Separator for electrochemical device and electrochemical device including the same

Abstract

The present invention relates to a separation membrane for an electrochemical element and an electrochemical element including the same. The present invention relates to a separation membrane for an electrochemical element and an electrochemical element including the same, in which a polymer resin contained in a porous polymer substrate is selected from specific types, and the polydispersity index, weight average molecular weight, content of an elution fraction at a specific temperature, and indentation depth of a polymer eluted at a high temperature are adjusted to improve the compression resistance and breakdown voltage of the separation membrane.

Description

[Technical Field]

[0001] This application claims priority to Korean Patent Applications Nos. 10-2023-0051176, 10-2023-0055916, and 10-2023-0065754, filed with the Korean Intellectual Property Office on April 19, 2023, April 28, 2023, and May 22, 2023, respectively, the contents of which are incorporated herein by reference in their entireties.

[0002] The present invention relates to a separator for an electrochemical device and an electrochemical device including the same. [Background technology]

[0003] Among the components of an electrochemical device, the separator is a porous polymer matrix located between the positive and negative electrodes, which serves to separate the positive and negative electrodes, prevent electrical shorts between the two electrodes, and allow electrolyte and ions to pass through. Although the separator itself does not participate in the electrochemical reaction, its physical properties, such as its wettability with the electrolyte, porosity, and thermal shrinkage, affect the performance and safety of the electrochemical device.

[0004] Therefore, various methods have been attempted to add a coating layer to a porous polymer substrate to enhance the physical properties of the separator, and to change the physical properties of the coating layer by adding various substances to the coating layer. For example, an inorganic substance may be added to the coating layer to improve the mechanical strength of the separator, or an inorganic substance or hydrate may be added to the coating layer to improve the flame retardancy and heat resistance of the polymer substrate. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a separator for an electrochemical device, which can improve the breakdown voltage of the separator by preventing deformation of the separator and damage to pores caused by pressure applied during a lamination process for bonding the separator to an electrode, and an electrochemical device including the separator.

[0006] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0007] One embodiment of the present invention provides a separator for an electrochemical device, comprising a porous polymer substrate, the porous polymer substrate comprising an amorphous polymer resin and a crystalline polymer resin, and a weight-average molecular weight (Mw) of an eluate obtained by subjecting the porous polymer substrate to temperature rising elution fractionation (TREF) is about 100,000 or more.

[0008] According to one embodiment of the present invention, the porous polymer substrate may contain about 40% by weight or less of a fraction eluted at a temperature of 35° C. or less by temperature rising elution fractionation.

[0009] According to one embodiment of the present invention, the content of the amorphous polymer resin in the porous polymer substrate may be about 40% by weight or less.

[0010] According to one embodiment of the present invention, the content of the crystalline polymer resin in the porous polymer substrate may be about 60% by weight or more.

[0011] According to one embodiment of the present invention, the weight ratio of the amorphous polymer resin to the crystalline polymer resin in the porous polymer substrate may be about 1:1 to 10:1.

[0012] According to one embodiment of the present invention, the deviation in indentation depth in the porous polymer substrate may be about −5 nm or more and 5 nm or less.

[0013] According to one embodiment of the present invention, the porous polymer substrate includes a polyolefin-based resin, the amorphous polymer resin may be an amorphous polyolefin-based resin, and the crystalline polymer resin may be a crystalline polyolefin-based resin.

[0014] According to one embodiment of the present invention, the polyolefin resin may be one selected from the group consisting of polyethylene; polypropylene; polybutylene; polypentene: polyhexene: polyoctene; copolymers of one or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; and combinations thereof.

[0015] According to one embodiment of the present invention, the polyolefin resin may have an average of about 500 or less short chain branches (SCB) per 1000 total carbon atoms.

[0016] According to one embodiment of the present invention, the polyolefin resin may have a melt index (ASTM D1238, 190° C., 2.16 kg) of about 0.1 g / 10 min to 0.3 g / 10 min.

[0017] According to one embodiment of the present invention, the weight average molecular weight (Mw) of the porous polymer substrate may be about 500,000 or more and 1,000,000 or less.

[0018] According to one embodiment of the present invention, the polydispersity index (PDI) of the eluate may be about 5 or greater.

[0019] According to one embodiment of the present invention, when a pressure of 8 MPa is applied at 70° C., any one or more of the following (i) to (iii) can be satisfied.

[0020] (i) the thickness reduction rate of the porous polymer substrate is about 10% or less, as defined by the following Equation 1:

[0021] [Formula 1] Thickness reduction rate (%) = (thickness of porous polymer substrate before applying pressure - thickness of porous polymer substrate after applying pressure) / thickness of porous polymer substrate before applying pressure x 100

[0022] (ii) the increase in air permeability of the porous polymer substrate after compression is about 185% or less, as defined by the following Equation 2:

[0023] [Formula 2] Air permeability increase rate (%) = (air permeability after compression - air permeability before compression) / (air permeability before compression) x 100

[0024] (iii) The dielectric breakdown voltage of the porous polymer substrate is about 1,000 V or more.

[0025] According to one embodiment of the present invention, the porous polymer substrate may have a thickness of about 1 μm or more and 30 μm or less.

[0026] One embodiment of the present invention provides an electrochemical device comprising: a positive electrode; a negative electrode; and the separator interposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0027] A separator for an electrochemical device according to an embodiment of the present invention can improve the weight-average molecular weight and polydispersity index of an eluate eluted at high temperatures, minimize deformation due to pressure applied during a lamination process, and improve the breakdown voltage.

[0028] An electrochemical device according to an embodiment of the present invention can prevent Hi-Pot failure and low voltage failure, thereby improving battery performance. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a diagram illustrating a schematic diagram of a method for measuring indentation depth.

[0030] In some of the accompanying drawings, corresponding components are given the same reference numerals. Those skilled in the art will understand that the drawings illustrate elements simply and clearly and are not necessarily drawn to scale. For example, to facilitate understanding of the various embodiments, the dimensions of some elements shown in the drawings may be exaggerated relative to other elements. Furthermore, elements of the known art that are useful or essential in commercially viable embodiments are often not depicted so as not to obscure the spirit of the various embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0032] In this specification, "A and / or B" means "A and B, or A or B."

[0033] In this specification, when a component is said to be "provided on" another component, this does not exclude other components from being disposed therebetween, but means that other components may be further disposed thereon, unless otherwise specified.

[0034] As used in this specification, the terms "about," "approximately," and "substantially" are used to mean a range of or close to a numerical value or degree, taking into consideration inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly exploiting the disclosure content in which exact or absolute numerical values ​​are mentioned, which are provided to aid in the understanding of the present invention.

[0035] As used herein, the characteristic of "having pores" means that an object contains a plurality of pores, and the pores are interconnected to allow gas and / or liquid fluids to pass from one side of the object to the other side.

[0036] In this specification, the separator has a porous property including a large number of pores, and serves as a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode in the electrochemical device.

[0037] The present invention will be described in further detail below.

[0038] In a secondary battery electrode assembly, the separator may be bonded to the electrode through a lamination process, and a polymer binder may be added to the coating layer composition of the separator to ensure adhesion between the electrode and the separator.

[0039] On the other hand, when the process speed is increased to improve yield in the lamination process, the time for applying heat is reduced, resulting in a problem of reduced adhesive strength. Although this problem is solved by increasing pressure during the lamination process to improve adhesive strength, the high pressure applied to the separator reduces its thickness and causes deformation, and damages pores, resulting in a decrease in the separator's breakdown voltage, leading to problems such as high-pot defects and low-voltage defects.

[0040] The present invention provides a separator that can prevent a decrease in thickness of the separator and improve the breakdown voltage by adjusting the polymer resin contained in the porous polymer substrate.

[0041] In the case of polyethylene used for the porous substrate of a separator, crystalline and amorphous components are mixed, and the higher the crystalline content and the narrower the molecular weight distribution, the better the compression resistance, which affects the degree of deformation in the thickness of the raw sheet after compression. Meanwhile, when propylene is added during the polyethylene polymerization process to improve processability during the production of polyethylene film, the amorphous content increases. Therefore, in one embodiment of the present invention, propylene is not added during the polyethylene polymerization process or is added in a small amount below the standard value, thereby increasing or adjusting the crystalline content in the manufactured porous substrate and improving various properties of the separator, such as compression resistance.

