KR20210144145A - Electrode assembly and secondary battery including the same - Google Patents

Abstract

The present invention relates to an electrode assembly and a secondary battery including the same. An electrode assembly, according to an embodiment of the present invention, comprises: an electrode sheet including an uncoated part formed by exposing a current collector; an electrode tab including a body part positioned on the uncoated part and an externally-exposed part extending outwardly from the body part; and first and second boundary tapes positioned between the uncoated part and the body part. The body part includes: a junction part joined to the uncoated part; a first extension part extending from the junction part to one side; and a second extension part extending from the junction part to the other side. The first boundary tape is positioned between the uncoated part and the first extension part, and the second boundary tape is positioned between the uncoated part and the second extension part. The present invention is to solve the problem of damage to the current collector due to the step structure formed by the electrode tab.

Description

Electrode assembly and secondary battery including the same

The present invention relates to an electrode assembly and a secondary battery including the same, and more particularly, to an electrode assembly having improved safety and a secondary battery including the same.

Recently, an increase in the price of an energy source due to the depletion of fossil fuels, interest in environmental pollution is amplified, and the demand for an eco-friendly alternative energy source is becoming an indispensable factor for future life. Accordingly, research on various power generation technologies such as nuclear power, solar power, wind power, and tidal power is continuing, and power storage devices for using the generated energy more efficiently are also of great interest.

In particular, as technology development and demand for mobile devices increase, the demand for batteries as an energy source is rapidly increasing, and accordingly, many studies on batteries capable of meeting various needs are being conducted.

Typically, there is a high demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, which have advantages such as high energy density, discharge voltage, and output stability.

In addition, depending on the shape of the battery case, the secondary battery consists of a cylindrical battery and a prismatic battery in which the electrode assembly is embedded in a cylindrical or prismatic metal can, and a pouch-type battery in which the electrode assembly is embedded in a pouch-type case of an aluminum laminate sheet. classified.

In addition, secondary batteries are classified according to the structure of the electrode assembly having a structure in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are stacked.

Typically, a jelly roll (winding type) electrode assembly in which a long sheet-shaped anode and anode are wound in a state in which a separator is interposed, and a plurality of cathodes and anodes cut in units of a predetermined size are interposed with a separator. and a stack-type (stack-type) electrode assembly, which is sequentially stacked in one state, and the like. Recently, in order to solve the problems of the jelly roll type electrode assembly and the stack type electrode assembly, it is an electrode assembly having an advanced structure, which is a mixed type of the jelly roll type and the stack type. A stack/folding electrode assembly having a structure in which the unit cells stacked in a state of being placed on a separation film are sequentially wound has been developed.

1 is an exploded perspective view showing a state before a conventional electrode assembly is wound.

Referring to FIG. 1 , a conventional electrode assembly 10 inserted into a secondary battery includes a first electrode sheet 20 , a second electrode sheet 30 , and a first electrode sheet 20 and a second electrode sheet 30 . and a separation membrane 40 interposed therebetween. In addition, in order to prevent the first electrode sheet 20 and the second electrode sheet 30 from contacting each other when wound in the form of a jelly roll, a separator 40 is additionally disposed under the second electrode sheet 30 it is preferable

Here, the first electrode sheet 20 and the second electrode sheet 30 may correspond to a positive electrode sheet and a negative electrode sheet, respectively.

An active material layer 22 to which an active material is applied and an uncoated region 23 to which an active material is not applied may be formed on the first electrode sheet 20 . Specifically, the active material layer 22 may be formed by applying an active material to the current collector of a thin metal plate, and the uncoated region 23 may be formed by exposing a portion of the current collector without applying the active material. The first electrode tab 21 may be joined to the uncoated region 23 by welding or the like.

Similarly, the active material layer 32 to which the active material is applied and the uncoated area 33 to which the active material is not applied may be formed on the second electrode sheet 30 . Specifically, the active material layer 32 may be formed by applying an active material to the current collector of a thin metal plate, and the uncoated portion 33 may be formed by exposing a portion of the current collector without applying the active material. The second electrode tab 31 may be joined to the uncoated region 33 by welding or the like.

