Separator for lithium-ion batteries, and method for manufacturing the same.

Abstract

The present invention provides a lithium-ion battery separator with high-temperature resistance, a manufacturing method thereof, and a lithium-ion battery manufactured thereby. The separator, which belongs to the field of lithium-ion battery separators, has a thickness of 3.5 to 30 μm, a porosity of 30 to 80%, a pore size adjustable from 20 to 2000 nm, a bidirectional stretch strength of 50 MPa or more, an air permeability of 400 s / 100 cc or less, and a rupture temperature of 160°C or more. The manufacturing method involves blending and melt-plasticizing 20 to 60% polypropylene base material, 2 to 10% solubilizing agent, 30 to 80% solvent, 0.1 to 5% nucleating agent, and / or 0.1 to 1% antioxidant. The mixture is then extruded using a twin-screw screw, followed by thermally induced phase separation to obtain a cast. The cast is then stretched, extracted, and post-treated, or directly extracted and post-treated.

Description

Technical Field

[0001] The present invention relates to the field of separators for lithium-ion batteries, and particularly to separators for lithium-ion batteries having high-temperature resistance characteristics. The present invention further provides a method for manufacturing a separator for a lithium-ion battery having the high-temperature resistance characteristics. The present invention also further provides a lithium-ion battery manufactured by the separator for a lithium-ion battery having the high-temperature resistance characteristics.

Background Art

[0002] The separators for lithium-ion batteries developed to date are mainly divided into two processes: polypropylene dry-process films and polyethylene wet-process films. Among them, polypropylene is used as the main raw material for the dry-process separators, and the melt stretching process is adopted. Furthermore, it is divided into dry-process unidirectional stretching and dry-process bidirectional stretching. The main raw material of the wet-process separator is polyethylene, and it is divided into wet-process bidirectional simultaneous stretching and non-simultaneous stretching according to the stretching method.

[0003] Conventional dry-process separators primarily use polypropylene, which has a high melting point. As a result, these separators have relatively high melting points and rupture temperatures, and relatively good heat resistance. Typical dry-process polypropylene films can maintain thermal shrinkage stability above 140°C and rupture temperatures above 160°C. However, due to the molding process, mainstream dry-process separators still mainly undergo low-magnification stretching in the longitudinal and transverse directions, or unidirectional stretching. This results in clear non-uniformity in the longitudinal and transverse directions, insufficient transverse stretching strength, and relatively low puncture strength, which can only be compensated for by increasing the thickness. The mechanism of pore formation in dry-process films involves crystallization under high stress during melt-extrusion of the polymer, forming layered crystals perpendicular to the stretching direction. Subsequently, heat treatment is performed to obtain a hard elastic material. Further stretching then causes dislocation separation between the layered crystals, forming micropores, and finally, thermoforming is performed to obtain a microporous film. The pore diameter is through-hole, and the porosity is generally 35-45%. This method forms through-holes, and because there are few curved or twisted sections in the holes, it results in a large equivalent hole diameter and a short equivalent hole length. This makes it particularly prone to micro-short circuits between the positive and negative electrodes and excessive self-discharge. Due to these problems, dry-process films are mainly low-end products consisting of thicker films, making their application to high-end fields difficult.

[0004] Conventional wet-process separators primarily use polyethylene with a relatively high molecular weight, resulting in relatively high bidirectional tensile strength and puncture strength. Because they employ a combination of thermally induced phase separation and oil film stretching as the pore formation principle, the pores are formed by stretching and dislocating dense, uniform spherulites or layered crystals, constantly creating a multilayer network structure. This results in a fine and uniform pore size distribution, small equivalent pore diameters, and large equivalent pore lengths. Even at extremely thin thicknesses (e.g., 4-9 μm), they maintain relatively good resistance characteristics, allowing for a wider range of high-end applications. However, because the polyethylene itself has relatively low softening and melting points, wet-process polyethylene separators have relatively poor heat resistance and low film rupture temperatures. Typical wet-process polyethylene separators can only guarantee thermal shrinkage stability up to 120°C and film rupture temperatures up to 140°C. Most high-end lithium-ion battery products employ a high-nickel ternary system, and the active properties of the positive electrode active material require a high degree of thermal stability from the separator. These contradictions lead to an increased safety risk for the battery.

