JPH07226205A - Alkaline secondary battery - Google Patents

Abstract

PURPOSE:To provide an alkaline secondary battery having a negative electrode containing a binder by which dispersion stability of paste, retainability of hydrogen storage alloy powder, and mechanical strength are increased. CONSTITUTION:An alkaline secondary battery has a positive electrode 2, a negative electrode 1 obtained by filling paste containing a negative active material and a binder in a conductive substrate, a separator interposed between the positive electrode 2 and the negative electrode 1, and an alkaline electrolyte. The binder of the negative electrode 1 contains a copolymer of acrylic acid or acrylate and vinyl alcohol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery having a paste type negative electrode, and more particularly to an alkaline secondary battery having an improved binder for the negative electrode.

[0002]

2. Description of the Related Art A cylindrical nickel-hydrogen secondary battery, which is an example of an alkaline secondary battery, is an electrode group made by spirally winding a nickel positive electrode and a hydrogen storage alloy negative electrode with a separator interposed therebetween. Has a structure in which is stored in a container together with an alkaline electrolyte. The negative electrode is prepared by adding a conductive agent and a binder to hydrogen absorbing alloy powder and kneading in the presence of water to prepare a paste, and filling the paste into a conductive substrate such as punched metal or reticulated sintered fiber substrate. It is manufactured by

Conventionally, the binder is polyvinyl alcohol (PVA), polyacrylate, methyl cellulose (MC) or carboxymethyl cellulose (CM).
C), hydroxypropyl methylcellulose (HPM
C) and other water-soluble cellulose derivatives, polyacrylamide (PA), polyvinylpyrrolidone (PV
P), polyethylene oxide (PEO) and the like are used, but each of them has the following problems.

That is, although the paste containing polyvinyl alcohol has a high holding power for the hydrogen storage alloy powder,
Dispersion stability is low, and since the polyvinyl alcohol has low compatibility with other polymers, the hydrogen storage alloy powder having a large specific gravity tends to aggregate, and the hydrogen storage alloy powder can be uniformly dispersed in the negative electrode. It will be very difficult.

Although the paste containing the polyacrylic acid salt has high dispersion stability, the hydrogen storage alloy powder falls off from the negative electrode because the holding power of the hydrogen storage alloy powder is low. As a result, the hydrogen storage alloy powder that has fallen off may come into contact with the positive electrode to cause a short circuit. Moreover, the amount of the hydrogen storage alloy powder falling off from the negative electrode becomes extremely large when the negative electrode is wound together with the positive electrode and the separator to form the electrode group. Further, since the moldability is poor, it becomes difficult to apply the paste to the conductive substrate with a uniform thickness.

Since the paste containing the water-soluble cellulose derivative has low dispersion stability, the hydrogen storage alloy powder having a large specific gravity aggregates, and it becomes difficult to uniformly disperse the hydrogen storage alloy powder in the negative electrode. . Further, since the holding power of the hydrogen storage alloy powder is low, the coating film strength of the paste is low, and the paste is easily peeled off from the conductive substrate.

A paste containing the polyacrylamide,
In both the paste containing the polyvinylpyrrolidone and the paste containing the polyethylene oxide, the hydrogen storage alloy powder having a large specific gravity is agglomerated because the dispersion stability is low, and the hydrogen storage alloy powder is uniformly dispersed in the negative electrode. Becomes difficult.

Moreover, since the above-mentioned binder has poor strength, any negative electrode containing the binder swells in the electrolytic solution. Therefore, the secondary battery including the negative electrode has a problem that the internal pressure increases as the charging / discharging cycle progresses, and the cycle life is shortened.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems and provides a negative electrode containing a binder having improved dispersion stability of paste, retention of hydrogen-absorbing alloy powder, and strength. It is intended to provide a provided alkaline secondary battery.

[0010]

According to the present invention, a positive electrode, a negative electrode having a structure in which a paste containing a negative electrode active material and a binder is filled in a conductive substrate, and the negative electrode is interposed between the positive electrode and the negative electrode. In the alkaline secondary battery comprising a separator and an alkaline electrolyte, the binder of the negative electrode is an alkaline secondary battery characterized by containing a copolymer of acrylic acid or acrylate and vinyl alcohol. is there.