FIG. 2 is a plan view of a portion “A” of FIG. 1 viewed on the xy plane.

Referring to FIG. 2 , as the first electrode tab 21 is bonded to the uncoated region 23 , a stepped structure is formed on both sides of the first electrode tab 21 in the width direction (y-axis direction). Due to the step structure, cracks may occur in the current collector of the uncoated region 23 in the jelly roll structure formed by winding the first electrode sheet 20 , the second electrode sheet 30 , and the separator 40 .

In particular, in order to develop a high-capacity secondary battery, development is in progress in the direction of increasing the silicon content in the negative electrode or decreasing the thickness of the current collector of the positive electrode. At this time, due to the high silicon content, the volume expansion of the negative electrode during charging and discharging is severe, and stress may be concentrated on both sides of the positive electrode tab attached to the positive electrode uncoated region in the width direction. As a result, cracks in the current collector due to both sides of the positive electrode tab may be further aggravated. The crack generation may lead to cutting of the current collector, which may cause damage to the electrode assembly.

Accordingly, there is a need for a technology capable of solving the problem of damage to the current collector due to the step structure of the electrode tab.

An object of the present invention is to provide an electrode assembly capable of solving a problem of damage to a current collector due to a step structure formed by an electrode tab, and a secondary battery including the same.

However, the problems to be solved by the embodiments of the present invention are not limited to the above problems and may be variously expanded within the scope of the technical idea included in the present invention.

An electrode assembly according to an embodiment of the present invention includes: an electrode sheet including an uncoated region formed by exposing a current collector; an electrode tab including a body positioned on the uncoated part and an external exposed part extending outwardly from the body part; and first and second boundary tapes positioned between the uncoated portion and the body portion. The body portion includes a bonding portion bonding to the uncoated portion, a first extension portion extending from the bonding portion to one side, and a second extension portion extending from the bonding portion to the other side. The first boundary tape is positioned between the uncoated region and the first extension, and the second boundary tape is positioned between the uncoated region and the second extension.

The first boundary tape may be positioned between the uncoated portion and one side of the first extension, and the second boundary tape may be positioned between the uncoated portion and one side of the second extension.

A length between one side of the first extension and one side of the second extension may be longer than a length between both sides of the external exposed portion.

The electrode sheet may include a first active material layer and a second active material layer formed by coating an active material on the current collector, and the uncoated portion may be positioned between the first active material layer and the second active material layer.

The first boundary tape may extend to cover a boundary between the uncoated region and the first active material layer.

The second boundary tape may extend to cover a boundary between the uncoated region and the second active material layer.

The first boundary tape and the second boundary tape may include at least one of polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP).

The electrode assembly may further include a first protective tape covering the main body.

The first protective tape may include at least one of polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP).

The electrode tab may be positioned on one surface of the electrode sheet, and the electrode assembly may further include a second protective tape attached to the other surface of the electrode sheet opposite to the one surface of the electrode sheet.

When viewed from a direction perpendicular to the other surface of the electrode sheet, the second protective tape may be positioned to cover an area in which the body part is formed.

The electrode sheet may be formed in plurality, and the electrode assembly may further include a separator interposed between the electrode sheets, and the electrode sheets and the separator may be wound to form a jelly roll structure.

According to embodiments of the present invention, damage to the current collector may be prevented through the boundary tape positioned under both sides of the electrode tab.

In addition, by forming the extension portion on the electrode tab, it is easy to secure a region for bonding the electrode tab to the current collector, thereby improving manufacturing processability.

Effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

1 is an exploded perspective view showing a state before a conventional electrode assembly is wound.
FIG. 2 is a plan view of a portion “A” of FIG. 1 viewed on the xy plane.
3 is an exploded perspective view illustrating an electrode assembly according to an embodiment of the present invention before being wound.
4 is a plan view of the portion “B” of FIG. 3 viewed on the xy plane.
FIG. 5 is a cross-sectional view taken along line C-C' of FIG. 4 .
6 is a plan view illustrating first and second boundary tapes according to a modified embodiment of the present invention.
7 is a cross-sectional view taken along the cutting line D-D' of FIG. 6 .
8 is a plan view illustrating a first protective tape according to another embodiment of the present invention.
9 is a plan view illustrating a second protective tape according to another embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, various embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly explain the present invention, parts irrelevant to the description are omitted, and the same reference numerals are given to the same or similar elements throughout the specification.

