KR20160034884A - Prismatic Secondary Battery Employed with Safety Plate - Google Patents

Abstract

The present invention relates to a square secondary battery, wherein an electrode assembly comprising an anode, a cathode, and a separation film is sealed in a square cell case. The cell case comprises: a rectangular case main body formed of a metal material, wherein the upper end is open; and a case cap including an electrode terminal and connected to the open upper end of the case main body. A safety plate, which is fractured when high pressure is generated in the battery, is formed on the case main body. The safety plate has a linear groove crossing a vertical center axis on both sides of the case main body, and the left part and the right part of the groove is asymmetry based on the vertical center axis of the case main body. A residual thickness (the depth of the groove is deducted from the thickness of the case main body) on the vertical center axis in the groove is the thinnest.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a Prismatic Secondary Battery Employed with Safety Plate,

The present invention relates to a prismatic secondary battery having a safety plate, and more particularly, to a prismatic secondary battery in which an electrode assembly composed of an anode, a cathode and a separator is sealed in a rectangular battery case, The safety plate is a linear notch groove formed on both sides of the case body so as to cross the vertical center axis. The notch groove has a vertical center axis of the case body, The left side portion and the right side portion of the notch groove are asymmetric with respect to each other and the remaining thickness on the vertical center axis in the notch groove is the thinnest.

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 shown in Fig. 1 is formed in a small contour on the side edge of the rectangular-type secondary battery case 20, and is 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, so that the curve shape is designed to break when the internal pressure of the battery rises excessively.

The notched groove having such a structure has an advantage of being sensitive to a high pressure generated in the battery relatively, but it is difficult to accurately set an intended pressure threshold in designing the battery.

That is, as mentioned above, since the high stress is applied to the side edge portion of the case, the notch groove can be easily broken even at a low pressure. In particular, when the thickness of the battery case is thin, So that unintended fracture occurs.

Therefore, it is necessary to make the size and depth of the notch grooves formed in the portion having a large stress value relatively small. If the size and depth of the notch grooves are made small, the notch grooves are not smoothly broken .

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, in such a structure, a safety plate made of a notch groove is formed at the upper central portion of the battery case having a relatively small stress, so that the breaking pressure of the safety plate can be increased with respect to a thin plate having a large area and a small thickness. However, There is a problem that unnecessary breakage such as propagation or deformation may be caused. Furthermore, since it is difficult to predict the directionality of the fracture with respect to the center portion, it is difficult to design the battery structure.

Therefore, it is a very important technology for a prismatic secondary battery having a safety plate structure that can solve the complicated problems of the conventional prismatic secondary battery as described above.

In addition, the shape of the notch groove is expected to be a very important factor for reliably operating under abnormal conditions.

Therefore, in consideration of the thickness of the battery case, the position of the notch groove according to the stress value, the shape of the notch groove, the length, the depth, and the like in a comprehensive manner, when the internal pressure increases, the gas is quickly discharged It is necessary to develop a prismatic secondary battery which can be used as a secondary battery.

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

The present inventors have conducted intensive research and various experiments and have found that the left side portion and the right side portion of the notch groove are asymmetrical with respect to the vertical center axis of the case body and the remaining thickness on the vertical center axis in the notch groove is made the thinnest It is possible to easily manufacture the notch grooves and to prevent unnecessary breakage such as crack propagation or deformation in the surrounding area when the safety plate is operated and to predict the directionality of the breakage and to design the battery accordingly Respectively.

In addition, when notch grooves having a specific structure are formed in a region where the stress value is relatively small on the surface of the battery case and at the same time, notched grooves having a specific shape are formed, the notch grooves can be reliably broken under proper conditions, Can be improved.

Accordingly, an object of the present invention is to provide a prismatic secondary battery having a safety plate with an improved structure that can be effectively broken at a necessary point.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a prismatic secondary battery includes a prismatic secondary battery in which an electrode assembly composed of an anode, a cathode, and a separator is sealed in a rectangular battery case, 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 main body to break when a high pressure inside the battery is generated,

The safety plate is a linear notch groove which intersects the vertical center axis on both sides of the case body. The left and right sides of the notch groove are asymmetrical with respect to the vertical center axis of the case body, (The thickness after the depth of the notch groove is subtracted from the thickness of the case main body) on the central axis is the thinnest.

