Separator and electrochemical device including the same

Abstract

The present disclosure relates to a separator, an electrode assembly including the same, and an electrochemical device, and the separator according to one embodiment of the present disclosure comprises a porous substrate and a porous coating layer on each of both surfaces of the porous substrate, the porous coating layer comprising inorganic particles, in which a total thickness of the separator remains constant throughout the separator, wherein an aspect ratio of the separator is 1 or more, and wherein an interface between each of the porous coating layers and the porous substrate has a curved shape protruding toward an adjacent porous coating layer based on a width direction of the separator.

Description

Technical Field

[0001] The present disclosure relates to a separator and an electrochemical device including the same. More particularly, the present disclosure relates to a separator used in an electrode assembly manufactured by an advanced-Z-stacking (AZS) method.

[0002] This application claims priority to Korean Patent Application No. 2023-0050320 filed in Korea on April 17, 2023, the disclosure of which is incorporated herein by reference. Background Art

[0003] Secondary batteries can be classified according to the structure of the electrode assembly of the positive electrode / separator / negative electrode structure. Representative examples may include a jelly roll (winding) electrode assembly in which a long sheet positive electrode and a long sheet negative electrode are wound together with a separator inserted therebetween; a lamination and stacking (Lamination and Stacking, L&S) electrode assembly in which a plurality of positive electrodes and a plurality of negative electrodes obtained by cutting into a predetermined size are arranged together with a separator inserted therebetween to form a unit cell and a plurality of unit cells are stacked in a continuous order; and a zigzag stacking (Z-stacked) electrode assembly in which a plurality of positive electrodes and a plurality of negative electrodes obtained by cutting into a predetermined size are stacked layer by layer in a zigzag shape together with a long sheet separator inserted therebetween. However, these existing electrode assemblies have some problems.

[0004] Since the jelly roll (wound) electrode assembly is manufactured by tightly winding a long sheet positive electrode and a long sheet negative electrode to form a cylindrical or oval or elliptical cross-sectional structure, the stress caused by the expansion and contraction of the electrode during charge / discharge accumulates in the electrode assembly, and when the accumulated stress exceeds a predetermined limit, deformation occurs in the electrode assembly. The deformation in the electrode assembly causes the distance between the electrodes to be uneven, resulting in rapid performance degradation of the battery and internal short circuits that threaten the safety of the battery. In addition, when the long sheet positive electrode and the long sheet negative electrode are wound, it is difficult to quickly wind the positive and negative electrodes with a constant distance between the positive and negative electrodes, resulting in low productivity.

[0005] In contrast, L&S electrode assemblies and Z-stack electrode assemblies have higher stability and productivity than jelly-roll electrode assemblies and are gaining more attention. Nevertheless, research on these methods continues.

[0006] However, the L&S electrode assembly has the advantages of high sequential stacking speed of a plurality of positive electrode units and a plurality of negative electrode units and high space efficiency of the battery, but separator misalignment may cause defects in the battery, so the sequential stacking process requires a lot of time and effort. Despite the high productivity, there is still a risk of instability.

[0007] Furthermore, the Z-stack electrode assembly provides a more stable structure than the L&S electrode assembly due to the use of a long sheet type separator, but has low process efficiency due to process complexity.

[0008] Therefore, new electrode assembly manufacturing methods are continuously being researched and developed in an effort to obtain the advantages of L&S and the advantages of Z-stack and to compensate for their disadvantages.

[0009] For example, methods for manufacturing advanced Z-stack (AZS) electrode assemblies are being developed, and efforts are ongoing to improve productivity and stability of AZS electrode assemblies having large lengths.

[0010] Reference Figure 2b and 2d , the electrode assembly that is long in the length direction (Y direction) is kept rigid at both ends by the tab welding, but since there is nothing to hold or support the center part, it may sag at the center part due to weight. Therefore, it is difficult to transport the electrode assembly during the process, resulting in low process efficiency, or the sag may cause defects, resulting in low stability. Summary of the invention

[0011] Technical issues

[0012] The present disclosure is directed to providing a separator for use in an electrode assembly having improved productivity and stability, and an electrochemical device using the same.

[0013] In particular, the present disclosure is directed to providing a separator for use in an advanced Z-stack (AZS) electrode assembly. More particularly, the present disclosure is directed to providing a separator having improved stability throughout an AZS electrode assembly having a large length.

[0014] For example, the present disclosure is directed to providing a new structural divider for reducing or preventing sagging of a center portion.

[0015] Technical Solution

[0016] In order to solve the above problems, according to one aspect of the present disclosure, there is provided:

[0017] The separator of the following embodiment.

[0018] A separator according to a first embodiment includes a porous substrate and a porous coating layer on each of both surfaces of the porous substrate,

[0019] The porous coating comprises inorganic particles,

[0020] wherein the total thickness of the separator remains constant throughout the separator, wherein the aspect ratio of the separator is 1 or greater, and wherein the interface between each of the porous coating layers and the porous substrate has a curved shape convex toward the adjacent porous coating layer based on the width direction of the separator.

[0021] According to a second embodiment, in the first embodiment,

[0022] The porous substrate may be thickest at the center of the separator in the width direction.

[0023] According to a third embodiment, in the first embodiment or the second embodiment,

[0024] The porous base may be thinnest at the outermost end of the separator in the width direction.

[0025] According to a fourth embodiment, in any one of the first to third embodiments,

[0026] The curved shape of the interface between the porous substrate and the porous coating layer may be symmetrical with respect to the center of the separator in the width direction.

[0027] According to a fifth embodiment, in any one of the first to fourth embodiments,

[0028] The curved shapes of the two interfaces may be symmetrical with respect to the center of the separator in the thickness direction.

[0029] According to a sixth embodiment, in any one of the first to fifth embodiments,

[0030] The thickness of the porous substrate may be 40% to 90% of 100% of the total thickness of the separator.

[0031] According to a seventh embodiment, in any one of the first to sixth embodiments,

[0032] The thickness of the porous substrate may be 60% to 80% of 100% of the total thickness of the separator.

[0033] According to an eighth embodiment, in any one of the first to seventh embodiments,

[0034] At 50% of the total width of the separator, the thickness of the porous substrate may be 70% to 95% of the total thickness of the separator.

