A ceramic coating diaphragm with high thermal stability and its preparation method and application

Abstract

The application relates to the technical field of lithium battery diaphragm, and discloses a ceramic coating diaphragm with high thermal stability and a preparation method and application thereof. A polyethylene diaphragm is coated with high-thermal-stability slurry, and the ceramic coating diaphragm is obtained after drying after volatilization of a solvent; the high-thermal-stability slurry comprises raw material components according to mass parts: 1-4 parts of modified poly(4-styrene sulfonic acid) lithium salt, 5-15 parts of polyacrylate, 20-30 parts of mercapto silane modified nano alumina, 60-80 parts of nano alumina, 0.005-0.03 parts of 1-vinyl-2-butylimidazole tetrafluoroborate, 0.5-3 parts of sodium ethoxide and 50-100 parts of solvent A. The slurry with high thermal stability is prepared by combining mercapto silane modified nano alumina, propylene modified adhesive and fluorine-containing ionic liquid, the problem of diaphragm shrinkage caused by high temperature is effectively improved, the coating layer is prevented from falling off, and the performance of lithium ion batteries applied to the diaphragm is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, specifically to a ceramic-coated separator with high thermal stability, its preparation method, and its application. Background Technology

[0002] Polyethylene (PE) was initially used as the primary material for lithium-ion battery separators due to its high strength, resistance to solvent corrosion, and low cost. Although research has focused on using other materials to prepare lithium-ion battery separators in recent years, most separators currently used in batteries are still polyethylene microporous films. Since the separator may shrink or soften when the battery's internal temperature rises, this occurs when the battery is in an abnormal operating state or when the external temperature exceeds 120°C. Such conditions can directly lead to internal short circuits, potentially causing fires or explosions. Therefore, improving the thermal stability of the separator can effectively improve the safety performance of lithium-ion batteries.

[0003] CN109411682A discloses a lithium battery separator with high thermal stability and its preparation method. The separator is composed of a polyimide core-porous membrane, a ceramic layer, and an electrospun nanofiber layer. The polyimide, which has high heat resistance and high insulation, serves as the base membrane. The ceramic layer and the electrospun nanofiber layer are sequentially coated on top of the base membrane. The porous alumina in the ceramic layer has good thermal conductivity, which can effectively conduct heat from the separator, avoiding short circuits caused by excessive local thermal shrinkage. The electrospun nanofiber layer not only improves the pore size uniformity of the separator surface and enhances the thermal stability of the lithium battery separator, but also tightly bonds with the ceramic layer, preventing the porous alumina in the ceramic layer from falling off. The prepared lithium battery separator exhibits good thermal stability and excellent thermal conductivity.

[0004] However, using high-melting-point polymers, such as cellulose membranes, polyimide membranes, and aramid membranes, to prepare new lithium-ion battery separators through electrospinning or phase inversion techniques to improve the high-temperature resistance of the separators has drawbacks such as complex film-forming processes, immature technology, and high prices.

[0005] CN108735953A discloses a SiO2 PS core-shell structure ceramic diaphragm coating, which, through the... Monodisperse nano-SiO2 particles prepared by this method are in-situ grafted with γ-methacryloxypropyltrimethoxysilane (MPS) for modification. The modified SiO2 particles are then coated with a mixture of polyvinylpyrrolidone ethanol solution and styrene-azobisisobutyronitrile (AIBN) to form a stable core-shell structure. This structure can be uniformly dispersed in the coating slurry system without excessive aggregation, resulting in a membrane with excellent overall mechanical properties. The membrane maintains a stable morphology at high temperatures, effectively preventing thermal shrinkage. Furthermore, the SiO2 particles in the core layer, coated with a glassy polymer, do not detach from the ceramic powder or clog the membrane pores, thus improving the heat resistance and stability of the lithium-ion battery membrane and enhancing the safety of the lithium-ion battery. However, the preparation process is complex and difficult to scale up for industrial production. Summary of the Invention

[0006] This invention addresses the problem of insufficient thermal stability in lithium-ion battery separators by providing a method for preparing a ceramic-coated separator with high thermal stability. The method combines mercaptosilane-modified nano-alumina, fluorine-containing ionic liquid, and modified binder to improve the thermal stability of the separator. When applied to lithium-ion batteries, this method can extend battery life and improve battery safety performance.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A ceramic-coated diaphragm with high thermal stability is obtained by coating a polyethylene diaphragm with a high thermal stability slurry, evaporating the solvent, and then drying.

