High-heat-resistance and high-infiltration lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a high-heat-resistance and high-infiltration lithium battery diaphragm and a preparation method thereof, the high-heat-resistance and high-infiltration lithium battery diaphragm comprises a base membrane and a coating on the base membrane, the coating is obtained by coating slurry, the slurry comprises flaky wollastonite fibers, a silane coupling agent, an adhesive and a dispersing agent, and the silane coupling agent is vinyltriethoxysilane. The width of the flaky wollastonite fiber is less than 1.5 mu m, the length is 2.0-7.0 mu m, and the thickness is 0.1-0.5 mu m. The high-heat-resistance and high-infiltration lithium battery diaphragm disclosed by the invention has excellent heat resistance and wettability, relatively high breakdown voltage and relatively low water content.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separators, and in particular relates to a highly heat-resistant and highly wettable lithium battery separator and a preparation method thereof. Background Art

[0002] As environmental problems become increasingly severe, more and more new energy projects have attracted social attention, among which electric vehicles are particularly popular. As the power source of electric vehicles, the safety and service life of lithium-ion batteries are not only the focus of scientific research, but also the focus of people's attention, and lithium battery separators play an important role in this.

[0003] Based on the above, the safety and service life of lithium-ion batteries have become the focus of more attention. Conventional lithium battery separators are PP or PE separators, which have the disadvantage of low heat resistance. By coating the separator with ordinary inorganic ceramics (alumina, boehmite, silicon oxide, etc.), its heat resistance will be improved, but the water content will also be greatly increased, which will cause the decomposition of the electrolyte lithium salt in the battery, resulting in a more obvious deterioration in the chemical properties of the lithium battery such as capacity, internal resistance, product characteristics, etc., and at the same time affect the battery safety performance. Summary of the invention

[0004] In view of the deficiencies in the prior art, the object of the present invention is to provide a highly heat-resistant and highly wettable lithium battery separator.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned high-heat-resistant and high-wetting lithium battery separator.

[0006] Another object of the present invention is to provide a slurry.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] A high-heat-resistant and high-wetting lithium battery separator comprises: a base film and a coating on the base film, wherein the coating is obtained by coating a slurry, wherein the slurry comprises: flaky wollastonite fibers, a silane coupling agent, an adhesive and a dispersant, wherein the ratio of the flaky wollastonite fibers, the silane coupling agent, the adhesive and the dispersant is (25-30): (2.5-4): (2.5-4): (0.1-0.5) by weight, and the silane coupling agent is vinyl triethoxysilane.

[0009] In the above technical solution, the width of the flaky wollastonite fiber is less than 1.5 μm, the length of the flaky wollastonite fiber is 2.0 to 7.0 μm, and the thickness of the flaky wollastonite fiber is 0.1 to 0.5 μm.

[0010] In the above technical solution, the width of the flaky wollastonite fiber at its widest point is 0.8 to 1.5 μm.

[0011] In the above technical solution, the dispersant is ammonium polyacrylate, and the adhesive is polyacrylate.

[0012] The method for preparing the above-mentioned high-heat-resistant and high-wetness lithium battery diaphragm comprises: coating the slurry on the base film, drying, obtaining a coating on the base film, and obtaining the high-heat-resistant and high-wetness lithium battery diaphragm.

[0013] In the above technical solution, the coating speed is 30 to 50 m / min.

[0014] In the above technical solution, the coating thickness is 1 to 2 μm.

[0015] In the above technical solution, the drying temperature is 50-70° C., and the drying time is 1-3 minutes.

[0016] A slurry comprises: flaky wollastonite fiber, water, silane coupling agent, adhesive and dispersant. The ratio of the flaky wollastonite fiber, water, silane coupling agent, adhesive and dispersant is (25-30): (61.5-69.9): (2.5-4): (2.5-4): (0.1-0.5) by weight, and the silane coupling agent is vinyl triethoxysilane.

[0017] The method for preparing the slurry comprises: mixing flaky wollastonite fibers, water, a silane coupling agent, an adhesive and a dispersant until they are uniform to obtain the slurry.

