KR101326186B1 - Prismatic Secondary Battery Employed with Safety Plate - Google Patents

Abstract

The present invention is a rectangular secondary battery in which an electrode assembly consisting of a positive electrode, a negative electrode and a separator is sealed in a rectangular battery case, the battery case is open at the top and a rectangular case body made of a metal material, the case body is opened It is composed of a case cap coupled to the top and including an electrode terminal, a safety plate is formed on the case body when the high pressure inside the battery is generated, the safety plate is notched groove of two or more discontinuous line It provides a rectangular secondary battery, characterized in that consisting of.

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 the upper side of the battery case is open. A rectangular case body made of a metal 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 when the high pressure inside the battery is generated, the safety plate Relates to a square secondary battery consisting of two or more discontinuous linear notches.

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 on the side edge of the rectangular secondary battery case 20, and is formed to be partially open. That is, the notch groove is formed in a portion where the stress value is relatively large in the stress distribution of the case, and is designed to break the curved shape when the battery is excessively increased in internal pressure.

This notch groove 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 high stress is applied to the side edges of the case, breakage of the notch groove can easily occur even at low pressure, and above all, it is particularly sensitive to high pressure when the battery case is thin. As a result, unintentional breakage occurs.

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. .

On the other hand, when the safety plate is long in the conventional rectangular secondary battery, excessive deformation or tearing may occur in the notch grooves.

Therefore, by forming a notch groove in a section where cracks or breaks are difficult to propagate, there is a great need for a technology capable of appropriately controlling energy release after the safety plate is operated.

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 square 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 in-depth study and various experiments, the present inventors can effectively control the energy relaxation phenomenon after the operation of the safety plate and easily solve the high pressure when the safety plate is composed of two or more non-continuous line notches. It was confirmed that there is.

In addition, when a notch groove having a specific structure is formed in a portion where the stress value is relatively small on the side of the battery case, and at the same time, when a notch groove having a specific shape is formed, breakage of the notch groove occurs reliably under appropriate conditions. It was confirmed that the safety 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 upper end of the case body and including an electrode terminal, a safety plate is formed on the case body when the high pressure inside the battery is generated, the safety plate is two It consists of the above-mentioned non-continuous notch grooves.

Therefore, the safety plate of the square battery according to the present invention is formed on the case body so as to break when a high pressure occurs inside the battery, and consists of two or more discontinuous line notches, so that energy relaxation after the safety plate is operated. Can be effectively controlled.

In the present invention, the notch grooves are formed in the shape of "non-continuous line" means that a portion where the depth (or residual thickness) is significantly different than the notch grooves are located between the notch grooves. In other words, it means that the depth or residual thickness at the notched grooves and their mutually spaced areas shows a discontinuous gradient. Therefore, after the high pressure is generated inside the battery and the notch groove (a) of one side is broken, the residual breaking stress is concentrated in the adjacent notch groove (b) to be resolved in the process of causing the notch groove (b) to be broken. Uneven progress may cause deformation, or excessive propagation of the break may prevent the battery case from tearing.

The notches may be, for example, curved and / or straight. That is, the shape of the notch groove can be designed in a curve, a straight line, or a combination of curves and straight lines according to the specifications of the desired battery.

In one preferred example, at least one of the notch grooves has a gradient in the remaining thickness (the thickness after subtracting the depth of the notch groove from the thickness of the case body) on a vertical cross section, thereby facilitating stress concentration for fracture. Can be controlled.

In another preferred embodiment, the case body has a thickness of 0.4 mm or less, and the notched grooves are formed on the case body exhibiting a stress distribution of 40% or less based on the maximum stress S _MAX of the case under high pressure. Can be.

Therefore, the notch grooves of the rectangular secondary battery according to the present invention are formed at relatively small portions having a stress value of 40% or less in the stress distribution of the case body, thereby preventing the notch grooves from easily breaking even at low pressure. It is possible to provide a high breaking pressure and to form a deep notch.

Preferably, as demonstrated in the following experimental example, the depth of the notch groove at a specific position is formed in a thinner structure from both ends to the center portion in the longitudinal direction, whereby the notch groove exhibits high operating reliability and uniform notch groove. Due to the rupture of the gas, the gas is quickly discharged to the outside of the battery to ensure the safety of the battery.

In another example, the notch grooves are located at least partially within the region of [(length of case body (L) minus jelly-roll anode width (W) relative to case length) X 2] from the top of the case body. It can be a structure. In addition, preferably 50% or less of the notched grooves may be located within a specific area of the case body.

Therefore, when the gas of high pressure is ejected through the notch grooves, the electrode may block the notch grooves by the fluid flow due to the high pressure, so that the notch grooves can be prevented from clogging when the notch grooves are located at the specific part defined above. have.