The alkaline secondary battery according to the present invention will be described with reference to FIG. The negative electrode 1 is spirally wound with the separator 3 interposed between the negative electrode 1 and the positive electrode 2, and is housed in a bottomed cylindrical container 4. The negative electrode 1 is arranged on the outermost periphery of the prepared electrode group and is in electrical contact with the container 4. The alkaline electrolyte is contained in the container 4. A circular sealing plate 6 having a hole 5 in the center is arranged in the upper opening of the container 4. The ring-shaped insulating gasket 7 is arranged between the peripheral edge of the sealing plate 6 and the inner surface of the upper opening of the container 4, and the sealing plate is attached to the container 4 by caulking to reduce the diameter of the upper opening inward. 6 is airtightly fixed via the gasket 7. One end of the positive electrode lead 8 is connected to the positive electrode 2, and the other end is the sealing plate 6.
Is attached to the underside of. Hat-shaped positive terminal 9
Is mounted on the sealing plate 6 so as to cover the hole 5. The rubber safety valve 10 is arranged so as to close the hole 5 in a space surrounded by the sealing plate 6 and the positive electrode terminal 9.

The negative electrode 1 is manufactured by preparing a paste containing a negative electrode active material, a binder, a conductive material powder, and water, applying the paste to a conductive substrate, drying the paste, and roller pressing.

Examples of the negative electrode active material include cadmium compounds such as cadmium metal and cadmium hydroxide, and hydrogen storage alloys. Among them, the negative electrode containing the hydrogen storage alloy is preferable because it has a higher capacity than the case of using the cadmium compound. The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in the electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ , MmNi ₅ (Mm means La, Ce,
It means a misch metal that is a mixture of lanthanum-based elements such as Pr, Nd, and Sm), LnNi ₅ (Ln; lanthanum-enriched misch metal), and some of these Nis are Al, Mn, Co, Ti, Cu, Zn, Zr, C
a multi-element system substituted with an element such as r or B, or T
Examples thereof include iNi type and TiFe type. Above all, the general formula LnNi _x Mn _y A _z (However, A is A
At least one metal selected from l and Co, and the atomic ratios x, y, and z have a total value of 4.8 ≦ x + y + z ≦ 5.4.
It is desirable to use a hydrogen storage alloy represented by

The binder is composed of a copolymer of acrylic acid or acrylate and vinyl alcohol alone or a mixture of the copolymer and another polymer. As the copolymer, it is desirable to use one having a viscosity of 10,000 cP or less when an aqueous solution having a concentration of 1% by weight is formed. Such a copolymer can improve the dispersion stability of the paste. If the viscosity exceeds 10,000 cP, the paste may be gelated, and it may be difficult to apply the paste to the conductive substrate. It is more preferable to use the copolymer having the viscosity of 500 cP to 10000 cP. The viscosity is 500c
If it is less than P, the fluidity of the paste becomes too high, and it may be difficult to apply the paste to the conductive substrate. The copolymer has a viscosity of 100.
It is more preferable to use one with 0 cP to 10,000 cP.

Specific examples of the copolymer include those having a straight-chain structure such as Sumikagel L-5H manufactured by Sumitomo Chemical Co., Ltd., and Sumikagel S manufactured by Sumitomo Chemical Co., Ltd. -50, Sumikagel S-80, Sumikagel S-100, Sumikagel SP-510, Sumikagel SP-520, and the like having a three-dimensional crosslinked structure can be mentioned. The linear copolymer improves the fluidity of the paste. On the other hand, although the three-dimensional cross-linked copolymer has poor solubility, it improves the water absorption and viscosity of the paste. In particular, the copolymer having the three-dimensional crosslinked structure is preferable because it can improve the dispersion stability of the paste and the strength of the negative electrode 1. Especially, it is preferable to use the said Sumika gel SP-520.

Examples of the acrylic acid salt of the copolymer of the acrylic acid salt and vinyl alcohol include monovalent salts such as sodium acrylate, potassium acrylate and lithium acrylate. Among them, a copolymer of the above-mentioned sodium salt of acrylic acid and vinyl alcohol is preferable. In addition, the water absorbency of the copolymer of acrylate and vinyl alcohol introduces a crosslinked structure into the molecule by copolymerizing a small amount of a divalent acrylate such as calcium acrylate in the copolymer. It can be adjusted by

The copolymer of acrylic acid or acrylate and vinyl alcohol may be copolymerized with a small amount of styrene having water repellency or butadiene having elasticity for the purpose of adjusting hydrophilicity and strength.

