[0009] According to an embodiment of the present application, the organic matrix material contains one or more of a carboxyl group, an acrylate group, a cyano group, a carbonyl group, a sulfonic acid group, a siloxane group, a mercapto group, an ether bond, a sulfone group, an amide group.

[0010] According to an embodiment of the present application, the organic matrix material contains an imide group, and the molar content of the imide group in the organic matrix material is 3% to 15%.

[0011] According to an embodiment of the present application, the organic matrix material includes one or more of a polyamide-imide, a carbonyl-type polyimide, a bismaleimide polymer, a polyetherimide sulfone, a carboxylic acid-type polyimide, a modified polyimide, a polyesterimide, a polyetherimide, a polyacrylonitrile; preferably, the modified polyimide includes one or more of a cyano-modified polyimide, a mercapto-modified polyimide, a sulfonic acid group-modified polyimide, a siloxane group-modified polyimide.

[0012] According to an embodiment of the present application, the mass content of the organic matrix material in the adhesive layer is 30% to 100%.

[0013] According to an embodiment of the present application, the adhesive layer further includes one or more of a ceramic particle, a co-adhesive, a wetting agent; preferably, in the adhesive layer, the mass content of the ceramic particle is 0 to 70%, preferably 30% to 65%; preferably, in the adhesive layer, the mass content of the co-adhesive is 0 to 50%, preferably 2% to 25%; preferably, in the adhesive layer, the mass content of the wetting agent is 0.01% to 0.5%; preferably, the ceramic particle includes one or more of alumina, boehmite, silica, magnesium oxide, titanium dioxide; preferably, the co-adhesive includes a polyvinylidene fluoride homopolymer and / or a polyvinylidene fluoride-hexafluoropropylene copolymer; preferably, the wetting agent includes an alkylammonium salt of an organosilicon polymer and / or an acid group-containing copolymer.

[0014] According to an embodiment of the present application, the glass transition temperature of the organic matrix material is 148 to 158°C.

[0015] According to an embodiment of the present application, the thickness of the adhesive layer is 0.5-3 μm. According to another aspect of the present application, there is provided a slurry for forming the adhesive layer of the separator, comprising a solvent, the organic matrix material, ceramic particles, a co-binder and a wetting agent, wherein the mass fraction of the organic matrix material is 30-100%, the mass fraction of the co-binder is 0-50%, the mass fraction of the ceramic particles is 0-70%, and the mass fraction of the wetting agent is 0.01-0.5%, based on the total mass of the organic matrix material, the ceramic particles, the co-binder and the wetting agent.

[0016] According to an embodiment of the present application, the mass fraction of the co-binder is 2-25%, based on the total mass of the organic matrix material, the ceramic particles, the co-binder and the wetting agent.

[0017] According to an embodiment of the present application, the solvent comprises one or more of acetone, N-methyl pyrrolidone and dimethylacetamide; and / or, in the slurry, the mass content of the solvent is 70-90%.

[0018] According to an embodiment of the present application, the slurry further comprises a pore-expanding agent; preferably, the pore-expanding agent comprises one or more of water, ethanol, polyethylene glycol and methanol; preferably, in the slurry, the mass content of the pore-expanding agent is 0.5-4%.

[0019] According to another aspect of the present application, there is provided a method for preparing the separator, comprising the following steps: applying a slurry containing a solvent and the organic matrix material to at least one surface of the base film to form the adhesive layer, thereby obtaining the separator.

[0020] According to an embodiment of the present application, the slurry comprises the above-mentioned slurry.

[0021] According to an embodiment of the present application, the process for forming the adhesive layer comprises: drying the slurry containing a solvent and the organic matrix material after applying the slurry to at least one surface of the base film, thereby forming the adhesive layer; wherein the drying temperature is 0-30°C, and the drying time is 2-60 s.

[0022] According to another aspect of the present application, there is provided a battery comprising a positive electrode sheet, a negative electrode sheet and the above-mentioned separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and at least one of the positive electrode sheet and the negative electrode sheet is adhered to the separator through the adhesive layer of the separator.

[0023] In another aspect of the present application, the battery further comprises an electrolyte; preferably, the positive electrode sheet is bonded to the separator through the bonding layer of the separator, and the wet-state adhesion between the separator and the positive electrode sheet is greater than or equal to 1 gf / mm, preferably 1-10 gf / mm; preferably, the negative electrode sheet is bonded to the separator through the bonding layer of the separator, and the wet-state adhesion between the separator and the negative electrode sheet is greater than or equal to 1 gf / mm, preferably 1-10 gf / mm.

[0024] The separator provided by the present application and the preparation method and application thereof can effectively improve the adhesion between the separator and the electrode sheet (such as the positive electrode sheet and / or the negative electrode sheet), specifically, the dry-state adhesion between the separator and the electrode sheet (i.e. the adhesion between the separator and the electrode sheet before the electrolyte is soaked), which is beneficial to the bonding and assembly between the separator and the electrode sheet during the preparation of the battery, thereby improving the production efficiency and yield of the battery. At the same time, the wet-state adhesion between the separator and the electrode sheet after the electrolyte is soaked can also be improved, the cycle stability of the battery is improved, and the design requirements of higher capacity density of the battery are met, and the battery can be applied to high-end application scenarios such as 3C digital electronic products and smart wearable devices. BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 is a schematic diagram of the stacking structure of the positive electrode sheet, the separator and the negative electrode sheet in an embodiment of the present application.

[0026] Label explanation: 1: positive electrode sheet; 11: positive electrode current collector; 12: positive electrode coating; 2: negative electrode sheet; 21: negative electrode current collector; 22: negative electrode coating; 3: separator; 31: base film; 32: bonding layer. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to better understand the scheme of the present application, the present application is further described in detail below.

[0028] As described above, in the related art, the adhesion between the separator and the electrode sheet is poor, which is usually manifested as poor dry-state adhesion and poor wet-state adhesion after the electrolyte is soaked.

[0029] For example, in the field of electronic products such as 3C digital electronic products and smart wearable products, electronic products are gradually developing towards thinness and smallness, and higher requirements are put forward for the volume, capacity, weight and energy density of the battery (such as a lithium ion battery). At the same time, the development of 5C technology also puts forward further requirements for the performance of the 3C digital lithium ion battery, such as the endurance time and the charging and discharging speed.

[0030] The separator is an important component of the battery, which is interposed between the positive electrode sheet and the negative electrode sheet to avoid short circuit of the positive and negative electrodes, and to allow active ions such as lithium ions to pass through, so as to ensure the charge and discharge cycle performance of the battery. Therefore, the separator is an important factor affecting the capacity development and cycle stability of the battery, and the capacity development and cycle performance of the battery can be improved by functionalizing the separator to meet the application requirements of the above 3C electronic products, digital electronics, smart wear and other electronic products.

