Lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a lithium battery diaphragm and a preparation method thereof, the lithium battery diaphragm comprises a base membrane and a ceramic coating coated on the base membrane, the lithium battery diaphragm also comprises an ion exchange resin coating coated on the ceramic coating, and the lithium battery diaphragm comprises the following components in parts by weight: 1-10 parts of an ion exchange resin coating, the ion exchange resin coating comprises the following raw materials in parts by weight: 70-90 parts of a solvent and 1-10 parts of ion exchange resin. The lithium battery diaphragm is relatively high in lithium ion conductivity and battery capacity retention rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery separators, and in particular relates to a lithium battery separator and a preparation method thereof. Background Art

[0002] With the development of new energy vehicles, battery safety performance, battery capacity, battery cycle performance, etc. have received widespread attention. The most common safety problem faced by lithium batteries is lithium dendrites, which are formed when lithium ions are reduced during the charging process of lithium batteries. Furthermore, the growth of lithium dendrites will lead to instability of the electrode and electrolyte interface during the cycle of lithium-ion batteries, destroying the generated solid electrolyte interface (SEI) film. During the growth process, lithium dendrites will continuously consume electrolyte and cause irreversible deposition of metallic lithium to form dead lithium, which will eventually manifest as low coulomb efficiency and battery capacity decay; the formation of lithium dendrites will even pierce the diaphragm and cause internal short circuits in lithium-ion batteries, causing thermal runaway of the battery and causing combustion and explosion. Therefore, improving lithium dendrites has become an important issue.

[0003] Currently, adding iodine-containing additives to lithium batteries can improve lithium dendrites. Iodide ions and iodite ions spontaneously react with Li and Li2O at the initial interface to make the Li metal surface smooth, ultimately leading to significant improvements in interface resistance and dendrite suppression. However, they will react with the lithium anode through the separator, causing lithium loss. Summary of the invention

[0004] In view of this, the present invention provides a lithium battery separator and a preparation method thereof, which solves the problem of lithium dendrites without causing loss of battery capacity. The lithium battery separator is beneficial to improving the lithium ion conductivity and battery capacity retention rate of the lithium battery.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A lithium battery separator comprises a base film and a ceramic coating coated on the base film. The lithium battery separator also comprises an ion exchange resin coating coated on the ceramic coating. The raw materials of the ion exchange resin coating comprise 70-90 parts of a solvent and 1-10 parts of an ion exchange resin in parts by weight.

[0007] In one embodiment, the weight proportion of the solvent may be, for example, 70 parts, 80 parts or 90 parts. In a preferred embodiment, the weight proportion of the solvent is 80-90 parts.

[0008] In one embodiment, the weight proportion of the ion exchange resin can be, for example, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts. In a preferred embodiment, the weight proportion of the ion exchange resin is 1-5 parts.

[0009] In a preferred embodiment, the solvent includes a first solvent and a second solvent. The ion exchange resin and the first solvent are pre-mixed and prepared into ion exchange resin particles, and then the ion exchange resin particles and the second solvent are mixed.

[0010] In a preferred embodiment, the mass fraction of the ion exchange resin in the ion exchange resin particles is 10%-20%; and / or, the particle size of the ion exchange resin particles is 0.3 μm - 0.6 μm; and / or, the ion exchange resin and the first solvent are mixed and then ground by a sand mill to obtain particles.

[0011] In a preferred embodiment, the volume ratio of the first solvent to the second solvent is (5 - 10):(20 - 40), and the first solvent and the second solvent are independently selected from one or more combinations of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or N-methylpyrrolidone.

[0012] In a preferred embodiment, the ion exchange resin includes one or more combinations selected from strongly acidic cation resins and weakly acidic cation resins.

[0013] In a preferred embodiment, the raw materials of the ion exchange resin coating further include 5 - 20 parts of a binder; the binder includes one or more combinations selected from polyvinylidene fluoride, carboxymethyl cellulose, polymethyl methacrylate, pectin, polyamideimide, polyimide, and lithium polyacrylate.

[0014] In an embodiment, the weight parts of the binder can be, for example: 5 parts, 6 parts, 7 parts, 9 parts, 13 parts, 17 parts, or 20 parts; in a preferred embodiment, the weight parts of the binder are 5 - 10 parts.

