Lithium Ion Battery Separator and Method for Manufacturing the Same

Abstract

The present disclosure relates to the technical field of lithium-ion battery separators and provides a method for manufacturing a lithium-ion battery separator. The method includes: (1) mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore-forming agent into a molten mixture, extruding the mixture through a die, and then cooling it to form a cast piece; (2) sequentially performing a first longitudinal stretching and a first transverse stretching on the cast piece to obtain a stretched film; (3) performing a second longitudinal stretching on the stretched film; (4) performing a second transverse stretching; (5) extracting the pore-forming agent in the separator to obtain an extracted separator; (6) performing a third longitudinal stretching on the extracted separator; (7) performing a third transverse stretching; and (8) sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator. The separator manufactured by the method of the present disclosure has significantly improved tensile strengths in the longitudinal and transverse directions, and its puncture strength can also be much higher than that of other separators of the same thickness.

Description

Technical Field

[0001] The present disclosure relates to the field of lithium-ion battery separators, and more particularly, to lithium-ion battery separators and methods for manufacturing the same.

Background Art

[0002] Lithium-ion batteries have been widely used in the fields of electronic devices, new energy vehicles, and wind energy storage in recent years; lithium-ion battery separators are important components of lithium-ion batteries; separators play an important role in separating the positive and negative electrodes to prevent short circuits and allowing the electrolyte solution to pass through to generate current; the main roles of separators include porosity, air permeability, tensile strength, puncture strength, shutdown temperature, etc. The characteristics of the separator directly affect the capacity, cycle performance, and safety of the battery. Therefore, improving the characteristics of the separator is very important for the performance of lithium-ion batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Currently, the main process of the most common wet method for manufacturing separators is: extruder → die → cast → machine direction (MD) → first transverse direction stretching (TD1) → extraction → second transverse direction stretching (TD2) → heat curing. This method is mature, controllable, and a common method for manufacturing conventional base films. However, due to the footprint of the equipment and the limitations of the method, the stretching ratios in the machine direction (abbreviated as "MD" hereinafter in this specification, which is the casting direction) and the transverse direction (abbreviated as "TD" hereinafter in this specification, which is perpendicular to the casting direction) of the separators produced by this traditional method are usually less than 15 times, subject to certain limitations, which restrict the tensile strength and puncture strength of the separators. In recent years, due to growing safety concerns regarding lithium-ion batteries in general, research on the safety of lithium-ion batteries has received even more attention. For some separators, the requirements for tensile strength and puncture strength are becoming increasingly high, and sometimes it is required to minimize the thickness of the separator while increasing its puncture strength. Therefore, it has become more desirable to develop an ultra-thin separator that has the basic physical properties of the separator while maintaining ultra-high strength, which is not yet available.

Means for Solving the Problem

[0004] The content of the present disclosure To achieve the objectives as shown, the technical solution of the present disclosure is implemented as follows.

[0005] In one aspect, the present disclosure is a method for manufacturing a lithium-ion battery separator, comprising: (1) mixing and heating a composition comprising a polyolefin resin, an antioxidant, and a pore former to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast sheet; and (2) sequentially performing a first machine direction stretching and a first transverse direction stretching on the cast sheet to obtain a stretched film. (3) Performing a second longitudinal stretching on the stretched film; (4) Performing a second transverse stretching; (5) Extracting the pore former in the separator to obtain the separator after extraction; (6) Performing a third longitudinal stretching on the separator after extraction; (7) Performing a third transverse stretching; (8) Sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator; A method is provided that includes the above steps.

[0006] In some embodiments, for both the first longitudinal stretching and the first transverse stretching in step (2), the stretching temperature ranges from 60°C to 150°C, and the stretching ratio ranges from 3 to 15 times.

[0007] Furthermore, in some embodiments, for the second longitudinal stretching in step (3), the stretching temperature ranges from 60°C to 140°C, and the stretching ratio ranges from 2 to 10 times.

[0008] Furthermore, in some embodiments, for the second transverse stretching in step (4), the stretching temperature ranges from 90°C to 140°C, and the stretching ratio ranges from 2 to 10 times.

[0009] Furthermore, in some embodiments, for the third longitudinal stretching in step (6), the stretching temperature ranges from 90°C to 150°C, and the stretching ratio ranges from 1.5 to 6 times.

[0010] Furthermore, in some embodiments, for the third transverse stretching in step (7), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.5 to 6 times.

[0011] Furthermore, in some embodiments, for the fourth transverse stretching in step (8), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.1 to 2 times.

[0012] Furthermore, in some embodiments, the temperature of the heat curing in step (8) ranges from 110°C to 150°C.

[0013] In another aspect, the present disclosure provides a method for manufacturing a lithium-ion battery separator, comprising: (1) mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore-forming agent to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast film; (2) sequentially performing a first longitudinal stretching and a first transverse stretching on the cast film to obtain a stretched film; (3) performing a second longitudinal stretching on the stretched film; (4) performing a second transverse stretching; (5) extracting the pore-forming agent in the separator to obtain an extracted separator; (6) performing a third longitudinal stretching on the extracted separator; (7) performing simultaneous biaxial stretching (SBS); (8) sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator. The method is provided.

[0014] In some embodiments, for both the first longitudinal stretching and the first transverse stretching in step (2), the stretching temperature ranges from 60°C to 150°C, and the stretching ratio ranges from 3 to 15 times.

[0015] Furthermore, in some embodiments, for the second longitudinal stretching in step (3), the stretching temperature ranges from 60°C to 140°C, and the stretching ratio ranges from 2 to 10 times.

[0016] Furthermore, in some embodiments, for the second transverse stretching in step (4), the stretching temperature ranges from 90°C to 140°C, and the stretching ratio ranges from 2 to 10 times.

[0017] Furthermore, in some embodiments, for the third longitudinal stretching in step (6), the stretching temperature ranges from 90°C to 150°C, and the stretching ratio ranges from 1.5 times to 6 times.

[0018] Furthermore, in some embodiments, for the simultaneous biaxial stretching in step (7), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.5×1.5 times to 6×6 times.

[0019] Furthermore, in some embodiments, for the fourth transverse stretching in step (8), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.1 times to 2 times.

[0020] Furthermore, in some embodiments, the temperature for heat curing in step (8) ranges from 110°C to 150°C.

[0021] In another aspect, the present disclosure is a method for manufacturing a lithium-ion battery separator, comprising: (1) mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore-forming agent to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast film; (2) sequentially performing a first longitudinal stretching and a first transverse stretching on the cast film to obtain a stretched film; (3) performing a second longitudinal stretching on the stretched film; (4) performing a simultaneous biaxial stretching; (5) extracting the pore-forming agent in the separator to obtain the separator after extraction; (6) performing a third longitudinal stretching on the separator after extraction; (7) performing a third transverse stretching; (8) sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator. A method as described above is provided.

[0022] In some embodiments, for both the first longitudinal stretching and the first transverse stretching in step (2), the stretching temperature ranges from 60°C to 150°C, and the stretching ratio ranges from 3 to 15 times.

[0023] Furthermore, in some embodiments, for the second longitudinal stretching in step (3), the stretching temperature ranges from 60°C to 140°C, and the stretching ratio ranges from 2 to 10 times.

[0024] Furthermore, in some embodiments, for the simultaneous biaxial stretching in step (4), the stretching temperature ranges from 90°C to 140°C, and the stretching ratio ranges from 1.5×1.5 to 12×12 times.

[0025] Furthermore, in some embodiments, for the third longitudinal stretching in step (6), the stretching temperature ranges from 90°C to 150°C, and the stretching ratio ranges from 1.5 to 6 times.

[0026] Furthermore, in some embodiments, for the third transverse stretching in step (7), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.5 to 6 times.

[0027] Furthermore, in some embodiments, for the fourth transverse stretching in step (8), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.1 to 2 times.

[0028] Furthermore, in some embodiments, the temperature of heat curing in step (8) ranges from 110°C to 150°C.

