JP2018125089A - Collector lead and manufacturing method of secondary battery including collector lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a collector lead capable of obtaining a secondary battery in which the occurrence of an inner short circuit is less than the conventional one, while maintaining an excellent high rate discharge characteristic, and a manufacturing method of the secondary battery including the collector lead.SOLUTION: A collector lead 34 includes: a top wall part 36 that is interposed between the sealing body 14 and a positive electrode collector 28, for connecting a sealing body 14 including a positive electrode terminal 22 and the positive electrode collector 28 attached with an electrode group 4, and is positioned at the side of the sealing body 14; leg parts 50 and 52 that are opposite to the top wall part 36, and are positioned at the side of the positive electrode collector 28; and a pair of side wall parts 42 and 44 that are extended between a side edge of the top wall part 36 and the side edges of the leg parts 50 and 52, and which are opposite each other. A first corner part 39 and a second corner part 41 formed by the top wall part 36 and the side wall parts 42 and 44, and a third corner part 47 and a fourth corner part 49 formed by the leg parts 50 and 52, and the side wall parts 42 and 44, are formed as curved round corners.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a current collecting lead and a method for manufacturing a secondary battery including the current collecting lead.

  As for secondary batteries that can be charged, the type of battery that can be charged and discharged at a high rate has been developed. As such a battery, for example, a cylindrical alkaline secondary battery as shown below is known.

  The cylindrical alkaline secondary battery is formed by accommodating an electrode group together with an alkaline electrolyte in a bottomed cylindrical outer can and sealing the opening of the outer can with a sealing body including a positive electrode terminal.

  The electrode group described above is formed by spirally winding a positive electrode and a negative electrode that are overlapped with a separator interposed therebetween, and has a substantially cylindrical shape as a whole. Here, the positive electrode and the negative electrode are arranged so as to be slightly shifted from each other in the direction along the axis of the electrode group during the winding operation, and a separator of a predetermined size is provided between the positive electrode and the negative electrode. Is arranged at a predetermined position. In this state, the positive electrode, the separator, and the negative electrode are wound. As a result, the edge of the positive electrode protrudes spirally from one end surface side of the electrode group, and the edge of the negative electrode protrudes spirally from the other end surface side of the electrode group.

  A positive electrode current collector plate is welded to the protruding positive electrode edge portion, and a negative electrode current collector plate is welded to the protruded negative electrode edge portion. Thereby, the positive electrode current collector plate is electrically connected to the positive electrode in a wide range, and the negative electrode current collector plate is electrically connected to the negative electrode in a wide range, so that the current collection efficiency is improved. As a result, the battery can be charged / discharged at a high rate.

  As a procedure for assembling the cylindrical alkaline secondary battery, for example, an electrode group is first inserted into the outer can, and the inner surface of the bottom wall of the outer can and the negative electrode current collector plate are welded. Thereby, the outer can which also serves as the negative electrode terminal and the negative electrode are electrically connected. Next, one end of a positive electrode ribbon made of a thin metal plate is welded to a predetermined position of the positive electrode current collector plate. Further, the other end of the positive electrode ribbon is welded to a predetermined position of the sealing body. As a result, the positive electrode terminal and the positive electrode are electrically connected. Thereafter, the sealing body is attached in a state where an insulating gasket is interposed in the upper end opening of the outer can, and the upper end opening of the outer can is caulked to seal the outer can. Thereby, a cylindrical alkaline secondary battery is formed.

  For the positive electrode ribbon as described above, a relatively long one is used in order to facilitate welding to the sealing body. Further, when the sealing body is attached to the upper end opening of the outer can, the positive ribbon is accommodated in the outer can so as to bend between the sealing body and the electrode group. For this reason, a comparatively thin thing is used for a positive electrode ribbon so that it may be bent easily.

  Incidentally, in recent years, higher performance is desired for alkaline secondary batteries, and in particular, it is desired to further improve the high-rate discharge characteristics so that a large current can be efficiently output.

  In order to improve the high rate discharge characteristics, it is necessary to make the internal resistance of the battery as low as possible. However, when the above-described thin and long strip-like positive electrode ribbon is used, the specific resistance of the positive electrode ribbon is high, and the positive electrode ribbon causes the internal resistance of the battery to increase.

  Therefore, various studies have been made to shorten the energization path as compared with the prior art in order to lower the internal resistance of the battery and to obtain a battery excellent in high rate discharge characteristics. For example, a battery as disclosed in Patent Document 1 is known as a battery in which measures for shortening the energization path are taken.

  In the battery represented by Patent Document 1, a measure using a current collecting lead that is thicker and shorter than a conventional positive electrode ribbon is taken. Specifically, when the battery of Patent Document 1 is assembled, a current collecting lead having a predetermined shape as shown in FIG. 1 of Patent Document 1 is welded onto the positive electrode current collector plate. Next, the sealing body is disposed at the opening of the outer can through an insulating gasket, and the battery is sealed by caulking the opening edge of the outer can inward to assemble the battery. At the time of sealing, the current collecting lead and the sealing body are in contact with each other. Thereafter, the current collector lead and the sealing body of the positive electrode are resistance spot welded by energizing between the positive electrode terminal and the negative electrode terminal of the battery.

  Since the battery of Patent Document 1 can weld the current collecting lead and the sealing body after sealing the outer can, it is necessary to weld the current collecting lead and the sealing body before sealing the outer can. Disappears. This makes it possible to easily attach the sealing body to the opening of the outer can even if the current collecting lead is short. Thus, if the current collecting lead is shortened, the energization path can be shortened, so that the internal resistance of the battery can be reduced. In addition, since the battery of Patent Document 1 does not need to bend the current collecting lead in the outer can, it is possible to use the current collecting lead that is thicker than the positive ribbon. Thus, if the current collecting lead having a large thickness is used, the energization path can be made thicker, and the internal resistance of the battery can also be reduced.

  Thus, since the battery of patent document 1 becomes low in internal resistance of a battery compared with the conventional battery, it is excellent in the high rate discharge characteristic.

Japanese Patent No. 3547931

  By the way, when attaching the sealing body to the outer can by caulking the upper end opening edge of the outer can, or when resistance collector welding the current collector plate, the current collecting lead, and the sealing body, the battery is along the axial direction. Compressive load is applied. When such a compressive load is applied, the current collector plate is deformed and presses the electrode group. If it does so, in a battery, there exists a possibility that the edge part of the positive electrode of a electrode group or a negative electrode may bend | fold, and an internal short circuit will be caused.

