Reaction inhibitor-based lithium battery separator and method for manufacturing same

Abstract

The present invention discloses a lithium battery based on a reaction control agent and a method for manufacturing the same. [Solution] A lithium battery separator is produced from a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight. The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight includes adding a reaction inhibitor to a process for synthesizing poly(paraphenylene terephthalamide) from p-phenylenediamine and terephthaloyl dichloride to obtain a para-aramid polymerization liquid containing the reaction inhibitor, which has a low apparent viscosity and a high molecular weight. The concentration of the reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is less than 300 ppm, and the concentration of water in a first solvent used to synthesize poly(paraphenylene terephthalamide) is 100 ppm or less. The reaction inhibitor is miscible with the first solvent and can simultaneously solidify poly(paraphenylene terephthalamide). According to the present invention, a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight exhibits a reduced apparent viscosity, coarsened fibers, increased porosity, improved wettability, and improved thermal stability.

Description

[Technical Field]

[0001] The present invention relates to the technical field of battery separators, and more particularly to a lithium battery separator based on a reaction inhibitor and a method for manufacturing the same. [Background technology]

[0002] With the development of social economy, the demand for lithium ion batteries is becoming increasingly large, so the safety issues of lithium ion batteries during use are undoubtedly becoming an issue that needs to be resolved at present.

[0003] Lithium-ion batteries are prone to combustion and explosion during use. For example, under abnormal operating conditions such as a collision, the lithium-ion battery separator can be destroyed, causing direct contact between the positive and negative electrodes, leading to short-circuiting of the battery and more serious consequences such as thermal runaway, spontaneous combustion, or explosion. Therefore, the separator must have good thermal stability and mechanical performance. Furthermore, the separator must have high ion permeability to ensure the electrochemical performance of the lithium-ion battery.

[0004] Para-aramid has high heat resistance (a glass transition temperature of over 300°C, a thermal decomposition temperature as high as 560°C, and 84% strength retention after 48 hours in air at 180°C), high tensile strength, and initial modulus of elasticity (fiber strength of 0.215 Newtons / denier, modulus of elasticity of 4.9-9.8 Newtons / denier, specific strength five times that of steel). It also has stable thermal shrinkage and creep properties, and excellent insulating properties and chemical corrosion resistance, making it an excellent separator material. Therefore, the use of separator slurries containing para-aramid to manufacture battery separators has become an important research direction.

[0005] CN115295961A proposes dissolving a para-aramid product in a solvent together with a dissolution promoter (strong base) to prepare a slurry, coating the slurry on a base film to form a composite membrane, and then curing the separator slurry containing the para-aramid in the composite membrane by steam-induced phase separation to form pores. This method uses a strong base as a solvent, which has a relatively high risk factor, and the cost of the para-aramid product is relatively high, and the steam-induced phase separation method is relatively cumbersome.

[0006] CN114388985A proposes producing a separator containing para-aramid by directly using a para-aramid polymerization solution to prepare a wet-process porous aramid film layer and then coating both sides of the film layer with an aqueous solution of para-aramid nanofibers. While this separator can effectively demonstrate the performance advantages of para-aramid, the para-aramid content used in this method is relatively high, the cost is relatively high, and the process is relatively complicated.

[0007] CN111019124A proposes adding polyethylene glycol and gas-phase nanoceramic particles during the synthesis of para-aramid, and then adding dimethyl carbonate as a pore-forming agent after the polymerization is complete. While this method effectively extends the shelf life of the slurry, the resulting slurry has a high apparent viscosity, which is unfavorable for coating, and the coating thickness is large, resulting in a relatively thick separator, which is unfavorable for ion migration. On the other hand, the addition of the pore-forming agent increases the difficulty of recovering the extractant at a later stage.

[0008] CN109411676A proposes that adding a non-solvent to a para-aramid solution as a pore-forming agent for the coating slurry can effectively improve the thermal stability and heat shrinkage resistance of separators. However, in actual production, this method results in a slurry with a too high apparent viscosity, which makes it difficult to smoothly supply the slurry and makes mass production difficult. Furthermore, adding a pore-forming agent is equivalent to introducing a new substance, which is disadvantageous for the separation and recovery of the extractant (solvent), increasing production costs. Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the drawbacks of the prior art, an object of the present invention is to provide a method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight.

[0010] Another object of the present invention is to provide a slurry for coating separators in lithium batteries.

[0011] Another object of the present invention is to provide a method for producing a slurry for coating separators of lithium batteries.

[0012] Another object of the present invention is to provide a method for manufacturing a lithium battery separator. [Means for solving the problem]

[0013] The object of the present invention is achieved by the following technical solutions. A method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, comprising the step of adding a reaction inhibitor to a process for synthesizing polyparaphenylene terephthalamide (PPTA) from p-phenylenediamine and terephthaloyl dichloride to obtain a para-aramid polymerization liquid containing the reaction inhibitor, the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, wherein the concentration of the reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is 300 ppm or less (the concentration of the reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is preferably 200 ppm or less, and more preferably 150 ppm or less), the concentration of water in a first solvent used to synthesize polyparaphenylene terephthalamide is 100 ppm or less, and the reaction inhibitor is a solvent that dissolves in the first solvent and is capable of simultaneously solidifying polyparaphenylene terephthalamide (PPTA, para-aramid).

[0014] In the above technical solution, the reaction control agent is deionized water, alcohols, esters or ethers.

[0015] Specifically, the method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight includes the following steps:

[0016] Step 1: A step of mixing a solubility-promoting salt and a first solvent under a nitrogen or inert gas atmosphere and stirring until the solubility-promoting salt is uniformly dispersed in the first solvent to obtain a first mixed solution, wherein the ratio of the first solvent to the solubility-promoting salt is (100 to 103):(3 to 8) parts by mass.

