A molybdenum carbide@PMMA coaxial nanotube coated lithium ion battery diaphragm and a preparation method thereof

Abstract

The application discloses a kind of molybdenum carbide@PMMA coaxial nanotube coated lithium ion battery separator, the separator includes base film and adheres in the coating layer of base film one side or two sides membrane surface, wherein the base film is polyolefin film, the coating layer slurry is prepared according to following method, first, 0.7%~1.2% dispersing agent, 18%~38% molybdenum carbide@PMMA coaxial nanotube are premixed in ultrapure water according to mass ratio;2%~10% thickening agent, 1%~8% binder, 0.1%~0.5% wetting agent and 0.05%~0.25% defoaming agent are added respectively and stirred uniformly, finally, iron is removed by filtration, and molybdenum carbide@PMMA coaxial nanotube coating layer slurry is obtained;Then using micro-gravure roll coating process, coating slurry is uniformly roll coated on polyolefin separator by coating machine, after 70 DEG C oven baking, it is rewound for standby, i.e. molybdenum carbide@PMMA coaxial nanotube coated lithium ion battery separators are obtained.The separator prepared by the application has excellent heat shrinkage performance, pole piece bonding performance and electrolyte wetting performance, and also has high mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separator preparation, specifically to a molybdenum carbide@PMMA coaxial nanotube coated lithium-ion battery separator and its preparation method. Background Technology

[0002] Lithium-ion batteries, as a new type of rechargeable battery, have advantages such as high energy density and long cycle life. Their applications are constantly expanding, and they are widely used in portable electronic devices, energy storage, and electric vehicles. Especially with the rapid development of the new energy industry, lithium-ion batteries are increasingly being used in electric vehicles. The separator, as a crucial component of lithium-ion batteries, effectively prevents short circuits between the positive and negative electrodes, and has a very important impact on the safety of lithium-ion batteries. Therefore, the improvement of lithium-ion battery performance and safety requirements place higher demands on the performance of the separator.

[0003] Polyolefin separators are currently the most widely used lithium-ion battery separators. However, existing polyolefin separators on the market also have some drawbacks: ① Low ionic conductivity, resulting in high internal resistance of the battery, which is not conducive to high-rate charging and discharging of lithium-ion batteries; ② Low mechanical strength and poor puncture resistance, making them easily punctured and causing short circuits between the positive and negative electrodes, leading to thermal runaway; ③ Polyolefin materials have very low melting points, making the separator prone to rupture when thermal runaway occurs, which can exacerbate the thermal runaway and lead to battery combustion or even explosion; ④ Poor adhesion to electrodes and insufficient electrolyte affinity, resulting in a series of problems such as poor cycle performance, low thermal stability, unstable electrode-separator interface, poor battery hardness, and difficulties in processing and transportation. This greatly limits the improvement of battery energy density and the development of high-performance ultra-thin batteries. To address the issues of poor adhesion between polyolefin separators and electrodes and poor electrolyte wettability, the main current solution is to coat one or both sides of the polyolefin separator with an aqueous PVDF adhesive layer. This coating layer can effectively improve the separator's adhesion while maintaining good wettability with the electrolyte. Regarding the problems of low ionic conductivity, poor mechanical properties, and poor heat resistance of polyolefin separators, the main current solution is to coat one or both sides of the polyolefin separator with a high-temperature resistant ceramic coating. This can delay the separator's pore-closing temperature to 150°C. However, a pore-closing temperature of 150°C cannot completely prevent short circuits and spontaneous combustion of lithium batteries at high temperatures. Therefore, it is necessary to further improve the heat resistance of the separator to reduce the risk of separator rupture and thus improve battery safety.

[0004] Therefore, developing lithium-ion battery separators with high heat resistance, high mechanical strength, high electrolyte wettability, and high adhesion has become a common goal pursued by the industry. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the technical defects of existing lithium-ion battery separators, such as low liquid absorption and retention capacity, low heat resistance, low electrode bonding performance and low mechanical strength, and to provide a lithium-ion battery separator with high electrolyte wettability, high bonding, high heat resistance and high mechanical strength.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A molybdenum carbide@PMMA coaxial nanotube coated lithium-ion battery separator is characterized in that the separator includes a base film and a coating layer adhered to one or both sides of the base film, wherein the base film is a polyolefin film, and the coating layer includes molybdenum carbide@PMMA coaxial nanotubes, a dispersant, a thickener, a binder, a wetting agent, and a defoamer.