[0005] Regarding improvements to dry-process polypropylene separators to simultaneously consider aspects such as heat resistance, mechanical performance, and electrochemical function, conventional techniques mainly involve increasing the lateral stretch ratio to enhance lateral strength and coating with small-particle ceramics to compensate for the deficiency of large pore size. However, there are limits to the improvement in strength, and the uniformity of pores cannot reach the level of wet-process polyethylene separators. Regarding improvements to wet-process polyethylene separators, conventional techniques mainly involve coating the wet-process polyethylene separator with inorganic or organic materials (e.g., ceramics, aramid fibers, boehmite, PI, etc.). However, coating the separator surface with inorganic or organic materials causes some degree of pore blockage, and the rapid decrease in the mechanical strength of the polyethylene separator itself under high-temperature conditions causes a degradation effect where the attached material collapses. When the temperature approaches the melting point of 140°C, even if shrinkage is prevented by the protection of the coating layer, the melting of the separator itself causes a large-area short circuit at the positive and negative electrodes.

[0006] Therefore, in order to solve the aforementioned technical problems, a lithium-ion battery separator is needed that takes into account high temperature stability and good mechanical performance, has high porosity, and has uniform and adjustable pore size.

[0007] In light of the above circumstances, I hereby submit this application. [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to solve the above-mentioned problems by providing a separator for lithium-ion batteries having high-temperature resistance characteristics and a method for manufacturing the same. [Means for solving the problem]

[0009] To achieve the above objectives, the present invention employs the following technical solutions. A separator for lithium-ion batteries having high temperature resistance, wherein the separator has a thickness of 3.5 to 30 μm, a porosity of 30 to 80%, an adjustable pore size of 20 to 2000 nm, a bidirectional stretch strength of 50 MPa or more, an air permeability of 400 s / 100 cc or less, and a fracture temperature of 160°C or higher.

[0010] Preferably, the separator has a thickness of 3.5 to 20 μm, a porosity of 35 to 60%, a pore diameter of 30 to 100 nm, a bidirectional stretch strength of 100 MPa or more, an air permeability of 300 s / 100 cc or less, and a fracture temperature of 170°C or higher.

[0011] The present invention further provides a method for manufacturing a lithium-ion battery separator having the aforementioned high-temperature resistance characteristics. The material may be obtained by mixing 20-60% polypropylene main material, 2-10% solubilizer, 30-80% solvent, 0.1-5% nucleating aid, and / or 0.1-1% antioxidant by mass percentage, melt-plasticizing, extruding with a twin-screw, obtaining a slab by thermally induced phase separation, and then post-processing such as stretching the slab, extracting mineral oil from the oil film of the slab, and stretching, relaxing, and thermoforming the resulting dry film. Alternatively, the material may be obtained by directly extracting mineral oil from the slab obtained by thermally induced phase separation without going through the slab stretching process, and then post-processing such as stretching, relaxing, and thermoforming the resulting dry film.

[0012] Preferably, the mass percentages of the polypropylene main material, solubilizer, solvent, nucleation aid, and antioxidant are 25-40%, 3-6%, 50-70%, 0.2-3%, and 0.1-0.5%, respectively.

[0013] Furthermore, the polypropylene is either a single component with a melt index of 20 g / 10 min or less, or a compound of multiple polypropylenes with different melt indices.

[0014] Preferably, the polypropylene is a single component with a melt index of 2 g / 10 min or less, or is a compound thereof with polypropylene having a melt index of 0.5 g / 10 min or less.

[0015] The solubilizer has a solubilizer component that simultaneously exhibits good eutectic properties with long linear hydrocarbon chain segments and / or branched hydrocarbon chain segments.

[0016] Preferably, the solubilizer comprises a polyolefin copolymer and / or a polyolefin wax. Preferably, the solubilizer comprises a mixture of one or more of the following: polyethylene / propylene copolymer, polypropylene / ethylene-butene copolymer, polypropylene / ethylene-hexene copolymer, polyethylene wax, polypropylene wax, and polyester wax. A solubilizer with this configuration can significantly improve the plasticizing effect.

[0017] The solvent comprises one or more mixtures of alkanes, esters, ethers, and aromatic hydrocarbon compounds.

[0018] Preferably, the solvent comprises a mixture of one or more of the following: liquid paraffin, solid paraffin, paraffin oil, natural vegetable oil, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, dioctyl sebacate, methyl salicylate, diphenyl ether, and diphenylmethane. The solvent is suitable for thermally induced phase separation.

