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

Abstract

An embodiment of the present invention provides a single-sided electrode for a secondary battery, a method for manufacturing same, an electrode assembly comprising same, and a secondary battery, wherein the single-sided electrode comprises a current collector and an active material layer formed on one surface of the current collector. The active material layer comprises a flat portion having a constant thickness of the active material layer and an inclined portion having a reduced thickness of the active material layer compared to the flat portion. A tape is attached to the other surface of the current collector of the single-sided electrode so as to correspond to the inclined portion.

Description

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

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0119928, filed September 8, 2023, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a cross-sectional electrode for a secondary battery, a method for manufacturing the same, and an electrode assembly and a secondary battery including the same.

[0004] As technological developments and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. In particular, secondary batteries are attracting significant attention as an energy source not only for mobile devices such as cell phones, digital cameras, laptops, and wearable devices, but also for powertrains such as electric bicycles, electric cars, and hybrid electric vehicles.

[0005] Secondary batteries are classified into cylindrical batteries in which the electrode assembly is built into a cylindrical metal can, square batteries in which the electrode assembly is built into a square metal can, and pouch-type batteries in which the electrode assembly is built into a pouch-type case made of aluminum laminate sheet, depending on the shape of the battery case.

[0006] Meanwhile, the electrode assembly built into the battery case is a rechargeable power plant having a stacked structure of a positive electrode, a separator, and a negative electrode, and is classified into a jelly-roll type, a stack type, and a stack / folding type. The jelly-roll type is a form in which a separator is interposed between long sheet-shaped positive and negative electrodes coated with active materials and wound, the stack type is a form in which a plurality of positive and negative electrodes of a predetermined size are sequentially stacked with a separator interposed between them, and the stack-and-folding type is a form in which unit cells are arranged on a separator film and wound as a composite structure of the jelly-roll type and the stack type.

[0007] An electrode assembly including a laminate excluding a double jelly-roll type includes a laminated form of unit electrodes including tabs.

[0008] At this time, the positive and negative electrodes used are manufactured by mixing materials such as active materials, conductive materials, and binders with a solvent to prepare a slurry, applying the slurry to a current collecting sheet, drying and rolling it, and then slitting it into unit electrodes. In this case, since the slurry is a viscous liquid substance, the slurry flows on the current collecting sheet at the boundary between the coated area and the uncoated area, and a sliding phenomenon occurs in which the thickness of the flowing portion becomes thinner.

[0009] This sliding phenomenon occurs between the uncoated area, i.e., the bare area, formed to secure the tab area, and the maintenance area of ​​the coated area, and is therefore generally located at the top of the electrode assembly.

[0010] However, due to the sliding phenomenon, the adhesive strength between the electrode and the separator at the upper portion of the thin electrode assembly is weakened or not adhered at all, increasing the distance between the anode, separator, and cathode, thereby increasing resistance and promoting side reactions, resulting in local swelling. Consequently, these problems ultimately lead to a decline in battery performance.

[0011] Accordingly, recently, to solve the above problem, a roller tilt method has been developed in which the rolling roller is twisted to roll the entire surface, a sub-roller method in which the top is pressed once more using an additional roller, and a JF taping method in which tape is attached to the slit in the jig formation stage so that the top of the cell receives pressure similar to that of the center of the cell.

[0012] However, the roller tilt method has a problem that although the upper adhesion can be improved, the lower adhesion is weakened or there is an increased possibility of non-adhesion, the sub-roller method has a problem that fine adjustment is difficult and there is no guide for optimal conditions, so there is a problem of side effects due to over-pressing, and the JF taping method has a problem that a pressure difference may occur when a tolerance occurs in the cell position within the jig formation device, which may cause a performance deviation between cells.

[0013] Therefore, there is a need to develop a secondary battery technology that resolves the problem of sliding of the upper part of the electrode assembly without causing additional problems.

[0014] The purpose of the present invention is to provide an electrode, an electrode assembly, and a secondary battery that can improve swelling and life characteristics by reducing the gap between components by compensating for the thickness of the sloped portion where the thickness of the active material layer formed by sliding during the electrode manufacturing process becomes thinner, thereby preventing an increase in resistance or side reaction due to this.

