Diaphragm coating material capable of being quickly bonded with pole piece as well as preparation method and application of diaphragm coating material

Abstract

The invention provides a diaphragm coating material quickly bonded with a pole piece as well as a preparation method and application thereof, and belongs to the technical field of thin film preparation. The film comprises the following components in parts by mass: 1-20 parts of modified PVDF, 1-15 parts of an acrylonitrile multipolymer, 1-5 parts of a dispersant, 2-10 parts of a water-based polymer binder, 0.1-1 part of a wetting agent and 55-185 parts of deionized water. The preparation method comprises the following steps: uniformly mixing the acrylonitrile multipolymer, the dispersant, the deionized water and the modified PVDF, grinding, heating while stirring, adding the aqueous polymer binder, continuously heating and stirring, cooling to room temperature, and adding the wetting agent to obtain the coating material which can be used for surface coating of a polyolefin base film or a film with a coating. The pretreated PVDF is coated with the water-based polymer binder, the expansion rate and the bonding strength are optimized, rapid bonding is achieved, the method can be used for rapid production of laminated batteries, the production efficiency and the qualification rate of the batteries are greatly improved, and the method has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of thin film preparation, and in particular to a diaphragm coating material capable of rapid bonding to a pole piece, and a preparation method and application thereof. Background Art

[0002] With the increasing popularity of electronic devices and the rise of the electric vehicle market, the demand for and performance requirements for lithium-ion batteries continue to increase. Separators are crucial in lithium-ion batteries, separating the positive and negative electrodes, preventing short circuits, and providing pathways for lithium ion migration. Their performance impacts battery charge and discharge performance, cycle life, and safety. High-quality separators ensure a stable interface, low internal resistance, and the ability to close micropores during abnormal temperature increases to prevent thermal runaway, making them key to the efficient and safe operation of lithium batteries.

[0003] Lithium-ion batteries are primarily manufactured in two ways: wound and laminated. The advantages of wound batteries lie in their mature process, high production efficiency, regular shape for easy installation, relatively low equipment costs, and high product consistency. However, their energy density is limited, their internal structure is unstable, they are prone to wave-like deformation at corners, and their heat dissipation is poor, making them unsuitable for special-shaped batteries. Laminated batteries offer high energy density, a stable internal structure, and a long cycle life, making them suitable for large-sized and special-shaped batteries. They also have excellent charge and discharge performance, but they have lower production efficiency, require large equipment investments, and are difficult to manufacture. They require high equipment precision and operator skill, and their yield rate is relatively low. During laminated battery production, the separator and electrode need to be precisely and firmly bonded together. With the continuous improvement of laminated battery processing technology and the increasing speed of production, higher requirements have been placed on the bonding strength and speed between the separator and electrode.

[0004] The current mainstream technologies for coating lithium-ion battery diaphragms can be divided into three major systems: inorganic coating, organic coating, and composite coating. Among them, inorganic coating mostly uses inorganic ceramic materials such as alumina and boehmite (such as CN118712657B). By constructing a high-temperature resistant protective layer, it significantly improves the heat resistance and puncture resistance of the diaphragm. While enhancing the safety performance of the battery, its unique microporous maze structure can effectively extend the lithium ion migration path, thereby reducing the battery self-discharge rate. The organic coating system is represented by polymer materials such as polyvinylidene fluoride (PVDF) (such as CN202310349038.9), polymethyl methacrylate (PMMA) (such as CN202411169892.8) and aramid. This type of coating can significantly enhance the interfacial bonding between the diaphragm and the electrode sheet, which is beneficial to improving the battery cycle life. However, due to the limitations of traditional processes, the above-mentioned organic materials require high temperature and high pressure conditions to achieve effective interface bonding, which cannot meet the process requirements of rapid bonding. As a result, relative displacement between the pole pieces and the diaphragm is very likely to occur during the production process of stacked batteries. This technical bottleneck seriously restricts the production efficiency of the stacking process.

