Coating diaphragm and preparation method thereof

Abstract

The invention discloses a coating diaphragm and a preparation method thereof, the coating diaphragm comprises a base film, a first coating and a second coating, the first coating and the second coating are respectively located on two sides of the base film; the first coating comprises sodium carboxymethyl cellulose, a metal organic framework, a modified solid electrolyte and a first pressure-sensitive adhesive, and the modified solid electrolyte is obtained by modifying a solid electrolyte with silicon resin; and the second coating comprises sodium carboxymethyl cellulose, a polyvinylidene fluoride-hexafluoropropylene copolymer, an emulsion type binder and a second pressure-sensitive binder. The solid electrolyte has a rigid framework to provide a rapid conduction channel, and the metal organic framework has a high specific surface area and can cooperate with the solid electrolyte to construct a three-dimensional network, so that the stable performance of the coating diaphragm is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, and specifically relates to a coated separator and its preparation method. Background Technology

[0002] With the booming development of the new energy industry, the demand for lithium-ion batteries in fields such as electric vehicles and energy storage systems is increasing. These applications require batteries to have higher energy density, better cycle performance, and higher safety. As a key component of the battery, the performance of the separator also needs to be improved accordingly to meet the overall battery performance requirements.

[0003] Solid electrolytes possess excellent electrical conductivity, but their heat resistance is typically poor, impacting battery safety. Improving the heat resistance of solid electrolytes through modifications such as incorporating heat-resistant components and controlling microstructure, and then using them as coating materials, can significantly enhance the heat resistance of the separator, reduce its shrinkage rate at high temperatures, and decrease the risk of short circuits caused by separator thermal deformation, effectively improving battery thermal stability and safety. However, existing solid electrolyte coatings still have core performance limitations: they struggle to simultaneously meet multiple performance requirements such as heat resistance, conductivity, and adhesion, and their electrolyte adsorption capacity is also insufficient. Therefore, there is an urgent need to develop a coated separator that combines high lithium-ion migration rate, efficient electrolyte adsorption capacity, and high-temperature structural stability to meet the demands for high energy density and high safety in batteries. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a coated diaphragm.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned coated diaphragm.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] A coated membrane includes: a base membrane, a first coating, and a second coating, wherein the first coating and the second coating are respectively located on two sides of the base membrane;

[0008] The first coating comprises: sodium carboxymethyl cellulose, metal-organic framework (MOF), modified solid electrolyte, and a first pressure-sensitive adhesive. The modified solid electrolyte is obtained by modifying a solid electrolyte with a silicone resin, wherein the silicone resin is methylphenyl silicone resin. The first pressure-sensitive adhesive is one or a mixture of several of the following: vinyl acetate emulsion pressure-sensitive adhesive, natural rubber emulsion pressure-sensitive adhesive, acrylate emulsion pressure-sensitive adhesive, and water-dispersible polyurethane pressure-sensitive adhesive.

[0009] The second coating comprises: sodium carboxymethyl cellulose, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), an emulsion adhesive, and a second pressure-sensitive adhesive. The emulsion adhesive is polymethyl methacrylate, and the second pressure-sensitive adhesive is one or a mixture of several of the following: vinyl acetate emulsion pressure-sensitive adhesive, natural rubber emulsion pressure-sensitive adhesive, acrylate emulsion pressure-sensitive adhesive, and water-dispersible polyurethane pressure-sensitive adhesive.

[0010] In the above technical solution, the method for preparing modified solid electrolyte includes: mixing solid electrolyte (particle size: D50=300~800nm), milling solvent and polymeric dispersant to obtain a mixture; subjecting the mixture to high-speed milling (speed: 500~1500rpm) to obtain a nano-dispersion (the particle size of the solid electrolyte in the nano-dispersion is: D50=250~780nm); adding silicone resin to the nano-dispersion and subjecting it to low-speed milling (speed: 500~1000rpm) to coat the surface of the solid electrolyte with silicone resin; and spray drying to obtain modified solid electrolyte (powder), wherein the mass of silicone resin is 0.1~5wt% of the solid electrolyte; and in the mixture, the ratio of solid electrolyte, milling solvent and polymeric dispersant by mass is (10~60):(38~89.9):(0.1~2).

[0011] In the method for preparing modified solid electrolytes, the inlet temperature of spray drying is 130~210℃, and the feed rate is 5~500kg / h.

