Separator substrate, preparation method thereof, and separator including same

Abstract

The present invention relates to a separator substrate, a separator, an electrode assembly, and an electrochemical device. A separator substrate according to one embodiment of the present invention has a surface roughness value (Sa) in a predetermined range. Accordingly, a separator using the separator substrate maintains excellent adhesive strength, and the abrasion resistance of the separator is improved.

Description

Membrane substrate, manufacturing method thereof, and membrane comprising the same

[0001] The present invention relates to a separator substrate, a method for manufacturing the same, and a separator comprising the same. Specifically, the present invention relates to a separator with improved adhesive strength and wear resistance, an electrode assembly comprising the same, and electrochemical testing.

[0002] This application claims priority to Korean Patent Application No. 2023-0095292, filed with the Korean Intellectual Property Office on July 21, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] Lithium secondary batteries are manufactured through a process of inserting an electrode assembly consisting of a cathode / separator / cathode as a single unit into a battery case, then injecting and sealing the electrode assembly. Polyolefin-based porous substrates are typically used as separators for lithium secondary batteries. To address the problem of short circuits between the cathode and anode due to the thermal shrinkage behavior of the polyolefin-based porous substrate, separators have been developed that enhance the strength and heat resistance of the separator by forming a coating layer made of a mixture of inorganic particles and binder polymers on the surface of the porous substrate. Examples include the Safety Reinforced Separator (SRS) and the Ceramic Coated Separator (CCS).

[0004] These SRS or CCS particles act as spacers, allowing the inorganic particles within the coating layer to maintain the physical form of the separator. This prevents the porous substrate from shrinking when exposed to high temperatures, thereby preventing direct contact between the anode and cathode. This allows for the manufacture of electrode assemblies by bonding the anode and cathode with a separator having porous coating layers on both sides.

[0005] Meanwhile, known types of secondary battery unit cells include cylindrical, square, and pouch-shaped. In the case of a cylindrical secondary battery cell, an insulator separator is interposed between the positive and negative electrodes, and this is wound to form a jelly-roll-shaped electrode assembly, which is then inserted into a battery can to form the battery.

[0006] At this time, due to the volume expansion of the cathode caused by repeated charging and discharging of the battery, the porous coating layer of the separator is continuously scratched, ultimately damaging the separator and causing an internal short circuit, or impingement. This internal short circuit can cause the cylindrical battery cell to catch fire.

[0007] In addition, if the porous coating layer of the separator is scratched, the inorganic particles and / or binder polymers that make up the porous coating layer may drift as foreign substances within the battery, which may cause a phenomenon in which a voltage drop behavior exceeding the self-discharge rate of the battery is exhibited.

[0008] This requires the development of a separator that can exhibit excellent friction durability while improving heat resistance by having a porous coating layer.

[0009] Accordingly, the problem to be solved by the present invention is to provide a separator that solves the above-described problem and an electrode assembly and electrochemical device including the same.

[0010] Specifically, the present invention aims to provide a separator having excellent frictional durability while stably bonding a porous coating layer, and an electrochemical device, such as a lithium secondary battery, having improved voltage drop behavior by applying the same.

[0011] In particular, the present invention aims to provide a membrane substrate having surface properties with improved wear resistance against friction and a method for manufacturing the same by maintaining an excellent degree of impregnation of a slurry for forming a coating layer when forming a porous coating layer on a membrane substrate, thereby providing excellent adhesion between the membrane substrate and the porous coating layer.

[0012] To solve the above problem,

[0013] According to one aspect of the present invention, a membrane substrate of the following embodiments is provided.

[0014] The membrane substrate according to the first embodiment is

[0015] A porous polymer substrate having a roughness value (Sa) of at least one surface of 80 nm to 160 nm.

[0016] According to the second embodiment, in the first embodiment,

[0017] The surface roughness value (Sa) of both sides of the above porous polymer substrate may be 85 nm to 150.

[0018]

[0019] According to another aspect of the present invention, a separation membrane of the following embodiments is provided.

[0020] The separation membrane according to the third embodiment is

[0021] A membrane substrate according to the first embodiment or the second embodiment and

[0022] A porous coating layer formed on at least one of the surfaces having a surface roughness value (Sa) of 80 nm to 160 nm, and including inorganic particles and a binder polymer;

[0023] According to the fourth embodiment, in the third embodiment,

[0024] The adhesive strength between the above-mentioned separator substrate and the above-mentioned porous coating layer may be 100 gf / 15 mm or more.

[0025] According to the fifth embodiment, in the third embodiment or the fourth embodiment,

[0026] The adhesive strength between the above-mentioned separator substrate and the above-mentioned porous coating layer may be 100 gf / 15 mm to 300 gf / 15 mm.

[0027] According to the sixth embodiment, in any one of the third to fifth embodiments,

[0028] The friction coefficient of the above separator may be 0.25 or more.

[0029] According to the seventh embodiment, in any one of the third to sixth embodiments,

[0030] The friction coefficient of the above separator may be 0.5 to 1.0.

[0031] According to the eighth embodiment, in any one of the third to seventh embodiments,

[0032] The puncture strength of the above membrane may be 450 gf or more.

[0033] According to the ninth embodiment, in any one of the third to eighth embodiments,

[0034] The puncture strength of the above membrane may be 500 gf to 600 gf.

[0035]

[0036] According to another aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0037] An electrode assembly according to the 10th embodiment,

[0038] A separation membrane according to any one of the third to ninth embodiments,

[0039] It may include a positive electrode and a negative electrode formed on each side of the above separator.

[0040] According to the 11th embodiment, in the 10th embodiment,

[0041] The above electrode assembly may have a voltage drop over voltage (dOCV) of 2.0 or less within 48 hours.

[0042] According to the 12th embodiment, in the 10th embodiment or the 11th embodiment,

[0043] The electrode assembly may have a voltage drop over 48 hours (dOCV) of 1.5 or less.