[0005] While some approaches have been taken to improve the performance of the battery, such as increasing the binder ratio in the coating or adding other types of adhesive, there is a lack of targeted development for rapid bonding between battery separators and electrode plates. Increasing the amount of adhesive has little effect and can actually lead to a loss of separator permeability and increased battery internal resistance, which in turn affects battery energy density and negatively impacts the rate discharge and cycling performance of lithium-ion batteries.

[0006] In summary, the defects of the existing technology mainly include: 1) slow bonding speed and low bonding ability, which cannot meet the high-speed production requirements of stacked batteries; 2) in order to ensure the bonding type, excessive adhesive is used, resulting in a decrease in the permeability of the diaphragm; 3) lack of adaptability design for the negative electrode material, and the interface is prone to failure due to volume expansion.

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

[0008] The purpose of the present invention is to provide a diaphragm coating material that can quickly bond to the pole piece, as well as its preparation method and application. By coating the pretreated PVDF with an aqueous polymer binder, the expansion rate and bonding strength are optimized to achieve rapid bonding. It can be used for the rapid production of laminated batteries, greatly improving the battery production efficiency and qualified rate, and has broad application prospects.

[0009] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a diaphragm coating material that quickly bonds to the electrode: in parts by mass, it includes 1-20 parts of modified PVDF, 1-15 parts of acrylonitrile multipolymer, 1-5 parts of dispersant, 2-10 parts of aqueous polymer binder, 0.1-1 part of wetting agent, and 55-185 parts of deionized water.

[0011] In a second aspect, the present invention also provides a method for preparing the diaphragm coating material that quickly bonds to the electrode. According to the mass parts, the acrylonitrile multipolymer, dispersant, deionized water and modified PVDF are evenly mixed and ground. The obtained modified PVDF dispersion is heated while stirring, and then an aqueous polymer binder is added. The heating and stirring are continued to effectively knead and coat the PVDF. After cooling to room temperature, a wetting agent is added to obtain the coating material.

[0012] Optionally, the acrylonitrile multipolymer includes one or more of acrylonitrile-acrylamide-acrylate copolymer, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer or acrylonitrile-methacrylate copolymer.

[0013] Optionally, the dispersant includes one or more of a nonionic dispersant, a fluorine-containing aqueous dispersant, a polyurethane dispersant or a polyester dispersant.

[0014] Optionally, the water-based polymer binder includes one or more of PAA (polyacrylic acid), PMMA (polymethyl methacrylate), PAM (polyacrylamide), SBR (styrene-butadiene rubber), and WPU (water-based polyurethane). The water-based polymer binder has high bonding strength, a certain degree of toughness, and a relatively fast curing speed, and can effectively coat PVDF, achieving rapid bonding between the diaphragm and the electrode while providing high bonding strength. This allows the diaphragm and electrode to fit tightly together, thereby increasing the production speed and yield rate of laminated batteries and significantly reducing battery manufacturing costs.

[0015] Optionally, the wetting agent includes one or more of an organosilicon-modified wetting agent, a polyether wetting agent, an acetylene alcohol wetting agent or an alcohol wetting agent.

[0016] PVDF, as a traditional adhesive, is the most widely used adhesive in commercial lithium-ion batteries for manufacturing positive electrodes. PVDF has excellent electrochemical stability, mechanical properties, processing properties, oxidation resistance of high-energy C-F bonds, and corrosion resistance. PVDF can provide close adhesion between the electrode and the diaphragm and ion transport in lithium-ion batteries. PVDF itself does not conduct lithium ions. To facilitate ion transport, PVDF expands as it absorbs the electrolyte. However, this expansion reduces its adhesive properties. PVDF is effectively coated with a water-based polymer binder. A certain coating ratio can achieve an optimal degree of PVDF expansion. The water-based polymer binder can also provide initial adhesion to the positive and negative electrodes of lithium-ion batteries, ensuring that the electrode and diaphragm do not shift during the battery production process. After hot pressing, the diaphragm and electrode are tightly bonded together with PVDF. Good adhesion can reduce voids within the battery and improve the battery's energy density and cycle life.

