JP7161373B2 - secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a secondary battery, and more particularly to a secondary battery including current collecting leads and current collectors.

In rechargeable secondary batteries, applications are expanding, and batteries that can be charged and discharged at a high rate are being 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 housing 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, which are superimposed 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 displaced from each other in the direction along the axis of the electrode group during the winding work, and a separator of a predetermined size is placed between the positive electrode and the negative electrode. is placed in place. In this state, the positive electrode, separator and negative electrode are wound. As a result, the edge of the positive electrode spirally protrudes from one end surface of the electrode group, and the edge of the negative electrode spirally protrudes from the other end surface of the electrode group.

A positive electrode current collector formed of a metal plate is welded to the protruding positive electrode edge, and a negative electrode current collector formed of a metal plate is welded to the protruding negative electrode end. . As a result, the positive electrode is electrically connected to the positive electrode current collector over a wide range, and the negative electrode is electrically connected to the negative electrode current collector over a wide range, so that current collection efficiency is enhanced. As a result, the battery can be charged and discharged at a high rate.

As a procedure for assembling this cylindrical alkaline secondary battery, for example, first, the electrode group is inserted into the outer can, and the inner surface of the bottom wall of the outer can and the negative electrode current collector are welded. As a result, 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. Furthermore, the other end of the positive electrode ribbon is welded to a predetermined position of the sealant. As a result, the positive electrode terminal and the positive electrode are electrically connected. After that, the sealing member is attached to the upper end opening of the outer can with an insulating gasket interposed therebetween, and the upper end opening of the outer can is crimped to seal the outer can. A cylindrical alkaline secondary battery is thus formed.

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

By the way, in recent years, alkaline secondary batteries are desired to have higher performance. For example, it is desired to have a performance capable of efficiently outputting a large current and a performance capable of rapid charging. In other words, it is desired to further improve the high rate charge/discharge characteristics.

In order to improve high rate charge/discharge characteristics, it is necessary to reduce the internal resistance of the battery as much as possible. However, when a thin and long belt-like positive electrode ribbon as described above is used, the specific resistance of the positive electrode ribbon is high, and the positive electrode ribbon increases the internal resistance of the battery.

Therefore, in order to lower the internal resistance of the battery and obtain a battery with excellent high-rate charging/discharging characteristics, various studies have been conducted to shorten the current-carrying path. For example, a battery disclosed in Japanese Unexamined Patent Application Publication No. 2002-100001 is known as a battery in which measures are taken to shorten the current-carrying path.

In a battery represented by Patent Document 1, current collecting leads are used instead of conventional positive electrode ribbons. The current collecting lead is formed by bending a nickel-plated steel plate, which is a steel plate thicker than the positive electrode ribbon and nickel-plated, into a cylindrical shape. It has a bottom that is welded to the positive current collector.

In this way, the current collecting lead is interposed between the sealing body and the positive electrode current collector, and by connecting them, the sealing body and the positive electrode current collector are separated from each other by a nickel-plated steel sheet that is thicker than the conventional positive electrode ribbon. Since it is connected in the shortest distance, the energization path can be thicker and shorter than before. Thereby, the internal resistance of the battery can be reduced. As a result, the battery of Patent Document 1 is superior to conventional batteries in high-rate charge/discharge characteristics.

In the battery of Patent Document 1, projection welding is performed when welding between the positive electrode collector and the collector lead. In this projection welding, the welding current flows intensively between the projection and the part that abuts on this projection, and this part is melted to form a weld. Such projections are usually formed at four locations, as described in Patent Document 1.

JP 2011-119039 A

By the way, the plate surface of the positive electrode current collector may have slight distortion. In addition, the positive electrode current collector may be slightly inclined with respect to the current collection lead. If there is such a distortion or inclination, the current collector and the current collection lead do not come into stable contact, and welding defects may occur in some of the four locations where welds should be formed. . Such poor welding results in a decrease in yield in battery production.

The present invention has been made based on the above circumstances, and its object is to provide a secondary battery that can improve the yield in production while maintaining excellent high-rate charge-discharge characteristics. That's what it is.

In order to achieve the above object, according to the present invention, there is provided an armored can having an opening, and a sealing body sealing the opening of the armored can, wherein the cover plate is disposed at the opening. and a sealing body including a terminal of one electrode attached to the cover plate, and an electrode group formed by superimposing the one electrode and the other electrode with a separator interposed therebetween, wherein the electrolysis is performed inside the outer can In order to electrically connect the electrode group accommodated with the liquid, the current collector joined to the one electrode of the electrode group, and the current collector and the sealing body, the sealing body and the and a current collecting lead interposed between the current collector and joined to the sealing body and the current collector, wherein the current collecting lead is positioned on the side of the sealing body and is located on the side of the sealing body. a top wall welded to the body, a bottom wall located on the side of the current collector opposite the top wall and welded to the current collector, between the top wall and the bottom wall and a pair of side walls facing each other, and the bottom wall has a bottom wall center assumed to be the center position of the bottom wall and a welded portion with the current collector. A secondary battery is provided, comprising three bottom wall portions to be welded arranged to surround the center of the bottom wall.