  The present invention has been made on the basis of the above circumstances, and the object of the present invention is to obtain a secondary battery in which the occurrence of an internal short circuit is less than that in the past while maintaining excellent high rate discharge characteristics. An object of the present invention is to provide a current collecting lead that can be produced and a method for manufacturing a secondary battery including the current collecting lead.

  In order to achieve the above object, according to the present invention, in order to connect a sealing body including a terminal and a current collector plate attached to an electrode group, the sealing body and the current collector plate are connected to each other. In a current collecting lead for a secondary battery interposed therebetween, a top wall located on the sealing body side, a bottom wall facing the top wall and located on the current collecting plate side, and the top wall And a pair of side walls facing each other, and a corner portion formed by the top wall and the side walls and the bottom wall A current collecting lead is provided in which a corner formed by the side wall is a rounded corner.

  Further, when the amount of descending the sealing body when assembling the secondary battery is A, the thickness of the material constituting the current collecting lead is B, and the thickness of the current collecting plate is C, the round corner It is preferable that the minimum required value Dmin of the radius of curvature satisfies a relationship represented by the following expression.

  However, the constants α, β, γ, and δ are α = −13.128, β = −4.8986, γ = 20.978, δ = 6.8538, and B and C are B > 0.25 mm, 0.25 mm <C ≦ 0.40 mm.

  In addition, when the thickness of the material constituting the current collecting lead is 0.30 mm and the descending amount of the sealing body when assembling the secondary battery is 0.6 mm, the curvature radius D of the round corner is , 0.7 mm ≦ D ≦ 1.2 mm is preferably satisfied.

  According to the present invention, the current collecting lead preparing step for preparing the current collecting lead described above, the electrode group preparing step for preparing the electrode group in which the positive electrode and the negative electrode are superposed via the separator, and the electrode group, Between the electrode group accommodation step of accommodating in an outer can and the electrode group and a current collector plate placed on the electrode group, the current collector plate and the current collector plate placed on the current collector plate A welding step of welding while pressing between the current collecting lead and between the current collecting lead and a sealing body including a terminal placed on the current collecting lead; and There is provided a method for manufacturing a secondary battery including a current collecting lead, comprising: a step of sealing and mounting and sealing the outer can.

  Since the current collecting lead of the present invention is a round corner with a curved corner, it is easily deformed. For this reason, when a compressive load acts in the manufacturing process of a battery, a current collection lead deforms preferentially. Thereby, since a deformation | transformation of a current collecting plate is suppressed, it is also suppressed that an electrode group is pressed. In addition, since the current collecting lead of the present invention has a structure that can be easily deformed, it is easy to deform the current collecting lead even if the thickness of the metal plate constituting it is relatively thick. . For this reason, since the thickness of a current collection lead can be made comparatively thick, the internal resistance of a battery can be suppressed low. Therefore, according to the present invention, a current collecting lead capable of obtaining a secondary battery in which occurrence of an internal short circuit is less than that of the conventional one while maintaining excellent high rate discharge characteristics, and a secondary battery including the current collecting lead are provided. A manufacturing method can be provided.

1 is a partial cross-sectional view showing a cylindrical nickel-metal hydride secondary battery according to the present invention. It is the top view which showed the positive electrode current collecting plate. It is the perspective view which showed the current collection lead. It is sectional drawing along the IV-IV line in FIG. It is the top view which showed the intermediate product of the current collection lead. It is the graph which showed the relationship between descent | fall amount A and the total load (sigma) to an electrode group. 3 is a graph showing a relationship between a coefficient and a radius of curvature D in the first relational expression. It is the graph which showed the relationship between current collection board thickness C and the buckling generation load of a positive electrode current collection board. 10 is a graph showing a relationship between a coefficient and a lead thickness B in the second relational expression. 6 is a graph showing a relationship between a curvature radius D and a current collector plate thickness C in Calculation Example 1. It is the graph which showed the relationship between the curvature radius D in calculation example 1, and part total height (2D + C). 6 is a graph showing a relationship between a radius of curvature D and a current collector plate thickness C in Calculation Example 2. It is the graph which showed the relationship between the curvature radius D in calculation example 2, and part total height (2D + C). It is an analysis figure which shows the analysis result of the change of the shape of a sealing body, a current collection lead, a current collection board, and an electrode group.

  Hereinafter, an alkaline secondary battery including a current collecting lead according to the present invention will be described with reference to the drawings.

  As a secondary battery according to an embodiment to which the present invention is applied, an AA size cylindrical nickel-hydrogen secondary battery (hereinafter referred to as a battery) 1 shown in FIG. 1 will be described as an example.

  The battery 1 includes an outer can 2 having a bottomed cylindrical shape with an open upper end. The outer can 2 has conductivity, and its bottom wall functions as a negative electrode terminal. In the outer can 2, an electrode group 4 is accommodated together with a predetermined amount of an alkaline electrolyte (not shown).

  As shown in FIG. 1, the opening 3 of the outer can 2 is closed by a sealing body 14. The sealing body 14 includes a disc-shaped lid plate 16 having conductivity, a valve body 20 disposed on the lid plate 16, and a positive electrode terminal 22. A ring-shaped insulating gasket 18 is disposed on the outer periphery of the cover plate 16 so as to surround the cover plate 16, and the insulating gasket 18 and the cover plate 16 are formed by caulking the opening edge 17 of the outer can 2. 2 is fixed to the opening edge 17. That is, the cover plate 16 and the insulating gasket 18 cooperate with each other to seal the opening 3 of the outer can 2. Here, the lid plate 16 has a central through hole 19 in the center, and a rubber valve body 20 is disposed on the outer surface of the lid plate 16 so as to close the central through hole 19. Furthermore, a flanged cylindrical positive terminal 22 is electrically connected to the outer surface of the cover plate 16 so as to cover the valve body 20. The positive electrode terminal 22 presses the valve body 18 toward the lid plate 16. Further, the positive electrode terminal 22 has a gas vent hole 23 on a side surface.

  Normally, the central through hole 19 is airtightly closed by the valve body 20. On the other hand, when gas is generated inside the outer can 2 and the pressure of the gas increases, the valve body 20 is compressed by the pressure of the gas, and the central through hole 19 is opened. As a result, gas is released from the outer can 2 to the outside through the central through hole 19 and the gas vent hole 23 of the positive terminal 22. That is, the central through hole 19, the valve body 20, and the gas vent hole 23 of the positive electrode terminal 22 form a safety valve for the battery 1.