The copolymer of acrylic acid or acrylic acid salt and vinyl alcohol can be produced by copolymerizing an acrylic ester and vinyl acetate and then saponifying the copolymer. The copolymer is allowed to contain unreacted acrylic ester or vinyl acetate as a copolymer component.

The polymer used in combination with the above-mentioned copolymer is, for example, polytetrafluoroethylene (PTFE),
Hydrophobic polymers such as polyethylene and polypropylene, such as carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), such as sodium polyacrylate (S
Examples thereof include polyacrylic acid salts such as PA), polyvinyl alcohol (PVA), hydrophilic polymers such as polyethylene oxide, and rubber-based polymers such as LATEX. In particular, it is preferable to use the hydrophilic polymer. Among such hydrophilic polymers, 1 selected from carboxymethyl cellulose and polyvinyl alcohol
It is more preferable to use one or more species. The polyethylene and polypropylene are used in the form of dispersion.

The binder consisting of a copolymer of acrylic acid or an acrylic acid salt and vinyl alcohol is preferably added in an amount of 0.5 to 2.0 parts by weight based on 100 parts by weight of the negative electrode active material. This is due to the following reasons. If the added amount is less than 0.5 part by weight, the viscosity of the paste may be reduced, and it may be difficult to apply the paste to the conductive substrate. On the other hand, if the amount added exceeds 2.0 parts by weight, the hydrogen storage alloy powder may agglomerate, and the dispersion stability of the paste may decrease. In particular,
It is more preferable to add 0.5 to 1.0 part by weight of the binder to 100 parts by weight of the negative electrode active material.

When the binder comprises a mixture of the copolymer and the polymer, the copolymer is added in an amount of 0.05 to 2.0 parts by weight based on 100 parts by weight of the negative electrode active material,
It is preferable that 0.1 to 3.0 parts by weight of the polymer is added to 100 parts by weight of the negative electrode active material. This is due to the following reasons. If the amount of the copolymer added is less than 0.05 part by weight, the dispersion stability of the paste may be reduced and the negative electrode 1 may be swollen in the electrolytic solution. If the amount of the copolymer added exceeds 2.0 parts by weight, the capacity of the negative electrode 1 may decrease. On the other hand, the addition amount of the polymer is 0.
If the amount is less than 1 part by weight, it may be difficult to improve the holding power of the hydrogen storage alloy powder of the binder. If the amount of the polymer added exceeds 3.0 parts by weight, the dispersion stability of the paste may be reduced. In particular,
To improve the dispersion stability of the paste and prevent the negative electrode 1 from swelling, 0.2 to 0.5 parts by weight of the copolymer is added, and 0.1 part by weight of the polymer is added. ~
It is more preferable to add 0.125 parts by weight. Among them, the paste in which carboxymethyl cellulose is used as the polymer can remarkably improve the dispersion stability.

Examples of the conductive material include carbon black. Examples of the conductive substrate include those having a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and those having a three-dimensional structure such as foam metal and mesh-like sintered metal fiber.

For the positive electrode 2, for example, a conductive material and a binder are added to nickel hydroxide powder, these are kneaded in the presence of water to prepare a paste, and the paste is filled in a conductive substrate. After being dried, it is manufactured by roller pressing.

Examples of the conductive material include cobalt compounds such as cobalt oxide and cobalt hydroxide. Examples of the binder include a copolymer of acrylic acid or an acrylic acid salt and vinyl alcohol, for example, a hydrophobic polymer such as polytetrafluoroethylene (PTFE), polyethylene, polypropylene, for example, carboxymethyl cellulose (CMC), methyl cellulose (MC). ), Hydroxypropyl methylcellulose (HP
MC), polyacrylic acid salts, polyvinyl alcohol, polyethylene oxide, and other hydrophilic polymers, such as latex, and other rubber-based polymers. The polyethylene and polypropylene are used in the form of dispersion.

Examples of the conductive material include cobalt compounds such as cobalt oxide and cobalt hydroxide. Examples of the conductive substrate include a porous substrate having a three-dimensional structure such as a nickel fiber sintered body, a felt-like nickel porous body, and a sponge-like nickel porous body.

Examples of the separator 3 include a nonwoven fabric made of polyamide fiber and a nonwoven fabric made of polyolefin fiber such as polyethylene and polypropylene to which a hydrophilic functional group is added.

As the electrolytic solution, for example, a mixed solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH) and potassium hydroxide (KOH), a mixed solution of KOH and LiOH and the like can be used.

