JP3005423B2 - Alkaline secondary battery - Google Patents

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 provided with a paste-type nickel positive electrode, and more particularly to an alkaline secondary battery in which the binder of the positive electrode is improved.

[0002]

2. Description of the Related Art A cylindrical nickel-metal hydride secondary battery, which is an example of an alkaline secondary battery, is an electrode group manufactured by spirally winding a nickel positive electrode and a hydrogen storage alloy negative electrode with a separator interposed therebetween. Is stored in a container together with an alkaline electrolyte. Conventionally, the nickel positive electrode is formed by molding and sintering carbonyl nickel powder, impregnating the sintered substrate with a nickel salt solution, and forming the same.
It is manufactured by a so-called sintering method. However,
The sintered nickel positive electrode has a problem in that mass production is inferior because an extremely complicated operation is required when manufacturing the sintered substrate or impregnating the sintered substrate with the solution.

[0003] For this reason, a paste-type nickel positive electrode is widely used in the secondary battery. The paste-type nickel positive electrode is prepared by dispersing nickel hydroxide powder as an active material using a binder to form a paste, and filling the paste into a conductive core made of, for example, a three-dimensional mesh-like porous body. It is manufactured by drying, rolling, and cutting to a desired size.

As the binder, conventionally, for example, carboxymethylcellulose, polytetrafluoroethylene,
Polyacrylate, polyvinyl alcohol and the like are used.

[0005] However, since the binder has a poor retention of the active material, the active material falls off the positive electrode containing the binder, and the dropped active material comes into contact with the negative electrode to cause an internal short circuit. was there. In addition, when the binding agent has poor holding power of the active material, cracks occur in the positive electrode when the positive electrode is wound, and the conductive core is easily released from the positive electrode. For this reason, when the positive electrode was wound together with the negative electrode and the separator to form the electrode group, the amount of the active material dropped from the positive electrode was extremely large.

Further, the strength of the binder is poor, so that the positive electrode swells when the secondary battery is charged. As a result, the internal pressure of the secondary battery is increased and the electrolyte is leaked, so that the capacity of the secondary battery is reduced and the cycle life is reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the conventional problems, and has been made in consideration of an alkaline battery provided with a positive electrode containing a binder having improved strength for holding an active material and improved strength. It is intended to provide a secondary battery.

[0008]

SUMMARY OF THE INVENTION The present invention provides a positive electrode having a structure in which a paste containing nickel hydroxide powder and a binder is filled in a conductive core, a negative electrode, and an interposed space between the positive electrode and the negative electrode. A separator to be mounted, in an alkaline secondary battery including an alkaline electrolyte, the binder of the positive electrode,
An alkaline secondary battery comprising a copolymer of acrylic acid or an acrylate and vinyl alcohol.

An alkaline secondary battery according to the present invention will be described with reference to FIG. The nickel positive electrode 1 is wound with a separator 3 made of synthetic resin fiber interposed between the nickel positive electrode 1 and the negative electrode 2, and is housed in a bottomed cylindrical container 4. The negative electrode 2 is arranged at the outermost periphery of the electrode group and is in electrical contact with the container 4. The alkaline electrolyte is contained in the container 4. A circular sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 4. 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 4, and the sealing plate is attached to the container 4 by caulking to reduce the diameter of the upper opening inward. 7 is hermetically fixed via the gasket 8. The positive electrode lead 9 has one end connected to the positive electrode 1 and the other end connected to the sealing plate 7.
Is connected to the lower surface. Hat-shaped positive electrode terminal 10
Is mounted on the sealing plate 7 so as to cover the hole 6. A rubber safety valve 11 is disposed in a space surrounded by the sealing plate 7 and the positive electrode terminal 10 so as to close the hole 6.

The positive electrode 1 is prepared by preparing a paste containing nickel hydroxide powder, a conductive agent, a binder, and water, filling the paste into a conductive core, drying and pressing the paste. Manufactured by cutting or punching to a desired size.

The nickel hydroxide powder allows zinc and cobalt to be coprecipitated with metallic nickel and contained as a solid solution. The binder may be composed of a copolymer of acrylic acid or acrylate and vinyl alcohol alone, or may be composed of a mixture of the copolymer and another polymer.

Specific examples of the copolymer include those having a straight-chain structure such as Sumikagel L-5H manufactured by Sumitomo Chemical Co., Ltd., and those of 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 cross-linkable structure. The linear copolymer improves the fluidity of the paste. On the other hand, the three-dimensionally crosslinked copolymer has poor solubility, but improves the water absorption and viscosity of the paste. The copolymer having the three-dimensional cross-linking structure is preferable because the water absorption of the electrolyte solution of the positive electrode 1 can be improved. Among the copolymers having a three-dimensional crosslinked structure, it is preferable to use the Sumikagel SP-520.

