KR102279224B1 - Electrode assembly for rechargeable battery and rechargeable battery including the same - Google Patents

Abstract

An electrode assembly for a secondary battery according to an embodiment of the present disclosure includes a first electrode including a first coating part and a first uncoated part positioned on at least one side of the first coating part, a second coating part, and the second coating part a second electrode including a second uncoated region positioned on at least one side, a separator interposed between the first electrode and the second electrode, and a first stress relief portion positioned in at least a partial region of the first uncoated region; and at least one of a second stress relieving unit positioned in at least a partial region of the second uncoated region, wherein the first stress relieving unit and the second stress relieving unit include an ethylene propylene copolymer, a hydrogenated hydrocarbon polymer, and polyethylene It may consist of a film.

Description

Electrode assembly for a secondary battery and a secondary battery including the same {ELECTRODE ASSEMBLY FOR RECHARGEABLE BATTERY AND RECHARGEABLE BATTERY INCLUDING THE SAME}

The present disclosure relates to an electrode assembly for a secondary battery and a secondary battery including the same.

The secondary battery is configured to include, for example, a case in which an electrode assembly composed of a positive electrode and a negative electrode and a separator interposed between the positive electrode and the negative electrode is accommodated. In addition, electrode tabs electrically connected to the positive and negative electrodes are drawn out of the case.

Recently, attention has been focused on the development and commercialization of flexible electronic devices such as flexible displays, wearable mobile phones, and watches. Accordingly, there is an increasing demand for implementing flexible characteristics even for a secondary battery, which is a power supply device for such a flexible electronic device.

In particular, research to realize a flexible secondary battery having a flexible characteristic and having excellent durability even in repeated bending is active.

SUMMARY Embodiments of the present disclosure provide an electrode assembly for a secondary battery having excellent flexibility and durability, and a secondary battery including the same.

In one aspect, the present disclosure provides a first electrode including a first coating part and a first uncoated part positioned on at least one side of the first coating part, a second coating part, and at least one side of the second coating part. a second electrode including a second uncoated region, a separator interposed between the first electrode and the second electrode, and at least a first stress relief portion and at least a second uncoated region positioned in at least a partial region of the first uncoated region At least one of the second stress relieving unit positioned in a partial region, wherein the first stress relieving unit and the second stress relieving unit are composed of a film including an ethylene propylene copolymer, a hydrogenated hydrocarbon polymer, and polyethylene; an electrode for a secondary battery assembly is provided.

In another aspect, the present disclosure provides a secondary battery including the above-described electrode assembly for a secondary battery and a casing for accommodating the electrode assembly for the secondary battery.

The electrode assembly for a secondary battery according to embodiments of the present disclosure and a secondary battery including the same may have excellent flexibility and remarkably improve durability even during repeated bending.

1 is an exploded perspective view of an electrode assembly for a secondary battery according to a first embodiment of the present disclosure;
FIG. 2 is a horizontal cross-sectional view illustrating an xy plane of the electrode assembly for a secondary battery according to FIG. 1 .
FIG. 3 shows a modified example of the electrode assembly in which positions of the first electrode tab and the second electrode tab are changed in FIG. 2 .
4 shows a modified example of the electrode assembly in which the shapes of the first electrode tab and the second electrode tab are changed in FIG. 1 .
5 is an exploded perspective view of an electrode assembly for a secondary battery according to a second exemplary embodiment of the present disclosure.
6 is a horizontal cross-sectional view illustrating an xy plane of the electrode assembly for a secondary battery according to FIG. 5 .
7 is a perspective view of a secondary battery according to a first embodiment of the present disclosure.
8 is an exploded perspective view of the secondary battery of FIG. 7 .
9 is an exploded perspective view of a secondary battery according to a second embodiment of the present disclosure;

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 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.

1 is an exploded perspective view of an electrode assembly for a secondary battery according to a first embodiment of the present disclosure, and FIG. 2 is a horizontal cross-sectional view illustrating an xy plane of the electrode assembly for a secondary battery according to FIG. 1 .

