Secondary battery and device including the same

Abstract

A secondary battery according to one embodiment of the present disclosure includes an electrode assembly including electrode sheets having electrode tabs and separators between the electrode sheets, a battery case in which the electrode assembly is accommodated, and an electrode lead connected to the electrode tabs and protruding to the outside of the battery case. The electrode lead includes a flexible portion having stretchability in a direction parallel to a protruding direction of the electrode lead, and the flexible portion is located inside the battery case.

Description

TECHNICAL FIELD

[0001] Cross Reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0165723, filed December 1, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

[0003] The disclosure relates to a secondary battery and a device including the same, and more particularly, to a secondary battery that prevents an electrode tab from being disconnected and a device including the same. BACKGROUND

[0004] Recently, as energy prices are rising due to depletion of fossil fuels and environmental pollution is increasingly being concerned, demand for environmentally friendly alternative energy is bound to play an important role in future life. Accordingly, research on various power generation technologies such as nuclear power, solar power, wind power, and tidal power is in progress, and energy storage devices that more effectively utilize generated energy are also attracting attention.

[0005] In particular, along with the technological development and increasing demand for mobile devices, the demand for batteries as energy sources has rapidly increased, and accordingly, a great deal of research has been conducted on batteries that can satisfy various needs.

[0006] In general, there is a high demand for lithium secondary batteries such as lithium ion batteries or lithium ion polymer batteries, which have advantages such as high energy density, discharge voltage, output stability, etc.

[0007] In addition, secondary batteries can be classified based on the structure of an electrode assembly having a structure in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween. In general, for example, a jelly-roll type electrode assembly having a structure in which a long positive electrode tab and a long negative electrode tab are wound in a state in which a separator is interposed therebetween, a stacked type electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes cut in a certain size unit are sequentially stacked with a separator interposed therebetween, etc. can be mentioned. In recent years, in order to solve problems caused by the jelly-roll type electrode assembly and the stacked type electrode assembly, a stacked / folded type electrode assembly, which is a combination of the jelly-roll type electrode assembly and the stacked type electrode assembly, having a structure in which unit cells in which positive electrodes and negative electrodes of a predetermined unit are stacked are sequentially wound with a separator interposed therebetween are disposed on a separator film, has been developed.

[0008] In addition, based on the shape of the battery case, secondary batteries can be classified into cylindrical batteries in which an electrode assembly is installed in a cylindrical case, prismatic batteries in which an electrode assembly is installed in a prismatic can, and pouch-type batteries in which an electrode assembly is installed in a pouch-type case of an aluminum laminate sheet.

[0009] Figure 1 is a perspective view of a conventional pouch-type secondary battery, and Figure 2 is a cross-sectional view taken along a cutting line A-A' of Figure 1 .

[0010] Referring to Figure 1 and Figure 2 , a conventional pouch-type battery cell 10 can be manufactured by accommodating an electrode assembly 20 inside a pouch case 300 and then sealing the case. The electrode assembly 20 can include electrodes and a separator disposed between the electrodes. The electrodes include electrode tabs 21t, and the electrode tabs 21t can be joined to electrode leads 40 by a method such as welding. When the electrode leads 40 are exposed to the outside of the pouch-type battery case 30, electrical connection of the electrode assembly 20 can be made.

[0011] In this case, the electrode assembly 20 can be a stacked-type electrode assembly in which a plurality of electrodes cut in a predetermined size unit are sequentially stacked with a separator interposed therebetween. All of the electrode tabs 21t extending from the respective electrodes can be joined to the electrode leads 40.

[0012] When repeatedly charged and discharged, the electrode assembly 20 repeatedly shrinks and swells. As shown in Figure 2 , the electrode assembly 20 causes swelling in the thickness direction thereof (a direction parallel to the z-axis). Since the electrode leads 40 included in the conventional secondary battery 10 are not flexible and are interposed between the sealed battery cases 30, there is no choice but to fix the positions except in a state in which the electrode tabs 21t are joined. At this time, when the electrode assembly 20 swells in the thickness direction thereof (a direction parallel to the z-axis), the electrode leads 40 are fixed, and thus a large tension is generated on the electrode tabs 21t. In particular, in the stacked-type electrode assembly, the outermost electrode tabs 21t exert the greatest tension when the electrode assembly 20 swells, and thus, in the worst case, this can cause disconnection.

