JP2000164192A - Alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold sufficient quantity of electrolyte when incorporating an electrode of a highly tensely binding degree into a vessel by providing a separator composed of a synthetic resin fiber sheet containing syndiotactic polypropylene fiber at a specific rate. SOLUTION: A separator is composed of a synthetic resin fiber sheet containing syndiotactic polypropylene fiber by 80 volume % or more. The syndiotactic polypropylene fiber independent or the other polyolefine fiber, for example, mixed fiber of polypropylene fiber and polyethylene fiber can be cited as synthetic resin fiber. These average fiber diameter is desirably set to 1 to 20 μm from the viewpoint of mechanical strength and of preventing a short circuit between a positive electrode and a negative electrode. A sheet may be nonwoven fabric and woven fabric or these composite sheet. A copolymer having a hydrophilic radical on a surface of fiber for revealing a hydrophilic property, for example, a structure covered with an ethyle vinyl alcohol copolymer is desirable as the separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an alkaline storage battery.

[0002]

2. Description of the Related Art Generally, an alkaline storage battery has a structure in which a spirally wound electrode group is housed in a battery outer can (container) with a separator interposed between a positive electrode and a negative electrode and sealed. For example, a nickel-metal hydride storage battery, which is a type of alkaline storage battery, is manufactured by the following method. First, a positive electrode in which an active material such as nickel hydroxide powder is supported on a current collector made of a three-dimensional substrate such as nickel fiber or foamed nickel, and a hydrogen storage alloy powder is applied to a current collector such as a nickel net or punched metal. Is wound spirally while a separator is interposed between the anode and the negative electrode on which an electrode is supported to produce an electrode group. Subsequently, the electrode group is housed in a container, an alkaline electrolyte is injected into the container, and after the electrode group is connected to an external terminal, the opening of the container is sealed. Manufacture hydrogen storage batteries.

[0003] In response to the demand for higher capacity of such an alkaline storage battery, it has been practiced to increase the number of turns of the positive and negative electrodes constituting the electrode group and to increase the thickness of the positive and negative electrodes themselves.

[0004] As a separator incorporated in the alkaline storage battery, a nonwoven fabric made of synthetic resin fibers such as polyamide and polyolefin has conventionally been used.

[0005]

However, since the separator made of the nonwoven fabric of the synthetic resin fiber described above has a low compressive strength, when used for a storage battery with a high degree of binding for the purpose of increasing the capacity, the electrolyte is sufficiently retained. There is a problem that the cycle characteristics cannot be obtained and the cycle characteristics are deteriorated.

The present invention is to provide an alkaline storage battery provided with a separator capable of holding a sufficient amount of electrolyte when a separator is disposed between a positive electrode and a negative electrode and a high-tightness electrode is incorporated in a container. It is assumed that.

[0007]

The alkaline storage battery according to the present invention comprises a syndiotactic polypropylene fiber of 8%.
A separator made of a synthetic resin fiber sheet containing 0% by volume or more is provided.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An alkaline storage battery (for example, a cylindrical nickel-metal hydride storage battery) according to the present invention will be described below with reference to FIG.

An electrode group 5 produced by stacking 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. Sealing plate 7 having hole 6 in the center
Are arranged in 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 attached to 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 attached on the sealing plate 7 so as to cover the hole 6. The rubber safety valve 11 is provided with the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10.
It is arranged so as to close. A circular holding plate 12 made of an insulating material having a hole in the center is arranged on the positive electrode terminal 10 such that a protrusion of the positive electrode terminal 10 projects from the hole of the holding plate 12. Exterior tube 13
Covers the periphery of the holding plate 12, the side surface of the container 1, and the bottom periphery of the container 1.

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

1) Positive electrode 2 The positive electrode 2 is prepared by kneading, for example, nickel hydroxide powder as an active material, a conductive material, and a polymer binder together with water to prepare a paste. It is produced by applying or filling the mixture, drying and molding.

The nickel hydroxide particles may be nickel hydroxide alone or a solid solution of a different element such as Co or Zn.

Examples of the conductive material include metallic cobalt, cobalt oxide, cobalt hydroxide and the like.

Examples of the polymer binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

The current collector may be, for example, a conductive two-dimensional substrate such as a mesh formed of nickel, stainless steel, or nickel-plated metal, or a sponge.
A conductive three-dimensional substrate such as a fibrous or felt-like porous metal body can be used.

2) Negative electrode 4 The negative electrode 4 is prepared, for example, by adding a conductive material to a hydrogen storage alloy powder, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a current collector, After drying, it is produced by molding.