Further, the length from the center of the current collector to the outer edge of the current collector is A, the center of the bottom wall of the current collection lead is Cb, and the bottom wall is the first portion to be welded on the bottom wall. The center of the first bottom wall-to-be-welded portion is C1, the center of the second bottom-wall-to-be-welded portion, which is the second of the bottom wall-to-be-welded portions, is C2, and the three of the bottom-wall-to-be-welded portions are C2. Let C3 be the center of the third bottom wall to-be-welded portion, L1 be the length from Cb to C1, L2 be the length from Cb to C2, and L2 be the length from Cb to C3. When the length is L3, the configuration satisfies the following relationships: L1/A × 100 = 50 ± 5%, L2 / A × 100 = 50 ± 5%, L3 / A × 100 = 50 ± 5% is preferred.

Moreover, it is preferable that the L1, the L2, and the L3 satisfy the relationship of L1=L2=L3.

A virtual line passing through C1 and Cb is assumed to be a virtual line H, a virtual line passing through C2 and C3 is assumed to be a virtual line V, and a point at which the virtual line H and the virtual line V intersect is an intermediate point. If the point Pm is the point Pm, the length from C2 to Pm is Ly2, and the length from C3 to Pm is Ly3, Ly2 and Ly3 are the same value Ly, and Ly/A× It is preferable to have a configuration that satisfies the relationship of 100≧25%.

ADVANTAGE OF THE INVENTION According to this invention, the secondary battery which can improve the yield in production, maintaining the outstanding high rate charge/discharge characteristic can be provided.

1 is a partial cross-sectional view showing a cylindrical nickel-hydrogen secondary battery according to the present invention; FIG. FIG. 3 is a plan view showing a positive electrode current collector; FIG. 4 is a perspective view showing a current collecting lead; FIG. 4 is a plan view showing the current collecting lead viewed from the bottom side; FIG. 3 is a plan view showing a current collecting lead of a comparative example viewed from the bottom wall side;

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

As an embodiment of a secondary battery to which the present invention is applied, a 4/3 FA size cylindrical nickel-hydrogen secondary battery (hereinafter referred to as battery) 1 shown in FIG. 1 will be described as an example.

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

As shown in FIG. 1 , the opening 3 of the outer can 2 is closed by a sealing member 14 . The sealing body 14 includes a disc-shaped lid plate 16 having conductivity, a valve body 20 disposed on the outer surface 16 a of the lid plate 16 , and a positive electrode terminal 22 . A ring-shaped insulating gasket 18 is arranged on the outer periphery of the lid plate 16 so as to surround the lid plate 16. The insulating gasket 18 and the lid plate 16 are formed by crimping the opening edge 17 of the outer can 2 to form the outer can. 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 arranged on the outer surface 16a of the lid plate 16 so as to close the central through hole 19. there is Furthermore, a flanged cylindrical positive electrode terminal 22 is electrically connected to the outer surface 16 a of the cover plate 16 so as to cover the valve body 20 . The positive electrode terminal 22 presses the valve body 20 toward the cover plate 16 . Moreover, this positive electrode terminal 22 has a gas vent hole 23 on its 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 element 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 electrode 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-shaped positive electrode 6, a negative electrode 8, and a separator 10, which are spirally wound with the separator 10 sandwiched between the positive electrode 6 and the negative electrode 8. As shown in FIG. That is, the positive electrode 6 and the negative electrode 8 are overlapped with each other with the separator 10 interposed therebetween. Such an electrode group 4 has a cylindrical shape as a whole.

In the electrode group 4, the edge of the positive electrode 6 is spirally exposed from one end face, and the edge of the negative electrode 8 is spirally exposed from the other end face. Here, the exposed edge portion of the positive electrode 6 is referred to as a positive electrode connection edge portion 32, and the exposed edge portion of the negative electrode 8 is referred to as a negative electrode connection edge portion (not shown). A positive electrode current collector 28 and a negative electrode current collector (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 strip-shaped conductive negative electrode core, and the negative electrode mixture is held on the negative electrode core.

The negative electrode core is a strip-shaped metal material, and is provided with a large number of through holes (not shown) penetrating in the thickness direction thereof. As such a negative electrode core, for example, a punching metal sheet can be used.

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

The negative electrode mixture contains particles of a hydrogen-absorbing alloy, a conductive material, a binder, and the like. Here, the hydrogen-absorbing alloy is an alloy capable of absorbing and releasing hydrogen, which is the negative electrode active material, and hydrogen-absorbing alloys commonly used in nickel-metal hydride secondary batteries are preferably used. The above-described binding agent functions to bind the particles of the hydrogen storage alloy and the conductive material together and to bind the negative electrode mixture to the negative electrode substrate. Here, as the conductive material and the binder, those commonly used in nickel-metal hydride secondary batteries are preferably used.

The negative electrode 8 can be manufactured, for example, as follows.
First, a negative electrode mixture paste is prepared by kneading a hydrogen-absorbing alloy powder, which is an aggregate of hydrogen-absorbing alloy particles, a conductive material, a binder, and water. The obtained negative electrode mixture paste is applied to the negative electrode substrate and dried. After drying, the negative electrode substrate to which the negative electrode mixture containing hydrogen-absorbing alloy particles and the like adheres is rolled and cut. Thereby, an intermediate product of the negative electrode is obtained. This negative electrode intermediate product has a rectangular shape as a whole. Then, the negative electrode mixture is removed from a predetermined edge portion to be the negative electrode connection edge portion in the intermediate product of the negative electrode. As a result, the predetermined edge portion becomes a negative electrode connection edge portion where the negative electrode core is exposed. Thus, a negative electrode 8 having a negative electrode connection edge is obtained. Here, the method for removing the negative electrode mixture is not particularly limited, but, for example, it is preferably removed by applying ultrasonic vibrations. It should be noted that the negative electrode mixture is still held in the region other than the negative electrode connection edge portion.

