Double-sided coated para-aramid separator and preparation method therefor

Abstract

Disclosed in the present invention are a double-sided coated para-aramid separator and a preparation method therefor. The double-sided coated para-aramid separator comprises: a base membrane and a coating coated on the base membrane, wherein the coating is obtained by coating a para-aramid slurry. The para-aramid slurry comprises: a gas-phase powder, a ceramic powder, a first solvent, a styrene-butadiene latex solution, nano calcium carbonate and a para-aramid polymerization solution, wherein prior to the use of the para-aramid polymerization solution, hydrogen chloride produced during the synthesis of para-aramid from para-phenylenediamine and terephthaloyl chloride is removed, and the gas-phase powder is one or a mixture of more of gas-phase aluminum oxide, gas-phase silicon dioxide and gas-phase barium titanate. In the present invention, the coating is subjected to pore forming by means of a solid space-occupying method, thereby increasing the porosity of the coating, such that the para-aramid separator has a larger porosity and a smaller air permeability value.

Description

Double-sided coated para-aramid diaphragm and preparation method thereof Technical Field

[0001] The present invention belongs to the technical field of battery separators, and in particular relates to a double-sided coated para-aramid separator and a preparation method thereof. Background Art

[0002] Double-sided coated para-aramid has great advantages in high temperature resistance. A very thin coating can provide good high temperature resistance. However, because the air permeability of double-sided para-aramid coating is high, the pore size problem of the coating is difficult to solve, and double-sided para-aramid coating is rarely used.

[0003] Single-sided coated para-aramid is more commonly used because the single-sided coated para-aramid diaphragm has better air permeability. However, the cost of the coating machine for producing single-sided para-aramid is extremely high. The cost of the coating machine for single-sided para-aramid mainly lies in eliminating the stress problem of the coating on the diaphragm. If it is directly coated on the diaphragm, the stress of the coating will cause the diaphragm to have serious edge warping. The thicker the coating thickness, the more serious the warping phenomenon. The warped diaphragm cannot be wound into the battery, so it must undergo sufficient ironing during the coating process to eliminate the stress of the para-aramid coating. Another major disadvantage of single-sided coated para-aramid is that if the coating thickness is relatively thin, the high temperature resistance of the diaphragm will deteriorate. The diaphragm must reach a sufficient thickness (≥5μm) to achieve high temperature resistance. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a para-aramid slurry.

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

[0006] Another object of the present invention is to provide a double-sided coated para-aramid diaphragm.

[0007] Another object of the present invention is to provide a method for preparing the double-sided coated para-aramid diaphragm.

[0008] The purpose of the present invention is achieved through the following technical solutions.

[0009] A para-aramid slurry comprises: gas phase powder, ceramic powder, a first solvent, styrene-butadiene latex solution, nano-calcium carbonate and a para-aramid polymer solution, wherein, by mass, the ratio of the gas phase powder, ceramic powder, the first solvent, styrene-butadiene latex solution, nano-calcium carbonate and the para-aramid in the para-aramid polymer solution is (3-5):(15-18):(66-76):(1-2):(3-5):(2-4); hydrogen chloride produced when para-aramid (poly(p-phenylene terephthalamide, PPTA)) is synthesized from para-phenylenediamine and terephthaloyl chloride is removed from the para-aramid polymer solution before use; and the gas phase powder is a mixture of one or more of gas phase alumina, gas phase silica and gas phase barium titanate.

[0010] In the above technical solution, when synthesizing para-aramid in the para-aramid polymer solution, a deacidifying agent is added to absorb the hydrogen chloride produced when para-phenylenediamine and terephthaloyl chloride are synthesized into para-aramid.

[0011] In the above technical solution, the deacidifying agent is one or a mixture of pyridine, sodium hydroxide and calcium hydroxide.

[0012] In the above technical solution, the para-aramid polymer solution comprises: para-aramid, calcium chloride and a second solvent. The concentration of para-aramid in the para-aramid polymer solution is 2-5wt%, and the concentration of calcium chloride in the para-aramid polymer solution is 3-8wt%.

[0013] In the above technical solution, the first solvent is NMP, and the water content of the first solvent is ≤0.2 wt%.

[0014] In the above technical solution, the ceramic powder is one or a mixture of several of aluminum oxide, aluminum hydroxide, boehmite and barium sulfate.

[0015] In the above technical solution, the particle size of the nano calcium carbonate is 20 to 80 nm.

[0016] The preparation method of the above-mentioned para-aramid slurry includes: mixing a first solvent and a styrene-butadiene latex solution evenly to obtain a B solution, mixing nano-calcium carbonate and the B solution evenly, sand-milling to obtain a C solution, mixing the C solution and the second solution, stirring until uniform, to obtain a para-aramid slurry, wherein the method for preparing the second solution is: mixing a gas phase powder, a ceramic powder and the first solvent evenly, sand-milling to obtain a A solution, mixing the A solution and a para-aramid polymer liquid, stirring until uniform, to obtain a second solution.

[0017] In the above technical solution, the gas phase powder, ceramic powder and the first solvent are mixed and then stirred for 40 to 80 minutes to achieve uniform mixing.

[0018] In the above technical solution, the C solution and the second solution are mixed and stirred for 30 to 40 minutes until they are uniform.

[0019] In the above technical solution, the first solvent and the styrene-butadiene latex solution are mixed and then stirred for 5 to 10 minutes to achieve uniform mixing, thereby obtaining solution B.

