Preparation method of lithium battery diaphragm, lithium battery diaphragm and application

Abstract

The invention provides a preparation method of a lithium battery diaphragm, the lithium battery diaphragm and application, and the preparation method of the lithium battery diaphragm comprises the following steps: adding a polyethylene raw material with a mass ratio of 18-22% and paraffin oil with a mass ratio of 78-82% into a twin-screw extruder, mixing and melting to form a homogeneous system; wherein the molecular weight of the polyethylene raw material is 1450,000-1550,000; extruding the homogeneous system through a die head, and performing phase separation to obtain a sheet; sequentially carrying out longitudinal stretching, primary transverse stretching, synchronous stretching, extraction, secondary transverse stretching and rolling on the sheet to obtain an initial diaphragm; wherein the stretching multiple of the longitudinal stretching is 2.5-3 times, and the stretching multiple of the primary transverse stretching is 1.7-2 times; the transverse stretching multiple of the synchronous stretching is 9-10, and the longitudinal stretching multiple of the synchronous stretching is 7-8; the stretching multiple of the secondary transverse stretching is 1.4 to 1.8 times; the speed of the film penetrating process is 25m / min, and the temperature is 126 + / -1 DEG C; preparing a final diaphragm by utilizing the initial diaphragm; wherein the speed of the film penetrating process is changed to be 30m / min, and the temperature is changed to be 124 + / -1 DEG C.

Description

Technical Field

[0001] The present application relates to the field of lithium battery technology, and in particular to a method for preparing a lithium battery separator, a lithium battery separator and applications. Background Art

[0002] Battery separator refers to a layer of separator material between the positive and negative electrodes of the battery. It is a very critical part of the battery and has a direct impact on the safety and cost of the battery. Its main function is to isolate the positive and negative electrodes and prevent the electrons in the battery from passing freely, allowing the ions in the electrolyte to pass freely between the positive and negative electrodes. Common lithium-ion battery separators have certain functional limitations when in use. Most research in the field of lithium-ion batteries focuses only on separators between 7-25μm to achieve a balance between battery safety and performance. However, the cost of this thick separator is that there is less free space inside the battery to accommodate active materials, which hinders the further development of the next generation of lithium-based batteries with high energy density. The strength of thin separators does not meet the requirements, and the porosity must be sacrificed to improve the strength, which affects the battery performance. How to significantly reduce the thickness of lithium battery separators, increase the porosity, and at the same time not reduce the tensile strength of the separator has become a problem to be solved. Summary of the invention

[0003] The present application provides a preparation method of a lithium battery separator, a lithium battery separator and an application, which solves the problem of how to significantly reduce the thickness of the lithium battery separator and increase the porosity without reducing the tensile strength of the separator.

[0004] In a first aspect, the present application provides a method for preparing a lithium battery separator, comprising:

[0005] 18-22% by mass of polyethylene raw material and 78-82% by mass of paraffin oil are added into a twin-screw extruder to mix and melt into a homogeneous system; wherein the molecular weight of the polyethylene raw material is 1.45 million to 1.55 million;

[0006] After the homogeneous system is extruded through a die head, phase separation is performed to obtain a sheet;

[0007] The sheet is sequentially subjected to longitudinal stretching, primary transverse stretching, synchronous stretching, extraction, secondary transverse stretching and winding to obtain an initial diaphragm; wherein the longitudinal stretching has a stretching multiple of 2.5 to 3 times, the primary transverse stretching has a stretching multiple of 1.7 to 2 times; the synchronous transverse stretching has a stretching multiple of 9 to 10 times, and the longitudinal stretching has a stretching multiple of 7 to 8 times; the secondary transverse stretching has a stretching multiple of 1.4 to 1.8 times; the speed of the film-penetrating process is 25 m / min, and the temperature is 126±1°C;

[0008] The final diaphragm is prepared by using the initial diaphragm; wherein the speed of the membrane penetration process is changed to 30 m / min, and the temperature is changed to 124±1°C.

[0009] Furthermore, the mass ratio of the polyethylene raw material is 20%, and the mass ratio of the paraffin oil is 80%.

[0010] Furthermore, the molecular weight of the polyethylene raw material is 1.5 million.

