KR20140042837A - Prismatic secondary battery employed with safety plate - Google Patents

Abstract

The present invention relates to a prismatic secondary battery where an electrode assembly which comprises an anode and a cathode and a separator is sealed in a prismatic battery case. The battery case includes a square case body which is made of a metallic material and has an open upper end, and a case cap which is combined with the open upper end of the case body and includes an electrode terminal. A safety plate which is broken when a high voltage is generated in the battery is formed on the case body. The safety plate is a line-shaped notch groove which is formed at a position which includes a vertical center axis in both sides of the case body. The notch groove includes at least one part of a curve part and generally has a line-shaped structure of a closed type.

Description

Square secondary battery with safety plate {Prismatic Secondary Battery Employed with Safety Plate}

The present invention relates to a rectangular secondary battery provided with a safety plate, and more particularly, a rectangular secondary battery in which an electrode assembly composed of a positive electrode, a negative electrode, and a separator is sealed in a rectangular battery case, and a battery case has an open top and a metal It consists of a rectangular case body made of a material, and a case cap coupled to an open upper end of the case body and including an electrode terminal. A safety plate is formed on the case body to break when a high pressure occurs inside the battery. A linear notch groove formed at a position including a vertical central axis on both sides of the notch groove, the notch groove includes at least a portion of the curved portion, and relates to a rectangular secondary battery having a closed linear structure as a whole.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Many researches have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries. .

The secondary battery is classified into a cylindrical battery and a prismatic battery in which the electrode assembly is housed in a cylindrical or rectangular metal can according to the shape of the battery case, and a pouch-shaped battery in which the electrode assembly is housed in a pouch-shaped case of an aluminum laminate sheet .

The electrode assembly incorporated in the battery case is a charge / dischargeable power generating element formed of a laminate structure of a positive electrode / separator / negative electrode. The electrode assembly is composed of a jelly-roll type in which a separator is interposed between a positive electrode and a negative electrode coated with an active material, A stacked type in which a plurality of positive and negative electrodes of a size are stacked in a state in which a separator is interposed, and stacked / folded type stacked units in which unit cells such as bi-cells or pull cells are wound in separate films.

Such a secondary battery may be exposed to various environments depending on usage conditions and conditions, and it is required to prevent the risk of explosion especially for the safety of the user. Generally, the high temperature and high pressure inside the battery, which can be caused by an abnormal operating condition of the battery such as an internal short, an allowable current, a charging state exceeding a voltage, exposure to a high temperature, . Therefore, the secondary battery is provided with a high-voltage relieving means capable of relieving the high voltage which is a direct cause of the explosion of the battery despite the difference in the shape of the battery.

For example, in a cylindrical battery, a safety plate having a specific structure is installed in a cap assembly, a prismatic battery has a notch groove formed in a cap or a case of the battery, and the pouch type battery has a notch groove Sealing portion) are separated from each other.

In a general prismatic secondary battery, a closed type or a partially open type notch groove is formed in the aluminum battery case so as to be cutable.

For example, as shown in Fig. 1, the prismatic secondary battery includes a notch groove of a partially open type on the side surface of the battery case.

The notch groove 30 of FIG. 1 is formed in a small outline at the side edge of the rectangular secondary battery case 20, and is partially formed in an open shape. That is, the notch groove 30 is formed in a portion where the stress value is relatively large in the stress distribution of the case, and is designed such that a curved shape breaks when the internal pressure of the battery increases excessively.

The notch groove 30 of this structure has the advantage of relatively sensitive to the high pressure generated inside the battery, but there is a problem that it is difficult to accurately set the intended pressure threshold value in the design of the battery.

That is, as mentioned above, since a high stress is applied to the side edge portion of the battery case, the breakage of the notch groove may easily occur even at low pressure, and above all, particularly when the battery case is thin, it is particularly sensitive to high pressure. Unresponsive breaks occur because of the reaction.

