KR20190067083A - Electrode assembly for rechargeable battery and rechargeable battery including the same - Google Patents

Abstract

The present invention relates to an electrode assembly with excellent flexibility and durability for a secondary battery, and a secondary battery including the same. According to one embodiment of the present invention, the electrode assembly for a secondary battery comprises: a first electrode including a first coating part and a first uncoated part placed on at least one side of the first coating part; a second electrode including a second coating part and a second uncoated part placed on at least one side of the second coating part; a separate interposed between the first and second electrodes; and at least one between a first stress relief part placed in at least a part of region of the first uncoated part and a second stress relief part placed in at least a part of region of the second uncoated part. The first and second stress relief parts are formed with a film including ethylene propylene copolymer, hydrogenated hydrocarbon polymer, and polyethylene.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrode assembly for a secondary battery and a secondary battery including the electrode assembly.

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

The secondary battery includes, for example, a case accommodating an electrode assembly composed of an anode and a cathode, and a separator interposed between the anode and the cathode. Also, an electrode tab electrically connected to the positive electrode and the negative electrode is drawn out from 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 a growing demand for a flexible secondary battery, which is a power supply device for such a flexible electronic device, to realize flexible characteristics.

Particularly, researches are actively carried out to realize a flexible secondary battery having excellent durability with repeated bending while having flexible characteristics.

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

In one aspect, the present disclosure provides a method of forming a coating comprising a first electrode comprising a first coating portion and a first uncoated portion located on at least one side of the first coating portion, a second coating portion and a second coating portion located on at least one side of the second coating portion A second electrode including a second uncoated portion, a separator interposed between the first electrode and the second electrode, and a first stress relieving portion located at least in a partial region of the first uncocked portion, Wherein the first stress relieving portion and the second stress relieving portion comprise at least one of a first stress relieving portion and a second stress relieving portion located in a partial region, wherein the first stress relieving portion and the second stress relieving portion are made of a film comprising an ethylene propylene copolymer, a hydrogenated hydrocarbon polymer and a polyethylene, Assembly.

In another aspect, the disclosure provides a rechargeable battery including the above-described electrode assembly for a secondary battery and an exterior member accommodating the electrode assembly for the secondary battery.

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

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 sectional view showing the xy plane of the electrode assembly for a secondary battery according to FIG. 1;
FIG. 3 shows a modification of the electrode assembly in which the positions of the first electrode tab and the second electrode tab are changed in FIG.
FIG. 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.
5 is an exploded perspective view of an electrode assembly for a secondary battery according to a second embodiment of the present disclosure.
6 is a horizontal sectional view showing the xy plane of the electrode assembly for a secondary battery according to FIG.
7 is a perspective view of a secondary battery according to the first embodiment of the present invention.
8 is an exploded perspective view of the secondary battery according to FIG.
9 is an exploded perspective view of a secondary battery according to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

In addition, since the sizes and thicknesses of the respective components shown in the drawings are arbitrarily shown for convenience of explanation, the present invention is not necessarily limited to those shown in the drawings.

Also, throughout the specification, when an element is referred to as "including" an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

FIG. 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 sectional view showing an xy plane of the electrode assembly for a secondary battery according to FIG.

1 and 2, an electrode assembly 10 for a secondary battery according to a first embodiment of the present invention includes a first electrode 11, a second electrode 12, a first electrode 11, And a separator (13) interposed between the electrodes (12).

The electrode assembly 10 includes a first electrode 11 and a second electrode 12 in the form of a rectangular sheet and is stacked in a stacked manner with the separator 13 interposed therebetween .

Although only one first electrode 11 and one second electrode 12 are illustrated in FIGS. 1 and 2 for convenience, a plurality of the first and second electrodes 11 and 12 may be stacked with the separator 13 interposed therebetween to form the electrode assembly 10 Of course.

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 a cathode. Hereinafter, a case where the first electrode 11 is an anode and the second electrode 12 is a cathode will be described as an example for convenience.

First, the separator 13 separates the first electrode 11 and the second electrode 12 and provides a passage for lithium ion. Any separator may be used as long as it is commonly used in a secondary battery. That is, a material having a low resistance to ion movement of an electrolyte and having an excellent ability to impregnate an electrolyte can be used.

