JP2013143331A - Method for manufacturing alkaline secondary battery, and alkaline secondary battery manufactured by this manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an alkaline secondary battery capable of achieving higher capacity of a battery due to thinning of a bottom wall of an exterior can, and simultaneously capable of suppressing the occurrence of a bulge of the bottom wall of the exterior can associated with the rise of an internal pressure.SOLUTION: A method for manufacturing an alkaline secondary battery includes: a bottom wall thinning process of pressing a first punch body 56 having a convexly curved bottom end 60 to a center portion 70 of a disc 44, and processing the center portion 70 of the disc 44 into a curved shape to thin it; an intermediate product formation process of applying drawing process to the convexly curved disc 44 to form a first intermediate product 50; a flattening process of sandwiching the curved bottom of the first intermediate product 50 between a lower end face 82 of a second punch body 78 and an upper end face 96 of a receiving tool 76 to flatten the curved bottom of the first intermediate product; a deep drawing process of applying drawing process to the first intermediate product having the flattened bottom; and a finish process of applying final drawing process to the second intermediate product 100 obtained through the deep drawing process to form an exterior can 10.

Description

  The present invention relates to a method for producing an alkaline secondary battery and an alkaline secondary battery produced by the production method.

  A nickel metal hydride secondary battery is known as one of alkaline secondary batteries, and this nickel metal hydride secondary battery is superior in environmental safety compared to a nickel cadmium secondary battery, so that it can be used in various applications. It has become. For the nickel metal hydride secondary battery used for such various applications, improvement in various characteristics is desired, and in particular, a higher capacity is desired.

  Here, a general nickel metal hydride secondary battery contains an electrode group consisting of a positive electrode containing nickel hydroxide, a negative electrode containing a hydrogen storage alloy and a separator in an outer can that also serves as a negative electrode terminal, and then an alkaline electrolyte solution. It is manufactured by pouring and then sealing the upper end opening of the outer can with a sealing body. One means for increasing the capacity of such a nickel metal hydride secondary battery is to reduce the thickness of the outer can. Specifically, when the thickness of the outer can of the battery is made thinner than before, the internal volume of the outer can increases accordingly, so that the size of the electrode group can be increased, and the positive and negative electrode active materials contained in the electrode group The amount of battery can be increased, and the capacity of the battery can be increased.

  Here, as a method for manufacturing an outer can that thins the peripheral wall, for example, a method for manufacturing an outer can shown in Patent Document 1 is known. In the method of Patent Document 1, first, an iron cup-shaped material is prepared. On the other hand, a plurality of dies each having a through hole for restriction having a different diameter are prepared, and these dies are arranged in multiple stages on the coaxial line so that the diameters of the through holes are sequentially reduced. Then, after the material is introduced into the first-stage die, the material is pushed with a punch having an outer diameter substantially equal to the inner diameter of the outer can, and passed through the final-stage die at once. Thereby, a bottomed cylindrical outer can having a predetermined inner diameter is obtained. Here, the material is continuously drawn and ironed in the process of passing through each die. As a result of this processing, the bottom wall portion is only reduced in diameter and the thickness remains almost the same as that of the material, but the peripheral wall portion is made continuous by applying a large force when passing through the die. As a result, the thickness is significantly smaller than the thickness of the material. In addition, the peripheral wall is hardened because of work hardening.

  By the way, in recent years, due to the demand for long-time driving of various portable devices for mobile use, a further increase in capacity is desired for nickel-hydrogen secondary batteries. For this reason, it is desired to further increase the internal volume of the battery outer can, and an attempt has been made to reduce the thickness of the bottom wall together with the thickness of the peripheral wall.

  Here, when an exterior can is manufactured using the method of Patent Document 1 as described above, the thinning of the bottom wall can be dealt with by using a cup-shaped material made of a thin base material in advance. Generally done. That is, in the method of Patent Document 1, the thickness of the material substantially corresponds to the thickness of the bottom wall portion of the resulting outer can.

Japanese Patent Publication No. 07-099686

  By the way, in the nickel metal hydride secondary battery, the internal pressure of the battery is kept constant by reducing and consuming the oxygen gas generated from the positive electrode during overcharge by the hydrogen storage alloy negative electrode. However, if charging and discharging are repeated, oxygen gas cannot be sufficiently reduced and consumed at the negative electrode due to deterioration of the hydrogen storage alloy. For this reason, in a nickel metal hydride secondary battery, the internal pressure of the battery tends to increase as the number of charge / discharge cycles increases.

  In a battery using an outer can made of a thin material in order to increase the capacity as described above, when the internal pressure increases, the bottom wall portion of the outer can may be deformed and bulge outward. . This is considered to be because the strength of the bottom wall portion of the outer can becomes lower than the conventional one due to the thinning of the material, and sufficient pressure-resistant strength cannot be secured. When the bottom wall portion of the outer can is thus swelled, the size of the battery in the longitudinal direction increases, causing problems such as being unable to accommodate the battery in a battery chamber of a portable device or the like.

  In order to suppress the swelling of the bottom wall portion of the outer can due to the increase in the internal pressure of the battery, it is preferable to make the bottom wall as thick as possible in order to maintain the strength of the bottom wall. However, increasing the thickness of the bottom wall hinders the increase in battery capacity. That is, it has been difficult to achieve both high battery capacity and suppression of battery wall swelling.