[0017] In step 1, the solubility-promoting salt is calcium chloride and / or lithium chloride.

[0018] In step 1, the first solvent is a non-aqueous solvent or an aqueous solvent, the non-aqueous solvent being a mixture of one or more selected from N-methylpyrrolidone, hexamethylphosphoric triamide, dimethylacetamide, and tetramethylurea, and the aqueous solvent being a mixture of a non-aqueous solvent and water.

[0019] In step 1, the stirring speed is 300 to 1500 rpm, the stirring time is 60 to 120 minutes, and the stirring temperature is 50 to 90°C.

[0020] Step 2: A step of cooling the first mixed solution to 5 to 15°C under a nitrogen or inert gas atmosphere, adding p-phenylenediamine to the first mixed solution, and stirring until homogenous to obtain a second mixed solution, wherein the ratio of parts by mass of the first mixed solution to parts by mass of the p-phenylenediamine substance is 100:(16 to 20), the unit of parts by mass of the substance is mol, and the unit of parts by mass is kg.

[0021] In step 2, the stirring speed is 300 to 1500 rpm, and the stirring time is 20 to 50 minutes.

[0022] Step 3: A step of cooling the second mixed solution to −5 to 5° C. under a nitrogen or inert gas atmosphere, adding terephthaloyl dichloride to the second mixed solution, and stirring until homogenous, thereby obtaining a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, wherein the ratio of paraphenylenediamine to terephthaloyl dichloride is (1 to 1.05):1 in terms of parts by mass.

[0023] In the steps 1 to 3, the reaction inhibitor is added once or in multiple portions in any of the steps 1 to 3 so that the concentration of the reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is 300 ppm or less.

[0024] In the step 3, the stirring speed is 300 to 1500 rpm, and the stirring time is 10 to 30 minutes.

[0025] A slurry for coating separators of lithium batteries, comprising: a second solvent, ceramic solid particles, and a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, wherein the ratio of the ceramic solid particles to the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is (5 to 30):(50 to 80) parts by mass, and the ceramic solid particles are a mixture of one or more materials selected from alumina, fumed alumina, silica, zirconium oxide, aluminum hydroxide, magnesium hydroxide, barium sulfate, boehmite, boron nitride, silicon nitride, and silicon carbide.

[0026] In the above technical solution, the slurry for coating separator of lithium battery further comprises a dispersant, and the ratio of the dispersant to the ceramic solid particles is (0.01-5):(5-30) in parts by mass, and the dispersant is a mixture of one or more selected from a polymer block copolymer dispersant, a polyacrylic acid sodium salt, a polyacrylic acid potassium salt, a polyacrylic acid ammonium salt, and a polycarboxylic acid sodium salt.

[0027] In the above technical solution, the second solvent is the non-aqueous solvent or the aqueous solvent, and preferably, the second solvent is the same as the first solvent.

[0028] In the above technical solution, the ratio of the second solvent to the ceramic solid particles is (60-90):(5-30) in parts by mass.

[0029] In the above technical solution, the particle size of the ceramic solid particles is 0.05-10 μm, and the particle size of the fumed alumina is 50-600 nm.

[0030] The method for producing the slurry for coating separators of lithium batteries includes the following steps: uniformly mixing a second solvent, ceramic solid particles, and a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight to obtain a slurry for coating separators of lithium batteries.

[0031] When the slurry for coating separators of lithium batteries further contains a dispersant, the method for producing the slurry for coating separators of lithium batteries includes the following steps: uniformly mixing the dispersant, the second solvent, the ceramic solid particles, and the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight to obtain the slurry for coating separators of lithium batteries.

[0032] Specifically, the method for producing a slurry for coating separators of lithium batteries includes the following steps: S1: Providing a solution A, said solution A comprising a second solvent.

[0033] In the above S1, the above solution A further contains a dispersant. The method for preparing the second solvent is to mix the dispersant and the second solvent and stir until the dispersant is uniformly dispersed in the second solvent to obtain the solution A.

[0034] In the step S1, the stirring speed is 300 to 800 rpm, and the stirring time is 15 to 45 minutes.

[0035] S2: A step of adding ceramic solid particles to solution A obtained in S1, stirring, and sand milling to obtain solution B.

[0036] In S2, the stirring speed is 300 to 800 rpm, and the stirring time is 15 to 50 minutes.

[0037] In S2, the sand mill time is 30 to 60 minutes, and the sand mill speed is 1000 to 2000 rpm.

[0038] S3: A step of mixing and stirring the solution B described in S2 with a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight to obtain a slurry for coating separators of lithium batteries.

[0039] In S3, the stirring speed is 500 to 2000 rpm, and the stirring time is 20 to 60 minutes.

[0040] A lithium battery separator comprising a base film and a coating coated on one or both sides of the base film, the coating being prepared from a slurry for coating separators for lithium batteries.

[0041] In the above technical solution, the base film is a polyethylene separator, a PP / PE / PP three-layer separator, a nonwoven fabric or a polyimide separator.

[0042] The manufacturing method of the lithium battery separator includes the following steps: coating the lithium battery coating separator slurry on one side or both sides of the base film, performing solvent content gradient extraction, and drying to obtain the lithium battery separator.

[0043] In the above technical solution, the coating method is a microgravure coating method, a dip coating method or a slit coating method, and the thickness of the applied single-sided coating is 1-10 μm.

[0044] In the above technical solution, the thickness of the base film is 5 to 25 μm.

[0045] In the above technical solution, the solvent content gradient extraction is carried out by sequentially using an extractant containing an extracting liquid and water, and when using an extractant containing an extracting liquid, the concentration of the extracting liquid in the extractant used sequentially decreases.