[0015] In a preferred embodiment, the raw materials of the ion exchange resin coating further include 1 - 5 parts of an ionic liquid; the ionic liquid includes one or more combinations selected from imidazole-based, pyridine-based, quaternary ammonium-based, quaternary phosphonium-based, pyrrolidine-based, piperidine, and functional ionic liquids.

[0016] In a preferred embodiment, the base film includes a polyethylene separator, and the thickness of the base film is 4 - 12 μm; and / or, the thickness of the ceramic coating is 1 - 2 μm; and / or, the thickness of the ion exchange resin coating is 0.5 - 1.5 μm.

[0017] In a preferred embodiment, the ceramic coating is made from a ceramic slurry, and the raw materials of the ceramic slurry include one or more combinations selected from alumina, boehmite, silica, and lithium titanium aluminum phosphate.

[0018] The present invention also adopts the following technical solution:

[0019] A method for preparing a lithium battery separator comprises the following steps:

[0020] S1. providing a base film having a ceramic coating on its surface;

[0021] S2, dispersing the ion exchange resin in the first solvent to prepare ion exchange resin particles;

[0022] S3, mixing the ion exchange resin and the second solvent to prepare a slurry, coating the slurry on the ceramic coating, and obtaining the lithium battery separator after drying.

[0023] In a preferred embodiment, in step S1, the ceramic coating is obtained by coating and drying a ceramic slurry containing lithium aluminum titanium phosphate;

[0024] In step S2, the ion exchange resin and the first solvent are mixed and sand-milled into particles with a particle size of 0.3 μm-0.6 μm to obtain the ion exchange resin particles, wherein the mass fraction of the ion exchange resin in the ion exchange resin particles is 10%-20%;

[0025] In step S3, the ion exchange resin particles, the binder, the ionic liquid and the second solvent are mixed to obtain an ion exchange resin slurry, the ion exchange resin slurry is coated on the ceramic coating, and dried to obtain an ion exchange resin coating;

[0026] The ion exchange resin comprises a strongly acidic styrene cation exchange resin, the total weight of the first solvent and the second solvent is 70-90 parts, the weight of the ion exchange resin is 1-10 parts, the weight of the binder is 5-20 parts, and the weight of the ionic liquid is 1-5 parts.

[0027] The present invention adopts the above solution, which has the following advantages compared with the prior art:

[0028] The lithium battery separator of the present invention first coats a ceramic coating on at least one side of the base film, and then coats an ion exchange resin coating on the ceramic coating. The ion exchange resin contains abundant sulfonic acid groups and carboxylic acid groups, which help to strengthen the interaction between the separator and the electrolyte, promote the conduction of lithium ions, and limit the transfer of anions, thereby preventing iodine ions and harmful byproducts from corroding the lithium negative electrode through the separator. At the same time, the sulfonic acid group is a polar functional group, which has the function of stabilizing ion pairs, making the charge distribution of the ion pairs more stable, further improving the ionic conductivity of the lithium battery, and at the same time can improve the liquid absorption of the separator to the electrolyte, improve the contact angle to optimize the performance of the lithium ion battery. DETAILED DESCRIPTION

[0029] The following elaborates in detail in combination with the preferred embodiments of the present invention, so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The present disclosure provides a lithium battery separator and a preparation method thereof. The separator includes a base film, a ceramic coating coated on the base film, and an ion exchange resin coating coated on the ceramic coating. The thickness of the ceramic coating is 1-2 μm, and the thickness of the ion exchange resin coating is 0.5-1.5 μm.

[0031] The ceramic coating is coated on at least one side surface of the base film. Specifically, the ceramic coating is coated on both side surfaces of the base film. The raw materials of the ceramic slurry include one or more combinations selected from alumina, boehmite, silica, and lithium aluminum titanium phosphate. Further, the base film is a polyethylene separator, and the thickness specification of the polyethylene separator is 4-12 μm.

[0032] The raw materials of the ion exchange resin coating include 70-90 parts of solvent, 1-10 parts of ion exchange resin, 5-20 parts of binder, and 1-5 parts of ionic liquid by weight fraction. The ion exchange resin coating is coated on the ceramic coating and dried to obtain the lithium battery separator of the present disclosure. The addition of the ionic liquid makes the ion exchange resin coating have more microporous structures, which not only enhances its selective permeation function, but also can improve the air permeability of the separator, accelerate the absorption of the electrolyte, and improve its liquid retention rate.

