Separation membrane and electrochemical element containing the same

Abstract

The present invention relates to a separation membrane, an electrode assembly, and an electrochemical element including the same. A separation membrane according to one embodiment of the present invention comprises a porous substrate and porous coating layers formed on each of the two surfaces of the porous substrate and containing inorganic particles, wherein the total thickness of the separation membrane is maintained constant over its entire surface, the aspect ratio of the separation membrane is 1 or greater, and each interface between the porous substrate and the porous coating layer has a convex curved shape toward the adjacent porous coating layer, with respect to the width direction of the separation membrane.

Description

[Technical Field]

[0001] The present invention relates to a separation membrane and an electrochemical element containing the same. Specifically, the present invention relates to a separation membrane for use in electrode assemblies manufactured by the Advanced Z-Stacking (AZS) method.

[0002] This application is a priority application claiming based on Korean Patent Application No. 2023-0050320 filed on April 17, 2023, and all contents disclosed in the specification and drawings of said application are incorporated into this application. [Background technology]

[0003] Secondary batteries can be classified according to the structure of their electrode assemblies, which consist of a positive electrode, a separator membrane, and a negative electrode. Typical examples include the jelly roll (wound type) electrode assembly, in which long sheet-like positive and negative electrodes are wound together with a separator membrane in between; the lamination and stacking (L&S) electrode assembly, in which multiple positive and negative electrodes cut to predetermined sizes are used to form unit cells with a separator membrane in between, and then multiple unit cells are stacked in sequence; and the zigzag stacking (Z-stacking) electrode assembly, in which multiple positive and negative electrodes cut to predetermined sizes are stacked in a zigzag pattern with a long sheet-like separator membrane in between. However, these conventional electrode assemblies have several problems.

[0004] First, in jelly roll (winding type) electrode assemblies, long sheet-like positive and negative electrodes are wound together to form a cylindrical or elliptical cross-section. As a result, stress caused by the expansion and contraction of the electrodes during charging and discharging accumulates inside the electrode assembly. When such stress accumulation exceeds a certain limit, deformation of the electrode assembly occurs. This deformation of the electrode assembly leads to uneven spacing between electrodes, causing a rapid decrease in battery performance and threatening battery safety due to internal short circuits. Furthermore, because long sheet-like positive and negative electrodes must be wound together, it is difficult to wind them quickly while maintaining a constant spacing between the positive and negative electrodes, resulting in reduced productivity.

[0005] On the other hand, lamination and stacking (L&S) electrode assemblies and zigzag stacking (Z-stacking) electrode assemblies have attracted considerable attention due to their superior stability and productivity compared to jelly roll electrode assemblies, and research into their manufacturing methods is currently ongoing.

[0006] However, while lamination and stacking (L&S) electrode assemblies have the advantage of high space efficiency in the manufactured batteries due to the rapid stacking speed of multiple positive and negative electrode units, misalignment of the separator membranes can lead to defects in the battery, and the sequential stacking process requires a lot of time and effort, so there is a risk of stability defects compared to the high productivity.

[0007] Furthermore, while zigzag stacking (Z-stacking) electrode assemblies offer a more stable structure compared to L&S electrode assemblies because they use long, sheet-like separation membranes, they suffer from low process efficiency due to the complexity of the manufacturing process.

[0008] Therefore, research and development are continuously being conducted to develop novel electrode assembly manufacturing methods that utilize the advantages of both lamination and stacking (L&S) and zigzag stacking (Z-stacking) while complementing the shortcomings of each.

[0009] For example, a manufacturing method for Advanced Z-Stacking (AZS) electrode assemblies is under development, and research is progressing to ensure the productivity and stability of AZS electrode assemblies, which are manufactured in elongated lengths.

[0010] Referring to Figures 2b and 2d, while the ends of an electrode assembly with a long overall length (Y direction) can maintain rigidity through welding of the tab sections, the central section lacks a fixing point and may sag downwards due to its weight, resulting in a drooping phenomenon. This can make it difficult to transport the electrode assembly during the process, potentially reducing process efficiency, and may also lead to defects in the sagging section, resulting in reduced stability. [Overview of the project] [Problems that the invention aims to solve]

[0011] Therefore, the problem that the present invention aims to solve is to provide a separation membrane that can be used in electrode assemblies with improved productivity and stability, and an electrochemical element using the same.

[0012] Specifically, the present invention provides a separation membrane that can be used in advanced-Z-stacking (AZS) electrode assemblies. More specifically, it provides a separation membrane that offers improved stability throughout the entire length of an electrode assembly when used in a long AZS electrode assembly.

[0013] As an example, the present invention provides a separation membrane with a novel structure that can improve the sagging (drooping) phenomenon in the central part. [Means for solving the problem]

[0014] To solve the above problems, According to one aspect of the present invention, a separation membrane of the following embodiment is provided.

[0015] The separation membrane according to the first embodiment is A separation membrane comprising a porous substrate and porous coating layers containing inorganic particles formed on each of both surfaces of the porous substrate, The separation membrane has a constant total thickness over the entire surface, the separation membrane has an aspect ratio of 1 or more, and with respect to the width direction of the separation membrane, each of the interfaces between the porous substrate and the porous coating layer has a convex curved surface shape toward the adjacent porous coating layer.

[0016] According to a second embodiment, in the first embodiment, With respect to the width direction of the separation membrane, the thickness of the porous substrate may be the thickest at the center.

[0017] According to a third embodiment, in the first embodiment or the second embodiment, With respect to the width direction of the separation membrane, the thickness of the porous substrate may be the thinnest at the outermost ends.

[0018] According to a fourth embodiment, in any one of the first to third embodiments, With respect to the center in the width direction of the separation membrane, the curved surface shapes of the interfaces between the porous substrate and the porous coating layer may be symmetric.

[0019] According to a fifth embodiment, in any one of the first to fourth embodiments, With respect to the center in the thickness direction of the separation membrane, the curved surface shapes of the two interfaces may be symmetric.

