Crosslinked polyolefin lithium ion battery diaphragm and preparation method thereof
Through the method of multi-stage stretching and gamma-ray irradiation cross-linking, the problem that the cross-linked polyolefin membrane in the existing technology cannot have both high membrane rupture temperature and ultra-thin and high strength is solved, and a high-performance cross-linked polyolefin lithium-ion battery membrane is prepared.
Patent Information
- Application Number
- CN202510917860.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-03
- Publication Date
- 2025-10-28
AI Technical Summary
The cross-linked polyolefin membranes prepared in the prior art are limited by the low stretching ratio and cannot simultaneously achieve high membrane rupture temperature and ultra-thin high strength properties.
A multi-stage stretching and gamma-ray irradiation crosslinking method was adopted, including casting at different temperatures, multiple stretching, diluent elution and heat setting, and finally crosslinking by gamma rays to prepare crosslinked polyolefin lithium-ion battery separators.
A cross-linked polyolefin lithium-ion battery separator with a thickness of 3.5 to 7.5 μm was prepared, with a membrane rupture temperature ≥ 220°C, a puncture strength ≥ 300 gf, and a tensile strength ≥ 150 MPa, combining high membrane rupture temperature with ultra-thin and high-strength performance.
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Figure CN120854843A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery separator technology, and in particular to a cross-linked polyolefin lithium-ion battery separator and its preparation method. Background Technology
[0002] Polyolefin separators have advantages such as high strength, good air permeability and low cost, and are widely used in lithium-ion batteries in the power, energy storage and 3C fields. However, the low melting point of polyolefin materials (such as polyethylene melting point 134-140℃) results in a low membrane breakage temperature (about 140℃), which further leads to a greater risk of thermal runaway during battery application.
[0003] Cross-linked polyolefins are one of the effective methods to increase their film breaking temperature.
[0004] Patent CN111081949B discloses a cross-linked polyolefin membrane and its preparation method. The method involves melt-blending polyolefin, a pore-forming agent, a grafting agent, an initiator, and a catalyst for 5–25 minutes, followed by extrusion, stretching, extraction, and heat setting to obtain a membrane with a thickness of 9–16 μm and a tensile strength of 1273–1861 kg / cm². 2 A polyethylene diaphragm with a breathability of 90sec / 100ml~150sec / 100ml and a rupture temperature of 162.2~188℃;
[0005] Patent CN116207440A discloses a cross-linked lithium-ion battery separator and its preparation method. The method involves mixing ultra-high molecular weight polyethylene, high-density polyethylene, diluent, silane cross-linking agent, free radical initiator, water absorbent and antioxidant and adding them into a twin-screw extruder. After casting, stretching, extraction, secondary stretching, heat setting and self-cross-linking at room temperature for 24 hours, a cross-linked polyethylene separator with a thickness of 9.0-9.2 μm and a film breaking temperature of 183-198℃ is obtained.
[0006] Patent CN111433264B discloses a cross-linked polyolefin separator and its manufacturing method. The method involves introducing a non-grafted polyolefin with a weight-average molecular weight of 300,000 to 1,500,000, a silane-grafted polyolefin with a weight-average molecular weight of 300,000 to 1,000,000, a diluent, an initiator, an alkoxysilane compound, and a cross-linking catalyst into an extruder for extrusion. After stretching, extraction, heat fixation, and cross-linking under water conditions for 6 to 50 hours, a cross-linked polyethylene separator with a rupture temperature ≥175℃ and a thickness of 12μm is obtained.
[0007] However, the cross-linked polyolefin membranes prepared by the above-mentioned prior art are limited by the low stretching ratio and cannot obtain polyolefin membranes that have both high rupture temperature and ultra-thin high strength properties. Summary of the Invention
[0008] The purpose of this invention is to provide a cross-linked polyolefin lithium-ion battery separator and its preparation method, aiming to solve the technical problem that the cross-linked polyolefin separators prepared in the prior art are limited by the low stretching ratio and cannot obtain polyolefin separators with both high rupture temperature and ultra-thin high strength properties.
[0009] To achieve the above objectives, the present invention provides a method for preparing a cross-linked polyolefin lithium-ion battery separator, comprising the following steps:
[0010] Polyolefin and diluent are added to a screw extruder, extruded through a die at temperature T1, and formed into a cast sheet under double-sided cooling by cooling rollers at temperature T2;
[0011] The cast sheet is stretched once at temperature T3 to obtain a stretched film.