  The electrode group 4 includes a strip-like positive electrode 6, a negative electrode 8, and a separator 10, which are wound in a spiral shape with the separator 10 sandwiched between the positive electrode 6 and the negative electrode 8. That is, the positive electrode 6 and the negative electrode 8 are overlapped with each other via the separator 10. Such an electrode group 4 has a cylindrical shape as a whole.

  In this electrode group 4, the edge of the positive electrode 6 is exposed in a spiral shape from one end surface, and the edge of the negative electrode 8 is exposed in a spiral shape from the other end surface. Here, the exposed edge of the positive electrode 6 is defined as a positive electrode connection edge 32, and the exposed edge of the negative electrode 8 is defined as a negative electrode connection edge (not shown). A positive electrode current collector plate 28 and a negative electrode current collector plate (not shown), which will be described later, are welded to the exposed positive electrode connection edge portion 32 and negative electrode connection edge portion, respectively.

  The negative electrode 8 has a conductive negative electrode core having a strip shape, and a negative electrode mixture is held in the negative electrode core.

  The negative electrode core is made of a band-shaped metal material in which a large number of through holes (not shown) penetrating in the thickness direction are distributed. For example, a punching metal sheet can be used as such a negative electrode core.

  The negative electrode mixture is not only filled in the through hole of the negative electrode core, but also held in layers on both surfaces of the negative electrode core.

  The negative electrode mixture includes particles of a hydrogen storage alloy, a conductive material, a binder, and the like. Here, the hydrogen storage alloy is an alloy capable of storing and releasing hydrogen, which is a negative electrode active material, and a hydrogen storage alloy generally used in nickel-hydrogen secondary batteries is preferably used. The above-described binder serves to bind the particles of the hydrogen storage alloy and the conductive material to each other and at the same time bind the negative electrode mixture to the negative electrode core. Here, as the conductive material and the binder, those generally used in nickel-hydrogen secondary batteries are preferably used.

  The negative electrode 8 can be manufactured as follows, for example.

  First, a hydrogen storage alloy powder composed of hydrogen storage alloy particles, a conductive material, a binder, and water are kneaded to prepare a paste of a negative electrode mixture. The obtained paste of the negative electrode mixture is applied to the negative electrode core and dried. After drying, the negative electrode core body to which the negative electrode mixture containing hydrogen storage alloy particles and the like is attached is subjected to roll rolling and cutting to obtain an intermediate product of the negative electrode. The intermediate product of this negative electrode has a rectangular shape as a whole. And about the predetermined | prescribed edge part which should become a negative electrode connection edge part in this intermediate product of a negative electrode, removal of a negative mix is performed. As a result, the predetermined edge portion becomes the negative electrode connection edge portion in which the negative electrode core is exposed. In this way, the negative electrode 8 having the negative electrode connection edge is obtained. Here, the method for removing the negative electrode mixture is not particularly limited, but for example, the removal is preferably performed by applying ultrasonic vibration. Note that the negative electrode mixture is still held in the region other than the negative electrode connection edge.

  Next, the positive electrode 6 will be described.

  The positive electrode 6 includes a conductive positive electrode base material having a porous structure and having a large number of pores, and a positive electrode mixture held in the pores and on the surface of the positive electrode base material.

  As the positive electrode base material, for example, foamed nickel can be used.

  The positive electrode mixture includes nickel hydroxide particles as positive electrode active material particles, a cobalt compound as a conductive material, a binder, and the like. The above-described binder serves to bind the nickel hydroxide particles and the conductive material to each other and simultaneously bind the positive electrode mixture to the positive electrode base material. Here, what is generally used for the nickel-hydrogen secondary battery is suitably used as the binder.

  The positive electrode 6 can be manufactured as follows, for example.

  First, a positive electrode mixture slurry containing a positive electrode active material powder composed of positive electrode active material particles, a conductive material, water, and a binder is prepared. The obtained positive electrode mixture slurry is filled in, for example, foamed nickel and dried. After drying, the foamed nickel filled with nickel hydroxide particles and the like is roll-rolled and then cut into a predetermined shape to obtain an intermediate product of the positive electrode. The intermediate product of this positive electrode has a rectangular shape as a whole. And about the predetermined | prescribed edge part which should become the positive electrode connection edge part 32 in this intermediate product of a positive electrode, the positive mix is removed and the positive electrode base material is exposed. Next, the edge part from which the positive electrode mixture has been removed is compressed in the thickness direction of the intermediate product of the positive electrode to become the positive electrode connection edge part 32. Since the positive electrode base material is in a dense state by being compressed in this manner, the positive electrode connection end edge portion 32 is easily welded. In this way, the positive electrode 6 having the positive electrode connection edge portion 32 is obtained. Here, the method for removing the positive electrode mixture is not particularly limited, but for example, it is suitably performed by applying ultrasonic vibration. It should be noted that the region other than the positive electrode connection edge portion 32 is still filled with the positive electrode mixture.

  Next, as the separator 10, for example, a polyamide fiber nonwoven fabric provided with a hydrophilic functional group, or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene provided with a hydrophilic functional group can be used.

  The positive electrode 6 and the negative electrode 8 produced as described above are spirally wound with the separator 10 interposed therebetween, whereby the electrode group 4 is formed. Specifically, during winding, the positive electrode 6 and the negative electrode 8 are arranged so as to be slightly shifted from each other in the direction along the axial direction of the electrode group 4, and between the positive electrode 6 and the negative electrode 8. The separator 10 having a predetermined size is disposed at a predetermined position, and the winding operation is performed in this state. As a result, a cylindrical electrode group 4 is obtained. As an aspect of the obtained electrode group 4, in one end side of the electrode group 4, the positive electrode connection edge 32 of the positive electrode 6 protrudes from the adjacent negative electrode 8 through the separator 10. On the other end side of the electrode group 4, the negative electrode connection edge portion of the negative electrode 8 is in a state of protruding from the adjacent positive electrode 6 with the separator 10 interposed therebetween.

  The electrode group 4 is formed by winding the positive electrode 6, the negative electrode 8, and the separator 10 with a core having a predetermined outer diameter, and the core is extracted after the winding operation. A through hole 9 is formed in the center of the electrode group 4.

  In the electrode group 4 as described above, the positive electrode current collector plate 28 is connected to one end side, and the negative electrode current collector plate is connected to the other end side.

  First, the negative electrode current collector plate is not particularly limited, and for example, a conventionally used disk-shaped metal plate is preferably used. The prepared negative electrode current collector plate is welded to the negative electrode connection edge on the other end side of the electrode group 4.

