Separator and electrochemical device including the same

Abstract

The present invention relates to a separator, an electrode assembly, and an electrochemical device including the same. A separator according to one embodiment of the present invention is a separator formed on each of a porous substrate and a porous coating layer containing inorganic particles, wherein the separator has a uniform overall thickness over the entire surface and an aspect ratio of 1 or greater, and, with respect to the width direction of the separator, each interface between the porous substrate and the porous coating layer has a convex curved shape toward the porous substrate.

Description

Technology Field

[0001] The present invention relates to a separator and an electrochemical device including the same. Specifically, the present invention relates to a separator for use in an electrode assembly manufactured by the Advanced-Z-Stacking (AZS) method. Background Technology

[0002] Secondary batteries can be classified according to the structure of the electrode assembly, which consists of a positive electrode, a separator, and a negative electrode. Representative examples include a jelly-roll (wound type) electrode assembly in which long sheet-type positive and negative electrodes are wound with a separator interposed; a lamination and stacking (L&S) electrode assembly in which multiple positive and negative electrodes cut into units of a predetermined size are formed into unit cells with a separator interposed, and then multiple unit cells are sequentially stacked; and a zigzag stacking (Z-stacking) electrode assembly in which multiple positive and negative electrodes cut into units of a predetermined size are stacked in a zigzag pattern with a long sheet-type separator interposed. However, these conventional electrode assemblies have several problems.

[0003] First, since the jelly-roll (wound-type) electrode assembly is formed by winding long sheet-type positive and negative electrodes in a dense manner to create a cylindrical or elliptical structure in cross-section, 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 results in uneven spacing between the electrodes, causing a rapid deterioration in battery performance and threatening the safety of the battery due to internal short circuits. Additionally, since long sheet-type positive and negative electrodes must be wound, it is difficult to wind them quickly while maintaining a constant spacing between them, which leads to a problem of reduced productivity.

[0004] On the other hand, laminate-stack (L&S) electrode assemblies and zigzag stacking (Z-stacking) electrode assemblies have shown superiority in terms of stability and productivity compared to jelly-roll electrode assemblies, and have been relatively popular, and research on these methods is still ongoing.

[0005] However, while the Laminated and Stacked (L&S) electrode assembly offers the advantages of rapid sequential stacking of multiple anode and cathode units and high space efficiency for manufactured batteries, it carries a risk of stability defects relative to its high productivity. This is because misalignment of the separator can cause battery defects, requiring significant time and effort for the sequential stacking process. Additionally, the Z-stacking electrode assembly provides a more stable structure compared to the L&S electrode assembly due to the use of long sheet-type separators, but it suffers from low process efficiency due to process complexity.

[0006] Therefore, new electrode assembly methods are continuously being researched and developed to combine the advantages of the Laminated and Stacked (L&S) type and the Zigzag Stacking (Z-stacking) type while compensating for each other's shortcomings.

[0007] For example, a manufacturing method for Advanced Z-Stacking (AZS) electrode assemblies is currently under development, and research is ongoing to ensure the productivity and stability of AZS electrode assemblies manufactured in long forms.

[0008] Referring to Fig. 2b, an electrochemical device including an AZS electrode assembly with a long length in the electric direction (Y direction) has a problem in that the central part of the separator is not sufficiently wetted by the electrolyte when the electrolyte is injected. Specifically, even after the electrolyte is injected, a region (un-wetting region) that is not wetted by the electrolyte is observed in the central part of the separator, and this may cause a problem in which the performance of the battery using it is degraded. The problem to be solved

[0009] Therefore, the problem that the present invention aims to solve is to provide a separator that can be used in an electrode assembly with improved productivity and stability, and an electrochemical device using the same.

[0010] Specifically, the present invention aims to provide a separator that can be used in an Advanced-Z-Stacking (AZS) electrode assembly. More specifically, the invention aims to provide a separator in which the electrolyte wetting properties of the separator are improved throughout the entire length of the electrode assembly, even when used in an AZS electrode assembly with a long length in the electric direction.

[0011] For example, the present invention aims to provide a separator with a novel structure capable of improving the phenomenon in which an electrolyte wetting region in the central part is observed. means of solving the problem

[0012] In order to solve the above problem,

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

[0014] The separator according to the first embodiment is,

[0015] porous substrate and

[0016] A separation membrane comprising a porous coating layer formed on each side of the above-mentioned porous substrate and containing inorganic particles,

[0017] The above separator maintains a constant overall thickness across the entire surface, and

[0018] The aspect ratio of the above separator is 1 or greater, and

[0019] Based on the width direction of the above separation membrane, each interface between the porous substrate and the porous coating layer is made to have a convex curved shape toward the porous substrate.

[0020] According to the second embodiment, in the first embodiment,

[0021] The thickness of the porous substrate may be thinnest at the center based on the width direction of the above separation membrane.

[0022] According to the third embodiment, in the first embodiment or the second embodiment,

[0023] Based on the width direction of the above separation membrane, the thickness of the porous substrate may be thickest at the outermost end.

[0024] According to the fourth embodiment, in any one of the first to third embodiments,

[0025] With respect to the center in the width direction of the above separation membrane, the curved shape of the interface between the porous substrate and the porous coating layer may be symmetrical.

[0026] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0027] With respect to the center of the thickness direction of the above separation membrane, the curved shape of the two interfaces may be symmetrical.

[0028] According to the 6th embodiment, in any one of the 1st to 5th embodiments,

[0029] Based on 100% of the total thickness of the above separator,

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

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

[0032] Based on 100% of the total thickness of the above separator,

[0033] The thickness of the above porous substrate may be 45% to 65%.

[0034] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0035] At the 50% point based on the total width of the above separator,

[0036] The thickness of the porous substrate may be 40% to 55% based on the total thickness of the separator.

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

[0038] At the 0% or 100% point based on the total width of the above separator,

[0039] The thickness of the porous substrate may be 50% to 70% based on the total thickness of the separator.