[0020] In the above technical solution, the nano-calcium carbonate and solution B are stirred for 40 to 80 minutes to achieve uniform mixing.

[0021] In the above technical solution, the solution A and the para-aramid polymer solution are mixed and stirred for 30 to 40 minutes until they are uniform.

[0022] In the above technical solution, the sand milling time is 20 to 30 minutes, and the sand milling speed is 1000 to 1500 r / min.

[0023] In the above technical solution, the ratio of the first solvent in solution B to the first solvent in solution A is (5-8):(14-18) in parts by mass.

[0024] In the above technical solution, the viscosity-average molecular weight of the para-aramid polymer solution is 5000-7000.

[0025] In the above technical solution, the method for preparing the para-aramid polymer solution includes: introducing a first slurry and a second slurry into a twin-screw extruder for synthesizing para-aramid, and introducing a third slurry into the twin-screw extruder for conveying the synthesized para-aramid to absorb the hydrogen chloride produced when para-phenylenediamine and terephthaloyl chloride are used to synthesize para-aramid, so as to obtain the para-aramid polymer solution, wherein the first slurry includes: calcium chloride, para-phenylenediamine and a second solvent; the second slurry is a molten liquid of terephthaloyl chloride; and the third slurry is a deacidifying agent.

[0026] In the above technical solution, the deacidifying agent is one or a mixture of pyridine, sodium hydroxide and calcium hydroxide.

[0027] In the above technical solution, the ratio of the second solvent to p-phenylenediamine is (90-96.4) to (1.6-2) by mass, and the ratio of calcium chloride to p-phenylenediamine is (2-8) to (1.6-2) by mass.

[0028] In the above technical solution, the speed ratio of the first slurry, the second slurry and the third slurry is (2-4): (0.6-0.8): (0.06-0.09).

[0029] In the above technical solution, the method for preparing the first slurry includes: mixing calcium chloride and a second solvent, stirring until the calcium chloride is dissolved in the second solvent to obtain a first solution, cooling the first solution to 5-20°C and then mixing with p-phenylenediamine, stirring until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry.

[0030] In the above technical solution, the calcium chloride is dehydrated before being mixed with the second solvent, and the dehydration method is calcining at 400-450° C. for 3-5 hours.

[0031] In the above technical solution, the second solvent is NMP, and the water content of the second solvent is ≤0.2 wt%.

[0032] In the above technical solution, calcium chloride is dissolved in the second solvent by stirring at 75-85° C. for 4-6 hours.

[0033] In the above technical solution, p-phenylenediamine is uniformly dispersed in the first solution by stirring at 5-20° C. for 3-5 hours.

[0034] In the above technical solution, solid terephthaloyl chloride is heated at 80-95° C. until terephthaloyl chloride is formed into a molten liquid.

[0035] In the above technical solution, the method for preparing the para-aramid polymer solution comprises the following steps:

[0036] Step 1, prepare a twin-screw extruder, the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, the left end of the polymerization zone is provided with a first feed port and a second feed port, the polymerization mixing zone is provided with a third feed port, and the right end of the heating zone is provided with a discharge port, the temperature of the polymerization zone is 0-5°C, the temperature of the polymerization mixing zone is 15-20°C, and the temperature of the heating zone is 20-30°C;

[0037] In step 1, the first feed port is located on the left side of the second feed port, and the material between the third feed port and the second feed port is used to synthesize para-aramid (poly(p-phenylene terephthalamide)).

[0038] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, then input the second slurry into the second feed port in a spraying state, and when the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1300-1500cp, input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1000-1300cp, and obtain the para-aramid polymer solution from the discharge port;

[0039] In the step 2, the slurry in the twin-screw extruder runs from the first feed port to the second feed port for 1 to 3 seconds, the slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 4 to 6 seconds, the slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 5 to 7 seconds, the slurry in the twin-screw extruder runs from the third feed port to the heating zone for 3 to 5 seconds, and the slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 4 to 6 seconds.

[0040] In the above technical solution, the rotation speed of the conveying rod in the twin-screw extruder is 20 to 30 r / min, and the rotation speed of the mixing rod stirring is 20 to 30 r / min.

[0041] A double-sided coated para-aramid diaphragm comprises a base film and a coating layer coated on the base film, wherein the coating layer is obtained by coating a para-aramid slurry.

[0042] In the above technical solution, the base film is a wet-process PE film.

[0043] The method for preparing the double-sided coated para-aramid membrane comprises: coating the para-aramid slurry on both sides of the base film, extracting to remove nano-calcium carbonate in the para-aramid slurry, and drying to obtain the double-sided coated para-aramid membrane.

[0044] In the above technical solution, the extraction first uses an acidic solution that can remove nano-calcium carbonate in the para-aramid slurry, and finally uses water.

[0045] In the above technical solution, the pH value of the acidic solution is 1-4.

[0046] In the above technical solution, the acidic solution is NMP whose pH value is adjusted by hydrogen chloride.

[0047] In the above technical solution, the coating thickness of the para-aramid slurry on each side of the base film (excluding the thickness of the base film) is 3 to 4 μm.

[0048] In the above technical solution, the coating is carried out under dry conditions, and the dry conditions are humidity <5% RH.