  Next, the positive electrode current collector plate 28 will be described.

  The positive electrode current collector plate 28 is a plate-like body made of a conductive material, and the shape in plan view is not particularly limited, and any shape such as a disc shape or a polygonal shape can be adopted. Further, the size of the positive electrode current collector plate 28 is smaller than the outer diameter size of the electrode group 4 and is large enough to cover the positive electrode connection edge 32 of the positive electrode 6 protruding from one end side of the electrode group 4. Is set.

  In the present embodiment, as shown in FIG. 2, a plate material having a decagonal shape in plan view is used. Specifically, the positive electrode current collector plate 28 is a thin plate made of Ni-plated steel having a decagonal shape as a whole, and has a circular central through hole 29 at the center and six radially extending so as to surround the central through hole 29. The slit 30 is included. The slit 30 is preferably formed by punching, and a protrusion (burr) extending downward (on the electrode group 4 side) is generated at an edge portion of the slit 30.

  In the battery 1, as shown in FIG. 1, a current collecting lead 34 is interposed between the positive electrode current collecting plate 28 and the sealing body 14, and this current collecting lead 34 is connected to the positive electrode 6 of the electrode group 4. The positive electrode current collector plate 28 and the sealing member 14 having the positive electrode terminal 22 are electrically connected.

  For example, as shown in FIG. 3, the current collecting lead 34 extends from a rectangular top wall (top wall) 36 connected to the sealing body 14, and predetermined side edges 38 and 40 of the top wall 36. A pair of side wall portions (side walls) 42 and 44 that face each other, and leg portions (bottom walls) that extend from end edges 46 and 48 opposite to the top wall portion 36 in the side wall portions 42 and 44, and face the top wall portion 36. ) 50 and 52. The leg portions (bottom walls) 50 and 52 are connected to the positive electrode current collector plate 28.

  The top wall portion 36 is provided with a circular through hole 54 at the center. The through hole 54 communicates with the central through hole 19 of the cover plate 16 when the current collecting lead 34 is connected to the sealing body 14. In addition, four protrusions 56 serving as welding points are provided around the through hole 54.

  As is apparent from FIG. 4 showing the cross section of the current collecting lead 34, the current collecting lead 34 has a first corner portion 39 formed by the side wall portion 42 and the top wall portion 36, and the top wall portion 36 and the side wall portion 44. And a second corner portion 41 formed by the side wall portion 44 and the leg portion 52, and a fourth corner portion 49 formed by the leg portion 50 and the side wall portion 42. Yes. These first to fourth corner portions 39, 41, 47, and 49 are round corners having a curved shape.

  Thus, when the first to fourth corner portions 39, 41, 47, 49 are round corners, the current collecting lead 34 is compressed when a load is applied in the directions of arrows A and B in FIG. It is easy to deform.

  As shown in FIG. 3, the leg portions 50 and 52 have extension portions 50 a, 50 b, 52 a and 52 b extending in the direction along the longitudinal direction of the side wall portions 42 and 44. These extending portions 50 a, 50 b, 52 a, 52 b extend outside a region facing the top wall portion 36 in the leg portions (bottom walls) 50, 52. For this reason, the extending portions 50 a, 50 b, 52 a, 52 b serve to increase the stability of the current collecting lead 34 when the current collecting lead 34 is connected to the positive current collecting plate 28. These extending portions 50a, 50b, 52a, 52b are provided with protruding portions 58 protruding toward the positive electrode current collector plate 28 side (see FIG. 4). This protrusion 58 also becomes a welding point.

  Here, the protruding portion 56 and the protruding portion 58 are formed by, for example, pressing. Note that reference numeral 60 in FIG. 3 indicates a recess formed on the back side of the protrusion 58 when the protrusions 58 are provided on the legs 50 and 52.

  The current collecting lead 34 can be manufactured as follows, for example.

  First, by processing a metal thin plate, a current collector lead intermediate product 62 made of a thin plate having a substantially H-shaped plan view as shown in FIG. 5 is prepared. In addition, this thin plate is sufficiently thick compared with the conventional positive electrode ribbon. In the intermediate product 62, the long portions positioned on both sides are leg portion planned regions 70 and 72 that become the leg portions 50 and 52. The regions that continue to the inside of the planned leg portions 70 and 72 are the side wall portions 74 and 76 that become the side walls 42 and 44. A region sandwiched between the side wall portion planned region 74 and the side wall portion planned region 76 is a top wall portion planned region 78 that becomes the top wall portion 36.

  Further, the intermediate product 62 is provided with a through hole 54 in the center of the planned top wall portion 78 by punching.

  Next, protrusions 56 and 58 are provided by pressing at a predetermined position around the through hole 54 and at predetermined positions on both ends of the planned leg portions 70 and 72.

  Thereafter, the portions of the virtual lines 80, 82, 84, 86 are bent to form the current collecting leads 34 as shown in FIG.

  In this embodiment, a gap is provided between the leg portion 50 and the leg portion 52, and the bottom wall portion is divided into two. However, the present invention is not limited to this aspect, and The part 50 and the leg part 52 may be connected to each other, and the leg part 50 and the leg part 52 may be integrated into one bottom wall part.

  Next, an example of the procedure for assembling the battery 1 will be described.

  The electrode group 4 as described above is prepared. And after connecting a negative electrode current collecting plate to the other end side of the electrode group 4, the said electrode group 4 is accommodated in an exterior can. Then, the negative electrode current collector plate is resistance spot welded to the bottom wall of the outer can.

  Next, the positive electrode current collector plate 28 is placed on one end side of the electrode group 4, and the current collector leads 34 are placed on the positive electrode current collector plate 28. At this time, the current collecting lead 34 is aligned with respect to the slit 30 of the positive electrode current collecting plate 28 so as to be disposed at a predetermined position. Then, the electrode group 4, the positive electrode current collector plate 28, and the current collector lead 34 are resistance spot welded. Thereby, the positive electrode connection edge 32 of the positive electrode 6 and the positive electrode current collector plate 28 are welded, and the positive electrode current collector plate 28 and the leg portions 50 and 52 of the current collector lead 34 are welded.

  Next, a predetermined amount of alkaline electrolyte is injected into the outer can 2. The alkaline electrolyte injected into the outer can 2 is held in the electrode group 4, and most of the alkaline electrolyte is held in the separator 10. This alkaline electrolyte advances an electrochemical reaction (charge / discharge reaction) during charge / discharge between the positive electrode 6 and the negative electrode 8. As the alkaline electrolyte, an alkaline electrolyte containing at least one of KOH, NaOH, and LiOH as a solute is preferably used.