[0033] Furthermore, the binder includes one or more combinations selected from polyvinylidene fluoride, carboxymethyl cellulose, polymethyl methacrylate, pectin, polyamideimide, polyimide, and lithium polyacrylate; the ion exchange resin includes one or more combinations selected from strongly acidic cation resins and weakly acidic cation resins, where the strongly acidic cation resin refers to a cation exchange resin containing a strongly acidic functional group and can efficiently perform ion exchange within a wide pH range (including acidic, neutral, and alkaline conditions), such as sulfonic acid type resins, etc.; the weakly acidic cation resin refers to a cation exchange resin containing a weakly acidic functional group and mainly works under neutral to alkaline conditions, having a strong affinity for H+, such as carboxylic acid type resins, phenolic hydroxyl type resins, etc.; the solvent includes a first solvent and a second solvent. The ion exchange resin and the first solvent are pre-mixed and prepared into ion exchange resin particles, and then the ion exchange resin particles and the second solvent are mixed. The volume ratio of the first solvent to the second solvent is (5 - 10):(20 - 40), and the first solvent and the second solvent are independently selected from one or more combinations of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or N-methylpyrrolidone; the ionic liquid includes one or more combinations selected from imidazoles, pyridines, quaternary ammonium salts, quaternary phosphonium salts, pyrrolidines, piperidines, and functional ionic liquids. The functional ionic liquid is a type of room-temperature molten salt compound that, through chemical modification or structural design, introduces specific functional groups or functional units on the basis of traditional ionic liquids, thereby endowing it with special physical, chemical, or biological functions.

[0034] The ion exchange resin of the present disclosure has abundant sulfonic acid groups and carboxylic acid groups, which helps to strengthen the interaction between the separator and the electrolyte, promote the conduction of lithium ions, and limit the transfer of anions, thereby preventing iodide ions and harmful by-products from permeating through the separator and corroding the lithium negative electrode.

[0035] When preparing the lithium battery separator, the following steps are included: S1, providing a base film with a ceramic coating on the surface; S2, dispersing the ion exchange resin in the first solvent and preparing it into ion exchange resin particles; S3, mixing the ion exchange resin and the second solvent to make a slurry, and coating the slurry on the ceramic coating, and drying to obtain the lithium battery separator.

[0036] In step S1, the ceramic coating is obtained by coating and drying a ceramic slurry containing lithium aluminum titanium phosphate; in step S2, the ion exchange resin and the first solvent are mixed and sanded into particles with a particle size of 0.3μm-0.6μm by a sand mill to obtain ion exchange resin particles, the mass fraction of the ion exchange resin in the ion exchange resin particles is 10%-20%, and grinding the ion exchange resin is conducive to its good combination with polyvinylidene fluoride, and its sulfonic acid group and carboxylic acid group can be evenly distributed in the polyvinylidene fluoride coating; in step S3, the ion exchange resin particles, the binder, the ionic liquid and the second solvent are mixed to obtain the ion exchange resin slurry, the ion exchange resin slurry is coated on the ceramic coating, and the ion exchange resin coating is obtained by drying; wherein, the ion exchange resin includes a strongly acidic styrene cation exchange resin, and the total weight of the first solvent and the second solvent is 70-90 parts.

[0037] The lithium battery diaphragm disclosed in the present invention is consistent with the existing diaphragm coating process, does not require additional special equipment, has a convenient process, low cost, and is highly operable.

[0038] In the above embodiment, the ceramic coating can not only increase the heat resistance of the diaphragm, but also the lithium source-rich lithium aluminum titanium phosphate can supplement lithium for the lithium battery, increase the battery capacity and cycle performance, and the strong and weak acid ion exchange resins are dispersed in the solvent and then sanded to become small particle size resins, which is conducive to their good combination with polyvinylidene fluoride, and its sulfonic acid group and carboxylic acid group can be evenly distributed in the polyvinylidene fluoride coating. The processing method is simple and easy to operate, and the product is stable and easy to improve. At the same time, the sulfonic acid group and the carboxylic acid group help to strengthen the interaction between the diaphragm and the electrolyte, promote the conduction of lithium ions, and limit the transfer of anions, thereby preventing iodine ions and harmful by-products from corroding the lithium negative electrode through the diaphragm, so that lithium dendrites are solved again, and the battery capacity will not be lost. The addition of ionic liquid makes the composite coating of strong and weak acid ion exchange resins doped with polyvinylidene fluoride have more microporous structures, which not only enhances its selective permeability function, but also improves the permeability of the diaphragm, accelerates the absorption of the electrolyte, and improves its liquid retention rate.

