A ceramic-coated separator of silsesquioxane, its preparation method and application

Abstract

The present invention relates to the technical field of lithium-ion battery separators, and discloses a ceramic-coated separator of silsesquioxane, a preparation method thereof, and an application thereof. The preparation includes the steps of: dissolving a modified polyacrylate in a solvent A to form a gel solution, adding nano-aluminum oxide and a dispersant to obtain a dispersion; coating the dispersion on a polyethylene separator, volatilizing to remove the solvent, immersing in a non-solvent and standing, and drying to obtain the ceramic-coated separator; wherein the modified polyacrylate includes raw material components: 50-100 parts of acrylate, 0.03-0.5 part of 1-vinyl-3-butylimidazolium tetrafluoroborate, 0.1-2 parts of methacryloxypropylcage poly(silsesquioxane), 0.1-1 part of polyvinyl alcohol, and 0.3-2 parts of a free radical initiator. In the present invention, a separator with a ceramic nano-coating is prepared by using a modified polyacrylate, which has an ultra-low moisture content, and the pores inside the separator are uniform, and the mechanical properties are excellent, and it has excellent performance in lithium batteries, effectively improving the cycle life and safety performance of lithium batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery separators, and particularly to a ceramic-coated separator of silsesquioxane, a preparation method thereof, and an application thereof. Background Art

[0002] Polyethylene has good thermoplasticity, mechanical strength, chemical stability, and transparency, and thus is widely used in light industry, instruments, toys, packaging, printing, construction, agriculture and other fields, and is also often used as a separation membrane material. The PE microporous membrane has the ability to resist electrolyte corrosion, is non-toxic, inexpensive, can be thermally closed at high temperatures, has good tear resistance and low surface resistance, and is an ideal material for battery separators. When used between the positive and negative electrodes of a lithium-ion battery, it only allows ions to pass through and is an insulator for electrons, which can prevent short circuits.

[0003] The performance of the PE separator determines the interface structure, internal resistance, etc. of the battery, and directly affects the capacity and cycle performance of the battery. However, the non-polar PE separator has a hydrophobic surface and a low surface energy, and it is difficult to wet and retain polar organic electrolytes such as ethylene carbonate and propylene carbonate. In order to improve the safety, service life, and wetting ability of the separator with liquid electrolyte, it is usually necessary to improve the existing separator, such as coating and modifying the surface of the PE separator.

[0004] CN104183805A discloses a preparation method of a separator material with a ceramic coating for a lithium-ion battery, including steps such as ceramic slurry preparation, separator pretreatment, precision coating, drying, etc.; the prepared product has the characteristics of a dense, uniform, firmly bonded ceramic coating and small thermal shrinkage of the separator, and has obvious effects on improving the safety performance of lithium-ion batteries and extending the battery life.

[0005] CN105552285A discloses a ceramic-coated separator, which is a symmetric five-layer laminated structure, including two outermost ceramic coatings, two sub-outermost chlorinated polyolefin coatings, and a middle matrix separator. In this method, ceramic particles are modified and then made into a ceramic coating slurry, and then the chlorinated polyolefin coating is applied to the matrix separator and dried to form a chlorinated polyolefin coating. Finally, the ceramic coating slurry is applied to the chlorinated polyolefin coating of the matrix separator and dried to make the ceramic-coated separator. Since the chlorinated polyolefin layer has a large number of polar groups Cl, it can not only improve the bonding strength between the matrix separator and the ceramic coating, but also chlorinated polyolefin has a similar crystal structure and size to polypropylene and polyethylene, so it has good adhesion performance to the matrix separator, thereby improving the adhesion between the ceramic coating and the substrate separator, and playing a role of being difficult to fall off and not shedding powder.

[0006] The above-mentioned ceramic coating solves the polarity problem of the PE separator to a certain extent. On the other hand, since the Al2O3 particles are extremely fine and generally have polar groups on their surfaces, with certain hydrophilicity, the water content of the generally Al2O3 ceramic-coated separator is higher than that of other polyolefin separators. As a result, there are certain risks during battery production and use. Therefore, reducing the water content of the separator is also extremely important.

