JP2001307722A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery with a high capacity and a long life. SOLUTION: This battery is equipped with a negative electrode 4 that contains a hydrogen storage alloy powder A with composition expressed by formula (1) and average particle size of 45 to 70 μm, and another hydrogen storage alloy powder B with composition expressed by the same formula (1) and average particle size of 10 to 40 μm, and blending ratio of A is larger than that of B and tap density of the mixture of the powders A and B is higher than 4.0 g/cc. (1) Ln1-xMgx(Ni1-yTy)z. Here, Ln is an element selected frong among lanthanoids, Ca, Sr, Y, Ti, Zr and Hf, while T is an element selected from among Li, V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and B, and atomic ratios x, y and z satisfy 0<x<1, 0<=y<=0.5 and 2.5<=z<=4.5.

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 Alkaline secondary batteries such as nickel-cadmium secondary batteries and metal oxide / hydrogen secondary batteries (for example, nickel-metal hydride secondary batteries) and lithium ion secondary batteries are available as secondary batteries capable of obtaining high capacity. Batteries are known. Among them, metal oxide / hydrogen secondary batteries are widely used in portable devices and the like because of their excellent environmental compatibility. With the development of portable devices in recent years, there has been a demand for higher capacity and longer life of metal oxide / hydrogen secondary batteries.

Incidentally, as a hydrogen storage alloy contained in a negative electrode of a metal oxide / hydrogen secondary battery, conventionally, an MmNi ₅ alloy (Mm represents a misch metal) or a TiMn ₂ alloy has been used.

However, MmNi ₅ alloys, Ti
In metal oxide / hydrogen secondary batteries equipped with a negative electrode containing an Mn ₂ alloy, the hydrogen storage / release capacity of the negative electrode is approaching the limit of the hydrogen storage capacity of the alloy. Is becoming less hopeful.

[0005] V-Ti, TiFe, Mg ₂ N
i-type alloys have been developed. These have excellent reactivity when reacted directly with hydrogen gas at high temperatures, but have poor reactivity with hydrogen at normal temperature and pressure, and are difficult to activate at the initial stage. And many other problems.

On the other hand, a hydrogen storage alloy containing magnesium, nickel and a rare earth element as main constituent elements is MmNi ₅
It has the feature of being superior in capacity density per volume and capacity density per weight as compared with the base alloy. For this reason, the metal oxide / hydrogen secondary battery provided with the negative electrode containing this hydrogen storage alloy can have a higher capacity as compared with the case of using the MmNi ₅ -based alloy, and has a higher capacity when using the TiMn ₂ -based alloy. As a result, the high-rate charge / discharge characteristics can be improved.

[0007]

However, in a secondary battery provided with a negative electrode containing a hydrogen storage alloy containing magnesium, nickel and a rare earth element as main constituent elements, the hydrogen storage alloy is liable to corrode, and an alkaline There is a problem that the cycle life is short because the electrolyte is quickly depleted by consumption of the electrolyte.

An object of the present invention is to provide an alkaline secondary battery having a high capacity and a long life.

[0009]

Means for Solving the Problems An alkaline secondary battery according to the present invention has a composition represented by the following general formula (1),
And a negative electrode comprising a hydrogen storage alloy powder A having an average particle size of 45 to 70 μm and a hydrogen storage alloy powder B having a composition represented by the following general formula (1) and having an average particle size of 10 to 40 μm. The mixing ratio of the powder A when the mixing ratio of the powder B is 1 is 1 or more, and the tap density of the mixed powder composed of the powder A and the powder B is 4.0 g / cc or more. It is a feature.

Ln _1-x Mg _x (Ni _1-y T _y ) _z (1) where Ln is a lanthanoid element, Ca, Sr, Y, T
i is at least one element selected from Zr and Hf, and T is Li, V, Nb, Ta, Cr, Mo, Mn,
Fe, Co, Al, Ga, Zn, Sn, In, Cu, S
i, at least one element selected from P and B,
The atomic ratios x, y and z are 0 <x <1, 0 ≦ y ≦ 0.5,
2.5 ≦ z ≦ 4.5.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An alkaline secondary battery according to the present invention has a composition represented by the following general formula (1), and has a hydrogen storage alloy powder A having an average particle size of 45 to 70 μm and the following general formula ( It has a composition represented by 1) and has an average particle size of 10 to 40 μm.
a positive electrode; a separator disposed between the positive electrode and the negative electrode; and an alkaline electrolyte. The amount of the powder B is 1
And the amount of the powder A is 1 or more, and the tap density of the mixed powder composed of the powder A and the powder B is 4.
0 g / cc or more.

