JP2000073134A - LaNi5 HYDROGEN STORAGE ALLOY AND ELECTRODE USING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydrogen storage alloy excellent in high temp. characteristics, high in capacity, high in discharging characteristics and rapid in charging characteristics by incorporating specified amounts of Ce and La into a mixture of rare earth elements to form into an LaNi5 hydrogen storage alloy. SOLUTION: This hydrogen storage alloy is expressed by the general formula of R(Ni)x-y-z(M1)y(M2)z(M3)w. In the formula, R denotes a mixture of rare earth elements at least contg. 41 to 50 wt.% Ce and 50 to 59 wt.% La, M1 denotes Mn and/or Al, M2 denotes at least one or more kinds selected from Co, Fe and Cu, M3 denotes Si and/or Ti, (x), (y) and (z) denote the atomic ratios to R and are controlled to 4.83<=x<=5.27, 0.3<=y<=1.0 and 0.4<=z<=1.0, and (w) is the value set in such a manner that M3 is controlled to 0.01 to 1 wt.%, preferably to 0.05 to 0.5 wt.% in the case the total of R, Ni, M1 and M2 is 100 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy and an electrode using the same, and more particularly to a hydrogen storage alloy suitable as a negative electrode for an alkaline storage battery and an electrode using the same.

[0002]

2. Description of the Related Art Since the discovery of a hydrogen storage alloy that absorbs and releases hydrogen, its application has been expanded not only to hydrogen storage means but also to heat pumps and batteries. In particular, alkaline storage batteries using a hydrogen storage alloy as a negative electrode have almost reached practical use, and the hydrogen storage alloys used have been continuously improved.

[0003] That is, the LaNi ₅ alloy studied at the beginning (see Japanese Patent Application Laid-Open No. 51-13934) has the advantage of a large amount of hydrogen storage, while the La metal is expensive and can store hydrogen. It has the drawback that it is easily pulverized by repeated release, and is easily corroded by an alkali solution or an acid solution. However, such drawbacks are that some of La are replaced by Ce, Pr, Nd and other rare earth elements and / or some of Ni is
o, Al, Mn and the like (for example, Japanese Patent Application Laid-Open Nos. 53-48918, 54).
-64014, 60-250558, 61-233969, and 62-43064).

[0004] Usually, part of La is Ce, Pr, N
Commercially available misch metal (Mm) was used as the metal substituted with d or the like. The misch metal is a mixture of rare earth elements, for example, Ce 45% by weight, La30
Wt%, Nd5 wt%, and other rare earth elements 20
% By weight.

In general, when a hydrogen storage alloy is used as a negative electrode for a battery, high-temperature characteristics are important conditions. In other words, when a negative electrode is manufactured using this alloy and used in a battery, if the battery is left in a car during charging or in a hot summer season, the temperature of the battery becomes high, so the life of the negative electrode is extended. It becomes shorter, and the function as a battery deteriorates. Such a drawback is particularly remarkable in a battery for an electric vehicle (EV) which is frequently exposed to high temperatures. Therefore, development of a hydrogen storage alloy that can be used as a negative electrode for a battery having high temperature characteristics has been desired.

Accordingly, it has been found that, with respect to a hydrogen storage alloy having excellent high-temperature characteristics when used as an electrode for a battery, the high-temperature characteristics of the electrode greatly depend on the content of Ce in the hydrogen storage alloy. A hydrogen storage alloy characterized by being contained in 45% by weight or more and an electrode using the same, and as a result of further examination, it was found that most of the rare earth elements were made of Ce and La, so that a high capacity was obtained. It has been found that an electrode having excellent high-temperature performance can be obtained.
306517 has been published. However, Ce and La
However, further improvement in the discharge capacity at a large current has been desired.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydrogen storage alloy which is excellent in high-temperature characteristics, and which has high capacity, high rate discharge characteristics and rapid charge characteristics. In addition, even when the battery is used at a high temperature, particularly at a high temperature of 30 ° C. or higher, the hydrogen storage alloy which does not deteriorate and has a high capacity, a high rate discharge characteristic, and an excellent rapid charge characteristic is used. It is to provide an electrode.