[0040] According to the 10th embodiment, in any one of the 1st to 9th embodiments,

[0041] The longitudinal length of the above separation membrane may be 1.5 to 5 m.

[0043] According to another aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0044] The preliminary electrode assembly according to the 11th embodiment is,

[0045] It includes a unit anode, a unit cathode, and a separator interposed between the unit anode and the unit cathode,

[0046] The above separator is folded in a zigzag manner, and

[0047] The unit anode and the unit cathode are alternately arranged in a plurality of areas where the above separator is folded and overlaps, and

[0048] The above separator is to be a separator according to any one of the first to ten embodiments.

[0049] According to the 12th embodiment, in the 11th embodiment,

[0050] Each of the above unit anode and the above unit cathode may include an electrode tab formed at one end.

[0052] According to another aspect of the present invention, electrochemical elements of the following embodiments are provided.

[0053] The electrochemical device according to the 13th embodiment is,

[0054] An electrode assembly according to the 11th embodiment or the 12th embodiment may be housed in a case.

[0055] According to the 14th embodiment, in the 13th embodiment,

[0056] The above electrochemical device may be a lithium secondary battery.

[0057] According to the 15th embodiment, in the 13th embodiment or the 14th embodiment,

[0058] The above case may be pouch-type, rectangular, cylindrical, or coated. Effects of the invention

[0059] A separator according to one embodiment of the present invention has a shape in which a porous substrate provided in a central portion in one direction is formed thinly, and a porous coating layer is formed thickly. Through this, even if the separator is formed in a large size, the electrolyte non-wetting area in the central portion is reduced, and furthermore, by being sufficiently wetted by the electrolyte over the entire area, the wetting performance of the separator can be improved.

[0060] A separator according to one embodiment of the present invention can be implemented with a long length by improving the wetting properties of the central portion and further the wetting properties of the front surface of the separator. Accordingly, it has the advantage of enabling the realization of a high-performance electrochemical device even when used in a ZZS electrode assembly or an AZS electrode assembly manufactured by a process in which a strip-shaped separator with a long length in the electric direction is folded in a zigzag shape and a unit electrode is inserted into the overlapping portion of the separator.

[0061] A separator according to one embodiment of the present invention has the advantage of being usable in an electrode assembly with improved stability and productivity. Brief explanation of the drawing

[0062] FIG. 1a is a schematic 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) formed on each of the two sides of the porous substrate. In FIG. 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). FIG. 1b is a cross-sectional view in the width direction of a conventional separator (1). Specifically, a separator (1) is shown having a first porous coating layer (11) and a second porous coating layer (12) provided on both sides of a porous substrate (10) without a thickness gradient. FIG. 2a is a schematic diagram of an electrode assembly (2) assembled in an AZS or ZZS manner. Specifically, it illustrates the structure of an electrode assembly (2) in which a separator (1) is folded in a zigzag manner and unit positive electrodes (21) and unit negative electrodes (22) are alternately interposed in the overlapping area where the separator (1) is folded. In FIG. 2a, the X direction represents the full width direction of the electrode assembly (2), the Y direction represents the full length direction of the electrode assembly (2), and the Z direction represents the thickness direction of the electrode assembly (2). FIG. 2b is a schematic diagram of an electrode assembly (3) having a positive electrode tab (211) and a negative electrode tab (222) respectively provided at both ends of an electrode assembly (2) in which only a positive electrode, a separator, and an electrode are stacked. In FIG. 2b, the X direction represents the full width direction of the electrode assembly (2), the Y direction represents the full length direction of the electrode assembly (2), and the Z direction represents the thickness direction of the electrode assembly (2). FIG. 2c is a cross-sectional view of an electrode assembly (2) assembled in an AZS or ZZS manner using a conventional separator (1). FIG. 3a is a schematic diagram of a separator (1) according to one embodiment of the present invention. Although the thickness of the entire separator is maintained constant with respect to the width direction of the separator (1), the interface (111, 121) between the porous substrate (10) and the first and second porous coating layers (11, 12) each has a convex curved shape toward the adjacent porous substrate. FIG. 3b is a schematic diagram of a separator (1) according to one embodiment of the present invention. In FIG. 3b, the dotted line (l) indicates the center of the separator (1) in the width direction (Y). FIG. 3c is a schematic diagram of a separator (1) according to one embodiment of the present invention. In FIG. 3c, the dotted line (m) indicates the center of the separator (1) in the thickness direction (Z). FIG. 4 is a cross-sectional view in the electric direction (Y) of an electrode assembly (2) assembled in an AZS or ZZS manner using a separator (1) according to one embodiment of the present invention. FIG. 5 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. Figure 6 is a photograph of the result of evaluating the electrolyte wetting performance of a separator according to Comparative Example 1 in this specification. Figure 7 is a photograph showing the result of evaluating the electrolyte wetting performance of the separator according to Example 1 in this specification. Specific details for implementing the invention

[0063] The present invention will be described in detail below with reference to the attached drawings.

[0064] In the drawings, the size of each component or a specific part constituting the component is exaggerated, omitted, or schematically depicted for the convenience and clarity of explanation. Accordingly, the size of each component does not entirely reflect its actual size. If it is determined that a specific description of related known functions or configurations could unnecessarily obscure the essence of the invention, such description shall be omitted. The invention is described in detail below.

[0065] In this specification, when a part is described as "comprising" a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0066] In this specification, the description of the term "A and / or B" means "A or B, or both."

[0067] Specific terms used in the following detailed description of the invention are for convenience only and are not intended to limit the invention. Additionally, words indicating direction, such as up, down, left, right, front, back, inside, and outside, indicate directions in the referenced drawings or directions toward or away from the geometric center of the respective designated device, system, and its components.

