High-density polyethylene nanofiber lithium ion battery separator and method of making the same

Abstract

This application provides a high-density polyethylene nanofiber lithium-ion battery separator and its preparation method, belonging to the field of battery separator technology. The lithium-ion battery separator involves melt-blending and spinning high-density polyethylene with cellulose acetate butyrate masterbatch, immersing the resulting composite fibers in a first solvent to obtain high-density polyethylene nanofibers; dispersing the high-density polyethylene nanofibers in a second solvent, performing shear pre-dispersion, and then homogenizing the resulting high-density polyethylene nanofiber suspension, which is then coated onto the upper and lower surfaces of a substrate to obtain the high-density polyethylene nanofiber lithium-ion battery separator. The extruder in the melt-blending spinning process has six temperature zones sequentially arranged along the material extrusion direction; the temperature gradually increases from the first to the fifth temperature zone, and decreases in the sixth temperature zone. This lithium-ion battery separator has high porosity, good electrolyte wettability, and exhibits excellent rate performance and cycle performance when applied to lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a high-density polyethylene nanofiber lithium-ion battery separator and its preparation method. Background Technology

[0002] With the rapid popularization of consumer electronics such as smartphones, new energy vehicles, and energy storage systems, lithium-ion batteries, with their core advantages such as high energy density and long cycle life, have gradually developed into the dominant electrochemical energy storage system, providing key technological support for the realization of the "dual-carbon strategy" goal. From a working mechanism perspective, lithium-ion batteries achieve energy storage and output through the reversible insertion and extraction of lithium ions between the positive and negative electrode materials, utilizing electrochemical redox reactions. The separator, as the core component of the battery, is located between the positive and negative electrodes. On the one hand, it provides physical isolation to prevent short circuits caused by direct contact between the positive and negative electrodes; on the other hand, it provides a transport channel for the directional migration of lithium ions. Therefore, the performance of the separator directly determines key indicators of the battery such as ionic conductivity, rate performance, cycle performance, and thermal safety performance. Currently, commercially available lithium-ion battery separators mainly use polyolefin separators, covering polyethylene (PE), polypropylene (PP), and their composites. Although these separator materials possess good chemical stability, they generally have limitations such as low porosity, poor thermal shrinkage performance, and poor electrolyte wettability.

[0003] In related technologies, lithium-ion battery separators are obtained by electrospinning polyvinylidene fluoride (PVDF) into a uniform spinning solution, followed by peeling off the tin foil after spinning. Compared to traditional unidirectional or bidirectional stretching processes, this method effectively improves the pore size, porosity, and pore structure of the separator, enhances electrolyte wettability, and helps improve ion permeability, battery rate performance, and cycle performance. However, this approach still has significant drawbacks: the prepared separator has low mechanical strength, and the volatilization of organic solvents during the spinning process poses safety hazards and environmental pollution risks. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a high-density polyethylene nanofiber lithium-ion battery separator and its preparation method. The high-density polyethylene nanofiber lithium-ion battery separator has high porosity, good electrolyte wettability, and exhibits good rate performance and cycle performance when applied to lithium-ion batteries.

[0005] To achieve the above objectives, in a first aspect, this application provides a method for preparing a high-density polyethylene nanofiber lithium-ion battery separator, comprising: providing high-density polyethylene, cellulose acetate butyrate, a first solvent, a second solvent, and a substrate; High-density polyethylene and cellulose acetate butyrate are melt-blended and spun to obtain composite fibers; The composite fibers were immersed in the first solvent to obtain high-density polyethylene nanofibers; High-density polyethylene nanofibers were dispersed in a second solvent and subjected to shear pre-dispersion to obtain a pre-dispersion liquid. The pre-dispersed liquid was homogenized to obtain a high-density polyethylene nanofiber suspension. A high-density polyethylene nanofiber suspension is coated onto a substrate to obtain a high-density polyethylene nanofiber lithium-ion battery separator; wherein... In melt blend spinning, the extruder is equipped with six temperature zones in sequence along the material extrusion direction; the temperature of the first to the fifth temperature zones gradually increases, and the temperature of the sixth temperature zone decreases.

