High-performance lithium battery diaphragm based on boehmite composite coating and preparation method thereof

Abstract

The invention discloses a boehmite composite coating-based high-performance lithium battery diaphragm and a preparation method thereof, the boehmite composite coating-based high-performance lithium battery diaphragm comprises a base membrane and a coating on the base membrane, the coating comprises nano boehmite, hexagonal boron nitride, ammonium polyacrylate, an acrylate copolymer and carboxymethyl cellulose, the preparation method of the high-performance lithium battery diaphragm comprises the following steps: coating a base membrane with slurry, drying, and forming the coating on the base membrane, so as to obtain the high-performance lithium battery diaphragm based on the boehmite composite coating. The nano boehmite and the hexagonal boron nitride synergistically improve the heat resistance, the liquid absorption rate, the liquid retention rate, the ionic conductivity, the needling strength and the tensile strength of the diaphragm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery separator, and particularly relates to a high-performance lithium battery separator based on a boehmite composite coating and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the new energy industry, lithium batteries, as an important energy storage device, have been widely used in electric vehicles, renewable energy storage and mobile electronic devices. The performance of lithium batteries, especially the energy density, cycle life and safety, has become a key factor restricting their widespread application. In lithium batteries, the separator material plays a crucial role, as it not only needs to have good electrolyte permeability to ensure ion conduction, but also needs to have sufficient mechanical strength, thermal stability and electrical insulation to prevent internal short circuits and improve the safety of the battery.

[0003] Currently, the commonly used lithium battery separator materials on the market are mainly polyolefin materials such as polyethylene and polypropylene films. However, polyolefin materials have poor stability at high temperatures and are prone to shrinkage and melting, which can lead to a decrease in the safety performance of the battery. Therefore, developing high-performance separator materials is one of the key factors in improving the performance of lithium batteries. Boehmite is an aluminum-based oxide that has good thermal stability, chemical stability and high specific surface area. The addition of boehmite to the separator can improve the thermal stability and mechanical strength of the separator and prevent deformation and melting of the separator under high temperature conditions. However, boehmite itself has poor ion conductivity, which limits its application in lithium battery separators. Therefore, how to prepare a separator with better performance has become a hot and difficult research topic. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a high-performance lithium battery separator based on a boehmite composite coating.

[0005] Another purpose of the present application is to provide a preparation method for the above-mentioned high-performance lithium battery separator based on a boehmite composite coating.

[0006] The purpose of the present application is achieved by the following technical solutions.

[0007] A high-performance lithium battery separator based on a boehmite composite coating, comprising a base film and a coating layer on the base film, wherein the coating layer comprises nano-boehmite, hexagonal boron nitride, ammonium polyacrylate, acrylate copolymer and carboxymethyl cellulose, and the mass ratio of nano-boehmite, hexagonal boron nitride, ammonium polyacrylate, acrylate copolymer and carboxymethyl cellulose is (25-30):(1-5):(0.2-0.5):(1.5-9):(5-10).

[0008] In the technical scheme, the nano-boehmite has a particle size of D50=0.4-0.5 mu m.

[0009] In the technical scheme, the hexagonal boron nitride is a nanosheet.

[0010] In the technical scheme, the nano-boehmite has an average value of D10 of 0.259 mu m, an average value of D50 of 0.432 mu m, and an average value of D90 of 0.978 mu m.

[0011] In the technical scheme, the hexagonal boron nitride has an average value of D10 of 0.215, an average value of D50 of 0.842 mu m, and an average value of D90 of 1.057 mu m.

[0012] The preparation method of the high-performance lithium battery diaphragm based on the boehmite composite coating comprises the following steps: coating a slurry on a base film, drying, and forming a coating layer on the base film to obtain the high-performance lithium battery diaphragm based on the boehmite composite coating.

[0013] In the technical scheme, the thickness of the coating layer is 2-3 mu m.

[0014] In the technical scheme, the coating speed is 20-50 m / min.

[0015] In the technical scheme, the drying temperature is 40-70 DEG C, and the drying time is 5-10 minutes.