[0029] In another aspect, the present disclosure is a method for manufacturing a lithium-ion battery separator, (1) mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore former to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast sheet; (2) sequentially performing a first longitudinal stretching and a first transverse stretching on the cast sheet to obtain a stretched film; (3) Performing a second longitudinal stretching on the stretched film; (4) Performing a first simultaneous biaxial stretching; (5) Extracting the pore former in the separator to obtain the separator after extraction; (6) Performing a third longitudinal stretching on the separator after extraction; (7) Performing a second simultaneous biaxial stretching; (8) Sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator; provided is a method including the above steps.

[0030] In some embodiments, for both the first longitudinal stretching and the first transverse stretching in step (2), the stretching temperature ranges from 60°C to 150°C, and the stretching ratio ranges from 3 to 15 times.

[0031] Further, in some embodiments, for the second longitudinal stretching in step (3), the stretching temperature ranges from 60°C to 140°C, and the stretching ratio ranges from 2 to 10 times.

[0032] Further, in some embodiments, for the first simultaneous biaxial stretching in step (4), the stretching temperature ranges from 90°C to 140°C, and the stretching ratio ranges from 1.5×1.5 to 12×12 times.

[0033] Further, in some embodiments, for the third longitudinal stretching in step (6), the stretching temperature ranges from 90°C to 150°C, and the stretching ratio ranges from 1.5 to 6 times.

[0034] Further, in some embodiments, for the second simultaneous biaxial stretching in step (7), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.5×1.5 to 6×6 times.

[0035] Further, in some embodiments, for the fourth transverse stretching in step (8), the stretching temperature ranges from 100°C to 150°C, and the stretching ratio ranges from 1.1 to 2 times.

[0036] Furthermore, in some embodiments, the temperature of the heat curing in step (8) ranges from 110°C to 150°C.

[0037] Furthermore, in some embodiments, the present disclosure also provides a lithium-ion battery separator having a thickness ranging from 3 μm to 8 μm, wherein the transverse tensile strength of the separator is greater than 5000 kgf / cm 2 sup, and the longitudinal tensile strength of the separator is greater than 5000 kgf / cm 2 sup, the puncture strength per unit thickness of the separator is greater than 120 gf / μm, the porosity of the separator ranges from 30% to 60%, and the median pore diameter of the separator is from 20 nm to 55 nm.

[0038] Furthermore, the transverse tensile strength of the lithium-ion battery separator disclosed herein ranges, for example, from 5000 kgf / cm 2 to 7500 kgf / cm 2 ; the longitudinal tensile strength of the separator ranges, for example, from 5000 kgf / cm 2 to 7500 kgf / cm 2 ; and the range of the puncture strength per unit thickness of the separator is, for example, from 120 gf / μm to 200 gf / μm.

[0039] The separator produced by the method of the present disclosure has significantly improved tensile strengths in both the MD and TD directions, and its puncture strength can also be much higher than that of other separators of the same thickness. When the separator disclosed herein is used inside a lithium-ion battery, it can provide better isolation and protection for the positive and negative electrodes of the battery, especially when the battery is subjected to an external impact. As a result, the risk of short circuit caused by separator breakage is avoided, and thus the safety performance of the lithium-ion battery is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0041] Legend of the figures: S1 - Extrusion; S2 - Cooling and sheet formation; S3 - MD1; S4 - TD1; S5 - MD2; S6 - TD2; S7 - SBS1; S8 - Extraction; S9 - MD3; S10 - TD3; S11 - SBS2; S12 - TD4; S13 - Heat curing.

[0042] **Specific Embodiments** Specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are used only for exemplifying and explaining the present disclosure and do not limit the present disclosure. The endpoints and any values of the ranges disclosed herein are not limited to the exact ranges or values, but should be understood to contain values close to those ranges or values. Ranges of values, the values of the endpoints of each range, the values of the endpoints of each range and the values of individual points, as well as the values of individual points, can be combined with each other to result in one or more new ranges of values, which will be considered as specifically disclosed herein.

[0043] As shown in FIG. 1, the main flow of the wet method for separator manufacturing in the prior art is S1 Extrusion → S2 Cooling and sheet formation → S3 MD1 → S4 TD1 → S8 Extraction → S6 TD2 → S13 Heat curing.

[0044] As shown in FIG. 2, in a specific embodiment of the present disclosure, a first method for manufacturing a lithium-ion battery separator, (1) Pre-mix the dry powder of high molecular weight polyethylene and an antioxidant, and then add the pre-mixed mixture together with an organic pore former to a twin-screw extruder. In S1, extrude the mixture through a die, and then in S2, cool it through a chill roll to form a cast sheet; (2) Sequentially perform S3 MD1 and S4 TD1 on the cast sheet to obtain a stretched film; (3) Perform S5 MD2 on the stretched film; (4) Perform S6 TD2; (5) By using an extraction solvent in S8, extract the organic pore former in the separator to obtain the separator after extraction; (6) Perform S9 MD3 on the separator after extraction; (7) Perform S10 TD3; (8) Sequentially perform S12 TD4 and S13 heat curing to obtain a lithium-ion battery separator. A method is provided that includes the above steps.

[0045] In some embodiments, the extrusion speed in die extrusion ranges from 60 kg / h to 350 kg / h, and the extrusion temperature ranges from 150 °C to 230 °C.

[0046] If the extrusion speed and / or extrusion temperature are too high or too low, this can easily lead to melt fracture or excessive casting defects; the morphology of the cast sheet plays an important role in maintaining a high draw ratio. Therefore, if the cast sheet contains many defects, this can easily lead to the breakage of the separator during stretching.

[0047] Furthermore, the molecular weight of the high molecular weight polyethylene in step (1) is, for example, in the range of 600,000 to 2,000,000; the concentration of the components is expressed in "parts by mass". For example, the amount of the high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant is, for example, in the range of 0.1 part by mass to 1 part by mass, and the amount of the organic pore former is, for example, in the range of 233 parts by mass to 400 parts by mass. In some embodiments, the amount of the high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant is in the range of 0.1 part by mass to 1 part by mass, and the amount of the organic pore former is in the range of 233 parts by mass to 360 parts by mass. In some embodiments, the amount of the high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant is in the range of 0.2 part by mass to 0.5 part by mass, and the amount of the organic pore former is in the range of 250 parts by mass to 360 parts by mass.

[0048] Furthermore, in some embodiments, the antioxidant in step (1) is one or more selected from amines, sulfur-containing compounds, nitrogen-containing compounds, phosphorus-containing compounds, and organic metal salts.

[0049] Furthermore, in some embodiments, the pore former in step (1) is one or more selected from white oil, paraffin oil, and polyethylene glycol.

[0050] Furthermore, in some embodiments, for both S3 MD1 and S4 TD1 in step (2), the stretching temperature is in the range of 60°C to 150°C, preferably 60°C to 125°C, for example 60°C to 120°C, and the stretching ratio is in the range of 3 to 15 times, preferably 8 to 15 times, for example, 8 to 10 times, or 10 to 15 times.

[0051] Furthermore, in some embodiments, for S5 MD2 in step (3), the stretching temperature is in the range of 60°C to 140°C, preferably 60°C to 130°C, and the stretching ratio is in the range of 2 to 10 times, preferably 2.5 to 10 times, for example, 6.7 to 10 times, or 7 to 10 times.

[0052] After the S4 TD1 stretching, the film may become much wider. Thus, the width of the film is then significantly reduced by the S5 MD2 stretching, thereby eliminating the process of separator slitting, improving production efficiency and equipment utilization rate, increasing the stretching ratio of the film, and facilitating subsequent stretching.

[0053] Furthermore, in some embodiments, for S6 TD2 in step (4), the stretching temperature ranges from 90 °C to 140 °C, preferably from 90 °C to 130 °C, and the stretching ratio ranges from 2 to 10 times, preferably from 2.5 to 10 times, for example, from 5.7 to 10 times, or from 6 to 10 times.

[0054] Since the S6 TD2 stretching is performed on the film with reduced width, the stretching ratio of the film can be further increased.

[0055] Furthermore, in some embodiments, for S9 MD3 in step (6), the stretching temperature ranges from 90 °C to 150 °C, preferably from 90 °C to 135 °C, and the stretching ratio ranges from 1.5 to 6 times, preferably from 2 to 5 times, for example, from 2.5 to 5 times, or from 3.3 to 5 times.

