Separator substrate, method for manufacturing the same, and separator containing the same

Abstract

The present invention relates to a separator substrate, a separator, an electrode assembly, and an electrochemical element, and a separator substrate according to one embodiment of the present invention is characterized by having a surface roughness value (Sa) within a predetermined range. This is characterized by improving the wear resistance of the separator while maintaining good adhesive strength of the separator using it.

Description

[Technical Field]

[0001] The present invention relates to a separator substrate, a method for producing the same, and a separator containing the same. Specifically, the present invention relates to a separator with improved adhesive strength and abrasion resistance, an electrode assembly containing the same, and an electrochemical element.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0095292, filed on 21 July 2023, and all contents disclosed in the specification and drawings of said application are incorporated herein by reference. [Background technology]

[0003] Lithium-ion batteries are manufactured using a process in which an electrode assembly, consisting of a positive electrode, separator, and negative electrode as a single unit, is inserted into a battery case, followed by the injection of electrolyte and sealing. Polyolefin-based porous substrates are typically used as separators in lithium-ion batteries. To address the problem of short circuits between the positive and negative electrodes due to the thermal shrinkage behavior of polyolefin-based porous substrates, separators have been developed that improve 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 safety-reinforced separators (SRS) and ceramic-coated separators (CCS).

[0004] Such SRS or CCS prevents direct contact between the positive and negative electrodes by suppressing the shrinkage of the porous substrate when exposed to high temperatures, as inorganic particles in the coating layer act as spacers that can maintain the physical shape of the separator. This makes it possible to manufacture an electrode assembly by bonding the positive and negative electrodes with a separator having porous coating layers on both sides in between.

[0005] On the other hand, cylindrical, prismatic, and pouch-type cell types are known for rechargeable batteries. In the case of a cylindrical rechargeable battery cell, an insulating separator is sandwiched between the positive and negative electrodes, and this is wound up to form a jelly roll-shaped electrode assembly, which is then inserted into a battery case to constitute the battery.

[0006] At this time, as the battery is repeatedly charged and discharged, the negative electrode becomes bulky, which can cause the porous coating layer of the separator to be continuously scratched. Ultimately, this can lead to the separator being damaged, resulting in an internal short circuit, or impingement. There are concerns that such an internal short circuit could cause the cylindrical battery cell to catch fire.

[0007] Furthermore, 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 float around inside the battery as foreign matter, potentially causing a voltage drop behavior that exceeds the battery's self-discharge rate.

[0008] Therefore, there is an urgent need for the development of a separator that, by incorporating a porous coating layer, can improve heat resistance while also exhibiting excellent durability against friction. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, the problem that the present invention aims to solve is to provide a separator, an electrode assembly containing the same, and an electrochemical element that can solve the above-mentioned problems.

[0010] Specifically, the present invention aims to provide a separator that has excellent durability against friction while stably bonding a porous coating layer, and an electrochemical element, such as a lithium secondary battery, in which the voltage drop behavior is improved by applying this separator.

[0011] In particular, when forming a porous coating layer on a separator substrate, the present invention aims to maintain a good degree of impregnation of the slurry for forming the coating layer, improve the adhesive strength between the separator substrate and the porous coating layer, and provide a separator substrate having surface characteristics with improved abrasion resistance against friction and a method for manufacturing the same.

Means for Solving the Problems

[0012] In order to solve the above problems, According to one aspect of the present invention, a separator substrate of the following embodiment is provided.

[0013] The separator substrate according to the first embodiment is a porous polymer substrate, wherein the surface roughness value (Sa) of at least one surface is 80 nm to 160 nm.

[0014] According to the second embodiment, in the first embodiment, the surface roughness values (Sa) of both surfaces of the porous polymer substrate can be 85 nm to 150.

[0015] ]>According to another aspect of the present invention, a separator of the following embodiment is provided.

[0016] The separator according to the third embodiment is a separator substrate according to the first embodiment or the second embodiment, and a porous coating layer formed on at least one of the surfaces having the surface roughness value (Sa) of 80 nm to 160 nm, and containing inorganic particles and a binder polymer.

[0017] According to the fourth embodiment, in the third embodiment, the adhesive strength between the separator substrate and the porous coating layer can be 100 gf / 15 mm or more.

[0018] According to the fifth embodiment, in the third embodiment or the fourth embodiment, The adhesive strength between the separator substrate and the porous coating layer may be 100 gf / 15 mm to 300 gf / 15 mm.

[0019] According to the sixth embodiment, in any one embodiment of the third to fifth embodiments, The friction coefficient of the separator may be 0.25 or higher.

[0020] According to the seventh embodiment, in any one embodiment of the third to sixth embodiments, The friction coefficient of the separator may be 0.5 to 1.0.

[0021] According to the eighth embodiment, in any one embodiment of the third to seventh embodiments, The perforation strength of the separator may be 450 gf or more.

[0022] According to the ninth embodiment, in any one embodiment of the third to eighth embodiments, The perforation strength of the separator may be 500 gf to 600 gf.

[0023] According to yet another aspect of the present invention, an electrode assembly of the following embodiment is provided.

[0024] The electrode assembly according to the tenth embodiment is A separator according to any one embodiment from the third to ninth embodiments, The separator may include a positive electrode and a negative electrode formed on both sides of the separator, respectively.