Therefore, the size and depth of the notch groove formed in the site where the stress value is large is inevitably small. However, when the size and depth of the notch groove are reduced, a problem of not breaking the notch groove is rather smooth. .

As another example of the prismatic secondary battery, there is a structure in which the notch groove is formed in the upper center portion of the battery case.

However, this structure forms a safety plate made of notch grooves in the upper center of the battery case with a relatively low stress, thereby increasing the breaking pressure of the safety plate for a thin battery having a large area and thickness, but the notch groove has a closed structure. Since it is not made there is a problem that can cause unnecessary fracture, such as propagation or deformation of cracks to the peripheral area of the notch groove during the operation of the safety plate.

Therefore, there is a great need for a technology related to a rectangular secondary battery having a safety plate structure that can solve the complex problems of the conventional rectangular secondary battery as described above.

In addition, the shape of the notch grooves is expected to be a very important factor for the reliable operation under abnormal conditions.

Therefore, in consideration of the thickness of the battery case, the location of the notch groove according to the stress value, the shape, the length, the depth of the notch groove, and the like, when the internal pressure increases, the gas is quickly discharged by uniform fracture of the notch groove. There is a high need for the development of a rectangular secondary battery that can be made.

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.

After the inventors have conducted extensive research and various experiments, the safety plate is a linear notch groove formed at a position including a vertical center axis on both sides of the case body, and the notch groove is generally formed at least partially including a curved portion. By constructing to have a closed linear structure, it was confirmed that notch grooves can be easily manufactured and that unnecessary breakage such as propagation or deformation of cracks to the surrounding area of the notch grooves can be prevented when the safety plate is operated. .

In addition, when a notch groove of a specific structure is formed in a portion where the stress value is relatively small on the surface of the battery case, and at the same time, a notch groove of a specific shape is formed, the notch groove breaks reliably under appropriate conditions, and as a result, safety It was confirmed that can be improved.

Accordingly, it is an object of the present invention to provide a rectangular secondary battery having a safety plate of an improved structure in which breakage can occur effectively when necessary.

According to the present invention, a rectangular secondary battery according to the present invention is a rectangular secondary battery in which an electrode assembly composed of a positive electrode, a negative electrode, and a separator is sealed in a rectangular battery case, and the battery case is open at the top and is made of a metallic material. It consists of a rectangular case body made of, and a case cap coupled to the open top of the case body and including an electrode terminal,

A safety plate is formed on the case body that breaks when a high pressure is generated inside the battery.

The safety plate is a linear notch groove formed at a position including a vertical center axis on both sides of the case body, and the notch groove includes a curved portion at least in part and has a closed linear structure as a whole. Consists of

Therefore, since the safety plate of the rectangular secondary battery according to the present invention has a structure in which the linear notch groove has a closed linear structure as a whole including a curved portion at least in part, the conventional notch groove is formed as an open straight or curved line. Compared with the structure formed in the case body, it is possible to prevent unnecessary deformation or tearing of the portion adjacent to the notch groove after the operation of the safety plate.

In addition, since the notch groove is formed at a position including the vertical central axis of the case body, which is a portion where the stress value is relatively small, breakage of the notch groove can occur reliably under appropriate conditions.

For reference, both sides of the case body in the present specification means the front or rear of the case body.

The closed linear structure is not particularly limited as long as it is a closed linear structure. Preferably, at least a portion of the linear linear structure is one selected from the group consisting of arcs of circles, arcs of ellipses, splines, and straight lines. It may be more preferably made of a closed curve of a circle or ellipse.

As one example of the structure, the closed linear structure may be a single closed curve in the form of an ellipse, and the ellipse may be a structure in which a long axis or a short axis is positioned in the width direction of the case body.

In this case, the ellipse may have a length of 20 to 80% of the length of the main body of the long axis, specifically, if the length of the long axis is less than 20% of the size of the width of the case body of the notch groove at a desired high pressure. Breakage is difficult to achieve and, on the contrary, exceeding 80% size is not desirable because the notch grooves can break at undesired low pressures.