[0008] As a limitation of the present invention, the mass percentages of each component in the coating layer are as follows: molybdenum carbide@PMMA coaxial nanotubes 18%–38%, dispersant 0.7%–1.2%, thickener 2%–10%, binder 1%–8%, wetting agent 0.1%–0.5%, defoamer 0.05%–0.25%, and the remainder is deionized water.

[0009] As a further limitation of the present invention, the dispersant is an aliphatic amide, the thickener is sodium hydroxymethyl cellulose (CMC adhesive), the binder is polyacrylic acid, the wetting agent is an alkyl sulfate, and the defoamer is a polyether defoamer.

[0010] As a limitation of the present invention, the molybdenum carbide@PMMA coaxial nanotubes of the present invention are prepared according to the following steps:

[0011] (1) Preparation of MnCO3 nanowires

[0012] 0.3–0.8 mmol potassium permanganate and 2–3 mmol manganese chloride were added to deionized water under constant stirring. After ultrasonic treatment, 0.1–0.3 g hexadecyltrimethylammonium bromide, 0.4–0.6 mL hydrogen peroxide (30% by mass), and 1–3 mmol lithium carbonate were added to the above solution. After stirring, the resulting mixture was transferred to a high-pressure reactor and then placed in an oven at 180°C for 20 h. After natural cooling to room temperature, the reaction product was filtered, washed, and dried to obtain the MnCO3 nanowires.

[0013] (2) Preparation of molybdenum carbide nanotubes

[0014] 1–3 g of the MnCO3 nanowires obtained in step (1) were added to deionized water under constant stirring. After stirring and ultrasonic dispersion, 2–4 g of (NH4)6Mo7O were added. 24·4H2O and 3-5g aniline, under constant stirring, 1.0mol·L -1 Hydrochloric acid was slowly added to the above mixture to adjust the pH to 4.5; the resulting mixture was transferred to a high-pressure reactor, and the reaction temperature was 75℃ for 10 hours; after the reaction, it was naturally cooled to room temperature, filtered, washed, and dried; the resulting powder was then calcined in a nitrogen atmosphere at 500–800℃ for 3–5 hours, and the calcined powder was added to a 2.0 mol·L⁻¹ solution. -1 The molybdenum carbide nanotubes were obtained by filtration, washing and drying after being kept in dilute hydrochloric acid for 40 hours.

[0015] (3) Preparation of molybdenum carbide@PMMA coaxial nanotubes

[0016] A. Add 1-2g of molybdenum carbide nanotubes obtained in step (2) and ultrapure water into a conical flask, and then stir magnetically and sonicate to obtain a uniformly dispersed molybdenum carbide nanotube dispersion.

[0017] B. Slowly add 0.3-0.8g of PMMA powder to 8-10g of ethyl acetate and seal the mixture to obtain a PMMA solution.

[0018] C. While continuously stirring, the PMMA solution obtained in step B is dispensed at a rate of 0.8 mL / min. -1 The solution is slowly added dropwise to the molybdenum carbide nanotube dispersion described in step A, and then subjected to magnetic stirring and ultrasonic treatment.

[0019] D. Centrifuge the mixture obtained in step C. The resulting precipitate is thoroughly washed and vacuum dried to obtain the PMMA-coated molybdenum carbide nanotube coaxial composite material, namely molybdenum carbide@PMMA coaxial nanotubes.

