High-puncture-strength and high-elongation lithium battery diaphragm as well as preparation method and application thereof

Abstract

The invention provides a high-puncture-strength and high-elongation lithium battery diaphragm and a preparation method and application thereof.The preparation method of the high-puncture-strength and high-elongation lithium battery diaphragm comprises the steps that 16%-18% by mass of polyethylene powder and 82%-84% by mass of white oil are added into an extruder to be subjected to melt extrusion, and a casting piece is obtained, the viscosity-average molecular weight of the polyethylene powder is 140 million to 160 million, the front pressure of a gear pump of the extruder is 1.5 to 1.8 Mpa, and the front pressure of a die head of the extruder is 1.7 to 1.9 Mpa; the casting piece passes through a cold roll and then is sequentially subjected to longitudinal stretching, primary transverse stretching, extraction and membrane surface drying, secondary transverse stretching, heat setting and rolling, the lithium battery diaphragm is obtained, the longitudinal stretching multiplying power is 500-600%, the primary transverse stretching multiplying power is 800-900%, and the secondary transverse stretching multiplying power is 140-150%. On the basis of ensuring that the lithium battery diaphragm has relatively high puncture strength, the elongation of the lithium battery diaphragm is further greatly improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery separator technology, and in particular to a lithium battery separator with high puncture strength and high elongation, its preparation method and application. Background Technology

[0002] High puncture strength means the separator can more effectively prevent punctures from sharp objects such as lithium dendrites and electrode burrs, thus avoiding short circuits caused by direct contact between the positive and negative electrodes. This significantly improves battery safety and reduces the risk of battery thermal runaway, fire, or explosion due to short circuits. Secondly, a separator with high elongation at break can better maintain its structural integrity when subjected to external impacts or vibrations. This characteristic helps reduce the risk of separator rupture during deformation, thereby ensuring stable battery operation in complex environments. Furthermore, a separator with high elongation is more likely to recover its original shape after deformation, which helps extend the overall battery life.

[0003] In summary, the high puncture strength and high elongation of lithium-ion battery separators jointly enhance the battery's safety, stability, and lifespan. These characteristics are crucial for meeting the application requirements of high-performance lithium-ion batteries in electric vehicles, energy storage systems, and other fields. Therefore, during the manufacturing process of lithium-ion batteries, key performance indicators such as puncture strength and elongation of the separator should be strictly controlled to ensure high battery quality and reliability. Conventional lithium-ion battery separator production often sacrifices elongation performance in pursuit of high puncture strength, resulting in poor elongation properties. Summary of the Invention

[0004] This application provides a lithium battery separator with high puncture strength and high elongation, its preparation method and application, which can achieve good elongation while ensuring puncture strength.

[0005] In a first aspect, this application provides a method for preparing a lithium battery separator with high puncture strength and high elongation, comprising: Polyethylene powder with a mass ratio of 16%-18% and white oil with a mass ratio of 82%-84% are added to an extruder and melt-extruded to obtain a cast sheet. The polyethylene powder has a viscosity-average molecular weight of 1.4 million to 1.6 million. The extruder has a gear pump pressure of 1.5-1.8 MPa and a die head pressure of 1.7-1.9 MPa. The cast sheet is subjected to longitudinal stretching, first transverse stretching, extraction and film drying, second transverse stretching, heat setting and winding after passing through cold rollers to obtain a lithium battery separator. The longitudinal stretching ratio is 500-600%, the first transverse stretching ratio is 800-900%, and the second transverse stretching ratio is 140%-150%.

[0006] Furthermore, the barrel temperature of the extruder is 180-200℃, and the extrusion rate / screw speed is 3.2-3.5.

[0007] Furthermore, the polyethylene powder has a specific mass ratio of 17%, the white oil has a specific mass ratio of 83%, and the polyethylene powder has a specific viscosity-average molecular weight of 1.5 million.

[0008] Furthermore, the barrel temperature of the extruder is specifically 200°C, and the extrusion rate / screw speed is specifically 3.2.

[0009] Furthermore, the pressure before the gear pump of the extruder is specifically 1.5 MPa, and the pressure before the die head is specifically 1.9 MPa.

[0010] Furthermore, the longitudinal stretch ratio is specifically 500%.

[0011] Furthermore, the specific transverse stretching ratio is 830%.