[0056] Furthermore, in some embodiments, for S10 TD3 in step (7), the stretching temperature ranges from 100 °C to 150 °C, preferably from 100 °C to 135 °C, and the stretching ratio ranges from 1.5 to 6 times, preferably from 2.5 to 5 times.

[0057] Furthermore, let the stretching ratio of S3 MD1 be "a", the stretching ratio of S4 TD1 be "b", the stretching ratio of S5 MD2 be "c", the stretching ratio of S6 TD2 be "d", the stretching ratio of S9 MD3 be "e", and the stretching ratio of S10 TD3 be "f". Define the product of a, c, and e as "m", that is, a × c × e = m. On the other hand, define the product of b, d, and f as "n", that is, b × d × f = n. The values of both "m" and "n" are independently in the range of, for example, 15 to 500, preferably 50 to 500, for example, 50 to 430, or 50 to 428.

[0058] As disclosed in this specification, the S5 MD2 operation, together with the S6 TD2 operation, is applied before the S8 extraction, and the S9 MD3 stretching, together with the S10 TD3 stretching operation, is applied after the S8 extraction, so that the stretching ratios of MD and TD are increased by cascade stretching. As a result, the total stretching ratios "m" and "n" of MD and TD can reach values in the range of 15 to 500 times. The separator manufactured by the method of the present disclosure thus has significantly improved tensile strengths in MD and TD, and its puncture strength can also be much higher than the puncture strength of other separators of the same thickness.

[0059] A method including the S9 MD3 stretching together with the S10 TD3 stretching after the S8 extraction can improve the mechanical strength of the separator while well controlling the porosity and pore diameter.

[0060] Furthermore, in some embodiments, for S12 TD4 in step (8), the stretching temperature is in the range of 100 °C to 150 °C, preferably 100 °C to 135 °C, and the stretching ratio is in the range of 1.1 times to 2 times, preferably 1.2 times to 2 times.

[0061] Furthermore, in some embodiments, the temperature of the S13 heat curing in step (8) is in the range of 110 °C to 150 °C, preferably 110 °C to 135 °C, for example 135 °C to 150 °C.

[0062] As shown in FIG. 3, in a specific embodiment of the present disclosure, a second method for manufacturing a lithium-ion battery separator, (1) Pre-mixing a dry powder of high molecular weight polyethylene and an antioxidant, and then adding the pre-mixed mixture together with an organic pore former to a twin-screw extruder, extruding the mixture through a die in S1, and then cooling it through a chill roll in S2 to form a cast piece; (2) Sequentially performing S3 MD1 and S4 TD1 on the cast piece to obtain a stretched film; (3) Performing S5 MD2 on the stretched film; (4) The step of performing S6 TD2, (5) The step of extracting the organic pore former in the separator by using an extraction solvent in S8 to obtain a separator after extraction, (6) The step of performing S9 MD3 on the separator after extraction, (7) The step of performing S7 SBS1, (8) The step of sequentially performing S12 TD4 and S13 heat curing to obtain a lithium ion battery separator A method is provided that includes.

[0063] In some embodiments, the extrusion speed in die extrusion is in the range of 60 kg / hour to 350 kg / hour, and the extrusion temperature is in the range of 150 °C to 230 °C.

[0064] If the extrusion speed and / or the extrusion temperature are too high or too low, this can easily lead to melt fracture or excessive casting defects; the morphology of the cast sheet plays an important role in maintaining a high draw ratio, and if the cast sheet contains many defects, this can easily lead to breakage of the separator during drawing.

[0065] Furthermore, in some embodiments, the molecular weight of the high molecular weight polyethylene in step (1) is in the range of 600,000 to 2,000,000; the concentration of the components is expressed in "parts by mass". For example, the amount of high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant is in the range of 0.1 part by mass to 1 part by mass, and the amount of the organic pore former is in the range of, for example, 233 parts by mass to 400 parts by mass. In some embodiments, the amount of high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant is in the range of 0.1 part by mass to 1 part by mass, and the amount of the organic pore former is in the range of 233 parts by mass to 360 parts by mass. In some embodiments, the amount of high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant is in the range of 0.2 part by mass to 0.5 part by mass, and the amount of the organic pore former is in the range of 250 parts by mass to 360 parts by mass.

[0066] Furthermore, in some embodiments, the antioxidant in step (1) is one or more selected from amines, sulfur-containing compounds, nitrogen-containing compounds, phosphorus-containing compounds, and organometallic salts.

[0067] Furthermore, in some embodiments, the pore former in step (1) is one or more selected from white oil, paraffin oil, and polyethylene glycol.

[0068] Furthermore, in some embodiments, for both S3 MD1 and S4 TD1 in step (2), the stretching temperature ranges from 60°C to 150°C, preferably from 60°C to 125°C, for example, in the range of 60°C to 120°C, and the stretching ratio ranges from 3 to 15 times, preferably from 8 to 15 times, for example, in the range of 8 to 10 times, or 10 to 15 times.

[0069] Furthermore, in some embodiments, for S5 MD2 in step (3), the stretching temperature ranges from 60°C to 140°C, preferably from 60°C to 130°C, and the stretching ratio ranges from 2 to 10 times, preferably from 2.5 to 10 times, for example, in the range of 3.3 to 10 times.

[0070] After the S4 TD1 stretching, the film may become much wider. Therefore, the width of the film is significantly reduced by the S5 MD2 stretching, thereby eliminating the process of separator slitting, improving the production efficiency and equipment utilization rate, increasing the stretching ratio of the film, and promoting subsequent stretching.

[0071] Furthermore, in some embodiments, for S6 TD2 in step (4), the stretching temperature ranges from 90°C to 140°C, preferably from 90°C to 130°C, and the stretching ratio ranges from 2 to 10 times, preferably from 2.5 to 10 times, for example, in the range of 6.7 to 10 times.

[0072] Since the S6 TD2 stretching is performed on the film with reduced width, the stretching ratio of the film can be further increased.

[0073] Furthermore, in some embodiments, for S9 MD3 in step (6), the stretching temperature ranges from 90°C to 150°C, preferably from 90°C to 135°C, and the stretching ratio ranges from 1.5 times to 6 times, preferably from 2 times to 5 times, for example, from 2.5 times to 5 times, or from 3.3 times to 5 times.

[0074] Furthermore, in some embodiments, for S7 SBS1 in step (7), the stretching temperature ranges from 100°C to 150°C, preferably from 100°C to 135°C, and the stretching ratio ranges from 1.5×1.5 times to 6×6 times, preferably from 2×2 times to 6×6 times, for example, from 2×2 times to 5×5 times.

[0075] Furthermore, let the stretching ratio of S3 MD1 be "a", the stretching ratio of S4 TD1 be "b", the stretching ratio of S5 MD2 be "c", the stretching ratio of S6 TD2 be "d", the stretching ratio of S9 MD3 be "e", and the stretching ratio of S7 SBS1 in any direction be "g". Define the product of "a", "c", "e", and "g" as "m", that is, a×c×e×g = m. On the other hand, define the product of "b", "d", and "g" as "n", that is, b×d×g = n. The values of both "m" and "n" are, independently, for example, in the range of 15 to 500, preferably 200 to 500, for example, 400 to 500, or 400 to 495.

[0076] As disclosed herein, the S5 MD2 operation is added together with the S6 TD2 operation before S8 extraction, and the S9 MD3 stretching is added together with the S7 SBS1 stretching operation after S8 extraction, so that the stretching ratios of MD and TD increase by cascade stretching. As a result, the total stretching ratios m and n of MD and TD can reach the range of 15 times to 500 times. The separator manufactured by the method of the present disclosure has significantly improved tensile strengths in MD and TD, and its puncture strength can also be much higher than that of other separators of the same thickness.

[0077] The method including S9 MD3 stretching together with S7 SBS1 stretching after S8 extraction can improve the mechanical strength of the separator while providing good control of porosity and pore diameter.

[0078] Furthermore, in some embodiments, for S12 TD4 in step (8), the stretching temperature ranges from 100°C to 150°C, preferably from 100°C to 135°C, and the stretching ratio ranges from 1.1 times to 2 times, preferably from 1.2 times to 2 times.

[0079] Furthermore, in some embodiments, the temperature of S13 heat curing in step (8) ranges from 110°C to 150°C, preferably from 110°C to 135°C, for example, from 135°C to 150°C.