[0031] In the preparation process of the battery, the positive electrode sheet, the separator and the negative electrode sheet are usually bonded to form a battery cell, and then the battery cell is packaged, injected with electrolyte (i.e. electrolyte is injected into the battery cell), and the like to form a battery.

[0032] However, the dry adhesion between the separator and the electrode sheet is poor, which is not conducive to the bonding and assembly between the electrode sheet and the separator during the preparation of the battery, affecting the production efficiency and yield of the battery. Although coating a bonding resin on the surface of the base film of the separator can improve the dry adhesion between the separator and the electrode sheet to some extent, the improvement effect is still limited. In addition, there is electrolyte in the battery, and after the electrolyte is soaked, due to the swelling of the polymer (such as the above-mentioned bonding resin) in the separator and other factors, the original interfacial mechanical anchoring and intermolecular force between the separator and the electrode sheet are opened, thereby reducing or even losing the interfacial adhesion between the separator and the electrode sheet (i.e. the wet adhesion between the separator and the electrode sheet after the electrolyte is soaked is basically zero), which is not conducive to the cycle stability and other performances of the battery (for example, after long-term cycle charging, the active ions (such as lithium ions) are easily blocked due to the interface misalignment between the separator and the electrode sheet, thereby affecting the cycle stability and capacity retention rate of the battery after the cycle).

[0033] Therefore, it is urgent to improve the dry adhesion between the separator and the electrode sheet and the wet adhesion after the electrolyte is soaked.

[0034] The separator 3 provided by the embodiment of the present application is shown in FIG. 1, which comprises a base film 31 and an adhesive layer 32 existing on at least one side surface of the base film 31; the adhesive layer 32 comprises an organic matrix material, and the organic matrix material contains a polar group; the molar content of the polar group in the organic matrix material (i.e. the molar proportion of the polar group in the organic matrix material) is greater than or equal to 3%.

[0035] According to the research and analysis of the inventor, the adhesive layer 32 as the interface layer of the separator 3, in which the organic matrix material contains polar groups with a molar content of not less than 3%, can effectively improve the dry-state adhesion and wet-state adhesion between the separator 3 and the electrode sheet (such as the positive electrode sheet 1 and / or the negative electrode sheet 2). The analysis reason is that the adhesive layer 32 formed by the above-mentioned organic matrix material can not only form mechanical anchoring effect and intermolecular force between the electrode sheet, but also the polar groups in the adhesive layer 32 can form chemical bonds and / or strong dipole-dipole forces (such forces are usually tens of times higher than van der Waals forces) with the electrode material, so that the separator 3 can also be connected with the electrode sheet through chemical bonds and / or strong dipole-dipole forces, thereby the dry-state adhesion and wet-state adhesion between the separator 3 and the electrode sheet can be improved at the same time. Specifically, even if the organic matrix material in the separator 3 may swell to a certain extent after being soaked in the electrolyte, and then may weaken the mechanical anchoring effect and intermolecular force between the separator 3 and the electrode sheet to a certain extent, the chemical bonds and strong dipole-dipole forces between the separator 3 and the electrode sheet are not easy to be destroyed, so that the wet-state adhesion between the separator 3 and the electrode sheet after being soaked in the electrolyte can still be maintained, thereby the stability and electrochemical performance of the battery cell structure assembled by the separator 3 and the electrode sheet can be improved.

[0036] In addition, the polar groups contained in the organic matrix material in the adhesive layer 32 can also form chemical bonds and / or strong dipole-dipole forces with the base film 31, so that the overall structural stability and other properties of the separator 3 can also be improved, and the stability and other properties of the battery cell structure assembled by the separator 3 and the electrode sheet can be further ensured.

[0037] In addition, according to the research of the inventor, if the molar content of the polar group in the organic matrix material is less than 3%, the adhesion between the separator 3 and the electrode sheet is poor, especially the wet-state adhesion between the separator 3 and the electrode sheet, and the reason is that there are too few polar groups in the organic matrix material, so that the chemical bond and / or strong dipole-dipole force cannot be effectively formed between the separator 3 and the electrode sheet, thereby the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet cannot be effectively improved. According to the further research of the inventor, the molar content of the polar group in the organic matrix material can be 3% to 40%, for example, 3%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range composed of any two of them, so that the dry-state adhesion and the wet-state adhesion of the separator and the electrode sheet can be improved, and the breakdown voltage of the separator can be further improved, thereby improving the cycle performance of the battery, and the reason is that when the molar content of the polar group in the organic matrix material is too high (>40%), the polarity is too large, and the electrolyte swelling degree of the separator is too large (generally up to about 150% or even more than 150%), which will reduce the breakdown voltage and other properties of the separator, and further affect the cycle performance of the battery.

[0038] Specifically, the molecular chain of the organic matrix material contains the above-mentioned polar group, which can contain one or at least two polar groups, and the above-mentioned organic matrix material can be a bonding type polymer resin containing one or at least two polar groups, and the polar group can be a strong polar group.

[0039] Specifically, the above-mentioned polar group can include one or more of carboxyl, acrylate group, cyano (-CN), carbonyl (-C=O), sulfonic acid group, siloxane group, mercapto group, ether bond, sulfone group, amide group (-CO-NH-), that is, the organic matrix material can contain one of these polar groups or at least two of these polar groups, and by introducing the polar group, the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet can be further improved, and the cycle performance of the battery can be improved, and the reason is that the introduction of the above-mentioned polar group in the bonding layer 32 is more conducive to the formation of chemical bonds and / or strong dipole-dipole forces between the separator and the electrode material of the electrode sheet, and the formation of mechanical anchoring and intermolecular forces between the separator and the electrode sheet, and at the same time, the separator has more suitable swelling properties, and the breakdown voltage and other properties of the separator can be improved, thereby improving the cycle performance of the battery.

[0040] In some embodiments, the imide group in the organic matrix material is conducive to further improving the dry adhesion and wet adhesion of the separator 3 and the electrode sheet, and can more significantly improve the wet adhesion of the separator 3 and the electrode sheet. The reason is that the imide group can provide hydrogen bonding force of the molecular chain in the interface layer (adhesion layer 32), enhance the adhesion of the separator 3, and thus enhance the adhesion between the separator 3 and the electrode sheet. At the same time, the imide group can also improve the breakdown voltage and other properties of the separator, thereby improving the cycle performance of the battery.

[0041] Specifically, the molar content of the imide group in the organic matrix material can be 3% to 15%, for example, 3%, 5%, 8%, 10%, 13%, 15%, or a range formed by any two of them. According to the research of the inventor, by controlling the molar content of the imide group in the organic matrix material within the above range (3% to 15%), the organic matrix material has better adhesion, significantly improves the dry adhesion and wet adhesion between the separator 3 and the electrode sheet, and at the same time, the organic matrix material has good swelling characteristics, improves the breakdown voltage and other properties of the separator, and further improves the cycle performance and other properties of the battery.