[0020] The preparation method of the molybdenum carbide@PMMA coaxial nanotube coated lithium-ion battery separator of the present invention is carried out according to the following steps:

[0021] (1) Premix 0.7% to 1.2% dispersant and 18% to 38% molybdenum carbide@PMMA coaxial nanotubes in ultrapure water according to the mass ratio; add 2% to 10% thickener, 1% to 8% binder, 0.1% to 0.5% wetting agent and 0.05% to 0.25% defoamer respectively and stir evenly. Finally, filter to remove iron to obtain molybdenum carbide@PMMA coaxial nanotube coating slurry;

[0022] (2) Using a micro-gravure roller coating process, the molybdenum carbide@PMMA coaxial nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70°C oven, it is rolled up for use, thus obtaining the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes for lithium-ion batteries.

[0023] The beneficial effects achieved by the present invention after adopting the above technical solution are as follows:

[0024] The composite diaphragm prepared by this invention exhibits excellent thermal shrinkage properties, electrode adhesion properties, and electrolyte wetting properties, while also possessing high mechanical strength. Specifically, this is reflected in the following aspects:

[0025] 1. The molybdenum carbide described in the technical solution of the present invention has good high temperature resistance and thermal conductivity. Selecting molybdenum carbide as a coating material and adding it to the slurry components is beneficial to improving the heat resistance of the coating, thereby improving the heat resistance of the diaphragm.

[0026] 2. The composite separator modified with molybdenum carbide@PMMA coaxial nanotubes provided by the present invention has the hollow nanotube structure improving the lithium-ion conductivity and greatly increasing the specific surface area of ​​the material, thereby significantly improving the liquid absorption and retention capacity of the separator.

[0027] 3. The composite membrane modified with molybdenum carbide@PMMA coaxial nanotubes provided by the present invention, wherein the introduction of molybdenum carbide@PMMA coaxial nanotubes, thanks to their excellent properties and the mutual cross-linking between different nanotubes, significantly improves the mechanical strength and thermal shrinkage performance of the membrane; in addition, PMMA and molybdenum carbide nanotubes can work synergistically, which further improves the mechanical properties and heat resistance of the membrane.

[0028] 4. The composite separator modified with molybdenum carbide@PMMA coaxial nanotubes provided by the present invention, wherein PMMA is combined with molybdenum carbide nanotubes by dissolving and then coating, and PMMA can adhere to its surface relatively firmly. That is, molybdenum carbide nanotubes can effectively fix PMMA on the surface of polyolefin separator, which also greatly improves the adhesion of the separator to the electrode and the wettability of the electrolyte. At the same time, this strategy also greatly improves the problem of PMMA powder shedding during the early coating and later cell manufacturing processes. Detailed Implementation

[0029] The technical solution of the present invention will be described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] First, molybdenum carbide@PMMA coaxial nanotubes were prepared using the following method.

[0031] (1) Preparation of MnCO3 nanowires:

[0032] 0.3–0.8 mmol of potassium permanganate and 2–3 mmol of manganese chloride were added to 45 mL of deionized water under constant stirring, and the mixture was ultrasonically treated for 20 min. Then, 0.1–0.3 g of hexadecyltrimethylammonium bromide, 0.4–0.6 mL of 30% hydrogen peroxide, and 1–3 mmol of lithium carbonate were added to the solution. After stirring for 36 min, the mixture was transferred to a 50 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), and then placed in an oven at 180 °C for 20 h. After the high-pressure reactor cooled naturally to room temperature, the mixture was filtered, and the precipitate was collected. The precipitate was thoroughly washed with anhydrous ethanol and deionized water, and then dried for 12 h to obtain MnCO3 nanowires.

[0033] (2) Preparation of molybdenum carbide nanotubes:

[0034] Under continuous stirring, 1–3 g of the MnCO3 nanowires prepared above were added to 45 mL of deionized water and magnetically stirred for 40 min (300 rpm). Then, the mixture was ultrasonically dispersed for 2 h (at 25 kHz and 300 W ultrasonic power). After dispersion, 2–4 g of (NH4)6Mo7O2 was added. 24 Add 4H₂O and 3–5 g of aniline, and continue stirring for 10 min (450 rpm), then ultrasonically disperse for 30 min (treated at 35 kHz and 600 W ultrasonic power). Subsequently, add 1.0 mol·L⁻¹ of aniline while continuously stirring. -1 Hydrochloric acid was slowly added to the resulting mixture to adjust the pH to 4.5. The mixture was then transferred to a PTFE-lined stainless steel autoclave for reaction at 75°C for 10 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The precipitate was then filtered and collected. The precipitate was thoroughly washed with anhydrous ethanol and deionized water, followed by vacuum drying (0.08 MPa vacuum, 50°C for 48 hours). The resulting powder was then calcined in a nitrogen atmosphere at 750°C for 4.5 hours. Finally, the calcined powder was added to a 2.0 mol·L⁻¹ solution. -1 The molybdenum carbide nanotubes were obtained by immersing them in dilute hydrochloric acid for 40 hours, then filtering, washing, and drying at 80°C for 12 hours.

[0035] (3) Preparation of molybdenum carbide@PMMA coaxial nanotubes:

[0036] A. Add 1-2g of the above-prepared molybdenum carbide nanotubes and ultrapure water to a 500mL stoppered conical flask and stir magnetically (stir at 380rpm for 90min). Then, perform ultrasonic treatment (treat at 25KHZ and 300w ultrasonic power for 6h) to obtain a uniformly dispersed molybdenum carbide nanotube dispersion.

[0037] B. Slowly add 0.3-0.8g of PMMA powder to 8-10g of ethyl acetate, then seal the mixture and stir it using a magnetic stirrer (stirring at 350rpm for 1.5h).

[0038] C. Under continuous stirring (650 rpm), the prepared PMMA solution was diluted at a rate of 0.8 mL / min. -1 The flow rate was slowly added dropwise to the above uniformly dispersed molybdenum carbide nanotube dispersion, and magnetic stirring was continued (stirring at 300 rpm for 2 h), followed by ultrasonic treatment (treatment at 35 kHz and 300 W ultrasonic power for 5 h).

[0039] D. Centrifuge the mixture obtained in step C (centrifuge at 8500 rpm for 20 min), wash the precipitate obtained by centrifugation thoroughly and vacuum dry (0.08 MPa vacuum, dry at 85℃ for 20 h), and after drying, you will get the PMMA-coated molybdenum carbide nanotube coaxial composite material, namely molybdenum carbide@PMMA coaxial nanotube.

[0040] The molybdenum carbide@PMMA coaxial nanotubes prepared above are used in the following examples.

[0041] Example 1

[0042] (1) 0.96% dispersant and 18% molybdenum carbide@PMMA coaxial nanotubes were premixed in ultrapure water for 85 min at 770 rpm. 6.8% thickener was added and stirring was continued for 90 min at 700 rpm. 6% binder was added and stirring was continued for 65 min at 1000 rpm. 0.35% wetting agent and 0.1% defoamer were added and stirring was continued for 45 min at 200 rpm. Finally, the mixture was filtered to remove iron to obtain the molybdenum carbide@PMMA coaxial nanotube coating slurry.

[0043] (2) Using a micro-gravure roller coating process, the molybdenum carbide@PMMA coaxial nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70°C oven, it is rolled up for use, thus obtaining the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes for lithium-ion batteries.

[0044] Example 2

[0045] (1) 0.96% dispersant and 28% molybdenum carbide@PMMA coaxial nanotubes were premixed in ultrapure water for 85 min at 770 rpm. 6.8% thickener was added and stirring was continued for 90 min at 700 rpm. 6% binder was added and stirring was continued for 65 min at 1000 rpm. 0.35% wetting agent and 0.1% defoamer were added and stirring was continued for 45 min at 200 rpm. Finally, the mixture was filtered to remove iron to obtain the molybdenum carbide@PMMA coaxial nanotube coating slurry.

[0046] (2) Using a micro-gravure roller coating process, the molybdenum carbide@PMMA coaxial nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70°C oven, it is rolled up for use, thus obtaining the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes for lithium-ion batteries.

[0047] Example 3

[0048] (1) 0.96% dispersant and 38% molybdenum carbide@PMMA coaxial nanotubes were premixed in ultrapure water for 85 min at 770 rpm. 6.8% thickener was added and stirring was continued for 90 min at 700 rpm. 6% binder was added and stirring was continued for 65 min at 1000 rpm. 0.35% wetting agent and 0.1% defoamer were added and stirring was continued for 45 min at 200 rpm. Finally, the mixture was filtered to remove iron to obtain the molybdenum carbide@PMMA coaxial nanotube coating slurry.