[0080] As shown in FIG. 4, in a specific embodiment of the present disclosure, a third method for manufacturing a lithium-ion battery separator, (1) preliminarily mixing a dry powder of high molecular weight polyethylene and an antioxidant, then adding the preliminarily mixed mixture together with an organic pore former to a twin-screw extruder, in S1, extruding the mixture through a die, and then, in S2, cooling it through a chill roll to form a cast piece; (2) sequentially performing S3 MD1 and S4 TD1 on the cast piece to obtain a stretched film; (3) performing S5 MD2 on the stretched film; (4) performing S7 SBS1; (5) in S8, extracting the organic pore former in the separator by using an extraction solvent to obtain an extracted separator; (6) performing S9 MD3 on the extracted separator; (7) performing S10 TD3; (8) sequentially performing S12 TD4 and S13 heat curing to obtain a lithium-ion battery separator; A method is provided that includes.

[0081] In some embodiments, the extrusion speed in die extrusion ranges from 60 kg / h to 350 kg / h, and the extrusion temperature ranges from 150°C to 230°C.

[0082] If the extrusion speed and / or extrusion temperature are too high or too low, this can easily lead to melt fracture or excessive casting defects; the morphology of the cast film plays an important role in maintaining a high draw ratio, and if the cast film contains many defects, this can easily lead to the breakage of the separator during drawing.

[0083] Furthermore, in some embodiments, the molecular weight of the high molecular weight polyethylene in step (1) ranges from 600,000 to 2,000,000; the concentrations of the components are expressed in "parts by mass". For example, the amount of high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant ranges from 0.1 part by mass to 1 part by mass, and the amount of the organic pore former ranges from, for example, 233 parts by mass to 400 parts by mass. In some embodiments, the amount of high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant ranges from 0.1 part by mass to 1 part by mass, and the amount of the organic pore former ranges from 233 parts by mass to 360 parts by mass. In some embodiments, the amount of high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant ranges from 0.2 part by mass to 0.5 part by mass, and the amount of the organic pore former ranges from 250 parts by mass to 360 parts by mass.

[0084] Furthermore, in some embodiments, the antioxidant in step (1) is one or more selected from amines, sulfur-containing compounds, nitrogen-containing compounds, phosphorus-containing compounds, and organic metal salts.

[0085] Furthermore, in some embodiments, the pore former in step (1) is one or more selected from white oil, paraffin oil, and polyethylene glycol.

[0086] Furthermore, in some embodiments, for both S3 MD1 and S4 TD1 in step (2), the drawing temperature ranges from 60°C to 150°C, preferably from 60°C to 125°C, for example from 60°C to 120°C, and the draw ratio ranges from 3 to 15 times, preferably from 8 to 15 times, for example from 8 to 10 times, or from 10 to 15 times.

[0087] Furthermore, in some embodiments, for S5 MD2 in step (3), the stretching temperature ranges from 60°C to 140°C, preferably from 60°C to 130°C, and the stretching ratio ranges from 2 to 10 times, preferably from 2.5 to 10 times.

[0088] After the S4 TD1 stretching, the film may become much wider. Therefore, the width of the film is significantly reduced by the S5 MD2 stretching, thereby eliminating the process of separator slitting, improving the production efficiency and equipment utilization rate, increasing the stretching ratio of the film, and promoting subsequent stretching.

[0089] Furthermore, in some embodiments, for S7 SBS1 in step (4), the stretching temperature ranges from 90°C to 140°C, preferably from 90°C to 130°C, and the stretching ratio ranges from 1.5×1.5 to 12×12 times, preferably from 2×2 to 12×12 times. For example, it ranges from 5×5 to 12×12 times, or from 2×2 to 5×5 times.

[0090] Since the S7 SBS1 stretching is performed on the film with reduced width, the stretching ratio of the film further increases.

[0091] Furthermore, in some embodiments, for S9 MD3 in step (6), the stretching temperature ranges from 90°C to 150°C, preferably from 90°C to 135°C, and the stretching ratio ranges from 1.5 to 6 times, preferably from 2 to 5 times. For example, it ranges from 2.5 to 5 times, or from 3.3 to 5 times.

[0092] Furthermore, in some embodiments, for S10 TD3 in step (7), the stretching temperature ranges from 100°C to 150°C, preferably from 100°C to 135°C, and the stretching ratio ranges from 1.5 to 6 times, preferably from 2.5 to 6 times.

[0093] Furthermore, let the draw ratio of S3 MD1 be "a", the draw ratio of S4 TD1 be "b", the draw ratio of S5 MD2 be "c", the draw ratio of S7 SBS1 in any direction be "g", the draw ratio of S9 MD3 be "e", and the draw ratio of S10 TD3 be "f". Define the product of "a", "c", "e", and "g" as "m", that is, a×c×e×g = m. On the other hand, define the product of "b", "g", and "f" as "n", that is, b×d×f = n. The values of both "m" and "n" are independently in the range of, for example, 15 to 500, preferably 40 to 500, for example, 80 to 500, 100 to 500, 200 to 500, or 200 to 495.

[0094] As disclosed in this specification, S5 MD2 is applied together with the S7 SBS1 operation before S8 extraction, and S9 MD3 drawing is applied together with the S10 TD3 drawing after S8 extraction, so that the draw ratios in MD and TD increase by cascade drawing. As a result, the total draw ratios "m" and "n" in MD and TD can reach values in the range of 15 times to 500 times. The separator manufactured by the method of the present disclosure has significantly improved tensile strengths in MD and TD, and its puncture strength can also be much higher than that of other separators of the same thickness.

[0095] The method including S9 MD3 drawing together with the S10 TD3 drawing after S8 extraction improves the mechanical strength of the separator while providing good control over the porosity and pore diameter.

[0096] Furthermore, in some embodiments, for S12 TD4 in step (8), the drawing temperature is in the range of 100°C to 150°C, preferably 100°C to 135°C, and the draw ratio is in the range of 1.1 times to 2 times, preferably 1.2 times to 2 times.

[0097] Furthermore, in some embodiments, the temperature of S13 heat curing in step (8) is in the range of 110°C to 150°C, preferably 110°C to 135°C, for example 135°C to 150°C.

[0098] As shown in FIG. 5, in a particular embodiment of the present disclosure, a fourth method for manufacturing a lithium-ion battery separator, (1) preliminarily mixing a dry powder of high molecular weight polyethylene and an antioxidant, and then adding the preliminarily mixed mixture together with an organic pore former to a twin-screw extruder, in S1, extruding the mixture through a die, and then, in S2, cooling it through a chill roll to form a cast piece; (2) sequentially performing S3 MD1 and S4 TD1 on the cast piece to obtain a stretched film; (3) performing S5 MD2 on the stretched film; (4) performing S7 SBS1; (5) in S8, extracting the organic pore former in the separator by using an extraction solvent to obtain a separator after extraction; (6) performing S9 MD3 on the separator after extraction; (7) performing S11 SBS2; (8) sequentially performing S12 TD4 and S13 heat curing to obtain a lithium-ion battery separator is provided.

[0099] In some embodiments, the extrusion speed in die extrusion ranges from 60 kg / h to 350 kg / h, and the extrusion temperature ranges from 150°C to 230°C.

[0100] If the extrusion speed and / or the extrusion temperature are too high or too low, this can easily lead to melt fracture or excessive casting defects; the morphology of the cast piece plays an important role in maintaining a high ratio of stretching, and if the cast piece contains many defects, this can easily lead to the breakage of the separator during stretching.

[0101] Furthermore, in some embodiments, the molecular weight of the high molecular weight polyethylene in step (1) ranges from 600,000 to 2,000,000; the concentrations of the components are expressed in "parts by mass". For example, the amount of the high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant ranges from 0.1 part by mass to 1 part by mass, and the amount of the organic pore former ranges from, for example, 233 parts by mass to 400 parts by mass. In some embodiments, the amount of the high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant ranges from 0.1 part by mass to 1 part by mass, and the amount of the organic pore former ranges from 233 parts by mass to 360 parts by mass. In some embodiments, the amount of the high molecular weight polyethylene is 100 parts by mass, the amount of the antioxidant ranges from 0.2 part by mass to 0.5 part by mass, and the amount of the organic pore former ranges from 250 parts by mass to 360 parts by mass.