The separator 13 may be a nonwoven fabric or a woven fabric selected from, for example, glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE) or a combination thereof. In order to secure heat resistance or mechanical strength, a separator coated with a composition containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a 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 portion 1 having a positive electrode active material coated on at least one surface of the positive electrode current collector. At this time, the cathode active material is not entirely coated on at least one surface of the cathode current collector.

That is, the first uncoated portion 2 is located on at least one side of the first coated portion 1. The first uncoated portion 2 is formed integrally with at least one surface of the positive electrode collector on a region where the positive electrode active material is not coated, that is, a region where the positive electrode collector is exposed and a region where the positive electrode collector is exposed, All of which serve as the electrode tabs 51. Therefore, the first electrode tab 51 is made of the same material as the positive electrode collector.

As a result, the first electrode 11 includes a first coating portion 1 coated with a cathode active material and a first non-coated portion (not shown) disposed on at least one side of the first coated portion 1 and not coated with the cathode active material 2). At this time, the first uncoated portion 2 is integrally connected to the exposed positive electrode current collector region and the positive electrode current collector without forming the first coated portion 1, and is divided into a region 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 anode current collector may be, for example, in the form of a mesh, or may be in the form of a metal foil. As the positive electrode collector, for example, aluminum or an aluminum alloy may be used.

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

The second electrode 12 includes a negative electrode current collector made of a thin metal plate having electrical conductivity and a second coating portion 3 coated with a negative electrode active material formed on at least one surface of the negative electrode current collector. At this time, the negative electrode 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 located on at least one side of the second coated portion 3.

The second uncoated portion 4 is formed integrally with at least one surface of the negative electrode collector on a region where the negative electrode active material is not coated, that is, a region where the negative electrode collector is exposed and a region where the negative electrode collector is exposed, All of which serve as the electrode tabs 52. Therefore, the second electrode tab 52 is made of the same material as the negative electrode collector.

As a result, the second electrode 12 is disposed on at least one side of the second coating portion 3 coated with the negative electrode active material and the second coated portion 3, and the second uncoated portion 4). At this time, the second uncoated portion 4 is formed with the exposed negative current collector region where the second coated portion 3 is not formed, and a region that is integrally connected to the negative electrode collector and functions as the second electrode tab 52 Respectively.

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

The anode current collector may be, for example, in the form of a mesh, or may be in the form of a metal foil. As the negative electrode collector, for example, copper or a copper alloy can be used.

The second coating portion 3 is formed using a material containing at least one of a carbon material such as crystalline carbon, amorphous carbon, carbon composite, and carbon fiber, a lithium metal, a metal oxide, and a lithium alloy But is not limited thereto.

The first electrode tab 51 and the second electrode tab 52 are formed in such a manner that the first electrode tab 11 and the second electrode tab 12 are stacked with the separator 13 interposed therebetween. Can be alternately arranged on both sides in the width direction (x-axis direction). 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 of the electrode assembly 10 The first electrode tab 51 may be spaced apart from the first electrode tab 51 by a predetermined distance.

On the other hand, in the electrode assembly 10 according to the present disclosure, the first stress relieving portion P1 is located at least in a region of the first uncoated portion 2. In addition, the second stress relieving portion P2 is located in at least a part of the second uncoated portion 4.

2, the first stress relieving portion P1 is located on the first non-coated portion 2 and is spaced apart from the first coated portion 1 by a predetermined distance, and the second stress relieving portion P2 is disposed on the second non- Is disposed on the non-coated portion (4) and is spaced apart from the second coating portion (3) by a predetermined distance.

That is, the first stress relieving portion P1 is located in a portion of the first uncoated portion 2 that functions as the first electrode tab 51 and the second stress relieving portion P2 is located in the second uncoated portion 4 Of the second electrode tab 52. The second electrode tab 52 is a part of the second electrode tab 52,

Needless to say, the electrode assembly of the present disclosure may include only one of the first stress relieving portion and the second stress relieving portion. However, it is preferable that both the first stress relieving portion P1 and the second stress relieving portion P2 are included in the electrode assembly 10 according to the present embodiment in terms of improving the durability of the secondary battery.

Specifically, the first stress relieving portion P1 and the second stress relieving portion P2 may be composed of a film containing an ethylene propylene copolymer, a hydrogenated hydrocarbon polymer, and polyethylene, respectively.