[0049] In the above technical solution, the extraction is carried out in sequence through acidic solutions with extractant concentrations from high to low, and finally through water. The acidic solutions with extractant concentrations from high to low include a first extracting liquid and a second extracting liquid. The first extracting liquid and the second extracting liquid are both mixtures of extracting agent and water. The concentration of the extracting agent in the first extracting liquid is 70-90wt%, and the concentration of the extracting agent in the second extracting liquid is 40-60wt%. The extracting agent is NMP.

[0050] In the above technical solution, the drying is carried out in an oven at 40-80°C, wherein the oven is equipped with a heating roller with a diameter of 600-800 mm, and the temperature of the heating roller is 60-100°C.

[0051] In the above technical solution, there is a blower inside the drying oven, wherein the blowing frequency is 15 to 25 Hz.

[0052] In the above technical solution, the length of the film line in the oven is 15 to 30 m, and the speed of passing through the hot roller is 25 to 50 m / min.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] 1. The present invention uses a solid space occupying method to form pores in the coating. Nano-calcium carbonate is added to the para-aramid slurry. During the preparation of the para-aramid membrane, the para-aramid slurry is coated on both sides of the base membrane. During extraction, the nano-calcium carbonate is decomposed into calcium ions and carbon dioxide through an acidic solution. After the nano-calcium carbonate disappears, voids are generated inside the coating, thereby increasing the porosity of the coating. The generated carbon dioxide gas expands the voids in the coating, increasing the porosity of the coating, so that the para-aramid membrane has a larger porosity and a smaller air permeability.

[0055] 2. During the synthesis of para-aramid from p-phenylenediamine and terephthaloyl chloride, a small amount of hydrogen chloride is generated. This hydrogen chloride reacts with calcium carbonate prematurely, reducing the pore-forming effect of calcium carbonate in the coating. Therefore, the hydrogen chloride generated during the synthesis of para-aramid from p-phenylenediamine and terephthaloyl chloride is removed from the para-aramid polymer solution of the present invention before use.

[0056] 3. The present invention discloses a method for preparing a para-aramid polymer solution, in which a deacidifying agent is added in the middle stage of the synthesis to absorb the hydrogen chloride generated during the synthesis of the para-aramid.

[0057] 4. Method for preparing para-aramid polymer solution: If the mixture is directly stirred and mixed according to the corresponding temperature conditions, the production cycle is long, the efficiency is low, and the production volume is relatively small. When the amount of para-aramid polymer is relatively large, because the polymerization reaction is an exothermic reaction, the temperature rise rate will be too fast when the amount is large, resulting in a large number of molecular chains being broken, making it difficult to increase the molecular weight. However, the method of preparing para-aramid polymer solution using a twin-screw extruder of the present invention can achieve continuous production with relatively high efficiency, and can also effectively control the heat generated during synthesis, thereby controlling and increasing the molecular weight of the para-aramid polymer solution, simplifying the production steps, and improving production efficiency.

[0058] 5. Since the para-aramid diaphragm of the present invention is coated on both sides, there is no need to eliminate the stress of the coating on the diaphragm, thereby reducing the mechanical cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG1 is a cross-sectional scanning electron micrograph of the double-sided coated para-aramid diaphragm prepared in Example 1;

[0060] FIG2 is a cross-sectional scanning electron microscope image of the double-sided coated para-aramid diaphragm prepared in Comparative Example 1;

[0061] FIG3 is a schematic diagram of the synthesis of para-aramid polymer solution by a twin-screw extruder of the present invention. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below with reference to specific embodiments.

[0063] The twin-screw extruder of the present invention pushes the slurry forward by rotating, realizing polymerization and transmission at the same time. A jacket is provided on the outside of the screw, and chilled water or hot water can be passed into the jacket to realize temperature control of the polymerization zone, polymerization mixing zone and heating zone. The twin screws in the twin-screw extruder are a conveying rod and a mixing rod. The conveying rod in the twin-screw extruder is mainly used to convey the slurry, and the mixing rod is mainly used to mix and stir the slurry.

[0064] In the following examples, the styrene-butadiene latex solution was purchased from BYK Chemical (Shanghai) Co., Ltd., model number LPN21954, which was obtained by modifying acrylonitrile. The styrene-butadiene latex solution, with the help of the strongly polar acrylonitrile group, the flexible polymer chain forms a water-oil dispersion interface layer on the surface of the nano-calcium carbonate, preventing the nano-calcium carbonate from agglomerating.

[0065] Liquid absorption rate test method: Cut the diaphragm into samples with a width of 30 mm and a length of 100 mm, weigh them and record them as the mass before immersion, soak them in electrolyte for 30 minutes, take them out and weigh them and record them as the mass after immersion, and calculate the liquid absorption rate. Liquid absorption rate = (mass after immersion - mass before immersion) / mass before immersion.

[0066] Liquid retention rate test method: Cut the diaphragm into samples with a width of 30 mm and a length of 100 mm, weigh them and record them as the mass before immersion, soak the diaphragm in the electrolyte for 30 minutes, take them out and hang them for 30 minutes, gently absorb the excess electrolyte on the surface with a non-woven cloth, weigh them and record them as the mass of the liquid-retaining diaphragm, calculate the liquid retention rate, liquid retention rate = (mass of liquid-retaining diaphragm - mass before immersion) / mass before immersion.

[0067] The electrolyte comprises lithium hexafluorophosphate and a solvent. The concentration of lithium hexafluorophosphate in the electrolyte is 6 mol / L, and the solvent is carbonate.