[0012] Furthermore, the secondary transverse stretching ratio is specifically 140%.

[0013] Secondly, this application provides a high puncture strength and high elongation lithium battery separator, which is obtained based on the preparation method of the high puncture strength and high elongation lithium battery separator described above.

[0014] Thirdly, this application provides the application of the high puncture strength and high elongation lithium battery separator described above in the field of lithium batteries.

[0015] The above-mentioned technical solution of this application has the following advantages: The method for preparing a high-puncture-strength, high-elongation lithium-ion battery separator provided in the first aspect of this application involves adding 16%-18% by mass of polyethylene powder and 82%-84% by mass of white oil to an extruder for melt extrusion to obtain a cast sheet. The polyethylene powder has a viscosity-average molecular weight of 1.4 million to 1.6 million, the extruder has a gear pump pressure of 1.5-1.8 MPa, and a die pressure of 1.7-1.9 MPa. After passing through a cold roller, the cast sheet undergoes longitudinal stretching, a first transverse stretching, extraction and film surface drying, and a second transverse stretching. The lithium battery separator is obtained by stretching, heat setting, and winding. The longitudinal stretching ratio is 500-600%, the primary transverse stretching ratio is 800-900%, and the secondary transverse stretching ratio is 140%-150%. By using raw materials with higher viscosity-average molecular weight, the puncture strength of the lithium battery separator is improved. By adjusting the raw material ratio, gear pump pressure, die pressure, and reducing the biaxial stretching ratio, the elongation of the lithium battery separator can be significantly improved while ensuring high puncture strength.

[0016] It is understood that the beneficial effects of the second and third aspects mentioned above can be found in the relevant descriptions in the first aspect above, and will not be repeated here. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the preparation method of the high puncture strength and high elongation lithium battery separator provided in this application. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0021] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. 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 this application.

[0022] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0023] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0024] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0025] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application.

[0026] like Figure 1 As shown, this application provides a method for preparing a lithium battery separator with high puncture strength and high elongation, comprising: adding 16%-18% by mass of polyethylene powder and 82%-84% by mass of white oil to an extruder for melt extrusion to obtain a cast sheet, wherein the viscosity-average molecular weight of the polyethylene powder is 1.4 million to 1.6 million, the pressure before the gear pump of the extruder is 1.5-1.8 MPa, and the pressure before the die head is 1.7-1.9 MPa; the cast sheet is subjected to longitudinal stretching, primary transverse stretching, extraction and film surface drying, secondary transverse stretching, heat setting and winding after passing through a cold roller to obtain a lithium battery separator, wherein the longitudinal stretching ratio is 500-600%, the primary transverse stretching ratio is 800-900%, and the secondary transverse stretching ratio is 140%-150%.

[0027] In some embodiments, the barrel temperature of the extruder is 180-200°C, and the extrusion rate / screw speed is 3.2-3.5.

[0028] In some embodiments, the mass ratio of the polyethylene powder is specifically 17%, the mass ratio of the white oil is specifically 83%, and the viscosity-average molecular weight of the polyethylene powder is specifically 1.5 million.

[0029] In some embodiments, the barrel temperature of the extruder is specifically 200°C, and the extrusion rate / screw speed is specifically 3.2.

[0030] In some embodiments, the pressure before the gear pump of the extruder is specifically 1.5 MPa, and the pressure before the die head is specifically 1.9 MPa.

[0031] In some embodiments, the longitudinal stretch ratio is specifically 500%.

[0032] In some embodiments, the lateral stretch ratio is specifically 830%.

[0033] In some embodiments, the secondary transverse stretch ratio is specifically 140%.

[0034] The polyethylene raw material used in this application embodiment is Daehan Oil & Chemical VH150U, with a viscosity-average molecular weight of 1.4 million to 1.6 million. Ultra-high molecular weight polyethylene can ensure high puncture strength of the product, but because its molecular weight distribution is narrow and its molecular chain branching is low, the elongation needs to be improved through a unique processing technology to achieve better elongation performance.

[0035] Key points for process improvement: Polyethylene powder content: 16%-18%; Extruder barrel temperature: 180-200℃; Extrusion rate / screw speed: 3.2-3.5; Gear pump inlet pressure: 1.5-1.8Mpa; Die inlet pressure: 1.7-1.9Mpa; MD stretch ratio: 500-600%; 1TD stretch ratio: 800-900%; 2TD stretch ratio: 140%-150%.