[0025] According to the 11th embodiment, in the 10th embodiment, The electrode assembly may have a voltage drop (dOCV) of 2.0 or less within 48 hours.

[0026] According to the 12th embodiment, in the 10th embodiment or the 11th embodiment, The electrode assembly may have a voltage drop (dOCV) of 1.5 or less within 48 hours.

[0027] According to yet another aspect of the present invention, an electrochemical element of the following embodiment is provided.

[0028] The electrochemical element according to the 13th embodiment is An electrode assembly according to any one of the tenth to twelfth embodiments is housed in a case.

[0029] According to the 14th embodiment, in the 13th embodiment, The aforementioned case may be a cylindrical case.

[0030] According to yet another aspect of the present invention, a method for manufacturing a separator substrate is provided in the following embodiment.

[0031] The method for manufacturing a separator substrate according to the 15th embodiment is: S1) A step of extruding a polymer slurry to obtain a polymer sheet, A method for producing a separator substrate, comprising the steps of S2) positioning the obtained polymer sheet on a casting roll and cooling it, Between step S1 and step S2, the step of placing the polymer sheet in a temperature atmosphere of 28°C to 45°C is further included. [Effects of the Invention]

[0032] A separator substrate according to one embodiment of the present invention has the effect of improving the adhesion between the separator substrate and the porous coating layer by improving the surface roughness value (Sa), thereby improving the degree of impregnation of the slurry for forming the coating layer when forming a porous coating layer on this surface.

[0033] This results in an effect that improves the wear resistance of the porous coating layer to friction due to the surface characteristics of the separator substrate, thereby improving mechanical properties such as puncture strength.

[0034] Therefore, electrochemical elements to which separators using this material are applied have the effect of preventing and / or improving the breakdown of the separator caused by the bulkiness of the electrodes, such as the negative electrode, due to repeated charging and discharging, and the resulting short-circuit phenomenon between the positive and negative electrodes.

[0035] Furthermore, by using a separator with a porous coating layer, not only can the heat resistance of the electrochemical element be improved, but the wear resistance of the separator can also be improved, thereby preventing and / or reducing the formation of foreign matter inside the element during charging and discharging, and thus improving the voltage drop phenomenon of the electrochemical element. [Brief explanation of the drawing]

[0036] [Figure 1] This is a schematic diagram of a conventional apparatus for manufacturing separator substrates. The apparatus in Figure 1 includes an extrusion section 200 for extruding polymer sheets and casting rolls 201 and 202 for cooling the extruded polymer sheets. [Figure 2] This is a schematic diagram of an apparatus for manufacturing a separator substrate according to one embodiment of the present invention. The apparatus in Figure 2 includes a cooling section 300 for cooling one surface of the separator substrate between the extrusion section 200 and the casting rolls 201 and 202. [Figure 3] This is a schematic diagram of an apparatus for manufacturing a separator substrate according to one embodiment of the present invention. The apparatus in Figure 3 includes a cooling section 300 for cooling both surfaces of the separator substrate between the extrusion section 200 and the casting rolls 201 and 202. [Modes for carrying out the invention]

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

[0038] Throughout this specification, when a part of a component is described as "including," this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specified.

[0039] Throughout this specification, the phrase "A and / or B" means "A or B, or both."

[0040] The specific terms used in the subsequent detailed description of the invention are for ease of explanation only and are not intended to limit the invention. Furthermore, directional words such as up, down, left, right, front, back, inside, and outside indicate directions in the referenced drawings, or directions toward or away from the geometric center of the specified device, system, and its components.

[0041] According to one aspect of the present invention, a separator substrate is provided which is a porous polymer substrate having a surface roughness value (Sa) of at least one surface of 30 nm to 160 nm.

[0042] Separator substrate and method for manufacturing the same According to one aspect of the present invention, a separator substrate is provided which is a porous polymer substrate having a surface roughness value (Sa) of at least one surface of 80 nm to 160 nm.

[0043] To explain this, first, one feature of the method for manufacturing a separator substrate according to one embodiment of the present invention will be described.

[0044] A method for manufacturing a separator substrate according to one aspect of the present invention is: S1) A step of extruding a polymer slurry to obtain a polymer sheet, S2) The process includes the step of placing the obtained polymer sheet on a casting roll and cooling it.

[0045] In this case, according to one aspect of the present invention, the step of placing the polymer sheet in a temperature atmosphere of 28°C to 45°C is further included between steps S1 and S2.

[0046] Figure 1 shows a schematic diagram of a part of a conventional apparatus for manufacturing separator substrates. The apparatus in Figure 1 comprises an extrusion unit 200 for extruding a polymer sheet and casting rolls 201 and 202 for conveying the polymer sheet for cooling and subsequent processes. Generally, the polymer sheet extruded through the extrusion unit is brought into contact with the casting rolls at a high temperature and cooled in air.

[0047] Figures 2 and 3 show schematic diagrams of parts of an apparatus for manufacturing separator substrates according to one embodiment of the present invention. The apparatus in Figures 2 and 3 includes a cooling section 300 between the extrusion section 200 and the casting rolls 201 and 202 to lower the temperature of the extruded polymer sheet. In Figure 2, the cooling section 300 is provided on only one side of the polymer sheet, while in Figure 3, the cooling section 300 is provided on both sides of the polymer sheet.

