KR20090016279A - Secondary battery of improved safety - Google Patents

Abstract

A secondary battery is provided to prevent the firing of a battery or the risk of explosion and to secure safety and reliability of operation by emitting high pressure gas inside a battery cell to the desired site. A secondary battery(100) has a structure sealed by heat welding an anode/separation film/cathode electrode assembly installed in a battery case(300). A cut-out part(210) indented from the outer side of the structure is formed in an outer circumference sealing part(310) of an electrode assembly receiving part, to eject high pressure gas to the outside while the sealing force is weaken. The sealing part of the site formed with the cut-out part has the small width compared with the width of the sealing part of the other site.

Description

Secondary Battery of Improved Safety

The present invention relates to an improved safety secondary battery, and more particularly, a plate-shaped secondary battery having a structure in which an electrode assembly having a cathode / separation membrane / cathode structure is mounted in a battery case and then sealed by heat fusion, and an electrode assembly in a battery case. The outer circumferential surface sealing portion of the housing portion is provided with a cutout having a structure indented from the outside to discharge the high pressure gas to the outside while the sealing force is preferentially released when the high pressure gas is generated inside the battery cell. The sealing part relates to a secondary battery configured to have a width smaller than the width (width) of other parts except for this.

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 formed by injecting or impregnating an electrolyte solution after embedding an electrode assembly composed of a positive electrode, a negative electrode, and an insulating film interposed between the positive electrode and the negative electrode in a battery case of a metal can or laminate sheet in a stacked or wound state. It is.

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. In particular, in the pouch type secondary battery, the sealing force of the battery case is lowered, so that the electrolyte leakage 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 thermally fusion bonding 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 the secondary battery reaches an abnormal operating state such as internal short circuit, overcharge, high temperature exposure, 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 seriously may cause fire 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 technique for forming a predetermined gas releasing mechanism in a battery that heat seals and seals the outer peripheral portion of a laminate film incorporating an electrode assembly.

In this regard, FIG. 2 schematically shows a perspective cross-sectional view of a battery case in which a gas discharge mechanism, which is an unfused portion, is formed as an example according to the above technique, and another example according to the above technique is illustrated in FIGS. 3 to 5. As a side cross-sectional view of the battery case sealing portion in which the gas discharge mechanism is formed in a modified form of a seal layer is shown.

Referring to these drawings, the technique is (i) as shown in FIG. 2, by forming the unfused portion 11 in a part of the sealing portion during thermal fusion, the stress of the internal gas is concentrated on the unfused portion 11 3) and (ii) a laminate layer composed of an outermost layer 41 / metal layer 42 / seal layer 43, as shown in FIGS. It discloses the method of deforming and making the adhesive strength by heat welding lower than another site | part. As an example of the method (ii), a part of the seal layer is removed 30 as in FIG. 3, or a polymer resin 31 having a relatively low bonding force is inserted into the removed seal layer as in FIG. 4, and FIG. As in 5, a method of bonding the polymer resin 32 having a low bonding strength to a part of the seal layer or the like is proposed.

However, according to the experiments performed by the inventors of the present application, the technique has a weak adhesive strength of the sealing portion in which the gas discharge mechanism is formed, and thus, even in normal operating conditions, water penetration into the battery cell and leakage of the electrolyte are continuously maintained through the portion. It was confirmed that there is a serious problem in the safety of the battery. Furthermore, in the case of the method (i), since it is difficult to precisely control the formation of the unfused portion in the battery manufacturing process, and the stress caused by the internal gas is concentrated, the method (i) is unfused even by the internal gas pressure generated in the normal operation of the battery. As the portion is gradually expanded, there is a problem that the operation reliability is greatly lowered and the sealability of the battery is lowered. In addition, in the case of the method (ii), a process of removing only a part of the laminate seal layer or inserting a separate resin itself requires a high level of precision, and thus there is a problem in that it is difficult to be applied to an actual mass production process.

On the other hand, 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 lead connected to the positive electrode plate and the negative electrode plate are drawn out from the sealing portion of the outer case. A technique of performing heat fusion in a state in which a heat-sealing resin sheet having a lower melting point than that of a laminate sheet is inserted in a part of a sealing portion of an exterior case is disclosed. 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. Such electrolytes are mostly strong in order 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, the secondary battery used in the medium-large battery pack as a power source for electric vehicles, hybrid vehicles, etc. is required to ensure safety because of the long-term life required and a large number of battery cells are concentrated.