1 and 2 , the electrode assembly 10 for a secondary battery according to the first embodiment of the present disclosure includes a first electrode 11 , a second electrode 12 , and a first electrode 11 and a second electrode assembly 10 . A separator 13 interposed between the electrodes 12 is included.

In the electrode assembly 10, for example, the first electrode 11 and the second electrode 12 formed in a rectangular sheet shape are sequentially stacked with a separator 13 interposed therebetween to form a stacked type. .

1 and 2 show only one first electrode 11 and one second electrode 12, respectively, for convenience, but a plurality of them are stacked with a separator 13 therebetween to constitute the electrode assembly 10 is of course

In addition, in the present disclosure, the polarities of the first electrode 11 and the second electrode 12 are not particularly limited. That is, the first electrode 11 may be an anode, the second electrode 12 may be a cathode, the first electrode 11 may be a cathode, and the second electrode 12 may be an anode. Hereinafter, for convenience, a case in which the first electrode 11 is an anode and the second electrode 12 is a cathode will be described as an example.

First, the separator 13 separates the first electrode 11 and the second electrode 12 and provides a passage for lithium ions to move, and any one commonly used in secondary batteries may be used. That is, one having a low resistance to ion movement of the electrolyte and excellent in the electrolyte moisture content may be used.

The separator 13 is selected from, for example, glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. In addition, in order to secure heat resistance or mechanical strength, a separator coated using a composition containing a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

Next, the first electrode 11 includes a positive electrode current collector made of a thin metal plate having electrical conductivity and a first coating part 1 in which a positive electrode active material is coated on at least one surface of the positive electrode current collector. In this case, the positive electrode active material is not entirely coated on at least one surface of the positive electrode current collector.

That is, the first uncoated portion 2 is positioned on at least one side of the first coating portion 1 . The first uncoated region 2 is integrally formed with a region where the positive electrode active material is not coated on at least one surface of the positive electrode current collector, that is, the region where the positive electrode current collector is exposed and the region where the positive electrode current collector is exposed. All regions serving as electrode tabs 51 are included. Accordingly, the first electrode tab 51 is made of the same material as the positive electrode current collector.

As a result, the first electrode 11 is located on at least one side of the first coating part 1 coated with the positive electrode active material and the first coating part 1, and the first uncoated area ( 2) is included. At this time, the first uncoated region 2 is divided into a positive electrode current collector area exposed because the first coating portion 1 is not formed and an area integrally connected to the positive electrode collector and functioning as the first electrode tab 51 . do.

The first electrode tab 51 may electrically connect the first electrode 11 to an external terminal.

The positive electrode current collector, for example, may be formed in a mesh (mesh) form or may be formed in a metal foil (foil) form. In addition, as a positive electrode collector, aluminum, an aluminum alloy, etc. can be used, for example.

The first coating portion 1 is, for example, cobalt, manganese, nickel, lithium cobaltate, lithium nickelate, lithium nickel cobaltate, lithium nickel cobalt aluminate, lithium nickel cobalt manganate, lithium manganate and iron phosphate. It may be formed using a lithium transition metal oxide such as lithium, and formed using a slurry containing a complex oxide of lithium and a metal selected from nickel sulfide, copper sulfide, sulfur, iron oxide, vanadium oxide, and combinations thereof. may be, but is not limited thereto.

The second electrode 12 includes an anode current collector made of a thin metal plate having electrical conductivity and a second coating part 3 coated with an anode active material formed on at least one surface of the anode current collector. In this case, the negative active material is not entirely coated on at least one surface of the negative electrode current collector.

That is, the second uncoated portion 4 is positioned on at least one side of the second coating portion 3 .

The second uncoated region 4 is integrally formed with a region on at least one surface of the negative electrode current collector on which the negative electrode active material is not coated, that is, an exposed region of the negative electrode current collector and an exposed region of the negative electrode current collector. All regions serving as electrode tabs 52 are included. Accordingly, the second electrode tab 52 is made of the same material as the negative electrode current collector.

