Preparation method of nitrogen-containing modified Ti3C2Tx material and application of nitrogen-containing modified Ti3C2Tx material in diaphragm

Abstract

The invention discloses a preparation method of a nitrogen-containing modified Ti3C2Tx material and an application of the nitrogen-containing modified Ti3C2Tx material in a diaphragm, and the preparation method comprises the following steps: firstly, adding a certain amount of MAX phase material and a pH regulator into deionized water, stirring at normal temperature, continuously performing ultrasonic treatment for 50-70 minutes, then adding a certain amount of etching agent, and stirring to fully hydrolyze the etching agent, thereby obtaining the nitrogen-containing modified Ti3C2Tx material. Adding a certain amount of nitrogen atom doped raw material, continuously stirring until the nitrogen atom doped raw material is completely dissolved, filling the obtained solution into a reaction kettle, controlling the temperature at 90-180 DEG C, carrying out hydrothermal reaction for 4-12 hours, naturally cooling to room temperature, washing with deionized water, and carrying out centrifugal treatment, so as to obtain a precursor; and drying and grinding a solid product obtained by centrifugation in vacuum, and finally performing high-temperature heat treatment under the protection of inert gas to obtain the nitrogen-containing modified Ti3C2Tx material with the two-dimensional layered structure. The surface adsorption energy of the Ti3C2Tx material can be improved, hole active sites on the surface of the material are increased, and the liquid retention capacity of the diaphragm is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and specifically relates to a preparation method of a nitrogen-containing modified Ti3C2T x material and its application in a separator. Background Art

[0002] As one of the four major main materials of a lithium-ion battery, the separator not only plays a particularly important role in preventing short circuits between the positive and negative electrodes, but also is crucial for electrochemical performance. Nowadays, in the industry, it is usually necessary to perform coating modification on the surface of separator base films such as PE, PP, and PI to balance safety and electrochemical performance. Ceramic inorganic materials have become one of the most widely used base modification coatings for separators on the market because of their good anti-shrinkage support effect.

[0003] Ti3C2T x As a new type of two-dimensional material, it itself has excellent ionic conductivity, flexibility, rich surface functional groups, and a large specific surface area, and has great opportunities and application development possibilities in the field of energy storage and conversion, where T x represents the surface groups (-O, -F, -OH) of the material. However, the existing Ti3C2T x material is prone to configuration overlap during the preparation process, resulting in a decrease in the adsorption energy on the surface of the separator when used as a battery separator coating, hindering ions from entering the material interlayer, and having insufficient surface hole active sites. During the charge and discharge process, it is also easy to reduce the high-valent titanium to zero-valent titanium or titanium-containing alloy, forming metal foreign substances, thereby reducing the cycle life of the lithium-ion battery. Summary of the Invention

[0004] In view of the deficiencies of the existing technology, the present invention provides a preparation method of a nitrogen-containing modified Ti3C2T x material and its application in a separator, which can increase the interlayer spacing, surface adsorption performance, and ionic conductivity of the Ti3C2T x material, improve the liquid retention capacity of the separator coating, and improve the cycle life of the battery.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method of a nitrogen-containing modified Ti3C2T x material, comprising the following steps:

[0007] First, a certain amount of MAX phase material and pH regulator are added to deionized water, stirred at room temperature, and continuously ultrasonically treated for 50 - 70 min. Then, a certain amount of etching agent is added, and stirred to fully hydrolyze the etching agent. Then, a certain amount of nitrogen atom doping raw material is added, and continuously stirred until the nitrogen atom doping raw material is completely dissolved. Next, the obtained solution is filled into a reaction kettle, and hydrothermal reaction is carried out at 90 - 180 °C for 4 - 12 h. Then, after natural cooling to room temperature, it is washed and centrifuged with deionized water. The centrifuged solid product is dried and ground under vacuum. Finally, high-temperature heat treatment is carried out under the protection of inert gas to obtain the nitrogen-modified Ti3C2T with a two-dimensional layered structure. x Material. By introducing the hydrothermal reaction, nitrogen atoms are adsorbed on the surface of the Ti3C2T x material surface, and a hybrid stable structure is formed during the subsequent high-temperature treatment, thereby reducing the risk of configuration overlap during the preparation process of the Ti3C2T x material, increasing the surface adsorption energy of the Ti3C2T x material, ensuring the smooth entry of ions into the material interlayer, and at the same time increasing the surface hole active sites.

