Lithium battery separator based on reaction control agent and method for manufacturing the 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 belongs to the technical field of battery separators, and specifically relates to a lithium battery separator based on a reaction control agent and a manufacturing method thereof. [Background Art]

[0002] With the development of social economy, the demand for lithium-ion batteries is increasing. Therefore, the safety issue during the use of lithium-ion batteries has undoubtedly become a problem that needs to be solved currently.

[0003] Lithium-ion batteries are prone to combustion and explosion during use. For example, under abnormal use conditions such as collision, the lithium-ion battery separator is damaged, and direct contact between the positive electrode and the negative electrode causes a short circuit in the battery, leading to thermal runaway and even more serious consequences such as spontaneous combustion or explosion. Therefore, the separator needs to have good thermal stability and mechanical properties. In addition, to guarantee the electrochemical performance of lithium-ion batteries, the separator needs to have higher ion permeability.

[0004] Para-aramid has high heat resistance (its glass transition temperature is above 300°C, the thermal decomposition temperature is as high as 560°C, and the strength retention rate after being left in air at 180°C for 48 hours is 84%), high tensile strength and initial elastic modulus (the strength of the fiber is 0.215 newton / denier, the elastic modulus is 4.9-9.8 newton / denier, and the specific strength is 5 times that of steel), stable thermal shrinkage and creep performance, as well as high insulation and chemical corrosion resistance. Therefore, it is a very excellent separator material. For this reason, manufacturing battery separators using separator slurry containing para-aramid has become an important research direction.

[0005] CN115295961A proposes a method in which a para-aramid product is dissolved using a solvent along with a dissolution accelerator (strong base), a slurry is prepared, the slurry is applied to a base film to form a composite film, and the separator slurry containing para-aramid in the composite film is cured by vapor induction phase separation to form pores. However, this method has a relatively high risk factor because a strong base is used as the solvent, the cost of the para-aramid product is relatively high, and the use of vapor induction phase separation is relatively cumbersome.

[0006] CN114388985A proposes a method for producing a porous aramid film layer using a para-aramid polymerization solution directly, and then applying an aqueous solution of para-aramid nanofibers to both sides of the film layer to create a para-aramid-containing separator. While this separator can effectively demonstrate the performance advantages of para-aramid, the para-aramid content used in this method is relatively high, resulting in relatively high costs and a relatively complex process.

[0007] CN111019124A proposes adding polyethylene glycol and gas-phase nanoceramic particles during the synthesis of para-aramid, and adding dimethyl carbonate as a pore-forming agent after polymerization is complete. While this method effectively extends the shelf life of the slurry, the slurry produced by this method has a high apparent viscosity, making it unsuitable for coating, resulting in a thick coating, a relatively thick separator, and unfavorable ion movement. On the other hand, the introduction of a pore-forming agent increases the difficulty of recovering the extractant in later stages.

[0008] CN109411676A proposes that adding a non-solvent as a pore-forming agent to the para-aramid solution can effectively improve the heat stability and thermal shrinkage resistance of the separator. However, in actual production, this method makes it difficult to supply the slurry smoothly due to its excessively high apparent viscosity, making mass production challenging. Furthermore, adding a pore-forming agent involves introducing a new substance, which is disadvantageous for the separation and recovery of the extractant (solvent), increasing production costs. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] In view of the shortcomings of the prior art, the present invention aims to provide a method for producing a paraaramid polymerization liquid with low apparent viscosity and high molecular weight.

[0010] Another objective of this invention is to provide a slurry for coating separators in lithium batteries.

[0011] Another objective of this invention is to provide a method for manufacturing a slurry for coating separators in lithium batteries.

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

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

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

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

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

[0017] In step 1, the dissolution-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 is a mixture of one or more selected from N-methylpyrrolidone, hexamethylphosphate triamide, dimethylacetamide, and tetramethylurea, and the aqueous solvent is a mixture of the non-aqueous solvent and water.

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

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

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

[0022] Step 3: A step in which the second mixed solution is cooled to -5 to 5°C under a nitrogen or inert gas atmosphere, terephthaloyl dichloride is added to the second mixed solution, and the mixture is stirred until homogeneous to obtain a para-aramid polymerization solution with low apparent viscosity and high molecular weight, wherein the ratio of paraphenylenediamine to terephthaloyl dichloride is (1 to 1.05):1 in parts by substance.