[0013] Therefore, there is a need to develop a technology that can prevent the electrode tabs from being disconnected when the electrode assembly swells. SUMMARY

[0014] TECHNICAL PROBLEM

[0015] An object of the present disclosure is to provide a secondary battery that can reduce a tension applied to electrode tabs and prevent outermost electrode tabs from being disconnected even when an electrode assembly swells.

[0016] However, the technical problems to be solved by embodiments of the present disclosure are not limited to the above problems, and can be variously extended within the scope of the technical idea included in the present disclosure.

[0017] Technical solution

[0018] According to one embodiment of the present disclosure, there is provided a secondary battery including: an electrode assembly including electrode tabs formed with electrode joints and separators between the electrode tabs; a battery case in which the electrode assembly is accommodated; and an electrode lead connected to the electrode joints and protruding to the outside of the battery case, wherein the electrode lead includes a flexible portion having stretchability in a direction parallel to a protruding direction of the electrode lead, and wherein the flexible portion is located inside the battery case.

[0019] The flexible portion can have a curved shape.

[0020] The flexible portion can be stretchable in a direction parallel to a protruding direction of the electrode lead.

[0021] The flexible portion can include at least one of gold (Au) and silver (Ag).

[0022] The battery case can include an upper case and a lower case, a sealing portion of the upper case and a sealing portion of the lower case can be heat-sealed to each other, and the flexible portion can be located between a portion of the electrode lead where the sealing portion is located and the electrode assembly.

[0023] The electrode lead can include a first portion connected to the flexible portion and the electrode joint; a second portion connected to the flexible portion and protruding to the outside of the battery case; and a fixing portion connected to each of the first portion and the second portion.

[0024] The flexible portion can include a first flexible portion and a second flexible portion, and the fixing portion can be located between the first flexible portion and the second flexible portion.

[0025] The fixing portion can include at least one of an alloy material having low flexibility, a glass material, a ceramic material, and carbon graphite.

[0026] The fixing portion can have a straight shape.

[0027] The electrode assembly can be a stacked-type electrode assembly in which the electrode tabs are stacked, and the flexible portion can be stretchable in a direction perpendicular to a thickness direction of the electrode tabs when the electrode tabs are expanded in the thickness direction.

[0028] Advantageous effects

[0029] According to the embodiments of the present disclosure, a flexible portion is formed on an electrode lead, thereby reducing tension applied to an electrode joint even when an electrode assembly is expanded. Thus, it is possible to prevent the outermost electrode joint from being disconnected.

[0030] Effects of the present disclosure are not limited to the above-mentioned effects, and other additional effects not described above will be clearly understood by those skilled in the art from the description of the appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a perspective view of a conventional pouch-type secondary battery;

[0032] Figure 2 is a cross-sectional view taken along a cutting line A-A' of Figure 1

[0033] Figure 3 is an exploded perspective view of a secondary battery according to an embodiment of the present disclosure;

[0034] Figure 4 is a perspective view showing an assembled state of a secondary battery of Figure 3

[0035] Figure 5 Figure 4

[0036] Figure 6 is a plan view of an electrode lead included in a secondary battery of Figure 5

[0037] Figure 7 is a cross-sectional view showing a state in which an electrode assembly swells with respect to an electrode lead and an electrode assembly included in a secondary battery of Figure 5

[0038] Figure 8 is a cross-sectional view showing an electrode assembly and an electrode lead according to a modified embodiment of the present disclosure;

[0039] Figure 9 is a plan view of an electrode assembly and an electrode lead viewed in a -z-axis direction on an xy plane of Figure 8

[0040] Figure 10 is a plan view showing an electrode lead according to another modified embodiment of the present disclosure. DETAILED DESCRIPTION

[0041] Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily perform them. The present disclosure can be modified in various different ways, and is not limited to the embodiments set forth herein.

[0042] ​​​​​​​For the sake of clarity of the disclosure, portions unrelated to description will be omitted and the same reference numbers designate the same elements throughout the description.

