Aramid composite lithium battery separator and preparation method thereof

Abstract

This invention discloses an aramid composite lithium battery separator and its preparation method, relating to the field of lithium-ion battery technology. Inorganic particles are added to PolarClean solvent and dispersed by high-temperature stirring. Then, a co-solvent, a phase separation promoter, and short aramid fibers are added and dissolved by high-temperature stirring to obtain an aramid solution. Under constant temperature drying conditions, the dissolved aramid solution is coated onto a substrate film, with a constant temperature plate placed underneath. The substrate film coated with the aramid solution is placed in a constant temperature and humidity chamber under a water vapor environment for a certain period of time, and then immersed in a gel bath composed of deionized water to wash away residual solvent, co-solvent, and phase separation promoter. The washed composite film is then dried in a hot roller or oven to obtain the aramid composite lithium battery separator. This invention utilizes PolarClean as a solvent for preparing the aramid composite lithium battery separator, which, in addition to being non-toxic and harmless, significantly improves the gas permeability and electrical performance of the battery separator.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an aramid composite lithium battery separator and its preparation method. 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 10%-50% NMP aqueous solution, and finally drying to form an aramid composite membrane. Patent 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. Then, an aqueous solution containing 70% solvent is used as the first gel bath, and a composite membrane is prepared by phase separation. Patent CN115207571A discloses a lithium-ion battery composite membrane and its preparation method. It dissolves aramid and polyacrylate materials in NMP, DMAC, or acetone, and uses a water-NMP mixed solution with a mass ratio of (1-9):10 as the gel bath, preparing a composite membrane by phase separation.

[0004] Given the reproductive toxicity of DMF, DMAc, and NMP, the need to find alternatives is becoming increasingly urgent. Therefore, there is a pressing need to develop a method for preparing aramid composite membranes using a non-toxic and harmless solvent. PolarClean, as a non-toxic and harmless aprotic polar green solvent, holds promise as a replacement for DMF, DMAc, and NMP, and researchers are currently investigating it. However, there are no studies yet on the application of PolarClean in the preparation of lithium-ion battery membranes. Summary of the Invention

[0005] The purpose of this invention is to provide an aramid composite lithium battery separator and its preparation method. PolarClean is used as the solvent required for preparing the aramid composite lithium battery separator. In addition to being non-toxic and harmless, it also significantly improves the air permeability and electrical performance of the battery separator.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing an aramid composite lithium battery separator includes the following steps:

[0008] (1) Inorganic particles are added to PolarClean solvent and dispersed by high temperature stirring. Then, cosolvent, phase separation promoter and aramid short fiber are added and dissolved by high temperature stirring to obtain aramid solution.

[0009] (2) Under constant temperature and drying conditions, the dissolved aramid solution is coated onto the base film, and a constant temperature plate is placed under the base film;

[0010] (3) Place the base film coated with aramid solution in a constant temperature and humidity chamber under water vapor for a certain period of time, and then immerse it in a gel bath composed of deionized water to wash away residual solvent, co-solvent and phase separation promoter.

[0011] (4) The washed composite membrane is dried in a hot roller or oven to obtain an aramid composite lithium battery separator.

[0012] Preferably, the PolarClean solvent is methyl 5-dimethylamino-2-methyl-5-oxovalerate.

[0013] Preferably, the inorganic particles are one of alumina with D50≤1um and boehmite with D90≤2um, accounting for 1-10wt% of the total mass of the solution, and the stirring and dispersion temperature is 50-100℃.

[0014] Preferably, the co-solvent is one of lithium chloride, lithium bromide, and lithium nitrate, accounting for 0.01-0.1 wt% of the total solution mass.

[0015] Preferably, the phase separation promoter is selected from one or more of polyethylene glycol 400 (PEG-400), polyethylene glycol 800 (PEG-800), polyvinylpyrrolidone K13 (PVP-K13), polyvinylpyrrolidone K16 (PVP-K16), and deionized water, accounting for 0.1-5 wt% of the total mass of the solution.

