High-heat-resistant high-liquid-absorption lithium battery separator and preparation method thereof

Abstract

The application discloses a high-heat-resistance high-liquid-absorption lithium battery diaphragm and a preparation method thereof. The preparation method of the slurry comprises the following steps: mixing porous alumina, first water, an ethyleneimine aqueous solution, a silane coupling agent solution, a polyvinyl alcohol aqueous solution, a dispersing agent and a binder until uniform to obtain a slurry. The slurry is coated on a base film, dried, and a coating layer is obtained on the base film, thereby obtaining the high-heat-resistance high-liquid-absorption lithium battery diaphragm. The high-heat-resistance high-liquid-absorption lithium battery diaphragm has good liquid absorption, liquid retention, ion conductivity, needle penetration strength and peeling strength, and good heat resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery separator, and particularly relates to a high-heat-resistance high-liquid-absorption lithium battery separator and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are a very popular technology in the field of electronic devices, mainly because they have higher energy density and longer cycle life. In lithium ion batteries, the function of the battery separator is to act as an isolation medium between the positive and negative electrodes, promoting the movement of lithium ions. At present, most commercial lithium ion battery separators use polyolefin separators, such as polyethylene film and polypropylene film. Polyolefin separators lack polarity and hydrophilic groups, resulting in poor hydrophilicity and ionic conductivity of the battery separator. The micropores on the surface of the battery separator are usually formed by a stretching process, which has poor heat resistance and electrolyte wettability. This is not conducive to the cycle performance and safety performance of the battery. At the present stage, the surface morphology and structure of the separator can be modified by coating or grafting to improve the thermal stability of the separator, and to improve the heat shrinkage resistance, mechanical strength, ionic conductivity and wettability of the separator, thereby improving the overall performance of the battery. However, the modification of the prior art still cannot completely meet the application requirements of lithium ion batteries. SUMMARY

[0003] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for preparing a slurry.

[0004] Another purpose of the present application is to provide a slurry obtained by the above method.

[0005] Another purpose of the present application is to provide a high-heat-resistance high-liquid-absorption lithium battery separator.

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

[0007] A method for preparing a slurry, comprising: mixing porous alumina, first water, an ethyleneimine aqueous solution, a silane coupling agent solution, a polyvinyl alcohol (PVA) aqueous solution, a dispersing agent and a binder to be uniform to obtain a slurry, wherein the ratio of the porous alumina, the first water, the ethyleneimine aqueous solution, the silane coupling agent solution, the polyvinyl alcohol aqueous solution, the dispersing agent and the binder is (20-30):(50-60):(1-5):(0.5-2):(1-5):(0.2-0.5):(5-10) by mass fraction.

[0008] In the technical solution, the ratio of the porous alumina, the first water, the ethyleneimine aqueous solution, the silane coupling agent solution, the polyvinyl alcohol aqueous solution, the dispersant and the binder is preferably (20-30) :(50-60) :(1-3) :(0.5-1.5) :(3-5) :(0.2-0.5) :(6-10) in terms of mass parts.

[0009] In the technical solution, the ratio of the porous alumina, the first water, the ethyleneimine aqueous solution, the silane coupling agent solution, the polyvinyl alcohol aqueous solution, the dispersant and the binder is preferably (20-30) :(50-60) :(1-3) :(0.5-1.5) :(3-5) :(0.2-0.5) :(6-10) in terms of mass parts.

[0010] In the technical solution, the content of ethyleneimine in the ethyleneimine aqueous solution is 5-15wt%.

[0011] In the technical solution, the content of silane coupling agent in the silane coupling agent solution is 1-10wt%.

[0012] In the technical solution, the content of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 5-15wt%.

[0013] In the technical solution, the binder is an acrylate copolymer solution, and the content of acrylate copolymer in the acrylate copolymer solution is 20-40wt%.

[0014] In the technical solution, the dispersant is polyacrylammonium.

[0015] In the technical solution, the silane coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane (KH560) and γ-aminopropyltriethoxysilane (KH550).