[0049] (2) Using a micro-gravure roller coating process, the molybdenum carbide@PMMA coaxial nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70°C oven, it is rolled up for use, thus obtaining the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes for lithium-ion batteries.

[0050] Example 4

[0051] (1) 0.7% dispersant and 20% molybdenum carbide@PMMA coaxial nanotubes were premixed in ultrapure water for 85 min at 770 rpm. 2% thickener was added and stirring was continued for 90 min at 700 rpm. 1% binder was added and stirring was continued for 65 min at 1000 rpm. 0.1% wetting agent and 0.05% defoamer were added and stirring was continued for 45 min at 200 rpm. Finally, the mixture was filtered to remove iron to obtain the molybdenum carbide@PMMA coaxial nanotube coating slurry.

[0052] (2) Using a micro-gravure roller coating process, the molybdenum carbide@PMMA coaxial nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70°C oven, it is rolled up for use, thus obtaining the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes for lithium-ion batteries.

[0053] Example 5

[0054] (1) 1.2% dispersant and 25% molybdenum carbide@PMMA coaxial nanotubes were premixed in ultrapure water for 85 min at 770 rpm. 10% thickener was added and stirring was continued for 90 min at 700 rpm. 8% binder was added and stirring was continued for 65 min at 1000 rpm. 0.5% wetting agent and 0.25% defoamer were added and stirring was continued for 45 min at 200 rpm. Finally, the mixture was filtered to remove iron to obtain the molybdenum carbide@PMMA coaxial nanotube coating slurry.

[0055] (2) Using a micro-gravure roller coating process, the molybdenum carbide@PMMA coaxial nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70°C oven, it is rolled up for use, thus obtaining the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes for lithium-ion batteries.

[0056] Comparative Example 1

[0057] The same polyolefin separator described above is without a coating.

[0058] Comparative Example 2

[0059] (1) 0.96% dispersant and 18% molybdenum carbide nanotubes were premixed in ultrapure water for 85 min at 770 rpm. 6.8% thickener was added and stirring was continued for 90 min at 700 rpm. 6% binder was added and stirring was continued for 65 min at 1000 rpm. 0.35% wetting agent and 0.1% defoamer were added and stirring was continued for 45 min at 200 rpm. Finally, the mixture was filtered to remove iron to obtain the molybdenum carbide nanotube coating slurry.

[0060] (2) Using a micro-gravure roller coating process, the molybdenum carbide nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70°C oven, it is rolled up for use, thus obtaining the separator modified with molybdenum carbide nanotubes for lithium-ion batteries.

[0061] The composite membranes prepared in Examples 1 to 5 and the membranes in Comparative Examples 1 to 2 were subjected to performance tests. The test results are shown in Table 1 below.

[0062] Table 1 Comparison of various properties of the composite membranes obtained in the examples and comparative examples

[0063]

[0064] As can be seen from Table 1, the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes obtained by the present invention has excellent thermal shrinkage performance, electrode adhesion performance and electrolyte wetting performance, and also has high mechanical strength. This type of coated separator has good application prospects in the field of lithium battery separators.

