JPH1197003A - Nickel hydrogen secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel hydrogen secondary cell which keeps its capacity as specified, and is excellent in charging/discharging cyclic characteristics. SOLUTION: This cell is a closed type nickel hydrogen secondary cell equipped with each negative electrode 4 containing hydrogen occluded alloy powder, each positive electrode 2 which contains nickel hydroxide as active material, and is located to each negative electrode 4 while each separator 3 is being held in between, and with alkaline electrolyte. In this case, the aforesaid hydrogen occluded alloy contains the following components such as manganese, cobalt, and aluminum, has a surface layer as thin as 1 to 3 μm which has no specified constituent as mentioned above, or is lower in concentration than its internal part, and furthermore, the aforesaid surface layer is sheathed with a metallic layer having oxygen gas reaction properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen secondary battery having an improved negative electrode containing a hydrogen storage alloy.

[0002]

2. Description of the Related Art A sealed nickel-metal hydride secondary battery is composed of a paste-type positive electrode containing nickel hydroxide as an active material and a paste-type negative electrode containing a hydrogen-absorbing alloy with an electrode group together with an alkaline electrolyte. It is housed in a container and has a closed structure. Such sealed nickel-metal hydride secondary batteries have been widely put into practical use as operating power supplies for various electronic devices such as portable telephones and portable imaging devices.

[0003] The characteristics of a nickel-metal hydride secondary battery are governed by the balance between the negative electrode, the positive electrode, and the alkaline electrolyte.

In the hydrogen storage alloy, if the equilibrium plateau pressure at the time of storing and releasing hydrogen is high, the internal pressure of the battery increases and the safety decreases. For this reason, LaNi ₅ based alloy, MmNi ₅
It is common to control the equilibrium pressure by substituting part of Ni in Mn-based alloys (Mm; misch metal which is a mixture of lanthanum-based elements such as La, Ce, Pr, Nd, and Sm) with Mn, Al, Co, etc. It is being done. Among these substituted metals, Mn can reduce the equilibrium pressure for hydrogen absorption and desorption with a small amount, and plays an important role. However, on the other hand, since Mn has a higher vapor pressure than other metals, it evaporates and segregates in the vicinity of the surface in the melting step when producing an alloy. For this reason, it is difficult to produce a uniform alloy with a hydrogen storage alloy containing Mn. A negative electrode containing a hydrogen-absorbing alloy having a heterogeneous composition is corroded and deteriorated when a charge / discharge cycle is repeated, and a non-alloyed metal is eluted in an alkaline electrolyte. The former corrosion of the hydrogen storage alloy inhibits a smooth consumption reaction of oxygen gas on the negative electrode surface. Elution of the latter alloy component poisons the alkaline electrolyte. As a result, the cycle characteristics of the secondary battery are significantly reduced.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a nickel-metal hydride secondary battery which maintains a predetermined capacity and has an increased charge / discharge cycle life.

[0006]

A nickel-hydrogen secondary battery according to the present invention comprises a negative electrode containing hydrogen-absorbing alloy powder, a positive electrode containing nickel hydroxide as an active material and having a negative electrode and a separator interposed therebetween. A sealed nickel-metal hydride secondary battery comprising an alkaline electrolyte, wherein the hydrogen-absorbing alloy has a composition containing manganese, cobalt, and aluminum, wherein the specific component does not exist or has a thickness less than that of the inside. It has a surface layer of about 3 μm, and is coated with a metal layer having oxygen gas reactivity on the surface.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A nickel-metal hydride secondary battery (cylindrical nickel-metal hydride secondary battery) according to the present invention will be described below with reference to FIG.

An electrode group 5 produced by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and spirally winding them is accommodated in a cylindrical container 1 having a bottom. 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
Is arranged between the periphery of the container and the inner surface of the upper opening of the container 1,
The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking to reduce 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. Rubber safety valve 1
1 is arranged so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 so that a protrusion of the positive electrode terminal 10 is provided on the holding plate 1.
2 so as to protrude from the holes. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

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

1) Negative Electrode 4 The negative electrode contains a hydrogen storage alloy having a composition containing manganese (Mn), cobalt (Co), and aluminum (Al) [these are referred to as specific components]. This hydrogen storage alloy
It has a structure in which the specific component does not exist or has a surface layer having a thickness of 1 to 3 μm at a lower concentration than the inside, and a surface is coated with a metal layer having oxygen gas reactivity.