[0042] In the embodiments of the present application, the polar group and its content in the organic matrix material can be measured by Fourier infrared spectrum analysis, nuclear magnetic resonance analysis and other analysis methods. Specifically, after obtaining the separator (or disassembling the separator from the battery), the separator can be soaked in an organic solvent (the organic solvent used includes N-methyl pyrrolidone (NMP), for example), so that the adhesion layer 32 falls off from the separator (the fallen adhesion layer 32 enters the organic solvent). After the adhesion layer 32 on the separator is basically completely removed, the obtained soaking liquid (organic solvent containing the adhesion layer 32 material) is dried, for example, the soaking liquid can be placed in a vacuum drying oven for drying until the organic solvent is basically completely removed, and a residual solid is obtained. Then, the residual solid is used for the following analysis:

[0043] (1) Take the residual solid as an infrared analysis sample and perform Fourier infrared spectrum analysis on it. The type of polar group contained in the residual solid (i.e. the type of polar group in the organic matrix material) is determined according to the group absorption peak (characteristic peak) in the measured infrared spectrum.

[0044] (2) Take the residual solid as a nuclear magnetic resonance analysis sample and perform nuclear magnetic resonance analysis on it. The molar content of the polar group is quantitatively analyzed according to the measured nuclear magnetic resonance spectrum. Specifically, the molar content of the polar group can be calculated according to the integral area of the characteristic peak of the group in the nuclear magnetic resonance spectrum (the molar content of the polar group is the integral area ratio of the characteristic peak of the polar group in the nuclear magnetic resonance spectrum). The calculation result is the molar content of the polar group in the organic matrix material.

[0045] It can be understood that when the organic matrix material contains multiple polar groups, the molar content of the polar groups in the organic matrix material according to the embodiments of the present application refers to the sum of the molar content of the polar groups in the organic matrix material.

[0046] In the embodiments of the present application, the organic matrix material can include a polymer containing the polar group described above, such as an imide-based polymer and / or polyacrylonitrile, etc., wherein the imide-based polymer contains an imide group, and can or can not contain other polar groups. For example, the imide-based polymer can include one or more of polyamide-imide, carbonyl-type polyimide (containing a carbonyl group), bismaleimide polymer, polyetherimide sulfone, carboxylic acid-type polyimide (containing a carboxyl group), modified polyimide, polyester imide, and polyether imide.

[0047] Further considering the dry-state adhesion and wet-state adhesion between the separator 3 and the electrode sheet, and the swelling properties of the organic matrix material, etc., in some preferred embodiments, the organic matrix material described above can include one or more of polyamide-imide, carbonyl-type polyimide (containing a carbonyl group), bismaleimide polymer, polyetherimide sulfone (containing a sulfone group), carboxylic acid-type polyimide (containing a carboxyl group), modified polyimide, polyester imide, polyether imide (containing an ether bond), and polyacrylonitrile (containing a cyano group).

[0048] The basic structural formula of the polyamide-imide is shown as follows:

[0049] In the basic structural formula of the polyamide-imide described above, n is a positive integer, and the polyamide-imide can be specifically formed by the repeating units shown in the structural formula.

[0050] Specifically, the modified polyimide can include one or more of cyano-modified polyimide (polyimide containing a cyano group), mercapto-modified polyimide (polyimide containing a mercapto group), sulfonic acid-modified polyimide (polyimide containing a sulfonic acid group), and siloxane-modified polyimide (polyimide containing a siloxane group).

[0051] Specifically, the polyester imide described above can include a polyester imide containing an acrylate group.

[0052] In the embodiments of the present application, the organic matrix material such as the amide-based polymer and polyacrylonitrile is a bonding-type polymer, which can be obtained by a conventional method in the art, such as being commercially available or being self-made by a conventional method, and is not particularly limited.

[0053] Further research shows that the glass transition temperature of the organic matrix material can be 148-158°C, for example 148°C, 150°C, 153°C, 155°C, 158°C, or a range between any two of them, so as to further improve the wet adhesion of the separator 3 and the electrode sheet. The glass transition temperature of the organic matrix material will affect the dry and wet adhesion of the separator and the electrode sheet. By using an organic matrix material with a glass transition temperature in the above range (148-158°C), the separator has more suitable electrolyte swelling properties and stronger adhesion, which can further improve the dry and wet adhesion of the separator 3 and the electrode sheet, while maintaining the high withstand voltage of the separator and other properties, and improving the cycle performance of the battery.

[0054] It should be noted that when the organic matrix material includes a plurality of polymers (for example, including at least one imide polymer and polyacrylonitrile, or including a plurality of imide polymers), the glass transition temperature of the organic matrix material is 148-158°C, and the glass transition temperature of each polymer is 148-158°C, respectively. The glass transition temperatures of these polymers can be the same or different. For example, the glass transition temperature of the imide polymer is 148-158°C, and the glass transition temperature of the polyacrylonitrile is 148-158°C.

[0055] The glass transition temperature of the organic matrix material can be measured by differential scanning calorimetry (DSC analysis method). In practice, after obtaining the separator, the adhesive layer 32 can be taken from the separator as a test sample, and the test sample can be subjected to DSC analysis to test the glass transition temperature, and the test result is the glass transition temperature of the organic matrix material.

[0056] In addition, the mass content of the organic matrix material in the adhesive layer 32 (i.e. the ratio of the mass of the organic matrix material to the total mass of the adhesive layer 32) can be 30%-100%, for example 30%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, 90%, 100%, or a range between any two of them.

[0057] In addition, the adhesive layer 32 can further include one or more of ceramic particles, co-binders, and wetting agents.

[0058] When the adhesive layer 32 includes the co-binder, the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet can be further improved. The reason is that, in the coexisting system of the organic matrix material and the co-binder, the organic matrix material mainly ensures the wet-state adhesion (but it can still maintain a high dry-state adhesion between the separator 3 and the electrode sheet), and the co-binder mainly enhances the dry-state adhesion, and the two can also synergistically act to further improve the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet.

[0059] Specifically, the co-binder can include polyvinylidene fluoride homopolymer (PVDF) and / or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), which is conducive to synergistic effect with the above-mentioned organic matrix material, and further improves the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet.

[0060] In some embodiments, the mass content of the co-binder in the adhesive layer 32 can be 0-50%, for example, 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of them, preferably 2%-25%, which is conducive to further improving the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet. When the adhesive layer 32 includes ceramic particles, the heat resistance of the separator can be improved while improving the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet, and it is also conducive to increasing the porosity and improving the electrolyte wettability of the separator, thereby further improving the heat dissipation and cycle performance of the battery.