In addition, since the size and thickness of each component shown in the drawings are arbitrarily indicated for convenience of description, the present invention is not necessarily limited to the illustrated bar. In order to clearly express various layers and regions in the drawings, the thicknesses are enlarged. And in the drawings, for convenience of description, the thickness of some layers and regions are exaggerated.

Also, when a part of a layer, film, region, plate, etc. is said to be “on” or “on” another part, it includes not only cases where it is “directly on” another part, but also cases where another part is in between. . Conversely, when we say that a part is "just above" another part, we mean that there is no other part in the middle. In addition, to be "on" or "on" the reference part means to be located above or below the reference part, and it means to be located "on" or "on" the direction opposite to gravity. no.

In addition, throughout the specification, when a part "includes" a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated.

In addition, throughout the specification, when referring to "planar", it means when the target part is viewed from above, and "in cross-section" means when viewed from the side when a cross-section of the target part is vertically cut.

3 is an exploded perspective view showing an electrode assembly according to an embodiment of the present invention before being wound, FIG. 4 is a plan view of a portion “B” of FIG. 3 viewed on an xy plane, and FIG. 5 is a cut line of FIG. It is a cross-sectional view taken along C-C'.

3 to 5 , the electrode assembly 100 according to an embodiment of the present invention may include electrode sheets 200 and 300 and a separator 400 interposed between the electrode sheets 200 and 300 . have. When wound in the form of a jelly roll, it is preferable that the separator 400 is additionally disposed under the electrode sheet 300 .

The electrode sheets 200 and 300 may include a first electrode sheet 200 and a second electrode sheet 300 , and the first electrode sheet 200 and the second electrode sheet 300 are a positive electrode sheet and a negative electrode sheet. It may correspond to one of each. Hereinafter, description will be made based on the first electrode sheet 200 .

The electrode assembly 100 according to the present embodiment includes an electrode sheet 200 including an uncoated area 230 formed by exposing a current collector and an electrode tab 210 bonded to the uncoated area 230 . The electrode tab 210 includes a body part 211 positioned on the uncoated part 230 and an external exposed part 212 extending outwardly from the body part 211 . In addition, the electrode assembly 100 according to the present embodiment includes first and second boundary tapes 510 and 520 positioned between the uncoated region 230 and the main body 211 .

Specifically, the main body 211 includes a bonding portion 211c bonded to the uncoated portion 230 , a first extension portion 211a extending from the bonding portion 211c to one side, and a second extension portion extending from the bonding portion 211c to the other side. It includes two extensions 211b. The one side and the other side may correspond to the y-axis direction and the -y-axis direction in FIG. 4 . That is, the first extension 211a and the second extension 211b may extend in a direction perpendicular to the extension direction (x-axis direction) of the external exposed portion 212 with respect to the junction portion 211c.

The active material layers 221 and 222 may be formed by applying an active material to the current collector of the thin metal plate, and the uncoated region 230 may be formed by exposing a portion of the current collector without applying the active material. The electrode tab 210 , in particular the bonding portion 211c of the main body 211 , may be bonded to the uncoated region 230 by welding or the like.

In this case, the first boundary tape 510 is positioned between the uncoated region 230 and the first extension 211a, and the second boundary tape 520 is positioned between the uncoated region 230 and the second extension 211b. located in More specifically, the first boundary tape 510 may be positioned between the uncoated region 230 and one side of the first extension 211a, and the second boundary tape 520 may be disposed between the uncoated region 230 and the second boundary tape 520 . It may be located between one side of the two extension parts 211b. One side of the first extension part 211a may correspond to a side in the y-axis direction among the sides constituting the body part 211 , and one side of the second extension part 211b is a side constituting the body part 211 . It may correspond to a side in the -y-axis direction.