[0068] The air permeability test is defined as: in an environment of 25°C, 60% RH, and normal pressure, a pressure of 1.21 kPa is applied to the test instrument, and 100 mL of air passes through an area of ​​6.45 cm 2 The time required for the diaphragm.

[0069] Ionic conductivity: tested at 25°C.

[0070] In the following examples, the base film is a wet-process PE film, and the thickness of the base film is 9 μm.

[0071] In the following examples, water is deionized water.

[0072] In the following examples, the second solvent is NMP with a water content of 0.2 wt %.

[0073] In the following examples, the first solvent is NMP, and the water content is 0.2 wt %.

[0074] In the following examples, a deacidifying agent is added to the para-aramid polymer solution to absorb the hydrogen chloride produced during the synthesis of para-aramid from p-phenylenediamine and terephthaloyl chloride.

[0075] In the following examples, the calcium chloride in the para-aramid polymer solution occupies the chlorine bonds of the acyl chlorides in the para-aramid fibers, preventing or reducing hydrogen bonding and thus preventing agglomeration of the para-aramid fibers. If calcium chloride is omitted or added in small amounts, the para-aramid polymer solution will become extremely viscous, making it unusable.

[0076] Example 1

[0077] A method for preparing a para-aramid polymer solution comprises the following steps:

[0078] Step 1, prepare a twin-screw extruder, as shown in Figure 3, the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, a first feed port and a second feed port are provided at the left end of the polymerization zone (the first feed port is located on the left side of the second feed port), a third feed port is provided on the polymerization mixing zone, the third feed port is located at 1 / 2 of the polymerization mixing zone, and the third feed port and the second feed port are used to synthesize poly(p-phenylene terephthalamide) (PPTA), a discharge port is provided at the right end of the heating zone, the temperature of the polymerization zone is 0°C, the temperature of the polymerization mixing zone is 15°C, and the temperature of the heating zone is 20°C;

[0079] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, and then input the second slurry into the second feed port in a spraying state. When the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1300cp, input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1000cp, and obtain a para-aramid polymer solution with a viscosity-average molecular weight of 5000 from the discharge port. The speed ratio of the first slurry, the second slurry and the third slurry is 2:0.6:0.06, and the speed ratio of the first slurry, the second slurry and the third slurry is 2:0.6:0.06. The flow rate of a slurry is 2L / min. The slurry in the twin-screw extruder runs from the first feed port to the second feed port for 3s. The slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 6s. The slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 7s. The slurry in the twin-screw extruder runs from the third feed port to the heating zone for 5s. The slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 6s. The speed of the conveying rod in the twin-screw extruder is 20r / min, and the speed of the mixing rod stirring is 20r / min.

[0080] The method for preparing a first slurry comprises: mixing calcium chloride and a second solvent, stirring at 80° C. for 6 hours until the calcium chloride is dissolved in the second solvent to obtain a first solution, cooling the first solution to 5° C. and then mixing with p-phenylenediamine, stirring at 5° C. for 3 hours until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein the ratio of the second solvent, calcium chloride and p-phenylenediamine is 90:2:1.6 by mass, and the calcium chloride is dehydrated before being mixed with the second solvent by calcining in a muffle furnace at 420° C. for 4 hours;

[0081] The second slurry is a molten liquid of terephthaloyl chloride, which is obtained by heating the solid terephthaloyl chloride in a tank at 80°C until the molten liquid of terephthaloyl chloride is formed;

[0082] The third slurry is a deacidifying agent (pyridine), which is used to absorb the hydrogen chloride produced during the synthesis of p-phenylenediamine and terephthaloyl chloride, to prevent the hydrogen chloride from reacting with the nano-calcium carbonate in advance and reduce the pore-forming effect of the nano-calcium carbonate in the coating.

[0083] The concentration of para-aramid in the para-aramid polymer solution is 2 wt %, and the concentration of calcium chloride in the para-aramid polymer solution is 3 wt %.

[0084] The method for preparing a para-aramid slurry comprises: mixing a first solvent and a styrene-butadiene latex solution, stirring for 5 minutes until uniform, to obtain a B solution; mixing nano-calcium carbonate (the particle size of the nano-calcium carbonate is 20 to 40 nm) and the B solution, stirring for 40 minutes until uniform, sand milling for 20 minutes at a speed of 1000 r / min in a sand mill to obtain a C solution; mixing the C solution with a second solution, stirring for 30 minutes until uniform, to obtain a para-aramid slurry, wherein the method for preparing the second solution is: mixing a gas phase powder, a ceramic powder and the first solvent, stirring for 40 minutes until uniform, The mixture was sand milled at a speed of 1000 r / min for 20 minutes to obtain solution A, and solution A and para-aramid polymer solution were mixed and stirred for 30 minutes until uniform to obtain a second solution, wherein the gas phase powder was fumed silica, and the ceramic powder was boehmite. The ratio of the gas phase powder, the ceramic powder, all the first solvents in the para-aramid slurry, the styrene-butadiene latex solution, the nano-calcium carbonate and the para-aramid in the para-aramid polymer solution was 3:15:76:1:3:2 by mass, wherein the ratio of the first solvent in solution B to the first solvent in solution A was 5:14 by mass.

