JP2002093421A - Positive electrode for alkaline secondary battery and alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode for an alkaline secondary battery with improved welding strength between a conductive base and a collector. SOLUTION: This positive electrode has a conductive substrate having a three-dimensional porous structure, in which an average hole diameter of one surface is larger than that of the other surface, and when the number of holes of the surface having a larger average hole diameters is 1, the number of holes of the surface having a smaller average hole diameters is in the range of 1.1 to 2, and the collector 8 welded on a collector welding area 4 of the surface of the conductive substrate having a larger average hole diameter, and a positive mix filled in the conductive substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode for an alkaline secondary battery and an alkaline secondary battery.

[0002]

2. Description of the Related Art As alkaline secondary batteries, nickel cadmium secondary batteries and nickel hydrogen secondary batteries are known. Due to the increasing demand for high-capacity batteries due to the recent spread of PCs (personal computers) and mobile phones, and environmental issues, nickel-metal hydride secondary batteries have become mainstream as alkaline secondary batteries.

[0003] In the automobile industry, electric vehicles (EVs) which replace gasoline engine vehicles due to environmental problems,
The development of assist type electric vehicles (HEVs) is active and some of them have been commercialized.

The positive electrode of an alkaline secondary battery is composed of a positive electrode mixture containing nickel hydroxide as an active material filled in a conductive substrate having a three-dimensional structure. A current collector such as a band-shaped metal plate for electrically connecting the positive electrode and the positive electrode terminal is welded to the conductive substrate of the positive electrode. Various proposals have been made for the method of attaching the current collector to the conductive substrate as described below.

Japanese Patent Application Laid-Open No. 9-22704 discloses that one corner of a porous substrate made of foamed nickel is compressed by a press machine, filled with an active material paste, then roll-pressed, heated, and collected. It is described that a paste nickel electrode is manufactured by spot welding an electric body.

Japanese Unexamined Patent Publication No. 9-204911 discloses that when a tab is spot-welded to a current collector having a three-dimensional network structure carrying an active material mixture mainly composed of nickel hydroxide. A predetermined portion of the current collector is compressed to provide a tab attaching portion, and then the active material paste is filled into the current collector and then dried, and the tab attaching portion is continuously beaten by an impact applying means in which a plurality of needles are bundled. Thus, it is disclosed that a positive electrode is manufactured.

On the other hand, Japanese Patent Application Laid-Open No. 8-255611 discloses that an ultrasonic vibration horn is pressed against at least one surface of a predetermined portion of a three-dimensional porous substrate filled with an active material to remove the active material at the predetermined portion. A method for manufacturing a battery electrode plate in which a current collecting tab is welded to a portion where the active material is removed, wherein a high-pressure fluid injection hole or a powder suction hole is provided in the ultrasonic vibration horn, and the active material is ultrasonically vibrated. And a method for manufacturing a battery electrode plate for removing the crushed active material by injecting a high-pressure fluid from the injection hole or removing the active material by suction into the powder suction hole. ing.

[0008]

In these paste-type positive electrodes, a current collector is welded to one end of the conductive substrate, and the current is collected by the current collector. Although it is easy to increase the filling amount, the contact area between the current collector and the conductive substrate is small, and the current collection efficiency is apt to be significantly reduced due to slight welding failure. Therefore, in order to obtain higher current collection performance, it is necessary to increase the welding strength between the current collector and the conductive substrate.

An object of the present invention is to provide a positive electrode for an alkaline secondary battery having improved welding strength between a conductive substrate and a current collector.

[0010] The present invention provides a positive electrode having excellent current collecting performance,
An object is to provide an alkaline secondary battery having excellent charge / discharge characteristics.

[0011]

The positive electrode for an alkaline secondary battery according to the present invention has a three-dimensional porous structure, in which the average pore diameter on one surface is larger than the average pore diameter on the other surface, and When the number of holes on the surface having a large pore diameter is 1, the number of holes on the surface having a small average pore diameter is in the range of 1.1 to 2, and the number of holes on the surface of the conductive substrate having the large average hole diameter is less than 1.1. A current collector welded to a current collector welding region, and a positive electrode mixture filled in the conductive substrate are provided.