[0007] CN109888155A discloses a ceramic-coated separator and a preparation method thereof. The separator includes a base film and a ceramic coating coated on at least one surface of the base film. The ceramic coating is formed by coating an alumina slurry. The binder used in the alumina slurry is a silicone resin with polar groups or a polysiloxane polyacrylate copolymer emulsion; the polar groups are at least one of amino, carboxyl, hydroxyl, and derivatives of these groups. The binder used is a binder containing a hydrophobic silane segment and polar groups, which greatly reduces the water content of the prepared ceramic-coated separator, avoids the safety hazards of battery use and production caused by high water content of the separator, and also avoids the influence of the high water content separator on battery performance, laying a foundation for the preparation of high-quality battery separators and batteries.

[0008] However, in the above patent, acetone is used as a solvent to prepare a composite film by the phase inversion method. However, due to the relatively fast evaporation rate of acetone, there will be losses during the preparation process of the coating solution, resulting in difficult control of the preparation process; another method uses water as a single non-solvent to prepare a composite film, which easily makes the coating form an irregular pore shape, affecting the performance of the separator. Summary of the Invention

[0009] Aiming at the problems of high water content and uneven pore formation in ceramic-coated PE separators, the present invention provides a preparation method of a ceramic-coated separator based on silsesquioxane, which can obtain a ceramic-coated separator with an ultra-low water content, and the pores inside the separator are uniform, and the mechanical properties remain excellent, showing excellent performance in lithium batteries, effectively improving the cycle life and safety performance of lithium batteries.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A preparation method of a ceramic-coated separator based on silsesquioxane, comprising the steps of:

[0012] Step 1, dissolve a modified polyacrylate in solvent A to form a gel solution, add nano-alumina and a dispersant to obtain a nano-alumina gel dispersion;

[0013] Step 2, coat the nano-alumina gel dispersion on a polyethylene separator, volatilize and remove the solvent, immerse it in a non-solvent and let it stand, and obtain the ceramic-coated separator after drying.

[0014] The modified polyacrylate, by weight, comprises raw material components: 50 - 100 parts of acrylate, 0.03 - 0.5 part of 1 - vinyl - 3 - butylimidazolium tetrafluoroborate, 0.1 - 2 parts of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 0.1 - 1 part of polyvinyl alcohol, and 0.3 - 2 parts of free radical initiator.

[0015] Preferably, by weight, the feedstock in the preparation process comprises: 15 - 20 parts of modified polyacrylate, 40 - 60 parts of solvent A, 3 - 7 parts of nano - alumina, and 1 - 4 parts of dispersant.

[0016] The preparation process of the modified polyacrylate includes: adding 50 - 100 parts of acrylate, 0.03 - 0.5 part of 1 - vinyl - 3 - butylimidazolium tetrafluoroborate, 0.1 - 2 parts of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 0.1 - 1 part of polyvinyl alcohol, 0.3 - 2 parts of free radical initiator, and 400 - 500 parts of solvent B into a reaction kettle, reacting at 70 - 80 °C for 60 - 120 min, and distilling off solvent B to obtain the modified polyacrylate.

[0017] In the modification of polyacrylate, adding a small amount of 1 - vinyl - 3 - butylimidazolium tetrafluoroborate and methacryloxypropylcage polyhedral oligomeric silsesquioxane can, on the one hand, avoid the decline of the mechanical properties of the material caused by a large addition amount, and on the other hand, only a small amount needs to be added in the present invention to effectively reduce the water content of the separator.

[0018] The solvent A is N - methylpyrrolidone; this solvent has low volatility and slower evaporation, which is more conducive to obtaining a separator with uniform pores.

[0019] The dispersant includes polyethylene glycol;

[0020] The coating thickness of the nano - alumina gel dispersion is 2 - 4 μm;

[0021] The non - solvent is an aqueous solution of ethanol, in which the mass concentration of ethanol is 10 - 30%. In the present invention, using an aqueous solution of ethanol to soak the separator instead of pure water makes the fibers in the separator looser and more porous, and it is not easy to shrink during the drying process, with a higher porosity and more uniform pore formation. The higher the porosity, the more micropores in the separator, and the easier it is for lithium ions to migrate from the negative electrode to the positive electrode, so the battery rate discharge performance is better.

