High-purity polypropylene having excellent electrical properties for secondary battery separator, manufacturing method thereof, and secondary battery separator using same

Abstract

Disclosed are high-purity polypropylene for a secondary battery separator, a method for manufacturing same, and a secondary battery separator using same, the high-purity polypropylene having excellent insulation properties due to few electrical defects and being capable of improving productivity in separator production. The present invention provides polypropylene for a secondary battery separator, a method for manufacturing same, and a secondary battery separator using same, the polypropylene having an inorganic residue content of 30 ppm or less, a low-molecular-weight content of 0.5 wt% or less with a molecular weight of 1,000 g / mol or less, and a GC-FID value of n-C15 or less of 15 pA·s or less.

Description

High-purity polypropylene for secondary battery separators with excellent electrical properties, a method for manufacturing the same, and a secondary battery separator using the same

[0001] The present invention relates to polypropylene for secondary battery separators, and more specifically, to high-purity polypropylene for secondary battery separators having excellent electrical properties, a method for manufacturing the same, and a secondary battery separator using the same.

[0002] This application claims priority and interest to Korean Patent Application No. 10-2024-0164426 filed on November 18, 2024, the full text of which is incorporated herein by reference.

[0003] Since the commercialization of lithium-ion batteries, the development of new separators exhibiting excellent mechanical and electrical properties has continued. Currently, microporous separators utilizing polyolefin-based materials form the mainstream of lithium-ion battery separators. In the case of existing polyolefin-based materials used for microporous separators, various inorganic residues remain from the catalysts, co-catalysts, and various additives used during manufacturing. When separators are formed using these materials, these inorganic residues often act as electrical defects within the separator, leading to a decrease in insulation performance. While wet separator manufacturing processes, which primarily use polyethylene, include an extraction step utilizing organic solvents to partially reduce these inorganic residues, dry separator manufacturing processes, which primarily use polypropylene, lack this step, resulting in the inorganic residues remaining within the separator.

[0004] In addition, small molecular weight oligomers, which are inevitably generated during polyolefin polymerization, are easily oxidized by high heat and friction during the extrusion process for separator manufacturing, leading to the generation of fumes harmful to the human body. Inorganic residues are also known to be closely linked to the oxidation of polypropylene. The generation of excessive fumes causes discomfort to workers, and particularly during long-term production, the accumulation of these oxidized substances can lead to the formation of oil deposits on the manufacturing line, thereby reducing productivity.

[0005] To address these issues, a separate de-ashing process may be applied within the polypropylene manufacturing process itself to separate and purify inorganic residues, oligomers, etc., using organic solvents and water; however, applying such a process has the disadvantage of increasing facility investment, maintenance costs, and waste disposal costs.

[0006] Korean registered patent No. 10-2624224 discloses a method for producing polypropylene with low organic solvent solubility, high purity, low odor, and excellent mechanical and electrical properties by utilizing a hexane slurry process, but it describes a method for producing polypropylene using a metallocene catalyst with low catalytic activity.

[0007] In addition, Korean published patent No. 10-2015-0091326 relates to a high-performance Ziegler-Natta catalyst system and discloses a highly active catalyst used in polypropylene polymerization, but does not mention the improvement of electrical characteristics when applied as a secondary battery separator.

[0008] The present invention aims to provide high-purity polypropylene for secondary battery separators that has excellent insulation properties due to a small number of electrical defect sites and can improve productivity during separator production, a method for manufacturing the same, and a secondary battery separator using the same.

[0009] To solve the above problem, the present invention provides an inorganic residue content of 30 ppm or less measured according to the following method, a content of low molecular weight having a molecular weight of 1,000 g / mol or less of 0.5 wt% or less, and nC 15 The present invention provides polypropylene for secondary battery separators having a GC-FID value of 15ρA·s or less.