[0023] In steps 1 to 3, the reaction control agent is added in one or more steps during any of steps 1 to 3 so that the concentration of the reaction control agent in the paraaramid polymerization solution, which has low apparent viscosity and high molecular weight, is 300 ppm or less.

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

[0025] A slurry for a coated separator of a lithium battery, comprising a second solvent, ceramic solid particles, and a para-aramid polymerization solution with low apparent viscosity and high molecular weight, wherein the ratio of the ceramic solid particles to the para-aramid polymerization solution with low apparent viscosity and high molecular weight is (5~30):(50~80) in parts by mass, and the ceramic solid particles are one or more mixtures selected from the group consisting of 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 a coated separator of a lithium battery further comprises a dispersant, the ratio of the dispersant to the ceramic solid particles is (0.01~5):(5~30) in parts by mass, and the dispersant is one or more mixtures selected from the group consisting of polymer block copolymer dispersants, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, and sodium polycarboxylate.

[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 diameter of the ceramic solid particles is 0.05~10 μm, and the particle diameter of the fumed alumina is 50~600 nm.

[0030] A method for producing the above slurry for a coated separator of a lithium battery comprises the following step: uniformly mixing the second solvent, ceramic solid particles, and a para-aramid polymerization solution with low apparent viscosity and high molecular weight to obtain the slurry for a coated separator of a lithium battery.

[0031] If the slurry for the coating separator of a lithium battery further contains a dispersant, the method for producing the above-mentioned slurry for the coating separator of a lithium battery includes the following steps: a step of uniformly mixing a dispersant, a second solvent, ceramic solid particles, and a para-aramid polymerization solution with low apparent viscosity and high molecular weight to obtain a slurry for the coating separator of a lithium battery.

[0032] Specifically, the method for manufacturing a slurry for a lithium battery coating separator includes the following steps: S1: A step of providing solution A, wherein solution A includes a second solvent.

[0033] In S1, the A solution 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 A solution.

[0034] In S1, the stirring speed is 300-800 rpm, and the stirring time is 15-45 min.

[0035] S2: A step in which ceramic solid particles are added to solution A obtained in S1, the mixture is stirred, and a sand mill is performed to obtain solution B.

[0036] In step S2, the stirring speed is 300-800 rpm, and the stirring time is 15-50 min.

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

[0038] S3: A step of mixing solution B described in S2 with a para-aramid polymerization solution that has low apparent viscosity and high molecular weight, stirring, and obtaining a slurry for a lithium battery coating separator.

[0039] In step S3, the stirring speed is 500-2000 rpm, and the stirring time is 20-60 min.

[0040] A lithium battery separator comprising a base film and a coating applied to one or both sides of the base film, wherein the coating is prepared from a slurry for lithium battery coating separators.

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

[0042] The above-mentioned method for manufacturing a lithium battery separator includes the following steps: applying a slurry for lithium battery coating separators to one or both sides of a base film, performing solvent content gradient extraction, and drying to obtain a lithium battery separator.

[0043] In the above proposed technology, 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 to 10 μm.

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

[0045] In the above proposed technology, the solvent content gradient extraction is performed by sequentially using an extractant containing the extract and water. When extraction is performed using an extractant containing the extract, the concentration of the extract in the extractant used sequentially decreases.

[0046] In the above proposed technology, the solvent content gradient extraction is performed by sequentially using a first extractant, a second extractant, a third extractant, and a fourth extractant. Here, the first, second, and third extractants are each mixtures of extractant and water, the concentration of the extractant in the first extractant is 80-95 wt%, the concentration of the extractant in the second extractant is 40-55 wt%, the concentration of the extractant in the third extractant is 20-35 wt%, and the fourth extractant is water.

[0047] In the above proposed technology, the drying temperature is 60-80°C, and the drying time is 30-120 seconds.

[0048] In the above proposed technology, when the first solvent is a non-aqueous solvent, the extract is the same as that of the first solvent, and when the first solvent is an aqueous solvent, the extract is the same as that of the non-aqueous solvent.

[0049] Application of the above lithium battery separator to lithium batteries.

