A polyoxometalate-intercalated hydrotalcite aramid-coated lithium-ion battery separator and its preparation method

Abstract

The present invention relates to the technical field of lithium-ion battery materials, and specifically relates to a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator and a preparation method thereof. The preparation method is as follows: preparing polyoxometalate intercalated hydrotalcite by a peeling and recombination method: adding hydrotalcite into formamide, vigorously stirring under the protection of an inert gas to obtain a suspension, centrifuging the suspension to obtain exfoliated hydrotalcite lamellae, then adding a polyoxometalate aqueous solution to the exfoliated hydrotalcite lamellae and stirring for self-assembly, and finally performing solid-liquid separation to obtain polyoxometalate intercalated hydrotalcite; mixing the polyoxometalate intercalated hydrotalcite with an aramid slurry uniformly to obtain a polyoxometalate intercalated hydrotalcite aramid-coated slurry; coating the polyoxometalate intercalated hydrotalcite aramid-coated slurry on the surface of a base film, passing through a coagulation bath and then drying to obtain a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator. The lithium-ion battery separator has higher thermal stability, and the preparation method is simple and has strong practicability.

Description

Technical Field

[0001] The present invention relates to a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator and a preparation method thereof, belonging to the technical field of lithium-ion battery materials. Background Art

[0002] In recent years, with the rapid development of technology, energy crisis and environmental pollution problems have also emerged one after another. As a green and renewable energy source, lithium-ion batteries have received extensive attention. Due to their advantages such as high working voltage, long cycle life, and no memory effect, lithium-ion batteries are widely used in fields such as digital products, electric vehicles, and energy storage. Among them, the separator, as one of the four main materials in lithium-ion batteries, is particularly important for the performance of the battery, especially the safety performance. Therefore, higher requirements are put forward for separator products.

[0003] Aramid-coated separators have advantages such as high safety, wettability, and antioxidant properties, and are a new type of high-end separator product. Aramid coating can improve the thermal stability of the separator, but still cannot meet the growing market demand. Hydrotalcite is a new type of functional material with a two-dimensional layered structure. Due to the exchangeability of the interlayer anions of hydrotalcite, various guest anions can be introduced into the interlayer to prepare intercalated hydrotalcite. Therefore, it is possible to choose to composite the intercalated hydrotalcite material with the aramid separator to improve the thermal stability of the separator. Chinese Patent Application CN114479654A discloses a preparation method of an organic intercalated hydrotalcite-aramid coating solution and its application in the coating of lithium battery separators. An organic intercalated hydrotalcite is added during the aramid polymerization process to prepare the coating solution. The separator prepared by this method can improve the temperature resistance performance, but the ability of this method to improve the temperature resistance of the separator is also limited. At present, the requirements for the thermal stability of aramid-coated separators are getting higher and higher. Therefore, it is of great value to provide a lithium-ion battery separator with higher thermal stability. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator and a preparation method thereof. The lithium-ion battery separator has higher thermal stability, and the preparation method is simple and has strong practicability.

[0005] The technical solution for the present invention to solve the above technical problems is as follows: A preparation method of a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator, and the preparation method is as follows:

[0006] S1. Preparation of polyoxometalate intercalated hydrotalcite:

[0007] Prepare polyoxometalate intercalated hydrotalcite by the exfoliation-reassembly method: Add hydrotalcite to formamide, stir vigorously under the protection of an inert gas to obtain a suspension, centrifuge the suspension to obtain exfoliated hydrotalcite layers, then add a polyoxometalate aqueous solution to the exfoliated hydrotalcite layers and stir for self-assembly, and finally perform solid-liquid separation to obtain polyoxometalate intercalated hydrotalcite;

[0008] S2. Preparation of Coating Slurry:

[0009] Mix the polyoxometalate-intercalated hydrotalcite with the aramid slurry evenly to obtain the polyoxometalate-intercalated hydrotalcite aramid coating slurry;

[0010] S3. Preparation of Separator:

[0011] Coat the polyoxometalate-intercalated hydrotalcite aramid coating slurry on the surface of the base film, dry it after passing through the coagulation bath to obtain the polyoxometalate-intercalated hydrotalcite aramid coated lithium-ion battery separator.

[0012] Furthermore, the hydrotalcite is at least one of nickel-cobalt hydrotalcite and magnesium-aluminum hydrotalcite.