  Here, as a measure to suppress the swelling of the bottom wall portion of the outer can due to an increase in internal pressure, it is conceivable to use a base material that is thin but high in strength, but in this case, it becomes difficult to process the base material itself, Even if the can can be manufactured, it causes a significant decrease in manufacturing efficiency and causes adverse effects such as an increase in manufacturing cost.

  The present invention has been made on the basis of the above circumstances, and its object is to increase the capacity of the battery by thinning the bottom wall of the outer can and the bottom wall of the outer can as the internal pressure increases. An object of the present invention is to provide a method for producing an alkaline secondary battery that can simultaneously suppress the occurrence of blistering, and an alkaline secondary battery using this production method.

  To achieve the above object, according to the present invention, an outer can manufacturing process for manufacturing a bottomed cylindrical outer can, an electrode group storing process for storing an electrode group consisting of a positive electrode, a negative electrode, and a separator in the outer can, Manufacture of an alkaline secondary battery comprising an electrolyte injection step of injecting an alkaline electrolyte into an outer can in which an electrode group is housed, and a sealing step of sealing the opening of the outer can with a cover plate after the injection of the alkaline electrolyte In the method, the outer can manufacturing process includes a punching process of punching a disk as a starting material of the outer can from a metal plate as a base material, and a cup-shaped intermediate product by drawing the disk An intermediate product forming process for forming the intermediate product, a deep drawing process in which the intermediate product is subjected to drawing to reduce the diameter and the peripheral wall is thinned, and the intermediate product that has undergone the deep drawing process is finished to the drawing A finishing process for forming the outer can by applying a can bottom forming portion to be a bottom wall of the outer can in the disk or the intermediate product between the punching process and the finishing process. A method of manufacturing an alkaline secondary battery, further comprising: a bottom wall thinning process for thinning the protrusion by deforming it into a convex shape and a flattening process for flattening the can bottom forming planned portion deformed into the convex shape. (Claim 1).

  Here, the bottom wall thinning process forms a convexly curved disk by pressing a punch having a convexly curved pressing surface against a central portion of the disk, and the intermediate product forming process Forming a cup-shaped intermediate product having a curved bottom by subjecting the circularly curved disk to a flat shape, and the flattening process pressing the curved bottom of the intermediate product flat It is preferable to flatten by sandwiching between a punch having a surface and a receiving tool having a flat receiving surface.

  Further, the base material is a plate mainly composed of iron having a Vickers hardness of 80 Hv to 120 Hv, and in the bottom wall thinning process, the bottom wall has a Vickers hardness of 100 Hv to 180 Hv. It is preferable to cause work hardening as much as possible and to cause work hardening as much as possible in the deep drawing process so that the hardness of the peripheral wall is 190 to 210 Hv in terms of Vickers hardness.

  Moreover, according to this invention, the alkaline secondary battery manufactured using the manufacturing method in any one of Claims 1-3 mentioned above is provided (Claim 4).

  Here, it is preferable that the hardness of the bottom wall of the outer can is in a range of 50% to 90% with respect to the hardness of the peripheral wall of the outer can.

  The method for producing an alkaline secondary battery according to the present invention includes a bottom wall thinning process and a flattening process in the outer can manufacturing process. This bottom wall thinning process is performed by deforming the can bottom forming planned portion to be the bottom wall of the outer can in the circular plate as the starting material of the outer can or the intermediate product obtained by drawing the disc into a convex shape. It is a process to convert. On the other hand, the flattening process is a step of flattening the can bottom forming planned portion deformed into a convex shape. In this way, in the process of manufacturing the outer can, if the can bottom forming planned portion to be the bottom wall of the outer can is processed, the can bottom forming planned portion is thinned and causes work hardening, and the hardness is increased. Enhanced. As a result, since the bottom of the outer can is thinned, the internal volume is increased, the size of the electrode group can be increased correspondingly, and the capacity of the battery can be increased. In addition, since the strength of the bottom portion of the outer can increases as the hardness increases, even if the internal pressure of the battery increases, the bottom wall portion can be prevented from being deformed and swollen. That is, according to the manufacturing method of the present invention, it is possible to achieve both higher battery capacity by reducing the thickness of the bottom wall of the outer can and suppressing the occurrence of swelling of the bottom wall of the outer can due to the increase in internal pressure. . Therefore, the battery provided by the present invention has a high capacity and high quality because the swelling of the bottom of the can during the charge / discharge cycle is suppressed.

  Further, in the present invention, the base wall is processed together with the peripheral wall in the process of forming the outer can using the base material having a relatively low hardness, and work hardening is caused on the peripheral wall and the bottom wall, so that it is finally obtained. Despite the high hardness of the outer can, the outer can can be manufactured relatively easily without causing a decrease in manufacturing efficiency.

It is the perspective view which fractured | ruptured and showed the nickel-hydrogen secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows the aspect which punches out the disc as a starting material of an exterior can. It is sectional drawing which shows the aspect which processes a disc into 1st intermediate product. It is sectional drawing which shows the aspect which planarizes the bottom part of a 1st intermediate product. It is sectional drawing which shows the aspect which gives a drawing process to the 1st intermediate product and manufactures the 2nd intermediate product. It is sectional drawing which shows the aspect which performs a drawing process to the 2nd intermediate product. It is sectional drawing which shows the aspect which processes a 2nd intermediate product into an exterior can.