  Then, the sealing body 14 is arrange | positioned through the insulating gasket 18 in the upper-end opening part of the armored can 2. At this time, the current collecting lead 34 and the sealing body 14 are in contact with each other.

  Thereafter, a current is passed between the positive electrode terminal 22 and the negative electrode terminal of the battery 1 while performing resistance indirect spot welding. Thereby, the top wall part 36 of the current collection lead 34 and the cover plate 16 of the sealing body 14 are welded.

  Then, the opening 3 of the outer can 2 is sealed by caulking the opening edge 17 of the outer can 2.

  Here, in the top wall portion 36 of the current collecting lead 34, the protruding portion 56 is disposed so as to contact the lid plate 16 of the sealing body 14. When resistance indirect spot welding is performed, the welding current concentrates on the portion of the protruding portion 56, and a portion of the protruding portion 56 is melted to connect the top wall portion 36 of the current collecting lead 34 and the cover plate 16. Is done.

  As described above, the positive electrode 6 and the positive electrode terminal 22 are electrically connected via the positive electrode current collector plate 28, the current collector lead 34, and the lid plate 16 to form the battery 1.

  At the time of resistance spot welding and caulking as described above, a compressive load acts on the battery 1 in a direction along its axis. Along with this, the compressive load also acts on components constituting the battery 1 such as the electrode group 4, the positive electrode current collector plate 28, and the current collector leads 34. Here, in the current collecting lead 34, the first to fourth corner portions 39, 41, 47, and 49 are round corners as described above, so that the top wall portion 36 and the leg portions 50 and 52 approach each other. That is, when a compressive load acts in the directions indicated by arrows A and B in FIG. 4 (hereinafter referred to as the compression direction), the side wall portions 42 and 44 are likely to be deformed. That is, the current collecting lead 34 has a shape that easily deforms. When the current collecting lead 34 is easily deformed in this way, the current collecting lead 34 is preferentially deformed, the deformation of the positive current collecting plate 28 is suppressed, and the positive current collecting plate 28 is prevented from pressing the electrode group 4. can do. As a result, occurrence of an internal short circuit can be suppressed.

  In the present invention, in order to facilitate the deformation of the current collecting lead 34, the first to fourth corner portions 39, 41, 47, and 49 are round corners as described above. Here, it is considered that the degree of ease of deformation of the current collecting lead 34 generally depends on the radius of curvature of the round corner. That is, the smaller the radius of curvature of the round corner, the larger the area of the flat surface of the side walls 42, 44. Therefore, the side walls 42, 44 are less likely to bend even when a load is applied in the compression direction. The larger the radius of curvature, the smaller the area of the flat surface of the side walls 42, 44. Therefore, when a load is applied in the compression direction, the side walls 42, 44 are easily bent.

  The inventor of the present application has made the following studies in order to obtain a preferable radius of curvature of a round corner.

  First, before and after a series of operations of resistance spot welding and caulking, the amount by which the sealing body is pushed into the outer can 2, that is, the lowering amount of the sealing body is “falling amount A”, and the metal constituting the current collecting lead 34 The thickness of the thin metal plate is “lead thickness B”, the thickness of the metal thin plate constituting the positive electrode current collector plate 28 is “current collector plate thickness C”, and the curvature of the round corner of the current collector lead 34 is The radius is “curvature radius D”.

The amount of drop A [mm] and the total load σ [kgf / cm ² ] when the radius of curvature of the round corner of the current collecting lead is changed every 0.1 mm from 0.4 mm to 0.9 mm. Sought a relationship. The result is shown in FIG. FIG. 6 shows that the amount of drop A and the total load σ on the electrode group are in a proportional relationship.

FIG. 7 approximates the obtained load curve by a quadratic expression when plotting the relationship between the drop amount A [mm] at the curvature radius D [mm] and the total load σ [kgf / cm ² ] to the electrode group. The relationship between slope and intercept is shown. Here, the relational expression of A, D, and σ is shown below as the first relational expression (I).

  Here, in the first relational expression (I), a portion of −2.456D + 3.9243 represents an approximate expression of inclination, and a portion of −1.673D + 2.3413 represents an approximate expression of intercept. In FIG. 7, the vertical axis represents the coefficient in the first relational expression, and the horizontal axis represents the curvature radius D.

  From FIG. 7, it can be seen that when the radius of curvature D increases, an increase in load is suppressed.

The relationship between the current collector plate thickness C [mm] and the buckling generation load [kgf / cm ² ] of the positive electrode collector plate is as shown in FIG. FIG. 8 shows that the limit of the buckling occurrence load is raised when the current collector plate thickness C is increased.

FIG. 9 shows a load curve obtained by plotting the relationship between the descent amount A [mm] and the total load σ [kgf / cm ² ] on the electrode group at the lead thickness B [mm]. The relationship between the slope and intercept approximated by the formula of thickness 2.5 is shown. Here, a correction term (relational expression) obtained by adding B to the relational expressions of A, D, and σ is shown below as a second relational expression (II).

Here, the second relation formula (II), (- 49.82D + 79.61) parts of the ^{B 2.5} represents the slope of the approximate expression, (- 18.59D + ^26.01) parts of the ^{B 2.5} Represents an approximate expression of the intercept. In FIG. 9, the vertical axis represents the coefficient in the second relational expression, and the horizontal axis represents the lead thickness B.

  From FIG. 9, it can be seen that the load load increases as the lead thickness B increases.

  When the relationship between each parameter of the above-mentioned descent amount A, lead thickness B, current collector plate thickness C, and radius of curvature D is formulated, it can be expressed as the following formula (III).

  By using this formula (III), for example, the minimum required radius of curvature D can be obtained.

  In addition, when the lead thickness B is set from the limit thickness at which a good reduction effect of the internal resistance of the battery is obtained, and the limit drop A is set from the manufacturing tolerance, by using the formula (III), A combination of the curvature radius D and the current collector plate thickness C that can suppress deformation (buckling) of the positive electrode current collector plate can be obtained.

  By the way, in recent years, various devices have been miniaturized, and even a small device is required to be discharged at a high rate. Under these circumstances, small batteries such as AA type (corresponding to R6 type, AA type) and AAA type (corresponding to R03 type, AA type) used for small devices are also at a higher rate. Discharge is required.