[0012] A first-stretched film is subjected to a second stretching at temperature T4 to obtain a second-stretched film.
[0013] The double-stretched film was placed in an extraction tank at temperature T5 to completely wash off the diluent, then placed in an oven at temperature T6 to dry completely, and finally stretched a third time at temperature T7 to obtain a triple-stretched film.
[0014] The three-stretched film is heat-set at temperature T8 to obtain a heat-set film;
[0015] Crosslinked polyolefin lithium-ion battery separators are obtained by crosslinking heat-set films with gamma-ray irradiation at temperature T9.
[0016] The polyolefins used include ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 400,000 to 3,000,000, and the total solids content is 15% to 35% of the total mass of polyolefins and diluents.
[0017] The diluent includes one or more of white oil, paraffin oil, alkane compounds, or ester compounds;
[0018] The diluent can fully melt and mix with the polyolefin at a temperature of +50 to 100°C (the melting point of the polyolefin material) to form a uniform liquid without undergoing a chemical reaction.
[0019] The extractant includes one of dichloromethane, carbon tetrachloride, and diethyl ether, or a volatile solvent that is completely miscible with the diluent.
[0020] Wherein, the T1 temperature is the melting point of the polyolefin material +50 to 100℃, the T2 temperature is 5 to 30℃, and the T3 temperature is the melting point of the polyolefin material -10 to 40℃.
[0021] Wherein, the T4 temperature is the melting point of the polyolefin material from -10 to 40°C, the T5 temperature is the boiling point of the extractant from -10 to 30°C, and the T6 temperature is the boiling point of the extractant from +0 to 20°C.
[0022] Wherein, the T7 temperature is the melting point of the polyolefin material from -10 to 40°C, the T8 temperature is the melting point of the polyolefin material from -40 to 60°C, and the T9 temperature is 20 to 30°C.
[0023] The first stretching ratio is 2 to 3 times, the second stretching ratio is 9 to 13 times, and the third stretching ratio is 1.5 to 2.9 times.
[0024] The gamma-ray irradiation crosslinking dose is 100–200 kGy.
[0025] The present invention also provides a cross-linked polyolefin lithium-ion battery separator, which is prepared by the cross-linked polyolefin lithium-ion battery separator and preparation method described above.
[0026] The cross-linked polyolefin lithium-ion battery separator has a thickness of 3.5–7.5 μm, a rupture temperature ≥220℃, a puncture strength ≥300 gf, and a tensile strength ≥150 MPa.
[0027] The cross-linked polyolefin lithium-ion battery separator has a porosity of 28% to 45% and an air permeability of 80 to 165 s / 100cc.
[0028] This invention discloses a cross-linked polyolefin lithium-ion battery separator and its preparation method. In practical use, polyolefin and a diluent are first added to a screw extruder and extruded through a die at temperature T1. The mixture is then cooled on both sides by cooling rollers at temperature T2 to form a cast sheet. The cast sheet is stretched once at temperature T3 to obtain a first-stretched film. The first-stretched film is then stretched a second time at temperature T4 to obtain a second-stretched film. The second-stretched film is placed in an extraction tank at temperature T5 to completely wash away the diluent, then placed in an oven at temperature T6 for complete drying, and finally stretched a third time at temperature T7 to obtain a third-stretched film. The third-stretched film is heat-set at temperature T8 to obtain a heat-set film. The heat-set film is then cross-linked by gamma-ray irradiation at temperature T9 to obtain the cross-linked polyolefin lithium-ion battery separator. The cross-linked polyolefin lithium-ion battery separator prepared by this invention possesses both high rupture temperature and ultra-thin, high-strength properties, solving the technical problem that existing cross-linked polyolefin separators are limited by low stretching ratios and cannot achieve both high rupture temperature and ultra-thin, high-strength properties. Attached Figure Description
[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0030] Figure 1 This is a flowchart of the preparation method of the cross-linked polyolefin lithium-ion battery separator of the present invention. Detailed Implementation
[0031] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.
[0032] Please see Figure 1 , Figure 1 This is a flowchart of the preparation method of the cross-linked polyolefin lithium-ion battery separator of the present invention.
[0033] This invention provides a method for preparing a cross-linked polyolefin lithium-ion battery separator, comprising the following steps:
[0034] Polyolefin and diluent are added to a screw extruder, extruded through a die at temperature T1, and formed into a cast sheet under double-sided cooling by cooling rollers at temperature T2;
[0035] The cast sheet is stretched once at temperature T3 to obtain a stretched film.