[0061] Specifically, the ceramic particles can include one or more of alumina, boehmite, silicon dioxide, magnesium oxide, and titanium dioxide, wherein the alumina can include nano-alumina (i.e., its particle size is nanoscale). By using the ceramic particles, the adhesive layer 32 system containing the above-mentioned organic matrix material and the like components can be adapted, and the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet, and the heat dissipation performance of the separator 3 and the battery can be improved. In some embodiments, the mass content of the ceramic particles in the adhesive layer 32 can be 0-70%, for example, 0%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of them, preferably 30%-65%, which is conducive to further improving the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet, and the heat dissipation performance of the separator 3.

[0062] When the wetting agent is included in the adhesive layer 32, the lubricant can be used to reduce the interfacial static surface tension and dynamic surface tension, facilitate the adhesive layer 32 to more fully wet the surface of the base film, make the adhesive layer 32 more fully combined with the surface of the base film, and improve the bonding strength (peeling strength) between the adhesive layer 32 and the base film.

[0063] Specifically, the wetting agent can include an alkyl ammonium salt of an organosilicon polymer and / or an acidic group copolymer, etc., which is conducive to adapting the adhesive layer 32 system containing the above-mentioned organic matrix material and other components, improving the stability of the slurry used to form the adhesive layer 32, and avoiding the slurry from settling, thereby facilitating the formation of the adhesive layer 32.

[0064] Specifically, the organosilicon polymer can include a modified organosilane polymer.

[0065] In the embodiments of the present application, the above-mentioned lubricant and other components can be commercially available, for example, the modified organosilane polymer (lubricant) can be a modified organosilane polymer from BASF.

[0066] In some embodiments, the mass content of the wetting agent in the adhesive layer 32 can be 0.01% to 0.5%, for example, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.45%, 0.5% or a range consisting of any two of them.

[0067] In addition, the thickness of the adhesive layer 32 can be 0.5 μm to 3 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or a range consisting of any two of them.

[0068] In contrast, if the thickness of the adhesive layer 32 is too small (<0.5 μm), the improvement effect on the dry adhesion and wet adhesion of the separator and the electrode sheet is limited; and if the thickness of the adhesive layer 32 is too large (>3 μm), it will affect the porosity and air permeability of the base film to some extent, and then affect the penetration of active ions (such as lithium ions in lithium ion batteries) through the separator, and then affect the cycle performance of the battery. Therefore, the thickness of the adhesive layer 32 is within the above-mentioned range (0.5 μm to 3 μm), which is conducive to improving the dry adhesion and wet adhesion of the separator and the electrode sheet, and at the same time, better battery cycle performance is taken into account.

[0069] In the embodiments of the present application, the adhesive layer 32 can be formed on one side surface of the base film 31, or the adhesive layer 32 can be respectively formed on the opposite two side surfaces of the base film 31. The side surface of the base film 31 or the opposite two side surfaces of the base film 31 are substantially perpendicular to the thickness direction of the base film 31, the adhesive layer 32 and the base film 31 are stacked, and the thickness direction of the adhesive layer 32, the thickness direction of the base film 31, the thickness direction of the separator 3, and the direction from the adhesive layer 32 to the base film 31 (or the direction from the base film 31 to the adhesive layer 32) are parallel to each other.

[0070] In the embodiments of the present application, the base film 31 used can be a conventional separator 3 material in the art. For example, the base film 31 can include one or more of a polypropylene (PP) film, a polyethylene (PE) film, a first composite film, and a second composite film.

[0071] The first composite film is a base film 31 composed of at least two layers of polymer films. For example, the first composite film includes a PP / PE / PP composite film and / or a PP / PE composite film. The first composite film can be a multi-layer co-extruded base film prepared by a co-extrusion process.

[0072] The second composite film includes a substrate and a coating layer present on at least one side surface of the substrate. The coating layer can include one or more of a ceramic film, an ultraviolet (UV) cross-linked ceramic film, and a nanofiber film. The coating layer on the surface of the substrate can be formed by a coating method or other conventional method in the art. The coating layer can be formed on one side surface of the substrate (single-sided coating), or the coating layer can be formed on the opposite two side surfaces of the substrate (double-sided coating).

[0073] The embodiments of the present application also provide a slurry for forming the adhesive layer 32 of the separator 3. The slurry includes a solvent, an organic matrix material, ceramic particles, a co-binder, and a wetting agent. Based on the total mass of the organic matrix material, the ceramic particles, the co-binder, and the wetting agent, the mass fraction of the organic matrix material (i.e., the proportion of the mass of the organic matrix material to the sum of the masses of the organic matrix material, the ceramic particles, the co-binder, and the wetting agent) is 30% to 100%, the mass fraction of the co-binder is 0 to 50%, the mass fraction of the ceramic particles is 0 to 70%, and the mass fraction of the wetting agent is 0.01% to 0.5%.

[0074] In some embodiments, based on the total mass of the organic matrix material, the ceramic particles, the co-binder, and the wetting agent, the mass fraction of the co-binder can be 2% to 25%. In this way, the mass content of the co-binder in the adhesive layer 32 formed using the above-mentioned slurry is also substantially 2% to 25%, which is beneficial for further taking into account the improvement of the dry-state adhesion and the wet-state adhesion between the separator 3 and the electrode sheet.

[0075] The solvent is used to dissolve or disperse the organic matrix material, ceramic particles, co-binders, wetting agents, and the like, so as to uniformly disperse these components. The solvent can include an organic solvent, and specifically can include one or more of acetone, N-methyl pyrrolidone (NMP), dimethylacetamide (DMAc).

[0076] Specifically, the mass content of the solvent in the slurry (i.e., the ratio of the mass of the solvent to the total mass of the slurry) can be 70% to 90%, such as 70%, 75%, 80%, 85%, 90%, or a range defined by any two of these values.

[0077] In addition, the slurry can further include a pore-expanding agent (or coating pore-expanding agent), which can increase the porosity of the adhesive layer 32, increase the number of ion channels in the adhesive layer 32, and improve the rate performance of the battery.

[0078] Specifically, the pore-expanding agent can include one or more of water, ethanol, polyethylene glycol, and methanol.

[0079] Specifically, the mass content of the pore-expanding agent in the slurry (i.e., the mass content of the pore-expanding agent in the slurry) can be 0.5% to 4%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or a range defined by any two of these values.

[0080] In specific implementations, the slurry described above can be applied to at least one side surface of the base film 31 to form the adhesive layer 32 on at least one side surface of the base film 31, thereby producing the separator 3.

[0081] The present embodiments also provide a method for producing the separator 3 described above, which includes the following steps: applying a slurry containing a solvent and an organic matrix material to at least one surface of the base film 31 to form the adhesive layer 32, thereby producing the separator 3.

[0082] The slurry used can include the slurry described above, which will not be described in detail here.

[0083] Specifically, the slurry described above is applied to at least one surface of the base film 31 and then dried to form the adhesive layer 32, thereby producing the separator 3. The drying temperature can be 0 to 30°C, such as 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, or a range defined by any two of these values. The drying time can be 2 seconds to 60 seconds, such as 2 seconds, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, 30 seconds, 35 seconds, 40 seconds, 45 seconds, 50 seconds, 55 seconds, 60 seconds, or a range defined by any two of these values.