Examples of the acrylate of the copolymer of acrylate and vinyl alcohol include monovalent ones such as sodium acrylate, potassium acrylate and lithium acrylate. Among them, a copolymer of the above-mentioned sodium acrylate and vinyl alcohol is preferable. In addition, the water absorption of the copolymer of the acrylate and the vinyl alcohol is such that a small amount of a divalent acrylate such as a calcium acrylate is copolymerized with the copolymer to introduce a crosslinked structure into the molecule. Can be adjusted.

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

The above-mentioned copolymer of acrylic acid or acrylate and vinyl alcohol can be produced by copolymerizing an acrylate and vinyl acetate and then saponifying the copolymer. Note that the copolymer is allowed to contain unreacted acrylate or vinyl acetate as a copolymer component.

The polymer used in combination with the copolymer includes, for example, polytetrafluoroethylene (PTFE),
Hydrophobic polymers such as polyethylene and polypropylene such as carboxymethylcellulose (CMC), methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) such as sodium polyacrylate (S
PA) and other hydrophilic polymers such as polyvinyl alcohol (PVA) and polyethylene oxide, and rubber polymers such as latex. In particular, it is preferable to use the hydrophobic polymer and the hydrophilic polymer. Among such hydrophobic polymers and hydrophilic polymers, it is more preferable to use one or more selected from polytetrafluoroethylene, carboxymethylcellulose, methylcellulose, and polyvinyl alcohol. The polyethylene and the polypropylene are used in the form of a dispersion.

The binder consisting of the copolymer of acrylic acid or acrylate and vinyl alcohol alone is used in an amount of 0.2 parts by weight to 100 parts by weight of the nickel hydroxide powder.
It is desirable to add 10 parts by weight. This is due to the following reasons. If the amount is less than 0.2 parts by weight, the strength of the positive electrode may be reduced,
The nickel hydroxide powder may fall off from the positive electrode and come into contact with the negative electrode, causing an internal short circuit. On the other hand, if the amount exceeds 10 parts by weight, the paste may be thickened, so that the amount of water added to the paste may increase and the active material density of the positive electrode may decrease.
In particular, the binder is more preferably added in an amount of 0.3 to 3 parts by weight based on 100 parts by weight of the nickel hydroxide powder.

When the binder comprises a mixture of the copolymer and the polymer, the copolymer is added in an amount of 0.05 to 5 parts by weight based on 100 parts by weight of the nickel hydroxide powder. It is desirable to add 0.1 to 5 parts by weight to 100 parts by weight of the nickel hydroxide powder.
This is due to the following reasons. If the amount of the copolymer is less than 0.05 parts by weight, the strength of the binder may be reduced. On the other hand, if the amount of the copolymer exceeds 5 parts by weight, the active material density in the positive electrode may decrease, and the battery performance such as battery capacity may deteriorate. If the amount of the polymer is less than 0.1 part by weight, the fluidity and stability of the paste may be reduced. On the other hand, if the amount of the polymer exceeds 5 parts by weight, there is a possibility that the battery performance may be seriously affected, such as the internal pressure characteristics of the secondary battery being reduced. In particular, it is more preferable that the addition amount of the copolymer is in the range of 0.1 to 2.0 parts by weight, and the addition amount of the polymer is in the range of 0.3 to 3 parts by weight.

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

The negative electrode 2 is manufactured by adding a conductive material to a negative electrode active material, kneading it with a binder and water to prepare a paste, filling the conductive substrate with the paste, drying, and molding. Is done.

Examples of the negative electrode active material include cadmium compounds such as metal cadmium and cadmium hydroxide, and hydrogen storage alloys. Especially, it is preferable to use a hydrogen storage alloy. The hydrogen storage alloy is not particularly limited, as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. For example, La
Ni _5, MmNi ₅ (and Mm is, La, Ce, Pr, N
d, Sm, etc.), LnNi ₅ (Ln; lanthanum-enriched misch metal), and a part of these Ni
l, Mn, Co, Ti, Cu, Zn, Zr, Cr, a multi-element system substituted with elements such as B, or TiNi
And TiFe-based ones. Among them,
Formula LnNi _x Mn _y A _z (However, A is Al, Co
At least one metal selected from the group consisting of: atomic ratio x, y, z
It is desirable to use a hydrogen storage alloy represented by the following formula: 4.8 ≦ x + y + z ≦ 5.4.