[0039] The present invention is further described in detail below with reference to specific embodiments.

[0040] Example 1

[0041] The steps for preparing lithium battery separator are as follows:

[0042] (1) Coating ceramic diaphragm on polyethylene diaphragm: Set the coating machine parameters to 70m / min coating speed, 50°C oven temperature, 160LPI gravure roller line count, and 65μm depth. Coat alumina slurry on 7μm polyethylene diaphragm with a coating thickness of 2μm.

[0043] (2) Strong acidic ion exchange resin sanding: For better grinding effect, first evenly disperse strong acidic styrene cation exchange resin in N-methylpyrrolidone. The mass fraction of the ion exchange resin in N-methylpyrrolidone is 20%; set the sand mill parameters: the air pressure of the feed pump is 0.1 MPa, the rotation speed is 1000 ± 20 rpm, the discharge temperature < 40 °C, and the cylinder pressure < 0.15 MPa. Sand the strong acidic styrene cation exchange resin dispersed in N-methylpyrrolidone until the particle size reaches 0.5 μm.

[0044] (3) Preparation of slurry: Take the sanded strong acidic styrene cation exchange resin, 28 kg of N-methylpyrrolidone solvent, 10 kg of polyvinylidene fluoride, and 2 kg of ionic liquid 1-butyl-3-methylimidazolium chloride and put them into the pulping tank. Set the revolution speed of the stirrer to 30 rpm and the rotation speed to 1500 rpm to homogenize the slurry for 1.5 hours.

[0045] (4) Preparation of the finished diaphragm: Set the coating machine parameters: the coating speed is 70 m / min, the oven temperature is 50 °C, the number of lines of the gravure roll is 160 LPI, and the depth is 65 μm. Continuously coat the strong acidic styrene cation exchange resin-doped polyvinylidene fluoride slurry on both sides of the diaphragm with an alumina coating on both sides, and the coating thickness is 2 μm.

[0046] In step (2), the weight of the ion exchange resin is 2 kg, and the weight of N-methylpyrrolidone is 8 kg; in steps (2) and (3), the N-methylpyrrolidone solvent is used for grinding the strong acidic styrene cation exchange resin and making the slurry respectively.

[0047] The polyethylene diaphragm of this example has a thickness of 7 μm; the ion exchange resin is a strong acidic ion exchange resin; the solvent is N-methylpyrrolidone; the ionic liquid is an imidazole type; the main ceramic material is alumina.

[0048] Example 2

[0049] Replace the alumina in Example 1 with lithium titanium aluminum phosphate powder, and the others are the same as Example 1.

[0050] Example 3

[0051] Change the thickness of the polyethylene diaphragm in Example 1 to 4 μm, and the others are the same as Example 1.

[0052] Example 4

[0053] Change the thickness of the polyethylene diaphragm in Example 1 to 12 μm, and the others are the same as Example 1.

[0054] Example 5

[0055] Replace the strongly acidic styrene cation exchange resin in Example 1 with a weakly acidic cation exchange resin of the acrylic series.

[0056] Example 6

[0057] The weight fraction of the strongly acidic styrene cation exchange resin is 1 part, the weight fraction of the ionic liquid 1-butyl-3-methylimidazolium chloride is 5 parts, and the weight fraction of polyvinylidene fluoride is 20 parts. Other conditions are the same as in Example 1.

[0058] Example 7

[0059] The weight fraction of the strongly acidic styrene cation exchange resin is 10 parts, the weight fraction of the ionic liquid 1-butyl-3-methylimidazolium chloride is 1 part, and the weight fraction of polyvinylidene fluoride is 5 parts. Other conditions are the same as in Example 1.