[0043] Also, in the drawings, the size and the thickness of each element are arbitrarily illustrated for the convenience of description, and the disclosure is not necessarily limited to those illustrated in the drawings. In the drawings, the thickness of layers, regions, and the like is exaggerated for clarity. In the drawings, the thickness of some layers and regions is exaggerated for the convenience of description.

[0044] Also, it will be understood that when an element such as a layer, film, region, or plate is referred to as being "on" or "above" another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being "directly on" another element, then there are no intervening elements present. Also, the word "on" or "above" means that an element is positioned above or below the reference portion, and does not necessarily mean that the element is positioned at the upper end of the reference portion in the direction opposite to the direction of gravity.

[0045] Also, throughout the description, when a portion is referred to as "including" or "comprising" a certain component, it means that the portion can further include other components without excluding the other components, unless otherwise specified.

[0046] Also, throughout the description, when referred to as "planar", it means that the target portion is observed from the upper side, and when referred to as "cross-sectional", it means that the target portion is observed from the side of the cross-section cut vertically.

[0047] Figure 3 is an exploded perspective view of a secondary battery according to an embodiment of the disclosure. Figure 4 is a perspective view showing Figure 3 an assembled state of the secondary battery of Figure 5 is a cross-sectional view taken along Figure 4 cutting line B-B' of

[0048] Referring to Figures 3 to 5 , the secondary battery 100 according to an embodiment of the disclosure includes an electrode assembly 200, a battery case 300 in which the electrode assembly 200 is accommodated, and electrode leads 400 and 500 protruding to the outside of the battery case 300.

[0049] The electrode assembly 200 includes electrode tabs 210 and 220 formed with electrode terminals 210t and a separator 230 positioned between the electrode tabs 210 and 220. Specifically, the electrode assembly 200 according to the present embodiment can be a stacked-type electrode assembly, a jelly-roll type electrode assembly, or a stacked / folded-type electrode assembly, but is preferably a stacked-type electrode assembly. Specifically, the stacked-type electrode assembly can have a structure in which a plurality of electrode tabs 210 and 220 are stacked with the separator 230 interposed therebetween.

[0050] Each of the electrode sheets 210 and 220 can be formed by coating an electrode active material onto an electrode current collector, and a portion of the electrode current collector can protrude to provide the electrode tab 210t. The electrode sheets 210 and 220 can be divided into a positive electrode sheet and a negative electrode sheet, and the separator 230 can be interposed between the positive electrode sheet and the negative electrode sheet. As an example, the electrode sheet 210 can be a positive electrode sheet, and the electrode tab 210t protruding therefrom can be a positive electrode tab. The other electrode sheet 220 can be a negative electrode sheet, and an electrode tab (not shown) protruding therefrom can be a negative electrode tab.

[0051] In addition, the electrode tab according to the present embodiment can be connected to an electrode lead. As an example, the electrode tab 210t having either polarity can be joined to either electrode lead 400, and the electrode tab (not shown) having the other polarity can be joined to the other electrode lead 500. These electrode leads 400 and 500 can protrude from both end portions of the battery case 300. Figure 3 and Figure 4 It is shown that the two electrode leads 400 and 500 protrude in opposite directions to each other, but the direction of protrusion is not particularly limited. That is, a structure in which the two electrode leads 400 and 500 protrude in the same direction from one side of the secondary battery 100 is also possible. One of the two electrode leads 400 and 500 can be a positive electrode lead, and the other can be a negative electrode lead.

[0052] Furthermore, the battery case 300 according to the present embodiment can be a pouch-type case. The battery case 300 can include an upper case 310 and a lower case 320 that are heat-sealed to each other. Although not specifically shown in the figure, the battery case 300 including the upper case 310 and the lower case 320 can be a laminate sheet including a resin layer and a metal layer. Specifically, each of the upper case 310 and the lower case 320 can include an inner resin layer for sealing, a metal layer for preventing material permeation, and an outer resin layer located at the outermost side.

[0053] The outer resin layer has excellent tensile strength and weather resistance compared to its thickness, and can have electrical insulation so as to protect the pouch-type secondary battery 100 from external influences. The outer resin layer can contain a polyethylene terephthalate (PET) resin or a nylon resin. The metal layer can prevent air, moisture, etc. from flowing into the pouch-type secondary battery 100. The metal material can include aluminum (Al). The inner resin layers can be heat-sealed to each other by applied heat and pressure in a state in which the electrode assembly 200 is mounted. The inner resin layers can include cast polypropylene (CPP) or polypropylene (PP).