At this time, the film constituting the first stress relieving portion P1 and the second stress relieving portion P2 is, for example, based on the entirety of the film, from 35 to 45% by weight of an ethylene propylene copolymer, From 35 to 45% by weight of a hydrocarbon polymer, and from 10 to 25% by weight of the polyethylene.

More specifically, the film constituting the first stress relieving portion (P1) and the second stress relieving portion (P2) is, for example, from 35 to 45% by weight of an ethylene propylene copolymer based on the whole film, 35 to 45 wt% of a hydrogenated hydrocarbon polymer, and 10 to 25 wt% of the polyethylene.

On the other hand, the film may have an adhesive strength in a range of 80 ° C to 200 ° C, more specifically 170 ° C to 190 ° C. Therefore, after the film is melted by applying heat to the above-mentioned range, the film is coated on at least a part of the first uncoated portion 2 and at least a part of the second uncoated portion 4, The first stress relieving portion P1 and the second stress relieving portion P2 can be formed.

Generally, when a secondary battery having a flexible characteristic is repeatedly bended, compressive stress and tensile stress (tensile stress) are applied to an uncoated region having a function of being electrically connected to an external terminal, tensile stress) can be easily damaged. If the uncoated region is damaged, an internal short circuit may occur due to direct contact between the positive electrode and the negative electrode.

Or the uncoated region does not maintain the adhesive force in the electrolyte, so that an internal short circuit may occur due to direct contact between the positive electrode and the negative electrode.

However, in the present disclosure, as described above, the first stress relieving portion P1 and the second stress relieving portion (first stress relieving portion) are provided in at least a part of the first uncoated portion 2 and at least a part of the second uncoated portion 4, P2, the above-described problems can be solved when the electrode assembly 10 according to the present disclosure is applied to a secondary battery having a flexible characteristic.

In other words, by applying the electrode assembly 10 according to the present disclosure to a secondary battery having a flexible characteristic, it is possible to electrically connect each electrode in the non-solid portion to the external terminal in spite of repeated bending while having excellent flexibility And the durability of the electrode tab region can be remarkably improved.

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

3, the first and second electrode tabs 51 and 52 in the electrode assembly 10 of the present disclosure can be positioned facing each other in the longitudinal direction (y-axis direction) of the electrode assembly 10. That is, the first electrode tab 51 is located on one side in the longitudinal direction (y-axis direction) of the electrode assembly 10, and the second electrode tab 52 is located on the side of the electrode assembly 10 in the longitudinal direction Can be located on the other side.

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

FIG. 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.

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. The first and second electrode tabs 51 and 52 may be structurally resilient by including the bent portions 511 and 521 so that the first and second electrode tabs 51 and 52 Lead tabs (not shown) can be connected more stably.

4, the first and second stress relieving portions P1 and P2 may be overlapped with the bending portions 511 and 521 or may be overlapped with the bending portions 511 and 521, And is not particularly limited.

1 and 2, except that the first electrode tab 51 and the second electrode tab 52 include the bent portions 511 and 521 in this modified example, Which is the same as the configuration of the electrode assembly, is omitted here.

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

In the present embodiment, the same configurations as those described in Figs. 1 to 4 will not be described, and different configurations will be described.

5 and 6, in the present embodiment, the first stress relieving portion P1 is located on the first uncoated portion 2, and one side of the first stress relieving portion is connected to the first coating portion .

Specifically, in the present embodiment, the first coating portion 1 is located on at least one entire surface of the cathode current collector, and does not include the region where the cathode current collector is exposed because the cathode active material is not coated. The first stress relieving portion P1 is formed in a region extending from the first uncoated portion 1 which functions as the first electrode tab 51 to a region in contact with the first coated portion 1, .

On the other hand, the second coating portion 3 is located on at least one entire surface of the negative electrode current collector and does not include a region where the negative electrode current collector is exposed because the negative electrode active material is not coated. The second stress relieving portion P2 is located in the region of the second uncoated portion 3 functioning as the second electrode tab 52 and formed in a shape extending to the region in contact with the second coating portion 3 .

Therefore, in this embodiment, the area of each of the first and second stress relieving portions P1 and P2 is the same as that of the first and second stress relieving portions P1, and P2, respectively.

When the first and second stress relieving portions P1 and P2 are formed as in this embodiment, the durability of the secondary battery electrode assembly 10 can be further improved.

