JPH11265712A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the current collecting efficiency of a positive electrode, to prevent an internal short circuit and attain a high capacity and a long life by providing the positive electrode carried with a mix containing an active material and conductive flake-like powder having the length and thickness of specific values on a conductive substrate having a two-dimensional structure. SOLUTION: A paste containing nickel hydroxide powder, a conductive material, conductive flake-like powder having the length of 10-30 μm and the thickness of 0.5-3.0 μm, a binder and water is prepared, and it is filled or applied to a conductive substrate and dried to manufacture a positive electrode 2 by pressure molding, for example. Grains made of nickel or a nickel alloy are rolled by a ball mill then heat-treated in the reducing atmosphere as required to manufacture the flake-like powder, for example. The blended quantity of the flake-like powder is preferably set to 2.0-13.0 wt.% against an active material. Polytetrafluoroethylene can be used for the binder, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery having an improved positive electrode.

[0002]

2. Description of the Related Art A paste-type positive electrode used in a nickel-metal hydride secondary battery is prepared by kneading, for example, nickel hydroxide powder as an active material, a conductive material and a binder in the presence of water to prepare a paste. Is filled in a conductive substrate, dried, and roll-pressed if necessary. Further, the paste type negative electrode used in the secondary battery is prepared, for example, by kneading a hydrogen storage alloy and a binder in the presence of water to prepare a paste, filling the paste into a conductive substrate, drying, and then drying. It is produced by performing a roll press according to.

Conventionally, the conductive substrate is a two-dimensional substrate such as an expanded metal or a perforated steel sheet (a punched metal sheet), a fibrous metal porous body (non-plated type) by chattering vibration, and a plated type. A three-dimensional substrate such as a sponge-like porous metal body or a felt-like porous metal body is used.

By the way, in order to make a secondary battery of higher capacity, it is necessary to reduce the basis weight of the substrate by using a two-dimensional substrate as the conductive substrate.

[0005]

However, the positive electrode including the two-dimensional substrate as the conductive substrate has a problem that the current collection efficiency between the active material and the conductive substrate is inferior.

In view of the above, it has been considered to mix short fibers made of nickel or the like into the paste of the positive electrode. However, the current collection efficiency of such a positive electrode was still insufficient. When a separator (for example, a nonwoven fabric made of synthetic resin) is interposed between the positive electrode and the negative electrode and spirally wound to form an electrode group, the short fibers included in the positive electrode break through the separator and the negative electrode And short-circuiting may occur.

The present invention can improve the current collection efficiency of a positive electrode using a two-dimensional substrate as a conductive substrate,
An object of the present invention is to provide a high capacity, long life alkaline secondary battery capable of preventing internal short circuit.

[0008]

The alkaline secondary battery according to the present invention comprises an active material, a conductive flake powder having a length of 10 to 30 μm and a thickness of 0.5 to 3.0 μm. Wherein the mixture comprises a positive electrode supported on a conductive substrate having a two-dimensional structure.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an alkaline secondary battery of the present invention will be described with reference to FIG.

An electrode group 5 produced by laminating a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral is accommodated in a cylindrical container 1 having a bottom. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is supplied in the container 1
Housed within. A circular first sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 1. The ring-shaped insulating gasket 8 is disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is formed on the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is hermetically fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is provided on the sealing plate 7 with the hole 6.
It is attached to cover. Rubber safety valve 11
Is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 with a protrusion of the positive electrode terminal 10.
Are arranged to protrude from the holes. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described.

1) Positive electrode 2 The positive electrode 2 has an active material composed of nickel hydroxide powder and a conductive agent, and has a length of 10 to 30 μm and a thickness of 0.5 to 30 μm.
It has a structure in which a mixture containing conductive flake powder having a thickness of 3.0 μm is supported on a conductive substrate having a two-dimensional structure.

The positive electrode 2 is prepared, for example, by preparing a paste containing nickel hydroxide powder, a conductive agent, the flake powder, a binder, and water, filling or applying the paste to a conductive substrate, and drying the paste. It is manufactured by press molding.

