Single-sided electrode for secondary battery, method for manufacturing same, and electrode assembly and secondary battery comprising same

Abstract

Embodiments of the present invention provide a single-sided electrode of a secondary battery, a method for manufacturing the same, an electrode assembly including the same, and a secondary battery, in which the single-sided electrode includes a current collector and an active material layer formed on one surface of the current collector, the active material layer including a flat portion and an inclined portion, the flat portion has an active material layer having a constant thickness, and the inclined portion has a reduced thickness compared to the flat portion. The ribbon is attached to the other surface of the current collector of the single-sided electrode so as to correspond to the inclined portion.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2023-0119928, filed on September 8, 2023, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This disclosure relates to a single-sided electrode for a secondary battery and a method for manufacturing the same, as well as an electrode assembly and a secondary battery including the single-sided electrode. Background Technology

[0004] With the development of mobile device technology, the demand for mobile devices is increasing, and the demand for secondary batteries as an energy source is rapidly increasing. In particular, secondary batteries have attracted considerable attention as an energy source for electrically powered devices (such as electric bicycles, electric vehicles, and hybrid electric vehicles) and for mobile devices (such as mobile phones, digital cameras, laptops, and wearable devices).

[0005] Based on the shape of the battery casing, secondary batteries can be classified as: cylindrical batteries, in which the electrode assembly is constructed into a cylindrical metal container; prismatic batteries, in which the electrode assembly is constructed into a prismatic metal container; or pouch batteries, in which the electrode assembly is constructed into a pouch-shaped casing made of aluminum laminate.

[0006] Additionally, the electrode assembly installed within the battery casing is a power generation element with a stacked structure capable of charging / discharging and including a positive electrode, a negative electrode, and a separator. Electrode assemblies can be classified as wound-core type, stacked type, and stacked / folded type. A wound-core type electrode assembly is configured with a structure in which long sheet-shaped positive and negative electrodes coated with active material are wound together with a separator inserted between the positive and negative electrodes. A stacked type electrode assembly is configured with a structure in which a large number of positive and negative electrodes of predetermined size are sequentially stacked with a separator inserted between the positive and negative electrodes. A stacked / folded type electrode assembly is a combination of wound-core and stacked electrode assemblies, in which a unit cell is arranged on the separator and wound up.

[0007] Among these components, in addition to the core type, the electrode assembly including the stacked components includes a stacked form of unit electrodes containing connectors.

[0008] The positive and negative electrodes used here are manufactured by mixing materials such as active materials, conductive materials, and binders with a solvent to prepare a slurry, then coating the slurry onto a current collector sheet, drying, rolling, and then slitting it into unit electrodes. In this case, because the slurry is a viscous liquid, a sliding phenomenon occurs where the slurry flows on the current collector sheet at the boundary between the coated and uncoated areas, and the thickness becomes thinner in the flow area.

[0009] Since this sliding phenomenon occurs between the uncoated area (i.e., the flat portion forming the fixed joint area) and the coated portion of the coated area, it is usually located at the upper end of the electrode assembly.

[0010] However, due to slippage, the upper part of the thin electrode assembly exhibits weakened or non-adhesion between the electrode and the separator, thus increasing the distance between the positive electrode, separator, and negative electrode. This increases resistance and promotes side reactions, leading to localized expansion. Ultimately, this problem results in reduced battery performance.

[0011] Therefore, in recent years, various methods have been developed to solve the above problems, such as the roller tilting method, which twists the rolling roller to roll the entire cell; the secondary roller method, which presses the upper end again by an additional roller; and the JF strip method, which applies a strip to the liner during the fixture forming stage so that the upper end of the cell receives the same pressure as the center of the cell.

[0012] However, while the roller tilting method can improve the adhesion at the upper end, it has the problem of weakened adhesion or increased possibility of non-adhesion at the lower end. The secondary roller method is difficult to fine-tune, lacks guidance on optimal conditions, and leads to side reaction problems due to excessive pressing. The JF strip method has the problem of pressure difference when there is a tolerance in the cell position within the fixture forming device, which may lead to performance deviations between cells.

