JPH0773880A - Metal oxide-hydrogen secondary battery - Google Patents

Abstract

PURPOSE:To lengthen the cycle life of a battery and to decrease dispersion of the cycle life by making the amount of a hydrogen storage alloy per negative electrode constant. CONSTITUTION:A negative electrode is made of a rare earth hydrogen storage alloy powder having 1. a mean particle size as determined by laser diffraction of 35+ or -10mum, a ratio of particles having particle size of 10mum or less of 13 volume percent or less, and a ratio of particles over 200 mesh screen of 1wt.% or less, and 2. a BET specific surface area of 0.04-0.12m<2>/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide / hydrogen secondary battery using a metal oxide as a positive electrode active material and hydrogen as a negative electrode active material.

[0002]

2. Description of the Related Art At present, metal oxide / hydrogen secondary batteries of the type in which the negative electrode is composed of a hydrogen storage alloy are drawing attention. The reason is that this battery system originally has a high energy density, is advantageous in volumetric efficiency, can be operated safely, and is excellent in characteristics and reliability. .

As a hydrogen storage alloy used for the negative electrode material of this type of battery, LaNi ₅ has been frequently used. Such a hydrogen storage alloy containing only La element as a rare earth component is excellent as a battery negative electrode material, but it is not practical because La is expensive. Therefore, an alloy of Misch metal (hereinafter referred to as Mm), which is a mixture of lanthanum elements such as La, Ce, Pr, Nd, and Sm, and Ni, that is, MmNi ₅ is also widely used.

Regarding LaNi ₅ and MmNi ₅ , a part of Ni is Al, Mn, Fe, Co, Ti, C.
A multi-element system in which an element such as u, Zn, Zr, Cr, V or B is substituted is also used. As such a hydrogen storage alloy, an alloy ingot is manufactured by a method such as high frequency melting of the constituents, and powdered by a method such as mechanical crushing.

However, the conventional metal oxide / hydrogen secondary battery has a problem that the charge / discharge cycle life is short and varies. The variation in cycle life is due to the coating state of the kneading paste on the conductive core during the production of the negative electrode. The hydrogen storage alloy negative electrode is generally manufactured by the following method. First, the hydrogen storage alloy is mechanically pulverized or hydrogenated to be powdered. Then, the hydrogen storage alloy powder is kneaded with a polymer binder and a conductive agent to prepare a paste. Subsequently, the conductive core body serving as a current collector is immersed in a coating tank containing this paste and then pulled up vertically to remove excess paste through a slit. Further, after drying this, the whole is subjected to pressure molding treatment by a press to obtain a hydrogen storage alloy negative electrode.

However, in the above manufacturing method,
Even if the paste composition and kneading conditions are kept constant, the state of application of the paste to the conductive core varies due to the difference in the properties of the hydrogen storage alloy powder used, so a negative electrode with a constant thickness cannot be obtained. There was a problem. That is, since it is difficult to obtain a negative electrode in which the amount of hydrogen storage alloy contained per electrode is constant, a battery incorporating the negative electrode has variations in performance such as cycle life. It is considered that the variation in the coating state of the paste on the conductive core is due to the difference in the fluidity of the paste.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a negative electrode having a constant thickness containing a predetermined amount of rare earth-based hydrogen storage alloy, and having a long charge / discharge cycle life,
In addition, it is to provide a metal oxide / hydrogen secondary battery with less variation.

[0008]

Means for Solving the Problems The present invention includes a positive electrode, an alkaline electrolyte, and the general formula LmNi _w Co _X Mn _y Al
_z (where Lm is one or more elements selected from rare earth elements including La, and w, x, y, and z are
3.90 ≦ w ≦ 4.50, 0.38 ≦ x ≦ 0.50,
0.28 ≤ y ≤ 0.50, 0.28 ≤ z ≤ 0.50 and 5.10 ≤ w + x + y + z ≤ 5.50), the metal having a negative electrode containing a rare earth hydrogen storage alloy as a main material. In the oxide / hydrogen secondary battery, the negative electrode is (1)
Average particle size by laser diffraction method is 35 ± 10μm, 1
The ratio of particles having a particle size of 0 μm or less is 13% by volume or less, the ratio of particles that do not pass through a 200-mesh sieve is 1% by weight or less; and (2) the specific surface area according to the BET method is 0.04 to 0.12 m ^2. / g; a metal oxide characterized by being composed of a rare earth-based hydrogen storage alloy powder
The present invention relates to a hydrogen secondary battery.

The rare earth-based hydrogen storage alloy has the general formula LmNi
(where, Lm is at least one or two or more rare earth elements including _{La) w Co X Mn y Al} z having composition represented by are preferred from the hydrogen storage capacity. For example,
In the above equation, w = 4.2, x = 0.4, y = 0.3,
The one having z = 0.3 (w + x + y + z = 5.2) is used.