[0009] The high thermal stability slurry comprises the following raw material components by weight: 1-4 parts modified poly(4-styrenesulfonic acid) lithium salt, 5-15 parts polyacrylate, 20-30 parts mercaptosilane modified nano alumina, 60-80 parts nano alumina, 0.005-0.03 parts 1-vinyl-2-butylimidazolium tetrafluoroborate, 0.5-3 parts sodium ethoxide, and 50-100 parts solvent A;

[0010] The preparation process of the modified poly(4-styrenesulfonic acid) lithium salt includes: dissolving the poly(4-styrenesulfonic acid) lithium salt in solvent B, adding aluminum trichloride as a catalyst, and adding acryloyl chloride dropwise under stirring to obtain the modified poly(4-styrenesulfonic acid) lithium salt.

[0011] The preparation process of the mercaptosilane-modified nano-alumina includes: mixing mercaptosilane and nano-alumina in water and stirring, filtering and drying the product to obtain mercaptosilane-modified nano-alumina.

[0012] In the preparation of the modified poly(4-styrenesulfonic acid) lithium salt, the mass ratio of poly(4-styrenesulfonic acid) lithium salt to acryloyl chloride is 20-30:15-19; the mass ratio of aluminum trichloride to poly(4-styrenesulfonic acid) lithium salt is 2-5:20-30.

[0013] The mass ratio of mercaptosilane to nano-alumina in the preparation process of mercaptosilane-modified nano-alumina is 3-6:200-300.

[0014] The reaction conditions during the preparation of the modified poly(4-styrenesulfonic acid) lithium salt are -20 to 0°C and the reaction time is 50 to 100 min.

[0015] The mixing and stirring process for preparing the mercaptosilane-modified nano-alumina is carried out at 20-30℃ for 2-4 hours.

[0016] Solvent A includes one or more of water, N,N-dimethylacetamide, ethanol, methanol, n-butanol, isobutanol, and tert-butanol;

[0017] Solvent B includes one or more of N,N-dimethylacetamide, ethanol, methanol, n-butanol, isobutanol, and tert-butanol.

[0018] Preferably, solvent A is a mixed solvent of water and N,N-dimethylacetamide, wherein the volume ratio of water to N,N-dimethylacetamide is 3-10:90-97.

[0019] The mercaptosilane includes one or more of mercaptopropyl dimethoxymethylsilane, mercaptomethyl dimethoxymethylsilane, and mercaptoethyl dimethoxymethylsilane; the mercaptosilane contains mercapto groups, and reacts with nano-alumina to introduce a mercapto structure on the surface of the alumina. Subsequently, it undergoes a mercapto-olefin Michael addition reaction with a poly(4-styrenesulfonic acid) lithium salt containing propylene groups to form a mercapto-propylene adduct, thereby improving the thermal stability of the membrane.

[0020] The polyacrylic acid includes one or more of polymethyl acrylate, polyethyl acrylate, and polyisopropyl acrylate.

[0021] Preferably, the particle size of the nano-alumina is 10. -5 -10 -1 Micron-sized and nano-sized alumina have a higher specific surface area, more pores and channels, which can effectively improve the liquid retention capacity of the diaphragm, thereby further improving the thermal stability of the diaphragm.

[0022] Preferably, the polyethylene diaphragm is a pre-oxidized polyethylene diaphragm, and the preparation process includes: immersing the polyethylene diaphragm in an oxidation solution prepared by K2Cr2O7, H2SO4 and H2O, and then taking it out, cleaning and drying it to obtain the pre-oxidized polyethylene diaphragm; the pre-oxidized polyethylene diaphragm is more conducive to the adhesion of the coating layer, making the coating layer and the polyethylene diaphragm bond more tightly.

