Aramid fiber coated lithium ion battery diaphragm and preparation method thereof

Abstract

The invention discloses an aramid fiber coated lithium ion battery diaphragm and a preparation method thereof, and belongs to the technical field of battery diaphragms. The preparation method comprises the following steps: S1, mixing and stirring aramid fiber, DMSO, KOH and deionized water, carrying out centrifugal washing, cooling to room temperature, filtering the obtained product, dispersing the product in deionized water, and carrying out dialysis until the pH value is 7 to obtain an aramid nanofiber aqueous dispersion liquid; s2, carboxymethyl chitosan, carboxylated multi-walled carbon nanotubes and 2, 2 '-dithiodiacetic acid are dissolved in the aramid nanofiber water-based dispersion liquid obtained in the S1, then a condensing agent is added for polymerization, and aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel is obtained; s3, at least one surface of a base membrane is coated with the hydrogel obtained in the step S2, a coating is obtained after coating is finished, the diaphragm is placed in a drying oven for 1 h at the temperature of 50 DEG C, the solvent is volatilized, and the lithium ion battery diaphragm is obtained. The prepared diaphragm is excellent in comprehensive performance.

Description

Technical Field

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

[0002] Lithium-ion batteries are rechargeable batteries that rely primarily on the movement of lithium ions between the positive and negative electrodes. In the structure of lithium batteries, the separator is one of the key internal components.

[0003] Lithium-ion battery separators are porous membranes. Their primary function in lithium-ion batteries is to isolate the positive and negative electrodes, preventing internal short circuits. They also provide pathways for lithium ions to migrate during charging and discharging, allowing them to pass through.

[0004] Polyolefins (such as PE and PP) are the main materials used in commercial lithium-ion battery separators. Although they have certain advantages in chemical stability, mechanical properties, cost, etc., as lithium-ion batteries continue to penetrate the field of electric vehicles, the shortcomings of polyolefins in terms of high temperature resistance have become increasingly prominent, seriously reducing the safety performance of lithium-ion batteries, especially hindering their application in power batteries.

[0005] To further improve the high-temperature resistance of lithium battery separators, a high-temperature resistant coating is typically applied to the separator surface. Aramid, short for poly(p-phenylene isophthalamide), possesses exceptional properties such as ultra-high strength, high modulus, high-temperature resistance, acid and alkali resistance, and lightweight. Its thermal decomposition temperature can reach 400-430°C. As a separator coating for lithium-ion batteries, it can significantly improve the battery's heat resistance and safety. However, aramid slurry tends to form a dense stacking structure during film formation, resulting in a decrease in the separator's porosity. This not only affects the efficiency of lithium ion migration but also leads to a decrease in electrochemical performance. Summary of the Invention

[0006] The present invention provides an aramid-coated lithium-ion battery separator and a preparation method thereof, which can solve the problem in the prior art that aramid slurry easily forms a dense stacking structure during the film-forming process, resulting in a decrease in the porosity of the separator, which not only affects the migration efficiency of lithium ions but also leads to a decrease in electrochemical performance.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing an aramid-coated lithium-ion battery separator, comprising the following steps:

[0009] S1: Aramid fibers, DMSO, KOH, and deionized water were mixed and stirred, washed by centrifugation, cooled to room temperature, filtered, dispersed in deionized water, and dialyzed until the pH was 7 to obtain an aqueous dispersion of aramid nanofibers;

[0010] S2: dissolving carboxymethyl chitosan, carboxylated multi-walled carbon nanotubes and 2,2'-dithiodiacetic acid into the aramid nanofiber aqueous dispersion obtained in S1, and then adding a condensing agent for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0011] S3: coating the hydrogel obtained in step S2 on at least one surface of the base film to obtain a coating. After the coating is completed, the separator is placed in an oven at 50° C. for 1 hour to volatilize the solvent, thereby obtaining the lithium-ion battery separator.