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

[0051] (Effects of the invention) Compared to the prior art, the present invention has the following beneficial effects. 1. In this invention, a para-aramid polymerization solution with low apparent viscosity and high molecular weight is infused with a reaction control agent at a concentration of 300 ppm or less, and the addition of a corresponding amount of the reaction control agent and the first solvent during the para-aramid synthesis process is calculated and reverse-estimated. The reaction control agent can be added in one or more stages. The method for producing a para-aramid polymerization solution with low apparent viscosity and high molecular weight according to this invention includes the step of adding a reaction control agent. This controls the rate of the polymerization reaction, makes the chain length of the polymerization chains more uniform, and makes the distribution of polymerization chains more regular, thereby lowering the apparent viscosity of the para-aramid polymerization solution with low apparent viscosity and high molecular weight, roughening the fibers, increasing the porosity, further improving the penetrating properties, and improving the thermal stability; 2. Because the fibers become rougher and the porosity increases, there is no need to add a pore-forming agent separately to the slurry, which is advantageous for cost reduction and efficiency improvement. 3. Since no pore-forming agent is required, the solid and liquid can be separated by distillation simply by neutralizing the extract with an alkali. At the same time, water and the first / second solvent are also separated due to the large difference in boiling points, which is advantageous for the separation and recycling of the extract. [Brief explanation of the drawing]

[0052] [Figure 1] This data shows the electrolytic permeability of the lithium battery separators manufactured in Examples 1 and 2 and the lithium battery separators manufactured in Comparative Examples 1 and 2. [Figure 2] This is a scanning electron microscope image of the lithium battery separator manufactured in Example 1. [Figure 3] This is a scanning electron microscope image of the lithium battery separator manufactured in Comparative Example 1. [Figure 4] This is a scanning electron microscope image of the para-aramid separator CN109411676A. [Figure 5] This is a scanning electron microscope image of the lithium battery separator manufactured in Example 2. [Figure 6] This is a scanning electron microscope image of the lithium battery separator manufactured in Comparative Example 2. [Figure 7] This is a cross-sectional electron microscope image of the lithium battery separator manufactured in Example 1. [Modes for carrying out the invention]

[0053] In this invention, a paraaramid polymerization solution with low apparent viscosity and high molecular weight is obtained by adding a reaction control agent. The reaction control agent can control the reaction rate of the polymerization reaction. Under the premise that the weight-average molecular weight remains unchanged or decreases slightly, the apparent viscosity is reduced to the maximum extent, making slurry preparation easier and more suitable for mass production by companies.

[0054] By mixing a para-aramid polymerization solution with low apparent viscosity and high molecular weight with ceramic solid particles to produce a slurry for lithium battery coating separators, it is possible to ensure that the coating proceeds smoothly and at the same time maximize the performance advantages of para-aramid. Furthermore, since no pore-forming agent is used in the production of the lithium battery coating separator slurry, the extractant after extraction contains only water and the extract, in addition to the acid produced in the synthesis reaction, which is advantageous for the separation and recycling of the extractant.

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

[0056] The basic information regarding the raw materials and equipment for the following examples is as follows: [Table 1]

[0057] [Table 2]

[0058] The electrolyte immersion test was performed using an electrolyte solution containing LiPF6 (purchased from Zhuhai Guangrui), with a LiPF6 concentration of 1 mol / L in the electrode solution.

[0059] Example 1

[0060] A method for producing a para-aramid polymerization solution with low apparent viscosity and 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 to uniformly disperse the dissolution-promoting salt in the first solvent to obtain the first mixed solution. During the stirring process, deionized water was added as a reaction control agent so that the concentration of the reaction control agent in the para-aramid polymerization solution, which has low apparent viscosity and high molecular weight, was 100 ppm. The ratio of the first solvent to the dissolution-promoting salt was 100:6 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: The first mixed solution was cooled to 11°C in a nitrogen atmosphere, p-phenylenediamine was added to the first mixed solution, and the mixture was stirred at a rotational speed of 600 rpm for 25 minutes until homogeneous to obtain the second mixed solution. The ratio of parts by mass of the first mixed solution to parts by volume of p-phenylenediamine was 100:16.5, with parts by mass being in kg and parts by volume being in moles. Step 3: The second mixed solution was cooled to 1.2°C in a nitrogen atmosphere, terephthaloyl dichloride was added to the second mixed solution, and the mixture was stirred at a rotational speed of 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 parts by substance.

[0061] The slurry for lithium battery coating separators contains a second solvent, a dispersant, ceramic solid particles, and a para-aramid polymerization solution with low apparent viscosity and high molecular weight. The ratio of the dispersant, ceramic solid particles, and para-aramid polymerization solution with low apparent viscosity and high molecular weight was 0.5:15:60 by mass, and the ratio of the second solvent to the ceramic solid particles was 83.5:15. In this example, the dispersant was BYK-LPN21954, and the ceramic solid particles were alumina (solid particles) and fumed alumina (powder). The mass ratio of alumina to fumed alumina was 5:10, 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.