[0060] Comparative Example 1

[0061] (1) Coating a ceramic separator on a polyethylene separator: Set the coating machine parameters as a coating speed of 70 m / min, an oven temperature of 50 °C, an intaglio roller line count of 160 LPI, and a depth of 65 μm. Coat alumina slurry on a 7-μm polyethylene separator with a coating thickness of 2 μm.

[0062] (2) Grinding the strongly acidic ion exchange resin: For better grinding effect, first evenly disperse the strongly acidic styrene cation exchange resin in N-methylpyrrolidone, and the mass fraction of the ion exchange resin in N-methylpyrrolidone is 20%; Set the sand mill parameters as the feed pump air pressure of 0.1 MPa, the rotation speed of 1000 ± 20 rpm, the discharge temperature < 40 °C, and the cylinder pressure < 0.15 MPa. Grind the strongly acidic styrene cation exchange resin dispersed in N-methylpyrrolidone to a particle size of 0.5 μm.

[0063] (3) Preparing the slurry: Take the ground strongly acidic styrene cation exchange resin, 30 kg of N-methylpyrrolidone solvent, and 10 kg of polyvinylidene fluoride and put them into the pulping tank. Set the mixer to rotate at 30 rpm for revolution and 1500 rpm for rotation to homogenize the slurry for 1.5 hours.

[0064] (4) Preparing the finished separator: Set the coating machine parameters as a coating speed of 70 m / min, an oven temperature of 50 degrees Celsius, an intaglio roller line count of 160 LPI, and a depth of 65 μm. Continuously coat the slurry of strongly acidic styrene cation exchange resin doped with polyvinylidene fluoride on both sides of the separator with a double-sided alumina coating, with a coating thickness of 2 μm.

[0065] That is, in Comparative Example 1, the ionic liquid 1-butyl-3-methylimidazolium chloride in Example 1 was not added, and 2 kg more of N-methylpyrrolidone solvent was added.

[0066] Comparative Example 2

[0067] (1) Coating ceramic diaphragm on polyethylene diaphragm: Set the coating machine parameters to 70m / min coating speed, 50°C oven temperature, 160LPI gravure roller line count, and 65μm depth. Coat alumina slurry on 7μm polyethylene diaphragm with a coating thickness of 2μm.

[0068] (2) Preparation of slurry: 38 kg of N-methylpyrrolidone solvent, 10 kg of polyvinylidene fluoride, and 2 kg of ionic liquid 1-butyl-3-methylimidazolium chloride were put into a slurry tank, and the stirrer was set to rotate at 30 rpm and 1500 rpm for homogenization for 1.5 hours.

[0069] (3) Preparation of finished diaphragm: Set the coating machine parameters to a coating speed of 70 m / min, an oven temperature of 50 degrees Celsius, a gravure roller line number of 160 LPI, and a depth of 65 μm. Continue to double-side coat the diaphragm coated with alumina coating with a strong acid styrene cation exchange resin doped with polyvinylidene fluoride slurry, with a coating thickness of 2 μm.

[0070] That is, in Comparative Example 2, the sand grinding and addition of the strong acid styrene cation exchange resin in Example 1 were eliminated, and an equal amount of N-methylpyrrolidone solvent was added, and normal coating was performed.

[0071] Comparative Example 3

[0072] Coating ceramic diaphragm on polyethylene diaphragm: Set the coating machine parameters to 70m / min coating speed, 50°C oven temperature, 160LPI gravure roller line number, and 65μm depth. Coat alumina slurry on 7μm polyethylene diaphragm with a coating thickness of 2μm, that is, comparative example 3 cancels the polymer coating in Example 1. Strong acid styrene cation exchange resin doped with polyvinylidene fluoride coating.

[0073] Detection of lithium ion conductivity and battery capacity retention rate after 500 cycles in the embodiments and comparative examples:

[0074] (1) Preparation of positive electrode sheets: active material lithium cobalt oxide, conductive carbon black, binder polyvinylidene fluoride, and solvent N-methylpyrrolidone NMP are stirred and mixed in a mass ratio of 64:3:3:30 to form a slurry, which is then coated on aluminum foil, dried, cold pressed, and cut into strips to prepare positive electrode sheets.