Therefore, the safety plate of the prismatic secondary battery according to the present invention has a structure in which the notch grooves on the lines crossing the vertical central axis on both sides of the case body are asymmetric with respect to the left side portion and the right side portion of the notch groove with respect to the vertical central axis of the case body It is possible to solve the problem that it is difficult to form a symmetrical structure by making the notch thinner toward the center of the battery case as compared with the safety plate structure in which the left side portion and the right side portion of the conventional notch groove are symmetrical to each other. Further, by making the notch grooves of the left side portion or the right side portion relatively large relative to the vertical central axis of the case body, the break directionality of the notch groove can be predicted, and the design of the battery or the battery pack .

In addition, since the residual thickness on the vertical center axis in the notch groove is the thinnest, when the high pressure inside the battery is generated, the portion located on the vertical central axis among the notch grooves is torn first so that the safety plate is unnecessary at portions other than the desired notch grooves And the gas can be effectively discharged to the outside after the operation of the safety plate.

For reference, both surfaces of the case body in the present specification mean the front or rear surface of the case body.

The notch grooves may, for example, be curved and / or straight. That is, the shape of the notch groove can be designed as a curve, a straight line, or a combination of a curve and a straight line according to the specification of a desired battery.

In one preferred example, the notch groove is formed at least partially within the region of the upper end of the case body ((length L of the case body - positive electrode width W of the jelly-roll with respect to the longitudinal direction of the case) X 2] It can be a structure located. Preferably, not more than 50% of the notch grooves may be located within a specific region of the case body.

Therefore, when the high pressure gas is ejected through the notch groove, the electrode can block the notch groove by the fluid flow due to the high pressure. Therefore, when the notch groove is located at the specific region defined above, the notch groove can be prevented from being clogged have.

In some cases, the line-shaped notch grooves may be formed on the case body which exhibits a stress distribution of 40% or less based on the maximum stress (S _MAX ) of the case under a high pressure.

The stress distribution can be variously changed depending on the shape, structure, and the like of the battery case, and the stress distribution in a typical prismatic secondary battery is shown in Fig.

In one specific example, the thickness of the case body is 0.4 mm or less, and the notch groove is formed on the case body which exhibits a stress distribution of 40% or less based on the case maximum stress (S _MAX ) at a high pressure Structure.

Therefore, the notch groove of the prismatic secondary battery according to the present invention is formed in a relatively small region where the stress value in the stress distribution of the case body is 40% or less, so that the notch groove can be prevented from being easily broken even under low pressure It is possible to provide a high breaking pressure and to form a deep notch groove.

Preferably, the depth of the notch groove at a specific position is formed to be thinner from the both ends toward the vertical center axis of the case body with respect to the longitudinal direction, so that the notch groove exhibits high operation reliability, The gas can be quickly discharged to the outside of the battery to secure the safety of the battery.

On the other hand, 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 in accordance with the enlargement of the case due to the high capacity and the processing into the thin material. Therefore, the notch groove having the specific position and shape can achieve a reliable rupture at an appropriate threshold value even though the case body is thinner than the general case body.

It has been confirmed by the present inventors that the notch grooves are easily broken even at low pressures when the notch grooves are formed on the case body showing a stress distribution exceeding 40% with respect to the case S _MAX . As a result, by satisfying the above-described conditions, it is possible to obtain a higher stress distribution than the case where the notch grooves are formed on the case body that exhibits a stress distribution exceeding 40% based on S _MAX , .

Such a notch groove may be a structure formed on the case main body, which preferably exhibits a stress distribution of 10 to 40% of S _MAX , more preferably a stress distribution of 25 to 35%.

On the other hand, the structure in which the left side portion and the right side portion of the notch groove are asymmetric with respect to the vertical center axis of the case body may be variously formed as needed.

In one preferred example, the length of the left side portion or the right side portion of the notch groove with respect to the vertical center axis of the case body may be larger than the length of the corresponding right side portion or the left side portion.

Specifically, the length of the left side portion or the right side portion of the notch groove may be 10% to 80% larger than the length of the corresponding right side portion or the left side portion with respect to the vertical central axis of the case body.