[0006] Furthermore, the temperatures in the first to fifth temperature zones are 180℃-225℃, and the temperature in the sixth temperature zone is 190℃-200℃.

[0007] Furthermore, the mass ratio of high-density polyethylene to cellulose acetate butyrate is (10:90) to (50:50).

[0008] Furthermore, the first solvent includes at least one of ethyl acetate, formic acid, acetone, and tetrahydrofuran; and / or, The second solvent includes at least one of deionized water, ethanol, isopropanol, n-butanol, tert-butanol, and n-propanol.

[0009] Furthermore, in the pre-dispersion liquid, the mass fraction of high-density polyethylene nanofibers is 0.1wt%-5wt%.

[0010] Furthermore, the shear pre-dispersion time is 2h-4h; and / or, The homogenization process takes 9-11 hours.

[0011] Furthermore, the substrate includes at least one of meltblown nonwoven fabric, spunbond nonwoven fabric, spunlace nonwoven fabric, needle-punched nonwoven fabric, and flash-spun nonwoven fabric.

[0012] Furthermore, the coating weight is 1 g / m². 2 -20 g / m 2 .

[0013] Furthermore, high-density polyethylene and cellulose acetate butyrate are melt-blended and spun to obtain composite fibers, including: High-density polyethylene and cellulose acetate butyrate are dried to obtain dried high-density polyethylene and dried cellulose acetate butyrate. The dried high-density polyethylene and the dried cellulose acetate butyrate were melt-blended and spun to obtain composite fibers.

[0014] Secondly, this application also provides a battery, including a high-density polyethylene nanofiber lithium-ion battery separator prepared by the preparation method of the high-density polyethylene nanofiber lithium-ion battery separator of any of the above claims.

[0015] The beneficial effects of this application are as follows: In this application, high-density polyethylene (HDPE) is used as the dispersed phase and cellulose acetate butyrate (CET) as the continuous phase. HDPE / CET composite fibers are obtained through melt blending and extrusion, and gradient heating ensures thorough plasticization and uniform dispersion of the materials. Utilizing the principle of similar compatibility, the difference in solubility between CET and HDPE in solvents is used to completely dissolve and remove the CET matrix phase, resulting in HDPE nanofibers. High-speed shearing is then used to initially de-agglomerate and disperse the nanofibers, and homogenization further breaks down the entanglement and aggregation between fibers, resulting in a uniformly dispersed HDPE nanofiber suspension. A coating method is then used to obtain a HDPE nanofiber lithium-ion battery separator. The operation is simple and easy to implement. Furthermore, the fiber diameter, pore size, structure, and morphology of the HDPE nanofiber membrane are easily controlled, resulting in higher porosity, better electrolyte wettability, higher liquid absorption rate, higher ionic conductivity, and lower interfacial impedance. Consequently, the assembled lithium-ion battery exhibits superior rate performance and cycle performance.

[0016] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

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

[0018] Figure 1 This is a SEM image of the high-density polyethylene nanofiber lithium-ion battery separator from Example 1. Figure 2 The contact angle of the high-density polyethylene nanofiber lithium-ion battery separator to the electrolyte in Example 1; Figure 3 AC impedance spectrum of high-density polyethylene nanofiber lithium-ion battery separator in Example 1 (stainless steel sheet / separator / stainless steel sheet simulated battery). Figure 4The rate performance diagram of the high-density polyethylene nanofiber lithium-ion battery separator in Example 1 is shown. Figure 5 The graph shows the cycle performance of the high-density polyethylene nanofiber lithium-ion battery separator in Example 1. Detailed Implementation