[0013] Furthermore, the polyoxometalate is any one of Keggin-type polyoxometalate and Weakley-type polyoxometalate.

[0014] Furthermore, the solid content in the suspension is 1-3%.

[0015] Furthermore, the concentration of the polyoxometalate aqueous solution is 5-15 mmol / L, and the mass ratio of the hydrotalcite to the polyoxometalate is 1:(1-4).

[0016] Furthermore, in step S1, when preparing the suspension, the vigorous stirring speed is 1500-2000 r / min, and the vigorous stirring time is 24-48 h; when performing self-assembly, the stirring speed is 800-1200 r / min, and the stirring time is 12-24 h.

[0017] Furthermore, the aramid slurry is para-aramid slurry or meta-aramid slurry, and the solid content of the aramid slurry is 5%-10%;

[0018] The mass content of the polyoxometalate-intercalated hydrotalcite in the coating slurry is 1%-3%.

[0019] Furthermore, in step S3, the coating thickness of the polyoxometalate-intercalated hydrotalcite aramid coating slurry is 1-2 μm.

[0020] Furthermore, the coagulation bath is a two-stage coagulation bath. The first-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath is 50-60%; the second-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath is 75-85%.

[0021] Furthermore, the difference in the volume content of water between the first-stage coagulation bath and the second-stage coagulation bath is not higher than 25%.

[0022] The present invention also discloses a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator, and the polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator is prepared according to the preparation method described in the present invention.

[0023] The beneficial effects of the present invention are as follows:

[0024] In the preparation method of the present invention, polyoxometalate intercalated hydrotalcite is introduced into the separator coating layer. Since the particle size of polyoxometalate intercalated hydrotalcite is nanoscale, the introduction of polyoxometalate intercalated hydrotalcite will not change the original morphology and thickness of the coating layer. In addition, the unique layered structure of hydrotalcite and the stable embedding of polyoxometalate can enhance the thermal stability of the separator. The present invention selects the exfoliation-reassembly method to prepare polyoxometalate intercalated hydrotalcite, which can reduce the steric hindrance during the intercalation-reassembly process, reduce impurity phases, and improve the performance of polyoxometalate intercalated hydrotalcite. Introducing polyoxometalate intercalated hydrotalcite into the lithium-ion battery separator reduces the thermal shrinkage rate of the separator and improves the thermal stability of the separator, having extremely high application value.

[0025] In the preparation method of the present invention, a lithium-ion battery separator is prepared by introducing polyoxometalate intercalated hydrotalcite into the separator coating layer. With suitable exfoliation-reassembly and coagulation bath conditions, a separator product with more excellent thermal stability is finally obtained. Polyoxometalate intercalated hydrotalcite is combined with aramid fibers through intermolecular forces to improve the thermal stability of the aramid-coated lithium-ion battery separator. Description of the Drawings

[0026] Figure 1 It is a scanning electron microscope image of the polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator of Example 1;

[0027] Figure 2 It is a comparison diagram before and after the thermal shrinkage rate test heating of Example 1 and Comparative Example 1. Detailed Embodiments

[0028] The following makes a detailed description of the specific embodiments of the present invention. The present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing the specific embodiments and are not intended to limit the present invention.

[0030] A preparation method of a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator, and the preparation method is as follows:

[0031] S1. Preparation of polyoxometalate intercalated hydrotalcite:

[0032] Preparation of polyoxometalate intercalated hydrotalcite by exfoliation-reassembly method: Hydrotalcite is added to formamide, and exfoliation is carried out by vigorous stirring under the protection of inert gas to obtain a suspension. The suspension is centrifuged to obtain exfoliated hydrotalcite layers, and then an aqueous polyoxometalate solution is added to the exfoliated hydrotalcite layers and stirred for self-assembly. Finally, centrifugation, washing, and drying are carried out to obtain polyoxometalate intercalated hydrotalcite;

[0033] S2. Preparation of coating slurry:

[0034] The polyoxometalate intercalated hydrotalcite and aramid slurry are mixed evenly to obtain a polyoxometalate intercalated hydrotalcite aramid coating slurry;

[0035] S3. Preparation of separator:

[0036] The polyoxometalate intercalated hydrotalcite aramid coating slurry is coated on the surface of the base film, dried after passing through the coagulation bath, and a polyoxometalate intercalated hydrotalcite aramid coated lithium-ion battery separator is obtained.