Next, the positive electrode 6 will be explained.
The positive electrode 6 includes a conductive positive electrode base material and a positive electrode material mixture held on the positive electrode base material. Specifically, the positive electrode substrate has a porous structure having a large number of pores, and the positive electrode material mixture is held in the pores and on the surface of the positive electrode substrate.
Foamed nickel, for example, can be used as the positive electrode substrate.

The positive electrode mixture contains nickel hydroxide particles as positive electrode active material particles, a cobalt compound as a conductive material, a binder, and the like. The binder described above functions to bind the nickel hydroxide particles and the conductive material to each other and to bind the nickel hydroxide particles and the conductive material to the positive electrode substrate. Here, as the binder, one commonly used in nickel-metal hydride secondary batteries is preferably used.

The positive electrode 6 can be manufactured, for example, as follows.
First, a positive electrode mixture slurry containing positive electrode active material powder, which is an aggregate of positive electrode active material particles (nickel hydroxide particles), a conductive material, water and a binder is prepared. The resulting positive electrode mixture slurry is, for example, filled into nickel foam and dried. After that, the foamed nickel filled with nickel hydroxide particles or the like is rolled and cut. This yields a positive electrode intermediate product. This positive electrode intermediate product has a rectangular shape as a whole. Then, the positive electrode material mixture is removed from a predetermined edge portion to be the positive electrode connection edge portion 32 in the intermediate product of the positive electrode, and the positive electrode base material is exposed. Next, the edge portion 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 portion 32 . By being compressed in this way, the positive electrode base material becomes dense, so that the positive electrode connection end edge portion 32 becomes a state in which it is easy to weld. In some cases, a thin plate of Ni-plated steel is connected to the positive electrode connecting edge portion 32 by resistance welding to facilitate welding. In this manner, 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, a method of removing by applying ultrasonic vibration is preferably used. 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 to which a hydrophilic functional group is added, or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene to which a hydrophilic functional group is added can be used.

The positive electrode 6 and the negative electrode 8 manufactured as described above are spirally wound with the separator 10 interposed therebetween, thereby forming the electrode group 4 . Specifically, during winding, the positive electrode 6 and the negative electrode 8 are arranged so as to be slightly displaced 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 1, a separator 10 of a predetermined size is arranged at a predetermined position, and the winding operation is performed in this state. As a result, a cylindrical electrode group 4 is obtained. As for the form of the obtained electrode group 4 , on one end side of the electrode group 4 , the positive electrode connection edge portion 32 of the positive electrode 6 protrudes from the adjacent negative electrode 8 with the separator 10 interposed therebetween. At the other end of the electrode group 4 , the negative electrode connection edge portion of the negative electrode 8 protrudes from the adjacent positive electrode 6 with the separator 10 interposed therebetween.

The electrode group 4 is formed by winding the above-described positive electrode 6, negative electrode 8, and separator 10 around a winding core having a predetermined outer diameter. 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 28 is connected to one end side, and the negative electrode current collector is connected to the other end side.

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

Next, the positive electrode current collector 28 will be described.
The positive electrode current collector 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 disk shape, a polygonal shape, or the like can be adopted. . In addition, the size of the positive electrode current collector 28 is smaller than the outer diameter of the electrode group 4 and is large enough to cover the positive electrode connection edge portion 32 of the positive electrode 6 protruding from one end side of the electrode group 4. set.

In this embodiment, as shown in FIG. 2, a plate member having a circular shape in plan view is used. Specifically, the positive electrode current collector 28 is a generally circular thin plate made of Ni-plated steel, and includes a circular central through-hole 29 in the center.

Here, in the circular positive electrode current collector 28, as shown in FIG. 2, the center of the circle is the current collector center Ca, and the length from the current collector center Ca to the outer edge of the circle Let the radius of the circle be the radius A of the current collector. The central through-hole 29 is formed at a position where its center coincides with the current collector center Ca.

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

1, the current collecting lead 34 has a first top wall 50 and a second top wall 52 connected to the cover plate 16 of the sealing body 14, and a bottom wall connected to the positive electrode current collector 28. It has a wall 36 , a first side wall 42 extending between the first top wall 50 and the bottom wall 36 , and a second side wall 44 extending between the second top wall 52 and the bottom wall 36 .

The current collecting lead 34 will be described in detail with reference to FIGS.
As is clear from FIG. 3, the bottom wall 36 of the current collecting lead 34 has a rectangular shape, and a circular bottom wall through-hole 51 is provided in the center.

A pair of first side walls 42 extending in a direction orthogonal to the plate surface of the bottom wall 36 at first short edges 60 and second short edges 62 positioned at portions corresponding to the short sides of the rectangle of the bottom wall 36 . and a second side wall 44 are provided. The side view shape of these 1st side wall 42 and the 2nd side wall 44 is a rectangle.

At the first upper edge 64 and the second upper edge 66 on the side of the first side wall 42 and the second side wall 44 opposite to the side connected to the first short edge 60 and the second short edge 62 of the bottom wall 36, A pair of first top wall 50 and second top wall 52 extending in directions parallel to the plate surface of the bottom wall 36 and in directions away from each other are provided. The planar shape of the first top wall 50 and the second top wall 52 is rectangular.

Here, a plurality of slightly protruding circular top wall projections 56 are provided on the upper surfaces 68 and 70 of the first top wall 50 and the second top wall 52 that are joined to the sealing member 14 . These top wall projection 56 portions are intended to be welded portions where welding current flows intensively when resistance welding is performed. In this embodiment, two top wall projections 56 are positioned on the first top wall 50 and two top wall projections 56 are positioned on the second top wall 52 . The number of top wall projections 56 is not particularly limited.