[0013] Therefore, there is a need to develop a secondary battery technology that solves the problem related to slippage at the upper end of the electrode assembly without causing additional problems. Summary of the Invention

[0014] Technical issues

[0015] The purpose of this disclosure is to provide an electrode, an electrode assembly, and a secondary battery that compensate for the thickness of tilted portions where the active material layer is thinned due to slippage that occurs during the electrode manufacturing process, and reduces the gaps between components. This prevents an increase in resistance and side reactions, and improves expansion and lifespan characteristics.

[0016] Another object of this disclosure is to provide a preparation method that enables the thickness compensation element to be covered throughout the sliding area to achieve the desired effect.

[0017] The technical objectives to be addressed by the embodiments of this disclosure are not limited to those disclosed above, and those skilled in the art can clearly understand other objectives not mentioned herein based on the following detailed description and accompanying drawings.

[0018] Technical solution

[0019] According to embodiments of this disclosure, a single-sided electrode for a secondary battery is provided, wherein:

[0020] The single-sided electrode includes a current collector and an active material layer formed on one surface of the current collector.

[0021] The active material layer includes a flat portion and an inclined portion. In the flat portion, the thickness of the active material layer is constant, and in the inclined portion, the thickness of the active material layer decreases compared to the flat portion.

[0022] The strip is attached to the portion of the current collector on the other surface of the single-sided electrode that corresponds to the inclined portion.

[0023] The current collector is provided with a connector, and the connector may be located in the direction in which the inclined portion is formed.

[0024] In this case, the strip formed on the other surface of the single-sided electrode can be formed to have a length equal to the width of the single-sided electrode, the width being perpendicular to the direction in which the connector of the single-sided electrode protrudes.

[0025] The strip may be cast polypropylene (CPP).

[0026] Furthermore, the thickness of the strip can be 30% to 100% of the thickness of the flat portion.

[0027] Furthermore, according to another embodiment of this disclosure, a method for manufacturing a single-sided electrode according to claim 1 is provided.

[0028] Wherein: an electrode paste containing active material is coated onto one surface of a current collector sheet, dried and rolled to form an active material layer having a flat portion and an inclined portion, the flat portion having a constant thickness, the inclined portion having a reduced thickness compared to the flat portion, and a strip corresponding to the inclined portion is attached to the other surface of the current collector sheet before the slitting process of cutting the sheet into unit electrodes.

[0029] The inclined portion formed by coating the electrode paste can be formed on the uncoated side of the current collector sheet that is not coated with the electrode paste and subsequently forms the connector.

[0030] In addition, the joint is formed by a grooving process, which can be performed simultaneously with the slitting process or after the slitting process.

[0031] Furthermore, according to another embodiment of this disclosure, an electrode assembly for a secondary battery is provided, the electrode assembly comprising: a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode, wherein the single-sided electrode is located at one or both of the outermost parts of the electrode assembly.

[0032] The single-sided electrode can be a single-sided positive electrode.

[0033] In this case, the active material layer of the single-sided positive electrode can be formed in the direction facing the negative electrode located inside the electrode assembly.

[0034] The electrode assembly may be in the form of a stack of unit electrodes, for example, a stacked and folded electrode assembly, a laminated and stacked electrode assembly, or a Z-shaped stacked electrode assembly. The stacked and folded electrode assembly has a structure in which a unit cell including an electrode and a separator is wound in one direction through a separation membrane. The laminated and stacked electrode assembly has a structure in which the unit cell and the separator are stacked and laminated. In the Z-shaped stacked electrode assembly, the unit cell or unit electrode is folded in a Z-shape through the separation membrane.

[0035] Furthermore, according to yet another embodiment of this disclosure, a secondary battery including an electrode assembly is provided. Attached Figure Description

[0036] Figure 1 This is a cross-sectional view of a single-sided electrode according to an embodiment of the present disclosure.

[0037] Figure 2 This is a plan view of the other surface of the current collector of a single-sided electrode according to an embodiment of the present disclosure.

[0038] Figure 3 This is a schematic diagram illustrating some steps of a method for manufacturing a single-sided electrode according to yet another embodiment of the present disclosure.

[0039] Figure 4 This is a cross-sectional view of an electrode assembly according to yet another embodiment of the present disclosure.

[0040] Figure 5 This is a schematic diagram illustrating various types of electrode assemblies according to yet another embodiment of the present disclosure. Detailed Implementation

[0041] In the following description, various embodiments of the present disclosure will be detailed to the extent that those skilled in the art can readily practice it. The present disclosure may be implemented in many different forms and is not limited to the embodiments described herein.