As a result, the second electrode 12 is located on at least one side of the second coating part 3 coated with the anode active material and the second coating part 3, and the second uncoated part ( 4) is included. At this time, the second uncoated region 4 includes a negative electrode current collector area exposed because the second coating portion 3 is not formed, and an area integrally connected to the negative electrode collector and functioning as a second electrode tab 52 . are separated

The second electrode tab 52 may electrically connect the second electrode 12 to an external terminal.

The negative electrode current collector, for example, may be formed in a mesh (mesh) form or may be formed in a metal foil (foil) form. Moreover, as a negative electrode collector, copper, a copper alloy, etc. can be used, for example.

The second coating part 3 may be formed using, for example, a material including at least one of a carbon material such as crystalline carbon, amorphous carbon, carbon composite material, carbon fiber, lithium metal, a metal oxide, and a lithium alloy. However, the present invention is not limited thereto.

In a state in which the first electrode 11 and the second electrode 12 are stacked with the separator 13 interposed therebetween, the first electrode tab 51 and the second electrode tab 52 are formed of the electrode assembly 10 . They may be alternately disposed on both sides of the width direction (x-axis direction). That is, in FIG. 2 , the first electrode tab 51 is disposed on the right side in the width direction (x-axis direction) of the electrode assembly 10 , and the second electrode tab 52 is disposed on the right side in the width direction (x-axis direction) of the electrode assembly 10 . direction) may be spaced apart from the first electrode tab 51 at a predetermined interval on the left side.

Meanwhile, in the electrode assembly 10 according to the present disclosure, the first stress relief portion P1 is positioned in at least a partial region of the first uncoated region 2 . In addition, the second stress relaxation portion P2 is positioned in at least a partial region of the second uncoated region 4 .

In FIG. 2 , the first stress relief portion P1 is positioned on the first uncoated portion 2 , and is disposed to be spaced apart from the first coating portion 1 by a predetermined distance, and the second stress relief portion P2 is disposed on the second uncoated portion 2 . It is located on the uncoated part 4 and is spaced apart from the second coating part 3 by a predetermined distance.

That is, the first stress relieving portion P1 is located in a portion of the region functioning as the first electrode tab 51 of the first uncoated region 2 , and the second stress relieving portion P2 is located in the second uncoated region 4 . ) in a portion of the region functioning as the second electrode tab 52 .

Although not shown, it goes without saying that the electrode assembly of the present disclosure may include only one of the first stress relieving unit and the second stress relieving unit. However, in terms of improving durability of the secondary battery, it is preferable that the electrode assembly 10 according to the present embodiment includes both the first stress relief part P1 and the second stress relief part P2 .

Specifically, the first stress relieving unit (P1) and the second stress relieving unit (P2) may be each formed of a film including an ethylene propylene copolymer, a hydrogenated hydrocarbon polymer, and polyethylene.

At this time, the film constituting the first stress relief portion (P1) and the second stress relief portion (P2) is, for example, based on the entire film, ethylene propylene copolymer 35% by weight to 45% by weight, the hydrogenation 35 wt% to 45 wt% of the hydrocarbon polymer, and 10 wt% to 25 wt% of the polyethylene may be included.

More specifically, the film constituting the first stress relief portion (P1) and the second stress relief portion (P2) is, for example, based on the entire film, 35 wt% to 45 wt% of the ethylene propylene copolymer, the 35 wt% to 45 wt% of the hydrogenated hydrocarbon polymer, and 10 wt% to 25 wt% of the polyethylene may be included.

On the other hand, the film may have an adhesive strength in the range of 80 °C to 200 °C, more specifically, in the range of 170 °C to 190 °C. Therefore, the film is melted by applying heat in the above-described range, and then coated on at least a partial area of the first uncoated area 2 and at least a partial area of the second uncoated area 4, respectively, and then cooled to cool the first stress relief area. (P1) and the second stress relief portion P2 may be formed.

