Preparation method of lithium battery diaphragm

Abstract

The invention relates to the technical field of battery diaphragms, and provides a preparation method of a lithium battery diaphragm. The lithium battery diaphragm comprises the following raw materials in parts by weight: 22-32 parts of polyethylene, 6-14 parts of a bisphenol compound, 65-75 parts of an organic solvent, 3-8 parts of a dispersing agent, 8-12 parts of hectorite powder and 5-8 parts of a pore forming agent, the bisphenol compound is prepared from p-tert-butylcatechol and ethyl 3, 4-dihydroxybenzoate according to the weight ratio of (1 to 9) to 1. According to the technical scheme, the problem of low tensile strength of the lithium battery diaphragm in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and specifically, to a preparation method of a lithium battery separator. Background Art

[0002] With the continuous development of technology, people have higher and higher requirements for the performance of lithium-ion batteries. As one of the important component parts of lithium batteries, the lithium battery separator is of great significance to the charge and discharge cycle performance, safety performance, and service life of the battery.

[0003] On the one hand, the material of the polyolefin lithium battery separator can isolate the electron conduction between the positive and negative electrodes of the lithium battery to prevent internal short circuits; on the other hand, the polyolefin lithium battery separator usually has a suitable porosity, and the three-dimensional holes therein can provide a migration channel for lithium ions. Therefore, the polyolefin lithium battery separator usually has the dual functions of electron insulation and ion conduction. However, the current polyolefin separators used have low tensile strength. Polyolefins such as polyethylene and polypropylene have relatively large flexibility in their molecular chains. This flexible structure will make the interaction between molecular chains weak. When only polyolefin components are used in the polyolefin lithium battery separator, when subjected to external tensile force, the molecular chains are prone to relative slippage, resulting in the separator being deformed or even broken under relatively low external force, which limits the improvement of its tensile strength; in order to overcome the defects of the separator using only polyolefin, some additives are usually added, such as plasticizers, antioxidants, or other auxiliaries. However, if the types and contents of the additives are not selected properly, it may also have a negative impact on the tensile strength of the separator. The low tensile strength of the polyolefin separator will restrict the improvement of battery performance, and thus cannot meet some application scenarios with high requirements for battery performance and safety, such as electric vehicles, aerospace, energy storage power stations and other fields.

[0004] In view of this, reasonably exploring the components of the polyolefin separator can obtain a lithium battery separator with good tensile performance, which has an important role in expanding the application of lithium batteries in some high-end fields. Summary of the Invention

[0005] The present invention provides a preparation method of a lithium battery separator, which solves the problem of low tensile strength of the lithium battery separator in the related art.

[0006] The technical solution of the present invention is as follows: The present invention provides a lithium battery separator, comprising the following raw materials in parts by weight: 22-32 parts of polyethylene, 6-14 parts of bisphenol compound, 65-75 parts of organic solvent, 3-8 parts of dispersant, 8-12 parts of lithium soapstone powder, 5-8 parts of pore former; The bisphenol compound comprises 1-9:1 of p-tert-butylcatechol and ethyl 3,4-dihydroxybenzoate by weight.

[0007] As a further technical solution, the weight ratio of p-tert-butylcatechol to ethyl 3,4-dihydroxybenzoate is 2-4:1.

[0008] When the weight ratio of p-tert-butylcatechol to ethyl 3,4-dihydroxybenzoate is 2-4:1, the tensile strength of the lithium battery separator can be further improved, and the longitudinal tensile strength of the lithium battery separator is increased to 3112-3133 Kgf / cm 2 , and the transverse tensile strength is increased to 3137-3145 Kgf / cm 2 ; when the weight ratio of p-tert-butylcatechol to ethyl 3,4-dihydroxybenzoate is outside the range of 2-4:1, the tensile strength of the lithium battery separator is relatively lower.

[0009] As a further technical solution, the bisphenol compound further includes 2-(3,4-dihydroxyphenyl)ethylamine.

[0010] In the present invention, when the bisphenol compound further includes 2-(3,4-dihydroxyphenyl)ethylamine, by using p-tert-butylcatechol, ethyl 3,4-dihydroxybenzoate and 2-(3,4-dihydroxyphenyl)ethylamine together, while maintaining the good tensile strength of the lithium battery separator, the puncture strength of the lithium battery separator can be improved. The possible reason is speculated as follows: the addition of 2-(3,4-dihydroxyphenyl)ethylamine can promote the formation of a relatively strong interfacial bonding effect between p-tert-butylcatechol, ethyl 3,4-dihydroxybenzoate and the matrix material, thereby improving the puncture strength of the lithium battery separator.