[0035] According to a ninth embodiment, in any one of the first to eighth embodiments,

[0036] At 0% or 100% of the total width of the separator, the thickness of the porous substrate may be 50% to 70% of the total thickness of the separator.

[0037] According to a tenth embodiment, in any one of the first to ninth embodiments,

[0038] The length of the partition in the length direction may be 1.5 m to 5 m.

[0039] According to another aspect of the present disclosure, an electrode assembly according to the following embodiment is provided.

[0040] The electrode assembly according to the eleventh embodiment includes a unit positive electrode, a unit negative electrode, and a separator between the unit positive electrode and the unit negative electrode.

[0041] wherein the separator is folded in a zigzag shape, wherein the unit positive electrodes and the unit negative electrodes are arranged in an alternating manner in a plurality of regions where the separator is folded and overlapped, and wherein the separator is as defined in any one of the first to tenth embodiments.

[0042] According to the twelfth embodiment, in the eleventh embodiment,

[0043] The cell positive electrode and the cell negative electrode may each include an electrode tab at an end.

[0044] According to still another aspect of the present disclosure, an electrochemical device according to the following embodiments is provided.

[0045] An electrochemical device according to a thirteenth embodiment includes:

[0046] The electrode assembly according to the eleventh embodiment or the twelfth embodiment and a case accommodating the electrode assembly.

[0047] According to the fourteenth embodiment, in the thirteenth embodiment,

[0048] The electrochemical device may be a lithium secondary battery.

[0049] According to a fifteenth embodiment, in the thirteenth embodiment or the fourteenth embodiment, the case may have a bag-type shape, a prism shape, a cylindrical shape, or a coin-type shape.

[0050] Beneficial Effects

[0051] The separator according to one embodiment of the present disclosure may have a reduced weight of the central portion by reducing the thickness of the porous coating layer at the central portion in one direction and conversely increasing the thickness of the relatively lightweight porous substrate.

[0052] When a separator according to an embodiment of the present disclosure is applied to a battery cell having a large length in the length direction, the weight of the central portion of the long battery cell can be reduced, thereby preventing the central portion from sagging. Specifically, when a ZZS (zigzag stacking) electrode assembly or an advanced Z-stack (AZS) electrode assembly is manufactured by folding a long strip-type separator in a zigzag shape and inserting a unit electrode at the folded and overlapping portion of the separator, even if it is manufactured to have an increased length in the length direction with electrode tabs provided at both ends, the central portion can be significantly prevented from sagging.

[0053] A separator according to one embodiment of the present disclosure may be used in an electrode assembly with improved stability and productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1a is a diagram of a conventional separator 1. The separator 1 may include a porous substrate 10 and a first porous coating layer 11 and a second porous coating layer 12 each present on each of two surfaces of the porous substrate. Figure 1a , the X direction represents the length direction of the separator 1 , the Y direction represents the width direction of the separator 1 , and the Z direction represents the thickness direction of the separator 1 .

[0055] Figure 1b 1 shows a cross section of a conventional separator 1 in the width direction. Specifically, Figure 1b A separator 1 having a first porous coating layer 11 and a second porous coating layer 12 on both surfaces of a porous substrate 10 without a thickness gradient is shown.

[0056] Figure 2a FIG. 2 is a diagram of an electrode assembly 2 assembled by a ZZS (zigzag stacking) method. Specifically, Figure 2a The structure of the electrode assembly 2 is shown, in which the separator 1 is folded in a zigzag shape, and the unit positive electrodes 21 and the unit negative electrodes 22 are arranged in an alternating manner at the folded and overlapped regions. Figure 2a , the X direction represents the width direction of the electrode assembly 2 , the Y direction represents the length direction of the electrode assembly 2 , and the Z direction represents the thickness direction of the electrode assembly 2 .

[0057] Figure 2b FIG. 3 is a diagram of an electrode assembly 3 having a positive electrode tab 211 and a negative electrode tab 222, each electrode tab being at each of the two ends of an electrode assembly 2 including a stack of positive electrode / separator / electrode. Figure 2b , the X direction represents the width direction of the electrode assembly 2 , the Y direction represents the length direction of the electrode assembly 2 , and the Z direction represents the thickness direction of the electrode assembly 2 .

[0058] Figure 2cis a cross-sectional view of an electrode assembly 2 assembled by a ZZS method using a conventional separator 1.

[0059] Figure 2d 3 is a diagram showing the drooping center portion of the electrode assembly 3 in the length direction (Y).

[0060] Figure 3a The total thickness of the separator 1 is kept constant based on the width direction of the separator 1, but the interface between the porous substrate 10 and the first and second porous coating layers 11 and 12 has a curved shape convex toward the adjacent porous coating layer.

[0061] Figure 3b FIG. 1 is a diagram of a separator 1 according to an embodiment of the present disclosure. Figure 3b In FIG. 1 , the dotted line 1 represents the center of the separator 1 in the width direction (Y).

[0062] Figure 3c FIG. 1 is a diagram of a separator 1 according to an embodiment of the present disclosure. Figure 3c , the dotted line m represents the center of the separator 1 in the thickness direction (Z).

[0063] Figure 4 A cross section of an electrode assembly 2 in a length direction (Y) is shown, and the electrode assembly 2 is assembled by a ZZS method using the separator 1 according to one embodiment of the present disclosure.

[0064] Figure 5 : is a diagram of a method for evaluating a sagging center portion of an electrode assembly according to an experimental example in the specification. Specifically, Figure 5 A method for evaluating the vertical distance h to the position (dashed line) where the electrode assembly 3 sags is shown, wherein the electrode tabs at both ends of the electrode assembly 3 are fixed to tables b, b' using weights a, a'.

[0065] Figure 6 is a diagram of a coating rod 4 for forming a porous coating layer according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0066] Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings.

[0067] In the accompanying drawings, for the convenience and clarity of description, the size of each element or a specific part of an element is enlarged, omitted or schematically shown. Therefore, the size of each element does not fully reflect the actual size. When it is determined that the detailed description of the relevant known function or element may unnecessarily obscure the subject matter of the present disclosure, the description is omitted.