[0008] As a preferred technical solution, the MAX phase material is selected from one or more of titanium aluminum carbon, titanium silicon carbon, and titanium tin carbon; the pH regulator is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid; the etching agent is selected from one or more of ammonium fluoride, ammonium bifluoride, sodium fluoride decahydrate, calcium fluoride, magnesium fluoride, aluminum fluoride, and ferrous fluoride; the nitrogen atom doping raw material is selected from one of urea, melamine, dopamine, or phthalocyanine.

[0009] As a preferred technical solution, the temperature of vacuum drying is controlled at 58 - 62 °C.

[0010] As a preferred technical solution, during the hydrothermal reaction, the temperature is controlled at 120 - 160 °C, and the reaction time is 6 - 10 h.

[0011] As a preferred technical solution, the temperature of high-temperature heat treatment is 500 - 800 °C, and the treatment duration is 2 - 6 h.

[0012] A preparation method of a coated separator includes the following steps:

[0013] (1) Preparation of the coating slurry: The nitrogen-modified Ti3C2T x material prepared by the above-mentioned preparation method and ceramic material are used as the main body, mutually doped and mixed to prepare the coating slurry;

[0014] (2) Coating the separator: The coating slurry prepared in the previous step is coated on the surface of the separator by a conventional coating method and dried to obtain a coated separator with nitrogen-modified Ti3C2T xCoated separator of materials.

[0015] By incorporating nitrogen-containing modified Ti3C2T into ceramic materials x materials, thus utilizing the good interlayer spacing, large specific surface area, ionic conductivity, flexibility, and rich adjustable surface functional groups of the nitrogen-containing modified Ti3C2T x materials, thereby enhancing the electrolyte adsorption and liquid retention capacity of the separator coating, the migration and conduction capacity of lithium ions during charge and discharge, promoting the formation of enriched ion carriers of lithium ions during charge and discharge, being beneficial to ion migration, and improving the charge and discharge rate performance of the battery cell; while the interface between the nitrogen-containing modified Ti3C2T x materials and the ceramic materials is stable, forming a riveted state with high mutual force, being more stable during the long-term cyclic use of the battery cell, further improving the safety performance, and being able to improve the brittle stress of ceramic particles by virtue of the good flexibility of the materials themselves, enhancing the coating tortuous toughness, and increasing the service life under long cycles.

[0016] As a preferred technical solution, the coating method of the separator is selected from one of dip coating, wire bar coating, and microgravure coating, and the separator is selected from one of polyethylene film, polypropylene film, polyamide film, or polyolefin multi-layer co-extruded composite porous film.

[0017] As a preferred technical solution, the coating slurry contains 5-25 parts by mass of nitrogen-containing modified Ti3C2T x materials, 20-40 parts by mass of ceramic alumina materials, 40-70 parts by mass of deionized water, 0.1-3 parts by mass of dispersant, 2-10 parts by mass of binder, and 0.1-3 parts by mass of wetting agent.

[0018] As a preferred technical solution, the dispersant is one or more of polyacrylate, sodium dodecylbenzenesulfonate, polyoxyethylene stearate, sodium citrate, sodium polyphosphate, polyacrylamide, and sodium hexametaphosphate, the binder is one or more of polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate, styrene-butadiene rubber, polyurethane, epoxy resin, polyvinyl alcohol, polyvinyl acetate, acrylic polymer, and acrylonitrile polymer, and the wetting agent is one or more of polymethylsiloxane, polyacrylate, oxyethylene ether, polyoxyethylene fatty alcohol ether, fluorine-containing polyoxyethylene ether, and lauryl alcohol polyoxyethylene ether.

[0019] A coated separator, which is prepared by the aforementioned method for preparing a coated separator.