[0011] As a further technical solution, the weight ratio of the sum of the weights of p-tert-butylcatechol and ethyl 3,4-dihydroxybenzoate to 2-(3,4-dihydroxyphenyl)ethylamine is 5-11:1.

[0012] By regulating the content ratio of p-tert-butylcatechol, ethyl 3,4-dihydroxybenzoate and 2-(3,4-dihydroxyphenyl)ethylamine, when the weight ratio of the sum of the weights of p-tert-butylcatechol and ethyl 3,4-dihydroxybenzoate to 2-(3,4-dihydroxyphenyl)ethylamine is 5-11:1, the puncture strength of the lithium battery separator can be further improved, and the puncture strength is increased to 627-636 gf. When the weight ratio of the sum of the weights of p-tert-butylcatechol and ethyl 3,4-dihydroxybenzoate to 2-(3,4-dihydroxyphenyl)ethylamine is outside the range of 5-11:1, the puncture strength of the lithium battery separator is relatively lower.

[0013] As a further technical solution, the organic solvent includes one or more of acetone, N,N-dimethylformamide, and N-methylpyrrolidone; The dispersant includes one or more of polyvinyl alcohol, polyethylene glycol, and polyvinylpyrrolidone; The pore-forming agent includes white oil.

[0014] In the present invention, the addition of the dispersant can, to a certain extent, improve the dispersibility of solid particles in the organic matrix material, laying a foundation for the uniformity of the internal structure of the separator; The addition of the pore-forming agent can ensure the formation of uniform and appropriate pores during the preparation of the separator, thereby endowing the lithium battery separator with breathability and the basic requirements for ion transport.

[0015] As a further technical solution, the viscosity-average molecular weight of the polyethylene is 600,000 to 4 million.

[0016] As a further technical solution, the particle size of the lithium saponite powder is 15 to 50 μm.

[0017] The present invention provides a method for preparing a lithium battery separator, used to prepare the lithium battery separator described above, including the following steps: S1. Blend the raw materials of the lithium battery separator, extrude, and cool to obtain a cast film; S2. After subjecting the cast film to the first stretching process or the second stretching process, perform heat setting to obtain the lithium battery separator; The first stretching process specifically includes the following steps: first biaxial stretching, cooling, second biaxial stretching, extraction, and transverse stretching; The second stretching process specifically includes the following steps: first biaxial stretching, extraction, and second biaxial stretching.

[0018] The present invention also provides a method for preparing a lithium battery separator, used to prepare the lithium battery separator described above, including the following steps: S0. Dissolve the bisphenol compound in ethanol, add the lithium saponite powder, mix evenly, concentrate, dry, and ball mill to obtain a mixture; S1. Blend the polyethylene, organic solvent, dispersant, pore-forming agent, and the mixture, extrude, and cool to obtain a cast film; S2. After subjecting the cast film to the first stretching process or the second stretching process, perform heat setting to obtain the lithium battery separator.

[0019] In the present invention, by first performing pretreatment such as mixing and ball milling on the bisphenol compound and the lithium saponite powder, the composite of the bisphenol compound with the lithium saponite powder can be achieved to a certain extent, making the lithium saponite powder more uniformly dispersed in the organic system, so that a cast film with a tightly combined internal structure can be obtained, further improving the tensile strength and puncture strength of the lithium battery separator.

[0020] As a further technical solution, during the ball milling, the speed is 300 - 500 rpm and the time is 35 - 55 min.

[0021] As a further technical solution, in the first stretching process, the transverse stretching ratio and the longitudinal stretching ratio of the first biaxial stretching and the second biaxial stretching are each independently 1 - 20 times, and the transverse stretching ratio of the transverse stretching is 1 - 1.5 times; In the second stretching process, the transverse stretching ratio and the longitudinal stretching ratio of the first biaxial stretching are each independently 1 - 20 times, and the transverse stretching ratio and the longitudinal stretching ratio of the second biaxial stretching are each independently 1 - 2 times.