[0084] The battery provided by the embodiment of the present application also comprises a positive electrode sheet 1, a negative electrode sheet 2 and the above-mentioned separator 3, the separator 3 is located between the positive electrode sheet 1 and the negative electrode sheet 2, and at least one of the positive electrode sheet 1 and the negative electrode sheet 2 is bonded to the separator 3 through the bonding layer 32 of the separator 3.

[0085] Specifically, in the separator 3, when one side surface of the base film 31 is provided with the above-mentioned bonding layer 32, the bonding layer 32 can be located on the side surface of the base film 31 facing the positive electrode sheet 1 (i.e. the separator 3 is bonded to the positive electrode sheet 1 through the bonding layer 32), or the bonding layer 32 is located on the side surface of the base film 31 facing the negative electrode sheet 2 (i.e. the separator 3 is bonded to the negative electrode sheet 2 through the bonding layer 32); when both side surfaces of the base film 31 are provided with the above-mentioned bonding layer 32, the separator 3 is bonded to the positive electrode sheet 1 through the bonding layer 32 located on one side surface of the base film 31, and is bonded to the negative electrode sheet 2 through the bonding layer 32 located on the other side surface of the base film 31.

[0086] Generally, the battery comprises a battery cell and a packaging body for packaging the battery cell, the battery cell comprises the above-mentioned positive electrode sheet 1, the separator 3 and the negative electrode sheet 2. The battery cell can be a wound battery cell, i.e. the positive electrode sheet 1, the separator 3 and the negative electrode sheet 2 are sequentially stacked and wound to form a wound structure (winding core); or the battery cell can also be a stacked battery cell (as shown in FIG. 1), i.e. the battery cell comprises a plurality of positive electrode sheets 1 and a plurality of negative electrode sheets 2 which are stacked and arranged in an interleaved manner, and the positive electrode sheets 1 and the negative electrode sheets 2 are separated by the separator 3.

[0087] In the embodiment of the present application, the packaging body can be a conventional packaging material in the art, for example, the packaging body can comprise a soft packaging material (i.e. the battery can be a soft packaging battery), and the soft packaging material can comprise an aluminum plastic film and the like, but is not limited thereto.

[0088] In specific implementation, the positive electrode sheet 1, the separator 3 and the negative electrode sheet 2 can be sequentially stacked to form a stacked structure, and then the positive electrode sheet 1, the separator 3 and the negative electrode sheet 2 are bonded through hot pressing treatment to obtain the battery cell; then the battery cell is packaged by the packaging body, and then the battery is obtained after processes such as liquid injection and formation, which are all conventional operations in the process of preparing the battery in the art, and the present application does not particularly limit them.

[0089] In addition, the battery also comprises an electrolyte, and the electrolyte can be a non-aqueous electrolyte, which comprises an organic solvent, an electrolyte salt and an additive.

[0090] The organic solvent can comprise one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC).

[0091] The electrolyte salt can include lithium salt, and the lithium salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6).

[0092] The additive can include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinonitrile (SN), adiponitrile (ADN).

[0093] In some embodiments, the positive electrode sheet 1 is adhered to the separator 3 by the adhesive layer 32 of the separator 3, and the wet adhesion between the separator 3 and the positive electrode sheet 1 is greater than or equal to 1 gf / mm, and can be 1-10 gf / mm, for example, 1 gf / mm, 2 gf / mm, 3 gf / mm, 4 gf / mm, 5 gf / mm, 6 gf / mm, 7 gf / mm, 8 gf / mm, 9 gf / mm, 10 gf / mm, or a range consisting of any two of them.

[0094] In some embodiments, the negative electrode sheet 2 is adhered to the separator 3 by the adhesive layer 32 of the separator 3, and the wet adhesion between the separator 3 and the negative electrode sheet 2 is greater than or equal to 1 gf / mm, and can be 1-10 gf / mm, for example, 1 gf / mm, 2 gf / mm, 3 gf / mm, 4 gf / mm, 5 gf / mm, 6 gf / mm, 7 gf / mm, 8 gf / mm, 9 gf / mm, 10 gf / mm, or a range consisting of any two of them.

[0095] In the embodiments of the present application, the wet adhesion (peeling strength after electrolyte immersion) between the electrode sheet (positive electrode sheet 1 or negative electrode sheet 2) and the separator 3 in the battery can be measured by conventional methods in the art. For example, the process for testing the wet adhesion of the electrode sheet and the separator 3 can include:

[0096] (1) The electrode sheet is cut into a sheet sample with a length of 70 mm and a width of 15 mm, and the separator is cut into a separator sample with a length of 92 mm and a width of 20 mm, and a total of 5 sheet samples and 4 separator samples are cut;

[0097] (2) The 5 sheet samples and 4 separator samples are fully immersed in the electrolyte, and specifically, the sheet sample and the separator sample are soaked in the electrolyte for about 24 h;

[0098] (3) The 5 pieces of the electrode tab samples and 4 pieces of the separator samples infiltrated with the electrolyte solution are alternately stacked (i.e., every two adjacent electrode tab samples are separated by one separator sample, and every two adjacent separator samples are separated by one electrode tab sample), and then hot-pressed at 85°C and 1 MPa for about 1 hour, followed by natural cooling at room temperature, to obtain a laminate in which 5 layers of the electrode tab samples and 4 layers of the separator samples are alternately stacked; wherein the length direction of the separator sample is parallel to the length direction of the electrode tab sample;

[0099] (4) A 1-cm-wide adhesive tape is attached to the surface of the electrode tab sample of the laminate (i.e., the adhesive tape is attached to the surface of the electrode tab sample away from the separator sample), and the other surface of the adhesive tape is attached to a 3-mm-thick, 150-mm-long, and 50-mm-wide substrate, so that the length direction of the separator sample is parallel to the length direction of the substrate, to obtain a peel test piece; wherein the adhesive tape used can be a 3M tape (a type of high-performance adhesive tape produced by 3M Company), and the substrate used can be a SUS stainless steel plate or a glass plate;

[0100] (5) A universal testing machine is used to sandwich the separator sample in the load cell side chuck, and a 90° peel test is performed at a test speed of 50 mm / min; the average of the values measured from 20 mm to 70 mm of the stroke in the peel test is taken as the average value, which is taken as the peel force of the peel test piece. Wherein, 8 peel tests are performed on each layer of the laminate from top to bottom (in each peel test, one electrode tab sample and the separator sample are peeled off), and the average value F of the peel forces is converted to a value (i.e., F / w) by the width w of the electrode tab sample, which is taken as the wet-state adhesive force (gf / mm) of the separator 3 and the electrode tab. Wherein, the width w is the width of the electrode tab sample.