[0016] Preferably, the aramid short fiber is meta-aramid short fiber, accounting for 5-10 wt% of the total mass of the solution, and the stirring and dissolving temperature is 50-100℃.

[0017] Preferably, the constant temperature drying conditions are 20-60℃.

[0018] Preferably, the coating method is blade coating, dip coating, or micro-groove roller coating, and the coating thickness is 1-5 μm.

[0019] Preferably, the constant temperature plate is at the same temperature as the coating temperature, which is 20-60℃.

[0020] Preferably, the bottom membrane is a commercial lithium battery separator made of polyethylene or polypropylene.

[0021] Preferably, the temperature and humidity chamber is 40-80℃, the relative humidity is 40%-95%, and the placement time is 10-60s.

[0022] Preferably, the drying temperature is 40-70℃.

[0023] An aramid composite lithium battery separator is prepared by the above method.

[0024] The beneficial effects of this invention are:

[0025] 1. PolarClean is a non-toxic, harmless, and biodegradable green solvent. Using this solvent to prepare aramid coated membranes can reduce environmental pollution and improve the working environment for technicians.

[0026] 2. High-temperature coating can increase the film-forming properties of aramid / PolarClean solution, resulting in thinner aramid composite membranes.

[0027] 3. Adding a phase separation promoter to the aramid / PolarClean solution causes it to undergo cyclotron phase separation when immersed in a non-solvent, resulting in a structure with better pore connectivity and a lower gas permeability increment in the coated film.

[0028] 4. No solvent is added to the non-solvent phase; phase separation is initiated only by steam and water. The process is environmentally friendly, and the resulting coated film has a low increase in air permeability.

[0029] 5. Aramid coating can significantly improve the heat resistance and electrolyte wettability of polyolefin membranes.

[0030] 6. Thanks to the advantages of the aramid membrane structure brought by PolarClean, the battery cycle and rate performance can be further improved. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for preparing an aramid composite lithium battery separator according to the present invention. Detailed Implementation

[0032] To make the above features and advantages of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings.

[0033] Example 1

[0034] 1. Take 1 wt% of alumina with D90 of 2 μm and D50 of 1 μm and add it to PolarClean. Stir and disperse at 100 °C. Then add 0.1 wt% lithium chloride, 5 wt% PEG-400 and 10 wt% aramid short fiber. Stir until completely dissolved and let stand at ambient temperature to obtain aramid solution.

[0035] 2. Apply the aramid solution to one side of a commercial polyethylene separator (coating thickness 5µm, coating temperature 20℃), then immerse it in a constant temperature and humidity chamber at 40℃ and 95% humidity for 10 seconds. Next, immerse it in deionized water to wash away the solvent, co-solvent, and phase separation promoter. Finally, dry the membrane at 70℃ to obtain the aramid composite separator.

[0036] Example 2

[0037] 1. Take 10wt% of alumina with D90 of 0.6um and D50 of 0.2um and add it to PolarClean. Stir and disperse at 60℃. Then add 0.1wt% lithium chloride, 0.1wt% deionized water, 1wt% PVP-K13, and 8wt% aramid short fiber. Stir until completely dissolved and let stand at ambient temperature to obtain aramid solution.

[0038] 2. Apply the aramid solution to one side of a commercial polyethylene membrane (coating thickness 1µm, coating temperature 60℃), then immerse it in a constant temperature and humidity chamber at 60℃ and 75% for 30 seconds. Next, immerse it in deionized water to wash away the solvent, co-solvent, and phase separation promoter. Finally, dry the membrane at 60℃ to obtain the aramid composite membrane.

[0039] Example 3

[0040] 1. Take 10wt% of alumina with D90 of 0.6um and D50 of 0.2um and add it to PolarClean. Stir and disperse at 50℃. Then add 0.1wt% lithium chloride, 0.1wt% deionized water, 1wt% PVP-K13, and 5wt% aramid short fibers. Stir until completely dissolved and let stand at ambient temperature to obtain aramid solution.