[0010] [Method for Measuring Inorganic Residue Content]

[0011] The content of each inorganic residue was measured for 0.1 g of the above polypropylene sample through ICP (inductively coupled plasma) analysis;

[0012] [Method for Measuring Low Molecular Weight Content]

[0013] The content of low molecular weight compounds extracted by immersing 5 g of the above polypropylene in heptane solvent in an oil bath at 101°C for 15 hours was measured to have a molecular weight of 1,000 g / mol or less using Gel Permeation Chromatography (GPC, Agilent) according to ASTM D3536 standard;

[0014] [GC-FID Value Measurement Method]

[0015] The peak area of ​​the portion having a hydrocarbon with 3 to 15 carbon atoms was measured in a graph obtained by gas chromatography flame ionization detector analysis after pre-treating the above 5 g of polypropylene by immersing it in 30 ml of hexane solvent at 80°C for 15 hours.

[0016] To solve the above additional problem, the present invention provides a separator for a secondary battery comprising the polypropylene.

[0017] In addition, the above separator has an electrical defect count of 50 or fewer measured according to the following method, and an initial resistance of 3×10 after voltage application. 10A separator for a secondary battery is provided, characterized by having a value of Ω or higher.

[0018] [measurement method]

[0019] The above polypropylene for the separator is extruded using a twin-screw extruder at 220 to 250°C using a T-die method to form a sheet, and then sequentially stretched in the MD and TD directions within a stretcher to manufacture a single-layer porous separator with a thickness of 15 μm; a voltage of 1,000 V is applied to a separator sample measuring 10×10 cm (applied once every 0.1 seconds, for a total of 100 times over 10 seconds) and each resistance is measured, wherein the resistance immediately after application is taken as the initial resistance, and each resistance is 10 7 If Ω or less, it is counted as a defect.

[0020] To solve the above additional problem, the present invention provides a method for producing polypropylene for a secondary battery separator according to claim 1 by polymerizing a propylene monomer in the presence of a Ziegler-Natta catalyst, wherein the catalyst has an activity of 30 kg-PP / g-cat or more, the amount of the catalyst used is 0.05 g-catalyst / kg-propylene or less, and the amount of the co-catalyst used is 0.2 g-co-catalyst / kg-propylene or less.

[0021] In addition, the present invention provides a method for manufacturing polypropylene for a secondary battery separator, characterized in that the above-mentioned co-catalyst is one or more selected from the group consisting of trimethylaluminum, triethylaluminum, triisobutylaluminum, and trioctylaluminum.

[0022] In addition, a method for manufacturing polypropylene for a secondary battery separator is provided, comprising the step of adding a neutralizing agent to the polymer produced by the above polymerization reaction and kneading, wherein the amount of the neutralizing agent added is less than 300 ppm with respect to the weight of the polymer.

[0023] In addition, the present invention provides a method for manufacturing polypropylene for a secondary battery separator, characterized in that the above neutralizing agent is one or more selected from the group consisting of calcium stearate, hydrotalcite, and zinc oxide.

[0024] According to the present invention, by reducing the amount of inorganic residue contributed from the catalyst and co-catalyst and minimizing the amount of neutralizing agent used as an additive, the overall inorganic residue content can be reduced by more than 40% compared to the existing amount, and by applying a highly active catalyst, the effect of relatively reducing the oligomer content can be obtained. Thus, by manufacturing a separator using polypropylene with reduced inorganic residue, the electrical defect sites are reduced, thereby exhibiting excellent insulation properties. Furthermore, along with the reduction in oligomer content, high-purity polypropylene, a method for manufacturing the same, and a separator for a secondary battery using the same can be provided, which can improve productivity by reducing fumes and oil precipitates generated during separator production.

[0025] Figure 1 is a photograph showing whether fumes were generated during the process of manufacturing a separator using polypropylene prepared according to the examples and comparative examples.