[0015] In addition, a manufacturing method is provided that enables the thickness compensation to be covered throughout the entire sliding area to achieve the above effect.

[0016] The problems to be solved by the present invention are not limited to the problems described above, and problems not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention pertains from this specification and the attached drawings.

[0017] As a cross-sectional electrode for a secondary battery according to one embodiment of the present invention,

[0018] The above cross-sectional electrode includes a current collector and an active material layer formed on one surface of the current collector,

[0019] The above active material layer includes a flat portion where the thickness of the active material layer is constant and a sloped portion where the thickness of the active material layer decreases compared to the flat portion,

[0020] It is characterized in that a tape is attached to a portion corresponding to the inclined portion on the other side of the current collector of the above-mentioned cross-sectional electrode.

[0021] Here, a tab is formed on the entire body, and the tab can be positioned in the direction in which the inclined portion is formed.

[0022] At this time, the tape formed on the other side of the cross-sectional electrode can be formed to have a length equal to the width of the cross-sectional electrode in a direction perpendicular to the direction in which the tab of the cross-sectional electrode protrudes.

[0023] The above tape may be casted polypropylene (CPP).

[0024] Additionally, the forming thickness of the tape may be 30% to 100% of the thickness of the flat portion.

[0025] Moreover, according to another embodiment of the present invention, as a method for manufacturing a cross-sectional electrode,

[0026] A method for manufacturing a single-sided electrode is provided, which includes applying, drying, and rolling an electrode slurry containing an active material to one surface of a current collecting sheet to form an active material layer including a flat portion having a constant thickness and an inclined portion having a reduced thickness compared to the flat portion, and attaching a tape to the other surface of the current collecting sheet corresponding to the inclined portion before a slitting process for cutting the active material layer into unit electrodes.

[0027] The inclined portion formed by applying the electrode slurry may be formed on the non-coated side of the current collecting sheet where the electrode slurry is not applied and where the tab will be formed later.

[0028] Meanwhile, the tab is formed by a notching process, and the notching process can be performed simultaneously with the slitting process or after the slitting process.

[0029] Furthermore, according to another embodiment of the present invention, an electrode assembly for a secondary battery is provided, which includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the electrode assembly has a cross-sectional electrode positioned on one or both outermost sides of the electrode assembly.

[0030] Here, the cross-sectional electrode may be a cross-sectional positive electrode.

[0031] At this time, the active material layer of the cross-sectional electrode may be formed in a direction facing the negative electrode located on the inside of the electrode assembly.

[0032] The electrode assembly may be in a form including a stacking of unit electrodes, for example, a stack-and-fold type electrode assembly having a structure in which unit cells including electrodes and separators are wound in one direction by a separator film, a lamination-and-stack type electrode assembly having a structure in which the unit cells and separators are stacked and laminated, or a zigzag stack type electrode assembly in which the unit cells or unit electrodes are folded in a zigzag shape by the separator film.

[0033] In addition, according to another embodiment of the present invention, a secondary battery including such an electrode assembly and an electrolyte is provided.

[0034] Figure 1 is a cross-sectional view of a cross-sectional electrode according to one embodiment of the present invention.

[0035] Figure 2 is a plan view of the other surface of the current collector of a cross-sectional electrode according to one embodiment of the present invention.

[0036] Figure 3 is a schematic diagram showing some steps of a method for manufacturing a cross-sectional electrode according to another embodiment of the present invention.

[0037] Figure 4 is a cross-sectional view of an electrode assembly according to another embodiment of the present invention.

[0038] Figure 5 is a schematic diagram showing various types of electrode assemblies according to another embodiment of the present invention.

[0039] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0040] In order to clearly explain the present invention, parts that are not related to the description are omitted, and the same reference numerals are used for identical or similar components throughout the specification.

[0041] Furthermore, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to the illustrated components. In the drawings, the thicknesses are enlarged to clearly represent various layers and regions. Furthermore, in the drawings, the thicknesses of some layers and regions are exaggerated for convenience of explanation.