[0022] In the present invention, the first stretching process adopts a stretching process of double stretching + double stretching + extraction + transverse stretching, and the second stretching process adopts a stretching process of double stretching + extraction + double stretching. Whether the first stretching process or the second stretching process is adopted, it replaces the traditional processes of double stretching + transverse stretching or longitudinal stretching + transverse stretching + secondary transverse stretching, can improve the performance adjustment space of the lithium battery separator, reduce the problem of limited stretching ratio adjustment caused by the traditional stretching process, so that a good balance can be achieved between the pores and the compactness inside the separator, and further improve the strength performance of the lithium battery separator and the service life of the lithium battery.

[0023] As a further technical solution, in the first stretching process, the transverse stretching retraction ratio and the longitudinal stretching retraction ratio of the second biaxial stretching are each independently < 10%, and the transverse stretching retraction ratio of the transverse stretching is 10% - 25%; In the second stretching process, the transverse stretching retraction ratio and the longitudinal stretching retraction ratio of the first biaxial stretching are each independently < 10%, the longitudinal stretching retraction ratio of the second biaxial stretching is 5% - 15%, and the transverse stretching retraction ratio is 10% - 25%.

[0024] As a further technical solution, in the first stretching process, the temperature of the second biaxial stretching is 3 - 10 °C higher than the temperature of the first biaxial stretching; The temperature of the second biaxial stretching is 124 - 130 °C.

[0025] As a further technical solution, the temperature of the transverse stretching in the first stretching process is 124 - 130 °C.

[0026] In the present invention, when the stretching process is the first stretching process, the as-cast film has high toughness and low modulus before stretching. Through a slightly high temperature, the molecular chains of the substrate can be activated and easily stretched. However, after the first biaxial stretching, its toughness becomes relatively poor and the modulus increases. At this time, a higher stretching temperature than the first biaxial stretching is required to break the bondage between the molecular chains of the substrate. Therefore, the two biaxial stretching temperatures before extraction need to show an increasing change. When the second biaxial stretching temperature in the first stretching process is 3 - 10 °C higher than the first biaxial stretching temperature, the two biaxial stretching temperatures before extraction can present appropriate stretching temperatures, facilitating better stretching of the separator.

[0027] As a further technical solution, during extrusion, the temperature is 170 - 230 °C and the extrusion amount is 100 - 700 kg / h.

[0028] As a further technical solution, during extraction in the first stretching process or the second stretching process, the extractant is dichloromethane.

[0029] As a further technical solution, the temperature of the extraction is 18 - 25 °C.

[0030] As a further technical solution, the temperature of the heat setting is 80 - 125 °C and the time is 15 - 25 min.

[0031] The working principle and beneficial effects of the present invention are as follows: 1. In the present invention, the lithium battery separator uses polyethylene as the substrate, which can endow the lithium battery separator with a stable matrix structure, providing basic flexibility for the separator. Combined with bisphenol compounds, dispersants, lithium saponite powder, and pore-forming agents, with the reasonable cooperation of each component, a lithium battery separator with good stretching properties can be obtained, thereby improving the safety and stability of the lithium battery.

[0032] 2. The bisphenol compounds include p-tert-butylcatechol and ethyl 3,4-dihydroxybenzoate, and the two have a synergistic effect. By using p-tert-butylcatechol and ethyl 3,4-dihydroxybenzoate together and controlling the weight ratio of p-tert-butylcatechol to ethyl 3,4-dihydroxybenzoate to be 1 - 9:1, the interaction between polyethylene matrices can be improved, and the adhesion between polyethylene and each component can be enhanced, thereby improving the tensile strength of the lithium battery separator and avoiding the adverse effects on the tensile strength of the lithium battery separator caused by coating a coating on the surface of the separator to increase the thickness of the separator. Specific Embodiments

[0033] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0034] In the following examples and comparative examples, the model of polyethylene is GHR 8110; the white oil is 50# white oil; the CAS number of p-tert-butylcatechol is 98-29-3; the CAS number of ethyl 3,4-dihydroxybenzoate is 3943-89-3; the average particle size of lithium saponite powder is 38 μm; the model of polyvinyl alcohol is PVA2488; the model of polyethylene glycol is PEG-1000; the model of polyvinylpyrrolidone is K30.

