JP2014041718A - Case for secondary battery and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a case for a secondary battery having a structure which can cleave a safety valve with a predetermined specified pressure and high accuracy even if it is used for a long period of time, and which is achieved at a low cost.SOLUTION: A safety valve 14 having a thin wall part 28 which has a thinner wall than a case body 12 for sealing a positive electrode, a negative electrode and an electrolyte in the inside thereof, and which forms a dome shape is provided to the case body 12 so as to be bulged into the inside thereof, and on only one surface in the thickness direction of the safety valve 14, a cleavage groove 32 is formed which is cleaved when the inner pressure of the case body 12 reaches a predetermined specified pressure.

Description

  The present invention relates to a secondary battery case and a secondary battery, and more particularly, to an improvement of a secondary battery case used for a sealed secondary battery and a secondary battery case using such a secondary battery case. The present invention relates to a new structure of a secondary battery.

  In recent years, portable electronic devices such as notebook PCs and mobile phones have been widely used as light sources for nickel-cadmium secondary batteries, nickel-hydrogen secondary batteries, lithium ion secondary batteries, etc. that can be charged at high speed. Has been. Among these secondary batteries, in particular, nickel-hydrogen secondary batteries and lithium ion secondary batteries have higher energy density, so they can also be used as in-vehicle high-output power sources for hybrid cars and electric cars. Has begun to be.

  By the way, such a secondary battery has a so-called hermetically sealed structure in which a positive electrode, a negative electrode, and an electrolyte are sealed in a case. Large amounts of gas may be generated. In such a case, the pressure in the case increases abnormally and the case may burst, which is extremely dangerous.

  Therefore, a conventional case for a sealed secondary battery is usually provided with a safety valve in a case body that seals the positive electrode, the negative electrode, and the electrolyte inside. This safety valve can be opened when the pressure in the case body reaches a preset specified pressure due to the generation of gas in the case body, and the gas in the case body (internal pressure) can be released to the outside. It has a structure. By providing such a safety valve in the case, it is possible to prevent the case from being ruptured.

  As one type of such a safety valve, a destructive safety valve is known. This destructive safety valve is thinner than the case body, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-185113 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2010-282855 (Patent Document 2). It is made of a thin flat plate, and a part of the case body is thinned and formed integrally with the case body, or is fixed to the case body so as to close the opening provided in the case body. When the pressure in the case body becomes equal to or higher than the specified pressure, the case body is cleaved (destructed) to release the internal pressure of the case body to the outside.

  Such a destructive safety valve has an advantage that it can be easily and inexpensively provided to the case body. However, the present inventor has examined such a destructive safety valve from various angles, and depending on the type of secondary battery provided with the destructive safety valve, there is a possibility that the operation accuracy may deteriorate due to long-term use. It became clear that there was.

  That is, for example, when a destructive safety valve is provided in a case body such as a lithium ion secondary battery, the operation accuracy is stably ensured even with long-term use, and the safety valve is reliably secured at a predetermined specified pressure. Cleave. On the other hand, for example, when a destructible safety valve is provided in a case body such as a nickel-hydrogen secondary battery, the internal pressure of the case body abnormally increases after a long period of use. It has been found that there is a possibility that the safety valve may be broken before the internal pressure of the valve reaches a predetermined specified pressure.

  This is considered to be due to the following reasons. That is, in the lithium ion secondary battery, no gas is generated at the positive electrode or the negative electrode during normal charging / discharging, and therefore the inside of the case body is maintained at a substantially constant pressure in a normal use state. On the other hand, in the nickel-hydrogen secondary battery, while oxygen gas is generated at the positive electrode due to the side reaction at the end of charging, such oxygen gas is absorbed by the negative electrode, so every time charging is performed, The pressure in the case body fluctuates. If a reversible safety valve consisting of a thin flat plate is provided in the case of a secondary battery in which internal pressure fluctuations normally occur during charging or discharging, such as this nickel-hydrogen secondary battery, the charging of the secondary battery The tensile load is repeatedly input to the safety valve based on the internal pressure fluctuation of the case main body that occurs every time the battery is discharged or discharged. Therefore, if the usage period of the secondary battery in which such internal pressure fluctuations occur is prolonged, fatigue due to repeated occurrence of tensile stress accumulates in the safety valve provided in the case body, and the safety valve's breaking strength (breaking strength) Gradually decreases. For this reason, in such a secondary battery, when the pressure rises abnormally in the case body after long-term use, the destruction strength of the destructive safety valve is reduced, so the inside of the case body is predetermined. Before reaching the specified pressure, the safety valve may break without being able to withstand the internal pressure of the case body.

  In addition to the destructive type, the safety valve includes a self-return type. The self-returning safety valve includes, for example, a valve body that opens and closes an opening provided in a case body, and a peripheral portion of the opening as disclosed in Japanese Patent Laid-Open No. 2001-185113. And an elastic body such as a coil spring or rubber that exerts an urging force on the valve body so as to maintain the closed state of the opening by the valve body. When the pressure in the case body becomes equal to or higher than the specified pressure, the valve body opens against the urging force of the elastic body and discharges the gas generated in the case body to the outside from the opening. It is like that. Further, when the pressure inside the case body falls below the specified pressure due to such gas discharge, the valve body returns to the position where the opening is closed by the urging force of the elastic body, and the inside of the case body is sealed again. It is configured to be in a state.