[0017] Preferably, the modified PVDF is obtained by soaking PVDF in an alkaline solution at a certain temperature and then washing it with deionized water.

[0018] Furthermore, the concentration of the alkaline solution is 1-6 mol / L.

[0019] Furthermore, the soaking temperature is 25-80°C, and the soaking time is 5-30 minutes. Preferably, the soaking temperature is 45-80°C.

[0020] It can be speculated that treatment with an alkaline solution at the aforementioned temperature triggers a dehydrofluorination reaction (HDF) of the PVDF molecular chain, forming a carbon-carbon double bond structure. This process partially destroys the original fluorine-carbon bond network, creating conjugated double bonds and some oxygen-containing groups on the material's surface. This increases the material's surface polarity, resulting in more uniform dispersion in water and smaller particle size. It also increases the material's chemical activity, improving its subsequent binding ability with different polymer materials, enhancing the coating effect, and making it suitable for various coating processes.

[0021] Optionally, the alkaline solution includes one or more of an aqueous solution of sodium hydroxide, potassium hydroxide, ammonia water, barium hydroxide, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate or sodium carbonate.

[0022] Furthermore, the temperatures of the heating and continued heating are both 40-80°C.

[0023] Preferably, the heating temperature is 65-80°C; and the continued heating temperature is 50-65°C.

[0024] Furthermore, preferably, the mass ratio of the modified PVDF to the aqueous polymer binder is 6:1-2:1; preferably, the mass ratio of the modified PVDF to the aqueous polymer binder is 4:1-3:1.

[0025] In a third aspect, the present invention further provides a lithium-ion battery separator, comprising a polyolefin-based film or a coated film, wherein at least one surface of the separator is coated with the coating material or the coating material obtained by the preparation method.

[0026] Optionally, the coating can be one of micro-concave roller coating, spin spray coating or dot matrix coating, with a single-side coating thickness of 0.5-5 μm, and after drying, a coated lithium-ion battery separator that can quickly adhere to the pole piece is obtained.

[0027] Compared with the existing technology, the present invention adopts a solution of coating PVDF with a water-based polymer binder, which solves the contradiction between expansion rate and bonding strength. While meeting the bonding strength with the electrode material, it improves the bonding speed and realizes rapid bonding with the battery electrode. It can be firmly bonded to the battery electrode in a short time, greatly improving battery production efficiency, adapting to the rapid production requirements of modern battery production, reducing the bonding time and process in the production of stacking equipment, and can greatly save battery manufacturing costs.

[0028] The product of the present invention has high adaptability and can quickly bond not only to the positive electrode material of a battery, but also to the negative electrode material of a battery. It is well known that the positive electrode material of a battery has high surface energy and activity, making it easier to quickly bond, while the surface of the negative electrode material is relatively smooth and difficult to bond. Furthermore, during the battery's charge and discharge process, the negative electrode material undergoes relatively large volume changes, and during lithium insertion and removal, it undergoes a certain degree of volume expansion and contraction, which can easily damage the bonding interface. The present invention uses a water-based polymer binder to coat pre-treated PVDF, solving the problem of slow and weak bonding between the separator and the negative electrode.

[0029] At the same time, the use of water-based coating has low raw material and equipment costs, is environmentally friendly and safe, does not cause the problem of clogging the diaphragm gaps, dries quickly, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 The coating materials prepared in Examples 1-5 and Comparative Examples 1-2 of the present invention were used to compare the peel strength with the negative electrode materials after hot pressing;

[0032] Figure 2 The coating materials prepared for Examples 1-5 of the present invention and Comparative Examples 1-2 were used to compare the peel strength with the positive electrode materials after hot pressing. DETAILED DESCRIPTION

[0033] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0034] As used herein:

[0035] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0036] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0037] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0038] In these examples, parts and percentages are by mass unless otherwise indicated.