[0012] In the method for preparing modified solid electrolytes, the milling solvent is one or a mixture of several of N-methylpyrrolidone, methanol, ethanol, isopropanol, n-butanol, acetone, dimethylacetamide (DMAC), p-xylene, and mixed xylenes.

[0013] In the method for preparing modified solid electrolytes, the polymeric dispersant includes one or more of ammonium polyacrylate, sodium polyacrylate, and polyvinylpyrrolidone.

[0014] In the above technical solution, the first coating is obtained by coating with a first slurry, which includes: first water, first dispersant, metal-organic framework (MOF), modified solid electrolyte, first pressure-sensitive binder, and wetting agent. The ratio of first water, first dispersant, metal-organic framework (MOF), modified solid electrolyte, first pressure-sensitive binder, and wetting agent by mass parts is (23~28):(0.3~0.6):(21~24):(5.3~7.8):(3~5):(0.015~0.030). Preferably, the ratio is (27~28):(0.3~0.35):(21~22):(5.3~5.8):(3~5):(0.015~0.030).

[0015] In the above technical solution, the second coating is obtained by coating with a second slurry, which includes: second water, second dispersant, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), emulsion binder and second pressure-sensitive binder. By mass parts, the ratio of second water, second dispersant, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), emulsion binder and second pressure-sensitive binder is (20~30):(0.3~0.5):(10~15):(7~10):(3~5).

[0016] In the above technical solution, the solid electrolyte is at least one of NASICON-type solid electrolyte and garnet-type solid electrolyte.

[0017] In the above technical solutions, the NASICON-type solid electrolyte is lithium titanium phosphate (LiTi2(PO4)3), lithium germanium phosphate (LiGe2(PO4)3), lithium zirconium phosphate (LiZr2(PO4)3), or sodium zirconium silicate phosphate (Na3Zr2Si2PO4). 12 ) and lithium titanium aluminum phosphate (Li 1.3 Al 0.3 Ti 1.7 One or a mixture of several of (PO4)3, preferably lithium aluminum titanium phosphate.

[0018] In the above technical solution, the garnet-type solid electrolyte is lithium lanthanum zirconium oxide (Li7La3Zr2O). 12 One or a mixture of several of lithium lanthanum zirconium oxide and its doped derivatives, preferably lithium lanthanum zirconium oxide.

[0019] In the above technical solution, the metal-organic framework (MOF) is ZIF-8.

[0020] In the above technical solution, the first dispersant and the second dispersant are the same, both being sodium carboxymethyl cellulose aqueous solution, and the content of sodium carboxymethyl cellulose in the sodium carboxymethyl cellulose aqueous solution is 5 wt%.

[0021] In the above technical solution, the first pressure-sensitive adhesive is preferably an acrylic emulsion pressure-sensitive adhesive.

[0022] In the above technical solution, the second pressure-sensitive adhesive is preferably an acrylic emulsion pressure-sensitive adhesive.

[0023] In the above technical solution, the thickness of the base film is 4.5~5.5μm, the thickness of the first coating is 1~5μm, and the thickness of the second coating is 1~5μm.

[0024] In the above technical solution, the base film, the first coating, and the second coating have the same area.

[0025] The above-mentioned method for preparing the coated diaphragm includes: coating a first slurry onto one side of a base membrane and drying it; coating a second slurry onto the other side of the base membrane and drying it; and obtaining a first coating and a second coating on both sides of the base membrane respectively, thereby obtaining a coated diaphragm.

[0026] In the above technical solution, the method for preparing the first slurry includes: mixing the first water, the first dispersant, the metal-organic framework (MOF), the modified solid electrolyte, the first pressure-sensitive binder and the wetting agent until uniform to obtain the first slurry. The ratio of the first water, the first dispersant, the metal-organic framework (MOF), the modified solid electrolyte, the first pressure-sensitive binder and the wetting agent by mass parts is (23~28):(0.3~0.6):(21~24):(5.3~7.8):(3~5):(0.015~0.030).

[0027] In the above technical solution, the method for preparing the second slurry includes: mixing the second water, the second dispersant, the polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the emulsion binder and the second pressure-sensitive binder until uniform to obtain the second slurry. The ratio of the second water, the second dispersant, the polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the emulsion binder and the second pressure-sensitive binder by mass parts is (20~30):(0.3~0.5):(10~15):(7~10):(3~5).

