KR101123061B1 - Secondary Battery of Improved Safety - Google Patents

Abstract

In the secondary battery according to the present invention, an electrode assembly having a cathode / separation membrane / cathode structure is sealed in a case of a laminate sheet, and the sealing is performed by heat-sealing the outer circumferential surface of the housing in a state where the electrode assembly is mounted in the housing of the case. And at least a part of the sealing portion formed by the thermal fusion is in a state in which a polymer resin having a melting point lower than that of the thermal fusion polymer of the sheet is added at a position not in contact with the electrolyte solution within a range of 50% of the width width of the sealing portion. Provided is a secondary battery characterized in that thermal fusion is performed.

Therefore, the secondary battery according to the present invention does not weaken the sealing property of the battery and at the same time, it effectively releases the high-pressure gas inside the battery to effectively block the risk of ignition or explosion on the battery and improve the safety of the battery. There is.

Description

Secondary Battery of Improved Safety

1 is an exploded perspective view of a general structure of a conventional pouch type secondary battery;

2 is an exploded perspective view of a secondary battery according to one embodiment of the present invention;

3A is a cross-sectional view illustrating a heat fusion process of a conventional secondary battery, and FIG. 3B is a sectional view showing a heat fusion process of a secondary battery according to one embodiment of the present invention;

4 to 10 are front views illustrating structures of secondary batteries according to embodiments of the present invention, respectively.

A secondary battery in which an electrode assembly having a cathode / separation membrane / cathode structure according to the present invention is sealed in a case of a laminate sheet, wherein the outer circumferential surface of the housing is heat-sealed to seal the electrode assembly in an accommodating portion of the case. At least a portion of the sealing portion formed by the heat fusion is heat in a state in which a polymer resin having a melting point lower than that of the heat fusion polymer of the sheet is added at a position not in contact with the electrolyte solution within 50% of the width width of the sealing portion. It relates to a secondary battery composed of fusion welding.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches on lithium secondary batteries with high energy density and discharge voltage have been conducted and commercialized. It is widely used.

In general, a secondary battery is composed of an electrode assembly composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode in a stacked or wound state, embedded in a battery case of a metal can or laminate sheet, and then injected or impregnated with an electrolyte solution. have.

One of the major research tasks in such secondary batteries is to improve safety. For example, secondary batteries may be subjected to high temperatures inside the cell, which may be caused by abnormal operating conditions of the battery, such as internal short circuits, overcharge conditions exceeding the allowed currents and voltages, exposure to high temperatures, deformation due to drops or external shocks, and High pressure can cause the battery to explode.

As one of the safety problems, the internal short circuit due to shrinkage or breakage of the separator generated when the battery is exposed to high temperature is a very serious situation, and many studies have been made on the cause and alternatives.

Generally, a porous polymer film such as polyethylene or polypropylene is used as the separator, and the separator has an advantage of being inexpensive and excellent in chemical resistance, and thus desirable for operation of a battery, but easily shrinkable in a high temperature environment.

In order to solve this problem, a method of applying and attaching an adhesive layer between the separator and the electrode is generally used. As such an adhesive layer, PVdF etc. which are used also as a binder of an electrode active material are mainly used. However, such an adhesive layer has a disadvantage in that the mobility of ions is lowered than in the case where it is not applied, thereby showing low rate characteristics. In addition, since the work of applying the adhesive layer itself must be added as a separate process, it also causes many problems with the increase in the number of work processes.

On the other hand, in the pouch type secondary battery, the sealing force of the battery case is lowered, so that the problem of leakage of the electrolyte frequently occurs. FIG. 1 is a schematic exploded perspective view of a general structure of a conventional representative pouch type secondary battery.

Referring to FIG. 1, the pouch type secondary battery 10 may include an electrode assembly 30, electrode tabs 40 and 50 extending from the electrode assembly 30, and electrodes welded to the electrode tabs 40 and 50. And a battery case 20 accommodating the leads 60 and 70 and the electrode assembly 30.

The electrode assembly 30 is a power generator in which a positive electrode and a negative electrode are sequentially stacked in a state where a separator is interposed therebetween, and has a stack type or a stack / fold type structure. The electrode tabs 40, 50 extend from each pole plate of the electrode assembly 30, and the electrode leads 60, 70 are welded, for example, with a plurality of electrode tabs 40, 50 extending from each pole plate. Each is electrically connected to each other, and part of the battery case 20 is exposed to the outside. In addition, an insulating film 80 is attached to a portion of the upper and lower surfaces of the electrode leads 60 and 70 in order to increase the sealing degree with the battery case 20 and to secure an electrical insulating state.