[0042] Additionally, throughout the specification, whenever a part is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0043] Additionally, throughout the specification, when we say "in plan", we mean when the target portion is viewed from above, and when we say "in cross section", we mean when the target portion is viewed from the side in a cross-section cut vertically.

[0044] The terms "about," "substantially," and the like used throughout this specification are used in a sense of or near to the numerical values ​​when manufacturing and material tolerances inherent in the meanings referred to are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that mention exact or absolute values ​​to aid understanding of this specification.

[0045] The terms “width,” “length,” and “width” used in this specification are based on the definitions in the specification.

[0046]

[0047] FIG. 1 illustrates a cross-sectional view of a cross-sectional electrode according to one embodiment of the present invention, and FIG. 2 illustrates a plan view of the other side of the current collector of the cross-sectional electrode.

[0048] Referring to FIGS. 1 and 2, a cross-sectional electrode (100) according to one embodiment of the present invention includes a current collector (111), an active material layer (120) formed on one surface of the current collector (111), and the active material layer (120) has a structure including a flat portion (121) in which the thickness of the active material layer (120) is constant and an inclined portion (122) in which the thickness of the active material layer (120) decreases compared to the flat portion (121). In addition, a tab (112) is formed on the current collector (111), and the tab (112) is positioned in the direction in which the inclined portion (122) is formed.

[0049] Not only the single-sided electrode (100), but also the double-sided electrodes that are subsequently laminated together with the single-sided electrode (100) are formed by coating the active material slurry, so that they have a flat portion and an inclined portion in the direction of the non-coated portion where the tab is to be formed, and since the electrode assembly is manufactured in a direction in which the inclined portions are laminated and wound so that they are positioned on the same line, a gap cannot but occur between the components of the electrode assembly at the portions where the inclined portions are positioned.

[0050] However, the occurrence of such a gap can significantly threaten the safety of the secondary battery by reducing the adhesion between the electrode and the separator and forming a space between the electrodes, which not only actively causes the subsequent formation of lithium dendrites and side reactions with the electrolyte, but also causes local swelling due to gas generation resulting from the acceleration of the side reaction.

[0051] Accordingly, active research is being conducted on methods to solve these problems, and the present invention solves these problems by attaching tape to the cross-sectional electrode present at the outermost surface.

[0052] Referring again to FIGS. 1 and 2, a cross-sectional electrode (100) according to one embodiment of the present invention has a structure in which a tape (130) is attached to a portion corresponding to an inclined portion (122) on the other surface of a current collector (111) on which an active material layer (120) is not formed.

[0053] By attaching such tape (130), the thickness difference occurring at the inclined portion (122) can be reduced, and accordingly, the pressure deviation can be reduced to ensure the safety of the secondary battery and improve its performance.

[0054] At this time, in order to effectively cover the inclined portion (122), the tape (130) may be formed with a length (l) corresponding to the inclined portion (122), and may be formed with a length equal to the width (w) of the cross-sectional electrode (100) in a direction perpendicular to the direction in which the tab (112) of the cross-sectional electrode (100) protrudes.

[0055] In addition, the thickness (T1) of the tape (130) must have a thickness that can offset the thickness difference between the flat portion (121) and the inclined portion (122). At this time, it may vary depending on the number of electrodes laminated, and is not limited thereto, but specifically, it may be 30% to 100% of the thickness (T0) of the flat portion, specifically, it may be 50% to 100%, and more specifically, it may be 70% to 90%.

[0056] If the thickness of the tape (130) is too thin, outside the above range, it is not desirable because it cannot sufficiently cover the thickness difference due to the stacking of electrodes in the electrode assembly, and if it is too thick, it may cause an increase in the volume of the electrode assembly, which is not desirable.

[0057] The type of such tape is not limited to a material that does not cause a side effect in the operation of the secondary battery, and an insulating tape used in a conventionally known battery may be used, and in detail, it may be cast polypropylene (CPP).

