JPH11297325A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the release of powder, such as an active material from a substrate, and to apply proper flexibility by containing a binder constituted of a copolymer of a monomer having a vinyl alcohol-COOX group and hydroxypropyl methyl cellulose in at least one of a positive electrode and a negative electrode. SOLUTION: A binder constituted of a copolymer of a monomer having the vinyl alcohol-COOX group (X is hydrogen, alkaline metal), and hydroxypropyl methyl cellulose is contained in at least one of a positive electrode and a negative electrode. A paste containing nickel hydroxide powder and an aqueous solution (with a concentration of 0.1-5 wt.% with respect to nickel hydroxide powder of 90 wt.%)) of a copolymer of a monomer, which has the vinyl alcohol-COOX group and hydroxypropyle methyl cellulose is filled in a conduvtive substrate to manufacture the positive electrode for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an alkaline secondary battery.

[0002]

2. Description of the Related Art Paste type electrodes are used for positive electrodes and negative electrodes of alkaline secondary batteries and lithium ion secondary batteries. For example, a paste-type nickel positive electrode is usually manufactured as follows. First, a conductive agent such as a nickel powder or a cobalt compound powder and a binder are added to nickel hydroxide powder as an active material, and the mixture is stirred to prepare a thixotropic active material paste. The paste is filled in a three-dimensional porous substrate such as a foam metal or a felt metal, dried, cut, and rolled to obtain the paste-type nickel positive electrode.

Examples of the binder include water-soluble cellulose derivatives such as methylcellulose, carboxymethylcellulose and polyvinyl alcohol, and rubbers such as EPDM (ethylene-propylene-diene terpolymer, SBR (styrene-butadiene rubber)). A binder or a copolymer of a monomer having a COOX group and vinyl alcohol (where X represents hydrogen, an alkali metal, or an alkaline earth metal) is used.

[0004]

However, a paste-type nickel positive electrode containing a water-soluble cellulose derivative or a rubber-based binder as a binder has a weak ability to capture the binder, so that the active material powder falls off the substrate. However, there is a problem that the charge / discharge characteristics such as a utilization rate and a charge / discharge cycle are lowered. In addition, if the powder is often dropped, the frequency of cleaning the equipment used in the rolling process and the punching becomes high, and thus the mass productivity is lacking.

On the other hand, when a paste-type nickel positive electrode is manufactured using a copolymer of a monomer having a COOX group and vinyl alcohol as a binder, the active material is firmly held on the substrate by the binder. Powder fall-off from the substrate is suppressed, and although a decrease in charge / discharge characteristics such as charge / discharge cycles is not seen, the separator is interposed between the positive electrode and the negative electrode because of low flexibility, and is spirally wound. There is a problem that an internal short circuit is likely to occur when an electrode group is manufactured.

[0006] The present invention provides an alkaline secondary battery having a high utilization factor and a long life, comprising a positive electrode and / or a negative electrode, in which powder of an active material or the like is prevented from falling off a substrate and having appropriate flexibility. What you want to do.

[0007]

According to the alkaline secondary battery of the present invention, at least one of the positive electrode and the negative electrode contains a copolymer of a vinyl alcohol-COOX group-containing monomer and hydroxypropyl methylcellulose. It is characterized by containing a binder.

[0008] An alkaline secondary battery according to the present invention comprises a positive electrode and a negative electrode, wherein the positive electrode comprises nickel hydroxide powder,
A copolymer of a monomer having a vinyl alcohol-COOX group (where X is at least one element selected from hydrogen, alkali metal and alkaline earth metal) and an aqueous solution of hydroxypropylmethylcellulose (the concentration of the aqueous solution is A paste containing 0.1 to 5% by weight with respect to 90% by weight of nickel oxide powder).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery according to the present invention will be described in detail with reference to FIG.

That is, an electrode group 5 produced by laminating the positive electrode 2, the separator 3, and the negative electrode 4 and winding them in a spiral shape is accommodated in the 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 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 with the sealing plate 7.
It is attached so as to cover the hole 6 above. A 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.
Circular holding plate 12 made of an insulating material having a hole in the center
Are arranged on the positive electrode terminal 10 such that the protrusions of the positive electrode terminal 10 protrude from the holes of the holding plate 12. The outer tube 13 is provided on the periphery of the holding plate 12,
The side surface of the container 1 and the periphery of the bottom of the container 1 are covered.

Hereinafter, the positive electrode 2, the negative electrode 4, the separator 3
And the alkaline electrolyte will be described in detail.