[0016] In the technical solution, the particle size of the slurry is D50=0.25-0.5 microns and D90=0.8-1.2 microns.

[0017] The method for preparing the slurry comprises the following steps:

[0018] Step 1, mixing the first water, the silane coupling agent solution and the dispersant to be uniform to obtain a first solution;

[0019] In step 1, the first water, the silane coupling agent solution and the dispersant are mixed and stirred to be uniform. The self-rotation speed of stirring is 500-1500r / min, the revolution speed is 30-50r / min, and the stirring time is 10-20 minutes.

[0020] Step 2, mix the first solution, the aqueous ethyleneimine solution and the porous alumina to be uniform to obtain a second solution;

[0021] In step 2, the first solution, the aqueous ethyleneimine solution and the porous alumina are mixed and stirred to be uniform. The self-rotation speed of stirring is 1500-2500 r / min, the revolution speed is 30-50 r / min, and the stirring time is 20-30 minutes.

[0022] Step 3, mix the second solution, the binder and the aqueous polyvinyl alcohol solution to be uniform to obtain a slurry.

[0023] In step 3, the second solution, the binder and the aqueous polyvinyl alcohol solution are mixed and simultaneously ultrasonicated and stirred in a vacuum environment for 15-25 minutes to be uniform, wherein the vacuum degree of the vacuum environment is 500-1500 pa. The self-rotation speed of stirring is 1000-2500 r / min, the revolution speed is 30-50 r / min, and the ultrasonic frequency is 5-10 kHz.

[0024] The slurry obtained by the above method.

[0025] A preparation method of a high-heat-resistance high-liquid-absorption lithium battery separator, comprising: coating the slurry on a base film, drying to obtain a coating layer on the base film, and obtaining the high-heat-resistance high-liquid-absorption lithium battery separator.

[0026] In the above technical solution, the base film is a hydrophilic film, and the water contact angle of the base film is 20-50°, preferably 20-30°.

[0027] In the above technical solution, the method for obtaining the hydrophilic film comprises: immersing a PE film in a first mixed solution at room temperature for 30-40 minutes, washing, and drying to obtain the hydrophilic film, wherein the first mixed solution comprises: ethanol, water and lithium citrate, and the ratio of the volume fraction of ethanol, the volume fraction of water in the first mixed solution and the mass fraction of lithium citrate is (50-60):(20-30):20, the unit of mass fraction is g, and the unit of volume fraction is mL.

[0028] In the above technical solution, the lithium citrate is introduced by a hydrated lithium citrate solution, and the content of lithium citrate in the hydrated lithium citrate solution is 5-10 wt%.

[0029] In the above technical solution, the coating speed is 20-40 m / min.

[0030] In the above technical solution, the thickness of the coating layer is 2-3 μm.

[0031] Application of porous alumina, ethyleneimine, silane coupling agent and polyvinyl alcohol in synergistically improving the liquid absorption and / or liquid retention rate of a separator.

[0032] Application of porous alumina, ethylene imine, silane coupling agent and polyvinyl alcohol in synergistically improving ion conductivity of the separator.

[0033] Application of porous alumina, ethylene imine, silane coupling agent and polyvinyl alcohol in synergistically improving wettability of the separator.

[0034] Application of porous alumina, ethylene imine, silane coupling agent and polyvinyl alcohol in synergistically improving needle punching strength and / or peeling strength of the separator.

[0035] Application of porous alumina, ethylene imine, silane coupling agent and polyvinyl alcohol in synergistically improving heat resistance of the separator.

[0036] Application of porous alumina, ethylene imine, silane coupling agent and polyvinyl alcohol in synergistically reducing interface resistance.

[0037] Compared with the prior art, the application has the beneficial effects that:

[0038] Porous alumina, ethylene imine, silane coupling agent and polyvinyl alcohol synergistically improve the liquid absorption rate, liquid retention rate, ion conductivity, needle punching strength, peeling strength and heat resistance of the separator.