[0019] The nucleation aid comprises a mixture of one or more of the following: adipic acid, calcium stearate, aluminum stearate, sorbitol benzylidene derivative, sodium benzoate, and bis(4-tert-butylbenzoato-κO)hydroxyaluminum.

[0020] Preferably, the nucleation aid is 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol.

[0021] The nucleating aid is generally only used in the manufacture of dry process separators. In the present invention, by adopting the configuration of combining polypropylene or formulations with different melt indices and the solubilizing agent and solvent, not only can the plasticizing effect and the casting effect be balanced and both be maintained normally, but it also helps to control the nucleation and crystallization effects in the thermal-induced phase separation process of the wet process, control the crystal morphology and size, and is useful for subsequent treatments such as stretching. The combination of the main raw material, solubilizing agent, solvent and nucleating aid can achieve a precise balance, thereby maintaining the high strength in two directions of the separator and having advantages such as a high porosity, a uniform pore size and being adjustable.

[0022] The antioxidant includes one of antioxidant 1076, antioxidant 1010 and antioxidant 168.

[0023] The supply method of the polypropylene main material, the solubilizing agent, the solvent, the nucleating aid, and / or the antioxidant before extrusion adopts simultaneous supply or non-simultaneous supply.

[0024] Preferably, in the biaxial screw extrusion process, the screw temperature is 140 - 240 °C, the pipe temperature of the melt is 190 - 230 °C, and the die temperature is 180 - 220 °C.

[0025] Preferably, the thickness of the extruded melt is 0.7 - 5 mm.

[0026] Preferably, in the manufacturing process of the cast sheet, the rotational speed of the co-rotating biaxial screw is 60 - 100 rmp.

[0027] Preferably, it further includes a cooling process after extrusion, and the cooling methods are rapid cooling roll cooling at 10 - 80 °C, rapid cooling roll cooling + draw roll cooling at 10 - 80 °C, rapid cooling roll + water cooling at 5 - 80 °C, water cooling + bottom roll cooling at 5 - 80 °C, rapid cooling roll + oil cooling at 5 - 80 °C and / or oil cooling + bottom roll cooling at 5 - 80 °C.

[0028] Preferably, in the stretching step of the cast slab, an air temperature of 130 to 165°C and a film surface temperature of 124 to 140°C are maintained, and the slab is stretched (1 to 30) times in the longitudinal direction, (1 to 30) times in the transverse direction, and / or (1 to 30) × (1 to 30) times simultaneously in two directions at a stretching speed of 3 to 40 m / min. "1x stretching" means that the slab is not stretched in that direction. The stretching step can achieve stretching of the crystals within the cast slab by different combinations of longitudinal stretching, transverse stretching, simultaneous longitudinal and transverse stretching, and multiple longitudinal and transverse stretchings, as well as different air temperatures, wind speeds, and stretching speeds. The layered crystals undergo expansion, dislocation, and sliding, ultimately realizing a fibrous spatial network structure, thereby obtaining oil film precursors of high-temperature resistant polyolefin porous separators with different porosity, pore diameters, and strengths.

[0029] Preferably, the stretched end material is not cut off beforehand during the extraction process. During extraction and drying, the stretched end material is not cut off beforehand, and the greater tension of the thicker end material suppresses lateral shrinkage of the thin film during the extraction process. This is because shrinkage during extraction increases the lateral polarity difference of the thin film, leading to problems such as poor uniformity, which can seriously affect the stability of the polypropylene thin film.

[0030] Preferably, the post-treatment includes bidirectional stretching and relaxation of the dry film, and thermoforming.

