JP2001236930A - Secondary alkaline battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary alkaline battery that suppresses or prevents corrosion on the inner face of its can body, bent portions of the bottom corner of the can body in particular, in use at a high temperature. SOLUTION: The secondary alkaline battery houses positive and negative poles, separator and alkaline electrolyte in the can body, and at least bent portions at the bottom corner on the inner face of the said can body are covered with alkaliproof coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As high-capacity secondary batteries, nickel-cadmium secondary batteries, nickel-hydrogen secondary batteries and lithium ion secondary batteries are known. Of these, nickel
Hydrogen secondary batteries are widely used in portable devices and the like, replacing small nickel-cadmium secondary batteries as small sealed secondary batteries having excellent environmental compatibility.

[0003] In recent years, the number of devices that continuously charge a secondary battery with a small current for a long period of time has been increasing. However, secondary batteries containing an alkaline electrolyte have been used under severe conditions, particularly under extremely high temperatures. If the battery is left in a charged state for a long period of time, local deep corrosion occurs on the inner surface of the can (particularly, the curved bottom surface of the can). The cause of this corrosion is not clear, but when nickel plating is applied to a can body made of steel, if the nickel plating film on the inside of the can body is thin or pinholes are present, when charging is continued It is considered that the pressure inside the can increases and a very large stress is applied locally, resulting in local corrosion.

[0004] When such local deep corrosion occurs in the can body, iron constituting the can body elutes into the electrolytic solution, resulting in deterioration of battery characteristics and, in extreme cases, leakage of liquid. .

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an alkaline secondary battery which suppresses or prevents corrosion of the inner surface of a can, particularly the curved portion of the bottom corner of the can, when used at a high temperature.

[0006]

An alkaline secondary battery according to the present invention is an alkaline secondary battery in which a positive electrode, a negative electrode, a separator and an alkaline electrolyte are housed in a can body, wherein at least a bottom corner of the inner surface of the can body is provided. The curved surface portion is characterized by being covered with an alkali-resistant film.

[0007] In the alkaline secondary battery according to the present invention,
Preferably, the positive electrode contains a nickel compound as an active material, and the negative electrode contains a hydrogen storage alloy.

[0008] In the alkaline secondary battery according to the present invention,
It is preferable that the material of the can is made of iron, and the inner bottom surface curved surface portion is covered with a nickel plating layer having a thickness of 0.5 μm or less or a plating layer containing nickel as a main component.

In the alkaline secondary battery according to the present invention,
The alkali-resistant coating is preferably made of an organic substance. In particular, the organic substance is preferably selected from any of synthetic resin, rubber, bitumen, and silicone.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (cylindrical nickel-metal hydride secondary battery) according to the present invention will be described with reference to FIGS.

An electrode group 5 produced by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a bottomed cylindrical can body 1. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the can 1. The alkaline electrolyte is contained in the can 1.

A circular sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the can 1. The ring-shaped insulating gasket 8 is provided on the periphery of the sealing plate 7 and the can body 1.
The sealing plate 7 is airtightly fixed to the can body 1 via the gasket 8 by caulking processing for reducing the diameter of the upper opening inward. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. The rubber safety valve 11 is provided with the sealing plate 7.
And a hole surrounded by the positive electrode terminal 10 so as to cover the hole 6. 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 projection of the positive electrode terminal 10 projects from the hole of the holding plate 12. The outer tube 13 includes a periphery of the holding plate 12, a side surface of the can 1, and the can 1.
Of the bottom portion of the cover.

In the nickel-hydrogen secondary battery having the structure shown in FIG. 1 described above, the can 1 is made of, for example, steel, and the entire inner surface thereof is nickel-plated. This nickel plating film preferably has a thickness of 0.5 μm or less. Further, as shown in FIG. 2, the can body 1 has at least a bottom curved surface portion, for example, a bottom curved surface portion of its inner surface covered with an alkali-resistant coating 14.

Next, the negative electrode 4, the positive electrode 2, the separator 3, the electrolyte and the alkali-resistant coating 14 will be described.

1) Negative electrode 4 The negative electrode contains a hydrogen storage alloy.

The hydrogen storage alloy is not particularly limited. For example, LaNi ₅ , MmNi ₅ (M
m; misch metal), LmNi ₅ (Lm; lanthanum-enriched misch metal), or a part of these Nis as Al, Mn, Co, Fe, Ti, Cu, Zn, Zr, C
a multi-element system substituted by elements such as r and B, TiN
i-based, TiFe-based, ZrNi-based, and MgNi-based ones. Among them, the general formula ANi _v Co _w Mn _x
Al _y (However, A is a rare earth element consisting of La70 wt% or more, preferably Lm, atomic ratio v, w, x, y respectively 3.30 ≦ v ≦ 4.50,0.30 ≦ w ≦ 1.1
0, 0.05 ≦ x ≦ 0.40, 0.20 ≦ y ≦ 0.50
And the total value is 4.90 ≦ v + w + x + y ≦ 5.
50 is preferably used.
More preferable values of the atomic ratios v, w, x, y are 3.80 ≦ v ≦ 4.20, 0.60 ≦ w ≦ 0.90, respectively.
0.08 ≦ x ≦ 0.30, 0.30 ≦ y ≦ 0.40,
And the total value is 5.00 ≦ w + x + y ≦ 5.30.