[0037] Specifically, the hydrotalcite is at least one of nickel-cobalt hydrotalcite and magnesium-aluminum hydrotalcite.

[0038] Specifically, the polyoxometalate is any one of Keggin-type polyoxometalate and Weakley-type polyoxometalate.

[0039] More specifically, the polyoxometalate used in the examples of the present invention is phosphotungstic acid.

[0040] Specifically, the solid content in the suspension is 1-3% (mass content).

[0041] Specifically, the concentration of the aqueous polyoxometalate solution is 5-15 mmol / L, and the mass ratio of the hydrotalcite to the polyoxometalate is 1:(1-4).

[0042] More specifically, the speed of vigorous stirring during the preparation of the suspension is 1500-2000 r / min, and the time of vigorous stirring is 24-48 h; during self-assembly, the stirring speed is 800-1200 r / min, and the stirring time is 12-24 h. During the preparation of the suspension, vigorous stirring is beneficial to the smooth exfoliation of hydrotalcite. During self-assembly, appropriately reducing the stirring speed can ensure the uniformity of the system while avoiding the fragmentation of hydrotalcite layers, and finally obtain excellent polyoxometalate intercalated hydrotalcite, which is more conducive to application in the separator.

[0043] Specifically, the aramid slurry is para-aramid slurry or meta-aramid slurry, and the solid content of the aramid slurry is 5%-10%; in the examples of the present invention, the solvent in the aramid slurry is DMAC.

[0044] The mass content of the polyoxometalate intercalated hydrotalcite in the coating slurry is 1%-3%.

[0045] Specifically, in step S3, the coating thickness of the polyoxometalate intercalated hydrotalcite aramid coating slurry is 1-2 μm, and the coating is double-sided coating or single-sided coating.

[0046] More specifically, the coating method in step S3 can be spraying, roll coating, knife coating, etc. In the embodiment of the present invention, the coating method adopted is knife coating, but it does not limit the present invention.

[0047] Specifically, the coagulation bath is a two-stage coagulation bath. The first-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath is 50-60%; the second-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath is 75-85%.

[0048] Specifically, the difference in the volume content of water between the first-stage coagulation bath and the second-stage coagulation bath is not higher than 25%.

[0049] More specifically, the coagulation baths in the embodiments of the present invention are all at room temperature.

[0050] Specifically, the drying temperature in step S3 is 55-65 °C.

[0051] Specifically, the base film material is an organic polymer base film, including polyethylene, polypropylene, polytetrafluoroethylene, etc. The base film is a dry or wet separator, and the thickness of the base film can be 5-13 μm. The base film used in the embodiment of the present invention is a PE base film purchased from Xingyuan Materials, but it does not limit the present invention.

[0052] A polyoxometalate intercalated hydrotalcite aramid coated lithium-ion battery separator, and the polyoxometalate intercalated hydrotalcite aramid coated lithium-ion battery separator is prepared according to the preparation method described in the present invention.

[0053] Example 1

[0054] A preparation method of a polyoxometalate intercalated hydrotalcite aramid coated lithium-ion battery separator, and the preparation method is as follows:

[0055] S1. Preparation of polyoxometalate intercalated hydrotalcite:

[0056] Prepare polyoxometalate intercalated hydrotalcite by the exfoliation-reassembly method: Add magnesium-aluminum hydrotalcite to formamide, and stir vigorously under nitrogen protection to obtain a suspension. The solid content in the suspension is 2%; the vigorous stirring speed is 1500 r / min, and the vigorous stirring time is 48 h;

[0057] The suspension is centrifuged to obtain exfoliated hydrotalcite layers, and then an aqueous phosphotungstic acid solution is added to the exfoliated hydrotalcite layers and stirred for self-assembly. Finally, it is centrifuged, washed, and dried to obtain polyoxometalate-intercalated hydrotalcite; wherein, the concentration of the aqueous phosphotungstic acid solution is 7 mmol / L, the mass ratio of magnesium-aluminum hydrotalcite to phosphotungstic acid is 1:1, the stirring speed during self-assembly is 1000 r / min, and the stirring time is 24 h.