In the case of the conventional electrode assembly 10 shown in FIGS. 1 and 2 , as described above, cracks may occur in the current collector of the uncoated area 23 due to the step structure formed by the first electrode tab 21 . have. In particular, when the direction in which the first electrode sheet 20 is wound is considered, a stepped structure formed by both sides of the first electrode tab 21 in the width direction (y-axis direction) may be a major cause of crack formation.

Accordingly, according to the present embodiment, the first and second boundary tapes are respectively between the uncoated region 230 and one side of the first extension 211a and between the uncoated region 230 and one side of the second extension 211b. By positioning the 510 and 520 , stress that may be applied by the stepped structure of both sides of the electrode tab 210 may be relieved. Accordingly, it is possible to prevent cracks from occurring in the current collector of the uncoated region 230 .

Each of the first boundary tape 510 and the second boundary tape 520 may include at least one of polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP). have.

On the other hand, as a comparative example of the present invention, the electrode tab may be configured in a straight shape without an extended region, and boundary tapes may be formed under sides of a junction part bonded to the uncoated part among the straight electrode tabs. In general, electrode tabs are generally formed to have a thin width. For example, the width of the electrode tab may be 4 mm to 5 mm. It is inevitably difficult in the manufacturing process to configure the tape under the sides of the junction without providing a separate extension part for the electrode tab having such a thin width, and the tape cannot be accurately positioned under the sides of the junction to prevent cracks. It may not have much effect. In addition, it is difficult to sufficiently secure a welding area for the joint portion to be joined to the uncoated portion.

On the contrary, the electrode tab 210 according to the present embodiment includes the first extension portion 211a and the second extension portion 211b extending to one side and the other side opposite to each other of the bonding portion 211c. was trying to solve the problem. That is, a length between one side of the first extension part 211a and one side of the second extension part 211b may be longer than a length between both sides of the external exposed part 212 . For example, a length between one side of the first extension part 211a and one side of the second extension part 211b may be 1.2 to 1.5 times the length between both sides of the external exposed part 212 . Accordingly, the first boundary tape 510 and the second boundary tape 520 may be accurately positioned under both sides of the main body 211 forming the stepped structure. That is, manufacturing processability is improved and a crack prevention effect can be easily implemented. In addition, since it is not necessary to reduce the area of the joint portion 211c, a sufficient welding area can be secured.

Hereinafter, the first and second boundary tapes 510a and 520a according to a modified embodiment of the present invention will be described with reference to FIGS. 6 and 7 .

6 is a plan view for explaining the first and second boundary tapes according to a modified embodiment of the present invention, and FIG. 7 is a cross-sectional view taken along the cutting line D-D' of FIG. 6 . Specifically, FIG. 6 shows a view of the electrode tab 210 on the xy plane as in FIG. 4 .

6 and 7 , the electrode sheet according to the present embodiment may include a first active material layer 221 and a second active material layer 222 formed by coating an active material on a current collector, and an uncoated region ( 230 may be positioned between the first active material layer 221 and the second active material layer 222 . That is, the uncoated region 230 may be formed to be spaced apart from both ends of the electrode sheet.

At this time, the first boundary tape 510a according to the modified embodiment of the present invention may extend to cover the boundary between the uncoated region 230 and the first active material layer 221 , and The second boundary tape 520a according to an embodiment may extend to cover the boundary between the uncoated region 230 and the second active material layer 222 .

In forming the active material layers 221 and 222 by coating the active material on the current collector, the boundary between the uncoated area 230 and the first active material layer 221 and the uncoated area 230 and the second active material layer 222 The boundary between them may correspond to the beginning or the end of the active material application. The application of the active material may be non-uniform at the beginning or the end of the application of the active material, and the electrochemical reaction may be unstable in the portion where the application of the active material is non-uniform. Accordingly, the first and second boundary tapes 510a and 520a according to the present embodiment cover the beginning or the end of the application of the active material, thereby making it an unreacted zone. Accordingly, the electrochemical reaction through the active material layers 221 and 222 may be more stably maintained.