[0012] During this process, aramid nanofibers form a fiber-reinforced network with the hydrogel. The surface of the aramid nanofibers contains polar groups. Carboxymethyl chitosan reacts with the carboxyl groups of carboxylated multi-walled carbon nanotubes and 2,2'-dithiodiacetic acid through amino groups to form amide bonds, which match the polar groups on the surface of the aramid nanofibers, promote the uniform dispersion of the aramid nanofibers in the hydrogel network, and combine the high strength of the aramid nanofibers with the flexibility of the hydrogel network, thereby improving the mechanical properties of the composite material.

[0013] Furthermore, in step S1, the usage ratio of the aramid fiber, DMSO, KOH and deionized water is 3 g:200 mL:4.5 g:40-50 mL.

[0014] Furthermore, in step S1, the aramid fiber is aramid fiber poly(p-phenylene terephthalamide) fiber.

[0015] Furthermore, in step S2, the mass ratio of the carboxymethyl chitosan to the carboxylated multi-walled carbon nanotubes is (20-40): 1. The present invention achieves the best performance by precisely controlling the mass ratio of carboxymethyl chitosan to carboxylated multi-walled carbon nanotubes. When the amount of carboxylated multi-walled carbon nanotubes is small, the reinforcing effect of the carboxylated multi-walled carbon nanotubes is difficult to exert, thereby reducing the overall performance of the membrane. When the amount of carboxylated multi-walled carbon nanotubes is large, agglomeration may occur to destroy the network structure, and the overall performance of the membrane will also be reduced.

[0016] Furthermore, in step S2, the molar ratio of the carboxymethyl chitosan to 2,2'-dithiodiacetic acid is (1-4):1.

[0017] Furthermore, in step S2, the molar ratio of the total amount of the condensing agent to 2,2'-dithiodiacetic acid is 2:1.

[0018] Furthermore, in step S2, the condensing agent is any one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and dicyclohexylcarbodiimide in combination with any one of 4-dimethylaminopyridine, N-hydroxysuccinimide, and 1-hydroxybenzotriazole, and the molar ratio of the two condensing agents when used in combination is 1:1.

[0019] Furthermore, in step S2, the viscosity-average molecular weight of the carboxymethyl chitosan is 350,000-500,000, and the degree of substitution is 0.7-0.95.

[0020] Furthermore, in step S3, the base film is one or more of a polyolefin film, a polypropylene film, and a polypropylene-polyethylene-polypropylene composite film; the base film has a thickness of 5-11 microns; and the coating has a thickness of 1-3 microns.

[0021] In a second aspect, the present invention provides an aramid-coated lithium-ion battery separator, which is prepared by any one of the preparation methods described above.

[0022] Beneficial effects of the present invention:

[0023] The present invention uses aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel as the coating material of the diaphragm, which can significantly improve the comprehensive performance of the diaphragm, as follows:

[0024] 1. Aramid nanofibers have high strength and high modulus properties, forming a rigid network skeleton to improve the tensile strength and puncture resistance of the diaphragm; COOH-MWNTs, as nano-reinforced fillers, are entangled with aramid fibers through interfacial interactions to form a "fiber-nanotube" composite reinforcement structure, further enhancing toughness and bending resistance, that is, the overall mechanical properties of the diaphragm are improved.

[0025] 2. Chitosan releases large amounts of nitrogen-containing, non-combustible gases during combustion, which dilute the oxygen concentration around the burning surface and inhibit the combustion rate. Carbon nanotubes form a dense carbon layer during combustion, providing insulation, oxygen isolation, and a barrier to combustible gases. The sulfur element in DTT synergizes with the flame-retardant properties of CMC / COOH-MWNTs, enhancing the flame-retardant properties of the separator. Furthermore, DTT contains dynamic disulfide bonds, which possess self-healing properties, enhancing the self-healing capabilities of the separator.