[0046] In the above technical solution, the solvent content gradient extraction is carried out by sequentially using the first extractant, the second extractant, the third extractant, and the fourth extractant, where the first extractant, the second extractant, and the third extractant are mixtures of extractant and water, respectively, the concentration of extractant in the first extractant is 80-95 wt%, the concentration of extractant in the second extractant is 40-55 wt%, the concentration of extractant in the third extractant is 20-35 wt%, and the fourth extractant is water.

[0047] In the above technical solution, the drying temperature is 60 to 80°C, and the drying time is 30 to 120 seconds.

[0048] In the above technical solution, when the first solvent is a non-aqueous solvent, the extraction liquid is the same as the first solvent, and when the first solvent is an aqueous solvent, the extraction liquid is the same as the non-aqueous solvent.

[0049] The application of the lithium battery separator to lithium batteries.

[0050] In the above technical proposal, the positive electrode active material of the lithium battery is a ternary material composite of lithium cobalt oxide, lithium manganese oxide, and lithium nickel oxide. The negative electrode material is one selected from graphite and SiC. The electrolyte of the electrolyte solution in the lithium battery is a mixture of one or more selected from LiPF6, LiBF4, LiAsF6, and LiSbF6.

[0051] (Effects of the Invention) The present invention has the following advantageous effects compared to the prior art. 1. In the present invention, a reaction inhibitor is added to a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight at a concentration of 300 ppm or less, and the corresponding amounts of the reaction inhibitor and first solvent are added during the para-aramid synthesis process by reverse calculation. The reaction inhibitor can be added in one or more batches. The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight of the present invention includes a step of adding a reaction inhibitor. This controls the polymerization reaction rate, makes the chain lengths of the polymerized single chains more uniform, and makes the distribution of the polymer chains more regular, thereby reducing the apparent viscosity of the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, resulting in coarsening of the fibers, increasing porosity, further improving wettability, and improving thermal stability; 2. Because the fibers become coarse and the porosity increases, there is no need to add a pore-forming agent to the slurry, which is advantageous for reducing costs and improving efficiency. 3. Since no pore-forming agent is required, the extract can be simply neutralized with alkali and the solid and liquid can be separated by distillation. At the same time, due to the large difference in boiling points, water and the first and second solvents are also separated, which is advantageous for separating and recycling the extract. [Brief explanation of the drawings]

[0052] [Figure 1] 1 shows data on electrolytic wettability of lithium battery separators produced in Examples 1 and 2 and lithium battery separators produced in Comparative Examples 1 and 2. [Figure 2] 1 is a scanning electron microscope image of the lithium battery separator produced in Example 1. [Figure 3] 1 is a scanning electron microscope image of the lithium battery separator produced in Comparative Example 1. [Figure 4] CN109411676A is a scanning electron microscope image of a para-aramid separator. [Figure 5] 1 is a scanning electron microscope image of the lithium battery separator produced in Example 2. [Figure 6] 1 is a scanning electron microscope image of the lithium battery separator produced in Comparative Example 2. [Figure 7] 1 is a cross-sectional electron microscope image of the lithium battery separator produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0053] In the present invention, a reaction inhibitor is added to obtain a para-aramid polymerization liquid with low apparent viscosity and high molecular weight. The reaction inhibitor can control the reaction rate of the polymerization reaction. Under the condition that the weight average molecular weight remains unchanged or slightly decreases, the apparent viscosity can be reduced to the maximum extent, making the preparation of the slurry easier and more suitable for mass production by enterprises.

[0054] The slurry for coating separators for lithium batteries is produced by mixing a para-aramid polymerization liquid, which has a low apparent viscosity and a high molecular weight, with ceramic solid particles, ensuring that the coating can proceed smoothly and at the same time maximizing the performance advantages of para-aramid; on the other hand, since no pore-forming agent is used in the production of the slurry for coating separators for lithium batteries, the extractant after extraction contains only water and the extractant, in addition to the acid produced in the synthesis reaction, which is advantageous for separating and recycling the extractant.

[0055] The technical solution of the present invention will be further described below with reference to specific examples.

[0056] Basic information on raw materials and equipment for the following examples is as follows: [Table 1]

[0057] [Table 2]

[0058] The electrolyte permeability was measured in an electrolyte solution containing LiPF6 (purchased from Zhuhai Guangrui), and the LiPF6 concentration in the electrode solution was 1 mol / L.

[0059] Example 1

[0060] A method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight includes the following steps: Step 1: In a nitrogen atmosphere, the dissolution-promoting salt and the first solvent were mixed and stirred for 80 minutes at a temperature of 80°C and a rotation speed of 600 rpm until the dissolution-promoting salt was uniformly dispersed in the first solvent, yielding a first mixed solution. During the stirring process, deionized water was added as a reaction inhibitor so that the concentration of the reaction inhibitor in the para-aramid polymerization liquid, which had a low apparent viscosity and a high molecular weight, was 100 ppm. The ratio of the first solvent to the dissolution-promoting salt was 100:6 in parts by mass, the first solvent was an N-methylpyrrolidone solution, the water content in the first solvent was 62.3 ppm, and the dissolution-promoting salt was calcium chloride. Step 2: In a nitrogen atmosphere, the first mixed solution was cooled to 11°C, p-phenylenediamine was added to the first mixed solution, and the mixture was stirred at 600 rpm for 25 minutes until homogenous, yielding a second mixed solution. The ratio of parts by mass of the first mixed solution to parts by mass of the p-phenylenediamine substance was 100:16.5, with the units of parts by mass being kg and parts by mass of the substance being mol. Step 3: In a nitrogen atmosphere, the second mixed solution was cooled to 1.2°C, and terephthaloyl dichloride was added to the second mixed solution. The mixture was stirred at 600 rpm for 20 minutes until homogeneous, yielding a para-aramid polymerization solution with low apparent viscosity and high molecular weight. The ratio of p-phenylenediamine to terephthaloyl dichloride was 16.5:16 in terms of parts.