[0039] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0040] The test method of hot pressing peel strength in the following examples and comparative examples is as follows:

[0041] (1) Cut the positive and negative plates into strips of fixed width (20*200mm), place the strips on an electric roller machine and compact and roll them twice to make plate strips for use.

[0042] (2) Cut the coating film sample into strips slightly wider than the electrode sample (30*200mm).

[0043] (3) Center the prepared plate sample on the cut membrane sample and place both on a hot press tester. The hot press tester settings are: hot press temperature 80°C, pressure 1 MPa, and hot press time 5 seconds. Start the equipment to prepare the sample and remove the sample after the hot press is completed.

[0044] (4) Replace the peel strength test fixture on the testing machine and adjust the fixture so that the fixture spacing (the lower edge of the upper fixture and the upper edge of the lower fixture) is 30 mm. Fix the sample to be tested after hot pressing on the fixture, clamp the electrode at one end of the fixture and clamp the coating film sample at the other end, and tighten the fixture to fix the sample.

[0045] (5) Clear all force and displacement values ​​and click the start button to start the test. The test stroke is 100 mm. After the test, the average peeling force of the test stroke is measured. Finally, the peeling strength of the hot pressing sample under the specified hot pressing conditions (80°C, 1 MPa, 5 s) is obtained = peeling force / electrode width, unit N / m.

[0046] Hot pressing peel strength is greatly affected by the front-end hot pressing conditions. Under the condition of constant hot pressing temperature and hot pressing pressure, the shorter the hot pressing time, the lower the hot pressing peel strength. The greater the hot pressing peel strength, the stronger the adhesion between the coating and the electrode.

[0047] Example 1

[0048] (1) PVDF was soaked in a 2 mol / L NaOH aqueous solution at 60°C for 15 min and then washed with deionized water to obtain modified PVDF.

[0049] (2) 10 g of acrylonitrile-acrylamide-ammonium acrylate copolymer and 2 g of fluorine-containing aqueous dispersant hexafluorobutyl acrylate were added to 163 g of deionized water in sequence to form an aqueous solution, and then 20 g of modified PVDF was added and stirred rapidly for 90 min. After mixing evenly, it was ground using a sand mill to obtain a uniform modified PVDF dispersion, which was heated to 70 ° C and stirred slowly for 2 h. Then, 5 g of aqueous PMMA binder was added, and heating and stirring were continued at 70 ° C for 1 h to effectively coat the modified PVDF. After cooling to room temperature, 0.2 g of wetting agent polyether-modified siloxane was added and mixed evenly to obtain a coating slurry.

[0050] (3) The prepared coating slurry was applied to both sides of the polyolefin base film using a spin spray coating method, with a single-side coating thickness of 2 μm. After drying, sample 1 was obtained. The performance test results are shown in Table 1. The comparison of the positive and negative electrode peel strength is shown in Table 1. Figure 1 and Figure 2 .

[0051] Example 2

[0052] (1) PVDF was soaked in a 2 mol / L NaOH aqueous solution at 60°C for 15 min and then washed with deionized water to obtain modified PVDF.

[0053] (2) 10 g of acrylonitrile-acrylamide-ammonium acrylate copolymer and 2 g of fluorine-containing aqueous dispersant hexafluorobutyl acrylate were added to 163 g of deionized water in sequence to form an aqueous solution, and then 20 g of modified PVDF was added and stirred rapidly for 90 min. After mixing evenly, it was ground using a sand mill to obtain a uniform modified PVDF dispersion, which was heated to 70 ° C and stirred slowly for 2 h. Then, 5 g of aqueous SBR binder was added and continued to heat and stir at 55 ° C for 1 h to effectively coat the modified PVDF. After cooling to room temperature, 0.2 g of wetting agent polyether-modified siloxane was added and mixed evenly to obtain a coating slurry.

[0054] (3) The prepared coating slurry was applied to both sides of the polyolefin base film using a spin spray coating method, with a single-side coating thickness of 2 μm. After drying, sample 2 was obtained. The performance test results are shown in Table 1. The comparison of the positive and negative electrode peel strength is shown in Table 1. Figure 1 and Figure 2 .