[0039] 1. Ethylene imine has a certain flexibility, and the synergistic effect of ethylene imine and porous alumina enables the coating to have better flexibility while maintaining a certain mechanical strength. The amine group of ethylene imine can react with the hydroxyl group on the surface of porous alumina to form a hydrogen bond, thereby enhancing the polarity and hydrophilicity of the coating surface, helping to reduce the contact angle of the liquid on the coating surface, enabling the liquid to more fully contact the coating, and improving the adsorption and retention capacity of the coating for the liquid.

[0040] 2. Ethylene imine interacts with the active groups (hydroxyl group, carboxyl group) on the surface of the hydrophilic membrane through the amine group to form a hydrogen bond, thereby improving the adhesion of the coating to the base film. The porous alumina is filled in the surface pores of the separator, increasing the contact area of the coating and the base film, and further improving the adhesion.

[0041] 3. The citrate ion in the hydrated lithium citrate solution is a group with a certain hydrophilicity. Using the hydrated lithium citrate solution to treat the PE film can reduce the surface tension of the PE film, making the electrolyte more easily spread and penetrate on the surface of the PE film, and the hydrophilicity of the separator is significantly improved.

[0042] 4. The chemical bonds in lithium citrate can absorb part of the heat at high temperature, which can prevent the excessive shrinkage or melting of the separator at high temperature, and both porous alumina and ethylene imine have high thermal stability, which can maintain good structural stability in a high-temperature environment and effectively resist the destruction of thermal stress to the separator. The interface impedance between the separator and the electrode is also significantly reduced. This is because there are a large number of polar groups (hydroxyl and amine groups) on the surface of the high-heat-resistant and high-liquid-absorption lithium battery separator, which enhances the polarity of the surface of the separator, making the ion migration process in the separator easier, thereby effectively reducing the impedance related to ion migration. The improvement of such comprehensive performance provides a strong guarantee for the high-performance operation of lithium batteries and provides a new idea and method for the development of lithium batteries in terms of high energy density, high safety, etc. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The contact angle of the lithium battery separator prepared for Comparative Example 3;

[0044] Figure 2 The contact angle of the high-heat-resistant and high-liquid-absorption lithium battery separator prepared for Example 8;

[0045] Figure 3 SEM of the high-heat-resistant and high-liquid-absorption lithium battery separator prepared from the slurry of Example 2. DETAILED DESCRIPTION

[0046] The technical solutions of the present application will be further illustrated below in combination with specific examples.

[0047] Porous alumina: Shanghai Yingcheng New Material Co., Ltd.;

[0048] Polyvinyl alcohol aqueous solution: Guangzhou Xiangqian Chemical Co., Ltd.;

[0049] Acrylate copolymer (acrylate and vinylidene fluoride) solution: Ningbo Xinfeng Plastic Co., Ltd.;

[0050] Ammonium polyacrylate: Shanghai Sanrui High Polymer Material Science and Technology Co., Ltd.;

[0051] Hydrated lithium citrate solution: Hubei Watson Chemical Technology Co., Ltd.;

[0052] Silane coupling agent solution: Shandong Jinyu Feng New Material Co., Ltd.

[0053]

[0054] Double planetary mixer: XFZH-30L.

[0055] In the following examples and comparative examples, the method for preparing the hydrophilic film is: immersing the PE film in the first mixture at room temperature for 30 minutes, washing (rinsing with deionized water three times), drying at 75°C for 20 min to obtain a hydrophilic film (water contact angle of 24.6°), wherein the method for obtaining the first mixture is: adding ethanol and deionized water in a beaker, stirring at room temperature, the stirring speed is 1000 r / min, the stirring time is 10 min, then adding lithium citrate hydrate solution (the content of lithium citrate in the lithium citrate hydrate solution is 5wt%), stirring at 40°C at a speed of 1000 r / min for 30 min until clear, to obtain the first mixture. In the first mixture, the volume fraction of ethanol, the volume fraction of water and the mass fraction of lithium citrate are in the ratio of 50:30:20, the unit of mass fraction is g, and the unit of volume fraction is mL.

[0056] Ionic conductivity: the test temperature is 25°C, and the relative humidity is 50%.