[0085] The invention discloses a method for preparing a double-sided coated para-aramid diaphragm, comprising: coating a para-aramid slurry on a base film on both sides, wherein the coating thickness of the para-aramid slurry on each side of the base film is 3 μm; extracting to remove nano-calcium carbonate in the para-aramid slurry; drying to obtain a coating on the base film, and obtaining a double-sided coated para-aramid diaphragm, wherein the coating is performed under dry conditions to prevent the slurry from being deteriorated due to contact with moisture in the air, and the drying condition is a humidity of 4% RH; extracting by sequentially passing through acidic solutions with extractant concentrations from high to low, and finally passing through water, wherein the water is used to wash out calcium ions decomposed by the nano-calcium carbonate, wherein the acidic solutions with extractant concentrations from high to low are sequentially a first extracting liquid and a second extracting liquid, wherein the first extracting liquid and the second extracting liquid are both mixtures of extractant and water, and during extraction, the diaphragm sequentially passes through a first extraction tank, a second extraction tank, ..., a fifth extraction tank, wherein the first extraction tank is a first extraction tank, a second extraction tank, ..., a fifth extraction tank, and the first extraction tank is a second ... The extract and the second extract are placed in a first extraction tank. A partition is provided in the middle of the first extraction tank to divide the first extraction tank into a first zone and a second zone. The first extract is located in the first zone, the second extract is located in the second zone, and water is located in the second to fifth extraction tanks, respectively. The concentration of the extractant in the first extract is 90 wt %, the concentration of the extractant in the second extract is 60 wt %, and the extractant is NMP. The pH values ​​of the first extract and the second extract are adjusted to 1 by hydrogen chloride. The hydrogen chloride is used to decompose the nano-calcium carbonate into calcium ions and carbon dioxide. The drying is carried out in an oven at 40° C. The oven is equipped with four hot rollers with a diameter of 750 mm. The heating temperature of the hot rollers is 60° C. A blower is provided inside the drying oven. The blowing frequency is 20 Hz. The length of the film line in the oven is 15 m, and the speed passing through the hot rollers is 25 m / min.

[0086] Example 2

[0087] A method for preparing a para-aramid polymer solution comprises the following steps:

[0088] Step 1, prepare a twin-screw extruder, as shown in Figure 3, the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, a first feed port and a second feed port are provided at the left end of the polymerization zone (the first feed port is located on the left side of the second feed port), a third feed port is provided on the polymerization mixing zone, the third feed port is located at 1 / 2 of the polymerization mixing zone, and the third feed port and the second feed port are used to synthesize poly(p-phenylene terephthalamide) (PPTA), a discharge port is provided at the right end of the heating zone, the temperature of the polymerization zone is 3°C, the temperature of the polymerization mixing zone is 18°C, and the temperature of the heating zone is 25°C;

[0089] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, and then input the second slurry into the second feed port in a spraying state. When the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1300cp, input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1200cp, and obtain a para-aramid polymer solution with a viscosity-average molecular weight of 6000 from the discharge port. The speed ratio of the first slurry, the second slurry and the third slurry is 3:0.7:0.08, and the speed ratio of the first slurry, the second slurry and the third slurry is 3:0.7:0.08. The flow rate of a slurry is 3L / min. The slurry in the twin-screw extruder runs from the first feed port to the second feed port for 2s. The slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 5s. The slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 6s. The slurry in the twin-screw extruder runs from the third feed port to the heating zone for 4s. The slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 5s. The speed of the conveying rod in the twin-screw extruder is 25r / min, and the speed of the mixing rod stirring is 25r / min.

[0090] The method for preparing a first slurry comprises: mixing calcium chloride and a second solvent, stirring at 80° C. for 6 hours until the calcium chloride is dissolved in the second solvent to obtain a first solution, cooling the first solution to 10° C. and then mixing with p-phenylenediamine, stirring at 10° C. for 3 hours until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein the ratio of the second solvent, calcium chloride and p-phenylenediamine is 93.2:5:1.8 by mass, and the calcium chloride is dehydrated before being mixed with the second solvent by calcining in a muffle furnace at 420° C. for 4 hours;

[0091] The second slurry is a molten liquid of terephthaloyl chloride, which is obtained by heating the solid terephthaloyl chloride in a tank at 90°C until the molten liquid of terephthaloyl chloride is formed;

[0092] The third slurry is a deacidifying agent (sodium hydroxide), which is used to absorb hydrogen chloride produced during the synthesis of p-phenylenediamine and terephthaloyl chloride, to prevent hydrogen chloride from reacting with nano-calcium carbonate in advance and reduce the pore-forming effect of nano-calcium carbonate in the coating.

[0093] The concentration of para-aramid in the para-aramid polymer solution is 3 wt %, and the concentration of calcium chloride in the para-aramid polymer solution is 5 wt %.

[0094] The method for preparing a para-aramid slurry comprises: mixing a first solvent and a styrene-butadiene latex solution, stirring for 8 minutes until uniform, to obtain a B solution; mixing nano-calcium carbonate (the particle size of the nano-calcium carbonate is 40 to 60 nm) and the B solution, stirring for 60 minutes until uniform, sand milling for 25 minutes at a speed of 1300 r / min in a sand mill to obtain a C solution; mixing the C solution with a second solution, stirring for 35 minutes until uniform, to obtain a para-aramid slurry, wherein the method for preparing the second solution is: mixing a gas phase powder, a ceramic powder and the first solvent, stirring for 60 minutes until uniform, The mixture was sand milled at a speed of 1300 r / min for 25 minutes to obtain solution A, and solution A and para-aramid polymer solution were mixed and stirred for 35 minutes until uniform to obtain a second solution, wherein the gas phase powder was gas phase alumina, and the ceramic powder was alumina. The ratio of the gas phase powder, the ceramic powder, all the first solvents in the para-aramid slurry, the styrene-butadiene latex solution, the nano-calcium carbonate and the para-aramid in the para-aramid polymer solution was 4:16:71:2:4:3 by mass, wherein the ratio of the first solvent in solution B to the first solvent in solution A was 7:15 by mass.