  If such a self-recovering type safety valve is provided in a case for a secondary battery in which internal pressure fluctuations are normally generated during charging or discharging, the above-described problems caused when a destructive type safety valve is provided in such a case. It can be advantageously eliminated. However, the self-returning safety valve is more expensive than the destructive safety valve because it has a more complicated structure and more parts. Therefore, when such a self-returning safety valve is provided in the secondary battery case, a new problem arises that the cost of the secondary battery case, and hence the secondary battery, rises.

JP 2001-185113 A JP 2010-282851 A

  Here, the present invention has been made in the background of the above-mentioned circumstances, and the problem to be solved is to ensure that the safety valve is maintained at a predetermined specified pressure even when the service period is long. An object of the present invention is to provide a sealed secondary battery case in which a cleavable structure is realized at low cost. In addition, the present invention provides an improved structure in a sealed secondary battery that can prevent the case from bursting due to an increase in internal pressure at a low cost and reliably even when the service period is long. Is also a problem to be solved.

  In the present invention, in order to solve such a problem, the case body has a case body that seals the positive electrode, the negative electrode, and the electrolyte therein, and the internal pressure of the case body becomes a preset specified pressure. A safety valve that is cleaved to release the internal pressure of the case body to the outside is a case for a secondary battery provided in the case body, and the safety valve bulges inside the case body The cleaving groove that is cleaved when the internal pressure of the case body becomes the specified pressure is formed in the thickness direction of the thin part. The gist of the case is a secondary battery case that is provided only on the surface.

  According to one advantageous aspect of the present invention, the inner surface of the cleavage groove is a curved surface.

  Further, according to one of the preferred embodiments of the present invention, the inner surface of the cleavage groove is formed by connecting a plurality of curved surface portions having different curvature radii to each other in the width direction of the cleavage groove. The curvature radius of the plurality of curved surface portions is gradually increased from the center in the width direction of the cleavage groove toward the opening side of the cleavage groove.

  Furthermore, according to one of the desirable aspects of the present invention, the cleavage groove is formed on the surface of the thin portion opposite to the inside of the case body.

  Furthermore, according to one of the preferable aspects of the present invention, the cleavage groove is constituted by a main groove portion extending in a straight line and a sub groove portion extending so as to intersect the main groove portion.

  And in this invention, in order to solve an above-described subject, the secondary battery characterized by sealing the positive electrode, the negative electrode, and electrolyte in the above-mentioned case for secondary batteries. Is also the gist of this.

  In other words, in the case for a secondary battery according to the present invention, the safety valve is configured with a destructive structure having a thin portion provided with a cleavage groove on one surface in the thickness direction. Thus, for example, the cost can be advantageously reduced as compared with a case for a secondary battery provided with a self-returning safety valve.

  And in this case for secondary batteries, especially the thin part of a safety valve has the dome shape which bulged inside the case body. Therefore, for example, when the internal pressure of the case main body rises during charging or discharging of the secondary battery, the thin wall portion is pushed by the pressure in the case main body and bulges toward the outside of the case main body. Until the deformation, only the compressive load is applied to the entire thin portion. As a result, even if the internal pressure of the case body repeatedly fluctuates with a magnitude that does not reach the specified pressure, only the compressive stress is always generated in the thin portion of the safety valve. For this reason, in the case for a secondary battery according to the present invention, for example, unlike a conventional case for a secondary battery provided with a destructive safety valve made of a thin flat plate, the safety valve is In thin-walled parts, fatigue due to repeated occurrence of tensile stress does not accumulate, and therefore the safety valve may deteriorate over time due to long-term use, and its fracture strength may gradually decrease. It can be effectively avoided.

  Therefore, in the case for a secondary battery according to the present invention, the formation cost of the safety valve, and thus the manufacturing cost of the case, can be advantageously reduced, and the thin portion of the safety valve is preliminarily provided over a long period of use. It can be cleaved accurately and reliably at a prescribed pressure. As a result, the rupture of the case main body due to an abnormal increase in internal pressure can be reliably prevented at a sufficiently low cost by the destruction of a safety valve that is inexpensive and has high operation accuracy.

  And in the secondary battery according to the present invention, since the case having the excellent characteristics as described above is used, even if the service period is long, the case is sufficiently ruptured due to an abnormal increase in internal pressure. It can be reliably and stably prevented at a low cost.

It is front explanatory drawing which shows an example of the secondary battery which has a structure according to this invention. FIG. 2 is an explanatory top view of the secondary battery shown in FIG. 1. FIG. 3 is a partially enlarged explanatory view of an end surface of a III-III cross section in FIG. 2. FIG. 4 is a partial end surface explanatory view of a IV-IV cross section in FIG. 3. FIG. 5 is a view corresponding to FIG. 4 for explaining the state of the safety valve when the pressure in the case abnormally increases in the secondary battery shown in FIG. 1, and FIG. The state which deform | transformed so that it may bulge toward the outer side of a case is shown, (b) has shown the state which the thin part cut | disconnected. FIG. 5 is an enlarged explanatory view of a VI part in FIG. 4. It is a figure corresponding to FIG. 3 which shows another example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 6 which shows another example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 2 which shows the other example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 2 which shows the further another example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 2 which shows another example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 2 which shows another example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 2 which shows the other example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 2 which shows the further another example of the secondary battery which has a structure according to this invention. It is a figure corresponding to FIG. 2 which shows another example of the secondary battery which has a structure according to this invention.