[0042] One embodiment of the present invention provides a separator for an electrochemical device, comprising a porous polymer substrate prepared by the above method, the porous polymer substrate comprising an amorphous polymer resin and a crystalline polymer resin, and when the porous polymer substrate is analyzed by temperature rising elution fractionation (TREF), the weight average molecular weight (Mw) of the eluate is about 100,000 or more.

[0043] In the preparation of a separator for an electrochemical device according to one embodiment of the present invention, as described above, by not adding or adding a small amount of propylene during the polyethylene polymerization process, the crystalline content can be increased or adjusted, thereby improving the weight average molecular weight and polydispersity index of the eluate eluted at high temperatures and minimizing deformation due to pressure applied during the lamination process, thereby improving the breakdown voltage.

[0044] One embodiment of the present invention relates to a separator for an electrochemical device, which may be applied as a separator itself or as a component. Therefore, in the separator according to one embodiment of the present invention, other layers may be disposed on at least one surface of the porous polymer substrate, as needed, depending on the material or function. For example, in one embodiment of the present invention, the separator may have a coating layer, such as an organic / inorganic composite coating layer, containing inorganic particles and / or a polymer binder formed on at least one or both surfaces of the porous polymer substrate.

[0045] According to one embodiment of the present invention, the separator for an electrochemical device includes a porous polymer substrate. As described above, the separator for an electrochemical device includes a porous polymer substrate, which allows lithium ions to pass through while blocking electrical contact between the positive electrode and the negative electrode, thereby achieving a shutdown function at an appropriate temperature. In this specification, the "shutdown function" may refer to the porous polymer substrate's pores being blocked under abnormally high temperature conditions, thereby preventing lithium ions from passing through the separator.

[0046] According to one embodiment of the present invention, the porous polymer substrate includes an amorphous polymer resin and a crystalline polymer resin. For example, the polymer resin included in the porous polymer substrate may include both crystalline and amorphous polymer resins, and the amorphous polymer resin and the crystalline polymer resin may be uniformly mixed, or may include both amorphous and crystalline structures within a single molecule. As described above, the porous polymer substrate includes an amorphous polymer resin and a crystalline polymer resin, which can improve the uniformity of the porous polymer substrate and increase its compression resistance.

[0047] According to one embodiment of the present invention, the porous polymer substrate of the present invention is a porous polymer substrate containing both crystalline and amorphous polymer resins by adjusting the presence or absence of propylene addition during polyethylene polymerization, and when the porous polymer substrate is analyzed by temperature rising elution fractionation (TREF), the weight average molecular weight (Mw) of the eluate is about 100,000 or more. For example, when the porous polymer substrate is eluted by temperature rising elution fractionation (TREF), the weight average molecular weight (Mw) of the eluate may be about 100,000 to 10,000,000, 200,000 to 9,000,000, 300,000 to 8,000,000, 400,000 to 7,000,000, 500,000 to 6,000,000, 600,000 to 5,000,000, 700,000 to 4,000,000, 800,000 to 3,000,000, 900,000 to 2,000,000, or 900,000 to 1,000,000. When the porous polymer substrate is eluted by temperature rising elution fractionation (TREF) within the above range, the weight average molecular weight (Mw) of the eluate is controlled within the above range, thereby improving the uniformity of the porous polymer substrate and increasing its compression resistance.

[0048] According to one embodiment of the present invention, the eluate may be eluted by temperature rising elution fractionation (TREF) at a temperature of about 90° C. to 110° C. For example, the eluate may be eluted by temperature rising elution fractionation (TREF) at a temperature of about 90° C. to 110° C., 91° C. to 109° C., 92° C. to 108° C., 93° C. to 107° C., 94° C. to 106° C., 95° C. to 105° C., 96° C. to 104° C., 97° C. to 103° C., 98° C. to 102° C., or 99° C. to 101° C. The porous polymer substrate of the present invention contains both crystalline and amorphous polymer resins by controlling the addition or absence of propylene during polyethylene polymerization. By controlling the temperature at which the eluate of the porous polymer substrate is eluted by temperature rising elution fractionation (TREF) within the above range, the uniformity and compression resistance of the porous polymer substrate can be improved. Furthermore, the mechanical properties of the porous polymer substrate can be improved.

[0049] As used herein, "temperature rising elution fractionation (TREF)" analysis can be performed using a PolymerChar TREF instrument. Specifically, temperature rising elution fractionation involves dissolving a sample and injecting it into a column at a high temperature. The temperature is then gradually lowered to induce crystallization of the sample. Once the sample precipitates within the column, the temperature is raised and the molecular weight of the eluted sample is measured. For example, 40 mg of polymer sample is dissolved in 20 mL of trichlorobenzene solvent at 150°C for 120 minutes and then stabilized at 100°C for 45 minutes. This is then loaded onto a TREF column, cooled to 35°C at a rate of 0.5°C per minute, and maintained at this temperature for 15 minutes. Then, the sample is heated from 35°C to 80°C at a rate of 20°C per minute, maintained at 5°C intervals for 20 minutes, and then heated from 80°C to 120°C at a rate of 20°C per minute, maintained at 2°C intervals for 20 minutes, and the weight average molecular weight of the polymer sample eluted is measured. A TREF analysis graph can be derived from the results of these concentration measurements.

[0050] According to one embodiment of the present invention, the porous polymer substrate may contain about 40 wt. % or less of a fraction eluted at 35°C or less by temperature rising elution fractionation. For example, when analyzed by temperature rising elution fractionation, the porous polymer substrate may contain a first fraction eluted at 35°C or less and a second fraction eluted at a temperature above 35°C. The first fraction may contain a non-crystalline polymer resin. The second fraction may contain a crystalline polymer resin eluted from the porous polymer substrate at a temperature above 35°C by temperature rising elution fractionation. For example, the second fraction may be eluted at a temperature above 35°C and 100°C or less, 40°C to 90°C, 50°C to 80°C, or 60°C to 70°C. Alternatively, the second fraction may be eluted at a temperature above 98°C.

[0051] According to one embodiment of the present invention, the content of the amorphous polymer resin in the porous polymer substrate may be about 40 wt% or less. For example, the content of the amorphous polymer resin in the porous polymer substrate may be about greater than 0 wt% and less than 40 wt%, 2 wt% to 38 wt%, 4 wt% to 36 wt%, 6 wt% to 34 wt%, 8 wt% to 32 wt%, 10 wt% to 30 wt%, 12 wt% to 28 wt%, 14 wt% to 26 wt%, 16 wt% to 24 wt%, or 18 wt% to 22 wt%. Adjusting the content of the amorphous polymer resin in the porous polymer substrate within the above ranges can improve the uniformity and compression resistance of the porous polymer substrate. Furthermore, the mechanical properties of the porous polymer substrate can be improved.

[0052] According to one embodiment of the present invention, the content of the crystalline polymer resin in the porous polymer substrate may be about 60 wt% or more. For example, the content of the crystalline polymer resin in the porous polymer substrate may be about 60 wt% or more but less than 100 wt%, 62 wt% or more but less than 98 wt%, 64 wt% or more but less than 96 wt%, 66 wt% or more but less than 94 wt%, 68 wt% or more but less than 92 wt%, 70 wt% or more but less than 90 wt%, 72 wt% or more but less than 88 wt%, 74 wt% or more but less than 86 wt%, 76 wt% or more but less than 84 wt%, or 78 wt% or more but less than 82 wt%. Alternatively, the content of the crystalline polymer resin in the porous polymer substrate may be about 70 wt% or more but less than 85 wt%. Adjusting the content of the crystalline polymer resin in the porous polymer substrate within the above ranges can improve the uniformity of the porous polymer substrate and increase its compression resistance. Furthermore, the mechanical properties of the porous polymer substrate can be improved.

[0053] According to one embodiment of the present invention, the weight ratio of the amorphous polymer resin to the crystalline polymer resin in the porous polymer substrate may be about 1:1 to 10:1. For example, the weight ratio of the amorphous polymer resin to the crystalline polymer resin in the porous polymer substrate may be about 1.5:1 to 9.5:1, 2.0:1 to 9.0:1, 2.5:1 to 8.5:1, 3.0:1 to 8.0:1, 3.5:1 to 7.5:1, 4.0:1 to 7.0:1, 4.5:1 to 6.5:1, or 5.0:1 to 6.0:1. By adjusting the weight ratio of the amorphous polymer resin to the crystalline polymer resin in the porous polymer substrate within the above ranges, the uniformity of the porous polymer substrate and its compression resistance can be improved. Furthermore, the mechanical properties of the porous polymer substrate can be improved.