As is clear from FIG. 4 showing the current collecting lead 34 viewed from the side of the bottom surface 72 facing the positive electrode current collector 28, the bottom wall 36 has a rectangular shape as a whole. On the bottom wall 36, a point at which diagonal lines of the rectangle (indicated by virtual lines La and Lb in FIG. 4) intersect is assumed, and this virtual point is defined as a bottom wall center Cb. Here, the bottom wall through hole 51 is formed at a position where its center coincides with the bottom wall center Cb. Also, as shown in FIG. 4, three slightly projecting circular bottom wall projections are provided on the bottom surface 72 of the bottom wall 36 . These bottom wall projections are referred to as a first bottom wall projection 81 , a second bottom wall projection 82 and a third bottom wall projection 83 .

The first bottom wall projection 81, the second bottom wall projection 82, and the third bottom wall projection 83 are to be welded by a concentrated welding current when resistance welding is performed. Department. That is, in the present invention, the number of bottom wall welding planned portions on the bottom wall 36 of the current collecting lead 34 is set to three.

If there are three portions to be welded on the bottom wall, three welded portions are formed when the collector lead 34 and the positive electrode collector 28 are joined together. Even if the positive electrode current collector 28 is slightly distorted or tilted, the current collecting lead 34 is in contact with the current collecting lead 34 at three points, so that the connection is stable and the occurrence of poor welding can be suppressed. As a result, the yield is improved in battery production.

Here, the position where the bottom wall projection as the portion to be welded on the bottom wall is formed, that is, the position where the welded portion is formed is preferably set based on the following conditions. With this setting, even if the number of welded portions on the bottom wall 36 is reduced from four to three, a significant increase in the internal resistance of the battery can be avoided, which is preferable.

First, as shown in FIG. 4, the centers of the circular first bottom wall projection 81, the second bottom wall projection 82 and the third bottom wall projection 83 are set to the first projection center C1, the second projection center C2 and the third projection center C2, respectively. Let the center be C3. The length of the straight line connecting the bottom wall center Cb and the first projection center C1 is defined as L1, the length of the straight line connecting the bottom wall center Cb and the second projection center C2 is defined as L2, and the bottom wall center Cb and the third projection center C3 is the length of the straight line L3. When A is the current collector radius of the positive electrode current collector 28 joined to the current collection lead 34, L1/A×100=50±5%, L2/A×100=50±5%, L3 It is preferable that the portion to be welded (bottom wall projection), that is, the welded portion is positioned at a position that satisfies the relationship of /A×100=50±5%. More preferably, the lengths of L1, L2 and L3 are set to a constant value L. That is, the relationship of L1=L2=L3=L is satisfied. Then, the portion to be welded (bottom wall projection), that is, the welded portion is positioned at a position satisfying the relationship of L/A×100=50±5%.

Here, the longer the lengths of L1, L2, and L3, the more they contribute to the reduction of the internal resistance value. Considering the energization from the positive electrode current collector to the electrode group, the position of the welded portion is efficient when it is near the middle (50%) of the radius A of the positive electrode current collector 28. Therefore, the optimum range is as follows. The ratio with A described above is preferably 50±5%.

Furthermore, as shown in FIG. 4, an extension line (virtual line H) obtained by further extending the straight line connecting the first projection center C1 and the bottom wall center Cb, and connecting the second projection center C2 and the third projection center C3. A midpoint Pm is a point at which the straight line (virtual line V) intersects. Then, the length of the straight line connecting the bottom wall center Cb and the intermediate point Pm is Lx, the length of the straight line connecting the second projection center C2 and the intermediate point Pm, and the length of the straight line connecting the third projection center C3 and the intermediate point Pm Let Ly be the length of the straight line connecting Then, the portion to be welded (bottom wall projection), ie the weld is preferably positioned. More preferably, Ly and Lx are equal, that is, Ly=Lx.

Here, as the second projection center C2 and the third projection center C3 are separated from each other, the internal resistance value decreases, but a saturation tendency appears when Ly/A×100 is 25% or more. Therefore, it is preferable to satisfy Ly/A×100≧25%.

From the above, it is more preferable to satisfy L/A×100=50±5% and Ly/A×100≧25% in the aspect of reducing the internal resistance value.

In addition, the thickness of the current-carrying path through which the current flows in the battery 1 affects the internal resistance of the battery 1 . A part of this current path includes a welded portion of the current collecting lead 34 . Since the welded portion of the current collecting lead 34 is formed by the top wall projection 56, the first bottom wall projection 81, the second bottom wall projection 82 and the third bottom wall projection 83, the diameters of these projections correspond to the internal resistance of the battery 1. It can be said that it affects Normally, these projections have a diameter of 0.9 mm, but increasing the diameter to about 1.2 mm contributes to lowering the internal resistance. Therefore, it is preferable to set the diameter of these projections to about 1.2 mm if possible.

The collector lead 34 described above can be manufactured, for example, as follows.
First, a rectangular metal thin plate is prepared, and the thin plate is bent to form the first top wall 50, the first side wall 42, the bottom wall 36, the second side wall 44, and the second top wall 52. do. A bottom wall through hole 51 is formed in the center of the bottom wall 36 . Further, for example, by press working, the top wall projection 56 is provided at a predetermined position of the first top wall 50 and the second top wall 52, and the first bottom wall projection 81 and the second bottom wall projection are provided at predetermined positions of the bottom wall 36. 82, forming a third bottom wall projection 83; In this way, the collector lead 34 as shown in FIG. 3 can be obtained.