  Hereinafter, in order to clarify the present invention more specifically, embodiments of the present invention will be described in detail with reference to the drawings.

  First, FIG. 1 and FIG. 2 show a nickel-hydrogen secondary battery as an embodiment of a secondary battery having a structure according to the present invention in a front form and a top form, respectively. As is clear from FIGS. 1 and 2, the nickel-hydrogen secondary battery of this embodiment has a case 10. Although not shown in the figure, the case 10 contains a positive electrode, a negative electrode, a separator interposed between them, an electrolytic solution as an electrolyte, and the like, as in the conventional product, and is sealed. ing. And in the nickel-hydrogen secondary battery of this embodiment, such a case 10 is comprised with the special structure which is not seen conventionally.

  More specifically, the case 10 includes a case main body 12 and a safety valve 14 provided in the case main body 12. The case body 12 includes a housing body 16 formed of a longitudinal rectangular housing that opens upward, and a lid body 18 that covers the upper opening of the housing body 16.

  The container 16 of the case body 12 is made of a press-formed product obtained by performing press working such as deep drawing on a nickel-plated steel plate, for example, and includes four side wall portions and one bottom wall portion. Have. In the container 16, the positive electrode, the negative electrode, the separator, the electrolyte, and the like described above are accommodated through the upper opening.

  The lid 18 is a flat plate formed using a nickel-plated steel plate, and has a longitudinal rectangular shape that can cover the entire upper opening of the container 16. The lid body 18 is fixed to the housing body 16 by, for example, laser welding in a state of covering the upper opening of the housing body 16 in which the positive electrode, the negative electrode, the separator, the electrolytic solution, and the like are housed.

  Thus, the case main body 12 is configured as an integrated product of the housing 16 and the lid 18, and the positive electrode, the negative electrode, the separator, the electrolytic solution, and the like are sealed inside the case main body 12. It should be noted that positive electrodes connected to the positive electrode and the negative electrode sealed in the case main body 12 are provided at both ends in the length direction of the lid 18 of the case main body 12 (left and right direction in FIGS. 1 and 2). The terminal 20 and the negative electrode terminal 22 are penetrating positions, and upper ends of the positive electrode and the negative electrode terminals 20 and 22 protrude upward from the lid body 18. Here, the container 16 has a thickness of about 0.2 to 0.4 mm, and the lid 18 has a thickness of about 0.2 to 2.0 mm. Thereby, in the case main body 12, the pressure | voltage resistance which can endure the pressure of about 2.5 MPa is ensured.

  As shown in FIGS. 2 to 4, in the case main body 12, an opening 24 that penetrates the central portion is provided in the central portion in the length direction of the lid body 18. Here, the opening 24 has a longitudinal rectangular shape having a length that is less than 1/3 of the length of the lid 18 and a width that is about half the width of the lid 18, and the surface of the lid 18. It has a sufficiently large opening area with respect to the area.

  And the safety valve 14 is attached to the cover body 18 so that the opening part 24 provided in the cover body 18 of such a case main body 12 may be obstruct | occluded completely.

  The safety valve 14 is formed using a nickel-plated steel plate having a long rectangular flat plate shape having a constant thickness that is thinner than the housing 16 and the lid 18. And the part except the outer peripheral part of this safety valve 14 is shaped so that it may bulge in the curved direction toward the thickness direction one side by press molding or the like.

  Thus, while the outer peripheral portion of the safety valve 14 is a mounting frame portion 26 having a flat rectangular frame shape that is slightly larger than the opening 24 of the lid 18, the inner portion of the mounting frame portion 26 is As a whole, the bulging portion 28 is formed as a thin-walled portion having a dome shape that bulges toward one side in the thickness direction of the safety valve 14. That is, the bulging portion 28 has a longitudinal cross-sectional shape (cross-sectional shape shown in FIG. 3) cut by a cutting line extending in the length direction of the safety valve 14 (left and right direction in FIG. 3), and the width direction (FIG. 4). (The left-right direction) of the safety valve 14 cut by a cutting line extending in a direction crossing the length direction and the width direction of the safety valve 14 (cross-sectional shape shown in FIG. 4). All the shapes are mountain-shaped.

  As described above, the bulging portion 28 is thinner than the housing body 16 and the lid body 18 of the case main body 12, and the overall shape thereof has a curved shape and swells on one side in the thickness direction of the safety valve 14. Although it is necessary to have a shape, the specific shape is not particularly limited. That is, the vertical cross-sectional shape of the safety valve 14 (the cross-sectional shape cut in the height direction of the bulging portion 28) is not limited to the mountain shape, for example, an arc shape, a semicircular shape, a shape consisting of a part of an ellipse, It is sufficient that the overall shape, such as a shape consisting of a part of an ellipse, is curved toward the inside of the case body 12 and does not have any concave portions. Among these, it is desirable that the longitudinal cross-sectional shape of the safety valve 14 is a curved shape that draws a suspension line. Thus, as will be described later, when pressure is applied to the bulging portion 28 from the distal end side in the height direction toward the proximal end side as the internal pressure of the case 10 increases, the bulging portion 28. This is because only the compressive stress is generated more stably in the interior.