An alkaline secondary battery according to the present invention is an alkaline secondary battery comprising an electrode group in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween, wherein the positive electrode has a three-dimensional porous structure. The average pore diameter of the surface located on the inside during winding is larger than the average pore diameter of the surface located on the outside during winding, and the number of pores on the surface having a large average pore diameter is 1
When the number of pores on the surface having a small average pore diameter is 1.1 to 2
Having a positive electrode mixture filled in the conductive substrate, a current collector welded to a current collector welding area of the surface having a large average hole diameter of the conductive substrate, and a positive electrode mixture filled in the conductive substrate. It is characterized by the following.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The positive electrode for an alkaline secondary battery according to the present invention has a three-dimensional porous structure, the average pore size of one surface is larger than the average pore size of the other surface, and the average pore size is When the number of holes in the large surface is set to 1, the number of holes in the surface having the small average hole diameter is in the range of 1.1 to 2; and the current collection in the surface of the conductive substrate in which the number of holes is large. A current collector welded to the body welding region; and a positive electrode mixture filled in the conductive substrate.

In the positive electrode according to the present invention, when the positive electrode and the negative electrode are spirally wound with a separator interposed therebetween, it is preferable that the surface to which the current collector is welded is positioned inside at the time of the winding.

FIG. 1 shows a schematic view of an example of this conductive substrate.
You. In FIG. 1, the size relationship of the skeleton of the conductive substrate is understood.
Circular holes are used to make the surface structure of the conductive substrate easier to understand.
The structure is evenly opened, but the surface structure of the conductive substrate
Is not limited to the structure shown in FIG. The conductivity
The substrate 1 comprises a layer 2 having a three-dimensional porous structure having a large average pore diameter.
And a layer 3 having a three-dimensional porous structure having a small average pore diameter.
Is done. The conductive substrate 1 has an average pore diameter of one surface 2.
Is larger than the average pore diameter of the other surface 3. The average pore size
The average pore diameter is small when the number of pores on
By making the number of holes in the main surface 3 1.1 or more,
Hole spacing R on surface 2 with large uniform diameter₁(Skeleton thickness)
Is the hole interval R in the surface 3 having the small average hole diameter._Two(Skeleton
Thickness), and the conductive substrate
Apparent porosity can be increased. However
When the number of holes of the surface 2 having a large average pore diameter is set to 1,
When the number of holes on the surface 3 having a small average pore diameter is larger than 2,
The difference between the thickness of the skeleton on one side and the thickness of the skeleton on the other side is large.
And the strength of the substrate decreases, or the mixture
The packing density differs greatly from the mixture packing density on the other side.
Therefore, the substrate may be warped at the time of pressing. Ma
In addition, the hole interval R on the surface 3 having the small average hole diameter _Two(Bone
(Thickness of the case) is thinner, so the separator between the positive and negative electrodes
When making an electrode group by spirally winding
The surface 3 having a small average pore diameter is easily broken. others
As a result, the internal short-circuiting rate increases,
And the high rate discharge characteristics are impaired. The average pore size
The average pore diameter is small when the number of pores on
The number of holes on the surface 3 should be in the range of 1.1 to 1.5.
preferable. The conductive substrate 1 has a large average pore diameter.
At the center of the longitudinal side end of the surface 2, a current collector weld
Region 4 exists.

The number of holes on the surface of the conductive substrate is, for example,
It is measured by the method described below. Photomicrographs are taken at any three locations on each surface of the conductive substrate. For each microscope image, the number of holes per inch is measured, and the average value of three places is calculated to be the number of holes on the surface of the conductive substrate.

This conductive substrate is produced, for example, by the method described below. First, a foamed resin sheet having a large average pore size and a foamed resin sheet having a small average pore size are prepared. The number of holes on the surface of the foamed resin sheet having a large average pore diameter is 1
In this case, the number of pores on the surface of the foamed resin sheet having a small average pore diameter is in the range of 1.1 to 2. After the two foamed resin sheets are integrated by heat fusion, electroless plating (for example, electroless nickel plating) is performed, and then electroplating (for example, nickel electroplating) is performed, followed by heating and firing. Is produced by thermally decomposing and removing the resin in the nickel plating, followed by firing in a reducing atmosphere. The obtained conductive substrate has a three-dimensional porous structure. This structure is obtained by transferring the structure of a foamed resin sheet as a raw material.