As the nickel hydroxide powder, for example, a single nickel hydroxide powder or a nickel hydroxide powder in which zinc and / or cobalt are eutectic can be used. The latter positive electrode containing nickel hydroxide powder can improve charging efficiency and cycle characteristics in a high temperature state.

The average particle size of the nickel hydroxide powder is 5
It is preferable to set the range to 30 μm.

Examples of the conductive agent include cobalt compounds such as cobalt monoxide, dicobalt trioxide and cobalt hydroxide.

The flake powder has, for example, a structure as shown in FIG. The flaky powder 14 is
A thin plate having a shape of a circle, an ellipse, or a shape similar thereto has a curved shape.

The thickness of the flake powder is limited to the above range for the following reason. When the thickness is less than 0.5 μm, the flake-like powder is broken at the time of pressure molding, and it is difficult to improve the contact area. On the other hand, if the thickness exceeds 3.0 μm, the flake-like powder is less likely to be deformed during pressure molding in the positive electrode preparation step, and the contact area with the active material is reduced, so that the current collection efficiency is reduced. A more preferable range of the thickness is 1.0 to 2.5 μm.
m.

The length of the flake powder is limited to the above range for the following reason. If the length is less than 10 μm, it is difficult to increase the contact point and the contact area between the active material and the flake powder, so that the current collection efficiency of the positive electrode cannot be improved. On the other hand, if the length exceeds 30 μm, workability during paste preparation may be significantly impaired. A more preferable range of the length is 15 to 25 μm.

The flake powder can be formed of, for example, nickel or a nickel alloy.

The flake powder preferably has a dynamics hardness (DH) of 150 to 400. This is due to the following reasons. If the dynamics hardness (DH) exceeds 400, the flake-like powder is less likely to be deformed during the pressure molding in the positive electrode preparation step, so that the contact area between the active material and the flake-like powder is reduced, and the current collection of the positive electrode is performed. Efficiency may be reduced. On the other hand, if the dynamics hardness (DH) is less than 150, the flake powder is crushed at the time of pressure molding, and it may be difficult to improve the contact area between the active material and the flake powder. The dynamics hardness (D
A more preferred range for H) is from 200 to 350.

The flake powder can be produced, for example, by rolling particles made of nickel or a nickel alloy by a ball mill and, if necessary, heat-treating the particles in a reducing atmosphere. By performing the heat treatment, the hardness of the flaky powder can be reduced, and the contact points and the contact area between the flaky powder and the active material can be improved.

The amount of the flake powder is preferably in the range of 2.0 to 13.0% by weight based on the active material (comprising nickel hydroxide powder and conductive agent). This is due to the following reasons. If the amount is less than 2.0% by weight, it may be difficult to improve the current collection efficiency of the positive electrode. On the other hand, if the amount exceeds 13.0% by weight, the amount (absolute capacity) of nickel hydroxide may decrease, and the production cost may increase. A more preferable range of the compounding amount is 5.0 to 10.0% by weight.

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

As the conductive substrate having the two-dimensional structure, for example, an expanded metal, a perforated steel plate, a two-dimensional substrate having a large number of holes obtained by forming a metal powder by a powder rolling method, or the like is used. be able to. Above all,
It is preferable to use a two-dimensional substrate formed through the powder rolling method.

Hereinafter, the two-dimensional substrate will be described.

The two-dimensional substrate is made of, for example, nickel. It is preferable that the thickness of the two-dimensional substrate is 60 μm or less. When the thickness of the two-dimensional substrate exceeds 60 μm, the volume of the conductive substrate increases, the filling rate of the paste decreases, and as a result, the capacity of the paste-type positive electrode having the conductive substrate can be improved. It can be difficult.
More preferably, the thickness of the two-dimensional substrate is 10 to 50 μm.
It is.

The aperture ratio of the two-dimensional substrate is 30-80%
Is preferable.

The hole of the two-dimensional substrate is not limited to a circular shape.
Any shape such as a rectangular shape and an elliptical shape is possible.

The above-described two-dimensional substrate is manufactured, for example, by the following method.