The hydrogen storage alloy is not particularly limited, and may be any alloy capable of storing hydrogen electrochemically generated in an electrolytic solution and easily releasing the stored hydrogen during discharge. . As this hydrogen storage alloy,
For example LaNi _5, MmNi ₅ (Mm; misch metal), LmNi ₅ (Lm; lanthanum enriched misch metal), or some of these Ni Al, Mn, C
o, Ti, Cu, Zn, Zr, Cr, B, etc.
e-type ones can be mentioned. Among them, the general formula Lm
Ni _x Mn _y A _z (However, A is shown Al, at least one metal selected from Co, the atomic ratio x, y, z is the total value of 4.8 ≦ x + y + z ≦ 5.4) is represented by It is preferable to use one.

Examples of the polymer binder include those similar to those used in the positive electrode 2.

As the conductive material, for example, carbon black or the like can be used.

Examples of the current collector include conductive two-dimensional substrates such as punched metal, expanded metal, perforated rigid plate, and nickel net; and conductive tertiary substrates such as felt-like metal porous materials and sponge-like metal substrates. The original substrate can be mentioned.

3) Separator 3 The separator 3 is made of a sheet made of synthetic resin fiber containing at least 80% by volume of syndiotactic polypropylene fiber.

The synthetic resin fiber may be a syndiotactic polypropylene fiber alone or a mixture of 80% by volume or more of this fiber with another polyolefin fiber, for example, a polypropylene fiber or a polyethylene fiber, or a core material made of syndiotactic polypropylene. Core-sheath composite fibers coated with polyolefin fibers different from the fibers, and split-structure composite fibers in which syndiotactic polypropylene fibers and polyolefin fibers are joined to each other in a circular shape can be exemplified. The average fiber diameter of the syndiotactic polypropylene fiber and the polyolefin fiber is 1 from the viewpoint of mechanical strength and prevention of short circuit between the positive electrode and the negative electrode.
It is preferable to set it to 20 μm.

The ratio of the syndiotactic polypropylene fiber in the synthetic resin fiber sheet is specified because if the ratio of the fiber is less than 80% by volume, it is difficult to impart high elasticity and strength to the separator. become. A more preferable ratio of the syndiotactic polypropylene fiber is 80% by volume or more.

Examples of the sheet include a nonwoven fabric made of the above-mentioned syndiotactic polypropylene fiber alone or mixed with other fibers, a woven fabric made of the same fiber, or a composite sheet made of these nonwoven fabrics and a woven fabric. be able to. The nonwoven fabric is produced by, for example, a dry method, a wet method, a spun bond method, a melt blow method, or the like.

The sheet has a basis weight of 40 to 70 g /
It is preferable that m ² and the thickness be 0.1 to 0.2 mm.

The separator 3 includes a copolymer having a hydrophilic group on the surface of the syndiotactic polypropylene fiber or polyolefin fiber in order to exhibit hydrophilicity.
For example, those having a structure coated with an ethyl vinyl alcohol copolymer or the like and those obtained by graft copolymerizing a vinyl monomer having a hydrophilic group on the sheet-like material are preferable. Here, as the vinyl monomer having a hydrophilic group, for example, acrylic acid, methacrylic acid, esters of the acrylic acid and the methacrylic acid, vinyl pyridine, styrene sulfonic acid,
Examples thereof include those having a functional group capable of forming a salt by directly reacting with an acid or base such as styrene, and those having a functional group capable of forming a salt upon hydrolysis after graft copolymerization. Acrylic acid is preferred among the vinyl monomers.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH. In particular, an electrolytic solution obtained by mixing an aqueous KOH solution with an aqueous NaOH solution or an aqueous LiOH solution is preferable.

The alkaline storage battery according to the present invention described above comprises a separator made of a synthetic resin fiber sheet containing at least 80% by volume of syndiotactic polypropylene fiber having high elasticity and high strength. When the degree of binding is increased by interposing the separator therebetween, the separator has a high compressive strength and can sufficiently hold the electrolytic solution.
As a result, the depletion of the electrolyte in the separator during the charge / discharge cycle can be suppressed, and the cycle life can be improved.

Further, by using the fiber subjected to the hydrophilic treatment as the synthetic resin sheet, the retention of the electrolyte in the separator can be further improved, so that an alkaline storage battery having a longer cycle life can be realized.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIG.

Example 1 <Preparation of Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide particles and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 part by weight of carboxymethyl cellulose and 0.175 parts by weight of sodium polyacrylate. A paste was prepared by adding 0.2 parts by weight of a polytetrafluoroethylene dispersion, 45 parts by weight of pure water, and kneading them. Subsequently, the paste was filled in a nickel fiber substrate, dried, and roller-pressed to a predetermined thickness to produce a paste-type positive electrode.

<Preparation of Paste Type Negative Electrode> LmNi _4.0 C
o _0.4 Mn _0.3 Al _0.3 (where Lm is a lanthanum-enriched misch metal) composition and 100 parts by weight of a hydrogen storage alloy powder with sodium polyacrylate 0.5
Parts by weight, carboxymethylcellulose (CMC) 0.1
A paste was prepared by mixing 25 parts by weight, 1.0 part by weight of polytetrafluoroethylene and 1.0 part by weight of carbon powder with 50 parts by weight of water. This paste was applied to punched metal, dried and then molded under pressure to produce a paste type negative electrode.