[0020] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, by introducing a hydrothermal reaction, nitrogen atoms are adsorbed on the surface of the Ti3C2T x materials, and a hybrid stable structure is formed during the subsequent high-temperature treatment, thereby reducing the Ti3C2Tx During the material preparation process, the risk of configuration overlap occurs, improving Ti3C2T x The surface adsorption energy of the material ensures the smooth entry of ions into the material interlayer, while increasing the active hole sites on the material surface; by doping nitrogen-containing modified Ti3C2T into the ceramic material x material, thus utilizing the nitrogen-containing modified Ti3C2T x The material has good interlayer spacing, large specific surface area, ion conductivity, flexibility, and rich adjustable surface functional groups, thereby enhancing the electrolyte adsorption and liquid retention capacity of the separator coating, the migration and conduction capacity of lithium ions during charge and discharge, promoting the formation of enriched ion carriers of lithium ions during charge and discharge, being beneficial to ion migration, and improving the charge and discharge rate performance of the battery cell; while the nitrogen-containing modified Ti3C2T x The interface between the material and the ceramic material is stable, forming a riveted state with high mutual force, being more stable during the long-term cyclic use of the battery cell, further improving the safety performance, and also being able to improve the brittle stress of the ceramic particles by virtue of the good flexibility of the material itself, enhancing the coating tortuous toughness, and increasing the service life under long cycles.

[0021] To more clearly elaborate on the structural features, technical means, and the specific purposes and functions achieved by the present invention, the following further details the present invention in conjunction with the drawings and specific embodiments: Description of the Drawings

[0022] Figure 1 is the apparent morphology diagram of the nitrogen-containing modified Ti3C2T x material prepared by the present invention. Detailed Embodiments

[0023] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the indicated position or element must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention.

[0024] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "mounted", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] The present invention provides a preparation method of a nitrogen-containing modified Ti3C2T x material, comprising the following steps:

[0026] First, a certain amount of MAX phase material and a pH regulator are added to deionized water, stirred at room temperature, and continuously ultrasonically treated for 50 - 70 min. Then, a certain amount of etching agent is added, and the etching agent is stirred to be fully hydrolyzed. Then, a certain amount of nitrogen atom doping raw material is added, and stirring is continued until the nitrogen atom doping raw material is completely dissolved. Next, the obtained solution is filled into a reaction kettle, and a hydrothermal reaction is carried out at 90 - 180 °C for 4 - 12 h. Then, after natural cooling to room temperature, it is washed and centrifuged with deionized water. The centrifuged solid product is dried and ground under vacuum, and finally, high-temperature heat treatment is carried out under the protection of inert gas to obtain a nitrogen-containing modified Ti3C2T with a two-dimensional layered structure x material. The mass ratio of Ti3C2T in the nitrogen-containing modified Ti3C2T x material is 15 - 35%. By introducing a hydrothermal reaction, nitrogen atoms are adsorbed on the surface of the Ti3C2T x material, and a hybrid stable structure is formed during the subsequent high-temperature treatment, thereby reducing the risk of configuration overlap during the preparation process of the Ti3C2T x material, improving the surface adsorption energy of the Ti3C2T x material, ensuring the smooth entry of ions into the material interlayer, and at the same time increasing the surface hole active sites of the material. x In the present invention, the MAX phase material is selected from one or more of titanium aluminum carbon, titanium silicon carbon, and titanium tin carbon; the pH regulator is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid; the etching agent is selected from one or more of ammonium fluoride, ammonium bifluoride, sodium fluoride decahydrate, calcium fluoride, magnesium fluoride, aluminum fluoride, and ferrous fluoride; the nitrogen atom doping raw material is selected from one of urea, melamine, dopamine, or phthalocyanine.

[0027] Specifically, the temperature of vacuum drying is controlled at 58 - 62 °C, and preferably, the temperature of vacuum drying is controlled at 60 °C. When carrying out the hydrothermal reaction, the temperature is controlled at 120 - 160 °C, and the reaction time is 6 - 10 h. The temperature of high-temperature heat treatment is 500 - 800 °C, and the treatment duration is 2 - 6 h. In the present invention, the inert gas can be selected from nitrogen or argon.