[0044]

[0045] According to another aspect of the present invention, electrochemical devices of the following embodiments are provided.

[0046] The electrochemical device according to the 13th embodiment,

[0047] An electrode assembly according to any one of the 10th to 12th embodiments is housed in a case.

[0048] According to the 14th embodiment, in the 13th embodiment,

[0049] The above case may be a cylindrical case.

[0050]

[0051] According to another aspect of the present invention, a method for manufacturing a membrane substrate of the following embodiments is provided.

[0052] The method for manufacturing a membrane substrate according to the 15th embodiment is as follows:

[0053] S1) A step of extruding a polymer slurry to obtain a polymer sheet; and

[0054] S2) A method for manufacturing a membrane substrate, comprising the step of positioning the obtained polymer sheet on a casting roll and cooling it;

[0055] The method further includes a step of placing the polymer sheet in an atmosphere at a temperature of 28°C to 45°C between steps S1 and S2.

[0056] According to one embodiment of the present invention, a membrane substrate can exhibit an effect of improving the adhesion between the membrane substrate and the porous coating layer by improving the degree of impregnation of a slurry for forming a coating layer when forming a porous coating layer on its surface through improvement of the surface roughness value (Sa).

[0057] Accordingly, the surface properties of the membrane substrate can improve the wear resistance of the porous coating layer against friction and enhance mechanical properties such as puncture strength.

[0058] Through this, an electrochemical device using a separator can exhibit the effect of preventing and / or improving the destruction of the separator caused by volume expansion of an electrode, for example, a cathode, due to repeated charge and discharge, and the resulting short circuit phenomenon between the anode and cathode.

[0059] In addition, by using a separator having a porous coating layer, not only can the heat resistance of the electrochemical device be improved, but also the wear resistance of the separator can be improved, thereby preventing and / or reducing the formation of foreign substances inside the electrochemical device during charging and discharging, thereby improving the voltage drop phenomenon of the electrochemical device.

[0060] Figure 1 is a schematic diagram of a conventional device for manufacturing a membrane substrate. The device of Figure 1 comprises an extrusion section (200) for extruding a polymer sheet and casting rolls (201, 202) for cooling the extruded polymer sheet.

[0061] Fig. 2 is a schematic diagram of an apparatus for manufacturing a membrane substrate according to one embodiment of the present invention. The apparatus of Fig. 2 includes a cooling unit (300) for cooling one surface of the membrane substrate between an extrusion unit (200) and casting rolls (201, 202).

[0062] Fig. 3 is a schematic diagram of an apparatus for manufacturing a membrane substrate according to one embodiment of the present invention. The apparatus of Fig. 3 includes a cooling unit (300) for cooling both surfaces of the membrane substrate between an extrusion unit (200) and casting rolls (201, 202).

[0063] Hereinafter, the present invention will be described in detail.

[0064] In this specification, when a part is said to "include" a certain component, this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specifically stated.

[0065] In this specification, the term “A and / or B” means “A or B, or both.”

[0066] Certain terminology used in the following detailed description of the invention is for convenience only and is not intended to limit the invention. Furthermore, directional words such as "up," "down," "left," "right," "front," "back," "inside," and "outside" indicate directions within the drawings to which reference is made, or indicate directions toward or away from the geometric center of the designated device, system, or its components, respectively.

[0067] According to one aspect of the present invention, a membrane substrate is provided as a porous polymer substrate, wherein at least one surface has a roughness value (Sa) of 30 nm to 160 nm.

[0068]

[0069] Membrane substrate and manufacturing method thereof

[0070] According to one aspect of the present invention, a membrane substrate is provided as a porous polymer substrate, wherein at least one surface has a roughness value (Sa) of 80 nm to 160 nm.

[0071] To explain this, one feature of a method for manufacturing a membrane substrate according to one embodiment of the present invention will first be described.

[0072] A method for manufacturing a membrane substrate according to one aspect of the present invention is as follows:

[0073] S1) A step of extruding a polymer slurry to obtain a polymer sheet; and

[0074] S2) A step of cooling the obtained polymer sheet by placing it on a casting roll.

[0075] At this time, according to one aspect of the present invention, it is characterized in that it further includes a step of placing the polymer sheet in an atmosphere at a temperature of 28°C to 45°C between the steps S1 and S2.

[0076] Figure 1 schematically illustrates a portion of a conventional device for manufacturing a membrane substrate. The device of Figure 1 comprises an extrusion unit (200) for extruding a polymer sheet and casting rolls (201, 202) for transporting the polymer sheet for cooling and subsequent processing. Typically, a polymer sheet extruded through the extrusion unit is brought into contact with the casting roll while at a high temperature and cooled in the air.

[0077] FIGS. 2 and 3 schematically illustrate a portion of an apparatus for manufacturing a membrane substrate according to one embodiment of the present invention. The apparatus of FIGS. 2 and 3 is provided with a cooling unit (300) for lowering the temperature of a polymer sheet extruded between an extrusion unit (200) and casting rolls (201, 202). FIG. 2 has the cooling unit (300) only on one side of the polymer sheet, while FIG. 3 has the cooling units (300) on both sides of the polymer sheet.

[0078] First, in one embodiment of the present invention, the step of extruding the polymer slurry S1) to obtain a polymer sheet may include melt-extruding a polymer resin as a raw material.

[0079] In one embodiment of the present invention, the polymer resin may be used without particular limitation as long as it is used as a raw material for manufacturing a membrane substrate. The polymer resin may include a resin such as polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or a mixture of two or more thereof as a raw material for manufacturing a membrane substrate. The polyolefin resin is a polymerization of olefin, and refers to a resin polymerized using an olefin generally used in a membrane substrate as a monomer. For example, the polyolefin resin may be a homopolymer of a monomer selected from polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; A copolymer of two or more of these; or a mixture thereof, but is not limited thereto.

[0080] In one embodiment of the present invention, the porous polymer substrate may be a polyolefin substrate.