[0057] Peeling strength: a standard size sample (width 10-25 mm, length 150 mm) is prepared, 3M transparent tape is pasted on the coating side of the sample, and enough peeling end (at least 20 mm) is left, a standard roller is uniformly pressed through the sample 3 times, both ends of the sample are fixed in the upper and lower clamps respectively, the peeling direction is 180°, and one end of the 3M transparent tape is torn off by using a tensile machine, so as to obtain the peeling strength.

[0058] The electrolyte used in the contact angle test is a mixture of electrolyte and solvent, the electrolyte is LiPF6, the electrolyte concentration is 1M, and the solvent is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1:1:1.

[0059] Examples 1-3

[0060] A method for preparing a slurry, comprising the following steps:

[0061] Step 1, mixing the first water (pure water), silane coupling agent solution and dispersant in a double planetary mixer, stirring until uniform (the rotation speed of stirring is 1000 r / min, the revolution speed is 40 r / min, and the stirring time is 10 minutes), to obtain a first solution, the dispersant is polyacrylammonium, the content of silane coupling agent in the silane coupling agent solution is 5wt%, and the silane coupling agent is γ-glycidoxypropyltrimethoxysilane (KH560);

[0062] Step 2, adding ethyleneimine aqueous solution and porous alumina (powder) into the first solution, stirring until uniform (stirring speed of 2000 r / min, revolution speed of 40 r / min, stirring time of 30 minutes), to obtain a second solution, the content of ethyleneimine in the ethyleneimine aqueous solution is 10 wt%;

[0063] Step 3, adding a binder and polyvinyl alcohol aqueous solution into the second solution, stirring and ultrasonic oscillation in a double planetary mixer with high-speed dispersion ultrasonic oscillation function under vacuum environment for 20 minutes until uniform, to obtain a slurry, wherein the vacuum degree of the vacuum environment is 1000 pa, the stirring speed is 2000 r / min, the revolution speed is 40 r / min, the ultrasonic wave frequency is 5 kHz, the binder is an acrylate copolymer solution, the content of the acrylate copolymer in the acrylate copolymer solution is 30 wt% (the acrylate copolymer is polymerized from acrylate and vinylidene fluoride), the content of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 10 wt%, and the ratio of the porous alumina, the first water, the ethyleneimine aqueous solution, the silane coupling agent solution, the polyvinyl alcohol aqueous solution, the dispersant and the binder is X in mass fraction.

[0064] The value of X is shown in Table 1.

[0065] Table 1

[0066] Slurry X Example 1 25：60：1：1：4.5：0.5：8 Example 2 25：60：2：1：3.5：0.5：8 Example 3 25：60：5：2：2.5：0.5：5

[0067] The particle size of the slurry prepared in Example 1 is D50: 0.454 microns, D90: 1.035 microns; the particle size of the slurry prepared in Example 2 is D50: 0.420 microns, D90: 1.055 microns; and the particle size of the slurry prepared in Example 3 is D50: 0.454 microns, D90: 1.103 microns.

[0068] Example 4

[0069] A method for preparing a slurry is basically the same as that in Example 1, except that the method for preparing the slurry in Example 4 does not add a silane coupling agent solution.

[0070] Example 5

[0071] A method for preparing a slurry is basically the same as that in Example 1, except that the method for preparing the slurry in Example 5 does not add an ethyleneimine aqueous solution.

[0072] Example 6

[0073] A method for preparing a slurry is basically the same as that in Example 1, except that the method for preparing the slurry in Example 6 does not add a polyvinyl alcohol aqueous solution.

[0074] Comparative Example 1

[0075] A method for preparing a slurry, comprising the following steps:

[0076] Step 1, put pure water and dispersant into a double planetary mixer, first stir at a rotation speed of 1000 r / min and a revolution speed of 40 r / min for 10 minutes to obtain solution A;

[0077] Step 2, add porous alumina (powder) to solution A, first stir at a rotation speed of 2000 r / min and a revolution speed of 40 r / min for 30 minutes to obtain solution B;

[0078] Step 3, add a binder to solution B, and simultaneously ultrasonic and stir in a double planetary mixer with high-speed dispersion ultrasonic oscillation function under vacuum environment for 20 minutes until uniform to obtain a slurry, wherein the rotation speed of stirring is 2000 r / min, the revolution speed is 40 r / min, the ultrasonic frequency is 5 kHz, and the vacuum degree is 1000 pa;

[0079] The ratio of porous alumina, pure water, dispersant and binder is 35:60:0.5:9.5 by mass fraction, and the dispersant and binder in Comparative Example 1 are the same as those in Example 1.