[0028] The present invention also provides a preparation method of a coated separator, comprising the following steps:

[0029] (1) Preparation of the coating slurry: Using the nitrogen-containing modified Ti3C2T

[0030] material prepared by the aforementioned preparation method and a ceramic material as the main body, intermixing and mixing to obtain the coating slurry; x material and a ceramic material as the main body, intermixing and mixing to obtain the coating slurry;

[0031] (2) Coating: Coating the coating slurry prepared in the previous step on the surface of the separator by a conventional coating method, and drying to obtain a coated separator with a nitrogen-containing modified Ti3C2T x material. The coating can be coated on one or both sides of the separator, and can be coated by one of dip coating, wire bar coating, or microgravure coating, and the thickness of the coating can be obtained by one-time coating or multiple coatings.

[0032] By incorporating a nitrogen-containing modified Ti3C2T x material into the ceramic material, thereby utilizing the good interlayer spacing, large specific surface area, ionic conductivity, flexibility, and rich adjustable surface functional groups of the nitrogen-containing modified Ti3C2T x material, so as to improve the electrolyte adsorption and liquid retention ability of the separator coating and the migration and conduction ability of lithium ions during charge and discharge, promote the formation of enriched ion carriers of lithium ions during charge and discharge, facilitate ion migration, and improve the charge and discharge rate performance of the battery cell; and the interface between the nitrogen-containing modified Ti3C2T x material and the ceramic material is stable, forming a riveting state with high mutual force, which is more stable during the long-term cyclic use of the battery cell, further improving the safety performance, and can also improve the brittle stress of the ceramic particles by virtue of the good flexibility of the material itself, improve the tortuosity toughness of the coating, and increase the service life under long cycles.

[0033] In the present invention, the separator is selected from one of a polyethylene film, a polypropylene film, a polyamide film, or a polyolefin multi-layer co-extruded composite porous film. The coating slurry contains 5-25 parts by mass of a nitrogen-containing modified Ti3C2T x material, 20-40 parts by mass of a ceramic alumina material, 40-70 parts by mass of deionized water, 0.1-3 parts by mass of a dispersant, 2-10 parts by mass of an adhesive, and 0.1-3 parts by mass of a wetting agent.

[0034] The dispersant is one or more of polyacrylate, sodium dodecylbenzenesulfonate, polyoxyethylene stearate, sodium citrate, sodium polyphosphate, polyacrylamide, and sodium hexametaphosphate. The adhesive is one or more of polyacrylic acid, polymethacrylic acid, polyacrylate methyl ester, polymethacrylate methyl ester, styrene-butadiene rubber, polyurethane, epoxy resin, polyvinyl alcohol, polyvinyl acetate, acrylic polymer, and acrylonitrile polymer. The wetting agent is one or more of polymethylsiloxane, polyacrylate, oxyethylene ether, polyoxyethylene fatty alcohol ether, fluorine-containing polyoxyethylene ether, and lauryl alcohol polyoxyethylene ether.

[0035] The present invention also provides a coated separator, which is prepared by the aforementioned method for preparing a coated separator.

[0036] Example 1

[0037] Preparation of a coated separator, comprising the following steps:

[0038] (1) Preparation of nitrogen-containing modified Ti3C2T x material

[0039] At room temperature, 50 g of titanium aluminum carbide is dissolved in 500 mL of deionized water, and then 1 g of glacial acetic acid is added as a pH regulator. Continuously stir rapidly and ultrasonically disperse for 60 min for later use; in the above dispersion, 5 g of NH4F is added as an etchant, and stir rapidly for 30 min to promote the full hydrolysis of the etchant. Then, 10 g of urea is added as a nitrogen atom doping raw material and continuously stirred until completely dissolved; subsequently, the dispersion added with the nitrogen atom doping raw material is transferred to a hydrothermal reaction kettle, and the reaction is continuously carried out at a stable 90 °C for 4 h. After the reaction is completed, naturally cool to room temperature, collect the product by centrifugal washing with deionized water several times, with a centrifugal speed of 10000 rpm and a time of 10 min. Finally, place the collected product in a vacuum drying oven and dry at 60 °C. After drying, take out the solid product and grind it with a mortar for 10 - 30 min, and heat-treat it at 500 °C for 4 h under nitrogen protection to finally obtain the nitrogen-containing modified Ti3C2T x material