[0075] (2) Preparation of negative electrode sheets: Active material graphite, binder styrene-butadiene rubber, thickener sodium carboxymethyl cellulose, and deionized water are stirred and mixed in a mass ratio of 62:2:1:35 to form a slurry, which is then coated on copper foil and dried, cold pressed, and cut into strips to form negative electrode sheets.

[0076] (3) Lamination: The positive electrode sheets, negative electrode sheets and coated separators are cut twice according to the size of the battery to be produced, and the conductive tabs for the battery cells are formed using a die-cutting machine; the cut positive and negative electrode sheets and separators are assembled together, and after gluing, the electrode core is formed.

[0077] (4) Assembling soft-pack batteries: Using special welding equipment, the tabs of the stacked battery cells are welded; the electrode cores produced in the previous step are placed into the aluminum-plastic film with holes punched in it for packaging; the electrolyte is injected into the packaged battery cells from the reserved injection port to obtain a lithium-ion soft-pack battery, wherein the electrolyte is a 1 mol / L LiPF6 solution of ethylene carbonate EC / dimethyl carbonate DEC (the volume ratio of EC to DEC is 1:1).

[0078] At 25°C, the battery was charged at a constant current of 1C to 4.4V, then charged at a constant voltage of 4.4V to 0.05C, and then discharged at a discharge current of 1C to 2.0V. The above process was repeated to test the lithium ion conductivity after 500 cycles.

[0079] Next, the thermal shrinkage, puncture strength and liquid absorption rate of the batteries in the embodiments and comparative examples were measured, wherein the thermal shrinkage was based on GB / T12027-2004 Plastics-Film and Sheet-Test Method for Dimensional Change Rate after Heating; the puncture strength was measured according to GB / T36363-2018; the liquid absorption rate was measured according to QB / T2303.11-2008 "Battery Pulp Layer Paper Part 11: Determination of Liquid Absorption".

[0080] The test results of the above embodiments and comparative examples are as follows:

[0081] Table 1

[0082]

[0083]

[0084] It can be seen from all the examples and comparative examples that, except for the slightly higher thermal shrinkage of the diaphragm in Example 3, the thermal shrinkage resistance of the other diaphragms coated with ceramic coatings is very excellent.

[0085] It can be seen from Examples 1 and 2 that the measured performances of both are very excellent. However, after the ceramic powder is replaced with lithium aluminum titanium phosphate, since lithium aluminum titanium phosphate has its own lithium ions and has more lithium sources, the lithium source can be replenished in time when lithium ions are consumed during the cycle of the lithium battery. Therefore, Example 2 has higher lithium ion conductivity and battery capacity retention rate.

[0086] Comparing Example 1 with Examples 3 and 4, it can be obtained that reducing the diaphragm thickness can increase the capacity of the active substances in the lithium battery. Therefore, the ionic conductivity is improved to a certain extent. However, due to the reduced thickness, the voids in the diaphragm decrease, so the liquid absorption property and puncture strength are reduced to a certain extent. An overly low puncture strength may increase the safety hazards of the battery. Similarly, after the thickness of the polyvinyl film in Example 4 increases, the puncture strength increases, and the lithium ion conductivity decreases to a certain extent.

[0087] Comparing Example 1 with Examples 5 and Comparative Example 2, it can be obtained that strong and weak acidic ion exchange resins have the effect of improving ionic conductivity and battery capacity, can promote the conduction of lithium ions, limit the transfer of anions, thereby preventing iodide ions and harmful by-products from permeating through the diaphragm to corrode the lithium negative electrode. While the lithium dendrites are resolved, the battery capacity will not be lost. Among them, the strong acidic ion exchange resin has a better effect.

[0088] From the data of Example 1 and Comparative Example 1, it can be obtained that after canceling the addition of the ionic liquid, the microporous structure of the ion exchange resin coating is greatly reduced, and its performance is reduced to a certain extent.

[0089] From the data of Example 1 and Comparative Example 3, it can be obtained that after canceling the doping of the strong acidic ion exchange resin in the polyvinylidene fluoride coating, not only the excellent functions of the sulfonic acid group and carboxylic acid group are missing, but also the binding property between the polyvinylidene fluoride and the positive and negative electrodes is reduced, the battery consistency becomes poor, and its performance is reduced.

[0090] It can be understood that the same or similar parts in the above-mentioned embodiments can be referred to each other. For the content not detailed in some embodiments, reference can be made to the same or similar content in other embodiments.