The conductive substrate may have a structure in which two or more layers having a three-dimensional porous structure having different average pore diameters are laminated. A two-dimensional substrate may be arranged between layers having a three-dimensional porous structure having a small pore diameter. When the two-dimensional substrate is interposed in this way, the hole can be prevented from expanding when tension is applied to the conductive substrate, so that the mixture filling density of the conductive substrate can be increased, and mass production can be performed. Performance can be improved. Further, such a conductive substrate is manufactured by, for example, a method described below. First, a foamed resin sheet having a large average pore size and a foamed resin sheet having a small average pore size are prepared. When the number of holes on the surface of the foamed resin sheet having a large average pore diameter is 1, the number of holes on the surface of the foamed resin sheet having a small average pore diameter is in the range of 1.1 to 2. After interposing a sheet of the same material between the two foamed resin sheets and integrating them by heat fusion,
Electroless plating (for example, electroless nickel plating) is applied, followed by electroplating (for example, nickel electroplating), which is heated and fired to thermally decompose and remove the resin in the nickel plating, and then fired in a reducing atmosphere. It is produced by doing.

The positive electrode is produced, for example, by the method described below.

First, a paste is prepared by kneading an active material, a conductive agent and a binder in the presence of water. It has a three-dimensional porous structure, the average pore size of one surface is larger than the average pore size of the other surface, and the average pore size is smaller when the number of pores on the larger surface is 1. Number 1.1
After filling the paste into the conductive substrates in the range of ~ 2, the paste is dried and pressed to obtain a conductive substrate filled with the positive electrode mixture.

The positive electrode mixture filled in the current collector welding area 4 of the mixture-filled substrate 5 is removed by, for example, ultrasonic vibration. The removal by the ultrasonic vibration can be performed, for example, by the method shown in FIG. First, the horn 6 is arranged on the surface of the conductive substrate of the mixture-filled substrate 5 having the smaller average hole diameter, and the anvil 7 is arranged on the surface of the mixture substrate 5 having the larger average hole diameter.
Ultrasonic vibration is applied from the surface opposite to the current collector welding area 4 by the horn 6 to crush the positive electrode mixture filled in the current collector welding area 4. The positive electrode mixture filled in the current collector welding area 4 is removed by sucking the pulverized material of the positive electrode mixture by the anvil 7. When the mixture is removed by such a method, the pulverized material of the mixture can be quickly sucked by the anvil, so that damage to the conductive substrate can be minimized. Further, since the mixture can be prevented from remaining in the current collector welding region 4, the rate of occurrence of splash at the time of welding can be reduced.

Next, a current collector 8 made of a strip-shaped metal plate is provided on the current collector welding area 4 on the surface of the conductive substrate having a large average hole diameter.
To obtain a paste-type nickel positive electrode having the structure shown in FIG. Such a current collector can be formed, for example, from nickel.

The welding area of the current collector 8 is determined by setting the width of the current collector 8 to L.
_1, and when the length from the lower end of the current collector 8 to the positive electrode terminal was L _2, it is calculated by L ₁ × L _2. This welding area is 30 times the area of the current collector welding area 4 on the surface of the conductive substrate having a large average hole diameter (the area is calculated by length L ₃ × length L ₄ ).
% To 80%. If the welding area is less than 30% of the current collector welding area, it may be difficult to sufficiently improve the welding strength between the conductive substrate and the current collector. Also, because the current collector welding area is excessive,
There is a possibility that a high positive electrode capacity cannot be obtained. Furthermore, when the separator is interposed between the positive electrode and the negative electrode and spirally wound, a crack is easily generated in the current collector welding area. On the other hand, if the welding area exceeds 80% of the current collector welding area, the position accuracy of the current collector is reduced and splash is likely to occur during welding. A more preferable range of the welding area is 40 to
70%.

The active material, conductive agent and binder contained in the positive electrode mixture will be described.