[0023] The volume ratio of K2Cr2O7, H2SO4 and H2O is 1:16-20:2; the soaking time is 1-5 min.

[0024] The present invention also provides a method for preparing the high thermal stability ceramic-coated diaphragm, comprising the steps of:

[0025] Step 1: Dissolve lithium poly(4-styrenesulfonic acid) in solvent B, add aluminum trichloride to it, and add acryloyl chloride dropwise under stirring to prepare modified lithium poly(4-styrenesulfonic acid).

[0026] Step 2: Mix and stir mercaptosilane and nano-alumina in water, filter and dry the product to obtain mercaptosilane-modified nano-alumina;

[0027] Step 3: Modified poly(4-styrenesulfonic acid) lithium salt, polyacrylate, mercaptosilane modified nano-alumina, nano-alumina, 1-vinyl-2-butylimidazolium tetrafluoroborate and sodium ethoxide are mixed and dispersed in solvent A to obtain a high thermal stability slurry.

[0028] Step 4: Coat both sides of the polyethylene diaphragm with a high thermal stability slurry, evaporate the solvent, and then dry to obtain the ceramic-coated diaphragm.

[0029] In step 3, the mixture is dispersed and then ball-milled at 30-40℃ for 20-50 minutes;

[0030] In step 4, the coating thickness of the high thermal stability slurry is 2-4 μm; the volatile solvent evaporates in air at room temperature for 10-20 min, and the drying is carried out under vacuum at 60-80℃ for 24-30 h.

[0031] This invention employs mercaptosilane-modified nano-alumina, reacting acryloyl chloride with lithium poly(4-styrenesulfonic acid) salt, followed by a mercapto addition reaction. The resulting coating exhibits higher stability in its tetrafluoroborate groups, silane groups, and styrenesulfonic acid structure. The synergistic effect of these three components enhances the membrane's thermal stability. Furthermore, the ultra-large specific surface area and interparticle porosity and channels of the nano-alumina particles improve the membrane's electrolyte retention capacity, further enhancing the thermal stability of the polyethylene membrane.

[0032] This invention also provides the application of the high thermal stability ceramic-coated separator in lithium batteries. The ceramic-coated separator of this invention exhibits improved thermal stability and enhanced hydrophobicity. The mixed particles have a high specific surface area, resulting in a high electrolyte absorption rate, reducing the possibility of overheating, short circuits, and other hazards in lithium-ion batteries, thus improving the safety performance of lithium-ion batteries. The compactly packed nanoparticles also provide better thermal shrinkage performance, i.e., less thermal shrinkage, effectively reducing the adverse consequences caused by thermal shrinkage of the separator.

[0033] On the other hand, although the coating cannot prevent the porous polyolefin membrane from melting at high temperatures, it can still self-support itself as a separate layer after the porous polyolefin melts, thus preventing physical contact between the positive and negative electrodes. The coating has good heat shrinkage resistance and has little impact on ion permeability and the stability of the coating film in the battery, thereby improving the safety performance of lithium-ion batteries.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) This invention combines mercaptosilane-modified nano-alumina, propylene-modified adhesive and fluorine-containing ionic liquid to prepare a slurry with high thermal stability. When coated on the surface of polyethylene separator, it effectively improves the problem of separator shrinkage due to high temperature, avoids coating peeling, improves the cycle life of lithium-ion battery, and extends the service life of lithium-ion battery; reduces the internal resistance of lithium-ion battery and improves battery discharge efficiency.

[0036] (2) In this invention, nano-alumina is used. Its high specific surface area and porosity are utilized to improve the liquid retention capacity of the separator, thereby improving the thermal stability of the separator and reducing the possibility of overheating, short circuit and other dangers in lithium-ion batteries, thus improving the safety performance of lithium-ion batteries.

[0037] (3) The ceramic-coated diaphragm in this invention has the advantages of low air permeability, low moisture content, and high thermal stability. Attached Figure Description

[0038] Figure 1 The image shows a scanning electron microscope (SEM) image of the highly stable ceramic coating prepared in Example 1.