In general, when a rechargeable battery having a flexible characteristic is also repeatedly bent, compressive stress and tensile stress ( It can be easily damaged because it is continuously subjected to tensile stress. When the uncoated region is damaged as described above, an internal short circuit may occur due to direct contact between the positive electrode and the negative electrode.

Alternatively, an internal short circuit may occur due to direct contact between the positive electrode and the negative electrode because the adhesive force is not maintained in the uncoated region in the electrolyte.

However, in the present disclosure, as described above, in at least a partial region of the first uncoated region 2 and at least a partial region of the second uncoated region 4 , the first stress relaxation portion P1 and the second stress relaxation portion ( P1 ) and the second stress relaxation portion ( By locating P2), when the electrode assembly 10 according to the present disclosure is applied to a rechargeable battery having flexible characteristics, the above-described problems can be solved.

That is, by applying the electrode assembly 10 according to the present disclosure to a secondary battery having a flexible characteristic, it has excellent flexibility and electrically connects each electrode of the uncoated region to an external terminal despite repeated bending. By preventing the electrode tab area from being damaged, durability can be remarkably improved.

3 shows a modified example of the electrode assembly in which the positions of the first electrode tab and the second electrode tab are changed in FIG. 2 .

Referring to FIG. 3 , in the electrode assembly 10 of the present disclosure, the first and second electrode tabs 51 and 52 may be positioned to face each other in the longitudinal direction (y-axis direction) of the electrode assembly 10 . That is, the first electrode tab 51 is positioned on one side in the longitudinal direction (y-axis direction) of the electrode assembly 10 , and the second electrode tab 52 is positioned on one side in the longitudinal direction (y-axis direction) of the electrode assembly 10 . It may be located on the other side.

In this modified example, except for the positions of the first electrode tab 51 and the second electrode tab 52 , other configurations are the same as the respective configurations of the electrode assembly according to the embodiment described above with reference to FIGS. 1 and 2 . to be omitted.

4 shows a modified example of the electrode assembly in which the shapes of the first electrode tab and the second electrode tab are changed in FIG. 1 .

Referring to FIG. 4 , in the electrode assembly 10 of the present disclosure, the first and second electrode tabs 51 and 52 may include bent portions 511 and 521 bent in the longitudinal direction thereof. By including the bent portions 511 and 521 in the first and second electrode tabs 51 and 52 , structural elasticity may be formed, and accordingly, the first and second electrode tabs 51 and 52 and A lead tab (not shown) may be connected more stably.

In this case, the first and second stress relief portions P1 and P2 may overlap the bent portions 511 and 521 as shown in FIG. 4 , or overlap the bent portions 511 and 521 . It may be formed so as not to do so, it is not particularly limited.

In this modified example, other configurations except that the first electrode tab 51 and the second electrode tab 52 include the bent portions 511 and 521 are according to the embodiment described above with reference to FIGS. 1 and 2 . Since each configuration of the electrode assembly is the same, it will be omitted herein.

5 is an exploded perspective view of an electrode assembly for a secondary battery according to a second exemplary embodiment of the present disclosure, and FIG. 6 is a horizontal cross-sectional view illustrating an xy plane of the electrode assembly for a secondary battery according to FIG. 5 .

In this embodiment, descriptions of the same components as those described with reference to FIGS. 1 to 4 will be omitted and different components will be described.

5 and 6 , in the present embodiment, the first stress relief portion P1 is located on the first uncoated portion 2 , and one side of the first stress relief portion is formed with the first coating portion and placed in contact.