Therefore, by effectively discharging the high-pressure gas that can be generated due to unexpected development by a simple process to a desired site, it is possible to prevent the ignition or explosion of the battery cell in advance, thereby ensuring the life and stability of the battery. There is a high need for technology.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, an object of the present invention is to effectively discharge the high-pressure gas inside the battery cell to the desired site through a structure that can be easily manufactured, thereby preventing the risk of ignition or explosion on the battery, thereby improving safety and operation. It is to provide a secondary battery that can secure the reliability, and can solve the problems caused by the indiscriminate discharge of harmful gases.

Accordingly, the secondary battery according to the present invention is a plate-shaped secondary battery having a structure in which an electrode assembly having a cathode / separation membrane / cathode structure is mounted in a battery case and sealed by heat fusion, and the sealing part of the battery case has an outer circumferential surface sealing portion thereof. When the high pressure gas is generated inside the battery cell, the sealing force is preferentially released, so that the high pressure gas can be discharged to the outside, and a cutout part formed from the outside is formed. It is comprised by having a width smaller than the width (width) of a sealing part.

According to the present invention, when a high-pressure gas is generated in an abnormal operating state of the battery and the sealing property of the sealing portion is gradually released, the cut portion having a relatively short width of the sealing portion is opened earlier than other portions so that the gas can be effectively discharged. Therefore, it is possible to lower the battery internal pressure and to prevent ignition and explosion of the battery in advance. In addition, since the discharge position of the gas can be easily adjusted by the position of the cutout, it is possible to solve the problem that may be caused by the indiscriminate discharge of harmful gas.

Furthermore, as described above, in the past, the process of forming the gas release mechanism was very difficult and precise control was difficult, but the cutout portion according to the present invention may be formed through a simple process such as cutting off a part of the sealing portion after manufacture of the battery. Therefore, there is an advantage that the manufacturing process is very simple and the production efficiency of the battery is high. In addition, since the sealing property of the inner sealing part is ensured, it is possible to prevent moisture infiltration and leakage of the electrolyte due to external sealing, a small amount of gas generated in a normal state, and the like that the sealing property of the sealing part is gradually released. Operational reliability is high.

In general, the sealing part is formed by joining the outer circumferential surface portion of the battery case by heat fusion, and it is not easy to control to have a uniform bonding force in all the heat fusion areas, and both ends of the sealing part (inner end and Relatively low coupling force).

In the present invention, the cutout portion is formed in a part of the sealing portion, and has a structure indented from the outside. That is, the cutout portion is indented in the inward direction in which the accommodating portion is formed from the outward direction of the sealing portion having a relatively low coupling force. Therefore, since the sealing property is maintained by the sealing portion on the center having a strong bonding force, it is possible to ensure the maximum sealing performance of the battery under normal operating conditions.

The position at which the cutout is formed is not particularly limited and may be appropriately determined depending on, for example, the desired gas discharge path. That is, in order to prevent harmful internal gas from being discharged indiscriminately, a predetermined exhaust member may be mounted on the battery cell itself or the pack case, and the cutout may be determined to communicate with the exhaust member.

In one preferred example, the cutout may be formed at the center of both sealing portions located on the short axis with respect to the center of the battery case. Here, the center of the battery case means a point at which the center of the long axis and the short axis of the battery case intersect and its vicinity. This is because the gas movement path within the battery is the shortest, and the volume expansion of the battery case is the largest area, so that rapid and efficient gas discharge can be achieved.

In addition, the sealing portion of the portion where the cutout is formed is configured to have a width smaller than the width (width) of the other portions except this.

Generally, in a plate-shaped secondary battery sealed by heat fusion, the gas generated in the battery pressurizes the heat fusion portion of the sealing portion, and when the gas pressure exceeds the bonding force of the sealing portion, the sealing portion is opened and discharged to the outside. do. Therefore, the time point at which the high-pressure gas is discharged is determined by the width of the sealing portion, and in the secondary battery according to the present invention, since the width of the sealing portion of the portion where the cut portion is formed is shorter than the width of the other sealing portion, the portion where the cut portion is formed is preferentially opened. Can be.

On the other hand, the cutout portion may be formed in a portion excluding the sealing portion having a high bonding strength by heat fusion in order to prevent the sealing of the battery from weakening in the normal operating range of the battery.