[0036] Because ultra-high molecular weight polyethylene (UHMWPE) is difficult to process, more processing aids, such as white oil, are needed to promote the melting and extrusion of polyethylene powder in the extruder. At this stage, the polyethylene powder is more easily sheared and broken by the screw, and as the molecular weight degrades and increases, the strength decreases, but the elongation increases. Increasing the gear pump speed achieves lower pressure, and the melt is further sheared by the gear pump as it passes through, resulting in a loss of strength and an increase in elongation.

[0037] By reducing the die lip gap, the die pressure is increased. This slows down the melt flow rate, reduces the flow orientation, and widens the cast sheet width. When the final film width after transverse stretching is the same, it's equivalent to a smaller stretch ratio. This results in lower tensile strength and higher elongation. Reducing the biaxial stretch ratio decreases the biaxial orientation of the product, significantly reducing puncture strength and tensile strength. However, due to the characteristics of polyethylene raw materials, requirements can still be met, resulting in a substantial increase in elongation.

[0038] The testing instrument is an electronic universal testing machine. For puncture strength testing, a 1mm spherical ruby ​​needle is used; for elongation testing, the sample width is 15mm, the clamp spacing is 50.8mm, and the testing speed is 508mm / min. This application produces a 9μm product with a thickness of 9μm and an area of ​​5.3g / m², simultaneously meeting the requirements of puncture strength > 600gf, MD elongation > 55%, and TD elongation > 55%.

[0039] The technical solution of this application will be further described below with reference to specific embodiments.

[0040] Example The main production processes of wet-process lithium-ion battery separators are: 1. raw material melt extrusion; 2. cold roll casting; 3. longitudinal stretching; 4. primary transverse stretching; 5. extraction and membrane drying; 6. secondary transverse stretching; 7. heat setting and winding.

[0041] Control Group 1: Raw material: Daehan Oil & Chemical VH035 (viscosity-average molecular weight 600,000); Powder percentage: 30%; Extruder barrel temperature: 190℃; Extrusion rate / screw speed: 3.5; Gear pump inlet pressure: 2.5 MPa; Die inlet pressure: 3.5 MPa; MD drawing ratio: 700%; 1TD drawing ratio: 900%; 2TD drawing ratio: 130% Improvement Group 2: Raw Material: Daehan Oil & Chemical VH150U (viscosity-average molecular weight 1.5 million); Powder content: 22%; Extruder barrel temperature: 200℃; Extrusion rate / screw speed: 3.2; Gear pump inlet pressure: 2.5 MPa; Die inlet pressure: 3.5 MPa; MD drawing ratio: 1000%; 1TD drawing ratio: 1200%; 2TD drawing ratio: 150% Improvement Group 3: Raw Material: Daehan Oil & Chemical VH150U; Powder Ratio: 17%; Extruder Barrel Temperature: 200℃; Extrusion Rate / Screw Speed: 3.2; Gear Pump Pre-pressure: 2.5 MPa; Die Pre-pressure: 1.7 MPa; MD Drawing Ratio: 1000%; 1TD Drawing Ratio: 1200%; 2TD Drawing Ratio: 150% Improvement Group 4: Raw Material: Daehan Oil & Chemical VH150U; Powder Ratio: 17%; Extruder Barrel Temperature: 200℃; Extrusion Rate / Screw Speed: 3.2; Gear Pump Pre-pressure: 1.5 MPa; Die Pre-pressure: 1.9 MPa; MD Drawing Ratio: 1000%; 1TD Drawing Ratio: 1200%; 2TD Drawing Ratio: 150% Improvement Group 5: Raw Material: Daehan Oil & Chemical VH150U; Powder Ratio: 17%; Extruder Barrel Temperature: 200℃; Extrusion Rate / Screw Speed: 3.2; Gear Pump Pre-pressure: 1.5 MPa; Die Pre-pressure: 1.9 MPa; MD Drawing Ratio: 800%; 1TD Drawing Ratio: 1000%; 2TD Drawing Ratio: 150% Improvement Group 6: Raw Material: Daehan Oil & Chemical VH150U; Powder Ratio: 17%; Extruder Barrel Temperature: 200℃; Extrusion Rate / Screw Speed: 3.2; Gear Pump Pre-pressure: 1.5 MPa; Die Pre-pressure: 1.9 MPa; MD Drawing Ratio: 500%; 1TD Drawing Ratio: 830%; 2TD Drawing Ratio: 140% The experimental results are shown in the table below: Based on the experimental results, we can conclude that: Control group 1 used raw materials with a viscosity-average molecular weight of 600,000, which had good elongation but low puncture strength; Improved group 2 used raw materials with a viscosity-average molecular weight of 1,500,000, which had high puncture strength but low elongation; Improved group 3 reduced the proportion of raw materials, which increased the elongation; Improved group 4 reduced the pressure before the gear pump and increased the pressure of the die head, which increased the elongation; Improved groups 5-6 reduced the biaxial stretching ratio, which significantly improved the elongation.