[0028] In the above technical solution, the method for preparing the first slurry includes the following steps:

[0029] Step 1: Mix the first water and the first dispersant until homogeneous to obtain solution A;

[0030] Step 2: Mix solution A and metal-organic framework (MOF) until homogeneous to obtain solution B;

[0031] Step 3: Mix solution B and the modified solid electrolyte until homogeneous to obtain solution C;

[0032] Step 4: Mix solution C and the first pressure-sensitive adhesive until homogeneous to obtain solution D;

[0033] Step 5: Mix solution D and wetting agent until homogeneous to obtain the first slurry.

[0034] In the above technical solution, the method for preparing the second slurry includes the following steps:

[0035] S1, mix the second water and the second dispersant until homogeneous to obtain the first solution;

[0036] S2, mix the first solution and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) until homogeneous to obtain the second solution;

[0037] S3, mix the second solution and the emulsion-type adhesive until homogeneous to obtain the third solution;

[0038] S4. Mix the third solution and the second pressure-sensitive adhesive until homogeneous to obtain the second slurry.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] The modified solid electrolyte of this invention has a rigid framework to provide a fast conduction channel, while the metal-organic framework (MOF) has a high specific surface area and can synergistically build a three-dimensional network with the solid electrolyte. The unsaturated metal sites of the MOF can anchor lithium salts in the electrolyte, promoting dissociation and increasing the lithium-ion transference number. Furthermore, the rigid framework of the modified solid electrolyte can suppress the structural collapse of the MOF, maintaining the integrity of the three-dimensional network and thus ensuring the stability of the coated separator. Simultaneously, the first coating has good adhesion to the base film, and the second coating also has good adhesion to the base film (the first coating contains a first pressure-sensitive adhesive, resulting in good adhesion between the first coating and the base film; the second coating contains a second pressure-sensitive adhesive, thus also resulting in good adhesion between the second coating and the base film). These factors together improve the adhesion between the coated separator and the electrode, as well as the adhesion between the coating and the base film, maintaining battery performance over long-term use. Attached Figure Description

[0041] Figure 1 The image shows a SEM image of the surface containing the first coating of the coated membrane prepared in Example 1. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0043] Methylphenyl silicone resin: Shin-Etsu Chemical KR-251, colorless transparent liquid, refractive index (25℃) 1.518, viscosity (25℃) 18. .

[0044] Polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP): purchased from Arkema (Changshu) Fluorochemicals Co., Ltd., Kynar Flex LBG 8200, CAS No. 24937-79-9, density 1.77~1.80 g / cm³. 3 It has a melting point of 148-155℃, a weight-average molecular weight of 500,000-600,000 g / mol, and a number-average molecular weight of 200,000-300,000 g / mol.

[0045] Polymethyl methacrylate: Chi Mei Industrial Co., Ltd., ACRYREX ® CM-211.

[0046] Acrylic emulsion hydraulic adhesive: Purchased from Dongguan Wanjiang Jianda Adhesive Products Co., Ltd., Tiger Brand 3808A, milky white liquid, solid content 54~56wt%, viscosity 50~80. .

[0047] Liquid absorption rate and liquid retention rate: The diaphragm was cut into samples 30 mm wide and 100 mm long, weighed and recorded as the mass before soaking (m0). It was then soaked in an electrolyte solution at 20–25℃ for 30 min, removed and weighed, recorded as the mass after soaking (m1). It was then placed at 20–25℃ for 1 h, and the mass was recorded as m2. The liquid retention rate and liquid absorption rate were calculated as follows: Liquid retention rate = ((m2-m0) / m0)*100%, Liquid absorption rate = ((m1-m0) / m0)*100%. The electrolyte used for testing the liquid absorption rate and liquid retention rate included an electrolyte and a solvent. The electrolyte was lithium hexafluorophosphate, and the solvent was a mixture of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, with a volume ratio of 1:1:1. The concentration of the electrolyte in the electrolyte solution was 1.0 mol / L.

[0048] The standard for ionic conductivity and heat shrinkage testing is GB / T 36363-2018. In this invention, the temperature for testing ionic conductivity is 40℃, and the relative humidity is 45~50%.

[0049] The standard for moisture (water content) testing is GB / T 6283-2008.

[0050] The standard for peel strength testing is GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes".