1) Positive Electrode 2 The positive electrode 2 has a structure in which a mixture containing nickel hydroxide powder and a binder as active materials is carried on a conductive substrate. The binder includes a copolymer of a monomer having a vinyl alcohol-COOX group (where X is at least one element selected from hydrogen, an alkali metal, and an alkaline earth metal), and hydroxypropyl methylcellulose. .

For the positive electrode, for example, a paste containing nickel hydroxide powder as a main component, a conductive agent, a binder and water is prepared, and the paste is filled in a conductive substrate, which is dried and pressed. It is produced by doing.

As the nickel hydroxide powder, for example, non-eutectic nickel hydroxide powder or nickel hydroxide powder in which zinc and / or cobalt are eutectic with metallic nickel can be used.

[0015] As the conductive agent, for example, at least one selected from cobalt and a cobalt compound can be used. Examples of the cobalt compound include cobalt monoxide, dicobalt trioxide, and cobalt hydroxide. The conductive agent can be added to the paste by attaching it as a layer to the surface of powder or nickel hydroxide powder.

The number of moles of the propyl group substituted in the hydroxypropyl methylcellulose is preferably 0.1 to 0.3. This is due to the following reasons. When the number of moles of substitution is less than 0.1, the flexibility of the positive electrode is reduced, and the internal short-circuit rate at the time of producing a spiral electrode group may be increased. On the other hand, when the number of moles of substitution exceeds 0.3, the viscosity of the paste increases, making it difficult for the paste to be filled in the substrate. A more preferred range of the number of moles of substitution is 0.15 to 0.25.

The average degree of polymerization of the hydroxypropyl methylcellulose is preferably from 4,000 to 30,000. This is due to the following reasons. If the average degree of polymerization is less than 4000, the flexibility of the positive electrode may be reduced, and the internal short-circuit rate when producing a spiral electrode group may be increased. On the other hand, when the average degree of polymerization exceeds 30,000, it becomes difficult to obtain a paste having a desired viscosity. A more preferable range of the average degree of polymerization is 8,000 to 15
000.

In the copolymer of a monomer having a COOX group and vinyl alcohol, the monomer having a COOX group includes, for example, acrylic acid, maleic acid, fumaric acid, acrylate, maleate, fumarate And the like. Among them, acrylic acid is preferred.

The hydroxypropyl methylcellulose and the copolymer are preferably added to the paste in the form of an aqueous solution. The concentration of the aqueous solution in which the hydroxypropyl methylcellulose and the copolymer are dissolved is preferably 0.1 to 5% by weight based on 90% by weight of the nickel hydroxide powder. This is due to the following reasons. When the concentration is less than 0.1% by weight,
The flexibility and strength of the positive electrode may be reduced, and winding defects such as an internal short circuit may increase during the production of the spiral electrode group, or the paste may peel off from the substrate. On the other hand, when the concentration is 5
If the content is more than 10% by weight, a film of the copolymer is formed on the surface of the nickel hydroxide powder or the like, which may cause a decrease in the utilization rate of the positive electrode. A more preferable range of the concentration is 0.5 to 3% by weight.

The binder may be carboxymethylcellulose (CMC) or methylcellulose (M) in addition to the hydroxypropylmethylcellulose and the copolymer.
Other cellulosic polymers such as C) may be included. The cellulose polymer is preferably added to the paste in the form of an aqueous solution.

The binder is preferably added to the paste in an amount of 20 to 25 parts by weight based on 90 parts by weight of the nickel hydroxide powder. This is due to the following reasons. If the amount of the binder is less than 20 parts by weight, the paste may flow downward by its own weight when the conductive substrate is filled with the paste, and the paste may be unevenly filled in the substrate. On the other hand, when the amount of the binder added is 25
If the amount exceeds the weight part, the amount of the active material contained in the paste decreases, and the fluidity of the paste decreases, so that the efficiency of filling the substrate may be reduced.

Examples of the conductive substrate include a net-like two-dimensional substrate made of a metal such as nickel and stainless steel, a nickel-plated resin, and the like, and a sponge-like, fiber-like, felt-like porous material made of the same material. A three-dimensional substrate having a porous structure, a composite substrate including the two-dimensional substrate and the three-dimensional substrate, and the like.

2) Negative Electrode 4 The negative electrode 4 has a structure in which a mixture containing a hydrogen storage alloy and a binder is supported on a conductive substrate.