[0061] The slurry for coating separators for lithium batteries contains a second solvent, a dispersant, ceramic solid particles, and a para-aramid polymer liquid having a low apparent viscosity and a high molecular weight. The ratio of the dispersant, ceramic solid particles, and para-aramid polymer liquid having a low apparent viscosity and a high molecular weight, in parts by mass, was 0.5:15:60, and the ratio of the second solvent to the ceramic solid particles was 83.5:15. In this example, the dispersant was BYK-LPN21954, the ceramic solid particles were alumina (solid particles) and fumed alumina (powder), the mass ratio of the alumina to the fumed alumina was 5:10, the particle size of the alumina was 0.05-1 μm, and the particle size of the fumed alumina was 50-150 nm. The second solvent was the same as the first solvent.

[0062] The method for producing a slurry for a coating separator of a lithium battery includes the following steps: S1: The dispersant and the second solvent were mixed and stirred at a rotation speed of 500 rpm for 25 minutes until the dispersant was uniformly dispersed in the second solvent, thereby obtaining solution A; S2: After adding alumina to solution A, the mixture was stirred at 500 rpm for 25 minutes, then fumed alumina was added and the mixture was stirred at 600 rpm for 25 minutes. After all the ceramic solid particles were added, the mixture was sand-milled at 1700 rpm for 50 minutes to obtain solution B; S3: The B solution was mixed with a para-aramid polymerization solution having a low apparent viscosity and a high molecular weight, and the mixture was stirred at a rotation speed of 600 rpm for 30 minutes to obtain a slurry for coating separators of lithium batteries.

[0063] The method for manufacturing a lithium battery separator includes the following steps: Using a microgravure coating method, the lithium battery separator coating slurry was applied to one side of a base film at a speed of 8 m / min, followed by solvent content gradient extraction. The resulting film was dried at 80 °C for 60 seconds to obtain a lithium battery separator. The coating thickness was 3 μm, and the base film was a 12 μm-thick PE film. The solvent content gradient extraction was performed using the first, second, third, and fourth extractants in sequence (the separator was immersed in each extractant for 9 s). The first, second, and third extractants were each a mixture of extractant and water. The extractant was N-methylpyrrolidone, with the extractant concentration in the first extractant being 90 wt%, the extractant concentration in the second extractant being 50 wt%, the extractant concentration in the third extractant being 30 wt%, and the fourth extractant being water.

[0064] Comparative Example 1

[0065] The method for producing the para-aramid polymerization liquid was basically the same as that in Example 1, except for the following difference: in this comparative example, deionized water was not added as a reaction inhibitor during the stirring process, and the water content in the first solvent was 55.4 ppm.

[0066] The slurry for coating separators of lithium batteries was basically the same as the slurry for coating separators of lithium batteries in Example 1, but the only difference was that the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight in the slurry for coating separators of lithium batteries in Example 1 was replaced with the "para-aramid polymerization liquid" in this comparative example.

[0067] The method for producing a slurry for coating separators of lithium batteries in this comparative example was basically the same as the method for producing a slurry for coating separators of lithium batteries in Example 1, with the only difference being the following: the para-aramid polymerization liquid with a low apparent viscosity and a high molecular weight in the method for producing a slurry for coating separators of lithium batteries in Example 1 was replaced with the "para-aramid polymerization liquid" in this comparative example.

[0068] The manufacturing method of the lithium battery separator was basically the same as the "manufacturing method of the lithium battery separator" of Example 1, but the differences were as follows: the slurry for coating separator of the lithium battery obtained using the para-aramid polymerization liquid obtained in Comparative Example 1 had an apparent viscosity that was too high, and the supply speed during the on-machine coating process was slow and could not be matched to the coating speed, resulting in serious coating leakage, and furthermore, the thickness of the coating on one side of the lithium battery separator after coating was 2 μm.

[0069] Example 2

[0070] A method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight includes the following steps: Step 1: In a nitrogen atmosphere, the dissolution-promoting salt and the first solvent were mixed and stirred for 80 minutes at a temperature of 80°C and a rotation speed of 600 rpm until the dissolution-promoting salt was uniformly dispersed in the first solvent, yielding a first mixed solution. The ratio of the first solvent to the dissolution-promoting salt was 100:6.5 in parts by mass, the first solvent was an N-methylpyrrolidone solution, the water content in the first solvent was 61.2 ppm, and the dissolution-promoting salt was calcium chloride. Step 2: In a nitrogen atmosphere, the first mixed solution was cooled to 9.2°C, p-phenylenediamine was added to the first mixed solution, and the mixture was stirred at 600 rpm for 35 minutes until homogeneous, yielding a second mixed solution. During the stirring process, deionized water was added as a reaction inhibitor to achieve a reaction inhibitor concentration of 200 ppm in the para-aramid polymerization solution, which had a low apparent viscosity and a high molecular weight. The ratio of parts by mass of the first mixed solution to parts by mass of the p-phenylenediamine substance was 100:17.5, with the units of parts by mass being kg and parts by mass being mol. Step 3: In a nitrogen atmosphere, the second mixed solution was cooled to -1.0°C, and terephthaloyl dichloride was added to the second mixed solution. The mixture was stirred at 600 rpm for 10 minutes until homogeneous, yielding a para-aramid polymerization solution with low apparent viscosity and high molecular weight. The ratio of paraphenylenediamine to terephthaloyl dichloride was 17.5:17 in terms of parts.