The break of the notch groove starts from the vertical central axis portion of the case body having the thinnest remaining thickness, and propagates to a relatively large size portion (for example, the right side portion), so that the fracture progresses. Therefore, by designing such an arrangement that a separate safety element, detection element or the like is placed in the relevant region by the prediction of such breaking direction, or an additional member is added to the outer surface of the case body or the inner surface of the battery pack case corresponding thereto .

As described above, the remaining thickness of the notch groove on the vertical center axis of the case body is the thinnest, for example, 50% or less based on the thickness of the case body, Can be easily broken.

The remaining thickness of such a notch groove can be variously formed within a range satisfying the above conditions.

In one example, the residual thickness of the notch groove may be such that the first differential value of the residual thickness along the length of the notch groove is discontinuous on the vertical central axis of the case body and increases toward the end of the notch groove .

In another example, the residual thickness of the notch groove may be such that the first derivative of the residual thickness along the length of the notch groove is continuous on the vertical center axis of the case body and increases toward the end of the notch groove.

In some cases, in the above structure, the remaining thickness of the notch groove may be changed by one or more times in the end direction. For example, the structure may be changed by one to five times.

On the other hand, the present inventors have experimentally confirmed that when the remaining thickness of the notch groove is constant, even when the notch groove is formed in the portion where the stress is relatively small in the case body, effective rupture of the notch groove is not achieved.

That is, in the case of forming a notch groove with a certain residual thickness, it is very difficult to form a uniform residual thickness, so that a portion where pressure is concentrated is set at an arbitrary position, The shape of the surface of the substrate is deformed. As a result, it was confirmed that the stress value and the residual thickness of the case body are closely related to the rupture of the notch groove and the gas discharge.

In one preferred example, the average value of the remaining thickness of the notch groove can 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.

Specifically, the residual thickness of the notch groove on the vertical center axis of the case body is preferably 20 to 70% based on the thickness of the case body, in the range of 40 to 70% 50% size.

That is, the remaining thickness of the notch groove is preferably 20 to 50% of the thickness of the case body on the vertical center axis of the case body. If the size is less than 20%, the notch groove may easily break even under a small pressure. If the size is more than 50%, the notch groove of the vertical central axis and the notch groove of the both end portions may have a difference in the desired degree The operation reliability can be lowered.

In addition, the residual thickness may be a gradient structure in which the thickness gradually decreases from both ends of the notch groove to the vertical center axis. Here, " sequentially " means gradually becoming gradually thinner. Accordingly, it is possible to prevent the pressure from concentrating only in a specific region and to minimize the pressure deviation when the notch groove is broken.

The remaining thickness of the notch grooves on the vertical central axis of the case body is not particularly limited as long as the remaining thickness of the notch grooves is thinner than the remaining thickness of the both ends so that the notch grooves can be easily broken. Preferably, the remaining thickness is 40 to 70% . ≪ / RTI >

As described above, it has been experimentally confirmed that a prismatic secondary cell having a notch groove having a structure in which the residual thickness is thinned from both ends to the vertical central axis can exhibit effective operation reliability.

In another example, the high pressure inside the cell in which the notch grooves are broken may be at least twice the internal pressure of the cell under normal conditions, and the normal condition herein means a state of atmospheric pressure (1 atm) to 3 atm.

Meanwhile, the notch groove may be formed at a central position of 1/4 to 1/2 size with respect to the lateral width of the case body.

If the position of the notch groove deviates from the above range, breakage of the notch groove and discharge of gas at high pressure may be difficult to expect, and breakage of the notch groove may occur even at a small pressure, .

According to the experiments performed by the present inventors, as described above, when the pressure continuously increases and becomes higher than a predetermined level, the notch groove can be uniformly broken, so that gas is quickly discharged to the outside of the battery, It can be improved.

The notch groove may be formed on the case body of the space corresponding to the range of the forming position and preferably between the upper opening of the case body and the upper end of the electrode assembly mounted inside the case body . In one specific example, the notch groove is formed in a space corresponding to an upper end opening of the case body within a maximum of 5 mm from the upper end of the anode of the electrode assembly to the electrode assembly in the direction of the electrode assembly Or may be formed on the case body. The notch groove formed at such a position is located in the surplus space inside the case, specifically, at the upper end of the electrode assembly mounting portion, thereby facilitating gas discharge and minimizing breakage of the electrode assembly.