In order to form the unreacted region as described above, the first boundary tape 510a covers all the boundaries between the uncoated region 230 and the first active material layer 221 , and the second boundary tape 520a is formed on the uncoated region ( It is preferable to cover both the boundary between the 230 and the second active material layer 222 . That is, it is preferable that the first and second boundary tapes 510a and 520a have a length corresponding to the length of the electrode sheet in the height direction (x-axis direction). In FIG. 6 , the vertical length of the first and second boundary tapes 510a and 520a is shown to be slightly shorter than the length of the electrode sheet in the height direction (x-axis direction) for convenience of explanation, but as described above, the first and second boundary tapes 510a and 520a are shown in FIG. Preferably, the second boundary tapes 510a and 520a are formed to cover all of the boundaries.

6 and 7 show that the uncoated region 230 is located between the first active material layer 221 and the second active material layer 222, that is, spaced apart from both ends of the electrode sheet, but according to the present embodiment The position of the uncoated region is not limited thereto and may be formed to contact one end of the electrode sheet 200 . Accordingly, the active material layer may be formed on only one side of the uncoated region. In this case, the boundary tape according to the modified embodiment covering the active material layer may be formed only on one side of the electrode tab.

Hereinafter, the first protective tape 610 according to another embodiment of the present invention will be described with reference to FIG. 8 .

8 is a plan view illustrating a first protective tape according to another embodiment of the present invention. Specifically, FIG. 8 shows a view of the electrode tab 210 on the xy plane as in FIG. 4 .

Referring to FIG. 8 , the electrode assembly according to the present embodiment may further include a first protective tape 610 covering the body portion 211 of the electrode tab 210 . The first protective tape 610 is preferably formed to cover the entire body portion 211 .

As described above, in the electrode assembly according to the present embodiment, the electrode sheets 200 and 300 and the separator 400 may be wound to form a jelly roll structure. In the jelly roll structure, the step structure formed by the sides of the body part 211 of the electrode tab 210 damages not only the current collector of the uncoated part 230 to which the body part 211 is attached, but also other electrode sheets or separators. can be added Accordingly, by providing the first protective tape 610 covering the main body 211 , it was attempted to minimize damage due to the step structure formed by the sides of the main body 211 . The first protective tape 610 may include at least one of polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP).

Meanwhile, when the first protective tape 610 is attached to the main body 211 , the first and second boundary tapes 510a and 520a covering the active material layers 221 and 222 are shown in FIGS. 3 to 5 as well as FIGS. Of course, the first and second boundary tapes 510 and 520 may be applied.

Hereinafter, the second protective tape 620 according to another embodiment of the present invention will be described with reference to FIG. 9 .

9 is a plan view illustrating a second protective tape according to another embodiment of the present invention. Specifically, unlike FIG. 4 , FIG. 9 shows the other surface of the electrode sheet 200 , which is opposite to one surface to which the electrode tab 210 is attached, as viewed from the xy plane.

Referring to FIG. 9 , an electrode tab 210 is positioned on one surface of the electrode sheet 200 , and a second protective tape 620 is disposed on the other surface of the electrode sheet 200 opposite to the one surface of the electrode sheet 200 . can be attached. In particular, when viewed from a direction perpendicular to the other surface of the electrode sheet 200 , the second protective tape 620 is preferably positioned to cover the region where the body portion 211 is formed. As described above, in the electrode assembly according to the present embodiment, the electrode sheets 200 and 300 and the separator 400 may be wound to form a jelly roll structure, and the body portion ( 211 ) and the corresponding second protective tape 620 may be attached to minimize stress or damage applied to the other electrode sheet 300 or the separator 400 . The second protective tape 620 may include at least one of polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP).

On the other hand, in order to bond the electrode tab 210 through welding, not only the one surface of the electrode sheet 200 to which the electrode tab 210 is attached, but also the other surface of the electrode sheet 200, without applying an active material as shown. It is preferable to expose the current collector to form the uncoated region 230 .

