Preparation process of bio-based aramid fiber coated lithium battery diaphragm

Abstract

The invention belongs to the technical field of battery diaphragm processing, and provides a preparation process of a bio-based aramid fiber coated lithium battery diaphragm, and the preparation process comprises the following steps: 1, adding aramid fiber into N-methyl pyrrolidone, stirring until the mixture is uniform, adding modified alumina, continuously stirring, and filtering to obtain coating slurry; and 2, uniformly coating one side or two sides of a base membrane with the coating slurry, and carrying out coagulating bath curing, washing and drying by using an immersion phase inversion method to obtain the bio-based aramid fiber coated lithium battery diaphragm. The preparation process of the bio-based aramid fiber coated lithium battery diaphragm provided by the invention is simple in process, easy to operate, economical in cost and suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of battery separator processing technology, specifically relating to a preparation process of a bio-based aramid coated lithium battery separator. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density and good cycle performance, have been widely used in electric vehicles, energy storage, and other fields, and are a key new energy technology being developed by countries worldwide. The separator is one of the most important components of a lithium-ion battery, serving to prevent contact between the positive and negative electrodes while allowing the electrolyte to pass through. Polyolefins are currently the most commonly used separator material, but their heat resistance and electrolyte wettability are poor. Therefore, technicians often apply ceramic or heat-resistant polymer coatings to the surface to improve their performance.

[0003] Aramid is a high-performance specialty polymer material with excellent properties such as high temperature resistance, flame retardancy, high mechanical strength, and low density. Technicians in the membrane field typically dissolve it in polar organic solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), or N-methylpyrrolidone (NMP), then coat it onto the surface of a polyethylene or polypropylene membrane. Finally, it is immersed in a mixed gel bath of solvent and water to complete the phase inversion, resulting in an aramid composite membrane. Patent CN115064838A discloses a heat-resistant needle-punched aramid coated membrane and its preparation method. The method involves dissolving aramid in NMP and adding an appropriate amount of inorganic material, then coating it onto the surface of a base membrane, immersing it in a coagulation bath containing an aqueous solution of 10%–50% NMP, and finally drying it to form an aramid composite membrane.

[0004] Chinese patent application CN115295961A discloses a para-aramid membrane slurry, a para-aramid membrane, its preparation method, and a lithium battery. It uses DMF, DMAC, or NMP as solvents and adds a solubilizing agent to prepare an aramid slurry. A 70% solvent-containing aqueous solution is then used as the first gel bath, and a composite membrane is prepared through phase separation. Chinese patent application CN115207571A discloses a lithium-ion battery composite membrane and its preparation method. Aramid and polyacrylate materials are dissolved in NMP, DMAC, or acetone. A water-NMP mixture with a mass ratio of (1-9):10 is used as a gel, and a composite membrane is prepared through phase separation. Although coating a base membrane with aramid can effectively improve its heat resistance, aramid itself has low conductivity and porosity. Coating the base membrane with an aramid solution reduces its porosity and electrical properties. Therefore, a solution is proposed to address this technical deficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a preparation process for a bio-based aramid-coated lithium battery separator, in order to solve the technical problem in the prior art that the porosity of the base film is reduced due to the low porosity of aramid itself.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A process for preparing a bio-based aramid-coated lithium battery separator includes the following steps:

[0008] Step 1: Add aramid to N-methylpyrrolidone and stir until uniform. Add modified alumina and continue stirring for 2-3 hours. After filtration, the coating slurry is obtained.

[0009] Step 2: The coating slurry is evenly coated onto one or both sides of the base film. The coating is then cured in a coagulation bath, washed, and dried to obtain a bio-based aramid coated lithium battery separator.

[0010] Preferably, in step 1, the ratio of aramid, N-methylpyrrolidone, and modified alumina is 4-6g: 80g: 1.2-3g.

[0011] Preferably, the rotational viscosity of the aramid fiber in step 1 is 65,000–100,000 mPa·s. When the rotational viscosity of the aramid slurry is too high, its transport is difficult, and it is prone to solidification in the mixed system, affecting the porosity and air permeability of the resulting membrane. When the rotational viscosity of the aramid slurry is too low, it tends to float in the mixed system, and the membrane is prone to breakage during film formation. This invention optimizes the rotational viscosity range of the aramid slurry to ensure good processing performance and film formation stability, thereby obtaining a membrane material with uniform structure and excellent performance.