[0022] Preferably, in step 1, the temperature for dissolving the modified polyacrylate in the solvent is 60 - 70 °C;

[0023] In step 2, the volatilization is carried out by volatilizing in air at room temperature for 20 - 40 h; the standing in the non - solvent is carried out by standing at room temperature for 8 - 12 h;

[0024] The drying is carried out by vacuum drying at 40 - 60 °C for 2 - 4 h.

[0025] Preferably, the polyethylene separator is pretreated, and the pretreatment process includes:

[0026] S1, preparing an oxidation solution by mixing K2Cr2O7, H2SO4 and H2O at 60 - 80 °C;

[0027] S2, soaking 15 - 20 parts of the polyethylene separator in 40 - 60 parts of the oxidation solution, taking it out, washing and drying to obtain a pretreated polyethylene separator. Pretreating the polyethylene separator in advance can promote the resin coating to combine more tightly with the separator and have better performance.

[0028] More preferably, the volume ratio of K2Cr2O7, H2SO4 and H2O is 1:16 - 20:2.

[0029] In the modified polyacrylate, the acrylate includes one or more of octyl acrylate, methyl methacrylate, decyl acrylate, butyl acrylate, lauryl acrylate;

[0030] The solvent B is any one of toluene, dichloroethane, and xylene.

[0031] The radical initiator includes any one or more of azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and dimethyl azobisisobutyrate (AIBME).

[0032] The present invention also provides a ceramic-coated separator of silsesquioxane prepared according to the preparation method.

[0033] The present invention also provides the application of the ceramic-coated separator of silsesquioxane in a lithium battery.

[0034] In the present invention, 1-vinyl-3-butylimidazolium tetrafluoroborate and methacryloxypropylcage poly(silsesquioxane) are combined to prepare modified polyacrylic acid. Among them, the methacryloxypropylcage poly(silsesquioxane) copolymer undergoes a chain extension reaction with acrylate to obtain a polyacrylate containing siloxane functional groups. Then, through an addition polymerization reaction with 1-vinyl-3-butylimidazolium tetrafluoroborate, the tetrafluoroborate is introduced into the polyacrylate, effectively introducing a fluorine-containing structure and a POSS structure containing siloxane, improving the hydrophobicity. Finally, the prepared ceramic-coated separator has an extremely low water content, reduces mechanical micro-short circuits during cycling, effectively improves the cycle life, and has excellent performance in lithium batteries.

[0035] On the other hand, nano-aluminum oxide can form a solid solution in lithium batteries, improving the rate performance and cycle performance; high-purity nano-aluminum oxide also has very excellent thermal conductivity: when the battery temperature is too high, this material can conduct heat well, thus solving the problem of poor thermal conductivity of the separator material, and good wettability: high-purity nano-aluminum oxide powder has good liquid absorption and liquid retention capabilities.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) In the present invention, 1-vinyl-3-butylimidazolium tetrafluoroborate containing a hydrophobic group and methacryloxypropylcage polyhedral oligomeric silsesquioxane are combined and copolymerized to prepare a modified polyacrylate, effectively reducing the water content of the separator.

[0038] (2) In the present invention, a modified polyacrylate is dissolved in a low-volatility solvent, and a non-solvent such as an aqueous solution of ethanol is used instead of a single non-solvent of water, effectively preparing a separator with more uniform pore distribution and improving the mechanical properties of the separator to a certain extent.

[0039] (3) The ceramic-coated separator of the sesquioxane prepared by the present invention has an ultra-low water content and excellent performance in lithium batteries; the coated separator has excellent hydrophobic properties and can effectively block the penetration of water, thereby improving the cycle life and safety performance of lithium batteries; in addition, the use of the coated separator can reduce the internal resistance of lithium-ion batteries and the loss of electrolyte, thereby improving the energy output efficiency of lithium batteries; therefore, the modified polyacrylate has certain practical application prospects for improving the performance of lithium-ion batteries. Description of the Drawings

[0040] Figure 1 It is the test of the particle size of the separator slurry prepared in Example 4 by a laser particle size analyzer. Detailed Embodiments

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art make modifications or equivalent substitutions on the basis of understanding the technical solutions of the present invention, and without departing from the spirit and scope of the technical solutions of the present invention, they should all be covered within the protection scope of the present invention.

[0042] In the experimental methods of the following examples, unless otherwise specified, they are all conventional methods, carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels. The CAS number of methacryloxypropylcaged polyhedral oligomeric silsesquioxane is 160185-24-0, and for polyvinyl alcohol, the brand PVA17-92 is selected.