[0091] As shown in this specification and the claims, the terms "comprising" and "including" only indicate the inclusion of the clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements. The term "and / or" used herein includes any combination of one or more of the related listed items.

[0092] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0093] If a numerical range is recited herein, unless otherwise specified, the range is intended to include its endpoints and all integers and decimals within that range.

[0094] The above embodiments are only for illustrating the technical concept and features of the present invention, and are a preferred embodiment. The purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it is not intended to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A lithium battery separator, comprising a base film and a ceramic coating coated on the base film, characterized in that: The lithium battery separator also includes an ion exchange resin coating coated on the ceramic coating. The raw materials of the ion exchange resin coating include 70-90 parts of solvent and 1-10 parts of ion exchange resin in parts by weight.

2. The lithium battery separator according to claim 1, characterized in that The solvent includes a first solvent and a second solvent. The ion exchange resin and the first solvent are mixed in advance to prepare ion exchange resin particles, and then the ion exchange resin particles and the second solvent are mixed.

3. The lithium battery separator according to claim 2, characterized in that: The mass fraction of the ion exchange resin in the ion exchange resin particles is 10%-20%; and / or the particle size of the ion exchange resin particles is 0.3 μm-0.6 μm; and / or the ion exchange resin and the first solvent are mixed and then sand-milled to obtain particles.

4. The lithium battery separator according to claim 2, characterized in that: The volume ratio of the first solvent to the second solvent is (5-10):(20-40), and the first solvent and the second solvent are independently selected from a combination of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone.

5. The lithium battery separator according to any one of claims 1 to 4, characterized in that: The ion exchange resin includes a combination of one or more selected from a strong acid cation resin and a weak acid cation resin.

6. The lithium battery separator according to any one of claims 1 to 4, characterized in that: The raw materials of the ion exchange resin coating also include 5-20 parts of a binder; the binder includes a combination of one or more selected from polyvinylidene fluoride, carboxymethyl fiber, polymethyl methacrylate, pectin, polyamide-imide, polyimide and lithium polyacrylate.

7. The lithium battery separator according to claims 1 to 4, characterized in that: The raw materials of the ion exchange resin coating also include 1-5 parts of ionic liquid; the ionic liquid includes one or more combinations selected from imidazoles, pyridines, quaternary ammoniums, quaternary phosphoniums, pyrrolidines, piperidines and functional ionic liquids.

8. The lithium battery separator according to claim 1, characterized in that: The base film comprises a polyethylene diaphragm, and the thickness of the base film is 4-12 μm; and / or the thickness of the ceramic coating is 1-2 μm; and / or the thickness of the ion exchange resin coating is 0.5-1.5 μm.

9. The lithium battery separator according to claim 1, characterized in that: The ceramic coating is made of ceramic slurry, and the raw materials of the ceramic slurry include a combination of one or more selected from alumina, boehmite, silicon dioxide and lithium aluminum titanium phosphate.

10. A method for preparing a lithium battery separator according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. providing a base film having a ceramic coating on its surface; S2, dispersing the ion exchange resin in the first solvent to prepare ion exchange resin particles; S3, mixing the ion exchange resin and the second solvent to prepare a slurry, coating the slurry on the ceramic coating, and obtaining the lithium battery separator after drying.

11. The preparation method according to claim 10, characterized in that: In step S1, the ceramic coating is obtained by coating and drying a ceramic slurry containing lithium aluminum titanium phosphate; In step S2, the ion exchange resin and the first solvent are mixed and sand-milled into particles with a particle size of 0.3 μm-0.6 μm to obtain the ion exchange resin particles, wherein the mass fraction of the ion exchange resin in the ion exchange resin particles is 10%-20%; In step S3, the ion exchange resin particles, the binder, the ionic liquid and the second solvent are mixed to obtain an ion exchange resin slurry, the ion exchange resin slurry is coated on the ceramic coating, and dried to obtain an ion exchange resin coating; The ion exchange resin comprises a strongly acidic styrene cation exchange resin, the total weight of the first solvent and the second solvent is 70-90 parts, the weight of the ion exchange resin is 1-10 parts, the weight of the binder is 5-20 parts, and the weight of the ionic liquid is 1-5 parts.

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