[0081] In one embodiment of the present invention, the porous polymer substrate may be a polyethylene substrate.

[0082] In one embodiment of the present invention, a conventional diluent may be used to extrude the polymer resin by feeding it into an extruder. The diluent may be a liquid or solid paraffin oil, wax, soybean oil, or the like, which are commonly used in membrane manufacturing.

[0083] In one embodiment of the present invention, a conventional single-screw extruder or twin-screw extruder may be used for the melting and extrusion, but is not limited thereto. In one embodiment of the present invention, a mixture of the diluent and the polymer resin may be introduced into an extruder, and then mixed while melting the polymer resin at high temperatures to obtain a molten composition.

[0084] At this time, since the extrusion of the polymer sheet is generally performed at a high temperature, for example, 150°C to 300°C, the polymer sheet extruded through the extrusion section has a surface temperature of a high temperature, for example, 130°C to 200°C, immediately after extrusion, and comes into contact with the casting roll while having this surface temperature. Generally, considering that the temperature of the casting roll is 20°C to 45°C, 25°C to 45°C, 35°C to 45°C, or 25°C, the polymer sheet is rapidly cooled through contact with the casting roll, and crystal formation on the surface does not occur well.

[0085] According to one aspect of the present invention, the polymer sheet extruded through the extrusion section is first cooled through the cooling section (300) before it reaches the casting roll, thereby inducing crystal formation on the surface of the polymer sheet, thereby increasing the roughness of the surface.

[0086] In one embodiment of the present invention, the cooling unit may be referred to as a 'cooling unit' for cooling a polymer sheet at a high temperature, and the cooling unit may be equipped with, for example, a 'hot air blower' for bringing the polymer sheet into contact with a temperature higher than room temperature. In one embodiment of the present invention, the cooling unit may be equipped with a device for applying hot air of 28°C to 45°C to at least one surface of the polymer sheet.

[0087] Conventionally, when manufacturing a porous polymer substrate as a membrane substrate, a polymer slurry is extruded to obtain a polymer sheet, and the obtained polymer sheet is placed on a casting roll and cooled. The inventor of the present invention discovered that by placing the polymer sheet in an atmosphere having a specific temperature before cooling the polymer sheet, crystallization of the surface of the polymer sheet can be induced, thereby implementing different surface properties. Accordingly, in the manufacturing of the membrane substrate, by additionally performing a step of placing the polymer sheet in a specific temperature range before cooling, a membrane substrate having a surface roughness value (Sa) of 80 nm to 160 nm depending on the surface crystallization of the membrane substrate was obtained.

[0088] In one embodiment of the present invention, a step of placing the polymer sheet in an atmosphere having a temperature of 28°C to 45°C is performed between steps S1 and S2. Specifically, the step may be performed at a temperature of 30°C to 45°C or 30°C to 40°C. In addition, the step of placing the polymer sheet in air at atmospheric pressure within the above temperature range may be performed.

[0089] In one embodiment of the present invention, the additionally performed step may be performed continuously with steps S1 and S2 through a manufacturing device for a membrane substrate further equipped with a 'cooling unit (300)' between steps S1 and S2.

[0090] In one embodiment of the present invention, the speed at which the polymer sheet travels in the temperature range of 28°C to 45°C between steps S1 and S2 may be, for example, 5 m / min to 20 m / min, specifically 5 m / min to 15 m / min, or 10 m / min. However, the speed may vary depending on the speed of the entire process within a range that does not interfere with the implementation of surface roughness of the separation membrane substrate, and the present invention is not limited thereto.

[0091] When the polymer sheet is placed in the above temperature range before the cooling of the above step S2, the surface roughness value (Sa) can be implemented as 80 nm to 160 nm. In addition, if the temperature is too high, the surface roughness of the separator substrate may decrease, which may cause a decrease in the adhesive strength between the separator substrate and the porous coating layer, and if the temperature is too low, the surface roughness of the separator substrate may increase, which may cause a problem in that the adhesive strength between the separator substrate and the porous coating layer is implemented at an appropriate level or higher, and the impact resistance of the surface of the separator may be reduced, but the present invention is not limited thereto.

[0092] In one embodiment of the present invention, the method for manufacturing the membrane substrate may further include a step of stretching and heat-setting the polymer sheet formed through a casting roll S3) after the cooling step S2.

[0093] In one embodiment of the present invention, the stretching may include secondary stretching of the polymer sheets in the same direction or in different directions. For example, the stretching may include independently stretching the polymer sheets in a direction parallel to the machine direction (MD) and / or the transverse direction (TD).

[0094] In this specification, the 'machine direction' refers to a direction parallel to the running direction of the [extrusion->molding->stretching...] process in the manufacturing process of the membrane substrate. The machine direction can be confirmed through the fiber orientation direction of the polymer of the membrane substrate, and the direction parallel to the fiber orientation direction is the machine direction. Accordingly, the 'transverse direction' refers to a direction orthogonal to the machine direction. The transverse direction can also be confirmed as a direction orthogonal to the fiber orientation direction of the polymer of the membrane substrate.

[0095] In one embodiment of the present invention, the stretching can be performed, for example, by roll stretching, tenter stretching, or simultaneous stretching.

[0096] In one embodiment of the present invention, the stretching may be performed at a stretching ratio of, for example, 3 times or more, 5 to 12 times, or 6 to 7 times. When the stretching ratio satisfies the above numerical range, there may be advantageous effects in terms of thickness uniformity and physical property balance between longitudinal and transverse directions of the manufactured membrane substrate, but the present invention is not limited thereto.

[0097] In one embodiment of the present invention, a step of extracting a diluent from the stretched sheet after the stretching to form pores and then heat-setting may be included.

[0098] In one embodiment of the present invention, the extraction of the diluent may be performed using an organic solvent. Suitable organic solvents include, for example, methyl ethyl ketone, methylene chloride, hexane, or a mixture of two or more thereof, which have high extraction efficiency and rapid drying. However, the present invention is not limited thereto.