[0040] (2) Preparation of coating slurry

[0041] Mix 5 parts of polymethyl methacrylate emulsion glue and 65 parts of deionized water, and weigh 7.5 parts of nitrogen-doped modified Ti3C2T x material and 22.5 parts of Al3O2 ceramic material are added to the polymer glue solution, and continuously stir and disperse at 1500 rpm for 60 min; finally, 0.1 part of polyacrylate dispersant and 0.2 part of polymethylsiloxane wetting agent are added to the mixed solution, and slowly stir at 200 rpm for 60 min. Finally, an Al3O2 ceramic coating slurry of water-based N-doped modified Ti3C2T x material can be obtained

[0042] (3) Coating

[0043] The Al3O2 ceramic coating slurry of water-based N-doped modified Ti3C2T x material obtained in (2) is coated on the surface of a commercial polyolefin (PE, PP) separator through a microgravure. The coating grammage is 2.8 - 3.6 g / m 2 , the coating thickness is about 2 μm, the coating speed is 60 - 150 m / min, and it is dried and cured through an oven to obtain a coated separator with the surface modified by Al3O2 ceramic of N-doped Ti3C2T x material

[0044] Example 2

[0045] The difference from Example 1 is that in step (1), the hydrothermal reaction condition is continuous reaction at 90°C for 2 h, and other conditions are the same as those in Example 1.

[0046] Example 3

[0047] The difference from Example 1 is that in step (1), the hydrothermal reaction condition is continuous reaction at 90°C for 12 h, and other conditions are the same as those in Example 1.

[0048] Example 4

[0049] The difference from Example 1 is that in step (1), the hydrothermal reaction condition is continuous reaction at 90°C for 8 h, and other conditions are the same as those in Example 1.

[0050] Example 5

[0051] The difference from Example 1 is that in step (1), the hydrothermal reaction condition is continuous reaction at 120°C for 8 h, and other conditions are the same as those in Example 1.

[0052] Example 6

[0053] The difference from Example 1 is that in step (1), the hydrothermal reaction condition is continuous reaction at 140°C for 8 h, and other conditions are the same as those in Example 1.

[0054] Example 7

[0055] The difference from Example 1 is that in step (1), the hydrothermal reaction condition is continuous reaction at 180°C for 8 h, and other conditions are the same as those in Example 1.

[0056] Example 8

[0057] The difference from Example 1 is that in step (1), the hydrothermal reaction condition is continuous reaction at 200°C for 8 h, and other conditions are the same as those in Example 1.

[0058] Example 9

[0059] The difference from Example 6 is that in step (2), 0 parts of N-doped modified Ti3C2T x materials and 30 parts of Al3O2 ceramic materials are added to the polymer adhesive solution, and others are the same as those in Example 6.

[0060] Example 10

[0061] The difference from Example 6 is that in step (2), 4.5 parts of N-doped modified Ti3C2Tx 10.5 parts of N-doped modified Ti3C2T material and 25.5 parts of Al3O2 ceramic material are added to the polymer glue solution, and the others are the same as in Example 6.

[0062] Example 11

[0063] The difference from Example 6 is that in step (2), 10.5 parts of N-doped modified Ti3C2T x material and 19.5 parts of Al3O2 ceramic material are added to the polymer glue solution, and the others are the same as in Example 6.

[0064] Example 12

[0065] The difference from Example 6 is that in step (2), 12 parts of N-doped modified Ti3C2T x material and 18 parts of Al3O2 ceramic material are added to the polymer glue solution, and the others are the same as in Example 6.

[0066] Example 13

[0067] The difference from Example 6 is that in step (2), 15 parts of N-doped modified Ti3C2T x material and 15 parts of Al3O2 ceramic material are added to the polymer glue solution, and the others are the same as in Example 6.

[0068] Comparative Example 1

[0069] The difference from Example 6 is that in step (1), the Ti3C2T x material is not doped with nitrogen atoms by adding urea, and in step (2), 7.5 parts of undoped modified Ti3C2T x material and 22.5 parts of Al3O2 ceramic material are added to the polymer glue solution, and the others are the same as in Example 6.

[0070] Comparative Example 2

[0071] The difference from Example 6 is that in step (2), commercially available conventional boehmite (particle size about D50≤1.0μm, D90≤2.5μm) is selected to replace the Al3O2 ceramic material and mixed with the N-doped modified Ti3C2T x material, and the slurry is prepared and coated under the same conditions as in Example 6, and the same coating surface density range of 2.8 - 3.6 g / m 2 .