[0020] According to a sixth embodiment, in any one of the first to fifth embodiments, With respect to 100% of the total thickness of the separation membrane, the thickness of the porous substrate may be 40% to 90%.

[0021] According to a seventh embodiment, in any one of the first to sixth embodiments, With respect to 100% of the total thickness of the separation membrane, the thickness of the porous substrate may be 60% to 80%.

[0022] According to the eighth embodiment, in any one embodiment of the first to seventh embodiments, At a point 50% of the total width of the separation membrane, the thickness of the porous substrate can be 70% to 95% of the total thickness of the separation membrane.

[0023] According to the ninth embodiment, in any one embodiment of the first to eighth embodiments, At points representing 0% or 100% of the total width of the separation membrane, the thickness of the porous substrate may be 50% to 70% of the total thickness of the separation membrane.

[0024] According to the tenth embodiment, in any one embodiment of the first to ninth embodiments, The separation membrane may have a length of 1.5 m to 5 m in the longitudinal direction.

[0025] According to another aspect of the present invention, an electrode assembly of the following embodiment is provided.

[0026] The electrode assembly according to the 11th embodiment is The device includes a unit positive electrode, a unit negative electrode, and a separation membrane interposed between the unit positive electrode and the unit negative electrode, wherein the separation membrane is folded in a zigzag shape, and the unit positive electrode and the unit negative electrode are alternately arranged in a plurality of regions where the separation membrane is folded and overlapping, and the separation membrane may be a separation membrane according to any one embodiment of the first to tenth embodiments.

[0027] According to the 12th embodiment, in the 11th embodiment, Each of the unit positive electrode and the unit negative electrode may include an electrode tab formed at one end.

[0028] According to another aspect of the present invention, an electrochemical element of the following embodiment is provided.

[0029] The electrochemical element according to the 13th embodiment is The electrode assembly according to the 11th or 12th embodiment may be housed in a case.

[0030] According to the 14th embodiment, in the 13th embodiment, The electrochemical element may be a lithium secondary battery.

[0031] According to the 15th embodiment, in the 13th or 14th embodiment, The aforementioned case may be pouch-type, rectangular, cylindrical, or coin-type. [Effects of the Invention]

[0032] A separation membrane according to one embodiment of the present invention can reduce the weight of the central part by reducing the thickness of the porous coating layer provided in the central part in one direction and forming a thicker layer of a relatively light porous substrate.

[0033] When the separation membrane according to one embodiment of the present invention is applied to a cell with a long overall length, the weight of the central part of the long cell is reduced, thereby improving the sagging phenomenon in the central part. Specifically, when manufacturing a ZZS electrode assembly or AZS electrode assembly, which is produced by folding a long strip-shaped separation membrane in a zigzag pattern and inserting a unit electrode into the folded and overlapping portion of the separation membrane, the phenomenon of sagging in the central part can be dramatically improved even when the overall length in which electrode tabs are provided at both ends is increased.

[0034] A separation membrane according to one embodiment of the present invention has the advantage of being usable in electrode assemblies with improved stability and productivity. [Brief explanation of the drawing]

[0035] [Figure 1a]This is a schematic diagram of a conventional separation membrane 1. The separation membrane 1 may include a porous substrate 10, and a first porous coating layer 11 and a second porous coating layer 12 formed on both sides of the porous substrate, respectively. In Figure 1a, the X direction represents the length direction of the separation membrane 1, the Y direction represents the width direction of the separation membrane 1, and the Z direction represents the thickness direction of the separation membrane 1. [Figure 1b] This is a cross-sectional view in the width direction of a conventional separation membrane 1. Specifically, it shows a separation membrane 1 in which a first porous coating layer 11 and a second porous coating layer 12 are provided on both sides of a porous substrate 10 without a thickness gradient. [Figure 2a] This is a schematic diagram of the electrode assembly 2 assembled using the ZZS method. Specifically, it shows the structure of the electrode assembly 2 in which the separation membrane 1 is folded in a zigzag shape, and unit positive electrodes 21 and unit negative electrodes 22 are alternately interposed in the folded and overlapping regions. In Figure 2a, the X direction represents the overall width direction of the electrode assembly 2, the Y direction represents the overall length direction of the electrode assembly 2, and the Z direction represents the thickness direction of the electrode assembly 2. [Figure 2b] Figure 2b is a schematic diagram of an electrode assembly 3 in which a positive electrode tab 211 and a negative electrode tab 222 are provided at both ends of an electrode assembly 2, which consists only of a stacked positive electrode / separation membrane / electrode. In Figure 2b, the X direction represents the overall width direction of the electrode assembly 2, the Y direction represents the overall length direction of the electrode assembly 2, and the Z direction represents the thickness direction of the electrode assembly 2. [Figure 2c] This is a cross-sectional view of an electrode assembly 2 assembled using the ZZS method with a conventional separation membrane 1. [Figure 2d] This is a schematic diagram illustrating the phenomenon of the central part of the electrode assembly 3 bending relative to the overall length direction Y. [Figure 3a] This is a schematic diagram of a separation membrane 1 according to one embodiment of the present invention. The thickness of the entire separation membrane is kept constant with respect to the width direction of the separation membrane 1, but each interface between the porous substrate 10 and the first porous coating layer 11 and the second porous coating layer 12 has a convex curved shape toward the adjacent porous coating layer. [Figure 3b] This is a schematic diagram of a separation membrane 1 according to one embodiment of the present invention. In Figure 3b, the dotted line l indicates the center of the separation membrane 1 in the width direction Y. [Figure 3c]This is a schematic diagram of a separation membrane 1 according to one embodiment of the present invention. In Figure 3c, the dotted line m indicates the center of the separation membrane 1 in the thickness direction Z. [Figure 4] This is a cross-sectional view in the overall length direction Y of an electrode assembly 2 assembled using a separation membrane 1 according to one embodiment of the present invention in the ZZS method. [Figure 5] This is a schematic diagram of a method for evaluating the sag in the central part of an electrode assembly according to one embodiment of this specification. Specifically, it shows a method for evaluating the vertical distance h to the point where the electrode assembly sags downward (dotted line) by fixing the electrode tabs provided at both ends of the electrode assembly 3 on tables b and b' using weights a and a'. [Figure 6] This is a schematic diagram of the shape of a coating bar 4 for coating a porous coating layer according to one embodiment of the present invention. [Modes for carrying out the invention]

[0036] The present invention will be described in detail below with reference to the attached drawings.