[0043] Example 1

[0044] A preparation method of a ceramic-coated diaphragm of silsesquioxane, comprising the steps:

[0045] Step 1: Weigh 50 g of octyl acrylate, 0.03 g of 1-vinyl-3-butylimidazolium tetrafluoroborate, 0.1 g of methacryloxypropylcaged polyhedral oligomeric silsesquioxane, 0.1 g of polyvinyl alcohol and 0.3 g of azobisisobutyronitrile. Add 400 parts of toluene to a reaction kettle, introduce nitrogen to displace air, mix and stir evenly, heat up to 70 °C and react for 60 min, distill off toluene, and cool to room temperature to obtain modified polyacrylate.

[0046] Step 2: Measure K2Cr2O7, H2SO4, and H2O according to a volume ratio of 1:16:2, prepare an oxidation solution at 60 °C, immerse 15 g of a polyethylene diaphragm in 40 g of the oxidation solution for 1 min, then rinse it with deionized water multiple times and dry it to obtain a pretreated polyethylene diaphragm.

[0047] Step 3: Add 15 g of the modified polyacrylate to 40 g of N-methylpyrrolidone, heat up to 60 °C and stir to dissolve to form a gel solution. Then add 3 g of nano-aluminum oxide and 1 g of polyethylene glycol to the gel solution and continue to stir for 2 h to obtain a nano-aluminum oxide gel dispersion;

[0048] Step 4: Coat the nano-aluminum oxide gel dispersion on the pretreated polyethylene diaphragm, with a coating thickness of 2 μm. After coating, volatilize the solvent at room temperature in air for 20 h, then immerse it in an ethanol aqueous solution with an ethanol mass concentration of 25% and let it stand for 8 h. Finally, the diaphragm is vacuum-dried at 40 °C for 2 h to obtain the ceramic-coated diaphragm.

[0049] Example 2

[0050] A preparation method of a ceramic-coated diaphragm of silsesquioxane, comprising the steps:

[0051] Step 1, Weigh 60 g of methyl methacrylate, 0.2 g of 1-vinyl-3-butylimidazolium tetrafluoroborate, 1 g of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 0.4 g of polyvinyl alcohol, and 1 g of benzoyl peroxide. Add 430 parts of dichloroethane to the reaction kettle, introduce nitrogen to displace air, mix and stir evenly, heat up to 750 °C and react for 80 min, distill off toluene, and cool to room temperature to obtain modified polyacrylate.

[0052] Step 2, Measure K2Cr2O7, H2SO4, and H2O according to a volume ratio of 1:17:2, prepare the oxidation solution at 65 °C, soak 16 g of the polyethylene diaphragm in 45 g of the oxidation solution for 2 min, then rinse it with deionized water multiple times and dry it to obtain the pretreated polyethylene diaphragm.

[0053] Step 3, Add 18 g of the modified polyacrylate to 45 g of N-methylpyrrolidone, heat up to 65 °C and stir to dissolve to form a gel solution. Then add 4 g of nano-aluminum oxide and 2 g of polyethylene glycol to the gel solution and continue to stir for 3 h to obtain a nano-aluminum oxide gel dispersion.

[0054] Step 4, Coat the nano-aluminum oxide gel dispersion on the pretreated polyethylene diaphragm with a coating thickness of 3 μm. After coating, volatilize at room temperature in air for 30 h to remove the solvent, then immerse it in an ethanol aqueous solution with an ethanol mass concentration of 25% and let it stand for 9 h. Finally, dry the diaphragm in vacuum at 40 °C for 2 h to obtain the ceramic-coated diaphragm.

[0055] Example 3

[0056] A preparation method of a ceramic-coated diaphragm of silsesquioxane, comprising the steps:

[0057] Step 1, Weigh 85 g of decyl acrylate, 0.4 g of 1-vinyl-3-butylimidazolium tetrafluoroborate, 1.5 g of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 0.8 g of polyvinyl alcohol, and 1.5 g of benzoyl peroxide. Add 460 parts of xylene to the reaction kettle, introduce nitrogen to displace air, mix and stir evenly, heat up to 75 °C and react for 100 min, distill off toluene, and cool to room temperature to obtain modified polyacrylate.