[0068] It should be understood that, unless the context clearly indicates otherwise, “include” or “comprising” when used in the present specification specifies the presence of stated elements, but does not exclude the presence or addition of one or more other elements.

[0069] It should also be understood that "A and / or B", when used in this specification, specifies A or B, or both.

[0070] The terms used in the following detailed description are for convenience and are not intended to be limiting. The terms "upper", "lower", "left", "right", "front", "rear", "inner", and "outer" refer to directions in the drawings to which reference is made, or directions toward or away from the geometric center of the devices, systems, and elements described.

[0071] The present disclosure relates to a separator, an electrode assembly including the separator, and an electrochemical device including the separator. The electrochemical device may include, for example, a primary battery, a secondary battery, a supercapacitor, and a double-layer capacitor. More specifically, the secondary battery may be a lithium-ion secondary battery.

[0072] According to one aspect of the present disclosure, a separator for use in an electrochemical device is provided.

[0073] In the present specification, the separator may have various shapes. For example, the separator may have a strip shape that is longer in the length direction than in the width direction. However, the present disclosure is not limited thereto.

[0074] In this manual, reference is made to Figure 1a The length direction, width direction and thickness direction of the separator 1 are described. Figure 1a , the X direction represents the length direction of the separator 1 , the Y direction represents the width direction of the separator 1 , and the Z direction represents the thickness direction of the separator 1 .

[0075] In one embodiment of the present disclosure, the separator 1 may have a strip shape having an aspect ratio of 1 or more, and in this case, the long side of the separator may exist in the length direction (X direction) and the short side may exist in the width direction (Y direction).

[0076] Referring to the drawings, a separator 1 according to an embodiment of the present disclosure includes a porous substrate 10 and a porous coating 11, 12 on at least one surface of the porous substrate. In this case, the separator may be characterized in that the thickness in the thickness direction (Z direction) remains constant over the length direction of the entire separator.

[0077] Reference Figure 2aIn one embodiment of the present disclosure, the separator 1 can be used in a ZZS type electrode assembly or an advanced Z-stack (AZS) type electrode assembly, wherein the separator 1 is folded in a Z shape and the unit electrodes 21, 22 are inserted at the overlapping portion of the separator 1, but the use of the present disclosure is not limited thereto.

[0078] Reference Figure 2b , which shows an electrode assembly 3 in which a separator 1 is folded in a zigzag shape, unit electrodes 21 , 22 are inserted at the folded and overlapped portion of the separator, and each electrode tab 221 , 222 is formed at the end of each unit electrode.

[0079] In this manual, you can refer to Figure 2b Describe the length direction, width direction and thickness direction of the electrode assembly 3. Figure 2b , the X direction represents the width direction of the electrode assembly 2 , the Y direction represents the length direction of the electrode assembly 2 , and the Z direction represents the thickness direction of the electrode assembly 2 .

[0080] In one embodiment of the present disclosure, the separator-applied electrode assembly has a positive electrode tab 211 or a negative electrode tab 222 at each of both ends in the length direction, and can be applied to a battery cell that is long in the length direction. However, the present disclosure is not limited thereto.

[0081] In one embodiment of the present disclosure, an electrode assembly using a separator has a ZZS or AZS type electrode assembly structure including a plurality of unit electrodes and separators between the unit electrodes, wherein the aspect ratio of the separator is 1 or greater, the separator is folded in a Z shape, and the unit electrodes are inserted at the overlapping portions of the separator.

[0082] A separator according to one aspect of the present disclosure includes a porous substrate 10 and porous coating layers 11 , 12 containing inorganic particles, each on each of two surfaces of the porous substrate.

[0083] The porous substrate may include any type of substrate used for a separator without limitation, and will be described below.

[0084] The porous coating layer is a coating layer containing inorganic particles to improve the safety of the separator. Since the porous coating layer contains inorganic particles, the weight of the separator can be increased as the size of the separator increases (eg, the length of the separator increases).

[0085] The separator according to one aspect of the present disclosure includes a porous coating on each of the two surfaces of the porous substrate. In this case, in this specification, for the convenience of description, the porous coating on one surface of the porous substrate may be referred to as "first porous coating 11", and the porous coating on the other surface of the porous substrate may be referred to as "second porous coating 12".

[0086] Furthermore, in this specification, for convenience of description, the interface between the porous substrate and the first porous coating layer may be referred to as a “first interface”, and the interface between the porous substrate and the second porous coating layer may be referred to as a “second interface”.

[0087] In this specification, the "long side direction" of the separator refers to the direction on the side of the longer of the horizontal length and the vertical length of the separator. Specifically, the separator is a strip separator 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 separator. In this case, the long side direction means the direction in which the unit electrodes are arranged. Generally, the "long side direction" of the separator can match the direction in which the separator or the electrode assembly travels during the process of manufacturing the separator or the process of manufacturing the electrode assembly using the separator. With reference to the above description, the length direction (X direction) of the separator 1 can be the long side direction.

[0088] In this specification, the "short side direction" of the separator refers to the direction on the shorter side of the horizontal length and the vertical length of the separator. Referring to the above description, the width direction (Y direction) of the separator 1 may be the short side direction.

[0089] Figure 1b The side surface of the separator 1 in the width direction is shown, and the separator 1 has the first porous coating layer 11 and the second porous coating layer 12 , each on each of the two surfaces of the porous substrate 10 . Figure 1b The side surface of the separator 1 having an aspect ratio of 1 or more in the width direction is shown, and the porous coating layers 11 , 12 and the porous substrate 10 each have a uniform thickness in the width direction.

[0090] Figure 2d It is a side view of an electrode assembly formed by folding a long separator, when viewed from the length direction.

[0091] Reference Figure 2d , the electrode assembly 3 which is long in the length direction (Y direction) may have the risk of sagging in the center portion due to the weight. Figure 1bIn the case where each of the porous coating layer and the porous substrate has a uniform thickness based on the total width direction of the separator, the weight of the separator may increase due to the porous coating layer as described above, and the electrode assembly 3 may be more likely to sag in the center portion as the width of the separator increases.

[0092] To address this issue, the separator according to one aspect of the present disclosure has an aspect ratio of 1 or greater, the total thickness remains constant throughout the separator, and the interface between the porous substrate and each porous coating layer has a curved shape convex toward the adjacent porous coating layer based on the width direction of the separator.

