KR101347715B1 - 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 upper end 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 a notch groove of the linear shape formed by laser processing It provides a rectangular secondary battery, characterized in that.

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 TECHNICAL FIELD The present invention relates to a rectangular secondary battery that is constituted of a structure that is a linear notch groove formed by laser processing.

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 embedded in the battery case is a power generator capable of charging and discharging composed of a laminated structure of anode / separation membrane / cathode, a jelly-roll type wound through a separator between a long sheet-type anode and an anode coated with an active material, and It is roughly classified into a stack type in which a plurality of positive and negative electrodes of a predetermined size are sequentially stacked with a separator interposed therebetween, and a stack / folding type in which a unit cell such as a bicell or a full cell is wound with a separator film.

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, in spite of the above-mentioned difference in shape of the battery, there is provided a high-voltage relieving means capable of relieving the high pressure which is a direct cause of the battery explosion.

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 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.

The notch groove of this structure has the advantage of reacting relatively sensitive to the high pressure generated in the battery, but it is difficult to accurately set the pressure threshold intended 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. .

Meanwhile, in the conventional rectangular secondary battery, the notch groove is mainly formed by press working. However, when the depth of the notch groove is deeply processed in order to lower the pressure at which the notch groove breaks in the press working, deformation of the battery case such as the depression of the notch groove region and the protrusion of the adjacent notch groove after the processing of the safety plate occurs. This deformation is caused by the flow of the material (for example, aluminum) generated by the amount of deformation when the notch groove is processed into a press.

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.

The inventors, after extensive research and various experiments, confirmed that the notch grooves were excellent in dimensional stability before and after processing and the notch grooves were not deformed when the notch grooves were formed in the case body by laser processing.

In addition, when a notch groove having a specific structure is formed at a site 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 an improved notch groove having excellent dimensional stability and no deformation.

Square secondary battery according to the present invention for achieving this object,

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 that breaks when a high pressure is generated inside the battery is formed on the case body, and the safety plate has a structure that is a linear notch groove formed by laser processing.

Therefore, in the rectangular secondary battery according to the present invention, since the linear notch groove is formed in the case body by laser processing, compared with the structure of the rectangular secondary battery in which the conventional linear notch groove is formed in the case body by press working. It has excellent dimensional stability before and after processing and has the advantage that the notch groove is not deformed.

That is, the laser processing method of the notch groove according to the present invention can effectively suppress the appearance deformation and the dimensional deformation of the battery case generated during press working, and can effectively make the desired notch groove depth by repeatedly irradiating the laser.

For reference, laser processing in the present invention means processing the material by the focused laser beam. Therefore, the stamping method of the notch groove using the laser of the present invention as described above has a merit that there is no wear of the tool because the heat deformation layer is narrow and non-contact because a part of the case body is heated and processed at high speed. In addition, the notch groove can be accurately imprinted on the case body, there is an advantage that there is no noise and vibration during operation.

Preferably, the laser is not particularly limited as long as it does not cause deformation in the case body when the notch groove is formed. Preferably, the laser may be a pulse laser or a continuous wave laser.

Specifically, a pulsed laser is used to create the desired notch depth. In this case, the laser speed, overlap rate, power, etc. are adjusted in order to create the desired depth of the notched groove, and through one or several repeated laser processings. The working pressure of the desired safety valve can be made.

In addition, in order to make the depth of a notch groove uniform, it is preferable to use a continuous wave laser.

In some cases, the laser may be a carbon dioxide, ruby, or YAG laser.

In one preferred 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 under high pressure. Can be.

Therefore, the notch groove is formed in a relatively small portion where the stress value is 40% or less in the stress distribution of the case body, thereby preventing the notch groove from easily breaking even at low pressure, and providing a high breaking pressure. And the formation of deep notches.

Preferably, in the notch groove of the rectangular secondary battery, the remaining thickness of the case body (the thickness after subtracting the depth of the notch groove from the thickness of the case body) is formed in a structure that becomes thinner from both ends to the center portion in the longitudinal direction. Therefore, the notch groove exhibits high operating reliability, and gas is quickly discharged to the outside of the battery by the rupture of the uniform notch groove, thereby ensuring the safety of the battery.

According to the recent large capacity 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 be preferably 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 of a thin thickness than the general battery case.

The high pressure inside the battery where the notch groove is broken may be a pressure that is at least twice the internal pressure of the battery under normal conditions, and the normal condition means a state of atmospheric pressure (1 atm) to 3 atm.

As defined above, the linear notched 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 the high pressure state as described above.

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. 4.

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, the notch groove is formed in a portion where the stress value is relatively small in the stress distribution of the case main body, thereby preventing the notch groove from easily breaking even at low pressure, and providing high breaking pressure and deep notch. Formation is possible.

The notch groove may be formed in the vertical central axis portion on both sides (front or rear) of the case body, and more preferably, 1/4 to 1/2 size of the left and right width of the case body In the center position, it may be formed in the upper or lower position of 1/20 to 1/5 size based on the upper and lower lengths of the case body.

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 the notch groove may be broken 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.