In view of this, in one preferred example, the ratio (w '/ w) of the width w' of the cutout to the width w of the sealing part of the other portion except for the sealing portion in which the cutout is formed may be 20 to 70%. And more preferably 30 to 50%. Thus, the width of the sealing portion of the portion where the cutout is formed may be 30 to 80% of the width of the other sealing portion.

When the width of the cutout portion is too short, that is, when the value of w '/ w is too small, the degree of reduction of the gas discharge path is insignificant and the desired opening effect cannot be exerted. On the contrary, when the value of w '/ w is too large, the operation reliability becomes low and the sealing of the battery can be easily released even by a small amount of gas that may be generated by an external shock or in a normal state, and leakage of electrolyte may occur. Therefore, there is a problem in the safety of the battery.

In one preferred example, the sealing portion of the portion where the cutout is formed may be configured to further form an indentation ('inner indentation') of the structure indented from the inside. Accordingly, the stress of the gas inside the battery is concentrated on the inner indentation, so that the gas discharge from the cutout can be made more quickly.

However, this inner indentation has a smaller width than the case of Japanese Patent Application Laid-Open No. 2001-093489 described above. That is, the width w ″ of the inner indentation portion is sufficient to relatively concentrate the stress of the internal gas, and when large as in the above application, the sealability of the battery is lowered, so that water penetration or electrolyte leakage, etc. In consideration of this, it is preferable that the width of the inner indentation has a size of 1 to 10% based on the width of the other sealing part in a range smaller than the width of the cutout.

In the case of the cut-out portion formed with the inner indentation, as described above, it should be possible to ensure whether the sealability can be maintained in the normal state and the operation reliability, and therefore, it is preferable to have a width shorter than the width w 'of the cut-out portion. In addition, the sum of the width of the indentation and the cutout with respect to the width of the other sealing part, that is, (w '+ w ") / w is preferably 20 to 70%, as in the case where only the cutout is formed, and is 30 to 50%. More preferred.

The length (height) or the number of the cutouts and the indents is not particularly limited and may be appropriately adjusted in consideration of the size of the battery case, the expected gas pressure, workability and efficiency of the forming process. For example, when two or more cutouts are formed, the cutouts may be formed on sealing portions at positions facing each other based on the center of the battery case.

The cutout may be formed at the center of one or both sealing parts positioned on the short axis with respect to the center of the battery case. This is because the internal gas is mainly concentrated in the center of the battery, and the movement in the short axis phase is the fastest.

As another example, the cutout may be formed only on one side of the seal on the short axis, and the outer circumferential surface of the seal formed on the cutout may have a curved shape. In a specific example, the outer circumferential surface of the sealing portion formed side of the cut portion may be formed in a semi-circular curve around the cut portion. As described above, when the internal gas generated in the battery has a predetermined pressure or more, the sealing part is first separated from the cutout and the sealing property is released to release the gas. This is because the outer circumferential surface, including the outer end face of the cutout portion, is curved, and the selective sealing (separation of the seal portion) at the cutout can be ensured by the wide sealing area of the portion.

On the other hand, since almost no separation of the sealing portion occurs at the end (both ends) of the outer circumferential surface of the sealing portion, the width of the curved outer circumferential end portion may be shorter than the width of the other sealing portion on the side where the cutout is not formed.

Shapes of the cutout and the inner indentation may vary, for example, at least one selected from the group consisting of a semicircle, a triangle, a rectangle, or a trapezoid, and may preferably have a semicircular shape.

The method of forming the cutout is not particularly limited, and preferably, the electrode assembly is attached to the housing of the battery case, and heat-sealed on the outer circumferential surface sealing of the housing, and then has a structure indented from the outside of the sealing by a post-treatment process. It can be formed by cutting the sealing portion in the form. Therefore, it can be formed by a simple and easy method, and the work efficiency is excellent.

In addition, the formation of the inner indentation may, for example, consider a method of setting different heat fusion conditions such as heat treatment temperature, heat treatment time, pressure, and the like, but is not limited thereto.

The battery case may be preferably applied to a laminate sheet including a resin layer and a metal layer, in particular, a secondary battery in which an electrode assembly is embedded in a pouch type case of an aluminum laminate sheet.