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

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

[0064] Comparative Example 1

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

[0066] The slurry for the lithium battery coating separator was basically the same as the slurry for the lithium battery coating separator in Example 1. The only difference was that the para-aramid polymerization solution with low apparent viscosity and high molecular weight in the slurry for the lithium battery coating separator in Example 1 was replaced with the "para-aramid polymerization solution" in this comparative example.

[0067] The method for producing the lithium battery coating separator slurry in this comparative example was basically the same as the method for producing the lithium battery coating separator slurry in Example 1, except that the only difference was the following: the para-aramid polymerization solution with low apparent viscosity and high molecular weight in the method for producing the lithium battery coating separator slurry in Example 1 was replaced with the "para-aramid polymerization solution" in this comparative example.

[0068] The method for manufacturing the lithium battery separator was basically the same as the "Method for Manufacturing a Lithium Battery Separator" in Example 1, but the differences were as follows: The slurry for the lithium battery coating separator obtained using the para-aramid polymerization solution obtained in Comparative Example 1 had too high an apparent viscosity, resulting in a slow supply rate during the on-machine coating process, making it impossible to match the coating speed, and causing serious coating leakage. Furthermore, the thickness of the single-sided coating after coating the lithium battery separator was 2 μm.

[0069] Example 2

[0070] A method for producing a para-aramid polymerization solution with low apparent viscosity and 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 to obtain the first mixed solution. The ratio of the first solvent to the dissolution-promoting salt was 100:6.5 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: The first mixed solution was cooled to 9.2°C in a nitrogen atmosphere, p-phenylenediamine was added to the first mixed solution, and the mixture was stirred at a rotational speed of 600 rpm for 35 minutes until homogeneous to obtain the second mixed solution. During the stirring process, deionized water was added as a reaction control agent so that the concentration of the reaction control agent in the para-aramid polymerization solution, which has low apparent viscosity and high molecular weight, was 200 ppm. The ratio of parts by mass of the first mixed solution to parts by volume of p-phenylenediamine was 100:17.5, with parts by mass being in kg and parts by volume being in moles. Step 3: The second mixed solution was cooled to -1.0°C in a nitrogen atmosphere, terephthaloyl dichloride was added to the second mixed solution, and the mixture was stirred at a rotational speed of 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 by part of substance.

[0071] The slurry for lithium battery coating separators contains a second solvent, a dispersant, ceramic solid particles, and a para-aramid polymerization solution with low apparent viscosity and high molecular weight. The ratio of the dispersant, ceramic solid particles, and para-aramid polymerization solution with low apparent viscosity and high molecular weight was 1:10:55 by mass, and the ratio of the second solvent to the ceramic solid particles was 89:10. In this example, the dispersant was BYK-LPN21954, and the ceramic solid particles were alumina (solid particles) and fumed alumina (particles). The mass ratio of alumina to 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 manufacturing the slurry for the coating separator of the above-mentioned lithium battery includes the following steps: S1: The dispersant and the second solvent were mixed and stirred at room temperature at a rotational speed of 500 rpm for 25 minutes until the dispersant was uniformly dispersed in the second solvent to obtain solution A; S2: After adding alumina to solution A, the mixture was stirred at room temperature at a rotational speed of 600 rpm for 25 minutes, then fumed alumina was added and stirred at a rotational speed of 600 rpm for 25 minutes, and after adding all the ceramic solid particles, the mixture was sand-milled at a rotational speed of 1700 rpm for 50 minutes to obtain solution B; The S3:B solution was mixed with a para-aramid polymerization solution that had low apparent viscosity and 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 lithium battery coating separators.

[0073] The method for manufacturing a lithium battery separator includes the following steps: Using the microgravure coating method, a slurry for lithium battery coating separators was applied to one side of a base film at a speed of 8 m / min. Solvent content gradient extraction was performed, and the film was dried at 80°C for 60 seconds to obtain a lithium battery separator. The coated coating had a thickness of 3 μm, and the base film was a PE film with a thickness of 9 μm. Solvent content gradient extraction was performed using the first, second, third, and fourth extractants in order (the time the separator was immersed in each extractant was 9 s). The first, second, and third extractants were mixtures of extractant and water, respectively. The extractant was N-methylpyrrolidone, with an extractant concentration of 90 wt%, 50 wt%, 30 wt%, and water. The fourth extractant was water.

