JPH07153462A - Metal oxide-hydrogen secondary battery - Google Patents

Abstract

PURPOSE:To provide a metal oxide-hydrogen secondary battery capable of suppressing pulverization with the progress of charge/discharge cycles, capable of keeping the progress level of pulverization constant, and provided with a negative electrode by containing a specific alloy in the negative electrode. CONSTITUTION:This metal oxide-hydrogen secondary battery stores a positive electrode 2 containing a metal oxide, e.g. an unsintered nickel positive electrode, an alkaline electrolyte, and a negative electrode 1 containing a hydrogen storage alloy. The negative electrode 1 of this battery contains the hydrogen storage alloy expressed by the formula LmNinCoxMnyAlz and is provided with a hexagonal structure having the crystal lattice constants (a), (c) obtained by X-ray diffraction, where Lm is one or more selected from rare earth elements including La, the total value of atomic ratios indicates 4.8<=w+x+y+z<=5.5, 0.495 nm<=a<=0.510nm, and 0.400nm<=c<=0.410nm.

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, and more particularly to a metal oxide / hydrogen secondary battery with an improved negative electrode. It is a thing.

[0002]

2. Description of the Related Art At present, a metal oxide / hydrogen secondary battery of a type in which a hydrogen negative electrode is composed of a hydrogen storage alloy is drawing attention. The reason is that this battery system originally has a high energy-density and thus is advantageous in volumetric efficiency.
Moreover, it is possible to operate safely and is excellent in terms of characteristics and reliability. The negative electrode is manufactured by preparing a paste containing the powder of the hydrogen storage alloy and filling the paste into a conductive core body such as reticulated sintered metal fibers.

Conventionally, the hydrogen storage alloy has been L
aNi ₅ is often used. In addition, La, Ce, Pr,
An alloy of misch metal (hereinafter referred to as Mm), which is a mixture of lanthanum-based elements such as Nd and Sm, and Ni, that is, MmNi ₅ is also widely used. Since MmNi ₅ uses Mm as a rare earth component, it is cheaper and more practical than LaNi ₅ that uses only expensive La element as a rare earth component.

Regarding LaNi ₅ and MmNi ₅ , a part of Ni is Al, Mn, Fe, Co, Ti, C.
A multi-element system in which elements such as u, Zn, Zr, Cr, V and B are substituted is also used.

However, in the negative electrode prepared from the powder of the hydrogen storage alloy having the above-mentioned composition, the hydrogen storage alloy powder is hydro-pulverized and pulverized as the charge / discharge cycle progresses, and deteriorates. The secondary battery having the negative electrode has a problem that the charge / discharge cycle life is shortened. In addition, since the degree of progress of pulverization of the hydrogen storage alloy powder varies depending on the alloy lot, there is a problem that the charge / discharge cycle life of the secondary battery varies. This difference in the degree of pulverization is due to impurities contained in the hydrogen storage alloy, variations in the homogeneity of the alloy due to changes in the alloy manufacturing conditions, or the composition of the alloy due to changes in the yield of each alloy component during alloy production. This may be due to the variation in the ratio, but it is not clear at this stage.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the conventional problems, and it is possible to suppress pulverization with the progress of charge / discharge cycles, and further An object of the present invention is to provide a metal oxide / hydrogen secondary battery provided with a negative electrode capable of maintaining a constant degree of progress.

[0007]

The present invention provides a metal oxide / hydrogen secondary battery having a structure in which a positive electrode containing a metal oxide, a negative electrode containing an alkaline electrolyte and a hydrogen storage alloy are housed in a container. The negative electrode has a general formula of LmNi _w Co _x M
n _y Al _z (where Lm is at least one selected from La-containing rare earth elements, and the total atomic ratio is 4.
8 ≦ w + x + y + z ≦ 5.5), and X
The crystal lattice constants a and c obtained by line diffraction are 0.495 nm ≦ a ≦ 0.510 nm and 0.400 nm, respectively.
A metal oxide / hydrogen secondary battery comprising a hydrogen storage alloy having a hexagonal crystal structure with ≦ c ≦ 0.410 nm.

Lm, N blended with the hydrogen storage alloy
The five components of i, Co, Mn, and Al will be described in detail. (1) Lm Lm is made of at least one selected from rare earth elements including La and has a function of storing hydrogen.