As the active material, for example, nickel hydroxide powder in which at least one metal selected from zinc, cobalt, bismuth and copper is eutectic or non-eutectic nickel hydroxide powder can be used. .

Examples of the conductive agent include metal cobalt, cobalt compounds (for example, cobalt oxide such as CoO, and cobalt hydroxide such as Co (OH) ₂ ). As the conductive agent, one or more selected from the above-described types can be used. The conductive agent may be added to a paste described below in the form of a powder or a layered material covering the surface of the active material. To the paste, both a nickel hydroxide powder whose surface is coated with a conductive agent and a powder of a conductive agent may be added.

Examples of the binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

Hereinafter, an alkaline secondary battery provided with the positive electrode according to the present invention will be described.

This alkaline secondary battery comprises an electrode group in which the positive electrode and the negative electrode according to the present invention are spirally wound with a separator interposed therebetween, and an alkaline electrolyte.

The surface of the conductive substrate having a large average pore diameter is disposed on the side located inside when the positive electrode is wound. When a surface having a large average pore diameter of the conductive substrate is arranged on the surface located outside at the time of winding the positive electrode, there is a possibility that the edge of the current collector rebounds at the time of winding and breaks through the separator to come into contact with the negative electrode. Because.

Hereinafter, the negative electrode, the separator, and the alkaline electrolyte will be described.

1) Negative electrode The negative electrode contains a hydrogen storage alloy.

This negative electrode is made of, for example, hydrogen storage alloy powder,
The paste is prepared by kneading a conductive material and a binder in the presence of water to prepare a paste, filling the paste into a conductive substrate, drying, and then pressing.

As the hydrogen storage alloy, for example, La
Ni _5, MmNi ₅ (Mm is misch metal), LmN
i ₅ (Lm is a La-enriched misch metal), and part of Ni of these alloys is Al, Mn, Co, Ti, Cu, C
at least one selected from a, Mg, Zr, Cr and B
Rare earth-based hydrogen storage alloys represented by multi-element-based alloys substituted with various elements can be given. Above all, the general formula _{LnNi v Co w Mn x Al y} Zr z ( However, Ln is one or more kinds of rare earth elements, preferably those containing La, total atomic ratio v, w, x, y and z Value is 5.
1 ≦ v + w + x + y + z ≦ 5.4) is preferably used.

As the conductive material, for example, graphite,
Carbon black or the like can be used.

Examples of the binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate, polytetrafluoroethylene, polyvinyl alcohol (PVA), and styrene butadiene rubber (SB).
R) and the like.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate.

2) Separator Examples of the separator include a nonwoven fabric made of a polyamide fiber, a nonwoven fabric made of a polyolefin fiber such as polyethylene and polypropylene, or a nonwoven fabric provided with a hydrophilic functional group.

3) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH.

FIG. 1 shows an example of this cylindrical alkaline secondary battery.
Shown in

That is, in the bottomed cylindrical container 10,
An electrode group 13 produced by laminating the positive electrode 9, the separator 11, and the negative electrode 12 and winding them in a spiral shape is stored. The surface of the conductive substrate having a large average pore diameter is disposed on the side of the surface 14 located inside when the positive electrode 9 is wound. The negative electrode 12 is arranged at the outermost periphery of the electrode group 13 and is in electrical contact with the container 10. The alkaline electrolyte is contained in the container 10. A circular sealing plate 16 having a hole 15 in the center is
Is arranged in the upper opening. A ring-shaped insulating gasket 17 is disposed between the peripheral edge of the sealing plate 16 and the inner surface of the upper opening of the container 10, and the sealing plate is attached to the container 10 by caulking to reduce the diameter of the upper opening inward. 16 is hermetically fixed via the gasket 17. The positive electrode lead 8 has one end connected to the positive electrode 9 and the other end connected to the lower surface of the sealing plate 16. The hat-shaped positive electrode terminal 18 is mounted on the sealing plate 16 so as to cover the hole 15. The rubber safety valve 19
The hole 15 is disposed so as to close the hole 15 in a space surrounded by the sealing plate 16 and the positive electrode terminal 18. A circular holding plate 20 made of an insulating material having a hole in the center is provided on the positive terminal 18 with a protrusion of the positive terminal 18.
Are arranged to protrude from the holes. The outer tube 21 covers the periphery of the holding plate 20, the side surface of the container 10, and the periphery of the bottom of the container 10.