[0074] Comparative Example 2

[0075] The method for producing the paraaramid polymerization solution was basically the same as in Example 2, with the only difference being the following: In this comparative example, deionized water was not added as a reaction control agent during the stirring process, the water content in the first solvent was 61.6 ppm, and the step of "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 method for producing the slurry for the coating separator of lithium batteries was basically the same as the method for producing the slurry for the coating separator of lithium batteries in Example 2, but the only difference was the following: the para-aramid polymerization solution with low apparent viscosity and high molecular weight in the method for producing the slurry for the coating separator of lithium batteries in Example 2 was replaced with the "para-aramid polymerization solution" in this comparative example.

[0077] The method for manufacturing the lithium battery separator involved manually applying the slurry for the lithium battery coating separator of this comparative example to the surface of a 9 μm PE base film, followed by solvent content gradient extraction and drying to obtain the lithium battery separator. Here, the "solvent content gradient extraction and drying" in this comparative example was the same as the "solvent content gradient extraction and drying" in the "method for manufacturing the lithium battery separator" of Example 2. (The slurry for the lithium battery coating separator obtained using the para-aramid polymerization solution obtained in Comparative Example 2 had too high an apparent viscosity, making the supply operation difficult and requiring manual coating. Furthermore, significant material loss occurred during the solvent content gradient extraction process after application.)

[0078] Example 3

[0079] A method for producing a para-aramid polymerization solution with low apparent viscosity and 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 to obtain the first mixed solution. During the stirring process, deionized water was added as a reaction control agent. 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: The first mixed solution was cooled to 8.6°C in a nitrogen atmosphere, p-phenylenediamine was added to the first mixed solution, and the mixture was stirred at a rotational speed of 600 rpm for 40 minutes until homogeneous to obtain the second mixed solution. Deionized water was added as a reaction control agent during the stirring process. The ratio of parts by mass of the first mixed solution to parts by volume of p-phenylenediamine was 100:18.2, with parts by mass being in kg and parts by volume being in moles. Step 3: The second mixed solution was cooled to -2.3°C in a nitrogen atmosphere, terephthaloyl dichloride was added to the second mixed solution, and the mixture was stirred at a rotational speed of 600 rpm for 15 minutes until homogeneous, to obtain a para-aramid polymerization solution with low apparent viscosity and high molecular weight. Here, deionized water was added as a reaction control agent during the cooling process of the second mixed solution. The ratio of p-phenylenediamine to terephthaloyl dichloride was 18.2:18 by parts by mass. In this example, the ratio of the reaction control agent added in Step 1, the reaction control agent added in Step 2, and the reaction control agent added in Step 3 was 5:3:2 by mass so that the concentration of the reaction control agent in the para-aramid polymerization solution with low apparent viscosity and high molecular weight was 300 ppm.

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

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

[0082] The method for manufacturing a lithium battery separator includes the following steps: Using the microgravure coating method, a slurry for lithium battery coating separators was applied to one side of a base film at a speed of 8 m / min. Solvent content gradient extraction was performed, and the film was dried at 80°C for 60 seconds to obtain a lithium battery separator. The coated coating had a thickness of 3 μm, and the base film was a PE film with a thickness of 9 μm. Solvent content gradient extraction was performed using the first, second, third, and fourth extractants in order (the time the separator was immersed in each extractant was 9 s). The first, second, and third extractants were mixtures of extractant and water, respectively. The extractant was N-methylpyrrolidone, with an extractant concentration of 90 wt%, 50 wt%, 30 wt%, and water. The fourth extractant was water.

[0083] Comparative Example 3

[0084] The method for producing the paraaramid polymerization solution was basically the same as in Example 3, with the only differences being: in this comparative example, deionized water was not added as a reaction control agent, the water content in the first solvent was 57.6 ppm, and the step of "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 manufacturing the lithium battery coating separator slurry was carried out according to the method for manufacturing the lithium battery coating separator slurry of Example 3, but the para-aramid polymerization solution with low apparent viscosity and high molecular weight in the method for manufacturing the lithium battery coating separator slurry of Example 3 was replaced with the "para-aramid polymerization solution" in this comparative example. In the process of manufacturing the lithium battery coating separator slurry using the para-aramid polymerization solution obtained in Comparative Example 3, the para-aramid polymerization solution continued to polymerize, the apparent viscosity of the para-aramid polymerization solution continued to increase, and it gradually hardened, preventing the pulping process from proceeding smoothly. Therefore, it was not possible to successfully manufacture a lithium battery separator using the lithium battery coating separator slurry manufactured in Comparative Example 3 and perform the following measurements.