First, metal powder (for example, nickel powder)
Is supplied from a hopper onto a belt conveyor made of a material having high rigidity, and passes through a doctor blade arranged in the conveying direction of the belt conveyor to form a metal powder layer having a desired thickness on the belt conveyor. Subsequently, the metal powder layer on the belt conveyor is pressed at a desired pressure by an embossing roll having a large number of projections arranged on the upper side with the mating roll arranged on the lower side with the belt conveyor interposed therebetween, and the embossing roll is pressed onto the embossing. A dust sheet having a large number of holes opened at corresponding locations is produced. In this step, when the opening of the through hole to the dust sheet is not sufficiently made, a surfactant having high fluidity is added by adding a surfactant together with water to the nickel powder, or the embossed shape of the embossing roll is changed. Or other measures may be adopted. Subsequently, the compacted sheet is conveyed together with the belt conveyor to a firing furnace, where the compacted sheet is sintered to form a sintered metal sheet having a thickness of 60 μm or less, in which a large number of holes are opened, that is, a two-dimensional substrate. Is prepared.

Preferably, the nickel powder has an average particle size of 2 μm or less.

Preferably, the two-dimensional substrate has an uneven surface.

The average height of the irregularities is preferably in the range of 10 to 50 μm. This is due to the following reasons. When the height is less than 10 μm, it may be difficult to improve the positive electrode utilization factor and the discharge voltage by improving the adhesion to the mixture containing the nickel hydroxide powder. On the other hand, if the height exceeds 50 μm, the unevenness of the surface itself becomes like a burr, which breaks through the separator at the time of winding and comes into contact with the counter electrode, which may cause a short circuit. A more preferable range of the height (average) is 20 to 40 μm
It is.

The average interval between the irregularities is preferably in the range of 5 to 100 μm. This is due to the following reasons. If the distance is less than 5 μm, the contact area between the nickel hydroxide powder and the substrate becomes insufficient, so that it may be difficult to improve the positive electrode utilization rate and the discharge voltage. On the other hand, if the distance exceeds 100 μm, it may be difficult to improve the adhesion to the mixture.
A more preferable range of the interval (average) is 20 to 80 μm.
m.

The unevenness of the two-dimensional substrate can be formed by roughening. Specifically, after forming a layer composed of a conductive powder and a binder on the surface of the two-dimensional substrate,
By performing a heat treatment in an inert gas atmosphere to thermally decompose and remove the binder, irregularities can be formed on the surface of the two-dimensional substrate.

[0037] Examples of the conductive powder include nickel powder.

The conductive powder has an average particle size of 10 to 30.
It is preferable to set it in the range of μm. This is due to the following reasons. If the average particle size is less than 10 μm, the unevenness on the surface of the two-dimensional substrate is reduced, so that it may be difficult to improve the adhesiveness with the mixture to improve the positive electrode utilization rate and the discharge voltage. On the other hand, if the average particle size exceeds 30 μm, it may be difficult to control the average height and the interval of the irregularities. In addition, a short circuit may be caused when the spiral electrode group is manufactured, and productivity may be impaired. A more preferred range of the average particle size is 20 to
30 μm.

As the binder, a thermoplastic resin such as polyethylene, polypropylene, and polystyrene can be used.

2) Negative Electrode 4 The negative electrode 4 includes a conductive substrate and a negative electrode layer held on the substrate and containing a hydrogen storage alloy.

The negative electrode 4 is kneaded with a hydrogen storage alloy powder, a conductive material, a binder and water to prepare a paste,
The paste is filled in a conductive substrate, dried, and then molded.

The hydrogen storage alloy is not particularly limited, and may be any alloy that can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ , MmNi
₅ (Mm is misch metal), LmNi ₅ (Lm is La
At least one element selected from the group consisting of rare earth elements containing Al), Mn, Co, Ti, Cu,
Examples thereof include a multi-element-based material substituted with an element such as Zn, Zr, Cr, and B, a TiNi-based material, and a TiFe-based material. In particular, the general formula LmNi _w Co _x Mn _y A
l _z (the total value of the atomic ratios w, x, y, z is 5.00 ≦ w +
(x + y + z ≦ 5.50) The hydrogen storage alloy having the composition represented by the formula (1) is preferable because it suppresses the pulverization accompanying the progress of the charge / discharge cycle and can improve the charge / discharge cycle life.