In order to improve the coating state of the kneading paste on the conductive core when the negative electrode having a constant thickness containing the hydrogen storage alloy is produced, the hydrogen storage alloy powder used in the present invention has an average particle size measured by a laser diffraction method. Particle size is 35 ± 10μm, 10
The proportion of particles having a particle size of μm or less is 13% by volume or less,
And the specific surface area by BET method is 0.04 to 0.12 m ² / g
belongs to. Alloy powders having an average particle size of more than 45 μm or a specific surface area of less than 0.04 m ² / g have low fluidity when made into a paste, and therefore the thickness of the paste applied to the conductive core is uneven. This is because it tends to occur. On the other hand, if the ratio of particles having an average particle size of less than 25 μm or 10 μm or less is larger than 13% by volume, or if the specific surface area is larger than 0.12 m ² / g, the fluidity is too high. This is because the paste applied to the conductive core runs down. As described above, outside the above range, the coating state of the negative electrode paste becomes unstable, and the battery capacity and cycle life are reduced, which is not preferable. Particularly preferable specific surface area of the hydrogen storage alloy powder is 0.06 to 0.10.
It is in the range of m ² / g.

The reason why the proportion of particles that do not pass through the 200-mesh screen is set to 1% by weight or less is that the flowability of the paste is increased due to the presence of a trace amount of particles of 200-mesh or more, and the same problem as above. Is to cause. A more desirable ratio is 0.5% by weight or less.

In order to obtain such a hydrogen storage alloy powder, any method such as mechanical pulverization, hydrogenation pulverization and spray pulverization can be used. In actual production, mechanical crushing is preferable because the equipment is simple and the work is easy, and safety is ensured. In particular, stable particle size can be obtained,
From the viewpoint of cost, it is desirable to use those crushed by an impact crusher. As the impact type crusher, for example, a hammer mill or the like can be used.

The negative electrode is formed by kneading the hydrogen-absorbing alloy powder with a polymer binder or a conductive agent to form a paste, and immersing a conductive core as a current collector in a coating tank containing the paste, and then vertically It is manufactured by pulling up to 1, removing excess paste through a slit, further drying, and subjecting to pressure molding by a press.

Examples of the polymer binder include sodium polyacrylate and polytetrafluoroethylene (PTF).
E), carboxymethyl cellulose (CMC) and the like can be mentioned, and these may be used in combination. The blending ratio of the polymer binder is preferably in the range of 0.5 to 5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder. Examples of the conductive powder blended in the paste include carbon black and graphite. The blending ratio of such conductive powder is preferably in the range of 0.1 to 4 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder.

The conductive core which is the above current collector is
For example, one having a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and one having a three-dimensional structure such as foam metal and reticulated sintered metal fiber can be mentioned.

A metal oxide electrode such as a non-sintered nickel oxide electrode is used as the positive electrode of the present invention. That is, it is manufactured by a method of filling a paste containing a polymer binder and the like in addition to nickel hydroxide into, for example, a sintered fiber substrate, a foam metal, a non-woven fabric plated substrate or a punched metal substrate. Examples of the polymer binder include the same as the polymer binder for the negative electrode. Examples of the alkaline electrolyte used in the present invention include potassium hydroxide (KOH) and lithium hydroxide (LiOH).

[0017]

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition,% of composition is% by weight
Means

Examples 1 to 5 (1) Preparation of sample Rare earth element with purity 99.9% (La 45.1%, Ce
4.6%, Pr 12.1%, Nd 37%, other rare earth elements 1.1%), Ni, Co, Mn and Al are alloyed by high frequency melting to have a composition represented by LmNi _4.2 Co _0.4 Mn _0.3 Al _0.3 , This was mechanically pulverized to obtain an alloy powder. Next, the particle size of this alloy powder was measured by the laser diffraction method and the screen residue method, and the specific surface area was measured by the BET method. The results are shown in Table 1. In addition, Examples 1-3
In the above, after the mechanical pulverization, particles having a large particle size were removed by a 200-mesh sieve.

(2) Preparation of Negative Electrode and Test of Paste Application State Hydrogen storage alloy powder 100 having the above composition and specific surface area
g, 1.6 ml of a suspension of polytetrafluoroethylene as a polymer binder and 0.5 of sodium polyacrylate.
g, 0.05 g of carboxymethyl cellulose, 1 g of carbon black as a conductive agent, and 60 ml of water were added and mixed to prepare five kinds of pastes. continue,
The punched metal as a current collector is conveyed into a coating tank in which each of the pastes is housed, and after being pulled up from the coating tank in the vertical direction, excess paste is removed through a slit to form a punched metal surface. The paste was applied. Then, after drying, compression molding was performed by a roller press, and then cut, 100 hydrogen storage alloy negative electrodes were produced. The electrode weight and thickness were measured as the applied state of the paste in the production of each hydrogen storage alloy negative electrode described above. The results are shown in Table 1. The control values for each are 10.0 ± 0.5 g and 0.40 ± 0.02 mm.
Also described in. The thickness is 3 for each electrode.
Measurements were made at one location, and even one location was out of range and judged to be defective.