[0058] S2. Preparation of the coating slurry:

[0059] The polyoxometalate-intercalated hydrotalcite is mixed uniformly with the aramid slurry to obtain a polyoxometalate-intercalated hydrotalcite aramid coating slurry; wherein the aramid slurry is a para-aramid slurry with a solid content of 8%, and the mass content of the polyoxometalate-intercalated hydrotalcite in the coating slurry is 3%.

[0060] S3. Preparation of the separator:

[0061] A PE-based membrane with a thickness of 7 μm is taken, cut into a size of 30*50 cm, and an appropriate amount of slurry is used to coat both sides of the membrane on the surface with a doctor blade. The coating thickness is 2 μm. After passing through two-stage coagulation baths and drying at 60 °C, a polyoxometalate-intercalated hydrotalcite aramid-coated lithium-ion battery separator is obtained.

[0062] Among them, the first-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath is 55%; the second-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath is 80%.

[0063] Example 2

[0064] A preparation method of a polyoxometalate-intercalated hydrotalcite aramid-coated lithium-ion battery separator, and the preparation method is as follows:

[0065] S1. Preparation of polyoxometalate-intercalated hydrotalcite:

[0066] Polyoxometalate-intercalated hydrotalcite is prepared by the exfoliation-reassembly method: Nickel-cobalt hydrotalcite is added to formamide, and it is vigorously stirred under nitrogen protection for exfoliation to obtain a suspension, and the solid content in the suspension is 1%; the vigorous stirring speed is 2000 r / min, and the vigorous stirring time is 48 h;

[0067] The suspension is centrifuged to obtain exfoliated hydrotalcite layers, and then an aqueous phosphotungstic acid solution is added to the exfoliated hydrotalcite layers and stirred for self-assembly. Finally, it is centrifuged, washed, and dried to obtain polyoxometalate-intercalated hydrotalcite; wherein, the concentration of the aqueous phosphotungstic acid solution is 12 mmol / L, the mass ratio of magnesium-aluminum hydrotalcite to phosphotungstic acid is 1:3.5, the stirring speed during self-assembly is 1200 r / min, and the stirring time is 24 h.

[0068] S2. Preparation of the coating slurry:

[0069] Mix the polyoxometalate-intercalated hydrotalcite with the aramid slurry evenly to obtain the polyoxometalate-intercalated hydrotalcite aramid coating slurry; wherein the aramid slurry is a para-aramid slurry with a solid content of 5%, and the mass content of the polyoxometalate-intercalated hydrotalcite in the coating slurry is 1%.

[0070] S3. Separator preparation:

[0071] Take a PE-based film with a thickness of 9 μm, cut it into a size of 30*50 cm, take an appropriate amount of slurry and perform double-sided coating of the separator on the surface of the base film with a doctor blade, the coating thickness is 1 μm, pass through two-stage coagulation baths, and obtain a polyoxometalate-intercalated hydrotalcite aramid-coated lithium-ion battery separator after drying at 60°C;

[0072] Among them, the first-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath is 50%; the second-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath is 75%.

[0073] Example 3

[0074] A preparation method of a polyoxometalate-intercalated hydrotalcite aramid-coated lithium-ion battery separator, and the preparation method is as follows:

[0075] S1. Preparation of polyoxometalate-intercalated hydrotalcite:

[0076] Prepare the polyoxometalate-intercalated hydrotalcite by the exfoliation-reassembly method: add magnesium-aluminum hydrotalcite to formamide, stir vigorously under nitrogen protection to obtain a suspension, and the solid content in the suspension is 3%; the vigorous stirring speed is 2000 r / min, and the vigorous stirring time is 48 h;

[0077] The suspension is centrifuged to obtain exfoliated hydrotalcite layers, then an aqueous phosphotungstic acid solution is added to the exfoliated hydrotalcite layers and stirred for self-assembly, and finally centrifuged, washed, and dried to obtain the polyoxometalate-intercalated hydrotalcite; among them, the concentration of the aqueous phosphotungstic acid solution is 15 mmol / L, the mass ratio of magnesium-aluminum hydrotalcite to phosphotungstic acid is 1:2.5, the stirring speed during self-assembly is 1200 r / min, and the stirring time is 12 h.