The laminate sheet is composed of an outer coating layer of a polymer film, a barrier layer of a metal foil, and an inner sealant layer of a polyolefin series, and the outer coating layer must have excellent resistance from an external environment, and thus, it is necessary to have a predetermined tensile strength and weather resistance. Do. In such aspect, a stretched nylon film or polyethylene terephthalate (PET) may be preferably used as the polymer resin of the outer resin layer. The barrier 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. The inner sealant layer has a heat sealability (heat adhesion), low hygroscopicity to suppress the penetration of the electrolyte solution, polyolefin resin that is not expanded or eroded by the electrolyte solution may be preferably used. Preferably, unstretched polypropylene (cPP) can be used.

The electrode assembly is not particularly limited as long as it is a structure consisting of a cathode and an anode, and a separator interposed therebetween, and examples thereof include a folding type, a stack type, or a stack / folding type structure. Details of the electrode assembly of the stack / foldable structure are disclosed in Korean Patent Application Publication Nos. 2001-0082058, 2001-0082059, and 2001-0082060, which are described in the context of the present invention. Incorporated by reference.

The secondary battery according to the present invention may preferably be a lithium secondary battery, and in particular, may be preferably applied to a so-called lithium ion polymer battery in which a lithium-containing electrolyte is impregnated into the electrode assembly in the form of a gel.

The present invention also provides a medium-large battery pack including the secondary battery as a unit cell.

In particular, the secondary battery according to the present invention can be preferably used in a high output large capacity battery requiring long life and excellent durability, or a medium and large battery pack including a plurality of such batteries as a unit cell. The medium-large battery pack may be used as a power source of, for example, an electric vehicle, a hybrid electric vehicle, an electric motorcycle, and an electric bicycle.

Since the structure and manufacturing method of such a medium-large battery pack are known in the art, a detailed description thereof is omitted herein.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

6 is a perspective cross-sectional view of a secondary battery having a cutout structure according to one embodiment of the present invention, and FIG. 7 is a perspective view of the secondary battery of FIG. 6.

Referring to these drawings, the secondary battery 100 includes an electrode assembly (not shown), a battery case 300 accommodating the same, and two electrode leads 420 and 421 electrically connected to electrode tabs of the electrode assembly. It consists of doing.

The two electrode leads 420 and 421 are electrically connected to electrode tabs (not shown) extending from each electrode plate of the electrode assembly by welding or the like, and partly exposed to the outside of the battery case 300. . In addition, an insulating film 430 is attached to upper and lower portions of the electrode leads 420 and 421 to increase the sealing force with the battery case 300 and to secure an electrical insulation state. The two electrode leads 420 and 421 of the positive and negative electrodes may be formed at positions facing each other, as shown in this figure, or may be positioned side by side in the same direction.

The battery case 300 is formed of an aluminum laminate sheet, and has an accommodating part for accommodating an electrode assembly, and the upper battery case and the lower battery case are combined by heat fusion in the outer peripheral surface sealing part of the accommodating part to form a pouch as a whole. Have

The sealing portion 310 is formed with a cutout portion 210 having a structure indented from the outside to the inward direction. Typically, when gas is generated inside the battery, the battery case 300 expands the greatest in the center (M), so that the deformation force due to expansion in both sealing portions 310 located on its short axis (S) is the most. It becomes big. Therefore, the cutout 210 is positioned at the center of both sealing parts 310 positioned on the short axis S with respect to the center M of the battery case 300. Therefore, the sealing part is first released from the cutout 210 by the internal pressure of the internal gas of the battery, so that the sealing is released, thereby discharging the gas.

The width w-w 'of the sealing portion at the portion where the cutout 210 is formed is smaller than the width w of the other sealing portion, and the width w' of the cutout 210 is the width w of the other sealing portion. It is preferred to have a size of 20 to 70% on the basis.

Meanwhile, in this drawing, the electrode leads 420 and 421 protrude outward from both sealing parts 310 positioned on the long axis L based on the center M of the battery case 300. That is, since the portions where the electrode leads 420 and 421 are formed need to maintain high sealing property and insulation, it is preferable that the positions of the cutout portions 210 are different from those where the electrode leads 420 and 421 are formed.

8 is a perspective cross-sectional view of a secondary battery according to a second embodiment of the present invention.

Referring to FIG. 8, the outer circumferential surface sealing portion 310 of the battery case 300 is formed with a cutout portion 211 having a structure indented from the outside, and a sealing portion 310 at a position opposite to the cutout portion 211. The inner indentation 212 of the structure indented from the inner side of is formed.