[0086] The apparent viscosity of the para-aramid polymerization solutions produced in Examples 1-3 above, which had low apparent viscosity and high molecular weight, and the para-aramid polymerization solutions produced in Comparative Examples 1-3 were measured. After extrusion deposition of the para-aramid polymerization solutions with low apparent viscosity and high molecular weight, they were washed and dried with water, and the heat loss and weight-average molecular weight were measured. A comparison of the results is shown in Table 1.

[0087] Table 1 [Table 3]

[0088] Analysis in Table 1 shows that when a reaction control agent is added during the synthesis of poly(p-phenylene terephthalamide) (PPTA), the resulting para-aramid polymerization solution has a low apparent viscosity and a high molecular weight. However, the apparent viscosity decreases significantly, and the weight-average molecular weight decreases slightly. Furthermore, the distribution of weight-average molecular weight is relatively uniform, and the percentage of components that do not decompose below 600°C increases, indicating improved heat resistance.

[0089] Performance measurements were performed on the lithium battery separators manufactured in Examples 1-3 and Comparative Examples 1-2 described above. The results are shown in Tables 2 and 3 and Figure 1.

[0090] Table 2 [Table 4]

[0091] Table 3 [Table 5]

[0092] Tables 2 and 3 show that the measurement data for the examples and their corresponding comparative examples are similar to or better than those of the comparative examples, specifically that thermal stability is maintained and mechanical tensile strength is improved. Figure 1 shows that the electrolyte penetration properties of the examples are superior to those of the corresponding comparative examples.

[0093] The lithium battery separators produced in Examples 1-3 and Comparative Example 1 were assembled into lithium-ion batteries. The positive electrode material was a ternary material (purchased from Filipium Energy) composed of lithium cobalt oxide, lithium manganese oxide, and lithium nickelate. The negative electrode material was graphite. The electrolyte in the electrolyte solution was LiPF6. The results are shown in Table 4.

[0094] Table 4 [Table 6]

[0095] Comparative Example 4

[0096] For information on the manufacturing method of para-aramid separators, refer to CN109411676A.

[0097] Compared to patent CN10941676A, the present invention does not use a pore-forming agent, is more advantageous for extractant recovery, and improves aeration, thermal shrinkage, and needle-pierce resistance performance, achieving the objectives of cost reduction and improved efficiency.

[0098] Figures 2-3 and 5-6 show that in the example, the addition of the reaction control agent resulted in relatively thicker fibers, a uniform distribution of ceramics and fibers, and a significant increase in porosity. In contrast, in the comparative example, the fibers were relatively fine, leading to aggregation and an uneven distribution of ceramics and fibers.

[0099] As can be seen from Figure 4, the fibers of the paraaramid separator manufactured with CN109411676A are clearly visible and stacked in layers, but only a small amount of ceramic particles are shown on the right side. Because the distribution of fibers and ceramics is non-uniform, it can be inferred that stratification may occur between the fibers and ceramics.

[0100] As can be seen from Figure 7, the fibers and ceramics of the paraaramid separator manufactured in Example 1 of the present invention are alternately distributed, and because they are uniform and orderly, the coated separator can better combine the performance advantages of fibers and ceramics.

[0101] As can be seen from the above analysis, adding a reaction control agent during the PPTA synthesis process effectively reduces the apparent viscosity of the synthesized product while maintaining the molecular weight of the synthesized product. A lithium battery separator obtained by mixing the reaction control agent with ceramics, preparing a slurry for lithium battery coating separators, and applying it to a base film maintains thermal stability, improves mechanical tensile strength, significantly increases porosity, and improves electrolyte wetting properties.

[0102] Example 4 (Comparison)

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

[0104] Example 5

[0105] The method for producing the paraaramid polymerization solution was basically the same as in Example 4, with the only difference being the water content of the first solvent. 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 solution was basically the same as in Example 4, with the only difference being the water content of the first solvent. 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 solution was basically the same as in Example 4, with the only difference being the water content of the first solvent. 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 solution was basically the same as in Example 4, with the only difference being the water content of the first solvent. 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 solution was basically the same as in Example 4, with the only difference being the water content of the first solvent. 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 solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 50 ppm (amount added: the reaction control agent is added to achieve the desired concentration of the reaction control agent in the para-aramid polymerization solution with low apparent viscosity and high molecular weight).