[0078] S2. Preparation of coating slurry:

[0079] Mix the polyoxometalate-intercalated hydrotalcite with the aramid slurry evenly to obtain the polyoxometalate-intercalated hydrotalcite aramid coating slurry; wherein the aramid slurry is a meta-aramid slurry with a solid content of 5%, and the mass content of the polyoxometalate-intercalated hydrotalcite in the coating slurry is 2%.

[0080] S3. Separator preparation:

[0081] Take a PE base film with a thickness of 7 μm, cut it into a size of 30 * 50 cm, take an appropriate amount of slurry, and perform double-sided coating of the separator on the surface of the base film with a doctor blade. The coating thickness is 2 μm. After passing through two-stage coagulation baths and drying at 60 °C, a polyacid intercalated hydrotalcite aramid-coated lithium-ion battery separator is obtained;

[0082] Among them, the first-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath is 60%; the second-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath is 85%.

[0083] Example 4

[0084] A preparation method of a polyacid intercalated hydrotalcite aramid-coated lithium-ion battery separator, and the preparation method is as follows:

[0085] S1. Preparation of polyacid intercalated hydrotalcite:

[0086] Prepare polyacid intercalated hydrotalcite by the exfoliation-reassembly method: Add magnesium-aluminum hydrotalcite to formamide, and vigorously stir under nitrogen protection to obtain a suspension. The solid content in the suspension is 2%; the vigorous stirring speed is 1500 r / min, and the vigorous stirring time is 24 h;

[0087] The suspension is centrifuged to obtain exfoliated hydrotalcite layers, and then an aqueous phosphotungstic acid solution is added to the exfoliated hydrotalcite layers and stirred for self-assembly. Finally, it is centrifuged, washed, and dried to obtain polyacid intercalated hydrotalcite; among them, the concentration of the aqueous phosphotungstic acid solution is 5 mmol / L, the mass ratio of magnesium-aluminum hydrotalcite to phosphotungstic acid is 1:2, the stirring speed during self-assembly is 800 r / min, and the stirring time is 24 h.

[0088] S2. Preparation of coating slurry:

[0089] Mix the polyacid intercalated hydrotalcite and the aramid slurry evenly to obtain a polyacid intercalated hydrotalcite aramid-coated slurry; among them, the aramid slurry is a meta-aramid slurry, the solid content is 7%, and the mass content of the polyacid intercalated hydrotalcite in the coating slurry is 1.5%.

[0090] S3. Separator preparation:

[0091] Take a PE base film with a thickness of 7 μm, cut it into a size of 30 * 50 cm, take an appropriate amount of slurry, and perform double-sided coating of the separator on the surface of the base film with a doctor blade. The coating thickness is 2 μm. After passing through two-stage coagulation baths and drying at 60 °C, a polyacid intercalated hydrotalcite aramid-coated lithium-ion battery separator is obtained;

[0092] Among them, the first-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath is 50%; the second-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath is 75%.

[0093] Comparative Example 1

[0094] The lithium-ion battery separator was prepared by the same method as in Example 1, except that: instead of adding the polyacid-intercalated hydrotalcite, the aramid slurry was directly coated onto the base film. The specific preparation process is as follows:

[0095] S1. Preparation of the coating slurry:

[0096] The aramid slurry was used as the coating slurry, where the aramid slurry was para-aramid slurry with a solid content of 8%;

[0097] S2. Separator preparation:

[0098] A PE base film with a thickness of 7 μm was taken and cut into a size of 30 * 50 cm. An appropriate amount of slurry was used to perform double-sided coating of the separator on the surface of the base film with a doctor blade, and the coating thickness was 2 μm. After passing through two-stage coagulation baths and drying at 60 °C, a lithium-ion battery separator coated with polyacid-intercalated hydrotalcite aramid was obtained;

[0099] Among them, the first-stage coagulation bath was a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath was 55%; the second-stage coagulation bath was a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath was 80%.