[0080] The particle size of the slurry prepared in Comparative Example 1 is D50: 0.441 microns and D90: 1.054 microns.

[0081] Comparative Example 2

[0082] A method for preparing a slurry, which is basically the same as Comparative Example 1, except that "porous alumina" is replaced by "conventional alumina", and the particle size of the conventional alumina is D10: 0.336 μm, D50: 0.537 μm, D90: 1.079 μm, the specific surface area is 11.5 m 2 / g, and the pore size is 9.1 nm.

[0083] The particle size of the slurry prepared in Comparative Example 2 is D50: 0.487 microns and D90: 1.335 microns.

[0084] Examples 7-12

[0085] A method for preparing a high-heat-resistant high-liquid-absorption lithium battery separator, comprising: placing a base film on a coating machine, coating a slurry on one side of the base film at a speed of 30 m / min, and entering an oven under the traction of a traction roller, and drying at 50℃ for 10 minutes to obtain a coating layer on the base film, thereby obtaining a high-heat-resistant high-liquid-absorption lithium battery separator. The base film is a hydrophilic film, and the slurry is one of Examples 1-6.

[0086] Table 2

[0087] High heat resistance and high liquid absorption lithium battery separator Slurry for preparing high heat resistance and high liquid absorption lithium battery separator Example 7 Example 1 Example 8 Example 2 Example 9 Example 3 Example 10 Example 4 Example 11 Example 5 Example 12 Example 6

[0088] Comparative Examples 3 and 4

[0089] A method for preparing a lithium battery separator, comprising: placing a base film on a coating machine, coating a slurry on one side of the base film at a speed of 30 m / min, entering an oven under the traction of a traction roller, drying at 50℃ for 10 minutes, obtaining a coating layer on the base film, and obtaining the lithium battery separator. The base film is a PE film (non-hydrophilic film), and the slurry is one of Comparative Examples 1 and 2.

[0090] Table 3

[0091] Lithium battery separator Slurry for preparing lithium battery separator Comparative Example 3 Comparative Example 1 Comparative Example 4 Comparative Example 2

[0092] Comparative Example 5

[0093] A method for preparing a lithium battery separator, which is basically the same as Comparative Example 4, except that the base film used in Comparative Example 5 is a hydrophilic film.

[0094] The parameters of the high-heat-resistant and high-liquid-retention lithium battery separator (Example 7) prepared from the slurry of Example 1 are as follows:

[0095]

[0096] The parameters of the high-heat-resistant and high-liquid-retention lithium battery separator (Example 8) prepared from the slurry of Example 2 are as follows:

[0097]

[0098]

[0099] The parameters of the high-heat-resistant and high-liquid-retention lithium battery separator (Example 9) prepared from the slurry of Example 3 are as follows:

[0100]

[0101] The parameters of the high-heat-resistant and high-liquid-retention lithium battery separator (Example 10) prepared from the slurry of Example 4 are as follows:

[0102]

[0103]

[0104] The parameters of the high-heat-resistant and high-liquid-retention lithium battery separator (Example 11) prepared from the slurry of Example 5 are as follows:

[0105]

[0106] The parameters of the high heat resistance and high liquid absorption and retention rate lithium battery separator (Example 12) prepared from the slurry of Example 6 are as follows:

[0107]

[0108] The parameters of the lithium battery separator (Comparative Example 3) prepared from the slurry of Comparative Example 1 are as follows:

[0109]

[0110] The parameters of the lithium battery separator (Comparative Example 4) prepared from the slurry of Comparative Example 2 are as follows:

[0111]