[0042] For clarity of description, descriptions of components not related to this disclosure will be omitted, and identical or similar components will be indicated by the same reference numerals throughout the specification.

[0043] Because the dimensions and thicknesses of each component are arbitrarily shown in the accompanying drawings for ease of description, this disclosure is not necessarily limited to what is shown in the drawings. The drawings depict thicknesses at an enlarged scale to clearly show different layers and regions. Furthermore, the drawings exaggerate the thickness of a particular layer or region for ease of description.

[0044] When layers, films, regions, plates, etc., are disposed "on" a specific portion, this description includes not only cases where layers, films, regions, plates, etc., are disposed on the specific portion, but also cases where layers, films, regions, plates, etc., are disposed on the specific portion via another portion. When one portion is "directly disposed" on another portion, this indicates that there is no new portion between the two portions. Furthermore, when a component is disposed "on" a reference portion, this indicates that the component is present at the top or bottom of the reference portion, and does not necessarily indicate that the component is disposed only at the top of the reference portion opposite to the direction of gravity.

[0045] Throughout this description, when a section “includes” a component, it does not indicate that the section does not include other components, but rather that the section may further include other components, unless otherwise stated.

[0046] Throughout this text, the term "in a plan view" refers to an object viewed from above, and the term "in a cross-sectional view" refers to a vertical cross-section of an object viewed from the side.

[0047] Throughout this description, the terms “approximately” or “substantially” are intended to mean close to a numerical value or range specified with permissible error, and are intended to prevent the unlawful or unfair use by any unrestrained third party of the precise or absolute numerical values ​​disclosed for the purpose of understanding this invention.

[0048] Throughout this description, the term "ribbon" refers to an object that is narrow in width and long in length.

[0049] Figure 1 A cross-sectional view of a single-sided electrode according to an embodiment of the present disclosure is illustrated, and Figure 2 A plan view of the other surface of the current collector of a single-sided electrode according to an embodiment of the present disclosure is shown.

[0050] Reference Figure 1 and Figure 2 According to an embodiment of the present disclosure, a single-sided electrode 100 includes a current collector 111 and an active material layer 120 formed on one surface of the current collector 111. The active material layer 120 includes a flat portion 121 and an inclined portion 122, wherein the thickness of the active material layer 120 is constant in the flat portion 121, and the thickness of the active material layer 120 is reduced compared to the flat portion 121 in the inclined portion 122. Furthermore, the current collector 111 is formed with a connector 112, and the connector 112 is located in the direction in which the inclined portion 122 is formed.

[0051] Not only the single-sided electrode 100, but also the double-sided electrode subsequently stacked with the single-sided electrode 100 is formed by coating with an active material slurry. As described above, the electrode assembly has a flat portion and an inclined portion in the direction of the uncoated portion forming the joint, and is manufactured in the direction of stacking and winding such that the inclined portions are on the same line. Therefore, in the portion where the inclined portions are located, gaps inevitably arise between the components of the electrode assembly.

[0052] However, the formation of this gap reduces the adhesion between the electrode and the separator and creates space between the electrodes. As a result, not only do lithium dendrites form and side reactions with the electrolyte occur actively, but local expansion also occurs due to gas generation caused by the acceleration of the side reactions. This can significantly threaten the safety of the secondary battery.

[0053] Therefore, methods to solve this problem have been actively studied, and this disclosure solves the problem by attaching a strip to the single-sided electrode located on the outermost side.

[0054] Refer again Figure 1 and Figure 2 According to an embodiment of the present disclosure, the single-sided electrode 100 has a structure in which a strip 130 is attached to a portion of the other surface of the current collector 111 that corresponds to the inclined portion 122.

[0055] By attaching this strip 130, the thickness difference occurring at the inclined portion 122 can be reduced, and thus the pressure deviation can be reduced, thereby ensuring the safety of the secondary battery and improving its performance.

[0056] At this time, in order to effectively cover the inclined portion 122, the strip 130 can be formed to have a width l corresponding to the inclined portion 122, and can be formed to have a length equal to the width w of the single-sided electrode 100, the width w of which is perpendicular to the direction in which the connector 112 of the single-sided electrode 100 protrudes.