[0054] The recessed storage portions 310R and 320R in which the electrode assembly 200 can be disposed can be formed in each of the upper case 310 and the lower case 320, and the electrode assembly 200 can be stored in the storage portions 310R and 320R. A method of forming the storage portions 310R and 320R is not particularly limited, and a deep drawing process using a punch can be applied.

[0055] Sealing portions 310S and 320S can be provided along the outer periphery of each of the storage portions 310R and 320R of the upper case 310 and the lower case 320. The sealing portion 310S of the upper case 310 and the sealing portion 320S of the lower case 320 can be heat-sealed to each other to seal the battery case 300. More specifically, the inner resin layer of the sealing portion 310S of the upper case 310 and the inner resin layer of the sealing portion 320S of the lower case 320 can be heat-sealed in a state of facing each other. In addition, Figure 3 The upper case 310 and the lower case 320 that form the storage portions and are separated from each other are exemplified, but can be a laminate in which one side portion of the upper case 310 and one side portion of the lower case 320 are integrally formed, and can be a plate-shaped structure in which the storage portions are formed only in one of the upper case and the lower case and the storage portions are not formed in the other.

[0056] Next, the flexible portion formed on the electrode lead according to the embodiment of the disclosure will be described in detail with reference to Figure 5 and Figure 6 . To avoid repetitive description, either one of the two electrode leads 400 and 500 will be mainly described, but it is needless to say that the structure of the flexible portion according to the present embodiment can also be formed in the other electrode lead 500.

[0057] Figure 6 is a plan view of an electrode lead included in a secondary battery viewed in the -z-axis direction on an xy plane. Figure 5

[0058] With reference to Figure 3 , Figure 5 and Figure 6 , the electrode lead 400 according to the present embodiment has a flexible portion 400f that has stretchability in a direction parallel to the protruding direction of the electrode lead 400 (a direction parallel to the y-axis) and that is located inside the battery case 300.

[0059] Specifically, the flexible portion 400f according to the present embodiment has a curved shape and can be stretched in a direction parallel to the protruding direction of the electrode lead 400 (a direction parallel to the y-axis). In other words, the flexible portion 400f according to the present embodiment can be in a form that is compressed in a direction parallel to the protruding direction of the electrode lead 400 (parallel to the y-axis). ​

[0060] The flexible portion 400f is preferably made of a material having excellent ductility, malleability, elasticity, and toughness, and can include, for example, at least one of gold (Au) and silver (Ag). Such a flexible portion 400f can be formed in the middle of the electrode lead 400. Specifically, as shown in Figure 5 and Figure 6 indicated, the existing plate-shaped metal material constituting the electrode lead 400 can be joined to both ends of the metal material constituting the flexible portion 400f by a method such as welding. That is, for example, the electrode lead 400 including the flexible portion 400f can be manufactured by welding a metal member including aluminum (Al) or copper (Cu) to both ends of a metal member including silver (Ag).

[0061] Figure 7 is a cross-sectional view showing the state of expansion of the electrode lead and the electrode assembly included in the secondary battery of Figure 5 with respect to

[0062] In the conventional electrode assembly 20 (see Figure 2 ), since the electrode lead 40 is not flexible and its position is fixed, a large tension is generated in the electrode tab 21t along with the expansion of the electrode assembly 20, and the outermost electrode tab 21t is at risk of being broken. On the other hand, referring to Figure 7 along with Figure 5 and Figure 6 , since the flexible portion 400f of the electrode lead 400 according to the present embodiment has stretchability, it can stretch in a direction perpendicular to the thickness direction when the electrode assembly 200 expands in the thickness direction (a direction parallel to the z-axis). In other words, along with the expansion of the electrode assembly 200, the flexible portion 400f according to the present embodiment can stretch in a direction parallel to the protruding direction of the electrode lead 400 (parallel to the y-axis), particularly, in a direction in which the electrode assembly 200 is located (-y-axis direction).

[0063] By stretching the flexible portion 400f, it is possible to prevent an excessive tension from being generated in the electrode tab 210t, and it is possible to prevent the outermost electrode tab 210t from being broken.