The positive electrode for an alkaline secondary battery according to the present invention described above has a three-dimensional porous structure, and the average pore diameter on one side is larger than the average pore diameter on the other side, and the average pore diameter is large. A conductive substrate in which the number of holes on the surface having a small average pore diameter is 1.1 to 2 when the number of holes on the surface is 1;
A current collector welded to the current collector welding area on the surface of the conductive substrate having the large average hole diameter; and a positive electrode mixture filled in the conductive substrate.

In such a positive electrode, since the current collector is welded to the thick surface of the skeleton of the conductive substrate, the welding strength between the conductive substrate and the current collector can be improved, and the current collection of the positive electrode can be improved. Performance can be improved. Further, the positive electrode, after filling a conductive substrate with a paste containing an active material, drying and pressing to obtain a conductive substrate filled with a positive electrode mixture by pressing, and then filled in the current collector welding area. When the positive electrode mixture is removed and the current collector is welded to the current collector welding area, the positive electrode mixture filled in the current collector welding area can be easily removed. That is, the higher the mixture filling density is to increase the positive electrode capacity, the more difficult it is to remove the positive electrode mixture from the conductive substrate. For example, when the mixture is removed by ultrasonic vibration, it is necessary to increase the frequency or lengthen the time for applying the vibration, which increases the possibility of damaging the conductive substrate such as cracks. According to the present invention, the mixture can be easily removed because the average hole diameter of the surface to which the current collector is welded is large.

Further, when the positive electrode and the negative electrode according to the present invention are spirally wound with a separator interposed therebetween, a surface having a large average pore diameter of the conductive substrate is arranged on the side located inside when the positive electrode is wound. Thereby, although the surface located outside when the positive electrode is wound has a large amount of deformation, the surface having a small average pore diameter having high flexibility is arranged on this surface side, so that the surface located outside during the winding is large. Cracks can be avoided. In addition, since the current collector is welded to the inner surface when the positive electrode is wound, it is possible to prevent the edge of the current collector from rebounding during the winding. as a result,
The internal short-circuit occurrence rate at the time of manufacturing the electrode group can be reduced. In addition, an alkaline secondary battery including such an electrode group can improve charge / discharge characteristics such as positive electrode utilization and high-rate discharge characteristics.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Paste-Type Positive Electrode> After a nickel net was placed between two types of foamed resin sheets having different average pore sizes, these were integrated by heat fusion. Subsequently, nickel electroplating was applied after nickel electroless plating, and the resin inside the nickel plating layer was thermally decomposed and removed by firing, whereby the basis weight was 400 g / m ² and the porosity was 98%.
And the thickness is 1.5 mm and the average pore diameter on one side is 500
A conductive substrate having a three-dimensional porous structure in which the average number of pores on the other surface is 300 μm, and the number of holes on the surface having a small average diameter is 1.2 when the number of holes on the surface having a large average diameter is 1 Was prepared.

On the other hand, 3% by mass of carboxymethylcellulose (CMC) and polytetrafluoroethylene were added to a mixed powder consisting of 90% by mass of nickel hydroxide powder and 10% by mass of cobalt monoxide powder (D50: 3 μm, distribution of 7 μm at 7 μm). 5% by mass of fluoroethylene was added, and 45% by mass of water was added thereto.
A paste was prepared by adding and kneading. Subsequently, by filling this paste into the above-described conductive substrate, drying it, and then performing roller pressing and rolling molding,
A conductive substrate filled with the positive electrode mixture was obtained. The horn was arranged on the side of the conductive substrate of the mixture-filled substrate having the smaller average hole diameter, and the anvil was arranged on the side of the larger average hole diameter of the conductive substrate. Ultrasonic vibration is applied to the mixture-filled substrate with a horn to pulverize the mixture, the pulverized mixture is suctioned by the anvil, and the mixture is electrically conductive to 4 mm x 4 mm at the center of the longitudinal end of the substrate. A surface of the substrate having a large average hole diameter was exposed to form a current collector welding region.