In some cases, the remaining thickness of the notch groove located at the center portion of the case main body has a size of 50% or less based on the thickness of the case main body, so that the notch groove can be easily broken at a desired pressure.

Meanwhile, the notch grooves in the rectangular secondary battery according to the present invention may have various structures.

In one preferred example, the safety plate is composed of two non-continuous curve notch grooves, the notch grooves may be of a structure that is separated on both sides with respect to the vertical center axis of the case body.

In the above structure, the notch grooves may each have a gradient in the remaining thickness on the vertical cross section, and as a specific example, the notch grooves each have a gradient in which the residual thickness becomes thinner from both ends of the case body toward the center of the case body. Can be.

In another preferred example, the notch grooves are connected to bridge notch grooves having a relatively thick residual thickness, so that after the notch grooves are broken, stress can be propagated to the adjacent notch grooves via the bridge notch grooves. Can be.

In the above structure, it is preferable that the residual thickness of the bridge notch grooves is 10 to 90% thicker than the average residual thickness of the notch grooves.

For example, if the residual thickness of the bridge notch grooves is less than 10% thicker than the average residual thickness of the other notch grooves, there is no substantially residual thickness gradient with respect to the notch grooves, thereby implementing a discontinuous line safety plate. On the contrary, having a thick size of more than 90% is not preferable because the selectivity to the propagation direction of the fracture stress as described above may be inferior.

In another example, the safety plate is composed of three discontinuous notch grooves, and the remaining thicknesses of the notch grooves may be the same or different from each other.

In the above structure, for example, the safety plate may be composed of a straight notched groove located in the vertical center axis of the case body, and two curved notched grooves spaced apart from both ends of the straight notched 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 of the specific position and shape can achieve a reliable rupture at an appropriate threshold despite the case body of a thin thickness than the general case body.

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.

As mentioned above, the linear notch grooves may have a structure formed on the case body exhibiting a stress distribution of 40% or less based on the maximum stress S _MAX of the case under the high pressure.

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 battery is shown in FIG. 8.

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 .

Therefore, since the stress value is formed at a relatively small portion of the stress distribution of the case body, it is possible to prevent the notch grooves from being easily broken even at low pressure, and to provide a high breaking pressure and to form a deep notch. Do.

These notched grooves may be formed in the vertical central axis portion on both sides (front or rear) of the case body, and more preferably, 1/5 to 1/2 size of the left and right width of the case body It may be formed in a central position.

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

According to the experiments performed by the present inventors, as described above, when the pressure continuously rises to a predetermined level or more, the notch grooves may 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.

Such notched grooves 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 grooves are 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 between the corresponding top openings. It may be formed on the case body. Notched grooves formed in such a position can be located in the surplus space inside the case, specifically, the upper end of the electrode assembly mounting portion, to facilitate gas discharge and minimize the breakage of the electrode assembly.

In particular, when at least one notch groove is formed in an arc or ellipse shape, the gas discharge is prevented from being excessively biased in any part of the notch groove, thereby minimizing the pressure deviation when the notch groove is broken, and the thin case body The strength of the case itself can be assured.

The arc shape of the notch groove may preferably have a radius of curvature of 1/3 to 1.5 times the vertical length of the case body.

If the radius is too small, the curvature becomes large and the width of the arc shape becomes relatively small. On the contrary, if the radius is too large, the notch groove may be difficult to break even if a high pressure occurs, which is not preferable.

In addition, if the location and curvature of the notch groove do not deviate from the above range, the notch groove may be formed in an upward arc shape in which the center of curvature of the arc is located at the top, or in a downward arc shape in which the center of curvature of the arc is at the bottom thereof. have.

On the other hand, according to the inventors confirmed experimentally, even if the residual thickness of the notch groove is constant, even when formed in an arc shape in a relatively small portion of the stress in the case body, it was not suitable for rupture of the effective notch groove.

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, and as a result, the operation reliability is low and the Problems such as the appearance of deformation occurs. 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 may be determined in the range of 40 to 70% based on the thickness of the body case. This is determined as a range capable of providing an optimal state in consideration of various factors as described above.

In addition, the lowest residual thickness of the portion adjacent to the center of the notched grooves may be 20 to 50% in size based on the thickness of the body case. If the depth is 20% or less, the notch groove can be easily broken even under a small pressure. If the depth is 50% or more, as described above, the difference between the area adjacent to the center of the notch groove and the thickness of both ends of the notch groove are desired. Since it may not have the operation reliability can be lowered, it is not preferable.

In addition, the remaining thickness may have a gradient structure that is sequentially thinned from both ends of the notched groove toward a portion adjacent to the center portion. 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.