[0035] Example 1 A method for preparing a lithium battery separator, comprising the following steps: S1. Blend 22 parts of polyethylene, 3 parts of p-tert-butylcatechol, 3 parts of ethyl 3,4-dihydroxybenzoate, 65 parts of N-methylpyrrolidone, 3 parts of polyvinyl alcohol, 8 parts of lithium saponite powder and 5 parts of white oil, and extrude at an extrusion rate of 100 kg / h at 170 °C. After cooling, a cast sheet is obtained; S2. Perform the first biaxial stretching on the cast sheet at 121 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 1 time, and neither the transverse stretching nor the longitudinal stretching retracts. After cooling, perform the second biaxial stretching at 124 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 1 time, and neither the transverse stretching nor the longitudinal stretching retracts. After extraction with dichloromethane with a mass fraction of 99.9% at 18 °C, perform transverse stretching at 124 °C, with the transverse stretching ratio being 1 time and the transverse stretching retraction ratio being 10%. Then, perform heat setting treatment at 80 °C for 25 min to obtain a lithium battery separator with a thickness of 7.0 μm.

[0036] Example 2 A method for preparing a lithium battery separator, comprising the following steps: S1. Blend 27 parts of polyethylene, 6 parts of p-tert-butylcatechol, 6 parts of ethyl 3,4-dihydroxybenzoate, 70 parts of N-methylpyrrolidone, 5 parts of polyethylene glycol, 10 parts of lithium saponite powder and 7 parts of white oil, and extrude at an extrusion rate of 500 kg / h at 190 °C. After cooling, a cast sheet is obtained; S2. Perform the first biaxial stretching on the cast film at 121°C. The transverse stretching ratio and the longitudinal stretching ratio are both 3 times, and the transverse stretching retraction ratio and the longitudinal stretching retraction ratio are both 4%. Cool it, then perform the second biaxial stretching at 127°C. The transverse stretching ratio and the longitudinal stretching ratio are both 3 times, and the transverse stretching retraction ratio and the longitudinal stretching retraction ratio are both 4%. After extraction with dichloromethane with a mass fraction of 99.9% at 20°C, perform transverse stretching at 127°C. The transverse stretching ratio is 1.2 times, and the transverse stretching retraction ratio is 15%. Then, perform heat setting treatment at 110°C for 20 min to obtain a lithium battery separator with a thickness of 7.1 μm.

[0037] Example 3 A preparation method of a lithium battery separator includes the following steps: S1. Blend 32 parts of polyethylene, 12.6 parts of p-tert-butylcatechol, 1.4 parts of ethyl 3,4-dihydroxybenzoate, 75 parts of N-methylpyrrolidone, 8 parts of polyvinylpyrrolidone, 12 parts of lithium saponite powder, and 8 parts of white oil, and extrude at an extrusion rate of 700 kg / h at 230°C. After cooling, obtain a cast film. S2. Perform the first biaxial stretching on the cast film at 120°C. The transverse stretching ratio and the longitudinal stretching ratio are both 20 times, and the transverse stretching retraction ratio and the longitudinal stretching retraction ratio are both 8%. Cool it, then perform the second biaxial stretching at 130°C. The transverse stretching ratio and the longitudinal stretching ratio are both 20 times, and the transverse stretching retraction ratio and the longitudinal stretching retraction ratio are both 8%. After extraction with dichloromethane with a mass fraction of 99.9% at 25°C, perform transverse stretching at 130°C. The transverse stretching ratio is 1.5 times, and the transverse stretching retraction ratio is 25%. Then, perform heat setting treatment at 125°C for 15 min to obtain a lithium battery separator with a thickness of 7.2 μm.

[0038] Example 4 A preparation method of a lithium battery separator includes the following steps: S1. Blend 32 parts of polyethylene, 12.6 parts of p-tert-butylcatechol, 1.4 parts of ethyl 3,4-dihydroxybenzoate, 75 parts of N-methylpyrrolidone, 8 parts of polyvinyl alcohol, 12 parts of lithium saponite powder, and 8 parts of white oil, and extrude at an extrusion rate of 700 kg / h at 230°C. After cooling, obtain a cast film. S2. The cast film is subjected to the first biaxial stretching at 120 °C, with the transverse stretching ratio and the longitudinal stretching ratio both being 20 times, the transverse stretching retraction ratio and the longitudinal stretching retraction ratio both being 8%. After extraction with dichloromethane with a mass fraction of 99.9% at 25 °C, the second biaxial stretching is carried out at 130 °C, with the longitudinal stretching retraction ratio being 15% and the transverse stretching retraction ratio being 25%. Then, heat setting treatment is carried out at 125 °C for 15 min to obtain a lithium battery separator with a thickness of 7.2 μm.