[0011] Furthermore, the model of the paraffin oil is No. 50.

[0012] Furthermore, the temperature at which the polyethylene raw material and the paraffin oil are mixed and melted is 205°C.

[0013] Furthermore, the stretching ratio of the longitudinal stretching is 2.55 times; the stretching ratio of the first transverse stretching is 1.8 times; the transverse stretching ratio of the synchronous stretching is 9.95 times, and the longitudinal stretching ratio is 7 times; the stretching ratio of the second transverse stretching is 1.5 times.

[0014] Furthermore, the inlets of the stretching machines used for the longitudinal stretching, the primary transverse stretching, the synchronous stretching and the secondary transverse stretching are all provided with trimming edges.

[0015] Furthermore, the method of preparing a final diaphragm using the initial diaphragm comprises:

[0016] The initial diaphragm is tested for physical properties and appearance, and if the requirements are met, the initial diaphragm is prepared as a final diaphragm.

[0017] In a second aspect, the present application provides a lithium battery separator, which is obtained based on the preparation method of the lithium battery separator as described above.

[0018] In a third aspect, the present application provides a lithium battery separator obtained by the preparation method of the lithium battery separator as described above or the application of the lithium battery separator as described above in the field of lithium batteries.

[0019] The above technical solution of the present application has the following advantages:

[0020] The first aspect of the present application provides a method for preparing a lithium battery separator. The method comprises the following steps: melting ultra-high molecular weight polyethylene and low viscosity paraffin oil into a homogeneous system and then extruding the resulting sheet into a sheet. After the sheeted material is cooled for phase separation, high stretching ratio longitudinal stretching, primary transverse stretching, synchronous stretching, extraction, secondary transverse stretching and winding are sequentially performed to obtain an initial lithium battery separator. After the membrane is stabilized, the line speed is increased to prepare the final separator. The thickness of the lithium battery separator is greatly reduced, and the porosity is increased. At the same time, the tensile strength of the separator is not reduced, and the puncture strength and thermal shrinkage performance of the separator are not deteriorated, thereby significantly improving the battery performance.

[0021] It can be understood that the beneficial effects of the second and third aspects mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A flow chart of the method for preparing the lithium battery separator provided in the present application. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0026] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0028] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0029] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0030] This application aims to solve the technical problem of the difficulty in producing 3μm high-porous diaphragms, that is, the 3μm product sheet becomes thinner during production, and is easy to be pulled off by double pulling; the production stability is poor, and it is difficult to penetrate the membrane; the porosity is low, the strength is insufficient; the transparency becomes larger, and the defects are obvious. Through this application, the thickness of the lithium battery diaphragm can be greatly reduced, the porosity is increased, and the tensile strength of the diaphragm is not reduced.

[0031] The specific implementation methods of the present application are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not intended to limit the scope of the present application.

[0032] The present application provides a method for preparing a lithium battery separator. Figure 1 As shown, the following steps are included:

[0033] 18-22% by mass of polyethylene raw material and 78-82% by mass of paraffin oil are added into a twin-screw extruder to mix and melt into a homogeneous system; wherein the molecular weight of the polyethylene raw material is 1.45 million to 1.55 million;

[0034] After the homogeneous system is extruded through a die head, phase separation is performed to obtain a sheet;

[0035] The sheet is sequentially subjected to longitudinal stretching, primary transverse stretching, synchronous stretching, extraction, secondary transverse stretching and winding to obtain an initial diaphragm; wherein the longitudinal stretching has a stretching multiple of 2.5 to 3 times, the primary transverse stretching has a stretching multiple of 1.7 to 2 times; the synchronous transverse stretching has a stretching multiple of 9 to 10 times, and the longitudinal stretching has a stretching multiple of 7 to 8 times; the secondary transverse stretching has a stretching multiple of 1.4 to 1.8 times; the speed of the film-penetrating process is 25 m / min, and the temperature is 126±1°C;

[0036] The final diaphragm is prepared by using the initial diaphragm; wherein the speed of the membrane penetration process is changed to 30 m / min, and the temperature is changed to 124±1°C.