[0054] According to one embodiment of the present invention, the content of the crystalline polymer resin in the porous polymer substrate may be about 70 wt % to 85 wt % based on 100 wt % of the porous polymer substrate. By adjusting the content of the crystalline polymer resin in the porous polymer substrate within the above range, the indentation depth of the porous polymer substrate can be reduced, and the deviation in the indentation depth can be minimized, thereby improving the breakdown voltage.

[0055] According to one embodiment of the present invention, the indentation depth of the porous polymer substrate may be about 20 nm or less. For example, the indentation depth of the porous polymer substrate may be about 0 to 20 nm, more than 0 to 19 nm, 1 to 18 nm, 2 to 17 nm, 3 to 16 nm, 4 to 15 nm, 5 to 14 nm, 6 to 13 nm, 7 to 12 nm, 8 to 11 nm, or 9 to 10 nm. Adjusting the indentation depth of the porous polymer substrate within the above ranges can improve the compression resistance of the porous polymer substrate, improve the thickness uniformity of the porous polymer substrate after lamination, and minimize thickness deformation.

[0056] As used herein, "indentation" refers to a method for analyzing the mechanical properties of materials. It is an experimental method in which diamond indenters of various shapes are pressed into a material, and then the indentation marks and the load applied during the indentation are compared and analyzed. Indentation tests are not only used to measure the fracture toughness and hardness of materials, but have also recently been used in a variety of other areas, including the elastic-plastic behavior of materials, analysis of residual stress states, adhesion strength tests for thin films, fracture characteristics, and phase transformation analysis. For example, when performing indentation on a fine material such as a separator, nanoindentation can be used, in which a load of less than N (Newton) is applied using an indenter.

[0057] FIG. 1 is a diagram illustrating a method for measuring indentation depth. In this specification, the "indentation depth" is measured by setting a Dimension Icon (Bruker) under the following conditions, and then moving the tip relative to the surface of the sample as shown in FIG. 1, while measuring the peak tapping force. The peak tapping force (PTF) is measured, and the depth of the tip that penetrated into the surface of the sample at the time when the peak tapping force was measured may be measured using an atomic force microscope (AFM, OSTESPA-R3, Bruker, f=300 kHz, k=26 N / m).

[0058] -Mode: Tapping (Peak Force QNM)

[0059] -Scan speed (0.3Hz)

[0060] -Peak Force setpoint: 100 nN, Amplitude: 300 nm

[0061] -Scan angle: 90°

[0062] According to one embodiment of the present invention, the deviation in indentation depth of the porous polymer substrate may be about -5 nm to 5 nm. For example, the deviation in indentation depth of the porous polymer substrate may be about -4 nm to 4 nm, -3 nm to 3 nm, -2 nm to 2 nm, -1 nm to 1 nm, -0.5 nm to 0.5 nm, or -0.1 nm to 0.1 nm. As used herein, deviation refers to the difference in a variable from the average, and may refer to the difference in indentation depth at a specific position on the porous polymer substrate from the average indentation depth of the porous polymer substrate. By adjusting the deviation in indentation depth of the porous polymer substrate within the above range, the breakdown voltage of the porous polymer substrate can be improved.

[0063] According to one embodiment of the present invention, the porous polymer substrate may include a polyolefin-based resin. As described above, the porous polymer substrate may include a polyolefin-based resin, which facilitates the formation of the separator for the electrochemical device and enables a shutdown function when high temperatures occur during battery operation.

[0064] According to one embodiment of the present invention, the amorphous polymer resin may be an amorphous polyolefin-based resin. As used herein, "amorphous" may mean that the molecules are arranged randomly. As described above, by selecting an amorphous polyolefin-based resin as the amorphous polymer resin, a shutdown function can be achieved when high temperatures occur during battery operation.

[0065] According to one embodiment of the present invention, the crystalline polymer resin may be a crystalline polyolefin-based resin. As used herein, "crystalline" may refer to a structure in which molecules are regularly arranged. As described above, by selecting a crystalline polyolefin-based resin as the crystalline polymer resin, the mechanical properties and compression resistance of the porous polymer resin can be improved.

[0066] As used herein, the term "crystallinity" may refer to the content of crystals eluted at about 98°C or higher during TREF measurement.

[0067] According to one embodiment of the present invention, the polyolefin-based resin may be one selected from the group consisting of polyethylene; polypropylene; polybutylene; polypentene:polyhexene:polyoctene; copolymers of one or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; and combinations thereof. For example, the polyolefin-based resin may be polyethylene. By selecting the polyolefin-based resin from the above, the porous polymer substrate can contain a crystalline polymer resin and an amorphous polymer resin, thereby improving the mechanical properties and compression resistance of the porous polymer.

[0068] According to one embodiment of the present invention, the polyolefin resin may have an average short chain branch (SCB) of about 500 or less per 1,000 total carbon atoms of the polyolefin contained therein. The short chain branch may be the number of methyl groups per 1,000 total carbon atoms (CH3 / 1,000TC). The short chain branch may interfere with the formation of a crystalline structure during the crystallization process of the polymer, thereby affecting the physical properties of the substrate. The number of short chain branches can be controlled by adjusting the type and content of monomers contained in the polyolefin substrate. For example, the number of short chain branches in the polyolefin substrate can be controlled by adjusting the type and content of polyolefin polymer resin used in the polymerization process of the polymer resin used in the polyolefin substrate and / or the film formation process using the polymer resin. For example, the number of short chain branches can be increased by increasing the content of propylene, butylene, etc. during polymerization of the polyolefin polymer resin, or by adding polypropylene, etc. during the film formation process. The number of short chain branches can be determined by comparing resins contained in fractions eluted at different temperatures during analysis using temperature rising elution fractionation. For example, the number of CH3 atoms per approximately 1,000 carbon atoms can be determined using an IR detector and CH, CH2, and CH3 filters used in temperature rising elution fractionation. For example, the polyolefin substrate may have an average number of short chain branches per approximately 1,000 total carbon atoms of approximately 100 to 500, 150 to 450, 200 to 400, or 250 to 350. Alternatively, the polyolefin substrate may have an average number of short chain branches per 1,000 total carbon atoms of approximately 400 or less. If the average number of short chain branches exceeds the above range, it is detrimental to the orientation of the polyolefin polymer resin contained in the polyolefin substrate. By adjusting the average number of short chain branches within the above range, orientation of the crystalline polyolefin polymer resin can be achieved, providing a polyolefin substrate with compression resistance during the lamination process.

[0069] According to one embodiment of the present invention, the polyolefin resin may have a melt index of about 0.1 / 10 min to 0.3 g / 10 min. The melt index can be measured according to ASTM D1238 by placing a sample in a cylinder and heating it to about 190°C, or by placing a piston with a load of about 2.16 kg in the heated sample in the cylinder and measuring the weight of the resin extruded through an orifice (inner diameter: 2.09 mm, length: 8 mm) located on the opposite side of the piston, and converting the weight into the amount extruded per 10 minutes. By adjusting the melt index of the polyolefin within the above range, the rigidity of a porous polymer substrate containing the polyolefin resin can be determined, thereby providing a porous polymer substrate with compression resistance during the lamination process.

[0070] According to one embodiment of the present invention, the weight-average molecular weight (Mw) of the porous polymer substrate may be about 500,000 to 3,000,000. For example, the weight-average molecular weight (Mw) of the porous polymer substrate may be about 500,000 to 2,500,000, or about 1,000,000 to 2,000,000. By adjusting the weight-average molecular weight (Mw) of the porous polymer substrate within the above range, the mechanical properties and compression resistance of the porous polymer substrate can be improved. Furthermore, when different polyolefin resins are mixed or a separator membrane is formed with a multilayer structure composed of different polyolefin resins, the weight-average molecular weight of the polyolefin resin can be calculated by adding the weight-average molecular weights of the respective polyolefin resins according to their content ratio.

[0071] In this specification, the weight average molecular weight (Mw) and polydispersity index can be measured by gel permeation chromatography (GPC, PL GPC220, Agilent Technologies), and the measurement conditions can be set as follows.

