JP2000251871A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery, having Ion internal resistance and capable of large- current discharge by providing a current collecting plate having a diameter smaller than that of an electrode group, by forming lead parts of a positive and negative electrodes in the peripheral part of the end part of the electrode group by projecting them from the end part, and by welding the lead parts to the current collecting plate in a form bent toward the current collecting plate. SOLUTION: Each lower end part 4B of a negative electrode 4 is shifted downward, rolled and projected from a positive electrode 2, and a current collecting plate 6b is welded to the projecting part and thus electrically connected to the negative electrode 4. Similarly, each upper end part 2A of the positive electrode is projected from the negative electrode 4 and welded to a current collecting plate 6a. The diameter of the current collecting plate 6a is smaller than that of an electrode group 5, so that the peripheral part of the positive electrode 2 is exposed. A plurality of lead parts 2L projected from the upper end parts 2A are formed in the peripheral part, and the lead parts 2L are welded to the current collecting plate 6a by bending them toward the current collecting plate 6a. A connection area is increased, as compared with the case in which the peripheral part of the upper end parts 2A are directly abutted on the current collecting plate 6a, and welding heat is easy to outflow, and welding defects are reduced. Likewise, lead parts 4L are formed on the lower end parts 4B of the negative electrode 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery, and more particularly, to an alkaline secondary battery having a low internal resistance and capable of discharging a large current.

[0002]

2. Description of the Related Art Various electric tools and bicycles with electric assist,
Further, as a driving power source for an electric vehicle or the like that is being developed recently, a secondary battery that can be charged and discharged and that is portable is used. In particular, in the above-mentioned applications, a characteristic that a large current discharge is possible is required, and from this point, nickel cadmium secondary batteries are often used.

Further, in recent years, nickel-hydrogen secondary batteries having a discharge capacity of about 1.5 to 2 times as large as that of nickel-cadmium secondary batteries have been used. This nickel
A hydrogen secondary battery is an electrode group formed by applying a paste including an electrode active material and a binder to a conductive current collector sheet to form a positive electrode and a negative electrode, and winding the positive electrode and the negative electrode through a separator. Is sealed in a battery can together with an alkaline electrolyte.

[0004] Since nickel-hydrogen secondary batteries have a larger discharge capacity and volume energy density than nickel-cadmium secondary batteries, when batteries of the same size are discharged at the same time rate, nickel-cadmium secondary batteries are used. The discharge current can be increased as compared with the battery. However,
When the above-mentioned alkaline secondary battery is discharged at a high discharge rate (large current), a phenomenon occurs in which the operating voltage of the battery decreases due to the internal resistance of the battery. In particular, this phenomenon is remarkable in nickel-metal hydride rechargeable batteries, and when used as a power source for electric tools and electric vehicles, the operation voltage of the batteries does not decrease even when operated at a high discharge rate. It is necessary to reduce the internal resistance.

The internal resistance of a battery is greatly affected by the connection between the electrode and the external terminal. Conventionally, the outer periphery of the negative electrode is brought into contact with the inner surface of the battery can, or a tab provided on the positive electrode is connected to the positive terminal. The method of connecting was adopted. For this reason, when discharging is performed with a large current such as 20 to 50 A, the contact resistance between each electrode and the external terminal may significantly increase in the above-described contact method or tab method.

For this reason, a connection method has been proposed in which a current collector plate is welded to an end of an electrode group to establish conduction with an external terminal. In this connection method, for example, the current collector is welded to the electrode group as follows. First, a region where the current collector sheet was exposed in a band shape without the paste being carried on the ends of the positive electrode and the negative electrode was formed, and the ends of the positive electrode and the negative electrode were overlapped by being slightly shifted in the width direction. It is spirally wound in the longitudinal direction. In this case, one end of either the positive electrode or the negative electrode protrudes from the end (end surface) of the obtained pseudo-cylindrical electrode group, and the current collector is brought into contact with the protruding portion to perform spot welding. .

When the current collector plate is welded, it is ideal to weld all the portions where the ends of the electrode groups and the current collector plate are in contact with each other. A plurality of projections are arranged at equal intervals, and the burrs are used as welding points so that the end and the current collector plate are welded at as many parts as possible.