[0058] Step 2, Measure K2Cr2O7, H2SO4, and H2O according to a volume ratio of 1:19:2, prepare the oxidation solution at 60 °C, soak 19 g of the polyethylene diaphragm in 55 g of the oxidation solution for 4 min, then rinse it with deionized water multiple times and dry it to obtain the pretreated polyethylene diaphragm.

[0059] Step 3: Add 18 g of modified polyacrylate into 55 g of N-methylpyrrolidone, heat up to 65 °C and stir to dissolve to form a gel solution. Then add 6 g of nano-aluminum oxide and 2 g of polyethylene glycol into the gel solution and continue stirring for 4 h to obtain a nano-aluminum oxide gel dispersion.

[0060] Step 4: Coat the nano-aluminum oxide gel dispersion on the pretreated polyethylene separator with a coating thickness of 3 μm. After coating, volatilize at room temperature in air for 30 h to remove the solvent. Then immerse it in an ethanol aqueous solution with an ethanol mass concentration of 25% and let it stand for 11 h. Finally, the separator is vacuum dried at 55 °C for 3 h to obtain the ceramic-coated separator.

[0061] Example 4

[0062] A preparation method of a ceramic-coated separator of sesquisiloxane, comprising the steps:

[0063] Step 1: Weigh 100 g of butyl acrylate, 0.5 g of 1-vinyl-3-butylimidazolium tetrafluoroborate, 2 g of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 1 g of polyvinyl alcohol and 2 g of dimethyl 2,2'-azobis(2-methylpropionate). Add 500 parts of xylene into a reaction kettle, introduce nitrogen to displace air, mix and stir evenly, heat up to 80 °C and react for 120 min, distill off toluene, and cool to room temperature to obtain modified polyacrylate.

[0064] Step 2: Measure K2Cr2O7, H2SO4, and H2O according to a volume ratio of 1:20:2, prepare an oxidation solution at 80 °C, immerse 20 g of polyethylene separator in 60 g of the oxidation solution for 5 min, then rinse it with deionized water multiple times and dry it to obtain the pretreated polyethylene separator.

[0065] Step 3: Add 20 g of modified polyacrylate into 60 g of N-methylpyrrolidone, heat up to 70 °C and stir to dissolve to form a gel solution. Then add 7 g of nano-aluminum oxide and 4 g of polyethylene glycol into the gel solution and continue stirring for 5 h to obtain a nano-aluminum oxide gel dispersion.

[0066] Step 4: Coat the nano-aluminum oxide gel dispersion on the pretreated polyethylene separator with a coating thickness of 4 μm. After coating, volatilize at room temperature in air for 40 h to remove N-methylpyrrolidone. Then immerse it in an ethanol aqueous solution with an ethanol mass concentration of 25% and let it stand for 12 h. Finally, the separator is vacuum dried at 60 °C for 4 h to obtain the ceramic-coated separator.

[0067] Comparative Example 1

[0068] A preparation method of a ceramic-coated separator of sesquisiloxane, comprising the steps:

[0069] Step 1: Measure K2Cr2O7, H2SO4, and H2O according to a volume ratio of 1:16:2, prepare an oxidation solution at 60°C, soak 15 g of a polyethylene diaphragm in 40 g of the oxidation solution for 1 min, then rinse it with deionized water multiple times and dry it to obtain a pretreated polyethylene diaphragm.

[0070] Step 2: Add 15 g of polyacrylate to 40 g of N-methylpyrrolidone, heat to 60°C and stir to dissolve to form a gel solution, then add 3 g of nano-aluminum oxide and 1 g of polyethylene glycol to the gel solution and continue stirring for 2 h to obtain a nano-aluminum oxide gel dispersion;

[0071] Step 3: Coat the nano-aluminum oxide gel dispersion on the pretreated polyethylene diaphragm, with a coating thickness of 2 μm. After coating, volatilize at room temperature in air for 20 h to remove N-methylpyrrolidone, then immerse it in an ethanol aqueous solution with an ethanol mass concentration of 25% and let it stand for 8 h. Finally, the diaphragm is vacuum-dried at 40°C for 2 h to obtain the ceramic-coated diaphragm.