At this time, as shown, the second protective tape 620 covers the boundary between the uncoated region 230 and the first active material layer 221 and the boundary between the uncoated region 230 and the second active material layer 222 . may be extended to The second protective tape 620 covers the beginning or end of the active material application, that is, the non-uniformly applied portion of the active material, thereby making it an unreacted area to more stably maintain the electrochemical reaction through the active material layers 221 and 222 . can Although the vertical length of the second protective tape 620 is shown to be somewhat shorter than the length of the electrode sheet in the height direction (x-axis direction) in FIG. 9 , this is for convenience of explanation, and the second protective tape 620 is It is preferably formed so as to cover all of the boundaries.

Meanwhile, referring again to FIG. 3 , the active material layer 320 and the uncoated area 330 may be formed on the second electrode sheet 300 , and the electrode tab 310 may be bonded to the uncoated area 330 . , first and second boundary tapes 510 and 520 may be positioned between the uncoated region 330 and the electrode tab 310 . That is, the same or similar structure to the first electrode sheet 200 and the electrode tab 210 bonded thereto may be applied to the second electrode sheet 300 and the electrode tab 310 bonded thereto. Since the detailed description overlaps with the description based on the first electrode sheet 200 , it will be omitted.

Meanwhile, as described above, in the electrode assembly according to the present embodiment, the electrode sheets 200 and 300 and the separator 400 may be wound to form a jelly roll structure. Damage to the current collector may be severe. Accordingly, when the first and second boundary tapes or the first and second protective tapes according to the present embodiments are applied to the electrode assembly having a jelly roll structure, the effect of preventing damage to the current collector may be more clearly realized.

Although not specifically illustrated, the electrode assembly according to the present embodiments may be accommodated in a battery case together with an electrolyte to form a secondary battery, and the battery case may be a cylindrical or prismatic case.

Such a secondary battery may be applied to various devices. Specifically, it may be applied to transportation means such as an electric bicycle, an electric vehicle, a hybrid, etc., but is not limited thereto and may be applied to various devices that can use a secondary battery.

In this embodiment, terms indicating directions such as front, back, left, right, up, and down are used, but these terms are for convenience of explanation only, and may vary depending on the position of the object or the position of the observer. .

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

100: electrode assembly
200: electrode sheet
211a: first extension
211b: second extension
211c: junction
510: first boundary tape
520: second boundary tape

Claims (13)

an electrode sheet including an uncoated region formed by exposing a current collector;
an electrode tab including a body positioned on the uncoated part and an external exposed part extending outwardly from the body part; and
and first and second boundary tapes positioned between the uncoated portion and the body portion,
The body part includes a junction part joined to the uncoated part, a first extension part extending to one side from the junction part, and a second extension part extending from the junction part to the other side,
the first boundary tape is positioned between the uncoated part and the first extension part;
The second boundary tape is positioned between the uncoated portion and the second extended portion. In claim 1,
The first boundary tape is positioned between the uncoated part and one side of the first extension part,
The second boundary tape is positioned between the uncoated portion and one side of the second extension portion. In claim 1,
A length between one side of the first extension part and one side of the second extension part is longer than a length between both sides of the external exposure part. In claim 1,
The electrode sheet includes a first active material layer and a second active material layer formed by coating an active material on the current collector,
The uncoated portion is an electrode assembly positioned between the first active material layer and the second active material layer. In claim 4,
The first boundary tape extends to cover a boundary between the uncoated region and the first active material layer. In claim 4,
The second boundary tape extends to cover a boundary between the uncoated region and the second active material layer. In claim 1,
The first boundary tape and the second boundary tape may include at least one of polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP). In claim 1,
The electrode assembly further comprising a first protective tape covering the body portion. In claim 8,
The first protective tape may include at least one of polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP). In claim 1,
The electrode tab is positioned on one surface of the electrode sheet,
The electrode assembly further comprising a second protective tape attached to the other surface of the electrode sheet opposite to the one surface of the electrode sheet. In claim 10,
When viewed from a direction perpendicular to the other surface of the electrode sheet, the second protective tape is positioned to cover an area in which the body part is formed. In claim 1,
The electrode sheet is formed in plurality,
Further comprising a separator interposed between the electrode sheets,
An electrode assembly in which the electrode sheets and the separator are wound to form a jelly roll structure. A secondary battery comprising the electrode assembly according to claim 1 .

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