(3) Preparation of positive electrode Further, a paste containing nickel hydroxide and cobalt oxide was prepared, and this was filled in a nickel sintered fiber substrate,
A non-sintered nickel positive electrode was produced through drying, pressing and cutting steps.

(4) Assembly of Battery Next, as shown in FIG. 1, the five types of hydrogen storage alloy negative electrodes 1 produced by the above-mentioned method are respectively placed together with the non-sintered nickel oxide positive electrode 2 via the separator 3. It was wound and inserted into the AA size battery can 4. Further, after pouring an 8N potassium hydroxide aqueous solution, the battery can was sealed, and five types of storage batteries having a capacity of 1000 mAh were assembled into test cells. In the upper opening of the battery can 4,
A sealing plate 7 having a hole 6 in the center and also serving as a positive electrode terminal is supported and fixed via an insulating gasket 8. The sealing plate 7
Includes a safety valve 9 and a cap 10 for holding the safety valve 9.
Is equipped with an explosion-proof mechanism. The negative electrode 1 is directly connected to the inner surface of the battery can 4 which also functions as the negative electrode terminal, and the positive electrode 2 is connected through a tab 5 to a sealing plate 7 which also functions as the positive electrode terminal.

(5) Charge / Discharge Cycle Test Each of these test cells was subjected to a charge / discharge cycle test. Table 1 shows the number of cycles required for the battery capacity to become 1/2 of the initial capacity after repeating 1C discharge and 1C charge. Also, this cycle number is for each type of battery 1
It is an average value of 0 pieces. It should be noted that the cycle life is not affected only by the amount of alloy, and changes even when the amount of alloy is the same or due to alloy abnormality such as segregation of alloy components. For example,
The cycle life correlates with the surface area of the alloy powder when hydro-ground. Therefore, in order to keep this condition constant, the specific surface area of the alloy powder when hydro-pulverized is 0.04.
A material having a thickness of 0.12 m ² / g was used.

Comparative Examples 1 to 4 Examples except that alloys having the same composition as used in Examples 1 to 5 and having the grain sizes and specific surface areas shown in Comparative Examples 1 to 4 of Table 1 were used. (1) sample preparation similar to 1-5,
(2) Preparation of negative electrode and paste application state test, (3) Preparation of positive electrode, (4) Battery assembly, and (5) Charge / discharge cycle test. The results are shown in Table 1.

[0024]

[Table 1]

[0025]

According to the present invention, since the kneading paste can be applied to the conductive core in a uniform thickness, it is possible to obtain a negative electrode in which the amount of hydrogen storage alloy contained in one electrode is constant. As a result, it has become possible to provide a metal oxide / hydrogen secondary battery having a long charge / discharge cycle life and little variation. It

[Brief description of drawings]

FIG. 1 is a sectional view of a test battery assembled in an embodiment of the present invention.

[Explanation of symbols] 1 ... Hydrogen storage alloy negative electrode 2 ... Non-sintered nickel oxide positive electrode 3 ... Separator 4 ... Battery can 5 ... Tab 6 ... Hole 7 ... Sealing plate 8 ... Insulation gasket 9 ... Safety valve 10 ... Cap

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuaki Chiba 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Co., Ltd.

Claims (1)

[Claims] 1. A positive electrode, an alkaline electrolyte, and a general formula Lm.
In _{Ni w Co x Mn y Al z} ( wherein, Lm represents one or more elements selected from rare earth elements including La, w, x, y, z is, 3.90 ≦ w ≦ 4.50 , 0.
38 ≦ x ≦ 0.50, 0.28 ≦ y ≦ 0.50, 0.2
8 ≦ z ≦ 0.50 and 5.10 ≦ w + x + y + z ≦ 5.
In a metal oxide / hydrogen secondary battery including a negative electrode containing a rare earth-based hydrogen storage alloy as a main material, the negative electrode has: (1) an average particle diameter of 35 ± 10 μm measured by a laser diffraction method.
And the proportion of particles having a particle diameter of 10 μm or less is 13% by volume or less, and the proportion of particles that do not pass through a 200-mesh screen is 1% by weight or less; 12m ²
/ g; a metal oxide / hydrogen secondary battery comprising a rare earth-based hydrogen storage alloy powder.