Since the stress of the internal gas of the battery is concentrated to the inner indentation 212, the gas pressure applied to the cutout 211 is increased, so that discharge may be performed more quickly. The width w ″ of the inner indentation 212 may be enough to concentrate the stress of the internal gas, so that the width w ″ may be about 1 to 10% based on the width w of the other sealing part. The width w ″ of the inner indentation 212 is smaller than the width w ′ of the cutout 211 so as to ensure the sealing property of the cutout 211, and the width w ′ and the inner indentation of the cutout 211. The sum of the widths w ″ of the portions 212 preferably has a size of 20 to 70% based on the width w of the other sealing portions, that is, the width of the sealing portion at the cutout portion 211 forming portion, It is preferable that w- (w '+ w ") is 40 to 80% with respect to the width w of another sealing part.

Meanwhile, the shapes of the cutout 211 and the inner indentation 212 are illustrated in an elliptical shape, but the shape of the cutout 211 and the inner indentation 212 may be formed in various shapes, and the electrode terminals 420 and 421 may be formed. Of course, it can be formed in any position of the sealing portion 310 except the protruding portion.

9 is a perspective cross-sectional view of a secondary battery according to a third embodiment of the present invention.

Referring to FIG. 9, the cutout 212 may be located only at the center of the right sealing part 311 among the sealing parts 311 and 312 positioned on the short axis S based on the center M of the battery case 300. Formed. In addition, the outer circumferential surface of the right sealing portion 311 in which the cutout portion 212 is formed has an upper and lower outer circumferential surfaces having a semicircular curve shape around the cutout portion 212. Thereby, the width W ₂ of the outer peripheral surface end of the right sealing part 311 becomes smaller than the width W ₁ of the end of the left sealing part 312 in which the cutout is not formed. Accordingly, since the upper and lower sealing portions 311 have a large sealing area around the cutout portion 212, the gas generated therein can be discharged to the outside through the cutout portion 212 with high reliability.

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.

The electrode assembly was assembled between the positive electrode and the negative electrode through a separator cut to a larger size than these, and the electrode assembly was mounted inside the pouch-type battery case of the laminate sheet including the upper case and the lower case in which the accommodating parts were formed.

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.

In the upper case and the lower case, the sealing parts formed on the outer circumferential surface of the housing part are thermally bonded to each other, and as shown in FIG. 6, the outer and inner parts of the left and right sealing parts in the longitudinal direction, which are shortened with respect to the center of the battery case, are shortened. The cutout portion was formed by cutting off. The shape of the cutout was oval, and the width of the cutout was about 30% based on the width of the other sealing part.

Example 2

Except for changing the shape of the heating jig at the time of heat fusion, an inner indentation portion of the structure indented from the inside having a width of 5% in the sealing portion of the portion to be formed in the cutout portion was further formed. A secondary battery was completed in the same manner as in Example 1.

Example 3

Example 1, except that the cutout was formed only at the center of the right sealing part, and the outer peripheral surface of the right sealing part in which the cutout was formed was cut in a semicircular curve around the cutout as shown in FIG. 9. A secondary battery was completed in the same manner as described above.

Comparative Example 1

A secondary battery was completed in the same manner as in Example 1, except that no cutout was formed.

Comparative Example 2

A secondary battery was completed in the same manner as in Example 1, except that no cutout was formed and only an inner indentation having a width of 30% was formed during thermal fusion.

Experimental Example 1

30 batteries prepared in Examples 1 to 3 and Comparative Examples 1 and 2, respectively, were placed in a chamber at about 90 degrees, causing expansion of the battery, and then firing or explosion of the battery, discharge direction of internal gas, and gas. The cell expansion deviation at the time of discharge was confirmed. The discharge direction was determined by the number of positions of the sealing portion that was open when the internal gas was discharged. That is, when all the batteries are opened at the same place, the sealing part is set to 1, and in the case of some batteries, when the sealing part is opened at other positions, the number of such opening positions is added. In addition, the cell expansion deviation at the time of gas discharge was converted into a percentage of the width before the minimum degree of expansion based on the thickness of the battery showing the maximum degree of expansion at the time of gas discharge.

TABLE 1

As shown in Table 1, the batteries of Examples 1 to 3 of the present invention did not cause the battery to ignite or explode by the effective discharge of the internal gas even when the battery expanded under high temperature conditions. In addition, the internal gas was also discharged in one or both directions. However, the batteries of Comparative Example 1 were found to ignite or explode in a plurality of cells, and the sites opened when the internal gas was discharged were also different.