[0026] 3. The aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel has a highly porous structure, which can increase the diffusion and transmission rate of ions, thereby improving the ionic conductivity of the separator. The hydrogel contains a large number of polar groups such as hydroxyl, carboxyl, and amide groups that can coordinate with lithium ions, forming an efficient transmission structural unit, thereby constructing a high-speed lithium ion transmission channel in the separator, further improving the ionic conductivity of the separator. CMC contains a large number of hydrophilic groups, and the high porosity of the nanofiber network can improve the liquid absorption rate of the separator. DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0028] The carboxylated multi-walled carbon nanotubes used in the examples and comparative examples of the present invention were purchased from Suzhou Tanfeng Graphene Technology Co., Ltd., with the product brand HQNANO-CNTs-007-1C (outer diameter of 8-15 nm, length of 0.5-2 μm);

[0029] Example 1

[0030] A method for preparing an aramid-coated lithium-ion battery separator comprises the following steps:

[0031] S1: 3 g of poly (p-phenylene terephthalamide) fiber, 200 mL of DMSO, and 4.5 g of KOH were mixed and stirred at 95°C for 5 days on an electric stirrer. 50 mL of deionized water was then slowly added dropwise. The mixture was centrifuged and washed. After cooling to room temperature, the resulting product was filtered, dispersed in deionized water, and dialyzed until the pH reached 7 to obtain an aqueous dispersion of aramid nanofibers.

[0032] S2: 11 g of carboxymethyl chitosan (viscosity-average molecular weight of 350,000, degree of substitution of 0.7), 0.28 g of carboxylated multi-walled carbon nanotubes, and 0.91 g of 2,2'-dithiodiacetic acid were dissolved in the aqueous dispersion of aramid nanofibers obtained in S1, and then 0.96 g of 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride and 0.58 g of N-hydroxysuccinimide were added for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0033] S3: The hydrogel obtained in step S2 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0034] Example 2

[0035] A method for preparing an aramid-coated lithium-ion battery separator comprises the following steps:

[0036] S1: 3 g of poly (p-phenylene terephthalamide) fiber, 200 mL of DMSO, and 4.5 g of KOH were mixed and stirred at 95°C for 5 days on an electric stirrer. 40-50 mL of deionized water was then slowly added dropwise. The mixture was centrifuged and washed. After cooling to room temperature, the resulting product was filtered, dispersed in deionized water, and dialyzed until the pH reached 7 to obtain an aqueous dispersion of aramid nanofibers.

[0037] S2: 11 g of carboxymethyl chitosan (viscosity-average molecular weight of 350,000, degree of substitution of 0.7), 0.31 g of carboxylated multi-walled carbon nanotubes, and 0.91 g of 2,2'-dithiodiacetic acid were dissolved in the aqueous dispersion of aramid nanofibers obtained in S1, and then 0.96 g of 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride and 0.58 g of N-hydroxysuccinimide were added for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0038] S3: The hydrogel obtained in step S2 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0039] Example 3

[0040] A method for preparing an aramid-coated lithium-ion battery separator comprises the following steps:

[0041] S1: 3 g of poly (p-phenylene terephthalamide) fiber, 200 mL of DMSO, and 4.5 g of KOH were mixed and stirred at 95°C for 5 days on an electric stirrer. 50 mL of deionized water was then slowly added dropwise. The mixture was centrifuged and washed. After cooling to room temperature, the resulting product was filtered, dispersed in deionized water, and dialyzed until the pH reached 7 to obtain an aqueous dispersion of aramid nanofibers.

[0042] S2: 11 g of carboxymethyl chitosan (viscosity-average molecular weight of 350,000, degree of substitution of 0.7), 0.37 g of carboxylated multi-walled carbon nanotubes, and 1.46 g of 2,2'-dithiodiacetic acid were dissolved in the aqueous dispersion of aramid nanofibers obtained in S1, and then 1.5 g of 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride and 0.92 g of N-hydroxysuccinimide were added for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0043] S3: The hydrogel obtained in step S2 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0044] Example 4

[0045] A method for preparing an aramid-coated lithium-ion battery separator comprises the following steps:

[0046] S1: 3 g of poly (p-phenylene terephthalamide) fiber, 200 mL of DMSO, and 4.5 g of KOH were mixed and stirred at 95°C for 5 days on an electric stirrer. 50 mL of deionized water was then slowly added dropwise. The mixture was centrifuged and washed. After cooling to room temperature, the resulting product was filtered, dispersed in deionized water, and dialyzed until the pH reached 7 to obtain an aqueous dispersion of aramid nanofibers.