[0019] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0025] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0027] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0028] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0029] With the rapid popularization of consumer electronics such as smartphones, new energy vehicles, and energy storage systems, lithium-ion batteries, with their core advantages such as high energy density and long cycle life, have gradually developed into the dominant electrochemical energy storage system, providing key technological support for the realization of the "dual-carbon strategy" goal. From a working mechanism perspective, lithium-ion batteries achieve energy storage and output through the reversible insertion and extraction of lithium ions between the positive and negative electrode materials, utilizing electrochemical redox reactions. The separator, as the core component of the battery, is located between the positive and negative electrodes. On the one hand, it provides physical isolation to prevent short circuits caused by direct contact between the positive and negative electrodes; on the other hand, it provides a transport channel for the directional migration of lithium ions. Therefore, the performance of the separator directly determines key indicators of the battery such as ionic conductivity, rate performance, cycle performance, and thermal safety performance. Currently, commercially available lithium-ion battery separators mainly use polyolefin separators, covering polyethylene (PE), polypropylene (PP), and their composites. Although these separator materials possess good chemical stability, they generally have limitations such as low porosity, poor thermal shrinkage performance, and poor electrolyte wettability.

[0030] In related technologies, lithium-ion battery separators are obtained by electrospinning polyvinylidene fluoride (PVDF) into a uniform spinning solution, followed by peeling off the tin foil after spinning. Compared to traditional unidirectional or bidirectional stretching processes, this method effectively improves the pore size, porosity, and pore structure of the separator, enhances electrolyte wettability, and helps improve ion permeability, battery rate performance, and cycle performance. However, this approach still has significant drawbacks: the prepared separator has low mechanical strength, and the volatilization of organic solvents during the spinning process poses safety hazards and environmental pollution risks.

[0031] To address the aforementioned technical problems, in a first aspect, this application provides a method for preparing a high-density polyethylene nanofiber lithium-ion battery separator, comprising: providing high-density polyethylene, cellulose acetate butyrate, a first solvent, a second solvent, and a substrate; High-density polyethylene and cellulose acetate butyrate are melt-blended and spun to obtain composite fibers; The composite fibers were immersed in the first solvent to obtain high-density polyethylene nanofibers; High-density polyethylene nanofibers were dispersed in a second solvent and subjected to shear pre-dispersion to obtain a pre-dispersion liquid. The pre-dispersed liquid was homogenized to obtain a high-density polyethylene nanofiber suspension. A high-density polyethylene nanofiber suspension is coated onto a substrate to obtain a high-density polyethylene nanofiber lithium-ion battery separator; wherein... In melt blend spinning, the extruder is equipped with six temperature zones in sequence along the material extrusion direction; the temperature of the first to the fifth temperature zones gradually increases, and the temperature of the sixth temperature zone decreases.

[0032] In this application, high-density polyethylene (HDPE) is used as the dispersed phase and cellulose acetate butyrate (CET) as the continuous phase. HDPE / CET composite fibers are obtained through melt blending and extrusion, and gradient heating ensures sufficient plasticization and uniform dispersion of the materials. Utilizing the principle of similar compatibility, the difference in solubility between CET and HDPE in solvents is used to completely dissolve and remove the CET matrix phase, resulting in HDPE nanofibers. High-speed shearing is then used to initially de-agglomerate and disperse the nanofibers, and homogenization further breaks down the entanglement and aggregation between fibers, thus obtaining HDPE nanofibers. A coating method is then used to obtain a HDPE nanofiber lithium-ion battery separator. The operation is simple and easy to implement. Furthermore, the fiber diameter, pore size, structure, and morphology of the HDPE nanofiber membrane are easily controlled, resulting in higher porosity, better electrolyte wettability, higher liquid absorption rate, lower ionic conductivity, and lower interfacial impedance. Consequently, the assembled lithium-ion battery exhibits superior rate performance and cycle performance.

[0033] In some embodiments, the temperatures of the first to fifth temperature zones are 180°C-225°C, and the temperature of the sixth temperature zone is 190°C-200°C.