The battery case 20 is made of an aluminum laminate sheet, provides a space for accommodating the electrode assembly 30, and has a pouch shape as a whole.

The secondary battery 10 is manufactured by heat-sealing the contact portions of the outer circumferential surface of the battery case 20 with the electrode assembly 30 mounted on the accommodating portion of the battery case 20. When an abnormal operating state such as overcharge or exposure to high temperature is reached, the internal electrolyte is decomposed to generate high pressure gas. The generated high pressure gas may cause deformation of the battery case and shorten the life of the battery, and may seriously cause ignition or explosion of the battery.

Therefore, various attempts have been made to prevent the ignition or explosion of the battery and to discharge the gas efficiently when such a high pressure gas is generated. For example, Japanese Patent Application Laid-Open No. 2005-116235 discloses a battery in which the outer circumferential portion of a laminate film containing an electrode assembly is thermally fused to be sealed. The technique which has a gas discharge | release mechanism, such as making the width | variety of the sealing part fusion | melting relatively small is disclosed. However, since the above technique merely weakens the sealing force on a specific portion of the sealing portion that is heat-sealed to discharge the high pressure gas, moisture into the battery cell through the specific portion of which the sealing force is weakened during repeated charging and discharging processes. There is a problem that permeation and leakage of electrolyte solution are concerned.

Japanese Patent No. 3,638,765 discloses a battery in which a plate-shaped electrode assembly is accommodated in an exterior member and the outer peripheral portion of the exterior member is sealed by heat fusion or an adhesive layer. By sealing in the state which inserted the polymer resin sheet, the technique which comprises so that one side of the sealed part may have the breakdown-pressure performance compared with the other part is disclosed. In addition, Japanese Patent Application Laid-Open No. 2001-093489 discloses a battery in which an electrode assembly is embedded in a pouch type battery case of a laminate sheet, and at the same time, the positive and negative leads connected to the positive electrode plate and the negative electrode plate are drawn out from the sealing portion of the outer case to the outside. In this case, a technique is disclosed in which a part of the sealing portion of the outer case is thermally fused in a state in which a heat fusion resin sheet having a lower melting point than that of a laminate sheet is inserted.

However, all of the above techniques have serious problems since the resin fragments to be inserted are exposed to the electrolyte solution inside the battery cell at the inner end of the sealing portion. The problem is described below.

As the electrolyte of the secondary battery, a non-aqueous liquid electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used. These electrolytes are characterized by having a strong polarity in most cases to cause an electrochemical reaction with the active material applied to the positive electrode plate. The difference in the material between the case material of the battery cell itself and the polymer resin sheet to be inserted causes a difference in reactivity between the electrolyte with a strong polarity, which is directly connected to a weakening of the sealing part.

In addition, when the polymer resin of another material is inserted in the sealing portion to be heat-sealed, even if the heat-sealing process, a minute crack occurs in the junction between the different polymer resin, and the charge and discharge process repeatedly Due to such fine cracks in the process, the life of the battery may be shortened, and the problem may occur that the electrolyte may leak to the outside through the generated cracks.

In particular, a secondary battery used in a medium-large battery pack as a power source of an electric vehicle, a hybrid vehicle, etc. needs a long lifespan, and it is very important to secure safety due to the fact that many battery cells are concentrated.

Accordingly, by effectively releasing high pressure gas that may occur due to unexpected development while preventing the penetration of water and leakage of electrolyte, it is possible to prevent the ignition or explosion of the battery cell in advance, thereby prolonging the life and stability of the battery. There is a high necessity for a technology that can secure the safety.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

An object of the present invention is to prevent the water infiltration of the battery and leakage of the electrolyte, and at the same time to efficiently discharge the high-pressure gas inside the battery cell to prevent the risk of ignition or explosion on the battery in advance to ensure improved safety It is to provide a secondary battery.