[0102] Furthermore, in some embodiments, the antioxidant in step (1) is one or more selected from amines, sulfur-containing compounds, nitrogen-containing compounds, phosphorus-containing compounds, and organic metal salts.

[0103] Furthermore, in some embodiments, the pore former in step (1) is one or more selected from white oil, paraffin oil, and polyethylene glycol.

[0104] Furthermore, in some embodiments, for both S3 MD1 and S4 TD1 in step (2), the stretching temperature ranges from 60°C to 150°C, preferably from 60°C to 125°C, for example, from 60°C to 120°C, and the stretching ratio ranges from 3 times to 15 times, preferably from 3.75 times to 15 times, for example, from 8 times to 15 times, from 8 times to 10 times, or from 10 times to 15 times.

[0105] Furthermore, in some embodiments, for S5 MD2 in step (3), the stretching temperature ranges from 60°C to 140°C, preferably from 60°C to 130°C, and the stretching ratio ranges from 2 times to 10 times, preferably from 2.5 times to 10 times.

[0106] After the S4 TD1 stretching, the film may become much wider. Thus, the width of the film is then significantly reduced by the S5 MD2 stretching, thereby eliminating the separator slitting process, improving the production efficiency and equipment utilization rate, increasing the stretching ratio of the film, and facilitating subsequent stretching.

[0107] Furthermore, in some embodiments, for S7 SBS1 in step (4), the stretching temperature ranges from 90°C to 140°C, preferably from 90°C to 130°C, and the stretching ratio ranges from 1.5×1.5 times to 12×12 times, preferably from 2×2 times to 12×12 times. For example, it ranges from 5×5 times to 12×12 times, or from 2×2 times to 10×10 times.

[0108] Here, since the S7 SBS1 stretching is performed on the film with reduced width, the stretching ratio of the film further increases.

[0109] Furthermore, in some embodiments, for S9 MD3 in step (6), the stretching temperature ranges from 90°C to 150°C, preferably from 90°C to 135°C, and the stretching ratio ranges from 1.5 times to 6 times, preferably from 2 times to 5 times. For example, it ranges from 2.5 times to 5 times.

[0110] Furthermore, in some embodiments, for S11 SBS2 in step (7), the stretching temperature ranges from 100°C to 150°C, preferably from 100°C to 135°C, and the stretching ratio ranges from 1.5×1.5 times to 6×6 times, preferably from 2×2 times to 6×6 times. For example, it ranges from 2×2 times to 3.3×3.3 times, or from 2×2 times to 3×3 times.

[0111] Furthermore, let the draw ratio of S3 MD1 be "a", the draw ratio of S4 TD1 be "b", the draw ratio of S5 MD2 be "c", the draw ratio of S7 SBS1 in any direction be "g", the draw ratio of S9 MD3 be "e", the draw ratio of S11 SBS2 in any direction be "h", and define the product of "a", "c", "e", "g", and "h" as "m", that is, a×c×e×g×h = m. On the other hand, define the product of "b", "g", and "h" as "n", that is, b×d×h = n. The values of both "m" and "n" are independently in the range of, for example, 15 to 500, preferably 32 to 500, for example, 128 to 500, or 128 to 495.

[0112] As disclosed herein, S5 MD2 is applied together with the S7 SBS1 operation before S8 extraction, and S9 MD3 drawing is applied together with the S11 SBS2 drawing operation after S8 extraction, so that the draw ratios in MD and TD increase by cascade drawing. As a result, the total draw ratios "m" and "n" in MD and TD can reach values in the range of 15 times to 500 times. The separator manufactured by the method of the present disclosure has significantly improved tensile strengths in MD and TD, and its puncture strength can also be much higher than the puncture strength of other separators of the same thickness.

[0113] The method including S9 MD3 drawing together with S11 SBS2 drawing after S8 extraction can improve the mechanical strength of the separator while well controlling the porosity and pore diameter.

[0114] Furthermore, in some embodiments, for S12 TD4 in step (8), the drawing temperature is in the range of 100°C to 150°C, preferably 100°C to 135°C, and the draw ratio is in the range of 1.1 times to 2 times, preferably 1.2 times to 2 times.

[0115] Furthermore, in some embodiments, the temperature of S13 heat curing in step (8) is in the range of 110°C to 150°C, preferably 110°C to 135°C, for example 135°C to 150°C.

[0116] The lithium-ion battery separator obtained by any one of the methods of the above specific embodiments of the present disclosure has a thickness in the range of, for example, 3 μm to 8 μm, preferably 3 μm to 5 μm, for example, 4 μm to 5 μm; the transverse tensile strength of the separator is 5000 kgf / cm 2 super, preferably, 5000 kgf / cm 2 ~7500 kgf / cm 2 for example, 5200 kgf / cm 2 ~7500 kgf / cm 2 5500 kgf / cm 2 ~7500 kgf / cm 2 5800 kgf / cm 2 ~7500 kgf / cm 2 6300 kgf / cm 2 ~7500 kgf / cm 2 6600 kgf / cm 2 ~7500 kgf / cm 2 7100 kgf / cm 2 ~7500 kgf / cm 2 or 7200 kgf / cm 2 ~7500 kgf / cm 2 and is in the range of; the longitudinal tensile strength of the separator is more than 5000 kgf / cm 2 super, preferably 5000 kgf / cm 2 ~7500 kgf / cm 2 for example, 5700 kgf / cm 2 ~7500 kgf / cm 2 6300 kgf / cm 2 ~7500 kgf / cm 2 6500 kgf / cm 2 ~7500 kgf / cm 2 6900 kgf / cm 2 ~7500 kgf / cm 2 7000 kgf / cm 2 ~7500 kgf / cm 2 or 7100 kgf / cm 2 ~7500 kgf / cm 2is in the range of; the puncture strength per thickness of the separator is more than 120 gf / μm, preferably in the range of 121 gf / μm to 200 gf / μm, for example, in the range of 121 gf / μm to 190 gf / μm, 126 gf / μm to 190 gf / μm, 128 gf / μm to 190 gf / μm, 131 gf / μm to 190 gf / μm, 156 gf / μm to 190 gf / μm, or 187 gf / μm to 190 gf / μm; the porosity of the separator is, for example, in the range of 30% to 60%, preferably in the range of 40% to 60%, for example, in the range of 41% to 47%, 42% to 47%, 43% to 47%, 44% to 47%, 45% to 47%, or 46% to 47%; the median pore diameter of the separator is, for example, in the range of 20 nm to 55 nm, preferably in the range of 30 nm to 37 nm, for example, in the range of 32 nm to 37 nm, 33 nm to 37 nm, 34 nm to 37 nm, 35 nm to 37 nm, or 36 nm to 37 nm.

[0117] To further understand the present disclosure, the technical solutions provided by the present disclosure will be described in detail below with reference to examples.

[0118] In the following examples and comparative examples, the film performance or parameter tests are carried out according to the following methods.

[0119] 1. Thickness The thickness was measured according to the GB / T6672-2001 standard and tested as follows using a C1216 thickness gauge: The outer periphery of the produced base film was sampled, 40 mm×60 mm sample pieces were cut out, and they were tested at room temperature.

[0120] 2. Porosity 40 mm×60 mm sample pieces were cut out, the mass, thickness, and area of the sample pieces were measured respectively, and the density (ρ) of the sample pieces was calculated. The average porosity of the sample pieces was calculated using the following formula: Porosity (%) = [1 - ρ area ÷(ρ×d)]×100 obtained from the areal density.

[0121] 3. Median Pore Diameter When using the capillary flow porometer (CFP-1500AE) of PMI, the surface tension of the penetrant is 15.9 dynes / cm. The median pore diameter (φ mean ) is obtained from the semi-dry curve of the "dry-wet method".

[0122] 4. Puncture strength The puncture strength was measured according to ASTM D3736 standard and tested as follows using a KES-G5 manual compression tester: Cut out a 40 mm × 60 mm specimen piece, and test the specimen piece at room temperature with a test speed of 0.2 cm / second and a stroke of 20 mm.

