Lithium battery separator and method of making the same

Abstract

The application discloses a lithium battery diaphragm and a preparation method thereof. The diaphragm is obtained by coating slurry on a base film and drying. The preparation method of the slurry comprises the following steps: uniformly mixing ceramic powder, polyvinyl alcohol, a first substance and a crosslinking agent, drying to obtain a first powder, and the first substance being nanocellulose crystals and / or sodium carboxymethyl cellulose; uniformly mixing the first powder, water and an adhesive to obtain the slurry. The polyvinyl alcohol and the first substance are first crosslinked with the ceramic powder by using the crosslinking agent to form chemical bonds, a compact and stable three-dimensional crosslinked network structure is obtained, the solubility of the diaphragm in water is reduced, and the high-temperature resistance, wetting capacity and surface tension of the diaphragm are effectively improved. A large number of hydroxyl groups on the surface of the first substance and hydroxyl groups on the polyvinyl alcohol molecular chain can form intermolecular hydrogen bonds, promote crystallization, limit the movement of the polyvinyl alcohol molecular chain, and further improve the high-temperature resistance, wetting capacity and surface tension of the diaphragm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery separators, and particularly relates to a lithium battery separator and a preparation method thereof. BACKGROUND

[0002] With the development of the times, new energy electric vehicles have gradually become a part of people's life, and the safety and endurance of lithium ion batteries as the power source of electric vehicles are the focus of scientific research. The lithium battery separator plays an important role in the lithium ion battery.

[0003] The safety of electric vehicles has become the focus of more attention. The lithium ion battery separator in the prior art is not resistant to high temperature, causing loss of active material, reduction of battery capacity, excessive internal pressure of the battery, battery shell bulging, leakage, and even smoking and fire, affecting the normal use of the battery and endangering personal safety. Therefore, there is an urgent need to seek a lithium battery separator with good high-temperature resistance.

[0004] The lithium battery separator is crucial in the lithium battery. The conventional aluminum oxide coating separator has general high-temperature resistance and cannot meet the above requirements. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of slurry.

[0006] Another purpose of the present application is to provide a battery separator.

[0007] Another purpose of the present application is to provide a slurry obtained by the above preparation method.

[0008] The purpose of the present application is achieved by the following technical solutions.

[0009] A preparation method of slurry, comprising the following steps:

[0010] Step 1: mixing ceramic powder, polyvinyl alcohol (PVA), a first substance and a crosslinking agent to be uniform, drying to obtain a first powder, wherein the first substance is nano-cellulose crystal (CNC) and / or sodium carboxymethyl cellulose (CMC-Na);

[0011] In step 1, the crosslinking agent is glutaraldehyde (GD).

[0012] In step 1, the particle size of the first powder is 400-600 nm.

[0013] In step 1, the drying is to a moisture content of less than or equal to 0.8% (mass fraction).

[0014] In step 1, the ceramic powder is alumina and / or boehmite, and the particle size of the ceramic powder is 400-550 nm.

[0015] In step 1, the ceramic powder, polyvinyl alcohol (PVA), the first substance and the crosslinking agent are mixed and stirred for 10-30 min until uniform.

[0016] In step 2, the first powder, water and the adhesive are mixed until uniform to obtain a slurry, and the ratio of polyvinyl alcohol (PVA), the first substance, the crosslinking agent, water, the ceramic powder and the adhesive is (1-2.5):(2.5-4):(0.2-0.5):(65-74.8):(15-20):(5-10) by mass fraction.

[0017] In step 2, the adhesive is polyacrylate.

[0018] In step 2, the first powder and water are mixed until uniform to obtain a first solution, and the first solution and the adhesive are mixed until uniform to obtain a slurry.

[0019] In the above technical solution, the first powder and water are mixed, stirred at a self-rotation speed of 3100-3600 r / min and a revolution speed of 10-20 r / min for 10-15 min, and then ultrasonically treated at a frequency of 5-7 kHz for 10-30 min until uniform.

[0020] In step 2, the first solution and the adhesive are mixed and ultrasonically treated for 10-30 min until uniform under stirring, the self-rotation speed of stirring is 1000-1800 r / min, the revolution speed is 10-20 r / min, and the frequency of ultrasonic treatment is 5-7 kHz.

[0021] In step 2, the grinding speed is 400-600 r / min, and the grinding time is 10-15 min.

[0022] The slurry obtained by the above preparation method.

[0023] A separator is coated on a base film by the above slurry, and obtained after drying.

[0024] Application of polyvinyl alcohol (PVA), nanocellulose crystal (CNC) and ceramic powder in synergistically improving the wettability of the separator.