[0072] -Column: PL Olexis (Polymer Laboratories)

[0073] -Solvent: Trichlorobenzene (TCB)

[0074] -Flow rate: 1.0ml / min

[0075] -Sample concentration: 1.0mg / ml

[0076] -Injection volume: 200μl

[0077] -Column temperature: 160℃

[0078] -Detector: Agilent High Temperature Refractive Index Detector (RI detector)

[0079] -Standard: Polystyrene (corrected by a cubic function)

[0080] According to one embodiment of the present invention, other resin components may be further mixed in addition to the polyolefin-based resin, as needed, and filler particles, for example, may be included in addition to the resin components. The filler particles may be introduced for the purpose of a pressure barrier to prevent excessive reduction in the thickness, pore size, and porosity of the separator substrate due to the high pressure applied in the lamination process described below. The filler particles may include organic or inorganic fillers having a predetermined particle size, and are not limited to a specific component as long as they have strength equal to or greater than that of the polyolefin-based resin.

[0081] According to one embodiment of the present invention, the porous polymer substrate may be manufactured by a method (wet method) in which a polyolefin resin is kneaded with a plasticizer (diluents) at a high temperature to form a single phase, the polymer material and the plasticizer are phase-separated during a cooling process, the plasticizer is extracted to form pores, and then the resulting mixture is stretched and heat-set.

[0082] According to one embodiment of the present invention, the average pore size and the maximum pore size of the separator can be easily prepared by a person skilled in the art to meet the scope of the present invention by adjusting the mixing ratio of the plasticizer, the stretching ratio, the heat setting temperature, etc.

[0083] According to one embodiment of the present invention, the pore size can be calculated from the pore size distribution measured using a capillary flow porometer. For example, the separation membrane to be measured is first wetted with a wetting agent such as Galwick solution, and then air pressure is gradually increased on one side of the substrate. When the applied air pressure exceeds the capillary attraction of the wetting agent present in the pores, the wetting agent blocking the pores is forced out. The pore size and distribution can be measured based on the pressure and flow rate at the moment of extrusion, from which the average pore size and maximum size can be determined.

[0084] The porous polymer substrate may contain pores with an average diameter of about 0.01 μm to 1 μm. For example, the size of the pores contained in the porous polymer substrate may be about 0.01 μm to 0.09 μm, 0.02 μm to 0.08 μm, 0.03 μm to 0.07 μm, or 0.04 μm to 0.06 μm. By adjusting the pore size of the porous polymer substrate within the above ranges, the air permeability and ionic conductivity of the entire separator membrane can be controlled.

[0085] According to one embodiment of the present invention, the polydispersity index (PDI) of the eluate may be about 5 or more. For example, the polydispersity index (PDI) of the eluate may be about 6 to 19, 7 to 18, 8 to 17, 9 to 16, 10 to 15, 11 to 14, or 12 to 13. By adjusting the polydispersity index of the eluate within the above ranges, the uniformity and compression resistance of the crystalline polymer resin can be improved.

[0086] According to one embodiment of the present invention, when a pressure of 8 MPa is applied at about 70° C., the separation membrane may satisfy one or more of the following (i) to (iii):

[0087] (i) The thickness reduction rate of the porous polymer substrate, as defined by the following Equation 1, may be about 10% or less.

[0088] [Formula 1]

[0089] Thickness reduction rate (%) = (thickness of porous polymer substrate before applying pressure - thickness of porous polymer substrate after applying pressure) / thickness of porous polymer substrate before applying pressure x 100

[0090] For example, when a pressure of 8 MPa is applied at about 70° C., the thickness reduction rate of the porous polymer substrate may be about 0% to 10%, 1% to 9%, 2% to 8%, 3% to 7%, or 4% to 6%, as defined by the following Equation 1. By achieving a thickness reduction rate of the porous polymer substrate within the above range, the compression resistance of the separator can be improved.

[0091] (ii) The porous polymer substrate may have an increase in air permeability of about 185% or less after compression, as defined by the following Equation 2:

[0092] [Formula 2]

[0093] Air permeability increase rate (%) = (air permeability after compression - air permeability before compression) / (air permeability before compression) x 100

[0094] The compression resistance of a porous polymer substrate can be determined by the rate of change in air permeability before and after compression. The porous polymer substrate before compression may have an air permeability of about 10 s / 100 cc to about 100 s / 100 cc. For example, the air permeability of the porous polymer substrate may be about 10 s / 100 cc to about 90 s / 100 cc, 20 s / 100 cc to about 80 s / 100 cc, 30 s / 100 cc to about 70 s / 100 cc, or 40 s / 100 cc to about 60 s / 100 cc. Alternatively, the air permeability of the porous polymer substrate may be about 50 s / 100 cc to about 80 s / 100 cc. When the air permeability of the porous polymer substrate is within the above range, the air permeability of the resulting separator can be provided within a range suitable for ensuring the output and cycle characteristics of an electrochemical device.

[0095] Furthermore, when the porous polymer substrate is compressed at 70°C under a pressure of 8 MPa for about 10 seconds, the increase in air permeability after compression may be about 0% to 180%, 20% to 160%, 40% to 140%, 60% to 120%, or 80% to 100%. Alternatively, the porous polymer substrate after compression may have an air permeability of about 200 s / 100 cc or less. A porous polymer substrate satisfying the air permeability increase rate within the above range can reduce defects due to deformation of its shape during the lamination process. If a substrate with an air permeability exceeding about 200 s / 100 cc after compression under the above conditions is used, the output and cycle characteristics of the electrochemical device may be reduced.

[0096] The air permeability (s / 100cc) refers to the time (seconds) required for about 100cc of air to pass through a porous polymer substrate or separator with a predetermined area under a certain pressure. The air permeability can be measured using a Gurley densometer in accordance with ASTM D 726-58, ASTM D726-94, or JIS-P8117. For example, a Gurley 4110N device is used to measure air at a pressure of about 0.304 kPa or a pore size of about 1.215 kN / m. 2 About 100cc of air under water pressure fills about 1 square inch (or 6.54cm) 2 For example, using an Asahi Seiko EG01-55-1MR instrument, it is possible to measure the time it takes for approximately 100 cc of air to pass through a sample of approximately 1 square inch at room temperature under a constant pressure of 4.8 inches of water.

[0097] (iii) The porous polymer substrate may have a breakdown voltage of about 1,000 V or greater.

[0098] For example, when a pressure of 8 MPa is applied at about 70° C., the dielectric breakdown voltage of the porous polymer substrate may be about 1,000 V to 2,000 V, 1,100 V to 1,900 V, 1,200 V to 1,800 V, 1,300 V to 1,700 V, or 1,400 V to 1,600 V. By adjusting the dielectric breakdown voltage of the porous polymer substrate within the above range, the insulating properties of the porous polymer substrate can be improved.

[0099] As used herein, breakdown voltage may refer to the voltage when a test piece having a thickness of about 12 μm is subjected to a voltage increase rate of about 100 mV / s for more than about 0.5 mA and 3 seconds.

[0100] According to one embodiment of the present invention, the porous polymer substrate may have a thickness of about 1 μm to 30 μm. For example, the thickness of the porous polymer substrate may be about 2 μm to 29 μm, 3 μm to 28 μm, 4 μm to 27 μm, 5 μm to 26 μm, 6 μm to 25 μm, 7 μm to 24 μm, 8 μm to 23 μm, 9 μm to 22 μm, 10 μm to 21 μm, 11 μm to 20 μm, 12 μm to 19 μm, 13 μm to 18 μm, 14 μm to 17 μm, or 15 μm to 16 μm. Adjusting the thickness of the porous polymer substrate within the above ranges can improve the energy density of the separator for electrochemical devices.

[0101] A method for producing a porous polymer substrate according to one embodiment of the present invention may include the steps of kneading and extruding a composition for a porous polymer substrate containing a polymer resin; cooling the extruded composition for a porous polymer substrate to form a sheet; stretching the sheet; forming pores in the stretched sheet; and heat-setting the sheet with the pores formed therein to produce a porous polymer substrate. By producing a porous polymer substrate using the above method, a porous polymer substrate having uniform pores can be produced.

[0102] According to one embodiment of the present invention, the method for manufacturing the porous polymer substrate may include the steps of kneading and extruding a composition for the porous polymer substrate, including a polymer resin. By including the kneading and extruding steps as described above, a uniform composition for the porous polymer substrate can be manufactured, and a porous polymer substrate having uniform pore size can be manufactured.