Hereinafter, a nickel-hydrogen secondary battery (hereinafter simply referred to as a battery) 2 to which the present invention is applied will be described with reference to the drawings.
The battery to which the present invention is applied is not particularly limited. For example, a case where the present invention is applied to an AA size cylindrical battery 2 shown in FIG. 1 will be described as an example.

  As is clear from FIG. 1, the battery 2 includes an outer can 10 having a bottomed cylindrical shape with an open upper end. In the outer can 10, an electrode group 22 is accommodated together with a predetermined amount of an alkaline electrolyte (not shown). The outer can 10 has conductivity, and its bottom wall 35 functions as a negative electrode terminal. In the opening of the outer can 10, a disc-shaped cover plate 14 having conductivity and a ring-shaped insulating packing 12 surrounding the cover plate 14 are disposed. The insulating packing 12 caulks the opening edge 36 of the outer can 10. It is fixed to the opening edge 36 of the outer can 10 by processing. That is, the lid plate 14 and the insulating packing 12 cooperate with each other to airtightly close the opening of the outer can 10.

  Here, the cover plate 14 has a central through hole 16 in the center, and a rubber valve body 18 that closes the central through hole 16 is disposed on the outer surface of the cover plate 14. Further, a flanged cylindrical positive terminal 20 is fixed on the outer surface of the cover plate 14 so as to cover the valve body 18, and the positive terminal 20 presses the valve body 18 toward the cover plate 14. The positive electrode terminal 20 has a gas vent hole (not shown).

  Normally, the central through hole 16 is hermetically closed by the valve body 18. On the other hand, if gas is generated in the outer can 10 and its internal pressure increases, the valve body 18 is compressed by the internal pressure and opens the central through hole 16. As a result, the central through hole 16 and the positive electrode terminal 20 are opened from the outer can 10. Gas is released through the vent holes. That is, the central through hole 16, the valve body 18, and the positive electrode terminal 20 form a safety valve for the battery.

  Each of the electrode groups 22 is composed of a strip-like positive electrode 24, a negative electrode 26, and a separator 28, which are wound in a spiral shape with a separator 28 made of an insulating resin sandwiched between the positive electrode 24 and the negative electrode 26. Yes. That is, the positive electrode 24 and the negative electrode 26 are overlapped with each other via the separator 28. Here, the positive electrode 24 includes a conductive positive electrode substrate having a porous structure and a positive electrode mixture held in the pores of the positive electrode substrate. This positive electrode mixture contains nickel hydroxide. Further, the negative electrode 26 has a conductive negative electrode substrate (core body) having a strip shape, and a negative electrode mixture containing a hydrogen storage alloy is held on the negative electrode substrate.

The outermost periphery of the electrode group 22 is formed by a part of the negative electrode 26 (the outermost periphery), and is in contact with the inner surface of the peripheral wall of the outer can 10. That is, the negative electrode 26 and the outer can 10 are electrically connected to each other.
In the outer can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the lid plate 14, and both ends of the positive electrode lead 30 are connected to the inner end of the positive electrode 24 and the lid plate 14, respectively. . Accordingly, the positive electrode terminal 20 and the positive electrode 24 of the lid plate 14 are electrically connected to each other via the positive electrode lead 30 and the lid plate 14. A circular insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit provided in the insulating member 32. A circular insulating member 34 is also disposed between the electrode group 22 and the bottom of the outer can 10.

In manufacturing such a battery 2, first, an outer can 10 is prepared.
The outer can 10 according to the present invention is manufactured as follows.
First, a plate material 48 made of a metal material is prepared as a base material. Although it does not specifically limit as this board | plate material 48, the board | plate material which consists of material which has iron as a main body is used suitably, For example, a cold rolled steel plate etc. can be used. Preferably, the steel plate which consists of SPCD material prescribed | regulated to JIS G 3141 suitable for a drawing process is mentioned. And as this steel plate, it is more preferable to use what was nickel-plated beforehand. Here, it is preferable to use a base material having a Vickers hardness of 80 Hv to 120 Hv. This is because if the base metal hardness is lower than 80 Hv, the predetermined strength cannot be obtained, and if it exceeds 120 Hv, the processing becomes difficult and it becomes difficult to manufacture a predetermined outer can, resulting in a decrease in manufacturing efficiency. Moreover, it is preferable to use a base material having a thickness of 0.15 to 0.50 mm.

  As shown in FIG. 2, the prepared plate material 48 is punched by a punching die 40 and a punching punch 42 mounted on a press machine (not shown). Thereby, the disk 44 as a starting material of the outer can 10 is obtained. Specifically, as shown in FIG. 2A, a plate material 48 is provided between a punching die 40 having a through hole 46 having a predetermined inner diameter and a punching punch 42 having a predetermined outer diameter that can be inserted into the through hole 46. Is placed. The inner diameter of the through hole 46 of the punching die 40 and the outer diameter of the punching punch 42 are set to appropriate dimensions so that a disk 44 having a predetermined outer diameter can be obtained. Next, as shown in FIG. 2B, by operating the press machine, the punching punch 42 is lowered and inserted into the through hole 46 of the punching die 40. In this process, a predetermined disc 44 is punched from the plate 48.