[0036] A first-stretched film is subjected to a second stretching at temperature T4 to obtain a second-stretched film.
[0037] The double-stretched film was placed in an extraction tank at temperature T5 to completely wash off the diluent, then placed in an oven at temperature T6 to dry completely, and finally stretched a third time at temperature T7 to obtain a triple-stretched film.
[0038] The three-stretched film is heat-set at temperature T8 to obtain a heat-set film;
[0039] Crosslinked polyolefin lithium-ion battery separators are obtained by crosslinking heat-set films with gamma-ray irradiation at temperature T9.
[0040] The polyolefins used include ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 400,000 to 3,000,000, and the total solids content is 15% to 35% of the total mass of polyolefins and diluents.
[0041] The diluent includes one or more of white oil, paraffin oil, alkane compounds, or ester compounds;
[0042] The diluent can fully melt and mix with the polyolefin at a temperature of +50 to 100°C (the melting point of the polyolefin material) to form a uniform liquid without undergoing a chemical reaction.
[0043] The extractant includes one of dichloromethane, carbon tetrachloride, and diethyl ether, or a volatile solvent that is completely miscible with the diluent.
[0044] The T1 temperature is +50 to 100°C of the melting point of the polyolefin material, the T2 temperature is 5 to 30°C, and the T3 temperature is -10 to 40°C of the melting point of the polyolefin material.
[0045] The T4 temperature is the melting point of the polyolefin material from -10 to 40°C, the T5 temperature is the boiling point of the extractant from -10 to 30°C, and the T6 temperature is the boiling point of the extractant from +0 to 20°C.
[0046] The T7 temperature is the melting point of the polyolefin material from -10 to 40°C, the T8 temperature is the melting point of the polyolefin material from -40 to 60°C, and the T9 temperature is 20 to 30°C.
[0047] The first stretching ratio is 2 to 3 times, the second stretching ratio is 9 to 13 times, and the third stretching ratio is 1.5 to 2.9 times;
[0048] The gamma-ray irradiation crosslinking dose is 100–200 kGy.
[0049] During the preparation process, a temperature-stretching ratio correlation algorithm can be used to dynamically optimize and adjust the temperature and stretching ratio at each stretching stage. In addition, a real-time online monitoring system can be used to control key parameters such as film thickness and porosity. At the same time, a gamma-ray irradiation dose intelligent control algorithm can be used to ensure the uniformity of crosslinking. This serves as a characteristic process control method.
[0050] Before starting the preparation process, a comprehensive inspection was conducted on key equipment such as the screw extruder, cooling rollers, stretching equipment, extraction tank, drying oven, and irradiation device to ensure that the equipment was operating normally, all components were tightly connected, and there were no leaks or looseness issues. The screw extruder was also preheated.
[0051] During the preparation process, a detailed parameter recording table was established to record key parameters such as temperature, time, stretching ratio, and irradiation dose for each step. Data mining algorithms were also used to extract data to facilitate subsequent step optimization.
[0052] The present invention also provides a cross-linked polyolefin lithium-ion battery separator, which is prepared by the cross-linked polyolefin lithium-ion battery separator and preparation method described above.
[0053] The cross-linked polyolefin lithium-ion battery separator has a thickness of 3.5–7.5 μm, a rupture temperature ≥220℃, a puncture strength ≥300 gf, and a tensile strength ≥150 MPa.
[0054] The cross-linked polyolefin lithium-ion battery separator has a porosity of 28% to 45% and an air permeability of 80 to 165 s / 100cc.
[0055] For the testing of the cross-linked polyolefin lithium-ion battery separator of the present invention, the thickness, areal density, porosity, air permeability, puncture strength, tensile strength and heat shrinkage rate of the separator were tested according to GB / T 36363-2018.
[0056] The degree of crosslinking of polyolefin membranes was tested according to ASTM-D2765.
[0057] The rupture temperature of polyolefin diaphragms was tested using a thermomechanical analyzer.