[0095] The invention discloses a method for preparing a double-sided coated para-aramid diaphragm, comprising: coating a para-aramid slurry on a base film on both sides, wherein the coating thickness of the para-aramid slurry on each side of the base film is 3 μm; extracting to remove nano-calcium carbonate in the para-aramid slurry; drying to obtain a coating on the base film, and obtaining a double-sided coated para-aramid diaphragm, wherein the coating is performed under dry conditions to prevent the slurry from being deteriorated due to contact with moisture in the air, and the drying condition is a humidity of 3% RH; extracting by sequentially passing through acidic solutions with extractant concentrations from high to low, and finally passing through water, wherein the water is used to wash out calcium ions decomposed by the nano-calcium carbonate, wherein the acidic solutions with extractant concentrations from high to low are sequentially a first extracting liquid and a second extracting liquid, wherein the first extracting liquid and the second extracting liquid are both mixtures of extractant and water, and during extraction, the diaphragm sequentially passes through a first extraction tank, a second extraction tank, ..., a fifth extraction tank, wherein the first extraction tank is a first extraction tank, a second extraction tank, ..., a fifth extraction tank, and the first extraction tank is a second ... The extract and the second extract are placed in a first extraction tank. A partition is provided in the middle of the first extraction tank to divide the first extraction tank into a first zone and a second zone. The first extract is located in the first zone, the second extract is located in the second zone, and water is located in the second to fifth extraction tanks, respectively. The concentration of the extractant in the first extract is 80 wt %, the concentration of the extractant in the second extract is 50 wt %, and the extractant is NMP. The pH values ​​of the first extract and the second extract are adjusted to 2 by hydrogen chloride. The hydrogen chloride is used to decompose the nano-calcium carbonate into calcium ions and carbon dioxide. The drying is carried out in an oven at 60° C. The oven is equipped with four hot rollers with a diameter of 750 mm. The heating temperature of the hot rollers is 80° C. A blower is provided inside the drying oven. The blowing frequency is 20 Hz. The length of the film line in the oven is 25 m, and the speed passing through the hot rollers is 35 m / min.

[0096] Example 3

[0097] A method for preparing a para-aramid polymer solution comprises the following steps:

[0098] Step 1, prepare a twin-screw extruder, as shown in Figure 3, the twin-screw extruder is composed of a polymerization zone, a polymerization mixing zone and a heating zone from left to right, a first feed port and a second feed port are provided at the left end of the polymerization zone (the first feed port is located on the left side of the second feed port), a third feed port is provided on the polymerization mixing zone, the third feed port is located at 1 / 2 of the polymerization mixing zone, and the third feed port and the second feed port are used to synthesize poly(p-phenylene terephthalamide) (PPTA), a discharge port is provided at the right end of the heating zone, the temperature of the polymerization zone is 5°C, the temperature of the polymerization mixing zone is 20°C, and the temperature of the heating zone is 30°C;

[0099] Step 2: first input the first slurry into the first feed port of the twin-screw extruder to fill the twin-screw extruder with the first slurry, and then input the second slurry into the second feed port in a spraying state. When the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1500cp, input the third slurry into the third feed port until the viscosity of the slurry at the discharge port of the twin-screw extruder reaches 1300cp, and obtain a para-aramid polymer solution with a viscosity-average molecular weight of 7000 from the discharge port. The speed ratio of the first slurry, the second slurry and the third slurry is 4:0.8:0.09, and the speed ratio of the first slurry, the second slurry and the third slurry is 4:0.8:0.09. The flow rate of a slurry is 4L / min. The slurry in the twin-screw extruder runs from the first feed port to the second feed port for 1s. The slurry in the twin-screw extruder runs from the second feed port to the polymerization mixing zone for 4s. The slurry in the twin-screw extruder runs from the leftmost end of the polymerization mixing zone to the third feed port for 5s. The slurry in the twin-screw extruder runs from the third feed port to the heating zone for 3s. The slurry in the twin-screw extruder runs from the leftmost end of the heating zone to the discharge port for 4s. The speed of the conveying rod in the twin-screw extruder is 30r / min, and the speed of the mixing rod stirring is 30r / min.

[0100] The method for preparing a first slurry comprises: mixing calcium chloride and a second solvent, stirring at 80° C. for 6 hours until the calcium chloride is dissolved in the second solvent to obtain a first solution, cooling the first solution to 15° C. and then mixing with p-phenylenediamine, stirring at 15° C. for 3 hours until the p-phenylenediamine is uniformly dispersed in the first solution to obtain a first slurry, wherein the ratio of the second solvent, calcium chloride and p-phenylenediamine is 96.4:8:2 by mass, and the calcium chloride is dehydrated before being mixed with the second solvent by calcining in a muffle furnace at 420° C. for 4 hours;

[0101] The second slurry is a molten liquid of terephthaloyl chloride, which is obtained by heating the solid terephthaloyl chloride in a tank at 95°C until a molten liquid of terephthaloyl chloride is formed;

[0102] The third slurry is a deacidifying agent (pyridine), which is used to absorb the hydrogen chloride produced during the synthesis of p-phenylenediamine and terephthaloyl chloride, to prevent the hydrogen chloride from reacting with the nano-calcium carbonate in advance and reduce the pore-forming effect of the nano-calcium carbonate in the coating.