[0100] Comparative Example 2

[0101] The lithium-ion battery separator was prepared by the same method as in Example 2, except that: instead of adding the polyacid-intercalated hydrotalcite, the aramid slurry was directly coated onto the base film. The specific preparation process is as follows:

[0102] S1. Preparation of the coating slurry:

[0103] The aramid slurry was used as the coating slurry, where the aramid slurry was para-aramid slurry with a solid content of 5%;

[0104] S3. Separator preparation:

[0105] A PE base film with a thickness of 9 μm was taken and cut into a size of 30 * 50 cm. An appropriate amount of slurry was used to perform double-sided coating of the separator on the surface of the base film with a doctor blade, and the coating thickness was 1 μm. After passing through two-stage coagulation baths and drying at 60 °C, a lithium-ion battery separator coated with polyacid-intercalated hydrotalcite aramid was obtained;

[0106] Among them, the first-stage coagulation bath was a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath was 50%; the second-stage coagulation bath was a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath was 75%.

[0107] Comparative Example 3

[0108] Prepare polyoxometalate intercalated hydrotalcite according to Chinese Patent CN101898155B, and perform coating according to the coating method of Example 1 to obtain a polyoxometalate intercalated hydrotalcite aramid-coated separator. The specific preparation process is as follows:

[0109] S1. Preparation of polyoxometalate intercalated hydrotalcite:

[0110] Prepare polyoxometalate intercalated hydrotalcite according to the method of Example 1 of Chinese Patent CN101898155B;

[0111] S2. Preparation of coating slurry:

[0112] Mix polyoxometalate intercalated hydrotalcite with aramid slurry evenly to obtain a polyoxometalate intercalated hydrotalcite aramid coating slurry; wherein the aramid slurry is para-aramid slurry with a solid content of 8%, and the mass content of polyoxometalate intercalated hydrotalcite in the coating slurry is 3%.

[0113] S3. Separator preparation:

[0114] Take a PE base film with a thickness of 7 μm, cut it into a size of 30*50 cm, take an appropriate amount of slurry and perform double-sided coating of the separator on the surface of the base film with a doctor blade, with a coating thickness of 2 μm, pass through two-stage coagulation baths, and dry at 60°C to obtain a polyoxometalate intercalated hydrotalcite aramid-coated lithium-ion battery separator;

[0115] Among them, the first-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the first-stage coagulation bath is 55%; the second-stage coagulation bath is a mixed solution of DMAC and water, and the volume content of water in the second-stage coagulation bath is 80%.

[0116] Comparative Example 4

[0117] Prepare a lithium-ion battery separator by the same method as in Example 1, except that: in step S1, increase the concentration of the phosphotungstic acid aqueous solution. The concentration of the phosphotungstic acid aqueous solution in this Comparative Example 4 is 20 mmol / L. Other process conditions are exactly the same as those in Example 1.

[0118] Comparative Example 5

[0119] Prepare a lithium-ion battery separator by the same method as in Example 1, except that: in step S1, reduce the concentration of the phosphotungstic acid aqueous solution. The concentration of the phosphotungstic acid aqueous solution in this Comparative Example 5 is 2 mmol / L. Other process conditions are exactly the same as those in Example 1.

[0120] Comparative Example 6

[0121] Prepare a lithium-ion battery separator by the same method as in Example 1, except that: in step S1, increase the dosage ratio of phosphotungstic acid. In this Comparative Example 6, the mass ratio of magnesium-aluminum hydrotalcite to phosphotungstic acid is 1:5. Other process conditions are exactly the same as those in Example 1.

[0122] Comparative Example 7

[0123] The lithium-ion battery separator was prepared by the same method as in Example 1, except that: in step S1, the dosage ratio of phosphotungstic acid was reduced. In this Comparative Example 7, the mass ratio of magnesium-aluminum hydrotalcite to phosphotungstic acid was 1:0.5. Other process conditions were exactly the same as those in Example 1.

[0124] Comparative Example 8

[0125] The lithium-ion battery separator was prepared by the same method as in Example 1, except that: in step S2, the addition ratio of polyoxometalate-intercalated hydrotalcite was increased. In this Comparative Example 8, the content of polyoxometalate-intercalated hydrotalcite in the coating slurry was 5%.

[0126] Comparative Example 9

[0127] The lithium-ion battery separator was prepared by the same method as in Example 1, except that: in step S3, there was only a primary coagulation bath. In this Comparative Example 9, the water volume content in the coagulation bath was 80%.