[0058] Meanwhile, FIG. 3 schematically illustrates some steps in manufacturing such a cross-sectional electrode (100). Specifically, it illustrates a step of attaching a tape, with (a) illustrating the surface where the active material layer is formed and (b) illustrating the surface where the tape is attached.

[0059] Referring to FIGS. 1 and 2 together with FIG. 3, in order to manufacture a cross-sectional electrode (100), an electrode slurry containing an active material is first applied to one surface of a current collecting sheet (210), dried, and rolled to form an active material layer (220) including a flat portion (221) having a constant thickness and an inclined portion (222) having a reduced thickness compared to the flat portion (221).

[0060] Afterwards, a slitting (240) process is performed to cut the current collecting sheet (210) into unit electrodes. Before this slitting (240) process, a tape (230) is attached to the other side of the current collecting sheet (210), that is, the side where the active material layer (220) is not formed, so that the tape (230) covers the area corresponding to the inclined portion (222).

[0061] At this time, the inclined portion (222) is formed at the interface between the non-coated portion where the electrode slurry is not applied and the holding portion where the electrode slurry is applied, so it is formed on the non-coated portion side where the tab (112) is to be formed in the active material layer (220), and therefore, the tape (230) is attached adjacent to the tab (112).

[0062] And, after the attachment of the tape (230) is completed, a process of slitting (240) the current collecting sheet (210) on which the active material layer (220) is formed on one side into unit electrodes is performed, and also, a notching process for forming a tab (112) is also performed simultaneously with the slitting (240) process or after the slitting (240) process, thereby manufacturing a single-sided electrode (100).

[0063] In this way, according to the present invention, since the tape (230) is attached before the slitting (240) process into the unit electrode, as described above, the width (w) of the unit electrode (100) and the length of the tape (230) are made to match, so that, compared to the case where the tape is attached after the manufacturing of the unit electrode or after the manufacturing of the electrode assembly, there is no process dispersion in the attachment position or size of the tape (130), so that an electrode assembly of similar quality can be manufactured.

[0064] In addition, it is more preferable because it can cover the entire area of ​​the inclined portion (122) of the cross-sectional electrode (100), and an uncovered portion that may occur at the end of the width of the cross-sectional electrode (100) is not formed.

[0065] Meanwhile, according to another embodiment of the present invention, an electrode assembly for a secondary battery is provided, including the unit electrode, a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0066] Fig. 4 illustrates such an electrode assembly, and specifically, Fig. 4 illustrates a cross-sectional view of an electrode assembly (300) according to another embodiment of the present invention.

[0067] Referring to Fig. 4, an electrode assembly (300) according to another embodiment of the present invention has a structure in which single-sided electrodes are formed on both sides of the outermost surface, and double-sided electrodes are formed between them. At this time, the single-sided electrode located at the outermost surface may be a single-sided positive electrode (310), and the double-sided electrodes on the inner side may be stacked so that the facing electrodes have different polarities.

[0068] For convenience of explanation, only cathodes (320) facing the cross-sectional anodes (310) are illustrated in FIG. 4, and the illustration and description of other electrodes located between them are omitted.

[0069] If the cross-sectional electrode located at the outermost side is a cathode, an unnecessary cathode active material layer is added for capacity expression, which may reduce the energy density per volume, which is not desirable. Therefore, the cross-sectional electrode may be a cross-sectional positive electrode (310).

[0070] In addition, even if the electrode located at the outermost side is a double-sided positive electrode including active material layers on both sides of the current collector, there is no negative electrode to accept Li ions desorbed from the outermost active material layer facing the battery case, so corrosion of the battery case and lithium plating problems may occur. Therefore, it is preferable that a single-sided positive electrode (310) be located at the outermost side. Accordingly, at this time, the active material layer (312) of the single-sided positive electrode (310) can be laminated so as to be formed in a direction facing the negative electrode (320) located on the inside of the electrode assembly (300).

[0071] Moreover, as described above, the active material layer (312) of the cross-sectional positive electrode (310) has a flat portion (312a) having a constant thickness of the active material layer (312) and an inclined portion (312b) having a thickness that decreases from the flat portion (312a), as described above. Therefore, a gap is generated in which the distance between the components of the electrode assembly (300) widens in the direction of forming the tab (313) in which the inclined portion (312b) is formed.