[0048] First, in one embodiment of the present invention, the step of S1) extruding the polymer slurry to obtain a polymer sheet may include melt extruding a polymer resin as a raw material.

[0049] In one embodiment of the present invention, the polymer resin can be used without particular limitations as long as it is used as a raw material for manufacturing a separator substrate. The polymer resin may include resins such as polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or mixtures of two or more of these as raw materials for manufacturing a separator substrate. The polyolefin resin refers to a polymer of an olefin, specifically one obtained by polymerizing an olefin that is commonly used in separator substrates as a monomer. For example, the polyolefin resin may be, but is not limited to, polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; homopolymers of monomers selected from ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; copolymers of two or more of these; or mixtures thereof.

[0050] In one embodiment of the present invention, the porous polymer substrate may be a polyolefin substrate.

[0051] In one embodiment of the present invention, the porous polymer substrate may be a polyethylene substrate.

[0052] In one embodiment of the present invention, a conventional diluent can be used to feed the polymer resin into an extruder and perform extrusion. Suitable diluents include liquid or solid paraffin oil, wax, soybean oil, and other substances commonly used in the manufacture of separators.

[0053] In one embodiment of the present invention, a conventional single-screw or twin-screw extruder can be used for melting and extrusion, but is not limited thereto. In one embodiment of the present invention, after introducing the mixture of the diluent and the polymer resin into the extruder, the mixture is mixed while melting the polymer resin at a high temperature to obtain a molten composition.

[0054] In this case, since the extrusion of the polymer sheet is generally carried out under high temperature conditions, for example, 150°C to 300°C, the polymer sheet extruded through the extrusion section has a high surface temperature, for example, 130°C to 200°C immediately after extrusion, and comes into contact with the casting roll while having such a 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 upon contact with the casting roll, and the formation of surface crystals does not occur properly.

[0055] According to one aspect of the present invention, the polymer sheet extruded through the extrusion section is temporarily cooled through the cooling section 300 before it comes into contact with the casting roll, thereby inducing the formation of crystals on the surface of the polymer sheet and thereby increasing the surface roughness.

[0056] In one embodiment of the present invention, the cooling unit may also be referred to as a "cooler unit" for cooling a polymer sheet in a high-temperature state, and the cooling unit may include, 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 include a device for applying hot air at 28°C to 45°C to at least one side of the polymer sheet.

[0057] Conventionally, when manufacturing porous polymer substrates as separator substrates, a polymer slurry was extruded to obtain a polymer sheet, and the obtained polymer sheet was placed on a casting roll and cooled. The inventors of the present invention have found that by placing the polymer sheet in an atmosphere with a specific temperature before cooling, crystallization of the surface of the polymer sheet can be induced, thereby achieving different surface properties. Accordingly, by further performing the step of placing the polymer sheet within a specific temperature range before cooling during the manufacturing of the separator substrate, a separator substrate having a surface roughness value (Sa) of 80 nm to 160 nm was obtained through surface crystallization of the separator substrate.

[0058] In one embodiment of the present invention, between steps S1 and S2, the polymer sheet is placed in a temperature atmosphere of 28°C to 45°C. Specifically, this can be carried out under temperature conditions of 30°C to 45°C or 30°C to 40°C. Alternatively, the sheet may be placed in air within the aforementioned temperature range and at normal pressure.

[0059] In one embodiment of the present invention, this additional step may be carried out in conjunction with steps S1 and S2 using a separator substrate manufacturing apparatus further comprising a "cooling section 300" between steps S1 and S2.

[0060] In one embodiment of the present invention, the speed at which the polymer sheet travels through 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 overall process speed within a range that does not hinder the realization of the surface roughness of the separator substrate, and the present invention is not limited thereto.

[0061] When the polymer sheet is placed within the temperature range before cooling in step S2, a surface roughness value (Sa) of 80 nm to 160 nm can be achieved. Furthermore, if the temperature is too high, the surface roughness of the separator substrate may decrease, potentially leading to a decrease in the adhesive strength between the separator substrate and the porous coating layer. If the temperature is too low, the surface roughness of the separator substrate may be too high, resulting in an adhesive strength between the separator substrate and the porous coating layer exceeding an appropriate level, as well as a decrease in the impact resistance of the separator surface. However, the present invention is not limited to these conditions.

[0062] In one embodiment of the present invention, the method for manufacturing the separator substrate may further include, after cooling in step S2, step S3) stretching and heat-fixing the polymer sheet formed using a casting roll.

[0063] In one embodiment of the present invention, the stretching may include secondarily stretching the polymer sheet in the same direction or in different directions. For example, it may include independently stretching the polymer sheet in directions parallel to the machine direction (MD) and / or the transverse direction (TD).

[0064] In this specification, the term "machine direction" means the direction parallel to the running direction of the [extrusion → molding → stretching…] process in the manufacturing process of the separator substrate. The machine direction can be determined using the orientation direction of the polymer fibers of the separator substrate, and the direction parallel to the fiber orientation direction is the machine direction. Accordingly, the term "lateral direction" means the direction perpendicular to the machine direction. The lateral direction can also be determined by the direction perpendicular to the orientation direction of the polymer fibers of the separator substrate.