[0112] The parameters of the lithium battery separator (Comparative Example 5) prepared from the slurry of Comparative Example 2 are as follows:

[0113]

[0114] Silane coupling agents can hydrolyze hydroxyl groups on the surface of porous alumina to form silanols (-Si-OH), which then further form covalent bonds (-Si-O-Al), achieving chemical modification of the alumina surface. Through modification with silane coupling agents, active epoxy groups are introduced into the porous alumina surface, providing chemical reaction sites for subsequent bonding with ethyleneimine. The silane coupling agent establishes a chemical link between the porous alumina and ethyleneimine. The epoxy groups introduced by the silane coupling agent undergo ring-opening reactions in the ethyleneimine aqueous solution, forming stable amide bonds with the abundant primary amine groups on the ethyleneimine surface, thus combining the porous alumina with ethyleneimine (the porous alumina is successfully grafted onto the macromolecular chain of ethyleneimine). Subsequently, an aqueous solution of polyvinyl alcohol (PVA) is added. The hydroxyl groups in PVA can combine with the active groups on the hydrophilic membrane surface to form hydrogen bonds, thereby ensuring the coating adheres firmly to the base film.

[0115] like Figure 1 and Figure 2 As shown, the contact angle of the lithium-ion battery separator prepared in Comparative Example 3 was 15.136°, while the contact angle of the high heat resistance and high liquid absorption and retention rate lithium-ion battery separator prepared in Example 8 was 4.35°. This indicates that the modified porous alumina has excellent wettability. Figure 3 SEM image of the high heat resistance and high liquid absorption and retention rate lithium battery separator prepared from the slurry of Example 2.

[0116] The ceramic (porous alumina) particles attached to the surface of the base film can store a large amount of electrolyte and facilitate the absorption of the electrolyte by the separator, and in addition, a large number of hydrophilic hydroxyl (-OH) polar groups exist on the surface of the porous alumina, which facilitates the improvement of the wettability of the electrolyte by the separator. The present application improves the heat resistance, wettability and ionic conductivity of the separator through the synergistic effect of ethyleneimine, porous alumina, silane coupling agent and polyvinyl alcohol, thereby improving the overall performance of the battery.

[0117] The above has exemplarily described the present application, it should be explained that, in not departing from the core of the present application, any simple transformation, modification or other equivalent replacement which can not spend the creative labor of the person skilled in the art falls into the protection scope of the present application.

Claims

1. A method for preparing a high-heat-resistant high-liquid-absorption lithium battery separator, characterized in that, The application relates to a high-heat-resistance high-liquid-absorption lithium battery diaphragm. The silane coupling agent is at least one of gamma-glycidoxypropyltrimethoxysilane and gamma-aminopropyltriethoxysilane. The method for preparing the slurry comprises: mixing porous alumina, first water, an aqueine solution, a silane coupling agent solution, a polyvinyl alcohol aqueous solution, a dispersing agent and a binder to be uniform to obtain the slurry, wherein the ratio of the porous alumina, the first water, the aqueine solution, the silane coupling agent solution, the polyvinyl alcohol aqueous solution, the dispersing agent and the binder is (20-30):(50-60):(1-5):(0.5-2):(1-5):(0.2-0.5):(5-10) by mass fraction; and the base film is a hydrophilic film, and the water contact angle of the base film is 20-50 ° .

2. The production method according to claim 1, characterized by, The content of ethylene imine in the aqueous ethylene imine solution is 5-15 wt%.

3. The preparation method according to claim 1, characterized in that, The content of the silane coupling agent in the silane coupling agent solution is 1-10 wt%.

4. The method of claim 1, wherein, The content of polyvinyl alcohol in the aqueous polyvinyl alcohol solution is 5-15 wt%.

5. The preparation method according to claim 1, characterized in that, The binder is an acrylate copolymer solution, and the content of the acrylate copolymer in the acrylate copolymer solution is 20-40 wt%.

6. The method of claim 1, wherein, 7. The high-heat-resistance high-liquid-absorption lithium battery diaphragm obtained by the preparation method in claim 1. ​

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