[0034] In this embodiment, the temperatures of the first to fifth temperature zones are set to 180℃-225℃, and the temperature of the sixth temperature zone is set to 190℃-200℃. The gradient heating in the first five zones allows the high-density polyethylene / cellulose acetate butyrate composite fiber to be fully melted, plasticized, and uniformly dispersed. The temperature of the sixth zone is then suddenly dropped. The cooling and thickening effect of the melt is used to build a stable back pressure in front of the spinneret to eliminate bubbles and pressure fluctuations. This also precisely pre-compensates for the temperature rise caused by the high shear rate at the spinneret orifice, thereby preventing the melt from overheating and degrading and the viscosity from dropping suddenly, thus maintaining the fiber strength of the high-density polyethylene / cellulose acetate butyrate composite fiber.

[0035] In some embodiments, the mass ratio of high-density polyethylene to cellulose acetate butyrate is (10:90) to (50:50).

[0036] In this embodiment, the mass ratio of high-density polyethylene to cellulose acetate butyrate is set to (10:90)-(50:50). Cellulose acetate butyrate will be eluted to form micropores during subsequent extraction. This ratio enables the obtained battery separator to have high porosity while maintaining a certain fiber strength.

[0037] In some embodiments, the first solvent includes at least one of ethyl acetate, formic acid, acetone, and tetrahydrofuran.

[0038] In this embodiment, the above solvent is selected to extract the dispersed phase cellulose acetate butyrate, and the cellulose acetate butyrate matrix can be dissolved and removed to obtain high-density polyethylene nanofibers.

[0039] In some embodiments, the second solvent includes at least one of deionized water, ethanol, isopropanol, n-butanol, tert-butanol, and n-propanol.

[0040] In this embodiment, the above-mentioned solvent is selected as a dispersant and is used only as a carrier for high-density polyethylene fibers. Alcohol solvents are volatile and evaporate quickly after coating, so the obtained high-density polyethylene nanofibers can be dried quickly. At the same time, alcohols are relatively environmentally friendly and non-toxic.

[0041] In some embodiments, the mass fraction of high-density polyethylene nanofibers in the pre-dispersion liquid is 0.1wt%-5wt%.

[0042] In this embodiment, the mass fraction of high-density polyethylene nanofibers in the pre-dispersion liquid is set to 0.1wt%-5wt%, which can obtain a stable and dispersed high-density polyethylene nanofiber suspension. After coating, the porosity of the high-density polyethylene nanofiber lithium-ion battery separator is increased and the pore size distribution is more uniform.

[0043] In some embodiments, the shear pre-dispersion time is 2 h-4 h.

[0044] In this embodiment, the shearing pre-dispersion time is set to 2 h-4 h, so that the high-density polyethylene fibers can be dispersed in the second solvent and sheared into nanofibers of suitable length, thereby making the pore structure of the high-density polyethylene nanofiber lithium-ion battery separator uniform in the subsequent coating process.

[0045] In some embodiments, the homogenization process takes 9-11 hours.

[0046] In this embodiment, the homogenization treatment time is set to 9-11 h. The cavitation effect and shear force generated by the high-pressure jet can break the physical entanglement in the high-density polyethylene nanofibers, reduce nanofiber aggregation, and achieve a better dissociation state in the suspension while maintaining the nanofiber structure. This results in the coated high-density polyethylene nanofiber lithium-ion battery separator having high porosity and uniform pore size distribution.

[0047] In some embodiments, the substrate includes at least one of meltblown nonwoven fabric, spunbond nonwoven fabric, spunlace nonwoven fabric, needle-punched nonwoven fabric, and flash-spun nonwoven fabric.

[0048] In some embodiments, the coating weight is 1 g / m³. 2 -20 g / m 2 .

[0049] In this embodiment, the coating weight is set to 1 g / m³. 2 -20 g / m 2This allows the nanofiber coating to be defect-free, uniform in thickness, and provides sufficient pore structure, thereby improving the electrolyte wettability and ion conduction efficiency of high-density polyethylene nanofiber lithium-ion battery separators.