[0103] According to one embodiment of the present invention, the composition for a porous polymer substrate may further include a plasticizer. For example, the plasticizer may be liquid paraffin oil. As described above, the inclusion of a plasticizer makes it easy to remove the plasticizer from the sheet and prevents denaturation of the polymer resin.

[0104] According to one embodiment of the present invention, the liquid paraffin oil may have a kinematic viscosity of about 30 cSt or more and 50 cSt or less at 40° C. By adjusting the kinematic viscosity of the liquid paraffin oil within the above range, the concentration of the plasticizer in the composition for a porous polymer substrate can be uniformly adjusted.

[0105] According to one embodiment of the present invention, the weight ratio of the polymer resin to the plasticizer in the composition for a porous polymer substrate may be about 2:8 to 5:5. By adjusting the weight ratio of the polymer resin to the plasticizer in the composition for a porous polymer substrate within the above range, the porosity of the porous polymer substrate can be adjusted.

[0106] According to one embodiment of the present invention, the extrusion may be performed through a T-die using a biaxial extruder. By performing the extrusion as described above, the thickness of the sheet can be easily adjusted and cooling efficiency can be improved.

[0107] According to one embodiment of the present invention, the method for manufacturing the porous polymer substrate may include a step of cooling the extruded composition for the porous polymer substrate to form a sheet.

[0108] According to one embodiment of the present invention, the cooling temperature of the sheet may be about 40° C. to 80° C. For example, the temperature at which the sheet is cast through the T-die onto the roll may be about 40° C. to 80° C. By adjusting the cooling temperature of the sheet within the above range, the polymer resin can be made crystalline, and by adjusting the content of the crystalline polymer resin and the amorphous polymer resin in the porous polymer resin, the indentation depth can be reduced while minimizing the standard deviation of the indentation depth.

[0109] According to one embodiment of the present invention, the method for manufacturing the porous polymer substrate may include a step of stretching the sheet. By including the step of stretching the sheet as described above, the thickness of the porous polymer substrate can be adjusted to realize a thin film.

[0110] According to one embodiment of the present invention, the stretching step may be biaxial stretching using a tenter-type simultaneous stretching machine. For example, the stretching may be performed in the MD (machine direction) and then in the TD (transverse direction). By performing the stretching step as described above, the sheet can be manufactured into a large-area porous polymer substrate.

[0111] According to one embodiment of the present invention, the method for manufacturing the porous polymer substrate may include forming pores in the stretched sheet. For example, the forming pores in the stretched sheet may include removing plasticizers contained in the porous polymer substrate using a solvent. The solvent may be methylene chloride. By including the forming pores in the stretched sheet as described above, the porous polymer substrate can be manufactured and the residual plasticizer can be minimized.

[0112] In one embodiment of the present invention, the method may include heat-setting the pore-formed sheet to prepare a porous polymer substrate. For example, the heat-setting temperature may be about 100° C. to 150° C. As described above, heat-setting the sheet may improve the heat resistance of the separator.

[0113] According to one embodiment of the present invention, the separator for an electrochemical device may further include a coating layer formed on at least one surface of the porous polymer substrate.

[0114] According to one embodiment of the present invention, the coating layer comprises a polymer binder and inorganic particles and has porous properties.

[0115] According to one embodiment of the present invention, the coating layer may be a porous coating layer having a plurality of pores. For example, the coating layer may be a porous coating layer having a plurality of pores therein. As described above, the coating layer may have a plurality of pores, which may physically isolate the anode and cathode while allowing lithium ions to pass through to allow current to flow.

[0116] According to one embodiment of the present invention, the polymer binder and inorganic particles in the coating layer may be contained in a weight ratio of about 1:99 to 30:70. This ratio can be appropriately adjusted within the above range, and the polymer binder may be about 1 wt% or more, 5 wt% or more, or 10 wt% or more of the total of the polymer binder and inorganic particles (100 wt%), and the inorganic particles may be about 80 wt% or more, 85 wt% or more, 90 wt% or more, or 95 wt% or more of the inorganic particles.

[0117] According to one embodiment of the present invention, the coating layer may be formed by binding inorganic particles with a polymer binder and accumulating them in a layer, and the pores within the coating layer may be due to interstitial volumes, which are empty spaces between the inorganic particles.

[0118] In one embodiment of the present invention, the porosity of the coating layer may be about 30% to 70% by volume. When the porosity of the coating layer is about 70% by volume or less, it is possible to ensure mechanical properties that can withstand the pressing process for bonding to the electrode, and the surface opening ratio is not too high, which is suitable for ensuring adhesive strength. On the other hand, when the porosity is about 30% by volume or more, it is advantageous from the viewpoint of ion permeability.

[0119] In this specification, the porosity of the coating layer refers to the ratio of the volume occupied by pores to the total volume of the coating layer, and is expressed in volume %. The porosity may be used interchangeably with terms such as void ratio and porosity.

[0120] In this specification, the porosity corresponds to a value obtained by subtracting the weight and density of each component of the porous polymer substrate and the coating layer from the volume calculated in thickness, width, and length of the porous polymer substrate and the coating layer.

[0121] For example, the porous polymer substrate may have a porosity of about 10 vol% to 60 vol%. In one embodiment, the porosity of the porous polymer substrate may be about 15 vol% to 55 vol%, 20 vol% to 50 vol%, 25 vol% to 45 vol%, or 30 vol% to 40 vol%. When the porosity of the porous polymer substrate is within the above range, the ionic conductivity of the resulting separator may be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical device.

[0122] In one embodiment of the present invention, the porosity and pore size of the porous polymer substrate and coating layer can be measured using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) by a nitrogen gas adsorption flow method using a BET 6-point method. In this case, it may be advantageous to use a capillary flow porosimeter.

[0123] According to one embodiment of the present invention, the thickness of the coating layer may be formed on either side of the porous polymer substrate to a thickness of about 1 μm to 20 μm, but is not limited thereto. The thickness can be adjusted to an appropriate range by those skilled in the art in consideration of heat resistance and electrical resistance.

[0124] According to one embodiment of the present invention, the thickness of the porous polymer substrate and / or the coating layer may be measured using a contact-type thickness gauge, such as a Mitutoyo VL-50S-B.

[0125] According to one embodiment of the present invention, the polymer binder usable for the coating layer is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-co-vinyl acetate, polyethylene oxide, or the like. The polymer resin may be any one selected from the group consisting of polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more of these polymer resins, but is not limited thereto.

[0126] In one embodiment of the present invention, the inorganic particles that can be used for the coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in one embodiment of the present invention are those that can be used within the operating voltage range (e.g., Li / Li) of the applied electrochemical device. + There are no particular limitations on the voltage, as long as it does not undergo oxidation and / or reduction reactions at a voltage between 0 V and 5 V (based on the reference voltage).

[0127] According to one embodiment of the present invention, non-limiting examples of the inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1、0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, Al(OH)3, TiO2, aluminum peroxide, zinc tin hydroxide (ZnSn(OH)6), tin-zinc oxide (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), and the like can be mentioned, and one or more of these can be contained.

[0128] According to one embodiment of the present invention, the average diameter (D 50 Although there are no particular limitations on the thickness of the coating layer, it is preferably in the range of about 0.3 μm to 1 μm inclusive to form a coating layer of uniform thickness and to achieve a suitable porosity. For example, if the thickness is less than about 0.3 μm, the dispersibility of inorganic particles in the slurry prepared for forming the coating layer may decrease, and if the thickness is more than about 1 μm, the thickness of the formed coating layer may increase.

[0129] As used herein, the term "D50 particle size" refers to the particle size at approximately 50% of the cumulative distribution of particle numbers according to particle size. The particle size can be measured using a laser diffraction method. For example, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). When the particles pass through a laser beam, the difference in the diffraction pattern according to particle size is measured to calculate the particle size distribution. The D50 particle size can be measured by calculating the particle diameter at the 50% point of the cumulative distribution of particle numbers according to particle size measured by the analyzer.

[0130] According to one embodiment of the present invention, the coating layer can be formed, for example, as follows. First, a polymer binder is dissolved in a suitable organic solvent to prepare a polymer solution, or the polymer binder is dispersed in a suitable dispersing medium to prepare a polymer emulsion. The organic solvent or dispersing medium preferably has a solubility index similar to that of the polymer binder and a low boiling point. This facilitates uniform mixing and subsequent removal of the solvent or dispersing medium. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof.