[0065] In one embodiment of the present invention, the stretching can be performed, for example, by sequential or simultaneous stretching using a roll method or a tenter method.

[0066] In one embodiment of the present invention, the stretching may be performed, for example, by a stretch ratio of 3 times or more, or 5 to 12 times, or 6 to 7 times. When the stretch ratio satisfies the above numerical range, advantageous effects are obtained in terms of thickness uniformity of the manufactured separator substrate and balance of physical properties between the longitudinal and transverse directions, but the present invention is not limited thereto.

[0067] In one embodiment of the present invention, the process may include, after stretching, extracting a diluent from the stretched sheet to form pores, and then heat-fixing it.

[0068] In one embodiment of the present invention, the diluent may be extracted using an organic solvent. Suitable organic solvents include, for example, methyl ethyl ketone, methylene chloride, hexane, or mixtures of two or more thereof, which have high extraction efficiency and dry quickly, but the present invention is not limited thereto.

[0069] 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 formed porous substrate.

[0070] In one embodiment of the present invention, after stretching and extraction of the diluent, the porous sheet may be forcibly gripped and heat-set to remove residual stress within the sheet. However, the purpose of the heat-set is not limited to this.

[0071] 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 separator substrate. The heat-setting temperature may be, for example, 100°C to 180°C, more 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.

[0072] In one embodiment of the present invention, when heat is applied during thermal setting, the material may be uniaxially stretched in the MD or TD direction, or it may be biaxially stretched in both the MD and TD directions, and is not limited thereto.

[0073] According to one embodiment of the present invention, a separator substrate is provided in which the surface roughness value (Sa) of both sides of the porous polymer substrate is 80 nm to 160 nm.

[0074] 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. Furthermore, the surface roughness value (Sa) of at least both sides of the porous polymer substrate may be 85 nm to 150 nm.

[0075] 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 90 nm to 140 nm.

[0076] 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-mentioned range, excellent adhesive strength between the separator substrate and the porous coating layer is ensured when forming the porous coating layer, and advantageous effects are obtained in terms of the abrasion resistance and impact resistance of the porous coating layer. However, the effects of the present invention are not limited thereto.

[0077] On the other hand, in addition to measuring the Sa value, methods for measuring the surface roughness of separator substrates that indicate the roughness in the two-dimensional direction of the surface are also known, such as Ra (Center line average), Rmax (Maximum peak to valley roughness height), Rz (Ten Point Height), and Rg (Root Mean Square; RMS). However, in the case of Ra, Rmax, Rz, and Rg, the roughness of the surface is measured in two dimensions (linear direction), and the shape of the surface roughness cannot be confirmed by the value alone. In other words, even if at least one of the values ​​Ra, Rmax, Rz, and Rg is the same for two different surfaces, the three-dimensional roughness shape may differ. This can result in differences in the amount of slurry impregnated into the porous coating layer and differences in the shape of the porous coating layer, which can lead to differences in the adhesive strength between the separator substrate and the porous coating layer, as well as differences in the mechanical strength of the porous coating layer. Considering these problems, the present invention defines the surface roughness value of the separator substrate using Sa.

[0078] In one embodiment of the present invention, the surface roughness value (Sa) can be measured by performing surface analysis of a porous polymer substrate using an atomic force microscope (AFM). For example, a sample of 30 μm × 30 μm in size is obtained as a sample of the porous polymer substrate to be measured for surface roughness, and the surface properties of both sides are measured. At this time, the surface roughness value (Sa) is measured by analyzing the average height difference of the entire surface area with respect to the height average plane.

[0079] The following describes the composition of the porous polymer substrate in an illustrative manner. However, the porous substrate is not limited to the constituent components described later.

[0080] In one embodiment of the present invention, the porous polymer substrate is a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode, and the substrate has a plurality of pores formed inside. The pores are interconnected, and gas or liquid can pass from one surface of the substrate to the other.

[0081] In one embodiment of the present invention, a porous polymer film containing a thermoplastic resin can be used as the porous polymer substrate, from the viewpoint of providing a shutdown function. Here, the shutdown function refers to the function that, when the temperature of the battery rises, dissolves the thermoplastic resin and blocks the pores of the porous polymer substrate, thereby blocking ion movement and preventing thermal runaway of the battery.

[0082] 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-mentioned range based on the overall thickness of the separator, but may be, for example, 5 to 300 μm, specifically 5 to 100 μm, 5 to 50 μm, 5 to 20 μm, 5 to 15 μm, or 9 to 12 μm.

[0083] 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 component of the separator. For example, the thickness of the porous polymer substrate can be measured using a known thickness measuring device, such as a commercially available thickness measuring device (VL-50S-B, manufactured by Mitutoyo Corporation of Japan).

[0084] Separator According to one aspect of the present invention, a separator is provided which includes the above-described porous polymer substrate as a separator substrate, and which includes a porous coating layer formed on at least one side of the separator substrate and containing inorganic particles and a binder polymer. In this case, the porous coating layer may be formed on at least one of the surfaces of the separator substrate having a surface roughness value (Sa) of 30 nm to 160 nm.