[0051] Positive electrode bonding strength test: The coated separator and the positive electrode sheet were cut to a size of 25*150mm. The second coating surface of the coated separator was attached to the positive electrode sheet. The temperature of the hot press was adjusted to 80℃ and the pressure to X kg. The coated separator and the positive electrode sheet were preheated for 1 second and then hot-pressed for 1 second. The coated separator and the positive electrode sheet were peeled off using an electronic tensile testing machine at a speed of 300 mm / min and a peel angle of 180°. The positive electrode bonding strength was calculated as peel force divided by the sample width. Peel force was the average value of the force collected by the electronic tensile testing machine during the peeling process. The positive electrode material in the positive electrode sheet was lithium nickel cobalt aluminum oxide (LiNi). 0.8 Co 0.15 Al 0.05 O2), X = 500kg or 1000kg.

[0052] Negative electrode bonding strength test: This is basically the same as the "positive electrode bonding strength test", the only difference being that a negative electrode is used. The negative electrode is a carbon-based graphite electrode (containing 91% carbon).

[0053] In this invention, the base film is a wet-process polyethylene film with a thickness of 5.1 μm and an air permeability of 109 Sec / 100 ml. It should be noted that base films of other thicknesses can also be used.

[0054] The method for preparing ZIF-8 includes: mixing zinc acetate and methanol until homogeneous, and mixing 2-methylimidazole and methanol until homogeneous to obtain two solutions respectively. These two solutions are then mixed and stirred until homogeneous to ensure sufficient contact between zinc ions and 2-methylimidazole, resulting in a mixed liquid (in this mixed liquid, the molar ratio of zinc acetate, 2-methylimidazole, and methanol is 1:6.7:824). The mixed liquid is placed in a reaction vessel, sealed, and kept at 80℃ for 24 hours. After cooling to room temperature, the generated ZIF-8 crystals are collected by centrifugation, washed, dried, and sieved to obtain pure ZIF-8 (powder). The particle size of ZIF-8 is D50 = 0.5 μm, and the specific surface area is 1500~2200 m². 2 / g, with a pore size of 0.7~1.9nm.

[0055] The first and second dispersants are the same, both being an aqueous solution of sodium carboxymethyl cellulose, with a sodium carboxymethyl cellulose content of 5 wt%.

[0056] Example 1

[0057] A method for preparing a coated diaphragm includes: coating a first slurry onto one side of a base film by roller coating, drying at 50°C for 30 seconds to obtain a first coating on one side of the base film; coating a second slurry onto the other side of the base film by spray coating, drying at 70°C for 30 seconds to obtain a second coating on the other side of the base film (the thickness of the first coating is 2 μm, and the thickness of the second coating is 2 μm), thereby obtaining a coated diaphragm, wherein the base film, the first coating, and the second coating have the same area;

[0058] The method for preparing the first slurry includes the following steps:

[0059] Step 1: Mix the first water and the first dispersant, and stir at 3300 rpm for 30 minutes at room temperature until homogeneous to obtain solution A;

[0060] Step 2: Mix solution A with metal-organic framework (MOF, particles) and stir at 2000 rpm for 2 hours at room temperature until homogeneous to obtain solution B, wherein the metal-organic framework (MOF) is ZIF-8;

[0061] Step 3: Mix solution B and the modified solid electrolyte, and stir at 2000 rpm for 2 hours at room temperature until homogeneous to obtain solution C. The method for preparing the modified solid electrolyte includes: using NASICON-type solid electrolyte (LiTiAlP phosphate with D50 = 300 nm)... 1.3 Al 0.3 Ti 1.7 (PO4)3), a milling solvent, and a polymeric dispersant were mixed to obtain a mixture. This mixture was then subjected to high-speed milling (1500 rpm) for 2 hours to obtain a nano-dispersion (the particle size of lithium titanium aluminum phosphate in the nano-dispersion was D50 = 280 nm). Silicone resin was added to the nano-dispersion, and the mixture was then subjected to low-speed milling (700 rpm) for 1.5 hours to coat the surface of the NASICON-type solid electrolyte with the silicone resin. The mixture was then spray-dried (inlet temperature 180℃, feed rate 100 kg / h) to obtain a modified solid electrolyte. The mass of the silicone resin was 0.5 wt% of the NASICON-type solid electrolyte. In the mixture, the mass ratio of NASICON-type solid electrolyte, milling solvent, and polymeric dispersant was 40:58.5:1.5. The milling solvent was N-methylpyrrolidone, and the polymeric dispersant was ammonium polyacrylate solution (BASF Dispex). ® AA 4040 in the series has a solid content of 45% and a weight-average molecular weight of 20,000 to 60,000. The silicone resin is methylphenyl silicone resin.