[0026] The present invention will be described in detail below through preferred embodiments. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe their invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, the configurations of the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent all aspects of the technical spirit of the present invention; thus, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0027]

[0028] The present invention has an inorganic residue content of 30 ppm or less measured according to the following method, a low molecular weight content of 0.5 wt% or less with a molecular weight of 1,000 g / mol or less, and nC 15 A polypropylene for secondary battery separators having a GC-FID value of 15ρA·s or less is disclosed.

[0029] [Method for Measuring Inorganic Residue Content]

[0030] The content of each inorganic residue was measured for 0.1 g of the above polypropylene sample through ICP (inductively coupled plasma) analysis;

[0031] [Method for Measuring Low Molecular Weight Content]

[0032] The content of low molecular weight compounds extracted by immersing 5 g of the above polypropylene in heptane solvent in an oil bath at 101°C for 15 hours was measured to have a molecular weight of 1,000 g / mol or less using Gel Permeation Chromatography (GPC, Agilent) according to ASTM D3536 standard;

[0033] [GC-FID Value Measurement Method]

[0034] The peak area of ​​the portion having a hydrocarbon with 3 to 15 carbon atoms was measured in a graph obtained by gas chromatography flame ionization detector analysis after pre-treating the above 5 g of polypropylene by immersing it in 30 ml of hexane solvent at 80°C for 15 hours.

[0035] The present invention enables the polymerization of polypropylene with a small amount of main catalyst and co-catalyst by applying a highly active Ziegler-Natta catalyst, thereby reducing the amount of inorganic residue contributed by the catalyst and co-catalyst and reducing the content of oligomers, so that electrical properties are improved when manufacturing a separation membrane using the same, and productivity is improved by reducing fumes generated during separation membrane production.

[0036] In the polypropylene according to the present invention, the inorganic residue is not limited to any specific type as long as it is various inorganic substances remaining from catalysts, co-catalysts, and various additives, but may be, for example, aluminum (Al), titanium (Ti), calcium (Ca), magnesium (Mg), silicon (Si), phosphorus (P), etc. If the content of such inorganic residue exceeds 30 ppm, the inorganic residue portion acts as an electrical defect within the membrane formed by applying it, thereby degrading the electrical properties. In this regard, it is preferable that the content of the inorganic residue be 28 ppm or less, and more preferably 27 ppm or less.

[0037] In addition, the polypropylene according to the present invention has a significantly reduced inorganic residue content as described above, and also has a significantly reduced content of low molecular weight with a molecular weight of 1,000 g / mol or less, which is 0.5 weight% or less, and nC 15 The GC-FID value below is 15ρA·s or less, thereby improving process productivity without generating fumes during the extrusion process for membrane manufacturing, even without the addition of a separate process for separating and purifying such low molecular weights. In this regard, it is preferable that the content of the low molecular weight is 0.45 wt% or less and the GC-FID value is 10ρA·s or less.

[0038] In this way, the present invention provides a separator for a secondary battery with improved electrical characteristics by manufacturing a separator using polypropylene with reduced inorganic residue and low molecular weight content, thereby significantly reducing the generation of fumes, oil precipitates, etc. during separator production and having fewer electrical defect sites.

[0039] Specifically, the separator for a secondary battery according to the present invention has an electrical defect count of 50 or fewer measured according to the following method, and an initial resistance of 3×10 after voltage application. 10 It may be greater than Ω, preferably the number of electrical defects is 40 or less, and the initial resistance after voltage application is 4×10 10 It can be greater than Ω.

[0040] [measurement method]

[0041] The above polypropylene for the separator is extruded using a twin-screw extruder at 220 to 250°C using a T-die method to form a sheet, and then sequentially stretched in the MD and TD directions within a stretcher to manufacture a single-layer porous separator with a thickness of 15 μm; a voltage of 1,000 V is applied to a separator sample measuring 10×10 cm (applied once every 0.1 seconds, for a total of 100 times over 10 seconds) and each resistance is measured, wherein the resistance immediately after application is taken as the initial resistance, and each resistance is 10 7 If Ω or less, it is counted as a defect.