[0037] First, obtain ultra-high molecular weight polyethylene and low-viscosity paraffin oil, put the polyethylene raw material into the extruder, and mix it with paraffin oil during the extrusion and heating process to form a homogeneous system. After the homogeneous system is extruded through the die head, phase separation is performed to obtain a sheet; the sheet is stretched in the longitudinal, transverse, and synchronous stretching machines to obtain a stretched film, and the stretched film is extracted in the extraction tank, and dried after extraction to obtain an oil-free membrane sheet; the membrane sheet is stretched by a transverse stretching machine to obtain a diaphragm; the diaphragm is pulled and rolled. The film penetration process uses the process conditions of 4μm production, that is, a speed of 25m / min and a temperature of 126±1℃; after the entire line is penetrated to obtain the initial diaphragm, the 3μm process conditions, that is, a speed of 30m / min and a temperature of 124±1℃, are used to prepare the final diaphragm.

[0038] The method comprises the following steps: melting ultra-high molecular weight polyethylene and low viscosity paraffin oil into a homogeneous system and then extruding the resulting sheet into a sheet. After the sheet is cooled and the phases are separated, the sheet is sequentially subjected to longitudinal stretching with a high stretching ratio, primary transverse stretching, synchronous stretching, extraction, secondary transverse stretching and winding to obtain an initial lithium battery separator. After the membrane is stabilized, the line speed is increased to prepare the final separator. The thickness of the lithium battery separator is greatly reduced, and the porosity is increased. At the same time, the tensile strength of the separator is not reduced, and the puncture strength and thermal shrinkage performance of the separator are not deteriorated, thereby significantly improving the battery performance.

[0039] In some embodiments, the mass ratio of the polyethylene raw material is 20%, and the mass ratio of the paraffin oil is 80%.

[0040] In some embodiments, the molecular weight of the polyethylene feedstock is 1.5 million.

[0041] In some embodiments, the paraffin oil is No. 50.

[0042] In some embodiments, the temperature at which the polyethylene raw material and the paraffin oil are mixed and melted is 205°C.

[0043] In some embodiments, the stretching ratio of the longitudinal stretching is 2.55 times; the stretching ratio of the first transverse stretching is 1.8 times; the transverse stretching ratio of the synchronous stretching is 9.95 times, and the longitudinal stretching ratio is 7 times; the stretching ratio of the second transverse stretching is 1.5 times.

[0044] In some embodiments, the inlets of the stretching machines used for the longitudinal stretching, the primary transverse stretching, the synchronous stretching, and the secondary transverse stretching are all provided with trimming edges.

[0045] In some embodiments, the method of preparing a final diaphragm using the initial diaphragm comprises:

[0046] The initial diaphragm is tested for physical properties and appearance, and if the requirements are met, the initial diaphragm is prepared as a final diaphragm.

[0047] The preparation method of the lithium battery separator provided in the present application ensures the strength and heat shrinkage of the separator by adjusting the raw material formula; adopts the extrusion amount corresponding to 4μm in normal production to ensure stability, and increases the line speed to meet the 3μm product requirement; increases the trimming at the entrance of the stretching machine to avoid sheet slippage and declamping; while ensuring the high porosity of the product, it also ensures the high strength and ultra-thin characteristics of the product.

[0048] The following describes the invention in conjunction with specific embodiments.

[0049] Example

[0050] A polyethylene raw material with a mass fraction ratio of 20% and a molecular weight of 1.5 million is added to a twin-screw extruder and mixed with a mass fraction ratio of 80% paraffin oil (paraffin oil model 50#) to ensure strength and heat shrinkage, and fully melted at 205°C to form a homogeneous system.

[0051] After casting, the sheet is first stretched 2.55 times longitudinally, then stretched 1.8 times transversely, and then stretched in a synchronous stretching machine to obtain a stretched film. The transverse stretching multiple is 9.95 times before stretching, and the longitudinal stretching multiple is 7 times before stretching. The sheet is trimmed at the entrance of the stretching machine to prevent the sheet from slipping and unclamping. After extraction and 1.5 times of secondary transverse stretching, the initial diaphragm is rolled up. The membrane penetration process uses the process conditions of 4μm production, that is, the speed is set to 25m / min and the temperature is set to 126℃. After the membrane penetration is stable, the 3μm process conditions are used to produce the final diaphragm after the entire line is connected, that is, the speed is set to 30m / min and the temperature is set to 124℃.