[0008]

In the case of performing the above-mentioned welding, the welding can be performed well near the center of the electrode group. However, poor welding may occur at the periphery of the electrode group. It is considered that this is because the current collector plate exists only inside the welding point at the periphery of the electrode group, so that the welding heat becomes difficult to escape. The diameter cannot be increased.
As a result, welding failure occurs at that portion, but this has not been resolved to date.

If the welding is not performed uniformly at the center and the periphery of the electrode group, the contact resistance between the electrode and the current collector cannot be reduced, so that the internal resistance of the battery can be reduced. It becomes difficult. An object of the present invention is to provide an alkaline secondary battery which can solve the above-described problems in the alkaline secondary battery, has a low internal resistance, and can discharge a large current.

[0010]

SUMMARY OF THE INVENTION The present invention renews the electrode structure of an alkaline secondary battery and increases the contact area between the electrode and the current collector plate at the periphery of the electrode group under severe welding conditions. The technical idea is to improve welding defects at the peripheral edge. In order to achieve the above object, in the present invention according to claim 1, the current collector plate of the alkaline secondary battery has a smaller diameter than the electrode group, and the peripheral portion at the end of the electrode group has the positive electrode or the negative electrode. Wherein the lead portion is formed to project from the end portion, and the lead portion is welded to the current collector plate in a state where the lead portion is bent toward the current collector plate side.

Preferably, a lead portion and a current collecting plate according to claim 1 are provided at both ends of the electrode group (claim 2).

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cylindrical nickel-metal hydride secondary battery according to the present invention will be described below with reference to FIGS. In FIG. 1, a nickel-hydrogen secondary battery is formed by winding a sheet-shaped positive electrode 2 and a negative electrode 4 through a separator 3 to form a spiral electrode group 5, which is formed with a bottomed alkaline electrolyte together with an alkaline electrolyte (not shown). Cylindrical battery can 1
It is manufactured by being housed inside.

The positive electrode 2 and the negative electrode 4 are manufactured by applying a paste containing a predetermined electrode active material to a conductive current collector sheet described later. One end 2 A of the positive electrode 2 carries the paste. Instead, a region where the current collector sheet was exposed in a band shape was formed. Similarly, a current collector sheet is exposed in a band shape at one end 4 </ b> B of the negative electrode 4. Then, the positive electrode 2 and the negative electrode 4 are overlapped with the end 2A and the end 4B opposite to each other, and spirally wound so that the negative electrode 4 is on the outside to form an electrode group 5, which is housed inside the battery can 1. I do. Hereinafter, of the end portions of the electrode group 5, those located on the opening side of the battery can 1 are referred to as “upper end”, and those located on the bottom side of the battery can 1 are referred to as “lower end”.
Called.

Here, when the positive electrode 2 and the negative electrode 4 are overlapped with each other, the lower end 4B of the negative electrode 4 is shifted downward from the lower end of the positive electrode 2, and the lower end 4B of the negative electrode 4 is wound. It can protrude from the lower end of the positive electrode 2.
Then, the current collector plate 6b is welded to the protruding portion to establish conduction between the negative electrode 4 and the current collector plate 6b. Similarly, the upper end 2A of the positive electrode 2 protrudes from the upper end of the negative electrode 4, and the current collecting plate 6a is welded to this protruding portion. Note that the upper end of the separator 3 is preferably lower than the upper end 2A of the positive electrode 2 and protrudes from the upper end of the negative electrode 4, and the lower end of the separator 3 is
Preferably, it protrudes from the lower end of the positive electrode 2 above the lower end 4B of the negative electrode 4.

The current collectors 6a and 6b are formed in a disk shape smaller in diameter than the electrode group 5. More specifically, the current collector 6a is
, And the current collecting plate 6 b has a smaller diameter than the periphery of the negative electrode 4. Also, as the current collectors 6a and 6b,
For example, a conductive metal such as a Ni plate or a stainless steel plate can be used. In addition, as a method of welding the current collector plate to the end of the electrode group 5, the above-described protrusion may be formed.
A small tab terminal made of, for example, nickel may be welded to the lower end 4B of the negative electrode 4, and the lower end 4B may be welded to the current collector plate 6b via the tab terminal. Similarly, a tab terminal is welded to the upper end 2A of the positive electrode 2, and the upper end 2A is connected via the tab terminal.
May be welded to the current collecting plate 6a.