[0062] Step 4: Mix solution C and the first pressure-sensitive adhesive, and simultaneously sonicate and stir at room temperature for 10 minutes until homogeneous (stirring speed is 1000 r / min, revolution speed is 20 r / min, sonication frequency is 5 kHz) to obtain solution D. The first pressure-sensitive adhesive is an acrylic emulsion pressure-sensitive adhesive.

[0063] Step 5: Mix solution D and the wetting agent, stir at room temperature at a rotation speed of 3300 r / min and a revolution speed of 20 r / min for 10 min, and then grind in a grinder at a speed of 1500 r / min for 10 min to obtain the first slurry. The wetting agent is a nonionic polyether modified siloxane (Chemadd 6091 from Yueyang Kaimen Waterborne Additives Co., Ltd.).

[0064] The ratio of the first water, the first dispersant, the metal-organic framework (MOF), the modified solid electrolyte, the first pressure-sensitive binder, and the wetting agent by mass parts is 27.5:0.3:21:5.3:5:0.030.

[0065] The method for preparing the second slurry includes the following steps:

[0066] S1, mix the second water and the second dispersant, and stir at 3000 rpm for 60 minutes at room temperature until homogeneous to obtain the first solution;

[0067] S2, the first solution and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, powder) are mixed and stirred at 3300 rpm for 2 hours at room temperature until homogeneous to obtain the second solution;

[0068] S3, the second solution and the emulsion-type adhesive are mixed and simultaneously sonicated and stirred at room temperature for 1 hour (the rotation speed of the stirring is 1000 r / min, the revolution speed is 20 r / min, and the frequency of sonication is 5 kHz) to obtain the third solution, wherein the emulsion-type adhesive is polymethyl methacrylate;

[0069] S4, the third solution and the second pressure-sensitive adhesive are mixed and simultaneously ultrasonicated and stirred at room temperature for 1 hour (the rotation speed of the stirring is 1000 r / min, the revolution speed is 20 r / min, and the frequency of ultrasonication is 5 kHz), and then ground in a grinder at a speed of 600 r / min for 60 minutes to obtain the second slurry, wherein the second pressure-sensitive adhesive is an acrylic emulsion pressure-sensitive adhesive.

[0070] The ratio of the second water, the second dispersant, the polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the emulsion binder, and the second pressure-sensitive binder, by mass parts, is 20:0.3:15:7:3.

[0071] Example 2

[0072] A method for preparing a coated diaphragm is basically the same as in Example 1, except that the ratio of "by mass parts, the first water, the first dispersant, the metal-organic framework (MOF), the modified solid electrolyte, the first pressure-sensitive binder and the wetting agent is 27.5:0.3:21:5.3:5:0.030" is replaced with "by mass parts, the ratio of the first water, the first dispersant, the metal-organic framework (MOF), the modified solid electrolyte, the first pressure-sensitive binder and the wetting agent is 26:0.4:23:6:5:0.030".

[0073] In Example 2, the thickness of the first coating in the prepared coated membrane is 2 μm, and the thickness of the second coating is 2 μm.

[0074] Example 3 (as a comparison)

[0075] A method for preparing a coated membrane is basically the same as in Example 1, except that "metal-organic framework (MOF)" is replaced with "alumina".

[0076] Example 4 (as a comparison)

[0077] A method for preparing a coated diaphragm is basically the same as that in Example 1, except that no modified solid electrolyte is added to the first slurry in Example 4.

[0078] Example 5 (as a comparison)

[0079] A method for preparing a coated diaphragm is basically the same as in Example 1, except that the ratio of "by mass parts, the first water, the first dispersant, the metal-organic framework (MOF), the modified solid electrolyte, the first pressure-sensitive binder and the wetting agent is 27.5:0.3:21:5.3:5:0.030" is replaced with "by mass parts, the ratio of the first water, the first dispersant, the metal-organic framework (MOF), the modified solid electrolyte, the first pressure-sensitive binder and the wetting agent is 27.5:0.3:28:5.3:1:0.030".

[0080] Example 6 (as a comparison)

[0081] A method for preparing a coated diaphragm is basically the same as that in Example 1, except that the first pressure-sensitive adhesive is not added to the first slurry.