Accordingly, the secondary battery according to the present invention is a secondary battery in which an electrode assembly having a cathode / separation membrane / cathode structure is sealed in a case of a laminate sheet, and the outer circumferential surface of the accommodating portion is opened while the electrode assembly is mounted in the accommodating portion of the case. Sealing is performed, and at least a part of the sealing portion formed by the thermal fusion is formed at a position where the polymer resin having a melting point lower than that of the heat-sealing polymer of the sheet is not in contact with the electrolyte solution within 50% of the width width of the sealing portion. It consists of heat-sealing performed in the added state.

Therefore, the present invention by adding the polymer resin in the range within 50% of the width width of the sealing portion, when the gas is generated inside the battery cell to form a high pressure, the portion to which the polymer resin is added first open compared to other parts As a result, the internal gas is efficiently discharged. In other words, it is possible to prevent the ignition or explosion of the battery by inducing efficient release of the gas inside the battery cell while minimizing the deterioration of the sealing of the battery cell due to the addition of the polymer resin.

The laminate sheet has a structure including an inner resin layer that is heat-sealed, a barrier metal layer and an outer resin layer having excellent durability, and in the sealing portion where the laminate sheets are in contact with each other, the inner resin layers are mutually bonded by heat fusion. The metal layers are bonded to each other by welding in a structure surrounding the coupling parts of the inner resin layers, and the outer resin layers are mutually bonded by heat fusion or a separate resin in a structure surrounding the coupling parts of the metal layers. .

The polymer resin of the inner resin layer is preferably a polyolefin-based resin having heat sealability (heat adhesion), low hygroscopicity to suppress invasion of the electrolyte solution, and not expanded or eroded by the electrolyte solution. Can be used, more preferably unstretched polypropylene (cPP) can be used.

The barrier metal layer is preferably aluminum may be used to exhibit a function of improving the strength of the battery case in addition to the function of preventing the inflow or leakage of foreign substances such as gas, moisture.

Since the outer resin layer should have excellent resistance from the external environment, it is necessary to have a tensile strength and weather resistance of at least predetermined. In such aspect, a stretched nylon film or polyethylene terephthalate (PET) may be preferably used as the polymer resin of the outer resin layer.

Adhesion of the secondary battery sealing part should be a structure that can be easily opened when the volume changes due to the generation of internal gas, but if the volume expansion does not have to be strongly bonded. Therefore, the secondary battery according to the present invention was added to the low-melting point dissimilar polymer resin other than the non-stretched polypropylene (cPP) to the adhesive portion of the laminate sheet to ensure a sufficient adhesive force in the normal region, but can be opened quickly upon volume expansion.

The secondary battery according to the present invention is thermally fused in a state where a low melting polymer resin is added to a sealing portion of an internal resin layer. When the secondary battery is exposed to overcharge or high temperature, the internal temperature of the battery cell increases and the electrolyte is decomposed to generate gas. When the temperature of the battery rises above a certain level, the polymer resin having a low melting point is melted first to form an outlet of the internal gas. Therefore, the low melting point polymer resin is composed of a material having a melting point difference of more than a predetermined level with respect to the internal resin layer, the melting point difference is preferably between 10 to 50 ℃. If the melting point difference is less than 10 ℃, the difference in the breakdown voltage performance is not large, and the effect of preventing the ignition of the battery is insignificant, and if the melting point is higher than 50 ℃, the melting point of the polymer resin is too low to decrease the sealing of the battery This is because the effect of preventing the leakage of the electrolyte to the penetration of water is inferior.

As a preferred example, since the non-stretched polypropylene (cPP) used as the inner resin layer of the laminate sheet has a melting point of about 160 ° C., the polymer resin added to impart precise temperature selectivity thereto is Polyethylene (PE) with a melting point of about 135 ° C. may be used.

The low-melting polymer resin may be added without limitation of a particular shape, but may be added in the form of a film for the ease of manufacturing to the efficiency of the addition process of the polymer resin, particularly preferably coated in the form of a thin film is added It may be a structure.

In the secondary battery according to the present invention, the low melting point polymer resin is added to a position not in contact with the electrolyte, for example, the low melting point polymer resin is added to the sealing part and completely wrapped by the sealing part in a heat-sealed state. In some cases, the low melting polymer resin is added to the sealing portion and at least a portion of the low melting polymer resin is in contact with the outside of the battery or in the center portion of the sealing portion to be completely sealed. Can be.