[0064] At this time, as described above, the flexible portion 400f included in the electrode lead 400 is located inside the battery case 300. Specifically, referring again to Figure 5The sealing portions 310S of the upper case 310 and 320S of the lower case 320 are heat-sealed to each other, and the flexible portion 400f can be located between the portion of the electrode lead 400 in which the sealing portions 310S and 320S are located and the electrode assembly 200. If the flexible portion 400f is formed in an outer portion that is outside the portion of the electrode lead 400 in which the sealing portions 310S and 320S are located, because it is outside the portion fixed by the sealing portions 310S and 320S, the tension applied to the electrode tab 210t cannot be reduced when the electrode assembly 200 swells. Therefore, it is preferable that the flexible portion 400f according to the present embodiment be formed inside the battery case 300.

[0065] Next, the fixed portion according to the modified embodiment of the present disclosure will be described in detail with reference to Figures 8 to 9 .

[0066] Figure 8 is a cross-sectional view illustrating an electrode assembly and an electrode lead according to the modified embodiment of the present disclosure. Figure 9 is a plan view of the electrode assembly and the electrode lead viewed in the -z-axis direction on the xy plane. Figure 8 In particular, Figure 8 corresponds to a cross section taken along the yz plane, similar to Figure 5 or Figure 7 .

[0067] With reference to Figure 8 and Figure 9 , the formation of the flexible portion 400f' on the electrode lead 400' according to the modified embodiment of the present disclosure is similar to the above, but a fixed portion 430 can also be formed.

[0068] Specifically, the electrode lead 400' according to the present embodiment can include a first portion 410 connected to the flexible portion 400f' and the electrode tab 210t, a second portion 420 connected to the flexible portion 400f' and protruding to the outside of the battery case, and a fixed portion 430 connected to each of the first portion 410 and the second portion 420.

[0069] More specifically, the flexible portion 400f' according to the present embodiment can include a first flexible portion 400f1 and a second flexible portion 400f2. The first portion 410 can be joined to one end of each of the first flexible portion 400f1 and the second flexible portion 400f2, and the second portion 420 can be joined to the other end of each of the first flexible portion 400f1 and the second flexible portion 400f2. As a joining method, welding joining can be used as described above.

[0070] In this case, the fixing portion 430 can be connected to each of the first portion 410 and the second portion 420 while being positioned between the first flexible portion 400fl and the second flexible portion 400f2. Among them, the fixing portion 430 can also be connected to each of the first portion 410 and the second portion 420 by a method such as welding, respectively.

[0071] Any material that can be easily cut or broken can be applied to the fixing portion 430 without particular limitation. In one example, the fixing portion 430 can include at least one of an alloy material having low flexibility, a glass material, a ceramic material, and carbon graphite. In addition, unlike the flexible portion 400f' having a serpentine shape, the fixing portion 430 can have a straight shape.

[0072] Since the flexible portion 400f' includes a material having excellent ductility, forgeability, elasticity, and toughness, the flexible portion 400f' is not fixed during welding of the electrode tip 210t to the electrode lead 400', so that the welding cannot be smoothly performed. Therefore, in the present embodiment, the fixing portion 430 having a straight shape can be provided to fix the compressed form of the flexible portion 400f'. In addition, since the fixing portion 430 can maintain the distance between the first portion 410 and the second portion 420 constant, it is possible to prevent the flexible portion 400f' from being stretched even before the electrode assembly 200 is expanded. Alternatively, since the fixing portion 430 according to the present embodiment includes a metal material having slightly weak strength, it is cut off as the electrode assembly 200 is expanded, without hindering the stretching of the flexible portion 400f'.

[0073] Further, Figure 10 is a plan view showing an electrode lead according to another modified embodiment of the present disclosure, which specifically shows the position of the deformed fixing portion 430. The electrode lead 400" according to the present embodiment can include a first portion 410, a second portion 420, and a fixing portion 430. The position and the number of the fixing portion 430 according to the present embodiment are not limited as long as it connects the first portion 410 and the second portion 420. As an example, with reference to Figure 10 , one flexible portion 400f" connected to the first portion 410 and the second portion 420 is formed, and two fixing portions 430 can be connected to each of the first portion 410 and the second portion 420 with one flexible portion 400f" interposed therebetween. That is, the two fixing portions 430 can be disposed on both sides in the x-axis direction of the flexible portion 400f". Figure 10 The fixing portion 430 shown in

[0074] Further, referring again to Figure 3 and Figure 5 The lead film 600 can be positioned on each of the electrode leads 400 and 500. The lead film 600 can be positioned between the upper case 310 and the lower case 320 in the form of being wrapped around the electrode leads 400 and 500, respectively.