[0028]

According to the alkaline secondary battery of the present invention, a paste containing a negative electrode active material such as hydrogen-absorbing alloy powder and a copolymer of acrylic acid or an acrylate and vinyl alcohol as a binder is used as a conductive substrate. Since the dispersion stability of the paste can be improved by providing the negative electrode having the filled structure, the hydrogen storage alloy powder can be uniformly dispersed in the negative electrode.

The copolymer may be a COOH group, which is an adsorptive functional group of acrylic acid or an acrylic acid salt, C
Since it has an OOM group (M represents one or more elements selected from Na, K, Li, and Ca) and an OH group that is an adsorptive functional group of vinyl alcohol, the kind of adsorptive functional group is more than that of a conventional binder. Can be a lot. As a result, the plurality of adsorptive functional groups are different from each other in the position of adsorbing to the hydrogen storage alloy powder, and the copolymer adhered to the conductive substrate is adsorbed to various parts of the hydrogen storage alloy powder. Therefore, the hydrogen storage alloy powder can be firmly captured on the conductive substrate.

Further, since the copolymer has high strength,
Swelling of the negative electrode in the electrolytic solution can be prevented.
As a result, the secondary battery including the negative electrode can suppress an increase in internal pressure with charge / discharge cycles,
The cycle life can be improved.

Since the binder containing the copolymer is more flexible than the conventional binder made of a polymer of a single monomer, the flexibility of the negative electrode containing the copolymer is improved. It is possible to improve the winding property of the negative electrode when the above-mentioned spiral electrode group shown in FIG. 1 is produced.

[0032]

Embodiments of the present invention will be described in detail with reference to the drawings. Examples 1 to 11 First, Ln (Ln is La; 50% by weight, Ce; 4% by weight, Pr; 11% by weight, Nd; rare earth element consisting of 35% by weight) and Ni, Co, Mn, Al from the formula Ln _w Ni
A hydrogen storage alloy represented by _4.0 Co _0.4 Mn _0.3 Al _0.3 was prepared and pulverized. To 100 parts by weight of the obtained hydrogen storage alloy powder, 1.0 part by weight of carbon black and 50 parts by weight of water were added, and further, sodium acrylate of Sumikagel SP520 manufactured by Sumitomo Chemical Co., Ltd. and vinyl alcohol were added. Copolymer (SPA-PVA copolymer), carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), polyvinyl alcohol (PVA),
One or more kinds selected from sodium polyacrylate (SPA) were added at a mixing ratio shown in Table 1 below, and these were kneaded to prepare 15 kinds of pastes. In addition, the SP
The A-PVA copolymer used had a viscosity of 1500 cP when a 1 wt% aqueous solution was formed.

[0033]

[Table 1]

Next, each of the obtained pastes was applied to a punched metal, dried, pressed, and cut into 15 types of negative electrodes. Further, 90 parts by weight of nickel hydroxide powder, 10 parts by weight of cobalt monoxide, 3.5 parts by weight of polytetrafluoroethylene as a binder, 0.15 parts by weight of carboxymethyl cellulose (CMC), and 0 sodium polyacrylate. 0.175 parts by weight. To this, 60 parts by weight of pure water was added and kneaded to prepare a paste. The paste is coated and filled in a sintered fiber substrate as a conductive core, dried, and rolled by a roller press to have a thickness of 0.6 mm and a capacity per unit volume of 670 mAH / cc. A positive electrode was produced.

Next, a separator made of a polyamide fiber non-woven fabric was interposed between the positive electrode and each negative electrode, and these were spirally wound to prepare an electrode group. A cylindrical nickel metal hydride of AA size having a capacity of 1000 mAH and having the structure shown in FIG. 1 in which an electrolytic solution composed of such an electrode group and 7 N KOH and 1 N LiOH is housed in a cylindrical container having a bottom. The secondary battery was assembled.

The obtained Examples 1 to 11 and Comparative Examples 1 to 4
The secondary battery of (1) was aged at 45 ° C. for 24 hours, and then subjected to initial charging to make it accustomed. Next, after charging 150% at 1C, set the cutoff voltage to 1V and discharge at 1C. Repeat the charging / discharging cycle 7 times. After charging 480% at 1C, set the cutoff voltage to 1V and discharge at 1C. The capacity and voltage when the charge / discharge cycle was repeated 10 times were measured, and the results are shown in Table 2 below.