Examples of the conductive material include carbon black and graphite.

Examples of the binder include polyacrylates such as sodium polyacrylate and potassium polyacrylate, fluorine resins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (C).
MC) and the like.

As the conductive substrate, for example, an expanded metal, a perforated steel plate, a two-dimensional substrate similar to that described for the positive electrode, or the like can be used.

As the binder, the same binder as described for the positive electrode can be used.

3) Separator 3 Examples of the separator 3 include a nonwoven fabric made of a polyamide fiber and a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group.

4) Alkaline Electrolyte This alkaline electrolyte has a composition in which potassium hydroxide (KOH) is used alone, or one or both of sodium hydroxide (NaOH) and lithium hydroxide (LiOH) are added thereto. .

The above-described alkaline secondary battery according to the present invention comprises an active material and a conductive flake powder having a length of 10 to 30 μm and a thickness of 0.5 to 3.0 μm. The agent includes a positive electrode supported on a conductive substrate having a two-dimensional structure. According to such a secondary battery, the flake-like powder can be uniformly present between the active materials of the positive electrode (particularly, nickel hydroxide powder), so that the contact area between the nickel hydroxide powder and the flake-like powder can be particularly reduced. It is possible to form a conductive net by the contact between the flake-like powders. As a result, conduction between the active material and conduction between the active material and the conductive substrate can be improved,
The current collection efficiency of the positive electrode can be improved. In addition, by using a conductive substrate having a two-dimensional structure, the volume ratio of the substrate in the positive electrode can be reduced, so that the mixture filling amount can be increased and the filling density of the active material can be reduced. Can be improved. Therefore, the secondary battery can suppress a decrease in the discharge voltage due to the progress of the charge / discharge cycle, and can improve the positive electrode utilization rate, the discharge capacity, the cycle life, and the like.

In the secondary battery, the flake powder is mixed with the active material in the positive electrode mixture in an amount of 2.0 to 2.0%.
By adding 13.0% by weight, the current collection efficiency of the positive electrode can be improved without lowering the absolute capacity of the positive electrode, so that the positive electrode utilization rate, the discharge capacity, and the cycle life can be further increased.

Further, the thickness of the conductive substrate is reduced by using a two-dimensional substrate having a large number of holes and having a thickness of 60 μm or less, which is obtained by molding a metal powder by a powder rolling method. Warpage and burrs can be avoided. As a result, the filling amount of the mixture can be improved, so that the capacity and life of the secondary battery can be further improved. Further, according to this two-dimensional substrate, an internal short circuit can be prevented when the electrode group is manufactured by spirally winding a separator between the positive electrode and the negative electrode. Further, the spirally wound electrode group thus obtained has excellent adhesion to the positive and negative electrodes and has few voids, so that the spirally wound electrode group can be housed at a high density in a bottomed cylindrical container. Can be further increased in capacity.

Further, by forming irregularities on the surface of the two-dimensional substrate obtained by the powder rolling method and filling or applying the positive electrode paste to the substrate, it is possible to improve the adhesion between the paste and the substrate. As a result, the paste can be prevented from peeling from the substrate, and the contact area between the paste and the substrate can be increased. As a result, the positive electrode having the conductive substrate,
Since the current collection efficiency can be improved, the alkaline secondary battery including such a positive electrode can further improve the positive electrode utilization rate, the capacity, and the charge / discharge cycle life.

The height of the irregularities on the surface of the two-dimensional substrate obtained by the powder rolling method is set to 10 to 50 μm, and the interval is set to 5 to 100 μm. Can be improved, so that the paste can be prevented from peeling off from the conductive substrate at the time of rolling and during the charge / discharge cycle. At the same time, the contact area between the nickel hydroxide powder and the substrate can be increased, so that the current collection efficiency of the positive electrode can be improved, and the nickel hydroxide utilization rate can be improved. Therefore, the alkaline secondary battery including the positive electrode can have an improved charge / discharge cycle life.