Next, an example of the procedure for assembling the battery 1 will be described.
First, the electrode group 4 as described above is prepared. Then, after connecting the negative electrode current collector to the other end side of the electrode group 4, the electrode group 4 is accommodated in the outer can. Then, the negative electrode current collector is resistance-welded to the bottom wall of the outer can.

Next, the positive electrode current collector 28 is placed on one end side of the electrode group 4, and the positive electrode connecting edge portion 32 and the positive electrode current collector 28 in the electrode group 4 are resistance-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 by the electrode group 4 and most of it is held by the separator 10 . This alkaline electrolyte advances an electrochemical reaction (charging/discharging reaction) during charging/discharging between the positive electrode 6 and the negative electrode 8 . As this alkaline electrolyte, it is preferable to use an alkaline electrolyte containing at least one of KOH, NaOH and LiOH as a solute.

On the other hand, in another step, the first top wall 50 and the second top wall 52 of the current collecting lead 34 are resistance-welded to the inner surface 16b of the cover plate 16 of the sealing body 14 to form a composite of the sealing body 14 and the current collecting lead 34. form. More specifically, the current concentrates on the portion where the top wall projection 56 of the first top wall 50 and the second top wall 52 of the current collecting lead 34 and the inner surface 16b of the cover plate 16 of the sealing body 14 contact, forming a welded portion. Thus, a composite body in which the sealing member 14 and the current collecting lead 34 are welded together is obtained.

Next, the composite described above is placed on top of the positive electrode current collector 28 . At this time, it is preferable to align the bottom wall center Cb of the bottom wall 36 of the current collecting lead 34 with the current collector center Ca of the positive electrode current collector 28 . An insulating gasket 18 is provided on the outer peripheral edge of the lid plate 16 of the sealing member 14 , and the lid plate 16 is positioned at the upper end opening of the outer can 2 via the insulating gasket 18 .

After that, a current is passed between the positive electrode terminal 22 and the negative electrode terminal of the battery 1 while applying pressure to perform resistance welding (projection welding). At this time, the current concentrates on the portions where the positive electrode current collector 28 contacts the first bottom wall projection 81, the second bottom wall projection 82, and the third bottom wall projection 83, and welded portions are formed. Body 28 and bottom wall 36 of current collecting lead 34 are welded together.

After the welding as described above is completed, the opening 3 of the outer can 2 is sealed by crimping the opening edge 17 of the outer can 2 . Thus, the battery 1 is formed.

In the present invention, since the positive electrode current collector 28 and the current collecting lead 34 are welded at three points, even if the plate surface of the positive electrode current collector 28 is slightly distorted or tilted, the welded portion can be stably welded. is formed, and the production yield of the battery is improved. Further, in the current collecting lead 34 according to the battery 1 of the present invention, by positioning the bottom wall projection as the welded portion to be welded at a predetermined position, even if the number of welded portions is reduced from four in the conventional art to three. The internal resistance value of the battery 1 can be maintained at a value equivalent to the conventional one. Therefore, the battery 1 according to the present invention can also maintain excellent high-rate charge/discharge characteristics.

Therefore, according to the present invention, it is possible to obtain a secondary battery capable of improving the production yield in a secondary battery that uses a current collector and a current collecting lead to enable high-rate charging and discharging.

Here, in recent years, various devices have been miniaturized, and even small devices are required to charge and discharge at a high rate. In line with this situation, even small batteries such as FA type, AA type, and AAA type used in small devices are required to charge and discharge at a higher rate.

In these small batteries, the component parts must be made smaller than in the case of large batteries, such as D-type and C-type batteries, whose outer diameter exceeds 19 mm. With the miniaturization of component parts, the welding stability between the positive electrode current collector and the current collecting lead is lowered, and welding defects are likely to occur, resulting in a decrease in the production yield of small batteries.

In response to this situation, the present invention can stabilize the weldability between the positive electrode current collector and the current collection lead, so that it can be used particularly for small batteries with excellent high-rate charge-discharge characteristics, specifically, diameters of less than 19 mm. It is effective in improving the yield in the production of batteries.

[Example]
1. Production of secondary battery Example 1

(1) Manufacture of current collecting leads

A Ni-plated steel sheet was prepared by coating a thin sheet of steel corresponding to a so-called SPCC (cold-rolled steel sheet) with Ni to a thickness of 2 μm. The thickness of this Ni-plated steel sheet is 0.30 mm. Then, the current collecting lead 34 as shown in FIG. 3 was manufactured by punching and pressing the Ni-plated steel sheet.

Here, the dimensions of each portion of the current collecting lead 34 will be described below with reference to FIGS.
The length X1 of the bottom wall 36 in the direction of arrow X is 10.2 mm, the length X2 of the first top wall 50 in the direction of arrow X is 1.45 mm, and the length of the second top wall 52 in the direction of arrow X is 1.45 mm. X3 is 1.45 mm, and the length Y1 of the current collecting lead 34 in the arrow Y direction is 7.0 mm. The dimension of the height H1 of the first side wall 42 and the second side wall 44 is 1.95 mm (see FIG. 3). The diameter of the bottom wall through hole 51 is 3 mm, and the diameters of the top wall projection 56, the first bottom wall projection 81, the second bottom wall projection 82 and the third bottom wall projection 83 are 0.9 mm. L1=L2=L3=L=2.55 mm, Lx=1.8 mm and Ly=1.8 mm. A line passing through C1, Cb, and Pm is orthogonal to a line passing through C2, Pm, and C3.