[0016] A slurry comprises nano-boehmite, hexagonal boron nitride, water, a dispersing agent, a binder, and a thickening agent, and the ratio of the nano-boehmite, the hexagonal boron nitride, the water, the dispersing agent, the binder, and the thickening agent is (25-30):(1-5):(50-60):(0.2-0.5):(5-10):(5-10) in mass fraction.

[0017] In the technical scheme, the ratio of the nano-boehmite, the hexagonal boron nitride, the water, the dispersing agent, the binder, and the thickening agent is preferably (25-30):(2-4):(50-60):(0.2-0.5):(6-8):(5-7) in mass fraction.

[0018] In the technical scheme, the dispersing agent is polyacrylammonium.

[0019] In the technical scheme, the binder is an acrylic ester copolymer solution, and the content of the acrylic ester copolymer in the acrylic ester copolymer solution is 30-90 wt%.

[0020] In the technical scheme, the thickening agent is carboxymethyl cellulose.

[0021] In the technical scheme, the particle size of the slurry is D50: 1.0-2.0 microns, and D90: 2.0-3.5 microns.

[0022] A method for preparing a slurry comprises: mixing nano-boehmite, hexagonal boron nitride, water, a dispersing agent, a binder and a thickening agent to be uniform to obtain the slurry, wherein the ratio of the nano-boehmite, the hexagonal boron nitride, the water, the dispersing agent, the binder and the thickening agent is (25-30) :(1-5) :(50-60) :(0.2-0.5) :(5-10) :(5-10) by mass fraction.

[0023] In the technical scheme, the ratio of the nano-boehmite, the hexagonal boron nitride, the water, the dispersing agent, the binder and the thickening agent is preferably (25-30) :(2-4) :(50-60) :(0.2-0.5) :(6-8) :(5-7) by mass fraction.

[0024] In the technical scheme, the method for preparing the slurry specifically comprises the following steps:

[0025] Step 1, mixing the water and the dispersing agent to be uniform, then adding the nano-boehmite and the hexagonal boron nitride and mixing to be uniform to obtain a first solution;

[0026] In step 1, the water and the dispersing agent are mixed and stirred to be uniform. The self-rotation speed of stirring is 500-1500 r / min, the revolution speed is 30-50 r / min, and the stirring time is 10-20 minutes.

[0027] In step 1, after adding the nano-boehmite and the hexagonal boron nitride, the mixture is stirred to be uniform under ultrasonic conditions.

[0028] After adding the nano-boehmite and the hexagonal boron nitride, the mixture is stirred to be uniform under ultrasonic conditions for 10-30 minutes, wherein the self-rotation speed of stirring is 1500-2500 r / min, the revolution speed is 30-50 r / min, and the frequency of ultrasonic is 5-10 kHz.

[0029] Step 2, mixing the first solution, the binder and the thickening agent to be uniform to obtain the slurry.

[0030] In step 2, the first solution, the binder and the thickening agent are mixed, and then are simultaneously ultrasonically treated and stirred in a vacuum environment, and then are sand-milled to be uniform. The vacuum degree of the vacuum environment is 500-1500 pa, wherein the frequency of ultrasonic is 5-10 kHz, the self-rotation speed of stirring is 1500-2500 r / min, and the revolution speed is 30-50 r / min.

[0031] In step 2, the mixture is simultaneously ultrasonically treated and stirred in the vacuum environment for 5-10 minutes to be uniform.

[0032] In the above technical solution, the sanding time is 30-60 minutes, and the sanding speed is 700-1000 r / min.

[0033] Application of nanometer boehmite and hexagonal boron nitride in synergistically improving heat resistance of a separator.