[0039] Figure 2 The thermal shrinkage of the diaphragms of Example 4 and Comparative Example 3 after baking at 130°C for 0.5 h is shown in (a) for Example 4 and (b) for Comparative Example 3. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0041] The raw materials used in the following specific embodiments were all purchased from the market: nano alumina CAS: 1344-28-1, average particle size 0.5-0.8um; 1-vinyl-3-butylimidazolium tetrafluoroborate CAS No. 1033461-44-7.

[0042] Example 1

[0043] The preparation of a ceramic-coated diaphragm with high thermal stability includes the following steps:

[0044] Step 1: Add 20g of lithium poly(4-styrenesulfonic acid) salt to 100g of N,N-dimethylacetamide, stir and mix evenly, then add 2g of aluminum trichloride, and then add 15g of acryloyl chloride under nitrogen protection. Stir and react at -20℃ for 50 minutes, filter, and obtain modified lithium poly(4-styrenesulfonic acid) salt.

[0045] Step 2: Weigh 3g of mercaptopropyl dimethoxymethylsilane and 200g of nano-Al2O3, add them to 1000g of water, and stir at 20℃ for 2h; filter the product, dry it, and obtain mercaptosilane modified nano-Al2O3.

[0046] Step 3: Measure out K2Cr2O7, H2SO4 and H2O in a volume ratio of 1:16:2 and prepare an oxidation solution at 60℃; immerse 15g of polyethylene membrane in 40g of oxidation solution for 1min, then rinse it several times with deionized water and dry it to obtain a pre-oxidized polyethylene membrane.

[0047] Step 4: Weigh 1g of the modified poly(4-styrenesulfonic acid) lithium salt prepared in Step 1 as a binder, 5g of polymethyl methacrylate, 20g of the mercaptosilane-modified nano-Al2O3 prepared in Step 2, 60g of nano-Al2O3, 0.005g of 1-vinyl-3-butylimidazolium tetrafluoroborate, and 0.5g of sodium ethoxide. Add these to a mixed solvent of 50g water / N,N-dimethylacetamide with a volume ratio of 5:95. Ball mill and disperse the mixture at 30°C for 20 minutes to obtain a slurry.

[0048] Step 5: Apply the slurry to both sides of the pretreated polyethylene membrane, controlling the thickness to 2 μm. Dry at room temperature for 10 min to evaporate the solvent, then vacuum dry at 60℃ for 10 h to obtain a ceramic-coated membrane with high thermal stability. The microstructure of the membrane is as follows: Figure 1As shown.

[0049] Example 2

[0050] The preparation of a ceramic-coated diaphragm with high thermal stability includes the following steps:

[0051] Step 1: Add 24g of lithium poly(4-styrenesulfonic acid) salt to 130g of ethanol, stir and mix evenly, then add 3g of aluminum trichloride, and then add 16g of acryloyl chloride under nitrogen protection. Stir and react at -15℃ for 60 minutes, filter, and obtain modified lithium poly(4-styrenesulfonic acid) salt.

[0052] Step 2: Weigh 4g of mercaptopropyl dimethoxymethylsilane and 240g of nano-Al2O3, add them to 1200g of ethanol, and stir at 25°C for 3h. Filter the product and dry it to obtain mercaptosilane-modified nano-Al2O3.

[0053] Step 3: Measure K2Cr2O7, H2SO4 and H2O in a volume ratio of 1:17:2 and prepare an oxidation solution at 65℃; immerse 16g of polyethylene membrane in 45g of oxidation solution for 2min, then rinse repeatedly with deionized water and dry to obtain a pre-oxidized polyethylene membrane.

[0054] Step 4: Weigh 2g of the modified poly(4-styrenesulfonic acid) lithium salt prepared in Step 1 as a binder, 8g of polyethyl acrylate, 30g of mercaptosilane-modified nano-Al2O3 from Step 2, 67g of nano-Al2O3, 0.01g of 1-vinyl-3-butylimidazolium tetrafluoroborate, and 1g of sodium ethoxide. Add these to a mixed solvent of 60g water / N,N-dimethylacetamide with a volume ratio of 5:95, and ball mill and disperse at 35°C for 30 minutes to obtain a slurry.