[0055] Example 3

[0056] (1) PVDF was soaked in a 2 mol / L NaOH aqueous solution at 60°C for 15 min and then washed with deionized water to obtain modified PVDF.

[0057] (2) 10 g of acrylonitrile-acrylamide-ammonium acrylate copolymer and 3 g of non-ionic dispersant polyethylene glycol were added to 162 g of deionized water in sequence to form an aqueous solution, and then 20 g of modified PVDF was added and stirred rapidly for 90 min. After mixing evenly, it was ground using a sand mill to obtain a uniform modified PVDF dispersion, which was heated to 70 ° C and stirred slowly for 2 h. Then, 5 g of aqueous PAA binder was added and continued to heat and stir at 70 ° C for 1 h to effectively coat the modified PVDF. After cooling to room temperature, 0.2 g of wetting agent polyether-modified siloxane was added and mixed evenly to obtain a coating slurry.

[0058] (3) The prepared coating slurry was applied to both sides of the polyolefin base film using a spin spray coating method, with a single-side coating thickness of 2 μm. After drying, sample 3 was obtained. The performance test results are shown in Table 1. The comparison of the positive and negative electrode peel strength is shown in Table 1. Figure 1 and Figure 2 .

[0059] Example 4

[0060] (1) PVDF was soaked in a 2 mol / L NaOH aqueous solution at 60°C for 15 min and then washed with deionized water to obtain modified PVDF.

[0061] (2) 10 g of acrylonitrile-butadiene copolymer and 3 g of nonionic dispersant polyacrylate were added to 162 g of deionized water in sequence to form an aqueous solution, and then 20 g of modified PVDF was added and stirred rapidly for 90 min. After mixing evenly, it was ground using a sand mill to obtain a uniform modified PVDF dispersion, which was heated to 70 ° C and stirred slowly for 2 h. Then, 5 g of water-based PAM binder was added and continued to heat and stir at 55 ° C for 1 h to effectively coat the modified PVDF. After cooling to room temperature, 0.2 g of wetting agent polyether-modified siloxane was added and mixed evenly to obtain a coating slurry.

[0062] (3) The prepared coating slurry was applied to both sides of the polyolefin base film using a spin spray coating method, with a single-side coating thickness of 2 μm. After drying, sample 4 was obtained. The performance test results are shown in Table 1. The comparison of the positive and negative electrode peel strength is as follows: Figure 1 and Figure 2 .

[0063] Example 5

[0064] (1) PVDF was soaked in a 2 mol / L NaOH aqueous solution at 60°C for 15 min and then washed with deionized water to obtain modified PVDF.

[0065] (2) 10 g of acrylonitrile-methyl acrylate copolymer and 1.5 g of non-ionic dispersant polyacrylate were added to 168 g of deionized water in sequence to form an aqueous solution, and then 14 g of modified PVDF was added and stirred rapidly for 90 min. After mixing evenly, it was ground using a sand mill to obtain a uniform modified PVDF dispersion, which was heated to 70 ° C and stirred slowly for 2 h. Then 6 g of water-based WPU binder was added and continued to heat and stir at 70 ° C for 1 h to effectively coat the modified PVDF. After cooling to room temperature, 0.2 g of wetting agent polyether-modified siloxane was added and mixed evenly to obtain a coating slurry.

[0066] (3) The prepared coating slurry was applied to both sides of the polyolefin base film using a spin spray coating method, with a single-side coating thickness of 2 μm. After drying, sample 5 was obtained. The performance test results are shown in Table 1. The comparison of the positive and negative electrode peel strength is as follows: Figure 1 and Figure 2 .

[0067] Comparative Example 1

[0068] The difference compared with Example 2 is that the PVDF in step (1) is immersed in a 2 mol / L NaOH aqueous solution at 30°C.

[0069] Comparative Example 2

[0070] The difference compared with Example 2 is that the PVDF modification in step (1) is not performed.