[0034] Application of nanometer boehmite and hexagonal boron nitride in synergistically improving liquid absorption rate, liquid retention rate, ion conductivity, needle punching strength and / or tensile strength of a separator.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] Nanometer boehmite and hexagonal boron nitride synergistically improve the performance of a separator, wherein the nanometer boehmite, with its porous layered structure and high thermal stability, effectively improves the heat shrinkage resistance of the separator by physically filling to inhibit the high-temperature movement of the polymer chains of the base film, and the hydroxyl groups on the surface and the hydration characteristics of the nanometer boehmite can also release crystal water at high temperatures, which is converted into water vapor after being heated, and the boehmite delays thermal runaway and reduces the risk of thermal runaway through dehydration decomposition heat absorption and water vapor release; at the same time, the hexagonal boron nitride forms a high-thermal-conductivity and high-mechanical-strength skeleton with its two-dimensional sheet structure, builds a physical barrier, and improves the mechanical strength and puncture resistance of the separator, and the high thermal conductivity can quickly conduct local heat away, inhibit local overheating caused by lithium dendrite growth, and effectively block the penetration of lithium dendrites through the separator. The synergistic effect of the two significantly enhances the structural stability and safety of the separator. The hydrophilic surface of the nanometer boehmite and the polar wettability of the hexagonal boron nitride together improve the electrolyte wettability of the separator. The nanopores of the boehmite and the interlayer channels of the hexagonal boron nitride provide more storage and diffusion paths for the electrolyte, significantly improving the lithium ion transmission efficiency. The synergistic doping of nanometer boehmite and hexagonal boron nitride optimizes the pore structure of the separator, reduces the ion migration resistance, and thus improves the lithium ion transmission efficiency of the separator. This synergistic effect also reduces the interface side reaction and inhibits the polarization phenomenon, further enhancing the long-term reliability of the battery separator. The synergistic effect of the two achieves multi-dimensional improvement of the performance of the separator and improves the safety of the lithium battery separator. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Contact angle of the base film (PE film) and the lithium battery separator prepared from the slurry of Example 1;

[0038] Figure 2 Scanning electron microscope image of the lithium battery separator prepared from the slurry of Example 1. DETAILED DESCRIPTION

[0039] The technical solutions of the present application are further illustrated below in conjunction with specific embodiments.

[0040] Nanometer boehmite (powder): Luoyang Zhongchao New Material Co., Ltd.;

[0041] Hexagonal boron nitride (nanosheets): Liaoning Boda Technology Co., Ltd., density of 2.1 g / cm 3 , Mohs hardness of 2;

[0042] Acrylate copolymer solution: Ningbo Xinfeng Plastic Co., Ltd., the acrylate copolymer in the acrylate copolymer solution is polymerized from butyl acrylate and vinylidene fluoride;

[0043] Ammonium polyacrylate: Shanghai Sansui High Polymer Material Science and Technology Co., Ltd., weight average molecular weight of 1000,000 g / mol;

[0044] Carboxymethyl cellulose (powder): Suzhou Derby New Energy Technology Co., Ltd., weight average molecular weight of 1.5 x 10 5 g / mol.

[0045] Nano boehmite:

[0046]

[0047] Hexagonal boron nitride:

[0048]

[0049] Stirrer: double planetary stirrer XFZH-30L.

[0050] Sand mill: Pelletron pin-type nanosand mill.

[0051] Peeling strength: a piece of separator with a width of 10-25 mm and a length of 150 mm is prepared as a sample, 3M tape is pasted on one side of the coating of the sample, a standard roller is uniformly pressed through the sample 3 times, both ends of the sample are fixed on the upper and lower clamps respectively, the peeling direction is 180°, and one end of the 3M tape is torn off by using a tensile machine at a speed of 100 mm / min, thereby obtaining the peeling strength.

[0052] The electrolyte is a mixture of electrolyte and solvent, the concentration of electrolyte (LiPF6) in the electrolyte is 1M, the solvent is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1:1:1.

[0053] Ionic conductivity: the test temperature is 25℃, and the test relative humidity is 50%.

[0054] Tensile elongation: performed on an electronic universal testing machine, tensile elongation = (length of gauge after fracture - original length of gauge) / original length of gauge x 100%.

[0055] In the following examples, the base film is a PE film, and the thickness of the PE film is 7 microns.