  The disc 44 thus obtained is then processed into a shallow cup-shaped intermediate product (hereinafter referred to as a first intermediate product) 50. In the step of manufacturing the first intermediate product 50, as shown in FIG. 3A, the first drawing die 52 is disposed on the same axis and mounted on a press machine (not shown) so as to face each other. And the 1st aperture punch 54 is used.

  The first drawing punch 54 includes a first punch main body 56 and a first wrinkle pressing member 58 disposed around the first punch main body 56.

  The first punch body 56 has a cylindrical shape with an outer diameter smaller than that of the punching punch 42, and the lower end 60 on the first drawing die 52 side protrudes in a curved shape. The first punch body 56 can be moved up and down by a drive device of a press machine.

  The first wrinkle pressing member 58 has a ring shape surrounding the outer periphery of the first punch body 56. The first wrinkle pressing member 58 has a flat bottom surface 62 on the first drawing die 52 side. The first wrinkle pressing member 58 is slidable in a direction along the axial direction of the first punch main body 56, and applies a predetermined wrinkle pressing force in a direction toward the first drawing die 52 by a control device (not shown). Can do.

  On the other hand, the first drawing die 52 is fixed and has a receiving hole 64 capable of receiving the first punch body 56 at the center thereof. The receiving hole 64 has an inner diameter that is slightly larger than the outer diameter of the first punch body 56, and the bottom 66 is recessed in a curved shape so as to match the lower end 60 of the first punch body 56. Yes.

  Next, the manufacturing procedure of the first intermediate product 50 will be described. FIG. 3A shows a state where the first aperture punch 54 is in the raised position. At this time, the first punch body 56 is accommodated in the first wrinkle pressing member 58, and the lower end portion 60 thereof is positioned above the lower end surface 62 of the first wrinkle pressing member 58. Here, the disc 44 is supplied to a predetermined position on the first aperture die 52. The disc 44 is preliminarily coated with oil for preventing seizure.

  Thereafter, as shown in FIG. 3B, the first punch body 56 and the first wrinkle holding member 58 move toward the first drawing die 52, and the first wrinkle holding member 58 and the first drawing die 52 are moved. The peripheral edge of the disc 44 is clamped by the upper end surface 68. At this time, a predetermined wrinkle pressing force indicated by an arrow F <b> 1 in FIG. 3 is applied to the disc 44 by the first wrinkle pressing member 58.

  Next, as the first punch body 56 moves through the first wrinkle pressing member 58 and further lowers, it enters the receiving hole 64 of the first drawing die 52 as shown in FIG. Go. As a result, the disc 44 held between the first drawing die 52 and the first wrinkle pressing member 58 is deformed. At this time, since the lower end portion 60 of the first punch body 56 protrudes in a curved shape, the disk 44 is deformed along the shape. That is, the central portion 70 of the disc 44 that is to become the bottom wall 35 of the outer can 10 is rounded and protrudes into the receiving hole 64. At this time, the central portion 70 of the disk 44 is stretched, the thickness is reduced, work hardening is caused, and the hardness is increased.

  On the other hand, the peripheral edge 72 of the disc 44 is pressed by the first wrinkle pressing member 58 and the first drawing die 52, but strictly speaking, the first drawing die is slipped little by little by the oil film applied to the surface. It is pushed into the receiving hole 64 of 52. By being pushed into the receiving hole 64 in this way, the peripheral wall 59 is gradually formed. Here, the peripheral edge portion 72 of the disk 44 that becomes the peripheral wall 59 is squeezed in the process of being pushed into the receiving hole 64, and the thickness is reduced and work hardening is caused to increase the hardness.

  3D, when the lower end portion 60 of the first punch body 56 reaches the bottom 66 of the receiving hole 64 of the first drawing die 52, the first punch body 56 and the first drawing die 52 are formed. The first intermediate product 50 that fits into the gap formed between the receiving hole 64 and the receiving hole 64 is obtained. The first intermediate product 50 has a shallow cup shape in which the bottom wall 51 is rounded and protrudes. In the present invention, by drawing the first punch body 56 having a rounded shape, work hardening is caused in both the portion that should become the bottom wall 35 and the portion that should become the peripheral wall 38 of the outer can 10. Is possible.

Next, the first intermediate product 50 is reworked into a flat state on the rounded bottom wall 51 and further drawn.
The process of reworking the bottom wall 51 of the first intermediate product 50 into a flat state will be described in detail below with reference to FIG.

  In this step, as shown in FIG. 4A, a second drawing punch 74 and a second drawing die 76 that are arranged on the same axis and mounted on a press machine (not shown) so as to face each other are used. It is done.

The second drawing punch 74 includes a second punch body 78 and a second wrinkle pressing member 80 disposed around the second punch body 78.
The second punch main body 78 has a cylindrical shape with an outer diameter smaller than that of the first punch main body 56 and has a flat lower end surface 82. The second punch body 78 can be moved up and down by a drive device of a press machine.

  The second wrinkle pressing member 80 has a ring shape surrounding the outer periphery of the second punch body 78. The second wrinkle pressing member 80 has a tapered portion 81 whose outer diameter is substantially the same as the inner diameter of the first intermediate product 50 and whose lower end on the second drawing die 76 side is tapered. The second wrinkle pressing member 80 is slidable in a direction along the axial direction of the second punch main body 78, and has a predetermined wrinkle pressing force in a direction toward the second drawing die 76 by a control device (not shown). Can be applied.