[0012] Preferably, the modified alumina in step 1 is prepared by the following steps:

[0013] S1. Add nano-alumina to deionized water, ultrasonically disperse until uniform, add tris(hydroxymethyl)aminomethane hydrochloride and dopamine hydrochloride, adjust the pH to 8-8.5, then stir and react for 4-5 hours, wash, filter, and vacuum dry to obtain pretreated alumina;

[0014] S2. Mix silane coupling agent KH-550, anhydrous ethanol, and deionized water, heat to 55-60℃ and stir for 10-15 min, add pretreated alumina, heat to 75-80℃ and continue stirring for 3-4 h, wash, centrifuge and filter, and dry to obtain modified alumina. In the above technical solution, nano-alumina has the characteristics of small size and large specific surface area. When alumina is introduced, the number of nucleation sites in the polymer increases, the internal pores of the coating are more uniform, and it is easier to form a lightweight coating. However, due to the high surface energy of alumina, it is prone to agglomeration during doping, resulting in poor dispersibility in the system. Therefore, in this invention, dopamine is first used to appropriately modify the surface of alumina to improve its dispersibility. Dopamine coating treatment can enhance the dispersibility of nanofillers and provide abundant attachment sites for coupling agent grafting, enabling stronger intermolecular interactions between the amide groups in the aramid molecular chain and alumina, effectively avoiding microphase separation within the system.

[0015] Preferably, the particle size of the nano-alumina in S1 is 100–300 nm.

[0016] Preferably, the ratio of nano-alumina, deionized water, tris(hydroxymethyl)aminomethane hydrochloride and dopamine hydrochloride in S1 is 10-12g: 200mL: 0.31-0.32g: 0.1-0.12g.

[0017] Preferably, the ratio of silane coupling agent KH-550, anhydrous ethanol, deionized water and pretreated alumina in S2 is 1.5-2 mL: 90 mL: 10 mL: 2-2.5 g.

[0018] Preferably, the mesh size of the filter screen in the first step of filtration is 300 to 500 mesh.

[0019] Preferably, the coating method in step 2 is one of blade coating, dip coating, or gravure coating.

[0020] Preferably, the coating thickness in step 2 is 2–5 μm.

[0021] Preferably, the base film in step 2 is one of polypropylene base film and polyethylene base film;

[0022] Preferably, the thickness of the base film in step 2 is 20–30 μm.

[0023] Preferably, the porosity of the base film in step 2 is 30% to 45%, and the pore size is 60 to 80 nm.

[0024] The beneficial effects of this invention are:

[0025] This invention provides a process for preparing a bio-based aramid-coated lithium battery separator. Modified nano-alumina is added to an aramid solution to obtain a slurry, which is then uniformly coated onto a base membrane surface to obtain the bio-based aramid-coated separator. Nano-alumina, characterized by its small size and large specific surface area, promotes heterogeneous nucleation in the slurry. Pore nuclei form simultaneously at the interface between the two phases, significantly increasing the nucleation rate. This reduces the density of the aramid, leading to larger pore size and a greater number of pores, thus increasing the porosity of the aramid coating and consequently improving the separator's porosity and enhancing lithium-ion permeability. Furthermore, the dopamine in the modified nano-alumina contains abundant amino and hydroxyl groups, which helps improve the poor hydrophilicity of the base membrane surface to the electrolyte. Dopamine can also exist as spherical particles on the base membrane surface, providing support between the coating layer and the separator.

