Lithium battery separator and method of making the same

Abstract

The application discloses a kind of lithium battery diaphragm and its preparation method, and the lithium battery diaphragm includes base film and coating on base film, and the coating is obtained by coating lithium battery diaphragm slurry, and the lithium battery diaphragm slurry includes: nano-aluminum oxide and sodium alginate composite hydrogel.The application is prepared by coating lithium battery diaphragm slurry with nano-aluminum oxide as main material and adding sodium alginate composite hydrogel solution on the surface of base film to obtain diaphragm, improve the heat resistance and insulation of base film, solve the problem of serious heat shrinkage of prior art diaphragm, thereby improve the safety of lithium battery, and also can improve the liquid absorption and liquid retention of diaphragm.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a lithium battery separator and its preparation method. Background Technology

[0002] With social development, environmental and energy crises are global issues, making energy conservation and emission reduction an inevitable choice for human survival and development. To change this situation and adapt to social development trends, all industries are changing and innovating. In the automotive industry, this innovation manifests as the development and use of electric vehicles. Battery technology has always been a bottleneck in the development of electric vehicles, and lithium batteries are the most widely used power batteries. Simultaneously, battery safety has become a major concern. In the structure of a lithium battery, the separator is one of the key internal components. The main function of the separator is to separate the positive and negative electrodes, preventing short circuits caused by contact between the electrodes. It also allows electrolyte ions to pass through. Currently, existing lithium battery separators on the market have poor high-temperature resistance and thermal stability. Separators inside lithium batteries are prone to thermal shrinkage when exposed to high temperatures, affecting the normal use of the battery. Therefore, there is an urgent need to design a new ultra-thin, high-temperature resistant separator for lithium batteries that maintains good thermal stability at high temperatures, has a low coefficient of thermal expansion, and is more resistant to high temperatures; this would result in a longer lifespan and greater stability and safety for lithium batteries in actual use. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a lithium battery separator.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned lithium battery separator.

[0005] Another object of the present invention is to provide a slurry.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned slurry.

[0007] The objective of this invention is achieved through the following technical solution.

[0008] A lithium battery separator includes: a base film and a coating on the base film, the coating being obtained by coating a lithium battery separator slurry, the lithium battery separator slurry comprising: nano-alumina and sodium alginate composite hydrogel, the ratio of nano-alumina to sodium alginate composite hydrogel by mass parts being (22-29):(0.1-0.45).

[0009] In the above technical solution, the particle size of nano-alumina is: D50 is 300-500nm, and D90 is <1200nm.

[0010] In the above technical solution, the thickness of the coating is 1 to 2 μm.

[0011] The method for preparing the above-mentioned lithium battery separator includes: coating a lithium battery separator slurry onto a base film, drying it, obtaining a coating on the base film, and obtaining a lithium battery separator.

[0012] In the above technical solution, the drying time is 2 to 4 minutes and the drying temperature is 80 to 100°C.

[0013] In the above technical solution, the coating speed is 30-40 m / min.

[0014] A lithium battery separator slurry includes: a composite hydrogel of nano-alumina and sodium alginate, wherein the ratio of nano-alumina to sodium alginate composite hydrogel by mass parts is (22-29):(0.1-0.45).

[0015] In the above technical solution, the lithium battery separator slurry further includes: dispersant, binder and wetting agent, and the ratio of nano alumina, dispersant, binder and wetting agent by mass parts is (22~29):(0.5~1.0):(5~8):(0.3~0.8).

[0016] In the above technical solution, the lithium battery separator slurry also includes water.

[0017] In the above technical solution, the dispersant is an acrylate copolymer solution, and the solid content of the acrylate copolymer solution is 38-45 wt%.

[0018] In the above technical solution, the adhesive is acrylate.

[0019] In the above technical solution, the wetting agent is alkylphenol polyoxyethylene ether.

[0020] In the above technical solution, the particle size of the lithium battery separator slurry is D50: 0.4-0.7 micrometers and D90: 1.2-1.5 micrometers.