[0065] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing a molybdenum carbide@PMMA coaxial nanotube coated lithium-ion battery separator, characterized in that... The diaphragm comprises a base membrane and a coating layer adhered to one or both sides of the base membrane. The base membrane is a polyolefin membrane, and the coating layer comprises molybdenum carbide@PMMA coaxial nanotubes, a dispersant, a thickener, a binder, a wetting agent, and an antifoaming agent. The molybdenum carbide@PMMA coaxial nanotubes mentioned above are prepared according to the following steps: (1) Preparation of MnCO3 nanowires 0.3-0.8 mmol potassium permanganate and 2-3 mmol manganese chloride were added to deionized water under constant stirring. After ultrasonic treatment, 0.1-0.3 g hexadecyltrimethylammonium bromide, 0.4-0.6 mL hydrogen peroxide (30% by mass), and 1-3 mmol lithium carbonate were added to the above solution. After stirring, the resulting mixture was transferred to a high-pressure reactor and then placed in an oven at 180 °C for 20 h. After natural cooling to room temperature, the reaction product was filtered, washed, and dried to obtain the MnCO3 nanowires. (2) Preparation of molybdenum carbide nanotubes 1-3 g of the MnCO3 nanowires obtained in step (1) were added to deionized water under constant stirring. After stirring and ultrasonic dispersion, 2-4 g of (NH4)6Mo7O were added. 24 ·4H2O and 3~5 g of aniline, under constant stirring, 1.0 mol·L -1 Hydrochloric acid was slowly added to the above mixture to adjust the pH to 4.5; the resulting mixture was transferred to a high-pressure reactor, and the reaction temperature was 75℃ for 10 h; after the reaction, it was naturally cooled to room temperature, filtered, washed, and dried; the resulting powder was then calcined in a nitrogen atmosphere at 500-800℃ for 3-5 h, and the calcined powder was added to 2.0 mol·L⁻¹ -1 The molybdenum carbide nanotubes were obtained by filtration, washing and drying after being kept in dilute hydrochloric acid for 40 h. (3) Preparation of molybdenum carbide@PMMA coaxial nanotubes A. Add 1-2 g of molybdenum carbide nanotubes obtained in step (2) and ultrapure water into a conical flask, and then stir magnetically and sonicate to obtain a uniformly dispersed molybdenum carbide nanotube dispersion. B. Slowly add 0.3~0.8 g of PMMA powder to 8~10 g of ethyl acetate, and seal the mixture to obtain a PMMA solution; C. While continuously stirring, the PMMA solution obtained in step B is dispensed at a rate of 0.8 mL / min. -1 The solution is slowly added dropwise to the molybdenum carbide nanotube dispersion described in step A, and then subjected to magnetic stirring and ultrasonic treatment. D. Centrifuge the mixture obtained in step C. The resulting precipitate is thoroughly washed and vacuum dried to obtain the PMMA-coated molybdenum carbide nanotube coaxial composite material, namely molybdenum carbide@PMMA coaxial nanotubes.

2. The method for preparing a molybdenum carbide@PMMA coaxial nanotube coated lithium-ion battery separator according to claim 1, characterized in that... The mass percentages of each component in the coating layer are as follows: molybdenum carbide@PMMA coaxial nanotubes 18%~38%, dispersant 0.7%~1.2%, thickener 2%~10%, binder 1%~8%, wetting agent 0.1%-0.5%, defoamer 0.05%~0.25%, and the remainder is deionized water.

3. The method for preparing a molybdenum carbide@PMMA coaxial nanotube coated lithium-ion battery separator according to claim 1, characterized in that... The dispersant is an aliphatic amide, the thickener is sodium hydroxymethyl cellulose, the binder is polyacrylic acid, the wetting agent is an alkyl sulfate, and the defoamer is a polyether defoamer.

4. The method for preparing a molybdenum carbide@PMMA coaxial nanotube coated lithium-ion battery separator according to any one of claims 1 to 3, characterized in that... The method is specifically carried out according to the following steps: (1) Premix 0.7%~1.2% dispersant and 18%~38% molybdenum carbide@PMMA coaxial nanotubes in ultrapure water according to the mass ratio; add 2%~10% thickener, 1%~8% binder, 0.1%~0.5% wetting agent and 0.05%~0.25% defoamer respectively and stir evenly. Finally, filter to remove iron to obtain molybdenum carbide@PMMA coaxial nanotube coating slurry; (2) Using a micro-gravure roller coating process, the molybdenum carbide@PMMA coaxial nanotube coating slurry obtained in step (1) is uniformly roller coated onto the polyolefin separator by a coating machine. After baking in a 70 ℃ oven, it is rolled up for use, thus obtaining the composite separator modified with molybdenum carbide@PMMA coaxial nanotubes for lithium-ion batteries.

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