  However, in these small batteries, the current collector leads must be downsized compared to large batteries of D type (equivalent to R20 type, single type 1) or C type (equivalent to R14 type, single type 2). I must. As the current collector lead becomes smaller, the flexibility of the current collector lead decreases. Therefore, if a compressive load is applied in the axial direction of the battery, the current collector lead will not be deformed sufficiently, and the load will be applied directly to the current collector plate. Works. If it does so, a positive electrode current collecting plate will deform | transform and it will press on an electrode group and it will become easy to generate | occur | produce a short circuit. Further, in a small battery, since the number of turns of the electrode group is small, the strength of the electrode group itself in the axial direction is also low. For this reason, in a small battery using a current collector lead that is simply reduced in size to obtain excellent high rate discharge characteristics, a short circuit due to deformation of the positive electrode current collector plate is more likely to occur than in a large battery. ing.

  For such a situation, the present invention preferentially deforms the current collector lead by making the corner portion of the current collector lead a round corner, thereby suppressing the deformation of the positive electrode current collector plate, and thereby to the electrode group. Since compression can be avoided, it is particularly effective in suppressing the occurrence of short circuits in small batteries with excellent high rate discharge characteristics, specifically, batteries having a diameter of 18 mm or less.

  A current collecting component formed by the combination of the positive electrode current collecting plate 28 and the current collecting lead 34 is disposed in a slight space between the sealing body 14 and the electrode group 4. In particular, the space between the sealing body 14 and the electrode group 4 in the small battery as described above is smaller than that in the large battery. For this reason, in a small battery, it is preferable to make the total height of the current collecting parts as small as possible. Here, in particular, when the total height of the current collecting component is (2D + C), the following formula (IV) is given as a calculation formula that takes into account the combination of reducing the value of (2D + C). From this equation (IV), Dmin which is the minimum necessary value of the curvature radius D can be obtained.

  Here, the procedure for obtaining the formula (IV) will be described below. First, the formula (III) is modified as follows to obtain the basic formula (V).

  In this basic formula (V), it is replaced with −13.128 = α, −4.8986 = β, 20.978 = γ, and 6.8538 = δ. Then, the basic formula (V) becomes the following (VI) formula.

Further, assuming that αA + β = n _A1 and γA + δ = n _A2 , the formula (VI) becomes the following formula (VII).

Note that n _A1 and n _A2 are linearly proportional to A.

  Here, in the current collecting lead 34, the curvature radius D of the corner portion (first corner portion 39, second corner portion 41) located on the top wall portion 36 side and the corner located on the leg portions 50, 52 side. Assuming that the radius of curvature D of the portion (the third corner portion 47 and the fourth corner portion 49) is maximized, the total height of the current collecting component formed by the combination of the positive electrode current collecting plate 28 and the current collecting lead 34 is 2D + C. It becomes. Then, when the formula (VII) is substituted into this 2D + C formula, the following formula (VIII) is obtained.

Next, formula (IX) is obtained by rearranging formula (VIII) as follows.

  Then, when Dmin, which is a necessary minimum value of the radius of curvature D, is obtained from formula (IX) or a quadratic equation, the following formula (IV) is obtained.

  Here, C can be eliminated by solving for Dmin. However, since equation (IV) is a relational expression that is established when C is set, it is a precondition that C is set. In the present embodiment, C is preferably 0.25 mm <C ≦ 0.40 mm.

  It should be noted that B> 0.25 mm is set due to the limit of the thickness at which a good effect of reducing the internal resistance of the battery can be obtained.

Here, a calculation example using specific numerical values is shown below.
(1) Calculation example 1

  When the lead thickness B is 0.35 mm and the drop amount A can withstand up to 0.80 mm, the current collector plate thickness is calculated from the drop amount A, the lead thickness B, and the curvature radius D using the formula (III). C was calculated. The resulting graph is shown in FIG. FIG. 10 shows that the load decreases as the curvature radius D increases, and the current collector plate thickness C can be reduced. For example, when the current collector plate thickness C is 0.4 mm, the curvature radius D needs to be 0.95 mm. If the limit descent amount A itself decreases, the curvature radius D can be reduced by that amount, or the current collector plate thickness C can be reduced. For example, when A = 0.6 mm, B = 0.35 mm, and C = 0.4 mm, D = 0.84 mm. Further, when A = 0.6 mm, B = 0.35 mm, and D = 0.95 mm, C = 0.28 mm.

As in the example of the graph of FIG. 10, there are innumerable combinations of the current collector plate thickness C and the curvature radius D with respect to the limit drop amount A and the lead thickness B. However, if the total height of the component is (2D + C) and calculation is performed using the formula (IV) from the viewpoint of a combination that minimizes the value of (2D + C), the result shown in the graph of FIG. 11 is obtained. From this graph, the radius of curvature Dmin when the value of (2D + C) is the smallest is Dmin = 0.73 mm. In this case, the current collector plate thickness C is 0.8 mm.
(2) Calculation example 2

  When the lead thickness B is 0.30 mm and the drop amount A can withstand up to 0.70 mm, the current collector plate thickness is calculated from the drop amount A, lead thickness B, and curvature radius D using the formula (III). C was calculated. The resulting graph is shown in FIG. FIG. 12 shows that the load decreases as the radius of curvature D increases, and the current collector plate thickness C can be reduced. For example, when the current collector plate thickness C is 0.3 mm, the curvature radius D is 0.74 mm. Since the limit drop amount A and the lead thickness B are smaller than those in the calculation example 1, the radius of curvature D can be made smaller or the current collector plate thickness C can be made thinner than in the case of the calculation example 1. .

  When Dmin is calculated using equation (IV) as in calculation example 1, the result shown in the graph of FIG. 13 is obtained. In this case, Dmin = −0.54 mm, which is a negative value. In other words, the result shows the behavior under the condition that does not have the optimum value. As shown in the graph of FIG. 12, it is necessary to increase the current collector plate thickness C as the curvature radius D is smaller. Nevertheless, the combination of the curvature radius D as small as possible and the current collector plate thickness C as thick as possible. It was calculated that the total height of the component (2D + C) is smaller as a whole.

  In the present invention, the radius of curvature of the current collecting lead is defined by an arc portion outside the corner portion when the current collecting lead is viewed in cross section.

  Further, in the assembly procedure of the battery 1 described above, the positive electrode current collector plate 28 was welded after the electrode group 4 was accommodated in the outer can 2. However, the present invention is not limited to this mode. The electric plate 28 may be welded.