[0021] The preparation method of the above-mentioned lithium battery separator slurry includes: mixing nano-alumina, water, dispersant, sodium alginate composite hydrogel solution, binder and wetting agent until uniform to obtain lithium battery separator slurry. The ratio of nano-alumina, water, dispersant, sodium alginate composite hydrogel solution, binder and wetting agent by mass parts is (22~29):(36.2~59.2):(0.5~1.0):(10~15):(5~8):(0.3~0.8).

[0022] In the above technical solution, the sodium alginate composite hydrogel solution includes: sodium alginate composite hydrogel, and the concentration of sodium alginate composite hydrogel in the sodium alginate composite hydrogel solution is 1-3 wt%.

[0023] In the above technical solution, the method for preparing sodium alginate composite hydrogel solution includes: mixing powdered sodium alginate and solvent, stirring at room temperature for at least 60 minutes until uniform, adjusting the pH to 8-10, and obtaining sodium alginate composite hydrogel solution. The ratio of sodium alginate to solvent by mass is (1-3):(97-99).

[0024] In the method for preparing sodium alginate composite hydrogel solution, the solvent is water.

[0025] In the method for preparing sodium alginate composite hydrogel solution, the pH is adjusted to 8-10 by adding ammonia.

[0026] In the method for preparing sodium alginate composite hydrogel solution, the rotation speed of the stirrer is 1000-1500 r / min, and the revolution speed of the stirrer is 25-35 r / min.

[0027] In the above technical solution, the preparation method of lithium battery separator slurry includes: mixing nano-alumina, water and dispersant until uniform to obtain a first solution, and mixing the first solution, sodium alginate composite hydrogel solution, binder and wetting agent until uniform to obtain lithium battery separator slurry.

[0028] In the above technical solution, nano-alumina, water and dispersant are mixed, stirred at a rotation speed of 2000-2500 r / min and a revolution speed of 35-45 r / min for at least 60 min, and then sonicated at a frequency of 5-8 kHz for at least 10 min until homogeneous to obtain the first solution.

[0029] In the above technical solution, the first solution, sodium alginate composite hydrogel solution, adhesive and wetting agent are mixed and simultaneously stirred and sonicated under vacuum conditions for 15 to 20 minutes until homogeneous to obtain lithium battery separator slurry. The stirring rotation speed is 2000 to 2500 r / min, the revolution speed is 35 to 45 r / min, the vacuum pressure is less than -0.1 MPa, and the ultrasonic frequency is 5 to 8 kHz.

[0030] Application of nano-alumina and sodium alginate in synergistic improvement of diaphragm liquid absorption and / or liquid retention rate.

[0031] Application of nano-alumina and sodium alginate in synergistic improvement of membrane heat resistance.

[0032] Application of nano-alumina and sodium alginate in synergistic improvement of membrane adhesion.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention relates to a lithium battery separator slurry prepared by coating a base membrane surface with a composite hydrogel solution containing nano-alumina as the main material and sodium alginate as the additive. This process improves the heat resistance and insulation of the base membrane, solves the problem of severe thermal shrinkage in existing separators, thereby enhancing the safety of lithium batteries. It also improves the liquid absorption and retention properties of the separator. The lithium battery separator slurry of this invention exhibits good adhesion to the base membrane, and under a microscopic scale, the battery separator demonstrates excellent support. Attached Figure Description

[0035] Figure 1 SEM image (magnification 5.00 kX) of the battery separator prepared in Comparative Example 5;

[0036] Figure 2 SEM image (magnification 5.00 kX) of the battery separator prepared in Comparative Example 4;

[0037] Figure 3 SEM image (magnification 5.00 kX) of the battery separator prepared in Example 4. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] The raw material information involved in the following examples is as follows:

[0040] Sodium alginate is a natural anionic organic compound containing carboxyl and hydroxyl groups.

[0041] Nano-alumina: The main component is Al2O3, with a purity of ≥99.99%, D50 of 300-500nm, and D90 <1200nm.

[0042] The water used in the following examples is deionized water.

[0043] The method for preparing sodium alginate composite hydrogel solutions is based on the principle of physical cross-linking. An alkaline environment is used to induce interactions between sodium alginate molecular chains, causing them to cross-link. Cross-linking points are formed between the sodium alginate molecular chains through interactions such as ionic bonds and hydrogen bonds, thereby forming a three-dimensional network structure of the sodium alginate composite hydrogel.

[0044] In the following examples, the base film is a PE film with a thickness of 9 μm.