[0039] Example 5 A preparation method of a lithium battery separator includes the following steps: S1. 22 parts of polyethylene, 3 parts of p-tert-butylcatechol, 3 parts of ethyl 3,4-dihydroxybenzoate, 65 parts of N-methylpyrrolidone, 3 parts of polyvinyl alcohol, 8 parts of lithium saponite powder and 5 parts of white oil are blended and extruded at an extrusion rate of 100 kg / h at 170 °C. After cooling, a cast film is obtained; S2. The cast film is subjected to the first biaxial stretching at 121 °C, with the transverse stretching ratio and the longitudinal stretching ratio both being 1 time, and neither the transverse stretching nor the longitudinal stretching retracts. After extraction with dichloromethane with a mass fraction of 99.9% at 18 °C, the second biaxial stretching is carried out at 124 °C, with the longitudinal stretching retraction ratio being 5% and the transverse stretching retraction ratio being 10%. Then, heat setting treatment is carried out at 80 °C for 25 min to obtain a lithium battery separator with a thickness of 7.0 μm.

[0040] Example 6 The difference between this example and Example 2 is only that, in this example, 10.8 parts of p-tert-butylcatechol and 1.2 parts of ethyl 3,4-dihydroxybenzoate are added.

[0041] Example 7 The difference between this example and Example 2 is only that, in this example, 8 parts of p-tert-butylcatechol and 4 parts of ethyl 3,4-dihydroxybenzoate are added.

[0042] Example 8 The difference between this example and Example 2 is only that, in this example, 9.6 parts of p-tert-butylcatechol and 2.4 parts of ethyl 3,4-dihydroxybenzoate are added.

[0043] Example 9 A preparation method of a lithium battery separator includes the following steps: S0. 9.6 parts of p-tert-butylcatechol and 2.4 parts of ethyl 3,4-dihydroxybenzoate are dissolved in 30 parts of ethanol, then 10 parts of lithium saponite powder are added, mixed evenly, concentrated, dried, and ball-milled at 400 rpm for 45 min to obtain a mixture; S1. Blend 27 parts of polyethylene, 70 parts of N-methylpyrrolidone, 5 parts of polyvinyl alcohol, 7 parts of white oil and the above mixture, and extrude at an extrusion rate of 500 kg / h at 190 °C. After cooling, a cast film is obtained; S2. Perform the first biaxial stretching on the cast film at 121 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 3 times, and both the transverse stretching retraction ratio and the longitudinal stretching retraction ratio being 4%. After cooling, perform the second biaxial stretching at 127 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 3 times, and both the transverse stretching retraction ratio and the longitudinal stretching retraction ratio being 4%. After extraction with dichloromethane with a mass fraction of 99.9% at 20 °C, perform transverse stretching at 127 °C, with the transverse stretching ratio being 1.2 times and the transverse stretching retraction ratio being 15%. Then, perform heat setting treatment at 110 °C for 20 min to obtain a lithium battery separator with a thickness of 7.1 μm.

[0044] Example 10 The difference between this example and Example 8 is only that, in this example, 7.2 parts of p-tert-butylcatechol, 1.8 parts of ethyl 3,4-dihydroxybenzoate, and 3 parts of 2-(3,4-dihydroxyphenyl)ethylamine are added; S1. Blend 27 parts of polyethylene, 7.2 parts of p-tert-butylcatechol, 1.8 parts of ethyl 3,4-dihydroxybenzoate, 3 parts of 2-(3,4-dihydroxyphenyl)ethylamine, 70 parts of N-methylpyrrolidone, 5 parts of polyvinyl alcohol, 10 parts of lithium soapstone powder and 7 parts of white oil, and extrude at an extrusion rate of 500 kg / h at 190 °C. After cooling, a cast film is obtained; S2. Perform the first biaxial stretching on the cast film at 121 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 3 times, and both the transverse stretching retraction ratio and the longitudinal stretching retraction ratio being 4%. After cooling, perform the second biaxial stretching at 127 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 3 times, and both the transverse stretching retraction ratio and the longitudinal stretching retraction ratio being 4%. After extraction with dichloromethane with a mass fraction of 99.9% at 20 °C, perform transverse stretching at 127 °C, with the transverse stretching ratio being 1.2 times and the transverse stretching retraction ratio being 15%. Then, perform heat setting treatment at 110 °C for 20 min to obtain a lithium battery separator with a thickness of 7.1 μm.