[0123] 5. MD tensile strength The MD tensile strength was measured according to GB / T6672-2001 standard and tested as follows using a tensile tester (AGS-X10KN) of Shimadzu Corporation: Cut out a 15 mm × 15 mm specimen piece, and test the specimen piece at room temperature under a test speed of 50 mm / minute and a test gauge length of 10 mm.

[0124] 6. TD tensile strength The TD tensile strength was measured according to GB / T6672-2001 standard and tested as follows using a tensile tester (AGS-X10KN) of Shimadzu Corporation: Cut out 15 mm × 15 mm specimen pieces, and test them at room temperature under a test speed of 50 mm / minute and a test gauge length of 10 mm. (Example 1)

[0125] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 part of antioxidant were blended and stirred in the mixture; then, the mixture was poured into the feed bin of the extruder, and 330 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; S1 extrusion was carried out through the die; S2 cooling and sheet forming were carried out with chill rolls.

[0126] The S3 MD1 stretching and S4 TD1 stretching were sequentially performed on the cast piece. At this time, the stretching ratio was 8 times for both, the stretching temperature of S3 MD1 was 120 °C, and the stretching temperature of S4 TD1 was 125 °C.

[0127] For the stretching separator, the S5 MD2 stretching was performed at a stretching ratio of 2.5 times and a stretching temperature of 130 °C, and then the S6 TD2 stretching was performed at a stretching ratio of 2.5 times and a stretching temperature of 130 °C.

[0128] Using dichloromethane as the extraction solvent, the white oil was extracted step by step with an extraction time of 30 minutes.

[0129] For the separator after extraction, the S9 MD3 stretching was performed at a stretching ratio of 2.5 times and a stretching temperature of 135 °C, and then the S10 TD3 stretching was performed at a stretching ratio of 2.5 times and a stretching temperature of 135 °C.

[0130] The S12 TD4 stretching was performed at a stretching ratio of 1.2 times and a stretching temperature of 135 °C, and then the S13 heat curing was performed at a heat curing temperature of 135 °C to obtain the lithium-ion battery separator of the present disclosure.

[0131] (Comparative Example 1) The blending of the same raw materials and the S1 extrusion were completed as in Example 1 by the same process; after forming the S2 piece, only the S3 MD1 and S4 TD1 stretchings were performed at the same temperature and stretching ratio; then, the S8 extraction was performed under the same conditions; after the S8 extraction, the S6 TD2 stretching was performed at the same temperature and stretching ratio as that of S12 TD4 in Example 1; then, the S13 heat curing was performed at the same temperature and time as that in Example 1 to obtain a comparative sample.

[0132] The test results of Example 1 and Comparative Example 1 are shown as follows.

[0133]

Table 1

[0134] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 parts of antioxidant were blended and stirred in a mixture; then, the mixture was poured into the feed bin of an extruder, and 330 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; S1 extrusion was carried out through a die; S2 cooling and sheet forming were carried out with chill rolls.

[0135] S3 MD1 stretching and S4 TD1 stretching were sequentially carried out on the cast sheet. At this time, the stretching ratio was 8 times for both, the stretching temperature of S3 MD1 was 120 °C, and the stretching temperature of S4 TD1 was 125 °C.

[0136] For the stretching separator, S5 MD2 stretching was carried out at a stretching ratio of 2 times and a stretching temperature of 130 °C, and then S7 SBS1 stretching was carried out at a stretching ratio of 2×2 times and a stretching temperature of 130 °C.

[0137] In S8, dichloromethane was used as the extraction solvent, and the white oil was extracted step by step with an extraction time of 30 minutes.

[0138] For the separator after S8 extraction, S9 MD3 stretching was carried out at a stretching ratio of 2.5 times and a stretching temperature of 135 °C, and then S10 MD3 stretching was carried out at a stretching ratio of 2.5 times and a stretching temperature of 135 °C.

[0139] S12 TD4 stretching was carried out at a stretching ratio of 1.2 times and a stretching temperature of 135 °C, and then S13 heat curing was carried out at a heat curing temperature of 135 °C to obtain the lithium ion battery separator of the present disclosure.

[0140] (Comparative Example 2) The blending of the same raw materials and S1 extrusion were completed in the same process as in Example 2; after forming the S2 sheet, only S3 MD1 and S4 TD1 stretching were carried out at the same temperature and stretching ratio; then, S8 extraction was carried out under the same conditions; after S8 extraction, S6 TD2 stretching was carried out at the same temperature and ratio as that of S12 TD4 in Example 2; then, S13 heat curing was carried out at the same temperature and time as that in Example 2 to obtain a comparative sample.

[0141] The test results of Example 2 and Comparative Example 2 are shown as follows.

[0142]

Table 2

[0143] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 parts of antioxidant were blended and stirred in the mixture; then, the mixture was poured into the feed bin of the extruder, and 300 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; S1 extrusion was carried out through the die; S2 cooling and sheet formation were carried out with a chill roll.

[0144] S3 MD1 stretching and S4 TD1 stretching were sequentially carried out on the cast sheet. At this time, the stretching ratio was 8 times for both, the stretching temperature of S3 MD1 was 120 °C, and the stretching temperature of S4 TD1 was 125 °C.

[0145] For the stretching separator, S5 MD2 stretching was carried out at a stretching ratio of 2 times and a stretching temperature of 130 °C, and then S7 SBS1 stretching was carried out at a stretching ratio of 5×5 times and a stretching temperature of 130 °C.

[0146] In S8, dichloromethane was used as the extraction solvent, and the white oil was extracted step by step with an extraction time of 30 minutes.

[0147] For the separator after S8 extraction, S9 MD3 stretching was performed at a stretching ratio of 2.5 times and a stretching temperature of 135 °C, and then S10 MD3 stretching was performed at a stretching ratio of 2.5 times and a stretching temperature of 135 °C.

[0148] S12 TD4 stretching was performed at a stretching ratio of 1.2 times and a stretching temperature of 135 °C, and then S13 heat curing was performed at a heat curing temperature of 135 °C to obtain the lithium-ion battery separator of the present disclosure.

[0149] (Comparative Example 3) The blending of the same raw materials and S1 extrusion were completed by the same process as in Example 3; after forming S2 pieces, only S3 MD1 and S4 TD1 stretching were performed at the same temperature and stretching ratio; then S8 extraction was performed under the same conditions; after S8 extraction, S6 TD2 stretching was performed at the same temperature and stretching ratio as that of S12 TD4 in Example 3; then S13 heat curing was performed at the same temperature and time as that of Example 3 to obtain a comparative sample.

[0150] The test results of Example 3 and Comparative Example 3 are shown as follows.

[0151]

Table 3

[0152] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 part of antioxidant were blended and stirred in a mixture; then the mixture was poured into the feed bin of an extruder, and 330 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; S1 extrusion was performed through a die; S2 cooling and sheet forming were performed with a chill roll.

[0153] S3 MD1 stretching and S4 TD1 stretching were sequentially performed on the cast sheet. At this time, the stretching ratio was 8 times for both, the stretching temperature of S3 MD1 was 120 °C, and the stretching temperature of S4 TD1 was 125 °C.

[0154] For the extended separator, the S5 MD2 extension was carried out at a draw ratio of 2 times and a draw temperature of 130 °C, and then the S7 SBS1 extension was carried out at a draw ratio of 2×2 times and a draw temperature of 130 °C.

[0155] In S8, dichloromethane was used as the extraction solvent, and the white oil was extracted step by step with an extraction time of 30 minutes.

[0156] For the separator after S8 extraction, the S9 MD3 extension was carried out at a draw ratio of 2 times and a draw temperature of 135 °C, and then the S11 SBS2 extension was carried out at a draw ratio of 2×2 times and a draw temperature of 135 °C.

[0157] The S12 TD4 extension was carried out at a draw ratio of 1.2 times and a draw temperature of 135 °C, and then the S13 heat curing was carried out at a heat curing temperature of 135 °C to obtain the lithium ion battery separator of the present disclosure.

[0158] (Comparative Example 4) The blending of the same raw materials and the S1 extrusion by the same process were completed as in Example 4; after forming the S2 sheet, only the S3 MD1 and S4 TD1 extensions were carried out at the same temperature and draw ratio; then, the S8 extraction was carried out under the same conditions; after the S8 extraction, the S6 TD2 extension was carried out at the same temperature and draw ratio as that of S12 TD4 in Example 4; then, the S13 heat curing was carried out at the same temperature and time as that of Example 4 to obtain a comparative sample.