[0055] Step 5: Apply the slurry to both sides of the pretreated polyethylene membrane with a thickness of 3 μm, dry at room temperature for 15 min to evaporate the solvent, and then vacuum dry at 65 °C for 16 h to obtain a ceramic-coated membrane with high thermal stability.

[0056] Example 3

[0057] The preparation of a ceramic-coated diaphragm with high thermal stability includes the following steps:

[0058] Step 1: Add 28g of lithium poly(4-styrenesulfonic acid) salt to 160g of n-butanol, stir and mix evenly, then add 4g of aluminum trichloride, and then add 18g of acryloyl chloride under nitrogen protection. Stir and react at -10℃ for 80 minutes, filter, and obtain modified lithium poly(4-styrenesulfonic acid) salt.

[0059] Step 2: Weigh 5g of mercaptopropyl dimethoxymethylsilane and 280g of nano-Al2O3, add them to 1400g of ethanol, and stir at 25°C for 3h. Filter the product and dry it to obtain mercaptosilane-modified nano-Al2O3.

[0060] Step 3: Measure K2Cr2O7, H2SO4 and H2O in a volume ratio of 1:19:2 and prepare an oxidation solution at 75℃; immerse 19g of polyethylene membrane in 55g of oxidation solution for 4min, then rinse repeatedly with deionized water and dry to obtain a pre-oxidized polyethylene membrane.

[0061] Step 4: Weigh 3g of the modified poly(4-styrenesulfonic acid) lithium salt prepared in Step 1 as a binder, 12g of polyethyl acrylate, 35g of the mercaptosilane-modified nano-Al2O3 from Step 2, 70g of nano-Al2O3, 0.02g of 1-vinyl-3-butylimidazolium tetrafluoroborate, and 2g of sodium ethoxide. Add these to a mixed solvent of 80g water / N,N-dimethylacetamide with a volume ratio of 5:95, and ball mill and disperse at 35°C for 25 minutes to obtain a slurry.

[0062] Step 5: Apply the slurry to both sides of the pretreated polyethylene membrane with a thickness of 3 μm, dry at room temperature for 15 min to evaporate the solvent, and then vacuum dry at 75 °C for 18 h to obtain a ceramic-coated membrane with high thermal stability.

[0063] Example 4

[0064] The preparation of a ceramic-coated diaphragm with high thermal stability includes the following steps:

[0065] Step 1: Add 30g of lithium poly(4-styrenesulfonic acid) salt to 180g of N,N-dimethylacetamide, stir and mix evenly, then add 5g of aluminum trichloride, and then add 19g of acryloyl chloride under nitrogen protection. Stir and react at 0℃ for 100 minutes, filter, and obtain modified lithium poly(4-styrenesulfonic acid) salt.

[0066] Step 2: Weigh 6g of mercaptopropyl dimethoxymethylsilane and 300g of nano-Al2O3, add them to 1600g of tert-butanol, and stir at 30°C for 4 hours; filter the product, dry it, and obtain mercaptosilane-modified nano-Al2O3.

[0067] Step 3: Measure K2Cr2O7, H2SO4 and H2O in a volume ratio of 1:20:2 and prepare an oxidation solution at 80℃; immerse 20g of polyethylene membrane in 60g of oxidation solution for 5min, then rinse repeatedly with deionized water and dry to obtain a pre-oxidized polyethylene membrane.

[0068] Step 4: Weigh 4g of the modified poly(4-styrenesulfonic acid) lithium salt prepared in Step 1 as a binder, 15g of polyisopropyl acrylate, 40g of mercaptosilane-modified nano-Al2O3 from Step 2, 80g of nano-Al2O3, 0.03g of 1-vinyl-3-butylimidazolium tetrafluoroborate, and 3g of sodium ethoxide. Add these to a mixed solvent of 100g water / N,N-dimethylacetamide with a volume ratio of 5:95, and ball mill and disperse at 40°C for 30 minutes to obtain a slurry.