Specifically, in this embodiment, the first coating part 1 is located on at least one surface of the positive electrode current collector, and does not include a region where the positive electrode current collector is exposed because the positive electrode active material is not coated. In addition, the first stress relief portion P1 is positioned in the region of the first uncoated region 1 functioning as the first electrode tab 51 , and is formed to extend to the region in contact with the first coating unit 1 . can be

Meanwhile, the second coating part 3 is disposed on at least one surface of the anode current collector, and does not include a region where the anode current collector is exposed because the anode active material is not coated. In addition, the second stress relief portion P2 is positioned in the region of the second uncoated region 3 functioning as the second electrode tab 52 , and is formed to extend to the region in contact with the second coating portion 3 . can be

Therefore, in the present embodiment, the area of each of the first and second stress relief portions P1 and P2 is the first and second stress relief portions ( P1 and P2 ) of the electrode assembly according to the first embodiment described with reference to FIGS. 1 and 2 . P1 and P2) may be formed to be relatively wider than the respective areas.

When the first and second stress relief portions P1 and P2 are formed as in the present embodiment, durability of the electrode assembly 10 for a secondary battery may be further improved.

7 is a perspective view of a secondary battery according to a first exemplary embodiment of the present disclosure, and FIG. 8 is an exploded perspective view of the secondary battery according to FIG. 7 .

Referring to FIGS. 7 and 8 , the secondary battery 100 according to the present embodiment may be in the form of one of the above-described electrode assemblies 10 , and a flexible exterior material accommodating the electrode assembly 10 ( 15). 8 exemplarily illustrates the electrode assembly described with reference to FIGS. 1 and 2 . Accordingly, it goes without saying that the electrode assembly described with reference to FIGS. 3, 4 and 5 and 6 may be accommodated.

Since the content of the electrode assembly 10 is the same as that described above with reference to FIGS. 1 to 6 , it will be omitted herein.

An electrolyte solution may be accommodated in the casing 15 together with the electrode assembly 10 .

The electrolyte is, for example, in an organic solvent such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), LiPF ₆ , LiBF ₄ such as It may consist of a lithium salt. The electrolyte may be liquid, solid or gel.

The electrode assembly 10 is accommodated in a pair of exterior materials 15 positioned above and below the electrode assembly 10 . In this case, the first electrode tab 51 and the second electrode tab 52 are formed to be drawn out of the exterior material 15 .

In the present embodiment, the first electrode tab 51 and the second electrode tab 52 are accommodated in the exterior material 15 after each portion in contact with the exterior material 15 is wrapped with an insulating tape (not shown) or the like. can be

Referring to FIG. 8 , the pair of exterior materials 15 includes an outer resin layer 15a, a moisture permeation barrier layer 15b and an inner resin layer 15c that are sequentially stacked from the outermost layer, respectively.

The outer resin layer 15a functions as a protective layer and is located at the outermost portion of the secondary battery 100 .

The outer resin layer 15a is, for example, made of at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate and nylon film. may be, but is not limited thereto.

The thickness of the outer resin layer 15a may be, for example, 10 μm to 100 μm, more specifically, 10 μm to 50 μm. When the thickness of the outer resin layer 15a is 10 μm or more, it is not easily damaged because it has excellent physical properties, and when it is 100 μm or less, the moldability such as injection and foaming is excellent, and when applied to the secondary battery 100 It is possible to secure excellent battery capacity per unit volume.

A moisture barrier layer 15b is positioned on one surface of the outer resin layer 15a on the side where the electrode assembly 10 is positioned. The moisture-permeable barrier layer 15b is an intermediate layer that acts as a barrier layer that can prevent the electrolyte from leaking or from penetrating moisture. The moisture permeation barrier layer 15b may be formed of a thin plate-shaped member.

The moisture barrier layer 15b may be made of, for example, aluminum and an aluminum alloy.

The thickness of the moisture barrier layer 15b may be, for example, 10 μm to 100 μm, and more specifically, 10 μm to 50 μm or 10 μm to 30 μm. When the thickness of the moisture-permeable barrier layer 15b satisfies the above range, it is possible to effectively prevent leakage of electrolyte or penetration of moisture from the outside while having excellent workability.

The inner resin layer 15c is located on one surface of the moisture barrier layer 15b, and is located on the opposite surface of the surface on which the outer resin layer 15a is located. In addition, the inner resin layer 15c may have insulating and heat sealing functions.