(2) Ni Ni has a function of releasing hydrogen stored in the hydrogen storage alloy. The atomic ratio of Ni blended in the hydrogen storage alloy is preferably in the range of 3.90 to 4.50. This is due to the following reasons. When the atomic ratio is less than 3.90, the hydrogen storage amount of the hydrogen storage alloy may deviate from the target amount. On the other hand, when the atomic ratio exceeds 4.50, the hydrogen storage amount of the hydrogen storage alloy is likely to decrease, and the cycle life of the secondary battery may decrease. A more preferable atomic ratio is
It is in the range of 4.00 to 4.30.

(3) Co Co has a function of improving the cycle life of the secondary battery. The atomic ratio of Co compounded in the hydrogen storage alloy is preferably in the range of 0.38 to 0.50.
This is due to the following reasons. If the atomic ratio is less than 0.38, it may be difficult to suppress pulverization of the negative electrode. On the other hand, when the atomic ratio exceeds 0.50, the hydrogen storage amount of the hydrogen storage alloy is likely to decrease, and the cycle life of the secondary battery may decrease. A more preferable atomic ratio is in the range of 0.40 to 0.45.

(4) Mn Mn has a function of increasing the capacity of the negative electrode and suppressing pulverization of the negative electrode. M mixed with the hydrogen storage alloy
The atomic ratio of n is preferably in the range of 0.28 to 0.50. This is due to the following reasons. When the atomic ratio is less than 0.28, it becomes difficult to optimize the equilibrium hydrogen pressure of the hydrogen storage alloy, and the capacity of the negative electrode may decrease. On the other hand, the atomic ratio is 0.5
When it exceeds 0, the hydrogen storage amount of the hydrogen storage alloy is likely to be reduced and the hydrogen storage alloy is likely to be corroded, which may reduce the cycle life of the secondary battery. A more preferable atomic ratio is in the range of 0.30 to 0.40.

(5) Al Al has a function of increasing the capacity of the negative electrode and improving the cycle life of the secondary battery. The atomic ratio of Al compounded in the hydrogen storage alloy is preferably in the range of 0.28 to 0.50. This is due to the following reasons. If the atomic ratio is less than 0.28, it may be difficult to optimize the equilibrium hydrogen pressure of the hydrogen storage alloy to increase the capacity of the negative electrode, and it may be difficult to suppress atomization of the negative electrode. There is a fear. On the other hand, when the atomic ratio exceeds 0.50, the hydrogen storage amount of the hydrogen storage alloy is reduced and the hydrogen storage alloy is likely to be corroded, which may reduce the cycle life of the secondary battery. A more preferable atomic ratio is in the range of 0.30 to 0.40.

Ni, Co, Mn, Al
The reason for limiting the total value of the atomic ratios w, x, y, z in the range of 4.8 to 5.5 is as follows. When the total value is less than 4.8, it becomes difficult to suppress pulverization of the negative electrode. On the other hand, when the total value exceeds 5.5, the equilibrium hydrogen pressure of the hydrogen storage alloy increases and the hydrogen storage amount decreases, so that the capacity of the secondary battery decreases. A more preferable total value is in the range of 5.00 to 5.40.

The crystal lattice constants a and c of the hydrogen storage alloy are defined for the following reasons. When the crystal lattice constant a is less than 0.495 nm, the equilibrium hydrogen pressure of the hydrogen storage alloy of the negative electrode increases and the hydrogen storage amount decreases, so the capacity of the secondary battery decreases. On the other hand, when the crystal lattice constant a exceeds 0.510 nm, it becomes difficult to suppress pulverization of the negative electrode.
Further, when the crystal lattice constant c is less than 0.400 nm, the equilibrium hydrogen pressure of the hydrogen storage alloy of the negative electrode increases and the hydrogen storage amount decreases, so the capacity of the secondary battery decreases. On the other hand, when the crystal lattice constant c exceeds 0.410 nm, it becomes difficult to suppress pulverization of the negative electrode.
More desirable crystal lattice constants a and c are 0.49, respectively.
9 nm ≦ a ≦ 0.505 nm, 0.403 nm ≦ c ≦
It is 0.407 nm.

The negative electrode is made of the hydrogen storage alloy powder,
Preferably, a polymer binder is mixed, and if necessary, conductive powder is mixed to prepare a paste, and the paste is filled in a conductive core body.