[0069] Step 5: Apply the slurry to both sides of the pretreated polyethylene membrane with a thickness of 4 μm, dry at room temperature for 20 min to evaporate the solvent, and then vacuum dry at 80 °C for 24 h to obtain a ceramic-coated membrane with high thermal stability.

[0070] Comparative Example 1: Unmodified alumina

[0071] The preparation of a ceramic-coated diaphragm with high thermal stability includes the following steps:

[0072] Step 1: Add 20g of lithium poly(4-styrenesulfonic acid) salt to 100g of N,N-dimethylacetamide, stir and mix evenly, then add 2g of aluminum trichloride, and then add 15g of acryloyl chloride under nitrogen protection. Stir and react at -20℃ for 50 minutes, filter, and obtain modified lithium poly(4-styrenesulfonic acid) salt.

[0073] Step 2: Measure out K2Cr2O7, H2SO4 and H2O in a volume ratio of 1:16:2 and prepare an oxidation solution at 60℃; immerse 15g of polyethylene membrane in 40g of oxidation solution for 1min, then rinse it several times with deionized water and dry it to obtain a pre-oxidized polyethylene membrane.

[0074] Step 3: Weigh 1g of the modified poly(4-styrenesulfonic acid) lithium salt prepared in Step 1 as a binder, 5g of polymethyl acrylate, 80g of nano-Al2O3, 0.005g of 1-vinyl-3-butylimidazolium tetrafluoroborate, and 0.5g of sodium ethoxide. Add these to a mixed solvent of 50g water / N,N-dimethylacetamide with a volume ratio of 5:95. Ball mill and disperse the mixture at 30°C for 20 minutes to obtain a slurry.

[0075] Step 4: Apply the slurry to both sides of the pretreated polyethylene membrane with a thickness of 2 μm, dry at room temperature for 10 min to evaporate the solvent, and then vacuum dry at 60 °C for 10 h to obtain a ceramic-coated membrane with high thermal stability.

[0076] Comparative Example 2: Unmodified Adhesive

[0077] The preparation of a ceramic-coated diaphragm with high thermal stability includes the following steps:

[0078] Step 1: Weigh 3g of mercaptopropyl dimethoxymethylsilane and 200g of nano-Al2O3, add them to 1000g of water, and stir at 20℃ for 2h. Filter the product and dry it to obtain mercaptosilane-modified nano-Al2O3.

[0079] Step 2: Measure out K2Cr2O7, H2SO4 and H2O in a volume ratio of 1:16:2 and prepare an oxidation solution at 60℃; immerse 15g of polyethylene membrane in 40g of oxidation solution for 1min, then rinse it several times with deionized water and dry it to obtain a pre-oxidized polyethylene membrane.

[0080] Step 3: Weigh 1g of lithium poly(4-styrenesulfonic acid) salt as binder, 5g of polymethyl methacrylate, 20g of mercaptosilane-modified nano-Al2O3 from Step 1, 60g of nano-Al2O3, 0.005g of 1-vinyl-3-butylimidazolium tetrafluoroborate, and 0.5g of sodium ethoxide. Add these to a mixed solvent of 50g water / N,N-dimethylacetamide with a volume ratio of 5:95. Ball mill and disperse the mixture at 30°C for 20 minutes to obtain a slurry.

[0081] Step 4: Apply the slurry to both sides of the pretreated polyethylene membrane with a thickness of 2 μm, dry at room temperature for 10 min to evaporate the solvent, and then vacuum dry at 60 °C for 10 h to obtain a ceramic-coated membrane with high thermal stability.

[0082] Comparative Example 3: Neither the adhesive nor the alumina was modified.

[0083] The preparation of a ceramic-coated diaphragm with high thermal stability includes the following steps:

[0084] Step 1: Measure out K2Cr2O7, H2SO4 and H2O in a volume ratio of 1:16:2 and prepare an oxidation solution at 60℃; immerse 15g of polyethylene membrane in 40g of oxidation solution for 1min, then rinse it several times with deionized water and dry it to obtain a pre-oxidized polyethylene membrane.