  Such a safety valve 14 causes the bulging portion 28 to bulge or protrude toward the inside of the housing body 16 of the case body 12 through the opening 24 of the lid body 18, and the mounting frame portion 26 is Over the entire circumference, the lid 18 is disposed so as to overlap the peripheral portion of the opening 24 on the upper surface (outer surface) of the lid 18. Further, under such an arrangement state, the mounting frame portion 26 is fixed to the peripheral portion of the opening 24 of the lid 18 over the entire circumference by, for example, laser welding. Further, here, in such a fixed state, at least the bulging tip portion of the bulging portion 28 is disposed so as to protrude into the housing 16 (inside the housing 16 from the position of the inner surface of the lid 18). Protruding). As a result, the radius of curvature of each portion of the bulging portion 28 of the safety valve 14 is advantageously reduced, and the amount of bulging or protrusion of the bulging portion 28 toward the inside of the housing 16 (the bulging portion of the mounting frame portion 26). (The height from the surface on the side of 28 to the tip of the bulging portion 28) is sufficiently secured, so that, as will be described later, only the compressive stress is applied to the bulging portion 28 when the internal pressure of the case 10 increases. Further, there is an advantage that it can be generated more stably. If a sufficient bulge amount or protrusion amount of the bulging portion 28 to the inside of the housing body 16 is ensured, it does not enter the housing body 16 at all (from the position of the inner surface of the lid body 18 to the housing body). 16 may be disposed entirely inside the opening 24 without projecting inside 16.

  Thus, the opening 24 of the lid 18 is fluid-tightly sealed with the safety valve 14. And while the side wall part of the case 10 is comprised by the four side wall parts of the container 16 of the case main body 12, the lower side bottom wall part of the case 10 is the bottom wall part of the case main body 12, and The upper bottom wall portion of the case 10 is constituted by the lid body 18 of the case body 12 and the bulging portion 28 of the safety valve 14 that seals the opening 24 of the lid body 18.

  Thereby, in the nickel-hydrogen secondary battery of this embodiment, it was comprised by the bulging part 28 of the safety valve 14 thinner than the container 16 and the cover body 18 among the side wall part and both side bottom wall part of the case 10. The breaking strength of a part of the upper bottom wall portion is set to be lower than the breaking strength of the side wall portion and the bottom wall portion of the case 10 constituted by the container 16 and the lid body 18. However, here, the bulging portion 28 of such a safety valve 14 has a dome shape that bulges or protrudes into the housing 16. Therefore, unlike the conventional safety valve in which the inner portion of the attachment portion of the lid 18 is formed in a flat plate shape, even if the internal pressure fluctuation of the case 10 repeatedly occurs, the safety valve 14, particularly the bulging portion 28 is thereby destroyed. It is possible to advantageously prevent the strength from gradually decreasing.

  That is, in the nickel-hydrogen secondary battery of the present embodiment, when oxygen gas is generated at the positive electrode at the end of charging and the internal pressure of the case 10 rises, it is indicated by a white arrow in FIGS. As described above, a predetermined pressure is applied to the inner surface of the housing body 16 and the lid body 18 of the case body 12, and the inner surface 29 (the housing body 16) of the bulging portion 28 of the safety valve 14 that closes the opening 24 of the lid body 18. Also, a predetermined pressure is applied from the distal end side in the height direction of the bulging portion 28 toward the proximal end side. At that time, the bulging portion 28 is convex toward the inside of the container 16, that is, a direction against the pressurization direction accompanying the increase in internal pressure of the case 10 (on the opposite side to the pressurization direction). Only the compressive stress is generated inside the bulging portion 28. Therefore, in the safety valve 14 having such a bulging portion 28, unlike the conventional safety valve in which the inner portion of the mounting portion of the lid 18 is flat, every time charging is performed, tensile stress is generated inside the safety valve 14. Therefore, it is possible to completely eliminate the fact that fatigue due to tensile stress accumulates in the safety valve 14, particularly the bulging portion 28, and the fracture strength gradually decreases. It has become.

  In such a bulging portion 28 of the safety valve 14, the surface that is exposed to the inside of the container 16 and is opposite to the inner surface 29 that is pressurized when the internal pressure of the case 10 is increased, that is, the lid 18. A cleavage groove 32 is provided on the outer surface 30 exposed to the outside. Thereby, the fracture | rupture strength is made still smaller in the bottom part site | part of the cleavage groove 32 among the bulging parts 28 than another site | part.

  Thus, in the nickel-hydrogen secondary battery of the present embodiment, a larger amount of gas than the amount of oxygen gas generated during charging is generated in the case 10 due to, for example, large current discharge or overcharge. When the internal pressure of the main body 10 rises abnormally, an extremely larger pressure is applied to the inner surfaces of the housing 16 and the lid 18 of the case body 12 than during normal charging, and the bulging portion 28 of the safety valve 14 When an extremely large pressure similar to the pressure applied to the container 16 and the lid 18 is applied to the inner side surface 29, first, as shown in FIG. The shape that bulges or protrudes toward the inside of the housing body 16 (the dome shape that protrudes toward the inside of the housing body 16), or the shape that bulges or projects toward the outside of the housing body 16 (the housing body 16). Doe that protrudes outward Deformed into a shape).

  Next, as shown in FIG. 5 (b), immediately after or almost simultaneously with the deformation of the bulging portion 28, the bottom portion of the cleavage groove 32 in the bulging portion 28 is added to the bulging portion 28. It cannot withstand the pressure applied and breaks. That is, the bulging portion 28 is cleaved starting from the cleaving groove 32. As a result, the gas in the case 10 is released to the outside of the case 10 from the cleavage portion of the bulging portion 28.