[0116] Example 11

[0117] The method for producing a paraaramid polymerization solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 100 ppm.

[0118] Example 12

[0119] The method for producing a paraaramid polymerization solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 150 ppm.

[0120] Example 13

[0121] The method for producing a paraaramid polymerization solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 200 ppm.

[0122] Example 14

[0123] The method for producing a paraaramid polymerization solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 250 ppm.

[0124] Example 15

[0125] The method for producing a paraaramid polymerization solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 300 ppm.

[0126] Example 16

[0127] The method for producing a paraaramid polymerization solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 350 ppm.

[0128] Example 17

[0129] The method for producing a paraaramid polymerization solution with low apparent viscosity and high molecular weight was basically the same as in Example 1, except for the following difference: the amount of reaction control agent added was different. In this example, the amount of reaction control agent added was 400 ppm.

[0130] The apparent viscosity was measured for the para-aramid polymerization solutions produced in Examples 4-9 and the para-aramid polymerization solutions with low apparent viscosity and high molecular weight produced in Examples 10-17. The para-aramid polymerization solutions (low apparent viscosity and high molecular weight) were extruded into films, washed with water, and dried. The heat loss and weight-average molecular weight were then measured. The results are shown in Table 5:

[0131] Table 5 [Table 7] TIFF0007927376000008.tif32170

[0132] The method for manufacturing the slurry for the coating separator of lithium batteries was the same as the method for manufacturing the slurry for the coating separator of lithium batteries in Example 1, except that the only difference was that the "para-aramid polymerization solution with low apparent viscosity and high molecular weight" in the method for manufacturing the slurry for the coating separator of lithium batteries in Example 1 was replaced with "one of the para-aramid polymerization solutions with low apparent viscosity and high molecular weight produced in Examples 10 to 17, or the para-aramid polymerization solutions 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, one of the slurries manufactured in Examples 6, 7, and 10-16 was used as the slurry for the lithium battery coating separator. (The slurry for lithium battery coating separators obtained using the para-aramid polymerization solution produced in Example 4 could not be smoothly pulped because the apparent viscosity of the polymerization solution was too high. The slurry for lithium battery coating separators obtained using the para-aramid polymerization solution produced in Example 5 could not be supplied because the apparent viscosity was too high. The slurry for lithium battery coating separators obtained using the para-aramid polymerization solution produced in Example 6 was supplied slowly because the apparent viscosity was too high. The slurry for lithium battery coating separators obtained using the para-aramid polymerization solution produced in Examples 8-9 dropped during the coating process. The slurry for lithium battery coating separators obtained using the para-aramid polymerization solution produced in Example 17, which had a low apparent viscosity and high molecular weight, dropped all at once during the coating process. Therefore, the slurries for lithium battery coating separators produced in Examples 4-5, 8-9, and 17 were not used in the production of lithium battery separators.)

[0134] The apparent viscosity of the lithium battery coating separator slurries produced in Examples 4-17 was measured (Table 6). The lithium battery separators produced in Examples 6, 7 and Examples 10-16 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 control agent so that the water content of the first solvent is 100 ppm or less, the apparent viscosity is low, and the concentration of the reaction control agent in the para-aramid polymerization solution, which has a high molecular weight, is 300 ppm or less. The para-aramid polymerization solution synthesized in this way has a low apparent viscosity and a relatively high weight-average molecular weight, making it suitable for preparing coating slurries for lithium batteries.

[0138] As can be seen from the data analysis above, the slurry for lithium battery coating separators obtained by adjusting the ratio of the reaction control agent to the water content of the first solvent can fully exhibit the excellent thermal stability and high strength performance of para-aramid. The coating properties are directly related to the molecular weight of para-aramid. The weight-average molecular weight range of para-aramid that is suitable for slurry preparation and exhibits sufficient performance as a lithium battery separator is 5000 to 10000. In the process of synthesizing the para-aramid polymerization solution, the optimal ratio of the water content of the reaction control agent to the first solvent itself is determined to prepare a para-aramid polymerization solution with low apparent viscosity and high molecular weight. A slurry for lithium battery coating separators is prepared from the para-aramid polymerization solution with low apparent viscosity and high molecular weight. The battery separator obtained by coating with this slurry has excellent performance, and its thermal shrinkage, puncture strength, and air permeability are all superior to those of patent CN109411676A.