[0047] S2: 11 g of carboxymethyl chitosan (viscosity-average molecular weight of 350,000, degree of substitution of 0.7), 0.44 g of carboxylated multi-walled carbon nanotubes, and 3.6 g of 2,2'-dithiodiacetic acid were dissolved in the aqueous dispersion of aramid nanofibers obtained in S1, and then 3.8 g of 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride and 2.3 g of N-hydroxysuccinimide were added for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0048] S3: The hydrogel obtained in step S2 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0049] Example 5

[0050] A method for preparing an aramid-coated lithium-ion battery separator comprises the following steps:

[0051] S1: 3 g of poly (p-phenylene terephthalamide) fiber, 200 mL of DMSO, and 4.5 g of KOH were mixed and stirred at 95°C for 5 days on an electric stirrer. 50 mL of deionized water was then slowly added dropwise. The mixture was centrifuged and washed. After cooling to room temperature, the resulting product was filtered, dispersed in deionized water, and dialyzed until the pH reached 7 to obtain an aqueous dispersion of aramid nanofibers.

[0052] S2: 11 g of carboxymethyl chitosan (viscosity-average molecular weight of 350,000, degree of substitution of 0.7), 0.55 g of carboxylated multi-walled carbon nanotubes, and 3.6 g of 2,2'-dithiodiacetic acid were dissolved in the aqueous dispersion of aramid nanofibers obtained in S1, and then 3.8 g of 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride and 2.3 g of N-hydroxysuccinimide were added for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0053] S3: The hydrogel obtained in step S2 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that 2,2'-dithiodiacetic acid is omitted. The specific steps are as follows:

[0056] S1: 3 g of poly (p-phenylene terephthalamide) fiber, 200 mL of DMSO, and 4.5 g of KOH were mixed and stirred at 95°C for 5 days on an electric stirrer. 50 mL of deionized water was then slowly added dropwise. The mixture was centrifuged and washed. After cooling to room temperature, the resulting product was filtered, dispersed in deionized water, and dialyzed until the pH reached 7 to obtain an aqueous dispersion of aramid nanofibers.

[0057] S2: 11 g of carboxymethyl chitosan (viscosity-average molecular weight of 350,000, degree of substitution of 0.7) and 0.28 g of carboxylated multi-walled carbon nanotubes were dissolved in the aqueous dispersion of aramid nanofibers obtained in S1, and then 0.96 g of 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride and 0.58 g of N-hydroxysuccinimide were added for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0058] S3: The hydrogel obtained in step S2 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0059] Comparative Example 2

[0060] The only difference between this comparative example and Example 1 is that the carboxylation of multi-walled carbon nanotubes is omitted. The specific steps are as follows:

[0061] S1: 3 g of poly (p-phenylene terephthalamide) fiber, 200 mL of DMSO, and 4.5 g of KOH were mixed and stirred at 95°C for 5 days on an electric stirrer. 50 mL of deionized water was then slowly added dropwise. The mixture was centrifuged and washed. After cooling to room temperature, the resulting product was filtered, dispersed in deionized water, and dialyzed until the pH reached 7 to obtain an aqueous dispersion of aramid nanofibers.

[0062] S2: 11 g of carboxymethyl chitosan (viscosity-average molecular weight of 350,000, degree of substitution of 0.7) and 0.91 g of 2,2'-dithiodiacetic acid were dissolved in the aqueous dispersion of aramid nanofibers obtained in S1, and then 0.96 g of 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride and 0.58 g of N-hydroxysuccinimide were added for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel;

[0063] S3: The hydrogel obtained in step S2 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0064] Comparative Example 3

[0065] The only difference between this comparative example and Example 1 is that the CMC / COOH-MWNTs / DTT hydrogel is omitted. The specific steps are as follows:

[0066] S1: 3 g poly (p-phenylene terephthalamide) fiber, 200 mL DMSO, and 4.5 g KOH were mixed and stirred at 95°C on an electric stirrer for 5 days. Then, 50 mL deionized water was slowly added dropwise and the mixture was centrifuged to obtain an aqueous dispersion of aramid nanofibers.