[0056] Examples 1-3

[0057] A method for preparing a slurry, comprising the following steps:

[0058] Step 1, mixing water and dispersant in a double planetary mixer, stirring at a rotation speed of 1000 r / min and a revolution speed of 40 r / min for 10 minutes until uniform, then adding nano-boehmite and hexagonal boron nitride, stirring under ultrasonic conditions for 30 minutes until uniform (stirring at a rotation speed of 2000 r / min and a revolution speed of 40 r / min, ultrasonic frequency of 5 kHz), to obtain a first solution, the dispersant being polyacrylammonium, and the hexagonal boron nitride being nanosheets;

[0059] Step 2, mixing the first solution, the binder and the thickening agent, under vacuum environment, while ultrasonic and stirring for 10 minutes, then sanding in a sand mill for 40 minutes until uniform (sanding at a speed of 700 r / min), to obtain the slurry, wherein the vacuum degree of the vacuum environment is 1000 pa, the ultrasonic frequency is 5 kHz, the rotation speed of stirring is 2000 r / min, the revolution speed is 40 r / min, the binder is an acrylate copolymer solution, the content of the acrylate copolymer in the acrylate copolymer solution is 30 wt%, and the thickening agent is carboxymethyl cellulose;

[0060] The ratio of nano-boehmite, hexagonal boron nitride, water, dispersant, binder and thickening agent is X by mass fraction.

[0061] The value of X is shown in Table 1.

[0062] Table 1

[0063]

[0064]

[0065] The particle size of the slurry prepared in Example 1 is D50: 1.289 microns, D90: 2.726 microns; the particle size of the slurry prepared in Example 2 is D50: 1.387 microns, D90: 2.835 microns; and the particle size of the slurry prepared in Example 3 is D50: 1.359 microns, D90: 2.836 microns.

[0066] Comparative Example 1

[0067] A method for preparing a slurry, comprising the following steps:

[0068] Step 1, water and dispersant (same as in Example 1) were mixed in a double planetary mixer, stirred at 1000 r / min of revolution speed and 40 r / min of revolution speed for 10 minutes until uniform, then the conventional boehmite (D10: 0.421 micron, D50: 0.746 micron, D90: 1.509 micron, specific surface area: 125 m 2 / g) was added, stirred for 30 minutes until uniform under ultrasonic condition (the revolution speed of stirring was 2000 r / min, the revolution speed was 40 r / min, the frequency of ultrasonic was 5 kHz), to obtain solution A;

[0069] Step 2, solution A, binder (same as in Example 1) and thickening agent (same as in Example 1) were mixed, stirred and ultrasonicated under vacuum for 10 minutes, then milled in a sand mill for 40 minutes until uniform (the rotation speed of sand milling was 700 r / min), to obtain a slurry, wherein the vacuum degree of the vacuum environment was 1000 pa, the frequency of ultrasonic was 5 kHz, the revolution speed of stirring was 2000 r / min, and the revolution speed was 40 r / min;

[0070] The ratio of the conventional boehmite, water, dispersant, binder and thickening agent was 30:50:0.5:9.5:10 by mass fraction.

[0071] The particle size of the slurry prepared in Comparative Example 1 was D50: 0.532 micron, D90: 1.267 micron.

[0072] Comparative Example 2

[0073] A method for preparing a slurry was basically the same as in Comparative Example 1, except that the “conventional boehmite” was replaced by “nano boehmite”.

[0074] The particle size of the slurry prepared in Comparative Example 2 was D50: 0.257 micron, D90: 0.421 micron.

[0075] Comparative Example 3

[0076] A method for preparing a slurry was basically the same as in Example 1, except that the “nano boehmite” was replaced by “conventional boehmite”.

[0077] The particle size of the slurry prepared in Comparative Example 3 was D50: 1.322 micron, D90: 2.853 micron.

[0078] Comparative Example 4

[0079] A method for preparing a slurry was basically the same as in Example 1, except that the “hexagonal boron nitride” was replaced by “cubic boron nitride”. The thickness of the cubic boron nitride was 19 nm, the length was 10 μm, and the width was 4 μm.