[0103] The concentration of para-aramid in the para-aramid polymer solution is 5 wt %, and the concentration of calcium chloride in the para-aramid polymer solution is 8 wt %.

[0104] The method for preparing a para-aramid slurry comprises: mixing a first solvent and a styrene-butadiene latex solution, stirring for 10 minutes until uniform, to obtain a B solution; mixing nano-calcium carbonate (the particle size of the nano-calcium carbonate is 60 to 80 nm) and the B solution, stirring for 80 minutes until uniform, sand milling for 30 minutes at a speed of 1500 r / min in a sand mill to obtain a C solution; mixing the C solution with a second solution, stirring for 40 minutes until uniform, to obtain a para-aramid slurry, wherein the method for preparing the second solution is: mixing a gas phase powder, a ceramic powder and the first solvent, stirring for 80 minutes until uniform, The mixture was sand milled at a speed of 1500 r / min for 30 minutes to obtain solution A, and solution A was mixed with the para-aramid polymer solution and stirred for 40 minutes until uniform to obtain a second solution, wherein the gas phase powder was gas phase barium titanate, and the ceramic powder was aluminum hydroxide. The ratio of the gas phase powder, the ceramic powder, all the first solvents in the para-aramid slurry, the styrene-butadiene latex solution, the nano-calcium carbonate and the para-aramid in the para-aramid polymer solution was 5:18:66:2:5:4 by mass, wherein the ratio of the first solvent in solution B to the first solvent in solution A was 8:18 by mass.

[0105] The invention discloses a method for preparing a double-sided coated para-aramid diaphragm, comprising: coating a para-aramid slurry on a base film on both sides, wherein the coating thickness of the para-aramid slurry on each side of the base film is 3 μm; extracting to remove nano-calcium carbonate in the para-aramid slurry; drying to obtain a coating on the base film, and obtaining a double-sided coated para-aramid diaphragm, wherein the coating is performed under dry conditions to prevent the slurry from being deteriorated due to contact with moisture in the air, and the drying condition is a humidity of 2% RH; extracting by sequentially passing through acidic solutions with extractant concentrations from high to low, and finally passing through water, wherein the water is used to wash out calcium ions decomposed by the nano-calcium carbonate, wherein the acidic solutions with extractant concentrations from high to low are sequentially a first extracting liquid and a second extracting liquid, wherein the first extracting liquid and the second extracting liquid are both mixtures of extractant and water, and during extraction, the diaphragm sequentially passes through a first extraction tank, a second extraction tank, ..., a fifth extraction tank, wherein the first extraction tank is a first extraction tank, a second extraction tank, ..., a fifth extraction tank, and ... fifth extraction tank, wherein the first extraction tank is a first extraction tank, a second extraction tank, ..., a fifth extraction tank, and the first extraction tank is a fifth extraction tank, wherein the first extraction tank is a first extraction tank, a second extraction tank, ..., The extract and the second extract are placed in a first extraction tank. A partition is provided in the middle of the first extraction tank to divide the first extraction tank into a first zone and a second zone. The first extract is located in the first zone, the second extract is located in the second zone, and water is located in the second to fifth extraction tanks, respectively. The concentration of the extractant in the first extract is 70 wt %, the concentration of the extractant in the second extract is 40 wt %, and the extractant is NMP. The pH values ​​of the first extract and the second extract are adjusted to 4 by hydrogen chloride. The hydrogen chloride is used to decompose the nano-calcium carbonate into calcium ions and carbon dioxide. The drying is carried out in an oven at 80° C. The oven is equipped with four hot rollers with a diameter of 750 mm. The heating temperature of the hot rollers is 100° C. A blower is provided inside the drying oven. The blowing frequency is 20 Hz. The length of the film line in the oven is 30 m, and the speed passing through the hot rollers is 50 m / min.

[0106] Comparative Example 1

[0107] A method for preparing a double-sided coated para-aramid membrane is basically the same as the "method for preparing a double-sided coated para-aramid membrane" in Example 1, the only difference being that no nano-calcium carbonate is added to the para-aramid slurry in this comparative example.

[0108] Comparative Example 2

[0109] The method for preparing a single-sided coated para-aramid membrane is basically the same as the "method for preparing a double-sided coated para-aramid membrane" in Example 1. The only difference is that in this comparative example, the para-aramid slurry is coated on one side of the base film, and the coating thickness of the para-aramid slurry on one side of the base film is 5um.

[0110] Table 1 is a comparison of basic data of the double-sided coated para-aramid membranes prepared in Examples 1 to 3, the double-sided coated para-aramid membrane prepared in Comparative Example 1, and the single-sided coated para-aramid membrane prepared in Comparative Example 2.