[0031] More preferably, the post-treatment includes sequentially stretching the dry film in both longitudinal and transverse directions, relaxing it in both longitudinal and transverse directions, and thermoforming. Stretching and relaxing the dry film after extraction can achieve effects such as the creation of microscopic secondary crystals of fibrous polypropylene, reduction of the denier number of fine fibers, and removal of internal stress, thereby achieving the objectives of pore expansion and thermoforming, and improving the permeability and thermal stability of the separator. The longitudinal and transverse relaxing treatment and thermoforming are based on the conventional transverse unidirectional relaxing treatment method, but by simultaneously relaxing the film material in the longitudinal direction, the thermal shrinkage stability in both directions can be simultaneously improved. The specific method is as follows. During the longitudinal and transverse stretching of the extracted dry film, an air temperature of 130-175°C and a film surface temperature of 125-150°C must be maintained, and the film must be stretched (1-30) times longitudinally and (1-30) times transversely at a stretching speed of 3-40 m / min, and / or (1-30) x (1-30) times simultaneously in both directions. "1x stretching" means not stretching in that direction, and the stretching process includes longitudinal stretching, transverse stretching, simultaneous longitudinal and transverse stretching, and multiple longitudinal and transverse stretching. A predetermined stretching ratio can be achieved by different combinations of overlapping layers. For two-directional relaxation, it is necessary to maintain an air temperature of 130-175°C and a film surface temperature of 125-150°C, and to perform vertical relaxation where the input side becomes (1-3) times the length of the output side, horizontal relaxation where the input side becomes (1-3) times the width of the output side, and / or simultaneous two-directional relaxation where the input side becomes (1-3) × (1-3) times the length of the output side, at a relaxation speed of 3-20 m / min. "1x relaxation" means that relaxation does not occur in that direction.

[0032] The present invention further provides a lithium-ion battery manufactured using a lithium-ion battery separator having the aforementioned high-temperature resistance characteristics. [Effects of the Invention]

[0033] Compared to conventional technologies, the present invention combines the advantages of dry-process polypropylene separators, which have excellent heat resistance, with wet-process bidirectional stretched polyethylene separators, which have a uniform microscopic structure and high strength. This novel approach enables the manufacture of wet-process bidirectional high-magnification stretched polypropylene separator products, achieving consideration for heat resistance, mechanical strength, and the uniformity and controllability of the microscopic pore structure. The result is a novel lithium-ion battery separator with characteristics such as high temperature resistance, high strength in both directions, high porosity, uniform and adjustable pore diameter, and high resistivity. Furthermore, due to its high-temperature resistance, high porosity, and controllable pore diameter, the separator according to the present invention can also be applied to fields such as filtration of liquids, gaseous dust particles, and waterproof and breathable films. [Brief explanation of the drawing]

[0034] To further explain the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments are briefly introduced below. Note that the following drawings only illustrate some embodiments of the present invention and should not be considered limitations on the scope. Those skilled in the art can obtain other relevant drawings from these drawings without performing any novel work. [Figure 1] This is a scanning electron microscope image of the polypropylene microporous film according to Example 2 of the present invention. [Figure 2] This is a scanning electron microscope image of the polypropylene microporous film according to Example 4 of the present invention. [Modes for carrying out the invention]

[0035] The embodiments of the present invention will be described in detail below. Examples of embodiments are shown in the drawings. The same or similar elements or elements having the same or similar functions are consistently represented by the same or similar reference numerals. The embodiments described below with reference to the drawings are illustrative and are for illustrative purposes only, and should not be understood as limitations on the present invention.

[0036] This specification uses the following terms: The term "manufactured by..." is synonymous with "includes." The terms "includes," "contains," "have," or any variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, product, or apparatus containing the listed elements is not necessarily limited to those elements and may include other elements not explicitly mentioned or elements specific to such a composition, step, method, product, or apparatus.

[0037] The term "...consisting of..." excludes all elements, steps, or components not described. When used in a claim, the use of the term makes the claim closed, excluding any materials other than those described, and common impurities associated with them. If the term "...consisting of..." appears in the description of the subject of the claim rather than immediately after the subject matter, it limits the claim to only the elements mentioned in that description, and does not exclude other elements from the claim as a whole.

[0038] When equivalents, concentrations, or other values ​​or parameters are expressed as a range, a preferred range, or a range limited by several preferred upper and lower limits, it is understood that all ranges formed by the combination of the upper or preferred values ​​of any range and the lower or preferred values ​​of any range are specifically disclosed, regardless of whether such ranges are disclosed individually. For example, if the range "1 to 5" is disclosed, the range described is interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. Where numerical ranges are described herein, unless otherwise specified, such ranges are intended to include their boundary values ​​and all integers and fractions within that range.

[0039] In the embodiments described below, unless otherwise specified, all parts and percentages are based on mass.

[0040] "And / or" indicates that either one or both of the described situations may occur. For example, A and / or B includes A and B, and A or B.