Particularly, when the notch groove is formed in an arc shape, it is possible to prevent the gas discharge from being excessively concentrated on a certain portion of the notch groove, thereby minimizing the pressure deviation when the notch groove is broken. It is advantageous in that the strength of the surface layer can be secured.

The arc shape of the notch groove preferably has a radius of curvature that is 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 other hand, if the radius is too large, the curvature becomes gentle, and even if high pressure is generated, it may be difficult to break the notch groove.

Further, if the position and the curvature of the notch groove do not deviate from the above range, the notch groove may have an upward arc shape in which the center of curvature of the arc is located at the upper portion, or a downward arc shape in which the center of curvature of the arc is located at the lower portion have.

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

The vertical cross section of the notch grooves is not particularly limited as long as the notch grooves can be easily broken at the time of internal pressure, and may be, for example, a downward wedge shape or a trapezoid shape. In the case of the downward wedge type, the upper end of the notch groove is fractured by a crack. In the case of a trapezoid, the short side is stretched and the shear stress causes the fracture. As a result, uniform and immediate breakage of the notch grooves can be induced, thus ensuring safety of the battery.

The electrode assembly may have a stacked structure or a stack / folding structure as well as a jelly-roll structure. Of these, the jelly-roll has advantages of easy manufacture and 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.

As described above, in the prismatic secondary battery according to the present invention, the left side portion and the right side portion of the notch groove are asymmetrical with respect to the vertical center axis of the case body, and the remaining thickness on the vertical center axis in the notch groove is the thinnest, It is possible to easily manufacture the notch grooves, easily control the breaking stress after the operation of the safety plate, prevent unnecessary breakage of the safety plate, and efficiently perform gas ejection after the operation of the safety plate. In addition, it is possible to predict the breaking direction, thereby providing flexibility in the design of the battery or the battery pack.

Furthermore, by forming the notch grooves having a specific structure on the side where the stress value is relatively small on the side surface of the battery case and at the same time forming at least one notch groove with a specific shape, the notch grooves can be reliably broken under proper conditions As a result, safety can be improved.

1 is a schematic view of a prismatic 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 prismatic secondary battery including a notch groove according to an embodiment of the present invention;
4 is a partial front view of the case body including the notch groove of Fig. 3;
Figures 5 and 6 are graphs showing various residual thicknesses along the length of the notch groove of Figure 3;
7 is a partial front view of a case body including a notch groove according to another embodiment of the present invention;
Figures 8 and 9 are graphs showing various residual thicknesses along the length of the notch grooves of Figure 7;
10 is a photograph showing the stress distribution of the prismatic secondary cell of FIG. 3;
11 is a photograph showing a stress distribution of a prismatic secondary battery including a notch groove according to another embodiment of the present invention;
12 is a photograph showing a vertical section of the notch groove in Fig. 3;
13 is a photograph showing a vertical section of the notch groove of Fig. 1; Fig.
FIG. 14 is a schematic diagram showing 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.

FIG. 2 shows the structure of a conventional prismatic secondary battery according to an embodiment of the present invention.

Referring to FIG. 2, the prismatic secondary battery 100 has a jelly-roll structure having a structure in which a sheet-like positive electrode and a negative electrode are wound with a separator interposed therebetween in a rectangular cell case 200 serving as a negative terminal An electrode assembly (see Fig. 14) is inserted.

The battery case 200 includes a rectangular case body 210 having an open top and made of a metal material and a case cap 220 having a cathode terminal 400 mounted on the open upper end of the case body 210 Structure. The cathode terminal may be the case body 210 or the case cap 220 itself, which is electrically insulated from the cathode terminal 400.

In order to manufacture such a prismatic secondary battery 100, the electrode assembly is first inserted into the case body 210, the case cap 220 is seated in the opening of the case body 210, The area is sealed by laser welding. The electrolyte solution is injected into the battery case 200 through the injection port 230 formed at one side of the case cap 220. In detail, after the electrolyte is injected into the injection port 230, a ball member made of aluminum or the like is inserted into the injection port 230, a separate thin metal plate is placed on the ball member 600 to completely close the injection port 230 Sealed via laser welding. The sealing method of the injection port 230 is not limited to the above, and various other methods may be possible.

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

FIG. 3 is a schematic view of a prismatic secondary battery including a notch groove according to an embodiment of the present invention, and FIG. 4 is a partial front view of a case body including a notch groove of FIG. 3 . 3 and 4, the size of the safety plate is relatively larger than that of the case body for convenience of understanding.