If the residual thickness of the portion adjacent to the center in the notch groove is thinner than the remaining thickness of both ends, the thickness is not particularly limited, and preferably, the residual thickness of the portion adjacent to the center portion is equal to the remaining thickness of the both ends. 40 to 70% in size.

As described above, it was confirmed by experiment that the rectangular battery having a notch groove having a structure in which the remaining thickness becomes thinner from the both ends to the portion adjacent to the center portion can exhibit effective operation reliability.

The notch groove may be formed by various methods, and preferably, may be formed by rolling using a separate punch. 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 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 be a jelly-roll (wound) structure having a structure in which long sheets of positive and negative electrodes are wound in a state where a separator is interposed therebetween, and has an advantage of easy manufacturing and high energy density per weight.

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

As described above, the rectangular secondary battery according to the present invention comprises two or more non-continuous notch grooves of the safety plate, to easily control the breaking stress after the operation of the safety plate and to prevent unnecessary breakage of the safety plate. It is possible to efficiently perform gas ejection after the operation of the safety valve.

In addition, by forming notch grooves of a specific structure in a portion where the stress value is relatively small on the side of the battery case, and simultaneously forming at least one notch groove in a specific shape, breakage of the notch grooves occurs reliably under appropriate conditions. 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 to 7 are partial front views of a case body including a notch groove according to another embodiment of the present invention;
FIG. 8 is a photograph showing a stress distribution of the rectangular secondary battery in FIG. 6; FIG.
9 is a photograph showing a stress distribution of a rectangular secondary battery including a notch groove according to another embodiment of the present invention;
10 is a photograph showing a vertical cross section of the notch groove of FIG. 3;
FIG. 11 is a photograph showing a vertical cross section of the notch groove of FIG. 1; FIG.
FIG. 12 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. An electrode assembly (not shown) 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, the rectangular secondary battery has a safety plate formed on the case body 40 that is broken when a high voltage is generated in the battery, and the safety plate is composed of two non-continuous linear notch grooves 60 and 62. .

Specifically, the notch grooves 60 and 62 are formed in two arc shapes, and the arc shape is a center position and a left end of about 1/3 size from the right end with respect to the width Q of the case body 40. From a central position of about one third size and an upper position of about 3/10 size relative to the length L of the case body 40. In addition, the arc-shaped curvature consists of a curvature formed at a radius R of about 3/10 based on the length L of the case body 40. By this arc shape, the notch grooves 60 and 62 can maintain a constant mechanical strength while making gas discharge uniform.

In addition, the notches grooves 60 and 62 have a gradient in the remaining thickness, which is the thickness after subtracting the depth of the notch grooves from the thickness of the case body 40 in the vertical cross section, and the center portion 3 of the case body 40. The remaining thicknesses of the portions 2 and 4 adjacent to each other have a size of 40% based on the thickness of the case body 40.

On the other hand, the notch grooves 60 and 62 are areas of [(length of case body L-anode width W of jelly-roll relative to case length direction) X 2] from the top of case body 40. They are all located within (A), and are separated on both sides with respect to the center part 3 which is the vertical center axis of the case main body 40. As shown in FIG. In addition, the jelly roll has a structure in which the cathode 32, the separator 36, and the anode 34 are wound.

The remaining thickness 80 is formed in a structure that is sequentially thinned from both ends 1 and 5 toward the center 3 based on the total length l of the notched groove. That is, the lowest residual thickness of the portions 2 and 4 adjacent to the center 3 of the notched grooves 60 and 62 forms a residual thickness t of about 30% based on the thickness T of the case body. In addition, the remaining thickness becomes thicker at both ends 1 and 5 to form a thickness of up to 80%.

In addition, according to the adjustment of the appropriate range and pressure of the notch groove, as shown in the graph of FIG.

5 to 7 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 safety plate of FIG. 5 includes a straight notch groove 66 positioned at a vertical center axis of the case body 40, and two curved notched grooves spaced apart from both ends of the straight notch groove 66. (64, 66). The separation distance may be 5 to 30% in size based on the length of the straight notch groove 66.

Next, the safety plate of FIG. 6 is 70% thicker than the arc-shaped notch grooves 61 and 63 and the remaining thickness of the arc-shaped notch grooves 61 and 63 in the case body 40. The bridge notch groove 65 is formed to connect the notch grooves 61 and 63, and the safety plate of FIG. 7 has nine notch grooves 67 formed in the case body 40.

FIG. 8 is a photograph showing a stress distribution of the rectangular secondary battery of FIG. 6, and FIG. 9 is a photograph showing a stress distribution of a rectangular secondary battery including a notch groove according to another embodiment of the present invention. It is.

First, referring to FIG. 8 together with FIG. 6, notch grooves 61, 63, and 65 of the case body 40 are cuttable members for discharging high-pressure gas, and the maximum stress S _MAX of the case is _measured . It is formed in the upward arc shape in which the center of curvature of a circular arc is located in the site | part of the case which shows the stress distribution of about 25 to 35% as a reference | standard.