[0072] Comparative Example 2

[0073] A preparation method of a ceramic-coated diaphragm of sesquisiloxane, comprising the steps:

[0074] Step 1: Weigh 50 g of octyl acrylate, 0.03 g of 1-vinyl-3-butylimidazolium tetrafluoroborate, 0.1 g of polyvinyl alcohol, and 0.3 g of azobisisobutyronitrile, add 400 parts of toluene to a reaction kettle, introduce nitrogen to displace air, mix and stir evenly, heat up to 70°C and react for 60 min, distill off toluene, and cool to room temperature to obtain a modified polyacrylate.

[0075] Step 2: Measure K2Cr2O7, H2SO4, and H2O according to a volume ratio of 1:16:2, prepare an oxidation solution at 60°C, soak 15 g of a polyethylene diaphragm in 40 g of the oxidation solution for 1 min, then rinse it with deionized water multiple times and dry it to obtain a pretreated polyethylene diaphragm.

[0076] Step 3: Add 15 g of the modified polyacrylate to 40 g of N-methylpyrrolidone, heat to 60°C and stir to dissolve to form a gel solution, then add 3 g of nano-aluminum oxide and 1 g of polyethylene glycol to the gel solution and continue stirring for 2 h to obtain a nano-aluminum oxide gel dispersion;

[0077] Step 4: Coat the nano-aluminum oxide gel dispersion on the pretreated polyethylene diaphragm, with a coating thickness of 2 μm. After coating, volatilize at room temperature in air for 20 h to remove N-methylpyrrolidone, then immerse it in an ethanol aqueous solution with an ethanol mass concentration of 25% and let it stand for 8 h. Finally, the diaphragm is vacuum-dried at 40°C for 2 h to obtain the ceramic-coated diaphragm.

[0078] Comparative Example 3

[0079] A preparation method of a ceramic-coated diaphragm of silsesquioxane, comprising the steps of:

[0080] Step 1, weigh 50 g of octyl acrylate, 0.1 g of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 0.1 g of polyvinyl alcohol and 0.3 g of azobisisobutyronitrile, add 400 parts of toluene to a reaction kettle, introduce nitrogen to displace air, mix and stir evenly, heat up to 70 °C and react for 60 min, distill off toluene, and cool to room temperature to obtain modified polyacrylate.

[0081] Step 2, measure K2Cr2O7, H2SO4, and H2O according to a volume ratio of 1:16:2, prepare an oxidation solution at 60 °C, immerse 15 g of a polyethylene diaphragm in 40 g of the oxidation solution for 1 min, then rinse it with deionized water multiple times and dry it to obtain a pretreated polyethylene diaphragm.

[0082] Step 3, add 15 g of the modified polyacrylate to 40 g of N-methylpyrrolidone, heat up to 60 °C and stir to dissolve to form a gel solution, then add 3 g of nano-aluminum oxide and 1 g of polyethylene glycol to the gel solution and continue to stir for 2 h to obtain a nano-aluminum oxide gel dispersion;

[0083] Step 4, coat the nano-aluminum oxide gel dispersion on the pretreated polyethylene diaphragm, with a coating thickness of 2 μm. After coating, volatilize it at room temperature in air for 20 h to remove N-methylpyrrolidone, then immerse it in an ethanol aqueous solution with an ethanol mass concentration of 25% and let it stand for 8 h. Finally, the diaphragm is vacuum dried at 40 °C for 2 h to obtain the ceramic-coated diaphragm.

[0084] Performance testing

[0085] Perform performance testing on the diaphragms prepared in Examples 1-4 and Comparative Examples 1-3.

[0086] 1: The moisture content of the diaphragm is detected according to GB / T6283-2008;

[0087] 2: Through the battery cell liquid injection test, use a Karl Fischer coulometric titrator to measure the moisture content of the battery cell sample. The test results are shown in Table 1.

[0088] 3: Use a laser particle size analyzer to test the particles of the diaphragm slurry prepared in Example 4. It can be seen from Figure 1 that: the particle size of the coated diaphragm is between 0.5 and 2 microns, with a smaller size, which is more conducive to improving the performance of the battery.