[0072] Comparative Example 3

[0073] The difference from Example 6 is that in step (2), only the N-doped modified Ti3C2T xThe materials were added to the polymer glue solution without doping ceramic particles, and the slurry was prepared under the same conditions as in Example 6 for coating, and the same coating surface density range of 2.8 - 3.6 g / m was maintained. 2 .

[0074] The following are the relevant performance tests on the coated diaphragms prepared in Examples 1 - 13 and Comparative Examples 1 - 3, and the test results are as follows:

[0075] 1. Comparison of air permeability and heat shrinkage of coated diaphragms

[0076] The air permeability value of the coated diaphragm was tested by Asahi Seiko, comparing Examples 1 - 13 and Comparative Examples 1 - 3, and the influence of the ceramic coating of the obtained nitrogen-doped modified Ti3C2T x material on the air permeability of the diaphragm. The air permeability test method is as follows: Take a coated diaphragm with a sample size of 100 mm × 100 mm (MD × TD), and use an air permeability tester for testing, with a test duration of 5 s. The test method for shrinkage rate is as follows: Take the coated diaphragms in Examples 1 - 13 and Comparative Examples 1 - 3 for thermal shrinkage test, with a sample size of 100 mm × 100 mm (MD × TD), MD is the longitudinal direction of the diaphragm, and TD is the transverse direction of the diaphragm. Thermal shrinkage test temperature: 130 °C / 1 h.

[0077] The test results are shown in Table 1.

[0078] Table 1 Comparison of air permeability and thermal shrinkage of coated diaphragms in Examples 1 - 13 and Comparative Examples 1 - 3

[0079]

[0080]

[0081] As can be seen from Examples 1 - 4, as the hydrothermal reaction time increases, the air permeability of the prepared coated diaphragm decreases from large to small. Among them, in Example 2, due to the short hydrothermal reaction time, the unpeeled Ti3C2T x material accumulates densely on the diaphragm surface, resulting in pore blockage, so the air permeability of the diaphragm is relatively large. In Example 3, due to the too long hydrothermal reaction, the highest degree of peeling occurs, and more two-dimensional sheets are separated, resulting in more local pore blockage on the coated diaphragm, so the air permeability of the diaphragm is relatively large. In Examples 4 - 8, as the hydrothermal temperature increases, the overall peeling reaction degree of the Ti3C2T x material is different, affecting the surface pore structure of the material itself, and thus the air permeability of the coated finished diaphragm is also different. In Examples 9 - 13, the proportion of the nitrogen-doped modified Ti3C2T x material in the coating was changed. As the amount of the nitrogen-doped modified Ti3C2T x material increases, the thermal shrinkage of the coated diaphragm increases accordingly. This is because Ti3C2T xThe material presents a two-dimensional layered structure, with certain losses on the multi-dimensional support and the lack of ceramic particles resulting in Ti3C2T x The material is more closely packed. In Comparative Example 1 for Ti3C2T x The material was not nitrogen-doped and modified. Compared with Example 6, there is basically no difference in diaphragm air permeability and thermal shrinkage. The main change caused by N doping is Ti3C2T x The active sites and electrolyte affinity of the material, as well as the better ionic conductivity of the material. Comparative Examples 2-3 represent coatings composed of different inorganic substances and single Ti3C2T x The coatings have slightly worse thermal shrinkage than the Ti3C2T x doped ceramic composite diaphragms.

[0082] 2. Comparison of liquid absorption rate of coated diaphragms

[0083] The liquid absorption rate of the diaphragm was calculated by the weighing method to compare the electrolyte retention amounts per unit area of the coated diaphragms in Examples 1-13 and Comparative Examples 1-3. The test method is as follows: Take a coated diaphragm with a sample size of 100 mm × 100 mm (MD × TD) and weigh it as m0. Immerse it in the electrolyte at room temperature for 24 h, then take it out, wipe the electrolyte on the surface of the diaphragm, and weigh it as m1. The liquid absorption rate calculation formula is: x = (m1 - m0) / m0. The final test results are shown in Table 2.