[0080] The particle size of the slurry prepared in Comparative Example 4 was D50: 1.425 microns, and D90: 2.796 microns.

[0081] Comparative Example 5

[0082] A method for preparing a slurry was substantially the same as that of Example 1, except that "nanometer boehmite" was replaced by "alumina". The particle size of the alumina was D10 = 0.243 microns, D50 = 0.489 microns, and D90 = 1.246 microns, the specific surface area was 42 m2 / g, and the pore size was 300 nm. 2

[0083] The particle size of the slurry prepared in Comparative Example 5 was D50: 1.322 microns, and D90: 2.853 microns.

[0084] Examples 4 to 6 and Comparative Examples 6 to 10

[0085] A method for preparing a lithium battery separator included: placing a base film on a coating machine for coating a slurry, coating the slurry on one side of the base film at a speed of 40 m / min, and under the traction of a traction roller, entering a drying device, drying at 60°C for 10 minutes to form a coating layer on the base film, and obtaining a lithium battery separator. The slurry was one of Examples 1 to 3 and Comparative Examples 1 to 5.

[0086] Table 2

[0087] Lithium battery separator Slurry employed in the preparation of lithium battery separator Example 4 Example 1 Example 5 Example 2 Example 6 Example 3 Comparative Example 6 Comparative Example 1 Comparative Example 7 Comparative Example 2 Comparative Example 8 Comparative Example 3 Comparative Example 9 Comparative Example 4 Comparative Example 10 Comparative Example 5

[0088] The test results of the lithium battery separator prepared from the slurry of Example 1 were as follows:

[0089]

[0090]

[0091] The test results of the lithium battery separator prepared from the slurry of Example 2 were as follows:

[0092]

[0093]

[0094] The test results of the lithium battery separator prepared from the slurry of Example 3 were as follows:

[0095]

[0096] The test results of the lithium battery separator prepared from the slurry of Comparative Example 1 were as follows:

[0097] ​

[0098]

[0099] The test results of the lithium battery separator prepared from the slurry of Comparative Example 2 are as follows:

[0100]

[0101] The test results of the lithium battery separator prepared from the slurry of Comparative Example 3 are as follows:

[0102]

[0103] The test results of the lithium battery separator prepared from the slurry of Comparative Example 4 are as follows:

[0104]

[0105]

[0106] The test results of the lithium battery separator prepared from the slurry of Comparative Example 5 are as follows:

[0107]

[0108] Figure 1 For base film ( Figure 1 The "PE film" and the lithium battery separator prepared from the slurry of Example 1 (in the middle) Figure 1 The contact angle of the electrolyte with the "boron nitride + nano-boehmite coated membrane" is determined by... Figure 1 It can be seen that the lithium battery separator prepared from the slurry in Example 1 has good electrolyte wettability.

[0109] The application adopts a slurry containing hexagonal boron nitride and nanometer boehmite to prepare a separator, and the comprehensive performance of the lithium battery separator is improved through the synergistic effect of the characteristics of hexagonal boron nitride and nanometer boehmite. The two-dimensional sheet structure of hexagonal boron nitride endows the separator with excellent heat diffusion capacity, which can quickly disperse local heat, while the porous layered structure of nanometer boehmite forms a physical thermal resistance barrier to reduce the transfer of heat to the electrode, thereby constructing a heat conduction-heat insulation double protection mechanism. The structural stability of the separator under high temperature is significantly improved, and the risk of short circuit caused by the thermal shrinkage of the separator is effectively inhibited. At the same time, the hydrophilicity of nanometer boehmite optimizes the infiltration distribution of the electrolyte in the separator, and the hydrophobic surface of hexagonal boron nitride balances the water absorption swelling of organic substances in the coating, and its ordered layered structure also provides a high-efficiency directional migration channel for lithium ions, further reducing the interface impedance and improving the ion transmission efficiency. Hexagonal boron nitride forms a skeleton with high thermal conductivity and high mechanical strength due to its two-dimensional sheet structure, which significantly enhances the puncture resistance of the separator and reduces the risk of damage caused by lithium dendrite growth or mechanical stress; and the flexibility and stress dispersion effect of nanometer boehmite alleviate the impact of volume change during battery cycling. At the electrochemical level, the nanopore structure and surface charge characteristics of nanometer boehmite (the boehmite surface is rich in Al-OH hydroxyl groups, which will dissociate in the electrolyte, and the electrolyte (containing LiPF6) is weakly acidic, the boehmite surface tends to be positively charged) can physically block the expansion of lithium dendrites and regulate the uniform distribution of free lithium ions, and boron nitride stabilizes the SEI through low lattice mismatch, periodic adsorption sites and low diffusion energy barrier, realizing the ordered deposition of lithium metal, and synergistically inhibiting dendrite formation.