Further, Examples 1 to 11 after the aging are performed.
Also, the secondary batteries of Comparative Examples 1 to 4 were charged at 150% at 1C, then the charge-discharge cycle of discharging at 1C with the cutoff voltage set to 1V was repeated, and the number of cycles required for the capacity to become 900 mA or less was measured. The results are shown in Table 2 below.
Also described in.

On the other hand, Examples 1 to 11 and Comparative Examples 1 to 1
The dispersibility, stability, and coating film strength of the paste contained in the negative electrode of the secondary battery of Example No. 4 were evaluated in 5 grades from the appearance.

The negative electrodes of the secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 4 were soaked in ion-exchanged water for 30 minutes, and the surface thereof was lightly wiped with water-absorbent paper 5 times and weighed to obtain the water absorption rate. (Increase rate of weight from before water immersion) was determined, and the state of swelling of these negative electrodes was relatively evaluated in terms of appearance on a 5-point scale. Also,
The operation of winding each of the negative electrodes in a spiral shape is repeated 5 times, and the weight is weighed to obtain the weight reduction rate from before the winding due to the dropping of the hydrogen storage alloy powder, and the result, the water absorption rate, and the swelled state are calculated. It is also shown in Table 3 below.

[0040]

[Table 2]

[0041]

[Table 3]

As is clear from Tables 2 and 3, the secondary batteries of Examples 1 to 11 provided with the negative electrode containing the SPA-PVA copolymer as the binder had high capacity and voltage, and low internal pressure. Further, it can be seen that the cycle life is long. Also,
It can be seen that the pastes contained in the negative electrodes of the secondary batteries of Examples 1 to 11 have excellent dispersibility and stability and high coating strength. Further, it can be seen that the negative electrodes of the secondary batteries of Examples 1 to 11 have little swelling after absorbing water and a small amount of hydrogen storage alloy powder that has fallen off during winding. In particular, 0.2 to 0.5 parts by weight of the SPA-PVA copolymer and 0.125 parts by weight of C incorporated in the secondary batteries of Examples 8 to 10 were used.
It can be seen that the negative electrode containing the binder made of MC does not swell after absorbing water, and the pastes contained in these negative electrodes have high dispersibility and stability.

On the other hand, SPA as a binder and CM
The secondary batteries of Comparative Examples 1 to 4 provided with the negative electrode containing one selected from C, MC, HPMC, and PVA have high capacity and voltage as in Examples 1 to 11, but have a significantly high internal pressure, and It can be seen that the cycle life is extremely short. Further, the negative electrode of the secondary battery of Comparative Example 1 includes SPA and CM.
It can be seen that the paste containing the binder made of C has good dispersibility, stability, and coating film strength, but the negative electrode swells after absorbing water and has a very large amount of hydrogen storage alloy powder that has fallen off during winding. On the other hand, the secondary batteries of Comparative Examples 2 to 4 were incorporated with SPA as a binder, MC, HPMC, and P.
The negative electrode containing one selected from VA does not swell after absorbing water,
Moreover, although the amount of the hydrogen storage alloy powder that fell off during winding was small, the pastes contained in these negative electrodes were inferior in dispersibility, stability, and coating film strength.

[0044]

As described in detail above, according to the alkaline secondary battery of the present invention, it is provided with a negative electrode containing a binder having improved paste dispersion stability, hydrogen storage alloy powder retention and strength. It has a high discharge capacity and discharge voltage, further suppresses an increase in internal pressure, and has a remarkable effect of improving cycle life.

[Brief description of drawings]

FIG. 1 is a perspective view showing a nickel-hydrogen secondary battery of the present invention.

[Explanation of symbols]

1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Container, 6 ...
Seal plate, 7 ... Insulation gasket.

Claims (3)

[Claims] 1. A positive electrode, a negative electrode having a structure in which a paste containing a negative electrode active material and a binder is filled in a conductive substrate, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. The alkaline secondary battery according to claim 1, wherein the binder of the negative electrode contains a copolymer of acrylic acid or an acrylic acid salt and vinyl alcohol. 2. The alkaline secondary battery according to claim 1, wherein the binder of the negative electrode is composed of a copolymer of acrylic acid or an acrylic acid salt and vinyl alcohol, and carboxymethyl cellulose and / or polyvinyl alcohol. 3. The copolymer of acrylic acid or acrylic acid salt and vinyl alcohol having a viscosity of 10000 cP or less when an aqueous solution having a concentration of 1% by weight is formed is used. Alkaline secondary battery.