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

Referring to FIGS. 7 and 8, the secondary battery 100 according to the present embodiment may be in the form of one of the electrode assemblies 10 described above, 15). In FIG. 8, the electrode assembly described with reference to FIG. 1 and FIG. 2 is exemplarily shown. Therefore, it goes without saying that the electrode assembly described with reference to Figs. 3, 4, 5, and 6 may be housed.

The details of the electrode assembly 10 are the same as those described above with reference to Figs. 1 to 6, and thus will not be described here.

The electrolyte 15 can be accommodated together with the electrode assembly 10.

Electrolyte solution, for example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), in an organic solvent such as dimethyl carbonate (DMC), such as LiPF _6, LiBF ₄ Lithium salt. The electrolytic solution may be liquid, solid or gel.

The electrode assembly 10 is housed in a pair of facings 15 located at the top and bottom of the electrode assembly 10. At this time, the first electrode tab 51 and the second electrode tab 52 are formed to be drawn out to the outside of the casing member 15.

The first electrode tab 51 and the second electrode tab 52 are formed so that the portion of the first electrode tab 51 and the second electrode tab 52 which are in contact with the case member 15 is covered with an insulating tape .

Referring to Fig. 8, the pair of outer casings 15 includes an outer resin layer 15a, a moisture permeation preventive layer 15b, and an inner resin layer 15c, which are stacked in order from the outermost portion.

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 composed of at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymerized polyester, polycarbonate and nylon film But is not limited thereto.

The thickness of the external resin layer 15a may be, for example, in the range of 10 탆 to 100 탆, more specifically in the range of 10 탆 to 50 탆. When the thickness of the external resin layer 15a is 10 mu m or more, it is not easily damaged because of its excellent physical properties. When the thickness is 100 mu m or less, the moldability such as injection and forming is excellent. When applied to the secondary battery 100 An excellent battery capacity per unit volume can be secured.

The moisture permeation preventive layer 15b is located on one side of the side of the external resin layer 15a where the electrode assembly 10 is located. The moisture permeation preventive layer 15b is an intermediate layer serving as a barrier layer that can prevent leakage of electrolyte or penetration of moisture and the like. The moisture permeation preventive layer 15b may be formed of a thin plate-like member.

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

The thickness of the moisture permeation prevention layer 15b may be, for example, 10 占 퐉 to 100 占 퐉, and more specifically, 10 占 퐉 to 50 占 퐉 or 10 占 퐉 to 30 占 퐉. When the thickness of the moisture permeation prevention layer 15b satisfies the above range, it is possible to effectively prevent penetration of electrolyte leakage and moisture or the like from the outside with excellent workability.

The inner resin layer 15c is located on one surface of the moisture permeation preventive layer 15b and is located on the opposite surface of the surface where the outer resin layer 15a is located. In addition, the inner resin layer 15c may have insulation and heat fusion function.

The inner resin layer 15c may be formed of, for example, a copolymer of a polyolefin or a polyolefin. More specifically, the polyolefin may be composed of polyethylene (PE) or polypropylene (PP) But is not limited thereto.

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

The pair of outer sheaths 15 may be sealed with a gasket interposed therebetween after the electrode assembly 10 is positioned in the inner portion. Alternatively, the inner resin layers 15c may be sealed and sealed without providing a separate gasket have.

9 is an exploded perspective view of a secondary battery according to a second embodiment of the present invention. In the present embodiment, the same configurations as those described in Figs. 7 and 8 are not described, and different configurations will be described.

Referring to FIG. 9, at least one of the first stress relieving portion P1 and the second stress relieving portion P2 in the electrode assembly 10 included in the secondary battery 100 according to the present embodiment includes a pair of And may extend to a region in contact with a part of the rim of the casing 15.

FIG. 9 exemplarily shows a case where the first stress relieving portion P1 and the second stress relieving portion P2 of the electrode assembly of FIG. 5 are extended to a region contacting with a part of the rim of the casing 15 . Therefore, even when the electrode assembly described with reference to FIGS. 2 to 4 is accommodated, the first stress relieving portion P1 and the second stress relieving portion P2 extend to a region where they contact with a part of the rim of the casing 15 Of course.

In this case, in the step of housing the electrode assembly 10 in the casing 15, it is not necessary to cover the insulating tape 15 or the like at the portion where the first and second electrode tabs 51 and 52 are in contact with the casing 15, do.