[0099] In one embodiment of the present invention, the temperature at which the extraction is performed is not particularly limited as long as it does not change the surface roughness value of the porous substrate formed.

[0100] In one embodiment of the present invention, after the stretching and extraction of the diluent, heat setting may be performed to forcibly hold the porous sheet and remove residual stress within the sheet. However, the purpose of the heat setting is not limited thereto.

[0101] In one embodiment of the present invention, the heat setting temperature may vary depending on the type of polymer resin used in the manufacture of the membrane substrate. The heat setting temperature may be, for example, 100°C to 180°C, specifically 110°C to 150°C, more specifically 120°C to 140°C, for example, 130°C, but the present invention is not limited thereto.

[0102] In one embodiment of the present invention, heat may be applied while uniaxially stretching in the MD or TD direction during the heat fixation, or heat may be applied while biaxially stretching in the MD and TD directions, but is not limited thereto.

[0103] According to one embodiment of the present invention, a membrane substrate having a surface roughness value (Sa) of 80 nm to 160 nm on both sides of the porous polymer substrate can be provided.

[0104] According to one embodiment of the present invention, the surface roughness value (Sa) of at least one side of the porous polymer substrate may be 85 nm to 150 nm. In addition, the surface roughness value (Sa) of at least both sides of the porous polymer substrate may be 85 nm to 150 nm.

[0105] According to one embodiment of the present invention, the surface roughness value (Sa) of at least one surface of the porous polymer substrate may be 90 nm to 140 nm.

[0106] According to one embodiment of the present invention, when the surface roughness value (Sa) of at least one side of the porous polymer substrate is within the above-described range, excellent adhesive strength between the membrane substrate and the porous coating layer is secured when forming the porous coating layer, and advantageous effects can be exhibited in terms of wear resistance and impact resistance of the porous coating layer, but the effects of the present invention are not limited thereto.

[0107] Meanwhile, in addition to measuring the Sa value, there are known methods for measuring the surface roughness of a membrane substrate, such as Ra (center line average), Rmax (maximum peak to valley roughness height), Rz (ten point height), and Rg (root mean square, RMS), which represent the two-dimensional roughness of the surface. However, Ra, Rmax, Rz, Rg, etc. are measures of the two-dimensional (linear) roughness of the surface, and the roughness shape of the surface cannot be confirmed with the values ​​alone. That is, even if at least one of Ra, Rmax, Rz, and Rg is the same for two different surfaces, the three-dimensional roughness shape may be different, and as a result, the impregnation amount of the slurry for forming the porous coating layer may be different, or the shape of the porous coating layer may be different, so that the adhesive strength between the membrane substrate and the porous coating layer and the mechanical strength of the porous coating layer may be implemented differently. Considering these problems, the present invention defines the surface roughness value of the membrane substrate through Sa.

[0108] In one embodiment of the present invention, the surface roughness value (Sa) can be measured by analyzing the surface of a porous polymer substrate using atomic force microscopy (AFM). For example, a sample of a porous polymer substrate to be measured for surface roughness is obtained in a size of 30 ㎛ X 30 ㎛, and then the surface characteristics of each side are measured. At this time, the surface roughness value (Sa) is measured by analyzing the difference in the average height of the surface of the entire area based on the average height surface.

[0109] Hereinafter, the composition of the porous polymer substrate will be exemplarily described. However, the porous substrate is not limited to the constituent components described below.

[0110] In one embodiment of the present invention, the porous polymer substrate refers to a substrate having a plurality of pores formed therein as a porous ion-conducting barrier that allows ions to pass while blocking electrical contact between the cathode and the anode. The pores are structured to be interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0111] In one embodiment of the present invention, the porous polymer substrate may be a porous polymer film containing a thermoplastic resin, from the perspective of imparting a shutdown function. Here, the shutdown function refers to a function in which, when the battery temperature rises, the thermoplastic resin melts and closes the pores of the porous polymer substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery.

[0112] In one embodiment of the present invention, the thickness of the porous polymer substrate is not particularly limited as long as it satisfies the above-described range based on the total thickness of the separator, but may be, for example, 5 to 300 ㎛, specifically 5 to 100 ㎛, 5 to 50 ㎛, 5 to 20 ㎛, 5 to 15 ㎛, or 9 to 12 ㎛.

[0113] In one embodiment of the present invention, the "thickness" of the porous polymer substrate can be measured by a known method for measuring the thickness of each membrane component. For example, the thickness of the porous polymer substrate can be measured using a known thickness measuring device, and for example, the thickness can be measured using a commercially available thickness measuring device (Mitutoyo, VL-50S-B).

[0114]

[0115] membrane

[0116] According to one aspect of the present invention, a separator is provided, which comprises a porous polymer substrate as a separator substrate and a porous coating layer formed on at least one surface of the separator substrate, the porous polymer substrate comprising inorganic particles and a binder polymer. In this case, the porous coating layer may be formed on at least one surface of the separator substrate having a roughness value (Sa) of 30 nm to 160 nm.

[0117] According to another aspect of the present invention, a separator is provided, which comprises a porous polymer substrate as a separator substrate and a porous coating layer formed on at least one surface of the separator substrate, the porous polymer substrate comprising inorganic particles and a binder polymer. In this case, the porous coating layer is formed on at least one surface of the separator substrate having a roughness value (Sa) of 80 nm to 160 nm.

[0118] The above porous coating layer includes a large amount of inorganic particles and a binder polymer that binds them to improve the safety of the separator. The inorganic particles can improve the heat resistance of the separator, and the binder polymer can provide adhesive strength to the surface of the separator. At this time, if the surface of the separator substrate on which the porous coating layer is formed is flat, there may be a problem of poor adhesive strength at the interface between the separator substrate and the porous coating layer. However, if the surface of the separator substrate is too rough, the adhesive strength at the interface between the separator substrate and the porous coating layer is very strong, and as the amount of binder present at the interface between the separator substrate and the porous coating layer increases compared to the surface portion of the porous coating layer, the impact resistance of the surface portion of the porous coating layer is lowered, which may cause a problem of lowering the mechanical properties of the separator. Accordingly, a separator having a porous coating layer formed on a separator substrate according to one aspect of the present invention can exhibit improved wear resistance and impact resistance of the separator while maintaining excellent adhesion between the separator substrate and the porous coating layer by implementing a certain level of surface roughness.