[Example]

Example 1
A positive electrode 6, a negative electrode 8, and a separator 10 used for a general nickel metal hydride secondary battery were prepared. Each of the positive electrode 6, the negative electrode 8, and the separator 10 has a strip shape. With the separator 10 interposed between the prepared positive electrode 6 and negative electrode 8, it was wound in a spiral shape to form an AA size electrode group 4. At the time of winding, the positive electrode 6 and the negative electrode 8 are arranged so as to be slightly shifted from each other in the direction along the axial direction of the electrode group 4, and a separator is provided at a predetermined position between the positive electrode 6 and the negative electrode 8. 10 was placed and the winding operation was performed in this state to obtain a cylindrical electrode group 4. The obtained electrode group 4 is in a state in which the positive electrode connection edge 32 of the positive electrode 6 protrudes from the adjacent negative electrode 8 through the separator 10 on one end side of the electrode group 4. On the other end side, the negative electrode connecting edge of the negative electrode 8 is in a state of protruding from the adjacent positive electrode 6 with the separator 10 interposed therebetween.

  Next, a negative electrode current collector plate for AA size having a disc shape and comprising a thin plate of Ni-plated steel was prepared. The negative electrode current collector plate was welded to the negative electrode connection edge of the electrode group 4.

  Next, as shown in FIG. 2, the whole has a decagonal shape, and includes a circular central through hole 29 in the center and six slits 30 extending radially so as to surround the central through hole 29. A positive electrode current collector plate 28 for AA size was prepared. The positive electrode current collector plate 28 is made of a Ni-plated steel plate obtained by applying Ni plating to a thin steel plate having a carbon content of 0.04% by mass. The thickness of the positive electrode current collector plate 28 is 0.40 mm. This thickness value is shown in Table 1 as the thickness of the current collector plate.

  Next, a Ni-plated steel sheet was prepared by applying Ni plating to a steel sheet having a carbon content of 0.04 mass%. The thickness of this Ni-plated steel sheet is 0.30 mm. Then, by punching the Ni-plated steel sheet, an approximately H-shaped current collecting lead intermediate product 62 as shown in FIG. 5 was manufactured. A through-hole 54 was formed in the center of the intermediate product 62, and projections 56 and 58 were formed at predetermined positions by pressing. And the current collection lead 34 as shown in FIG. 3 was formed by bending the part of the virtual lines 80, 82, 84, 86. Here, the imaginary lines 80, 82, 84, and 86 were bent so that the radius of curvature was 0.90 mm. Accordingly, the first to fourth corner portions 39, 41, 47, and 49 of the current collecting lead 34 become round corners having a curvature radius of 0.90 mm. The value of the thickness of the Ni-plated steel sheet used to manufacture the current collecting lead 34 is shown in Table 1 as the thickness of the current collecting lead 34.

  Next, the electrode group 4 to which the negative electrode current collector plate was welded was housed in a bottomed cylindrical outer can 2. And the inner surface of the bottom wall of the armored can 4 and the negative electrode current collector plate were welded.

  Next, a pressure sensor was disposed at the upper end of the electrode group 4 so that the compressive load applied to the electrode group 4 could be measured. The signal line of this pressure sensor is led out to the outside through a hole previously drilled at a predetermined position of the outer can 2 and connected to a compression load measuring device. Then, the positive electrode current collector plate 28 is placed on the pressure sensor, and the current collector lead 34 is further placed on the positive electrode current collector plate 28 to measure the compressive load acting on the electrode group 4. The intermediate product of the battery was manufactured. Then, the intermediate product of the battery for load measurement is set in a resistance spot welder, a load of 25 kgf, which is the same compression load as that during welding, is applied in the axial direction of the intermediate product of the battery without flowing a welding current, 1 simulated resistance spot welding was performed. Subsequently, the sealing body 14 was arrange | positioned through the insulating gasket 18 in the upper end opening part of the armored can 4 of the intermediate product of a battery. At this time, the sealing body 14 and the current collecting lead 34 are in contact with each other. Then, the battery intermediate product for load measurement in this state is set again in the resistance spot welder, and a load of 25 kgf, which is the same compressive load as that during welding, is applied in the axial direction of the battery intermediate product without flowing a welding current. In addition, second simulated resistance spot welding was performed. Thereafter, the opening edge 17 of the outer can 2 was caulked to seal the opening 3 of the outer can 2 to manufacture a battery for load measurement. In addition, the sealing body 14 arrange | positioned at the upper end opening part of the armored can 4 was dropped 0.60 mm to the electrode group 4 side by this 2nd simulation resistance spot welding and caulking.

  The compressive load applied to the electrode group 4 was measured through the pressurizing operation and the caulking process with a resistance spot welder using the above-described intermediate product of the battery for load measurement. The maximum value among the measured values is shown in Table 1 as the maximum load on the electrode group.

Example 2
Except that the current collecting lead 34 is formed so that the first to fourth corner portions 39, 41, 47, 49 of the current collecting lead 34 have a round corner with a radius of curvature of 0.70 mm, the same as in the first embodiment. A battery for load measurement was manufactured.

Example 3
Except that the current collecting lead 34 is formed so that the first to fourth corner portions 39, 41, 47, 49 of the current collecting lead 34 are round corners having a curvature radius of 0.40 mm, the same as in the first embodiment. A battery for load measurement was manufactured.

Comparative Example 1
The first to fourth corner portions 39, 41, 47, and 49 of the current collecting lead 34 are not round corners, but the current collecting lead 34 is formed so as to be a right angle. A battery for measurement was manufactured.

  Moreover, about the sealing body 14 of Examples 1-3, the current collection lead 34, the positive electrode current collection board 28, and the electrode group 4, the state before performing resistance spot welding and crimping (henceforth a state before a deformation | transformation), and The shape of the state after the sealing body was lowered by 0.6 mm, that is, the state after resistance spot welding and caulking (hereinafter referred to as the state after deformation) was analyzed. The analysis results are shown in FIG. 14A shows the results of Example 1 with a radius of curvature of 0.90 mm, FIG. 14B shows the results of Example 2 with a radius of curvature of 0.70 mm, and FIG. 14C shows the curvature. The results of Example 3 with a radius of 0.40 mm are shown. And the upper stage has shown the state before a deformation | transformation, and the lower stage has shown the state after a deformation | transformation, respectively.

[Discussion]
(1) Compared with the thickness of the conventional positive electrode ribbon, the thicknesses of the current collecting leads of Examples 1 to 3 and Comparative Example 1 are sufficiently thick. For this reason, it is thought that the batteries of Examples 1 to 3 and Comparative Example 1 using current collecting leads have lower internal resistance values and are basically excellent in high rate discharge characteristics as compared with conventional batteries.