[0057] Furthermore, the thickness T1 of the strip 130 must have a certain thickness to compensate for the thickness difference between the flat portion 121 and the inclined portion 122. In this case, the thickness T1 of the strip 130 can vary depending on the number of stacked electrodes, but is not limited thereto; specifically, it can be 30% to 100% of the thickness T0 of the flat portion, more specifically, 50% to 100%, and even more specifically, 70% to 90%.

[0058] If the thickness of the strip 130 is too thin (outside the range mentioned above), the thickness difference cannot be adequately covered because the electrodes are stacked in the electrode assembly, which is not preferred. If the thickness is too thick, it may lead to an increase in the volume of the electrode assembly, which is also not preferred.

[0059] This type of strip is not limited to materials that do not cause side reactions during the operation of secondary batteries, and insulating strips used in conventionally known batteries can be used, and specifically, cast polypropylene (CPP) can be used.

[0060] in addition, Figure 3 A schematic diagram of several steps for manufacturing this single-sided electrode 100 is shown. Specifically, Figure 3 The process of attaching a strip is shown, wherein (a) shows the surface on which the active material layer is formed, and (b) shows the surface on which the strip is attached.

[0061] Refer to together Figure 1 , Figure 2 and Figure 3 In order to manufacture the single-sided electrode 100, firstly, an electrode paste containing active material is coated onto one surface of the current collector sheet 210, dried and wound to form an active material layer 220, which includes a flat portion 221 of constant thickness and an inclined portion 222 of reduced thickness compared to the flat portion 221.

[0062] Subsequently, a slitting 240 process is performed to cut the current collector sheet 210 into unit electrodes. Prior to this slitting 240 process, a strip 230 is attached to another surface of the current collector sheet 210, i.e., the surface where the active material layer 220 is not formed (refer to (b)), such that the strip 230 covers the portion corresponding to the inclined portion 222.

[0063] At this time, the inclined portion 222 appears at the interface between the uncoated portion of the uncoated electrode paste and the coated portion of the coated electrode paste, and is thus formed on the uncoated portion side of the connector 112 formed in the active material layer 220, and the strip 230 is attached to the vicinity of the connector 112.

[0064] Then, after the attachment of the strip 230 is completed, the current collector sheet 210 with an active material layer 220 formed on one surface is slit 240 into unit electrodes, and the grooving process for forming the connector 112 is also performed simultaneously with or after the slit 240 process, thereby manufacturing the single-sided electrode 100.

[0065] In this manner, according to this disclosure, since the strip 230 is attached to the unit electrode before the slitting 240 process, the width w of the single-sided electrode 100 and the length of the strip 230 are matched as described above. Therefore, compared to the case where the strip is attached after the manufacturing of the single-sided electrode or after the manufacturing of the electrode assembly, there is no process dispersion in the attachment position or size of the strip 130, making it possible to produce electrode assemblies of similar quality.

[0066] Furthermore, it is even more preferable that the entire area of ​​the inclined portion 122 of the single-sided electrode 100 can be covered and that the uncovered portion generated at the end of the width of the single-sided electrode 100 is not formed.

[0067] In another embodiment of this disclosure, an electrode assembly for a secondary battery is provided, the electrode assembly comprising: a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode.

[0068] Figure 4 This electrode assembly is shown, and specifically, Figure 4 A cross-sectional view of an electrode assembly 300 according to yet another embodiment of the present disclosure is shown.

[0069] Reference Figure 4 According to another embodiment of the present disclosure, the electrode assembly 300 has a structure in which a single-sided electrode is formed on both sides of the outermost portion and a double-sided electrode is formed between them. In this case, the single-sided electrode located on the outermost portion can be a single-sided positive electrode 310, and the inner double-sided electrodes can be stacked such that the opposing electrodes have different polarities.

[0070] For ease of explanation, Figure 4 Only the negative electrode 320 facing the single-sided positive electrode 310 is shown, and the illustrations and descriptions of the other electrodes located between them are omitted.

[0071] Furthermore, even if the outermost electrode is a double-sided negative electrode comprising active material layers on both surfaces of the current collector, no negative electrode receives Li ions released from the outermost active material layer facing the battery casing, which may lead to battery casing corrosion and lithium plating problems. Therefore, it is preferable that the single-sided positive electrode 310 is located on the outermost side. Thus, the active material layer 312 of the single-sided positive electrode 310 can be stacked to form in the direction facing the negative electrode 320 located inside the electrode assembly 300.