[0131] Next, inorganic particles are added to and dispersed in the prepared polymer solution and / or polymer dispersion medium to prepare a slurry for the coating layer. According to one embodiment of the present invention, the content ratio of the inorganic particles to the polymer binder is as described above and is appropriately adjusted taking into consideration the thickness, pore size, and porosity of the final coating layer of the present invention.

[0132] Next, the slurry for the coating layer prepared as described above is applied to at least one side of the prepared porous polymer substrate and dried. The method for applying the slurry to the surface of the porous polymer substrate is not limited to any particular method, and any conventional method known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a combination thereof can be used.

[0133] The drying process is performed by appropriately setting temperature and time conditions to minimize the occurrence of surface defects in the coating layer, and the drying may be performed using auxiliary drying devices such as a drying oven or hot air within an appropriate range.

[0134] When the separator includes a coating layer, damage caused by pressure of inorganic particles on the surface of the porous polymer substrate facing the coating layer during the lamination process can be reduced.

[0135] According to one embodiment of the present invention, the separator is interposed between the anode and cathode and fabricated into an electrochemical device by a lamination process in which heat and / or pressure are applied to bond them together. In one embodiment of the present invention, the lamination process can be performed using a roll press device including a pair of pressure rollers. That is, the anode, separator, and cathode can be sequentially stacked and then inserted between the pressure rollers to achieve interlayer bonding. In this case, the lamination process can be performed using a hot press method.

[0136] One embodiment of the present invention provides an electrochemical device comprising: a positive electrode; a negative electrode; and the separator interposed between the positive electrode and the negative electrode.

[0137] An electrochemical device according to an embodiment of the present invention can prevent Hi-Pot failure and low voltage failure, thereby improving battery performance.

[0138] In the present invention, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a type of device that includes a primary battery and a secondary battery. The term "secondary battery" as used herein refers to a lithium secondary battery, a nickel-cadmium battery, a nickel-metal hydride battery, or the like, which can be charged and discharged. Examples of the lithium secondary battery include, but are not limited to, non-aqueous electrolyte secondary batteries using lithium ions as an ion conductor, including liquid electrolyte secondary batteries, all-solid-state batteries including solid electrolyte batteries, lithium polymer batteries including gel polymer electrolyte batteries, and lithium metal batteries using lithium metal as a negative electrode.

[0139] According to one embodiment of the present invention, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the current collector, the positive electrode active material layer including a positive electrode active material, a conductive material, and a binder resin. The positive electrode active material may be a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3) 1-x M xLithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; It may contain one or a mixture of two or more of Fe2(MoO4)3.

[0140] According to one embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. As the negative electrode active material, the negative electrode includes carbon such as lithium metal oxide, graphitized carbon, graphite-based carbon; LixFe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x [[ID=PR=]]Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; It may contain one or a mixture of two or more selected from titanium oxides.

[0141] According to one embodiment of the present invention, the conductive material may be, for example, any one selected from the group consisting of graphite, carbon black, carbon or metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials, or may be any one selected from the group consisting of natural graphite, artificial graphite, Super-P, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0142] According to one embodiment of the present invention, the current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, stainless steel, copper, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like can be used.

[0143] According to one embodiment of the present invention, the binder resin may be a polymer commonly used in electrodes in the art. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples of suitable polymers include, but are not limited to, cyanoethyl acetatepropionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose.

[0144] In one embodiment of the present invention, the positive electrode slurry for preparing the positive electrode active material layer may include a dispersant, and the dispersant may be a pyrrolidone-based compound, for example, N-methylpyrrolidone (ADC-01, LG Chemicals).

[0145] According to one embodiment of the present invention, the content of the dispersant in the positive electrode slurry may be greater than about 0 parts by weight and less than or equal to 0.5 parts by weight, relative to 100 parts by weight of the positive electrode slurry. For example, the content of the dispersant in the positive electrode slurry may be greater than about 0.05 parts by weight and less than or equal to 0.4 parts by weight, relative to 100 parts by weight of the positive electrode slurry.

[0146] According to one embodiment of the present invention, the negative electrode slurry for preparing the negative electrode active material layer may include a dispersant, and the dispersant may be a polypyrrolidone-based compound, for example, polyvinylpyrrolidone (available from Junsei).

[0147] According to one embodiment of the present invention, the content of the dispersant in the negative electrode slurry may be greater than about 0 parts by weight and less than or equal to 0.5 parts by weight, relative to 100 parts by weight of the negative electrode slurry. For example, the content of the dispersant in the negative electrode slurry may be greater than about 0.05 parts by weight and less than or equal to 0.4 parts by weight, relative to 100 parts by weight of the negative electrode slurry.

[0148] According to one embodiment of the present invention, the electrochemical device prepared as described above can be placed in a suitable case and filled with an electrolyte to fabricate a battery.

[0149] According to one embodiment of the present invention, the electrolyte is A + B - A salt having the structure: + Li + , Na + , K. + or a combination thereof, - is PF6 - , BF4- , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or a salt containing an anion such as, or a combination thereof, dissolved or dissociated in an organic solvent such as, but not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or a mixture thereof.

[0150] One embodiment of the present invention provides a battery module including a battery containing the electrochemical device as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Examples of the device include, but are not limited to, power tools powered by a battery-type motor, electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters, electric golf carts, and power storage systems.

[0151] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples in this specification are provided to more completely explain the present invention to those skilled in the art.

[0152] Example 1 30 parts by weight of a polymer resin (polyethylene resin, Mw: 800,000) with a log Mw of 5.5 and 70 parts by weight of liquid paraffin oil (kinematic viscosity at 40°C: 40 cSt) were mixed and extruded into a biaxial extruder. After extrusion, the mixture was formed into a sheet through a T-die and a cooling casting roll, and then biaxially stretched in a tenter-type simultaneous stretching machine, stretching in the MD direction followed by the TD direction. The liquid paraffin oil diluent was extracted from the stretched sheet with methylene chloride and heat-set at approximately 128°C to produce a porous polymer substrate. That is, in the production of the polyethylene film in Example 1, propylene was not added during the polymerization process to increase the crystalline content and improve compression resistance.

[0153] The weight-average molecular weight of the eluate from the porous polymer substrate was measured using a PolymerChar TREF instrument. For example, a 40 mg sample was prepared from the porous polymer substrate and dissolved in 20 mL of trichlorobenzene solvent at 150°C for 120 minutes, then stabilized at 100°C for 45 minutes. The sample was then loaded onto a TREF column and cooled to 35°C at a rate of 0.5°C / min and maintained for 15 minutes. The column was then heated from 35°C to 80°C at a rate of 20°C / min, maintaining the temperature in 5°C increments for 20 minutes, and heated from 80°C to 120°C at a rate of 20°C / min, maintaining the temperature in 2°C increments for 20 minutes. The weight-average molecular weight of the polymer sample eluted at 98°C was measured while trichlorobenzene (solvent) was passed through the column at a flow rate of 0.5 mL / min.

[0154] Furthermore, the weight average molecular weight measured for the porous polymer substrate and the number average molecular weight derived through gel permeation chromatography (GPC) analysis were determined, and the polydispersity index was calculated using the following Equation 3.

[0155] [Formula 3] Polydispersity index (PDI)=(weight average molecular weight) / (number average molecular weight)

[0156] The log value of the weight average molecular weight (log Mw) of the eluate of the porous polymer substrate was 5.5, and the polydispersity index (PDI) of the eluate of the porous polymer substrate was 6.0.

[0157] <Example 2> A porous polymer substrate was prepared in the same manner as in Example 1, except that the polymer resin had a log Mw of 6.2.

[0158] Example 3 A porous polymer substrate was prepared in the same manner as in Example 1, except that the polymer resin had a log Mw of 5.1 and a polydispersity index (PDI) of 5.2.

[0159] Example 4 A porous polymer substrate was prepared in the same manner as in Example 1, except that the polymer resin had a log Mw of 5.1 and a polydispersity index (PDI) of 9.9.

[0160] <Comparative Example 1> In Comparative Example 1, a porous polymer substrate was prepared in the same manner as in Example 1, except that propylene was not added during the polymerization of polyethylene resin. In Comparative Example 1, 7 parts by weight of propylene was added to 100 parts by weight of ethylene during the polymerization of polyethylene resin to prepare a polymer resin (Mw: 800,000). The log Mw of the polymer resin was 2.9.