[0071] The slurry for coating separators for lithium batteries contains a second solvent, a dispersant, ceramic solid particles, and a para-aramid polymer liquid having a low apparent viscosity and a high molecular weight. The ratio of the dispersant to the ceramic solid particles to the para-aramid polymer liquid having a low apparent viscosity and a high molecular weight, in parts by mass, was 1:10:55, and the ratio of the second solvent to the ceramic solid particles was 89:10. In this example, the dispersant was BYK-LPN21954, the ceramic solid particles were alumina (solid particles) and fumed alumina (particles), the mass ratio of the alumina to the fumed alumina was 5:5, the particle size of the alumina was 0.05 to 1 μm, and the particle size of the fumed alumina was 50 to 150 nm. The second solvent was the same as the first solvent.

[0072] The method for producing the slurry for coating separator of the lithium battery includes the following steps: S1: The dispersant and the second solvent were mixed and stirred at room temperature at a rotation speed of 500 rpm for 25 minutes until the dispersant was uniformly dispersed in the second solvent, thereby obtaining solution A; S2: Alumina was added to solution A, and the mixture was stirred at room temperature for 25 minutes at a rotation speed of 600 rpm. Then, fumed alumina was added and the mixture was stirred at a rotation speed of 600 rpm for 25 minutes. After all the ceramic solid particles were added, the mixture was sand-milled at a rotation speed of 1700 rpm for 50 minutes to obtain solution B; S3: The B solution was mixed with a para-aramid polymerization solution having a low apparent viscosity and a high molecular weight, and the mixture was stirred at room temperature at a rotation speed of 600 rpm for 30 minutes to obtain a slurry for coating separators of lithium batteries.

[0073] The method for manufacturing a lithium battery separator includes the following steps: Using a microgravure coating method, the lithium battery separator coating slurry was applied to one side of a base film at a speed of 8 m / min, followed by solvent content gradient extraction. The resulting film was dried at 80°C for 60 seconds to obtain a lithium battery separator. The coating thickness was 3 μm, and the base film was a 9 μm-thick PE film. The solvent content gradient extraction was carried out using the first, second, third, and fourth extractants in sequence (the separator was immersed in each extractant for 9 seconds). The first, second, and third extractants were each a mixture of extractant and water. The extractant was N-methylpyrrolidone, with the extractant concentration in the first extractant being 90 wt%, the extractant concentration in the second extractant being 50 wt%, the extractant concentration in the third extractant being 30 wt%, and the fourth extractant being water.

[0074] Comparative Example 2

[0075] The method for producing the para-aramid polymerization liquid was basically the same as that in Example 2, except for the following differences: in this comparative example, deionized water was not added as a reaction inhibitor during the stirring process, the water content in the first solvent was 61.6 ppm, and the "cooling the second mixed solution to -1.0°C" in Example 2 was replaced with "cooling the second mixed solution to -1.2°C."

[0076] The manufacturing method of the slurry for coating separators of lithium batteries was basically the same as the manufacturing method of the slurry for coating separators of lithium batteries in Example 2, with the only difference being that the para-aramid polymerization liquid with low apparent viscosity and high molecular weight in the manufacturing method of the slurry for coating separators of lithium batteries in Example 2 was replaced with the "para-aramid polymerization liquid" in this comparative example.

[0077] The lithium battery separator was manufactured by manually applying the lithium battery coating separator slurry of this comparative example to the surface of a 9 μm PE base film, followed by solvent gradient extraction and drying to obtain a lithium battery separator. The "solvent gradient extraction and drying" of this comparative example was identical to the "solvent gradient extraction and drying" of the "lithium battery separator manufacturing method" of Example 2. (The lithium battery coating separator slurry obtained using the para-aramid polymerization solution of Comparative Example 2 had such a high apparent viscosity that the supply operation was not smooth, and it could only be coated manually. The material was severely damaged during the solvent gradient extraction process after application.)

[0078] Example 3

[0079] A method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight includes the following steps: Step 1: In a nitrogen atmosphere, the dissolution-promoting salt and the first solvent were mixed and stirred for 80 minutes at 80°C and 600 rpm until the dissolution-promoting salt was uniformly dispersed in the first solvent, yielding a first mixed solution. During the stirring process, deionized water was added as a reaction inhibitor. The ratio of the first solvent to the dissolution-promoting salt was 100:7.5 by mass, the first solvent was an N-methylpyrrolidone solution, the water content in the first solvent was 56.4 ppm, and the dissolution-promoting salt was calcium chloride. Step 2: In a nitrogen atmosphere, the first mixed solution was cooled to 8.6°C, p-phenylenediamine was added to the first mixed solution, and the mixture was stirred at 600 rpm for 40 minutes until homogeneous, yielding a second mixed solution. During the stirring process, deionized water was added as a reaction inhibitor. The ratio of parts by mass of the first mixed solution to parts by mass of the p-phenylenediamine substance was 100:18.2, with units of parts by mass being kg and units of parts by mass being mol. Step 3: In a nitrogen atmosphere, the second mixed solution was cooled to -2.3°C, terephthaloyl dichloride was added to the second mixed solution, and the mixture was stirred at 600 rpm for 15 minutes until homogeneous, yielding a para-aramid polymerization liquid with low apparent viscosity and high molecular weight. During the cooling process, deionized water was added as a reaction inhibitor. The ratio of p-phenylenediamine to terephthaloyl dichloride was 18.2:18 in parts by mass. In this example, the ratio of the reaction inhibitor added in Step 1, Step 2, and Step 3 was 5:3:2 in parts by mass, so that the concentration of the reaction inhibitor in the para-aramid polymerization liquid with low apparent viscosity and high molecular weight was 300 ppm.

[0080] The slurry for coating separators for lithium batteries contained a second solvent, ceramic solid particles, and a para-aramid polymer liquid having a low apparent viscosity and a high molecular weight. The ratio of the second solvent, ceramic solid particles, and para-aramid polymer liquid having a low apparent viscosity and a high molecular weight was 3:1:4 in parts by mass. The ceramic solid particles were barium sulfate (solid particles), and the particle size of the barium sulfate was 0.05 to 1 μm. The second solvent was the same as the first solvent.