(2) Battery assembly

A positive electrode 6, a negative electrode 8, and a separator 10, which are used in a general nickel-hydrogen secondary battery, were prepared. The positive electrode 6, the negative electrode 8 and the separator 10 are strip-shaped. The prepared positive electrode 6 and negative electrode 8 were spirally wound with a separator 10 interposed between them to form an electrode group 4 for 4/3 FA size. During winding, the positive electrode 6 and the negative electrode 8 are arranged so as to be slightly shifted in the direction along the axis of the electrode group 4, and a separator is placed at a predetermined position between the positive electrode 6 and the negative electrode 8. 10 was placed and a winding operation was performed in this state to obtain a columnar electrode group 4 . In the obtained electrode group 4 , the positive electrode connection edge portion 32 of the positive electrode 6 protrudes from one end side of the electrode group 4 beyond the adjacent negative electrode 8 with the separator 10 interposed therebetween. The negative electrode connection edge portion of the negative electrode 8 protrudes from the adjacent positive electrode 6 with the separator 10 interposed therebetween.

Next, a disk-shaped negative electrode current collector for 4/3FA size formed of a thin plate of Ni-plated steel was prepared. This negative electrode current collector was welded to the negative electrode connection end edge of the electrode group 4 .

Next, as shown in FIG. 2, a 4/3 FA size positive electrode current collector 28 having a circular shape as a whole and including a circular central through-hole 29 in the center was prepared. The positive electrode current collector 28 is formed of a Ni-plated steel sheet obtained by applying Ni-plating to a thin steel sheet corresponding to a so-called SPCC (cold-rolled steel sheet). The positive electrode current collector 28 has a thickness of 0.40 mm and a radius A of 7.5 mm.

Next, the electrode group 4 to which the negative electrode current collector was welded was accommodated in the bottomed cylindrical outer can 2 . Then, the inner surface of the bottom wall of the outer can 2 and the negative electrode current collector were welded.

Next, the positive electrode current collector 28 was placed on the upper end portion of the electrode group 4, and the positive electrode connection edge portion 32 and the positive electrode current collector 28 in the electrode group 4 were resistance-welded.
Next, a predetermined amount of an alkaline electrolyte containing KOH as a solute was injected into the outer can 2 .

Next, the current collecting lead 34 manufactured as described above was resistance-welded to the sealing body 14 to form a composite of the sealing body 14 and the current collecting lead 34 . More specifically, the current concentrates on the portion where the top wall projection 56 on the first top wall 50 and the second top wall 52 of the current collecting lead 34 and the inner surface of the cover plate 16 of the sealing member 14 contact to form a welded portion. , thereby obtaining a composite in which the sealing member 14 and the current collecting lead 34 are welded together.

The resulting composite was placed on top of the positive electrode current collector 28 . At this time, the cathode current collector 28 and the composite were aligned so that the bottom wall center Cb of the bottom wall 36 of the current collection lead 34 and the current collector center Ca of the cathode current collector 28 were aligned.

After that, a current was passed between the positive electrode terminal 22 and the negative electrode terminal of the sealing member 14 while applying pressure to perform resistance welding (projection welding). At this time, the current is concentrated in the portion where the first bottom wall projection 81, the second bottom wall projection 82, and the third bottom wall projection 83 on the bottom wall 36 of the current collecting lead 34 and the positive electrode current collector 28 are in contact. A weld was formed, and the cathode collector 28 and the bottom wall 36 of the collector lead 34 were welded together.

After the welding as described above was completed, the opening 3 of the outer can 2 was sealed by crimping the opening edge 17 of the outer can 2 . By repeating the above procedure, 10 batteries 1 were manufactured.

A resistance value measurement sample was prepared separately by resistance welding (projection welding) the sealing member 14, the current collector lead 34, and the positive electrode current collector 28 for resistance measurement, which will be described later.

At this time, the value of the radius A of the positive electrode current collector 28, the percentage of the values of L1, L2, and L3 in the current collecting lead 34, the value of the radius A of the positive electrode current collector 28, and the value of the current collecting lead 34 The percentage with the value of Ly was determined, and the results are shown in Table 1.

Example 2
Battery 1 and resistance measurement were performed in the same manner as in Example 1, except that the top wall projection 56, the first bottom wall projection 81, the second bottom wall projection 82, and the third bottom wall projection 83 had a diameter of 1.2 mm. A sample was prepared.

Example 3
A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that L1=L2=L3=L=2.96 mm and Lx=2.35 mm.

Example 4
The top wall projection 56, the first bottom wall projection 81, the second bottom wall projection 82, and the third bottom wall projection 83 have a diameter of 1.2 mm, L1=L2=L3=L=2.96 mm, and Lx= A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that the thickness was 2.35 mm.

Example 5
A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that L1=L2=L3=L=3.75 mm, Lx=2.6 mm, and Ly=2.6 mm.

Example 6
A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1 except that L1=L2=L3=L=3.38 mm, Lx=2.4 mm, and Ly=2.4 mm.

Example 7
A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that L1=L2=L3=L=3.00 mm, Lx=2.1 mm, and Ly=2.1 mm.

Example 8
A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that L1=L2=L3=L=3.75 mm, Lx=3.62 mm, and Ly=0.98 mm.

Example 9
Battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that L1 = 3.00 mm, L2 = L3 = 3.75 mm, Lx = 3.62 mm, and Ly = 0.98 mm. did.