[0037] In the drawings, the size of each component or specific part of that component is exaggerated, omitted, or schematic for the sake of clarity and ease of explanation. Therefore, the size of each component does not fully reflect its actual size. Where a specific description of a relevant known function or configuration is deemed to unnecessarily obscure the gist of the invention, such description is omitted.

[0038] In this specification, when a part "includes" a component, unless otherwise stated, this means that it may include other components rather than excluding them.

[0039] In this specification, the terms "A and / or B" mean "A or B, or both."

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

[0041] The present invention relates to a separation membrane, an electrode assembly containing the same, and an electrochemical element containing the same. Examples of the electrochemical element include primary batteries, secondary batteries, supercapacitors, and electric double-layer capacitors. More specifically, the secondary battery may be a lithium-ion secondary battery.

[0042] According to one aspect of the present invention, a separation membrane for use in an electrochemical element is provided.

[0043] In this specification, the separation membrane can have various shapes, and for example, it may be provided in the form of a strip with a length greater in the length direction than in the width direction. However, the present invention is not limited thereto.

[0044] In this specification, the longitudinal, transverse, and transverse directions of the separation membrane 1 are described with reference to Figure 1a. In Figure 1a, the X direction represents the longitudinal direction of the separation membrane 1, the Y direction represents the transverse direction of the separation membrane 1, and the Z direction represents the transverse direction of the separation membrane 1.

[0045] In one embodiment of the present invention, the separation membrane 1 is provided in the form of a strip with an aspect ratio of 1 or more, and in this case, the long side of the separation membrane may be formed in the length direction (X direction) and the short side may be formed in the width direction (Y direction).

[0046] Referring to the drawings, the separation membrane 1 according to one embodiment of the present invention includes a porous substrate 10 and porous coating layers 11, 12 formed on at least one surface of the porous substrate. In this case, one feature of the separation membrane is that the thickness in the thickness direction (Z direction) is maintained constant over the entire length.

[0047] Referring to Figure 2a, in one embodiment of the present invention, the separation membrane 1 may be used in a ZZS type electrode assembly or an AZS type electrode assembly in which the separation membrane is folded in a zigzag shape and unit electrodes 21 and 22 are inserted in the overlapping portions of the separation membrane; however, the applications of the present invention are not limited thereto.

[0048] Referring to Figure 2b, a schematic diagram of an electrode assembly 3 is shown in which the separation membrane 1 is folded in a zigzag shape, unit electrodes 21 and 22 are inserted into the overlapping portions of the folded separation membrane, and electrode tabs 221 and 222 are formed at one end of each unit electrode.

[0049] In this specification, the overall length direction, overall width direction, and thickness direction of the electrode assembly 3 can be described with reference to Figure 2b. In Figure 2b, the X direction represents the overall width direction of the electrode assembly 2, the Y direction represents the overall length direction of the electrode assembly 2, and the Z direction represents the thickness direction of the electrode assembly 2.

[0050] In one embodiment of the present invention, the electrode assembly to which the separation membrane is applied is provided with a positive electrode tab 211 or a negative electrode tab 222 at both ends in the overall length direction, and can be applied to a long cell with a long overall length. However, the present invention is not limited thereto.

[0051] In one embodiment of the present invention, the electrode assembly using the separation membrane includes a plurality of unit electrodes and a separation membrane with an aspect ratio of 1 or more interposed between the unit electrodes, wherein the separation membrane is folded in a zigzag shape and the unit electrodes are inserted into the overlapping portions of the separation membrane, resulting in a ZZS type electrode assembly or AZS type electrode assembly structure.

[0052] A separation membrane according to one aspect of the present invention comprises a porous substrate 10 and porous coating layers 11 and 12 formed on both sides of the porous substrate, each containing inorganic particles.

[0053] The porous substrate can be any substrate used for a separation membrane, and this will be described later.

[0054] The porous coating layer is a coating layer containing a large amount of inorganic particles to improve the safety of the separation membrane. Because the porous coating layer contains a large amount of inorganic particles, this can increase the weight of the separation membrane as the scale of the separation membrane increases, for example, as the length of the separation membrane increases.

[0055] A separation membrane according to one aspect of the present invention includes porous coating layers formed on each of the two sides of the porous substrate. In this specification, for the convenience of explanation, the porous coating layer located on one side of the porous substrate may be referred to as the "first porous coating layer 11," and the porous coating layer located on the other side of the porous substrate may be referred to as the "second porous coating layer 12."

[0056] Furthermore, for the convenience of explanation, in this specification, the interface between the porous substrate and the first porous coating layer may be referred to as the "first interface," and the interface between the porous substrate and the second porous coating layer may be referred to as the "second interface."

[0057] In this specification, the "long side direction" of the separation membrane means the direction of the longer of the lateral and vertical lengths of the separation membrane. Specifically, the separation membrane is a strip-shaped separation membrane with an aspect ratio of 1 or more, more specifically, an aspect ratio greater than 1, and two or more unit electrodes are arranged on the separation membrane. In this case, the long side direction means the direction in which the unit electrodes are arranged. Generally, the "long side direction" of the separation membrane may coincide with the direction of travel of the separation membrane or electrode assembly in the manufacturing process of the separation membrane or the manufacturing process of an electrode assembly using the separation membrane. Referring to the above, the length direction (X direction) of the separation membrane 1 can also be called the long side direction.

[0058] In this specification, the "short side direction" of the separation membrane refers to the direction of the shorter length between the lateral and longitudinal lengths of the separation membrane. Based on the above, the width direction (Y direction) of the separation membrane 1 can also be referred to as the short side direction.