[0041] 2. Apply the aramid solution to one side of a commercial polyethylene separator (coating thickness 1µm, coating temperature 40℃), then immerse it in a constant temperature and humidity chamber at 40℃ and 40% humidity for 60 seconds. Next, immerse it in deionized water to wash away the solvent, co-solvent, and phase separation promoter. Finally, dry the membrane at 60℃ to obtain the aramid composite separator.

[0042] Example 4

[0043] 1. Take 10wt% of alumina with D90 of 0.6um and D50 of 0.2um and add it to PolarClean. Stir and disperse at 60℃. Then add 0.1wt% lithium chloride, 0.1wt% deionized water, 1wt% PVP-K13, and 5wt% aramid short fiber. Stir until completely dissolved and let stand at ambient temperature to obtain aramid solution.

[0044] 2. Apply the aramid solution to one side of a commercial polyethylene separator (coating thickness 1µm, coating temperature 60℃), then immerse it in a constant temperature and humidity chamber at 80℃ and 95% humidity for 10 seconds. Next, immerse it in deionized water to wash away the solvent, co-solvent, and phase separation promoter. Finally, dry the membrane at 40℃ to obtain the aramid composite separator.

[0045] Example 5

[0046] 1. Take 1 wt% of boehmite with D90 of 0.8 μm and D50 of 0.4 μm and add it to PolarClean. Stir and disperse at 60 °C. Then add 0.01 wt% lithium chloride, 0.1 wt% deionized water, 1 wt% PVP-K16, and 5 wt% aramid short fiber. Stir until completely dissolved and let stand at ambient temperature to obtain aramid solution.

[0047] 2. Apply the aramid solution to one side of a commercial polyethylene membrane (coating thickness 1µm, coating temperature 60℃), then immerse it in a constant temperature and humidity chamber at 60℃ and 75% for 30 seconds. Next, immerse it in deionized water to wash away the solvent, co-solvent, and phase separation promoter. Finally, dry the membrane at 60℃ to obtain the aramid composite membrane.

[0048] Example 6

[0049] 1. Take 5wt% of boehmite with D90 of 0.8um and D50 of 0.4um and add it to PolarClean. Stir and disperse at 60℃. Then add 0.05wt% lithium chloride, 0.5wt% deionized water, 1wt% PEG-800 and 8wt% aramid short fiber. Stir until completely dissolved and let stand at ambient temperature to obtain aramid solution.

[0050] 2. Apply the aramid solution to one side of a commercial polyethylene membrane (coating thickness 1µm, coating temperature 60℃), then immerse it in a constant temperature and humidity chamber at 60℃ and 75% for 30 seconds. Next, immerse it in deionized water to wash away the solvent, co-solvent, and phase separation promoter. Finally, dry the membrane at 60℃ to obtain the aramid composite membrane.

[0051] Example 7

[0052] 1. Take 10wt% of boehmite with D90 of 0.8um and D50 of 0.4um and add it to PolarClean. Stir and disperse at 60℃. Then add 0.1wt% lithium chloride, 0.1wt% PEG-800 and 10wt% aramid short fiber. Stir until completely dissolved and let stand at ambient temperature to obtain aramid solution.

[0053] 2. Apply the aramid solution to one side of a commercial polyethylene separator (coating thickness 2µm, coating temperature 60℃), then immerse it in a constant temperature and humidity chamber at 60℃ and 75% for 30 seconds. Next, immerse it in deionized water to wash away the solvent, co-solvent, and phase separation promoter. Finally, dry the membrane at 60℃ to obtain the aramid composite separator.

[0054] Comparative Example 1

[0055] In this comparative example, the solvent PolarClean in Example 2 was replaced with DMAC, and everything else remained the same.

[0056] Comparative Example 2

[0057] In this comparative example, the solvent PolarClean in Example 2 was replaced with NMP, and everything else remained the same.