For the negative electrode 4, for example, a paste is prepared by kneading a hydrogen storage alloy with a conductive agent, a binder and water.
The paste is manufactured by filling the paste into a conductive substrate, drying the paste, and then press-molding the paste.

Such a hydrogen storage alloy negative electrode is preferable because the capacity of the secondary battery can be improved as compared with the case where a cadmium negative electrode 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 , MmNi ₅
(Mm is a misch metal), LmNi ₅ (Lm is at least one selected from rare earth elements including La), and a part of Ni of these alloys is Al, Mn, Co, Ti, Cu,
Examples thereof include a multi-element-based material substituted with an element such as 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 the atomic ratios w, y, z is 5.00 ≦ w + x + y
+ Z ≦ 5.5) is preferable because the hydrogen storage alloy having the composition represented by the formula: can improve the charge / discharge cycle life.

Examples of the conductive agent include carbon black and graphite.

Examples of the binder include a cellulosic polymer such as carboxymethylcellulose (C
MC), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), polyacrylates (eg, sodium polyacrylate (SPA), potassium polyacrylate), polyvinyl alcohol (PVC)
A), polyethylene oxide, a copolymer of the above-described monomer having a COOX group and vinyl alcohol, a fluorine-based resin such as polytetrafluoroethylene (PTFE), and a rubber-based polymer such as polyethylene, polypropylene and latex. One type can be used.

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

When the binder for the positive electrode contains a copolymer of a monomer having a COOX group and vinyl alcohol and hydroxypropylmethylcellulose, it is necessary to use a binder free of these polymers as the binder for the negative electrode. Allow.

As the negative electrode, one containing a cadmium compound such as metal cadmium or cadmium hydroxide can be used in addition to the one containing a hydrogen storage alloy as described above.

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

4) Alkaline Electrolyte As the alkaline electrolyte, sodium hydroxide (Na)
OH), aqueous solution of lithium hydroxide (LiOH), aqueous solution of potassium hydroxide (KOH), NaOH and L
A mixed solution of iOH, a mixed solution of KOH and LiOH, a mixed solution of KOH, LiOH, and NaOH can be used.

As described in detail above, in the alkaline secondary battery according to the present invention, at least one of the positive electrode and the negative electrode contains a vinyl alcohol-COOX group-containing monomer copolymer and hydroxypropyl methylcellulose. It is characterized by containing a binder. In the hydroxypropyl methylcellulose, a part of the cellulose is substituted with a hydropropoxyl group. The OH group in the hydropropoxyl group is adsorbed by the active material (particularly the positive electrode active material), and the helical structure of the propyl molecule absorbs external strain, thereby weakening the elasticity of the electrode against bending ( The resilience decreases). As a result, the electrode containing the hydroxypropyl methylcellulose can have improved flexibility.

On the other hand, when the above-mentioned copolymer is used as a binder, after the conductive substrate (particularly, one having a three-dimensional structure) is filled with the paste, the paste flows downward by its own weight in the process of being transported to the drying step. Without this, the conductive substrate can be uniformly filled with the paste. Further, the copolymer can improve the adhesion between the paste and the conductive substrate. In particular, in a paste containing an acrylic acid-vinyl alcohol copolymer, the vinyl alcohol phase is stretched in a state where the acrylic acid portion has swollen with water,
Receiving the crystal under orientation, the crystallized vinyl alcohol part has a complex structure in which the acrylic acid part or acrylate part supporting high water absorption is supported, so that the active material capturing action can be remarkably produced.

Accordingly, by using a binder containing both a monomer-vinyl alcohol copolymer having a COOX group and hydroxypropylmethylcellulose for the positive electrode or the negative electrode, appropriate flexibility can be imparted. At the same time, the adhesion between the paste and the conductive substrate can be improved. As a result, such a positive electrode,
An alkaline secondary battery provided with a negative electrode or both electrodes can improve the charge / discharge cycle life. In addition, the secondary battery can suppress an internal short circuit when manufacturing a spiral electrode group and can reduce the frequency of cleaning equipment for manufacturing the electrode, thereby improving mass productivity. be able to.

In particular, an aqueous solution of nickel hydroxide powder, a copolymer of a monomer having a vinyl alcohol-COOX group, and hydroxypropyl methylcellulose (the concentration of the aqueous solution is 0.1% with respect to 90% by weight of the nickel hydroxide powder).
(1 to 5% by weight) into a conductive substrate, dried, and subjected to pressure molding, whereby the effects of both binders can be more remarkably exhibited. A positive electrode having appropriate flexibility, high adhesion between the paste and the conductive substrate, and high utilization can be obtained. Therefore, when an alkaline secondary battery is manufactured from the positive electrode, the discharge capacity and the cycle life can be improved, and the mass productivity is improved by reducing the frequency of cleaning the equipment and suppressing an internal short circuit during the production of the spiral electrode group. be able to.