[0072] The occurrence of such a gap can cause many problems within a secondary battery, and according to one embodiment of the present invention, each of the cross-sectional positive electrodes (310) located at the outermost side has tapes (314) attached to a portion corresponding to the inclined portion (312b) on the other side of the current collector (311) where the active material layer (312) is not formed.

[0073] Additional configurations such as the specific attachment location and size of the tape are as described in the above drawings 1 and 2.

[0074] In this way, since the electrode assembly (300) according to the present invention has tapes (314) attached to the other surface of the current collector (311) of the outermost cross-section positive electrodes (310) to correspond to the inclined portions (312b), the tapes (314) play a role in offsetting the thickness difference between the flat portions (312a) and the inclined portions (312b), so that uniform pressure can be applied to the flat portions (312a) and the inclined portions (312b), problems such as reduced adhesive strength between the electrode and the separator, increased side reactions, and swelling, which were previously problematic, can be solved.

[0075] Meanwhile, the electrode assembly to which such a configuration can be applied is not limited and is possible as long as it has a structure including a unit electrode, and in order to explain such examples, a schematic diagram showing the types of various electrode assemblies (410, 420, 430) to which the cross-sectional electrode of the present invention can be applied is illustrated in FIG. 5. At this time, the electrode assembly of FIG. 5 is shown as a cross-sectional view in a direction perpendicular to the direction in which the tab is formed, not in the direction in which it is formed, and therefore the portion where the tape is formed is not illustrated.

[0076] Referring to FIG. 5, (a) shows a stack and folding type electrode assembly (410), (b) shows a lamination and stack type electrode assembly (420), and (c) shows a zigzag stack type electrode assembly (430).

[0077] Specifically, the stack-and-fold type electrode assembly (410) has a structure in which unit cells (411) including electrodes and separators are wound in one direction by a separator film (412).

[0078] Here, the unit cells (411) may be a monocell including one electrode and a separator, a full cell having a structure in which electrodes of different polarities are positioned at the outermost surface, for example, an anode / separator / cathode structure, or a bicell having a structure in which electrodes of the same polarity are positioned at the outermost surface, for example, an anode / separator / cathode / separator / anode structure, or a cathode / separator / anode / separator / cathode structure, or a combination thereof.

[0079] Similarly, the laminated and stacked electrode assembly (420) may have a laminated structure in which the unit cells (421) are laminated with a separator (422).

[0080] Here, the stacking of unit cells (421) and separators (422) is a concept that includes a structure including a separator (422) on the outer surface of the unit cells (421), and the unit cells (421) are the same as the description of the unit cells (411).

[0081] Lastly, the zigzag stack type electrode assembly (430) may have a structure in which unit cells or unit electrodes (431) are folded in a zigzag shape by a separation film (432).

[0082] At this time, the unit cells (431) are as described above.

[0083] Meanwhile, the composition, structure, etc. of the positive electrode, negative electrode, and separator constituting other electrode assemblies are known in the art, and thus a detailed description thereof is omitted in this specification.

[0084] Furthermore, according to another embodiment of the present invention, a secondary battery including the electrode assembly and an electrolyte is provided.

[0085] As these secondary batteries are known in the art, detailed descriptions other than the above configuration are omitted in this specification.

[0086] Although the preferred embodiments of the present invention have been described in detail above with reference to the drawings, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0087] [Explanation of symbols]

[0088] 100: cross-sectional electrode

[0089] 120, 220, 312: active material layer,

[0090] 130, 230, 314: Tape,

[0091] 210: Current collection sheet,

[0092] 240: Slitting,

[0093] 250: Notching,

[0094] 300 410, 420, 430: Electrode assembly,

[0095] 310: cross-sectional positive electrode,

[0096] 320: Cathode,

[0097] 330: Membrane,

[0098] 411, 421, 431: Unit electrode or unit cell

[0099] 412, 422, 432: Separator or Separator Film

[0100] 1200, 2200: Separation film,

[0101] 1300: Double-sided tapes,

[0102] 1310: 1st double-sided tape,

[0103] 1320: Second double-sided tape

[0104] According to the present invention, the cross-sectional electrode of the present invention and the electrode assembly including the same can reduce the gap between components by compensating for the thickness of the sloped portion where the thickness of the active material layer is thinned due to sliding that occurs during the manufacturing process of the electrode, thereby preventing an increase in resistance or a side reaction resulting therefrom, thereby improving swelling and enhancing life characteristics.