[0111] Table 1

[0112] It can be clearly seen from the test data in Table 1 that the air permeability of the double-sided coated para-aramid membranes (para-aramid slurry with nano-calcium carbonate added) prepared in Examples 1 to 3 is reduced to below 130s / 100mL, while the air permeability of the double-sided coated para-aramid membrane (para-aramid slurry without nano-calcium carbonate added) prepared in Comparative Example 1 is directly increased to 256s / 100mL, and the air permeability of the single-sided coated para-aramid membrane prepared in Comparative Example 2 is lower than that of Comparative Example 1. However, in an environment of 200°C for 1h, the shrinkage rate of the single-sided coated para-aramid membrane reaches about 15.3%, and the high temperature resistance is poor. The air permeability value can prove the pore-forming effect of the membrane. The smaller the air permeability value, the higher the porosity of the coating.

[0113] Table 2 shows the ionic conductivities of the double-sided coated para-aramid membranes prepared in Examples 1 to 3, the double-sided coated para-aramid membrane prepared in Comparative Example 1, and the single-sided coated para-aramid membrane prepared in Comparative Example 2.

[0114] Table 2

[0115] Ionic conductivity primarily measures the rate at which ions shuttle through the separator. Ionic conductivity testing can measure the separator's efficiency in shuttling lithium ions within the battery. Table 2 shows that adding nano-calcium carbonate (a solid pore-forming agent) significantly increases the separator's ionic conductivity. This is because increased porosity increases the ion shuttle channels, thereby increasing the separator's ionic conductivity.

[0116] Table 3 shows the liquid absorption and liquid retention of the double-sided coated para-aramid membranes prepared in Examples 1 to 3, the double-sided coated para-aramid membrane prepared in Comparative Example 1, and the single-sided coated para-aramid membrane prepared in Comparative Example 2.

[0117] Table 3

[0118] It can be seen from the data in Table 3 that the double-sided coated para-aramid diaphragms prepared in Examples 1 to 3 have higher liquid absorption and liquid retention rates and better wettability.

[0119] FIG1 is a scanning electron microscope image of a cross section of a double-sided coated para-aramid diaphragm prepared in Example 1. As can be seen from FIG1 , the addition of calcium carbonate to the para-aramid slurry significantly increases the porosity of the coating and makes the aramid fibers more uniform.

[0120] FIG2 is a cross-sectional scanning electron microscope of the double-sided coated para-aramid diaphragm prepared in Comparative Example 1. As can be seen from FIG2 , no calcium carbonate is added to the para-aramid slurry, which causes the aramid fibers in the coating to be tightly attached together and have a low porosity.

[0121] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A para-aramid slurry, characterized in that: include: Gas phase powder, ceramic powder, a first solvent, styrene butadiene latex solution, nano-calcium carbonate and para-aramid polymerization liquid, wherein, by weight, the ratio of para-aramid in the gas phase powder, ceramic powder, the first solvent, styrene butadiene latex solution, nano-calcium carbonate and para-aramid polymerization liquid is (3-5):(15-18):(66-76):(1-2):(3-5):(2-4); hydrogen chloride produced when para-aramid is synthesized from para-phenylenediamine and terephthaloyl chloride is removed from the para-aramid polymerization liquid before use; the gas phase powder is a mixture of one or more of gas phase alumina, gas phase silica and gas phase barium titanate.

2. The para-aramid slurry according to claim 1, characterized in that: When synthesizing para-aramid in the para-aramid polymerization liquid, a deacidifying agent is added to absorb the hydrogen chloride produced when para-phenylenediamine and terephthaloyl chloride are synthesized into para-aramid.

3. The para-aramid slurry according to claim 2, characterized in that: The deacidifying agent is one or a mixture of pyridine, sodium hydroxide and calcium hydroxide.

4. The para-aramid slurry according to claim 1, characterized in that: The ceramic powder is one or a mixture of several of aluminum oxide, aluminum hydroxide, boehmite and barium sulfate.

5. The para-aramid slurry according to claim 1, characterized in that: The para-aramid polymer solution comprises: para-aramid, calcium chloride and a second solvent. The concentration of para-aramid in the para-aramid polymer solution is 2-5wt%, the concentration of calcium chloride in the para-aramid polymer solution is 3-8wt%, the second solvent is NMP, and the water content of the second solvent is ≤0.2wt%.

6. The para-aramid slurry according to claim 1, characterized in that: The particle size of the nano calcium carbonate is 20-80 nm.

7. The para-aramid slurry according to claim 1, characterized in that: The first solvent is NMP, and the water content of the first solvent is ≤0.2 wt %.

8. The method for preparing the para-aramid slurry according to claim 1, comprising: The first solvent and the styrene-butadiene latex solution are mixed evenly to obtain a B solution, the nano-calcium carbonate and the B solution are mixed evenly, sand-milled to obtain a C solution, the C solution and the second solution are mixed, stirred until uniform, and a para-aramid slurry is obtained, wherein the method for preparing the second solution is: the gas phase powder, the ceramic powder and the first solvent are mixed evenly, sand-milled to obtain an A solution, the A solution is mixed with a para-aramid polymer solution, stirred until uniform, and a second solution is obtained.

9. A double-sided coated para-aramid diaphragm, characterized in that: include: A base film and a coating coated on the base film, wherein the coating is obtained by coating the para-aramid slurry according to claim 1.

10. The para-aramid diaphragm according to claim 9, characterized in that: The method for preparing the double-sided coated para-aramid diaphragm comprises: double-sidedly coating the para-aramid slurry on the base film, extracting to remove the nano calcium carbonate in the para-aramid slurry, and drying to obtain the double-sided coated para-aramid diaphragm.

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