As the binder, for example, a copolymer of acrylic acid or acrylate and vinyl alcohol, for example, a hydrophobic polymer such as polytetrafluoroethylene (PTFE), polyethylene, or polypropylene, for example, carboxymethyl cellulose (CMC) , Methylcellulose (MC), hydroxypropylmethylcellulose (HPMC) such as sodium polyacrylate (SP
A) such as polyacrylates, polyvinyl alcohol,
Examples include hydrophilic polymers such as polyethylene oxide, and rubber-based polymers such as latex.
The polyethylene and the polypropylene are used in the form of a dispersion.

Examples of the conductive material include carbon black. Examples of the conductive substrate include punched metal, expanded metal, a perforated rigid plate, a two-dimensional substrate such as a nickel net, a felt-like metal porous body, and a three-dimensional substrate such as a sponge-like metal porous body. it can.

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.

Examples of the alkaline electrolyte include sodium hydroxide (NaOH) and lithium hydroxide (LiO
H), a mixed solution of potassium hydroxide (KOH) and LiOH, a mixed solution of KOH, LiOH and NaOH, and the like.

[0026]

The alkaline secondary battery of the present invention has a structure in which a conductive core is filled with a paste containing nickel hydroxide powder and a copolymer of acrylic acid or acrylate and vinyl alcohol as a binder. By providing a positive electrode, the copolymer can have a COOH group, a COOM group (MOM) which is an adsorptive functional group of acrylic acid or acrylate, for example.
Represents one or more elements selected from Na, K, Li and Ca) and OH which is an adsorptive functional group of vinyl alcohol.
Because of the presence of the group, the number of types of the adsorptive functional group can be increased as compared with the conventional binder. As a result, the places where the plurality of adsorptive functional groups adsorb to the nickel hydroxide powder are different, and the copolymer adhered to the conductive core is adsorbed to various places of the nickel hydroxide powder. Therefore, the nickel hydroxide powder can be firmly captured by the conductive core. Accordingly, it is possible to prevent the nickel hydroxide powder from dropping from the positive electrode, and to prevent an internal short circuit of the secondary battery including the positive electrode.

Further, since the copolymer has high strength, it is possible to prevent the positive electrode from swelling when the secondary battery is charged. As a result, an increase in the internal pressure of the secondary battery can be suppressed, and leakage of the electrolyte can be prevented, so that the cycle life of the secondary battery can be improved.

Further, since the binder containing the copolymer has higher flexibility than the conventional binder consisting of a single monomer polymer, the flexibility of the positive electrode containing the copolymer is improved. It is possible to improve the winding property of the positive electrode when producing the spiral electrode group shown in FIG. 1 described above.

[0029]

An embodiment of the present invention will be described below in detail with reference to FIG. Example 1 First, 90 parts by weight of spherical nickel hydroxide powder containing 2% by weight of zinc and 2% by weight of cobalt in terms of metal and having an average particle size of 18 μm, 10 parts by weight of cobalt monoxide,
As shown in Table 1 below, as a binder, a copolymer of sodium acrylate and vinyl alcohol (trade name: Sumikagel SP-520, manufactured by Sumitomo Chemical Co., Ltd.)
3 parts by weight of a PVA copolymer) were added. 60 pure water
A part by weight was added and kneaded to prepare a paste.

Next, the paste is applied 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.
Thus, a positive electrode having a capacity per unit volume of 670 mAH / cc was produced.

The composition is represented by the formula LnNi _4.0 Co _0.4 Mn.
_0.3 parts by weight of sodium polyacrylate, 0.125 parts by weight of carboxymethyl cellulose (CMC) based on 100 parts by weight of the hydrogen storage alloy powder represented by _0.3 Al _0.3 ,
A paste was prepared by mixing 2.5 parts by weight of a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60 wt%) and 1.0 part by weight of carbon powder as a conductive material together with 50 parts by weight of water. This paste was applied to a punched metal, dried, and then molded under pressure to produce a hydrogen storage alloy negative electrode.

Next, a separator made of a nonwoven fabric made of polyamide fiber was interposed between the positive electrode and the negative electrode, and these were spirally wound to form an electrode group. Such an electrode group and KOH having a composition ratio of KOH to LiOH of 7: 1
The electrolyte having the structure shown in FIG.
A cylindrical nickel-metal hydride secondary battery having an AA size of mAH was assembled. Examples 2 to 6 As the binder for the positive electrode, one selected from the above-mentioned SPA-PVA copolymer, polytetrafluoroethylene fine powder (PTFE), carboxymethylcellulose (CMC), methylcellulose (MC), and polyvinyl alcohol (PVA) Except that the above polymers were used in the compounding ratios shown in Table 1 below, the capacity was 110 in the same configuration as in Example 1.
An AA size cylindrical nickel-metal hydride secondary battery of 0 mAH was assembled. Comparative Examples 1-4 As a binder for the positive electrode, sodium polyacrylate (SPA) manufactured by Nippon Pure Chemical Co., Ltd.
A of the same configuration as in Example 1 except that one or more polymers selected from FE, CMC, MC, and PVA were used in the mixing ratio shown in Table 1 below, and the capacity was 1100 mAH.
An A-size cylindrical nickel-metal hydride secondary battery was assembled.