  Here, as described above, since the case body 12 has a pressure resistance that can withstand a pressure of about 2.5 MPa, the internal pressure of the case body 12 (case 10) is lower than the pressure. When the pressure reaches 0 MPa, the bulging portion 28 of the safety valve 14 is cleaved at the cleaving groove 32. In other words, the specified pressure of the case 10 (case body 12) when the bulging portion 28 of the safety valve 14 is cleaved at the cleavage groove 32 is set to about 2.0 MPa, which is lower than the pressure that the case body 12 can withstand. -ing

  In the present embodiment, as shown in FIG. 2, the cleavage groove 32 extends straight in the length direction of the longitudinal rectangular safety valve 14 (the left-right direction in FIG. 2) at the central portion of the bulging portion 28. The main groove portion 33 is provided. Further, from one end portion of the main groove portion 33 in the length direction, the two sub groove portions 34a and 34b extend obliquely in a straight line toward both sides of the safety valve 14 in the width direction (vertical direction in FIG. 2). ing. Furthermore, from the other end portion in the length direction of the main groove portion 33, two sub groove portions 34 c and 34 d extend obliquely in a straight line toward both sides in the width direction of the safety valve 14.

  That is, the cleavage groove 32 includes a main groove portion 33 that extends in a straight line and four sub groove portions 34 a, 34 b, 34 c, and 34 d that extend so as to intersect the main groove portion 33. Of the four sub-grooves 34a, 34b, 34c, 34d, two sub-grooves 34a, 34b extending from one end in the length direction of the main groove 33 are on one side in the length direction of the main groove 33 (see FIG. 2). It intersects at an acute angle with the extension line extending to the right). On the other hand, the two sub-grooves 34c and 34d extending from the other longitudinal end of the main groove 33 are at an acute angle with respect to an extension line extending to the other longitudinal side of the main groove 33 (left side in FIG. 2). , Each crossed.

  Here, the two sub-grooves 34 a and 34 b extending from one end portion in the length direction of the main groove portion 33 are positioned symmetrically with respect to the extension line extending to one side in the length direction of the main groove portion 33. The two sub-groove portions 34 c and 34 d extending from the other end portion in the length direction of the main groove portion 33 are positioned symmetrically with respect to an extension line extending to the other side in the length direction of the main groove portion 33. Further, of the four sub-grooves 34a, 34b, 34c, 34d, the two sub-grooves 34a, 34c extending obliquely toward one side in the width direction of the safety valve 14 (upper side in FIG. 2) are the length of the main groove 33. It passes through the center point of the direction, is perpendicular to the main groove 33, is symmetrical with respect to a straight line extending in the width direction of the main groove 33, and faces the other side of the safety valve 14 in the width direction (the lower side in FIG. 2). The two sub-grooves 34b and 34d that extend obliquely are also positioned symmetrically with respect to a straight line that passes through the center point in the length direction of the main groove 33, is orthogonal to the main groove 33, and extends in the width direction of the main groove 33. Yes.

  As a result, of the portion on one side in the width direction of the bulging portion 28, the portion surrounded by the main groove portion 33 and the two sub-groove portions 34 a and 34 c extending from both ends thereof, or the width direction of the bulging portion 28. Of the portions on the other side, the main groove portion of the portion on one side in the length direction of the bulging portion 28 surrounded by the main groove portion 33 and the two sub groove portions 34b and 34d extending from both ends thereof. 2 extending from the other end in the length direction of the main groove 33 out of the portion surrounded by the two sub-groove portions 34a and 34b extending from one end in the length direction of 33 and the portion on the other side in the length direction of the bulging portion 28 The portions surrounded by the sub-groove portions 34 c and 34 d are rolled up in a well-balanced manner toward the outside of the case 10 when the cleavage groove 32 is cleaved. As a result, the area of the opening formed when the cleavage groove 32 is cleaved is made sufficiently larger, so that the gas in the case 10 can be more quickly and efficiently emitted from such an opening. It can be discharged out of the case 10.

  In addition, the cleavage groove 32 has the same inner surface shape in any part in the extending direction without distinction between the main groove portion 33 and the sub groove portions 34a, 34b, 34c, 34d. That is, as is apparent from FIG. 6 showing the longitudinal section of the main groove portion 33, here, the inner surface of the cleavage groove 32 is a stepped curved surface formed by connecting a plurality of curved surface portions in the width direction of the cleavage groove 32. Configured.

More specifically, the cleaving groove 32 has a central inner surface portion 36 made of an arcuate surface whose inner surface is located at the center in the width direction (inner side in the width direction) of the cleaving groove 32, and the central inner surface portion 36. A first opening-side inner surface made of an arcuate surface located on both sides in the width direction (both sides on the opening side of the cleavage groove 32) and connected to both ends in the width direction of the cleavage groove 32 in the central inner surface portion 36, respectively. It consists of a portion 38 and a second opening side inner surface portion 40. The curvature of the first opening side inner surface portion 38 radius R ₁ of curvature of the second opening side inner surface portion 40 radius R ₂ and is, while being the same size to each other, the curvature of the central inner surface portion 36 radius: R ₃ is smaller than the radius of curvature of the first opening side inner surface portion 38: R ₁ and the radius of curvature of the second opening side inner surface portion 40: R ₂ .