[0161] <Comparative Example 2> In Comparative Example 2, a porous polymer substrate was prepared in the same manner as in Example 1, except that propylene was not added during the polymerization of polyethylene resin. In Comparative Example 2, 5.5 parts by weight of propylene was added per 100 parts by weight of ethylene during the polymerization of polyethylene resin to prepare a polymer resin (Mw: 800,000). The log Mw of the polymer resin was 4.4.

[0162] <Comparative Example 3> In Comparative Example 3, a polymer resin (Mw: 800,000) was prepared by adding 3 parts by weight of propylene per 100 parts by weight of ethylene during the polymerization of polyethylene resin, in contrast to Example 1 in which propylene was not added during the polymerization of polyethylene resin. The polymer resin had a log Mw of 5.1 and a polydispersity index (PDI) of 2.3. A porous polymer substrate was prepared in the same manner as in Example 1.

[0163] <Comparative Example 4> In Comparative Example 4, a polymer resin (Mw: 800,000) was prepared by adding 1.5 parts by weight of propylene per 100 parts by weight of ethylene during the polymerization of polyethylene resin, in comparison with Example 1, in which propylene was not added during the polymerization of polyethylene resin. The polymer resin had a log Mw of 5.1 and a polydispersity index (PDI) of 3.9. A porous polymer substrate was prepared in the same manner as in Example 1.

[0164] <Experimental Example 1: Measurement of thickness reduction rate> Using a contact-type thickness gauge (Mitutoyo Corporation, VL-50S-B), the thickness of the porous polymer substrates of Examples 1 to 4 and Comparative Examples 1 to 4 before and after applying a pressure of 8 MPa at 70°C was measured, and the thickness reduction rate of the porous polymer substrate was calculated according to the following equation 1. The measurement was performed by punching out a 5 x 5 cm porous substrate, and measurements were taken at a total of five points, four points 1 cm away from the corners and one point in the center. Samples were taken three times at the left, center, and right positions along the TD, and the arithmetic average was taken as the thickness of the porous polymer substrate.

[0165] [Formula 1] Thickness reduction rate (%) = (thickness of porous polymer substrate before applying pressure - thickness of porous polymer substrate after applying pressure) / thickness of porous polymer substrate before applying pressure x 100

[0166] [Table 1]

[0167] Referring to Table 1, it was confirmed that in Comparative Examples 1 and 2, the thickness reduction rate of the porous polymer substrate increased due to the low weight average molecular weight, while in Examples 1 and 2, the thickness reduction rate of the porous polymer substrate decreased as the weight average molecular weight increased.

[0168] Furthermore, in Comparative Examples 3 and 4, when the weight average molecular weight was the same, the thickness reduction rate of the porous polymer substrate increased due to the low polydispersity index, whereas in Examples 3 and 4, the thickness reduction rate of the porous polymer substrate decreased as the polydispersity index increased.

[0169] According to one embodiment of the present invention, the weight average molecular weight and polydispersity index of the crystalline polymer resin contained in the porous polymer substrate can be adjusted to improve compression resistance and reduce thickness change rate.

[0170] <Example 5> Polyolefin resin (a copolymer of ethylene and propylene in a weight ratio of 96:4, weight average molecular weight: 800,000) and liquid paraffin oil (kinematic viscosity at 40°C: 40 cSt) were mixed in a weight ratio of 3:7, and 5 wt% of polypropylene was further added based on the total weight of the polyolefin resin. The mixture was fed into a biaxial extruder, kneaded, and extruded. After extrusion, the sheet was formed by passing through a T-die and a cooling casting roll, and then biaxially stretched using a tenter-type sequential stretching machine, which stretched in the MD and then in the TD. The liquid paraffin oil was extracted from the stretched sheet with methylene chloride, and the sheet was heat-set at approximately 128°C to produce a polyolefin substrate (thickness: 9 μm).

[0171] Example 6 A polyolefin substrate (thickness 9 μm) was prepared in the same manner as in Example 5, except that a polyolefin resin (a copolymer containing ethylene and propylene in a weight ratio of 93:7) and liquid paraffin oil were mixed in a weight ratio of 3:7, and 5 wt % of polypropylene was further added based on the total weight of the polyolefin resin.

[0172] Example 7 A polyolefin substrate (thickness 9 μm) was prepared in the same manner as in Example 5, except that polyolefin resin (a copolymer containing ethylene and propylene in a weight ratio of 85:15) and liquid paraffin oil were mixed in a weight ratio of 3:7, and 2 wt % of polypropylene was further added based on the total weight of the polyolefin resin.

[0173] Example 8 A polyolefin substrate (thickness 9 μm) was prepared in the same manner as in Example 5, except that polyolefin resin (a copolymer containing ethylene and propylene in a weight ratio of 85:15) and liquid paraffin oil were mixed in a weight ratio of 3:7, and 3.5 wt % of polypropylene was further added based on the total weight of the polyolefin resin.

[0174] <Comparative Example 5> A polyolefin substrate (thickness 9 μm) was prepared in the same manner as in Example 5, except that a polyolefin resin (a copolymer containing ethylene and propylene in a weight ratio of 70:30) and liquid paraffin oil were mixed in a weight ratio of 3:7, and 5 wt % of polypropylene was further added based on the total weight of the polyolefin resin.

[0175] <Comparative Example 6> A polyolefin substrate (thickness 9 μm) was prepared in the same manner as in Example 5, except that polyolefin resin (a copolymer containing ethylene and propylene in a weight ratio of 85:15) and liquid paraffin oil were mixed in a weight ratio of 3:7, and 7 wt % of polypropylene was further added based on the total weight of the polyolefin resin.

[0176] <Experimental Example 2: Confirmation of the content of amorphous polymer resin contained in polyolefin substrate> In the examples and comparative examples, the content of amorphous polyolefin polymer resin in the polyolefin substrate was determined using a PolymerChar TREF instrument. For example, 40 mg of the polyolefin substrate was dissolved in 20 mL of trichlorobenzene solvent at 150°C for 120 minutes and then stabilized at 100°C for 45 minutes. This solution was then loaded onto a TREF column, cooled to 35°C at a rate of 0.5°C / min, and maintained for 15 minutes. The column was then heated from 35°C to 80°C at a rate of 20°C / min, maintaining the temperature in 5°C increments for 20 minutes, and then heated from 80°C to 120°C at a rate of 20°C / min, maintaining the temperature in 2°C increments for 20 minutes. The trichlorobenzene solvent was then passed through the column at a flow rate of 0.5 mL / min, and the weight of the fraction eluted at 35°C was measured. The results are shown in Tables 2 and 3.

[0177] In addition, the average number of CH3 atoms per 1000 carbon atoms was determined using an IR detector included in the machine, and the results are shown in Tables 2 and 3 below.

[0178] <Experimental Example 3: Confirmation of compression resistance according to the content of amorphous polymer resin contained in polyolefin substrate> The polyolefin substrates of Examples 5 and 6 and Comparative Example 5 were tested using an Asahi Seiko EG01-55-1MR device at room temperature under a constant pressure of 4.8 inches of water to measure the time it takes for 100 cc of air to pass through a 1 inch2 sample, thereby confirming the air permeability before compression.

[0179] Each of the polyolefin substrates was attached to a press and pressed at 70° C. and 8 MPa for 10 seconds, and then the air permeability after compression was measured in the same manner using the press.

[0180] The increase in air permeability was calculated according to the formula 1 based on the air permeability of the raw fabric before and after compression, and is shown in Table 2 below.

[0181] [Table 2]

[0182] As can be seen from Table 2, in the case of Comparative Example 5, the increase in air permeability was 364%, whereas in the cases of Examples 5 and 6, the increase in air permeability was 30% and 68%, respectively.

[0183] <Experimental Example 4: Confirmation of compression resistance depending on average short chain branching of polyolefin base material> Using the polyolefin substrates of Examples 7 and 8 and Comparative Example 6, the air permeability was measured before and after compression in the same manner as in Experimental Example 3.

[0184] Based on the air permeability of the raw fabric before and after compression, the increase rate of air permeability was calculated according to the above-mentioned formula 2, and is shown in Table 3 below.

[0185] [Table 3]

[0186] As shown in Table 3, in the case of Comparative Example 6, the increase in air permeability was 201%, whereas in the cases of Examples 7 and 8, the increase in air permeability was 27% and 147%, respectively.