A circular sealing plate 8 having a hole 8a in the center is disposed in the upper opening of the battery can 1 containing the electrode group 5, and further between the peripheral edge of the sealing plate 8 and the upper end inner surface of the battery can 1. A ring-shaped insulating gasket 9 is interposed, and the sealing plate 8 is airtightly fixed to the battery can 1 via the gasket 9 by caulking processing to reduce the diameter of the upper end inward. One end of the positive electrode lead 7a is connected to the positive electrode 2 via the current collector plate 6a, and the other end is connected to the lower surface of the sealing plate 8. On the other hand, one end of the negative electrode lead 7b is connected to the negative electrode 4 via the current collector plate 6b, and the other end is connected to the bottom surface of the battery can 1.

The positive electrode terminal 10 having a hat shape is mounted on the sealing plate 8 so as to cover the hole 8a, and a space surrounded by the positive electrode terminal 10 and the sealing plate 8 is used to close the hole 8a. A rubber safety valve 11 is filled. Then, a donut-shaped holding plate (not shown) made of an insulating material is disposed on the positive electrode terminal 10, and the positive electrode terminal 10 projects from a hole of the holding plate. Further, a predetermined outer tube covers the periphery of the holding plate and the side and bottom periphery of the battery can 1.

Next, the lead portions 2L and 4L formed on the periphery of the end of the electrode group 5 will be described. At the upper end of the electrode group 5, a current collecting plate 6a having a smaller diameter than the electrode group is provided. Therefore, the periphery of the positive electrode 2 is exposed outside the current collecting plate 6a. Further, a lead portion 2L made of, for example, nickel is formed on the peripheral edge portion and protrudes from the upper end portion 2A and extends above the current collector plate 6a. The number of the lead portions 2L is not particularly limited, but it is preferable that a plurality of the lead portions 2L are formed at equal intervals on the peripheral portion. Further, the length of the lead portion 2L is not limited, but may be any length as long as the lead portion 2L can be appropriately contacted with the current collector plate when the lead portion 2L is bent toward the current collector plate side. As a method of forming the lead 2L, the lead 2L may be welded to the upper end 2A.
As shown in FIG.
An L-shaped protrusion may be formed. Hereinafter, an embodiment in which the lead portion is formed on the current collector sheet itself will be described with reference to FIG.

In FIG. 2A, the right side of the current collector sheet 20 corresponds to a portion which becomes an outer peripheral side after winding the sheet. One end 2 </ b> L is formed on the end 20 </ b> A of the sheet (corresponding to the upper end 2 </ b> A of the positive electrode 2) at a position that becomes a peripheral edge after winding. This sheet shape is referred to as “shape A”. FIG. 2B shows the end portion 20 of the sheet.
4A shows an aspect in which four lead portions 2L are formed. The intervals and the number of the lead portions 2L are defined so that they are arranged at equal intervals on the peripheral edge portion after winding. This sheet shape is referred to as “shape B”.

FIG. 2C shows a portion of the end portion 20A of the sheet, which is to be a peripheral portion after winding, is projected, and a plurality of cuts are made in the projected portion, thereby forming a plurality of lead portions 2A.
This shows an aspect in which L is formed. In this case, the adjacent lead portions 2L partially overlap each other when bent toward the current collector plate side, but such a configuration is acceptable. This sheet shape is referred to as “shape C”.

In each of the above-described embodiments, the lead portion 2L is formed only in the portion of the sheet 20 that becomes the peripheral edge (outermost periphery) of the electrode group after winding, but if the lead portion 2L is located outside the outer edge of the current collector plate 6a. Alternatively, a lead portion may be formed in a portion inside the outermost periphery of the sheet 20. Similarly, a lead portion 4L is attached to the peripheral portion at the lower end of the electrode group 5, that is, the lower end 4B of the negative electrode 4.
To form

Next, as shown in FIG. 3, the lead 2L is welded to the current collector 6a. In FIG. 3, each lead portion 2L is bent toward the current collecting plate 6a (in the direction of arrow F in the drawing) and brought into contact with the current collecting plate 6a, and in this state, the lead portion 2L is welded to the current collecting plate 6a. At this time, the periphery of the upper end portion 2A is connected to the current collector plate 6 via a lead portion 2L of a predetermined size.
Therefore, the contact area between the positive electrode 2 and the current collecting plate 6a is increased as compared with the case where the peripheral portion is directly contacted with the current collecting plate 6a. And since welding heat flows out to the lead part 2L through the above-mentioned contact portion, heat does not stay near the welded part, and welding defects are reduced.