[0025] Application of polyvinyl alcohol (PVA), carboxymethyl cellulose sodium (CMC-Na) and ceramic powder in synergistically improving the wettability of the separator.

[0026] Application of polyvinyl alcohol (PVA), nanocellulose crystal (CNC) and ceramic powder in synergistically improving the capacity retention rate of lithium batteries.

[0027] Application of polyvinyl alcohol (PVA), carboxymethyl cellulose sodium (CMC-Na) and ceramic powder in synergistically improving the capacity retention rate of lithium batteries.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] The present application first uses a crosslinking agent to form a chemical bond between polyvinyl alcohol (PVA) and the first substance (nanocellulose crystals and / or sodium carboxymethyl cellulose) and ceramic powder by chemical crosslinking to obtain a dense and stable three-dimensional crosslinked network structure, which reduces the solubility of the separator in water and effectively improves the high temperature resistance, wetting ability and surface tension of the separator. A large number of hydroxyl groups on the surface of the first substance can form intermolecular hydrogen bonds with the hydroxyl groups on the polyvinyl alcohol (PVA) molecular chain, promote crystallization, limit the movement of the polyvinyl alcohol (PVA) molecular chain, and thus improve the high temperature resistance, wetting ability and surface tension of the separator (PVA-ceramic-CNC composite separator). BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Distribution diagram of the obtained separator prepared from the slurry of Example 1 under electron microscope scanning at 5KX;

[0031] Figure 2 Distribution diagram of the obtained separator prepared from the slurry of Example 1 under electron microscope scanning at 15KX;

[0032] Figure 3 Distribution diagram of the obtained separator prepared from the slurry of Example 4 under electron microscope scanning at 5KX;

[0033] Figure 4 Distribution diagram of the obtained separator prepared from the slurry of Example 4 under electron microscope scanning at 15KX. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be further described below in combination with specific examples.

[0035] The materials used in the specific embodiments of the present application are as follows:

[0036] Aluminium oxide is an inorganic substance with the chemical formula Al2O3, which is a high-hardness compound with a melting point of 2054℃ and a boiling point of 2980℃.

[0037] Boehmite, also known as soft water aluminum stone, has the molecular formula γ-AlOOH (hydrated aluminum oxide) and decomposes above 400℃.

[0038] Nanocellulose crystals (CNC) are a cellulose derivative with excellent properties such as large specific surface area, high crystallinity, strong hydrophilicity, high strength, large elastic modulus, and rich functional groups.

[0039] Polyvinyl alcohol (PVA) is a biodegradable water-soluble polymer, which has excellent film-forming property, good thermal stability, and high crystallinity.

[0040] Sodium carboxymethyl cellulose (CMC-Na) is an organic substance, which is a carboxymethylated derivative of cellulose and is the most important ionic cellulose glue. Sodium carboxymethyl cellulose is usually prepared by reacting natural cellulose, caustic soda and monochloroacetic acid, and is an anionic polymer compound. CMC-Na is a white fibrous or granular powder, odorless, tasteless, hygroscopic, and easy to disperse in water to form a transparent colloidal solution.

[0041] In the following examples, the water is deionized water.

[0042] In the following examples, the base film is a PE film, and the thickness of the base film is about 7 μm.

[0043] In the following examples, the polyacrylate is poly(methyl acrylate).

[0044] In the following examples, the size of the nanocellulose crystal used is 0.01-0.02 μm.

[0045] In the following examples, the electrolyte is a mixture of electrolyte and solvent, the electrolyte in the electrolyte is LiPF6, and the solvent is a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate), the volume ratio of ethylene carbonate and dimethyl carbonate is 1:1, and the concentration of the electrolyte in the electrolyte is 1 mol / L.

[0046] Example 1

[0047] A method for preparing a slurry, comprising the following steps:

[0048] Step 1: In a reaction kettle, ceramic powder, polyvinyl alcohol (PVA), a first substance and a crosslinking agent are mixed at 25°C, stirred for 30 min to uniform, pressure filtration, drying (drying to moisture content of 0.8% (mass fraction)), crushing, sieving, to obtain a first powder with a particle size of 400-600 nm, the first substance is nanocellulose crystal (CNC), the crosslinking agent is glutaraldehyde (GD), and the ceramic powder is alumina (particles), the particle size of the alumina (particles) is 400-500 nm;

[0049] Step 2, in a double planetary mixer, the first powder and water are mixed, stirred at a rotation speed of 3100 r / min and a revolution speed of 20 r / min for 10 min, and then ultrasonically treated at a frequency of 5 kHz for 10 min until uniform, to obtain a first solution, the first solution and the adhesive are mixed, ultrasonically treated under stirring for 30 min until uniform (the rotation speed of stirring is 1000 r / min, the revolution speed is 20 r / min, and the frequency of ultrasonic treatment is 5 kHz), and then put into a grinder and ground at a rotation speed of 400 r / min for 10 min to obtain a slurry, the ratio of polyvinyl alcohol (PVA), the first substance, the crosslinking agent, water, the ceramic powder and the adhesive is 2.5:2.5:0.2:74.8:15:5 by mass fraction, and the adhesive is polyacrylate.