Next, a width of 3 mm was applied to the current collector welding area.
The current collector made of the strip-shaped nickel plate was subjected to resistance welding to obtain a paste-type nickel positive electrode for AA size having the structure shown in FIG. 3 described above. The current collector welding area (L ₁ × L ₂ ) was 50% of the current collector welding area (L ₃ × L ₄ ).

<Preparation of Paste Type Hydrogen Storage Alloy Negative Electrode> 100% by mass of hydrogen storage alloy powder, 0.5% by mass of sodium polyacrylate, carboxymethyl cellulose (CM
C) 0.12% by mass, polytetrafluoroethylene
5% by mass and 1% by mass of carbon black,
A paste was prepared by kneading with 0% by mass. This paste was applied on both sides of a punched metal as a conductive substrate, dried, and then roll-formed by a roller press to produce a negative electrode.

Next, a separator made of a nonwoven fabric made of polyolefin subjected to a hydrophilic treatment was interposed between the positive electrode and the negative electrode and spirally wound to form an electrode group. At this time, the surface of the conductive substrate having a large average pore diameter was arranged on the side located inside when the positive electrode was wound. Such an electrode group was housed in a bottomed cylindrical metal container also serving as a negative electrode terminal. Next, an alkaline electrolyte mainly composed of KOH is injected into the container, and the container is subjected to a sealing treatment or the like, thereby having the above-described structure shown in FIG. 1 and a theoretical capacity of 1200 mA.
h, an AA-size cylindrical nickel-metal hydride secondary battery was manufactured.

(Comparative Example 1) The average pore diameter on both surfaces was equal (3
00 μm) A conductive substrate having a three-dimensional porous structure was prepared.
This conductive substrate was filled with a paste similar to that described in Example 1 described above, dried, and then roll-pressed to obtain a conductive substrate filled with a positive electrode mixture. A horn was arranged on one side of the mixture-filled substrate, and an anvil was arranged on the other side. Ultrasonic vibration is applied to the mixture-filled substrate with a horn to pulverize the mixture, the pulverized mixture is sucked by the anvil, and the conductive substrate is exposed at the center of the longitudinal end of the mixture-filled substrate. Thus, a current collector welding area was formed.

Next, a width of 3 mm was applied to the current collector welding area.
The current collector formed of the strip-shaped nickel plate was resistance-welded to obtain a paste-type nickel positive electrode for AA size. The current collector welding area was 50% of the current collector welding area area.

A separator similar to that described in the first embodiment is interposed between such a positive electrode and a negative electrode similar to the one described in the first embodiment, and spirally wound. An electrode group was prepared. At this time, the surface to which the current collector was welded was defined as a surface located inside during winding. From this electrode group, a cylindrical nickel-metal hydride secondary battery was assembled in the same manner as described in Example 1 above.

Comparative Example 2 A conductive substrate similar to that described in Example 1 was filled with a paste similar to that described in Example 1 above, dried, and then rolled by roller pressing. By molding, a conductive substrate filled with the positive electrode mixture was obtained. The horn was arranged on the side of the mixture-filled substrate having the larger average pore diameter, and the anvil was arranged on the side of the smaller average pore diameter. Ultrasonic vibration is applied to the mixture-filled substrate with a horn to pulverize the mixture, the pulverized material of the mixture is suctioned by the anvil, and the average pore diameter of the conductive substrate is provided at the center of the longitudinal end of the mixture-filled substrate. Was exposed to form a current collector welded area.

Next, a width of 3 mm was applied to the current collector welding area.
The current collector formed of the strip-shaped nickel plate was resistance-welded to obtain a paste-type nickel positive electrode for AA size. The current collector welding area was 50% of the current collector welding area area.

A separator similar to that described in Example 1 is interposed between such a positive electrode and a negative electrode similar to that described in Example 1 described above, and is spirally wound. An electrode group was prepared. At this time, the surface of the conductive substrate having a small average pore diameter was arranged on the side located inside when the positive electrode was wound. From this electrode group, a cylindrical nickel-metal hydride secondary battery was assembled in the same manner as described in Example 1 above.