5 and 6 schematically show graphs showing various residual thicknesses depending on the length of the notch grooves in FIG.

12, a prismatic secondary battery is formed on a case body 40, which is broken when a high pressure inside the battery is generated. The safety plate has a vertical center axis B on both sides of the case body 40, The left side portion 61 and the right side portion 62 of the notch groove 60 are asymmetrical with respect to the vertical center axis B of the case body.

Specifically, the notch groove 60 is formed in a circular arc shape. The circular arc shape has a central position of about 1/3 size from the right end with respect to the width Q of the case body 40, Is formed in an upper position of about 3/10 of the length L as a reference. The curvature of the arc shape is formed by a curvature formed by a radius R of about 3/10 with respect to the length L of the case body 40. By such an arc shape, the notch groove 60 can maintain constant mechanical strength while uniformly discharging the gas.

The notch groove 60 has a thinnest size on the vertical center axis B in a vertical sectional view in which the remaining thickness 80 after the depth of the notch groove 60 is subtracted from the thickness of the case body 40 have.

The residual thickness 80 is formed so as to be sequentially thinned from the both ends A and C toward the vertical central axis B with respect to the entire length l of the notch groove. That is, the minimum residual thickness of the vertical central axis B of the notch groove 60 forms a residual thickness t of about 30% based on the thickness T of the case main body, The residual thickness is thickened to form a maximum of 80% of the thickness.

3 to 6, the length of the right side region 62 of the notch groove 60 is greater than the length of the corresponding left side region 61 with respect to the vertical center axis B of the case body 40 It is 250% larger in size.

The residual thickness 80 of the notch groove 60 may vary depending on the length of the notch groove 60 while satisfying the condition that the remaining thickness of the vertical central axis portion is the thinnest (B-B '), 5, the first differential value of the residual thickness 80 forms a discontinuous shape on the vertical central axis B of the case body 40 and the first differential of the residual thickness 80, as in FIG. 6, All of the shapes are continuous on the vertical central axis B of the case body 40. [

5), the residual thickness of the right side portion and the left side portion is decreased by the slope of the straight line in the graph of the length to thickness of the notch groove based on the residual thickness (B-B ') of the vertical center axis portion Structure.

On the other hand, in the latter case (FIG. 6), the residual thicknesses of the right side portion and the left side portion are decreased by the slope of the curve in the graph of the length to thickness of the notch grooves, based on the residual thickness (B-B ' .

Moreover, in the latter case (Fig. 6), the residual thickness 80 of the notch groove 60 has a structure that changes once in the end direction.

On the other hand, the notch groove 60 is formed in a region (a) of the case body 40 (the length L of the case body - the width W of the positive electrode of the jelly roll with respect to the longitudinal direction of the case) Respectively. The jelly-roll has a structure in which the cathode 32, the separation membrane 36, and the anode 34 are wound.

7 is a partial front view of a case body including a notch groove according to another embodiment of the present invention, and FIGS. 8 and 9 show various remaining thicknesses according to the length of the notch groove of FIG. 7 The graphs are schematically shown. For reference, in FIG. 7, the size of the safety plate is relatively large compared with the case body for convenience of understanding.

Referring to these drawings, the notch groove 63 is formed in a straight line, and the length of the right side portion 64 of the notch groove 63 is equal to the length of the corresponding left side portion 64 with respect to the vertical center axis B of the case body 40 4 and 6, except that it has a size that is 200% larger than the length of the guide groove 65, and thus a detailed description thereof will be omitted.

FIG. 10 is a photograph showing a stress distribution of the prismatic secondary cell of FIG. 3, and FIG. 11 is a photograph showing a stress distribution of a prismatic secondary cell including a notch groove according to another embodiment of the present invention. .

First reference with the FIG 3, the notch groove 60 of the case main body 40 is a member of the incision possible forms for discharging high-pressure gas, about 25 relative to the maximum stress of the case (S _MAX) The center of curvature of the arc is formed in an upward arc shape in which the center of curvature of the arc is located at the portion of the case showing a stress distribution of 35%.