On the other hand, the second drawing die 76 includes a second die main body 84 and a receiving tool 86 accommodated in the second die main body 84.
The second die body 84 is fixed and has a through hole 88 at the center thereof. The through-hole 88 has a straight portion 90 having an inner diameter that can receive the second punch body 78, and an enlarged diameter that continues to the straight portion 90 and gradually increases in inner diameter toward the second drawing punch 74. Part 92.

  The enlarged diameter portion 92 has a shape that matches the tapered portion 81 of the second wrinkle pressing member 80 described above, and can sandwich the first intermediate product 50 in cooperation with the second wrinkle pressing member 80.

  The straight portion 90 is inserted with a receiving tool 86 that can move up and down in the straight portion 90. The receptacle 86 includes a head 94 having a cylindrical shape that is substantially the same diameter as the inner diameter of the straight portion 90. The upper end surface 96 of the head 94 is flat and fits with the lower end surface 82 of the second punch body 78. On the other hand, a drive shaft 98 is connected to the lower end of the head 94, and the drive shaft 98 is connected to a drive device (not shown). The driving device is controlled by a control device (not shown), and can fix the receiving tool 86 at a predetermined position in the straight portion 90, and the receiving device 86 is synchronized with the vertical movement of the second punch body 72. It can also be moved up and down.

Next, a procedure for flattening the bottom wall 51 of the first intermediate product 50 will be described. As shown in FIG. 4A, the first intermediate product 50 is supplied between the second drawing punch 74 and the second drawing die 76. Then, as shown in FIG. 4B, the second punch body 78 and the second wrinkle pressing member 80 are inserted from the opening end 53 side of the first intermediate product 50, and the second punch punch 74 is inserted into the tip 75 of the second end punch 75. One intermediate product 50 is fitted. At this time, the tapered portion 81 of the second wrinkle pressing member 80 and the peripheral edge portion 55 of the bottom wall 51 of the first intermediate product 50 are substantially matched, but the lower end surface 82 of the second punch body 80 and the first intermediate product 50 are matched. A gap is formed between the bottom wall 51 and the central portion 57 of the bottom wall 51. The lower surface of the central portion 57 of the bottom wall 51 of the first intermediate product 50 is in contact with the upper end surface 96 of the head 94 of the receiving tool 86. Here, the receiving tool 86 is fixed so that the upper end surface 96 of the head 94 is positioned at the boundary between the enlarged diameter portion 92 and the straight portion 90 of the second die body 84. From this state, the second punch body 78 and the second wrinkle pressing member 80 move toward the second drawing die 76 and apply a pressing force to the first intermediate product 50. As a result, as shown in FIG. 4C, the central portion 57 of the bottom wall 51 of the first intermediate product 50 is sandwiched between the second punch main body 78 and the head 94 of the receiving tool 86 to be deformed and flattened. Become. At the same time, the peripheral edge 55 of the bottom wall 51 of the first intermediate product 50 is deformed by being sandwiched between the second wrinkle holding member 80 and the enlarged diameter portion 92 of the second die body 84. It becomes a shape suitable for the taper portion 81 and the enlarged diameter portion 92 of the second die body 84.
In this way, the bottom wall 51 of the first intermediate product 50 is processed again and becomes a flat shape.

  Next, the first intermediate product 50 with the flat bottom wall 51 is drawn. In this drawing process, as shown in FIG. 4C, the first intermediate product 50 is pressed by the second wrinkle pressing member 80 and the enlarged diameter portion 92 of the second die body 84 as shown in FIG. As shown, the second punch body 78 is moved downward and inserted into the through hole 88 of the second die body 84. Note that the receptacle 86 also moves downward in synchronization with the downward movement of the second punch body 78. Further, a predetermined wrinkle pressing force indicated by an arrow F2 in FIG. 5A is applied to the first intermediate product 50 by the second wrinkle pressing member 80.

  In this way, as the second punch body 78 enters the second die body 84, the first intermediate product 50 also enters the second die body 84 while deforming. In this process, the diameter of the first intermediate product 50 is reduced, and the peripheral wall 59 is squeezed and stretched. As a result, as shown in FIG. 5B, the first intermediate product 50 becomes a cup-shaped second intermediate product 100 in which the height of the peripheral wall 59 is increased.

Next, the second intermediate product 100 is further deeply drawn, and deep drawing is performed in order to obtain the target outer can 10.
The step of deep drawing will be described in detail below with reference to FIGS.
In this step, as shown in FIG. 6A, a third drawing punch 102 and a third drawing die 104 which are arranged on the same axis and mounted on a press machine (not shown) so as to face each other are used. It is done.

The third squeeze punch 102 includes a third punch body 106 and a third wrinkle pressing member 108 disposed around the third punch body 106.
The third punch body 106 has a cylindrical shape with an outer diameter smaller than that of the second punch body 78. The outer diameter of the third punch body 106 is set to be approximately the same as the inner diameter of the outer can 10. The lower end surface 110 of the third punch body 106 is flat. The third punch body 106 can be moved up and down by a drive device of a press machine.