[0081] The method for producing a slurry for a coating separator of a lithium battery includes the following steps: The second solvent was provided as S1:A solution; S2: Ceramic solid particles were added to the second solvent, stirred at a rotation speed of 500 rpm for 35 minutes, and then sand milled at a rotation speed of 1700 rpm for 50 minutes to obtain solution B; S3: The B solution was mixed with a para-aramid polymer solution having a low apparent viscosity and a high molecular weight, and the mixture was stirred at room temperature at 600 rpm for 30 minutes to obtain a slurry for coating separators for lithium batteries.

[0082] The method for manufacturing a lithium battery separator includes the following steps: Using a microgravure coating method, the lithium battery separator coating slurry was applied to one side of a base film at a speed of 8 m / min, followed by solvent content gradient extraction. The resulting film was dried at 80°C for 60 seconds to obtain a lithium battery separator. The coating thickness was 3 μm, and the base film was a 9 μm-thick PE film. The solvent content gradient extraction was carried out using the first, second, third, and fourth extractants in sequence (the separator was immersed in each extractant for 9 seconds). The first, second, and third extractants were each a mixture of extractant and water. The extractant was N-methylpyrrolidone, with the extractant concentration in the first extractant being 90 wt%, the extractant concentration in the second extractant being 50 wt%, the extractant concentration in the third extractant being 30 wt%, and the fourth extractant being water.

[0083] Comparative Example 3

[0084] The method for producing the para-aramid polymerization liquid was basically the same as that in Example 3, except for the following differences: in this comparative example, deionized water was not added as a reaction inhibitor, the water content in the first solvent was 57.6 ppm, and the "cooling the second mixed solution to -2.3°C" in Example 3 was replaced with "cooling the second mixed solution to -2.6°C."

[0085] The method for producing a slurry for a lithium battery coating separator was performed according to the method for producing a slurry for a lithium battery coating separator of Example 3, except that the para-aramid polymerization liquid with a low apparent viscosity and a high molecular weight used in the method for producing a slurry for a lithium battery coating separator of Example 3 was replaced with the "para-aramid polymerization liquid" used in this comparative example. During the process of producing a slurry for a lithium battery coating separator using the para-aramid polymerization liquid obtained in Comparative Example 3, the para-aramid polymerization liquid continued to polymerize, the apparent viscosity of the para-aramid polymerization liquid continued to increase, and the slurry gradually hardened, preventing the pulping process from proceeding smoothly. Therefore, the following measurements could not be performed successfully when a lithium battery separator was produced using the slurry for a lithium battery coating separator produced in Comparative Example 3.

[0086] The apparent viscosity was measured for the para-aramid polymerization liquids having low apparent viscosity and high molecular weight produced in Examples 1 to 3 and the para-aramid polymerization liquids produced in Comparative Examples 1 to 3. The para-aramid polymerization liquids having low apparent viscosity and high molecular weight / para-aramid polymerization liquids were extruded to form films, which were then washed with water and dried, and the loss on heat and the weight average molecular weight were measured. A comparison of the results is shown in Table 1.

[0087] Table 1 [Table 3]

[0088] From the analysis of Table 1, it can be seen that after adding a reaction inhibitor during the synthesis of polyparaphenylene terephthalamide (PPTA), the resulting para-aramid polymerization solution has a low apparent viscosity and a high molecular weight. The apparent viscosity and weight-average molecular weight are significantly reduced, but the weight-average molecular weight distribution is relatively uniform, and the percentage of the polymer that does not decompose until temperatures exceed 600°C increases, thereby improving heat resistance.

[0089] The performance of the lithium battery separators produced in Examples 1 to 3 and Comparative Examples 1 and 2 was measured, and the results are shown in Tables 2 and 3 and FIG.

[0090] Table 2 [Table 4]

[0091] Table 3 [Table 5]

[0092] Tables 2 and 3 show that the measured data of the Examples and the corresponding Comparative Examples are similar to or even superior to the Examples, specifically, the thermal stability is maintained and the mechanical tensile strength is improved. Figure 1 shows that the electrolyte wettability of the Examples is superior to that of the corresponding Comparative Examples.

[0093] The lithium battery separators manufactured in Examples 1 to 3 and Comparative Example 1 were assembled into lithium ion batteries. The positive electrode material was a ternary material (purchased from Philips Lithium Energy) in which lithium cobalt oxide, lithium manganese oxide, and lithium nickel oxide were composited. The negative electrode material was graphite. The electrolyte in the electrolytic solution was LiPF6. The results are shown in Table 4.

[0094] Table 4 [Table 6]

[0095] Comparative Example 4

[0096] For the manufacturing method of para-aramid separator, please refer to CN109411676A.

[0097] Compared with Patent CN10941676A, the present invention does not use a pore-forming agent, which is more advantageous for extractant recovery, and has improved breathability, thermal shrinkage, and needle puncture resistance, thereby achieving the goals of cost reduction and efficiency improvement.

[0098] From Figures 2-3 and 5-6, it can be seen that in the examples, the addition of the reaction inhibitor resulted in relatively thick fibers, a uniform distribution of ceramics and fibers, and a significant increase in porosity, whereas in the comparative examples, the fibers were relatively fine, resulting in aggregation and an uneven distribution of ceramics and fibers.

[0099] As can be seen from Figure 4, the fibers of the para-aramid separator manufactured by CN109411676A are clearly visible and stacked layer by layer, but only a small amount of ceramic particles are shown on the right side. This indicates that the distribution of the fibers and ceramic is uneven, which suggests that stratification may occur between the fibers and ceramic.