[0050] In some embodiments, high-density polyethylene and cellulose acetate butyrate are melt-blended and spun to obtain composite fibers, comprising: High-density polyethylene and cellulose acetate butyrate are dried to obtain dried high-density polyethylene and dried cellulose acetate butyrate. The dried high-density polyethylene and the dried cellulose acetate butyrate were melt-blended and spun to obtain composite fibers.

[0051] In this embodiment, high-density polyethylene and cellulose acetate butyrate are dried separately at 80°C for 24 hours to fully remove residual moisture from the raw materials and reduce degradation caused by moisture during processing.

[0052] It should be noted that the drying methods include, but are not limited to, hot air circulation drying, microwave drying, and vacuum drying.

[0053] Secondly, this application also provides a battery, including a high-density polyethylene nanofiber lithium-ion battery separator prepared by the preparation method of the high-density polyethylene nanofiber lithium-ion battery separator of any of the above claims.

[0054] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0055] I. Preparation Method Example 1 200 g of high-density polyethylene (HDPE) masterbatch and 800 g of cellulose acetate butyrate masterbatch were weighed and placed separately in a forced-air drying oven at 80°C for 24 hours to completely remove adsorbed moisture from the raw materials. The dried HDPE and cellulose acetate butyrate were then thoroughly premixed at a mass ratio of 20:80 and subsequently fed into a twin-screw extruder for melt blending extrusion. The temperatures of each zone of the twin-screw extruder were set sequentially as follows: Zone 1 180°C, Zone 2 210°C, Zone 3 215°C, Zone 4 220°C, Zone 5 225°C, and Zone 6 195°C. After the melt was extruded through the die, it was simultaneously wound by a winding machine at an appropriate traction speed to obtain HDPE / cellulose acetate butyrate composite fibers. The obtained composite fibers were immersed in acetone solvent and extracted with stirring at room temperature for 24 hours to completely dissolve and remove the cellulose acetate butyrate matrix phase. After extraction, the remaining high-density polyethylene fibers were washed three times with fresh acetone and then dried in a vacuum drying oven at 60 °C for 12 hours to finally obtain continuous high-density polyethylene nanofibers.

[0056] Take 0.5 g of the prepared high-density polyethylene nanofibers and add 100 g of isopropanol / water mixed solvent (volume ratio of isopropanol to water is 50:50) to prepare an initial suspension with a mass fraction of 0.5 wt%. First, pre-dispersion is performed using a high-speed shear press for 3 hours; then, the pre-dispersion is transferred to a homogenizer and homogenized for 10 hours to obtain a uniform and stable high-density polyethylene nanofiber suspension.

[0057] The prepared high-density polyethylene nanofiber suspension was loaded into a high-pressure spray gun at a speed of 30 g / m³. 2 Using spunbond polyester (PET) nonwoven fabric as the substrate, 240 mL of suspension was uniformly sprayed onto both surfaces of the nonwoven fabric. After spraying, the composite diaphragm was placed in a 60°C forced-air oven to dry for 2 hours, resulting in a diaphragm with a basis weight of 6 g / m² on one side. 2 The total weight is 12 g / m³ 2 High-density polyethylene nanofiber lithium-ion battery separator.

[0058] Example 2 The difference from Example 1 is that high-density polyethylene and cellulose acetate butyrate are fully premixed at a mass ratio of 40:60. The remaining steps are the same as in Example 1 and will not be repeated here. This yields the high-density polyethylene nanofiber lithium-ion battery separator of Example 2.

[0059] Example 3 The difference from Example 1 is that the basis weight of one side of the coated high-density polyethylene nanofibers is 10 g / m². 2 The total weight is 20 g / m³ 2 The remaining steps are the same as in Example 1, and will not be repeated here, thus obtaining the high-density polyethylene nanofiber lithium-ion battery separator of Example 3.