Ln _1-x Mg _x (Ni _1-y T _y ) _z (1) where Ln is a lanthanoid element, Ca, Sr, Y, T
i is at least one element selected from Zr and Hf, and T is Li, V, Nb, Ta, Cr, Mo, Mn,
Fe, Co, Al, Ga, Zn, Sn, In, Cu, S
i, at least one element selected from P and B,
The atomic ratios x, y and z are 0 <x <1, 0 ≦ y ≦ 0.5,
2.5 ≦ z ≦ 4.5.

In the composition represented by the general formula (1), a more preferable range of the atomic ratio x is 0.1 ≦ x ≦ 0.
9 A more preferable range of the atomic ratio y is 0 ≦ y
≦ 0.3. Further, a more preferable range of the atomic ratio z is 2.9 ≦ z ≦ 3.6.

Next, the negative electrode, the positive electrode, the separator and the electrolyte will be described.

1) Negative Electrode For the negative electrode, for example, a conductive material is added to the hydrogen storage alloy powder A and the hydrogen storage alloy powder B and kneaded with a binder and water to prepare a paste. It is manufactured by filling a flexible substrate, drying and pressing.

In this negative electrode, when the average particle size of the hydrogen storage alloy powder A exceeds 70 μm, the initial activity of the secondary battery decreases. In addition, when manufacturing the negative electrode, the alloy powder easily falls off, or the alloy powder is easily crushed in the pressing step. When the alloy powder is pulverized at the time of pressing, the specific surface area of the alloy is increased, which promotes a corrosion reaction.

The hydrogen storage alloy powder B has an average particle size of 10 μm.
When it is less than the above value, the activity of the hydrogen storage alloy becomes high, so that it is easily oxidized in the air.

If the amount of the powder A is less than 1 when the amount of the powder B is set to 1, the reaction area between the alloy powder and the electrolytic solution is increased, so that the corrosion progresses quickly and the cycle life is increased. Decrease.

The tap density of the mixed powder composed of the powder A and the powder B is measured by a method for measuring bulk density of acetylene black specified in JIS K1469.

The method for measuring the bulk density of acetylene black specified in JIS K1469 will be described below.

(Summary) The bulk density is determined from the volume of the sample taken in a measuring cylinder, dropped on a rubber plate and compressed.

(Operation) (1) 100 ml of a dried sample is gradually put in using a spoon with a 100 ml measuring cylinder having a known mass obliquely, and the mass is weighed to 10 mg.
(2) After a rubber stopper is attached to the measuring cylinder, the sample cylinder is dropped 50 times from a height of about 5 cm on the rubber plate, and the volume of the compressed sample is read.

(Calculation) The bulk density is calculated by the following equation.

D = m / V where D is the bulk density (g / ml), m is the mass (g) of the sample, and V is the volume (ml) of the sample after falling 50 times. .

When the tap density is less than 4.0 g / cc, a gap is easily formed between the alloy particles, and the contact between the alloy particles becomes insufficient, so that the conductivity of the negative electrode decreases. As a result, the utilization rate of the negative electrode decreases, and the cycle life decreases.

Examples of the binder include carboxymethylcellulose (CMC), methylcellulose, sodium polyacrylate, polytetrafluoroethylene,
Examples thereof include polyvinyl alcohol (PVA) and styrene butadiene rubber (SBR).

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

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, and a wire mesh, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate.

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

As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles 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.

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

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

As the conductive substrate, for example, a two-dimensional substrate such as a mesh-like, sponge-like, fiber-like, or felt-like porous metal body or a punched metal made of nickel, stainless steel, or nickel-plated metal is used. Having irregularities on the periphery of the hole.

This positive electrode 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, filling the paste into a conductive substrate, and drying the paste. After that, it is produced by molding.

3) Separator Examples of the separator include a nonwoven fabric made of polyamide fiber, a nonwoven fabric made of polyolefin fiber such as polyethylene and polypropylene, or 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.

According to the alkaline secondary battery of the present invention described above, high initial activity, high capacity, and long life can be satisfied at the same time.

That is, since the hydrogen storage alloy having the composition represented by the general formula (1) has a higher capacity per unit volume and a higher capacity per unit weight than the LaNi ₅ series alloy, it is necessary to obtain a constant capacity. The volume of the negative electrode necessary for the secondary battery can be reduced, and the volume of the positive electrode can be increased by the reduced volume, so that the secondary battery can have a higher capacity. In addition, since the rate of decrease in voids in the container due to the increase in capacity can be reduced, a sufficient amount of alkaline electrolyte can be accommodated.