[0119] In one embodiment of the present invention, the separator may be characterized in that the adhesion strength between the surface of the separator substrate having a surface roughness value (Sa) of 80 nm to 160 nm, specifically 85 nm to 150 nm, and the porous coating layer is 30 gf / 15 mm or more. Specifically, the adhesion strength between the surface of the separator substrate having a surface roughness value (Sa) in the above-described range and the porous coating layer may be 50 gf / 15 mm to 300 gf / 15 mm, 100 gf / 15 mm to 300 gf / 15 mm, 150 gf / 15 mm to 300 gf / 15 mm, or 195 gf / 15 mm to 284 gf / 15 mm. When the adhesive strength between the separator substrate and the porous coating layer of the separator is within the above-described range, it can exhibit advantageous effects in terms of improving the manufacturing process of an electrode assembly using the separator and improving the stability of the separator.

[0120] The adhesive strength of the above separator can be measured, for example, by the following method. The separator to be measured for adhesive strength is sampled to a width of 15 mm and attached to a slide glass using 18 mm wide double-sided tape (3M) so that the side to be measured for adhesive strength is in contact with the glass. Then, the peel strength between the separator substrate and the porous coating layer is measured using a UTM device (Instron) at 180° and 300 mm / min.

[0121] In addition, in one embodiment of the present invention, the separator may be characterized by having a friction coefficient of 0.25 or more. In the present specification, the 'friction coefficient' refers to a friction coefficient when the porous coating layer is detached due to destruction or damage caused by the frictional force applied to the separator, thereby exposing the separator substrate to the surface. When the surface roughness value (Sa) of the separator substrate is in the above-described range, the degree of impregnation of the slurry for forming a porous coating layer on the separator substrate is improved, thereby increasing the adhesive force between the separator substrate and the porous coating layer, and increasing the force required for detachment of the separator substrate and the porous coating layer by friction, thereby exhibiting the advantage of increasing the friction coefficient.

[0122] According to one embodiment of the present invention, the friction coefficient of the separator may be 0.25 or greater. Specifically, the friction coefficient of the separator may be 0.5 to 1.0, 0.50 to 0.85, 0.60 to 0.80, or 0.64 to 0.78.

[0123] The friction coefficient of the above-mentioned separator can be measured, for example, using known friction and wear testing equipment. Specifically, the friction coefficient of the above-mentioned separator can be measured, for example, by measuring the friction coefficient when the porous coating layer is detached when repeated friction is applied using a 5g / dia tip using Heidon's friction and wear equipment.

[0124] In addition, in one embodiment of the present invention, the separator may be characterized by having a puncture strength of 450 gf or more. In the present specification, the 'puncture strength' represents the magnitude of the resistance of the separator to the normal force when the normal force is applied to the separator. When the surface roughness value (Sa) of the separator substrate is in the above-described range, the degree of impregnation of the slurry for forming a porous coating layer on the separator substrate is improved, thereby increasing the adhesive force between the separator substrate and the porous coating layer, and also exhibiting the advantage of excellent mechanical strength of the separator substrate. On the other hand, when the surface roughness value of the separator substrate is too high, the inside of the separator substrate may not be formed densely, which may result in a problem of lowered mechanical strength and poor puncture strength, but the present invention is not limited thereto.

[0125] According to one embodiment of the present invention, the puncture strength of the separator may be 450 gf or more. Specifically, it may be 450 gf to 650 gf, 500 gf to 600 gf, 530 gf to 590 gf, or 566 gf to 589 gf.

[0126] The puncture strength of the above-mentioned separator can be measured, for example, by a known method for measuring puncture strength. Specifically, the puncture strength of the above-mentioned separator can be measured, for example, by measuring the force required to penetrate the separator when a force is applied under the conditions of a 1 mm tip and 120 mm / min using Instron's UTM equipment.

[0127] Hereinafter, the composition of the porous coating layer will be exemplarily described. However, the composition of the porous coating layer is not limited thereto.

[0128] In one embodiment of the present invention, the porous coating layer may include inorganic particles and a binder polymer, such that the inorganic particles have all or at least a portion of their surfaces coated with the binder polymer. In this case, the inorganic particles are surface-bonded and / or point-bonded via the binder polymer.

[0129] For example, the inorganic particles and the binder resin in the porous coating layer may be included in a weight ratio of 95:5 to 50:50. Specifically, the inorganic particles and the binder resin in the porous coating layer may be included in a weight ratio of 99:1 to 50:50, 95:5 to 50:50, 95:5 to 70:30, 95:5 to 80:20, 95:5 to 90:10, but the present invention is not limited thereto. The porous coating layer has a structure in which a plurality of micropores are formed therein, and these micropores are connected to each other, and has a structural characteristic of a porous layer in which gas or liquid can pass from one side to the other side.

[0130] In one embodiment of the present invention, the porous coating layer may have a porous structure derived from pores formed by the interstitial volume between inorganic particles. The pore size and porosity (pore volume ratio) can be controlled depending on the particle size and size distribution. Through this structure, the resistance to metallic foreign substances present in the electrode is increased, and at the same time, the shrinkage of the porous polymer substrate is suppressed, thereby enhancing the safety of the electrochemical device.

[0131] In one embodiment of the present invention, the porous coating layer comprises a plurality of nodes including the inorganic particles and a binder polymer covering at least a portion of the surface of the inorganic particles; and one or more filaments formed in a thread shape from the binder polymer of the nodes, the filaments having a node connecting portion extending from the nodes and connecting other nodes; and the node connecting portion may have a structure in which a plurality of filaments derived from the binder polymer intersect with each other to form a three-dimensional network structure.