In FIG. 1, the positive electrode and the negative electrode are spirally wound with a separator interposed therebetween, and the obtained electrode group is housed in a bottomed cylindrical container.
The positive electrode and the negative electrode may be alternately laminated with a separator interposed therebetween, and the resulting laminated electrode may be housed in a bottomed rectangular cylindrical container.

[0055]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Paste Type Positive Electrode> 90 parts by weight of nickel hydroxide powder having an average particle diameter of 10 μm and 10 parts by weight of cobalt monoxide powder
A mixed powder (active material) consisting of 0.5 parts by weight of carboxymethylcellulose and a suspension of polytetrafluoroethylene (specific gravity: 1.
5, 60 parts by weight of solid content) in an amount of 3.0 parts by weight in terms of solid content, and after adding 45 parts by weight of pure water thereto and kneading,
A flake-like nickel powder having a thickness of 1 μm, a length of 10 μm, and a dynamics hardness (DH) of 200 is blended in an amount of 5% by weight based on the active material (which is not in a wet state before preparing the paste). A paste was prepared by further kneading.

On the other hand, nickel powder having an average particle size of 0.5 μm is supplied from a hopper onto a belt conveyor made of a material having high rigidity, and passed through a doctor blade arranged in the conveying direction of the belt conveyor, so as to be placed on the belt conveyor. A nickel powder layer having a desired thickness was formed. Subsequently, the metal powder layer on the belt conveyor is pressed at a desired pressure by an embossing roll having a large number of projections arranged on the upper side with the mating roll arranged on the lower side with the belt conveyor interposed therebetween, and the embossing roll is pressed onto the embossing. A dust sheet having a large number of holes opened at corresponding locations was prepared. Subsequently, the compacted sheet is conveyed to a firing furnace together with the belt conveyor, and the compacted sheet is sintered in an argon gas atmosphere at 1000 ° C. to form a sintered nickel sheet having a large number of holes, that is, A two-dimensional substrate was obtained. This two-dimensional substrate
The thickness was 40 μm, the hole diameter was 1.8 mm, the center-to-center pitch was 2.5 mm, and the aperture ratio was 60%.

Subsequently, after filling the paste into the two-dimensional substrate, the paste was dried and subjected to roller pressing to produce a paste-type positive electrode. The thickness of the flake powder was measured using Fisher's Sub-Sive Sizer air, and the length was measured using an average particle size measuring device of Shimadzu Laser SALD 1000. The value used was a 50% value. .

<Preparation of Paste Type Negative Electrode> A commercially available lanthanum-enriched misch metal Lm and Ni, Co, Mn,
LmNi _4.0 Co _0.4
A hydrogen storage alloy having a composition of Mn _0.3 Al _0.3 was produced. The hydrogen storage alloy was mechanically pulverized and passed through a 200-mesh sieve. 0.5 parts by weight of sodium polyacrylate with respect to 100 parts by weight of the obtained alloy powder,
0.125 parts by weight of carboxymethylcellulose (CMC) and a dispersion of polytetrafluoroethylene (specific gravity: 1.5, solid content: 60 wt%) were converted to a solid content of 1.
A paste was prepared by mixing 5 parts by weight and 1.0 part by weight of carbon powder as a conductive material with 50 parts by weight of water. Apply this paste to punching metal,
After filling, the paste-type negative electrode was manufactured by drying and pressing.

A separator made of a nonwoven fabric made of a polyolefin fiber subjected to a hydrophilic treatment was interposed between the obtained positive electrode and the negative electrode, and spirally wound to form an electrode group. Such an electrode group and an electrolytic solution composed of 7N KOH and 1N LiOH are housed in a bottomed cylindrical container, and the AA-type cylindrical nickel-hydrogen secondary battery having a theoretical capacity of 1200 mAh and having a structure shown in FIG. The battery was assembled.