[0069] The present invention relates to a separator, an electrode assembly including the same, and an electrochemical device including the same. Examples of the electrochemical device include a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. More specifically, the secondary battery may be a lithium-ion secondary battery.

[0070] According to one aspect of the present invention, a separator for use in an electrochemical device is provided.

[0071] In this specification, the separator may have various shapes and, for example, may be provided in the form of a strip in which the length in the longitudinal direction is longer than the width in the width direction. However, the present invention is not limited thereto.

[0072] In this specification, the longitudinal, width, and thickness directions of the separator (1) are described with reference to FIG. 1a. In FIG. 1a, the X direction represents the longitudinal 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).

[0073] In one embodiment of the present invention, the separator (1) may be provided in the form of a strip having an aspect ratio of 1 or more, wherein the long side of the separator may be formed in the length direction (X direction) and the short side may be formed in the width direction (Y).

[0074] Referring to the drawings, a separator (1) according to one embodiment of the present invention comprises a porous substrate (10) and a porous coating layer (11, 12) formed 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) is maintained constant over the entire surface in the longitudinal direction.

[0075] Referring to FIG. 2a, in one embodiment of the present invention, the separator (1) may be used in a ZZS type electrode assembly or an AZS type electrode assembly in which a unit electrode is inserted into the portion where the separator is folded in a zigzag manner, but the use of the present invention is not limited thereto.

[0076] Referring to FIG. 2b, a schematic diagram of an electrode assembly (3) is shown in which the separator (1) is folded in a zigzag manner, unit electrodes (21, 22) are inserted into the overlapping portions of the folded separator, and electrode tabs (221, 222) are formed at one end of each unit electrode.

[0077] In this specification, the full-length direction, full-width direction, and thickness direction of the electrode assembly (3) can be explained with reference to FIG. 2b. In FIG. 2b, the X direction represents the full-width direction of the electrode assembly (2), the Y direction represents the full-length direction of the electrode assembly (2), and the Z direction represents the thickness direction of the electrode assembly (2).

[0078] In one embodiment of the present invention, the electrode assembly to which the separator is applied is provided with an anode tab (211) or a cathode tab (222) at one end in the electric field direction, respectively, and may be applied to a long cell with a long length in the electric field direction. Additionally, the anode tab (211) and the cathode tab (222) may be provided at one end in the same direction relative to the electric field direction, or at each end. However, the present invention is not limited thereto.

[0079] In one embodiment of the present invention, the electrode assembly using the separator comprises a plurality of unit electrodes and a separator with an aspect ratio of 1 or more interposed between the unit electrodes, and the separator has a structure of a ZZS type electrode assembly or an AZS type electrode assembly in which the unit electrode is inserted in a portion where the separator is folded in a zigzag manner and the separator overlaps.

[0081] A separator (1) according to one aspect of the present invention comprises a porous substrate (10) and porous coating layers (11, 12) formed on each of the two sides of the porous substrate and containing inorganic particles.

[0082] The above porous substrate may be used without particular restriction as long as it is used as a substrate for a separation membrane, and this will be described later.

[0083] The porous coating layer described above is a coating layer containing a large amount of inorganic particles to improve the safety of the separation membrane. Since the porous coating layer contains a large amount of inorganic particles, this can become a factor that increases the weight of the separation membrane as the size of the separation membrane increases, for example, as the length of the separation membrane increases.

[0084] A separator according to one aspect of the present invention comprises a porous coating layer formed on each of the two sides of the porous substrate. In this specification, for convenience of description, the porous coating layer located on one side of the porous substrate may be named the 'first porous coating layer (11)', and the porous coating layer located on the other side of the porous substrate may be named the 'second porous coating layer (12)'.

[0085] Additionally, for convenience of description in this specification, the interface between the porous substrate and the first porous coating layer may be named the 'first interface (111)', and the interface between the porous substrate and the second porous coating layer may be named the 'second interface (121)'.

[0086] In the present specification, the "long side direction" of the separator refers to the direction of the longer side among the horizontal and vertical lengths of the separator. Specifically, the separator is a strip-shaped separator with an aspect ratio of 1 or more, more specifically, an aspect ratio greater than 1, and two or more unit electrodes are disposed on the separator. At this time, the long side direction indicates the direction in which the unit electrodes are disposed. Generally, the "long side direction" of the separator may coincide with the driving direction of the separator or the electrode assembly in the manufacturing process of the separator or the manufacturing process of the electrode assembly using the same. Referring to the above, the longitudinal direction (X direction) of the separator (1) may also be referred to as the long side direction.

[0087] In this specification, the "short side direction" of the separator refers to the direction of the shorter length between the horizontal and vertical lengths of the separator. Referring to the above description, the width direction (Y direction) of the separator (1) may also be referred to as the short side direction.

[0088] Meanwhile, FIG. 1b shows a schematic diagram of the side view in the width direction of a separator (1) having a first porous coating layer (11) and a second porous coating layer (12) on each side of a porous substrate (10). FIG. 1b shows the side view in the width direction of a conventional separator (1) with an aspect ratio of 1 or more, and has a structure in which the porous coating layers (11, 12) and the porous substrate (10) are each formed with a uniform thickness based on the width direction.

[0089] As shown in Fig. 1b, when the porous coating layer and the porous substrate are each formed with a uniform thickness based on the width direction of the separator, when the electrode assembly formed by folding is housed in a case and the electrolyte is injected, a problem may occur in which the injected electrolyte does not sufficiently wet the central part of the separator.

[0090] Referring to FIGS. 2a and 2c, this problem can be exacerbated as the thickness of the electrode assembly increases, that is, as the number of stacked separators increases, or as the size of the separator increases, for example, as the length of the separator in the width direction and / or length direction increases, which can eventually lead to a problem that causes a degradation of the battery's performance.