[0045] The increase in surface density of a single-micron coating is calculated as: (surface density of the battery separator - surface density of the base film) / coating thickness.

[0046] Peel strength: Select a flat battery separator and cut it into samples 30mm wide and 200mm long. Apply a 200mm long 3M tape flat to the coating surface of the sample. Use a standard roller to press the sample three times at a uniform speed. Tear off one end and use a tensile tester to perform a peel test to obtain the peel strength.

[0047] Examples 1-2

[0048] A method for preparing a lithium battery separator slurry includes: mixing nano-alumina, water, and a dispersant, and mixing the mixture in a dual planetary mixer at a rotation speed of A r / min and a B r / min. The mixture was stirred at a revolution speed of r / min for 60 min, and then sonicated at a frequency of 5 kHz for 10 min until homogeneous, to obtain the first solution. In a double planetary mixer, the first solution, sodium alginate composite hydrogel solution, binder and wetting agent were mixed under vacuum, stirring and sonication conditions, and stirred and sonicated simultaneously under vacuum conditions for 15 min until homogeneous (stirring speed was 2000 r / min, revolution speed was 35 r / min, vacuum pressure was -1 MPa, and sonication frequency was 5 kHz) to obtain lithium battery separator slurry (particle size of lithium battery separator slurry is C). The dispersant is acrylate copolymer solution (solid content of acrylate copolymer solution is 41 wt%), the binder is methyl acrylate, and the wetting agent is alkylphenol polyoxyethylene ether. The ratio of nano alumina, water, sodium alginate composite hydrogel solution, dispersant, binder and wetting agent by mass parts is D. The sodium alginate composite hydrogel solution has a concentration of 1.5 wt%. The method for preparing the sodium alginate composite hydrogel solution includes: mixing powdered sodium alginate and solvent (by mass, the ratio of sodium alginate to solvent is 1.5:98.5), stirring at room temperature at a rotation speed of 1000 r / min and a revolution speed of 30 r / min for 60 min until homogeneous, adding ammonia water (26 wt%) to adjust the pH to 8, and obtaining the sodium alginate composite hydrogel solution. The solvent is deionized water.

[0049] The values ​​of A, B, C, and D are shown in Table 1.

[0050] Table 1

[0051]

[0052]

[0053] Example 3

[0054] A method for preparing a lithium battery separator slurry includes: mixing nano-alumina, water, and a dispersant; stirring the mixture in a double planetary stirrer at a rotation speed of 2500 r / min and a revolution speed of 45 r / min for 60 min; and then sonicating it at a frequency of 5 kHz for 10 min until homogeneous, obtaining a first solution; mixing the first solution, sodium alginate composite hydrogel solution, binder, and wetting agent in a double planetary stirrer under vacuum, stirring, and sonication conditions; and simultaneously stirring and sonicating under vacuum conditions for 15 min until homogeneous (the rotation speed of the stirrer is 2000 r / min and the revolution speed is 45 r / min). The process was carried out at a speed of 35 r / min, a vacuum pressure of -1 MPa, and an ultrasonic frequency of 5 kHz to obtain a lithium battery separator slurry (particle size of D50: 0.544 μm, D90: 1.461 μm). The dispersant was an acrylate copolymer solution (the same as the acrylate copolymer solution in Example 1), the binder was methyl acrylate, and the wetting agent was alkylphenol polyoxyethylene ether. The ratio of nano-alumina, water, sodium alginate composite hydrogel solution, dispersant, binder, and wetting agent by mass parts was 28:48.5:15:0.9:8:0.7. The sodium alginate composite hydrogel solution was the same as the sodium alginate composite hydrogel solution in Example 1.