[0052] After testing, the thickness of the final separator is 3.6μm and the surface density is 2.13g / m 2 , air permeability is 50.9sec / 100ml, porosity is 35.3%, needle strength is 316gf, MD tensile strength is 4712kgf / cm 2 , TD tensile strength is 4871kgf / cm 2 , MD elongation is 49%, TD elongation is 59%; 105℃, 1h MD thermal shrinkage is 2.09%; 105℃, 1h TD thermal shrinkage is 1.55%; breakdown voltage is 0.419kV.

[0053] It can be seen from the above that this embodiment can significantly reduce the thickness of the lithium battery separator and increase the porosity, while the tensile strength of the separator does not decrease.

[0054] The embodiment of the present application also provides a lithium battery separator, which is obtained based on the preparation method of the lithium battery separator as described above.

[0055] The embodiments of the present application also provide a lithium battery separator obtained by the preparation method of the lithium battery separator as described above or the application of the lithium battery separator as described above in the field of lithium batteries.

[0056] It should be clear that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. The present application is not limited to the specific methods described above and shown in the figures. In addition, for the sake of brevity, detailed descriptions of known methods and technologies are omitted here.

[0057] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for preparing a lithium battery separator, characterized in that: include: 18-22% by mass of polyethylene raw material and 78-82% by mass of paraffin oil are added into a twin-screw extruder to mix and melt into a homogeneous system; wherein the molecular weight of the polyethylene raw material is 1.45 million to 1.55 million; After the homogeneous system is extruded through a die head, phase separation is performed to obtain a sheet; The sheet is sequentially subjected to longitudinal stretching, primary transverse stretching, synchronous stretching, extraction, secondary transverse stretching and winding to obtain an initial diaphragm; wherein the longitudinal stretching has a stretching multiple of 2.5 to 3 times, the primary transverse stretching has a stretching multiple of 1.7 to 2 times; the synchronous transverse stretching has a stretching multiple of 9 to 10 times, and the longitudinal stretching has a stretching multiple of 7 to 8 times; the secondary transverse stretching has a stretching multiple of 1.4 to 1.8 times; the speed of the film-penetrating process is 25 m / min, and the temperature is 126±1°C; The final diaphragm is prepared by using the initial diaphragm; wherein the speed of the membrane penetration process is changed to 30 m / min, and the temperature is changed to 124±1°C.

2. The method for preparing a lithium battery separator according to claim 1, characterized in that: The mass ratio of the polyethylene raw material is 20%, and the mass ratio of the paraffin oil is 80%.

3. The method for preparing a lithium battery separator according to claim 1, characterized in that: The molecular weight of the polyethylene raw material is 1.5 million.

4. The method for preparing a lithium battery separator according to claim 1, characterized in that: The model of the paraffin oil is No.

50.

5. The method for preparing a lithium battery separator according to claim 1, characterized in that: The temperature at which the polyethylene raw material and the paraffin oil are mixed and melted is 205°C.

6. The method for preparing a lithium battery separator according to claim 1, characterized in that: The stretching multiple of the longitudinal stretching is 2.55 times; the stretching multiple of the first transverse stretching is 1.8 times; the transverse stretching multiple of the synchronous stretching is 9.95 times, and the longitudinal stretching multiple is 7 times; the stretching multiple of the second transverse stretching is 1.5 times.

7. The method for preparing a lithium battery separator according to claim 1, characterized in that: The inlets of the stretching machines used for the longitudinal stretching, the primary transverse stretching, the synchronous stretching and the secondary transverse stretching are all provided with trimming edges.

8. The method for preparing a lithium battery separator according to claim 1, characterized in that: The method of preparing a final diaphragm by using the initial diaphragm comprises: The initial diaphragm is tested for physical properties and appearance, and if the requirements are met, the initial diaphragm is prepared as a final diaphragm.

9. A lithium battery separator, characterized in that: The method for preparing the lithium battery separator is based on any one of claims 1 to 8.

10. Use of the lithium battery separator obtained by the preparation method of the lithium battery separator according to any one of claims 1 to 8 or the lithium battery separator according to claim 9 in the field of lithium batteries.

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