[0018] In the above technical solution, the method for preparing the above slurry specifically includes:

[0019] Step 1, mixing flaky wollastonite fibers, water and a dispersant until uniform to obtain a first solution;

[0020] In step 1, flaky wollastonite fibers, water and a dispersant are mixed, first stirred at a rotation speed of 1500 to 3100 r / min and a revolution speed of 20 to 50 r / min for 10 to 20 min, and then ultrasonicated at a frequency of 10 to 50 kHz for 10 to 20 min until uniform, to obtain a first solution.

[0021] Step 2: Mix the first solution, the silane coupling agent and the adhesive until they are uniform to obtain a slurry.

[0022] In step 2, the first solution, the silane coupling agent and the adhesive are mixed, and stirred and ultrasonicated for 10 to 20 minutes in a vacuum environment until they are uniform, the vacuum pressure is 0.06 to 0.08 KPA, the ultrasonic frequency of the ultrasound is 5 to 8 kHz, the stirring rotation speed is 1000 to 3800 r / min, and the revolution speed is 20 to 40 r / min.

[0023] Application of flaky wollastonite fibers and silane coupling agents in synergistically improving the heat resistance, breakdown voltage and / or wettability of a separator.

[0024] Application of flaky wollastonite fibers and silane coupling agents in synergistically reducing the water content of separators.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Due to the special flaky structure of flaky wollastonite fiber, the conventional water-based adhesive has a small bonding effect between the flaky wollastonite fiber and the base film. The present invention uses a silane coupling agent (vinyl triethoxysilane) for modification. When the silane coupling agent is between the inorganic interface (flaky wollastonite fiber) and the organic interface (base film), a bonding layer of an organic matrix-silane coupling agent-inorganic matrix can be formed, which improves the bonding performance between the flaky wollastonite fiber and the base film, and greatly improves the bonding strength between the coating and the base film. At the same time, the flaky wollastonite fiber has a low water absorption rate. After modification with a silane coupling agent, it can not only improve the bonding strength between the coating and the base film, but also further improve the water resistance of the diaphragm, thereby reducing the water content of the diaphragm;

[0027] 2. The flaky wollastonite fiber has a small thermal expansion coefficient, good thermal insulation and good thermal stability. After being modified with vinyl triethoxysilane, the diaphragm is not easily deformed at high temperatures, which enhances the stability of the diaphragm at high temperatures and reduces the shrinkage rate of the diaphragm at high temperatures;

[0028] 3. The flaky wollastonite fibers can form a cross distribution, making the coating denser and with fewer gaps. The modification of the silane coupling agent makes the structure of the coating and the base membrane more stable, increasing the support of the coating to the diaphragm;

[0029] 4. The cross-distribution of flaky wollastonite fibers has more microporous structures and smooth surfaces. The microporous structure improves the liquid absorption performance of the diaphragm, and the smooth surface can effectively reduce the surface tension of the coating and the liquid-solid interface energy, reduce the contact angle of the diaphragm, increase the wettability of the diaphragm, and improve the liquid absorption and retention rate of the diaphragm. This allows the lithium battery to increase its cycle rate while improving safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the SEM of the diaphragm prepared in Example 4;

[0031] Figure 2 This is the SEM of the separator prepared in Comparative Example 5. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0033] Flaky wollastonite fiber: the width at the widest point is 0.8 to 1.5 μm, the length is 2.0 to 7.0 μm, and the thickness is 0.1 to 0.5 μm.

[0034] Needle-shaped wollastonite: diameter at the widest point: 0.8-1.5μm, length: 2.0-7.0μm.

[0035] Granular wollastonite: D50: 0.5-0.8μm, D90: 1.4-2.0μm.

[0036] Ammonium polyacrylate: polyvinyl alcohol.

[0037] Flaky wollastonite fiber: The main component is CaSiO3, which is in the form of flakes and fibers, has good insulation properties, and also has high whiteness, good dielectric properties, high temperature resistance, high strength, and low thermal expansion coefficient; generally, it is resistant to acid, alkali, and chemical corrosion, and has low water absorption and low oil absorption.