[0085] According to another aspect of the present invention, a separator is provided which includes the above-described porous polymer substrate as a separator substrate, and which includes a porous coating layer formed on at least one side of the separator substrate and containing inorganic particles and a binder polymer. In this case, the porous coating layer is formed on at least one of the surfaces of the separator substrate having a surface roughness value (Sa) of 80 nm to 160 nm.

[0086] The porous coating layer contains a large amount of inorganic particles and a binder polymer that binds them together in order to improve the safety of the separator. The inorganic particles can improve the heat resistance of the separator, and the binder polymer can provide adhesion to the surface of the separator. In this case, if the surface of the separator substrate on which the porous coating layer is formed is a flat surface, there is a possibility that the adhesive strength at the interface between the separator substrate and the porous coating layer will be poor. However, if the surface of the separator substrate is excessively rough, the adhesive strength at the interface between the separator substrate and the porous coating layer will become 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 of the porous coating layer, there is a risk that the impact resistance of the surface of the porous coating layer will decrease, leading to a decrease in the mechanical properties of the separator. As a result, a separator having a porous coating layer formed on a separator substrate according to one aspect of the present invention can exhibit improved abrasion resistance and impact resistance while maintaining good adhesion between the separator substrate and the porous coating layer by achieving a certain level of surface roughness.

[0087] In one embodiment of the present invention, the separator may be characterized in that the adhesive 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 adhesive strength between the surface of the separator substrate having a surface roughness value (Sa) in the above 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 range, it has advantageous effects in terms of improving the manufacturing process performance of the electrode assembly using the separator and improving the stability of the separator.

[0088] The adhesive strength of the separator can be measured, for example, by the following method. A sample of the separator to be measured is taken to a width of 15 mm, and attached to a glass slide using 18 mm wide double-sided tape (manufactured by 3M) so that the surface to be measured is in contact with the glass. Then, the peel strength between the separator substrate and the porous coating layer is measured using a universal testing machine (manufactured by Instron) under conditions of 180° and 300 mm / min.

[0089] Furthermore, in one embodiment of the present invention, the separator may be characterized by having a coefficient of friction of 0.25 or higher. In this specification, the "coefficient of friction" refers to the coefficient of friction when the porous coating layer is broken or damaged and peeled off by the frictional force applied to the separator, and as a result the separator substrate is exposed on the surface. When the surface roughness value (Sa) of the separator substrate is within the above range, the degree of impregnation of the slurry for forming the porous coating layer on the separator substrate is improved, which increases the adhesive strength between the separator substrate and the porous coating layer, and thus increases the force required when the separator substrate and the porous coating layer peel off due to friction, resulting in an increase in the coefficient of friction.

[0090] According to one embodiment of the present invention, the coefficient of friction of the separator may be 0.25 or higher. Specifically, the coefficient of friction 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.

[0091] The coefficient of friction of the separator can be measured, for example, using equipment known for friction and wear experiments. Specifically, the coefficient of friction of the separator can be measured, for example, by measuring the coefficient of friction at which the porous coating layer peels off when friction is repeatedly applied with a 5g / Dia tip using a friction and wear test and analysis instrument manufactured by HEIDON Shinto Scientific Co., Ltd.

[0092] Furthermore, in one embodiment of the present invention, the separator may be characterized by having a puncture strength of 450 gf or more. In this specification, "puncture strength" indicates the magnitude of the separator's resistance to a normal force when the normal force is applied to the separator. When the surface roughness value (Sa) of the separator substrate is within the above range, it is possible to improve the degree of impregnation of the slurry for forming a porous coating layer on the separator substrate, thereby increasing the adhesion between the separator substrate and the porous coating layer, and also resulting in good mechanical strength of the separator substrate. On the other hand, if the surface roughness value of the separator substrate is excessively high, the interior of the separator substrate cannot be formed densely, which may result in a decrease in mechanical strength and poor puncture strength, but the present invention is not limited thereto.

[0093] According to one embodiment of the present invention, the perforation 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.

[0094] The perforation strength of the separator can be measured, for example, by a known method for measuring perforation strength. Specifically, the perforation strength of the separator can be measured, for example, by using an Instron universal testing machine to measure the force required to penetrate the separator when a force is applied under conditions of a 1 mm tip and a flow rate of 120 mm / min.

[0095] The following describes the configuration of the porous coating layer in an illustrative manner. However, the configuration of the porous coating layer is not limited to this.

[0096] In one embodiment of the present invention, the porous coating layer may contain inorganic particles and a binder polymer, wherein all or at least part of the surface of the inorganic particles is coated with the binder polymer. In this case, the inorganic particles are bonded together via the binder polymer by plane and / or at points.

[0097] For example, the inorganic particles and binder resin in the porous coating layer may be present in a weight ratio of 95:5 to 50:50. Specifically, the inorganic particles and binder resin in the porous coating layer may be present in weight ratios of 99:1 to 50:50, 95:5 to 50:50, 95:5 to 70:30, 95:5 to 80:20, and 95:5 to 90:10, but the present invention is not limited thereto. The porous coating layer has a structure in which a large number of micropores are interconnected, and has the structural characteristics of a porous layer that allows gas or liquid to pass from one surface to the other.