The inner resin layer 15c may be formed of, for example, polyolefin or a copolymer of polyolefin, and more specifically, the polyolefin may be made of polyethylene (PE) or polypropylene (PP). However, the present invention is not limited thereto.

The thickness of the inner resin layer 15c may be in the range of 10 μm to 100 μm, more specifically, 20 μm to 50 μm. When the maximum thickness of the inner resin layer 15c satisfies the above numerical range, moldability, adhesion, and chemical resistance are excellent.

The pair of exterior materials 15 may be sealed by placing a gasket on the edge after positioning the electrode assembly 10 therein, or may be sealed by fusion bonding the internal resin layers 15c without a separate gasket. have.

9 is an exploded perspective view of a secondary battery according to a second exemplary embodiment of the present disclosure; In the present embodiment, descriptions of the same components as those described with reference to FIGS. 7 and 8 will be omitted and different components will be described.

Referring to FIG. 9 , in the electrode assembly 10 included in the secondary battery 100 according to the present embodiment, at least one of the first stress relief unit P1 and the second stress relief unit P2 includes a pair of It may be formed to extend to a region in contact with a portion of the edge of the exterior material 15 .

9 exemplarily illustrates a case in which the first stress relief portion P1 and the second stress relief portion P2 are formed to extend to a region in contact with a portion of the edge of the exterior material 15 in the electrode assembly of FIG. 5 . . Accordingly, even when the electrode assembly described with reference to FIGS. 2 to 4 is accommodated, the first stress relief part P1 and the second stress relief part P2 extend to a region in contact with a portion of the edge of the exterior material 15 . Of course, it can be formed.

In this case, in the process of accommodating the electrode assembly 10 in the casing 15 , it is not necessary to cover the portion where the first and second electrode tabs 51 and 52 contact the casing 15 with an insulating tape, etc., so that productivity is improved. do.

The present invention will be described in detail with reference to the following examples.

Example One

A plurality of square sheet-shaped positive electrodes, negative electrodes, and separators were prepared.

At this time, the positive electrode tab and the negative electrode tab were integrally formed in the positive electrode uncoated region and the negative electrode uncoated region, respectively.

After the film A is melted by heating it to 175° C., it is applied to a portion of the uncoated region (tab portion) spaced apart from the coating portion of each electrode by a predetermined interval to form a first stress relief portion and a second stress relief portion in the form shown in FIG. 1 . A positive electrode and a negative electrode respectively formed were prepared.

Thereafter, a plurality of stacked electrode assemblies were manufactured by interposing a separator between the positive electrode and the negative electrode.

A secondary battery was manufactured by placing the electrode assembly between a pair of exterior materials and sealing the edges of the exterior materials.

comparative example One

A film B capable of being melted by heating at 175° C. was prepared as a film to be used as the first stress relief portion and the second stress relief portion.

comparative example 2

A film C capable of being melted by heating at 175° C. was prepared as a film to be used as the first stress relief portion and the second stress relief portion.

comparative example 3

A film D capable of being melted by heating at 175° C. was prepared as a film to be used as the first stress relief portion and the second stress relief portion.

comparative example 4

A film E capable of being melted by heating at 175° C. was prepared as a film to be used as the first stress relief portion and the second stress relief portion.

comparative example 5

A film F capable of being melted by heating at 175° C. was prepared as a film to be used as the first stress relief portion and the second stress relief portion.

comparative example 6

A secondary battery was manufactured in the same manner as in Example 1, except that the first and second stress relief portions were not formed after the positive electrode tab and the negative electrode tab were respectively connected to the positive electrode uncoated region and the negative electrode uncoated region by welding.

The compositions of the films A to F used in Example 1 and Comparative Examples 1 to 5 are shown in Table 1 below.

division Configuration film A Polyolefin film (ethylene propylene copolymer 40wt% + hydrogenated hydrocarbon polymer 40wt% + polyethylene 20wt%) film B polyamide film film C polyester film film D polyurethane film film E Polyolefin film (ethylene propylene copolymer 50wt% + hydrogenated hydrocarbon polymer 40wt% + polyethylene 10wt%) film F Polyolefin film (ethylene propylene copolymer 50wt% + hydrogenated hydrocarbon polymer 50wt%)

Experimental Example 1 - Adhesion Test The adhesion test was performed on the films A to F prepared in Example 1 and Comparative Examples 1 to 5.