[0055] Comparative Example 1

[0056] A method for preparing a lithium battery separator slurry includes: first, mixing a dispersant, water, and nano-alumina in a double planetary mixer at a rotation speed of 2500 r / min and a revolution speed of 45 r / min for 60 min; then, ultrasonicating at a frequency of 5 kHz for 10 min; under ultrasonic mixing conditions, adding a binder and a wetting agent; and continuing ultrasonic mixing for 15 min to obtain a lithium battery separator slurry (D50 of 0.558 μm and D90 of 1.530 μm). The ultrasonic mixing is performed using a double planetary mixer. The equipment was stirred and ultrasonicated under vacuum conditions. The rotation speed of the double planetary stirrer was 2000 r / min, the revolution speed was 35 r / min, the ultrasonic frequency was 5 kHz, and the vacuum pressure was -1 MPa. By mass parts, the ratio of nano alumina, water, dispersant, binder and wetting agent was 32:48.5:0.9:8:0.7. The binder was methyl acrylate, the dispersant was an acrylate copolymer solution (the same as the acrylate copolymer solution in Example 1), and the wetting agent was alkylphenol polyoxyethylene ether.

[0057] Comparative Example 2

[0058] A method for preparing a lithium battery separator slurry includes: first mixing a dispersant, water, and conventional alumina (D50 = 1.1 μm, D90 = 1.9 μm) in a double planetary mixer at a rotation speed of 2000 r / min and a revolution speed of 40 r / min for 60 min, and then sonicating at a frequency of 5 kHz for 10 min. Under ultrasonic mixing conditions, binder and wetting agent were added, and ultrasonic mixing was continued for 15 min to obtain lithium battery separator slurry (D50 is 1.233 μm, D90 is 1.87 μm). The ultrasonic mixing was carried out by stirring and ultrasonicating in a double planetary mixer under vacuum conditions. The rotation speed of the double planetary mixer was 2000 r / min, the revolution speed was 35 r / min, the ultrasonic frequency was 5 kHz, and the vacuum pressure was -1 MPa. By mass parts, the ratio of conventional alumina, water, dispersant, binder and wetting agent was 32:46.3:0.8:7:0.6. The binder was methyl acrylate, the dispersant was an acrylate copolymer solution (the same as the acrylate copolymer solution in Example 1), and the wetting agent was alkylphenol polyoxyethylene ether.

[0059] Comparative Example 3

[0060] A method for preparing a lithium battery separator slurry includes: mixing conventional alumina (D50 = 1.1 μm, D90 = 1.9 μm), water, and a dispersant; stirring the mixture in a double planetary stirrer at a rotation speed of 2500 r / min and a revolution speed of 45 r / min for 60 min; and then sonicating it at a frequency of 5 kHz for 10 min until homogeneous, obtaining solution A; and mixing solution A, sodium alginate composite hydrogel solution, binder, and wetting agent in a double planetary stirrer under vacuum, stirring, and sonication conditions, and simultaneously stirring and sonicating under vacuum conditions for 15 min until homogeneous (the rotation speed of the stirrer is 2500 r / min). The process involved operating at 00 r / min, a revolution speed of 35 r / min, a vacuum pressure of -1 MPa, and an ultrasonic frequency of 5 kHz to obtain a lithium battery separator slurry (with particle sizes of D50: 1.154 μm and D90: 1.763 μm). The dispersant was an acrylate copolymer solution (the same as the acrylate copolymer solution in Example 1), the binder was methyl acrylate, and the wetting agent was alkylphenol polyoxyethylene ether. The ratio of conventional alumina, water, sodium alginate composite hydrogel solution, dispersant, binder, and wetting agent, by mass parts, was 28:43.5:14:0.8:8:0.6. The sodium alginate composite hydrogel solution was the same as that in Example 1.

[0061] Examples 4-6 and Comparative Examples 4-6

[0062] A method for preparing a battery separator includes: coating a slurry onto a base film using a coating machine (coating speed Z m / min), drawing it into a drying equipment via a traction roller, and drying it at X °C for Y min to obtain a coating on the base film, thereby obtaining a battery separator. The slurry is one of the lithium battery separator slurries prepared in Examples 1-3 and Comparative Examples 1-3. X, Y, and Z are shown in Table 2.

[0063] Table 2

[0064]

[0065]

[0066] The battery separators obtained in Examples 4-6 and Comparative Examples 4-6 were tested, and the test results are shown in Table 3.