(Example 2) A cylindrical nickel-metal hydride secondary battery similar to that of Example 1 was assembled except that the length of the flake powder of the positive electrode was set to 20 µm.

(Example 3) A cylindrical nickel-metal hydride secondary battery similar to that of Example 1 was assembled except that the length of the flake powder of the positive electrode was set to 30 µm.

Comparative Example 1 A cylindrical nickel-metal hydride secondary battery similar to that of Example 1 was assembled except that the length of the flake-like powder of the positive electrode was set to 5 μm.

Comparative Example 2 A cylindrical nickel-metal hydride secondary battery similar to that of Example 1 was assembled except that the length of the flake powder of the positive electrode was set to 40 μm.

With respect to the obtained secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, charging and discharging at 1 C and -ΔV and discharging at 1 C and 1 V were repeatedly performed. The capacity per unit volume of the positive electrode (mAh / c
c) was calculated and the result is shown in FIG.

For the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, the number of leaks was measured when 250 spiral electrode groups were produced, and the results are shown in Table 1 below.

Table 1 Length of flake-like powder Number of leaks (out of 250) Example 1 10 μm 0 Example 2 20 μm 0 Example 3 30 μm 0 Comparative Example 1 5 μm 1 Comparative Example 2 40 μm 3 It is clear from FIG. As such, the thickness is 0.5-3.0 μm
In addition, the secondary batteries of Examples 1 to 3 including the positive electrode including the flake-like powder having a length of 10 to 30 μm have a capacity per unit volume of the positive electrode of 600 to 700 mAh / cc, which is smaller than Comparative Examples 1 and 2. You can see that it is high.

As is clear from Table 1, Examples 1 to 3
It can be seen that the secondary battery has no internal short-circuit occurrence rate at the time of producing the spiral electrode group.

Comparative Example 3 A cylindrical nickel-hydrogen secondary battery was assembled in the same manner as in Example 1, except that the positive electrode described below was used.

A mixed powder (active material) consisting of 90 parts by weight of nickel hydroxide powder having an average particle diameter of 10 μm and 10 parts by weight of cobalt monoxide powder was mixed with 0.5 part by weight of carboxymethyl cellulose based on the nickel hydroxide powder. , Suspension of polytetrafluoroethylene (specific gravity 1.5, solid content 6
0% by weight) in terms of solid content, and after adding 45 parts by weight of pure water and kneading the mixture, the fiber diameter was 5 μm.
The paste was prepared by blending 5% by weight of a fibrous nickel powder having a length of 20 μm and a length of 20 μm with respect to the active material (which was not in a wet state before the preparation of the paste), followed by kneading. Subsequently, the paste was filled in a two-dimensional substrate similar to that described in Example 1, dried, and subjected to roller pressing to produce a paste-type positive electrode.

With respect to the obtained secondary battery of Comparative Example 3, the capacity per unit volume of the positive electrode and the leak occurrence rate at the time of manufacturing 250 electrode groups were measured in the same manner as described above. Shown in Table 2 also shows the results of Example 2 described above.

Table 2 Capacity per unit volume of positive electrode Number of leaks generated Example 2 700 (mAh / cc) 0 Comparative Example 3 610 (mAh / cc) 64 As is clear from Table 2, the thickness was 1 μm, Length 20
The secondary battery of Example 2 including the positive electrode including the conductive flake powder having a diameter of 5 μm has a fiber diameter of 5 μm and a length of 20 μm.
The capacity per unit volume of the positive electrode is higher than that of the secondary battery of Comparative Example 3 including the positive electrode including the conductive fibrous powder having a particle size of μm, and the number of leaks generated during the production of the spiral electrode group is negligible. I understand.

Example 4 A cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the positive electrode described below was used.