[0041] (Example 1) Using both simultaneous and non-simultaneous feeding methods, polypropylene with a melt index of 0.5 g / 10 min (based on mass percentage), 5% polyethylene / propylene copolymer, and 63.8% 100# mineral oil were fed into a twin-screw extruder using a powder weighing device and a plunger pump, respectively. Further additions included 1% 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (i.e., 3988 nucleating agent) and 2‰ of 1076 antioxidant, followed by plasticization by melting at 190°C. The screw temperature was 220°C, the pipe temperature of the molten material was 200°C, the die temperature was 195°C, and the rotation speed of the co-direction twin-screw was 90 rpm.

[0042] The molten material was extruded from the die into flakes, and the gel-like flakes were immediately passed through a pre-existing gap between the forming roll (rapid cooling roll) and the pull-in roll of the casting mill (the surface temperature of the forming roll and pull-in roll was set to 15°C). In this embodiment, an additional cooling tank was added (water as the cooling medium) to forcibly cool the back of the molten material, and the temperature of the cooling tank was 20°C, forming a slab with a thickness of 1.5 mm. Subsequently, with an air temperature of 160°C, the slab was stretched six times along the direction of travel (MD) using a longitudinal stretcher at a film surface temperature of 130°C and a speed of 30 m / min, and then stretched six times along the width direction (TD) using a transverse stretcher at a film surface temperature of 140°C and a speed of 30 m / min. Subsequently, the ends of the oil film formed by stretching were trimmed and trimmed, and then the film was divided into three sections using a cutting machine, with each section having a width of 800 mm. The stretched oil film was then passed through an extraction tank containing dichloromethane to extract the mineral oil from the film and dry it. The dried microporous film was placed in a transverse stretching machine and stretched 1.2 times along the TD direction at 135°C. Then, it was further relaxed to 1.1 times along the TD direction while simultaneously being thermoformed at 135°C. Subsequently, it was wound using a winding roll to obtain a polypropylene microporous film with a thickness of 15.6 μm.

[0043] The thickness, tensile strength, puncture strength, porosity, air permeability, and thermal shrinkage rate of the polypropylene microporous film manufactured as described above were measured, and the measurement results are shown in Table 1. Furthermore, a corresponding high-temperature resistant lithium-ion battery can be manufactured using this polypropylene microporous film.

[0044] (Example 2) Using both simultaneous and non-simultaneous feeding methods, 31% polypropylene, 6% polypropylene / ethylene-butene copolymer, and 61.55% 100# mineral oil were fed into a twin-screw extruder using a powder weighing device and a plunger pump, respectively, based on mass percentage. Further additions included 1.1% 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (i.e., 3988 nucleating agent) and 3.5‰ of 1076 antioxidant, followed by plasticization by melting at 185°C. The polypropylene compounds had melt indices of 0.5 g / 10 min and 2 g / 10 min, respectively, with a mixing ratio of 8:2. The screw temperature was 210°C, the molten pipe temperature was 200°C, the die temperature was 195°C, and the rotation speed of the coaxial twin-screws was 80 rpm.

[0045] The molten material was extruded from the die into flakes, and the gel-like flakes were immediately passed through a pre-existing gap between the forming roll (rapid cooling roll) and the pull-in roll of the casting mill (the surface temperature of the forming roll and pull-in roll was set to 10°C). In this embodiment, an additional cooling tank was added (water as the cooling medium) to forcibly cool the back of the molten material, and the temperature of the cooling tank was 15°C, forming a 0.8 mm thick cast slab. Subsequently, with an air temperature of 130°C, the cast slab was stretched nine times along the direction of travel (MD) using a longitudinal stretcher at a film surface temperature of 130°C and a speed of 35 m / min, and then stretched seven times along the width direction (TD) using a transverse stretcher at a film surface temperature of 140°C and a speed of 35 m / min. Subsequently, the oil film formed by stretching was divided into three sections using a divider, with each section having a width of 800 mm. The stretched oil film was then passed through an extraction tank containing dichloromethane to extract the mineral oil from the film and dry it. The dried microporous film was placed in a transverse stretcher and stretched 1.2 times along the TD direction at 135°C. Then, it was further relaxed to 1.1 times along the TD direction while simultaneously being thermoformed at 135°C. Subsequently, it was wound using a winding roll to obtain a polypropylene microporous film with a thickness of 9.4 μm.

[0046] The thickness, tensile strength, puncture strength, porosity, air permeability, and thermal shrinkage rate of the polypropylene microporous film manufactured as described above were measured, and the measurement results are shown in Table 1. A scanning electron microscope image of the film is shown in Figure 1. Furthermore, a corresponding high-temperature resistant lithium-ion battery can be manufactured using this polypropylene microporous film.