[0026] This invention provides a preparation process for a bio-based aramid-coated lithium battery separator. The process is simple, easy to operate, and cost-effective, making it suitable for large-scale production. Furthermore, the bio-based aramid-coated lithium battery separator, under the action of modified alumina, results in a coating layer with high porosity formed by the aramid coating on the base film, which is conducive to the migration of lithium ions and thus improves the electrical strength of the battery separator, showing broad application prospects. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] N-Methylpyrrolidone: Purchased from Shanghai Maclean Biochemical Technology Co., Ltd.;

[0029] Alumina: purchased from Jiangsu Lianlian Chemical Co., Ltd.;

[0030] Tris(hydroxymethyl)aminomethane hydrochloride: purchased from Wuhan Dechen Biochemical Technology Co., Ltd.;

[0031] Polypropylene base membrane: porosity 30%–45%, pore size 60–80 nm, self-made;

[0032] Deionized water: homemade;

[0033] All other reagents without a specified manufacturer can be obtained from commercially available products.

[0034] Example 1

[0035] This embodiment provides a modified alumina prepared through the following steps:

[0036] S1. Add 10g of nano-alumina (particle size 100nm) to 200mL of deionized water, and ultrasonically disperse until uniform. Add 0.31g of tris(hydroxymethyl)aminomethane hydrochloride and 0.1g of dopamine hydrochloride, adjust the pH to 8, and then stir the reaction for 4h. Wash with deionized water 3 times, filter, and finally dry in a vacuum drying oven at 120℃ for 5h to obtain pretreated alumina.

[0037] S2. Mix 1.5 mL of silane coupling agent KH-550, 90 mL of anhydrous ethanol and 10 mL of deionized water, heat to 55 °C and stir for 10 min, add 2 g of pretreated alumina, heat to 75 °C and continue stirring for 3 h, finally wash with deionized water, centrifuge and filter, and dry to obtain modified alumina.

[0038] Example 2

[0039] This embodiment provides a modified alumina prepared through the following steps:

[0040] S1. Add 11g of nano-alumina (particle size of 200nm) to 200mL of deionized water, and ultrasonically disperse until uniform. Add 0.315g of tris(hydroxymethyl)aminomethane hydrochloride and 0.11g of dopamine hydrochloride, adjust the pH to 8, and then stir the reaction for 4h. Wash with deionized water 3 times, filter, and finally dry in a vacuum drying oven at 120℃ for 5h to obtain pretreated alumina.

[0041] S2. Mix 1.7 mL of silane coupling agent KH-550, 90 mL of anhydrous ethanol and 10 mL of deionized water, heat to 55 °C and stir for 10 min, add 2.3 g of pretreated alumina, heat to 75 °C and continue stirring for 3 h, finally wash with deionized water, centrifuge and filter, and dry to obtain modified alumina.

[0042] Example 3

[0043] This embodiment provides a modified alumina prepared through the following steps:

[0044] S1. Add 12g of nano-alumina (particle size 300nm) to 200mL of deionized water, and ultrasonically disperse until uniform. Add 0.32g of tris(hydroxymethyl)aminomethane hydrochloride and 0.12g of dopamine hydrochloride, adjust the pH to 8, and then stir the reaction for 4h. Wash with deionized water 3 times, filter, and finally dry in a vacuum drying oven at 120℃ for 5h to obtain pretreated alumina.

[0045] S2. Mix 2 mL of silane coupling agent KH-550, 90 mL of anhydrous ethanol and 10 mL of deionized water, heat to 55 °C and stir for 10-15 min, add 2.5 g of pretreated alumina, heat to 75 °C and continue stirring for 3 h, finally wash with deionized water, centrifuge and filter, and dry to obtain modified alumina.

[0046] Example 4

[0047] This embodiment provides a preparation process for a bio-based aramid-coated lithium battery separator, and the preparation steps are as follows:

[0048] Step 1: Add 4g of aramid (rotational viscosity of 65000mPa·s) to 80g of N-methylpyrrolidone, stir until uniform, add 1.2g of modified alumina from Example 1, continue stirring for 2h, filter (filter mesh of 300 mesh) to obtain coating slurry;

[0049] Step 2: The coating slurry is uniformly coated onto one side of a polypropylene base film (porosity 30%–45%, pore size 60–80 nm, base film thickness 20 μm) using a scraping method. The coating thickness is 2 μm. The film is cured in a coagulation bath using an immersion-reverse method, washed three times with deionized water, and dried to obtain a bio-based aramid coated lithium battery separator.