[0159] The test results of Example 4 and Comparative Example 4 are shown as follows.

[0160]

Table 4

[0161] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 parts of antioxidant were blended and stirred in a mixture; then, the mixture was poured into the feed bin of an extruder, and 300 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; S1 extrusion was carried out through a die; S2 cooling and sheet forming were carried out with a chill roll.

[0162] For the cast sheet, S3 MD1 stretching and S4 TD1 stretching were sequentially carried out. At this time, the stretching ratio was 8 times for both, the stretching temperature of S3 MD1 was 120 °C, and the stretching temperature of S4 TD1 was 125 °C.

[0163] For the stretching separator, S5 MD2 stretching was carried out at a stretching ratio of 2 times and a stretching temperature of 130 °C, and then S6 TD2 stretching was carried out at a stretching ratio of 2.5 times and a stretching temperature of 130 °C.

[0164] In S8, dichloromethane was used as the extraction solvent, and the white oil was extracted step by step with an extraction time of 30 minutes.

[0165] For the separator after S8 extraction, S9 MD3 stretching was carried out at a stretching ratio of 1.5 times and a stretching temperature of 135 °C, and then S11 SBS2 stretching was carried out at a stretching ratio of 5×5 times and a stretching temperature of 135 °C.

[0166] S12 TD4 stretching was carried out at a stretching ratio of 2 times and a stretching temperature of 135 °C, and then S13 heat curing was carried out at a heat curing temperature of 135 °C to obtain the lithium ion battery separator of the present disclosure.

[0167] (Comparative Example 5) The blending of the same raw materials and the S1 extrusion were completed in the same process as in Example 5; after forming the S2 sheet, the S3 MD1, S4 TD1, S5 MD2, and S6 TD2 stretching were carried out at the same temperature and stretching ratio; then, the S8 extraction was carried out under the same conditions; after the S8 extraction, the S12 TD4 stretching was carried out at the same temperature and stretching ratio as that of S12 TD4 in Example 5; then, the S13 heat curing was carried out at the same temperature and time as that of Example 5 to obtain a comparative sample.

[0168] Compared with Example 5, the S9 MD3 and S11 SBS2 stretching were deleted in the method of Comparative Example 5, and the other steps of the method remained the same. This comparative example was used to demonstrate the effect of this stretching on the physical properties of the separator.

[0169] The test results of Example 5 and Comparative Example 5 are shown as follows.

[0170]

Table 5

[0171] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 parts of antioxidant were blended into the mixture; then, the mixture was poured into the feed bin of the extruder, and 330 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; the S1 extrusion was carried out through the die; the S2 cooling and sheet forming were carried out with a chill roll.

[0172] The S3 MD1 stretching and S4 TD1 stretching were sequentially carried out on the cast sheet. At this time, the stretching ratio was 15 times for both, the stretching temperature of S3 MD1 was 120 °C, and the stretching temperature of S4 TD1 was 125 °C.

[0173] For the stretched separator, the S5 MD2 stretching was carried out at a stretching ratio of 6.7 times and a stretching temperature of 130 °C, and then the S6 TD2 stretching was carried out at a stretching ratio of 5.7 times and a stretching temperature of 130 °C.

[0174] In S8, dichloromethane was used as an extraction solvent, and white oil was extracted step by step with an extraction time of 30 minutes.

[0175] For the separator after S8 extraction, S9 MD3 stretching was carried out at a stretching ratio of 5 times and a stretching temperature of 135 °C, and then S10 MD3 stretching was carried out at a stretching ratio of 5 times and a stretching temperature of 135 °C.

[0176] S12 TD4 stretching was carried out at a stretching ratio of 1.2 times and a stretching temperature of 135 °C, and then S13 heat curing was carried out at a heat curing temperature of 135 °C to obtain the lithium ion battery separator of the present disclosure.

[0177] (Comparative Example 6) The blending of the same raw materials and S1 extrusion by the same process were completed as in Example 6; after forming S2 pieces, only S3 MD1 and S4 TD1 stretching were carried out at the same temperature and stretching ratio; then, S8 extraction was carried out under the same conditions; after S8 extraction, S6 TD2 stretching was carried out at the same temperature and stretching ratio as that of S12 TD4 in Example 6; then, S13 heat curing was carried out at the same temperature and time as that in Example 6 to obtain a comparative sample.

[0178] The test results of Example 6 and Comparative Example 6 are shown as follows.

[0179]

Table 6

[0180] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 parts of antioxidant were blended and stirred in a mixture; then, the mixture was poured into the feed bin of an extruder, and 330 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; S1 extrusion was carried out through a die; S2 cooling and sheet forming were carried out with a chill roll.

[0181] The S3 MD1 stretching and the S4 TD1 stretching were sequentially performed on the cast piece. At this time, the stretching ratio was 15 times in both cases. The stretching temperature of S3 MD1 was 120°C, and the stretching temperature of S4 TD1 was 125°C.

[0182] For the stretching separator, the S5 MD2 stretching was performed at a stretching ratio of 2 times and a stretching temperature of 130°C, and then the S7 SBS1 stretching was performed at a stretching ratio of 5×5 times and a stretching temperature of 130°C.

[0183] In S8, dichloromethane was used as the extraction solvent, and the white oil was extracted step by step with an extraction time of 30 minutes.

[0184] For the separator after the S8 extraction, the S9 MD3 stretching was performed at a stretching ratio of 3.3 times and a stretching temperature of 135°C, and then the S10 MD3 stretching was performed at a stretching ratio of 6.7 times and a stretching temperature of 135°C.

[0185] The S12 TD4 stretching was performed at a stretching ratio of 1.2 times and a stretching temperature of 135°C, and then the S13 heat curing was performed at a heat curing temperature of 135°C to obtain the lithium-ion battery separator of the present disclosure.

[0186] (Comparative Example 7) The blending of the same raw materials and the S1 extrusion were completed as in Example 7 by the same process; after forming the S2 piece, only the S3 MD1 and S4 TD1 stretchings were performed at the same temperature and stretching ratio; then, the S8 extraction was performed under the same conditions; after the S8 extraction, the S6 TD2 stretching was performed at the same temperature and stretching ratio as that of S12 TD4 in Example 7; then, the S13 heat curing was performed at the same temperature and time as that in Example 7 to obtain a comparative sample.

[0187] The test results of Example 7 and Comparative Example 7 are shown as follows.

[0188]

Table 7

[0189] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 parts of antioxidant were blended and stirred in a mixture; then, the mixture was poured into the feed bin of an extruder, and 330 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; S1 extrusion was carried out through a die; S2 cooling and sheet forming were carried out with a chill roll.

[0190] S3 MD1 stretching and S4 TD1 stretching were sequentially carried out on the cast sheet. At this time, the stretching ratio was 15 times in both cases, the stretching temperature of S3 MD1 was 120 °C, and the stretching temperature of S4 TD1 was 125 °C.

[0191] For the stretching separator, S5 MD2 stretching was carried out at a stretching ratio of 3.3 times and a stretching temperature of 130 °C, and then S6 TD2 stretching was carried out at a stretching ratio of 6.7 times and a stretching temperature of 130 °C.

[0192] In S8, dichloromethane was used as the extraction solvent, and the white oil was extracted step by step with an extraction time of 30 minutes.

[0193] For the separator after S8 extraction, S9 MD3 stretching was carried out at a stretching ratio of 2 times and a stretching temperature of 135 °C, and then S11 SBS2 stretching was carried out at a stretching ratio of 5×5 times and a stretching temperature of 135 °C.

[0194] S12 TD4 stretching was carried out at a stretching ratio of 1.2 times and a stretching temperature of 135 °C, and then S13 heat curing was carried out at a heat curing temperature of 135 °C to obtain the lithium-ion battery separator of the present disclosure.

[0195] (Comparative Example 8) The blending of the same raw materials and the S1 extrusion were completed as in Example 8 by the same process; after forming the S2 sheet, only the S3 MD1 and S4 TD1 stretching were carried out at the same temperature and stretching ratio; then, the S8 extraction was carried out under the same conditions; after the S8 extraction, the S6 TD2 stretching was carried out at the same temperature and stretching ratio as that of S12 TD4 in Example 8; then, the S13 heat curing was applied at the same temperature and time as that in Example 8 to obtain a comparative sample.