[0058] Using the cross-linked polyolefin lithium-ion battery separator and its preparation method of the present invention, in specific use, polyolefin and diluent are first added to a screw extruder, extruded through a die at temperature T1, and formed into a cast sheet under double-sided cooling by cooling rollers at temperature T2; the cast sheet is stretched once at temperature T3 to obtain a first-stretched film; the first-stretched film is stretched a second time at temperature T4 to obtain a second-stretched film; the second-stretched film is placed in an extraction tank at temperature T5 to completely wash off the diluent, and then placed in an oven at temperature T6 for complete drying, and then stretched a third time at temperature T7 to obtain a third-stretched film; the third-stretched film is heat-set at temperature T8 to obtain a heat-set film; the heat-set film is cross-linked by γ-ray irradiation at temperature T9 to obtain a cross-linked polyolefin lithium-ion battery separator. The cross-linked polyolefin lithium-ion battery separator prepared by the present invention has both high membrane rupture temperature and ultra-thin high-strength performance, solving the technical problem that the cross-linked polyolefin separators prepared in the prior art are limited by the low stretching ratio and cannot obtain polyolefin separators with both high membrane rupture temperature and ultra-thin high-strength performance.
[0059] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.
Claims
1. A method for preparing a cross-linked polyolefin lithium-ion battery separator, characterized in that, The steps include: Polyolefin and diluent are added to a screw extruder, extruded through a die at temperature T1, and formed into a cast sheet under double-sided cooling by cooling rollers at temperature T2; The cast sheet is stretched once at temperature T3 to obtain a stretched film. A first-stretched film is subjected to a second stretching at temperature T4 to obtain a second-stretched film. The double-stretched film was placed in an extraction tank at temperature T5 to completely wash off the diluent, then placed in an oven at temperature T6 to dry completely, and finally stretched a third time at temperature T7 to obtain a triple-stretched film. The three-stretched film is heat-set at temperature T8 to obtain a heat-set film; Crosslinked polyolefin lithium-ion battery separators are obtained by crosslinking heat-set films with gamma-ray irradiation at temperature T9.
2. The method for preparing the cross-linked polyolefin lithium-ion battery separator as described in claim 1, characterized in that, The polyolefins used include ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 400,000 to 3,000,000, and the total solids content is 15% to 35% of the total mass of polyolefins and diluents.
3. The method for preparing the cross-linked polyolefin lithium-ion battery separator as described in claim 2, characterized in that, The diluent includes one or more of white oil, paraffin oil, alkane compounds, or ester compounds; The diluent can fully melt and mix with the polyolefin at a temperature of +50 to 100°C (the melting point of the polyolefin material) to form a uniform liquid without undergoing a chemical reaction.
4. The method for preparing the cross-linked polyolefin lithium-ion battery separator as described in claim 3, characterized in that, The extractant includes one of dichloromethane, carbon tetrachloride, and diethyl ether, or a volatile solvent that is completely miscible with the diluent.
5. The method for preparing the cross-linked polyolefin lithium-ion battery separator as described in claim 4, characterized in that, The T1 temperature is +50 to 100°C of the melting point of the polyolefin material, the T2 temperature is 5 to 30°C, and the T3 temperature is -10 to 40°C of the melting point of the polyolefin material.
6. The method for preparing the cross-linked polyolefin lithium-ion battery separator as described in claim 5, characterized in that, The T4 temperature is the melting point of the polyolefin material from -10 to 40°C, the T5 temperature is the boiling point of the extractant from -10 to 30°C, and the T6 temperature is the boiling point of the extractant from +0 to 20°C.
7. The method for preparing the cross-linked polyolefin lithium-ion battery separator as described in claim 6, characterized in that, The T7 temperature is the melting point of the polyolefin material from -10 to 40°C, the T8 temperature is the melting point of the polyolefin material from -40 to 60°C, and the T9 temperature is 20 to 30°C.
8. The method for preparing the cross-linked polyolefin lithium-ion battery separator as described in claim 7, characterized in that, The first stretching ratio is 2 to 3 times, the second stretching ratio is 9 to 13 times, and the third stretching ratio is 1.5 to 2.9 times; The gamma-ray irradiation crosslinking dose is 100–200 kGy.
9. A cross-linked polyolefin lithium-ion battery separator, prepared by the method described in claim 8, characterized in that, The cross-linked polyolefin lithium-ion battery separator has a thickness of 3.5–7.5 μm, a rupture temperature ≥220℃, a puncture strength ≥300 gf, and a tensile strength ≥150 MPa.
10. The cross-linked polyolefin lithium-ion battery separator as described in claim 9, characterized in that, The cross-linked polyolefin lithium-ion battery separator has a porosity of 28% to 45% and an air permeability of 80 to 165 s / 100cc.