[0082] Example 7 (as a comparison)

[0083] A method for preparing a coated diaphragm includes: coating a first slurry prepared in Example 1 onto a base film by roller coating on one side, drying at 50°C for 10 seconds, and obtaining a first coating with a thickness of 2 μm on the base film to obtain a coated diaphragm.

[0084] Example 8 (as a comparison)

[0085] A method for preparing a coated membrane is basically the same as in Example 1, except that "modified solid electrolyte" is replaced with "solid electrolyte". The solid electrolyte used in Example 8 is a NASICON-type solid electrolyte (lithium aluminum titanium phosphate with D50=300nm), which has not been modified in any way.

[0086] The ionic conductivity of the coated membranes prepared in Examples 1-8 is shown in Table 1.

[0087] Table 1

[0088]

[0089] As shown in Table 1, the coated membrane prepared in Example 1 exhibits the highest ionic conductivity. This invention constructs a three-dimensional ion transport channel through the pores of the metal-organic framework (MOF) and the grain boundaries of lithium titanium aluminum phosphate, shortening the lithium-ion migration path and improving transport efficiency. Both elements work together to enhance electrolyte retention, ensuring a sufficient supply of medium for ion transport.

[0090] Peel strength tests were performed on the first coating surface of the coated diaphragms prepared in Examples 1-8. The peel strength of the coated diaphragms prepared in Examples 1-8 is shown in Table 2.

[0091] Table 2

[0092]

[0093] As shown in Table 2, the coated membrane prepared in Example 1 exhibits the highest peel strength. This invention utilizes a combination of CMC and acrylate emulsion hydraulic binder to effectively chain-entangle MOF and lithium aluminum titanium phosphate, resulting in a first slurry that combines dispersion stability and strong adhesion.

[0094] The thermal shrinkage rates of the coated membranes prepared in Examples 1-8 are shown in Table 3.

[0095] Table 3

[0096]

[0097] As shown in Table 3, the coated membrane prepared in Example 1 exhibits the best heat resistance. The MOF framework contains micron-sized voids, which LATP particles can uniformly fill, forming a dense composite structure of "MOF framework + LATP filling," further reducing the exposed area of ​​the base membrane and blocking the shrinkage path.

[0098] The liquid absorption rate and liquid retention rate of the coated membranes prepared in Examples 1-8 are shown in Table 4.

[0099] Table 4

[0100]

[0101] As shown in Table 4, the coated membrane prepared in Example 1 has the highest liquid absorption rate and liquid retention rate. The porous structure of lithium titanium aluminum phosphate gives it a high electrolyte adsorption capacity, while the high specific surface area and hydrophilic functional groups (-OH) of MOF can further enhance electrolyte wettability and synergistically improve the electrolyte adsorption capacity of the membrane.

[0102] The water content of the coated membranes prepared in Examples 1-8 is shown in Table 5.

[0103] Table 5

[0104]

[0105] As shown in Table 5, the water content in Example 8 is 1378 ppm. Examples 1 and 2 of the present invention reduce the water content in the coating by modifying the solid electrolyte and through the synergistic effect of the metal-organic framework and the modified solid electrolyte, thereby reducing the water content in Examples 1 and 2 to about 800 ppm, thereby improving the safety performance of the diaphragm.

[0106] The bonding strength of the positive electrode and the bonding strength of the negative electrode were tested on the second coating surface of the coated separators prepared in Examples 1-6 and Example 8. The bonding strength of the positive electrode and the bonding strength of the negative electrode of the coated separators prepared in Examples 1-6 and Example 8 are shown in Table 6.

[0107] Table 6

[0108]

[0109] As shown in Table 6, the coated separator prepared in the embodiments of the present invention improves the adhesion between the separator and the electrode by using a pressure-sensitive adhesive. The bonding strength values ​​obtained by hot pressing at 1000 kg pressure and hot pressing at 500 kg pressure are basically the same, which greatly reduces the energy consumption when conventional batteries use hot pressing.