[0059] On the other hand, Figure 1b shows a schematic diagram of the side view of a separation membrane 1 in which a first porous coating layer 11 and a second porous coating layer 12 are provided on both sides of a porous substrate 10, respectively. Figure 1b shows the widthwise side view of a conventional separation membrane 1 with an aspect ratio of 1 or more, and has a structure in which both the porous coating layers 11, 12 and the porous substrate 10 are formed with a uniform thickness with respect to the width direction.

[0060] Figure 2d shows a schematic side view of an electrode assembly formed by folding a long separation membrane, viewed along its entire length.

[0061] Referring to Figure 2d, electrode assemblies 3 with a long overall length (Y direction) may have the problem of sagging in the center due to their weight. In this case, as shown in Figure 1b, if both the porous coating layer and the porous substrate are formed with a uniform thickness based on the overall width direction of the separation membrane, as described above, the weight of the separation membrane increases due to the porous coating layer, and the longer the width of the separation membrane, the more the sagging problem in the center may be induced.

[0062] To solve these problems, a separation membrane according to one aspect of the present invention is provided which has an aspect ratio of 1 or more, and whose total thickness is maintained constant over the entire surface of the separation membrane, but with respect to the width direction of the separation membrane, each interface between the porous substrate and the porous coating layer has a convex curved surface toward the adjacent porous coating layer.

[0063] Figure 3a shows a schematic side view of a separation membrane 1 according to one embodiment of the present invention. Specifically, the separation membrane 1 has an aspect ratio of 1 or more, and Figure 3a shows a side view of the separation membrane in the width direction.

[0064] Referring to Figure 3a, the separation membrane 1 has porous coating layers 11 and 12 on each of the two sides of the porous substrate 10. In this case, with respect to the width direction of the separation membrane, each interface between the porous substrate 10 and the porous coating layers 11 and 12 has a convex curved surface toward the adjacent porous coating layers 11 and 12.

[0065] Specifically, referring to Figure 3a, the first interface between the porous substrate 10 and the first porous coating layer 11 has a curved surface shape with a convex central portion toward the first porous coating layer 11, with respect to the width direction of the separation membrane. Also, the second interface between the porous substrate 10 and the second porous coating layer 12 has a curved surface shape with a convex central portion toward the second porous coating layer 12, with respect to the width direction of the separation membrane.

[0066] As a result, a separation membrane according to one aspect of the present invention can have a structure in which the thickness of the porous substrate gradually increases to a maximum thickness and then gradually decreases, with respect to the width direction from one end of the separation membrane to the other end.

[0067] According to one embodiment of the present invention, a porous substrate having a thickness gradient in the width direction as described above can be formed in a conventional method for manufacturing a separation membrane substrate by adjusting the thickness adjustment screw at the extrusion discharge port when forming an extruded sheet. Specifically, when a polymer resin is fed into an extruder as a raw material for the separation membrane substrate and extruded through a T-die, the screws at both ends of the T-die discharge section are further tightened, and the screw in the center is tightened relatively less. As a result, the extruded sheet is formed with a thinner thickness at both ends and a thicker thickness in the center in the width direction. After casting the formed extruded sheet, a separation membrane substrate having the above shape can be manufactured by stretching it in the width direction TD and the running direction MD (or length direction), respectively. However, the present invention is not limited thereto.

[0068] Furthermore, a separation membrane according to one aspect of the present invention may have a structure in which the thickness of the porous coating layer gradually decreases to a minimum thickness and then gradually increases, with reference to the width direction from one end of the separation membrane to the other end.

[0069] According to one embodiment of the present invention, in order to form a porous coating layer on a porous substrate having a thickness gradient in the width direction as described above, such that the total thickness of the separation membrane is maintained at a constant level, a coating bar with varying thicknesses depending on the position can be used to form the porous coating layer. Specifically, Figure 6 shows a schematic diagram of a coating bar 4 for forming a porous coating layer according to one embodiment of the present invention. Referring to Figure 6, a separation membrane with a constant total thickness can be manufactured by coating at least one side, preferably both sides, of a porous substrate with a slurry for forming a porous coating layer using a coating bar whose thickness at both ends is greater than that at the center. However, the present invention is not limited thereto.

[0070] As described above, a separation membrane according to one aspect of the present invention is characterized in that the thickness of the porous substrate and the porous coating layer varies depending on the position in the width direction, and the total thickness of the separation membrane, i.e., the sum of the thicknesses of the porous substrate and the first and second porous coating layers, is kept constant.

[0071] In this specification, "the total thickness of the separation membrane is maintained constant" means that when the thickness is measured at any position within a specific region using the same method, the measured thickness value is within an error range of 5% or less. Specifically, the thickness can be described as being maintained constant if the deviation of the thickness values ​​at any two positions within a specific region is within 5%, 4%, 3%, 2%, 1%, or 0% (i.e., no difference).

[0072] In this specification, “gradually increasing thickness” means that when the thickness is measured in the same manner in a certain direction within a particular region, the thickness value increases continuously or discontinuously. The rate at which the thickness value increases may be kept constant within an error range of 5% or less, or may change discontinuously, but “gradually increasing thickness” preferably means that the thickness value increases continuously at a constant rate.

[0073] In this specification, “gradual decrease in thickness” means that when the thickness is measured in the same manner in a certain direction within a particular region, the thickness value decreases continuously or discontinuously. The rate at which the thickness value decreases may be kept constant within an error range of 5% or less, or may change discontinuously, but “gradual decrease in thickness” preferably means that the thickness value decreases continuously at a constant rate.

[0074] In this specification, unless otherwise defined, the “thickness” of each component may represent the value measured using a known thickness measuring instrument capable of measuring the thickness of the separation film of a battery. For example, the thickness measuring instrument may be, but is not limited to, the VL-50S product from Mitutoyo.

[0075] In one embodiment of the present invention, the thickness of the porous substrate can be measured by a method that involves removing the porous coating layer from the separation membrane. For example, the thickness of the remaining porous substrate can be measured after removing the porous coating layer using a solvent capable of dissolving the porous coating layer contained in the separation membrane.

