JPH11162468A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lengthen the charge/discharge cycle life by including a conductive binder in at least one electrode of a positive electrode and a negative electrode. SOLUTION: A negative electrode 4 is prepared by kneading a negative active material comprising a hydrogen storage alloy, a conductive material, and a conductive binder with water, filling the kneaded mixture in a conductive substrate, and drying them. As the conductive binder, 0.3-3.0 pts.wt. water soluble sulphonated polyaniline is mixed to 100 pts.wt. hydrogen storage alloy to prevent the coming off of the negative active material and drop in discharge capacity. A positive electrode 2 is prepared in such a way that metal hydroxide powder such as nickel hydroxide, a conductive material such as cobalt hydroxide, and a binder are kneaded with water, the kneaded mixture is filled in a current collector of a conductive substrate, dried, then they are rolled. As the binder, the use of a conductive binder like the negative electrode is preferable. The active material is firmly held in the current collector, current collecting efficiency is enhanced, battery capacity is ensured, and cycle life is lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery in which a binder contained in a positive electrode or a negative electrode is improved.

[0002]

2. Description of the Related Art A negative electrode of a nickel-metal hydride secondary battery, which is an example of an alkaline secondary battery, includes, for example, a hydrogen storage alloy powder, a conductive agent (for example, carbon fine powder), and a binder (for example, polytetrafluoroethylene (for example, polytetrafluoroethylene)). PTFE) or a rubber-based binder, sodium polyacrylate and carboxymethylcellulose) and water are kneaded to prepare a paste, and the paste is filled in a current collector (for example, punched metal) and dried. , By rolling.

[0003] Polytetrafluoroethylene and rubber-based binders used in the binder have excellent binding properties, so that when the hydrogen storage alloy is pulverized as the charge-discharge cycle progresses, the alloy becomes a negative electrode. Can be prevented from falling off.

[0004]

However, since the above-mentioned polytetrafluoroethylene and the rubber-based binder are insulating materials, they become a factor that hinders the current collection efficiency of the negative electrode. Therefore, when these are used as a binder,
There is a problem that polarization at the time of charging / discharging becomes large and the original capacity of the battery cannot be obtained. In addition, since the electrochemical reaction at the time of charging and discharging at the negative electrode occurs unevenly, oxygen gas generated from the positive electrode at the time of charging cannot be absorbed by the negative electrode, and the internal pressure tends to increase. For this reason, there is a risk of liquid leakage. An object of the present invention is to provide an alkaline secondary battery having a battery's original discharge capacity and improved cycle life.

[0005]

The alkaline secondary battery according to the present invention comprises a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode contains a conductive binder. It is a feature.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an alkaline secondary battery (cylindrical alkaline secondary battery) according to the present invention will be described below with reference to FIG. An electrode group 5 produced by winding a positive electrode 2 and a negative electrode 4 with a separator 3 interposed therebetween is accommodated in a bottomed cylindrical container 1. 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 contained in the container 1. 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
Is arranged between the periphery of the container and the inner surface of the upper opening of the container 1,
The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking to reduce the diameter of the upper opening inward. 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 attached on the sealing plate 7 so as to cover the hole 6. Rubber safety valve 1
1 is arranged 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 so that a protrusion of the positive electrode terminal 10 is provided on the holding plate 1.
2 so as 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.

Hereinafter, the negative electrode 4, the positive electrode 2, the separator 3
And an alkaline electrolyte. 1) Negative Electrode 4 The negative electrode 4 includes a negative electrode active material and a conductive binder.

The negative electrode 4 is prepared, for example, by kneading a negative electrode active material, a conductive agent and a conductive binder together with water to prepare a paste, filling the paste into a conductive substrate, drying, and then forming the paste. It is manufactured by

Examples of the negative electrode active material include cadmium compounds such as metal cadmium and cadmium hydroxide, and hydrogen. Examples of the host matrix of hydrogen include a hydrogen storage alloy.