[0093] Figure 3a is a side view of a separator 1 according to one aspect of the present disclosure. Specifically, the separator 1 has an aspect ratio of 1 or greater, and Figure 3a The side view of the separator in the width direction is shown.

[0094] Reference Figure 3a , the separator 1 has porous coating layers 11, 12 each on each of the two surfaces of the porous substrate 10. In this case, the interface between each of the porous coating layers 11, 12 and the porous substrate 10 has a curved shape convex toward the adjacent porous coating layers 11, 12 based on the width direction of the separator.

[0095] Specifically, refer to Figure 3a , based on the width direction of the separator, the first interface between the porous substrate 10 and the first porous coating layer 11 has a curved shape convex toward the first porous coating layer 11 at the center portion. In addition, based on the width direction of the separator, the second interface between the porous substrate 10 and the second porous coating layer 12 has a curved shape convex toward the second porous coating layer 12 at the center portion.

[0096] Therefore, the separator according to one aspect of the present disclosure may have a structure in which the thickness of the porous substrate gradually increases to a maximum thickness from one end to the other end of the separator based on the width direction and then gradually decreases.

[0097] According to one embodiment of the present disclosure, when an extruded sheet is formed by a method commonly used to manufacture a separator substrate, a porous substrate with a thickness gradient in the width direction as described above can be formed by adjusting the thickness adjusting screw of the extruder outlet. Specifically, an extruded sheet with a smaller thickness at both ends and a larger thickness in the center portion in the width direction is formed by adjusting the screw so that when a polymer resin as a raw material of a separator substrate is fed into the extruder and extruded through a T-die, the screw at both ends of the T-die outlet is tighter, while the screw at the center portion is not too tight. The extruded sheet can be cast and stretched in each of the width direction (TD) and the direction of travel (or length direction, MD) to manufacture a separator substrate having the above-mentioned shape. However, the present disclosure is not limited thereto.

[0098] Furthermore, the separator according to one aspect of the present disclosure may have a structure in which the thickness of the porous coating layer gradually decreases to a minimum thickness from one end to the other end of the separator based on the width direction and then gradually increases.

[0099] According to one embodiment of the present disclosure, on a porous substrate having a thickness gradient in the width direction as described above, in order to form a porous coating layer to keep the total thickness of the separator constant, a coating rod having different thicknesses according to positions can be used to form the porous coating layer. Specifically, Figure 6 FIG. 4 is a diagram of a coating rod 4 for forming a porous coating according to an embodiment of the present disclosure. Figure 6 The separator having a constant total thickness can be manufactured by coating a slurry for forming a porous coating layer on at least one surface, preferably both surfaces, of the porous substrate using a coating rod having a thickness at both ends greater than that at the center. However, the present disclosure is not limited thereto.

[0100] As described above, a separator according to one aspect of the present disclosure may have a structural feature in which the thickness of each of the porous substrate and the porous coating layer varies according to the position in the width direction, and the total thickness of the separator, i.e., the sum of the thickness of the porous substrate and the thickness of the first porous coating layer and the second porous coating layer, remains constant.

[0101] In this specification, "the total thickness of the separator remains constant" means that the thickness value measured by the same method at any position within a certain area is within an error range of 5% or less. Specifically, when the difference between the thickness values ​​at two random positions within a certain area is 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, or 0% (i.e., no difference), the thickness can be said to remain constant.

[0102] In this specification, "gradual increase in thickness" means that the thickness value measured by the same method along a predetermined direction in a certain area increases continuously or discontinuously. The increase rate of the thickness value may be constantly maintained within an error range of 5% or less, and may vary discontinuously, but preferably, the gradual increase in thickness may mean that the thickness value increases continuously at a constant rate.

[0103] In this specification, "gradually decreasing thickness" means that the thickness value measured by the same method along a predetermined direction in a certain area decreases continuously or discontinuously. The reduction ratio of the thickness value may be constantly maintained within an error range of 5% or less, and may vary discontinuously, but preferably, the gradual decrease in thickness may mean that the thickness value decreases continuously at a constant ratio.

[0104] In this specification, unless otherwise specified, the "thickness" of each component may refer to a value measured using a thickness measuring tool generally used to measure the thickness of a separator of a battery. For example, the thickness measuring tool may be obtained from Mitutoyo VL-50S, but is not limited thereto.

[0105] In one embodiment of the present disclosure, the thickness of the porous substrate may be measured after removing the porous coating layer from the separator. For example, the thickness of the porous substrate remaining after removing the porous coating layer using a solvent that dissolves the porous coating layer included in the separator may be measured.

[0106] In one embodiment of the present disclosure, the thickness of the porous coating layer may be measured by measuring the thickness of the separator and subtracting the thickness of the porous substrate measured as described above from the thickness of the separator, but the measuring method is not limited thereto.

[0107] According to one embodiment of the present disclosure, the position where the thickness of the porous substrate is the maximum thickness (in other words, the position where the thickness of the porous coating is the minimum thickness) can be changed according to the position where the sag in the electrode assembly is minimized, according to the position of the electrode lug of the electrode assembly formed when the electrode assembly is manufactured using a separator.

[0108] For example, in the manufacture of an electrode assembly using a separator, when the separator is folded in a Z shape and each of the unit positive electrode and the unit negative electrode is inserted at the folded and overlapping portion to form an electrode assembly, and both ends of the electrode assembly in the length direction are fixed by equal force, when the tension applied to the center portion of the electrode assembly in the length direction is the largest, the position where the thickness of the porous substrate is the largest can be the center portion of the separator in the width direction.

[0109] In another embodiment of the present disclosure, when an electrode assembly is manufactured using a separator, when the tension is maximum at a position 1 / 3 in the length direction of the electrode assembly, the position where the thickness of the porous substrate is the maximum thickness can be a position 1 / 3 of the total length of the separator in the width direction.

[0110] According to one embodiment of the present disclosure, in the manufacture of an electrode assembly using a separator, preferably, both ends can be fixed by equal force, and the thickness of the porous substrate can be the largest at the center of the separator in the width direction. Specifically, the thickness of the porous substrate can be the largest at 50% of the total length 100% in the width direction.