[0110] When the battery separator only uses a PE film, the lithium dendrites grow rapidly and in large numbers, and such disordered growth is extremely dangerous, which can easily penetrate the separator and greatly threaten the safety and stability of the battery. When a boehmite coating is formed on the surface of the PE film by coating the slurry, it can inhibit the growth of lithium dendrites to some extent. However, a single boehmite coating generally has limited effect on inhibiting the growth of lithium dendrites. In contrast, the boehmite and boron nitride composite coating exhibits more excellent performance and significantly improves the inhibition effect on the growth of lithium dendrites. Under the action of this composite coating, the growth of lithium dendrites becomes relatively more uniform and controlled, which can effectively avoid the risk of excessive growth of lithium dendrites.

[0111] The above is an exemplary description of the present application, it should be noted that any simple modification, modification or other equivalent replacement without creative labor of those skilled in the art without departing from the core of the present application falls within the protection scope of the present application.

Claims

1. A high performance lithium battery separator based on a composite coating of boehmite, characterized in that, It comprises: a base film and a coating layer on the base film, the coating layer comprising: nanometer boehmite, hexagonal boron nitride, polyacrylamide, acrylate copolymer and carboxymethyl cellulose, the ratio of nanometer boehmite, hexagonal boron nitride, polyacrylamide, acrylate copolymer and carboxymethyl cellulose being (25-30):(1-5):(0.2-0.5):(1.5-9):(5-10) by mass fraction.

2. The high performance lithium battery separator of claim 1, wherein, The hexagonal boron nitride is a nanosheet.

3. A slurry characterized in that, It comprises: nanometer boehmite, hexagonal boron nitride, water, dispersant, binder and thickening agent, the ratio of nanometer boehmite, hexagonal boron nitride, water, dispersant, binder and thickening agent being (25-30):(1-5):(50-60):(0.2-0.5):(5-10):(5-10) by mass fraction.

4. The slurry of claim 3, wherein, The dispersant is polyacrylamide; the binder is acrylate copolymer solution; and the thickening agent is carboxymethyl cellulose.

5. A method of preparing a slurry, characterized by, It comprises: Mixing nanometer boehmite, hexagonal boron nitride, water, dispersant, binder and thickening agent uniformly to obtain a slurry, the ratio of nanometer boehmite, hexagonal boron nitride, water, dispersant, binder and thickening agent being (25-30):(1-5):(50-60):(0.2-0.5):(5-10):(5-10) by mass fraction.

6. A process for the preparation of high performance lithium battery separator based on boehmite composite coating characterized by, It comprises: Coating the slurry of claim 3 on a base film, drying to form a coating layer on the base film, thereby obtaining a high-performance lithium battery separator based on boehmite composite coating.

7. Application of nanometer boehmite and hexagonal boron nitride in synergistically improving the heat resistance of a separator.

8. Application of nanometer boehmite and hexagonal boron nitride in synergistically improving the liquid absorption rate and liquid retention rate of a separator.

9. Application of nanometer boehmite and hexagonal boron nitride in synergistically improving the ion conductivity of a separator.

10. Application of nanometer boehmite and hexagonal boron nitride in synergistically improving the needle puncture strength and / or tensile strength of a separator.

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