[0076] In one embodiment of the present invention, the thickness of the porous coating layer can be measured by the thickness difference of the porous substrate measured as described above, after measuring the thickness of the separation film, but the measurement method is not limited thereto.

[0077] According to one embodiment of the present invention, the point where the porous substrate has its maximum thickness, in other words, the point where the porous coating layer has its minimum thickness, can vary depending on the position where the tabs of the electrode assembly are formed when the electrode assembly is manufactured using the separation membrane, thereby minimizing the sagging of the electrode assembly.

[0078] For example, when manufacturing an electrode assembly using the separation membrane, if the separation membrane is folded in a zigzag shape, and a unit positive electrode and a unit negative electrode are inserted into the folded and overlapping portions to form an electrode assembly, and both ends of the electrode assembly in the overall direction are fixed with the same force, and the tension applied to the center of the electrode assembly in the overall direction is the greatest, then the point where the thickness of the porous substrate is greatest may be the center with respect to the width direction of the separation membrane.

[0079] In another embodiment of the present invention, when an electrode assembly is manufactured using the separation membrane, if the tension is maximum at a point 1 / 3 of the way along the entire length of the electrode assembly, the point where the thickness of the porous substrate is maximum may be at a point 1 / 3 of the way along the entire width of the separation membrane.

[0080] According to one embodiment of the present invention, when manufacturing an electrode assembly using the separation membrane, it is preferable that the same force be applied to both ends. Therefore, the thickness of the porous substrate may be greatest in the center, with respect to the width direction of the separation membrane. Specifically, with respect to 100% of the total length in the width direction, the thickness of the porous substrate may be greatest at the 50% point.

[0081] This may mean that the thickness of the porous substrate is thinnest at the very end, relative to the width direction of the separation membrane. Specifically, the thickness of the porous substrate may be thinnest at 50% of the total length in the width direction, relative to 100% of the total length.

[0082] In one embodiment of the present invention, the thickness of the porous substrate at the central point, for example, at the 50% point relative to the total width of the separation membrane, is 70% to 95% relative to the total thickness of the separation membrane. For example, at the 50% point relative to the total width of the separation membrane, the thickness of the porous substrate is 75% to 90%, 75% to 85%, or 80% relative to the total thickness of the separation membrane.

[0083] In one embodiment of the present invention, the thickness of the porous substrate at both ends, for example, at the 0% or 100% point relative to the total width of the separation membrane, is 50% to 70% relative to the total thickness of the separation membrane. For example, at the 0% or 100% point relative to the total width of the separation membrane, the thickness of the porous substrate is 55% to 65% or 60% relative to the total thickness of the separation membrane.

[0084] In one embodiment of the present invention, the porous substrate in the separation membrane has a maximum thickness and minimum thickness deviation of 1 μm to 5 μm, 2 μm to 4 μm, or 2.5 μm to 3.5 μm, specifically 3 μm.

[0085] In other words, the thickness difference between the central and peripheral portions of the porous substrate in the separation membrane is 1 μm to 5 μm, 2 μm to 4 μm, or 2.5 μm to 3.5 μm, specifically 3 μm.

[0086] According to one embodiment of the present invention, the curved shape of the interface between the porous substrate and the porous coating layer may be symmetrical with respect to the center in the width direction of the separation film.

[0087] Figure 3b shows a cross-sectional view in the width direction of a separation membrane according to one embodiment of the present invention, with the center in the width direction indicated by a dotted line l.

[0088] Referring to Figure 3b, in one embodiment of the present invention, the separation membrane may have a symmetrical shape at the first interface between the porous substrate 10 and the first porous coating layer 11, with respect to the center of the separation membrane 1 in the width direction (dotted line l). Furthermore, the second interface between the porous substrate 10 and the second porous coating layer 12 may have a symmetrical shape, with respect to the center of the separation membrane 1 in the width direction (dotted line l).

[0089] According to another embodiment of the present invention, the curved shapes of the two interfaces may be symmetrical with respect to the center in the thickness direction of the separation membrane.

[0090] Figure 3c shows a cross-sectional view in the width direction of a separation membrane according to one embodiment of the present invention, with the center in the thickness direction indicated by a dotted line m.

[0091] Referring to Figure 3c, in the separation membrane according to one embodiment of the present invention, the curved shapes of the first interface and the second interface may be symmetrical with respect to the center (dotted line m) in the thickness direction of the separation membrane 1.

[0092] According to yet another embodiment of the present invention, the separation membrane may have a structure in which the curved shapes of the first interface and the second interface are symmetrical with respect to the center l in the width direction, and the curved shapes of the first interface and the second interface are symmetrical with respect to the center m in the thickness direction.

[0093] According to one embodiment of the present invention, the separation membrane can have a structure that is symmetrical with respect to the center in the width direction (dotted line l in Figure 3b). Specifically, with respect to the center in the width direction of the separation membrane, the thickness of the porous substrate at any point separated by the same distance from the center to both ends may be the same, and the thickness of the porous coating layer may be the same. More specifically, when the center is at 50% of the total width length of the separation membrane, the thickness of the porous substrate at the 40% point and the 60% point may be the same. Furthermore, the thickness of the first porous coating layer at the 40% point and the 60% point may be the same. Furthermore, the thickness of the second porous coating layer at the 40% point and the 60% point may be the same.

[0094] According to one embodiment of the present invention, the porous coating layers formed on each of the two sides of the porous substrate may be formed symmetrically with respect to the center of the separation membrane in the thickness direction (dotted line m in Figure 3c). That is, the separation membrane 1 may have a structure that is symmetrical with respect to the center of the thickness direction. As a result, the thicknesses of the first porous coating layer and the second porous coating layer may be the same at the same arbitrary position in the direction perpendicular to the width direction of the separation membrane, i.e., in the length direction of the separation membrane.