[0111] This may mean that the thickness of the porous substrate is smallest at the outermost end of the separator based on the width direction. Specifically, the thickness of the porous substrate may be smallest at 50% of 100% of the total length in the width direction.

[0112] In one embodiment of the present disclosure, the thickness of the porous substrate at the center (e.g., 50% of the total width of the separator) can be 70% to 95% of the total thickness of the separator. For example, the thickness of the porous substrate at 50% of the total width of the separator can be 75% to 90%, 75% to 85%, or 80% of the total thickness of the separator.

[0113] In one embodiment of the present disclosure, the thickness of the porous substrate at both ends (e.g., 0% or 100% of the total width of the separator) can be 50% to 70% of the total thickness of the separator. For example, the thickness of the porous substrate at 0% or 100% of the total width of the separator can be 55% to 65%, or 60% of the total thickness of the separator.

[0114] In one embodiment of the present disclosure, the difference between the maximum thickness and the minimum thickness of the porous substrate in the separator may be 1 μm to 5 μm, 2 μm to 4 μm, or 2.5 μm to 3.5 μm, specifically 3 μm.

[0115] In other words, the thickness difference between the center portion and the end portion of the porous substrate in the separator may be 1 μm to 5 μm, 2 μm to 4 μm, or 2.5 μm to 3.5 μm, specifically 3 μm.

[0116] According to one embodiment of the present disclosure, the curved shape of the interface between the porous substrate and the porous coating layer may be symmetrical with respect to the center of the separator in the width direction.

[0117] exist Figure 3b , in a cross section of the separator in the width direction according to one embodiment of the present disclosure, the center in the width direction is indicated by a dotted line 1.

[0118] Reference Figure 3bIn the separator according to one embodiment of the present disclosure, the first interface between the porous substrate 10 and the first porous coating layer 11 may have a shape symmetrical with respect to the center (dashed line 1) in the width direction of the separator 1. In addition, the second interface between the porous substrate 10 and the second porous coating layer 12 may have a shape symmetrical with respect to the center (dashed line 1) in the width direction of the separator 1.

[0119] According to another embodiment of the present disclosure, the curved shapes of the two interfaces may be symmetrical with respect to the center of the separator in the thickness direction.

[0120] exist Figure 3c , in a cross section of the separator in the width direction according to one embodiment of the present disclosure, the center in the thickness direction is indicated by a dotted line m.

[0121] Reference Figure 3c , the separator according to one embodiment of the present disclosure may have a curved shape of the first interface and a curved shape of the second interface that are symmetrical with respect to the center (dashed line m) of the separator 1 in the thickness direction.

[0122] According to another embodiment of the present disclosure, the separator may have a structure in which the curved shape of each of the first interface and the second interface is symmetrical relative to the center (l) in the width direction, and the curved shape of the first interface and the second interface is symmetrical relative to the center (m) in the thickness direction.

[0123] According to one embodiment of the present disclosure, the partition may have a width relative to the center ( Figure 3b The structure is symmetrical about the dotted line 1 in the figure. Specifically, based on the center of the separator in the width direction, the thickness of the porous substrate at any point at equal distances from the center to both ends can be equal to each other, and the thickness of the porous coating can be equal to each other. More specifically, when the position of the center is 50% of the total length of the separator in the width direction of 100%, the thickness of the porous substrate at the 40% position and the 60% position can be equal to each other. In addition, the thickness of the first porous coating at the 40% position and the 60% position can be equal to each other. In addition, the thickness of the second porous coating at the 40% position and the 60% position can be equal to each other.

[0124] According to one embodiment of the present disclosure, the porous coating layer on each of the two surfaces of the porous substrate may be oriented with respect to the center of the separator in the thickness direction ( Figure 3c That is, the separator 1 may have a structure that is a line-symmetrical shape with respect to the center in the thickness direction. Therefore, the thickness of each of the first porous coating layer and the second porous coating layer at any same position in the length direction of the separator perpendicular to the width direction of the separator may be equal to each other.

[0125] In this specification, in view of errors in the manufacturing process or measurement errors as described above, "equal thickness" includes a thickness having a thickness difference of ±5% or less.

[0126] In one embodiment of the present disclosure, the thickness of the porous substrate may be, for example, 40% to 90% of the total thickness of the separator (100%). Specifically, the thickness of the porous substrate at both ends may be 40% of the total thickness of the separator (100%), and for the first interface and the second interface having a curved surface, the thickness of the porous substrate may gradually increase as it moves toward the center of the separator in the long side direction, and reach 90% at the center of the separator in the long side direction.

[0127] According to one embodiment of the present disclosure, when the thickness of the porous substrate is, for example, 40% to 90% of the total thickness of the separator (100%), the thickness of each of the first and second porous coating layers may be 5% to 30% of the total thickness of the separator (100%).

[0128] In another embodiment of the present disclosure, the thickness of the porous substrate may be, for example, 60% to 80% of the total thickness of the separator (100%). Specifically, the thickness of the porous substrate at both ends may be 60% of the total thickness of the separator (100%), and for the first interface and the second interface having a curved surface, the thickness of the porous substrate may gradually increase as it moves toward the center of the separator in the width direction, and reach 80% at the center of the separator in the width direction.

[0129] According to another embodiment of the present disclosure, when the thickness of the porous substrate is, for example, 60% to 80% of the total thickness of the separator (100%), the thickness of each of the first and second porous coating layers may be 10% to 20% of the total thickness of the separator (100%).

[0130] In one embodiment of the present disclosure, the separator may have a strip shape. Specifically, the strip separator may be a separator in a long strip shape with a predetermined width, and specifically, refers to a separator in a rectangular shape with an aspect ratio of 1 or more, specifically greater than 1. More specifically, the length of the long side of the separator may be 1.5m to 5m, specifically 1.8m to 4.8m.

[0131] Hereinafter, the porous substrate and the porous coating layer will be described by way of example. However, the separator according to one aspect of the present disclosure has the above-described novel shape and is not limited by the components of the porous substrate and the porous coating layer.