[0050] Example 5

[0051] The only difference compared to Example 4 is:

[0052] In step 1, the modified alumina in Example 1 is replaced with the modified alumina in Example 2, with the amount remaining the same.

[0053] Example 6

[0054] The only difference compared to Example 4 is:

[0055] In step 1, the modified alumina in Example 1 is replaced with the modified alumina in Example 3, with the amount remaining the same.

[0056] Example 7

[0057] The only difference compared to Example 4 is:

[0058] Step 1: Add 5g of aramid (rotational viscosity of 65000mPa·s) to 80g of N-methylpyrrolidone and stir until uniform. Add 2g of the modified alumina from Example 1 and continue stirring for 2 hours. After filtration (using a 300-mesh filter), the coating slurry is obtained.

[0059] Example 8

[0060] The only difference compared to Example 4 is:

[0061] Step 1: Add 6g of aramid (rotational viscosity of 65000mPa·s) to 80g of N-methylpyrrolidone and stir until uniform. Add 3g of the modified alumina from Example 1 and continue stirring for 2 hours. After filtration (using a 300-mesh filter), the coating slurry is obtained.

[0062] Example 9

[0063] The only difference compared to Example 4 is:

[0064] Step 1: Add 4g of aramid (rotational viscosity of 85000mPa·s) to 80g of N-methylpyrrolidone and stir until uniform. Add 1.2g of the modified alumina from Example 1 and continue stirring for 2 hours. After filtration (using a 300-mesh filter), the coating slurry is obtained.

[0065] Example 10

[0066] The only difference compared to Example 4 is:

[0067] Step 1: Add 4g of aramid (rotational viscosity of 100000mPa·s) to 80g of N-methylpyrrolidone and stir until uniform. Add 1.2g of the modified alumina from Example 1 and continue stirring for 2 hours. After filtration (using a 300-mesh filter), the coating slurry is obtained.

[0068] Comparative Example 1

[0069] The only difference compared to Example 4 is:

[0070] Step 1: Add 4g of aramid (rotational viscosity of 65000mPa·s) to 80g of N-methylpyrrolidone, stir until uniform, continue stirring for 2 hours, filter (filter mesh of 300 mesh) to obtain coating slurry;

[0071] Step 2: The coating slurry is uniformly coated onto one side of a polypropylene base film (porosity 30%–45%, pore size 60–80 nm, base film thickness 20 μm) using a scraping method. The coating thickness is 2 μm. The film is cured in a coagulation bath using an immersion-reverse method, washed three times with deionized water, and dried to obtain a bio-based aramid coated lithium battery separator.

[0072] Comparative Example 2

[0073] The only difference compared to Example 4 is:

[0074] In step 1, the modified alumina in Example 1 is replaced with alumina, with the amount remaining the same.

[0075] Comparative Example 3

[0076] The only difference compared to Example 4 is:

[0077] Replace 1.2g of modified alumina from Example 1 in step 1 with 1g of modified alumina from Example 2.

[0078] Comparative Example 4

[0079] The only difference compared to Example 4 is:

[0080] Replace 1.2g of modified alumina from Example 1 in step 1 with 3.3g of modified alumina from Example 2.

[0081] Comparative Example 5

[0082] The only difference compared to Example 4 is:

[0083] Step 1: Add 3.5g of aramid (rotational viscosity of 65000mPa·s) to 80g of N-methylpyrrolidone and stir until uniform. Add 1.2g of the modified alumina from Example 1 and continue stirring for 2 hours. After filtration (using a 300-mesh filter), the coating slurry is obtained.

[0084] Comparative Example 6

[0085] The only difference compared to Example 4 is:

[0086] Step 1: Add 3.5g of aramid (rotational viscosity of 65000mPa·s) to 60g of N-methylpyrrolidone, stir until uniform, add 1.2g of modified alumina from Example 1, continue stirring for 2 hours, filter (screen mesh of 300 mesh) to obtain coating slurry;

[0087] Comparative Example 7

[0088] The only difference compared to Example 4 is:

[0089] Replace the rotational viscosity of aramid in step 1, which is 65000 mPa·s, with the rotational viscosity of aramid, which is 60000 mPa·s.