[0060] Example 4 The difference from Example 1 is that high-density polyethylene and cellulose acetate butyrate are fully premixed at a mass ratio of 10:90. The remaining steps are the same as in Example 1 and will not be repeated here. This yields the high-density polyethylene nanofiber lithium-ion battery separator of Example 4.

[0061] Example 5 The difference from Example 1 is that high-density polyethylene and cellulose acetate butyrate are fully premixed at a mass ratio of 30:70. The remaining steps are the same as in Example 1 and will not be repeated here. This yields the high-density polyethylene nanofiber lithium-ion battery separator of Example 5.

[0062] Example 6 The difference from Example 1 is that the shear pre-dispersion time is 5 h, and the remaining steps are the same as in Example 1, which will not be repeated here. The high-density polyethylene nanofiber lithium-ion battery separator of Example 6 is obtained.

[0063] Example 7 The difference from Example 1 is that the shear pre-dispersion time is 1 h, and the remaining steps are the same as in Example 1, which will not be repeated here. The high-density polyethylene nanofiber lithium-ion battery separator of Example 7 is obtained.

[0064] Example 8 The difference from Example 1 is that the homogenization time is 8 hours, while the remaining steps are the same as in Example 1 and will not be repeated here. The high-density polyethylene nanofiber lithium-ion battery separator of Example 8 is obtained.

[0065] Example 9 The difference from Example 1 is that the homogenization time is 11 h, while the remaining steps are the same as in Example 1 and will not be repeated here. The high-density polyethylene nanofiber lithium-ion battery separator of Example 9 is obtained.

[0066] Comparative Example 1 The difference from Example 1 is that no homogenization process is performed. The remaining steps are the same as in Example 1 and will not be repeated here. The high-density polyethylene nanofiber lithium-ion battery separator of Comparative Example 1 is obtained.

[0067] Comparative Example 2 The difference from Example 1 is that no shear pre-dispersion is performed. The remaining steps are the same as in Example 1 and will not be repeated here. The high-density polyethylene nanofiber lithium-ion battery separator of Comparative Example 2 is obtained.

[0068] Comparative Example 3 The difference from Example 1 is that six temperature control zones are not set. The remaining steps are the same as in Example 1 and will not be repeated here. The high-density polyethylene nanofiber lithium-ion battery separator of Comparative Example 3 is obtained.

[0069] II. Testing Methods Electrolyte absorbance test method: High-density polyethylene nanofiber lithium-ion battery separators were cut into circular samples with a diameter of 16 mm, completely immersed in lithium-ion battery electrolyte, left to stand for 1 hour, removed, and the residual electrolyte on the surface was wiped off. The mass of the separator before and after immersion was measured.

[0070] Liquid absorption rate (%) = 100% in, W 2 The quality of the diaphragm after impregnation with electrolyte. W 1 The quality of the diaphragm before impregnation.

[0071] Methods for testing ionic conductivity: Electrochemical impedance spectroscopy (EIS) of the blocking battery was tested using an electrochemical workstation (Autolab semiconductor analyzer, PGSTAT302N). The blocking battery assembly sequence was: negative electrode shell, stainless steel sheet, separator (with electrolyte added), and stainless steel sheet again. The test frequency was 10 Hz. 6 Hz-10 -2 Hz, voltage amplitude is 5 mV / s.

[0072] 1000 in, The ionic conductivity of the membrane. L (cm) represents the thickness of the diaphragm. A (cm 2 () represents the contact area between the stainless steel sheet and the diaphragm. R (Ω) is the diaphragm volume resistivity obtained from the Nyquist plot.

[0073] Discharge specific capacity test method: The battery was tested using the LANHE CT2001A charge / discharge test system at 0.2C, 0.5C, 1C, and 2C conditions, with a test voltage range of 2.5 V to 4.2 V.

[0074] Capacity retention test method: The battery's cycle performance was tested using the Blue Battery Testing System, specifically by performing 100 constant current charge-discharge cycles at 0.5C. Capacity retention rate is the ratio of the discharge specific capacity after 100 cycles to the initial discharge specific capacity.