Example 10
Battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that L1 = 3.38 mm, L2 = L3 = 3.75 mm, Lx = 2.68 mm, and Ly = 2.63 mm. did.

Comparative example 1
As shown in FIG. 5, the fourth bottom wall projection 84 is added to provide four bottom wall projections, and the length from the bottom wall center Cb to the center of each bottom wall projection is L1=L2=L3=L4= A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that the thickness was 2.55 mm and Lx and Ly in each bottom wall projection were 1.8 mm.

Comparative example 2
As shown in FIG. 5, the fourth bottom wall projection 84 is added to provide four bottom wall projections, and the length from the bottom wall center Cb to the center of each bottom wall projection is L1=L2=L3=L4= A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that Lx and Ly in each bottom wall projection were set to 3.38 mm and Lx and Ly were set to 2.4 mm.

Comparative example 3
As shown in FIG. 5, the fourth bottom wall projection 84 is added to provide four bottom wall projections, and the length from the bottom wall center Cb to the center of each bottom wall projection is L1=L2=L3=L4= A battery 1 and a resistance value measurement sample were manufactured in the same manner as in Example 1, except that the thickness was 3.68 mm and Lx and Ly in each bottom wall projection were 2.6 mm.

2. Evaluation of Secondary Battery (1) Observation of Poor Welding The obtained battery 1 was disassembled, and the positive electrode current collector 28 and the current collection lead 34 were peeled off using a predetermined tool to conduct a destructive inspection. Observing the joint surface of the bottom wall 36 of the torn off positive electrode current collector 28 and the current collecting lead 34, if there is a scooped scar in the portion corresponding to the welded part, it is assumed that the welded part has been formed. The number of scars was counted. In Examples 1 to 10, 3 scars were confirmed as good products, and less than 3 scars were regarded as defective products, and in Comparative Examples 1 to 3, 4 scars were confirmed. were regarded as non-defective products, and those with less than four were regarded as defective products.

If there were no defective batteries among the 10 manufactured batteries, the yield was judged to be excellent, and the column of yield in Table 1 was marked with a mark. On the other hand, if even one defective product was found among the 10 manufactured products, the yield was determined to be poor, and a Δ mark was added to the yield column in Table 1.

(2) Measurement of Resistance Value The resistance value between the positive electrode terminal and the positive electrode current collector was measured for the resistance value measurement sample described above. The obtained resistance values are shown in Table 1 as internal resistance values of the battery. By measuring the resistance from the positive electrode terminal to the positive electrode current collector using such a resistance value measurement sample, it becomes easier to grasp the influence of the position of the welded portion on the internal resistance value. The lower the internal resistance value, the better the high rate charge/discharge characteristics.

(3) Consideration (i) The batteries of Comparative Examples 1 to 3, which have four bottom wall projections, that is, four welding portions between the current collecting lead and the positive electrode current collector, are defective products with poor welding. existed. On the other hand, the batteries of Examples 1 to 10, in which there are three bottom wall projections, that is, three welded portions between the current collecting lead and the positive electrode current collector, have no defective welding and improve the yield of the battery. I know you are. This is probably because the bottom wall of the current collecting lead has three welded portions, so that even if the positive electrode current collector is slightly distorted or tilted, it can be stably contacted and good bonding can be achieved.

(ii) Comparing Example 1 and Example 2, it can be seen that increasing the diameter of the bottom wall projection lowers the internal resistance of the battery.

(iii) Example 5 in which the ratio (L/A) of the length L (L1, L2, L3) from the center of the bottom wall to each bottom wall projection and the radius A of the positive electrode current collector is 50%; Comparing with Example 7 in which the L/A ratio is 40%, the internal resistance value of Example 5 was 0.305 mΩ, while the internal resistance value of Example 7 was 0.348 mΩ. From this, it can be seen that setting the ratio of L/A to about 50% is effective in reducing the internal resistance value.

(iv) In Example 8, the ratio of L/A is 50%, and the ratio of Ly to the radius A of the positive electrode current collector 28 (Ly/A) is 13%. The internal resistance value of Example 8 was 0.336 mΩ. In contrast, Example 5 has an L/A ratio of 50% and a Ly/A ratio of 35%. The internal resistance value of Example 5 was 0.305 mΩ. From this, it can be seen that increasing the ratio of Ly/A in addition to setting the ratio of L/A to about 50% is effective in reducing the internal resistance value.

(v) From the results of Example 1 and Comparative Example 1, it can be seen that simply increasing the number of bottom wall projections from four to three increases the internal resistance value. However, increasing the length from the bottom wall center to the bottom wall projection, i.e., increasing the ratio of L/A, and increasing the distance between the second and third bottom wall projections, i.e. , Ly/A, the internal resistance value can be reduced to 0.305 mΩ as in Example 5. The resistance value of Example 5 is equivalent to the internal resistance value of Comparative Example 3 in which four bottom wall projections were formed under the same L/A and Ly/A conditions. In other words, it can be said that the number of bottom wall projections can be reduced from 4 to 3 without significantly increasing the internal resistance value if the positions of the bottom wall projections are appropriately arranged.

In addition, the present invention is not limited to the above-described one embodiment and examples, and various modifications are possible. A secondary battery, a lithium ion secondary battery, or the like may be used.

In addition, in the above-described embodiment and examples, the projection is formed on the current collector lead, but the present invention is not limited to this aspect, and the projection can be formed on the positive electrode current collector as long as the welded portion can be formed at a predetermined position. or the sealing member.