Hereinafter, the present invention will be described in detail with reference to examples.

Example  One

A plurality of positive electrodes in the form of a rectangular sheet, a negative electrode and a separator were prepared.

At this time, the positive electrode tab and the negative electrode tab were integrally formed on the uncoated portion and the non-coated portion, respectively.

The film A was melted by heating at 175 DEG C and then applied to a part of the non-coated portion (tab portion) spaced apart from the coating portion of each electrode by a predetermined distance to form the first stress relieving portion and the second stress relieving portion Thereby preparing positive and negative electrodes, respectively.

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

The electrode assembly was placed between a pair of outer sheaths, and then the rim of the outer sheath was sealed to manufacture a secondary battery.

Comparative Example  One

A film B to be melted was prepared by heating at 175 캜 with a film to be used as the first stress relieving portion and the second stress relieving portion.

Comparative Example  2

A film C to be melted was prepared by heating at 175 ° C with a film to be used as the first stress relieving portion and the second stress relieving portion.

Comparative Example  3

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

Comparative Example  4

A film E to be melted was prepared by heating at 175 DEG C with a film to be used as the first stress relieving portion and the second stress relieving portion.

Comparative Example  5

A film F to be melted was prepared by heating at 175 DEG C with a film to be used as the first stress relieving portion and the second stress relieving portion.

Comparative Example  6

A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode tab and the negative electrode tab were respectively welded to the positive electrode tab and the negative electrode tab and then the first and second stress relieving portions were not formed.

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 40 wt% + hydrogenated hydrocarbon polymer 40 wt% + polyethylene 20 wt%) Film B Polyamide film Film C Polyester film Film D Polyurethane film Film E Polyolefin film (ethylene propylene copolymer 50 wt% + hydrogenated hydrocarbon polymer 40 wt% + polyethylene 10 wt%) Film F Polyolefin film (50 wt% of ethylene propylene copolymer + 50 wt% of hydrogenated hydrocarbon polymer)

Experimental Example 1-Adhesion Test Adhesion tests were conducted on Film A to Film F prepared in Example 1 and Comparative Examples 1 to 5.

The adhesion test was carried out by preparing an aluminum foil having a size of 80 mm x 20 mm and the films A to F used in Example 1 and Comparative Examples 1 to 5 and then attaching the aluminum foil and one end of each film to each other, And the other side is fixed to each of the tensile tester (HT400 of Tinius olsen).

The adhesive force is then measured by pulling the ends of each film with an unattached aluminum foil in different directions at a constant speed.

division Adhesive force (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

As can be seen from Table 2, it can be confirmed that the film A used in Example 1 has remarkably excellent adhesion to aluminum foil as compared with the films B to F used in Comparative Examples 1 to 5.

Experimental Example  2 - Tension Test

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

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

Each sample was then subjected to a tensile test using a tensile tester (HT400 from Tinius olsen).

As a result of the tensile strength test, in all the samples other than the sample prepared by attaching the film A used in Example 1, the fracture of the aluminum foil and the film did not proceed at the same time. This means that the film was not sufficiently adhered and the film failed to sufficiently retard the fracture of the aluminum foil, 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

As a result of the tensile test, the sample produced by attaching the film A used in Example 1 exhibiting the best adhesive force simultaneously fractured the aluminum foil and the film A, which caused the film A to delay the breaking of the aluminum foil as much as possible with sufficient adhesion . Further, with reference to Table 3, in the case of the sample with the film A used in Example 1, as compared with the result of the tensile test on the sample made only of the aluminum foil without the stress relieving portion as in Comparative Example 6, the elongation and the elastic strain It can be confirmed that remarkably improved.

Experimental Example  3 - Bending  Test

The performance of the secondary batteries according to Example 1 and Comparative Example 6 was measured before and after the bending test and the bending test.