[0132] In one embodiment of the present invention, as described above, the porous coating layer may be formed through a safety reinforced separator (SRS) manufacturing method, a ceramic coated separator (CCS) manufacturing method, or another known manufacturing method, but is not limited thereto.

[0133] In one embodiment of the present invention, the inorganic particles can be used without particular limitation as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). Non-limiting examples of such 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, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC and TiO2, and one or more of these may be included.

[0134] In one embodiment of the present invention, the average particle diameter (D) of the inorganic particles 50 ) may be, for example, 100 nm or more. Specifically, the average particle diameter (D) of the inorganic particles 50 ) may be 100 nm to 1 μm, or 100 nm to 500 nm. When the average particle diameter of the inorganic particles is within the above-described range, it may exhibit a beneficial effect in terms of suppressing an increase in resistance of the separation membrane, but the present invention is not limited thereto.

[0135] The particle size of the above inorganic particles can be measured by a known particle size measuring method, for example, using a particle size analyzer (PSA, Particle Size Analyzer) from Melbourne Co. In addition, the average particle size (D 50 ) refers to the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size, and may be measured using a known laser diffraction method. At this time, the laser diffraction particle size measuring device may be, for example, Microtrac S3500 from Microtrac Corporation.

[0136] In one embodiment of the present invention, the binder polymer may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin) and / or an acrylic binder. In one embodiment of the present invention, the PVdF-based resin may include at least one of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of a monomer copolymerizable with vinylidene fluoride, and a mixture thereof. In one embodiment of the present invention, the monomer may include, for example, a fluorinated monomer and / or a chlorinated monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); Perfluoro(alkylvinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethylvinyl) ether (PEVE), and perfluoro(propylvinyl) ether (PPVE); perfluoro(1,3-dioxole); and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), and more than one of these may be included. The acrylic binder may include, for example, polyacrylic acid (PA), polyacrylonitrile (PAN), polyacrylamide (PAA), or a (meth)acrylic polymer, or a mixture of two or more thereof, but the present invention is not limited thereto. The (meth)acrylic polymer refers to a polymer that includes a (meth)acrylic acid ester as a monomer. Such monomers may include, for example, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate or mixtures of two or more thereof, but the present invention is not limited thereto.

[0137] In one embodiment of the present invention, the thickness of the porous coating layer is not particularly limited as long as it satisfies the above-described ratio range relative to the total thickness of the separator, but may be, for example, 0.5 to 50 μm, specifically 0.5 to 10 μm, 0.5 to 5 μm, or 1.5 to 3 μm.

[0138]

[0139] electrode assembly

[0140] According to another aspect of the present invention, an electrode assembly is provided, which includes the above-described separator and an anode and a cathode formed on each side of the separator.

[0141] As described above, the separator according to one aspect of the present invention has improved heat resistance by having a porous coating layer, and not only has excellent adhesion between the separator substrate and the porous coating layer and wear resistance of the porous coating layer, but also has improved impact resistance due to the excellent mechanical properties of the separator substrate. An electrode assembly using the same is characterized in that the voltage drop phenomenon is prevented or delayed, thereby effectively improving the low voltage problem caused by the destruction of the separator.

[0142] In one embodiment of the present invention, the electrode assembly is characterized in that no voltage drop phenomenon occurs or the degree of the voltage drop is very small even after 200 cycles of charge and discharge repetition.

[0143] For example, the electrode assembly may exhibit a voltage drop (dOCV) of 2.0 or less within 48 hours, for example, the electrode assembly may exhibit a voltage drop of 2.0 or less within 48 hours after 200 cycles of charge and discharge. In addition, the electrode assembly may exhibit a voltage drop of 1.5 or less within 48 hours, specifically, a voltage drop of 1.5 or less within 48 hours after 200 cycles of charge and discharge. More specifically, the electrode assembly may exhibit a voltage drop of 1.0 or less within 48 hours, specifically, a voltage drop of 1.0 or less within 48 hours after 200 cycles of charge and discharge. For example, the electrode assembly may exhibit a voltage drop of 0.1 to 1.0, 0.1 to 0.8, 0.3 to 0.8, 0.3 to 0.7, or 0.4 to 0.6 within 48 hours.

[0144] In one embodiment of the present invention, the voltage drop is the OCV measured at a reference time point (t0) and 48 hours later (t) from the reference time point. 48 ) can be measured by calculating the difference in the measured OCV. Specifically, the OCV of the electrode assembly is measured by measuring the voltage drop for 48 hours after charging with the SOC set to 60% as the end point.

[0145] In one embodiment of the present invention, when a separator using the above-described separator substrate is applied, the wear resistance of the separator is excellent, and thus an electrochemical device having excellent battery safety and lifespan characteristics can be provided.

[0146] Hereinafter, the configuration of the electrode is exemplarily described. However, the present invention is not limited thereto.

[0147] In one embodiment of the present invention, the positive electrode and the negative electrode may each be a current collector coated with an electrode active material, and their size and shape are not particularly limited.

[0148] In one embodiment of the present invention, the positive electrode active material may include, but is not limited to, for example, a lithium transition metal oxide; a lithium metal iron phosphate; a lithium nickel-manganese-cobalt oxide; an oxide in which a portion of lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more thereof. Specifically, the positive electrode active material may include, but is not limited to, a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a compound having the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by O2 (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein M = Fe, Co, Ni, Cu or Zn); lithium metal phosphate LiMPO4 (wherein M = Fe, CO, Ni or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide partially substituted with aluminum a [Nib Co c Mn d Al e ] 1-f M1 f O2 (M1 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and 0.8≤a≤1.2, 0.5≤b≤0.99, 0 <c<0.5, 0<d<0.5, 0.01≤e≤0.1, 0≤f≤0.1); 리튬 니켈-망간-코발트 산화물에 일부가 다른 전이금속으로 치환된 산화물 Li 1+x (Ni a Co b Mn c M d ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg and Mo), disulfide compounds; Fe2(MoO4)3, etc., but are not limited thereto.