[0095] In this specification, "having the same thickness" includes having a thickness difference of ±5% or less, taking into account manufacturing errors or measurement errors, as described above.

[0096] In one embodiment of the present invention, the thickness of the porous substrate is, for example, 40% to 90% of the total thickness of the separation membrane, relative to 100% of the total thickness of the separation membrane. Specifically, the porous substrate has a thickness of 40% of the total thickness of the separation membrane at both ends, and the thickness of the porous substrate gradually increases toward the center in the long-side direction of the separation membrane, such that the first interface and the second interface have curved surfaces, and may have a thickness of 90% at the center in the long-side direction of the separation membrane.

[0097] According to one embodiment of the present invention, when the thickness of the porous substrate is, for example, 40% to 90% of the total thickness of the separation membrane (100%), the thicknesses of the first porous coating layer and the second porous coating layer are each 5% to 30% of the total thickness of the separation membrane (100%).

[0098] In another embodiment of the present invention, the thickness of the porous substrate is, for example, 60% to 80% of the total thickness of the separation membrane, relative to 100% of the total thickness of the separation membrane. Specifically, the porous substrate has a thickness of 60% of the total thickness of the separation membrane at both ends, and the thickness of the porous substrate gradually increases toward the center in the width direction of the separation membrane, such that the first and second interfaces have curved surfaces, and may have a thickness of 80% in the center in the width direction of the separation membrane.

[0099] According to another embodiment of the present invention, if the thickness of the porous substrate is, for example, 60% to 80% of the total thickness of the separation membrane (100%), then the thicknesses of the first porous coating layer and the second porous coating layer are each 10% to 20% of the total thickness of the separation membrane (100%).

[0100] In one embodiment of the present invention, the separation membrane may be in the shape of a strip. Specifically, the strip-shaped separation membrane is a long strip-shaped separation membrane having a predetermined width, and more specifically, a rectangular separation membrane having an aspect ratio of 1 or more, more specifically, greater than 1. More specifically, the separation membrane has a long side length of 1.5m to 5m, more specifically, 1.8m to 4.8m.

[0101] The configurations of the porous substrate and the porous coating layer will be described exemplified below. However, the separation membrane according to one aspect of the present invention relates to the novel shape described above and is not limited to the respective components of the porous substrate and the porous coating layer.

[0102] In one embodiment of the present invention, the porous substrate is an ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode, and has a plurality of pores formed inside. The pores have a structure in which they are interconnected, and gas or liquid can pass from one side of the substrate to the other side.

[0103] In one embodiment of the present invention, the porous substrate can be a porous polymer film containing a thermoplastic resin, from the viewpoint of providing a shutdown function. Here, the shutdown function refers to a function that, when the battery temperature rises, prevents thermal runaway of the battery by blocking ion movement through the melting of the thermoplastic resin and closing the pores of the porous substrate.

[0104] In one embodiment of the present invention, a thermoplastic resin with a temperature of less than 200°C is preferred as the thermoplastic resin used for the porous substrate. The thermoplastic resin can be used without particular limitation as long as it is used as a substrate for a separation membrane, for example, but is not limited to polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or a mixture of two or more of these.

[0105] In one embodiment of the present invention, the porous substrate may be a polyolefin substrate.

[0106] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited as long as it satisfies the above range based on the total thickness of the separation film, for example, 5 μm to 300 μm, specifically 5 μm to 100 μm, 5 μm to 50 μm, 5 μm to 20 μm, 5 μm to 15 μm, or 9 μm to 12 μm.

[0107] In one embodiment of the present invention, the porous coating layer contains inorganic particles and further contains a binder resin, so that the inorganic particles can be coated on all or at least part of their surface by the binder resin. In this case, the inorganic particles are surface-bonded and / or point-bonded via the binder resin. For example, the inorganic particles and the binder resin may be contained in the porous coating layer in a weight ratio of 95:5 to 50:50. The porous coating layer has a plurality of micropores inside, and these micropores are interconnected, and has the structural characteristics of a porous layer in which gas or liquid can pass from one surface to the other.

[0108] In one embodiment of the present invention, the porous coating layer may have a porous structure derived from pores created by interstitial volume between inorganic particles. The size and porosity (percentage of pore volume) of these pores can be adjusted according to the size and size distribution of the particles. Such a structure enhances the safety of the electrochemical element by increasing resistance to metallic foreign matter present on the electrodes and suppressing shrinkage of the porous polyolefin substrate.

[0109] 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 from the binder polymer of the nodes, wherein the filaments have 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 each other to form a three-dimensional network structure.

[0110] In one embodiment of the present invention, as described above, the porous coating layer may be formed by an SRS (Safety Reinforced Separator) manufacturing method, a CCS (Ceramic Coated Separator) manufacturing method, or other known manufacturing methods, but is not limited thereto.

[0111] 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 electrochemical element to which they are applied (for example, 0 to 5V relative to Li / Li+). 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.

[0112] In one embodiment of the present invention, if the porous coating layer contains a binder resin, the binder resin may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin). 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 monomers 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), as well as perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), and one or more of these may be included.

[0113] 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 ratio range with respect to the total thickness of the separation film, for example, 0.5 μm to 50 μm, specifically 0.5 μm to 10 μm, 0.5 μm to 5 μm, or 1.5 μm to 3 μm.

[0114] In one embodiment of the present invention, the first porous coating layer and the second porous coating layer may have the same composition, but may be formed with different compositions as needed, and the present invention is not limited thereto.

[0115] A separation membrane according to one aspect of the present invention, with the structure described above, can have the advantageous effect of improving the stability of the separation membrane itself and the stability of the electrochemical element using it by reducing the tension applied to the central part when both ends in the overall direction of the electrode assembly using the separation membrane are fixed. However, the effects of the present invention are not limited to this.

[0116] According to another aspect of the present invention, an electrode assembly using the separation membrane described above is provided.

[0117] Specifically, the electrode assembly has a structure in which the separation membrane described above is folded in a zigzag pattern, and unit positive electrodes and unit negative electrodes are alternately arranged in multiple regions where the separation membrane is folded and overlapping.