In addition, the ellipse may have a length of the short axis is 3 to 20% of the width of the case body, specifically, if the length of the short axis is less than 3% size based on the width of the case body notched groove at a desired predetermined pressure. It is difficult to achieve breakage, and on the contrary, if the size exceeds 20%, the overall notch groove size increases, which is not preferable.

In another example, the closed curve may be a single closed curve in the form of a circle, and preferably, the diameter of the circle may be 5 to 30% of the width of the case body. Specifically, if the diameter of the circle is less than 5% of the width of the case body, it is difficult to achieve notch groove breakage at a desired high pressure. On the contrary, if the diameter exceeds 30%, the notch groove may break at an undesired low pressure. Therefore, it is not preferable.

In some cases, the closed linear structure may be formed by a combination of a circle or an ellipse arc and a straight line, and in one specific example, arcs of a circle or ellipse are located at both sides and a pair of straight lines may be used. It can be made of a connected structure.

In the above structure, the straight lines may be a structure passing through the vertical central axis of the case body, wherein the closed linear structure has a length of the long axis is 20 to 80% of the width of the case body and the length of the short axis is 3 times the width of the case body To 30% in size.

On the other hand, the linear notch groove may be a structure formed on the case body showing a stress distribution of 40% or less based on the maximum stress (S _MAX ) of the case in a high pressure state.

The stress distribution may be variously changed by the shape, structure, and the like of the battery case, and the stress distribution shown in a general rectangular secondary battery is disclosed in FIG. 7.

In one specific example, the case body has a thickness of 0.4 mm or less, and the notch groove is formed on the case body exhibiting a stress distribution of 40% or less based on the maximum stress S _MAX of the case in a high pressure state. It may be a structure.

Therefore, the notch groove of the square secondary battery according to the present invention is formed in a relatively small portion where the stress value is 40% or less in the stress distribution of the case main body, thereby preventing the notch groove from being easily broken even at low pressure. It is possible to provide a high breaking pressure and to form a deep notch groove.

On the other hand, according to the large area of the case due to the high capacity and processing into a thin material, the thickness of the case body to which the present invention is applied may preferably be in the range of 0.2 to 0.4 mm. Therefore, the notch groove formed at the specific position as described above can achieve a reliable rupture at an appropriate threshold, although the case body is thinner than the general case body.

As confirmed by the present inventors, when the notch groove was formed on the case main body having a stress distribution exceeding 40% based on the S _MAX of the case, the notch groove was easily broken even at low pressure. As a result, by satisfying the above conditions, breakage at higher pressure than in the case where notch grooves are formed on the case body showing a high stress distribution, that is, a stress distribution exceeding 40% based on S _MAX as in the prior art, Can be.

This notch groove may be a structure that is formed on the case body preferably exhibiting a stress distribution of 10 to 40%, more preferably 25 to 35% of the S _MAX .

On the other hand, the notch groove may have a structure in which the remaining thickness (the thickness after subtracting the depth of the notch groove from the thickness of the case body) has a relatively thin portion on the closed line.

Specifically, the remaining thickness of the relatively thin portion in the notched groove may be 30 to 70% of the average residual thickness of the notched groove, thereby allowing the notched groove to be easily broken at a desired pressure.

Of course, the remaining thickness of the notch groove may be various forms in a range satisfying the above conditions.

In one preferred example, the relatively thin portion of the notch groove may be a structure located on the vertical central axis of the case body.

Therefore, the breakage of the notch groove starts at the vertical central axis of the case body with the smallest remaining thickness, and propagates to a relatively large size (eg, right or left side) and undergoes a process of breaking. . Such a break does not proceed outward due to the closed linear structure, thereby preventing the case from tearing, and the breaking force is concentrated in the notch groove, thereby enabling efficient breakage.