[0132] In one embodiment of the present disclosure, a porous substrate refers to a substrate having pores to act as a porous ion-conducting barrier that allows ions to pass through but prevents electrical contact between the negative electrode and the positive electrode. The pores are interconnected to allow gas or liquid to flow from one side of the substrate to the other.

[0133] In one embodiment of the present disclosure, the porous substrate may include a porous polymer film containing a thermoplastic resin for providing a shutdown function. Here, the shutdown function refers to a function in which when the temperature of the battery increases, the thermoplastic resin melts and the pores of the porous substrate are closed to block further ion transmission, thereby preventing thermal runaway in the battery.

[0134] In one embodiment of the present disclosure, the thermoplastic resin used in the porous substrate may preferably be a thermoplastic resin below 200°C. In addition, the thermoplastic resin may include, for example, those that can be used as a substrate for a separator, without limitation. For example, the thermoplastic resin may include polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylenenaphthalene or a mixture thereof, but is not limited thereto.

[0135] In one embodiment of the present disclosure, the porous substrate may be a polyolefin substrate.

[0136] In one embodiment of the present disclosure, when the thickness of the porous substrate satisfies the aforementioned range based on the total thickness of the separator, the thickness of the porous substrate is not limited to a specific range, but can be, 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.

[0137] In one embodiment of the present disclosure, the porous coating layer comprises inorganic particles, and may further comprise a binder resin, and all or at least a portion of the surface of the inorganic particles may be coated with the binder resin. In this case, the inorganic particles are held together by surface bonding and / or point bonding via the binder resin. For example, the inorganic particles and the binder resin in the porous coating layer may be included in a weight ratio of 95:5 to 50:50. The porous coating layer has micropores therein so that the micropores are interconnected, and has a porous layer structure feature that allows gas or liquid to flow from one side to the other side.

[0138] In one embodiment of the present disclosure, the porous coating may have a pore structure derived from pores corresponding to the voids (interstitial volume) between inorganic particles. The pore size or porosity (volume ratio of pores) can be adjusted according to the particle size and particle size distribution. This structure can improve the tolerance to metal impurities present in the electrode and inhibit the shrinkage of the porous polyolefin substrate, thereby improving the safety of the electrochemical device.

[0139] In one embodiment of the present disclosure, the porous coating may include a plurality of nodes, the plurality of nodes including inorganic particles and a binder polymer covering at least a portion of the surface of the inorganic particles; and at least one filament, the at least one filament being formed in a linear form by the binder polymer of the nodes, wherein the filament has a node connection portion extending from one node and connecting the node to another node, and the node connection portion has a three-dimensional network structure formed by the interconnection of the filaments derived from the binder polymer.

[0140] In one embodiment of the present disclosure, as described above, the porous coating layer may be formed by a Safety Reinforced Separator (SRS) manufacturing method, a Ceramic Coated Separator (CCS) manufacturing method, or any other known manufacturing method, but is not limited thereto.

[0141] In one embodiment of the present disclosure, the inorganic particles are not limited to a specific type and may include those that are electrochemically stable. That is, the inorganic particles that can be used in the present disclosure are not limited to a specific type and may include those that are within the operating voltage range of the applied electrochemical device (e.g., relative to Li / Li + Those that do not undergo oxidation and / or reduction reactions within a range of 0 V to 5 V. Non-limiting examples of inorganic particles may include at least one of the following: BaTiO 3 、Pb(Zr,Ti)O 3 (PZT), Pb 1- x La x Zr 1-y Ti y O 3 (PLZT, 0 <x<1,0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 ) 3 -PbTiO 3 (PMN-PT), hafnium dioxide (HfO 2 )、SrTiO 3 SnO 2 、CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 、SiO 2 , Y 2 O 3 、Al 2 O 3 , SiC or TiO 2 .

[0142] In one embodiment of the present disclosure, when the porous coating layer includes a binder resin, the binder resin may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin). In one embodiment of the present disclosure, the PVdF-based resin may include at least one of the following: a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride, or a mixture thereof. In one embodiment of the present disclosure, the monomer may include, for example, a fluorinated monomer and / or a chloride-based monomer. Non-limiting examples of fluorinated monomers can include at least one of the following: 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).

[0143] In one embodiment of the present disclosure, when the thickness of the porous coating layer satisfies the above-mentioned ratio range based on the total thickness of the separator, the thickness of the porous coating layer is not limited to a specific range, but can be, 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.

[0144] In one embodiment of the present disclosure, the first porous coating layer and the second porous coating layer may have the same composition, but may be formed to have different compositions if necessary, and the present disclosure is not limited thereto.

[0145] Through the above structure, when the two ends of an electrode assembly using a separator according to one aspect of the present disclosure are fixed in the length direction, the separator can reduce the tension applied to the central part, thereby improving the stability of the separator itself and the stability of the electrochemical device using it, but the effects of the present disclosure are not limited to this.

[0146] According to another aspect of the present disclosure, an electrode assembly using the above separator is provided.

[0147] Specifically, the electrode assembly has a structure in which the above-mentioned separator is folded in a zigzag shape, and the unit positive electrodes and the unit negative electrodes are arranged in an alternating manner at a plurality of regions in which the separator is folded and overlapped.

[0148] An electrode assembly according to one embodiment of the present disclosure may include a unit positive electrode, a unit negative electrode, and a separator between the unit positive electrode and the unit negative electrode, wherein the unit positive electrode includes a plurality of unit positive electrodes arranged spaced apart from each other on one surface of the separator, the unit negative electrode includes a plurality of unit negative electrodes arranged spaced apart from each other on another surface of the separator, based on the long side direction of the separator, the position where the unit positive electrode is arranged and the position where the unit negative electrode is arranged do not overlap, and the separator is the above-mentioned separator.

[0149] Figure 4 A cross section in the length direction (Y) of an electrode assembly 2 according to one embodiment of the present disclosure is shown.

[0150] Reference Figure 4 , the electrode assembly 2 includes a separator 1 folded in a zigzag shape, and a plurality of unit positive electrodes 21 and a plurality of unit negative electrodes 22 arranged in an alternating manner at a plurality of regions where the separator is folded and overlapped.