The negative electrode 4 is prepared, for example, by adding a conductive material to the hydrogen storage alloy powder, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate, and drying the paste. , Manufactured by molding.

Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

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

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

2) Positive Electrode 2 The positive electrode 2 contains a nickel compound as an active material.

As the nickel compound, for example, nickel hydroxide, nickel oxide and the like can be used. The nickel hydroxide may be used alone or may be a metal such as zinc, cobalt, bismuth or copper co-precipitated with metallic nickel. In particular, the latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high-temperature state.

The positive electrode 2 is prepared, for example, by adding a conductive material to a nickel compound (particulate) as an active material, kneading it with a polymer binder and water to prepare a paste, and filling this paste into a conductive substrate. After drying and drying, it is produced by molding.

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

Examples of the polymer binder include hydrophobic polymers such as polytetrafluoroethylene, polyethylene, and polypropylene; cellulosic materials such as carboxymethylcellulose, methylcellulose and hydroxypropylmethylcellulose; and acrylics such as sodium polyacrylate. Acid esters; hydrophilic polymers such as polyvinyl alcohol and polyethylene oxide; and rubber-based polymers such as latex.

Examples of the conductive substrate include a mesh-like, sponge-like, fibrous, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

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

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.

5) Alkali-resistant film 14 This alkali-resistant film 14 is preferably made of an organic substance. Specifically, polyamide, polyethylene,
Synthetic resins such as polypropylene, acrylic resin and fluororesin; rubbers such as styrene-butadiene rubber, nitrile rubber, fluororubber and silicone rubber;
Bitumens such as pitch and tar; and silicone coatings such as silicone oil and silicone varnish; and the like.

The thickness of the alkali-resistant coating is 5 to 10
Preferably, the thickness is 0 μm. If the thickness of the alkali-resistant coating is less than 5 μm, it becomes difficult to effectively prevent corrosion of the curved bottom surface of the can body. on the other hand,
If the thickness of the alkali-resistant coating exceeds 100 μm, the coating must be thickened and re-coating or the like must be performed. In addition to the reduction in workability, the internal volume of the battery is reduced, and the amount of electrolyte that can be filled is reduced. There is a possibility that the characteristics are deteriorated.

The above-described alkaline secondary battery according to the present invention has a structure in which at least a corner-curved portion at the bottom of the inner surface of the can in which the positive electrode, the negative electrode, the separator and the alkaline electrolyte are stored is coated with an alkali-resistant coating. According to such a configuration, it is possible to prevent the alkali electrolyte from coming into contact with the material of the can body at the bottom corner curved surface portion of the can body to which the internal pressure is applied or the residual stress during processing is applied, by coating the alkali-resistant film. As a result, it is possible to suppress or prevent the occurrence of local deep corrosion at the bottom corner curved surface portion of the can body. Therefore,
Since the iron constituting the can can be prevented from being eluted into the electrolytic solution, an alkaline secondary battery having excellent long-term charging characteristics at high temperatures can be realized.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Negative Electrode> Lm, Ni, Co, Mo, Al, Zr
LmNi consisting of each element of_4.0Co _0.4Mn_0.3Al
_0.3Was prepared. 1000 ° C
Heat treatment in an argon atmosphere for 10 hours to equalize the alloy composition
Quality. 100 parts by weight of the pulverized powder of this hydrogen storage alloy
0.5 parts by weight of sodium acrylate, carboxymethy
0.12 parts by weight of cellulose (CMC), polytetraf
Dispersion of fluoroethylene (specific gravity 1.5, solid
60% by weight) and 1.0 part by weight in terms of solid content.
Added 1.0 parts by weight of carbon black as an electrically conductive material
And paste it by mixing with 30 parts by weight of water.
Prepared. This paste has a porosity of 9 as a conductive substrate.
Fill in 5% foamed nickel and dry at 125 ° C
To produce a negative electrode.

<Preparation of Positive Electrode> A mixed powder comprising 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 parts of carboxymethyl cellulose (CMC).
A paste was prepared by adding 0.5 parts by weight of a polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60% by weight) in terms of solid content and mixing with 45 parts by weight of pure water. . Subsequently, the paste was filled in a foamed nickel substrate and dried to produce a positive electrode.

Next, the AA size steel bottomed cylindrical can body was subjected to electrolytic nickel plating to a nickel plating thickness of 0.2 to 0.5 μm at the bottom of the inner surface of the can body. Subsequently, a suspension obtained by dispersing polyethylene fine particles in water is applied to the bottom corner curved surface of the inner surface of the can, and then heat-treated at 120 ° C. for 1 hour to evaporate the water content of the coating film. 30μ thickness by melting
m of the alkali-resistant coating was formed on the bottom corner curved surface of the inner surface of the can. Next, a 0.2-mm-thick separator made of a nonwoven fabric made of polyamide fiber was interposed between the negative electrode and the positive electrode, and spirally wound to form an electrode group. After such an electrode group is housed in the bottomed cylindrical can body, an electrolyte solution made of potassium hydroxide having a specific gravity of 1.31 is housed, and the structure shown in FIG. ,
An AA-size cylindrical nickel-metal hydride secondary battery having a theoretical capacity of 1200 mAh was assembled.