[0038] Double planetary mixer: XFZH-30L.

[0039] In the following examples, water is pure water.

[0040] In the following examples, the base film is a PE film with a thickness of 9 μm.

[0041] Electrolyte: The electrolyte is a mixture of an electrolyte and a solvent, the electrolyte is lithium hexafluorophosphate, the solvent is a mixture of EC and DMC (the volume ratio of EC to DMC is 1:1), and the concentration of the electrolyte in the electrolyte is 1M.

[0042] Peel strength (used to characterize the bonding strength between the coating and the base film): Select a flat separator and cut it into samples with a width of 30 mm and a length of 200 mm. Stick a 3M adhesive tape with a length of 200 mm flatly on the coating surface of the sample. Use a standard roller to press the sample at a constant speed for 3 times. Tear open one end and use a tensile machine to perform a peel test to obtain the peel strength. The separator is one of Examples 4 to 6 and Comparative Examples 5 to 8.

[0043] Examples 1 to 3

[0044] A method for preparing a slurry comprises the following steps:

[0045] Step 1, mixing flaky wollastonite fibers, water and a dispersant in a double planetary mixer, stirring for 15 minutes at a rotation speed of A1 r / min and a revolution speed of A2 r / min, and then ultrasonicating for 15 minutes at a frequency of C1 kHz until uniform, to obtain a first solution;

[0046] Step 2, the first solution, the silane coupling agent and the adhesive are mixed, and the high-speed dispersion is 20 minutes in a double planetary mixer under a vacuum environment with an ultrasonic oscillation function until uniform, the vacuum pressure is 0.07KPA, the ultrasonic frequency of the ultrasound is C2kHz, the stirring rotation speed is A3 r / min, and the revolution speed is A4 r / min to obtain a slurry, in which the ratio of flaky wollastonite fiber, water, silane coupling agent, adhesive and dispersant is X by mass, the dispersant is polyvinyl alcohol, the silane coupling agent is vinyl triethoxysilane, and the adhesive is polyethyl acrylate.

[0047] A1, A2, A3, A4, C1, C2 and X are shown in Table 1.

[0048] Table 1

[0049]

[0050] Comparative Example 1

[0051] A method for preparing slurry, comprising: mixing 25 parts by mass of aluminum oxide, 69.8 parts by mass of pure water and 0.2 parts by mass of a dispersant in a double planetary mixer for 10 minutes (rotation speed of 3100 r / min, revolution speed of 20 r / min), and then ultrasonicating at a frequency of 50 kHz for 15 minutes; adding 5 parts by mass of an adhesive and simultaneously ultrasonically oscillating (ultrasonic frequency of 5 kHz) for 15 minutes under stirring conditions (rotation speed of 1000 r / min, revolution speed of 40 r / min) to obtain a slurry, wherein the adhesive is polyethyl acrylate and the dispersant is polyvinyl alcohol. Aluminum oxide: D50: 0.602 microns, D90: 1.279 microns.

[0052] Comparative Example 2

[0053] A method for preparing slurry is basically the same as that of Comparative Example 1, except that "alumina" is replaced by "needle-shaped wollastonite".

[0054] Comparative Example 3

[0055] A method for preparing slurry is basically the same as that of Comparative Example 1, except that "alumina" is replaced by "granular wollastonite".

[0056] Comparative Example 4

[0057] A method for preparing a slurry is basically the same as that of Example 1, except that "vinyltriethoxysilane" is replaced by "diphenyldihydroxysilane".

[0058] Examples 4 to 6 and Comparative Examples 5 to 8

[0059] A method for preparing a diaphragm comprises: placing a base film on a coating machine equipped with slurry, coating the slurry on one side of the base film (coating speed is E m / min), pulling the base film into a drying device through a pulling roller and drying it at F°C for G min, obtaining a coating on the base film, and obtaining a diaphragm. The slurry is one of Examples 1 to 3 and Comparative Examples 1 to 4.