[0075] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 1 shows the test data for Examples 1-9 and Comparative Examples 1-3. As shown in Table 1, increasing the basis weight of the coated high-density nanofibers can improve their electrolyte absorption rate, thereby enhancing the ionic conductivity, rate performance, and capacity retention of the high-density polyethylene nanofiber battery separator. Extending the homogenization time can reduce the nanofiber diameter, resulting in finer high-density polyethylene nanofibers, which further improves their electrolyte absorption rate and, consequently, the ionic conductivity, rate performance, and capacity retention of the high-density polyethylene nanofiber battery separator.

[0076] Comparing Examples 1-9 with Comparative Examples 1-3, it can be seen that pre-shearing dispersion and homogenization treatment of high-density polyethylene nanofibers can improve the dispersibility of nanofibers, break the entanglement and aggregation between fibers, thereby obtaining high-density polyethylene nanofibers. This makes it easier to control the fiber diameter, pore size, structure and morphology of the high-density polyethylene nanofiber membrane, resulting in higher porosity, better wettability to electrolyte, higher liquid absorption rate, higher ionic conductivity, and lower interfacial impedance. As a result, the assembled lithium-ion battery exhibits better rate performance and cycle performance.

[0077] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a high-density polyethylene nanofiber lithium-ion battery separator, characterized in that, include: It provides high-density polyethylene, cellulose acetate butyrate, a first solvent, a second solvent, and a substrate; The high-density polyethylene and the cellulose acetate butyrate ester are melt-blended and spun to obtain composite fibers; The composite fiber is immersed in the first solvent to obtain high-density polyethylene nanofibers; The high-density polyethylene nanofibers are dispersed in the second solvent and subjected to shear pre-dispersion to obtain a pre-dispersion liquid. The pre-dispersed liquid was homogenized to obtain a high-density polyethylene nanofiber suspension. The high-density polyethylene nanofiber suspension is coated onto the substrate to obtain a high-density polyethylene nanofiber lithium-ion battery separator; wherein... The extruder in the melt blend spinning process has six temperature zones arranged sequentially along the material extrusion direction; the temperature of the first to the fifth temperature zones gradually increases, and the temperature of the sixth temperature zone decreases.

2. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, The temperatures in the first to fifth temperature zones are 180℃-225℃, and the temperature in the sixth temperature zone is 190℃-200℃.

3. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, The mass ratio of the high-density polyethylene to the cellulose acetate butyrate is (10:90) to (50:50).

4. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, The first solvent includes at least one of ethyl acetate, formic acid, acetone, and tetrahydrofuran; and / or, The second solvent includes at least one of deionized water, ethanol, isopropanol, n-butanol, tert-butanol, and n-propanol.

5. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, In the pre-dispersion liquid, the mass fraction of the high-density polyethylene nanofibers is 0.1wt%-5wt%.

6. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, The shear pre-dispersion time is 2 h-4 h; and / or, The homogenization process takes 9-11 hours.

7. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, The substrate includes at least one of meltblown nonwoven fabric, spunbond nonwoven fabric, spunlace nonwoven fabric, needle-punched nonwoven fabric, and flash-spun nonwoven fabric.

8. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, The coating has a basis weight of 1 g / m³. 2 -20 g / m 2 .

9. The method for preparing the high-density polyethylene nanofiber lithium-ion battery separator according to claim 1, characterized in that, The process of melt-blending the high-density polyethylene with the cellulose acetate butyrate and then spinning the resulting composite fiber comprises: The high-density polyethylene and the cellulose acetate butyrate ester are dried to obtain dried high-density polyethylene and dried cellulose acetate butyrate ester. The dried high-density polyethylene and the dried cellulose acetate butyrate were melt-blended and spun to obtain composite fibers.

10. A battery, characterized in that, This includes high-density polyethylene nanofiber lithium-ion battery separators prepared by the method described in any one of claims 1-9.

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