[0105] In addition, by attaching a tape to the other side of the outermost cross-section electrode of the electrode assembly, i.e., the other side where the active material layer is not formed, the thickness is supplemented, so that the reaction area of ​​the active material layer is not reduced, and thus there is no capacity reduction, which is advantageous in securing high capacity.

[0106] Moreover, according to the method for manufacturing a cross-sectional electrode of the present invention, the above effect can be achieved with a very simple taping method, and the slitting process is performed after the tape is attached entirely before the slitting process into unit electrodes, so that the tape can cover the entire width direction of the cross-sectional electrode to match the shape of the cross-sectional electrode to which it is applied, and thus, compared to attaching the tape after lamination, process dispersion in the attachment position, size, etc. of the tape does not occur, making it more effective.

Claims

1. As a cross-sectional electrode for secondary batteries, The above cross-sectional electrode includes a current collector and an active material layer formed on one surface of the current collector, The above active material layer includes a flat portion where the thickness of the active material layer is constant and a sloped portion where the thickness of the active material layer decreases compared to the flat portion, A cross-sectional electrode having a tape attached to a portion corresponding to the inclined portion on the other surface of the current collector of the cross-sectional electrode.

2. In paragraph 1, A cross-sectional electrode having a tab formed on the above-mentioned collector, wherein the tab is positioned in the direction in which the inclined portion is formed.

3. In paragraph 1, The above tape is a cross-sectional electrode formed with a length equal to the width of the cross-sectional electrode in a direction perpendicular to the direction in which the tab of the cross-sectional electrode protrudes.

4. In paragraph 1, The above tape is a single-sided electrode made of casted polypropylene (CPP).

5. In paragraph 1, A cross-sectional electrode having a thickness of the tape of 30% to 100% of the thickness of the flat portion.

6. A method for manufacturing a cross-sectional electrode according to paragraph 1, A method for manufacturing a single-sided electrode, comprising: applying, drying, and rolling an electrode slurry containing an active material to one surface of a current collecting sheet to form an active material layer including a flat portion having a constant thickness and an inclined portion having a reduced thickness compared to the flat portion; and attaching a tape to the other surface of the current collecting sheet corresponding to the inclined portion before a slitting process for cutting the active material layer into unit electrodes.

7. In paragraph 6, A method for manufacturing a cross-sectional electrode, wherein the inclined portion formed by applying the electrode slurry is formed on the non-coated side of the current collecting sheet on which the electrode slurry is not applied and on which a tab is to be formed later.

8. In paragraph 7, A method for manufacturing a cross-sectional electrode, wherein the tab is formed by a notching process, and the notching process is performed simultaneously with the slitting process or after the slitting process.

9. An electrode assembly for a secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein a cross-sectional electrode according to claim 1 is positioned on one or both outermost sides of the electrode assembly.

10. In paragraph 9, The above cross-sectional electrode is an electrode assembly that is a cross-sectional positive electrode.

11. In paragraph 10, An electrode assembly in which the active material layer of the above cross-sectional positive electrode is formed in a direction facing the negative electrode located on the inside of the electrode assembly.

12. In paragraph 9, The electrode assembly is a stack-and-fold type electrode assembly having a structure in which unit cells including electrodes and separators are wound in one direction by a separation film, a lamination-and-stack type electrode assembly having a structure in which the unit cells and separators are laminated by stacking, or a zigzag stack type electrode assembly in which the unit cells or unit electrodes are folded in a zigzag shape by the separation film.

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

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