[0101] In step (1), the electrolyte used has the following composition: the organic solvent is DMC, EMC, EC, DEC, and PC, the volume ratio of DMC, EMC, EC, DEC, and PC is 15:35:35:10:5, and the mass content of LiPF6 in the electrolyte is 11wt%.

[0102] In step (1), a conventional hot-pressing device in the art can be used for hot-pressing, for example, a precision heating and pressing device (such as CYPT-10 manufactured by Xindong Industrial Co., Ltd.).

[0103] In step (5), the universal testing machine used is, for example, a universal testing machine of model EM6.202 from Shenzhen Tesmet Instrument Equipment Co., Ltd.

[0104] In step (5), the universal testing machine used is, for example, a universal testing machine of model EM6.202 from Shenzhen Tesmet Instrument Equipment Co., Ltd.

[0105] In the embodiments of the present application, the electrolyte swelling degree of the separator refers to the swelling degree of the separator after the separator is soaked in the electrode liquid. The testing method can be found in the specific embodiments section below, and will not be described in detail here.

[0106] In the embodiments of the present application, the breakdown voltage of the separator refers to the highest voltage that the separator (insulator) can withstand. Even if the critical voltage value (voltage threshold) at which the separator breaks and loses its insulating properties is reached when a voltage is applied to the separator, the breakdown voltage of the separator is the highest voltage that the separator can withstand. That is, when a voltage is applied to the separator, the separator breaks and loses its insulating properties when the voltage reaches the voltage threshold. The testing method of the breakdown voltage of the separator can be found in the specific embodiments section below, and will not be described in detail here.

[0107] In the embodiments of the present application, the above-mentioned battery can be a secondary battery, and specifically can be a lithium ion battery.

[0108] In general, the positive electrode sheet 1 includes a positive electrode current collector 11 and a positive electrode coating layer 12 located on at least one side surface of the positive electrode current collector 11. The positive electrode coating layer 12 can be provided on one side surface of the positive electrode current collector 11, or the positive electrode coating layer 12 can be respectively provided on both the front and back side surfaces of the positive electrode current collector 11. The positive electrode sheet 1 is bonded to the separator 3 through the positive electrode coating layer 12 (i.e., the positive electrode coating layer 12 is bonded to the bonding layer 32 of the separator 3).

[0109] Specifically, the positive electrode current collector 11 can be a conventional positive electrode current collector 11 in the art, for example, the positive electrode current collector 11 can include an aluminum foil, but is not limited thereto.

[0110] Specifically, the positive electrode coating layer 12 can include a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material, a first conductive agent, and a first binder.

[0111] The positive electrode active material can be a conventional positive electrode active material in the art, for example, the positive electrode active material includes a lithium-containing active material, and the lithium-containing active material includes one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium cobaltate, lithium nickel manganese acid, lithium-rich manganese-based solid solution, lithium manganese acid, etc.

[0112] The first conductive agent can be a conventional conductive material in the art, for example, the first conductive agent can include one or more of conductive carbon (Super P), acetylene black, graphene, Ketjen black, carbon fiber, but is not limited thereto.

[0113] The first binder can be a conventional binder material in the art, for example, the first binder can include one or more of polyvinylidene fluoride homopolymer (PVDF), polyvinylidene fluoride, polyfluoroethylene, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, etc., but is not limited thereto.

[0114] Specifically, in the positive electrode active material layer, the mass content of the positive electrode active material can be 70% to 99%, the mass content of the first conductive agent can be 0.5% to 15%, and the mass content of the first binder can be 0.5% to 15%.

[0115] In addition, the negative electrode sheet 2 includes a negative electrode current collector 21 and a negative electrode coating layer 22 present on at least one side surface of the negative electrode current collector 21. The negative electrode coating layer 22 can be provided on one side surface of the negative electrode current collector 21, or the negative electrode coating layer 22 can be respectively provided on both the front and back side surfaces of the negative electrode current collector 21. The negative electrode sheet 2 is bonded to the separator 3 through the negative electrode coating layer 22 (i.e., the negative electrode coating layer 22 is bonded to the bonding layer 32 of the separator 3).

[0116] Specifically, the negative electrode current collector 21 can be a conventional negative electrode current collector 21 in the art, for example, the negative electrode current collector 21 can include a copper foil, but is not limited thereto.

[0117] Specifically, the negative electrode coating layer 22 can include a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material, a second conductive agent, and a second binder.

[0118] The negative electrode active material can be a conventional negative electrode active material in the art, for example, the negative electrode active material can be graphite and / or a silicon-based material, the silicon-based material can include silicon-carbon and / or silicon-oxygen material, for example, and the graphite can include artificial graphite and / or natural graphite, but is not limited thereto.

[0119] The second conductive agent can be a conventional conductive material in the art, for example, the second conductive agent can include one or more of carbon black, acetylene black, ketjen black, carbon fiber, graphene, etc., but is not limited thereto.

[0120] The second binder can be a conventional binder material in the art, for example, the second binder can include one or more of carboxymethyl cellulose, styrene butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyfluoroethylene, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyvinyl alcohol, sodium polyacrylate, etc., but is not limited thereto.

[0121] In the embodiment of the present application, the positive electrode sheet 1 can be prepared by a conventional method in the art, for example, by a coating method. For example, the preparation process of the positive electrode sheet 1 includes: dispersing components for forming the positive electrode coating 12, such as a positive electrode active material, a first conductive agent, and a first binder, in a first solvent, for example, N-methyl pyrrolidone (NMP), to prepare a positive electrode slurry; coating the positive electrode material on the surface of the positive electrode current collector 11, and forming the positive electrode coating 12 on the surface of the positive electrode current collector 11 after drying, rolling, and other processes, to prepare the positive electrode sheet 1.

[0122] In the embodiment of the present application, the negative electrode sheet 2 can be prepared by a conventional method in the art, for example, by a coating method. For example, the preparation process of the negative electrode sheet 2 includes: dispersing components for forming the negative electrode coating 22, such as a negative electrode active material, a second conductive agent, and a second binder, in a second solvent, for example, water (specifically, deionized water), to prepare a negative electrode slurry; coating the negative electrode material on the surface of the negative electrode current collector 21, and forming the negative electrode coating 22 on the surface of the negative electrode current collector 21 after drying, rolling, and other processes, to prepare the negative electrode sheet 2.

[0123] The present application is further described below through specific examples. In the following examples and comparative examples, unless otherwise specified, the carboxylic acid type polyimide is from Shenzhen Yan Yi, the cyano-modified polyimide, the mercapto-modified polyimide, the sulfonic acid group-modified polyimide, and the polyamide-imide are from Shenzhen Hao Dian, the ketone anhydride type polyimide, the polyester imide, and the siloxane group-modified polyimide are from Zhongke Jiuyuan, the polyether imide and the polyether imide sulfone are from Saudi Industrial Base, the polyacrylonitrile is from Yingdile, and the modified organosilane polymer is from BASF.