On the other hand, the batteries of Comparative Example 2, like the batteries of Examples 1 and 2, did not ignite or explode, and the internal gas was discharged only to the portion where the indentation was formed. On the other hand, there was a large variation in the degree of expansion of the battery when discharge occurred, that is, when the sealing portion was opened. That is, as the stress due to the internal gas pressed into the indentation is concentrated, the phenomenon in which the sealing part is opened in the low flat window state is confirmed. This expansion deviation tended to be higher than that of the batteries of Comparative Example 1.

As described above, the secondary battery according to the present invention is formed with a cut portion of the structure indented from the outside of the sealing portion of the battery case, when the high pressure gas generated inside the battery cell, while the sealing force is preferentially released from the high pressure gas Since it can be selectively discharged to the desired site, the risk of ignition or explosion on the battery can be blocked in advance, thereby remarkably improving the safety of the battery and solving the problem due to the indiscriminate discharge of harmful gas. Moreover, since such cutout portion can be easily formed in the battery manufacturing process, it does not cause an increase in the manufacturing cost 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.

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

2 is a perspective sectional view of a battery case in which a gas release mechanism that is an unfused portion is formed, in one example according to the conventional method;

3 to 5 are side cross-sectional views of another case according to the related art, in the case of a battery case sealing portion in which a gas release mechanism is modified in a seal layer;

6 and 7 are perspective cross-sectional views and perspective views of a secondary battery having a cutout according to a first embodiment of the present invention;

8 is a perspective cross-sectional view of a secondary battery having a cutout according to a second exemplary embodiment of the present invention.

9 is a perspective cross-sectional view of a secondary battery having a cutout according to a third exemplary embodiment of the present invention.

Claims (15)

A plate-shaped secondary battery in which an electrode assembly having a cathode / separation membrane / cathode structure is mounted in a battery case and sealed by heat fusion, and sealed at the outer peripheral surface sealing portion of the electrode assembly accommodating portion of the battery case when high pressure gas is generated in the battery cell. A cutout portion having a structure indented from the outside is formed to discharge the high pressure gas to the outside while the force is released first, and the sealing portion of the portion where the cutout portion is formed is smaller than the width (width) of the sealing portion of the other portion except this. Secondary battery characterized by having a. The secondary battery of claim 1, wherein the cutout has a width of 20 to 70% based on the width of the seal of the other portion. The secondary battery of claim 1, wherein the cutout is formed at a center of one or both sealing parts positioned on a short axis with respect to the center of the battery case. The secondary battery according to claim 3, wherein when the cutout is formed on only one side, an outer circumferential surface of the sealing part on the side where the cutout is formed has a curved shape. The secondary battery according to claim 4, wherein a width of an end portion of the curved sealing portion outer peripheral surface is shorter than a width of an opposite sealing portion in which no cutout portion is formed. The secondary battery of claim 1, wherein a shape of the cutout is at least one selected from the group consisting of semicircles, triangles, rectangles, and trapezoids. The secondary battery according to claim 1, wherein an inner indentation portion of the structure indented from the inside is further formed in a sealing portion of the portion where the cutout portion is formed. The secondary battery of claim 7, wherein the inner indentation part has a width of 1 to 10% based on the width of the sealing part of the other part. The width of the inner indentation portion is smaller than the width of the cutout portion, and the sum of the width of the inner indentation portion and the width of the cutout portion has a size of 20 to 70% based on the width of the sealing portion of the other portion. Secondary battery. The method of claim 1, wherein the cutout portion is formed by cutting the sealing portion in a form having a structure indented from the outside of the sealing portion after mounting the electrode assembly on the housing portion of the battery case and heat-sealed the sealing portion of the outer peripheral surface of the housing portion Secondary battery. The secondary battery of claim 1, wherein the battery case is a laminate sheet including a resin layer and a metal layer. The secondary battery of claim 11, wherein the sheet is an aluminum laminate sheet. The secondary battery of claim 1, wherein the electrode assembly has a folding type, a stack type, or a stack / folding type structure. The secondary battery of claim 1, wherein the battery is a lithium ion polymer battery. A medium-large battery module comprising the secondary battery according to any one of claims 1 to 14 as a unit cell.

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