[0091] To solve these problems, a separator according to one aspect of the present invention is a separator having an aspect ratio of 1 or more, wherein the total thickness is maintained constant over the entire surface of the separator, and with respect to the width direction of the separator, the interface between the porous substrate and the porous coating layer is each provided to have a convex curved shape toward the porous substrate.

[0092] FIGS. 3a to 3c illustrate schematic side views of a separator (1) according to one aspect of the present invention. Specifically, the separator (1) has an aspect ratio of 1 or greater, and FIG. 3a illustrates a side view of the separator in the width direction (Y direction).

[0093] Referring to FIG. 3a, the separator (1) has porous coating layers (11, 12) on each of the two sides of the porous substrate (10). At this time, with respect to the width direction of the separator, each interface (111, 121) between the porous substrate (10) and the porous coating layers (11, 12) has a convex curved shape toward the porous substrate (10).

[0094] Specifically, referring to FIG. 3a, the first interface (111) between the porous substrate (10) and the first porous coating layer (11) with respect to the width direction of the separator has a curved shape with a convex center facing the porous substrate (10). Additionally, the second interface (121) between the porous substrate (10) and the second porous coating layer (12) with respect to the width direction of the separator has a curved shape with a convex center facing the porous substrate (10).

[0095] Accordingly, a separation membrane according to one aspect of the present invention may have a structure in which the thickness of the porous substrate gradually decreases to a minimum thickness and then gradually increases, based on the width direction from one end to the other end of the separation membrane.

[0096] According to one embodiment of the present invention, a porous substrate having a thickness gradient in the width direction as described above may be formed by adjusting a thickness control screw of an extrusion discharge port when forming an extrusion sheet in a conventional method of manufacturing a separator substrate. Specifically, the separator substrate may be manufactured by a conventional process after feeding a polymer resin as a raw material into an extruder and extruding it through a T-die. At this time, the extruder may be equipped with a plurality of control screws that control the thickness of the extruded material when discharged from the T-die. When discharging the polymer resin from the T-die, if the screw in the center of the T-die discharge section is tightened more and the screws at both ends are tightened less, the extruded sheet is formed such that the thickness in the center is thin and the thickness at both ends is thick in the width direction. Subsequently, a separator substrate having the shape described above may be manufactured by casting the extrusion sheet formed as described above and stretching it in the width direction (TD) and the travel direction (or length direction, MD), respectively. However, the present invention is not limited thereto.

[0097] In addition, a separator according to one aspect of the present invention may have a structure in which the thickness of the porous coating layer gradually increases to a maximum thickness and then gradually decreases based on the width direction from one end to the other end of the separator.

[0098] 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 so that the total thickness of the separation membrane is maintained constant, the porous coating layer may be formed using a coating bar having a thickness different depending on the location. Specifically, FIG. 5 illustrates a schematic diagram of a coating bar (4) for forming a porous coating layer according to one embodiment of the present invention. Referring to FIG. 5, a separation membrane with a total thickness maintained constant can be manufactured by coating a slurry for forming a porous coating layer on at least one surface, preferably both surfaces, of a porous substrate using a coating bar in which the thickness of the central portion is thicker than that of both ends. However, the present invention is not limited thereto.

[0099] As described above, a separator according to one aspect of the present invention may have a structural feature in that the thickness of the porous substrate and the porous coating layer, respectively, varies depending on the position in the width direction, and the total thickness of the separator, that is, the sum of the thicknesses of the porous substrate and the first and second porous coating layers, is maintained constant.

[0100] In this specification, the term “the total thickness of the separator is maintained constant” indicates that when the thickness at any location within a specific area is measured according to the same method, the measured thickness value is within an error range of 5% or less. Specifically, the thickness may be described as being maintained constant when the deviation between thickness values ​​at any two locations within a specific area is within 5%, within 4%, within 3%, within 2%, within 1%, or 0% (i.e., no difference).

[0101] In this specification, the term “thickness gradually increases” indicates that when thickness is measured in the same way according to a certain direction within a specific area, the thickness value increases continuously or discontinuously. The rate at which the thickness value increases may be maintained constant within an error range of 5% or may change discontinuously, but preferably, “thickness gradually increases” indicates that the thickness value increases continuously at a constant rate.

[0102] In this specification, the term “thickness is gradually reduced” indicates that when thickness is measured in the same way according to a certain direction within a specific area, the thickness value decreases continuously or discontinuously. The rate at which the thickness value decreases may be maintained constant within an error range of 5% or may change discontinuously, but preferably, “thickness is gradually reduced” indicates that the thickness value decreases continuously at a constant rate.

[0103] In this specification, the "thickness" of each component may represent a value measured using a known thickness gauge capable of measuring the thickness of a battery separator, unless otherwise defined. For example, the thickness gauge may use the VL-50S product from Mitutoyo, but is not limited thereto.

[0104] In one embodiment of the present invention, the thickness of the porous substrate may be measured by removing the porous coating layer from the separator. For example, the thickness of the remaining porous substrate may be measured after removing the porous coating layer using a solvent capable of dissolving the porous coating layer included in the separator.

[0105] In one embodiment of the present invention, the thickness of the porous coating layer may be measured by the difference value of the thickness of the porous substrate measured according to the above after measuring the thickness of the separator, but the measurement method is not limited thereto.

[0106] According to one embodiment of the present invention, the point where the thickness of the porous substrate has a minimum thickness, that is, the point where the thickness of the porous coating layer has a maximum thickness, may be variable depending on the location where the separator of the electrode assembly is not sufficiently wetted by the electrolyte when manufacturing an electrode assembly using the separator.

[0107] For example, when manufacturing an electrode assembly using the above-described separator and housing it in a case to inject an electrolyte, if the electrolyte is supplied at a uniform density across the entire front surface of the electrode assembly and the amount of electrolyte reaching the center of the separator decreases, it may be preferable that the point where the thickness of the porous coating layer has a maximum thickness is the center of the separator in the width direction.