[0128] Comparative Example 10

[0129] The lithium-ion battery separator was prepared by the same method as in Example 1, except that: in step S3, the difference in water volume content between the first-stage coagulation bath and the second-stage coagulation bath > 25%. In this Comparative Example 10, the water volume content in the first-stage coagulation bath was 55%; the second-stage coagulation bath was a mixed solution of DMAC and water, and the water volume content in the second-stage coagulation bath was 85%.

[0130] The lithium-ion battery separators prepared in the above examples and comparative examples were subjected to performance tests. The test method was as follows: referring to the GB / T 36363-2018 standard, the thickness and thermal shrinkage rate of the samples were tested. The specific test results are shown in Table 1 below.

[0131] Table 1 Performance test data of lithium-ion battery separators

[0132]

[0133] Note: MD in Table 1 represents the longitudinal direction, and TD represents the transverse direction.

[0134] From the above data, it can be seen that: the lithium-ion battery separators prepared by the preparation method described in Examples 1-4 of the present invention have good thermal stability. The polyoxometalate-intercalated hydrotalcite is combined with aramid fibers through intermolecular forces. The unique layered structure of the hydrotalcite and the stable embedding of the polyoxometalate can improve the thermal stability of the aramid-coated film. The thermal stability of the separator can be enhanced. Through the thermal shrinkage and film-breaking temperature tests of the comparative examples and the examples, the introduction of the polyoxometalate-intercalated hydrotalcite reduces the thermal shrinkage rate of the separator and improves the thermal stability of the separator, which has extremely high application value. In addition, since the particle size of the polyoxometalate-intercalated hydrotalcite is nanoscale, the introduction of the polyoxometalate-intercalated hydrotalcite does not change the original morphology and thickness of the coating layer. From Figure 1 it can be clearly seen.

[0135] From the data comparison between Comparative Examples 1-2 and Examples 1-2, it can be seen that: if the polyoxometalate-intercalated hydrotalcite is not added, the thermal stability of the lithium-ion battery separator will decrease significantly. From Figure 2 it can also be visually seen.

[0136] From the data comparison between Comparative Example 3 and Example 1, it can be seen that: the polyoxometalate-intercalated hydrotalcite prepared by the preparation method described in the present invention is more conducive to being applied in the coating slurry, and finally a lithium-ion battery separator with excellent thermal stability is obtained. Because compared with other preparation methods of polyoxometalate-intercalated hydrotalcite, the stripping-recombination method can destroy the hydrogen bond network structure of the hydrotalcite during the stripping process, reduce the intermolecular force between the lamellae, facilitate the insertion of polyoxometalate between the lamellae, and reduce the generation of impurity phases.

[0137] From the data comparison between Comparative Examples 4-5 and Example 1, it can be seen that: both too high and too low concentrations of the phosphotungstic acid aqueous solution will affect the thermal stability of the lithium-ion battery separator. When the concentration of the phosphotungstic acid aqueous solution is too low, the intercalation process is relatively slow and the intercalation amount is limited, because polyoxometalate molecules with low concentration are difficult to fully enter the interlayer structure of the hydrotalcite, resulting in low thermal stability of the lithium-ion battery separator; if the concentration of the phosphotungstic acid aqueous solution is too high, the polyoxometalate molecules cannot be evenly distributed between the layers, which may lead to incomplete intercalation or the formation of impurity phases. The polyoxometalate molecules with too high concentration may destroy the balance between the layers of the hydrotalcite, resulting in unstable structure, and finally the thermal stability of the lithium-ion battery separator will also decrease. Therefore, using the concentration of the polyoxometalate aqueous solution defined in the present invention is more conducive to obtaining a lithium-ion battery separator with excellent performance.

[0138] From the data comparison between Comparative Examples 6-7 and Example 1, it can be seen that: whether the dosage ratio of phosphotungstic acid decreases or increases, it will affect the thermal stability of the lithium-ion battery separator. When the dosage ratio of phosphotungstic acid is too small, the self-assembly of hydrotalcite and polyacid is less, and the intercalation amount is insufficient, resulting in low thermal stability of the lithium-ion battery separator; if the dosage ratio of phosphotungstic acid is too high, excessive polyacid molecules will be crowded between the layers, affecting the stability of the intercalation structure, and ultimately also reducing the thermal stability of the lithium-ion battery separator. Therefore, using the polyacid aqueous solution concentration defined in the present invention is more conducive to obtaining a lithium-ion battery separator with excellent performance.