[0045] Example 11 The difference between this example and Example 10 is only that, in this example, 9.2 parts of p-tert-butylcatechol, 2.3 parts of ethyl 3,4-dihydroxybenzoate, and 0.5 parts of 2-(3,4-dihydroxyphenyl)ethylamine are added.

[0046] Example 12 The difference between this example and Example 10 is only that in this example, 8.8 parts of p-tert-butylcatechol, 2.2 parts of ethyl 3,4-dihydroxybenzoate, and 1 part of 2-(3,4-dihydroxyphenyl)ethylamine are added.

[0047] Example 13 The difference between this example and Example 10 is only that in this example, 8 parts of p-tert-butylcatechol, 2 parts of ethyl 3,4-dihydroxybenzoate, and 2 parts of 2-(3,4-dihydroxyphenyl)ethylamine are added.

[0048] Example 14 A method for preparing a lithium battery separator includes the following steps: S0: After dissolving 8 parts of p-tert-butylcatechol, 2 parts of ethyl 3,4-dihydroxybenzoate, and 2 parts of 2-(3,4-dihydroxyphenyl)ethylamine in 30 parts of ethanol, 10 parts of lithium saponite powder are added, mixed evenly, concentrated, dried, and ball-milled at 400 rpm for 45 min to obtain a mixture; S1: 27 parts of polyethylene, 70 parts of N-methylpyrrolidone, 5 parts of polyvinyl alcohol, 7 parts of white oil, and the above mixture are blended and extruded at an extrusion rate of 500 kg / h at 190 °C. After cooling, a cast sheet is obtained; S2: The cast sheet is subjected to first biaxial stretching at 121 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 3 times, and both the transverse stretching retraction ratio and the longitudinal stretching retraction ratio being 4%. After cooling, it is subjected to second biaxial stretching at 127 °C, with both the transverse stretching ratio and the longitudinal stretching ratio being 3 times, and both the transverse stretching retraction ratio and the longitudinal stretching retraction ratio being 4%. After extraction with dichloromethane with a mass fraction of 99.9% at 20 °C, it is subjected to transverse stretching at 127 °C, with the transverse stretching ratio being 1.2 times and the transverse stretching retraction ratio being 15%. Then, it is heat-set at 110 °C for 20 min to obtain a lithium battery separator with a thickness of 7.1 μm.

[0049] Comparative Example 1 The difference between this comparative example and Example 2 is only that in this comparative example, p-tert-butylcatechol is replaced with an equal amount of ethyl 3,4-dihydroxybenzoate.

[0050] Comparative Example 2 The difference between this comparative example and Example 2 is only that in this comparative example, ethyl 3,4-dihydroxybenzoate is replaced with an equal amount of p-tert-butylcatechol.

[0051] Comparative Example 3 The difference between this comparative example and Example 2 is only that in this comparative example, neither p-tert-butylcatechol nor ethyl 3,4-dihydroxybenzoate is added.

[0052] Experimental Example 1 The lithium battery separators prepared in Examples 1 - 9 and Comparative Examples 1 - 3 were tested for longitudinal (MD) tensile strength and transverse (TD) tensile strength using a Shimadzu intelligent electronic tensile testing machine (model AGS - 50N). Among them, the size of the lithium battery separator specimen was 150 mm × 15 mm, and the test results are shown in Table 1: Table 1 Tensile strength test results of Examples 1 - 9 and Comparative Examples 1 - 3

[0053] Compared with Comparative Examples 1 - 3, the longitudinal and transverse tensile strengths of the lithium battery separators prepared in Examples 1 - 9 were significantly improved, indicating that the bisphenol compounds including p - tert - butylcatechol and ethyl 3,4 - dihydroxybenzoate have a synergistic effect. By using p - tert - butylcatechol and ethyl 3,4 - dihydroxybenzoate together, the tensile strength of the lithium battery separator can be increased.

[0054] Experimental Example 2 The lithium battery separators prepared in Example 8 and Examples 10 - 14 were tested for puncture strength using a Shimadzu intelligent electronic tensile testing machine (model AGS - 50N). Among them, the specimen size was 100 mm × 100 mm, and the test results are shown in Table 2: Table 2 Puncture strength test results of Example 8 and Examples 10 - 14

[0055] Compared with Example 8, the puncture strength of the lithium battery separators in Examples 10 - 14 was improved, indicating that when the bisphenol compounds also include 2 - (3,4 - dihydroxyphenyl)ethylamine, by using p - tert - butylcatechol, ethyl 3,4 - dihydroxybenzoate and 2 - (3,4 - dihydroxyphenyl)ethylamine together, the puncture strength of the lithium battery separator can be increased.