(2) In Comparative Example 1, the maximum load on the electrode group is 90.0 kgf, which is a higher value than Examples 1-3. Since the current collecting lead of Comparative Example 1 has a right-angle corner, it is difficult to deform during resistance spot welding and caulking, and the compressive load in the axial direction of the battery is transmitted almost directly to the electrode group. It is done.

  On the other hand, in Examples 1 to 3, the maximum load on the electrode group is lower than that in Comparative Example 1. Since the current collecting leads of Examples 1 to 3 have round corners, they are preferentially deformed during resistance spot welding and caulking. For this reason, it is considered that the compressive load in the axial direction of the battery is relaxed at the current collecting lead portion, and the maximum load on the electrode group is relatively low.

  From the above, making the corner portion of the current collector lead a round corner means that when a compressive load is applied, the current collector lead is preferentially deformed, and the load applied to the electrode group can be made relatively small. It is thought to contribute to the suppression of the occurrence.

(3) Here, when the maximum load on the electrode group exceeds 50.0 kgf, the positive electrode current collector plate is greatly deformed, and the degree of pressure on the electrode group is increased. As a result, it is considered that the occurrence of an internal short circuit due to the bending of the positive electrode or the negative electrode increases. If the maximum load on the electrode group is 50.0 kgf or less, the degree of pressure on the electrode group due to the deformation of the positive electrode current collector plate is within a sufficiently acceptable range, and the occurrence of internal short circuit due to bending of the positive electrode or the negative electrode is suppressed. it is conceivable that.

  Therefore, in order to reduce the maximum load on the electrode group to 50.0 kgf or less in order to suppress the occurrence of an internal short circuit, it is preferable that the radius of curvature of the current collecting lead is 0.70 mm or more from the results in Table 1. I can say that.

  As described above, the radius of curvature of the current collecting lead is preferably larger. However, if the radius of curvature of the current collecting lead becomes too large, it becomes difficult to form a current collecting lead having a predetermined shape. Further, if the radius of curvature of the current collecting lead is too large, the current collecting lead is likely to be deformed too much, which may cause a problem that a load necessary for resistance spot welding cannot be obtained. Therefore, it is preferable to apply a load of 25 kgf or more, which is a load necessary for resistance spot welding, to the electrode group. In order to make the maximum load on the electrode group 25 kgf or more, it is preferable that the radius of curvature of the current collecting lead is 1.2 mm or less.

(4) Further, from FIG. 14 showing the analysis results of the shape of the current collecting lead 34, the positive current collecting plate 28 and the electrode group 4 before and after resistance spot welding and caulking, the radius of curvature of the current collecting lead 34 is 0. In Example 3 of 40 mm, the amount of deformation of the current collecting lead 34 itself is not so large, but deformation is observed in the current collecting plate 28 and the electrode group 4 (positive electrode connecting edge portion 32).

  On the other hand, in Example 2 where the radius of curvature is 0.70 mm and Example 1 where the radius of curvature is 0.90 mm, the deformation of the current collecting lead 34 itself is larger than that of Example 3. However, almost no deformation of the current collector plate 28 and the electrode group 4 (positive electrode connection edge 32) is observed.

  Also from this, it is considered that the larger the radius of curvature of the current collecting lead 34 is, the more the deformation of the electrode group 4 is suppressed, and the radius of curvature is more preferably 0.70 mm or more.

(5) As described above, it can be said that by making the corner portion of the current collecting lead a round corner, it is possible to obtain an effect of suppressing the occurrence of an internal short circuit while maintaining excellent high rate discharge characteristics. And it can be said that the effect is further enhanced by limiting the radius of curvature of the round corner to some extent.

  The present invention is not limited to the above-described embodiment and examples, and various modifications are possible. For example, the type of battery is not limited to a nickel-metal hydride secondary battery, but nickel-cadmium. A secondary battery, a lithium ion secondary battery, etc. may be sufficient. In the present invention, the shape of the battery is not particularly limited, and may be a cylindrical secondary battery or a square secondary battery.

DESCRIPTION OF SYMBOLS 1 Nickel metal hydride secondary battery 2 Exterior can 4 Electrode group 6 Positive electrode 8 Negative electrode 10 Separator 14 Sealing body 18 Insulating gasket 22 Positive electrode terminal 28 Positive electrode current collecting plate 32 Positive electrode connection edge 34 Current collecting lead 39 First corner part 41 Second Corner part 47 Third corner part 49 Fourth corner part

Claims (4)

In a current collecting lead for a secondary battery interposed between the sealing body and the current collector plate in order to connect the sealing body including a terminal and the current collector plate attached to the electrode group ,
A top wall located on the side of the sealing body; a bottom wall facing the top wall and located on the current collector side; and extending between a side edge of the top wall and a side edge of the bottom wall. And has a pair of side walls facing each other,
The corner formed by the top wall and the side wall and the corner formed by the bottom wall and the side wall are rounded corners.
Current collector lead. Curvature of the round corner when the amount of descending of the sealing body when assembling the secondary battery is A, the thickness of the material constituting the current collecting lead is B, and the thickness of the current collecting plate is C The current collecting lead according to claim 1, wherein a necessary minimum value Dmin of the radius satisfies a relationship represented by the following expression.

However, the constants α, β, γ, and δ are α = −13.128, β = −4.8986, γ = 20.978, δ = 6.8538, and B and C are B > 0.25 mm, 0.25 mm <C ≦ 0.40 mm.   When the thickness of the material constituting the current collecting lead is 0.30 mm and the descending amount of the sealing body when assembling the secondary battery is 0.6 mm, the curvature radius D of the round corner is 0. The current collecting lead according to claim 1, wherein a relationship of 0.7 mm ≦ D ≦ 1.2 mm is satisfied. A current collecting lead preparing step for preparing the current collecting lead according to claim 1;
An electrode group preparation step of preparing an electrode group in which a positive electrode and a negative electrode are superimposed via a separator;
An electrode group housing step of housing the electrode group in an outer can;
Between the electrode group and a current collector plate placed on the electrode group, between the current collector plate and the current collector lead placed on the current collector plate, and the current collector A welding step of welding while pressurizing between a lead and a sealing body including a terminal placed on the current collecting lead; and
Caulking and attaching the sealing body to the outer can, and a sealing step of sealing the outer can;
A method for manufacturing a secondary battery including a current collecting lead.

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