[0084] Table 2 Comparison of the liquid absorption rates of the coated diaphragms in Examples 1-13 and Comparative Examples 1-3

[0085] Example Liquid absorption rate <![CDATA[Coating areal density (g / m 2 )]]> Example 1 579.96％ 3.32 Example 2 523.98％ 3.41 Example 3 611.56％ 3.25 Example 4 631.12％ 3.36 Example 5 679.36％ 3.28 Example 6 712.56％ 3.43 Example 7 682.74％ 3.26 Example 8 673.19％ 3.28 Example 9 451.33％ 3.35 Example 10 581.23％ 3.31 Example 11 781.73％ 3.27 Example 12 792.44％ 3.19 Example 13 822.37％ 3.33 Comparative Example 1 481.69％ 3.29 Comparative Example 2 726.28％ 3.42 Comparative Example 3 1005.12％ 3.24

[0086] For the obtained coated diaphragms in Examples 1-13, as the proportion of the added nitrogen-modified Ti3C2T x material increases, the adsorption and liquid retention amount of the coated diaphragm for the electrolyte is more, and the affinity for the electrolyte is better. In Comparative Example 1 for Ti3C2T x the material was not nitrogen-modified, with fewer active sites, weaker affinity for the electrolyte, and less adsorption of the electrolyte on the surface, so the liquid absorption rate of the coated diaphragm is not high. In Comparative Examples 2-3, the liquid retention of the electrolyte by the coatings of different inorganic material blends and single nitrogen-modified Ti3C2T x materials is good, especially for the coating of single nitrogen-modified Ti3C2T x material. The rich surface polar functional groups and large specific surface area show a more obvious adsorption effect on the electrolyte.

[0087] 3. Comparison of ionic conductivity of coated diaphragms

[0088] The coated separators prepared in the above Examples 1-13 and Comparative Examples 1-3, together with the lithium iron phosphate positive electrode sheet and the graphite negative electrode sheet, were made into button-shaped cylindrical lithium-ion batteries by a winding process, and electrochemical impedance tests were carried out, and the ionic conductivity of the separators was calculated. The results are shown in Table 3.

[0089] Table 3 Comparison of ionic conductivities of the coated separators in Examples 1-13 and Comparative Examples 1-3

[0090]

[0091]

[0092] In Examples 1-13, as the proportion of the added amount of the N-doped Ti3C2T x material increased, the ionic conductivity of the coated separator gradually increased. In Comparative Example 1, since the Ti3C2T x material was not N-doped and modified, there were fewer active sites in the material, and the formed separator showed poor performance in ion conduction. In Comparative Examples 2-3, the blending of different inorganic materials and the single N-doped Ti3C2T x material coating both had good effects on ionic conductivity. Especially for the single N-doped Ti3C2T x material coating, with rich surface polar functional groups and a large specific surface area, provided a transmission path for ion conduction during charge and discharge, showing the best ionic conductivity.

[0093] In summary, in the present invention, by introducing a hydrothermal reaction, nitrogen atoms are adsorbed on the surface of the Ti3C2T x material, and a hybrid stable structure is formed during subsequent high-temperature treatment, thereby reducing the risk of configurational overlap during the preparation process of the Ti3C2T x material, increasing the surface adsorption energy of the Ti3C2T x material, ensuring that ions can smoothly enter the interlayer of the material, and at the same time increasing the surface hole active sites; by doping the nitrogen-modified Ti3C2T x material into the ceramic material, the good layer spacing, large specific surface area, ionic conductivity, flexibility, and rich adjustable surface functional groups of the nitrogen-modified Ti3C2T x material are utilized to improve the adsorption and liquid retention ability of the separator coating for the electrolyte, the migration and conduction ability of lithium ions during charge and discharge, promote the formation of enriched ion carriers of lithium ions during charge and discharge, facilitate ion migration, and improve the charge and discharge rate performance of the battery cell; and the nitrogen-modified Ti3C2T xThe interface of the mixture formed by the material and the ceramic material is stable, forming a riveted state with high mutual interaction force, which is more stable during the long-term cyclic use of the battery cell, further improving the safety performance. Moreover, it can improve the brittle stress of ceramic particles by virtue of the good flexibility of the material itself, enhance the coating tortuous toughness, and increase the service life under long cycles.