[0100] As can be seen from Figure 7, the fibers and ceramics in the para-aramid separator produced in Example 1 of the present invention are distributed alternately, uniformly, and orderly, allowing the coated separator to better combine the performance advantages of fibers and ceramics.

[0101] As can be seen from the above analysis, the addition of a reaction inhibitor during the synthesis of PPTA can effectively reduce the apparent viscosity of the synthesized product while ensuring the molecular weight of the synthesized product. The lithium battery separator obtained by mixing the reaction inhibitor with ceramic and then preparing a lithium battery separator coating slurry and applying it to a base film maintains thermal stability, improves mechanical tensile strength, significantly increases porosity, and improves electrolyte wettability.

[0102] Example 4 (Comparative)

[0103] The method for producing the para-aramid polymerization liquid was basically the same as that of Comparative Example 1, except for the following difference: the water content in the first solvent of this example was 20 ppm.

[0104] Example 5

[0105] The method for producing the para-aramid polymerization liquid was basically the same as in Example 4, except for the following difference: the water content of the first solvent was different. In this example, the water content of the first solvent was 103 ppm.

[0106] Example 6

[0107] The method for producing the para-aramid polymerization liquid was basically the same as in Example 4, except for the following difference: the water content of the first solvent was different. In this example, the water content of the first solvent was 162 ppm.

[0108] Example 7

[0109] The method for producing the para-aramid polymerization liquid was basically the same as in Example 4, except for the following difference: the water content of the first solvent was different. In this example, the water content of the first solvent was 240 ppm.

[0110] Example 8

[0111] The method for producing the para-aramid polymerization liquid was basically the same as in Example 4, except for the following difference: the water content of the first solvent was different. In this example, the water content of the first solvent was 350 ppm.

[0112] Example 9

[0113] The method for producing the para-aramid polymerization liquid was basically the same as in Example 4, except for the following difference: the water content of the first solvent was different. In this example, the water content of the first solvent was 420 ppm.

[0114] Example 10

[0115] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as that in Example 1, except for the following difference: the amount of reaction inhibitor added. In this Example, the amount of reaction inhibitor added was 50 ppm (addition amount: the reaction inhibitor was added so as to achieve a concentration of reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight).

[0116] Example 11

[0117] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction inhibitor added. In this example, the amount of reaction inhibitor added was 100 ppm.

[0118] Example 12

[0119] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction inhibitor added. In this example, the amount of reaction inhibitor added was 150 ppm.

[0120] Example 13

[0121] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction inhibitor added. In this example, the amount of reaction inhibitor added was 200 ppm.

[0122] Example 14

[0123] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction inhibitor added. In this example, the amount of reaction inhibitor added was 250 ppm.

[0124] Example 15

[0125] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction inhibitor added. In this example, the amount of reaction inhibitor added was 300 ppm.

[0126] Example 16

[0127] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction inhibitor added. In this example, the amount of reaction inhibitor added was 350 ppm.

[0128] Example 17

[0129] The method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction inhibitor added. In this example, the amount of reaction inhibitor added was 400 ppm.

[0130] The apparent viscosity was measured for the para-aramid polymerization liquids produced in Examples 4 to 9 and the para-aramid polymerization liquids having low apparent viscosity and high molecular weight produced in Examples 10 to 17. The para-aramid polymerization liquids / para-aramid polymerization liquids having low apparent viscosity and high molecular weight were extruded to form films, washed with water, and dried, and the loss on heat and weight average molecular weight were measured. The results are shown in Table 5.

[0131] Table 5 [Table 7] TIFF2025535101000009.tif32170

[0132] The method for producing the slurry for coating separators of lithium batteries was the same as the method for producing the slurry for coating separators of lithium batteries in Example 1, except for the following difference: the "para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight" in the method for producing the slurry for coating separators of lithium batteries in Example 1 was replaced with "any one of the para-aramid polymerization liquids having a low apparent viscosity and a high molecular weight produced in Examples 10 to 17 and the para-aramid polymerization liquids produced in Examples 4 to 9."

[0133] The lithium battery separator was manufactured according to the "Method for manufacturing a lithium battery separator" in Example 1. Here, the slurry for coating the lithium battery separator was any one of the slurries manufactured in Examples 6, 7, and 10 to 16. (The slurry for coating separators for lithium batteries obtained using the para-aramid polymerization liquid produced in Example 4 could not be smoothly pulped because the apparent viscosity of the polymerization liquid was too high. The slurry for coating separators for lithium batteries obtained using the para-aramid polymerization liquid produced in Example 5 could not be fed because the apparent viscosity was too high. The slurry for coating separators for lithium batteries obtained using the para-aramid polymerization liquid produced in Example 6 had a too high apparent viscosity and was fed slowly. The slurries for coating separators for lithium batteries obtained using the para-aramid polymerization liquids produced in Examples 8 and 9 dropped material during the coating process. The slurry for coating separators for lithium batteries obtained using the para-aramid polymerization liquid produced in Example 17, which had a low apparent viscosity and a high molecular weight, dropped material all at once during the coating process. Therefore, the slurries for coating separators for lithium batteries produced in Examples 4 and 5, 8 and 9, and 17 were not used to produce lithium battery separators.)

[0134] The slurries for coating separators of lithium batteries produced in Examples 4 to 17 were subjected to apparent viscosity measurements (Table 6). The lithium battery separators produced in Examples 6, 7, and 10 to 16 were subjected to performance measurements (Table 7). The results are shown in Tables 6 and 7.

[0135] Table 6 [Table 8]

[0136] Table 7 [Table 9]

[0137] From the examples, it can be concluded that the appropriate synthesis conditions are to add a reaction inhibitor so that the water content of the first solvent is 100 ppm or less and the concentration of the reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is 300 ppm or less. The para-aramid polymerization liquid synthesized in this way has a low apparent viscosity and a relatively high weight-average molecular weight, making it suitable for preparing a coating slurry for lithium batteries.