[0124] Example 1

[0125] 1. Preparation of the separator

[0126] (1) Preparation of the slurry: mix the organic matrix material, PVDF-HFP, nano-aluminum oxide, and modified organosilane polymer in a mass ratio of 40:5:60:0.5, and add them to acetone to prepare a slurry;

[0127] (2) Coat the slurry on the surfaces of the opposite sides of the base film (PE film), and dry at about 25°C for about 40s to form an adhesive layer, thereby preparing the separator.

[0128] 2. Preparation of the positive electrode sheet

[0129] Mix lithium cobaltate, Super P, and PVDF in a mass ratio of 85:10:5, and add them to NMP to prepare a positive electrode slurry;

[0130] The positive electrode slurry is coated on the front and back surfaces of the aluminum foil, and after drying and rolling, the positive electrode active material layers are formed on the front and back surfaces of the aluminum foil respectively, to obtain the positive electrode sheet.

[0131] 3. Preparation of the negative electrode sheet

[0132] The graphite, Super P and PVDF are mixed in a mass ratio of 85:10:5, and then added into deionized water to prepare the negative electrode slurry.

[0133] The negative electrode slurry is coated on the front and back surfaces of the copper foil, and after drying and rolling, the negative electrode active material layers are formed on the front and back surfaces of the copper foil respectively, to obtain the negative electrode sheet.

[0134] 4. Preparation of the battery

[0135] The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, and then the obtained laminated body is hot-pressed to bond the one side surface of the separator to the positive electrode sheet and the other side surface of the separator to the negative electrode sheet, to obtain the stacked cell. The cell is packaged with an aluminum plastic film, and then subjected to processes such as liquid injection and formation, to obtain the lithium ion battery.

[0136] The electrolyte used is composed of organic solvents DMC, EMC, EC, DEC and PC, and the volume ratio of DMC, EMC, EC, DEC and PC is 15:35:35:10:5 (i.e. DMC: EMC: EC: DEC: PC = 15:35:35:10:5 (vol)), and the mass content of LiPF6 in the electrolyte is 11%.

[0137] Comparative Example 1: The difference from Example 1 is that the content of the polar group in the organic matrix material is < 3%, as shown in Table 1. Except for the difference shown in Table 1, the other conditions are the same as those in Example 1.

[0138] Examples 2-25: The difference from Example 1 is that the type of the organic matrix material, the molar content of the polar group in the organic matrix material, the type of the polar group, the content of the imino group (-NH-) in the organic matrix material, the glass transition temperature of the organic matrix material, and the like are different, as shown in Table 1. Except for the difference shown in Table 1, the other conditions are the same as those in Example 1.

[0139] Example 26: The difference from Example 1 is that the adhesion layer does not contain a co-adhesive (i.e. in the preparation of the separator, the organic matrix material, nano-alumina and modified organosilane polymer are mixed in a mass ratio of 40:60:0.5 and added into acetone to prepare a slurry), and the other conditions are the same as those in Example 1.

[0140] The performance of the separators and the batteries prepared in each example and comparative example is tested by the following process, and the results are shown in Table 2.

[0141] 1. The test procedure for the dry adhesion between the diaphragm and the electrode sheet (including the dry adhesion between the diaphragm and the positive electrode sheet, and the dry adhesion between the diaphragm and the negative electrode sheet) is as follows:

[0142] The diaphragm was cut into test strips with a width of 25 mm and a length of 60 mm, and the electrode sheet was cut into test strips with a width of 25 mm and a length of 40 mm. The cut diaphragm test strips and electrode sheet test strips were attached together and sandwiched between two strips of white paper (the size of the white paper strips was larger than the size of the diaphragm test strips). The strips were then pressed at 80℃ and 6.5 MPa for 20 seconds (hot pressing), and then allowed to cool naturally at room temperature. The hot-pressed diaphragm strips were then subjected to a 180° peel test using a tensile testing machine at a test speed of 300 mm / min and a gauge length of 100 mm. After the test, the test results (i.e., the dry adhesion force of the diaphragm and the electrode sheet) were recorded.

[0143] 2. The test procedure for wet adhesion between the diaphragm and electrode plates (including dry adhesion between the diaphragm and the positive electrode plate, and dry adhesion between the diaphragm and the negative electrode plate) is as described above.

[0144] 3. Breakdown voltage test method:

[0145] "Breakdown voltage" refers to the highest voltage that an insulator can withstand, and "breakdown" means that when a voltage is applied to an insulator, it breaks down above a certain voltage and loses its insulating properties.

[0146] The test was conducted using a DC breakdown tester, with the upper electrode having a diameter of [missing information]. A brass cylindrical electrode rod with a chamfer radius of 2.5 mm was used, with the lower electrode being a stainless steel plate. The test sample (diaphragm) was placed between the upper and lower electrodes (ambient temperature 25±3℃, humidity <10%), and a DC current of 1 mA and a voltage increase rate of 0.2 kV / s were set, with a voltage rise time of 30 s. When the test began, the voltage was continuously increased and the measurement was stopped when a short circuit occurred. The voltage value at this point was recorded as the breakdown voltage. The results are shown in Table 2.

[0147] 4. Diaphragm swelling test method:

[0148] After drying the diaphragm sample, weigh its mass M1. Then, soak the diaphragm in the electrolyte at 70℃ for 24 hours. After soaking, take out the diaphragm sample and weigh its mass M2. Then, take out the sample and weigh it every other day (to record the diaphragm swelling data at 24-hour intervals, to confirm the change in swelling rate, and to avoid the diaphragm failure during the 7-day soaking process). After 7 days, measure the final mass M7. The swelling rate is calculated by the following formula: Swelling rate = (M7-M1) / M1×100%. The results are shown in Table 2.

[0149] Table 1

[0150] Table 2

[0151] As can be seen from Table 2, compared with Comparative Example 1, Examples 1-25 can improve the dry and wet adhesion between the separator and the electrode sheet, and improve the breakdown voltage of the separator, thereby improving the battery cycle performance.

[0152] Further, as can be seen from Comparative Example 1 and Examples 1-7, the molar content of the polar group in the organic matrix material of Comparative Example 1 is too small (<3%), and the adhesion between the separator and the electrode sheet is poor, especially the wet adhesion between the separator and the electrode sheet (the wet adhesion between the separator and the positive electrode sheet is only 0.6 N / m, and the wet adhesion between the separator and the negative electrode sheet is only 0.5 N / m), while in Examples 1-7, the molar content of the polar group in the organic matrix material is greater than or equal to 3%, which can significantly improve the adhesion between the separator and the electrode sheet, especially the wet adhesion between the separator and the electrode sheet.