<Preparation of Separator> A syndiotactic polypropylene and a polypropylene were spunlaid using 80% by volume of syndiotactic polypropylene fiber having an average fiber diameter of 9 μm and 20% by volume of polypropylene fiber having the same fiber diameter, and the basis weight was 50 g / m ^{2, and} the
A nonwoven fabric having a thickness of 150 μm was produced. Subsequently, the nonwoven fabric was immersed in an aqueous solution of acrylic acid, and then irradiated with ultraviolet rays to graft copolymerize the acrylic acid monomer. Subsequently, the nonwoven fabric was washed to remove unreacted acrylic acid, and then dried to produce a separator.

Next, the separator was interposed between the negative electrode and the positive electrode, and spirally wound to form an electrode group. By storing such an electrode group and an electrolytic solution comprising 8N KOH in a cylindrical container having a bottom, a 4 / 3A-size cylindrical nickel-metal hydride battery having the above-described structure shown in FIG. 1 was assembled.

(Comparative Example 1) The same structure as in Example 1 except that a nonwoven fabric consisting of only polypropylene fibers having an average fiber diameter of 9 μm was graft-copolymerized with an acrylic acid monomer was used as a separator, and the structure shown in FIG. A 4 / 3A size cylindrical nickel-metal hydride battery having the following characteristics was assembled.

(Comparative Example 2) Except that a nonwoven fabric composed of 10% by volume of syndiotactic polypropylene fiber having an average fiber diameter of 9 μm and 90% by volume of polypropylene fiber having the same fiber diameter was graft-copolymerized with an acrylic acid monomer as a separator. FIG. 1 is similar to FIG.
A 4 / 3A size cylindrical nickel-metal hydride storage battery having the structure shown in FIG.

(Comparative Example 3) Except that a nonwoven fabric composed of 30% by volume of syndiotactic polypropylene fiber having an average fiber diameter of 9 μm and 70% by volume of polypropylene fiber having the same fiber diameter was graft-copolymerized with an acrylic acid monomer as a separator. FIG. 1 is similar to FIG.
A 4 / 3A size cylindrical nickel-metal hydride storage battery having the structure shown in FIG.

Comparative Example 4 A non-woven fabric consisting of 50% by volume of syndiotactic polypropylene fibers having an average fiber diameter of 9 μm and 50% by volume of polypropylene fibers having the same fiber diameter was graft-copolymerized with an acrylic acid monomer as a separator. FIG. 1 is similar to FIG.
A 4 / 3A size cylindrical nickel-metal hydride storage battery having the structure shown in FIG.

In the obtained storage batteries of Example 1 and Comparative Examples 1 to 4, charging and discharging were repeated at 150% charge at 1 CmA in an atmosphere of 20 ° C. until the battery voltage reached 1.0 V at 1 CmA. Battery voltage 1.0 V at 1 CmA
The discharge capacity was calculated from the time at which the battery voltage reached 1.0 V at 1 CmA in each cycle. The result is shown in FIG. The cycle number ratio on the horizontal axis in FIG. 2 indicates that the number of cycles at which the discharge capacity of the storage battery of Example 1 reached 80% of the discharge capacity in the first cycle was 10
As 0, the number of cycles of the storage batteries of Comparative Examples 1 to 4 is shown as a relative value.

As is apparent from FIG. 2, the storage battery of Example 1 provided with a separator made of a non-woven fabric containing 80% by volume or more of syndiotactic polypropylene fiber was the same as that of Comparative Example 1 provided with a separator made of a non-woven fabric of polypropylene fiber alone. It can be seen that the battery has a longer charge / discharge cycle life than the storage batteries and the storage batteries of Comparative Examples 2 to 4 including the nonwoven fabric separator having a content of syndiotactic polypropylene fiber of less than 80% by volume. This is because the nonwoven fabric containing 80% by volume or more of syndiotactic polypropylene fiber can sufficiently retain the electrolyte even in a compressed state in a high-tension storage battery due to the elasticity of the fiber, and the electrolyte in the separator during the cycle progresses. This is because depletion can be suppressed.

[0041]

As described above, according to the present invention, it is possible to hold a sufficient amount of electrolyte when a separator is disposed between a positive electrode and a negative electrode and a high-tightness electrode is incorporated in a container. It is possible to provide an alkaline storage battery including a separator, which suppresses the depletion of the electrolyte during a charge / discharge cycle and has an improved cycle life.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a cylindrical nickel-metal hydride storage battery which is an example of an alkaline storage battery according to the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the cycle number ratio and the capacity in the storage batteries of Example 1 of the present invention and Comparative Examples 1 to 4.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. An alkaline storage battery comprising a separator made of a synthetic resin fiber sheet containing at least 80% by volume of syndiotactic polypropylene fiber.