[0056] Experimental Example 3 The following performance tests were carried out on the lithium battery separators prepared in Examples 1 - 5; ① Air permeability: The air permeability of the separator was tested according to the method in GB / T 36363 - 2018 "Polyolefin Separator for Lithium - Ion Batteries". Among them, the size of the separator specimen was 100 mm × 100 mm, and the test result was the average value of 3 specimens; ② Shrinkage rate: The transverse (TD) and longitudinal (MD) thermal shrinkage rates were measured according to the method in GB / T 36363 - 2018 "Polyolefin Separator for Lithium - Ion Batteries". Among them, the size of the lithium battery separator specimen was 100 mm × 100 mm, and the test results were the average values of 3 specimens.

[0057] Table 3 Performance test results of Examples 1 to 5

[0058] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium battery separator, characterized in that Comprising the following raw materials in parts by weight: 22 - 32 parts of polyethylene, 6 - 14 parts of bisphenol compound, 65 - 75 parts of organic solvent, 3 - 8 parts of dispersant, 8 - 12 parts of lithium saponite powder, 5 - 8 parts of pore former; The bisphenol compound comprises p - tert - butylcatechol and ethyl 3,4 - dihydroxybenzoate with a weight ratio of 1 - 9:

1.

2. The lithium battery separator according to claim 1, wherein, The weight ratio of p - tert - butylcatechol to ethyl 3,4 - dihydroxybenzoate is 2 - 4:

1.

3. A lithium battery separator according to claim 1, wherein The bisphenol compound further comprises 2-(3,4 - dihydroxyphenyl)ethylamine.

4. A lithium battery separator according to claim 3, wherein, The weight ratio of the sum of the weights of p - tert - butylcatechol and ethyl 3,4 - dihydroxybenzoate to 2-(3,4 - dihydroxyphenyl)ethylamine is 5 - 11:

1.

5. A lithium battery separator according to claim 1, characterized in that, The organic solvent comprises one or more of acetone, N,N - dimethylformamide, N - methylpyrrolidone; The dispersant comprises one or more of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone; The pore former comprises white oil.

6. A preparation method of a lithium battery separator for preparing a lithium battery separator according to any one of claims 1 to 5, characterized in that, Comprising the following steps: S1. Blend the raw materials of the lithium battery separator, extrude, and cool to obtain a cast sheet; S2. After subjecting the cast sheet to the first stretching process or the second stretching process, perform heat setting to obtain the lithium battery separator; The first stretching process specifically comprises the following steps: first biaxial stretching, cooling, second biaxial stretching, extraction, transverse stretching; The second stretching process specifically comprises the following steps: first biaxial stretching, extraction, second biaxial stretching.

7. A method for preparing a lithium battery separator according to claim 6, wherein, In the first stretching process, the transverse stretching ratio and the longitudinal stretching ratio of the first biaxial stretching and the second biaxial stretching are each independently 1 - 20 times, and the transverse stretching ratio of the transverse stretching is 1 - 1.5 times; In the second stretching process, the transverse stretching ratio and the longitudinal stretching ratio of the first biaxial stretching are each independently 1 - 20 times, and the transverse stretching ratio and the longitudinal stretching ratio of the second biaxial stretching are each independently 1 - 2 times.

8. The preparation method of a lithium battery separator according to claim 6, characterized in that, In the first stretching process, the transverse stretching retraction ratio and the longitudinal stretching retraction ratio of the first biaxial stretching and the second biaxial stretching are each independently < 10%, and the transverse stretching retraction ratio of the transverse stretching is 10% - 25%; In the second stretching process, the transverse stretching retraction ratio and the longitudinal stretching retraction ratio of the first biaxial stretching are each independently < 10%, and the longitudinal stretching retraction ratio of the second biaxial stretching is 5% - 15% and the transverse stretching retraction ratio is 10% - 25%.

9. The preparation method of a lithium battery separator according to claim 6, characterized in that, In the first stretching process, the temperature of the second biaxial stretching is 3 - 10°C higher than the temperature of the first biaxial stretching; The temperature of the second biaxial stretching is 124 - 130°C.

10. The preparation method of a lithium battery separator according to claim 6, wherein, When performing extraction in the first stretching process or the second stretching process, the extractant is dichloromethane.

Images