[0042] The method for preparing a high-puncture-strength and high-elongation lithium battery separator provided in this application improves the puncture strength of the product by using raw materials with higher viscosity-average molecular weight. By adjusting the raw material ratio, gear pump pressure, die pressure, and reducing the biaxial stretching ratio, the puncture strength is maintained above 600gf and the biaxial elongation is increased to above 55%. While ensuring that the lithium battery separator has high puncture strength, the elongation of the lithium battery separator is further significantly improved.

[0043] This application also provides a high puncture strength and high elongation lithium battery separator, which is obtained based on the preparation method of the high puncture strength and high elongation lithium battery separator described above.

[0044] This application also provides the application of the high puncture strength and high elongation lithium battery separator described above in the field of lithium batteries.

[0045] It should be noted 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 mutually. Each embodiment focuses on describing the differences from other embodiments. This application is not limited to the specific methods described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0046] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing a lithium battery separator with high puncture strength and high elongation, characterized in that, include: Polyethylene powder with a mass ratio of 16%-18% and white oil with a mass ratio of 82%-84% are added to an extruder and melt-extruded to obtain a cast sheet. The polyethylene powder has a viscosity-average molecular weight of 1.4 million to 1.6 million. The extruder has a gear pump pressure of 1.5-1.8 MPa and a die head pressure of 1.7-1.9 MPa. The cast sheet is subjected to longitudinal stretching, first transverse stretching, extraction and film drying, second transverse stretching, heat setting and winding after passing through cold rollers to obtain a lithium battery separator. The longitudinal stretching ratio is 500-600%, the first transverse stretching ratio is 800-900%, and the second transverse stretching ratio is 140%-150%.

2. The method for preparing a high-puncture-strength, high-elongation lithium battery separator as described in claim 1, characterized in that, The barrel temperature of the extruder is 180-200℃, and the extrusion rate / screw speed is 3.2-3.

5.

3. The method for preparing a high-puncture-strength, high-elongation lithium battery separator as described in claim 1, characterized in that, The specific mass ratio of the polyethylene powder is 17%, the specific mass ratio of the white oil is 83%, and the specific viscosity-average molecular weight of the polyethylene powder is 1.5 million.

4. The method for preparing a high-puncture-strength, high-elongation lithium battery separator as described in claim 2, characterized in that, The extruder barrel temperature is specifically 200℃, and the extrusion rate / screw speed is specifically 3.

2.

5. The method for preparing a high-puncture-strength, high-elongation lithium battery separator as described in claim 1, characterized in that, The extruder has a gear pump pressure of 1.5 MPa and a die head pressure of 1.9 MPa.

6. The method for preparing a high-puncture-strength, high-elongation lithium battery separator as described in claim 1, characterized in that, The longitudinal stretch ratio is specifically 500%.

7. The method for preparing a high-puncture-strength, high-elongation lithium battery separator as described in claim 1, characterized in that, The specific transverse stretching ratio is 830%.

8. The method for preparing a high-puncture-strength, high-elongation lithium battery separator as described in claim 1, characterized in that, The secondary transverse stretching ratio is specifically 140%.

9. A lithium battery separator with high puncture strength and high elongation, characterized in that, The high puncture strength and high elongation lithium battery separator is prepared according to any one of claims 1 to 8.

10. The application of the high puncture strength and high elongation lithium battery separator as described in claim 9 in the field of lithium batteries.

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