In particular, the notch groove according to the present invention is formed in an arc shape, thereby preventing the gas discharge from being excessively biased in any part of the notch groove, thereby minimizing the pressure deviation during breakage of the notch groove, for a thin case body The strength of the case itself can be secured.

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 minimum remaining thickness of the center portion of the notched groove may be 20 to 50% size based on the thickness of the case body. If the depth is less than 20%, the notch groove can be easily broken even under a small pressure. If the depth is greater than 50%, as described above, the thickness of the center and both ends of the notched groove does not have a desired difference. It is not preferable because the reliability can be lowered.

In addition, the remaining thickness may be configured to be sequentially thinned from both ends toward the center portion. Here, 'sequentially' means gradually thinner in stages. Therefore, this residual thickness structure can prevent the pressure from concentrating only on a specific portion and can minimize the pressure deviation during breakage of the notch groove.

The remaining thickness of the center portion in the notch groove is not particularly limited as long as the thickness of the center portion is thinner than the remaining thickness of both ends, so that the notch groove is easily broken. Preferably, the thickness of the center portion may be 40 to 70% of the remaining thickness of both ends.

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 both ends toward the center part can exhibit effective operation reliability.

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 shape or a trapezoidal shape. 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 trapezoidal shape, the fracture occurs due to the shear stress while the short side is increased. 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.

The notch groove may be configured in various shapes as needed, for example, may be a branched or closed curve shape.

 Specifically, when the notch groove has a branched shape, the notch groove has a first notch groove formed at a vertical central axis portion on both sides of the case body, and one branched at at least one position of the first notch groove. It may be composed of two or more second notch grooves, and this structure can prevent unnecessary tearing of the notch grooves and efficiently perform the ejection of gas after the operation of the notch grooves.

In addition, when the notch groove has a closed curve shape, the notch groove may include a curved portion at least in part, and may have a circular or elliptic closed curve structure as a whole, and such a structure may include a conventional notch groove 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 some cases, the notch groove is a section in which the remaining thickness (the thickness after subtracting the depth of the notch groove from the thickness of the case body) is discontinuously decreased in the vertical central axis portion of the case body ("discontinuous reduction section"). This structure may be a structure including a deformation of the case body generated during the safety plate processing, compared with the safety plate structure in which the residual thickness of the conventional notched groove is continuously reduced from both ends of the case body toward the vertical central axis portion. Can improve the operating reliability of the safety valve.

In the above structure, the notch groove is preferably a structure having a 'U', 'V', or 'trapezoid' shape on the vertical cross section in the longitudinal direction.

As described above, in the rectangular secondary battery according to the present invention, by forming the linear notch grooves in the case body by laser processing, the dimensional stability of the notched grooves before and after processing can be excellent and the notch grooves can be prevented from being deformed.

In addition, the notch groove is formed in a specific portion of low stress, and the notch groove is formed in a circular arc shape and the thickness of the notch groove becomes thinner toward the center thereof based on the entire length of the notched groove. By operating reliably, it is possible to effectively discharge the high pressure gas inside the battery, thereby greatly improving the safety of the battery.

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 photograph showing a stress distribution of the square battery of FIG. 3;
5 is a photograph showing a stress distribution of a square battery including a notch groove according to another embodiment of the present invention;
FIG. 6 is a partial front view including the notch groove of FIG. 3; FIG.
7 is a photograph showing a vertical cross section of the notch groove of FIG. 3;
8 is a photograph showing a vertical cross section of the notch groove of FIG. 1;
9 is a schematic diagram showing a process of winding up a jelly-roll type electrode assembly mounted on the battery case of FIG. 2;
10 to 12 are partial front views of a case body including notched grooves according to another embodiment of the present invention;
FIG. 13 is a graph illustrating various residual thicknesses along the length of the notch groove of FIG. 12.

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. 9) 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.

3 is a front view showing the shape of a notch groove according to an exemplary embodiment of the present invention, and FIG. 4 is a photograph showing a stress distribution of the rectangular secondary battery of FIG. 3. For reference, in FIG. 3, 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 formed of a linear notch groove 60 formed by laser processing.

The notch groove 60 of the case body 40 is a cuttable member for discharging the high pressure gas, and is formed in a part of the case which exhibits a stress distribution of about 25 to 35% based on the maximum stress S _MAX of the case. The center of curvature of the arc is formed in the shape of an upward arc located at the top.

As shown in Figure 4, the stress distribution is a tensile stress appearing in each region when a constant pressure is applied as a contour line, the high brightness (light region) is a relatively high stress as 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.

The arc shape of the notch groove 60 is about one-tenth the size of the center position of about one-third the size of the case body 40 and the length L of the case body 40. It is formed in the upper position. In addition, the arc-shaped curvature is composed of a curvature formed with a radius R of about 1/2 of the length L of the case body 40. By this arc shape, the notch groove 60 can maintain a constant mechanical strength while making the gas discharge uniform.

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 longitudinal direction of case) X 2] from the top 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.