Similarly, the lead 4L of the negative electrode 4 is welded to the current collector 6b. In addition, at least one of the end portions of the electrode group may be provided with the above-described lead portion and the current collecting plate, but in order to further reduce the contact resistance, the above-described lead portion is provided at both end portions of the electrode group. Preferably, a current collector is provided. The positive electrode 2 and the negative electrode 4 of the present invention may be manufactured as follows.

First, as a positive electrode material used for the positive electrode 2,
For example, nickel compounds such as nickel oxide containing nickel hydroxide and cobalt oxide can be suitably used. Then, the positive electrode material is kneaded with a conductive agent, a binder, and water to form a paste, applied to a current collector sheet, dried, molded, processed into an arbitrary shape, and formed into a positive electrode 2. .

As the current collector sheet, for example, nickel,
Punched metal, expanded metal, plated perforated steel plate made of stainless steel or nickel-plated steel plate,
A substrate having a two-dimensional structure such as a nickel net or a substrate having a three-dimensional structure such as a felt-like porous metal body or a sponge-like metal substrate can be used. As the conductive agent, for example, metal cobalt, cobalt oxide, cobalt hydroxide and the like can be used.

As the binder, for example, carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, sodium polyacrylate, polytetrafluoroethylene and the like can be used. As the negative electrode material used for the negative electrode 4, a hydrogen storage alloy powder can be suitably used. The hydrogen storage alloy is not particularly limited as long as it can store and release hydrogen in the electrolytic solution.
AB ₅ system can be used TiNi system, TiFe based or Mg ₂ Ni-based alloy. Here, A is La, Mm (mish metal), or Lm (La-enriched misch metal). And B is Ni, or Ni and Al,
An alloy with an element selected from the group consisting of Mn, Co, Ti, Cu, Zn, Zr, Cr and B.

Such a negative electrode material is used as a conductive agent, a binder,
And kneaded with water to form a paste, applied to the above-mentioned current collector sheet, dried, formed, processed into an arbitrary shape,
And it is sufficient. As the conductive agent, for example, carbon black or the like can be used. The binder may be the same as that used in the production of the positive electrode, for example. Examples of the alkaline electrolyte used for the nickel-hydrogen secondary battery of the present invention include a mixed solution of NaOH and LiOH, KOH and LiOH
, A mixed solution composed of KOH, LiOH, and NaOH can be used.

In the above embodiment, the nickel-hydrogen secondary battery has been described. However, the present invention can be applied to other alkaline secondary batteries such as a nickel-cadmium secondary battery.

[0029]

EXAMPLES Examples 1 to 7 and Comparative Example 1. Production of Positive Electrode and Negative Electrode A current collector sheet made of a Ni foam was prepared, and one end thereof (corresponding to the upper end portion after winding) 2A was pressed to a region 2 mm inside from the end face to densify it. Next, a positive electrode mixture paste containing nickel hydroxide powder as a main component is applied and filled on the surface of the sheet excluding the densified region, and the paste is dried under a drying condition of 100 ° C. × 1 hour. The positive electrode 2 was rolled and cut into a predetermined size.

A negative electrode mixture paste mainly composed of a predetermined hydrogen storage alloy powder was applied and filled on a current collector sheet made of Ni punched metal, and the paste was dried under a drying condition of 80 ° C. × 1 hour. Thereafter, this sheet was rolled and cut into a predetermined size to obtain a negative electrode 4. Then, the paste carried on one end (corresponding to the lower end after winding) 4B of the sheet was removed.

As shown in Table 1, the current collector sheets used for the positive electrode 2 and the negative electrode 4 were provided with lead portions 2L and 4L, respectively.
And corresponds to any of the shapes A to C described in FIG.

[0032]

[Table 1]

2. Battery Assembly The upper end 2A of the positive electrode 2 and the lower end 4B of the negative electrode 4 are set to be opposite to each other, and the lower end 4B of the negative electrode 4 is shifted downward from the lower end of the positive electrode 2. , And wound so that the negative electrode 4 was on the outside, to form an electrode group 5.