Examples of the polymer binder include sodium polyacrylate and polytetrafluoroethylene (P
TFE), carboxymethyl cellulose and salts thereof (C
MC) and the like. 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 include carbon black and graphite. The blending ratio of the conductive powder is preferably 4 parts by weight or less with respect to 100 parts by weight of the hydrogen storage alloy powder.

Examples of the conductive core include those having a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and those having a three-dimensional structure such as foam metal and reticulated sintered metal fiber.

For the positive electrode, for example, a paste containing cobalt oxide, a polymer binder, etc. in addition to a metal oxide such as nickel hydroxide, for example, a sintered fiber substrate, a foam metal,
It is manufactured by filling a conductive core body such as a non-woven fabric plated substrate or a punched metal substrate. Examples of the polymer binder include those similar to the polymer binder in the negative electrode. Examples of the alkaline electrolyte include 25 to 31 wt% potassium hydroxide aqueous solution to which 15 to 50 g / l of lithium hydroxide is added.

[0020]

The present inventors have found that the above-mentioned general formula LmNi _w Co
In the hydrogen-absorbing alloy represented by _x Mn _y Al _z, its crystal structured and measured by X-ray diffraction was a crystal lattice constant and the charge-discharge cycle life was found to be correlated. That is, the crystal structure is hexagonal and its crystal lattice constants a and c are
A hydrogen storage alloy with a small size is hard to be crushed due to storage and release of hydrogen during charge / discharge cycles because the crystal is strong,
It was found that the charge / discharge cycle life can be extended, but if the crystal lattice constants a and c are too small, the hydrogen storage amount is reduced, and the charge / discharge cycle life is shortened.

From the above, the present inventors set the crystal lattice constants a and c to 0.495 nm ≦ a ≦ 0.
It has been found that a hydrogen storage alloy having sufficient hydrogen storage performance and high crystal strength can be obtained by defining 510 nm and 0.400 nm ≦ c ≦ 0.410 nm. As a result, the negative electrode containing the hydrogen storage alloy has a sufficient hydrogen storage capacity, and can be suppressed from being pulverized with the progress of charge / discharge cycles to suppress deterioration. Furthermore, by defining the crystal lattice constants a and c within the above ranges, the crystal strengths of the hydrogen storage alloy are made uniform, so that the negative electrode can have a constant degree of pulverization.

Therefore, the above-mentioned general formula LmNi _w Co _x
Mn _y Al _z , and the crystal lattice constants a and c obtained by X-ray diffraction are 0.495 nm ≦ a ≦ 0.
A secondary battery including a negative electrode containing a hydrogen storage alloy having a hexagonal crystal structure with 510 nm and 0.400 nm ≦ c ≦ 0.410 nm can have a long charge / discharge cycle life and reduce variations in the life. can do.

[0023]

EXAMPLES Examples of the present invention will be described in detail below. Examples 1 to 3 First, the rare earth element Lm having a purity of 99.9% (Lm is La
45.1%, Ce 4.6%, Pr 12.1%, N
d is 37.0%, other rare earth elements and unavoidable impurities are 1.1%), Ni, Co, Mn, and Al are constituent components, and the composition is LmNi by high frequency melting.
_4.0 Co _0.4 Mn _0.3 Al _0.3 (The total atomic ratio is 5.
30 hydrogen storage alloy ingots represented by 0) were produced. Subsequently, these hydrogen storage alloy ingots were mechanically crushed.

The crystal lattice constants of the obtained hydrogen storage alloy powders were measured by X-ray diffractometry (tube; Cu). Hexagonal crystal lattice constants a and c are the values shown in Table 1 below. Five kinds of hydrogen storage alloy powder were selected.

Then, polytetrafluoroethylene, sodium polyacrylate and sodium carboxymethyl cellulose are used as a polymer binder in combination with the above-mentioned five kinds of hydrogen storage alloy powders, and carbon black and water as conductive powders are added. Was added and kneaded to prepare 5 kinds of pastes. Subsequently, each of the above-mentioned pastes was applied to a punched metal which is a conductive core, dried, pressed, and then cut into five types of negative electrodes.

A paste containing nickel hydroxide and cobalt oxide was prepared. This paste was filled into a nickel sintered fiber substrate, further dried, and then pressed all over,
A non-sintered nickel positive electrode was produced by cutting.