In addition, the circular arc may have an upward arc shape in which the center of curvature of the arc is located at the upper side as in FIGS. 3 and 4, but on the contrary, as in FIG. 5, the circular arc in which the center of curvature of the arc is located at the bottom as in FIG. 5. It may be a shape.

Referring to FIG. 5 together with FIG. 3, the arc shape of the notch groove is the same as the position and curvature of the notch groove of FIG. 3 except that the center of curvature of the arc is formed in a downward arc shape having a lower portion. Detailed description will be omitted.

FIG. 6 is a partial front view showing the shape of the notch groove of FIG. 3, and FIG. 7 is a photograph showing a vertical cross section of the notch groove of FIG. 3.

Referring to these figures, the remaining thickness 80 is formed in a structure that is sequentially thinned from both ends 1 and 5 toward the central portion 3 based on the total length l of the notched groove. That is, the minimum remaining thickness of the center portion 3 of the notch groove 60 forms a transfer thickness t of about 30% based on the thickness T of the case body, and the remaining thickness becomes thicker toward both ends. Shape 80% of the thickness.

On the other hand, the vertical cross section of the notched groove 60 is formed in a downward wedge shape, and the average value of the remaining thickness is formed to a depth of about 40% based on the thickness T of the case body 40.

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 and is easily ruptured, thereby quickly discharging gas to the outside of the battery, and consequently, improving the stability of the battery. .

FIG. 9 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. 9, 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.

10 to 11 are partial front views of a case body including a notch groove according to still another embodiment of the present invention.

First, referring to FIG. 10, the notch groove has an arc-shaped first notch groove 61 and an amount of the first notch groove 61 formed at portions of the vertical central axis 3 on both sides of the case body 40. It consists of two straight second notched grooves 62 branched at the end portion.

Further, the second notched groove (62) is branched from the distance (L _a) to the end portion direction in the range of 0.4L for _a deflected position to the end portion from the central axis (3) of the first notched groove 61, and And the first notch groove 61.

Next, referring to FIG. 11, the safety plate is a linear notch groove 63 formed at a position including a vertical center axis B at the front or rear side of both sides of the case body 40, and the closed linear structure as a whole. Have

Specifically, the notch groove 63 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.

FIG. 12 is a partial front view of a case body including a notch groove according to another embodiment of the present invention. FIG. 13 is a graph showing various residual thicknesses according to the length of the notch groove of FIG. 12. It is.

Referring to these drawings, the safety plate is a linear notch groove 64 formed at a position including a vertical center axis (h-h ') at the front or rear of both surfaces of the case body 40, and the notch groove 64 ) Includes a section d in which the residual thickness b discontinuously decreases at the vertical central axis h-h 'of the case body 40.

In addition, the non-continuous reduction period d of the notch groove 64 is from the vertical center axis h-h 'of the case body in the size range of about 20% based on the length l of the notch groove 64. It is formed at the left side region 61 and the right side region 62 spaced apart.

Further, the residual thickness b on the case body vertical center axis h-h 'is about 30% of the residual thickness a at both ends of the notched groove, based on the non-continuous reduction interval d. Reference numeral 64 has a substantially 'U' shape in the vertical direction in the longitudinal 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 (21)

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,
The safety plate is broken on the case body when the high pressure inside the battery is generated, the safety plate consists of a linear notch groove formed by laser processing, the case notch groove is the maximum stress of the case under high pressure ( S _MAX ) is formed on the case body showing a stress distribution of 40% or less,
The notch grooves are formed on the case body portion corresponding to the space between the top opening of the case body and the top of the electrode assembly mounted inside the case body, while being located at the vertical central axis portions on both sides of the case body.
The notch groove has a downward arc shape in which the center of curvature of the arc is located below, and has a radius of curvature of 1/3 to 1.5 times the upper and lower lengths of the main body.
The thickness of the case main body secondary battery, characterized in that the remaining thickness after subtracting the depth of the notch groove is made thinner from both ends toward the center of the notch groove. The rectangular secondary battery of claim 1, wherein the laser is a pulse laser or a continuous wave laser. delete delete According to claim 1, wherein the thickness of the case body is a rectangular secondary battery, characterized in that in the range of 0.2 to 0.4 mm. The rectangular secondary battery according to claim 1, wherein the high pressure inside the battery where the notch groove is broken is at least twice the pressure of the battery under normal conditions. The rectangular rechargeable battery as claimed in claim 1, wherein the notch groove is formed on a case body exhibiting a stress distribution of 10 to 40% of the maximum stress S _MAX . delete delete delete delete delete The rectangular secondary battery of claim 1, wherein the average thickness of the remaining thickness is 40 to 70% based on the thickness of the case body. The rectangular secondary battery of claim 1, wherein a minimum remaining thickness of the center portion of the notch groove is 20 to 50% based on the thickness of the case body. delete The rectangular secondary battery of claim 1, wherein the remaining thickness of the center portion of the notch groove is 40 to 70% of the remaining thickness of both ends. The rectangular secondary battery of claim 1, wherein a vertical cross section of the notch groove has a downward wedge shape. The rectangular secondary battery of claim 1, wherein a vertical cross section of the notch groove has 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. delete

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