[0072] Furthermore, as described above, the active material layer 312 of the single-sided positive electrode 310 has a flat portion 312a and an inclined portion 312b. In the flat portion 312a, the thickness of the active material layer 312 is constant, and in the inclined portion 312b, the thickness decreases from that in the flat portion 312a, so that the spacing between the components of the electrode assembly 300 widens in the direction of forming the connector 313, and the inclined portion 312b is formed in this direction.

[0073] The occurrence of such gaps can lead to many problems in secondary batteries. Therefore, according to an embodiment of this disclosure, each of the outermost single-sided positive electrodes 310 has a strip 314 attached to a portion of the other surface of the current collector 311 that corresponds to the inclined portion 312b.

[0074] Other configurations for specific attachment locations and sizes of the strip, such as Figure 1 and Figure 2 As described in [the text].

[0075] Therefore, the electrode assembly 300 according to this disclosure has another surface of the current collector 311 attached to the outermost single-sided positive electrode 310 to correspond to the strip 314 of the inclined portion 312b, such that the strip 314 serves to offset the thickness difference between the flat portion 312a and the inclined portion 312b. Thus, uniform pressure can be applied to the flat portion 312a and the inclined portion 312b, thereby solving problems such as reduced adhesion strength between the electrode and the diaphragm, increased side reactions, and expansion, which are problematic under normal circumstances.

[0076] Furthermore, there are no restrictions on the electrode assemblies that can be used with this configuration, as long as they have a structure that includes unit electrodes. To explain these examples, in Figure 5 A schematic diagram is illustrated, showing various types of electrode assemblies 410, 420, and 430 to which the single-sided electrode of this disclosure can be applied. At this time, Figure 5 The electrode assembly is shown as a cross-sectional view in a direction perpendicular to the direction of forming the connector, rather than in the direction of forming the strip, so the part forming the strip is not shown.

[0077] Reference Figure 5 (a) shows a stacked and folded electrode assembly 410, (b) shows a laminated and stacked electrode assembly 420, and (c) shows a zigzag stacked electrode assembly 430.

[0078] Specifically, the stacked and folded electrode assembly 410 has a structure in which a unit cell 411, including electrodes and a separator, is wound in one direction by a separation membrane 412.

[0079] Here, the cell 411 can be a single cell including electrodes and a separator, a full cell with electrodes of different polarities located on the outermost side (e.g., a positive / separator / negative electrode structure), or a dual cell with electrodes of the same polarity located on the outermost side (e.g., a positive / separator / negative / separator / positive electrode structure, or a negative / separator / positive / separator / negative electrode structure, or a combination thereof).

[0080] Similarly, the laminated and stacked electrode assembly 420 may have a structure in which unit cells 421 and separators 422 are stacked and laminated.

[0081] Here, the stacking of cell 421 and separator 422 is a concept that includes a structure in which separator 422 is included at the outer corner of cell 421, and cell 421 is the same as that described for cell 411.

[0082] Finally, the Z-shaped stacked electrode assembly 430 may have a structure in which the unit cell or unit electrode 431 is folded in a Z-shape through the separation membrane 432.

[0083] At this time, the cell 431 is as described above.

[0084] Furthermore, the composition and structure of the positive electrode, negative electrode, and diaphragm constituting other electrode components are known in the art, and therefore their detailed description is omitted here.

[0085] Furthermore, according to another embodiment of this disclosure, a secondary battery including an electrode assembly and an electrolyte is provided.

[0086] Such secondary batteries are also known in the art, therefore, a detailed description of their exclusion of the above configuration is omitted here.

[0087] While preferred embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the scope of the present disclosure is not limited to the embodiments, but also includes various modifications and improvements made by those skilled in the art using the concepts defined in the appended claims.

[0088] [Explanation of reference numerals in the attached figures]

[0089] 100: Single-sided electrode

[0090] 120, 220, 312: Active material layer

[0091] 130, 230, 314: Strip-shaped objects

[0092] 210: Current collector sheet

[0093] 240: Slicing

[0094] 250: Grooving

[0095] 300, 410, 420, 430: Electrode assemblies

[0096] 310: Single-sided positive electrode

[0097] 320: Negative electrode

[0098] 330: Diaphragm,

[0099] 411, 421, 431: Unit electrode or unit cell

[0100] 412, 422, 432: Diaphragm or separation membrane

[0101] 1200, 2200: Separation membrane

[0102] 1300: Double-sided tape

[0103] 1310: First Double-Sided Adhesive Tape

[0104] 1320: Second double-sided tape

[0105] Industrial applicability

[0106] According to embodiments, the single-sided electrode and the electrode assembly including the single-sided electrode of this disclosure compensate for the thickness of the tilted portion of the active material layer that becomes thinner due to slippage during the electrode manufacturing process, and reduce the gap between components. This prevents an increase in resistance or side reactions, and improves expansion and enhances lifespan characteristics.