If the low-melting polymer resin is added in contact with the electrolyte, that is, in contact with the inside of the battery, the electrolyte becomes unstable as the interface becomes unstable due to the difference in the degree of swelling with the electrolyte between the different polymers. In addition to leakage, fine cracks may be generated at the joints between the polymers, thereby weakening the sealability of the sealing part. This weakening of sealability makes it easier to penetrate moisture into the battery, and may result in shortening the life of the battery.

Preferably, the low melting point polymer resin may be added to the center portion of the sealing portion to be completely sealed by the sealing portion of the battery in the heat-sealed state. When the low melting point polymer resin is interposed in the center portion of the sealing portion within 50% of the width of the sealing portion, the sealability of the battery is not weakened in the normal operating range of the battery, and high pressure gas is generated in an abnormal operating range. If the polymer resin having a relatively low breakdown performance is interposed first, the risk of the battery igniting or exploding can be removed beforehand.

The addition area of the low melting polymer resin is preferably in the range of 1 to 20% based on the entire area of the sealing portion. When the addition area of the low-melting polymer resin exceeds 20%, the sealing property of the battery is significantly weakened, which is not preferable because of the possibility of water penetration into the battery and leakage of the electrolyte solution. On the contrary, if the pressure is less than 1%, the sealing part is not opened even when the pressure is higher than a predetermined level, which is not preferable because it is difficult to achieve the object of the invention of preventing the explosion or explosion of the battery.

The laminate sheet of the pouch type battery is generally composed of a thickness of the outer resin layer of 5 to 40 µm, a thickness of the metal layer of 20 to 150 µm, and a thickness of the inner resin layer of 10 to 100 µm. The low melting point polymer resin which concerns on this invention is added between internal resin layers, and it is preferable to add in thickness of 1-50 micrometers. If the added thickness is too thin, the effect of lowering the breakdown voltage performance due to the addition of the polymer resin is insignificant. On the contrary, if the thickness is too thick, a step due to the thickness difference is formed on the laminate sheet, and this step weakens the physical strength of the sheet. It is unpreferable to reduce workability.

The battery case may be a secondary battery case having a thin thickness and a relatively wide width and length so as to minimize the overall size when the battery case is stacked for the configuration of the battery module. Such a preferable example may be a battery case of a laminate sheet including a resin layer and a metal layer having a structure in which an electrode assembly is embedded and electrode terminals protrude from upper and lower ends or one end thereof, and specifically, an electrode assembly is embedded. It may be a pouched case of aluminum laminate sheet.

The present invention is applicable to a battery of various forms and types, the battery may be preferably applied to a lithium secondary battery prepared by impregnating a lithium-containing electrolyte in the electrode assembly.

The present invention also relates to a medium-large battery module including the secondary battery as a unit cell.

The secondary battery according to the present invention can be preferably used as a unit cell for a high output large capacity battery or a battery pack due to high safety and excellent sealing properties.

Hereinafter, the present invention will be further described with reference to the drawings according to embodiments of the present invention, but the scope of the present invention is not limited thereto.

2 is an exploded perspective view of a secondary battery according to an embodiment of the present invention.

Referring to FIG. 2, in the pouch type secondary battery 200, an electrode assembly 210 including a cathode, an anode, and a solid electrolyte coating separator disposed therebetween is formed inside the pouch type battery case 300. Two electrode leads 222 and 232 electrically connected to the negative electrode tabs 220 and 230 are sealed to be exposed to the outside.

The battery case 300 includes a case body 310 including a concave accommodating portion 311 on which the electrode assembly 210 may be seated, and a cover 320 integrally connected to the body 310. have.

In the stacked electrode assembly 210, a plurality of positive electrode tabs 220 and a plurality of negative electrode tabs 230 are fused to each other and coupled to the electrode leads 222 and 232. In addition, when the excess portion 312 and the cover 320 of the case body 310 are heat-sealed by the heat welder, the short between the heat welder and the electrode leads 222 and 232 is prevented from occurring, and the electrode lead is prevented. In order to secure the sealing property between the 222 and 232 and the battery case 100, the insulating film 240 is attached to upper and lower surfaces of the electrode leads 222 and 232.

The case body 310 and the cover 320 are composed of an outer resin layer, a barrier metal layer, and an inner resin layer as described above, and the inner resin layer is a case body in which a segment 100 of a polymer resin is added. The outer surface of the 310 and the outer surface of the cover 320 may be tightly fixed by heat and pressure from a heat welding machine (not shown).