[0108] In one embodiment of the present invention, when an electrode assembly is manufactured using the separator and placed in a case to inject an electrolyte, if the amount of electrolyte reaching the 1 / 3 point in the electric direction of the electrode assembly is reduced due to the shape of the case, etc., the point where the thickness of the porous coating layer has a maximum thickness may be the 1 / 3 point in the width direction of the separator.

[0109] According to one embodiment of the present invention, when an electrode assembly is manufactured using the separator and placed in a case to inject an electrolyte, it is common for the amount of electrolyte reaching the halfway point in the electric direction of the electrode assembly to be reduced; therefore, the thickness of the porous coating layer may be thickest at the center based on the width direction of the separator. Specifically, the thickness of the porous coating layer may be thickest at the 50% point based on 100% of the total length in the width direction.

[0110] This may mean that the thickness of the porous coating layer is thinnest at the outermost end based on the width direction of the separator. Specifically, the thickness of the porous coating layer may be thickest at the 50% point based on 100% of the total length in the width direction.

[0111] In one embodiment of the present invention, at a central portion, for example, at 50% of the total width of the separator, the thickness of the porous substrate may be 40% to 55% of the total thickness of the separator. For example, at 50% of the total width of the separator, the thickness of the porous substrate may be 40% to 50% or 45% to 50% of the total thickness of the separator.

[0112] In one embodiment of the present invention, at both ends based on the total width of the separator, for example at 0% or 100%, the thickness of the porous substrate may be 50% to 70% based on the total thickness of the separator. For example, at 0% or 100% based on the total width of the separator, the thickness of the porous substrate may be 55% to 65% or 60% based on the total thickness of the separator.

[0113] In one embodiment of the present invention, the porous substrate in the separator may have a maximum thickness and a minimum thickness variation of 1 μm to 5 μm, 1.5 μm to 4 μm, or 2 μm to 3.5 μm, specifically 2 μm.

[0114] In one embodiment of the present invention, the difference in thickness between the central and terminal portions of the porous substrate with respect to the width direction of the separator may be 1 μm to 5 μm, 1.5 μm to 4 μm, or 2 μm to 3.5 μm, specifically 2 μm.

[0115] 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 membrane.

[0116] In FIG. 3b, the center of the width direction of the side view of the separator according to one embodiment of the present invention is indicated by a dotted line (ㅣ).

[0117] Referring to FIG. 3b, in one embodiment of the present invention, the first interface between the porous substrate (10) and the first porous coating layer (11) may have a symmetrical shape with respect to the center (dotted line l) in the width direction of the separator (1). Additionally, 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 (dotted line l) in the width direction of the separator (1).

[0118] According to another embodiment of the present invention, the curved shape of the two interfaces may be symmetrical with respect to the center of the thickness direction of the separation membrane.

[0119] In FIG. 3c, the center in the thickness direction is indicated by a dotted line (m) on a schematic diagram of the side view in the width direction of a separator according to one embodiment of the present invention.

[0120] Referring to FIG. 3c, in one embodiment of the present invention, the separator may have a curved shape of the first interface and the second interface symmetrical with respect to the center (dotted line m) in the thickness direction of the separator (1).

[0121] According to another embodiment of the present invention, the separator may have a structure in which the curved shapes of the first interface and the second interface are each symmetrical with respect to the center in the width direction (dotted line l in FIG. 3b), and the curved shapes of the first interface and the second interface are symmetrical with respect to the center in the thickness direction (dotted line m in FIG. 3c).

[0122] According to one embodiment of the present invention, the separator may have a structure that is symmetrical with respect to the center in the width direction (dotted line l in FIG. 3b). Specifically, with respect to the center in the width direction of the separator, the thickness of the porous substrate at any point spaced equally from the center to both ends may be equal, and the thickness of the porous coating layer may be equal. More specifically, when the center position is 50% with respect to 100% of the total length in the width direction of the separator, the thickness of the porous substrate at the point at 40% and the point at 60% may be equal. In addition, the thickness of the first porous coating layer at the point at 40% and the point at 60% may be equal. In addition, the thickness of the second porous coating layer at the point at 40% and the point at 60% may be equal.

[0123] According to one embodiment of the present invention, 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 thickness direction of the separator (dotted line m in FIG. 3c). That is, the separator (1) may have a structure with a line-symmetric shape with respect to the center of the thickness direction. Accordingly, the thicknesses of the first porous coating layer and the second porous coating layer, which are located on the same line as the direction orthogonal to the width direction of the separator, that is, the thickness direction (Z direction) of the separator, may be equal to each other.

[0124] In this specification, the phrase "the thicknesses are identical" includes having a thickness difference of within ±5%, taking into account manufacturing process errors or measurement errors as described above.

[0125] In one embodiment of the present invention, the thickness of the porous substrate may be, for example, 40% to 90% based on 100% of the total thickness of the separator. Specifically, the porous substrate may have a thickness of 40% based on 100% of the total thickness of the separator in the central part, and the thickness of the porous substrate may gradually increase as it approaches both ends in the width direction of the separator so that the first interface and the second interface have curved surfaces, and then have a thickness of 90% at both ends in the width direction of the separator.

[0126] According to one embodiment of the present invention, when the thickness of the porous substrate is, for example, 40% to 90% based on 100% of the total thickness of the separator, the thickness of the first porous coating layer and the second porous coating layer may each be 5% to 30% based on 100% of the total thickness of the separator.

[0127] In another embodiment of the present invention, the thickness of the porous substrate may be, for example, 40% to 70% based on 100% of the total thickness of the separator. Specifically, the porous substrate may have a thickness of 50% to 70%, for example 60%, based on 100% of the total thickness of the separator at both ends, and the thickness of the porous substrate may gradually decrease as it moves toward the center in the width direction of the separator so that the first interface and the second interface have curved surfaces, and then have a thickness of 40% to 60%, for example 40% to 55%, 40% to 50%, or 45% at the center in the width direction of the separator.