[0138] As can be seen from the above data analysis, the slurry for coating separators for lithium batteries obtained by adjusting the ratio of the reaction inhibitor and water content in the first solvent can fully utilize the excellent thermal stability and high strength performance of para-aramid. Coating properties are directly related to the molecular weight of para-aramid. The weight-average molecular weight range of para-aramid suitable for slurry preparation and sufficient performance for lithium battery separators is 5,000 to 10,000. During the synthesis of the para-aramid polymerization solution, the optimal ratio of the reaction inhibitor and water content in the first solvent itself is determined to prepare a para-aramid polymerization solution with low apparent viscosity and high molecular weight. A slurry for coating separators for lithium batteries is prepared from the para-aramid polymerization solution with low apparent viscosity and high molecular weight. Battery separators obtained by applying this slurry exhibit excellent performance, with thermal shrinkage, pinpoint strength, and breathability all superior to those of Patent CN109411676A.

[0139] Although the present invention has been described above by way of example, it should be understood that any simple variations, modifications, or equivalent conversions that can be made by those skilled in the art without expending any creative effort without departing from the spirit and scope of the present invention are all included within the scope of protection of the present invention.

Claims

1. The method includes a step of adding a reaction inhibitor to a process of synthesizing polyparaphenylene terephthalamide from p-phenylenediamine and terephthaloyl dichloride to obtain a para-aramid polymerization liquid containing the reaction inhibitor and having a low apparent viscosity and a high molecular weight, The concentration of the reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is 300 ppm or less, the concentration of water in the first solvent used to synthesize polyparaphenylene terephthalamide is 100 ppm or less; the reaction inhibitor is a solvent that dissolves in the first solvent and can simultaneously solidify the polyparaphenylene terephthalamide; A method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, characterized by the above.

2. The reaction control agent is deionized water, alcohols, esters, or ethers. The method according to claim 1 .

3. A method for producing a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight includes the following steps: Step 1: mixing a solubility-promoting salt and a first solvent under a nitrogen or inert gas atmosphere and stirring until the solubility-promoting salt is uniformly dispersed in the first solvent to obtain a first mixed solution, wherein the ratio of the first solvent to the solubility-promoting salt is (100 to 103):(3 to 8) parts by mass; Step 2: cooling the first mixed solution to 5 to 15°C under a nitrogen or inert gas atmosphere, adding p-phenylenediamine to the first mixed solution, and stirring until homogenous to obtain a second mixed solution, wherein the ratio of parts by weight of the first mixed solution to parts by weight of the p-phenylenediamine substance is 100:(16 to 20), the unit of parts by weight of the substance is mol, and the unit of parts by weight is kg; Step 3: cooling the second mixed solution to −5 to 5° C. under a nitrogen or inert gas atmosphere, adding terephthaloyl dichloride to the second mixed solution, and stirring until the mixture becomes uniform, thereby obtaining a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, wherein the ratio of paraphenylenediamine to the terephthaloyl dichloride is (1 to 1.05):1 in terms of parts by mass; In the steps 1 to 3, the reaction inhibitor is added once or in multiple portions in any of the steps 1 to 3 so that the concentration of the reaction inhibitor in the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is 300 ppm or less. The method according to claim 1 or 2.

4. In step 1, the first solvent is a non-aqueous solvent or an aqueous solvent, the non-aqueous solvent is a mixture of one or more solvents selected from N-methylpyrrolidone, hexamethylphosphoric triamide, dimethylacetamide, and tetramethylurea, and the aqueous solvent is a mixture of a non-aqueous solvent and water, In step 1, the stirring temperature is 50 to 90°C, and the dissolution-promoting salt is calcium chloride and / or lithium chloride. The method according to any one of claims 1 to 3.

5. a second solvent, ceramic solid particles, and a para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight, the para-aramid polymerization liquid being obtained by the production method according to any one of claims 1 to 4; the ratio of the ceramic solid particles to the para-aramid polymerization liquid having a low apparent viscosity and a high molecular weight is (5 to 30):(50 to 80) parts by mass, the ceramic solid particles are a mixture of one or more selected from alumina, fumed alumina, silica, zirconium oxide, aluminum hydroxide, magnesium hydroxide, barium sulfate, boehmite, boron nitride, silicon nitride, and silicon carbide; A slurry for coating separators of lithium batteries, characterized by:

6. Further comprising a dispersant, the ratio of the dispersant to the ceramic solid particles is (0.01 to 5):(5 to 30) parts by mass; the dispersant is a mixture of one or more selected from a polymer block copolymer dispersant, a polyacrylic acid sodium salt, a polyacrylic acid potassium salt, a polyacrylic acid ammonium salt, and a polycarboxylic acid sodium salt; The second solvent is the non-aqueous solvent or the aqueous solvent, and preferably the second solvent is the same as the first solvent.

6. The slurry for coating separators of lithium batteries according to claim 5.

7. The ratio of the second solvent to the ceramic solid particles is (60 to 90):(5 to 30) parts by mass.

7. The slurry for coating separators of lithium batteries according to claim 6.

8. A base film and a coating applied to one or both sides of the base film, The coating is prepared from the slurry for coating separators of lithium batteries according to any one of claims 5 to 7. A lithium battery separator comprising:

9. The method includes the steps of applying the slurry for a lithium battery coating separator to one or both sides of a base film, performing solvent content gradient extraction, and drying to obtain a lithium battery separator.

9. The method for manufacturing a lithium battery separator according to claim 8.

10. 9. The lithium battery separator obtained by the method of claim 8, wherein the separator is applied to a lithium battery.

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