(1) It is possible to maintain a capacity retention rate of 90% or more Bending  Number of times

The secondary battery for Example 1 and Comparative Example 6 was charged and discharged at 0.5 C, and the number of times of bending possible to maintain the capacity retention rate at 90% or more was measured and shown in Table 4 below.

division Bending times Example 1 More than 20,000 times Comparative Example 6 1,000 or less

(2) to respectively measure the discharging capacity and the capacity upkeep ratio of the discharge capacity and capacity retention ratio according to the number of times for bending the bending number of times shown in Table 5.

division 0 times 1000 times 20,000 times 50,000 times 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 Not measurable Not measurable

Referring to Tables 4 and 5, in the case of the lithium secondary battery according to Example 1 in which the film A containing the ethylene propylene copolymer, the hydrogenated hydrocarbon polymer and the polyethylene in a specific amount was applied as the first and second stress relieving portions, And the lithium secondary battery according to Comparative Example 6 in which the second stress relieving portion is not formed, as compared with the lithium secondary battery according to Comparative Example 6, and exhibits excellent capacity retention ratio.

While the preferred embodiments of the present invention have been described with reference to the drawings, it is to be understood that the present invention is not limited to the above-described embodiments, and various changes and modifications may be made by those skilled in the art And shall include all modifications of the scope which are deemed to be equivalent.

10: Secondary battery electrode assembly
1: first coating portion
2:
3: Second coating part
4:
11: first electrode
12: Second electrode
13: Separator
51: first electrode tab
52: second electrode tab
15: Outer material
P1: first stress relaxation portion
P2: the second stress relieving portion

Claims (16)

A first electrode including a first coating portion and a first non-coating portion located at least on one side of the first coating portion;
A second electrode including a second coating portion and a second non-coating portion located on at least one side of the second coating portion;
A separator interposed between the first electrode and the second electrode; And
At least one of a first stress relieving portion located in at least a part of the first uncoated portion and a second stress relieving portion located in at least a part of the second uncoated portion,
The first stress relieving portion and the second stress relieving portion may include:
An ethylene propylene copolymer, a hydrogenated hydrocarbon polymer, and polyethylene. The method according to claim 1,
The film has, on the basis of the entire film,
From 35 to 45% by weight of ethylene propylene copolymer,
35 to 45 wt% of the hydrogenated hydrocarbon polymer, and
And 10 wt% to 25 wt% of the polyethylene. The method according to claim 1,
Wherein the film has an adhesive strength in the range of 80 占 폚 to 200 占 폚. The method according to claim 1,
The first stress relieving portion includes:
Wherein the second coating part is disposed on the first non-coating part and is spaced apart from the first coating part by a predetermined distance. The method according to claim 1,
Wherein the second stress relieving portion comprises:
And a second coating unit disposed on the second uncoated portion and spaced apart from the second coating unit by a predetermined distance. The method according to claim 1,
The first stress relieving portion includes:
And the first stress relieving portion is disposed on the first uncoated portion, and one side of the first stress relieving portion contacts the first coated portion. The method according to claim 1,
Wherein the second stress relieving portion comprises:
Wherein the first stress relieving portion is located on the second uncoated portion and the one side of the second stress relieving portion is in contact with the second coated portion. The method according to claim 1,
Wherein the first unoided portion is integrally formed with the first electrode tab,
Wherein the second uncoated portion is integrally formed with the second electrode tab. 9. The method of claim 8,
Wherein the first electrode tab comprises:
A second electrode assembly disposed on one side in the width direction of the secondary battery assembly,
The second electrode tab may include:
Wherein the first electrode tab and the second electrode tab are disposed in the same direction as the first electrode tab, and are spaced apart from the first electrode tab by a predetermined distance. 9. The method of claim 8,
Wherein the first electrode tab comprises:
The electrode assembly for a secondary battery,
The second electrode tab may include:
And an electrode assembly for a secondary battery, the electrode assembly being located on the other side of the electrode assembly in the longitudinal direction of the secondary battery assembly. 9. The method of claim 8,
Wherein at least one of the first electrode tab and the second electrode tab includes a bent portion bent in the longitudinal direction of the first electrode tab and the second electrode tab. The method according to claim 1,
Wherein the first electrode and the second electrode are made of a metal,
Wherein a plurality of the electrode assemblies are stacked alternately with the separator interposed therebetween. An electrode assembly for a secondary battery according to any one of claims 1 to 12; And
An outer casing accommodating the electrode assembly for the secondary battery;
. ≪ / RTI > 14. The method of claim 13,
Wherein the first stress relieving portion is in contact with a part of the rim of the casing. 14. The method of claim 13,
And the second stress relieving portion is in contact with a part of the rim of the casing. 14. The method of claim 13,
Wherein the secondary battery has a flexible characteristic.

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