[0071] Table 1 Test results of the performance of the diaphragms after coating in the examples and comparative examples

[0072]

[0073] Through Table 1 and Figure 1 、 2 It can be seen that compared with Comparative Examples 1 and 2, the coating materials prepared by modifying the PVDF in Examples 1-5 and coating it with an aqueous polymer binder have much better hot pressing peel strength for both the positive and negative electrodes than those without PVDF modification or when the modified immersion temperature is too low.

[0074] Depend on Figure 1 and 2 It can be seen that the hot pressing time of the present application can be shortened to 5s, which is much shorter than the conventional hot pressing time of 1min-3min in the current market, reflecting the rapid bonding ability of the product of the present invention.

[0075] It can be seen from Examples 2 and 4 that when the modified PVDF dispersion is added with the aqueous polymer binder and the temperature at which it is heated and stirred is slightly lower, the effect is better.

[0076] As shown in Table 1, the coated separators of the present invention, while generally requiring 10-20% less coating than the control, offer stronger adhesion to both the positive and negative electrodes, maintaining relatively high bonding strength for both the positive and negative electrodes. This makes them suitable for various thermal composite rapid bonding battery devices, eliminating bonding limitations and fully accelerating battery production.

[0077] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0078] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A diaphragm coating material that quickly bonds to a pole piece, characterized in that: In parts by mass, the composition comprises 1-20 parts of modified PVDF, 1-15 parts of acrylonitrile multipolymer, 1-5 parts of dispersant, 2-10 parts of water-based polymer binder, 0.1-1 part of wetting agent, and 55-185 parts of deionized water.

2. A method for preparing the diaphragm coating material for rapid bonding with the electrode according to claim 1, characterized in that: According to the mass parts, the acrylonitrile multipolymer, dispersant, deionized water and modified PVDF are uniformly mixed, ground, heated while stirring, and then an aqueous polymer binder is added. The heating and stirring are continued. After cooling to room temperature, a wetting agent is added to obtain the coating material.

3. The preparation method according to claim 2, characterized in that The acrylonitrile multi-component copolymer includes one or more of acrylonitrile-acrylamide-acrylate copolymer, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer or acrylonitrile-methacrylate copolymer; and / or, the dispersant comprises one or more of a nonionic dispersant, a fluorine-containing aqueous dispersant, a polyurethane dispersant or a polyester dispersant; and / or, the aqueous polymer binder comprises one or more of polyacrylic acid, polymethyl methacrylate, polyacrylamide, styrene-butadiene rubber, and aqueous polyurethane; The wetting agent includes one or more of an organosilicon-modified wetting agent, a polyether wetting agent, an acetylene alcohol wetting agent or an alcohol wetting agent.

4. The preparation method according to claim 2, characterized in that The modified PVDF is obtained by soaking PVDF in an alkaline solution at a certain temperature and then washing it with deionized water.

5. The preparation method according to claim 4, characterized in that The concentration of the alkaline solution is 1-6 mol / L; And / or, the soaking temperature is 25-80° C., and the soaking time is 5-30 min.

6. The preparation method according to claim 4 or 5, characterized in that The alkaline solution includes one or more of an aqueous solution of sodium hydroxide, potassium hydroxide, ammonia water, barium hydroxide, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate or sodium carbonate.

7. The preparation method according to claim 2, characterized in that The temperatures for heating and continuing heating are both 40-80°C.

8. The preparation method according to claim 7, characterized in that The heating temperature is 65-80°C; And / or, the temperature of the continued heating is 50-65°C.

9. The preparation method according to claim 2, characterized in that The mass ratio of the modified PVDF to the aqueous polymer binder is 6:1-2:

1.

10. A lithium ion battery separator, characterized in that: The diaphragm comprises a polyolefin-based film or a coated film, and at least one surface of the diaphragm is coated with the coating material according to claim 1 or the coating material prepared by the preparation method according to any one of claims 2 to 8.

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