[0008]

SUMMARY OF THE INVENTION The above objects of the present invention.
Is LaNi_FiveR (Ni) of the system_xyz(M¹)_y(M^Two)
_z(M^Three)_wA hydrogen storage alloy represented by
At least 41 to 50% by weight of Ce and 50 to 59% of La
% By weight and a mixture of rare earth elements and Ti
And / or using a hydrogen storage alloy containing Si
More excellent high-rate discharge characteristics,
It has become possible to provide poles.

The hydrogen storage alloy of the present invention contains 41 to 50% by weight of Ce in R, which is a mixture of rare earth elements. By using an alloy having such a composition as the negative electrode of an alkaline storage battery, a battery having a high temperature history (hereinafter, referred to as “high temperature history”)
This is synonymous with a battery having excellent high-temperature performance. ) Can be manufactured. Further, the hydrogen storage alloy of the present invention contains La
Of 50 to 59% by weight. As a result, a high-capacity battery as well as excellent high-temperature performance can be obtained.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a compound represented by the general formula (1)
(Ni) _xyz (M ¹ ) _y (M ² ) _z A hydrogen storage alloy represented by (M ³ ) _w is provided. R is at least 4
It is a mixture of rare earth elements containing 1 to 50% by weight and 50 to 59% by weight of La. M ¹ represents Mn and / or Al, M ² represents at least one selected from Co, Fe, and Cu, and M ³ represents Si and / or Ti.
x, y, and z are atomic ratios with respect to R, and 4.83 ≦
x ≦ 5.27, 0.3 ≦ y ≦ 1.0, 0.4 ≦ z ≦ 1.
It is a number that satisfies 0. w is the atomic ratio to R, and when the total amount of R, Ni, M ¹ and M ² is 100% by weight, M ³ is 0.01 to 1% by weight, preferably 0.0% by weight.
The number is set to be 5 to 0.5% by weight. R
Represents at least 41 to 50% by weight of Ce and 50 to 50% of La.
It is a rare earth element mixture containing 59% by weight. R is
In addition to Ce and La, Pr, Nd, Sm, Y and the like can be contained, but it is particularly preferable that R be a mixture of Ce and La. Ce and La in R
The reason for setting the content of the above to the above range is that when La increases,
Although the discharge capacity is increased, the life is shortened, and when the La amount is reduced, the discharge capacity is reduced. Further, when most of R is composed of La and Ce, it is possible to obtain an alloy that is resistant to a high-temperature history. As M ¹ , Mn and Al can be substituted alone, but it is particularly preferable to selectively substitute both at the same time. When Mn, Al and M ² elements coexist, elution of alloy constituent elements in an alkaline aqueous solution is suppressed, and the corrosion resistance at high temperatures is further improved. As M ^3, it is particularly preferable to use Ti, which does not form a solid solution in the alloy due to the addition of Ti, exists as a Ti compound as a second phase other than the CaCu ₅ structure, and can increase the surface area. Thereby, the high rate discharge characteristics are further improved, and the characteristics of the alloy are improved.

When x is less than 4.83, the ratio of the rare earth element becomes large, the life is short, the corrosion resistance is reduced, and it is not practical. If x exceeds 5.27, the amount of hydrogen absorbed per unit weight of the alloy becomes small, which is not practical. y is 0.
If it is less than 3, the amount of hydrogen absorbed per unit weight of the alloy at a high temperature becomes small, which is not practical. If y exceeds 1.0, the amount of hydrogen occlusion per unit weight of the alloy at a normal temperature or lower becomes small, which is not practical. When z is less than 0.4, the life is shortened and is not practical. When z exceeds 1.0, the hydrogen storage amount per unit weight decreases, which is not practical. R, N
When the total amount of i, M ¹ and M ² is 100% by weight, M
^When w is set so that ³ is less than 0.01% by weight,
Effects such as improvement of high-rate discharge characteristics by addition of M ³ are not sufficiently exhibited. If w is set so that M ³ exceeds 1% by weight, the amount of hydrogen occlusion per unit weight of the alloy decreases, which is not practical.