[0090] Comparative Example 8

[0091] The only difference compared to Example 4 is:

[0092] Step 2: The coating slurry is uniformly coated onto one side of a polypropylene base film (porosity of 20%–25%, pore size of 40–50 nm, and base film thickness of 20 μm) using a scraping method. The coating thickness is 2 μm. The film is then cured in a coagulation bath using an immersion-reverse method, washed three times with deionized water, and dried to obtain a bio-based aramid-coated lithium battery separator.

[0093] Performance tests were conducted on the bio-based aramid-coated lithium battery separators obtained in Examples 4-10 and Comparative Examples 1-8:

[0094] (1) The porosity and mechanical properties of bio-based aramid coated lithium battery separators were tested according to standard GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries". The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] (2) The bio-based aramid-coated lithium battery separators obtained in Examples 4-10 and Comparative Examples 1-8 were respectively used to form half-cells with LiFePO4 / Li to investigate their electrochemical performance. The test results are shown in Table 2.

[0099] Table 2

[0100]

[0101]

[0102] As shown in Tables 1-2, compared to the bio-based aramid-coated lithium battery separators prepared in Comparative Examples 1-8, the bio-based aramid-coated lithium battery separators prepared in Examples 4-10 exhibit higher porosity and tensile strength, while also demonstrating excellent electrochemical performance. Therefore, the preparation process of the bio-based aramid-coated lithium battery separator provided by this invention, under the action of modified alumina, results in a coating layer with high porosity formed by the aramid coating on the base film, which is beneficial for lithium ion migration, thereby improving the electrical strength of the battery separator and showing broad application prospects.

[0103] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0104] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A preparation process for a bio-based aramid-coated lithium battery separator, characterized in that, Includes the following steps: Step 1: Add aramid to N-methylpyrrolidone and stir until uniform. Add modified alumina and continue stirring for 2-3 hours. After filtration, the coating slurry is obtained. Step 2: The coating slurry is evenly coated onto one or both sides of the base film. The coating is then cured in a coagulation bath, washed, and dried to obtain a bio-based aramid coated lithium battery separator.

2. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, In step 1, the ratio of aramid, N-methylpyrrolidone, and modified alumina is 4–6 g: 80 g: 1.2–3 g.

3. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, In step 1, the rotational viscosity of the aramid is 65,000 to 100,000 mPa·s.

4. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, The modified alumina described in step 1 is prepared through the following steps: S1. Add nano-alumina to deionized water, ultrasonically disperse until uniform, add tris(hydroxymethyl)aminomethane hydrochloride and dopamine hydrochloride, adjust the pH to 8-8.5, then stir and react for 4-5 hours, wash, filter, and vacuum dry to obtain pretreated alumina; S2. Mix silane coupling agent KH-550, anhydrous ethanol and deionized water, heat to 55-60℃ and stir for 10-15 min, add pretreated alumina, heat to 75-80℃ and continue stirring for 3-4 h, wash, centrifuge and filter, and dry to obtain modified alumina.

5. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, The particle size of nano-alumina in S1 is 100–300 nm.

6. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, The ratio of nano-alumina, deionized water, tris(hydroxymethyl)aminomethane hydrochloride and dopamine hydrochloride in S1 is 10-12g: 200mL: 0.31-0.32g: 0.1-0.12g.

7. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, The ratio of silane coupling agent KH-550, anhydrous ethanol, deionized water, and pretreated alumina in S2 is 1.5–2 mL: 90 mL: 10 mL: 2–2.5 g.

8. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, In step 1, the mesh size of the filter screen is 300-500.

9. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, The coating method described in step 2 is one of the following: blade coating, dip coating, or gravure coating; And / or, the coating thickness described in step 2 is 2–5 μm.

10. The preparation process of a bio-based aramid-coated lithium battery separator according to claim 1, characterized in that, The base film mentioned in step 2 is either a polypropylene base film or a polyethylene base film; And / or, the thickness of the base film described in step 2 is 20–30 μm; And / or, the porosity of the base film described in step 2 is 30% to 45%, and the pore size is 60 to 80 nm.

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