As shown in Figure 10, the stress distribution when applying a constant pressure appears as a tensile stress contour lines that appear in each part, the maximum stress as the area the stress is relatively high brightness, a high portion (light color portion) (S _MAX) (Dark area) is a relatively low stressed area, which means the lowest stress (S _MIN ) distribution area.

In addition, the arc may be an upward arc shape in which the center of curvature of the arc is located at the upper side as shown in Fig. 10, but it may be a downward arc shape in which the center of curvature of the arc is located at the lower side as shown in Fig. 11 .

Fig. 12 is a photograph showing a vertical section of the notch groove of Fig. 3.

12, the vertical cross section of the notch groove 60 is formed in a downward wedge shape. The average value of the remaining thickness 80 is about 40% of the thickness T of the case body 40 Respectively.

Accordingly, when the internal pressure gradually increases and a pressure of three times or higher than the normal internal withstand voltage is generated, cracks are generated in the notch groove 60 and rupture easily so that the gas is quickly discharged to the outside of the battery. As a result, .

FIG. 14 is a schematic view showing a process of winding up the jelly-roll type electrode assembly mounted on the battery case of FIG.

14, the jelly-roll 10a includes a negative electrode 32 and a negative electrode tab 31 and a positive electrode tab 33 on the uncoated portion 36 to which no electrode active material is applied at the left end of the positive electrode 34 And then winding the negative electrode 32 and the positive electrode 34 from the left end portion to the right end portion.

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 (16)

1. A prismatic secondary battery in which an electrode assembly composed of an anode, a cathode and a separator is sealed in a rectangular battery case, wherein the battery case has a rectangular case body made of a metal material and having an open upper end, And a case cap including an electrode terminal,
A safety plate is formed on the case main body to break when a high pressure inside the battery is generated,
Wherein the left and right sides of the notch groove are asymmetrical with respect to a vertical center axis of the case body,
The notch groove has a downward arc shape in which the center of curvature of the arc is located at the lower side,
The notch groove is formed on the case main body which exhibits a stress distribution of 40% or less based on the maximum stress (S _MAX ) of the case under a high pressure,
Wherein the remaining thickness on the vertical center axis in the notch groove (the thickness after subtracting the depth of the notch groove from the thickness of the case body) is the thinnest. The prismatic secondary battery according to claim 1, wherein the thickness of the case body is 0.4 mm or less. The prismatic secondary battery according to claim 1, wherein a length of a left side portion or a right side portion of the notch groove is greater than a length of a corresponding right side portion or a left side portion of the notch groove with respect to a vertical center axis of the case body. The prismatic secondary battery according to claim 1, wherein the remaining thickness of the notch groove on the vertical central axis of the case body is 50% or less based on the thickness of the case body. The method according to claim 1, wherein the remaining thickness of the notch groove is such that the first differential value of the residual thickness along the length of the notch groove is discontinuous on the vertical central axis of the case body and increases toward the end of the notch groove Characterized in that a rectangular secondary battery. The method as claimed in claim 1, wherein the residual thickness of the notch groove is characterized in that the first differential value of the residual thickness along the length of the notch groove is continuous on the vertical central axis of the case body and increases toward the end of the notch groove Shaped secondary battery. The prismatic secondary battery according to claim 6, wherein the residual thickness of the notch groove is changed at least once in the end direction. The prismatic secondary battery according to claim 1, wherein an average residual thickness of the notch groove is 40 to 70% of a thickness of the case body. 9. The method according to claim 8, wherein the residual thickness of the notch groove on the vertical center axis of the case body is such that the average value of the residual thickness is within the range of 40 to 70% Wherein the size of the prismatic secondary battery is 20 to 50%. The prismatic secondary battery according to claim 8, wherein the remaining thickness of the notch groove on the vertical center axis of the case body is 40 to 70% of the remaining thickness of the one end portion. The prismatic secondary battery according to claim 1, wherein the high pressure inside the battery in which the safety plate is broken is a pressure of three times or more the internal pressure of the battery under normal conditions. The prismatic secondary battery according to claim 1, wherein the notch groove is formed at a central position of 1/4 to 1/2 size with respect to the width of the case body. The prismatic secondary battery according to claim 1, wherein a vertical cross section of the notch groove has a downward wedge shape. The prismatic secondary battery according to claim 1, wherein a vertical section of the notch groove has a trapezoidal shape. The prismatic secondary battery according to 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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