As the hydrogen storage alloy, for example, LaN
i ₅ , MmNi ₅ (Mm; misch metal), LmNi
₅ A part of Ni of (Lm; lanthanum-enriched misch metal) is converted to Al, Mn, Co, Ti, Cu, Zn, Zr, C
A multi-element material selected from r and B and substituted with an element containing at least Al, Co and Mn can be given. Above all, the general formula _{LmNi w Co x Al y Mn z} ( where atomic ratios w, x, y, z are 3.30 ≦ w ≦ respectively
4.50, 0.50 ≦ x ≦ 1.10, 0.20 ≦ y ≦
0.50, 0.05 ≦ z ≦ 0.20, and the sum thereof is represented by 4.90 ≦ w + x + y + z ≦ 5.50). The hydrogen storage alloy represented by the general formula can further improve the cycle life. More preferable values of the atomic ratio w, x, y, z are 3.80 ≦ w ≦ 4.20, 0.7, respectively.
0 ≦ x ≦ 0.90, 0.30 ≦ y ≦ 0.40, 0.08
≦ z ≦ 0.130 and the total value is 5.00 ≦ w +
x + y + z ≦ 5.20.

[0012] When the specific component is present, the surface layer of the hydrogen storage alloy preferably has a concentration of 10% or less with respect to the specific component inside.

The reason why the thickness of the surface layer of the hydrogen storage alloy is specified is that, when the thickness is less than 1 μm, the specific component is easily diffused into the metal layer coated on the surface, and the poisoning of the alkaline electrolyte is prevented. Cause On the other hand, when the thickness of the surface layer is 3
If it exceeds μm, the original hydrogen storage properties of the hydrogen storage alloy may be impaired.

As the metal layer, for example, Ni, Ni-
P and the like. It is preferable that the thickness of such a metal layer be 1 to 3 μm.

The hydrogen storage alloy having the above structure is produced by, for example, the following method. First, given Mn,
A hydrogen storage alloy having a composition containing Co and Al is pulverized to obtain a hydrogen storage alloy powder having a desired particle size. Subsequently, the hydrogen storage alloy powder is immersed in an alkaline solution (preferably a heated alkaline solution) to elute and remove specific components such as Mn, Co and Al on the surface of the powder. Note that the surface of the powder is roughened by this elution treatment, and the specific surface area is increased. Subsequently, the hydrogen storage alloy is removed from the alkaline solution, washed with water, and dried. Next, a hydrogen storage alloy powder having a surface coated with the metal layer is prepared by subjecting the powder to electroless plating with a metal having oxygen gas reactivity by a known method.

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 has a structure in which a positive electrode material containing nickel hydroxide particles as an active material, a conductive material and a polymer binder is supported on a conductive substrate.

As the nickel hydroxide particles, for example, a single nickel hydroxide particle or a nickel hydroxide particle in which a metal such as zinc, cobalt, bismuth or copper is coprecipitated with metallic nickel can be used. In particular, the latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high-temperature state.

The nickel hydroxide particles have a peak half-value width of the (101) plane determined by an X-ray powder diffraction method of 0.8 ° / 2θ.
(Cu-Kα) or more is preferable. More preferable peak half width of nickel hydroxide particles is 0.9 to 1.0.
゜ / 2θ (Cu-Kα).

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

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

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

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

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.

The above-described nickel-metal hydride secondary battery according to the present invention comprises a negative electrode containing a hydrogen storage alloy powder, a positive electrode containing nickel hydroxide as an active material and having a separator interposed therebetween, and an alkaline electrolyte. A sealed nickel-metal hydride secondary battery comprising: the hydrogen storage alloy,
A composition containing manganese, cobalt, and aluminum, wherein the specific component is not present or has a surface layer having a thickness of 1 to 3 μm with a lower concentration than the inside, and a metal layer having oxygen gas reactivity is coated on the surface. I have.

Since the hydrogen storage alloy has a composition containing manganese, cobalt and aluminum, it has an appropriate equilibrium plateau pressure when storing and releasing hydrogen.

Further, the hydrogen storage alloy has a surface layer of a predetermined thickness in which the specific component does not exist or has a lower concentration than the inside, and a metal layer having oxygen gas reactivity is coated on the surface. Therefore, in the repetition of the charge / discharge cycle, the specific component can be prevented from being eluted into the alkaline electrolyte. In particular, since the specific component can be prevented from being diffused and taken into the metal layer when the metal layer is formed, it is possible to prevent the specific component from being eluted into the alkaline electrolyte during repeated charge / discharge cycles.

Further, the metal layer is coated on the surface of the alloy powder having a large specific surface area having the surface layer, and the coated area is increased, so that the reactivity of consumption of oxygen gas generated during a charge / discharge cycle can be improved.

Therefore, according to the present invention, it is possible to obtain a nickel-metal hydride secondary battery having a predetermined capacity and excellent charge-discharge cycle characteristics.

In FIG. 1 described above, the separator 3 is interposed between the positive electrode 2 and the negative electrode 4 and spirally wound and accommodated in the bottomed cylindrical container 1. The battery is not limited to such a structure. For example, a prismatic nickel-metal hydride secondary battery may be configured by interposing a separator between a positive electrode and a negative electrode, and stacking a plurality of the laminated members in a bottomed rectangular cylindrical container.