The adhesion test was conducted after preparing an aluminum foil having a size of 80 mm × 20 mm and films A to F used in Examples 1 and Comparative Examples 1 to 5, and then thermally attaching one end of the aluminum foil and each film to each other. Fix the other side to a tensile tester (HT400 by Tinius olsen).

Then, the adhesive force is measured by pulling the aluminum foil that is not thermally attached and the ends of each film at a constant speed in different directions.

division Adhesion (N/mm) Example 1 0.826 Comparative Example 1 0.219 Comparative Example 2 0.256 Comparative Example 3 0.401 Comparative Example 4 0.662 Comparative Example 5 0.531

Referring to Table 2, in the case of the film A used in Example 1, it can be seen that the adhesion with the aluminum foil is remarkably excellent compared to the films B to F used in Comparative Examples 1 to 5.

Experimental example 2 - Tensile force test

A tensile force test was performed on the films A to F prepared in Example 1 and Comparative Examples 1 to 5.

Samples were prepared in which an aluminum foil of a certain standard and films A to F used in Examples 1 and Comparative Examples 1 to 5 were attached, respectively. In the case of Comparative Example 6, a sample in which the film was made of only aluminum foil was prepared.

Thereafter, a tensile force test was performed for each sample using a tensile tester (HT400 manufactured by Tinius olsen).

As a result of the tensile force test, in all samples other than the sample prepared by attaching the film A used in Example 1, the aluminum foil and the film did not break at the same time, and the film layer was broken after the breakage of the aluminum foil occurred first. This means that the film did not sufficiently delay the breakage of the aluminum foil due to insufficient adhesion, and thus it was difficult to obtain elongation and elastic strain data.

Therefore, only the tensile test results for Example 1 and Comparative Example 6 are shown in Table 3 below.

division Elongation (%) Elastic strain (%) Example 1 6.3 0.85 Comparative Example 6 1.1 0.58

In the sample prepared by attaching the film A used in Example 1, which showed the best adhesion, fracture of the aluminum foil and the film A occurred simultaneously as a result of the tensile force test, which had sufficient adhesion and the film A delayed the fracture of the aluminum foil as much as possible. indicates In addition, referring to Table 3, in the case of the sample to which the film A used in Example 1 is attached, when compared with the tensile force test results for a sample made of only aluminum foil without a stress relief part as in Comparative Example 6, the elongation and elastic strain were It can be seen that a significant improvement

Experimental example 3 - bending Test

Performance of the secondary battery before and after performing the bending test and the bending test on the secondary batteries according to Example 1 and Comparative Example 6 was measured.

(1) possible until the capacity retention rate maintains 90% or more bending number of times

After charging and discharging the secondary batteries for Example 1 and Comparative Example 6 at 0.5C, the number of bending possible until the capacity retention rate was maintained at 90% or more was measured and shown in Table 4 below.

division number of bends Example 1 over 20,000 times Comparative Example 6 1,000 or less

(2) Discharge capacity and capacity retention rate according to the number of bending The discharge capacity and capacity retention rate according to the number of bending were measured, respectively, and are shown in Table 5 below.

division 0 times 1000 times 20,000 times 50,000 episodes Discharge
Volume
(mAh) discharge capacity
(mAh) Volume
retention rate
(%) Discharge
Volume
(mAh) Volume
retention rate
(%) Discharge
Volume
(mAh) Volume
retention rate
(%) Example 1 37.2 37.0 99.5 36.8 98.8 30.2 81.2 Comparative Example 6 39.4 19.7 50 Measurable Measurable

Referring to Tables 4 and 5, in the case of the lithium secondary battery according to Example 1 in which film A including an ethylene propylene copolymer, a hydrogenated hydrocarbon polymer, and polyethylene in a specific content is applied as the first and second stress relief units, the first And it can be confirmed that the lithium secondary battery according to Comparative Example 6 does not form the second stress relaxation portion has excellent bending properties and at the same time exhibits excellent capacity retention.