[0085] Step 2: Weigh 1g of lithium poly(4-styrenesulfonic acid) salt as binder, 5g of polymethyl methacrylate, 80g of nano Al2O3, 0.005g of 1-vinyl-3-butylimidazolium tetrafluoroborate, and 0.5g of sodium ethoxide. Add these to a mixed solvent of 50g water / N,N-dimethylacetamide with a volume ratio of 5:95. Ball mill and disperse the mixture at 30°C for 20 minutes to obtain a slurry.

[0086] Step 3: Apply the slurry to both sides of the pretreated polyethylene membrane with a thickness of 2 μm, dry at room temperature for 10 min to evaporate the solvent, and then vacuum dry at 60℃ for 10 h to obtain a ceramic-coated membrane with high thermal stability.

[0087] Performance testing

[0088] The diaphragms prepared in the examples and comparative examples were subjected to automatic air permeability, moisture content, and thermal stability tests. Automatic air permeability was tested according to GB / T 458-2008, moisture content was tested according to GB / T6283-2008, and the thermal shrinkage rate of the diaphragms was tested according to GB / T 36363—2018. Specifically:

[0089] 1. Use a craft knife to cut a 12cm*12cm square diaphragm, ensuring that the cut area is wrinkle-free;

[0090] 2. Use a ruler to measure the length of the central part of the square area in the longitudinal (MD) and transverse (TD) directions by 10cm respectively. Draw the measurement lines with a black pen and mark the measured dimensions. Take 3 samples.

[0091] 3. Open the oven, set the baking temperature, and after the temperature has risen, place the measured diaphragm on 10 sheets of A4 paper for baking, 5 sheets on the top and 5 sheets on the bottom.

[0092] 4. After baking, remove the A4 paper. When the temperature drops to around room temperature, remove the diaphragm and test the lengths of MD and TD after baking, which is C0. When testing, select the marked position before baking for measurement. If the diaphragm curls at high temperature, you need to manually smooth the curled part of the diaphragm first and test the size after smoothing, which is C1.

[0093] 5. Calculate the thermal shrinkage rate of the diaphragm = 100% * (C0 - C1) / C0.

[0094] As can be seen from Table 1, compared with the completely unmodified slurry in Comparative Example 1, the water content of the membranes prepared in Examples 1-4 was greatly reduced, and the thermal shrinkage rate was also greatly reduced, with the best longitudinal shrinkage being only 1.51% and the best transverse shrinkage being only 0.52%, showing significant improvement.

[0095] The thermal shrinkage of the diaphragms in Example 4 and Comparative Example 3 after baking at 130°C for 0.5 hours is as follows: Figure 2 As shown in the figure, (a) is Example 4 and (b) is Comparative Example 3. It can be clearly seen from the figure that the sample of Example 4 is smooth with few wrinkles, while the diaphragm of Comparative Example 3 has many wrinkles. It can be seen that the modified slurry can significantly and effectively improve the thermal stability of the diaphragm and reduce the thermal shrinkage rate of the diaphragm.

[0096] Table 1. Performance of the membranes prepared in the examples and comparative examples.

[0097]