[0107] Furthermore, since the thickness is compensated by attaching the strip to the other surface of the outermost single-sided electrode of the electrode assembly (i.e., the other surface where the active material layer is not formed), the reaction area of ​​the active material layer is not reduced, and therefore the capacity is not reduced, which helps to ensure high capacity.

[0108] Furthermore, according to the manufacturing method of the single-sided electrode disclosed herein, the above-mentioned effects can be achieved using a very simple strip method. The strip is attached as a whole before the process of slitting it into unit electrodes, and then the slitting process is performed. Therefore, the strip can cover the width direction of the single-sided electrode as a whole by matching the shape of the applied single-sided electrode. Thus, compared to attaching the strip after lamination, process dispersion in the attachment position, size, etc., of the strip does not occur, which is more efficient.

Claims

1. A single-sided electrode for a secondary battery, wherein, The single-sided electrode includes a current collector and an active material layer formed on one surface of the current collector. The active material layer includes a flat portion and an inclined portion. In the flat portion, the thickness of the active material layer is constant, and in the inclined portion, the thickness of the active material layer decreases compared to the flat portion. The strip is attached to the portion of the other surface of the current collector of the single-sided electrode that corresponds to the inclined portion.

2. The single-sided electrode according to claim 1, in, The current collector is formed with a connector, and the connector is located in the direction in which the inclined portion is formed.

3. The single-sided electrode according to claim 1, in, The strip is formed to have a length equal to the width of the single-sided electrode, the width being perpendicular to the direction in which the connector of the single-sided electrode protrudes.

4. The single-sided electrode according to claim 1, in, The strip is cast polypropylene (CPP).

5. The single-sided electrode according to claim 1, in, The thickness of the strip is 30% to 100% of the thickness of the flat portion.

6. A method for manufacturing a single-sided electrode, wherein the single-sided electrode is the single-sided electrode according to claim 1, wherein, An electrode paste containing active material is coated onto one surface of a current collector sheet, dried, and rolled to form an active material layer having a flat portion and a sloping portion. The flat portion has a constant thickness, and the sloping portion has a reduced thickness compared to the flat portion. Before a slitting process that cuts the sheet into unit electrodes, a strip is attached to another surface of the current collector sheet corresponding to the sloping portion.

7. The method for manufacturing a single-sided electrode according to claim 6: in, The inclined portion formed by coating the electrode paste is formed on the uncoated portion side of the current collector sheet where the electrode paste is not coated and subsequently a connector is formed.

8. The method for manufacturing a single-sided electrode according to claim 7, in, The joint is formed by a grooving process, and the grooving process is performed simultaneously with the slitting process or after the slitting process.

9. An electrode assembly for a secondary battery, the electrode assembly comprising: A positive electrode, a negative electrode, and a diaphragm inserted between the positive electrode and the negative electrode, wherein the single-sided electrode according to claim 1 is located at one or both of the outermost parts of the electrode assembly.

10. The electrode assembly according to claim 9, in, The single-sided electrode is a single-sided positive electrode.

11. The electrode assembly according to claim 10, in, The active material layer of the single-sided positive electrode is formed in a direction facing the negative electrode located inside the electrode assembly.

12. The electrode assembly according to claim 9, in, The electrode assembly is a stacked and folded electrode assembly, a laminated and stacked electrode assembly, or a Z-shaped stacked electrode assembly. The stacked and folded electrode assembly has a structure in which a unit cell, including an electrode and a separator, is wound in one direction through a separation membrane. The laminated and stacked electrode assembly has a structure in which the unit cell and the separator are stacked and laminated. In the Z-shaped stacked electrode assembly, the unit cell or unit electrode is folded in a Z-shape through the separation membrane.

13. A secondary battery comprising the electrode assembly according to claim 9 and an electrolyte.

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