[0128] According to another embodiment of the present invention, when the thickness of the porous substrate is, for example, 40% to 70% based on 100% of the total thickness of the separator, the thickness of the first porous coating layer and the second porous coating layer may each be 15% to 30% based on 100% of the total thickness of the separator.

[0129] In one embodiment of the present invention, the separator may be in the form of a strip. Specifically, the strip-shaped separator is a long strip-shaped separator having a predetermined width, specifically a rectangular separator having an aspect ratio of 1 or more, specifically greater than 1. More specifically, the separator may have a long side length of 1.5 to 5 m, specifically 1.8 to 4.8 m.

[0131] Hereinafter, the composition of the porous substrate and the porous coating layer is described by example. However, in one aspect of the present invention, a separator membrane is of the novel shape described above and is not limited by the respective constituent components of the porous substrate and the porous coating layer.

[0132] In one embodiment of the present invention, the porous substrate refers to a substrate having a plurality of pores formed therein, which acts as a porous ion-conducting barrier that blocks electrical contact between a cathode and an anode while allowing ions to pass through. The pores are structured to be interconnected, so that gas or liquid can pass from one side of the substrate to the other.

[0133] In one embodiment of the present invention, the porous substrate may be a porous polymer film containing a thermoplastic resin in order to provide a shutdown function. Here, the shutdown function refers to a function that prevents thermal runaway of the battery by blocking the movement of ions through the melting of the thermoplastic resin and closing the holes of the porous substrate when the battery temperature rises.

[0134] In one embodiment of the present invention, the thermoplastic resin used in the porous substrate may preferably be a thermoplastic resin with a temperature of less than 200°C. In addition, the thermoplastic resin may be used without particular limitation as long as it can be used as a substrate for a separator, for example, but may be polyolefin, 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, but is not limited thereto.

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

[0136] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited as long as it satisfies the above-described range based on the total thickness of the separation membrane, but, for example, it may be 5 to 300 μm, specifically 5 to 100 μm, 5 to 50 μm, 5 to 20 μm, 5 to 15 μm, or 9 to 12 μm.

[0137] In one embodiment of the present invention, the porous coating layer may comprise inorganic particles and further comprise a binder resin such that the inorganic particles have all or at least a portion of their surface coated 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 in the porous coating layer may be included 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 in a structure, and has the structural characteristics of a porous layer that allows gas or liquid to pass from one side to the other.

[0138] In one embodiment of the present invention, the porous coating layer may have a porous structure derived from pores resulting from the interstitial volume between inorganic particles. The size or porosity (ratio of pore volume) of the pores can be controlled according to the particle size and size distribution. Through this structure, resistance to metallic foreign substances present on the electrode is increased, and at the same time, shrinkage of the porous polyolefin substrate is suppressed, thereby enhancing the safety of the electrochemical device.

[0139] In one embodiment of the present invention, the porous coating layer comprises a plurality of nodes including a binder polymer covering at least a portion of the surface of the inorganic particles and the inorganic particles; and one or more filaments formed in a thread shape from the binder polymer of the nodes, wherein the filaments have a node connecting portion extending from the nodes to connect other nodes, and the node connecting portion 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.

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

[0141] In one embodiment of the present invention, the inorganic particles may be used without particular limitation as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). Non-limiting examples of such inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), 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 / 3Examples 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.

[0142] In one embodiment of the present invention, when a binder resin is included in the porous coating layer, 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 a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer with a monomer capable of copolymerizing with vinylidene fluoride, and a mixture thereof. In one embodiment of the present invention, the monomer may be, for example, a fluorinated monomer and / or a chlorinated monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); and hexafluoropropylene (HFP). Perfluoro(alkylvinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethylvinyl) ether (PEVE), and perfluoro(propylvinyl) ether (PPVE); perfluoro(1,3-dioxol); and perfluoro(2,2-dimethyl-1,3-dioxol) (PDD), etc., and one or more of these may be included.

[0143] In one embodiment of the present invention, the thickness of each of the porous coating layers is not particularly limited as long as it satisfies the ratio range described above relative to the total thickness of the separator, but may be, for example, 0.5 to 50 μm, specifically 1 to 10 μm, 1.5 to 5 μm, 2 to 4 μm, or 3 to 4 μm.

[0144] 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.

[0145] A separator according to one aspect of the present invention may have an advantageous effect in improving the performance of an electrochemical device using the same by improving the electrolyte wetting properties across the entire surface of the separator through the structure described above, but the effects of the present invention are not limited thereto.

[0147] According to another aspect of the present invention, an electrode assembly using the above-described separator is provided.

[0148] Specifically, referring to FIG. 2a, the electrode assembly (2) has a structure in which the separator (1) described above is folded in a zigzag manner, and unit positive electrodes (21) and unit negative electrodes (22) are alternately arranged in a plurality of areas where the separator is folded and overlapped.

[0149] An electrode assembly according to one embodiment of the present invention comprises a unit anode, a unit cathode, and a separator interposed between the unit anode and the unit cathode, wherein a plurality of unit anodes are spaced apart on one surface of the separator and a plurality of unit cathodes are spaced apart on the other surface of the separator, and the positions where the unit anodes and the unit cathodes are arranged do not overlap with each other with respect to the long side direction of the separator, and the separator may have a structure that is the separator described above.

[0150] FIG. 4 shows a cross-sectional view in the electric direction (Y) of the electrode assembly (2) according to one embodiment of the present invention.

[0151] Referring to FIG. 4, the electrode assembly (2) has a separator (1) that is folded in a zigzag manner, and a plurality of unit positive electrodes (21) and a plurality of unit negative electrodes (22) are alternately arranged in a plurality of areas where the separator is folded and overlapped.