[0098] In one embodiment of the present invention, the porous coating layer may have a porous structure resulting from pores due to interstitial volume between inorganic particles. The pore diameter and porosity (ratio of pore volume) can be adjusted according to the particle size and particle size distribution. By using such a structure, resistance to metallic foreign matter present on the electrode can be increased, and shrinkage of the porous polymer substrate can be suppressed, thereby enhancing the safety of the electrochemical element.

[0099] In one embodiment of the present invention, the porous coating layer includes a plurality of nodes, each containing 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-like manner and extending from the binder polymer of the nodes, wherein the filaments include node connection portions that extend from the nodes and connect to other nodes, and the node connection portions 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.

[0100] In one embodiment of the present invention, as described above, the porous coating layer may be formed using a manufacturing method for SRS (Safety Reinforced Separator), a manufacturing method for CCS (Ceramic Coated Separator), or other known manufacturing methods, but is not limited thereto.

[0101] In one embodiment of the present invention, the inorganic particles can be used without particular limitations, as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are within the operating voltage range of the electrochemical element to which they are applied (for example, Li / Li + There are no particular limitations as long as oxidation and / or reduction reactions do not occur in the range of 0 to 5V (based on the reference value). Non-limiting examples of such inorganic particles include BaTiO3, Pb(Zr,Ti)O3(PZT), and 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 Examples include 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.

[0102] In one embodiment of the present invention, the average particle size (D 50) can be, for example, 100 nm or more. Specifically, the average particle diameter (D 50 ) can be 100 nm to 1 μm, or can be 100 nm to 500 nm. When the average particle diameter of the inorganic particles is within the above-described range, an advantageous effect is exhibited from the aspect of suppressing an increase in the resistance of the separator, but the present invention is not limited thereto.

[0103] The particle diameter of the inorganic particles can be measured by a known particle size measurement method. For example, it can be measured using a particle size distribution measurement device (PSA; Particle Size Analyzer) manufactured by Malvern. Further, the average particle diameter (D 50 ) means the particle diameter at the 50% point of the particle number cumulative distribution according to the particle diameter, and can be measured using a known laser diffraction method. At this time, as the laser diffraction particle size distribution measurement device, for example, Microtrac (registered trademark) S3500 manufactured by Microtrac can be used.

[0104] 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 one or more of the following: a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride, and mixtures thereof. In one embodiment of the present invention, the monomer may be, for example, a fluorinated monomer and / or a chlorine-based monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), and one or more of these may be included. The acrylic binder may include, for example, polyacrylic acid (PA), polyacrylonitrile (PAN), polyacrylamide (PAA), or (meth)acrylic polymers or mixtures of two or more of these, but the present invention is not limited thereto. The (meth)acrylic polymer means a polymer containing (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 of these, but the present invention is not limited thereto.

[0105] 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-mentioned range of ratios to the total thickness of the separator, but for example it may be 0.5 to 50 μm, specifically 0.5 to 10 μm, 0.5 to 5 μm, or 1.5 to 3 μm.

[0106] electrode assembly According to yet another aspect of the present invention, an electrode assembly is provided which includes the above-described separator and a positive electrode and a negative electrode formed on both sides of the separator, respectively.

[0107] As described above, a separator according to one aspect of the present invention has improved heat resistance due to the presence of a porous coating layer, and not only does it have excellent adhesion between the separator substrate and the porous coating layer and excellent wear resistance of the porous coating layer, but it also has the effect of improving impact resistance due to the excellent mechanical properties of the separator substrate. One feature of an electrode assembly using this is that the phenomenon of voltage drop is prevented or delayed, and the problem of low voltage caused by the failure of the separator can be effectively solved.

[0108] In one embodiment of the present invention, the electrode assembly is characterized in that, even when repeatedly subjected to 200 charge-discharge cycles, the phenomenon of voltage drop does not occur, or the degree of such drop is extremely low.

[0109] For example, the electrode assembly may exhibit a voltage drop (dOCV) of 2.0 or less within 48 hours, or for example, a voltage drop of 2.0 or less within 48 hours after 200 charge-discharge cycles. Furthermore, 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 charge-discharge cycles. 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 charge-discharge cycles. 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.

[0110] In one embodiment of the present invention, the voltage drop is the OCV measured at a reference time (t0) and the OCV 48 hours after the reference time (t 48 The OCV can be measured by calculating the difference with the OCV measured at ). Specifically, the OCV of the electrode assembly is measured by measuring the voltage drop over 48 hours after charging with the SOC set to 60% as the endpoint.

[0111] In one embodiment of the present invention, by applying a separator using the separator substrate, the separator exhibits excellent wear resistance, thus providing an electrochemical element with superior battery safety and lifespan characteristics.

[0112] The following describes the configuration of the electrodes in an illustrative manner. However, the present invention is not limited thereto.

[0113] 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.

[0114] In one embodiment of the present invention, the positive electrode active material may include, for example, lithium transition metal oxide; lithium metallic iron phosphorus oxide; lithium nickel-manganese-cobalt oxide; an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these, but is not limited thereto. Specifically, the positive electrode active material may include, for example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; 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 as 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 as 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); Lithium metal phosphorus oxide LiMPO4 (where 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, in which part of the oxide is replaced by aluminum. a [Ni b Co c Mn d Al e ] 1-f M1 fO2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S; 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); an oxide in which a part of lithium nickel - manganese - cobalt oxide is substituted with another transition metal Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = ￥u30000~0.03, 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), a disulfide compound; examples include, but are not limited to, Fe2(MoO4)3.