On the other hand, according to the inventors experimentally confirmed, when the notch groove is constant thickness, even if the notched groove is formed in a relatively small portion of the stress in the case body, effective notch breakage was not achieved.

That is, in the case where the notched groove is to be formed with a constant residual thickness, it is very difficult to form a uniform residual thickness, so that the area where the pressure is concentrated is set at an arbitrary position, whereby the operation case is low and the battery case is low even under low pressure. It was confirmed that the problem occurs, such as the phenomenon that the shape of the deformation appears. Accordingly, it was confirmed that the stress value and the remaining thickness of the case body are closely related to the rupture of the notch grooves and the gas discharge.

In one preferred example, the average value of the remaining thickness of the notch groove may be determined in the range of 40 to 70% based on the thickness of the case body. This is determined as a range capable of providing an optimal state in consideration of various factors as described above.

As one example, the remaining thickness of the notched groove on the vertical center axis of the case body is based on the thickness of the case body in a range where an average value of the remaining thickness satisfies 40 to 70% of the size of the case body. 20 to 50% in size.

That is, the remaining thickness of the notch groove is preferably 20 to 50% of the size of the case body on the vertical center axis of the case body. If the size is less than 20%, the notch groove can be easily broken even under a small pressure. If the size is greater than 50%, as described above, the difference between the desired thickness of the notched groove on the vertical central axis and the notched groove on both ends is desired. Since it may not have the operation reliability can be lowered, it is not preferable.

In addition, the remaining thickness may be formed in a gradient structure that is sequentially thinned from both ends of the notched groove to the vertical central axis based on the width direction of the case body. Here, 'sequentially' means gradually thinner in stages. Therefore, it is possible to prevent the pressure from concentrating only on a specific part and to minimize the pressure deviation when the notch groove is broken.

The remaining thickness of the notch groove on the vertical central axis of the case body is not particularly limited as long as it is thinner than the remaining thickness of the both ends to facilitate breaking of the notch groove, and preferably 40 to 70% of the remaining thickness of both ends. It can be formed in size.

As described above, it was confirmed by experiment that the rectangular secondary battery provided with the notch groove having the remaining thickness thinned from the both ends to the vertical central axis can exhibit effective operation reliability.

In another example, the high pressure inside the battery where the notch grooves are broken may be at least twice the pressure of the battery under normal conditions, where the normal condition means atmospheric pressure (1 atm) to 3 atm.

On the other hand, the notch groove is a central position of 1/4 to 1/2 size based on the left and right width of the case body, and in the upper or lower position of 1/20 to 1/4 size based on the upper and lower lengths of the case body. It may be formed.

If the location of the notch groove is out of the above range, it may be difficult to expect breakage of the notch groove and gas discharge at high pressure, and breakage of the notch groove occurs even at a small pressure, which is not preferable in the safety and assembly processability of the high pressure. .

According to the experiments performed by the inventors, as described above, when the pressure continuously rises to a predetermined level or more, the notch grooves can be uniformly broken, so that the gas is quickly discharged to the outside of the battery, resulting in stability of the battery. It was confirmed that it could be improved.

The notch groove may be formed on the case body in a space corresponding to the upper end of the case body and the upper end of the electrode assembly mounted inside the case body, while satisfying the range of the formation position. . In one specific example, the notch groove is close to the top opening of the case body, and within a maximum of 5 mm in the direction of the electrode assembly from the top of the anode of the electrode assembly mounted inside the case body, and corresponding space between the top opening. It may be formed on the case body. The notch groove formed at such a position may be located at the upper portion of the surplus space inside the case, specifically, the electrode assembly mounting portion, to facilitate gas discharge and minimize damage of the electrode assembly.

The notch groove may be formed by various methods, and preferably, may be rolled using a separate punch or formed by laser processing. In some cases, a method of scraping off the surface of the case using a predetermined tool may be possible.