[0042] Hereinafter, a method for manufacturing polypropylene for a secondary battery separator according to the present invention will be described in detail.

[0043] The present invention discloses a method for producing polypropylene for a secondary battery separator according to claim 1 by polymerizing propylene monomers in the presence of a Ziegler-Natta catalyst, wherein the catalyst has an activity of 30 kg-PP / g-cat or more, the amount of the catalyst used is 0.05 g-catalyst / kg-propylene or less, and the amount of the co-catalyst used is 0.2 g-co-catalyst / kg-propylene or less.

[0044] In the present invention, the Ziegler-Natta catalyst is a solid catalyst prepared by, for example, reacting a magnesium compound with an alkanediol having 3 to 15 carbon atoms substituted or unsubstituted with an alkyl group having 1 to 5 carbon atoms and a benzoyl halide compound to prepare a magnesium compound solution, reacting the magnesium compound solution with a transition metal compound to prepare a support, and reacting the support with a transition metal compound. Regarding specific manufacturing methods, Registered Patent No. 1373775 in the name of the applicant is cited by reference.

[0045] In the present invention, a highly active Ziegler-Natta catalyst with an activity of 30 kg-PP / g-cat or more, preferably 35 kg-PP / g-cat or more, is applied to minimize the amounts of catalyst and co-catalyst applied to the polymerization to 0.05 g-catalyst / kg-propylene or less and 0.2 g-co-catalyst / kg-propylene or less, preferably 0.04 g-catalyst / kg-propylene or less and 0.1 g-co-catalyst / kg-propylene or less, respectively, and more preferably 0.03 g-catalyst / kg-propylene or less and 0.07 g-co-catalyst / kg-propylene or less, respectively, thereby enabling the polymerization of polypropylene with a small amount of main catalyst and co-catalyst, which reduces the amount of inorganic residue contributed by the catalyst and co-catalyst, and thereby improves the electrical properties of the separation membrane produced therefrom.

[0046] In the present invention, the production of polypropylene for secondary battery separators is not particularly limited, but preferably, the propylene monomer is polymerized in the presence of the solid catalyst, and a bimodal mode process may be applied. That is, the propylene monomer polymerization reaction may be made such that highly crystalline polypropylene is produced by including a) a step of obtaining high molecular weight polypropylene having a weight-average molecular weight of 500,000 to 800,000 g / mol in a first reactor and b) a step of obtaining low molecular weight polypropylene having a weight-average molecular weight of 150,000 to 450,000 g / mol in a second reactor.

[0047] In the present invention, the propylene polymerization reaction may be carried out in a gas phase, a liquid phase, or a solution phase. When performing the polymerization reaction in a liquid phase, a hydrocarbon solvent may be used, or propylene itself may be used as a solvent. The polymerization reaction temperature may be 0 to 200°C, preferably 50 to 150°C. If the reaction temperature is below 0°C, the activity of the catalyst may decrease, and if it exceeds 200°C, stereoregularity may decrease. The pressure conditions during polymerization may be 1 to 100 atmospheres, preferably 2 to 30 atmospheres. If the pressure exceeds 100 atmospheres, it is undesirable from an industrial and economic perspective. The polymerization reaction can be carried out by any of batch, semi-continuous, or continuous methods; however, in the present invention, a continuous bimodal mode process is applied so that high molecular weight polypropylene having a weight-average molecular weight of 500,000 to 800,000 g / mol in a first reactor and low molecular weight polypropylene having a weight-average molecular weight of 150,000 to 450,000 g / mol in a second reactor are produced in a weight ratio of 8:2 to 4:6, preferably high molecular weight polypropylene having a weight-average molecular weight of 550,000 to 750,000 g / mol in the first reactor and low molecular weight polypropylene having a weight-average molecular weight of 200,000 to 350,000 g / mol in the second reactor are produced in a weight ratio of 7:3 to 5:5, so that the weight-average molecular weight of the final polypropylene is 350,000 to It can be manufactured to have a molecular weight distribution (Mw / Mn) of 5 to 10 and a molecular weight of 650,000 g / mol.