[0050] Example 2

[0051] A method for preparing a slurry, which is basically the same as that in Example 1, except that the "first substance is nanocellulose crystal (CNC)" is replaced by "the first substance is sodium carboxymethyl cellulose (CMC-Na)".

[0052] Example 3

[0053] A method for preparing a slurry, comprising: in a double planetary mixer, mixing a ceramic powder, a first substance and water, stirring at a rotation speed of 3100 r / min and a revolution speed of 20 r / min for 10 min, and then ultrasonically treating at 3 kHz for 10 min, adding an adhesive, ultrasonically treating under stirring for 30 min until uniform (the rotation speed of stirring is 1000 r / min, the revolution speed is 20 r / min, and the frequency of ultrasonic treatment is 5 kHz), putting into a grinder and grinding at a rotation speed of 400 r / min for 10 min to obtain a slurry, the ratio of the first substance, water, the ceramic powder and the adhesive is 5:75:15:5 by mass fraction, the adhesive is polyacrylate, the first substance is sodium carboxymethyl cellulose (CMC-Na), and the ceramic powder is alumina (particles), and the particle size of the alumina (particles) is 400-500 nm.

[0054] Example 4

[0055] A method for preparing a slurry, which is basically the same as that in Example 1, except that the "ceramic powder is alumina (particles)" is replaced by "ceramic powder is boehmite (particles)". The particle size of the boehmite (particles) is 450-550 nm.

[0056] Example 5

[0057] A method for preparing a slurry, which is substantially the same as that of Example 2, except that "ceramic powder is alumina (particles)" is replaced by "ceramic powder is boehmite (particles)". The particle size of boehmite (particles) is 450-550 nm.

[0058] Example 6

[0059] A method for preparing a slurry, which is substantially the same as that of Example 3, except that "ceramic powder is alumina (particles)" is replaced by "ceramic powder is boehmite (particles)". The particle size of boehmite (particles) is 450-550 nm.

[0060] Examples 7-12

[0061] A lithium battery, comprising: a positive electrode, a negative electrode, a separator and an electrolyte, the positive electrode material in the positive electrode is ternary material (NCM523), the negative electrode material in the negative electrode is graphite, the positive electrode slurry is a mixture of N-methyl pyrrolidone, positive electrode material, conductive carbon black and positive electrode binder (polyvinylidene fluoride, PVDF), the ratio of N-methyl pyrrolidone, positive electrode material, conductive carbon black and positive electrode binder (PVDF) in the positive electrode slurry is 10:8:1:1 by mass fraction, the negative electrode slurry is a mixture of N-methyl pyrrolidone, graphite, conductive agent (ketchen carbon black) and negative electrode binder (styrene butadiene latex, SBR), the ratio of N-methyl pyrrolidone, graphite, conductive agent (ketchen carbon black) and negative electrode binder (styrene butadiene latex, SBR) in the negative electrode slurry is 10:8:0.8:1.2 by mass fraction, the preparation method of the positive electrode comprises: mixing N-methyl pyrrolidone, NCM523, conductive carbon black and positive electrode binder by wet process, stirring at a self-rotation speed of 1500 r / min and a revolution speed of 20 r / min, and then ultrasonicating at a frequency of 7 kHz for 30 min to obtain the positive electrode slurry, coating 1.5 g of the positive electrode slurry on an aluminum foil substrate (91.5 mm*1 m), drying in a constant temperature oven, forming a positive electrode coating on the aluminum foil substrate, and roll pressing to firmly press the positive electrode coating and the aluminum foil substrate together to obtain the positive electrode. The preparation method of the negative electrode comprises: mixing N-methyl pyrrolidone, graphite, conductive agent (ketchen carbon black) and negative electrode binder by wet process, stirring at a self-rotation speed of 1500 r / min and a revolution speed of 20 r / min, and then ultrasonicating at a frequency of 7 kHz for 30 min to obtain the negative electrode slurry. Coating 1.5 g of the negative electrode slurry on a copper foil substrate (91.5 mm*1.2 m), drying in a constant temperature oven, forming a negative electrode coating on the copper foil substrate, and roll pressing to firmly press the negative electrode coating and the copper foil substrate together to obtain the negative electrode. The method for preparing the separator comprises: coating the slurry on the base film in the form of roll coating, drying at 45℃ for 10 min to obtain a coating on the base film, and obtaining the separator. The slurry is one of the slurries prepared in Examples 1-6. The lithium batteries of Examples 7-12 are prepared in turn from the slurries in Examples 1-6.