[0067] S2: The aqueous dispersion of aramid nanofibers obtained in step S1 is coated on one surface of a polyolefin film (8 microns thick). After the coating is completed, a coating with a thickness of 2 microns is obtained. The membrane is placed in an oven at 50°C for 1 hour to evaporate the solvent, thereby obtaining the lithium-ion battery membrane.

[0068] Comparative Example 4

[0069] The only difference between this comparative example and Example 1 is that the mass ratio of carboxymethyl chitosan to carboxylated multi-walled carbon nanotubes is 45:1, that is, the amount of carboxylated multi-walled carbon nanotubes used is 0.24 g.

[0070] Comparative Example 5

[0071] The only difference between this comparative example and Example 5 is that the mass ratio of carboxymethyl chitosan to carboxylated multi-walled carbon nanotubes is 15:1, that is, the amount of carboxylated multi-walled carbon nanotubes used is 0.73 g.

[0072] The performance tests of the diaphragms prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were conducted. The test items are as follows, and the results are shown in Table 1:

[0073] 1. Tensile Strength: The lithium-ion battery separators obtained in each example and the comparative example were cut into strips of 5 mm×40 mm, and the tensile strength was tested using a universal tester.

[0074] 2. Flame retardant performance: The limiting oxygen index test is carried out using the ASTM D2863 standard.

[0075] III. Ionic Conductivity: An AC impedance test was performed. Specifically, the separators prepared in the above embodiments and comparative examples were cut into discs with a diameter of 17 mm, dried, and placed between two stainless steel (SS) electrodes. The discs were allowed to absorb a sufficient amount of electrolyte (the electrolyte contained 32.5 wt % EC (ethylene carbonate), 32.5 wt % EMC (ethyl methyl carbonate), 32.5 wt % DMC (dimethyl carbonate), 2.5 wt % VC (vinylene carbonate), and 1 mol / L LiPF6 (lithium hexafluorophosphate)). The discs were then sealed in 2016-type button cells and subjected to an AC impedance test. The intersection of the linear axis and the real axis was the bulk resistance of the electrolyte, from which the ionic conductivity could be calculated: σ = L / A·R (where L is the thickness of the separator (cm), A is the contact area between the stainless steel plate and the separator (cm2), and R is the bulk resistance of the electrolyte (mS)).

[0076] 4. Liquid absorption rate: The diaphragm was cut into discs with a diameter of 17 mm, dried, and weighed. After that, it was immersed in an electrolyte (the electrolyte contained 32.5 wt% EC (ethylene carbonate), 32.5 wt% EMC (ethyl methyl carbonate), 32.5 wt% DMC (dimethyl carbonate), 2.5 wt% VC (vinylene carbonate) and 1 mol / L LiPF6 (lithium hexafluorophosphate)) for 24 h. Then, the liquid on the surface of the membrane was removed and dried with filter paper and the mass at this time was weighed. All operations were carried out in an argon-filled glove box. Then, the liquid absorption rate was calculated according to the following formula:

[0077] Liquid absorption rate % = (Wi-W) / W×100%; where W is the mass of the dry film (g); Wi is the mass of the dry film after being immersed in the electrolyte for 24 hours (g).

[0078] 5. Self-healing performance: A microscopic scratch of approximately 200 μm in length was made on the surface of the diaphragm using a scalpel. The two cut surfaces of the membrane were then placed in contact at 25°C and 50% relative humidity for 1 hour. The damage to the diaphragm surface was observed and recorded using an optical microscope.

[0079] Table 1

[0080]

[0081]

[0082] It can be seen from Table 1 that the performance of the diaphragms prepared in Examples 1 to 5 is better than that of the diaphragms prepared in Comparative Examples 1 to 5.

[0083] Comparative Example 1, which lacks 2,2'-dithiodiacetic acid, exhibits significantly lower flame retardancy and self-healing properties than Example 1. This suggests that the sulfur element in DTT synergizes with the flame retardant properties of CMC / COOH-MWNTs, enhancing the flame retardancy of the membrane. Furthermore, DTT contains dynamic disulfide bonds, which possess self-healing properties, enhancing the membrane's self-healing capabilities.