[0048] Here, a co-catalyst and an external electron donor are introduced into the first reactor, and as the transition metal compound is reduced in the solid catalyst, a portion of the internal electron donor present in the solid catalyst is removed, and the external electron donor binds to this vacant space to allow the polymerization reaction to proceed.

[0049] The above co-catalyst and external electron donor are not particularly limited as long as they are components used in the manufacture of polypropylene for conventional secondary battery dry separators; for example, the above co-catalyst may include trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, etc., and the above external electron donor may include cyclohexylmethyldimethoxysilane, dicyclopentyldimethoxysilane, diisopropyldimethoxysilane, vinyltriethoxysilane, triethylmethoxysilane, trimethylethoxysilane, dicyclopentyldiethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, diphenyldiethoxysilane, phenylpropyldimethoxysilane, fennyltrimethoxysilane, tertiarybutyltrimethoxysilane, cyclohexylethyldimethoxysilane, cyclohexylmethyldimethoxysilane, etc. Cyclopentyltriethoxysilane, diisobutyldiethoxysilane, isobutyltriethoxysilane, normalpropyltrimethoxysilane, isopropyltrimethoxysilane, cycloheptylmethyldiethoxysilane, dicycloheptyldiethoxysilane, etc. may be used, and preferably, triethylaluminum (TEAL) may be used as the co-catalyst and dicyclopentyldimethoxysilane as the external electron donor.

[0050] Polypropylene is obtained through the above propylene polymerization reaction, and the polymerized polypropylene may be further coated with antioxidants, neutralizing agents, nucleating agents, etc. during the mixing process, and a porous film can be dry-manufactured by stretching the extruded sheet.

[0051] Here, the present invention has confirmed that the content of the neutralizing agent formulation among the additives significantly affects productivity and electrical characteristics of the separator during production. That is, the amount of the neutralizing agent added may be less than 300 ppm with respect to the weight of the polymerized polypropylene, preferably 200 ppm or less, and more preferably 150 ppm or less. If the neutralizing agent content is 300 ppm or more, the electrical characteristics may deteriorate during manufacturing into a separator, and productivity may decrease due to increased generation of fumes, etc.

[0052] Examples of such neutralizing agents may be used, such as calcium stearate, hydrotalcite, zinc oxide, etc., and preferably, calcium stearate may be used.

[0053] The method used to fabricate separation membranes using the dry process for the aforementioned polypropylene may involve orienting the polymer crystal portions in a specific direction and then rupturing the relatively weak amorphous portions through cold stretching to form pores. Additionally, the membranes may be fabricated due to differences in polymer crystal shape and crystallization temperature, and nucleating agents are added when fabricated in this manner. Therefore, it is believed that the characteristics of the manufactured microporous membranes are determined not only by the degree of orientation and the shape of the polymer crystal portions but also by the additives and modifiers added.

[0054] For example, in the present invention, the separation membrane can be manufactured by using the above-mentioned polypropylene to extrude it in a T-die manner at a temperature of 200 to 230°C using a twin-screw extruder to form a sheet, and then performing simultaneous and sequential stretching in the MD and TD directions in a stretching machine to form a porous film.

[0055] The present invention will be explained in more detail below through specific embodiments and comparative examples.

[0056]