[0089] Table 1 Performance of diaphragms prepared in examples and comparative examples

[0090]

[0091]

[0092] In comparison, in Comparative Example 1, since the polyacrylate was not modified and a pure resin was used, the water content of the product was as high as 1272 ppm; in Comparative Example 2 and Comparative Example 3, the polyacrylate modifications did not add methacryloxypropylcaged polyhedral oligomeric silsesquioxane or 1-vinyl-3-butylimidazolium tetrafluoroborate respectively, and the water content in the separator decreased slightly compared with that of the unmodified one, but the effect was far less than that of Example 1. The cell samples also showed similar effects. It can be seen that the method of the present invention can effectively reduce the water content of the separator.

Claims

1. A preparation method of a ceramic-coated separator of silsesquioxane, characterized in that Including the steps: Step 1: Dissolve the modified polyacrylate in solvent A to form a gel solution, add nano-aluminum oxide and a dispersant to obtain a nano-aluminum oxide gel dispersion; Step 2: Coat the nano-aluminum oxide gel dispersion on a polyethylene separator, volatilize to remove solvent A, immerse it in a non-solvent and let it stand, and obtain the ceramic-coated separator after drying; the non-solvent is an aqueous solution of ethanol; The modified polyacrylate, by weight, includes raw material components: 50-100 parts of acrylate, 0.03-0.5 part of 1-vinyl-3-butylimidazolium tetrafluoroborate, 0.1-2 parts of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 0.1-1 part of polyvinyl alcohol, 0.3-2 parts of a radical initiator; The preparation process of the modified polyacrylate includes: Add 50-100 parts of acrylate, 0.03-0.5 part of 1-vinyl-3-butylimidazolium tetrafluoroborate, 0.1-2 parts of methacryloxypropylcage polyhedral oligomeric silsesquioxane, 0.1-1 part of polyvinyl alcohol, 0.3-2 parts of a radical initiator, and 400-500 parts of solvent B into a reaction kettle, react at 70-80 °C for 60-120 min, and distill to remove solvent B to obtain the modified polyacrylate.

2. The preparation method of the ceramic-coated diaphragm of silsesquioxane according to claim 1, characterized in that, By weight, the feedstock in the preparation process includes: 15-20 parts of modified polyacrylate, 40-60 parts of solvent A, 3-7 parts of nano-aluminum oxide, and 1-4 parts of a dispersant.

3. The preparation method of the ceramic-coated diaphragm of silsesquioxane according to claim 1, characterized in that, The solvent A is N-methylpyrrolidone; the dispersant includes polyethylene glycol; And / or, the coating thickness of the nano-aluminum oxide gel dispersion is 2-4 μm; And / or, the mass concentration of ethanol in the non-solvent is 10-30%; 4. The method for preparing the ceramic-coated diaphragm of silsesquioxane according to claim 1, wherein In Step 1, the temperature for dissolving the modified polyacrylate in solvent A is 60-70 °C; in Step 2, the volatilization is carried out by volatilizing in air at room temperature for 20-40 h; the standing in the non-solvent is carried out by standing at room temperature for 8-12 h; the drying is carried out by vacuum drying at 40-60 °C for 2-4 h.

5. The preparation method of the ceramic-coated diaphragm of silsesquioxane according to claim 1, characterized in that, The polyethylene separator is pretreated, and the pretreatment process includes: S1: Prepare an oxidation solution by mixing K2Cr2O7, H2SO4 and H2O at 60-80 °C; S2: Immerse 15-20 parts of the polyethylene separator in 40-60 parts of the oxidation solution, take it out, wash and dry to obtain a pretreated polyethylene separator.

6. The preparation method of the ceramic-coated diaphragm of the silsesquioxane according to claim 5, characterized in that, The volume ratio of K2Cr2O7, H2SO4 and H2O is 1:(16-20):

2.

7. The preparation method of the ceramic-coated diaphragm of silsesquioxane according to claim 1, characterized in that, The acrylate includes one or more of octyl acrylate, methyl methacrylate, decyl acrylate, butyl acrylate, lauryl acrylate; And / or, the solvent B is any one of toluene, dichloroethane, and xylene; And / or, the radical initiator includes any one or more of azobisisobutyronitrile, benzoyl peroxide, and dimethyl azobisisobutyrate.

8. A ceramic-coated separator of silsesquioxane prepared by the preparation method according to any one of claims 1-7.

9. Application of the ceramic-coated separator of silsesquioxane according to claim 8 in a lithium battery.

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