In short, the inner surface of the cleavage groove 32 has a stepped curved surface shape composed of a central inner surface portion 36 and first and second opening-side inner surface portions 38 and 40, and the inner surface of the cleavage groove 32. The radius of curvature: R ₃ , R ₁ , R ₂ is larger on the opening side of the cleavage groove 32 than the central portion in the width direction of the cleavage groove 32. In this way, even when the inner surface of the cleavage groove 32 has a stepped curved surface shape, the central inner surface portion 36 and the first and second opening side inner surface portions 38 and 40 are not necessarily arcuate surfaces. It is not necessary to have a curved surface other than the circular arc surface that is convex toward the center of the bulging portion 28 in the thickness direction.

  Thus, in the nickel-hydrogen secondary battery of the present embodiment, when the internal pressure of the case 10 is abnormally increased and a pressure larger than the normal state is applied to the bulging portion 28 of the safety valve 14, in particular, the cleavage groove. 32, the stress concentration is surely and stably generated at a portion between the main groove portion 33 and the central inner surface portion 36 of each of the sub-groove portions 34a to 34d and the inner surface 29 portion of the bulging portion 28 positioned corresponding thereto. It has become. As a result, when the internal pressure of the case 10 becomes the above-mentioned prescribed pressure, the bulging portion 28 is surely cleaved with higher accuracy at the site where the cleavage groove 32 is formed.

As described above, when the internal pressure of the case 10 becomes a specified pressure, in order to accurately and accurately cleave the cleavage groove 32 of the bulging portion 28, the main groove portion 33 and each sub-groove portion 34 a in the cleavage groove 32. the first and second opening-side inner surface portions 38, 40 of the curvature radius of ~34d: R _1, the curvature of the R ₂ and the central inner surface portion 36 radius and R ₃ is that one has also been a 1.0mm or less desirable. They also first and second opening-side inner surface portions 38, 40 of the curvature radius: R _1, R ₂ and the curvature of the central inner surface portion 36 radius: when R ₃ is more than 1.0mm, for example, the rupturing groove 32 Is formed by press working, a larger pressing pressure is required, resulting in a problem that the equipment required for forming the cleavage groove 32 is increased in size and cost. Even if therefrom point, the curvature of the first and second opening-side inner surface portions 38, 40 radius that R ₃ is a 1.0mm or less of curvature of R _1, R ₂ and the central inner surface portion 36 radially It is desirable. In addition, those curvature radii: R ₁ , R ₂ , R ₃ are more preferably 0.07 mm or less.

Moreover, it is preferable that the curvature radii: R ₁ and R _{2 of} the first and second opening-side inner surface portions 38, 40 and the curvature radius: R ₃ of the central inner surface portion 36 are both 0.01 mm or more. This is because, for example, the cleavage groove 32 having the central inner surface portion 36 and the first and second opening-side inner surface portions 38, 40, which are curved surfaces having curvature radii: R ₁ , R ₂ , R ₃ of less than 0.01 mm, This is because, when a nickel-plated steel sheet, which is a material to be processed of the safety valve 14, is obtained by pressing, there is a possibility that breakage is likely to occur, and it is difficult to stably obtain the cleavage groove 32. Further, in order to reliably form the cleavage groove 32 by press working on the nickel-plated steel sheet, the first and second opening side inner surface portions 38 and 40 have radii of curvature: R ₁ and R ₂ and the inner inner surface portion 36 have radii of curvature: R ₃ is more preferably 0.05 mm or more. Furthermore, the curvature of the central inner surface portion 36 radius and R _3, the curvature of the first and second opening-side inner surface portions 38, 40 radius regardless magnitude of each of R _1, R _2, the former is smaller than the latter Need to be.

  As is clear from the above description, in the nickel-hydrogen secondary battery of the present embodiment, the safety valve 14 has a bulged portion 28 that is thin and provided with the cleavage groove 32, and is provided in the case 10. When the pressure becomes a specified pressure, the bulging portion 28 has a destructive structure in which it is cleaved. Therefore, for example, as compared with the case where the safety valve 14 is configured with a self-returning structure, the cost of the safety valve 14 can be reduced, and the cost of the nickel-hydrogen secondary battery as a whole can be advantageously reduced.

  Further, in such a nickel-hydrogen secondary battery, the bulging portion 28 of the safety valve 14 has a dome shape that bulges or protrudes inside the case main body 12, thereby repeatedly changing the internal pressure of the case main body 12. As a result, the breaking strength of the bulging portion 28 does not gradually become lower than the initial setting. Therefore, in the nickel-hydrogen secondary battery of the present embodiment, the bulging portion 28 of the safety valve 14 does not deteriorate over time even with a long period of use, and accurately at a predetermined specified pressure, It can be reliably cleaved.

  Therefore, in the nickel-hydrogen secondary battery of this embodiment as described above, the rupture of the case main body 10 due to an abnormal increase in internal pressure is caused at a sufficiently low cost due to the destruction of a safety valve that is inexpensive and has high operation accuracy. It can be surely prevented.

  Further, in the nickel-hydrogen secondary battery of the present embodiment, the cleavage groove 32 is formed on the outer surface 30 of the bulging portion 28. Also by this, the bulging part 28 of the safety valve 14 can be reliably cleaved with high accuracy at a predetermined specified pressure. Further, when the cleavage groove 32 is formed by pressing the bulging portion 28 (safety valve 14), even if the plating layer formed on the surface of the bulging portion 28 is somewhat damaged during pressing. The contact of the damaged part with the electrolyte sealed in the case main body 12 is avoided, so that the aging of the bulging portion 28 of the safety valve 14 can be further effectively prevented. Become.