A 2 μm-thick polyethylene (PE) resin 100 was deposited between the surplus portion 312 and the cover 320 of the case body 310 while the electrode assembly 210 impregnated with the electrolyte was seated on the accommodating portion 311. When the polyethylene (PE) fragment 100 cut to a width of 30% of the width of the surplus portion 312 is added, the sealing portion is formed by heat-sealing the contact portion between the surplus portion 312 and the cover 320.

The pouch battery 200 prevents penetration of moisture and leakage of electrolyte in the sealing portion, and when the pressure of the internal gas exceeds a predetermined level, the portion to which the PE fragment 100 is added is opened first, thereby causing abnormality of the battery. It is possible to prevent the ignition in the operating state in advance, and greatly improve the life and safety of the battery.

3A and 3B are cross-sectional views of a conventional secondary battery and a secondary battery according to one embodiment of the present invention, respectively.

In the conventional secondary battery, as shown in FIG. 3A, a heat seal between the excess portion 312 and the lid 320 of the main body 310 of the battery case is generally performed. However, in the secondary battery according to the present invention, as shown in FIG. 3B, a low melting polymer resin, that is, a polyethylene (PE) fragment is added between the surplus portion 312 and the lid 320 of the case body 310. In the state, heat-sealing is performed, so that the pressure resistance performance of the portion where the PE fragment 100 is added and the portion where the PE fragment 100 is not added differs, and when a high-pressure gas is generated inside the battery, rupture of the entire battery 200 occurs. It is possible to improve the safety of the battery by preventing and inducing efficient gas ejection.

4 and 5 respectively show a front view of a secondary battery according to one embodiment of the present invention.

In the case of FIG. 4, the polyethylene (PE) fragment 100a as the low melting polymer resin is added to the center portion based on the width of the excess portion 312 of the case body 310 to be heat-sealed. have. As another embodiment of the present invention, in FIG. 5, one side of the polyethylene (PE) fragment 300b is added on the surplus portion 311 in a state of being in contact with the outside of the battery 200.

6 and 7, respectively, as a secondary battery according to one embodiment of the present invention, unlike FIGS. 3B and 4, PE fragments 100c and 100d are disposed between the positive electrode leads 222 and 232 of the battery 200. It may be an added structure.

8 to 10 illustrate secondary batteries according to still another embodiment of the present invention. That is, two or more PE fragments 100e may be formed in one side direction or the other side direction of the surplus portion 312 that is thermally fused together of the battery 200, or one in the opposite side direction. .

In addition to the above case, one or more segments of the polymer resin are added in a width of 50% or less of the width of the excess portion to be thermally fused, and a part easily created by a person having ordinary skill in the art. It should also be construed as being included in the scope of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

The positive electrode was prepared by coating a slurry of lithium cobalt oxide, PVdF and a conductive material on an aluminum current collector in a generally known composition, and the negative electrode was prepared by coating a slurry of graphite, PVdF and conductive material on a copper current collector in a generally known composition.

An electrode assembly was assembled between the positive electrode and the negative electrode through a separator cut to a size slightly larger than these, and the electrode assembly was mounted inside the pouch-type battery case of the laminate sheet having a long width to width as shown in FIG. 1.

The laminate sheet has a structure including an inner resin layer of an unstretched polypropylene (cPP) material, a barrier aluminum metal layer, and an outer resin layer of a polyethylene terephthalate (PET) material.

A fragment of polyethylene (PE) resin was added between the heat-sealed inner resin layers in a width of 30% of the width of the heat-sealed portion of the inner resin layer as shown in FIG. 2.

In the sealing portion where the laminate sheets are in contact with each other, the inner resin layers were bonded to each other by thermal fusion to complete a secondary battery having a structure as shown in FIG. 4.

[Example 2]

A secondary battery was completed in the same manner as in Example 1, except that the fragment of the polyethylene (PE) resin to be added was brought into close contact with the outer side of the inner resin layer to be thermally fused as shown in FIG. 5.

Example 3

A secondary battery was completed in the same manner as in Example 1, except that segments of the polyethylene (PE) resin to be added were added between the protruding electrode leads of the electrode assembly as shown in FIG. 6.

Example 4

A secondary battery was completed in the same manner as in Example 1, except that two fragments of the polyethylene (PE) resin were added to one side of the inner resin layer that is thermally fused as shown in FIG. 8.