[0110] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A coated diaphragm, characterized in that, include: A base film, a first coating, and a second coating, wherein the first coating and the second coating are located on opposite sides of the base film; The first coating comprises: sodium carboxymethyl cellulose, a metal-organic framework, a modified solid electrolyte, and a first pressure-sensitive adhesive. The modified solid electrolyte is obtained by modifying a solid electrolyte with a silicone resin, wherein the silicone resin is a methylphenyl silicone resin. The first pressure-sensitive adhesive is one or a mixture of several of the following: vinyl acetate emulsion pressure-sensitive adhesive, natural rubber emulsion pressure-sensitive adhesive, acrylate emulsion pressure-sensitive adhesive, and water-dispersible polyurethane pressure-sensitive adhesive. The second coating comprises: sodium carboxymethyl cellulose, polyvinylidene fluoride-hexafluoropropylene copolymer, an emulsion adhesive, and a second pressure-sensitive adhesive. The emulsion adhesive is polymethyl methacrylate, and the second pressure-sensitive adhesive is one or a mixture of several of the following: vinyl acetate emulsion pressure-sensitive adhesive, natural rubber emulsion pressure-sensitive adhesive, acrylate emulsion pressure-sensitive adhesive, and water-dispersible polyurethane pressure-sensitive adhesive.

2. The coated diaphragm according to claim 1, characterized in that, The method for preparing modified solid electrolytes includes: mixing solid electrolytes, milling solvents, and polymeric dispersants to obtain a mixture; subjecting the mixture to high-speed milling to obtain a nano-dispersible solution; adding silicone resin to the nano-dispersible solution and performing low-speed milling to coat the surface of the solid electrolyte with silicone resin; and spray drying to obtain modified solid electrolytes. The mass of the silicone resin is 0.1~5 wt% of the solid electrolyte. In the mixture, the ratio of solid electrolyte, milling solvent, and polymeric dispersant by mass is (10~60):(38~89.9):(0.1~2).

3. The coated diaphragm according to claim 1, characterized in that, The first coating is obtained by coating with a first slurry, which includes: first water, first dispersant, metal-organic framework, modified solid electrolyte, first pressure-sensitive binder and wetting agent. By mass parts, the ratio of first water, first dispersant, metal-organic framework, modified solid electrolyte, first pressure-sensitive binder and wetting agent is (23~28):(0.3~0.6):(21~24):(5.3~7.8):(3~5):(0.015~0.030).

4. The coated diaphragm according to claim 1, characterized in that, The second coating is obtained by coating with a second slurry, which includes: second water, second dispersant, polyvinylidene fluoride-hexafluoropropylene copolymer, emulsion binder and second pressure-sensitive binder. By mass parts, the ratio of second water, second dispersant, polyvinylidene fluoride-hexafluoropropylene copolymer, emulsion binder and second pressure-sensitive binder is (20~30):(0.3~0.5):(10~15):(7~10):(3~5).

5. The coated diaphragm according to claim 2, characterized in that, The solid electrolyte is at least one of NASICON-type solid electrolyte and garnet-type solid electrolyte.

6. The coated diaphragm according to claim 1, characterized in that, The metal-organic framework is ZIF-8.

7. The coated diaphragm according to claim 3 or 4, characterized in that, The first and second dispersants are the same, both being an aqueous solution of sodium carboxymethyl cellulose.

8. The coated diaphragm according to claim 1, characterized in that, The thickness of the base film is 4.5~5.5μm, the thickness of the first coating is 1~5μm, and the thickness of the second coating is 1~5μm.

9. The method for preparing the coated diaphragm as described in claim 1, characterized in that, include: The first slurry is coated on one side of the base film and dried. The second slurry is coated on the other side of the base film and dried. The first coating and the second coating are obtained on the two sides of the base film, respectively, to obtain a coated diaphragm.

10. The preparation method according to claim 9, characterized in that, The method for preparing the first slurry includes: mixing first water, first dispersant, metal-organic framework, modified solid electrolyte, first pressure-sensitive binder and wetting agent until uniform to obtain the first slurry. The ratio of first water, first dispersant, metal-organic framework, modified solid electrolyte, first pressure-sensitive binder and wetting agent by mass parts is (23~28):(0.3~0.6):(21~24):(5.3~7.8):(3~5):(0.015~0.030). The method for preparing the second slurry includes: mixing second water, second dispersant, polyvinylidene fluoride-hexafluoropropylene copolymer, emulsion binder and second pressure-sensitive binder until uniform to obtain the second slurry. The ratio of second water, second dispersant, polyvinylidene fluoride-hexafluoropropylene copolymer, emulsion binder and second pressure-sensitive binder by mass parts is (20~30):(0.3~0.5):(10~15):(7~10):(3~5).

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