[0047] (Example 3) Using a simultaneous supply method, 35% polypropylene, 3% polyethylene wax, and 59.5% liquid paraffin, based on mass percentage, were fed into a twin-screw extruder using a powder weighing device and a plunger pump, respectively. Further additions of 2% adipic acid and 5‰ of 1010 antioxidant were added, and plasticization by melting was carried out at 190°C. The polypropylene was a compound with melt indices of 0.5 g / 10 min and 2 g / 10 min, respectively, with a mixing ratio of 6:4. The screw temperature was 205°C, the molten pipe temperature was 205°C, the die temperature was 190°C, and the rotation speed of the co-direction twin-screw was 100 rpm.

[0048] The molten material was extruded from the die into flakes, and the gel-like flakes were immediately passed through a pre-existing gap between the forming roll (rapid cooling roll) and the pull-in roll of the casting mill (the surface temperature of the forming roll and pull-in roll was set to 20°C). In this embodiment, an additional cooling tank was added (water as the cooling medium) to forcibly cool the back of the molten material, and the temperature of the cooling tank was 15°C, forming a 0.9 mm thick cast slab. Subsequently, at an air temperature of 165°C, the cast slab was stretched nine times along the direction of travel (MD) using a longitudinal stretcher at a film surface temperature of 130°C and a speed of 40 m / min, and then stretched seven times along the width direction (TD) using a transverse stretcher at a film surface temperature of 140°C and a speed of 40 m / min. Subsequently, the ends of the oil film formed by stretching were trimmed and trimmed, and then the film was divided into three sections using a cutting machine, with each section having a width of 800 mm. The stretched oil film was then passed through an extraction tank containing dichloromethane to extract the mineral oil from the film and dry it. The dried microporous film was placed in a transverse stretching machine and stretched 1.2 times along the TD direction at 135°C. Then, it was further relaxed to 1.1 times along the TD direction while simultaneously being thermoformed at 135°C. Subsequently, it was wound using a winding roll to obtain a polypropylene microporous film with a thickness of 10.7 μm.

[0049] The thickness, tensile strength, puncture strength, porosity, air permeability, and thermal shrinkage rate of the polypropylene microporous film manufactured as described above were measured, and the measurement results are shown in Table 1. Furthermore, a corresponding high-temperature resistant lithium-ion battery can be manufactured using this polypropylene microporous film.

[0050] (Example 4) Using both simultaneous and non-simultaneous feeding methods, polypropylene with a melt index of 0.5 g / 10 min (based on mass percentage), 5% polyethylene / propylene copolymer, and 63.8% 100# mineral oil were fed into a twin-screw extruder using a powder weighing device and a plunger pump, respectively. Further additions included 1% 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (i.e., 3988 nucleating agent) and 2‰ of 1076 antioxidant, followed by plasticization by melting at 190°C. The screw temperature was 220°C, the pipe temperature of the molten material was 200°C, the die temperature was 195°C, and the rotation speed of the coaxial twin-screw was 90 rpm.

[0051] The molten material was extruded from the die into flakes, and the gel-like flakes were immediately passed through a pre-existing gap between the forming roll (rapid cooling roll) and the pull-in roll of the casting mill (the surface temperature of the forming roll and pull-in roll was set to 40°C). In this embodiment, an additional cooling tank was added (water as the cooling medium) to forcibly cool the back of the molten material, and the temperature of the cooling tank was 20°C, forming a slab with a thickness of 0.7 mm. Subsequently, the obtained slab was passed through a pure dichloromethane ultrasonic extraction tank at a speed of 2 m / min for extraction. At an air temperature of 162°C, the extracted slab was stretched seven times along the direction of travel (MD) using a longitudinal stretcher at a film surface temperature of 133°C and a speed of 30 m / min, and then stretched seven times along the width direction (TD) using a transverse stretcher at a film surface temperature of 140°C and a speed of 30 m / min. Subsequently, the edges of the waterproof and breathable film formed by stretching were trimmed and trimmed to obtain the trimmed and trimmed film, which was then placed in a transverse stretching machine and stretched 1.2 times along the TD direction at 135°C. After that, it was further relaxed to 1.1 times along the TD direction, and at the same time, thermoforming was performed at 135°C. Next, it was wound up using a winding roll to obtain a polypropylene microporous film with a thickness of 14.3 μm.