The current collecting plate 6a is provided on the protruding upper end 2A.
And the current collector plate 6b was similarly welded to the lower end 4B protruding. Next, the lead portion 2L protruding from the upper end portion 2A is bent inward and welded to the current collecting plate 6a.
The lead 4L protruding from B was bent inward and welded to the current collector 6b.

The electrode group 5 is housed in the battery can 1, and an electrolyte containing KOH as a main component is injected and sealed. The cylindrical nickel-hydrogen secondary battery shown in FIG. I assembled them one by one. For comparison, a positive electrode 2 and a negative electrode 4 were manufactured using a conventional current collector sheet having no lead portion, and the other parts were assembled in the same manner as in the example. This is a comparative example.

3. Measurement of Intermediate Discharge Voltage The battery was charged at a predetermined rate and then discharged at a discharge rate of 5, 10, and 15 (CmA), respectively, to measure an intermediate discharge voltage (Mid CV). The result is shown in FIG. The higher the discharge intermediate voltage, the better the large current discharge characteristics. (1) As is clear from FIG. 4, the nickel-hydrogen secondary battery of the present invention has a discharge rate,
It has a high discharge intermediate voltage during large current discharge of CmA or more, and is excellent in large current discharge characteristics. (2) In the case of the comparative example in which the lead portion is not formed at the peripheral edge at the end of the electrode group, the discharge intermediate voltage is lower than that of the example, and the large current discharge characteristics are inferior. From this,
The advantage of the present invention in which a lead portion is formed on the peripheral edge at the end of the electrode group and the lead portion is welded to the current collector plate is apparent. (3) As is clear from comparison of Examples 1 to 3 and Examples 4 to 6, as the number of formed lead portions increases, the discharge intermediate voltage increases, and this tendency becomes more pronounced as the discharge rate increases. .
This indicates that it is preferable to form a plurality of leads. (4) As is clear from a comparison between Examples 4 to 6 and Example 7, Example 7 in which leads were formed at both ends of the electrode group,
Examples 1 to 3 in which the lead portion was formed only at the end of the positive electrode,
The discharge intermediate voltage is higher than in Examples 4 to 6 in which the lead portion is formed only at the end of the negative electrode. This indicates that it is preferable to form leads at both ends of the electrode group.

[0037]

As is apparent from the above description, according to the present invention, a lead portion is formed at the peripheral edge at the end of the electrode group, and this lead portion is welded to the current collector plate. A lead portion having a predetermined size is formed in the portion, and the contact area between the positive electrode or the negative electrode and the current collector plate is increased as compared with a case where the peripheral portion is directly connected to the current collector plate without providing the lead portion.

Since the welding heat flows to the lead portion through the above-mentioned contact portion, the heat does not stay in the vicinity of the welding portion, welding defects are reduced, and the contact resistance between the electrode and the current collector plate is reduced. I do. As a result, the internal resistance of the battery is reduced, and a high discharge operating voltage can be ensured. Therefore, the battery can be suitably used for a power supply requiring a large current discharge, such as an electric tool or an electric vehicle.

In particular, when the above-mentioned lead portions and current collectors are provided at both ends of the electrode group, this effect becomes remarkable.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a nickel-hydrogen secondary battery according to the present invention.

FIG. 2 is a development view showing a shape of a current collector sheet in which leads are formed in advance.

FIG. 3 is a perspective view showing a mode in which a lead portion is welded to a current collecting plate.

FIG. 4 shows a discharge intermediate voltage (Mid) when a battery is discharged.
It is a graph which shows CV).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery can 2 Positive electrode 2A Upper end of positive electrode 4 Negative electrode 4B Lower end of negative electrode 2L, 4L Lead part 5 Electrode group 6a, 6b Current collector plate

Claims (2)

[Claims] A spiral electrode group formed by winding a positive electrode and a negative electrode through a separator is enclosed in a battery can together with an alkaline electrolyte, and a current collector plate is provided at at least one end of the electrode group. In the alkaline secondary battery being welded, the current collector plate has a smaller diameter than the electrode group, and a lead portion of the positive electrode or the negative electrode is formed at a peripheral portion at an end of the electrode group so as to protrude from the end. An alkaline secondary battery, wherein the lead portion is welded to the current collector in a state where the lead is bent toward the current collector. 2. The alkaline secondary battery according to claim 1, wherein the lead portion and the current collecting plate according to claim 1 are provided at both ends of said electrode group.