[0115] In one embodiment of the present invention, as the negative electrode active material, 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 of these can be used, but is not limited thereto.

[0116] 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 the shape of a sheet and a separator sandwiched between them 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.

[0117] Electrochemical elements According to yet another aspect of the present invention, an electrochemical element is provided in which the above-described electrode assembly is housed in a case.

[0118] In one embodiment of the present invention, the electrochemical element can be a primary battery, a secondary battery, a supercapacitor, an electric double-layer capacitor, and the like. More specifically, the secondary battery may be a lithium-ion secondary battery.

[0119] In one embodiment of the present invention, the case can be one that is commonly used as a battery case, and is not particularly limited to an external shape that is appropriate for the battery's application. For example, the case may be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0120] In one embodiment of the present invention, the case may be a cylindrical case, and the electrochemical element may be a cylindrical battery.

[0121] In one embodiment of the present invention, the cylindrical battery includes a positive electrode plate, a jelly roll type electrode assembly having a structure in which a negative electrode plate and a separator sandwiched between the positive electrode plate and the negative electrode plate are wound in one direction, a battery can in which the electrode assembly is housed, and a sealant that seals the open end of the battery can, wherein the separator is the separator described above.

[0122] 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 diameter Φ to height H, i.e., the ratio of diameter Φ to height H) of 0.4 or more.

[0123] 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 indicating the form factor, the first two digits indicate the diameter of the cell, the next two digits indicate the height of the cell, and the last digit 0 indicates that the cross-section of the cell is circular.

[0124] Once the electrode assembly described above is completed, it can be housed in a case and sealed using a conventional method to manufacture an electrochemical element, which in this case may be, for example, a lithium secondary battery.

[0125] The present invention will be described in more detail below with reference to examples, but these examples are merely illustrative and the scope of the present invention is not necessarily limited to them.

[0126] [Manufacturing of separator substrates] A porous polymer substrate was manufactured using the following method.

[0127] After mixing a polyethylene polymer with 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 then extruded using a T-die. The resulting polymer sheet was then placed to pass through the temperature ranges listed in Table 1 below before being cooled using a stainless steel casting roll with a surface temperature of 25°C. The speed at which the sheet traveled through these temperature ranges was 10 m / min. Next, the polymer sheet that had passed through the casting roll was subjected to MD stretching (stretching ratio: 7 times, stretching temperature: 115°C) and TD stretching (stretching ratio: 6 times, stretching temperature: 125°C) using a tenter-type sequential stretcher located downstream of the casting roll. After extracting the diluent using methylene chloride, the sheet was held in the MD and TD directions and heat-fixed at a temperature of 130°C to obtain a porous polymer substrate. The thickness of the obtained porous polymer substrate was 9 μm and the porosity was 45 vol%.

[0128] [Table 1]

[0129] [Separator manufacturing] As separator substrates, the porous polymer substrates of Comparative Example 1, Comparative Example 2, and Examples 1 and 2, respectively, were used, and separators were manufactured by forming porous coating layers on both sides of the separator substrates using the method described below.

[0130] Manufacturing of porous coating layers A coating slurry was prepared by mixing a PAA (MW: 350,000 g / mol) binder and inorganic particles (Al2O3) in a weight ratio of 5:95 in an aqueous solvent. The inorganic coating slurry prepared above was applied to the entire surface of the porous substrate by bar coating and dried to form a porous coating layer with a thickness of 1.5 μm on both the upper and lower surfaces of the porous substrate prepared above.

[0131] This allowed us to manufacture a separator with an overall thickness of 12 μm.

[0132] [Manufacturing of electrode assemblies] Using the separators prepared above, the negative and positive electrodes were prepared as described below and attached to one side of each separator to manufacture the electrode assembly.

[0133] Manufacturing of negative electrodes A composition for forming a negative electrode was prepared by mixing distilled water with an active material (graphite), a binder polymer (SBR), and a conductive material (Super P) in a weight ratio of 95:0.5:4.5.

[0134] The negative electrode was prepared by applying the negative electrode formation composition to one side of a copper current collector and drying it. The loading amount of the negative electrode was 5.3 mAh / cm². 2 It was manufactured to achieve this.

[0135] Manufacturing of positive electrodes 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 weight ratio of 97:1:2 with a solvent (NMP).

[0136] A positive electrode was prepared by applying the positive electrode formation composition to one side of an aluminum current collector and drying it. The loading capacity of the positive electrode was 4.949 mAh / cm². 2 It was manufactured to achieve this.

[0137] Assembly of electrode assemblies After stacking the positive electrode / separator / negative electrode / separator in the order described above, the assembly was wound up using the core as a reference to produce a jelly roll-shaped electrode assembly.

[0138] [Evaluation of physical properties] The physical properties of the separator substrate, separator, and electrode assembly were evaluated using the following method in the manufacturing order described above, and the results are shown in Table 2 below.

[0139] The adhesive strength of the separators in Table 2 below was measured by the adhesive strength between the surface with the measured surface roughness value and the porous coating layer.