[0067] Table 3

[0068]

[0069]

[0070] Table 3 shows that the battery separator prepared using a slurry containing nano-alumina and sodium alginate composite hydrogel has a shrinkage rate of less than 3% after baking at 150°C for 1 hour. In contrast, the battery separator prepared using the slurry of Comparative Example 2 (conventional alumina, without sodium alginate composite hydrogel) (Comparative Example 5) has a shrinkage rate of approximately 40% after baking at 150°C for 1 hour, and the battery separator prepared using the slurry of Comparative Example 3 (containing conventional alumina and sodium alginate composite hydrogel) (Comparative Example 6) has a shrinkage rate of approximately 26% after baking at 150°C for 1 hour. This indicates that the synergistic effect of nano-alumina and sodium alginate composite hydrogel significantly improves the thermal shrinkage of the separator. The liquid absorption and retention rates of the battery separators in Examples 4-6 are also far superior to those in Comparative Examples 4-6. The synergistic effect of nano-alumina and sodium alginate composite hydrogel also significantly improves the liquid absorption and retention rates of the separator. This invention significantly improves the heat resistance of the separator without affecting other performance characteristics, and also greatly enhances its liquid absorption and retention properties, resulting in better electrolyte absorption. This avoids short circuits caused by large positive and negative contact areas due to separator shrinkage, and maximizes electrolyte absorption, thereby improving battery charge and discharge efficiency.

[0071] Figure 1 SEM image (magnification 5.00 kX) of the battery separator prepared in Comparative Example 5; Figure 2 SEM image (magnification 5.00 kX) of the battery separator prepared in Comparative Example 4; Figure 3 SEM image (magnification 5.00 kX) of the battery separator prepared in Example 4.

[0072] The lithium battery separator slurry containing nano-alumina and sodium alginate composite hydrogel, after drying, has a three-dimensional network structure in which the sodium alginate composite hydrogel encapsulates the nano-alumina and can also encapsulate and absorb the electrolyte. In this slurry system, the nano-alumina is responsible for improving the heat resistance of the separator, while the sodium alginate composite hydrogel acts as a supporting skeleton (scaffold). The nano-alumina fills the skeleton, much like adding steel bars to a brick wall, which can effectively improve the thermal shrinkage of the separator. Furthermore, the gaps in the skeleton can absorb and store the electrolyte, thereby improving the liquid absorption and retention performance of the separator.

[0073] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A lithium battery separator, characterized in that, include: The base film and the coating on the base film, wherein the coating is obtained by coating with lithium battery separator slurry, the lithium battery separator slurry comprising: nano-alumina, sodium alginate composite hydrogel solution, dispersant, binder and wetting agent, the ratio of nano-alumina to sodium alginate composite hydrogel solution by mass parts is (22~29):(10~15), the ratio of nano-alumina, dispersant, binder and wetting agent by mass parts is (22~29):(0.5~1.0):(5~8):(0.3~0.8); the particle size of nano-alumina is: D50 is 300~500nm, D90<1200nm, the dispersant is acrylate copolymer solution, the solid content of acrylate copolymer solution is 38~45wt%, the binder is acrylate, and the wetting agent is alkylphenol polyoxyethylene ether; The sodium alginate composite hydrogel solution has a sodium alginate composite hydrogel concentration of 1.5 wt%. The method for preparing the sodium alginate composite hydrogel solution includes: mixing powdered sodium alginate and a solvent, stirring until uniform at room temperature, adding ammonia to adjust the pH to 8, and obtaining the sodium alginate composite hydrogel solution. The solvent is deionized water and the concentration of ammonia is 26 wt%.

2. The lithium battery separator according to claim 1, characterized in that, The coating thickness is 1~2μm.

3. A method for preparing the lithium battery separator according to any one of claims 1 to 2, characterized in that, include: The lithium battery separator slurry is coated onto the base film and dried to obtain a coating on the base film, thus obtaining the lithium battery separator.

4. The lithium battery separator as described in claim 1, characterized in that, The preparation method of lithium battery separator slurry includes: mixing nano-alumina, water, dispersant, sodium alginate composite hydrogel solution, binder and wetting agent until uniform to obtain lithium battery separator slurry, wherein the sodium alginate composite hydrogel solution includes: sodium alginate composite hydrogel.

5. The lithium battery separator according to claim 4, characterized in that, The ratio of nano-alumina, water, dispersant, sodium alginate composite hydrogel solution, binder and wetting agent by mass parts is (22~29):(36.2~59.2):(0.5~1.0):(10~15):(5~8):(0.3~0.8).

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