[0196] The test results of Example 8 and Comparative Example 8 are shown as follows.

[0197]

Table 8

[0198] 100 parts of high molecular weight polyethylene (average molecular weight 600,000) and 0.3 parts of antioxidant were blended and stirred in the mixture; then, the mixture was poured into the feed bin of the extruder, and 330 parts of white oil were added simultaneously; the screw and extrusion speed were adjusted to completely mix and plasticize the high molecular weight polyethylene and white oil; the S1 extrusion was carried out through the die; the S2 cooling and sheet forming were carried out with a chill roll.

[0199] The S3 MD1 stretching and S4 TD1 stretching were sequentially carried out on the cast sheet. At this time, the stretching ratio of S3 MD1 was 3.75 times, the stretching temperature was 120 °C, the stretching ratio of S4 TD1 was 15 times, and the stretching temperature was 125 °C.

[0200] For the stretching separator, the S5 MD2 stretching was carried out at a stretching ratio of 2 times and a stretching temperature of 130 °C, and then the S7 SBS1 stretching was carried out at a stretching ratio of 10×10 times and a stretching temperature of 130 °C.

[0201] In S8, dichloromethane was used as the extraction solvent, and the white oil was extracted step by step with an extraction time of 30 minutes.

[0202] For the separator after S8 extraction, S9 MD3 stretching was carried out at a stretching ratio of 2 times and a stretching temperature of 135 °C, and then S11 SBS2 stretching was carried out at a stretching ratio of 3.3×3.3 times and a stretching temperature of 135 °C.

[0203] S12 TD4 stretching was carried out at a stretching ratio of 1.2 times and a stretching temperature of 135 °C, and then S13 heat curing was carried out at a heat curing temperature of 135 °C to obtain the lithium-ion battery separator of the present disclosure.

[0204] (Comparative Example 9) Blending of the same raw materials and S1 extrusion were completed as in Example 9 by the same process; after forming S2 pieces, only S3 MD1 and S4 TD1 stretching were carried out at the same temperature and stretching ratio; then S8 extraction was carried out under the same conditions; after S8 extraction, S6 TD2 stretching was carried out at the same temperature and stretching ratio as that of S12 TD4 in Example 9; then S13 heat curing was applied at the same temperature and time as that in Example 9 to obtain a comparative sample.

[0205] The test results of Example 9 and Comparative Example 9 are shown as follows.

[0206]

Table 9

Explanation of symbols

[0207] S1 Extrusion S2 Cooling and sheet formation S3, S5, S9 Longitudinal stretching S4, S6, S10, S12 Transverse stretching S7, S11 Simultaneous biaxial stretching S8 Extraction S13 Heat curing

Claims

1. A method for manufacturing a lithium-ion battery separator, comprising: (1) mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore-forming agent to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast sheet; (2) sequentially performing a first longitudinal stretching and a first transverse stretching on the cast sheet to obtain a stretched film; (3) performing a second longitudinal stretching on the stretched film; (4) performing a second transverse stretching; (5) extracting the pore-forming agent in the separator to obtain an extracted separator; (6) performing a third longitudinal stretching on the extracted separator; (7) performing a third transverse stretching; and (8) sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator. A method comprising the above steps.

2. A method for manufacturing a lithium-ion battery separator, comprising: (1) mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore-forming agent to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast sheet; (2) sequentially performing a first longitudinal stretching and a first transverse stretching on the cast sheet to obtain a stretched film; (3) performing a second longitudinal stretching on the stretched film; (4) performing a second transverse stretching; (5) extracting the pore-forming agent in the separator to obtain an extracted separator; (6) performing a third longitudinal stretching on the extracted separator; (7) performing simultaneous biaxial stretching; and (8) sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator. A method comprising the above steps.

3. A method for manufacturing a lithium-ion battery separator, comprising: (1) mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore-forming agent to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast sheet; (2) sequentially performing a first longitudinal stretching and a first transverse stretching on the cast sheet to obtain a stretched film; (3) performing a second longitudinal stretching on the stretched film; and (4) performing simultaneous biaxial stretching. Step of extracting the pore former in the separator to obtain the separator after extraction; Step of performing a third longitudinal stretching on the separator after extraction; Step of performing a third transverse stretching; Step of sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator; A method comprising the above steps. **Claim 4** A method for manufacturing a lithium-ion battery separator, comprising: Step of mixing and heating a composition containing a polyolefin resin, an antioxidant, and a pore former to form a molten mixture, extruding the mixture through a die, and then cooling it to form a cast film; Step of sequentially performing a first longitudinal stretching and a first transverse stretching on the cast film to obtain a stretched film; Step of performing a second longitudinal stretching on the stretched film; Step of performing a first simultaneous biaxial stretching; Step of extracting the pore former in the separator to obtain the separator after extraction; Step of performing a third longitudinal stretching on the separator after extraction; Step of performing a second simultaneous biaxial stretching; Step of sequentially performing a fourth transverse stretching and heat curing to obtain a lithium-ion battery separator; A method comprising the above steps. **Claim 5** For both the first longitudinal stretching and the first transverse stretching in step (2), the stretching temperature ranges from 60°C to 150°C, and the stretching ratio ranges from 3 times to 15 times. The method for manufacturing a lithium-ion battery separator according to any one of claims 1 to 4. **Claim 6** For the second longitudinal stretching in step (3), the stretching temperature ranges from 60°C to 140°C, and the stretching ratio ranges from 2 times to 10 times. The method for manufacturing a lithium-ion battery separator according to any one of claims 1 to 4. **Claim 7** For the second transverse stretching in step (4), the stretching temperature ranges from 90°C to 140°C, and the stretching ratio ranges from 2 times to 10 times. The method for manufacturing a lithium-ion battery separator according to claim 1 or 2. **Claim 8** For the simultaneous biaxial stretching or the first simultaneous biaxial stretching in step (4), the stretching temperature ranges from 90°C to 140°C, and the stretching ratio ranges from 1.5×1.5 times to 12×12 times. The method for manufacturing a lithium-ion battery separator according to claim 3 or 4. **Claim 9** For the third longitudinal direction extension of step (6), the production method of the lithium ion battery separator according to any one of claims 1 to 4, wherein the extension temperature is in the range of 90°C to 150°C and the extension ratio is in the range of 1.5 times to 6 times.

10. For the third transverse direction extension of step (7), the production method of the lithium ion battery separator according to claim 1 or 3, wherein the extension temperature is in the range of 100°C to 150°C and the extension ratio in each direction is in the range of 1.5 times to 6 times.

11. For the simultaneous biaxial extension or the second simultaneous biaxial extension of step (7), the production method of the lithium ion battery separator according to claim 2 or 4, wherein the extension temperature is in the range of 100°C to 150°C and the extension ratio is in the range of 1.5×1.5 times to 6×6 times.

12. For the fourth transverse direction extension of step (8), the production method of the lithium ion battery separator according to any one of claims 1 to 4, wherein the extension temperature is in the range of 100°C to 150°C and the extension ratio is in the range of 1.1 times to 2 times.

13. For the heat curing in step (8), the production method of the lithium ion battery separator according to any one of claims 1 to 4, wherein the temperature is in the range of 110°C to 150°C.

14. The thickness of the separator is in the range of 3 μm to 8 μm, and the transverse tensile strength of the separator is more than 5000 kgf / cm ２ exceeding, and the longitudinal tensile strength of the separator is more than 5000 kgf / cm ２ exceeding, the puncture strength per unit thickness of the separator is more than 120 gf / μm, the porosity of the separator is in the range of 30% to 60%, and the median pore diameter of the separator is in the range of 20 nm to 55 nm, a lithium-ion battery separator.

15. The transverse tensile strength of the separator is in the range of 5000 kgf / cm ２ to 7500 kgf / cm ２ and the longitudinal tensile strength of the separator is in the range of 5000 kgf / cm ２ to 7500 kgf / cm ２ and / or the puncture strength per unit thickness of the separator is in the range of 120 gf / μm to 200 gf / μm, the lithium ion battery separator according to claim 14.

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