  The third wrinkle pressing member 108 has a ring shape surrounding the outer periphery of the third punch body 106. The third wrinkle pressing member 108 has an outer diameter that is substantially the same as the inner diameter of the second intermediate product 100, and has a tapered portion 112 whose lower end on the third drawing die 104 side is tapered. The third wrinkle pressing member 108 is slidable in a direction along the axial direction of the third punch body 106, and has a predetermined wrinkle pressing force in a direction toward the third drawing die 104 by a control device (not shown). Can be applied.

  On the other hand, the third aperture die 104 is fixed and has a through hole 114 at the center thereof. The through-hole 114 has a straight portion 105 having an inner diameter dimension capable of receiving the third drawing punch 106, and an enlarged diameter that is continuous with the straight portion 105 and gradually increases toward the third drawing punch 102. Part 107.

The straight portion 105 is set to have substantially the same size as the outer diameter of the outer can 10.
The enlarged diameter portion 107 has a shape that matches the tapered portion 112 of the third wrinkle pressing member 108 described above, and can hold the second intermediate product 100 in cooperation with the third wrinkle pressing member 108.

  Next, a procedure for deep drawing will be described. First, as shown in FIG. 6A, the third punch body 106 and the third wrinkle pressing member 108 are inserted from the opening end 111 side of the second intermediate product 100, and the second punch 103 is inserted into the tip 103 of the third drawing punch 102. 2 The intermediate product 100 is in a fitted state. From this state, the third punch body 106 and the third wrinkle pressing member 108 move toward the third drawing die 104 and apply a pressing force to the second intermediate product 100. As a result, as shown in FIG. 6B, the peripheral edge 118 of the bottom wall 116 of the second intermediate product 100 is sandwiched between the third wrinkle pressing member 108 and the enlarged diameter portion 107 of the third drawing die 104. It is deformed and becomes a shape suitable for the tapered portion 112 of the third wrinkle pressing member 108 and the enlarged diameter portion 107 of the third drawing die 104. Here, the third wrinkle pressing member 108 is in a state where a force (indicated by an arrow F3 in FIG. 6) acting in the direction of the third aperture die 104 is applied by a control device (not shown). For this reason, the second intermediate product 100 is pressed by the third wrinkle pressing member 108 and the enlarged diameter portion 107 of the third drawing die 104. From this state, as shown in FIG. 6C, when the third punch body 106 is moved and inserted into the through hole 114 of the third drawing die 104, the second intermediate product 100 is It deforms and enters the through hole 114. In this process, the diameter of the second intermediate product 100 is reduced and the peripheral wall 120 is squeezed and stretched. When the third punch body 106 is further moved, as shown in FIG. 7A, the entire second intermediate product 100 is pushed into the through hole 114, and the peripheral wall 120 is stretched to a predetermined length. The outer can 10 is obtained. Then, as shown in FIG. 7B, the outer can 10 is taken out by pulling out the third punch body 106 from the third drawing die 104. The extracted outer can 10 has its opening end portion 11 appropriately cut and then cleaned in order to make the height equal to a prescribed dimension.

  The outer can 10 thus obtained is not only the portion of the peripheral wall 38 but also the portion of the bottom wall 35 is processed (stretching and flattening) in the manufacturing process, and thus has caused work hardening. Strength is increased.

Here, it is preferable that the bottom wall 35 is processed to such an extent that the hardness thereof is Vickers hardness and causes work hardening to be 100 Hv to 180 Hv. This is because if the hardness is lower than 100 Hv, the strength of the bottom of the can is not sufficient, and the bottom of the can tends to swell as the internal pressure of the battery increases. On the other hand, in order to cause work hardening exceeding 180 Hv, the degree of processing becomes too high, and it becomes difficult to process the outer can. In addition, the peripheral wall 38 is preferably subjected to processing that causes work hardening to be 190 Hv to 210 Hv in terms of Vickers hardness. This is because if the hardness is lower than 190 Hv, the strength of the peripheral wall portion is not sufficient. On the other hand, in order to cause work hardening to exceed 210 Hv, the degree of processing becomes too high, and it becomes difficult to process the outer can. Further, the hardness of the bottom wall 35 of the outer can 10 is preferably in the range of 50% to 90% with respect to the hardness of the peripheral wall 38 of the outer can 10. This is because if the ratio of the hardness of the bottom wall to the hardness of the peripheral wall is lower than 50%, the strength of the bottom wall is not sufficient, and if it exceeds 90%, it becomes difficult to process the outer can.
Moreover, it is preferable that the relationship between the thickness of the bottom wall 35 and the peripheral wall 38 in the outer can 10 is the relationship of the thickness of the bottom wall> the thickness of the peripheral wall.

  The outer can 10 obtained as described above contains the electrode group 22 formed by winding the positive electrode 24, the negative electrode 26, and the separator 28, and then an alkaline electrolyte is injected. Thereafter, the cover plate 14 is caulked and fixed to the opening edge 36 of the outer can 10 via insulating packing, and the outer can 10 is sealed to obtain the battery 2.

  According to the present invention, since the strength of the bottom of the outer can can be increased by increasing the hardness of the bottom wall of the outer can, the occurrence of swelling of the bottom wall due to an increase in battery internal pressure when the charge / discharge cycle is repeated It is suppressed and the quality of the battery can be improved. In addition, the bottom wall can be made thinner, which contributes to higher battery capacity.

  In addition, this invention is not limited to a nickel-hydrogen secondary battery, It can also be employ | adopted for another battery.