[0094] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical reality of the present invention still fall within the scope of the technical solutions of the present invention.

Claims

1. A nitrogen-modified Ti3C2T x The method for preparing the material is characterized in that: The following steps are involved: First, a certain amount of MAX phase material and pH regulator are added to deionized water, stirred at room temperature, and ultrasonically treated for 50-70 minutes, then a certain amount of etchant is added, stirred to fully hydrolyze the etchant, and then a certain amount of nitrogen atom doped raw material is added, and stirred continuously until the nitrogen atom doped raw material is completely dissolved, and then the obtained solution is charged into a reactor, and the temperature is controlled at 90-180°C for hydrothermal reaction for 4-12 hours, and then after naturally cooling to room temperature, it is washed with deionized water and centrifuged, and the solid product obtained by centrifugation is dried and ground under vacuum, and finally high-temperature heat treatment is performed under inert gas protection to obtain a two-dimensional layered structure of nitrogen-containing modified Ti3C2T x Material.

2. A nitrogen-modified Ti3C2T3 according to claim 1 x The method for preparing the material is characterized in that: The MAX phase material is selected from one or more of titanium aluminum carbon, titanium silicon carbon, and titanium tin carbon; the pH adjuster is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid; the etchant is selected from one or more of ammonium fluoride, ammonium hydrogen fluoride, sodium fluoride decahydrate, calcium fluoride, magnesium fluoride, aluminum fluoride, and ferrous fluoride; the nitrogen atom doping raw material is selected from one of urea, melamine, dopamine, or phthalocyanine.

3. A nitrogen-modified Ti3C2T3 according to claim 1 x The method for preparing the material is characterized in that: The temperature of vacuum drying was controlled at 58-62°C.

4. A nitrogen-modified Ti3C2T3 according to claim 1 x The method for preparing the material is characterized in that: During the hydrothermal reaction, the temperature is controlled at 120-160°C and the reaction time is 6-10h.

5. The method for preparing a diaphragm according to claim 1, characterized in that: The temperature of high temperature heat treatment is 500-800°C and the treatment time is 2-6h.

6. A method for preparing a coated diaphragm, characterized in that: The following steps are involved: (1) Preparation of coating slurry: Nitrogen-modified Ti3C2T prepared by the preparation method described in any one of claims 1 to 5 x The material and the ceramic material are used as the main body, mixed with each other, and the coating slurry is prepared; (2) Coating: The coating slurry prepared in the previous step is coated on the surface of the diaphragm by conventional coating method and dried to obtain a coating nitrogen-modified Ti3C2T x Material coated diaphragm.

7. The method for preparing a coated diaphragm according to claim 6, characterized in that: The coating method in step (2) is selected from one of dip coating, wire rod coating, and micro-gravure coating, and the diaphragm is selected from one of polyethylene film, polypropylene film, polyamide film or polyolefin multi-layer co-extruded composite porous film.

8. The method for preparing a coated diaphragm according to claim 6, characterized in that: The coating slurry contains 5-25 parts by mass of nitrogen-modified Ti3C2T x material, 20-40 parts by mass of ceramic alumina material, 40-70 parts by mass of deionized water, 0.1-3 parts by mass of dispersant, 2-10 parts by mass of adhesive, and 0.1-3 parts by mass of wetting agent.

9. The method for preparing a coated diaphragm according to claim 7, characterized in that: The dispersant is one or more of polyacrylate, sodium dodecylbenzene sulfonate, polyoxyethylene stearate, sodium citrate, sodium polyphosphate, polyacrylamide, and sodium hexametaphosphate; the adhesive is one or more of polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate, styrene-butadiene rubber, polyurethane, epoxy resin, polyvinyl alcohol, polyvinyl acetate, acrylic polymer, and acrylonitrile polymer; the wetting agent is one or more of polymethylsiloxane, polyacrylate, oxyethylene ether, polyoxyethylene fatty alcohol ether, fluorine-containing polyoxyethylene ether, and lauryl alcohol polyethylene ether.

10. A coated diaphragm, characterized in that: The coated diaphragm is prepared by the coated diaphragm preparation method according to any one of claims 6 to 9.

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