[0057] Example 1

[0058] Polypropylene polymerization was performed using a bimodal process via bulk polymerization with a highly active Ziegler-Natta catalyst and propylene as a solvent. In a pre-polymerization reactor at a reaction temperature of 20°C, while maintaining a propylene atmosphere, an active catalyst of approximately 36 kg-PP / g-cat was introduced in an amount of 0.02 g-catalyst / kg-propylene, in a weight ratio with respect to the propylene introduced into the pre- and first reactors. Simultaneously, triethylaluminum (TEAL) (co-catalyst) and dicyclopentyldimethoxysilane (external electron donor) were introduced. At this time, triethylaluminum was introduced in an amount of 0.04 g-teal / kg-propylene, in a weight ratio with respect to the propylene introduced into the pre- and first reactors. Subsequently, propylene was introduced into the first reactor at a reaction temperature of 70°C, and polymerization was carried out by operating a stirrer. Subsequently, the unreacted polypropylene was transferred to the second reactor, and additional propylene was added and the process was carried out in the same manner as above, but with the polymerization time adjusted to produce low molecular weight polypropylene having a relatively high melt index. The polypropylene produced by blending the polypropylene polymerized in the first and second reactors was obtained after drying, and subsequently, an additive containing 80 ppm of calcium stearate (neutralizing agent) and 1,500 ppm of a phenolic antioxidant was added to the polypropylene powder and granulated to produce pellet-shaped polypropylene.

[0059]

[0060] Example 2, Comparative Examples 1 to 3

[0061] Pellet-shaped polypropylene was prepared in the same manner as in Example 1, except that the catalyst exhibiting the activity listed in Table 1 below was used in Example 1, and the content of the co-catalyst, external electron donor, and neutralizing agent was adjusted as described in Table 1 below.

[0062]

[0063] Experimental Example

[0064] The polypropylene prepared in the above examples and comparative examples and the separator prepared using it were evaluated for inorganic residue content, molecular weight characteristics, low molecular weight content, GC-FID value, electrical characteristics, and fume generation according to the following method, and the results are shown in Table 1 and Figure 1 (fume generation).

[0065] [measurement method]

[0066] (1) Mineral residue content

[0067] The content of each inorganic residue was measured for 0.1 g of the above polypropylene sample through ICP (inductively coupled plasma) analysis.

[0068] (2) Molecular weight characteristics

[0069] The weight-average molecular weight (Mw) and molecular weight distribution (MWD, Mw / Mn) were measured using the GPC analysis method in accordance with ASTM D3536.

[0070] (3) Low molecular weight content

[0071] The content of the low molecular weight extracted by immersing 5 g of the above polypropylene in heptane solvent in an oil bath at a temperature of 101°C for 15 hours was measured using gel permeation chromatography (GPC, Agilent) according to ASTM D3536 standards to determine the molecular weight of 1,000 g / mol or less.

[0072] (4) GC-FID value

[0073] The peak area of ​​the portion having hydrocarbons with 3 to 15 carbon atoms was measured in a graph obtained through gas chromatography flame ionization detector analysis after pre-treating 5 g of the above polypropylene by immersing it in 30 ml of hexane solvent at 80°C for 15 hours.

[0074] (5) Electrical characteristics

[0075] The above polypropylene for the separator is extruded using a twin-screw extruder at 220 to 250°C using a T-die method to form a sheet, and then sequentially stretched in the MD and TD directions within a stretcher to manufacture a single-layer porous separator with a thickness of 15 μm; a voltage of 1,000 V is applied to a separator sample measuring 10×10 cm (applied once every 0.1 seconds, for a total of 100 times over 10 seconds) and each resistance is measured, wherein the resistance immediately after application is taken as the initial resistance, and each resistance is 10 7 If it is less than Ω, it was counted as a defect.

[0076] (6) Whether fumes are generated

[0077] The generation of fumes during the above sheet molding process was observed visually, and the generation of fumes during the separator manufacturing process using polypropylene prepared according to each example and comparative example is shown in the photograph of FIG. 1.

[0078]

[0079]

[0080]

[0081] Referring to Table 1, it can be seen that when the catalyst and co-catalyst content is minimized by applying a highly active Ziegler-Natta catalyst according to the present invention (Examples 1 and 2), the inorganic residue content is significantly reduced and the oligomer content is minimized, thereby achieving excellent electrical properties through improved insulation when manufacturing a separator, and significantly reducing the amount of fumes generated during extrusion, which also improves productivity.