The vertical cross section of the notch groove is not particularly limited as long as it can easily break the notch groove when internal pressure is generated, and may be, for example, a downward wedge or trapezoid. In the case of the downward wedge shape, the fracture occurs due to a crack in the upper end of the notch groove, and in the case of the trapezoid, the fracture occurs due to the shear stress as the short side increases. As a result, it is possible to induce uniform and immediate breakage of the notch groove, thereby ensuring the safety of the battery.

The electrode assembly may not only have a jelly-roll (wound) structure, but also a stacked structure or a stack / foldable structure. Among them, the jelly-roll may be easily manufactured and has a high energy density per weight. Of course, it is not limited.

The secondary battery having such a structure is more preferably a lithium secondary battery.

On the other hand, the notch groove is a structure in which at least part is located within the region of [(length of case body (L)-the width of the jelly-roll anode width (W)) X 2] from the top of the case body. Can be. In addition, preferably 50% or less of the notched groove may be located within a specific area of the case body.

Therefore, when the high pressure gas is ejected through the notch grooves, the electrode may block the notch grooves due to the fluid flow due to the high pressure. Therefore, the notch grooves may be prevented from being blocked when the notch grooves are located at the specific part defined above. have.

As described above, in the rectangular secondary battery according to the present invention, the linear notch grooves formed at positions including a vertical central axis on both sides of the case body include curved portions at least in part, and have a closed linear structure as a whole. It is possible to easily manufacture the notch grooves, and to prevent unnecessary breakage such as propagation or deformation of cracks to the peripheral area of the notch grooves when the safety plate is operated.

Furthermore, by forming a notch groove having a specific structure in a specific shape at a portion where the stress value is relatively small on the side of the battery case, breakage of the notch groove occurs reliably under appropriate conditions, and as a result, safety can be improved.

1 is a schematic diagram of a rectangular secondary battery including a conventional notch groove;
2 is a schematic view of a prismatic secondary battery used in the present invention;
3 is a schematic view of a rectangular secondary battery including a notch groove according to one embodiment of the present invention;
4 is a partial front view of the case body including the notch groove of FIG. 3;
5 and 6 are partial front views of a case body including a notch groove according to another embodiment of the present invention;
FIG. 7 is a photograph showing a stress distribution of the rectangular secondary battery of FIG. 3; FIG.
8 is a photograph showing a vertical cross section of the notch groove of FIG. 3;
9 is a photograph showing a vertical cross section of the notch groove of FIG. 1;
FIG. 10 is a schematic diagram illustrating a process of winding up a jelly-roll type electrode assembly mounted on the battery case of FIG. 2.

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

Figure 2 shows the structure of a conventional rectangular secondary battery according to one embodiment that can be used in the present invention.

Referring to FIG. 2, the rectangular secondary battery 100 is a inside of a rectangular battery case 200 serving as a negative electrode terminal, and has a jelly-roll structure having a structure in which a sheet-shaped positive electrode and a negative electrode are wound with a separator interposed therebetween. The electrode assembly (see FIG. 10) is inserted.

The battery case 200 has an open upper end and a rectangular case body 210 made of a metal material, and a case cap 220 in which an anode terminal 400 is installed at an open upper end of the case body 210. It consists of a structure. The negative electrode terminal may be the case body 210 or the case cap 220 itself electrically insulated from the positive electrode terminal 400.

In order to manufacture such a rectangular secondary battery 100, first, the electrode assembly is inserted into the case body 210, the case cap 220 is seated in the opening of the case body 210, and then its adhesive surface. The site is sealed by laser welding. Then, the electrolyte is injected into the battery case 200, the electrolyte is injected through the injection port 230 formed on one side of the case cap 220. In detail, after the electrolyte is injected into the injection hole 230, a ball member made of aluminum or the like is inserted into the injection hole 230, and a separate metal sheet is seated on the ball member 600 to completely block the injection hole 230. Seal through laser welding in the state. The sealing method of the injection hole 230 is not limited to the above, various other methods may be possible.