The average particle size having the above composition is 4
The negative electrode containing only the hydrogen storage alloy powder A having a diameter of 5 to 70 μm as the hydrogen storage alloy has a reduced contact area between the alloy and the electrolytic solution, but can suppress corrosion of the alloy.
This leads to a decrease in the initial activity. By adding a hydrogen storage alloy powder B having the above composition and having an average particle diameter of 10 to 40 μm to the powder A, the powder B can store and release hydrogen from the initial stage of the charge and discharge cycle, and thus a high initial activity can be obtained. .

When the compounding ratio of the powder B is set to 1 and the compounding ratio of the powder A is set to 1 or more, the contact area between the alloy and the electrolytic solution is greatly increased with the addition of the powder B. Therefore, corrosion of the alloy due to the electrolytic solution can be suppressed, and depletion of the electrolytic solution can be prevented. Furthermore, by setting the tap density of the mixed powder composed of the powder A and the powder B to 4.0 g / cc or more, the powder B enters the gap between the powders A having a large particle size, and thus the number of electrical contact points between the alloys is increased. , The conductivity of the negative electrode can be improved, and the utilization rate of the negative electrode can be improved. Therefore, corrosion of the alloy is suppressed and the utilization rate of the negative electrode is improved, so that deterioration of the negative electrode can be suppressed and the charge / discharge cycle life can be improved.

[0041]

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

(Examples 1-3 and Comparative Examples 1-6) <Preparation of Negative Electrode> The composition was La _0.7 Mg _0.3 (Ni _0.9 C
o _0.1 ) Each metal was mixed so as to be _3.0, and melted and cooled in an argon gas atmosphere in a high-frequency melting furnace to obtain an ingot. The ingot was heat-treated and homogenized, pulverized in an inert gas atmosphere, and had an average particle diameter (D ₅₀ ) measured by a laser diffraction method of ₅ , 20, 30, 35, ₅₀ , 6 or more.
Eight kinds of hydrogen storage alloy powders of 0, 80, and 100 μm were obtained. Two of these were selected, and the powder having the larger average particle diameter was designated as powder A, and the powder having the larger average particle diameter was designated as powder B. The mixing ratio (A: B) of powder A and powder B was as shown in Table 1 below. Were mixed so as to have the values shown in Table 1. The tap density of the obtained mixed powder was measured according to the tap density measurement method for acetylene black specified in JIS K1469, and the results are shown in Table 1 below.

To 100 parts by weight of each mixed powder, 0.5 parts by weight of sodium polyacrylate as a binder, 0.12 parts by weight of carboxymethylcellulose (CMC) and a dispersion of polytetrafluoroethylene (specific gravity 1.5,
(A solid content of 60% by weight) and 1.0 part by weight of a carbon black as a conductive material were added thereto, and mixed with 30 parts by weight of water to prepare a paste. This paste was filled into foamed nickel having a porosity of 95%, dried at 125 ° C., press-molded to 0.30 mm, and then cut into a width of 60 mm and a length of 168 mm to obtain 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 dispersion of polytetrafluoroethylene (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, this paste was filled in a foam substrate, dried, then rolled by a roller press, and cut to obtain a width of 60 mm and a length of 135 m.
m, and a positive electrode having a thickness of 0.75 mm was prepared.

Next, a separator made of a nonwoven fabric made of polypropylene and subjected to a hydrophilic treatment was interposed between each of the negative electrode and the positive electrode, and spirally wound to form an electrode group. After storing this electrode group in a cylindrical container having a bottom, 3.9 cc of an alkaline electrolyte comprising an aqueous solution of potassium hydroxide having a specific gravity of 1.31 is accommodated, and the structure shown in FIG. A 4/3 A size cylindrical nickel-metal hydride secondary battery having a capacity of 4200 mAh was assembled.

That is, 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. 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 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 provided with the sealing plate 7.
It is attached so as to cover the hole 6 above. A rubber safety valve 11 is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10.
Circular holding plate 12 made of an insulating material having a hole in the center
Are arranged on the positive electrode terminal 10 such that the projections of the positive electrode terminal 10 protrude from the holes of the holding plate 12. The outer tube 13 is provided on the periphery of the holding plate 12,
The side surface of the container 1 and the periphery of the bottom of the container 1 are covered.

The obtained Examples 1 to 3 and Comparative Examples 1 to 6
Of the secondary battery was subjected to predetermined initial charge and discharge. After charging at 25 ° C for 13 hours at a 10-hour rate,
The battery was discharged at a rate of 5 ° C. to a final voltage of 1.0 V, and the discharge capacity was measured. The results are shown in Table 1 below. Next, the battery was charged at a rate of 10 hours for 13 hours and then discharged at 25 ° C. at a rate of 5 hours to a final voltage of 1.0 V. The cycle life was measured, and the results were compared with the discharge capacity at the first cycle (initial capacity). ) And the maximum discharge capacity are shown in Table 1 below. However, the cycle life was the number of cycles until the battery capacity reached 80% of the initial capacity.

[0048]

[Table 1]

As is apparent from Table 1, the average particle size having the composition represented by the above general formula (1) is 45 to 70 μm.
m of the hydrogen storage alloy powder A and the hydrogen storage alloy powder B having a composition represented by the general formula (1) and having an average particle diameter of 10 to 40 μm, and the powder A with respect to the powder B
The secondary batteries of Examples 1 to 3 provided with negative electrodes having a mixing ratio of 1 or more and a tap density of a mixed powder composed of the powder A and the powder B of 4.0 g / cc or more, It can be seen that the maximum discharge capacity is high and the cycle life is long.

On the other hand, the average particle size of the powder A was 70 μm.
In addition, the secondary battery of Comparative Example 1 including the negative electrode in which the average particle diameter of the powder B is less than 10 μm and the tap density is less than 4.0 g / cc has a low initial capacity and a low cycle life. It turns out that it is short. Further, the secondary battery of Comparative Example 2 including the negative electrode in which the average particle diameter of the powder B exceeds 40 μm and the tap density is less than 4.0 g / cc has a long cycle life but a low initial capacity. Understand. on the other hand,
It can be seen that the secondary battery of Comparative Example 3 including the negative electrode in which the average particle size of the powder A is less than 45 μm can increase the initial capacity but shortens the cycle life. Further, it can be seen that the secondary battery of Comparative Example 4 including the negative electrode having an average particle diameter of powder A exceeding 70 μm has a long cycle life but a low initial capacity. In addition, it can be seen that the secondary batteries of Comparative Examples 5 and 6 including the negative electrodes in which the blending amount of the powder B is larger than that of the powder A can increase the initial capacity but shorten the cycle life.

In the above-described embodiment, the composition is
La_0.7Mg_0.3(Ni_0.9Co_0.1) _3.0Is hydrogen storage
Although the description has been made by taking the alloy as an example,
In the case of a hydrogen storage alloy having the following composition,
It was confirmed that a similar effect could be obtained.

In the above-described embodiment, the separator is interposed between the positive electrode and the negative electrode and spirally wound and housed in a cylindrical container having a bottom. However, the alkaline secondary battery of the present invention has such a structure. It is not limited to the structure. For example, the present invention can be similarly applied to a prismatic alkaline secondary battery in which a separator is interposed between a positive electrode and a negative electrode, and a laminate of a plurality of such layers is housed in a bottomed rectangular cylindrical container.

[0053]

As described above, according to the present invention, an alkaline secondary battery having excellent initial activity, high capacity, and long life can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a nickel-metal hydride secondary battery of Example 1. FIG.

[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.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuichiro Irie 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Corporation (72) Inventor Kazuta Takeno 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo No. Toshiba Battery Corporation F-term (reference) 5H028 AA01 CC12 EE01 HH01 HH03 HH05 5H050 AA07 AA08 BA14 CA03 CB17 EA23 EA24 FA17 HA02 HA05 HA08

Claims (1)

[Claims] 1. A hydrogen storage alloy powder A having a composition represented by the following general formula (1) and having an average particle size of 45 to 70 μm, and a composition represented by the following general formula (1), And a negative electrode containing a hydrogen storage alloy powder B having an average particle size of 10 to 40 μm, wherein the mixing ratio of the powder A is 1 or more when the mixing ratio of the powder B is 1, and the powder A and the powder An alkaline secondary battery, wherein the mixed powder composed of the powder B has a tap density of 4.0 g / cc or more. Ln _1-x Mg _x (Ni _1-y T _y ) _z (1) where Ln is a lanthanoid element, Ca, Sr, Y, T
i is at least one element selected from Zr and Hf, and T is Li, V, Nb, Ta, Cr, Mo, Mn,
Fe, Co, Al, Ga, Zn, Sn, In, Cu, S
i, at least one element selected from P and B,
The atomic ratios x, y and z are 0 <x <1, 0 ≦ y ≦ 0.5,
2.5 ≦ z ≦ 4.5.