1. Production of battery (Example 1)
(1) Production of an outer can In a transfer press machine (not shown), a pair of a punching punch 42 and a punching die 40 shown in FIG. 2, a first drawing punch 54 and a first drawing die 52 shown in FIG. 4, the pair of the second drawing punch 74 and the second drawing die 76 shown in FIG. 4, and the pair of the third drawing punch 102 and the third drawing die 104 shown in FIG. 6 were mounted in parallel. A steel plate (sheet material 48) as a base material is supplied to such a transfer press machine, and punching processing at each pair of punches and dies, thinning of the bottom wall portion, flattening processing and drawing processing are sequentially performed. The outer can 10 having a bottom wall thickness of 0.250 mm was manufactured.
Here, as a base material, a steel plate made of SPCD material defined in JIS 3141 was prepared. This steel plate has a thickness of 0.255 mm and a hardness of 80 Hv in terms of Vickers hardness.

(2) Preparation of positive electrode 100 parts by weight of nickel hydroxide particles, 10 parts by weight of cobalt hydroxide, 40 parts by weight of HPC (hydroxypropylcellulose) dispersion and 0.3 parts by weight of zinc oxide (positive electrode additive) ) To prepare a positive electrode mixture slurry, and this positive electrode mixture slurry was applied to and filled in a foamed nickel sheet as a positive electrode substrate. The foamed nickel sheet to which the positive electrode mixture slurry was adhered was dried and then rolled and cut to obtain the positive electrode 24.

(3) Production of negative electrode Dispersion of 0.4 parts by weight of sodium polyacrylate, 0.1 part by weight of carboxymethyl cellulose, and styrene butadiene rubber (SBR) with respect to 100 parts by weight of the rare earth-Mg-Ni hydrogen storage alloy powder 1.0 part by weight (solid content 50% by weight) (solid content conversion), 1.0 part by weight of carbon black, and 30 parts by weight of water were added and kneaded to prepare a negative electrode mixture slurry.

This negative electrode mixture slurry was applied to both surfaces of an iron perforated plate as a negative electrode substrate so that the thickness was uniform and constant. This perforated plate has a thickness of 60 μm, and its surface is plated with nickel.
After the slurry was dried, the perforated plate to which the hydrogen storage alloy powder was adhered was further rolled and cut to produce an AA size negative electrode 26 in which the amount of the hydrogen storage alloy per negative electrode was 9.0 g.

(4) Assembly of Nickel Metal Hydride Battery The obtained positive electrode 24 and negative electrode 26 were spirally wound with a separator 28 sandwiched between them, and an electrode group 22 was produced. The separator 28 used for production of the electrode group 22 here was made of a polypropylene fiber non-woven fabric, and its thickness was 0.1 mm (weight per unit area 40 g / m ² ).

  The electrode group 22 was housed in a bottomed cylindrical outer can 10 and an 8N (normality) alkaline electrolyte composed of a 30 wt% aqueous sodium hydroxide solution containing lithium and potassium was injected. Thereafter, the opening of the outer can 10 was closed with the cover plate 14 or the like, and the AA size nickel-hydrogen secondary battery 2 having a nominal capacity of 2000 mAh was assembled.

(Examples 2 to 7)
The battery of Example 1 was prepared using the outer can obtained in the same manner as in Example 1 except that the steel plate having the thickness shown in Table 1 was used as the base material of the outer can. The same nickel metal hydride secondary battery was assembled.

(Examples 8 to 14)
As the base material of the outer can, an outer can was produced in the same manner as in Example 1 except that a steel plate having a hardness of 100 Hv and a thickness shown in Table 2 was used. A nickel metal hydride secondary battery similar to the battery of Example 1 was assembled.

(Examples 15 to 21)
As the base material of the outer can, an outer can was produced in the same manner as in Example 1 except that a steel plate having a hardness of 120 Hv and a thickness shown in Table 3 was used. A nickel metal hydride secondary battery similar to that in Example 1 was assembled.

(Comparative Examples 1-4)
By using a steel plate having a thickness of 0.250 mm and a hardness as shown in Tables 1 to 3 as a base material of the outer can, the bottom wall portion is not subjected to thinning and flattening processing. Except that the thickness was kept as the base material thickness and the bottom wall hardness was kept as the base material hardness, an outer can was produced in the same manner as in Example 1, and the obtained outer can was used as in Example 1. A similar nickel metal hydride secondary battery was assembled.

2. Evaluation of Exterior Can and Nickel Metal Hydride Battery (1) About Exterior Can The ratio of the thickness of the bottom wall after processing to the thickness of the base material is shown in Tables 1 to 3 as the thickness change rate.
The Vickers hardness of the bottom wall portion and the peripheral wall portion was measured, and the results are shown in Tables 1 to 3. Further, from these values, the ratio of the hardness of the bottom wall to the hardness of the peripheral wall was obtained and shown in Tables 1 to 3 as the base wall / peripheral wall ratio.
In addition, Tables 1 to 3 also indicate whether or not the manufacture of the outer can 10 can be performed as “possible”, and the case where the specified outer can 10 cannot be manufactured is “impossible”. Indicated.