[0033]

[Table 1]

The obtained secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 4 were allowed to stand at room temperature for 48 hours to obtain a 0.2 CA
And then discharging to 1 V was repeated twice. Subsequently, after charging 150% at 1C, three charge / discharge cycles of discharging to 1V were performed, and the battery capacity was measured. The results are shown in Table 2 below. Further, the charge / discharge cycle was repeated, and the swelling ratio, internal pressure, operating voltage, liquid leakage occurrence ratio, and internal short circuit occurrence ratio of the positive electrode at the 20th cycle were measured, and the results are shown in Table 2 below.

The charge / discharge cycle of the secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 4 was repeated by performing 1C charging for cutting the charging current when the operating voltage dropped by 10 mV and then discharging at 1C. The cycle life (20 ° C.) was measured, and the results are shown in Table 2 below.

Further, the positive electrode pastes of Examples 1 to 6 and Comparative Examples 1 to 4 were allowed to stand at room temperature for 3 days, and the state of aggregation of the paste was evaluated in three stages of relatively good, slightly agglomerated and agglomerated from the appearance. The results are shown in Table 3 below.

After the positive electrodes of Examples 1 to 6 and Comparative Examples 1 to 4 were wound around a core shaft having a diameter of 4.0 mm, the process of rewinding was repeated three times, and the nickel hydroxide The amount of the powder falling off (relative amount) was measured, and the results are shown in Table 3 below.

[0038]

[Table 2]

[0039]

[Table 3]

As is clear from Tables 2 and 3, the secondary batteries of Examples 1 to 6 provided with a positive electrode containing a copolymer of sodium acrylate and vinyl alcohol as a binder had a large capacity and a high operating capacity. It can be seen that the voltage is high and the life is long, the swelling ratio of the positive electrode, the amount of the active material falling off of the positive electrode and the internal pressure of the battery are low, and there is no occurrence of electrolyte leakage and internal short circuit occurrence. Further, it can be seen that the secondary batteries of Examples 1 to 6 have high storage stability of the positive electrode paste. In contrast,
Comparative Example 1 provided with a positive electrode to which the copolymer was not added
4 are lower in battery capacity and operating voltage than the secondary batteries of Examples 1 to 6, and have a shorter cycle life,
Furthermore, the swelling ratio of the positive electrode, the amount of the active material falling off of the positive electrode, the internal pressure of the battery,
It can be seen that the rate of occurrence of electrolyte leakage and internal short circuit is high.
In addition, it can be seen that the secondary batteries of Comparative Examples 1 to 4 have poor storage stability of the positive electrode paste.

In the above embodiment, an example in which the present invention is applied to a cylindrical nickel-metal hydride secondary battery is described. However, the present invention can be similarly applied to a square nickel-metal hydride secondary battery. Further, the electrode group housed in the container of the secondary battery is not limited to a spiral shape, but a positive electrode,
A configuration in which a plurality of separators and negative electrodes are stacked in this order may be adopted.

[0042]

As described above in detail, according to the alkaline secondary battery of the present invention, the positive electrode having the paste having excellent storage stability is provided, and the fall of the active material of the positive electrode is reduced to cause an internal short circuit. Can be prevented, and furthermore, the swelling of the positive electrode is suppressed and the internal pressure can be suppressed from increasing,
This has the remarkable effect of preventing the electrolyte from leaking and improving the cycle life.

[Brief description of the drawings]

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

[Explanation of symbols]

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

Continuation of front page (72) Inventor Kunihiko Miyamoto 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (56) References JP-A-52-125723 (JP, A) JP-A-53- 70347 (JP, A) JP-A-57-23468 (JP, A) JP-A-57-136774 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4 / 32,4 / 62 H01M 10 / 24,10 / 30

Claims (2)

(57) [Claims] A positive electrode having a structure in which a paste containing nickel hydroxide powder and a binder is filled in a conductive core; a negative electrode; a separator interposed between the positive electrode and the negative electrode; Wherein the binder of the positive electrode contains a copolymer of acrylic acid or an acrylate and vinyl alcohol. 2. The alkaline secondary battery according to claim 1, wherein the copolymer of acrylic acid or acrylate and vinyl alcohol has a three-dimensional crosslinked structure.