[0052] The thickness, tensile strength, puncture strength, porosity, air permeability, and thermal shrinkage rate of the polypropylene microporous film manufactured as described above were measured, and the measurement results are shown in Table 1. The scanning electron microscope images are shown in Figure 2. Furthermore, this polypropylene microporous film can be used to manufacture corresponding high-porosity film materials.

[0053] (Example 5) Using both simultaneous and non-simultaneous feeding methods, polypropylene with a melt index of 0.5 g / 10 min (based on mass percentage), 5% polyethylene / propylene copolymer, and 63.8% 100# mineral oil were fed into a twin-screw extruder using a powder weighing device and a plunger pump, respectively. Further additions included 1% 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (i.e., 3988 nucleating agent) and 2‰ of 1076 antioxidant, followed by plasticization by melting at 190°C. The screw temperature was 220°C, the pipe temperature of the molten material was 200°C, the die temperature was 195°C, and the rotation speed of the co-direction twin-screw was 90 rpm.

[0054] The molten material was extruded from the die into flakes, and the gel-like flakes were immediately passed through a pre-existing gap between the forming roll (rapid cooling roll) and the pull-in roll of the casting mill (the surface temperature of the forming roll and pull-in roll was set to 15°C). In this embodiment, an additional cooling tank was added (water as the cooling medium) to forcibly cool the back of the molten material, and the temperature of the cooling tank was 20°C, forming a slab with a thickness of 1.9 mm. Subsequently, at an air temperature of 160°C, the slab was stretched 3 x 3 times in the direction of travel (MD x TD) at a speed of 10 m / min and a film surface temperature of 130°C using a two-way simultaneous stretcher to obtain a thick oil film. The thick oil film obtained by stretching was stretched seven times in the direction of travel (MD) at a film surface temperature of 129°C and a speed of 60 m / min using a longitudinal stretcher at an air temperature of 158°C, and then seven times in the width direction (TD) at a film surface temperature of 137°C and a speed of 60 m / min using a transverse stretcher. After that, the ends of the stretched oil film were trimmed and trimmed, and then it was divided into three sections using a divider, with each section having a width of 800 mm. The stretched oil film was then passed through an extraction tank containing dichloromethane to extract the mineral oil from the oil film and dry the oil film. The dried microporous film was placed in a transverse stretcher and stretched 1.2 times in the TD direction at 135°C, and then relaxed to 1.1 times in the TD direction while simultaneously being thermoformed at 135°C. Subsequently, it was wound using a winding roll to obtain a polypropylene microporous film with a thickness of 3.9 μm.

[0055] The thickness, tensile strength, puncture strength, porosity, air permeability, and thermal shrinkage rate of the polypropylene microporous film manufactured as described above were measured, and the measurement results are shown in Table 1. Furthermore, a corresponding high-temperature resistant lithium-ion battery can be manufactured using this polypropylene microporous film.

[0056] (Comparative Example 1) In contrast to Example 1, the main material is PE, and it was manufactured using a wet process.

[0057] (Comparative Example 2) In comparison to Example 1, the main material is PP, and it was manufactured using a dry process. Table 1: Measurement results of the examples and comparative examples [Table 1]

[0058] As can be seen from the comparison of data in Table 1 and Figure 1, the polypropylene separator of the present invention exhibits excellent heat resistance, a uniform microscopic structure, and high strength. It also realizes a novel wet-process bidirectional high-magnification stretched polypropylene separator product manufacturing method, achieving consideration for heat resistance, mechanical strength, microscopic uniformity, and controllability. This results in a novel lithium-ion battery separator with properties such as high temperature resistance, high strength in both directions, uniform pore size, and high resistivity. Furthermore, this process is fast and has low processing costs.

[0059] In this specification, any use of the terms “one embodiment,” “some embodiments,” “example,” “specific example,” or “some examples” means that the specific features, structures, materials, or properties described using that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the examples of the terms used do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or properties described can be appropriately combined in any one or more embodiments or examples. Furthermore, those skilled in the art can combine different embodiments or examples and features of different embodiments or examples described herein, provided they do not contradict each other.

[0060] Although embodiments of the present invention have been shown and explained above, it should be understood that these embodiments are illustrative and should not be understood as limitations on the present invention. Those skilled in the art can modify, correct, replace, and alter the embodiments within the scope of the present invention.