[0035]

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 Paste-Type Negative Electrode> Commercially available misch metal Mm and each element of Ni, Co, Mo, and Al were heated and melted in a high frequency furnace, and then cooled to obtain MmNi _4.0.
A hydrogen storage alloy having a composition of Co _0.4 Mn _0.3 Al _0.3 was produced. This alloy was mechanically pulverized to obtain a hydrogen storage alloy powder having an average particle size of 37 μm. Subsequently, the hydrogen storage alloy powder was immersed in an 8N-KOH aqueous solution at 120 ° C. for 1 hour to elute and remove specific components such as Mn, Co and Al on the surface of the powder. This elution treatment roughened the powder surface and increased the specific surface area. Subsequently, the supernatant was removed, washed with water, the pH of the solution was lowered, filtered, and dried to obtain a hydrogen storage alloy powder. Thereafter, the powder was subjected to electroless plating using a known Ni-based electroless plating bath to produce a hydrogen storage alloy powder having a surface coated with a 3 μm-thick Ni layer.

Next, the obtained hydrogen storage alloy powder 100
0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethylcellulose (CMC), and a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60% by weight) in terms of solid content were added to 2 parts by weight. A paste was prepared by adding 5 parts by weight and 1.0 part by weight of carbon black and mixing with 50 parts by weight of water. This paste was applied to a punched metal as a conductive substrate, dried, and then pressed to produce a negative electrode.

<Preparation of Paste-Type Positive Electrode> A mixture of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with carboxymethyl cellulose (CM).
C) 0.3 parts by weight of polytetrafluoroethylene dispersion (specific gravity 1.5, solids content 60% by weight) is added in an amount of 0.5 parts by weight in terms of solids, and mixed with 45 parts by weight of pure water. To prepare a paste. Subsequently, this paste was filled in a nickel-plated metal porous body, dried, and then rolled by roller pressing to produce a positive electrode.

Next, a separator made of a nonwoven fabric made of polypropylene fiber subjected to hydrophilic treatment was interposed between the negative electrode and the positive electrode, and spirally wound to form an electrode group. After storing such an electrode group in an AA-size cylindrical container with a bottom, an electrolytic solution composed of 7N potassium hydroxide and 1N lithium hydroxide is stored, and sealing is performed, as shown in FIG. 1 described above. With structure, positive electrode capacity 1200mA
h, a cylindrical nickel-metal hydride secondary battery having a negative electrode capacity of 2000 mAh was assembled.

(Comparative Example 1) A negative electrode produced by using a Ni-coated hydrogen storage alloy powder obtained by simply subjecting a hydrogen storage alloy having the same composition as in Example 1 to mechanical pulverization and electrolessly plating Ni. A cylindrical nickel-metal hydride secondary battery having the above-described structure shown in FIG.

(Comparative Example 2) A negative electrode having the same structure as in Example 1 except that the negative electrode was prepared by using a hydrogen storage alloy powder obtained by simply mechanically pulverizing a hydrogen storage alloy having the same composition as in Example 1 was used. The assembled cylindrical nickel-metal hydride secondary battery having the structure shown in FIG. 1 was assembled.

The obtained secondary batteries of Example 1 and Comparative Examples 1 and 2 were charged at a high temperature of 45 ° C .;
A, discharge for 90 minutes; 1200 mA, cutoff voltage 1
An accelerated cycle test under the condition of V was performed, and the discharge capacity was 900
The number of cycles when the value became equal to or less than mAh was determined. The results are shown in Table 1 below.

[0043]

[Table 1]

As is clear from Table 1, the secondary battery of Example 1 is a secondary battery of Comparative Example 1 provided with a negative electrode having a hydrogen storage alloy powder having a structure in which a Ni layer is simply coated on the surface.
The cycle life can be significantly increased as compared with the secondary battery of Comparative Example 2 including the negative electrode having the hydrogen storage alloy powder not covered with the Ni layer. This is because Co, Mn, A
The negative electrode of Example 1 having a hydrogen absorbing alloy powder having a structure in which a surface layer having a specific thickness lower than that of a specific component such as l and a Ni layer is formed on the surface thereof is formed by simply coating the Ni layer. This is because the oxygen gas consumption characteristics are superior to the hydrogen storage alloy described above.

[0045]

As described above, according to the present invention, it is possible to provide a nickel-hydrogen secondary battery which maintains a predetermined capacity and has excellent charge-discharge cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a perspective view of a nickel-metal hydride secondary battery as an example of a nickel-metal hydride secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket.

Claims (1)

[Claims] 1. A sealed nickel-metal hydride secondary battery comprising a negative electrode containing a hydrogen-absorbing alloy powder, a positive electrode containing nickel hydroxide as an active material disposed with a separator interposed between the negative electrode and an alkaline electrolyte. The hydrogen storage alloy has a composition containing manganese, cobalt, and aluminum, and has a surface layer having a thickness of 1 to 3 μm in which the specific component does not exist or has a lower concentration than the inside, and an oxygen gas reaction on the surface. A nickel-metal hydride secondary battery, which is covered with a metal layer having a property.