[0084] In Comparative Example 2, there are no carboxylated multi-walled carbon nanotubes, and the mechanical properties, flame retardant properties, ionic conductivity, and liquid absorption rate of the diaphragm have all decreased. This shows that COOH-MWNTs, as nano-reinforced fillers, are entangled with aramid fibers through interfacial interactions to form a "fiber-nanotube" composite reinforcement structure, which further enhances toughness and bending resistance, that is, the overall mechanical properties of the diaphragm are improved. Carbon nanotubes can form a dense carbon layer during the combustion process, which plays a role in heat insulation, oxygen isolation, and barrier to combustible gases. The aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel has a relatively high porosity structure, which can increase the diffusion and transmission rate of ions, thereby improving the ionic conductivity of the diaphragm. The high porosity of the nanofiber network can improve the liquid absorption rate of the diaphragm.

[0085] Comparative Example 3 does not contain CMC / COOH-MWNTs / DTT hydrogel, and its comprehensive performance is worse than that of Example 1.

[0086] The content of carboxylated multi-walled carbon nanotubes in Comparative Example 4 is lower than that in Example 1, and the overall performance is reduced, indicating that when the amount of carboxylated multi-walled carbon nanotubes used is small, it is difficult for the carboxylated multi-walled carbon nanotubes to exert their reinforcing effect; the content of carboxylated multi-walled carbon nanotubes in Comparative Example 5 is higher than that in Example 5, and the overall performance is reduced, indicating that when the amount of carboxylated multi-walled carbon nanotubes used is large, agglomeration may occur and the network structure may be destroyed.

[0087] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A method for preparing an aramid-coated lithium-ion battery separator, characterized in that: The following steps are involved: S1: Aramid fibers, DMSO, KOH, and deionized water were mixed and stirred, washed by centrifugation, cooled to room temperature, filtered, dispersed in deionized water, and dialyzed until the pH was 7 to obtain an aqueous dispersion of aramid nanofibers; S2: dissolving carboxymethyl chitosan, carboxylated multi-walled carbon nanotubes and 2,2'-dithiodiacetic acid into the aramid nanofiber aqueous dispersion obtained in S1, and then adding a condensing agent for polymerization to obtain an aramid fiber composite CMC / COOH-MWNTs / DTT hydrogel; S3: coating the hydrogel obtained in step S2 on at least one surface of the base film to obtain a coating. After the coating is completed, the separator is placed in an oven at 50° C. for 1 hour to volatilize the solvent, thereby obtaining the lithium-ion battery separator.

2. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S1, the usage ratio of the aramid fiber, DMSO, KOH and deionized water is 3 g:200 mL:4.5 g:40-50 mL.

3. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S1, the aramid fiber is aramid fiber poly(p-phenylene terephthalamide) fiber.

4. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S2, the mass ratio of the carboxymethyl chitosan to the carboxylated multi-walled carbon nanotubes is (20-40):

1.

5. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S2, the molar ratio of the carboxymethyl chitosan to 2,2'-dithiodiacetic acid is (1-4):

1.

6. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S2, the molar ratio of the total amount of the condensing agent to the 2,2'-dithiodiacetic acid is 2:

1.

7. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S2, the condensing agent is any one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, 1-(3-dimethylaminopropyl) 3-ethylcarbodiimide hydrochloride, and dicyclohexylcarbodiimide in combination with any one of 4-dimethylaminopyridine, N-hydroxysuccinimide, and 1-hydroxybenzotriazole, and the molar ratio of the two condensing agents when used in combination is 1:

1.

8. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S2, the viscosity-average molecular weight of the carboxymethyl chitosan is 350,000-500,000, and the degree of substitution is 0.7-0.

95.

9. The method for preparing an aramid-coated lithium-ion battery separator according to claim 1, characterized in that: In step S3, the base film is one or more of a polyolefin film, a polypropylene film, and a polypropylene-polyethylene-polypropylene composite film; the base film has a thickness of 5-11 microns; and the coating has a thickness of 1-3 microns.

10. An aramid-coated lithium-ion battery separator, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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