The notch groove according to the present invention is formed on the front side 211 or the rear side (not shown) of the case body of the rectangular secondary battery 100.

FIG. 3 is a schematic view of a rectangular secondary battery including a notch groove according to an embodiment of the present invention, and FIG. 4 is a partial front view of the case body including the notch groove of FIG. 3. . For reference, in FIGS. 3 to 7, the size of the safety plate is relatively large compared to the case body for convenience of understanding.

Referring to these drawings together with FIG. 8, the rectangular secondary battery has a safety plate formed on the case body 40 that is broken when a high pressure is generated in the battery, and the safety plate has a vertical center at the front or rear of both sides of the case body 40. As the linear notch groove 60 formed in the position including the axis B, it has a closed linear structure as a whole.

Specifically, the notch groove 60 is an elliptic closed curve having a closed linear structure, and the ellipse has a long axis D located in the width direction Q of the case body 40, and the length of the long axis D is the case body ( 40 is about 35% of the width Q, and the length of the short axis S is about 10% of the width Q of the case body 40.

The elliptic closed curve is about 1/2 of the center position from the right end with respect to the width Q of the case body 40 and an upper position of about 4/10 size with respect to the length L of the case body 40 ( It is formed in a).

In addition, the notch groove 60 has the thinnest size on the vertical center axis B, the thickness of which is the thickness after subtracting the depth of the notch groove 60 from the thickness of the case body 40 on the vertical cross section. have.

The remaining thickness 80 is formed in a structure that is sequentially thinned from both ends A and C toward the vertical central axis B based on the long axis D of the notched groove. That is, the lowest residual thickness of the vertical central axis B of the notched groove 60 forms a residual thickness t of about 30% based on the thickness T of the case body, and gradually increases to both ends A and C. The remaining thickness is thickened to form a thickness of up to 80%.

On the other hand, the notch groove 60 is a region (a) of [(length of case body L-anode width W of jelly-roll with respect to the length direction of case) X 2] from the upper end of the case body 40. Located within. In addition, the jelly roll has a structure in which the cathode 32, the separator 36, and the anode 34 are wound.

5 and 6 are partial front views of a case body including a notch groove according to still another embodiment of the present invention.

Referring to these drawings, the notch groove 61 of FIG. 5 is a single closed curve in a circle shape, and the diameter b of the circle is about 20% of the width W of the case body 40, and FIG. 6. The notch groove 62 of the ellipse has a structure in which the arcs 63 and 64 of the ellipse are located at both sides, and the pair of straight lines 65 and 66 connect the arcs 63 and 64 of the ellipse. ) Passes through the vertical central axis B of the case body 40.

In addition, in the notch groove 62 of FIG. 6, the closed linear structure has a length of the long axis D being about 40% of the width W of the case body 40, and a length of the short axis S is the case body 40. ) Is about 10% of the width (W).

FIG. 7 is a photograph showing the stress distribution of the rectangular secondary battery of FIG. 3.

Referring to FIG. 7 together with FIG. 3, the notch groove 60 of the case body 40 is a member that can be cut out to discharge the high pressure gas, based on the maximum stress S _MAX of the case body 40. An elliptic closed curve is formed at the site of the case showing a stress distribution of about 25 to 35%.

As shown in FIG. 7, the stress distribution has a tensile stress that appears in each region when a constant pressure is applied, and a high brightness portion (light color portion) is a portion having a relatively high stress as a maximum stress (S _MAX ). The site of distribution, the site of low brightness (dark site) is a site of relatively low stress, and means the site of minimum stress (S _MIN ) distribution.

8 is a photograph showing a vertical cross section of the notch groove of FIG. 3.

Referring to FIG. 8, the vertical cross section of the notch groove 60 is formed in a downward wedge shape, and the average value of the remaining thickness 80 is about 40% based on the thickness T of the case body 40. Formed.