[0062] Table 1

[0063]

[0064]

[0065] Figure 1 Figure 2 is an electron microscope image of the separator prepared from the slurry of Example 1 at 5KX, Figure 2 Figure 3 is an electron microscope image of the separator prepared from the slurry of Example 1 at 15KX.

[0066] Figure 3 Figure 6 is an electron microscope image of the separator prepared from the slurry of Example 4 at 5KX, Figure 4 Figure 7 is an electron microscope image of the separator prepared from the slurry of Example 4 at 15KX.

[0067] The separators prepared from the slurries of Examples 1-6 were tested under the conditions of standard atmosphere, i.e. temperature: 20℃; relative humidity: 50%; atmospheric pressure: 96kPa, and the test results are shown in Table 2.

[0068] Table 2

[0069] Separator in lithium battery Contact angle of electrolyte (°) Example 7 0.89 Example 8 1.10 Example 9 1.56 Example 10 0.97 Example 11 1.06 Example 12 1.63

[0070] As shown in Table 2, the contact angle of the separator prepared from the slurry of Example 7 is 0.89°, which is much smaller than the contact angles of the separators prepared from the slurries of Examples 8-12, and thus the separator prepared from the slurry of Example 1 has better wettability.

[0071] Table 3

[0072]

[0073] As shown in Table 3, the longitudinal (MD) and transverse (TD) shrinkage rates of the separator prepared from the slurry of Example 7 are both within 2.5%, which is better than those of Examples 8-12, and thus the separator prepared from the slurry of Example 1 has better thermal stability.

[0074] The capacity retention data of the lithium batteries prepared from Examples 7-12 are shown in the following table (3 groups of parallel experiments were performed for each example).

[0075] Table 4

[0076]

[0077] The lithium battery prepared from Example 7 still has a capacity retention rate of more than 94% after being cycled for more than 200 cycles at J=25.97A / m 2 ​

[0078] The test data for the separator in the lithium battery produced in Example 7 is as follows:

[0079]

[0080]

[0081] The test data for the separator in the lithium battery produced in Example 10 is as follows:

[0082]

[0083] The above has been described by way of example, it should be noted that, without departing from the core of the present application, any simple modification, modification or other equivalent replacement which can not cost the creative labor of those skilled in the art falls within the protection scope of the present application.

Claims

1. A method for preparing a slurry for a lithium battery separator, the lithium battery separator being coated on a base film from the slurry, characterized in that, The method comprises the following steps: Step 1, mixing ceramic powder, polyvinyl alcohol, a first substance and a crosslinking agent to be uniform, drying to obtain a first powder, wherein the first substance is nanocellulose crystal and / or sodium carboxymethyl cellulose; Step 2, mixing the first powder, water and an adhesive to be uniform to obtain a slurry, wherein the ratio of polyvinyl alcohol, the first substance, the crosslinking agent, water, ceramic powder and the adhesive is (1-2.5):(2.5-4):(0.2-0.5):(65-74.8):(15-20):(5-10) by mass fraction; The crosslinking agent is glutaraldehyde, and the ceramic powder is alumina and / or boehmite.

2. The production method according to claim 1, characterized by, The particle size of the ceramic powder is 400-550 nm.

3. The production method according to claim 1, characterized by, In step 2, the adhesive is polyacrylate.

4. The slurry for lithium battery separator membrane obtained by the preparation method of any one of claims 1-3.

5. A lithium battery separator, characterized by, The slurry of claim 4 is coated on a base film, and after drying, a coating layer is obtained.

6. A lithium battery separator characterized by, The method comprises the following steps: The base film and the coating layer, wherein the coating layer comprises ceramic powder, polyvinyl alcohol and a first substance, the first substance is nanocellulose crystal and / or sodium carboxymethyl cellulose, the polyvinyl alcohol and the first substance are chemically crosslinked by a crosslinking agent to form a chemical bond with the ceramic powder, forming a three-dimensional crosslinked network structure; the crosslinking agent is glutaraldehyde, and the ceramic powder is alumina and / or boehmite, and the ratio of polyvinyl alcohol, the first substance, the crosslinking agent and the ceramic powder is (1-2.5):(2.5-4):(0.2-0.5):(15-20) by mass fraction.

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