To a mixed powder (active material) consisting of 90 parts by weight of nickel hydroxide powder having an average particle size of 10 μm and 10 parts by weight of cobalt monoxide powder, 0.5 part by weight of carboxymethylcellulose with respect to the nickel hydroxide powder , Suspension of polytetrafluoroethylene (specific gravity 1.5, solid content 6
0% by weight) in terms of solid content, and 3.0 parts by weight of pure water, 45 parts by weight of pure water, and kneading.
A flake-like nickel powder having a length of 20 μm and a dynamics hardness (DH) of 200 was added in an amount of 1% by weight based on the active material (which was not in a wet state before preparing the paste).
A paste was prepared by mixing and kneading.
Subsequently, the paste was filled in a two-dimensional substrate similar to that described in Example 1, dried, and subjected to roller pressing to produce a paste-type positive electrode.

(Examples 5 to 9) In the secondary battery of Example 4,
2% by weight of flake-form nickel powder
%, 9%, 13% and 15% by weight to obtain the secondary batteries of Examples 5 to 9.

Comparative Example 4 A cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1, except that no flake-like nickel powder was added to the positive electrode.

With respect to the obtained secondary batteries of Examples 4 to 9 and Comparative Example 4, the capacity per unit volume of the positive electrode was measured in the same manner as described above, and the results are shown in FIG. FIG. 4 also shows the results of Example 2 described above.

As is clear from FIG. 4, the thickness is 1 μm.
In the secondary batteries of Examples 4 to 9 including the positive electrode including the flake-shaped powder having a length of 20 μm, the capacity per unit volume of the positive electrode was 600 to 700 mAh / cc, and the flake-shaped powder was not added. It can be seen that it is higher than the secondary battery of Comparative Example 3 including the positive electrode. Among them, the secondary batteries of Examples 2, 5 to 8 provided with the positive electrode in which the compounding amount of the flake-shaped nickel powder is 2 to 13% by weight, and the secondary batteries of Examples 2 to 8 provided with the positive electrode in which the compounding amount of the flake-shaped nickel powder is out of the above range. 4,
9 shows that the capacity per unit volume of the positive electrode is higher than that of the secondary battery of No. 9.

(Example 10) A cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the positive electrode described below was used.

A conductive paint was prepared by dispersing nickel powder having an average particle diameter of 20 μm and polystyrene fine powder in water. The two-dimensional substrate was coated by applying the coating material to the non-opening portion of the two-dimensional substrate similar to that described in Example 1, performing heat treatment in an inert gas atmosphere, and thermally decomposing and removing the polystyrene fine powder. Was roughened. The average height of the irregularities of the obtained two-dimensional substrate (based on the surface of the two-dimensional substrate before roughening) was 40 μm. Also,
The average interval between the irregularities was 80 μm.

Subsequently, a paste similar to that described in Example 2 was filled in the two-dimensional substrate, dried, and rolled by roller pressing to produce a paste-type positive electrode.

When the capacity per unit volume of the positive electrode of the obtained secondary battery of Example 10 was measured in the same manner as described above, it was 730 mAh / cc, which was higher than that of the secondary battery of Example 2.

[0083]

As described above in detail, according to the present invention, a positive electrode having improved current collection efficiency and utilization factor is provided, an internal short circuit is prevented when an electrode group is manufactured, and a high capacity, long life alkaline A secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an alkaline secondary battery according to the present invention.

FIG. 2 is a schematic view showing a conductive flake powder incorporated in a positive electrode of the secondary battery of FIG.

FIG. 3 is a characteristic diagram showing the relationship between the length of flake-like powder and the capacity per unit volume of a positive electrode in the nickel-metal hydride secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2.

FIG. 4 is a characteristic diagram showing the relationship between the blended amount of flake powder and the capacity per unit volume of the positive electrode in the nickel-metal hydride secondary batteries of Examples 2, 4 to 9 and Comparative Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 7 ... Sealing plate, 8 ... Insulating gasket.

Claims (2)

[Claims] 1. A mixture comprising an active material and a conductive flake powder having a length of 10 to 30 μm and a thickness of 0.5 to 3.0 μm comprises a conductive material having a two-dimensional structure. An alkaline secondary battery comprising a positive electrode supported on a substrate. 2. The alkaline secondary battery according to claim 1, wherein the flake powder is mixed in the mixture at 2.0 to 13.0% by weight based on the active material.