[0118] An electrode assembly according to one embodiment of the present invention includes a unit positive electrode, a unit negative electrode, and a separation membrane interposed between the unit positive electrode and the unit negative electrode, wherein a plurality of the unit positive electrodes are arranged spaced apart on one surface of the separation membrane, and a plurality of the unit negative electrodes are arranged spaced apart on the other surface of the separation membrane, and the positions in which the unit positive electrodes and the unit negative electrodes are arranged do not overlap with respect to the long side direction of the separation membrane, and the separation membrane can have the separation membrane structure described above.

[0119] Figure 4 shows a cross-sectional view of the electrode assembly 2 in the overall length direction Y according to one embodiment of the present invention.

[0120] Referring to Figure 4, the electrode assembly 2 has a separation membrane 1 folded in a zigzag pattern, and multiple unit positive electrodes 21 and multiple unit negative electrodes 22 are alternately arranged in multiple regions where the separation membrane is folded and overlapping.

[0121] According to one embodiment of the present invention, the electrode assembly has a structure in which a plurality of unit electrodes are arranged on one side and the other side of a strip-shaped separation membrane. Therefore, the total length of the electrode assembly when unfolded is, for example, 1 m to 4.5 m, specifically 1.2 m to 4.3 m.

[0122] As described above, the electrode assembly according to another aspect of the present invention, even if provided in a long strip shape, has an advantage that the sagging phenomenon at the central part is improved during the manufacturing process of the electrode assembly due to the structure peculiar to the separation membrane, and the stability and productivity are improved. However, the effects of the present invention are not limited thereto.

[0123] In one embodiment of the present invention, the unit electrode is a normal positive electrode and / or negative electrode used in an electrochemical element. The positive electrode and the negative electrode are each a current collector coated with an electrode active material, and their size and shape are not particularly limited.

[0124] In one embodiment of the present invention, when the electrode is a positive electrode, the positive electrode active material can include, for example, a lithium transition metal oxide, a lithium metal iron phosphate, a lithium nickel-manganese-cobalt oxide, an oxide in which a part 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 is, for example, a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), a compound substituted with one or more transition metals, and the chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, and the chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3), Ni-site type lithium nickel oxide represented by, and the chemical formula LiMn 2-x M xO2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 - 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn), a lithium manganese composite oxide, lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn), and 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), and an oxide Li a [Ni b Co c Mn d Al e ) 1-f M1 f O2 (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), and an oxide 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, and Fe2(MoO4)3, etc., but not limited thereto.

[0125] In one embodiment of the present invention, when the electrode is a negative electrode, the negative electrode active material may be, but is not limited to, lithium metal or 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, or a mixture of two or more of these.

[0126] In one embodiment of the present invention, each of the unit positive electrode and the unit negative electrode may include an electrode tab formed at one end.

[0127] According to one embodiment of the present invention, the electrode tabs formed on the unit positive electrode and the unit negative electrode may be formed on both opposing ends of the electrode assembly with respect to the overall length direction.

[0128] According to yet another aspect of the present invention, an electrochemical element can be provided in which the above-described electrode assembly is housed in a case.

[0129] 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-type, or coin-type using a can.

[0130] Once the electrode assembly described above is completed, it can be placed 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.

[0131] The present invention will be further described below with reference to embodiments, but these embodiments are for illustrative purposes only and the scope of the present invention is not limited to them.

[0132] [Manufacturing of separation membranes] The separation membranes for Example 1 and Comparative Example 1 were manufactured as described below.

[0133] The shape of the side surface of the separation membrane in Example 1 is shown in Figure 3a, and the shape of the side surface of the separation membrane in Comparative Example 1 is shown in Figure 1b.

[0134] Example 1 Manufacturing of porous substrates Three polyethylene polymers with different molecular weights, a polypropylene polymer, and an antioxidant were mixed in appropriate proportions in an extruder. An extruded sheet was produced by passing it through a T-die, and the resulting polyolefin precursor film was cast and stretched in the MD and TD directions to obtain a porous substrate. The three polyethylene polymers used were PE 40 (Mw 400,000 g / mol), PE 90 (Mw 900,000 g / mol), and PE 150 (Mw 1,500,000 g / mol), and the polypropylene polymer was PP 35 (Mw 350,000 g / mol).

[0135] Furthermore, when forming the extruded sheet through the T-die, the thickness adjustment screws at both ends of the T-die's discharge section were further tightened to obtain an extruded sheet having a shape in which the center of the porous substrate in the width direction was thicker and the ends in the width direction were thinner. The porosity of the porous substrate finally produced after stretching was 45 vol%.

[0136] The porous substrate had a total width (short side, Y direction) of 500 mm and a length (long side, X direction) of 4 m. The thickness (Z direction) measured at both ends of the short side was 9 μm at each end. The substrate was manufactured by adjusting the spacing of the T-dies so that the thickness increased curvedly from both ends to the 250 mm point, which is the center of the short side, so that the thickness at the 250 mm point was 12 μm.

[0137] Manufacturing of porous coating layers An inorganic coating slurry was prepared by mixing a PVDF-HFP binder (Mw 500,000 g / mol, HFP 15 wt%) and inorganic particles in a weight ratio of 5:95 in a suitable solvent.

[0138] The inorganic coating slurry prepared as described above was applied to both sides of the porous substrate using a coating bar having the shape shown in Figure 6 and dried to form a porous coating layer on the upper and lower surfaces of the porous substrate prepared as described above.

[0139] As a result, porous coating layers were manufactured such that the thickness of the porous coating layer formed on the upper and lower surfaces was 3 μm at each end, and the thickness decreased curvedly to 1.5 μm at a point 250 mm from both ends, which is the center of the shorter side.

[0140] This resulted in the production of a separation membrane in which the total thickness was consistently maintained at 15 μm across both the short and long sides.

[0141] Comparative Example 1 Manufacturing of porous substrates A porous substrate was manufactured using the same method as in Example 1, except that it was formed with a constant thickness of 9 μm throughout the entire width direction (short side).