As shown in FIG. 8, the stress distribution is represented by the contour lines of the tensile stress of each part when a constant pressure is applied, and the part with high brightness (light color part) is the part with relatively high stress and the 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.

In addition, although the circular arc may be an upward circular arc shape in which the center of curvature of a circular arc is located in the upper part like FIG. 8, the circular arc may be a downward circular arc shape in which the center of curvature of a circular arc is located in lower part as shown in FIG. .

FIG. 10 is a photograph showing a vertical section of the notch groove of FIG. 3.

Referring to FIG. 10, the vertical cross section of the notch groove 61 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 rises to generate a pressure greater than twice the normal battery internal pressure, a crack occurs in the notch groove 61 and is easily ruptured, thereby quickly discharging gas to the outside of the battery, resulting in improved battery stability. You can.

FIG. 12 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. 12, the jelly-roll 10a may include the negative electrode tab 31 and the positive electrode tab 33 on the uncoated portion 36 on 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 (24)

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 an electrode terminal,
A safety plate is formed on the case body when a high pressure inside the battery is generated, and the safety plate is composed of two or more notched grooves spaced apart from each other, and the two or more notch grooves are formed in a discontinuous line shape. Forming a safety plate, the notched grooves are rectangular secondary battery, characterized in that formed on the case body showing a stress distribution of 40% or less based on the maximum stress (S _MAX ). The rectangular secondary battery of claim 1, wherein the notch grooves have a curved line, a straight line, or a curved line and a straight line. The rectangular secondary battery according to claim 1, wherein at least one of the notch grooves has a gradient in a residual thickness (a thickness after subtracting the depth of the notch grooves from the thickness of the case body) on a vertical cross section. The thickness of the case body is 0.4 mm or less, and the notch grooves are formed on the case body exhibiting a stress distribution of 40% or less based on the maximum stress (S _MAX ) of the case under high pressure. Square secondary battery characterized by. 2. The notch groove according to claim 1, wherein all the notches are all or part within an area of [(length of case body L-anode width W of jelly-roll relative to case length) X 2] from the top of the case body. Rectangular secondary battery, characterized in that is located. The rectangular secondary battery of claim 1, wherein the remaining thickness of the notch groove located at the center of the case body has a size of 50% or less based on the thickness of the case body. The rectangular secondary battery of claim 1, wherein the safety plate is formed of two discontinuous curved notch grooves, and the notch grooves are separated at both sides with respect to the vertical center axis of the case body. The rectangular secondary battery of claim 7, wherein each of the notch grooves has a gradient at a residual thickness in a vertical cross section. The rectangular secondary battery of claim 8, wherein each of the notch grooves has a gradient in which the remaining thickness becomes thinner from both end portions of the case body toward the center portion of the case body. The rectangular secondary battery of claim 7, wherein the notch grooves are connected to bridge notch grooves having a relatively thick thickness. The secondary type secondary cell of claim 10, wherein the remaining thickness of the bridge notch grooves is 10 to 90% thicker than the average residual thickness of the notch grooves. The rectangular secondary battery of claim 1, wherein the safety plate is configured of three discontinuous notch grooves, and the remaining thicknesses of the notch grooves are the same or different from each other. The rectangular secondary battery of claim 12, wherein the safety plate comprises a straight notch groove positioned at a vertical center axis of the case body, and two curved notched grooves spaced apart from both ends of the straight notch groove. The rectangular secondary battery according to claim 4, wherein the case body has a thickness in a range of 0.2 to 0.4 mm. The rectangular secondary battery according to claim 4, wherein the high pressure inside the battery where the notch grooves are broken is at least twice the pressure of the battery under normal conditions. The rectangular secondary battery of claim 4, wherein the notch grooves are formed on a case body that exhibits a stress distribution of 10 to 40% of the maximum stress S _MAX . The rectangular secondary battery of claim 1, wherein the notch grooves are formed at vertical central axis portions on both sides of the case body. 18. The rectangular secondary battery according to claim 17, wherein the notch groove is formed on a case body in a space corresponding between an upper end opening of the case body and an upper end of an electrode assembly mounted inside the case body. The rectangular secondary battery of claim 2, wherein the curve has an arc or an ellipse shape. 20. The rectangular secondary battery of claim 19, wherein the notch groove has an upward arc shape having a center of curvature of the arc or a downward arc shape having a center of curvature of the arc. The rectangular secondary battery of claim 1, wherein the vertical cross sections of the notch grooves have a downward wedge shape. The rectangular secondary battery of claim 1, wherein the vertical cross sections of the notch grooves have a trapezoidal shape. 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.

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