  Furthermore, in this nickel-hydrogen secondary battery, the inner surface shape of the cleavage groove 32 is a curved surface shape. For this reason, for example, unlike the case where the inner surface shape of the cleavage groove 32 is a polygonal longitudinal section having an angular portion, a stress concentration occurs on a part of the inner surface of the cleavage groove 32, thereby causing the bulging portion. Such a variation in the pressure value when 28 is cleaved can be advantageously prevented.

  The specific configuration of the present invention has been described in detail above. However, this is merely an example, and the present invention is not limited by the above description.

  For example, in the above-described embodiment, the safety valve 14 is made of a separate member independent of the case body 12, but the safety valve 14 may be integrally formed with the case body 18.

  That is, for example, as shown in FIG. 7, the central portion of the lid 18 of the case body 12 is subjected to compression processing such as press processing, so that the central portion is thinner than the other portions. At the same time, the bulging portion 28 is formed there. As a result, it is possible to integrally form the thin destructive safety valve 14 at the center of the lid 18. In addition, although not shown, by compressing by pressing or the like on any one of the four side wall portions and one bottom wall portion of the housing 16 of the case body 12, The safety valve 14 can be formed integrally with the housing 16 of the case body 12 by reducing the thickness of the portion and forming the bulging portion 28.

  As described above, even when the safety valve 14 is formed integrally with the case main body 12, the central portion of the safety valve 14 is pressed toward the inside of the case main body 12 by, for example, pressing. Thus, a dome-shaped bulging portion 28 that protrudes or protrudes is formed. Thereby, even in the present embodiment, substantially the same operation / effect as the operation / effect achieved in the embodiment can be enjoyed effectively. In addition, regarding the embodiment shown in FIG. 7 and some of the embodiments shown in FIGS. 8 to 15, members and parts having the same structure as the first embodiment are shown in FIGS. The same reference numerals as those in FIG. 6 are given, and detailed descriptions thereof are omitted.

  Further, an opening 24 is formed in any one of the four side wall portions and one bottom wall portion of the housing 16 of the case body 12, and the safety valve 14 is provided so as to fluid-tightly seal the opening 24. You may adhere to the container 16 by laser welding etc., for example.

  As can be seen from FIG. 7, when the safety valve 14 is formed integrally with the lid 18, the inner surface of the lid 18 and the inner surface 29 of the safety valve 14 do not have a step or a recess between them. In addition, it is desirable that they are smoothly connected. That is, for example, when the safety valve 14 is formed by thinning the central portion of the lid body 18 by press working, it is preferable to perform press working for recessing only the outer surface of the lid body 18. As a result, when the internal pressure of the case body 12 rises above, stress concentration is prevented from occurring at the boundary portion between the safety valve 14 and the lid 18, and therefore, for example, the internal pressure of the case body 12 is defined. It is possible to effectively prevent the breakage at the boundary between the safety valve 14 and the lid 18 before reaching the pressure. As a result, when the internal pressure of the case main body 12 reaches the specified pressure, the bulging portion 28 of the safety valve 14 can be cleaved with higher accuracy.

  Further, the inner shape of the cleavage groove 32 provided in the bulging portion 28 is not limited at all. That is, for example, as shown in FIG. 8, a central inner surface portion 42 that is located at the center in the width direction of the cleavage groove 32 and constitutes the bottom of the cleavage groove 32 is configured by a curved surface or an arc surface. The first opening-side inner surface portion 44 and the second opening-side inner surface portion 46 that are located on both sides in the width direction with the central inner surface portion 42 interposed therebetween and are respectively connected to both ends in the width direction of the central inner surface portion 42. Each may be configured by inclined surfaces that are inclined in directions away from each other toward the opening side of the cleavage groove 32.

Such a cleavage groove 32 having an inner surface shape when forming the bulging portion 28, the curvature of the central inner surface portion 42 consisting of a curved surface and arcuate surface radius range R ₄ of about 0.01~1.0mm It is desirable that the value be within the range, and it is even more desirable that the value be within the range of about 0.05 to 0.07 mm. The reason for this is the same as described above. Moreover, it is preferable that the angle [theta] between the first opening side inner surface portion 44 and the second opening side inner surface portion 46 is 45 to 120 degrees. This is because, when the angle of the formed angle: θ is larger than 120 degrees, the cleavage groove 32 of the bulging portion 28 can be cleaved with high accuracy when the internal pressure of the case 10 reaches the specified pressure. In addition to the possibility of difficulty, when the cleavage groove 32 is formed by, for example, pressing the bulging portion 28, an extremely large press pressure is required, and the size of equipment required for forming the cleavage groove 32 is large. This is because there is a risk of increasing the cost and cost. Further, when the angle formed by the angle θ is smaller than 45 degrees, when the cleavage groove 32 is formed, for example, by pressing the bulging portion 28, the possibility of breakage increases. This is because it may be difficult to stably obtain the cleavage groove 32.

  Furthermore, even if the inner surface of the cleavage groove 32 is formed of a stepped curved surface formed by connecting three or more curved surface portions having different radii of curvature to each other in the width direction of the cleavage groove 32. good. The curvature radii of the three or more curved surface portions may be configured to gradually increase from the central portion in the width direction of the cleavage groove 32 toward the opening side of the cleavage groove 32.