100 secondary batteries of Example 1 and Comparative Examples 1 and 2 were prepared and subjected to a short-circuit test.
The failure rate due to an internal short circuit was measured, and the results are shown in Table 1 below.

Also, 100 positive electrodes of Example 1 and Comparative Examples 1 and 2 were prepared and subjected to a tensile test, and the average value of the tensile strength was calculated. The results are shown in Table 1 below.

[0059]

[Table 1]

As is clear from Table 1, the average pore diameter on one surface is larger than the average pore diameter on the other surface, and the average pore size is smaller when the number of pores on the surface with the larger average pore diameter is 1. The secondary battery of Example 1 in which the current collector was welded to the surface of the conductive substrate having a large average hole diameter in the range of 1.1 to 2 in the conductive substrate in comparison with the secondary batteries of Comparative Examples 1 and 2 As a result, the internal short-circuit occurrence rate can be reduced, and the tensile strength between the positive electrode conductive substrate and the current collector can be increased.

(Examples 2 to 5) The ratio of the current collector welding area to the current collector welding area was changed to 20%, 30%, 80%, and 90% by changing the area of the current collector welding area. A cylindrical nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1 except for the above.

Each of the obtained secondary batteries of Examples 2 to 5 was prepared, and a short-circuit test was carried out, and a defective rate due to an internal short-circuit was measured. The results are shown in Table 2 below.

Also, 100 positive electrodes of Examples 2 to 5 were prepared, and a tensile test was performed to calculate an average value of tensile strength. The results are shown in Table 2 below.

[0064]

[Table 2]

As is apparent from Table 2, the tensile strength between the positive electrode conductive substrate and the current collector can be improved by setting the welding area to 30 to 80% of the current collector welding area.

[0066]

As described above, according to the present invention, it is possible to provide a positive electrode for an alkaline secondary battery which has improved welding strength between a conductive substrate and a current collector and has excellent current collecting performance. Further, according to the present invention, it is possible to provide an alkaline secondary battery having excellent charge / discharge characteristics including a positive electrode having excellent current collecting performance.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a conductive substrate of a positive electrode for an alkaline secondary battery according to the present invention.

FIG. 2 is a perspective view showing a mixture removing step in a manufacturing step of the positive electrode for an alkaline secondary battery according to the present invention.

FIG. 3 is a plan view showing an example of a positive electrode for an alkaline secondary battery according to the present invention.

FIG. 4 is a partially cutaway perspective view showing an example of the alkaline secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Conductive board | substrate, 2 ... Layer of a three-dimensional porous structure with a large average pore diameter, 3 ... Layer of a three-dimensional porous structure with a small average pore diameter, 4 ... Current collector welding area, 5 ... Positive electrode mixture filled substrate, 8: current collector, 9: positive electrode.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H017 AA02 AS02 BB11 CC01 CC20 CC28 DD03 EE04 HH03 5H028 AA01 BB05 BB07 CC05 CC12 5H050 AA14 BA14 CA03 CB17 DA04 DA20 FA09 FA12 FA13 GA07 GA23 HA06

Claims (2)

[Claims] 1. An average pore size having a three-dimensional porous structure, wherein the average pore size on one surface is larger than the average pore size on the other surface, and when the number of pores on the surface having the larger average pore size is 1, A conductive substrate having a small number of holes in a range of 1.1 to 2; a current collector welded to a current collector welding region of the large average hole diameter of the conductive substrate; And a positive electrode mixture filled in a functional substrate. 2. An alkaline secondary battery comprising an electrode group in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween, wherein the positive electrode has a three-dimensional porous structure, and has a three-dimensional porous structure. The average pore diameter of the surface located is larger than the average pore diameter of the surface located outside at the time of winding, and when the number of pores of the surface having the larger average pore diameter is 1, the number of pores of the surface having the smaller average pore diameter is 1 A current collector welded to a current collector welding area on the surface of the conductive substrate having the large average pore diameter, and a positive electrode filled in the conductive substrate. Alkaline secondary battery comprising: