JP2000090921A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery with high discharge capacity at low temperature in addition to good charge/discharge cycle characteristics. SOLUTION: A negative electrode contains a mixture of alloy powder having a specific surface area by BET method of 0.05-0.07 m2/g obtained by mechanical crushing of a rare-earth family hydrogen storage alloy (A) having a large specific area by BET method when hydro-crushing is conducted once at 2-30 deg.C and at 5-10 atm. (gage pressure), and alloy powder having a specific surface area by BET method of 0.10-0.12 m2/g obtained by mechanical crushing of a rare-earth family hydrogen storage alloy (B) having a small specific surface area by BET method when hydro-crushing is conducted similarly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery having an improved negative electrode containing a hydrogen storage alloy.

[0002]

2. Description of the Related Art In recent years, an alkaline secondary battery provided with a negative electrode including a hydrogen storage alloy that stores and releases hydrogen has attracted attention. This secondary battery has a high energy density, has a high volumetric efficiency, can operate safely, and has high reliability in characteristics.

[0003] Examples of the hydrogen-absorbing alloy used in the negative electrode material, AB ₅ type LaNi ₅ has been frequently used conventionally. Although this hydrogen storage alloy has excellent characteristics as a negative electrode material, it is not practical because La is expensive. Therefore, misch metal (Mm), which is a mixture of lanthanum-based elements such as La, Ce, Pr, Nd, and Sm.
MmNi ₅ which is an alloy of Ni and Ni is also widely used. For LaNi ₅ and MmNi ₅ , N
Part of i is Co, Mn, Al, Cu, Zr, Fe, T
Multi-elements substituted with elements such as i, Cr, V and B have also been used.

In order to apply the above-mentioned hydrogen storage alloy as a negative electrode material, the constituent elements of the alloy are melted, for example, in response to intoxication by the public to form an alloy ingot, which is mechanically pulverized to a powder state.

[0005]

However, the alkaline secondary battery provided with the negative electrode containing the powder of the hydrogen storage alloy has a problem that the discharge capacity under low temperature conditions (-20 ° C.) at the beginning of the cycle is low.

An object of the present invention is to provide an alkaline secondary battery having a large discharge capacity under a low temperature condition while maintaining good charge / discharge cycle characteristics.

[0007]

The alkaline secondary battery according to the present invention has a specific surface area determined by the BET method when hydrogenated and pulverized once at a temperature of 2 to 30 ° C. and a pressure of 5 to 10 atm (gauge pressure). The specific surface area by the BET method obtained by mechanically pulverizing a large rare earth hydrogen storage alloy (A) is 0.05 to 0.07 m ² /
g alloy powder having a small specific surface area according to the BET method when crushed with hydrogen by the same hydrogen method. The specific surface area according to the BET method obtained by mechanically crushing the rare earth hydrogen storage alloy (B) is 0.10 to 0.12 m ^2.
/ G of an alloy powder.

[0008]

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 FIG.

An electrode group 5 produced by laminating 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 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. A circular 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 disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the container 1 is formed by caulking to reduce the diameter of the upper opening inward.
The sealing plate 7 is hermetically fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2,
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
The hole 6 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 circular holding plate 12 made of an insulating material having a hole in the center is
The projecting portion of the positive electrode terminal 10 is disposed on the reference numeral 0 so as to project from the hole of the holding plate 12. 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.

2) Negative Electrode 4 The negative electrode 4 has a structure in which a negative electrode material containing a hydrogen storage alloy and a conductive material is supported on a conductive substrate. The negative electrode 4 having such a structure is prepared by, for example, kneading a hydrogen storage alloy powder, a conductive material and a polymer binder together with water to prepare a paste, filling the conductive substrate with the paste, drying, and drying the paste. It is produced by press molding according to

[0012] The hydrogen storage alloy is at 2 to 30 ° C and 5 to 1 ° C.
When the rare earth-based hydrogen storage alloy (A) having a large specific surface area according to the BET method when subjected to hydrogenation and pulverization once under a pressure of 0 atm (gauge pressure) has a specific surface area according to the BET method of mechanical pulverization of 0.
The specific surface area of the rare earth-based hydrogen storage alloy (B) obtained by mechanically pulverizing a rare earth hydrogen absorbing alloy (B) having a small specific surface area by the BET method when the hydrogen powder is pulverized with an alloy powder of 0.5 to 0.07 m ² / g is 0.10 to 0.12 m. ^{It is} composed of a mixed powder with ² / g alloy powder.

The rare earth hydrogen storage alloys (A) and (B)
Is not particularly limited, as long as it can occlude electrochemically generated hydrogen in the electrolytic solution and can easily release the occluded hydrogen during discharge. Examples of the hydrogen storage alloy include LaNi ₅ and MmNi ₅
(Mm; misch metal made of a mixture of lanthanum elements such as La, Ce, Pr, Nd, and Sm), LmNi ₅
(Lm; lanthanum-enriched misch metal), or a part of these Nis is Al, Mn, Co, Ti, Cu, Z
Examples include multi-element materials substituted with elements such as n, Zr, Cr, and B. In particular, the general formula LmNi _x A
_y (where Lm is at least one rare earth element containing La, A is at least one metal selected from Co, Mn, Al, Cu, Zr, V and B, and the atomic ratio x, y has a total value of 4. A rare earth-based hydrogen storage alloy represented by the following formula: 5 ≦ x + y ≦ 5.5 is preferable.

The hydrogen storage alloy (A) is 2 to 30 ° C.
The specific surface area by the BET method when hydrogenating and pulverizing once under a pressure of 5 to 10 atm (gauge pressure) is 0.10 to 0.12.
It is preferably m ² / g. The hydrogen storage alloy (B) preferably has a specific surface area by the BET method of 0.05 to 0.07 m ² / g when subjected to the hydrogenation and pulverization.

The mixing ratio of the powder of the hydrogen storage alloy (A) and the powder of the hydrogen storage alloy (B) is from 4: 6 by weight.
Preferably, the ratio is 6: 4.

The mixed powder has an average particle size of 35 ± 10 μm.
Preferably, particles having a particle size of 10 μm or less have a particle size distribution of 13% by weight or less, and particles of 75 μm or more have a particle size distribution of 1% by weight or less.

As the conductive material, for example, carbon black such as acetylene black, Ketchan black and furnace black can be used. It is preferable to mix such a conductive material in an amount of 4 parts by weight or less with respect to 100 parts by weight of the hydrogen storage alloy.

Examples of the polymer binder include hydrophobic polymers such as polytetrafluoroethylene, polyethylene, and polypropylene; cellulosic materials such as carboxymethylcellulose, methylcellulose and hydroxypropylmethylcellulose; acrylic acid such as sodium polyacrylate Esters; hydrophilic polymers such as polyvinyl alcohol and polyethylene oxide; and rubber-based polymers such as latex. It is preferable to add 0.5 to 5 parts by weight of such a polymer binder to 100 parts by weight of the hydrogen storage alloy.

Examples of the conductive substrate include those having a two-dimensional structure such as a punched metal, an expanded metal, a perforated rigid plate, and a wire mesh, and a three-dimensional structure such as a foamed metal and a mesh metal sintered metal fiber. Can be.

2) Positive Electrode 2 The positive electrode 2 has a structure in which, for example, a nickel compound as an active material and a conductive material are supported on a conductive substrate. Such a positive electrode is prepared by, for example, kneading a nickel compound as an active material, a conductive material, and a polymer binder together with water to prepare a paste, filling the paste into a conductive substrate, drying, and, if necessary, It is produced by applying pressure molding.

Examples of the nickel compound include nickel hydroxide, nickel oxide and nickel oxide in which nickel hydroxide, zinc and cobalt are coprecipitated.
Particularly, nickel hydroxide in which zinc and cobalt are coprecipitated is preferable.

As the conductive material, for example, at least one selected from a cobalt compound and metallic cobalt is used. As the cobalt compound,
For example, cobalt hydroxide [Co (OH) ₂ ], cobalt monoxide (CoO), and the like can be given. In particular, it is preferable to use cobalt hydroxide, cobalt monoxide, or a mixture thereof as the conductive material.

Examples of the polymer binder include those similar to those used in the front negative electrode 4.

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.

3) Separator 3 This separator 3 is made of, for example, an olefin-based nonwoven fabric such as a nonwoven fabric made of polyethylene fiber, a nonwoven fabric made of ethylene-vinyl alcohol copolymer fiber, or a nonwoven fabric made of polypropylene fiber, or an olefin such as a nonwoven fabric made of polypropylene fiber. Examples thereof include nonwoven fabrics made of a nonwoven fabric made of a base fiber and hydrophilic functional groups, and nonwoven fabrics made of polyamide fibers such as nylon 6,6. In order to impart a hydrophilic functional group to the olefin fiber nonwoven fabric, for example, corona discharge treatment, sulfonation treatment, graft copolymerization, or application of a surfactant or a hydrophilic resin can be employed.

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 alkaline secondary battery according to the present invention is a rare earth-based battery having a large specific surface area by the BET method when subjected to hydrogenation and pulverization once at 2 to 30 ° C. and 5 to 10 atm (gauge pressure). B obtained by mechanically pulverizing the hydrogen storage alloy (A)
The specific surface area by the BET method obtained by mechanically pulverizing a rare earth hydrogen storage alloy (B) having a small specific surface area by the BET method when the same powder is alloyed with the specific surface area by the ET method of 0.05 to 0.07 m ² / g and hydrogen-ground. Is 0.10 to 0.12 m ² / g
With a negative electrode containing a mixed powder with an alloy powder of

In the alkaline secondary battery provided with the negative electrode having such a configuration, the discharge capacity at a low temperature is significantly improved while maintaining a good charge / discharge cycle life.

That is, by increasing the specific surface area of the hydrogen-absorbing alloy powder contained in the negative electrode, the contact area with the electrolytic solution is increased and the electrode reaction at a low temperature is promptly performed. As a result, the discharge at a low temperature is performed. Capacity can be improved. However, when only the hydrogen storage alloy powder having a large specific surface area is used as the negative electrode material, the progress of corrosion is promoted and the electrode reaction on the surface is inhibited, resulting in a reduction in cycle life.

From the above, according to the present invention, the rare earth-based hydrogen storage alloy (A) having a large specific surface area by the BET method at the time of hydropulverization, that is, pulverization proceeds due to repetition of charge and discharge, and the specific surface area An alloy powder obtained by mechanically pulverizing a hydrogen-absorbing alloy, which has the property of increasing the corrosion and accelerating the
By making the specific surface area by the ET method as small as 0.05 to 0.07 m ² / g, miniaturization and corrosion of the hydrogen storage alloy during charge / discharge cycles can be suppressed.

On the other hand, the rare earth-based hydrogen storage alloy (B) having a small specific surface area by the BET method at the time of the hydrogen pulverization is difficult to be miniaturized even after repeated charging and discharging, and the specific surface area does not increase so much. The specific surface area of the alloy powder obtained by mechanically pulverizing
By making it as large as 0 to 0.12 m ² / g, the contact area with the electrolytic solution increases, and the discharge capacity at low temperature can be improved.

Therefore, by using a negative electrode containing a mixed powder of the two alloy powders, it is possible to obtain an alkaline secondary battery having an increased discharge capacity at a low temperature while maintaining good charge / discharge cycle characteristics. it can.

In particular, when the hydrogen storage alloy (A) is subjected to the hydrogenation pulverization, the specific surface area by the BET method is 0.1%.
Used as a 0~0.12m ² / g, BET specific surface area upon grinding the hydride as the hydrogen storage alloy (B) by the use of 0.05~0.07m ² / g, It is possible to obtain an alkaline secondary battery having an increased discharge capacity at a low temperature while maintaining better charge / discharge cycle characteristics.

[0034]

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

(Examples 1 to 9 and Comparative Examples 1 to 12) <Preparation of Paste Type Negative Electrode> A rare earth element having a purity of 99.9% (La: 45.1%, Ce: 4.6%, Pr: 12. 1
%, Nd: 37.0%, other rare earth elements: 1.1
%), Ni, Co, Mn and Al constituent elements in a high-frequency furnace with an alloy (A) having a composition of LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3 and LmNi _4.0 Co _0.4 Mn _0.3 Al
An alloy (B) having a composition of _0.3 was produced.

The ingots of the alloys (A) and (B) were crushed into about 3 cm squares, and 500 g of the crushed pieces were crushed by a hydropulverizer. Grinding conditions are 60 ° C and 0.8 torr
Degassed under reduced pressure for 3.5 hours at 15 ° C., 9 kg / cm ²
Is maintained for 2.5 hours, then at 60 ° C. and 0.8 t
Degassing was performed for 7 hours under reduced pressure of orr to remove hydrogen gas.
The hydrogenated and pulverized alloy (A) and alloy (B) are BE
The specific surface area was measured by the T method. As a result, the specific surface area of each of the alloy (A) and the alloy (B) was 0.1
Was 2m ² /g,0.06m ² / g.

Next, the alloy (A) and the alloy (B)
Was mechanically pulverized by a hammer mill, and the pulverization time was adjusted so that the specific surface area by the BET method was 0.04.
m ² /g,0.05m ² /g,0.06m ² /g,0.0
A powder of the alloy of ^{7m 2 /g,0.08m 2 / g (A} ), 0.09m 2 /g,0.10m 2 /g,0.11m 2
Powder /g,0.12m ² /g,0.13m ² / g the alloy of (B) was prepared. Subsequently, the alloy (A) powder and the alloy (B) powder were combined as shown in Table 1 below, and the mixing ratio of the powders was 50:50.
And 21 kinds of hydrogen storage alloy mixed powders were prepared.

Next, the hydrogen storage alloy mixed powder 10
0.5 g of sodium polyacrylate as a polymer binder and 0 g of carboxymethyl cellulose (CMC) in 0 g.
21 kinds of pastes were prepared by adding and kneading 05 g, 1.6 ml of a dispersion of polytetrafluoroethylene (specific gravity: 1.5, solid content: 60 wt%), 1 g of carbon black, and 60 ml of water. These pastes are applied to a punched metal as a conductive substrate, dried, pressed and cut to obtain 1
Four kinds of paste type negative electrodes were produced.

<Preparation of Paste-Type Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 parts by weight of carboxymethylcellulose and A paste was prepared by adding 0.5 parts by weight of a dispersion of fluoroethylene (specific gravity: 1.5, solid content: 60% by weight) in terms of solid content, adding 45 parts by weight of pure water thereto, and kneading. Subsequently, after this paste was filled in a nickel-plated fiber substrate, the paste was further applied to both surfaces thereof, dried, and rolled by roller pressing to produce a paste-type positive electrode.

Next, a nonwoven fabric made of polypropylene fiber was interposed between each of the negative electrode and the positive electrode, and spirally wound to produce 21 kinds of electrode groups. After storing each such electrode group in a bottomed cylindrical container, 7N-KOH and 1N-L
An electrolytic solution composed of iOH was injected into the container, and the container was sealed and the like, whereby 21 kinds of AA-size cylindrical nickel-metal hydride secondary batteries having a structure shown in FIG.
00 mAh).

The obtained Examples 1 to 9 and Comparative Examples 1 to 1
The low-temperature discharge characteristics and the cycle characteristics described below were evaluated for each of the ten secondary batteries of No. 2 and shown in Table 1 below as an average value of the ten secondary batteries.

(1) Low-temperature discharge characteristics This low-temperature discharge characteristic is 1400 mA in an atmosphere of 20 ° C.
After charging at a current of (1C) for 90 minutes, the battery was discharged to a final voltage of 1 V at a current of 1C, and the discharge capacity was measured. Also, 1
After charging with a current of C for 90 minutes, the battery was discharged to a final voltage of 1 V at a current of 1 C in an atmosphere of -20 ° C, and the discharge capacity was measured. The latter discharge capacity was shown as a ratio (%) when the former discharge capacity (20 ° C.) was set to 100.

(2) Cycle Characteristics The cycle characteristics are as follows: charge / discharge is repeated at a current of 1 C for 90 minutes in an atmosphere at a temperature of 20 ° C., and discharge is performed at a current of 1 C to a cutoff voltage of 1 V. The number of cycles until the volume of the eye became 1/2 was shown.

[0044]

[Table 1]

As is apparent from Table 1, the specific surface area of the rare-earth hydrogen-absorbing alloy (A) having a large specific surface area by the BET method when subjected to hydrogenation and pulverization is 0.05 to 0.07 m ² by the mechanically pulverized BET method. / G alloy powder and an alloy having a specific surface area of 0.10 to 0.12 m ² / g by mechanically pulverizing a rare earth-based hydrogen storage alloy (B) having a small specific surface area by BET method when hydrogen pulverized. The secondary batteries of Examples 1 to 9 including the negative electrode including the mixed powder with the powder have excellent discharge capacity and charge / discharge cycle characteristics at low temperature compared to the secondary batteries of Comparative Examples 1 to 12. I understand.

In the above embodiment, an example in which the present invention is applied to a cylindrical nickel-metal hydride secondary battery has been described. However, a square nickel-metal hydride secondary battery in which a positive electrode, a separator and a negative electrode are laminated to form an electrode group is also described. The same can be applied.

[0047]

As described above, according to the present invention, it is possible to provide an alkaline secondary battery having a large discharge capacity under a low temperature condition while maintaining good charge / discharge cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a nickel-metal hydride secondary battery which is an example of an alkaline 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 (3)

[Claims] 1. 2-30 ° C., 5-10 atm (gauge pressure)
The rare-earth hydrogen-absorbing alloy (A) having a large specific surface area by the BET method when subjected to hydrogenation and pulverization once under the pressure of 0.05 to 0.07 m ² by the BET method when mechanically pulverized.
/ G of alloy powder having a small specific surface area by the BET method when pulverized with hydrogen by the same hydrogen method. The specific surface area by the BET method obtained by mechanically pulverizing the rare earth hydrogen storage alloy (B) is 0.10 to 0.12 m.
An alkaline secondary battery comprising a negative electrode containing a mixed powder of ² / g alloy powder. 2. The rare earth hydrogen storage alloy has a general formula L
mNi _x A _y (where Lm is at least one rare earth element containing La, and A is Co, Mn, Al, Cu, Z
2. The alkali according to claim 1, wherein at least one kind of metal selected from r, V and B, and the atomic ratio x, y are represented by the following expression: a total value of 4.5 ≦ x + y ≦ 5.5. Rechargeable battery. 3. The method according to claim 1, wherein the hydrogen storage alloy (A) is 2-30.
The specific surface area by the BET method when hydrogenated and pulverized once under a pressure of 5 to 10 atm (gauge pressure) is 0.10 to 0.
12 m ² / g, and the hydrogen storage alloy (B) has a specific surface area by the BET method of 0.05 to 500 when subjected to the same hydrogenation and pulverization.
^2. The alkaline secondary battery according to claim 1, wherein the content is 0.07 m ² / g.