[0139] From the data comparison between Comparative Example 8 and Example 1, it can be seen that: if the dosage of polyacid intercalated hydrotalcite in the coating slurry is too much, excessive polyacid intercalated hydrotalcite particles will affect the structural stability of aramid fibers, and the interaction between polyacid intercalated hydrotalcite and aramid may be weakened due to too high a ratio, which will also lead to a decrease in the thermal stability of the lithium-ion battery separator.

[0140] From the data comparison between Comparative Examples 9-10 and Example 1, it can be seen that: the coagulation bath conditions defined in the present invention are more conducive to controlling the coagulation and forming speed, so that the polyacid intercalated hydrotalcite is evenly distributed in the lithium-ion battery separator, and finally a lithium-ion battery separator with excellent thermal stability is obtained. If the coagulation bath concentration is not appropriate, it will affect the uniformity of the polyacid intercalated hydrotalcite, and ultimately lead to a decrease in the thermal stability of the lithium-ion battery separator.

[0141] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0142] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for preparing a polyacid intercalated hydrotalcite aramid coated lithium battery separator, characterized in that: The preparation method is: S1. Preparation of polyacid intercalated hydrotalcite: The polyacid intercalated hydrotalcite is prepared by exfoliation and recombination method: hydrotalcite is added to formamide, and vigorously stirred under the protection of inert gas to exfoliate to obtain a suspension, the suspension is centrifuged to obtain an exfoliated hydrotalcite sheet, and then a polyacid aqueous solution is added to the exfoliated hydrotalcite sheet and stirred to self-assemble, and finally the polyacid intercalated hydrotalcite is separated by solid-liquid separation; The concentration of the polyacid aqueous solution is 5-15 mmol / L, and the mass ratio of the hydrotalcite to the polyacid is 1:(1-4); S2. Preparation of coating slurry: The polyacid intercalated hydrotalcite and aramid slurry are mixed evenly to obtain a polyacid intercalated hydrotalcite aramid coating slurry; the mass content of the polyacid intercalated hydrotalcite in the coating slurry is 1%-3%; S3. Diaphragm preparation: The polyacid intercalated hydrotalcite aramid coating slurry is applied to the surface of the base film, and then dried after passing through a coagulation bath to obtain a polyacid intercalated hydrotalcite aramid coating lithium battery separator; The coagulation bath is a two-stage coagulation bath, wherein the first-stage coagulation bath is a mixed solution of DMAC and water, wherein the water volume content in the first-stage coagulation bath is 50-60%; the second-stage coagulation bath is a mixed solution of DMAC and water, wherein the water volume content in the second-stage coagulation bath is 75-85%; and the difference in water volume content between the first-stage coagulation bath and the second-stage coagulation bath is not higher than 25%.

2. The method for preparing a polyacid intercalated hydrotalcite aramid coated lithium battery separator according to claim 1, characterized in that: The hydrotalcite is at least one of nickel-cobalt hydrotalcite and magnesium-aluminum hydrotalcite; and the polyacid is any one of Keggin-type polyacid and Weakley-type polyacid.

3. The method for preparing a polyacid intercalated hydrotalcite aramid coated lithium battery separator according to claim 1, characterized in that: The solid content in the suspension is 1-3%.

4. The method for preparing a polyacid intercalated hydrotalcite aramid coated lithium battery separator according to claim 1, characterized in that: In step S1, the vigorous stirring speed when preparing the suspension is 1500-2000 r / min, and the vigorous stirring time is 24-48h; when performing self-assembly, the stirring speed is 800-1200 r / min, and the stirring time is 12-24h.

5. The method for preparing a polyacid intercalated hydrotalcite aramid coated lithium battery separator according to claim 1, characterized in that: The aramid slurry is para-aramid slurry or meta-aramid slurry, and the solid content of the aramid slurry is 5%-10%.

6. The method for preparing a polyacid intercalated hydrotalcite aramid coated lithium battery separator according to claim 1, characterized in that: In step S3, the coating thickness of the polyacid intercalated hydrotalcite aramid coating slurry is 1-2 μm.

7. A polyacid intercalated hydrotalcite aramid coated lithium battery separator, characterized in that: The polyacid intercalated hydrotalcite aramid coated lithium battery separator is prepared according to the preparation method according to any one of claims 1-6.

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