[0153] According to one embodiment of the present invention, the electrode assembly has a structure in which a plurality of unit electrodes are arranged on each of one side and the other side of a strip-shaped separator, so the total length when the electrode assembly is unfolded may be, for example, 1 to 4.5 m, specifically 1.2 to 4.3 m.

[0154] As described above, even if an electrode assembly according to another aspect of the present invention is provided in the form of a long strip, it can exhibit the advantage of being sufficiently wetted by the electrolyte across the entire surface of the separator due to the improved electrolyte wetting performance of the central portion caused by the unique structure of the separator. This can improve the electrolyte wetting performance of a long electrode assembly (or a thick electrode assembly) and improve the stability and productivity of the battery, but the effects of the present invention are not limited thereto.

[0155] In one embodiment of the present invention, the unit electrode may be a conventional anode and / or cathode used in an electrochemical device, and the anode and cathode may each have an electrode active material coated on a current collector, and their size or shape is not particularly limited.

[0156] In one embodiment of the present invention, when the electrode is a positive electrode, the positive electrode active material may comprise, for example, a lithium transition metal oxide; a lithium metal iron phosphate; a lithium nickel-manganese-cobalt oxide; an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these, but is not limited thereto. Specifically, the positive electrode active material may comprise, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; and a compound with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides represented as O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide, a lithium oxide in which a portion is substituted with aluminum Li a [Nib 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, and 0.8≤a≤1.2, 0.5≤b≤0.99, 0 <c<0.5, 0<d<0.5, 0.01≤e≤0.1, 0≤f≤0.1); 리튬 니켈-망간-코발트 산화물에 일부가 다른 전이금속으로 치환된 산화물 Li 1+x (Ni a Co b Mn c M d ) 1-x Examples include O2 (x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg and Mo), disulfide compounds; Fe2(MoO4)3, etc., but are not limited to these.

[0157] In one embodiment of the present invention, when the electrode is a negative electrode, the negative electrode active material may be, for example, 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, but is not limited thereto.

[0158] In one embodiment of the present invention, each of the unit anode and the unit cathode may include an electrode tab formed at one end.

[0159] According to one embodiment of the present invention, the electrode tabs formed on the unit anode and the unit cathode may be formed at the same end with respect to the electric field direction of the electrode assembly. Alternatively, the electrode tabs formed on the unit anode and the unit cathode may be formed at opposite ends with respect to the electric field direction of the electrode assembly. The present invention is not limited thereto.

[0161] According to another aspect of the present invention, an electrochemical element in which the above-described electrode assembly is housed in a case may be provided.

[0162] In one embodiment of the present invention, the case may be one that is conventionally used as a battery case, and is not particularly limited in its external shape according to the use of the battery. For example, the case may be a cylindrical, prismatic, pouch, or coin type using a can.

[0163] Once the electrode assembly described above is completed, it can be housed in a case using a conventional method, and an electrochemical device can be manufactured by injecting and sealing the electrolyte. At this time, the electrochemical device may be, for example, a lithium secondary battery.

[0165] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0166] [Manufacturing of Separator Membranes]

[0167] The separator membranes of Example 1 and Comparative Example 1 were prepared as follows.

[0168] At this time, the shape of the side of the separator of Example 1 is shown in FIG. 2, and the shape of the side of the separator of Comparative Example 1 is shown in FIG. 1.

[0170] Example 1

[0171] Manufacturing of porous substrates

[0172] Three types of polyethylene polymers and polypropylene polymers with different molecular weights and an antioxidant were mixed in appropriate proportions in an extruder and extruded through a T-die to produce an extruded sheet, and a polyolefin precursor film produced by casting was stretched in the MD and TD directions, respectively, to obtain a porous substrate. At this time, 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).

[0173] In addition, when forming an extrusion sheet through the above T-die, the screw in the central part of the T-die's discharge section was tightened more and the screws at both ends were tightened less, thereby obtaining an extrusion sheet having a shape in which the thickness in the central part of the porous substrate in the width direction is thin and the thickness increases in a curved shape toward both ends. The porosity of the porous substrate finally manufactured after stretching was 45 vol%.

[0174] The above porous substrate was manufactured by adjusting the spacing of the T-die so that the thickness decreases in a convex curved shape from both ends toward the center point, such that the total width (short side, Y direction) is 500 mm and the length (long side, X direction) is 4 m, the thickness measured at both ends of the short side is 9 μm each, and the thickness at the center point of the short side, 250 mm, is 7 μm.

[0175] Preparation of porous coating layer

[0176] An inorganic coating slurry was prepared by mixing 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.

[0177] The inorganic coating slurry prepared above was applied to both sides of the porous substrate using a coating bar having the shape shown in FIG. 5 and dried to form porous coating layers on the upper and lower surfaces of the porous substrate prepared above.

[0178] The porous coating layers formed on the upper and lower surfaces, respectively, were manufactured such that the thickness measured at both ends of the short side was 3 μm each, and the thickness in the center was 4 μm, and the thickness increased in a convex curved shape toward the porous substrate from both ends to the center (at a point of 250 mm).

[0179] Thus, a separation membrane was manufactured with a total thickness of 15 μm maintained uniformly across the entire surface.

[0181] Comparative Example 1

[0182] Manufacturing of porous substrates

[0183] A porous substrate was prepared according to the same method as in Example 1, except that it was formed with a uniform thickness of 9 μm without any change in thickness throughout the width direction (short side) direction.

[0185] Preparation of porous coating layer

[0186] A porous coating layer was formed according to the same method as in Example 1, except that it was formed with a uniform thickness of 3 μm without any change in thickness throughout the entire width direction (short side) direction.

[0187] Accordingly, a separation membrane with a total thickness of 15 μm in the width direction was manufactured.

[0188] Table 1 summarizes the thickness of each component at both ends (0%, 100%) and the center (50%) based on 100% of the total width direction length of the separator membranes of Example 1 and Comparative Example 1 prepared above.