[0142] Manufacturing of porous coating layers A porous coating layer was formed using the same method as in Example 1, except that the thickness remained constant at 3 μm throughout the entire width direction (short side).

[0143] This allowed us to produce a separation membrane with a constant total thickness of 15 μm in the width direction.

[0144] Table 1 summarizes the thickness of each component at both ends (0%, 100%) and the center (50%) of the separation membranes manufactured in Example 1 and Comparative Example 1 above, using 100% of the total width direction as a reference. Table 1 also shows the ratio of the thickness of the porous substrate to the total thickness of the separation membrane, depending on its position.

[0145] [Table 1] [Manufacturing and evaluation of electrode assemblies] Manufacturing of electrode assemblies Using the separation membranes of Example 1 and Comparative Example 1 manufactured as described above, electrode assemblies were fabricated as shown in the schematic diagram in Figure 2a. At this time, the separation membrane was folded so that the total length (Y direction) of the manufactured electrode assembly was 500 mm and the total width (X direction) was 100 mm.

[0146] Specifically, a positive electrode of 17ea and a negative electrode of 16ea were arranged intersecting the upper and lower surfaces of the separation membrane. At this time, the points where the ends of the positive electrode are located on one surface and the points where the ends of the negative electrode are located on the other surface were spaced apart so that the horizontal distance on the plane was 3 mm, and they were arranged alternately. Specifically, the separation membrane of Example 1 or Comparative Example 1 was folded in a zigzag shape, and the respective positive and negative electrodes were arranged such that a positive electrode 1ea or a negative electrode 1ea was interposed in the region where the separation membrane was folded and overlapped. The positive electrode was prepared to contain lithium cobalt oxide LCO as the positive electrode active material, and the negative electrode was prepared to contain graphite as the negative electrode active material (N / P ratio > 100).

[0147] Evaluation of sagging in the central area The sag in the central part of the electrode assembly manufactured above was evaluated using the method shown in Figure 5, with respect to the overall length direction (Y direction).

[0148] First, an electrode assembly manufactured using the separation membrane of Example 1 or Comparative Example 1 was prepared. Next, two tables b and b' of the same height were prepared, spaced 400 mm apart, so that both ends of the prepared electrode assembly in the overall length direction Y would be fixed. After placing both ends of the electrode assembly in the overall length direction 50 mm apart against the tables, weights a and a' of the same weight were placed on the electrode assembly and fixed in place.

[0149] After fixing for 30 minutes, the longest distance h (height) from a position horizontal to the table height where the electrode assembly hung down was measured, and the results are shown in Table 2 below.

[0150] [Table 2] As can be seen in Table 2 above, it was confirmed that using a separation membrane having the same structure as in Example 1 dramatically improves the phenomenon of sagging in the central part of the electrode assembly in the overall length direction.

[0151] As described above with reference to embodiments and drawings of the present invention, any person with ordinary skill in the art to which the present invention belongs should be able to make various applications and modifications within the scope of the present invention based on the above description. [Explanation of Symbols]

[0152] 1: Separation membrane 10: Porous base material 11: First porous coating layer 12: Second porous coating layer 2: Electrode assembly 21: Unit positive electrode 22: Unit negative electrode 211: Positive Tab 222: Negative electrode tab 3: Electrode assembly 4: Coating bar a, a': weight b, b': Table

Claims

1. A separation membrane comprising a porous substrate and a porous coating layer containing inorganic particles formed on each of the two surfaces of the porous substrate, The separation membrane maintains a constant overall thickness across its entire surface. The separation membrane has an aspect ratio of 1 or more. A separation membrane wherein, with respect to the width direction of the separation membrane, each interface between the porous substrate and the porous coating layer has a convex curved shape toward the adjacent porous coating layer.

2. The separation membrane according to claim 1, wherein the thickness of the porous substrate is greatest in the center, with reference to the width direction of the separation membrane.

3. The separation membrane according to claim 1, wherein the thickness of the porous substrate is thinnest at the outermost end, with respect to the width direction of the separation membrane.

4. The separation membrane according to claim 1, wherein the curved shape of the interface between the porous substrate and the porous coating layer is symmetrical with respect to the center of the separation membrane in the width direction.

5. The separation membrane according to claim 1, wherein the curved shapes of the two interfaces are symmetrical with respect to the center of the thickness direction of the separation membrane.

6. Based on 100% of the total thickness of the separation membrane, The separation membrane according to claim 1, wherein the thickness of the porous substrate is 40% to 90%.

7. Based on 100% of the total thickness of the separation membrane, The separation membrane according to claim 1, wherein the thickness of the porous substrate is 60% to 80%.

8. At a point 50% of the total width of the aforementioned separation membrane, The separation membrane according to claim 1, wherein the thickness of the porous substrate is 70% to 95% of the total thickness of the separation membrane.

9. At points where the entire width of the separation membrane is 0% or 100%, The separation membrane according to claim 1, wherein the thickness of the porous substrate is 50% to 70% of the total thickness of the separation membrane.

10. The separation membrane according to claim 1, wherein the separation membrane has a length in the longitudinal direction of 1.5 m to 5 m.

11. It includes a unit positive electrode, a unit negative electrode, and a separation membrane interposed between the unit positive electrode and the unit negative electrode, The separation membrane is folded in a zigzag pattern, The unit positive electrode and the unit negative electrode are alternately arranged in multiple regions where the separation membrane is folded and overlaps. The electrode assembly wherein the separation membrane is the separation membrane described in any one of claims 1 to 10.

12. The electrode assembly according to claim 11, wherein each of the unit positive electrode and the unit negative electrode includes an electrode tab formed at one end.

13. An electrochemical element in which the electrode assembly described in claim 11 is housed in a case.

14. The electrochemical element according to claim 13, wherein the electrochemical element is a lithium secondary battery.

15. The electrochemical element according to claim 13, wherein the case is pouch-type, rectangular-type, cylindrical-type, or coin-type.

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