Although preferred embodiments of the present invention have been described above with reference to the drawings, the present description is not limited to the above embodiments, and from the examples of the present description, it is easy for those of ordinary skill in the art to which the present invention pertains. It includes all changes within the scope recognized as equivalent.

10: electrode assembly for secondary battery
1: first coating part
2: 1st uncoated area
3: second coating part
4: 2nd uncoated area
11: first electrode
12: second electrode
13: separator
51: first electrode tab
52: second electrode tab
15: exterior material
P1: first stress relief part
P2: second stress relief part

Claims (16)

a first electrode including a first coating part and a first uncoated part positioned on at least one side of the first coating part;
a second electrode including a second coating part and a second uncoated part positioned on at least one side of the second coating part;
a separator interposed between the first electrode and the second electrode; And
at least one of a first stress relieving unit located in at least a partial region of the first uncoated region and a second stress relieving unit located in at least a partial region of the second uncoated region;
The first stress relieving unit and the second stress relieving unit,
Consists of a film comprising an ethylene propylene copolymer, a hydrogenated hydrocarbon polymer and polyethylene,
The film is based on the entire film,
35 to 45% by weight of an ethylene propylene copolymer;
35 wt% to 45 wt% of the hydrogenated hydrocarbon polymer, and
An electrode assembly for a secondary battery comprising 10% to 25% by weight of the polyethylene. delete According to claim 1,
The film is an electrode assembly for a secondary battery having an adhesive force in the range of 80 ℃ to 200 ℃. According to claim 1,
The first stress relief unit,
An electrode assembly for a secondary battery disposed on the first uncoated portion and spaced apart from the first coating portion by a predetermined distance. According to claim 1,
The second stress relief unit,
An electrode assembly for a secondary battery disposed on the second uncoated portion and spaced apart from the second coating portion by a predetermined distance. According to claim 1,
The first stress relief unit,
An electrode assembly for a secondary battery positioned on the first uncoated region, wherein one side of the first stress relief part is in contact with the first coating part. According to claim 1,
The second stress relief unit,
An electrode assembly for a secondary battery positioned on the second uncoated region, wherein one side of the second stress relief part is in contact with the second coating part. According to claim 1,
The first uncoated portion is integrally formed with the first electrode tab,
The second uncoated portion is an electrode assembly for a secondary battery configured integrally with the second electrode tab. 9. The method of claim 8,
The first electrode tab,
Located on one side in the width direction of the electrode assembly for the secondary battery,
The second electrode tab,
An electrode assembly for a secondary battery located in the same direction as the first electrode tab and spaced apart from the first electrode tab by a predetermined distance. 9. The method of claim 8,
The first electrode tab,
Located on one side in the longitudinal direction of the electrode assembly for the secondary battery,
The second electrode tab,
An electrode assembly for a secondary battery located on the other side in the longitudinal direction of the electrode assembly for a secondary battery. 9. The method of claim 8,
At least one of the first electrode tab and the second electrode tab includes a bent portion bent in a longitudinal direction of the first electrode tab and the second electrode tab. According to claim 1,
The first electrode and the second electrode are
A plurality of electrode assemblies for secondary batteries that are alternately stacked with the separator interposed therebetween. The electrode assembly for a secondary battery of any one of claims 1 and 3 to 12; And
a casing for accommodating the electrode assembly for the secondary battery;
A secondary battery comprising a. 14. The method of claim 13,
The first stress relief part is in contact with a portion of an edge of the exterior material. 14. The method of claim 13,
The second stress relief part is in contact with a portion of an edge of the exterior material. 14. The method of claim 13,
The secondary battery is a secondary battery having a flexible characteristic.

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