[0189] division Example 1 Comparative Example 1 Total length in width direction (100%) Total length in width direction (100%) End (0%) Central (50%) End (100%) End (0%) Central (50%) End (100%) First porous coating layer (㎛) 3 4 3 3 3 3 porous substrate (㎛) 9 7 9 9 9 9 Second porous coating layer (㎛) 3 4 3 3 3 3 Total thickness (㎛) 15 15 15 15 15 15

[0190] [Evaluation of Membrane Properties]

[0191] In order to evaluate the electrolyte wetting performance and battery capacity according to the evaluation method below, a battery was manufactured as follows.

[0192] Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for an anode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to produce an anode having an anode active material layer (thickness 120 μm).

[0193] Graphite (a blend of natural graphite and artificial graphite), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for a negative electrode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to manufacture a negative electrode having a negative electrode active material layer (thickness 120 μm).

[0194] Nineteen positive electrodes and twenty negative electrodes manufactured as described above were prepared, and a Z-folded electrode assembly was prepared by stacking the separator manufactured as described above in a zigzag manner, with positive electrodes and negative electrodes alternately inserted between the folds.

[0195] Subsequently, the electrode assembly prepared above was placed in a pouch-type case, and an electrolyte with a composition in which 1M LiPF6 was dissolved in a 1,3-dioxolane:dimethoxyethane (DOL:DME 1:1 v / v) mixed solvent was injected, and an aging process and a degassing process were performed to manufacture a battery.

[0197] Evaluation of the wetting properties of the electrolyte

[0198] Regarding the battery manufactured above, photographs of each separator when the battery was disassembled at an SOC of 60 are shown in FIG. 6 (Comparative Example 1) and FIG. 7 (Example 1). At this time, each separator was observed visually through the difference in brightness of the area not wetted by the electrolyte.

[0200] Initial capacity evaluation

[0201] The capacity of the battery was measured after repeating charging and discharging three times in a voltage range of 2.5 V to 4.3 V with a current of 0.33 C using an electrochemical charge / discharger, and the results are shown in Table 2 below.

[0202] division Theoretical capacity Initial capacity Separator Comparative Example 1 160 Ah 150 Ah Example 1 159 Ah

[0203] Through the results of FIGS. 6, FIGS. 7 and Table 2, it was confirmed that using a separator according to one embodiment of the present invention can exhibit excellent electrolyte wettability across the entire surface of the separator and can further enhance the effect of achieving the theoretical capacity of the battery.

[0204] In particular, according to the results in Fig. 6 and Table 2, when electrolyte wetting occurs unevenly, the capacity development relative to the theoretical capacity decreases, and Comparative Example 1 shows a significantly reduced initial capacity, whereas according to the results in Fig. 7 and Table 2, when electrolyte wetting occurs uniformly, a sufficient capacity relative to the theoretical capacity is developed, and it was confirmed that Example 1 shows a significantly higher initial capacity.

[0205] Although the present invention has been described above with reference to the embodiments and drawings, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above content. Explanation of the symbols

[0207] 1: Separator 10: Porous substrate 11: First porous coating layer 12: Second porous coating layer 111: First interface 121: Second interface 2: Electrode assembly 21: Unit anode 22: Unit cathode 211: Positive tab 222: Negative tab 3: Electrode assembly 4: Coating bar

Claims

Claim 1 An electrode assembly comprising a separator that folds in a zigzag manner, a unit anode, and a unit cathode, wherein the unit anode and the unit cathode are alternately arranged in a plurality of regions where the separator is folded and overlaps, and the separator is interposed between the unit anode and the unit cathode, wherein the separator comprises a porous substrate and a porous coating layer formed on each of the two sides of the porous substrate and containing inorganic particles, wherein the separator maintains a constant overall thickness over the entire surface, the aspect ratio of the separator is 1 or greater, wherein the porous substrate and the porous coating layer each have a continuously changing thickness gradient with respect to the width direction of the separator, wherein the interface between the porous substrate and the porous coating layer each have a convex curved shape toward the porous substrate with respect to the width direction of the separator, and wherein the curved shape of the interface between the porous substrate and the porous coating layer is symmetric with respect to the center of the thickness direction of the separator. Claim 2 An electrode assembly according to claim 1, characterized in that the thickness of the porous substrate is thinnest at the center with respect to the width direction of the separator. Claim 3 An electrode assembly according to claim 1, characterized in that the thickness of the porous substrate is thickest at the outermost end with respect to the width direction of the separator. Claim 4 An electrode assembly according to claim 1, characterized in that the curved shape of the interface between the porous substrate and the porous coating layer is symmetric with respect to the center in the width direction of the separator. Claim 5 delete Claim 6 An electrode assembly according to claim 1, characterized in that the thickness of the porous substrate is 40% to 90% based on 100% of the total thickness of the separator. Claim 7 An electrode assembly according to claim 1, characterized in that the thickness of the porous substrate is 45% to 65% based on 100% of the total thickness of the separator. Claim 8 An electrode assembly according to claim 1, characterized in that at a point 50% of the total width of the separator, the thickness of the porous substrate is 40% to 55% of the total thickness of the separator. Claim 9 An electrode assembly according to claim 1, characterized in that at a point of 0% or 100% based on the total width of the separator, the thickness of the porous substrate is 50% to 70% based on the total thickness of the separator. Claim 10 An electrode assembly according to claim 1, characterized in that the longitudinal length of the separator is 1.5 to 5 m. Claim 11 delete Claim 12 An electrode assembly according to claim 1, wherein each of the unit anode and the unit cathode comprises an electrode tab formed at one end. Claim 13 An electrochemical device characterized by an electrode assembly according to claim 1 being housed in a case. Claim 14 An electrochemical device according to claim 13, characterized in that the electrochemical device is a lithium secondary battery. Claim 15 An electrochemical device according to claim 13, wherein the case is pouch-type, prismatic-type, cylindrical-type, or coated-type.

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