Claims

1. A ceramic-coated diaphragm with high thermal stability, characterized in that, A ceramic-coated diaphragm is obtained by coating a polyethylene diaphragm with a high thermal stability slurry, followed by solvent evaporation and drying. The high thermal stability slurry comprises the following raw material components by weight: 1-4 parts modified poly(4-styrenesulfonic acid) lithium salt, 5-15 parts polyacrylate, 20-30 parts mercaptosilane modified nano alumina, 60-80 parts nano alumina, 0.005-0.03 parts 1-vinyl-3-butylimidazolium tetrafluoroborate, 0.5-3 parts sodium ethoxide, and 50-100 parts solvent A; The preparation process of the modified poly(4-styrenesulfonic acid) lithium salt includes: dissolving the poly(4-styrenesulfonic acid) lithium salt in solvent B, adding aluminum trichloride to it, and adding acryloyl chloride dropwise under stirring to obtain the modified poly(4-styrenesulfonic acid) lithium salt. The preparation process of the mercaptosilane-modified nano-alumina includes: mixing and stirring mercaptosilane and nano-alumina in water, filtering and drying the product to obtain mercaptosilane-modified nano-alumina; In the preparation of the modified poly(4-styrenesulfonic acid) lithium salt, the mass ratio of poly(4-styrenesulfonic acid) lithium salt to acryloyl chloride is (20-30):(15-19); the mass ratio of aluminum trichloride to poly(4-styrenesulfonic acid) lithium salt is (2-5):(20-30). The mass ratio of mercaptosilane to nano-alumina in the preparation process of mercaptosilane modified nano-alumina is (3-6):(200-300). Solvent A includes one or more of water, N,N-dimethylacetamide, ethanol, methanol, n-butanol, isobutanol, and tert-butanol; Solvent B includes one or more of N,N-dimethylacetamide, ethanol, methanol, n-butanol, isobutanol, and tert-butanol.

2. The high thermal stability ceramic-coated diaphragm according to claim 1, characterized in that, The reaction conditions during the preparation of the modified poly(4-styrenesulfonic acid) lithium salt are -20 to 0°C and the reaction time is 50 to 100 min. And / or, the mixing and stirring during the preparation of the mercaptosilane-modified nano-alumina is carried out at 20-30℃ for 2-4 hours.

3. The high thermal stability ceramic-coated diaphragm according to claim 1, characterized in that, Solvent A is a mixed solvent of water and N,N-dimethylacetamide, wherein the volume ratio of water to N,N-dimethylacetamide is (3-10):90-97.

4. The high thermal stability ceramic-coated diaphragm according to claim 1, characterized in that, The mercaptosilane includes one or more of mercaptopropyl dimethoxymethylsilane, mercaptomethyl dimethoxymethylsilane, and mercaptoethyl dimethoxymethylsilane; And / or, the polyacrylate includes one or more of polymethyl acrylate, polyethyl acrylate, and polyisopropyl acrylate.

5. The high thermal stability ceramic-coated diaphragm according to claim 1, characterized in that, The polyethylene diaphragm is a pre-oxidized polyethylene diaphragm, and the preparation process includes: immersing the polyethylene diaphragm in an oxidation solution prepared with K2Cr2O7, H2SO4 and H2O, and then taking it out, washing and drying it to obtain the pre-oxidized polyethylene diaphragm; the immersion time is 1-5 minutes.

6. The method for preparing a ceramic-coated diaphragm with high thermal stability according to any one of claims 1-5, characterized in that, Including the following steps: Step 1: Dissolve lithium poly(4-styrenesulfonic acid) in solvent B, add aluminum trichloride to it, and add acryloyl chloride dropwise under stirring to prepare modified lithium poly(4-styrenesulfonic acid). Step 2: Mix and stir mercaptosilane and nano-alumina in water, filter and dry the product to obtain mercaptosilane-modified nano-alumina; Step 3: Modified poly(4-styrenesulfonic acid) lithium salt, polyacrylate, mercaptosilane modified nano alumina, nano alumina, 1-vinyl-3-butylimidazolium tetrafluoroborate and sodium ethoxide are mixed and dispersed in solvent A to obtain a high thermal stability slurry. Step 4: Coat both sides of the polyethylene diaphragm with a high thermal stability slurry, evaporate the solvent, and then dry to obtain the ceramic-coated diaphragm.

7. The method for preparing a ceramic-coated diaphragm with high thermal stability according to claim 6, characterized in that, In step 3, the mixture is dispersed by ball milling at 30-40℃ for 20-50 min; in step 4, the high thermal stability slurry coating thickness is 2-4 μm; the volatile solvent is evaporated in air at room temperature for 10-20 min, and the drying is vacuum drying at 60-80℃ for 24-30 h.

8. The application of the high thermal stability ceramic-coated separator according to any one of claims 1-5 in lithium batteries.

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