Therefore, when the internal pressure gradually increases to generate a pressure three times greater than the normal battery internal pressure, cracks occur in the notch groove 60 and are easily ruptured, thereby quickly discharging gas to the outside of the battery, and consequently improving the stability of the battery. You can.

FIG. 10 is a schematic diagram illustrating a process of winding up a jelly-roll type electrode assembly mounted on the battery case of FIG. 2.

Referring to FIG. 10, the jelly-roll 10a may include the negative electrode tab 31 and the positive electrode tab 33 on the uncoated portion 36 to which the electrode active material is not coated at the left ends of the negative electrode 32 and the positive electrode 34. After attaching vertically, the cathode 32 and the anode 34 are manufactured by winding from the left end to the right end direction.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (19)

An electrode assembly composed of a positive electrode, a negative electrode, and a separator is a rectangular secondary battery sealed in a rectangular battery case, wherein the battery case is open at the top and is formed of a rectangular case body made of a metallic material, and coupled to an open upper end of the case body. It consists of a case cap containing the electrode terminal,
A safety plate is formed on the case body that breaks when a high pressure is generated inside the battery.
The safety plate is a linear notch groove formed at a position including a vertical central axis on both sides of the case body, wherein the notch groove includes a curved portion at least in part and has a closed linear structure as a whole. Square secondary battery characterized by. The rectangular secondary battery of claim 1, wherein the closed linear structure comprises at least one portion selected from the group consisting of arcs of circles, arcs of ellipses, splines, and straight lines. The rectangular secondary battery of claim 2, wherein the closed linear structure is formed of a closed curve of a circle or an ellipse. The rectangular secondary battery of claim 3, wherein the closed linear structure is a single closed curve having an ellipse shape, and the ellipse has a long axis or a short axis in a width direction of the case body. The rectangular secondary battery of claim 4, wherein the length of the ellipse is 20 to 80% of the width of the case body. The rectangular secondary battery of claim 4, wherein the length of the ellipse is about 3 to 20% of the width of the case body. 4. The rectangular rechargeable battery of claim 3, wherein the closed linear structure is a single closed curve in a circular shape. The rectangular secondary battery of claim 3, wherein the closed linear structure is a single closed curve in a circle shape, and the diameter of the circle is 5 to 30% of the width of the case body. 4. The rectangular rechargeable battery as claimed in claim 3, wherein the closed linear structure has a form in which an arc and a straight line of a circle or ellipse are combined. 10. The rectangular secondary battery of claim 9, wherein the closed linear structure has a structure in which arcs of circles or ellipses are located at both sides, and a pair of straight lines connect the arcs. The rectangular secondary battery of claim 10, wherein the straight lines pass through a vertical central axis of the case body. The rectangular secondary battery according to claim 10, wherein the closed linear structure has a length of 20 to 80% of the width of the case body and a length of 3 to 30% of the width of the case body. The case body according to claim 1, wherein the case body has a thickness of 0.4 mm or less, and the notch groove is formed on the case body exhibiting a stress distribution of 40% or less based on the maximum stress S _MAX of the case in a high pressure state. Rectangular secondary battery, characterized in that. The rectangular secondary battery according to claim 1, wherein the notch groove includes a portion having a relatively thin thickness on the closed line (the thickness after subtracting the depth of the notch groove from the thickness of the case body). 15. The rectangular secondary battery of claim 14, wherein the remaining thickness of the relatively thin portion of the notched groove is 30 to 70% of the average remaining thickness of the notched groove. 15. The rectangular rechargeable battery of claim 14, wherein a relatively thin portion of the notch groove is located on a vertical central axis of the case body. The prismatic secondary battery of claim 1, wherein the electrode assembly is a jelly roll. The prismatic secondary battery according to claim 1, wherein the secondary battery is a lithium secondary battery. The method of claim 1, wherein the notch groove is at least partially within an area of [(length of case body (L) minus width of jelly-roll in the length direction of case) X 2] from an upper end of the case body. Square secondary battery, characterized in that located.

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