[0151] According to one embodiment of the present disclosure, since the electrode assembly has a structure in which a plurality of unit electrodes are arranged on each of one surface and the other surface of a strip-type separator, the total length of the electrode assembly when unfolded can be, for example, 1m to 4.5m, specifically 1.2m to 4.3m.

[0152] As described above, the electrode assembly according to another aspect of the present disclosure has a long strip shape, but due to the unique structure of the separator, the central portion can be prevented from sagging during the manufacturing process of the electrode assembly, thereby improving stability and productivity, but the effects of the present disclosure are not limited thereto.

[0153] In one embodiment of the present disclosure, the unit electrode may be a positive electrode and / or a negative electrode commonly used in an electrochemical device, and each of the positive electrode and the negative electrode may include a current collector and an electrode active material coating on the current collector, and its size or shape is not limited to a specific size or shape.

[0154] In one embodiment of the present disclosure, when the electrode is a positive electrode, the positive electrode active material may include, for example, lithium transition metal oxide; lithium metal iron phosphate; lithium nickel-manganese-cobalt oxide; lithium nickel-manganese-cobalt oxide partially substituted by other transition metals; or two or more thereof, but is not limited thereto. Specifically, the positive electrode active material may include, for example, a layered compound, such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ) or a compound substituted by one or more transition metals; chemical formula Li 1+x Mn 2-x O 4 (x is 0 to 0.33), LiMnO 3, LiMn 2 O 3 , LiMnO 2 's lithium manganese oxides; lithium copper oxide (Li 2 CuO 2 ); vanadium oxides, such as LiV 3 O 8 , LiV 3 O 4 , V 2 O 5 , Cu 2 V 2 O 7 ; Ni-site type lithium nickel oxides represented by the chemical formula LiNi 1-x M x O 2 (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); lithium manganese composite oxides represented by the chemical formula LiMn 2-x M x O 2 (M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li 2 Mn 3 MO 8 (M = Fe, Co, Ni, Cu or Zn); lithium metal phosphate LiMPO 4 (M = Fe, Co, Ni or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O 2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1); lithium nickel-manganese-cobalt oxide partially substituted by aluminum Li a [Ni b Co c Mn d Al e 1-f M1 f O 2 (M1 is at least one selected from 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); lithium nickel-manganese-cobalt oxide partially substituted by other transition metals Li 1+x (Ni a Co b Mn​c M d ) 1-x O 2 (x=0 to 0.03, a=0.3 to 0.95, b=0.01 to 0.35, c=0.01 to 0.5, d=0.001 to 0.03, a+b+c+d=1, M is any one selected from Fe, V, Cr, Ti, W, Ta, Mg and Mo), disulfide compound; Fe 2 (MoO 4 ) 3 , but not limited to this.

[0155] In one embodiment of the present disclosure, when the electrode is a negative electrode, the negative electrode active material may include, for example, lithium metal or lithium alloy, soft carbon, hard carbon, natural graphite, crystalline graphite (Kish graphite), pyrolytic carbon, carbon fiber based on mesophase pitch, mesophase carbon microbeads, mesophase pitch, coke derived from petroleum or coal tar pitch, or a mixture thereof, but is not limited thereto.

[0156] In one embodiment of the present disclosure, the cell positive electrode and the cell negative electrode may each include an electrode tab at an end portion.

[0157] According to one embodiment of the present disclosure, an electrode tab of each of the unit positive electrode and the unit negative electrode may be disposed at each of two opposite ends of the electrode assembly in a length direction.

[0158] According to another aspect of the present disclosure, an electrochemical device including the electrode assembly and a case accommodating the electrode assembly may be provided.

[0159] In one embodiment of the present disclosure, the housing may include those commonly used as battery housings, and its shape is not particularly limited by the battery application. For example, the housing may be a cylindrical shape using a can, a prismatic shape, a bag shape, or a coin shape.

[0160] When the electrode assembly is completed, the electrode assembly may be placed in a case by a common method of manufacturing an electrochemical device, followed by injecting an electrolyte and sealing the case, and in this case, the electrochemical device may be, for example, a lithium secondary battery.

[0161] Hereinafter, the present disclosure will be described in more detail through embodiments, but the following description is provided to describe the present disclosure through examples, and the scope of the present disclosure is not limited thereto.

[0162] [Manufacturing of separator]

[0163] The separators of Example 1 and Comparative Example 1 were manufactured as follows.

[0164] in this case, Figure 3a shows the side shape of the separator of Example 1, and Figure 1b The side surface shape of the separator of Comparative Example 1 is shown.

[0165] Example 1

[0166] Fabrication of porous substrates

[0167] Three types of polyethylene polymers having different molecular weights, a polypropylene polymer, and an antioxidant were mixed in an appropriate ratio and extruded through a T-die to form an extruded sheet, which was then cast to form a polyolefin-based precursor film, and the polyolefin-based precursor film was stretched in each of the MD and TD directions to obtain a porous substrate. In this case, the three types of 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).

[0168] Furthermore, when the extruded sheet was formed through the T-die, the thickness adjusting screws at both ends of the T-die outlet were tightened more firmly to obtain an extruded sheet in a shape in which the central portion 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 manufactured after stretching was 45% by volume.

[0169] A porous substrate was manufactured while adjusting the gap of the T-die so as to increase the thickness in a curved shape from both ends to the 250 mm position so that the total width (short side, Y direction) was 500 mm, the length (long side, X direction) was 4 m, the thickness (Z direction) measured at each of the two ends of the short side was 9 μm, and the thickness at the center of the short side (i.e., at the 250 mm position) was 12 μm.

[0170] Fabrication of porous coatings

[0171] PVDF-HFP binder (Mw 500,000 g / mol, HFP 15 wt %) and inorganic particles were added to a proper solvent at a weight ratio of 5:95 and mixed to prepare an inorganic coating slurry.

[0172] Use with Figure 6 The inorganic coating slurry thus prepared is applied to both surfaces of the porous substrate by a coating bar of the shape shown, and dried to form a porous coating layer on each of the upper and lower surfaces of the porous substrate.

[0173] Therefore, the porous coating on each of the upper and lower surfaces was formed to decrease in thickness in a curved shape so that the thickness measured at each of both ends was 3 μm and the thickness at a position 250 mm from both ends corresponding to the center of the short side was 1.5 μm.