[0010] Above all, the hydrogen storage alloy is preferable because the capacity of the storage battery can be improved as compared with the case where the cadmium compound is used. The hydrogen storage alloy is not particularly limited, and may be any as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ , MmN
i ₅ (Mm is misch metal), LmNi ₅ (Lm is L
at least one selected from rare earth elements including a), and a part of Ni of these alloys is Al, Mn, Co, Ti, C
Examples thereof include a multi-element-based material substituted with an element such as u, Zn, Zr, Cr, and B, or a TiNi-based or TiFe-based material. In particular, the general formula LmNi _w Co _x Mn
_y Al _z (the total value of atomic ratios w, x, y, and z is 5.00 ≦
(W + x + y + z ≦ 5.50) The hydrogen storage alloy having the composition represented by the formula (1) is suitable because it can suppress the pulverization accompanying the progress of the charge / discharge cycle and improve the charge / discharge cycle life.

The conductive binder is preferably water-soluble from the viewpoint of improving the stability of the paste. Examples of such a binder include sulfonated polyaniline, polypyrrole, polyacene, and polyphenylene.

It is preferable that the amount of the conductive binder is in the range of 0.3 to 3.0 parts by weight based on 100 parts by weight of the negative electrode alloy. This is due to the following reasons. When the blending amount is less than 0.3 parts by weight, the falling of the negative electrode active material, particularly when the hydrogen storage alloy is used, the falling of the alloy during the charge / discharge cycle becomes remarkable, and the cycle life may be reduced. . On the other hand, if the amount exceeds 3.0 parts by weight, the amount of the negative electrode active material may decrease, and the discharge capacity may decrease.

[0013] From the viewpoint of improving the stability of the paste, a water-soluble or hydrophilic binder may be used in combination with the negative electrode. Such binders include, for example, carboxymethyl cellulose (CMC), methyl cellulose (M
C), hydroxymethylcellulose (HPMC), polyacrylate (for example, sodium polyacrylate (S
PA)), polyvinyl alcohol (PVA), polyethylene oxide, a copolymer of a vinyl alcohol and a monomer having at least one COOX group (where X is 1 selected from hydrogen, alkali metal and alkaline earth metal).
One or more selected from polymers).

Examples of the conductive agent include carbon black, graphite, and conductive fibers. As the conductive fiber, for example, a nickel fiber, a carbon fiber having fine metal particles adhered to the surface, or the like can be used. Examples of the metal fine particles include those made of nickel and copper. In particular, by using conductive fibers as the conductive agent, the contact area between the conductive agent and the active material can be increased, so that the current collection efficiency of the negative electrode can be significantly improved.

The average fiber diameter of the conductive fibers is 0.1 to
It is preferable that the thickness be in the range of 4.0 μm. The average fiber length of the conductive fibers is preferably in the range of 1 to 40 mm.

In the case where the conductive fiber is used as the conductive agent, the amount of the conductive fiber is adjusted according to the amount of the negative electrode alloy 100
It is preferable that the amount be in the range of 0.1 parts by weight to 3.0 parts by weight based on parts by weight. By setting the amount of the conductive fiber in such a range, the discharge capacity and the cycle life can be further improved.

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

2) Positive Electrode 2 The positive electrode 2 has a structure in which a mixture containing a metal oxide is supported on a current collector. The positive electrode is prepared, for example, by kneading a metal oxide powder, a conductive agent and a binder in the presence of water to prepare a paste, filling the paste into a current collector, drying, and rolling. It is manufactured by

Examples of the metal oxide include nickel hydroxide. As the conductive agent,
For example, there may be mentioned cobalt compounds such as cobalt hydroxide, cobalt monoxide, dicobalt trioxide and metallic cobalt.

Examples of the binder include a fluorine resin (for example, polytetrafluoroethylene), the above-mentioned water-soluble or hydrophilic binder, and the above-mentioned conductive binder.

Examples of the current collector include a net-like, sponge-like, fibrous, and felt-like conductive substrate made of an alkali-resistant material such as nickel, stainless steel, and nickel-plated resin.

3) Separator The separator can be formed, for example, from a nonwoven fabric made of polyolefin fiber or nylon fiber, a woven fabric made of the same fiber, or a composite sheet made of the nonwoven fabric and the woven fabric. When the separator is composed of polyolefin fibers, it is preferable to perform a hydrophilic treatment. As the hydrophilic treatment, for example, application of a surfactant, graft copolymerization of a vinyl monomer having a hydrophilic group, or the like can be employed.