[0153] Further, as can be seen from Comparative Example 1 and Examples 1-7, the molar content of the polar group in the organic matrix material of Comparative Example 1 is too small (<3%), and the adhesion between the separator and the electrode sheet is poor, especially the wet adhesion between the separator and the electrode sheet (the wet adhesion between the separator and the positive electrode sheet is only 0.6 N / m, and the wet adhesion between the separator and the negative electrode sheet is only 0.5 N / m), while in Examples 1-7, the molar content of the polar group in the organic matrix material is greater than or equal to 3%, which can significantly improve the adhesion between the separator and the electrode sheet, especially the wet adhesion between the separator and the electrode sheet.

[0154] Further, as can be seen from Examples 8 and 17, compared with Example 17 (the organic matrix material does not contain imino groups), the organic matrix material of Example 8 contains imino groups, which can more significantly improve the wet adhesion between the separator and the electrode sheet, and improve the breakdown voltage of the separator, thereby improving the battery cycle performance.

[0155] Further, as can be seen from Examples 18-22, compared with Example 18 (the content of imino groups in the organic matrix material is too small (<3%)) and Example 22 (the content of imino groups in the organic matrix material is too large (>15%)), the content of imino groups in the organic matrix material of Examples 19-21 is in the range of 3%-15%, which can further improve the dry and wet adhesion between the separator and the electrode sheet.

[0156] Further, the glass transition temperature of the organic matrix material in the above embodiments is in the range of 148 to 158°C, which can further improve the dry and wet adhesion of the separator and the electrode sheet, relative to the organic matrix material in Example 23 (the glass transition temperature of the organic matrix material is too small (< 148°C)), Example 24 (the glass transition temperature of the organic matrix material is too large (> 158°C)), Example 15, and the like.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A diaphragm, characterized in that, Includes a base film and an adhesive layer present on at least one surface of the base film; The adhesive layer includes an organic matrix material containing polar groups; The molar content of the polar groups in the organic matrix material is greater than or equal to 3%.

2. The diaphragm according to claim 1, characterized in that, The molar content of the polar groups in the organic matrix material is 3% to 40%.

3. The diaphragm according to claim 1, characterized in that, The organic matrix material contains one or more of the following groups: carboxyl, acrylate, cyano, carbonyl, sulfonic acid, siloxane, mercapto, ether, sulfone, and amide.

4. The diaphragm according to claim 1, characterized in that, The organic matrix material contains imide groups, and the molar content of the imide groups in the organic matrix material is 3% to 15%.

5. The diaphragm according to any one of claims 1-4, characterized in that, The organic matrix material includes one or more of the following: polyamide-imide, carbonyl polyimide, bismaleimide polymer, polyetherimide sulfone, carboxylic acid polyimide, modified polyimide, polyesterimide, polyetherimide, and polyacrylonitrile. Preferably, the modified polyimide includes one or more of cyano-modified polyimide, mercapto-modified polyimide, sulfonic acid-modified polyimide, and siloxane-modified polyimide.

6. The diaphragm according to any one of claims 1-4, characterized in that, The organic matrix material in the adhesive layer has a mass content of 30% to 100%.

7. The diaphragm according to any one of claims 1-4, characterized in that, The adhesive layer further includes one or more of ceramic particles, co-adhesives, and wetting agents; Preferably, the ceramic particles in the adhesive layer have a mass content of 0-70%, more preferably 30%-65%; Preferably, the co-adhesive content in the adhesive layer is 0-50% by mass, more preferably 2%-25%; Preferably, the wetting agent in the adhesive layer has a mass content of 0.01% to 0.5%. Preferably, the ceramic particles comprise one or more of alumina, boehmite, silicon dioxide, magnesium oxide, and titanium dioxide; Preferably, the co-adhesive comprises polyvinylidene fluoride homopolymer and / or polyvinylidene fluoride-hexafluoropropylene copolymer. Aggregates; Preferably, the wetting agent comprises an organosilicon polymer and / or an alkylammonium salt of a copolymer with acidic groups.

8. The diaphragm according to any one of claims 1-4, characterized in that, The glass transition temperature of the organic matrix material is 148–158 °C.

9. The diaphragm according to any one of claims 1-4, characterized in that, The thickness of the adhesive layer is 0.5μm to 3μm.

10. A slurry for forming the adhesive layer of the diaphragm according to any one of claims 1-9, characterized in that, The mixture includes a solvent, the organic matrix material, ceramic particles, a co-adhesive, and a wetting agent. Based on the total mass of the organic matrix material, ceramic particles, co-adhesive, and wetting agent, the mass fraction of the organic matrix material is 30% to 100%, the mass fraction of the co-adhesive is 0% to 50%, the mass fraction of the ceramic particles is 0% to 70%, and the mass fraction of the wetting agent is 0.01% to 0.5%.

11. The slurry according to claim 10, characterized in that, Based on the total mass of the organic matrix material, ceramic particles, co-adhesive, and wetting agent, the mass fraction of the co-adhesive is 2-25%.

12. The slurry according to claim 10, characterized in that, The solvent includes one or more of acetone, N-methylpyrrolidone, and dimethylacetamide; And / or, in the slurry, the solvent content is 70% to 90% by mass.

13. The slurry according to claim 10, characterized in that, The slurry also includes a pore-expanding agent; Preferably, the pore-expanding agent comprises one or more of water, ethanol, polyethylene glycol, and methanol; Preferably, the pore-expanding agent in the slurry has a mass content of 0.5% to 4%.

14. A method for preparing a diaphragm according to any one of claims 1-9, characterized in that, The process includes the following steps: applying a slurry containing a solvent and the organic matrix material to at least one surface of the base film to form the adhesive layer, thereby obtaining the diaphragm.

15. The method for preparing the diaphragm according to claim 14, characterized in that, The slurry includes the slurry according to any one of claims 10-13.

16. The method for preparing the diaphragm according to claim 14 or 15, characterized in that, The process of forming the adhesive layer includes: applying a slurry containing a solvent and the organic matrix material to at least one surface of the base film and then drying it to form the adhesive layer; wherein the drying temperature is 0℃~30℃ and the drying time is 2s~60s.

17. A battery, characterized in that, The device includes a positive electrode, a negative electrode, and a separator as described in any one of claims 1-9, wherein the separator is located between the positive electrode and the negative electrode, and at least one of the positive electrode and the negative electrode is bonded to the separator via the adhesive layer of the separator.

18. The battery according to claim 17, characterized in that, The battery also includes an electrolyte; Preferably, the positive electrode is bonded to the separator through the adhesive layer of the separator, and the wet adhesion force between the separator and the positive electrode is greater than or equal to 1 gf / mm, preferably 1 to 10 gf / mm; Preferably, the negative electrode sheet is bonded to the separator through the adhesive layer of the separator, and the wet adhesion force between the separator and the negative electrode sheet is greater than or equal to 1 gf / mm, preferably 1 to 10 gf / mm.

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