[0174] Thus, a separator having a total thickness constantly maintained at 15 μm over the entire short sides and long sides was manufactured.

[0175] Comparative Example 1

[0176] Fabrication of porous substrates

[0177] A porous substrate was manufactured by the same method as in Example 1, except that the porous substrate had a constant thickness of 9 μm without thickness variation throughout the width direction (short side).

[0178] Fabrication of porous coatings

[0179] A porous coating layer was formed by the same method as in Example 1, except that the porous coating layer had a constant thickness of 3 μm without thickness variation throughout the width direction (short side).

[0180] Thus, a separator having a constant total thickness of 15 μm in the width direction was manufactured.

[0181] Table 1 summarizes the thickness of each component at both ends (0%, 100%) and the center (50%) of the total length 100% in the width direction of the separator thus prepared based on Example 1 and Comparative Example 1. In Table 1, the ratio of the thickness of the porous substrate according to the position relative to the total thickness of the separator is shown.

[0182] [Table 1]

[0183]

[0184] [Manufacturing and evaluation of electrode assemblies]

[0185] Manufacturing of electrode assemblies

[0186] Using the separator thus prepared in each of Example 1 and Comparative Example 1, a Figure 2a In this case, the separator is folded so that the length of the electrode assembly in the length direction (Y direction) is 500 mm and the length in the width direction (X direction) is 100 mm.

[0187] Specifically, 17 positive electrodes and 16 negative electrodes are arranged on the upper and lower surfaces of the separator in an alternating manner. In this case, the position of the end of the positive electrode on one surface and the position of the end of the negative electrode on the other surface are arranged in an alternating manner, spaced apart from each other at a horizontal interval of 3 mm on the plane. Specifically, the separator of Example 1 or Comparative Example 1 is folded in a zigzag shape, and a positive electrode or a negative electrode is placed at each area where the separator is folded and overlapped. A positive electrode containing lithium cobalt oxide LCO as a positive electrode active material and a negative electrode containing graphite as a negative electrode active material (N / P ratio>100) are prepared.

[0188] Evaluation of center section sagging

[0189] pass Figure 5 The method shown is used to evaluate the sagging of the central portion of the electrode assembly in the length direction (Y direction).

[0190] First, an electrode assembly manufactured using the separator of Example 1 or Comparative Example 1 was prepared. Subsequently, two tables b and b' having the same height were arranged at an interval of 400 mm from each other to fix both ends of the electrode assembly thus prepared in the length direction (Y). A length of 50 mm at each of the two ends of the electrode assembly in the length direction was brought into contact with each of the tables spaced from each other, and weights a and a' having the same weight were placed on the electrode assembly to prevent the electrode assembly from moving.

[0191] After 30 minutes had passed since the electrode assembly was fixed, the longest distance (height, h) from the position flush with the height of the table to the position where the electrode assembly drooped was measured, and the results are shown in Table 2 below.

[0192] [Table 2]

[0193]

[0194] As can be seen from the above Table 2, it was confirmed that when the separator having the structure of Example 1 was used, the sagging of the central portion of the electrode assembly in the length direction could be significantly reduced.

[0195] Although the present disclosure has been described above with reference to the embodiments and the accompanying drawings, it will be apparent to one of ordinary skill in the art to which the present disclosure pertains that various changes and modifications may be made within the scope of the present disclosure based on the foregoing description.

[0196] [reference numerals list]

[0197] 1: Separator

[0198] 10: Porous substrate

[0199] 11: First porous coating

[0200] 12: Second porous coating 2: Electrode assembly

[0201] 21: Unit positive electrode

[0202] 22: Unit negative pole

[0203] 211: Positive electrode tab

[0204] 222: Negative electrode tab

[0205] 3: Electrode assembly

[0206] 4: Coating rod

[0207] a, a': heavy object

[0208] b, b': table

Claims

1. A separator, comprising: porous substrate; and a porous coating layer on each of the two surfaces of the porous substrate, the porous coating layer comprising inorganic particles, wherein the total thickness of the separator remains constant throughout the separator, wherein the aspect ratio of the partition is 1 or greater, and wherein an interface between each of the porous coating layers and the porous substrate has a curved shape that is convex toward an adjacent porous coating layer based on a width direction of the separator. 2 . The separator according to claim 1 , wherein the porous substrate is thickest at a center of the separator in the width direction. 3 . The separator according to claim 1 , wherein the porous substrate is thinnest at an outermost end of the separator in the width direction. 4 . The separator 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 a center of the separator in the width direction. The separator according to claim 1 , wherein the curved shapes of the two interfaces are symmetrical with respect to a center of the separator in a thickness direction. The separator according to claim 1 , wherein the thickness of the porous substrate is 40% to 90% of 100% of the total thickness of the separator. 7 . The separator according to claim 1 , wherein the thickness of the porous substrate is 60% to 80% of 100% of the total thickness of the separator. 8 . The separator according to claim 1 , wherein at 50% of the total width of the separator, the thickness of the porous substrate is 70% to 95% of the total thickness of the separator. 9 . The separator according to claim 1 , wherein at 0% or 100% of the total width of the separator, the thickness of the porous substrate is 50% to 70% of the total thickness of the separator. 10 . The separator according to claim 1 , wherein the length of the separator in the length direction is 1.5 m to 5 m.

11. An electrode assembly, comprising: a positive electrode unit, a negative electrode unit, and a separator between the positive electrode unit and the negative electrode unit, wherein the separator is folded in a Z-shape, wherein the unit positive electrodes and the unit negative electrodes are arranged in an alternating manner in a plurality of regions in which the separators are folded and overlapped, and Wherein the separator is as defined in any one of claims 1 to 10. 12 . The electrode assembly of claim 11 , wherein the unit positive electrode and the unit negative electrode each include an electrode tab at an end portion.

13. An electrochemical device comprising: The electrode assembly according to claim 11; and A casing for accommodating the electrode assembly.

14. The electrochemical device according to claim 13, wherein the electrochemical device is a lithium secondary battery. 15 . The electrochemical device according to claim 13 , wherein the case has a bag-type shape, a prism shape, a cylindrical shape, or a coin-type shape.

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