(2) Nickel metal hydride secondary battery The swelling amount of the bottom wall portion of the battery after 100 cycles was determined as follows.
After charging the battery of the example and the comparative example at a temperature of 25 ° C. with a charging current of 0.1 C for 16 hours, until the battery voltage becomes 0.5 V with a discharging current of 0.2 C The initial activation process for discharging was repeated twice.
The battery that had been subjected to the initial activation treatment was charged in a 25 ° C. atmosphere at a charging current of 1.0 C with a charging current of 1.0 C until the voltage decreased to 10 mV, and then left for 30 minutes.
Next, the battery was discharged at a discharge current of 1.0 C under the same atmosphere until the battery voltage became 0.8 V, and then left for 30 minutes.

  The charge / discharge cycle was defined as one cycle, and such a cycle was repeated 100 times. And the full length of the battery after 100 cycles was measured. The values obtained by subtracting the total length of the battery (50.2 mm) measured in advance before the initial activation process from the total length of the battery after 100 cycles are shown in Tables 1 to 3 as the amount of swelling at the bottom of the can after 100 cycles. .

(3) About the result of Tables 1-3 The following is clear from Tables 1-3.
First, the higher the hardness of the bottom wall of the outer can, the smaller the swollen amount of the can bottom after repeating the charge / discharge cycle 100 times. This is probably because the bottom wall portion is work hardened, and the strength increases accordingly, so that the internal pressure of the battery rises and can withstand pressure.

  In addition, when the base material having a hardness exceeding 140 Hv is used, it becomes difficult to process the steel sheet, and the specified outer can cannot be manufactured. From this, it can be said that it is not very effective to increase the hardness of the base material in advance, and it is effective to increase the hardness of the bottom wall portion in the process of processing into an outer can. Here, it can be said that the hardness of the base material is preferably set in the range of 80 Hv to 120 Hv.

  In this way, in the process of processing into an outer can, forming the bottom of the can while reducing the thickness of the base material is effective in increasing the hardness of the bottom wall portion. When the thickness change rate becomes lower than 89%, that is, when the thickness of the bottom wall after processing becomes thinner than 89% with respect to the thickness of the base material, the production of the can as specified is made. It turns out to be difficult. From this, it can be said that drastic reduction in thickness such that the rate of change in thickness from the base material is less than 89% is not effective.

  Further, in this embodiment, the thickness of the bottom wall is fixed to 0.25 mm, but it is considered that the same effect can be obtained even when the thickness is changed to other thicknesses.

  Here, in the outer can of the present invention, the bottom wall is also thinned along with the thinning of the peripheral wall, so that the capacity of the obtained battery is considered to be high.

2 Nickel Metal Hydride Battery 10 Exterior Can 22 Electrode Group 24 Positive Electrode 26 Negative Electrode 28 Separator 35 Bottom Wall 38 Peripheral Wall 40 Punching Die 42 Punching Punch 44 Disc 50 First Intermediate Product 52 First Drawing Die 54 First Drawing Punch 74 Second drawing punch 76 Second drawing die 100 Second intermediate product 102 Third drawing punch 104 Third drawing die

Claims (5)

An outer can manufacturing process for manufacturing a bottomed cylindrical outer can, an electrode group storing step for storing an electrode group composed of a positive electrode, a negative electrode and a separator in the outer can, an alkaline electrolyte in the outer can in which the electrode group is stored In a method for producing an alkaline secondary battery comprising an electrolyte injection step of injecting and sealing a step of sealing an opening of the outer can with a cover plate after injection of the alkaline electrolyte,
The outer can manufacturing process includes:
A punching process for punching a disc as a starting material of the outer can from a metal plate as a base material;
An intermediate product forming process for drawing the disk to form a cup-shaped intermediate product;
A deep drawing process in which the intermediate product is drawn to reduce the diameter and reduce the peripheral wall;
A finishing process for forming the outer can by subjecting the intermediate product that has undergone the deep drawing process to a final drawing process,
Between the punching process and the finishing process, the bottom wall is thinned by deforming the can bottom forming planned portion to be the bottom wall of the outer can in the disk or the intermediate product into a convex shape. A method of manufacturing an alkaline secondary battery, further comprising a flattening process for flattening the process and the can bottom forming scheduled portion deformed into a convex shape. The bottom wall thinning process is:
Forming a convexly curved disk by pressing a punch having a convexly curved pressing surface against the central part of the disk,
The intermediate product formation process includes:
Forming a cup-shaped intermediate product with a curved bottom by applying a drawing process to the convexly curved disc,
The planarization process includes:
2. The alkali secondary according to claim 1, wherein the curved bottom portion of the intermediate product is flattened by being sandwiched between a punch having a flat pressing surface and a receiving member having a flat receiving surface. Battery manufacturing method. For the base material, a plate material mainly composed of iron having a Vickers hardness in the range of 80 Hv to 120 Hv is used,
In the bottom wall thinning process, the bottom wall has a Vickers hardness of 100 Hv to 180 Hv to cause work hardening,
3. The method for producing an alkaline secondary battery according to claim 1, wherein in the deep drawing process, work hardening is caused so that the hardness of the peripheral wall is 190 to 210 Hv in terms of Vickers hardness.   The alkaline secondary battery manufactured using the manufacturing method in any one of Claims 1-3.   5. The alkaline secondary battery according to claim 4, wherein the hardness of the bottom wall of the outer can is in the range of 50% to 90% with respect to the hardness of the peripheral wall of the outer can.

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