[0149] In one embodiment of the present invention, the negative electrode active material may be, for example, lithium metal or a lithium alloy, soft carbon, hard carbon, natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, petroleum or coal tar pitch derived cokes, silicon (Si)-based compounds (M-SiOx (M=Li, Mg, Ca, Al or Ti, 0≤x<2)) or a mixture of two or more thereof, but is not limited thereto.

[0150] In one embodiment of the present invention, the electrode assembly may be a jelly roll type electrode assembly having a structure in which a first electrode plate and a second electrode plate having a sheet shape and a separator interposed therebetween are wound in one direction. In this case, the separator is the separator described above, and the first electrode plate and the second electrode plate may be a positive electrode plate and a negative electrode plate, respectively.

[0151]

[0152] electrochemical devices

[0153] According to another aspect of the present invention, an electrochemical device can be provided in which the above-described electrode assembly is housed in a case.

[0154] In one embodiment of the present invention, the electrochemical device may be, for example, a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. The secondary battery may be, more specifically, a lithium ion secondary battery.

[0155] In one embodiment of the present invention, the case may adopt a conventional battery case, and there are no particular limitations on the external shape depending on the intended use of the battery. For example, the case may be cylindrical, square, pouch-shaped, or coin-shaped, such as using a can.

[0156] In one embodiment of the present invention, the case may be a cylindrical case, and the electrochemical device may be a cylindrical battery.

[0157] In one embodiment of the present invention, the cylindrical battery comprises: a jelly-roll type electrode assembly having a structure in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive and negative electrode plates are wound in one direction; a battery can in which the electrode assembly is accommodated; and a sealing body for sealing an open end of the battery can, wherein the separator is the separator described above.

[0158] In one embodiment of the present invention, the cylindrical battery may be a large cylindrical battery cell having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of the cylindrical battery divided by the height) of 0.4 or more.

[0159] In one embodiment of the present invention, the cylindrical battery may be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 48750 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.418), a 48800 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), or a 46800 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575). In the numerical value representing the form factor, the first two numbers represent the diameter of the cell, the next two numbers represent the height of the cell, and the last number O represents that the cross-section of the cell is circular.

[0160] Once the electrode assembly as described above is completed, it can be housed and sealed in a case in a conventional manner to manufacture an electrochemical device. At this time, the electrochemical device can be, for example, a lithium secondary battery.

[0161]

[0162] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0163]

[0164] [Manufacture of membrane substrate]

[0165] A porous polymer substrate was manufactured by the following method.

[0166] After mixing a polyethylene polymer having a molecular weight of 600,000 (g / mol) and an antioxidant in an extruder, the mixture was melted at a temperature of 200°C and extruded through a T-shaft. The obtained polymer sheet was placed so that it passed through the temperature ranges described in Table 1 below before cooling through a casting roll made of stainless steel and having a surface temperature of 25°C, and then cooled. At this time, the speed of traveling through the temperature range below was 10 m / min. Next, the polymer sheet that passed through the casting roll was stretched in MD (stretch ratio 7 times, stretch temperature 115°C) and TD (stretch ratio 6 times, stretch temperature 125°C) using a tenter-type sequential stretching machine placed at the rear end of the casting roll, and then the diluent was extracted using methylene chloride. After that, the sheet was caught and heat-set in the MD and TD directions at a temperature of 130°C, thereby obtaining a porous polymer substrate. The thickness of the obtained porous polymer substrate was 9 μm, and the porosity was 45 vol%.

[0167] Temperature range before cooling (℃) Comparative Example 150 Example 140 Example 230 Comparative Example 220

[0168] [Manufacturing of membranes]

[0169] Using the porous polymer substrates of Comparative Examples 1 and 2 and Examples 1 and 2 manufactured above as a membrane substrate, a porous coating layer was formed on both sides of the membrane substrate by the following method to manufacture a membrane.

[0170]

[0171] Manufacturing of porous coating layers

[0172] A coating slurry was prepared by mixing PAA (MW 350,000 g / mol) binder and inorganic particles (Al2O3) in an aqueous solvent at a weight ratio of 5:95. The inorganic coating slurry prepared above was applied to the entire surface of the porous substrate by a bar coating method and dried to form a porous coating layer with a thickness of 1.5 μm on each of the upper and lower surfaces of the porous substrate prepared above.

[0173] In this way, a separation membrane with a total thickness of 12 ㎛ was manufactured.

[0174]

[0175] [Manufacturing of electrode assembly]

[0176] Each of the above-prepared separators was used as a separator, and a cathode and an anode were prepared as follows and attached to one side of the separator to manufacture an electrode assembly.

[0177]

[0178] Manufacturing of cathode

[0179] A composition for forming a negative electrode was prepared by mixing an active material (Graphite), a binder polymer (SBR), and a conductive material (Super P) in distilled water at a weight ratio of 95:0.5:4.5.

[0180] The negative electrode was prepared by applying and drying the above negative electrode forming composition on one side of a copper current collector. The loading amount of the negative electrode was 5.3 mAh / cm 2 It was manufactured to be.

[0181]

[0182] Manufacturing of anodes

[0183] A composition for forming a positive electrode was prepared by mixing an active material (NCMA), a binder polymer (PVDF), and a conductive material (CNT) in a solvent (NMP) at a weight ratio of 97:1:2.

[0184] The anode was prepared by applying and drying the composition for forming the anode on one side of an aluminum current collector. The loading amount of the anode was 4.949 mAh / cm 2 It was manufactured to be.

[0185]

[0186] Assembly of the electrode assembly

[0187] After the positive electrode / separator / cathode / separator prepared above were laminated in that order, they were wound around the core to manufacture a jelly roll-shaped electrode assembly.