[0060] The values ​​of E, F and G are shown in Table 2.

[0061] Table 2

[0062] Diaphragm Slurry for preparing diaphragm E(m / min) F(℃) G(min) Example 4 Example 1 30 50 3 Example 5 Example 2 40 60 2 Example 6 Example 3 50 70 1 Comparative Example 5 Comparative Example 1 30 50 3 Comparative Example 6 Comparative Example 2 30 50 3 Comparative Example 7 Comparative Example 3 30 50 3 Comparative Example 8 Comparative Example 4 30 50 3

[0063] The test data of the diaphragm prepared in Example 4 are as follows:

[0064]

[0065] The test data of the diaphragm prepared in Example 5 are as follows:

[0066]

[0067] The test data of the diaphragm prepared in Example 6 are as follows:

[0068]

[0069]

[0070] The test data of the diaphragm prepared in Comparative Example 5 are as follows:

[0071]

[0072] The test data of the diaphragm prepared in Comparative Example 6 are as follows:

[0073]

[0074]

[0075] The test data of the diaphragm prepared in Comparative Example 7 are as follows:

[0076]

[0077] The test data of the diaphragm prepared in Comparative Example 8 are as follows:

[0078]

[0079]

[0080] The peel strength of Example 4 is 134.3 N / m, the peel strength of Example 5 is 132.7 N / m, and the peel strength of Example 6 is 135.1 N / m; the peel strength of Comparative Example 5 is 83.2 N / m, the peel strength of Comparative Example 6 is 36.4 N / m, the peel strength of Comparative Example 7 is 54.6 N / m, and the peel strength of Comparative Example 8 is 89.6 N / m.

[0081] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A highly heat-resistant and highly wettable lithium battery separator, characterized in that: include: The base film and the coating on the base film are obtained by coating a slurry, the slurry includes: flaky wollastonite fiber, silane coupling agent, adhesive and dispersant, and the ratio of flaky wollastonite fiber, silane coupling agent, adhesive and dispersant is (25-30): (2.5-4): (2.5-4): (0.1-0.5) by weight, and the silane coupling agent is vinyl triethoxysilane.

2. The high heat-resistant and high-wetting lithium battery separator according to claim 1, characterized in that: The width of the flaky wollastonite fiber is less than 1.5 μm, the length of the flaky wollastonite fiber is 2.0 to 7.0 μm, and the thickness of the flaky wollastonite fiber is 0.1 to 0.5 μm.

3. The method for preparing a highly heat-resistant and highly wettable lithium battery separator according to any one of claims 1 to 2, characterized in that: include: The slurry is coated on the base film and dried to obtain a coating on the base film to obtain a high heat-resistant and high-wetness lithium battery separator.

4. The preparation method according to claim 3, characterized in that: The coating thickness is 1 to 2 μm.

5. A slurry, characterized in that: include: The flaky wollastonite fiber, water, silane coupling agent, adhesive and dispersant are in the ratio of (25-30) to (61.5-69.9) by weight: (2.5-4) to (2.5-4) and (0.1-0.5) by weight. The silane coupling agent is vinyl triethoxysilane.

6. A method for preparing the slurry according to claim 5, characterized in that: include: The flaky wollastonite fiber, water, a silane coupling agent, an adhesive and a dispersant are mixed until uniform to obtain a slurry.

7. Application of flaky wollastonite fiber and silane coupling agent to synergistically improve the heat resistance of diaphragm, characterized in that: The silane coupling agent is vinyltriethoxysilane.

8. Application of flaky wollastonite fibers and silane coupling agents to synergistically improve the breakdown voltage and / or peel strength of a diaphragm, characterized in that: The silane coupling agent is vinyltriethoxysilane.

9. Application of flaky wollastonite fiber and silane coupling agent to synergistically improve the wettability of diaphragm, characterized in that: The silane coupling agent is vinyltriethoxysilane.

10. Application of flaky wollastonite fiber and silane coupling agent in synergistically reducing the water content of diaphragm, characterized in that: The silane coupling agent is vinyltriethoxysilane.

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