In addition, in the embodiment and examples described above, the positive electrode current collector is disk-shaped, but the present invention is not limited to this aspect, and the positive electrode current collector may be polygonal. In this case, the center of the circumscribed circle of the polygon is the center of the current collector.

Furthermore, in the embodiment and examples described above, the electrode on the side connected to the outer can is the negative electrode, and the electrode on the side connected to the sealing body is the positive electrode, but the present invention is limited to this aspect. Alternatively, the electrode connected to the outer can may be the positive electrode, and the electrode connected to the sealing body may be the negative electrode.

Furthermore, in the present invention, the size of the battery is not particularly limited, and may be FA size, AA size, or other sizes.

<Aspect of the present invention>
A first aspect of the present invention is an armored can having an opening; A sealing body including a terminal of one electrode attached, and an electrode group formed by superimposing one electrode and the other electrode with a separator interposed therebetween, and are accommodated together with an electrolytic solution inside the outer can. a current collector joined to the one electrode of the electrode group; a current collecting lead interposed therebetween and joined to the sealing body and the current collector, wherein the current collecting lead is positioned on the side of the sealing body and welded to the sealing body a top wall, a bottom wall located on the side of the current collector opposite the top wall and welded to the current collector, extending between the top wall and the bottom wall; The bottom wall has a bottom wall center assumed to be the center position of the bottom wall and a bottom wall weld in which a welded portion with the current collector is formed. The secondary battery includes three bottom wall welding scheduled portions arranged so as to surround the center of the bottom wall.

According to a second aspect of the present invention, in the first aspect of the present invention described above, the length from the center of the current collector to the outer edge of the current collector is defined as A, and the center of the bottom wall of the current collection lead is is Cb, the center of the first bottom wall welding scheduled portion that is the first of the bottom wall welding scheduled portions is C1, and the second bottom wall welding scheduled portion that is the second bottom wall welding scheduled portion is C1 Let C2 be the center of the planned portion, let C3 be the center of the third bottom wall planned portion to be welded, and let L1 be the length from Cb to C1. to C2 is L2, and the length from Cb to C3 is L3, L1/A×100=50±5%, L2/A×100=50±5%, L3 /A×100=50±5%.

A third aspect of the present invention is the secondary battery according to the second aspect of the present invention, wherein the L1, the L2, and the L3 satisfy the relationship of L1=L2=L3.

According to a fourth aspect of the present invention, in the second aspect or the third aspect of the present invention described above, a virtual line passing through the C1 and the Cb is a virtual line H, and a virtual line passing through the C2 and the C3 A line is a virtual line V, a point where the virtual line H and the virtual line V intersect is a midpoint Pm, a length from C2 to Pm is Ly2, and a length from C3 to Pm is When Ly3, Ly2 and Ly3 have the same value Ly, and the secondary battery satisfies the relationship Ly/A×100≧25%.

1 Nickel Metal Hydride Secondary Battery 2 Armored 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 Collector 32 Positive Electrode Connecting Edge 34 Current Collecting Lead 36 Bottom Wall 42 First Side Wall 44 Second side wall 50 First top wall 52 Second top wall 81 First bottom wall projection 82 Second bottom wall projection 83 Third bottom wall projection

Claims (3)

an outer can having an opening;
a sealing body that seals the opening of the outer can, the sealing body including a lid plate disposed in the opening and a one-electrode terminal attached to the lid plate;
an electrode group formed by stacking one electrode and the other electrode with a separator interposed therebetween, the electrode group being housed inside the outer can together with an electrolytic solution;
a current collector joined to the one electrode of the electrode group;
a current collecting lead interposed between the sealing body and the current collector and joined to the sealing body and the current collector for electrically connecting the current collector and the sealing body; , and
The current collecting lead is located on the side of the sealing body and is located on a top wall welded to the sealing body, and is located on the side of the current collector opposite to the top wall and is on the side of the current collector. a bottom wall to be welded and a pair of opposing side walls extending between the top and bottom walls;
The bottom wall has a bottom wall center assumed at the center position of the bottom wall, and a bottom wall weld scheduled portion where a weld portion with the current collector is formed, and is arranged so as to surround the bottom wall center. and three bottom wall weld schedules ,
The length from the center of the current collector to the outer edge of the current collector is A, the center of the bottom wall of the current collection lead is Cb, and the first portion of the bottom wall to be welded is the first The center of the portion to be welded on the bottom wall is set to C1, the center of the portion to be welded on the second bottom wall, which is the second of the portions to be welded on the bottom wall, is set to C2, and the center of the portion to be welded on the bottom wall is the third one of the portions to be welded on the bottom wall. Let C3 be the center of the third bottom wall weld-scheduled portion, L1 be the length from Cb to C1, L2 be the length from Cb to C2, and L2 be the length from Cb to C3 is L3, the secondary battery satisfies the following relationships: L1/A×100=50±5%, L2/A×100=50±5%, and L3/A×100=50±5% . 2. The secondary battery according to claim 1 , wherein said L1, said L2 and said L3 satisfy the relationship of L1=L2=L3. A virtual line passing through the C1 and the Cb is defined as a virtual line H, a virtual line passing through the C2 and the C3 is defined as a virtual line V, and a point where the virtual line H and the virtual line V intersect is a midpoint Pm. When the length from C2 to Pm is Ly2 and the length from C3 to Pm is Ly3, Ly2 and Ly3 are the same value Ly, and Ly/A×100≧ 3. The secondary battery according to claim 1 , which satisfies the 25% relationship.

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