[0082] In this regard, it can be seen that when a relatively low-activity Ziegler-Natta catalyst is used (Comparative Examples 1 and 2), the inorganic residue content and oligomer content increase, the amount of fumes generated increases, and the electrical properties are significantly degraded.

[0083] Meanwhile, it is confirmed that electrical characteristics and productivity can be maximized during membrane manufacturing by minimizing the neutralizing agent content, as the amount of fumes generated increases and electrical characteristics also deteriorate when the neutralizing agent content is excessive even when a highly active Ziegler-Natta catalyst is applied (Comparative Example 3).

[0084]

[0085] Preferred embodiments of the present invention have been described in detail above. The description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without changing the technical concept or essential features of the present invention.

[0086] Accordingly, the scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning, scope, and equivalent concepts of the claims should be interpreted as being included within the scope of the present invention.

Claims

1. The inorganic residue content measured according to the following method is 30 ppm or less, and the content of low molecular weight substances with a molecular weight of 1,000 g / mol or less is 0.5 wt% or less, and nC 15 Polypropylene for secondary battery separators having a GC-FID value of 15ρA·s or less: [Method for Measuring Inorganic Residue Content] The content of each inorganic residue was measured for 0.1 g of the above polypropylene sample through ICP (inductively coupled plasma) analysis; [Method for Measuring Low Molecular Weight Content] The content of low molecular weight compounds extracted by immersing 5 g of the above polypropylene in heptane solvent in an oil bath at 101°C for 15 hours was measured to have a molecular weight of 1,000 g / mol or less using Gel Permeation Chromatography (GPC, Agilent) according to ASTM D3536 standard; [GC-FID Value Measurement Method] The peak area of ​​the portion having a hydrocarbon with 3 to 15 carbon atoms was measured in a graph obtained by gas chromatography flame ionization detector analysis after pre-treating the above 5 g of polypropylene by immersing it in 30 ml of hexane solvent at 80°C for 15 hours.

2. A separator for a secondary battery comprising the polypropylene of claim 1.

3. In Paragraph 2, The above separator has an electrical defect count of 50 or fewer measured according to the following method, and an initial resistance of 3×10 after voltage application. 10 Separator for secondary batteries characterized by having an Ω or greater: [measurement method] The above polypropylene for the separator is extruded using a twin-screw extruder at 220 to 250°C using a T-die method to form a sheet, and then sequentially stretched in the MD and TD directions within a stretcher to manufacture a single-layer porous separator with a thickness of 15 μm; a voltage of 1,000 V is applied to a separator sample measuring 10×10 cm (applied once every 0.1 seconds, for a total of 100 times over 10 seconds) and each resistance is measured, wherein the resistance immediately after application is taken as the initial resistance, and each resistance is 10 7 If Ω or less, it is counted as a defect.

4. A method for producing polypropylene for a secondary battery separator according to claim 1 by polymerizing propylene monomers in the presence of a Ziegler-Natta catalyst, A method for manufacturing polypropylene for a secondary battery separator, wherein the catalyst has an activity of 30 kg-PP / g-cat or more, the amount of the catalyst used is 0.05 g-catalyst / kg-propylene or less, and the amount of the co-catalyst used is 0.2 g-co-catalyst / kg-propylene or less.

5. In Paragraph 4, A method for manufacturing polypropylene for a secondary battery separator, characterized in that the above-mentioned co-catalyst is one or more selected from the group consisting of trimethylaluminum, triethylaluminum, triisobutylaluminum, and trioctylaluminum.

6. In Paragraph 4, A method for manufacturing polypropylene for a secondary battery separator, comprising the step of adding a neutralizing agent to the polymer produced by the above polymerization reaction and kneading, wherein the amount of the neutralizing agent added is less than 300 ppm with respect to the weight of the polymer.

7. In Paragraph 6, A method for manufacturing polypropylene for a secondary battery separator, characterized in that the above neutralizing agent is one or more selected from the group consisting of calcium stearate, hydrotalcite, and zinc oxide.

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