[0058] Comparative Example 3

[0059] In this comparative example, the solvent PolarClean in Example 2 was replaced with DMF, and everything else remained the same.

[0060] Comparative Example 4

[0061] In this comparative example, polyethylene diaphragm was used directly as a control.

[0062] The performance of the aramid composite membrane and polyethylene membrane in the examples and comparative examples is shown in Table 1, and the performance data of the membrane battery is shown in Table 2.

[0063] Table 1. Diaphragm performance data for examples and comparative examples.

[0064]

[0065] As can be seen from Table 1, the aramid composite membrane prepared using PolarClean (Example 2) has significantly lower air permeability and heat shrinkage rate than that prepared using conventional solvents (Comparative Examples 1, 2, and 3), and is also thinner.

[0066] Table 2 Performance data of membrane batteries in the examples and comparative examples

[0067]

[0068] The electrical performance of the present invention Example 2 and Comparative Examples 1, 2 and 3 was investigated by forming half-cells with LiFePO4 / Li. The results are shown in Table 2. Thanks to its thinner thickness and lower air permeability, the aramid composite membrane prepared by PolarClean (Example 2) has the best cycle capacity retention and its rate performance is also significantly better than that of the aramid membrane prepared by conventional solvents.

[0069] Test method: The membrane thickness, air permeability and heat shrinkage rate at 150℃ / 1h were tested according to GB / T 36363-2018.

[0070] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention should be covered within the protection scope of the present invention, which is defined by the claims.

Claims

1. A method of making an aramid composite lithium battery separator, characterized by, Includes the following steps: (1) Inorganic particles are added to PolarClean solvent and dispersed by high-temperature stirring. Then, a co-solvent, a phase separation promoter, and aramid short fibers are added and dissolved by high-temperature stirring to obtain an aramid solution. The PolarClean solvent is methyl 5-dimethylamino-2-methyl-5-oxovalerate. The co-solvent is one of lithium chloride, lithium bromide, and lithium nitrate, accounting for 0.01-0.1 wt% of the total mass of the solution. The phase separation promoter is one or more of polyethylene glycol 400, polyethylene glycol 800, polyvinylpyrrolidone K13, polyvinylpyrrolidone K16, and deionized water, accounting for 0.1-5 wt% of the total mass of the solution. (2) Under constant temperature and drying conditions, the dissolved aramid solution is coated onto the substrate film, and a constant temperature plate is placed under the substrate film; (3) Place the base film coated with aramid solution in a constant temperature and humidity chamber under water vapor for a certain period of time, and then immerse it in a gel bath composed of deionized water to wash away residual solvent, co-solvent and phase separation promoter. (4) The composite membrane after washing is dried in a hot roller or oven to obtain an aramid composite lithium battery separator.

2. The method as described in claim 1, characterized in that, The inorganic particles are either alumina or boehmite with D50≤1µm and D90≤2µm, accounting for 1-10wt% of the total mass of the solution; and / or The aramid short fibers are meta-aramid short fibers, accounting for 5-10 wt% of the total mass of the solution.

3. The method as described in claim 1, characterized in that, The stirring and dissolving temperature is 50-100℃.

4. The method as described in claim 1, characterized in that, The constant temperature drying conditions are 20-60℃; and / or The constant temperature plate is consistent with the coating temperature, which is 20-60℃.

5. The method as described in claim 1, characterized in that, The coating method is blade coating, dip coating, or micro-groove roller coating, and the coating thickness is 1-5 μm.

6. The method as described in claim 1, characterized in that, The bottom membrane is a commercial lithium battery separator made of polyethylene or polypropylene.

7. The method as described in claim 1, characterized in that, The temperature and humidity chamber is 40-80℃, the relative humidity is 40%-95%, and the placement time is 10-60s.

8. The method as described in claim 1, characterized in that, The drying temperature is 40-70℃.

9. An aramid composite lithium battery separator, characterized in that, Prepared by the method described in any one of claims 1-8.

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