4) Alkaline Electrolyte Examples of the alkaline electrolyte include a mixture of potassium hydroxide, sodium hydroxide and lithium hydroxide, a mixture of potassium hydroxide and lithium hydroxide, and a mixture of sodium hydroxide and lithium hydroxide. And the like.

In FIG. 1 described above, the positive electrode and the negative electrode are spirally wound with a separator interposed therebetween to produce an electrode group, and the electrode group is housed in a bottomed cylindrical container. Alternatively, a positive electrode and a negative electrode may be alternately stacked with a separator interposed therebetween to form an electrode group, and the electrode group may be housed in a bottomed rectangular cylindrical container.

As described in detail above, according to the alkaline secondary battery of the present invention, either the positive electrode, the negative electrode, or both electrodes contain a conductive binder. Such an electrode can improve current collection efficiency while firmly holding the active material on the current collector. As a result, the secondary battery
Sufficient battery capacity can be secured from the beginning, and cycle life can be improved.

Further, by using a sulfonated polyaniline as the conductive binder, it is possible to achieve a binding property equivalent to that of polytetrafluoroethylene and to achieve a paste that cannot be achieved by polytetrafluoroethylene. (2) The current collection efficiency of the electrode can be improved, so that the discharge capacity and cycle life of the secondary battery can be further improved.

When the negative electrode contains both the conductive binder and the conductive fibers, the current collection efficiency of the negative electrode can be greatly improved. As a result, the secondary battery can suppress the polarization at the time of charging and discharging, and thus can realize the original capacity. In addition, since the electrochemical reaction occurs uniformly in the negative electrode, the gas generated from the positive electrode during charging can be quickly absorbed by the negative electrode, and an increase in internal pressure during charging can be suppressed. Therefore, the charge / discharge cycle life can be improved.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail. Example 1 <Preparation of positive electrode> A mixture of 90 parts by weight of nickel hydroxide particles and 10 parts by weight of cobalt monoxide particles was mixed with 0.3 parts by weight of carboxymethyl cellulose as a binder and a dispersion of polytetrafluoroethylene (specific gravity: 1). (0.5 wt.%, 60 wt%) in terms of solid content, and 0.5 part by weight of solid content, and further 45 parts by weight of water were added and kneaded to prepare a paste. This paste was filled in a nickel-plated fiber substrate, and the paste was applied to both sides of the substrate, dried, and roller-pressed to produce a paste-type nickel positive electrode. <Preparation of Negative Electrode> LmNi _4.35 Co _0.40 Mn _0.29 Al _0.30
(Where Lm is La-enriched misch metal) 100 parts by weight of the hydrogen storage alloy powder having the composition of 0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethylcellulose, 1.0 part by weight of sulfonated polyaniline
0 parts by weight, 1.00 parts by weight of carbon powder and 50 parts by weight of water were added to prepare a paste. Thereafter, the paste was applied to punched metal, dried, and molded to produce a paste-type hydrogen storage alloy negative electrode. <Preparation of Electrode Group> A nonwoven fabric made of polyolefin subjected to a hydrophilic treatment was prepared as a separator. The above-described positive electrode and negative electrode were spirally wound while the separator was interposed therebetween, thereby producing a spiral electrode group. <Assembly of battery> After the electrode group is housed in a bottomed cylindrical metal container, an alkaline electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide is housed in the container, and a metal cover, etc. A cylindrical nickel-metal hydride secondary battery having a size of 4 / 3A and a nominal capacity of 3000 mAh was assembled using the above members.

Comparative Example 1 <Preparation of Negative Electrode> LmNi _4.35 Co _0.40 Mn _0.29 Al _0.30
100 parts by weight of a hydrogen storage alloy powder having the following composition: 0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethylcellulose, a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60 wt.
%) In terms of solid content, and 1.00 part by weight of carbon powder.
A paste was prepared by adding 00 parts by weight and 50 parts by weight of water. Then, apply the paste to the punched metal,
The paste-type hydrogen storage alloy negative electrode was manufactured by drying and molding.

A cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the obtained negative electrode was used.
Regarding the obtained secondary batteries of Example 1 and Comparative Example 1, 3
After charging to 120% of the nominal capacity at the current value of A, 3A
The charge / discharge cycle of discharging until the discharge potential becomes 1 V at the current value of 1 is repeated, and the number of cycles until the battery capacity becomes 80% of the nominal capacity is obtained. The results are shown in Table 1 below.
Table 1 also shows the initial capacity of the battery and the potential at the time of discharging.

[0031]

[Table 1]

As is clear from Table 1, the secondary battery of Example 1 provided with the negative electrode containing sulfonated polyaniline as the conductive binder was the same as that of Comparative Example 1 provided with the negative electrode containing no binder. It can be seen that the initial capacity, discharge potential and cycle life can be improved as compared with the secondary battery.

Example 2 <Preparation of Negative Electrode> LmNi _4.35 Co _0.40 Mn _0.29 Al _0.30
100 parts by weight of a hydrogen storage alloy powder having the following composition: 0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethylcellulose, 1.00 parts by weight of sulfonated polyaniline, an average fiber length of 10 mm, and an average fiber diameter 1.00 part by weight of nickel fiber having a particle size of 1.0 μm and water 50
The paste was prepared by adding parts by weight. Thereafter, the paste was applied to punched metal, dried, and molded to produce a paste-type hydrogen storage alloy negative electrode.

A cylindrical nickel-hydrogen secondary battery similar to that of Example 1 was assembled except that the obtained negative electrode was used. Example 3 0.5 part by weight of sodium polyacrylate and 0.5 part by weight of carboxymethyl cellulose were added to 100 parts by weight of a hydrogen storage alloy powder having a composition of LmNi _4.35 Co _0.40 Mn _0.29 Al _0.30 .
12 parts by weight, 1.00 parts by weight of sulfonated polyaniline,
A paste was prepared by adding 1.00 part by weight of carbon fiber whose surface was coated with nickel fine particles and 50 parts by weight of water. Thereafter, the paste was applied to punched metal, dried, and molded to produce a paste-type hydrogen storage alloy negative electrode. The carbon fiber has an average fiber length of 10 m.
m, the average fiber diameter was 1.0 μm, and the thickness of the nickel fine particle layer was 0.1 μm.

A cylindrical nickel-metal hydride secondary battery similar to that of Example 1 was assembled except that the obtained negative electrode was used. Comparative Example 2 <Preparation of Negative Electrode> LmNi _4.35 Co _0.40 Mn _0.29 Al _0.30
100 parts by weight of a hydrogen storage alloy powder having the composition of 0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethyl cellulose, and 1.00 parts by weight of a dispersion of polytetrafluoroethylene in terms of solid content.
A paste was prepared by adding 1.00 part by weight of nickel fiber having an average fiber length of 10 mm and an average fiber diameter of 1.0 μm and 50 parts by weight of water. Thereafter, the paste was applied to punched metal, dried, and molded to produce a paste-type hydrogen storage alloy negative electrode.

A cylindrical nickel-metal hydride secondary battery similar to that of Example 1 was assembled except that the obtained negative electrode was used.
The charge and discharge cycle of charging the obtained secondary batteries of Examples 2 to 3 and Comparative Example 2 at a current value of 3 A to 120% of the nominal capacity and then discharging at a current value of 3 A until the discharge potential becomes 1 V Is repeated until the battery capacity reaches 80% of the nominal capacity.
%, And the result is shown in Table 2 below.
Shown in Table 2 also shows the initial capacity of the battery and the potential at the time of discharging.

[0037]

[Table 2]

As is clear from Table 2, the secondary batteries of Examples 2 and 3 provided with the negative electrode using both the conductive binder and the conductive fiber did not contain the conductive binder, It can be seen that the initial capacity, discharge potential, and charge / discharge cycle life can be significantly improved as compared with the secondary battery of Comparative Example 2 including the negative electrode containing only the conductive fiber.

[0039]

As described in detail above, according to the alkaline secondary battery of the present invention, a remarkable effect such as realization of the original capacity of the battery and improvement of the cycle life can be obtained.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate.

Claims (2)

[Claims] 1. An alkaline secondary battery comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode contains a conductive binder. 2. The method according to claim 1, wherein the negative electrode includes a conductive binder and a conductive fiber.