In FIG. 1 described above, the electrode group 5 produced by spirally winding the separator 3 between the positive electrode 2 and the negative electrode 4 was housed in the bottomed cylindrical container 1. However, an electrode group produced by alternately stacking a positive electrode and a negative electrode with a separator interposed therebetween may be stored in a bottomed rectangular cylindrical container.

[0038]

Embodiments of the present invention will be described below in detail.

Example 1 <Preparation of Positive Electrode> In a mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 5.5 parts by weight of cobalt monoxide powder, the substitution polymerization number of propyl group was 0.25 and the average polymerization was carried out. Degree 10
000 hydroxypropyl methylcellulose (HPM
A paste was prepared by adding 27.3 parts by weight of an aqueous solution in which C) and an acrylic acid-vinyl alcohol copolymer were dissolved to a concentration of 1% by weight, and kneading.
The paste was filled in a nickel three-dimensional substrate, dried, cut, rolled by a roller press, and punched to a predetermined size to produce a positive electrode.

<Preparation of Negative Electrode> LaNi _4.0 Co _0.4 Mn
_To 3 parts by weight of polytetrafluoroethylene powder, 1 part by weight of carbon powder, and 1 part by weight of carboxymethylcellulose as a binder are added to 95 parts by weight of a hydrogen storage alloy powder having a composition of _0.3 Al _0.3 , and 50 parts by weight of water are added. A paste was prepared by mixing. This paste was applied to a nickel net, dried, and then pressed to form a negative electrode.

Next, a separator made of a nonwoven fabric mainly composed of polypropylene was interposed between the positive electrode and the negative electrode, and spirally wound to form an electrode group. These electrode groups and an alkaline electrolyte composed of 8.0 M KOH were housed in a cylindrical container having a bottom, and an AA-size cylindrical nickel-metal hydride secondary battery was assembled.

Example 2 AA-size cylindrical nickel metal hydride was prepared in the same manner as in Example 1 except that the concentration of the aqueous solution of hydroxypropylmethylcellulose and acrylic acid-vinyl alcohol copolymer was adjusted to 5.0% by weight. The secondary battery was assembled.

Example 3 An AA-size cylindrical nickel-metal hydride was prepared in the same manner as in Example 1 except that the concentration of the aqueous solution of hydroxypropylmethylcellulose and acrylic acid-vinyl alcohol copolymer was 7.0% by weight. The secondary battery was assembled.

Example 4 AA-size cylindrical nickel metal hydride was prepared in the same manner as in Example 1 except that the concentration of the aqueous solution of hydroxypropylmethylcellulose and acrylic acid-vinyl alcohol copolymer was changed to 10.0% by weight. The secondary battery was assembled.

Comparative Example 1 A paste was prepared by kneading a mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 5.5 parts by weight of cobalt monoxide powder in the presence of water. Since it was difficult to fill the obtained paste into a nickel three-dimensional substrate, a positive electrode could not be obtained.

Comparative Example 2 An AA-size 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 consisting of 90 parts by weight of nickel hydroxide powder and 5.5 parts by weight of cobalt monoxide powder, the same kind of hydroxypropyl methylcellulose as described in Example 1 was added to a concentration of 2.0% by weight. A paste was prepared by adding 27.5 parts by weight of the aqueous solution dissolved as described above and kneading. The paste was filled in a nickel three-dimensional substrate, dried, cut, rolled by a roller press, and punched to a predetermined size to produce a positive electrode.

Comparative Example 3 An AA-size 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 consisting of 90 parts by weight of nickel hydroxide powder and 5.5 parts by weight of cobalt monoxide powder, concentrations of hydroxypropyl methylcellulose and polyvinyl alcohol (PVA) similar to those described in Example 1 were used. 2.0% by weight of an aqueous solution
A paste was prepared by adding 7.5 parts by weight and kneading. This paste is filled in a nickel three-dimensional substrate, dried, cut, and rolled by a roller press,
A positive electrode was produced by punching to a predetermined size.