Comparative Example 1

A secondary battery was completed in the same manner as in Example 1, except that no segment of polyethylene (PE) resin was added between the heat-sealed inner resin layers.

Comparative Example 2

In the same manner as in Example 1, except that the fragments of the polyethylene (PE) resin to be added were brought into close contact with the inner side of the inner resin layer to be thermally fused to be in contact with the embedded electrode assembly. The secondary battery was completed.

Experimental Example 1

30 batteries prepared in Examples 1 to 3 and Comparative Examples 1 and 2, respectively, were subjected to an overcharge test of 1 C and 10 V to confirm whether the batteries were ignited.

TABLE 1

As shown in Table 1, it can be seen that the battery according to the embodiments of the present invention is significantly reduced in the case of ignition under overcharge conditions compared to Comparative Example 1.

This is because the battery decomposes the electrolyte under overcharging conditions and the internal gas is generated with an increase in temperature. This is because the sealing portion is opened while the added polymer resin is melted at 135 ° C. or higher, thereby igniting the battery while ejecting a high-pressure gas therein.

In the case of Example 4 compared to Example 1, it can be seen that by adding two polymer resin fragments, the function of preventing the fire of the battery is further improved. However, the effectiveness of the moisture permeation prevention by the following Experimental Example 2 should be reviewed.

Experimental Example 2

Relative humidity of the batteries prepared in Examples 1 to 3 and Comparative Example 2, respectively, was stored at 90% for one week at a temperature of 60 ° C., and then the remaining capacity was measured.

TABLE 2

As shown in Table 2, it can be seen that the battery according to the embodiments of the present invention has a higher residual capacity since the moisture permeation phenomenon is suppressed as compared with Comparative Example 2.

In Example 4, by adding two polymer resin fragments, it was confirmed that the effect of suppressing the ignition of the battery was the highest in Experimental Example 1, but in Experimental Example 2 compared with Examples 1 to 3 It can be seen that the residual capacity is relatively decreased due to the increase.

Therefore, in consideration of the risk of ignition of the battery and the required battery life, an appropriate case should be selected and applied.

As described above, the secondary battery according to the present invention does not weaken the sealability of the battery for preventing water penetration, and at the same time efficiently discharges the high-pressure gas inside the battery, thereby reducing the risk of fire or explosion for the battery. Blocking in advance is effective to significantly improve the high temperature safety of the battery.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (14)

A secondary battery in which an electrode assembly having a cathode / separation membrane / cathode structure is sealed in a case of a laminate sheet, wherein the outer circumferential surface of the housing is heat-sealed to seal the battery in a state in which the electrode assembly is mounted in the housing of the case. At least a portion of the sealing portion formed by the heat-sealing is performed in a state in which a polymer resin having a melting point lower than that of the heat-sealing polymer of the sheet is added at a position not in contact with the electrolyte solution within a range of 50% of the width width of the sealing portion, The laminate sheet includes an inner resin layer that is heat-sealed, a barrier metal layer, and an outer resin layer having excellent durability, The low melting polymer resin is a secondary battery characterized in that the coating is added in the form of a thin film on the inner resin layer. delete The secondary battery of claim 1, wherein the inner resin layer comprises cPP, the barrier metal layer comprises aluminum, and the outer resin layer comprises stretched nylon or PET. The secondary battery of claim 1, wherein the low melting polymer resin has a melting point difference of 10 to 50 ° C. with respect to an internal resin layer. The secondary battery of claim 1, wherein the low melting polymer resin is PE. delete delete The secondary battery of claim 1, wherein the low melting polymer resin is completely encapsulated by the sealing part in a state of being heat-sealed in addition to the sealing part. The secondary battery of claim 1, wherein the low-melting polymer resin is added to a sealing part and at least a part of the low melting polymer resin is in contact with the outside of the battery or is located at the center of the sealing part to be completely sealed. . The secondary battery of claim 9, wherein the low-melting polymer resin is completely sealed by the sealing part of the battery in a state of being heat-sealed by being added to a central portion of the sealing part. The secondary battery of claim 1, wherein an additional area of the low melting polymer resin is in a range of 1 to 20% based on the entire area of the sealing part. The secondary battery of claim 1, wherein an additional thickness of the low melting polymer resin is 1 to 50 μm. The secondary battery of claim 1, wherein the case is a pouch type case. The secondary battery of claim 1, wherein the battery is a lithium secondary battery.

Images