[0075] The lead film 600 can not only prevent a short circuit from occurring between the electrode leads 400 and 500 and the metal layer of the battery case 300, but also improve the sealing property of the pouch-type battery case 300. The electrode leads 400 and 500 made of a metal material have a slightly large contact resistance when heat-sealed to the inner resin layer of the pouch-type battery case 300, which can cause a decrease in surface adhesion. However, if the lead film 600 is provided as in the present embodiment, such a decrease in adhesion phenomenon can be prevented. In addition, the lead film 600 includes an insulating material, and thus can prevent an electric current from being applied from the electrode leads 400 and 500 to the pouch-type battery case 300.

[0076] The lead film 600 can be formed of a film having insulating properties and heat-sealing properties. The lead film 600 can include, for example, at least one of polyimide (PI), polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET).

[0077] Although terms indicating directions such as front, rear, left, right, upper, and lower directions are used herein, these are merely proposed for the convenience of explanation, and can differ depending on the position of an observer, the position of an object, etc.

[0078] The secondary battery according to the embodiment of the present disclosure mentioned above can be gathered in a plurality to form a battery module. Such a battery module can be installed together with various control and protection systems such as a BMS (Battery Management System) and a cooling system to form a battery pack.

[0079] The secondary battery, the battery module, and the battery pack can be applied to various devices. Such a device can be applied to a vehicle device such as an electric bicycle, an electric vehicle, or a hybrid vehicle, but the present disclosure is not limited thereto, and is applicable to various devices in which a secondary battery can be used.

[0080] Although preferred embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present disclosure defined in the appended claims also fall within the scope of the present disclosure.

[0081] Explanation of Reference Numerals

[0082] 200: electrode assembly

[0083] 300: battery case

[0084] 400, 500: electrode lead

[0085] 400f: flexible portion

Claims

1.A secondary battery comprising: an electrode assembly including electrode sheets in which electrode tabs are formed and separators between the electrode sheets; a battery case in which the electrode assembly is accommodated; and an electrode lead connected to the electrode tabs and protruding to the outside of the battery case, wherein the electrode lead includes a flexible portion having stretchability in a direction parallel to a protruding direction of the electrode lead, and wherein the flexible portion is located inside the battery case, wherein the electrode lead includes a first portion connected to the flexible portion and the electrode tabs, a second portion connected to the flexible portion and protruding to the outside of the battery case, and a fixed portion connected to each of the first portion and the second portion, wherein the fixed portion is cut off as the electrode assembly swells without hindering the stretchability of the flexible portion. 2.The secondary battery of claim 1, wherein the flexible portion has a curved shape. 3.The secondary battery of claim 1, wherein a material of the flexible portion includes at least one of gold (Au) and silver (Ag). 4.The secondary battery of claim 1, wherein the battery case includes an upper case and a lower case, a sealing portion of the upper case and a sealing portion of the lower case are heat-sealed to each other, and the flexible portion is located between the portion of the electrode lead in which the sealing portion is located and the electrode assembly. 5.The secondary battery of claim 4, wherein the flexible portion includes a first flexible portion and a second flexible portion, and the fixed portion is located between the first flexible portion and the second flexible portion. 6.The secondary battery of claim 4, wherein the fixed portion includes at least one of an alloy material, a glass material, a ceramic material, and carbon graphite. 7.The secondary battery of claim 4, wherein the fixed portion has a straight shape. 8.The secondary battery of claim 1, wherein the electrode assembly is a stacked-type electrode assembly in which the electrode sheets are stacked, and when the electrode sheets swell in a thickness direction, the flexible portion stretches in a direction perpendicular to the thickness direction. 9.An apparatus comprising the secondary battery of any one of claims 1-8.

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