Comparative Example 4 AA size 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 mixed powder composed of 90 parts by weight of nickel hydroxide powder and 5.5 parts by weight of cobalt monoxide powder was mixed with hydroxypropylmethylcellulose and carboxymethylcellulose (CM) of the same type as described in Example 1.
A paste was prepared by adding 27.4 parts by weight of an aqueous solution in which C) was dissolved to a concentration of 1.5% by weight and kneading. The paste was filled in a nickel three-dimensional substrate, dried, cut, rolled by a roller press, and punched to a predetermined size to produce a positive electrode.

For each of the secondary batteries of Examples 1 to 4 and Comparative Examples 2 to 4, the positive electrode before being subjected to the roller press was vibrated for 30 minutes using a vibration tester (manufactured by Tabi, trade name: EV-20). The amount of body loss was measured, and the minimum amount and the maximum amount (of 5 positive electrodes) are shown in FIG.

[0053]

[Table 1]

As is apparent from FIG. 2, the secondary batteries of Examples 1 to 4 have a smaller amount of powder falling off from the positive electrode than the secondary batteries of Comparative Examples 2 to 4. Table 1 below
The following shows the number of times the positive electrode manufacturing equipment was cleaned when producing 100,000 positive electrodes for each of the secondary batteries of Examples 1 to 4 and Comparative Examples 2 to 4. As is clear from Table 1, Examples 1 to 4
It can be understood that the secondary battery of No. can reduce the cleaning frequency of the positive electrode manufacturing equipment as compared with the secondary batteries of Comparative Examples 2 to 4.

The secondary batteries of Examples 1 to 4 and Comparative Examples 2 to 4 were charged at 0.2 C for 10 hours, and then charged at 0.2 C, 1.0 C and 3.0 C at each rate. The positive electrode utilization when discharging to 5 V was measured, and the results are shown in FIG.

As is clear from FIG. 3, the secondary batteries of Examples 1 to 4 have a low degree of decrease in the positive electrode utilization factor when the discharge rate is increased to 1.0 C and 3.0 C.

Further, with respect to the secondary batteries of Examples 1 to 4 and Comparative Examples 2 to 4, the internal short-circuit rate when a spiral electrode group was produced was measured, and the results are shown in FIG.

As is clear from FIG. 4, the secondary batteries of Examples 1 to 4 can suppress an internal short circuit when producing a spiral electrode group as compared with the secondary batteries of Comparative Examples 2 to 4. .

Accordingly, as is apparent from FIGS. 2 to 4 and Table 1, the secondary batteries of Examples 1 to 4 have a reduced amount of powder falling off from the positive electrode while maintaining excellent positive electrode utilization. It can be seen that internal short-circuiting during production of the electrode group can be suppressed, and mass productivity can be improved. It is estimated that the reason why the amount of powder falling off was reduced is that the network structure of polyvinyl alcohol stretched under the crystals of the acrylic acid-vinyl alcohol copolymer contained in the positive electrode paste covered the active material. It is considered that the reason why the internal short circuit was suppressed was that the flexibility of the positive electrode was improved by the hydroxypropyl methylcellulose contained in the paste, and the spiral shape when the spiral electrode group was produced became uniform.

[0060]

As described above in detail, according to the present invention, a positive electrode and / or a negative electrode having a suitable flexibility is provided, in which the powder of the active material or the like is prevented from falling off the substrate. And a long-life alkaline secondary battery can be provided.

[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.

FIG. 2 is a characteristic diagram showing the amount of powder falling off of a positive electrode in the nickel-hydrogen secondary batteries of Examples 1 to 4 and Comparative Examples 2 to 4.

FIG. 3 is a characteristic diagram showing a relationship between a positive electrode utilization rate and a discharge rate in the nickel-hydrogen secondary batteries of Examples 1 to 4 and Comparative Examples 2 to 4.

FIG. 4 is a characteristic diagram showing an internal short-circuit occurrence rate when producing an electrode group in the nickel-hydrogen secondary batteries of Examples 1 to 4 and Comparative Examples 2 to 4.

[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] At least one of a positive electrode and a negative electrode contains a binder containing a copolymer of a monomer having a vinyl alcohol-COOX group and a hydroxypropylmethylcellulose. battery. 2. An anode comprising a positive electrode and a negative electrode, wherein the positive electrode comprises an aqueous solution of nickel hydroxide powder, a copolymer of a monomer having a vinyl alcohol-COOX group, and hydroxypropyl methylcellulose (the concentration of the aqueous solution is the nickel hydroxide). An alkaline secondary battery comprising a conductive substrate filled with a paste containing 0.1% to 5% by weight with respect to 90% by weight of powder.