Claims

1. A method for manufacturing a lithium-ion battery separator having high temperature resistance, comprising mixing 25-40% polypropylene main material, 3-6% solubilizer, 50-70% solvent, 0.2-3% nucleating aid and / or 0.1-0.5% antioxidant by mass percentage, melt-plasticizing the mixture, extruding it with a twin-screw, and obtaining a cast slab by thermally induced phase separation. Subsequently, the cast slab is stretched, mineral oil is extracted from the oil film on the cast slab, and post-treatment is performed to obtain it. In the stretching process of the cast slab, the air temperature is maintained at 130 to 165°C and the film surface temperature at 124 to 140°C, and the slab is stretched (1 to 30) times in the longitudinal direction, (1 to 30) times in the transverse direction, and / or (1 to 30) × (1 to 30) times simultaneously in both directions at a stretching speed of 3 to 60 m / min. The post-processing includes sequentially stretching the dry film in both longitudinal and transverse directions, relaxing it in both longitudinal and transverse directions, and thermoforming, wherein in the longitudinal and transverse stretching step of the dry film, an air temperature of 130 to 175°C and a film surface temperature of 125 to 150°C are maintained, and the film is stretched longitudinally by (1 to 30) times, stretched transversely by (1 to 30) times, and / or simultaneously stretched in both directions by (1 to 30) × (1 to 30) times at a stretching speed of 3 to 40 m / min, and in the longitudinal and transverse relaxation step, an air temperature of 130 to 175°C and a film surface temperature of 125 to 150°C are maintained, and the film is relaxed longitudinally at a relaxation speed of 3 to 20 m / min so that the entry side is (1 to 3) times the length of the exit side, and the entry side is relaxed transversely so that the entry side is (1 to 3) times the width of the exit side, and / or simultaneously relaxed in both directions so that the entry side is (1 to 3) × (1 to 3) times the width of the exit side. The aforementioned polypropylene is a compound made from polypropylene with a melt index of 2 g / 10 min or less and polypropylene with a different melt index of 0.5 g / 10 min or less. The nucleation aid comprises a mixture of one or more of adipic acid, calcium stearate, aluminum stearate, sorbitol benzylidene derivative, sodium benzoate, and bis(4-tert-butylbenzoato-κO)hydroxyaluminum. The solubilizer comprises a mixture of one or more of polyethylene / propylene copolymer, polypropylene / ethylene-butene copolymer, polypropylene / ethylene-hexene copolymer, polyethylene wax, polypropylene wax, and polyester wax. The manufacturing method is characterized in that the separator has a thickness of 3.5 to 30 μm, a porosity of 30 to 80%, an adjustable pore size of 20 to 2000 nm, a bidirectional stretch strength of 50 MPa or more, an air permeability of 400 s / 100 cc or less, and a film rupture temperature of 160°C or higher.

2. The manufacturing method according to claim 1, characterized in that the solvent comprises a mixture of one or more alkanes, esters, ethers, and aromatic hydrocarbon compounds.

3. The method for producing the product according to claim 2, characterized in that the solvent comprises one or more of the following: liquid paraffin, solid paraffin, paraffin oil, natural vegetable oil, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, dioctyl sebacate, methyl salicylate, diphenyl ether, and diphenylmethane.

4. The production method according to claim 1, characterized in that the nucleation aid is 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol.

5. The manufacturing method according to claim 1, characterized in that the antioxidant comprises one of antioxidant 1076, antioxidant 1010, and antioxidant 168.

6. The supply method for the polypropylene main material, the solubilizer, the solvent, the nucleation aid, and / or the antioxidant before extrusion may be either simultaneous supply or non-simultaneous supply. In the aforementioned twin-screw extrusion process, the screw temperature is 140 to 240°C, the molten pipe temperature is 190 to 230°C, and the die temperature is 180 to 220°C. The thickness of the extruded molten material is 0.7 to 5 mm. In the manufacturing process of the aforementioned cast slab, the rotational speed of the coaxial twin-screw is 60 to 100 rpm. The process after extrusion further includes a cooling step, the cooling method of which is rapid cooling roll cooling 10 to 80°C, rapid cooling roll cooling + pull roll cooling 10 to 80°C, rapid cooling roll + water cooling 5 to 80°C, water cooling + bottom roll cooling 5 to 80°C, rapid cooling roll + oil cooling 5 to 80°C and / or oil cooling + bottom roll cooling 5 to 80°C. The manufacturing method according to any one of claims 1 to 5, characterized in that the stretched end material is not cut off in advance during the extraction.

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