Using the five types of negative electrodes and the non-sintered nickel positive electrode, five types of test cells having a capacity of 1000 mAh shown in FIG. 1 were assembled. That is, the negative electrode 1 is spirally wound with the separator 3 interposed between the negative electrode 1 and the positive electrode 2, and is housed in the AA size cylindrical container 4. The negative electrode 1 is arranged on the outermost periphery of the prepared electrode group and is in electrical contact with the container 4. An alkaline electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide is contained in the container 4. A circular sealing plate 6 having a hole 5 in the center is arranged in the upper opening of the container 4. The ring-shaped insulating gasket 7 is
The sealing plate 6 is attached to the container 4 by caulking, which is disposed between the peripheral edge of the sealing plate 6 and the inner surface of the upper opening of the container 4, and is caulked to reduce the diameter of the upper opening inward.
It is fixed airtightly through. Positive electrode terminal 8 having a collar portion
The lower surface of the collar portion is welded to the sealing plate 6 via a ring-shaped spacer 9. The positive electrode lead 10 has one end connected to the positive electrode 2 and the other end connected to the positive electrode terminal 8.

Then, one of each of the five types of test cells is provided.
For 0 cells each, charge the battery for 1000 minutes at 1000 mAh for 90 minutes, then set the final voltage to 1 V and discharge at 1000 mAh. Repeat the charge-discharge cycle to measure the number of cycles required until the battery capacity becomes half of the initial charge-discharge cycle. Then, the average number of cycles was determined, and the results are shown in Table 1 below.

The pressure-composition isotherms of the above-mentioned 5 kinds of hydrogen storage alloy powders were measured at 60 ± 5 ° C. according to JIS H7201, and the hydrogen storage capacity (10
H / M (atomic ratio of hydrogen and hydrogen storage alloy) at atm was determined, and the results are also shown in Table 1 below.

[0030]

[Table 1]

As is apparent from Table 1, the composition is represented by the above-mentioned formula LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3 , and the crystal lattice constants a and c are 0.495 nm ≦ a ≦ 0.
Examples 1 to 10 provided with a hydrogen storage alloy having a hexagonal crystal structure of 510 nm and 0.400 nm ≤ c ≤ 0.410 nm.
It can be seen that the secondary battery of No. 3 can have a long cycle life and can reduce variations in the life. It is considered that this is because the negative electrode can be suppressed from being pulverized as the charge / discharge cycle progresses, and the degree of pulverization can be made constant. On the other hand, the composition is the same as in Examples 1 to 3, but the crystal lattice constant a is less than 0.495 nm and c is 0.400 nm.
It can be seen that the secondary battery of Comparative Example 1 including the negative electrode containing the hydrogen storage alloy having the hexagonal crystal structure of less than 1 has a short cycle life because the hydrogen storage amount of the negative electrode is low. On the other hand, Comparative Example 2 having the same composition as in Examples 1 to 3, but including a negative electrode containing a hydrogen storage alloy having a hexagonal crystal structure in which the crystal lattice constant a exceeds 0.510 nm and c exceeds 0.410 nm. It can be seen that, in the secondary battery of No. 3, although the hydrogen storage amount of the negative electrode is high as in Examples 1 to 3, the cycle life is shortened. This is because the negative electrode is one of Examples 1-3.
It is considered that this is because the pulverization progresses faster than that.

[0032]

As described above in detail, according to the present invention, it is possible to suppress pulverization with the progress of charge / discharge cycles, and to make the degree of pulverization constant. It is possible to provide a metal oxide / hydrogen secondary battery that includes such a negative electrode, has a long cycle life, and has reduced variations.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a test cell used in an example of the present invention.

[Explanation of symbols]

1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Cylindrical container with a bottom.

Claims (1)

[Claims] 1. In a metal oxide / hydrogen secondary battery having a structure in which a positive electrode containing a metal oxide, a negative electrode containing an alkaline electrolyte and a hydrogen storage alloy are housed in a container, the negative electrode is of the general formula LmNi _w. Co _x Mn _y Al _z (where, Lm
Is at least one selected from rare earth elements including La, and the total atomic ratio is 4.8 ≦ w + x + y + z ≦
5.5) and the crystal lattice constants a and c obtained by X-ray diffraction are 0.495 nm ≦ a ≦.
0.510 nm, 0.400 nm ≦ c ≦ 0.410 nm
A metal oxide / hydrogen secondary battery comprising a hydrogen storage alloy having a hexagonal crystal structure of