Example 2 Example 1 was repeated except that a bottomed cylindrical can having an alkali-resistant coating described below was used.
AA nickel-metal hydride secondary battery having the same AA size was assembled.

That is, an AA size steel bottomed cylindrical can body was subjected to electrolytic nickel plating to make the nickel plating thickness at the bottom of the inner surface of the can body 0.2 to 0.5 μm. Subsequently, a suspension obtained by dispersing styrene-butadiene rubber latex microparticles in water was applied to the bottom curved surface of the inner surface of the can, and then heat-treated at 100 ° C. for 1 hour to evaporate the water content of the coating. An alkali-resistant coating having a thickness of 30 μm was formed on the bottom corner curved surface of the inner surface of the can. (Example 3) AA similar to Example 1 except that a bottomed cylindrical can having an alkali-resistant coating described below was used.
A cylindrical nickel-metal hydride secondary battery having a size was assembled.

That is, electrolytic nickel plating was applied to an AA-size steel bottomed cylindrical can body so that the nickel plating thickness at the bottom of the inner surface of the can was 0.2 to 0.5 μm. Subsequently, an asphalt solution obtained by dissolving asphalt with toluene was applied to the bottom corner curved surface of the inner surface of the can, and then
By performing a heat treatment at 0 ° C. for 30 minutes, an alkali-resistant film having a thickness of 30 μm was formed on the curved surface at the bottom corner of the inner surface of the can. (Example 4) AA similar to that of Example 1 except that a bottomed cylindrical can having an alkali-resistant coating described below was used.
A cylindrical nickel-metal hydride secondary battery having a size was assembled.

That is, an AA size steel bottomed cylindrical can body was subjected to electrolytic nickel plating so that the nickel plating thickness at the bottom of the inner surface of the can was 0.2 to 0.5 μm. Subsequently, a silicone varnish was applied to the bottom corner curved surface of the inner surface of the can, and then heat-treated at 50 ° C. for 30 minutes to form a 30 μm thick alkali-resistant film on the bottom corner curved surface of the inner surface of the can. (Comparative Example 1) A cylindrical nickel-metal hydride secondary battery having the same AA size as in Example 1 was assembled except that a cylindrical can body with a bottom was used in which an alkali-resistant coating was not formed on the inner bottom curved surface.

The obtained secondary batteries of Examples 1 to 4 and Comparative Example 1 were charged and discharged to 25% at 25 ° C. and 1 C, and then discharged to 1.0 V three times. Further, 30 secondary batteries charged to 150% at 1C were prepared, and charged at 0.1C at a high temperature of 90 ° C for 50 days. After the charging for 50 days, the secondary battery was disassembled, and the bottom curved surface of the inner surface of the bottomed cylindrical can was observed with a microscope. The results are shown in Table 1 below.

[Table 1]

As is clear from Table 1, the secondary batteries of Examples 1 to 4 in which the curved surface at the bottom corner of the inner surface of the bottomed cylindrical can was coated with an alkali-resistant coating, were charged at a high temperature. It can be seen that the number of occurrences of corrosion at the curved surface portion is significantly lower than that of the secondary battery of Comparative Example 1 in which the bottom corner curved surface portion of the inner surface of the bottomed cylindrical can is not coated with the alkali-resistant coating.

[0042]

As described above, according to the present invention, corrosion of the inner surface of a can, particularly the curved portion of the bottom corner of the can at the time of use at a high temperature is suppressed or prevented, and excellent long-term charging characteristics at a high temperature are obtained. The alkaline secondary battery can be provided.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view of a main part of the can body of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Can body, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket, 14 ... Alkali-resistant coating.

Claims (5)

[Claims] 1. An alkaline secondary battery in which a positive electrode, a negative electrode, a separator, and an alkaline electrolyte are housed in a can body, wherein at least a bottom corner curved surface portion of the inside of the can body is covered with an alkali-resistant film. Characteristic alkaline secondary battery. 2. The alkaline secondary battery according to claim 1, wherein the positive electrode contains a nickel compound as an active material, and the negative electrode contains a hydrogen storage alloy. 3. The method according to claim 1, wherein the can body is made of iron, and the inner surface of the can body is covered with a nickel plating layer having a thickness of 0.5 μm or less or a nickel-based plating layer. The alkaline secondary battery according to claim 1, wherein: 4. The alkaline secondary battery according to claim 1, wherein the alkali-resistant coating is made of an organic material. 5. The alkaline secondary battery according to claim 4, wherein the organic substance is selected from synthetic resin, rubber, bitumen, and silicone.