[0187] Example 9

[0188] 30 parts by weight of polymer resin (polyethylene resin, Mw: 1.5 million) and 70 parts by weight of liquid paraffin oil (kinematic viscosity at 40°C: 40 cSt) were charged into a biaxial extruder, kneaded, and then extruded. After extrusion, the mixture was formed into a sheet through a T-die and a cooling casting roll, and then biaxially stretched in a tenter-type simultaneous stretching machine, stretching in the MD and then the TD. The liquid paraffin oil diluent was extracted from the stretched sheet with methylene chloride, and the sheet was heat-set at approximately 128°C to produce a porous polymer substrate.

[0189] The weight ratio of the eluate eluted at 98°C for the porous polymer substrate was determined using a PolymerChar TREF machine. For example, a 40 mg sample was prepared for the porous polymer substrate and dissolved in 20 mL of trichlorobenzene solvent at 150°C for 120 minutes, then stabilized at 100°C for 45 minutes. The sample was then loaded onto a TREF column and cooled to 35°C at a temperature ramp rate of 0.5°C / min and maintained for 15 minutes. The column was then heated from 35°C to 80°C at a ramp rate of 20°C / min, maintaining the temperature at 5°C intervals for 20 minutes, and heated from 80°C to 120°C at a ramp rate of 20°C / min, maintaining the temperature at 2°C intervals for 20 minutes. The weight of the polymer sample eluted at 98°C was measured while the trichlorobenzene solvent was flowed through the column at a flow rate of 0.5 mL / min. The content of the crystalline polymer resin in the porous polymer substrate was determined to be 72 wt%.

[0190] Example 10 A porous polymer substrate was produced in the same manner as in Example 9, except that the content of the crystalline polymer resin contained in the porous polymer substrate was 83 wt %.

[0191] <Comparative Example 7> In Example 9, 7 parts by weight of polypropylene (Mw: 350,000) was added to 100 parts by weight of polyethylene (Mw: 600,000) to produce a polymer resin (Mw: 580,000), and the content of the crystalline polymer resin contained in the porous polymer substrate was 66% by weight. A porous polymer substrate was produced in the same manner as in Example 9.

[0192] <Comparative Example 8> In Example 9, 0.5 parts by weight of polypropylene (Mw: 350,000) was added to 100 parts by weight of polyethylene (Mw: 600,000) to produce a polymer resin (Mw: 600,000), and a porous polymer substrate was produced in the same manner as in Example 9, except that the content of the crystalline polymer resin contained in the porous polymer substrate was 90% by weight.

[0193] <Experimental Example 5: Measurement of indentation depth and standard deviation> Using a nanoindenter (Fischerscope, HM2000), an indenter (Vickers Indenter, tip width 0.5 μm) was pressed into the porous polymer substrate with a force of 100 nN, and then the depth of the indenter was measured using an atomic force microscope (AFM).

[0194] The surfaces of the porous polymer substrates of Examples 9 and 10 and Comparative Examples 7 and 8 were subjected to a Dimension Icon (Bruker) under the following conditions, and the tip was moved relative to the surface of the sample as shown in FIG. 1 while applying a peak tapping force. The peak tapping force was measured, and the depth of the tip that penetrated into the sample surface at the time when the peak tapping force was measured was measured using an atomic force microscope (AFM, Atomic Force Microscope, OSTESPA-R3, Bruker, f=300 kHz, k=26 N / m).

[0195] -Mode: Tapping (Peak Force QNM)

[0196] -Scan speed (0.3Hz)

[0197] -Peak Force setpoint: 100nN, Amplitude: 300nm

[0198] -Scan angle: 90°

[0199] <Experimental Example 6: Measurement of Breakdown Voltage> For Examples 9 and 10 and Comparative Examples 7 and 8 having a thickness of 12 μm, a pressure of 8 MPa was applied at 70° C., and then the voltage was measured at 0.5 mA and over 3 seconds while increasing the pressure at a rate of 100 mV / s.

[0200] [Table 4]

[0201] Referring to Table 4, it was confirmed that in Examples 9 and 10, the crystalline polymer resin was contained in the porous polymer substrate at an appropriate content greater than the reference value, resulting in a relatively low indentation depth, a reduced standard deviation of the indentation depth, and an increased breakdown voltage after compression.

[0202] In contrast, in Comparative Example 7, the porous polymer substrate contained only a small amount of crystalline polymer resin, at 66 wt %, resulting in a sharp increase in indentation depth and a relatively small increase in breakdown voltage after compression, below 1,000 V. In Comparative Example 8, the porous polymer substrate contained an excessive amount of crystalline polymer resin, at 90 wt %, resulting in an increase in the standard deviation of indentation depth and a relatively small increase in breakdown voltage after compression, below 1,000 V.

[0203] Therefore, in the separator for an electrochemical device according to one embodiment of the present invention, the content of the crystalline polymer resin contained in the porous polymer substrate can be adjusted to control the indentation depth and its standard deviation, thereby improving the breakdown voltage after lamination.

[0204] Although the present invention has been described above with reference to preferred embodiments, it will be understood by those skilled in the art or those having ordinary knowledge in the art that various modifications and changes can be made to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. a porous polymer substrate; the porous polymer substrate includes an amorphous polymer resin and a crystalline polymer resin; the weight average molecular weight (Mw) of the eluate obtained by subjecting the porous polymer substrate to temperature rising elution fractionation (TREF) is 100,000 or more; A separator for an electrochemical device, wherein the content of the amorphous polymer resin in the porous polymer substrate is 40% by weight or less.

2. 2. The separator for an electrochemical device according to claim 1, wherein the porous polymer substrate contains 40% by weight or less of a fraction eluted at a temperature of 35° C. or less by temperature rising elution fractionation.

3. 2. The separator for an electrochemical device according to claim 1, wherein the content of the crystalline polymer resin in the porous polymer substrate is 60% by weight or more.

4. 2. The separator for an electrochemical device according to claim 1, wherein the weight ratio of the amorphous polymer resin to the crystalline polymer resin in the porous polymer substrate is 1:1 to 10:

1.

5. 2. The separator for an electrochemical device according to claim 1, wherein the deviation of the indentation depth in the porous polymer substrate is −5 nm or more and 5 nm or less.

6. the porous polymer substrate contains a polyolefin resin; the amorphous polymer resin is an amorphous polyolefin resin, 2. The separator for an electrochemical device according to claim 1, wherein the crystalline polymer resin is a crystalline polyolefin resin.

7. 7. The separator for an electrochemical device according to claim 6, wherein the polyolefin resin is one selected from the group consisting of polyethylene; polypropylene; polybutylene; polypentene: polyhexene: polyoctene; copolymers of one or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; and combinations thereof.

8. 8. The separator for an electrochemical device according to claim 7, wherein the polyolefin resin has an average of 500 or less short chain branches (SCB) per 1000 total carbon atoms.

9. 8. The separator for an electrochemical device according to claim 7, wherein the polyolefin resin has a melt index (ASTM D1238, 190° C., 2.16 kg) of 0.1 g / 10 min to 0.3 g / 10 min.

10. 2. The separator for an electrochemical device according to claim 1, wherein the weight average molecular weight (Mw) of the porous polymer substrate is 500,000 or more and 3,000,000 or less.

11. 2. The separator for an electrochemical device according to claim 1, wherein the polydispersity index (PDI) of the eluate is 5 or more.

12. The separator for electrochemical elements according to claim 1, which satisfies any one or more of the following (i) to (iii) when a pressure of 8 MPa is applied at 70°C: (i) The thickness reduction rate of the porous polymer substrate is 10% or less, as defined by the following Equation 1: [Formula 1] Thickness reduction rate (%) = (thickness of porous polymer substrate before applying pressure - thickness of porous polymer substrate after applying pressure) / thickness of porous polymer substrate before applying pressure x 100 (ii) the increase in air permeability of the porous polymer substrate after compression is 185% or less, as defined by the following formula 2: [Formula 2] Air permeability increase rate (%) = (air permeability after compression - air permeability before compression) / (air permeability before compression) x 100 (iii) The dielectric breakdown voltage of the porous polymer substrate is 1,000 V or more.

13. The separator for an electrochemical element according to claim 1, which has a thickness of 1 μm or more and 30 μm or less.

14. An electrochemical device comprising: a positive electrode; a negative electrode; and the separator for an electrochemical device according to claim 1 interposed between the positive electrode and the negative electrode.

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