[0188]

[0189] [Physical property evaluation]

[0190] The properties of the separator substrate, separator, and electrode assembly were evaluated in the manufacturing order above using the following method, and the results are shown in Table 2 below.

[0191] The adhesive strength of the separator in Table 2 below was measured by measuring the adhesive strength between the surface on which the surface roughness value was measured and the porous coating layer.

[0192]

[0193] Measurement of surface roughness value (Sa) of membrane substrate

[0194] A surface analysis of a porous polymer substrate was performed using atomic force microscopy (AFM), a height map of the surface was obtained, and the difference in the average height of the entire surface area based on the average height plane was analyzed to measure the roughness value (Sa).

[0195] Roughness values ​​were measured on both sides of the membrane substrate.

[0196]

[0197] Measurement of the adhesive strength of the separator

[0198] The separator was sampled to a width of 15 mm and attached to a slide glass using 18 mm wide double-sided tape (3M) so that the side to be measured for adhesive strength was in contact with the glass. Then, the peel strength between the separator substrate and the porous coating layer was measured using a UTM device (Instron) at 180° and 300 mm / min.

[0199] The adhesive strength was performed on both sides of the separator.

[0200]

[0201] Measurement of friction coefficient of separator

[0202] When friction was repeatedly applied to the above membrane using Heidon's friction and wear equipment with a 5g / Dia tip, the coefficient of friction was measured when the porous coating layer was detached.

[0203]

[0204] Measurement of puncture strength of membrane

[0205] The force required to penetrate the membrane was measured using Instron's UTM equipment when a force was applied under the conditions of a 1 mm tip and 120 mm / min.

[0206]

[0207] Measurement of self-discharge

[0208] The self-discharge characteristics of the above separator were evaluated using the following method.

[0209] The jelly roll-shaped electrode assembly manufactured above was placed in a cylindrical case and an electrolyte (DME / DOL 1:1 v / v, 1M LiFSI) was injected to manufacture a cylindrical battery.

[0210] Afterwards, the voltage drop was measured for 48 hours after setting the SOC to 60% through charging.

[0211] Separator substrateSeparator electrode assemblySa(nm)Adhesive strength(gf / 15mm)Friction coefficientPuncture strength(gf)Voltage drop(mV)(dOCV / 2day)Comparative example 164.3510.216512.2Example 190.11950.645890.6Example 2138.42840.785660.4Comparative example 2163.6Over road0.894020.3

[0212] As confirmed in Tables 1 and 2 above, the porous polymer substrate obtained by placing it in a temperature range of 25°C to 45°C before cooling during the manufacture of the separator substrate and then cooling it exhibited a surface roughness value (Sa) of 80 nm to 160 nm, thereby confirming that it had excellent wear resistance while maintaining an appropriate level of adhesive strength. Furthermore, it was confirmed that the phenomenon of eye drop (low voltage) due to self-discharge of the electrode assembly using this could be significantly improved.

[0213] On the other hand, it was confirmed that the porous polymer substrate obtained by cooling after being placed in a range outside the above temperature before cooling as a membrane substrate had a surface roughness value (Sa) of 80 nm to 160 nm. In particular, in the case of Comparative Example 1 in which the surface roughness value (Sa) was less than 80 nm, the adhesive strength between the membrane substrate and the porous coating layer of the separator was implemented low, and the mechanical strength of wear resistance and impact resistance was also confirmed to be poor, and a voltage drop phenomenon of the electrode assembly using the same was observed, and in the case of Comparative Example 2 in which the surface roughness value (Sa) exceeded 160 nm, not only did the adhesive strength appear very high, but also the separator exhibited poor physical properties in terms of impact resistance.

[0214] [Explanation of symbols]

[0215] 200 - Extrusion section

[0216] 201, 202 - Casting roll

[0217] 300 - Cooling Unit

Claims

1. A membrane substrate characterized in that the roughness value (Sa) of at least one surface of the porous polymer substrate is 80 nm to 160 nm.

2. In claim 1, A membrane substrate characterized in that the surface roughness value (Sa) of both sides of the porous polymer substrate is 85 nm to 150 nm.

3. A membrane substrate according to claim 1; and A separation membrane characterized by comprising a porous coating layer formed on at least one surface having a surface roughness value (Sa) of 80 nm to 160 nm and containing inorganic particles and a binder polymer.

4. In claim 3, A separator characterized in that the adhesive strength between the separator substrate and the porous coating layer is 100 gf / 15 mm or more.

5. In claim 4, A separator characterized in that the adhesive strength between the separator substrate and the porous coating layer is 100 gf / 15 mm to 300 gf / 15 mm.

6. In claim 3, A separation membrane characterized in that the friction coefficient of the separation membrane is 0.25 or more.

7. In claim 6, A separation membrane characterized in that the friction coefficient of the separation membrane is 0.5 to 1.

0.

8. In claim 3, A separation membrane characterized in that the puncture strength of the above separation membrane is 450 gf or more.

9. In claim 8, A separation membrane characterized in that the puncture strength of the separation membrane is 500 gf to 600 gf.

10. A separator according to any one of claims 3 to 9; An electrode assembly characterized by including a positive electrode and a negative electrode formed on each side of the separator.

11. In claim 10, The electrode assembly is characterized in that the voltage drop (dOCV) within 48 hours is 2.0 or less.

12. In claim 11 The electrode assembly is characterized in that the voltage drop (dOCV) within 48 hours is 1.5 or less.

13. An electrochemical device characterized in that the electrode assembly according to claim 10 is housed in a case.

14. In claim 13, An electrochemical device characterized in that the above case is a cylindrical case. 15.S1) A step of extruding a polymer slurry to obtain a polymer sheet; and S2) A method for manufacturing a membrane substrate, comprising the step of positioning the obtained polymer sheet on a casting roll and cooling it; A method for manufacturing a membrane substrate, characterized in that it further comprises a step of placing the polymer sheet under a temperature atmosphere of 28°C to 45°C between the steps S1 and S2.

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