  Furthermore, in the above-described embodiment, the cleavage groove 32 is provided only on the outer side surface 30 of the bulging portion 28, but it may be provided only on the inner side surface 29 of the bulging portion 28.

  Further, the shape and structure of the cleavage groove 32 can be variously changed. That is, for example, as shown in FIG. 9, a portion of the main groove portion 33 that has a predetermined dimension deviation from one end in the length direction to the center portion side, and a portion that has a predetermined dimension deviation from the other end portion in the length direction to the center portion side, The four sub-grooves 34a, 34b, 34c, and 34d are extended obliquely toward both sides in the width direction of the main groove 33 (the width direction of the safety valve 14 and the vertical direction in FIG. 9). The cleavage groove 32 may be configured.

  Further, as shown in FIG. 10, the four sub-grooves 34 a, 34 b, 34 c, 34 d are convex toward the center in the length direction of the main groove 33 toward both sides in the width direction of the main groove 33. The cleavage groove 32 may be formed by extending with a curved shape. Of course, the four sub-grooves 34 a, 34 b, 34 c, 34 d can be extended with a curved shape that is concave on the center side in the longitudinal direction of the main groove 33 to constitute the cleavage groove 32.

  Further, as shown in FIG. 11, the four sub-groove portions 34 a, 34 b, 34 c, 34 d are respectively connected to the main groove portion 33 from both ends in the length direction of the main groove portion 33 toward both sides in the width direction of the main groove portion 33. Alternatively, the cleavage groove 32 may be configured to extend at a right angle.

  Furthermore, as shown in FIG. 12, only one sub-groove 34 a extends obliquely from one end in the length direction of the main groove 33 toward one side in the width direction of the main groove 33 (the upper side in FIG. 12). On the other hand, from the other end in the length direction of the main groove portion 33, only one sub groove portion 34b is obliquely extended toward the other side in the width direction of the main groove portion 33 (the lower side in FIG. 12). It is also possible to configure.

  Furthermore, as shown in FIG. 13, the cleavage groove 32 may be configured by only one main groove portion 33 extending in a straight line in the length direction of the safety valve 14.

  Further, as shown in FIG. 14, the first main groove portion 33 a extending in a straight line in the length direction of the safety valve 14 and the second main groove portion 33 b extending in a straight line in the width direction of the safety valve 14 are respectively extended. It is also possible to form the cleavage groove 32 by crossing each other at the center of the direction.

  Further, as shown in FIG. 15, the first main groove portion 33 a that extends in a straight line in the direction intersecting both the length direction and the width direction of the safety valve 14, the length direction, the width direction, and the first direction of the safety valve 14. A second main groove portion 33b extending in a straight line in a direction intersecting all the extending directions of the main groove portion 33a is formed so as to intersect with each other in the center portion of each extending direction, and the cleavage groove 32 is formed. It can also be configured.

  Further, the overall shape of the safety valve 14 is not limited to the illustrated longitudinal rectangular shape. For example, the shape of the opening 24 provided in the case body 12 and sealed by the safety valve 14 is, for example, Accordingly, it can be appropriately changed. That is, there is no problem even if the overall shape of the safety valve 14 is, for example, a square shape, a circular shape, an oval shape, an elliptical shape, or the like.

  Furthermore, the overall shape of the case 10 can be variously changed. For example, the overall shape of the case 10 may be a cylindrical shape.

  Furthermore, the material of the housing 16 and the lid 18 of the case body 12 or the material of the safety valve 14 can be changed as appropriate according to, for example, the type of the secondary battery. Therefore, the case main body 12 and the safety valve 14 can be formed of, for example, aluminum (including pure aluminum and aluminum alloy), or a metal material such as nickel, iron, and stainless steel in addition to the illustrated nickel-plated steel plate.

  In addition, in some of the embodiments described above, specific examples of applying the present invention to a nickel-hydrogen secondary battery and a case for a nickel-hydrogen secondary battery have been shown. Of course, the present invention can be advantageously applied to any secondary battery other than the secondary battery and the case for the secondary battery.

  In addition, although not enumerated one by one, the present invention can be carried out in a mode to which various changes, modifications, improvements, etc. are added based on the knowledge of those skilled in the art. It goes without saying that all are included in the scope of the present invention without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Case 12 Case main body 14 Safety valve 16 Container 18 Cover body 24 Opening part 28 Swelling part 32 Cleavage groove

Claims (4)

A safety valve that has a case body that seals the positive electrode, the negative electrode, and the electrolyte inside, and that is cleaved when the internal pressure of the case body reaches a preset specified pressure, and releases the internal pressure of the case body to the outside. A case for a secondary battery provided in the case body,
When the safety valve is configured to have a dome shape that bulges inside the case body, and is thinner than the case body, and the internal pressure of the case body becomes the specified pressure A case for a secondary battery, wherein a cleavage groove that is cleaved is provided only on one surface in the thickness direction of the thin portion.   The case for a secondary battery according to claim 1, wherein an inner surface of the cleavage groove is a curved surface.   The inner surface of the cleavage groove is composed of a plurality of curved surface portions having mutually different curvature radii, which are connected to each other in the width direction of the cleavage groove, and the plurality of curved surface portions. 3. The secondary battery case according to claim 2, wherein the curvature radius is gradually increased from the center in the width direction of the cleavage groove toward the opening side of the cleavage groove. 4. A secondary battery comprising a case for a secondary battery according to claim 1, wherein a positive electrode, a negative electrode, and an electrolyte are sealed.

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