[0139] Although the present invention has been described in an illustrative manner, it should be understood that any simple modification, alteration, or equivalent transformation that can be performed by those skilled in the art without expending creative effort, without departing from the spirit and scope of the invention, is within the scope of protection of the present invention.

Claims

1. The process of synthesizing polyparaphenylene terephthalamide from p-phenylenediamine and terephthaloyl dichloride includes a step of adding a reaction control agent to obtain a paraaramid polymerization solution containing the reaction control agent, which has low apparent viscosity and high molecular weight. In paraaramid polymerization solutions with low apparent viscosity and high molecular weight, the concentration of the reaction control agent is 300 ppm or less. The concentration of water in the first solvent used to synthesize poly(p-phenylene terephthalamide) is 100 ppm or less. The reaction control agent is deionized water. A method for producing a paraaramid polymerization solution characterized by low apparent viscosity and high molecular weight.

2. A method for producing a para-aramid polymerization solution with low apparent viscosity and high molecular weight includes the following steps: Step 1: A step of mixing a dissolution-promoting salt and a first solvent under a nitrogen or inert gas atmosphere, stirring until the dissolution-promoting salt is uniformly dispersed in the first solvent, thereby obtaining a first mixed solution, wherein the ratio of the first solvent to the dissolution salt is (100-103):(3-8) by parts by mass. Step 2: A step of cooling the first mixed solution to 5-15°C under a nitrogen or inert gas atmosphere, adding p-phenylenediamine to the first mixed solution, and stirring until homogeneous to obtain a second mixed solution, wherein the ratio of parts by mass of the first mixed solution to parts by amount of p-phenylenediamine is 100:(16-20), the unit of parts by amount of the substance is mol, and the unit of parts by mass is kg. Step 3: A step in which the second mixed solution is cooled to -5 to 5°C under a nitrogen or inert gas atmosphere, terephthaloyl dichloride is added to the second mixed solution, and the mixture is stirred until homogeneous to obtain a para-aramid polymerization solution with low apparent viscosity and high molecular weight, wherein the ratio of paraphenylenediamine to the terephthaloyl dichloride is (1 to 1.05):1 in parts by amount of substance. In steps 1 to 3, the reaction control agent is added in one or more steps in any of steps 1 to 3 such that the concentration of the reaction control agent in the paraaramid polymerization solution, which has low apparent viscosity and high molecular weight, is 300 ppm or less. The manufacturing method according to claim 1, characterized in that it

3. 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 selected from N-methylpyrrolidone, hexamethylphosphate triamide, dimethylacetamide, and tetramethylurea, and the aqueous solvent is a mixture of the 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 manufacturing method according to claim 2, characterized in that it

4. A method for producing a coating separator slurry for a lithium battery, comprising the steps of uniformly mixing a second solvent, ceramic solid particles, and a paraaramid polymerization solution having low apparent viscosity and high molecular weight obtained by the production method described in claim 1, to obtain a slurry for a coating separator slurry for a lithium battery, The ratio of the ceramic solid particles to the paraaramid polymerization liquid, which has low apparent viscosity and high molecular weight, is (5-30):(50-80) in 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 manufacturing method characterized by the following features.

5. The slurry for the coating separator of the lithium battery further comprises a dispersant, The ratio of the dispersant to the ceramic solid particles is (0.01 to 5) : (5 to 30) in parts by mass. The dispersant is a mixture of one or more selected from polymer block copolymer dispersants, sodium polyacrylate salts, potassium polyacrylate salts, ammonium polyacrylate salts, and sodium polycarboxylate salts. The second solvent is a non-aqueous solvent or an aqueous solvent. The non-aqueous solvent is a mixture of one or more selected from N-methylpyrrolidone, hexamethylphosphate triamide, dimethylacetamide, and tetramethylurea. The aqueous solvent is a mixture of a non-aqueous solvent and water. The manufacturing method according to feature 4.

6. The second solvent is the same as the first solvent. The manufacturing method according to claim 5, characterized in that it

7. The ratio of the second solvent to the ceramic solid particles is (60-90):(5-30) by mass. The manufacturing method according to claim 6.

8. A lithium battery coating separator slurry manufactured by the manufacturing method described in any one of Claims 4 to 7 is applied to one or both sides of a base film, solvent content gradient extraction is performed, and drying is performed to obtain a lithium battery separator. A method for manufacturing a lithium battery separator, characterized by the following:

9. Use of a lithium battery separator obtained by the manufacturing method described in claim 8 in a lithium battery.

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