[0140] Measurement of the surface roughness value (Sa) of the separator substrate Surface analysis of a porous polymer substrate was performed using AFM (atomic force microscopy) to obtain a surface height map. The roughness value (Sa) was measured by analyzing the difference in average surface height across the entire area, using the average height plane as a reference.

[0141] Roughness values ​​were measured on both sides of the separator substrate.

[0142] Measurement of the adhesive strength of the separator A 15mm wide sample of the separator was taken and attached to a glass slide using 18mm wide double-sided tape (3M) so that the side to be measured for adhesive strength was in contact with the glass. Subsequently, the peel strength between the separator substrate and the porous coating layer was measured using a universal testing machine (Instron) under conditions of 180° and 300mm / min.

[0143] Adhesion strength was measured on both sides of the separator.

[0144] Measurement of the friction coefficient of the separator When friction was repeatedly applied to the separator using a friction and wear testing and analysis instrument manufactured by HEIDON Shinto Scientific Co., Ltd. with a tip of 5 g / Dia, the coefficient of friction at which the porous coating layer peeled off was measured.

[0145] Measurement of the perforation strength of the separator When a force was applied to the aforementioned separator using an Instron universal testing machine under the conditions of a 1 mm tip and a force flow rate of 120 mm / min, the force required to penetrate the separator was measured.

[0146] Measurement of self-discharge The self-discharge characteristics of the aforementioned separator were evaluated using the following method.

[0147] After housing the jelly-roll-shaped electrode assembly manufactured above into a cylindrical case, an electrolyte (DME / DOL = 1:1v / v, 1M LiFSI) was injected to manufacture a cylindrical battery.

[0148] Afterward, the device was charged to set the State of Charge (SOC) to 60%, and the voltage drop over 48 hours was measured.

[0149] [Table 2]

[0150] As can be clearly seen from Tables 1 and 2 above, the porous polymer substrate obtained by placing the separator substrate in the temperature range of 25°C to 45°C before cooling during manufacturing exhibited a surface roughness value (Sa) of 80 nm to 160 nm. This confirmed that it possesses excellent abrasion resistance while maintaining an appropriate level of adhesive strength. Furthermore, it was confirmed that the phenomenon of voltage drop (low voltage) due to self-discharge in electrode assemblies using this substrate can be significantly improved.

[0151] In contrast, a porous polymer substrate obtained by placing the separator substrate within a temperature range deviating from the above before cooling and then cooling it was confirmed that the surface roughness value (Sa) deviated from 80 nm to 160 nm. In particular, in Comparative Example 1, where the surface roughness value (Sa) was less than 80 nm, the adhesive strength between the separator substrate and the porous coating layer of the separator was low, and it was confirmed that the mechanical strength in terms of abrasion resistance and impact resistance was also poor, and a voltage drop phenomenon was observed in the electrode assembly using it. In Comparative Example 2, where the surface roughness value (Sa) exceeded 160 nm, not only was the adhesive strength extremely high, but the physical properties were also poor in terms of the impact resistance of the separator. [Explanation of Symbols]

[0152] 200 Extrusion section Casting Rolls 201, 202 300 Cooling section

Claims

1. A separator substrate comprising a porous polymer substrate, wherein the surface roughness value (Sa) of at least one surface is 80 nm to 160 nm.

2. The separator substrate according to claim 1, wherein the surface roughness value (Sa) of both sides of the porous polymer substrate is 85 nm to 150 nm.

3. A separator substrate according to claim 1, A porous coating layer is formed on at least one of the surfaces having a surface roughness value (Sa) of 80 nm to 160 nm, and comprises inorganic particles and a binder polymer. A separator that includes this.

4. The separator according to claim 3, wherein the adhesive strength between the separator substrate and the porous coating layer is 100 gf / 15 mm or more.

5. The separator according to claim 4, wherein the adhesive strength between the separator substrate and the porous coating layer is 100 gf / 15 mm to 300 gf / 15 mm.

6. The separator according to claim 3, wherein the coefficient of friction of the separator is 0.25 or more.

7. The separator according to claim 6, wherein the coefficient of friction of the separator is 0.5 to 1.

0.

8. The separator according to claim 3, wherein the perforation strength of the separator is 450 gf or more.

9. The separator according to claim 8, wherein the perforation strength of the separator is 500 gf to 600 gf.

10. A separator according to any one of claims 3 to 9, A positive electrode and a negative electrode are formed on both sides of the separator, An electrode assembly, including the electrode assembly.

11. The electrode assembly according to claim 10, wherein the voltage drop (dOCV) within 48 hours is 2.0 or less.

12. The electrode assembly according to claim 11, wherein the voltage drop (dOCV) within 48 hours is 1.5 or less.

13. An electrochemical element in which the electrode assembly described in claim 10 is housed in a case.

14. The electrochemical element according to claim 13, wherein the case is a cylindrical case.

15. S1) A step of obtaining a polymer sheet by extruding a polymer slurry, S2) The step of placing the obtained polymer sheet on a casting roll and cooling it, A method for producing a separator substrate, including, A method for producing a separator substrate, further comprising the step of placing the polymer sheet in a temperature atmosphere of 28°C to 45°C between step S1 and step S2.

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