Further, the present invention provides a compound represented by the general formula (2):
(Ni)_x-y1-y2-z(Mn)_y1(Al)_y2(M^Two)
_z(M^Three)_wA hydrogen storage alloy represented by the formula: R,
M^Two, M ^Three, X, z, and w are the same as in the general formula (1).
The reason for setting x, z, and w in this range is also the same as in the general formula (1).
is there. Further, y1 and y2 are atomic ratios to R,
y1 is a number in the range of 0.1 to 0.5, and y2 is 0.1
It is a number in the range of 0.6. Let y1 and y2 be this range
The reason is to adjust the equilibrium dissociation pressure of the alloy and
It is necessary to secure the amount, and y1 and y2 are large.
This is disadvantageous for corrosion resistance. M^ThreeTi and / or S
i is added and dissolved simultaneously with each element, or R is added.
It may be re-dissolved and put together with other metals to dissolve
And R (Ni)_xyz(M¹)_y(M^Two)_zIf
It may be charged when gold is produced and the alloy is melted again.
No.

The hydrogen storage alloy of the present invention can be easily obtained by adding and dissolving each element of the above composition by a known method. Specifically, a predetermined amount of each element is weighed, and is evacuated using a crucible or the like in a high-frequency melting furnace, an arc melting furnace, or the like (in a low pressure of 0.01 torr or less) or in an inert gas atmosphere such as argon or helium. Below 200-800
After melting under torr, it is cooled and cast into an ingot or the like. Further, in vacuum (under a low pressure of 0.01 torr or less) or in an atmosphere of an inert gas such as argon or helium (600 to
5 to 2 at 800 to 1200 ° C in 1000 torr)
Heat treatment is performed for 0 hours. Also, not only the above casting method,
The alloy of the present invention can be obtained by quenching the molten alloy by a quenching method such as a roll quenching method and an atomizing method.

An alloy powder having an average particle size of 5 to 50 μm can be easily obtained from the hydrogen-absorbing alloy produced by the above-mentioned method under an inert gas atmosphere of argon, nitrogen or the like by an impact-type or grinding-type pulverizer. Further, the alloy powder of the present invention is subjected to a surface treatment with an alkali solution such as potassium hydroxide or an acidic solution such as hydrochloric acid or the like to activate the alloy powder, or a metal layer is formed on the alloy surface with a transition metal such as Ni or Co to make electrical contact. Alternatively, the catalytic ability may be improved.

The electrode of the present invention uses a known binder such as polyvinyl alcohol, carboxymethyl cellulose or the like, a binder such as PTFE or a polymer latex in an amount of 0.1 to 20% by weight based on the alloy, and further contains carbon or graphite powder if necessary. , Ni powder, Cu powder, etc., may be added in an amount of 0.5 to 10% by weight, and may be made into a paste, easily filled and applied to a current collecting support such as punched metal, foamed nickel, nickel fiber, and the like. Can be obtained. Therefore, an alkaline storage battery can be obtained by incorporating the negative electrode of the present invention, a known nickel positive electrode, a separator, and the like.

[0016] The hydrogen storage alloy of the present invention, as described above,
When used as an electrode for an alkaline storage battery, its characteristics can be best exhibited, but it goes without saying that it can be used as an original hydrogen storage means or as a heat pump for applications other than the above electrodes.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. Examples 1 to 5 Each element was weighed so as to have the composition shown in Table 1, and they were melted in an arc melting furnace under argon gas to obtain an alloy. In Table 1, "wt%" of Ti is La,
Ce, Ni, Mn, Al, Co and, where applicable, percentages by weight relative to the total amount of Fe and Cu. The obtained alloy is subjected to a heat treatment at 1000 ° C. × 5 hours in an argon gas atmosphere, and then the alloy is pulverized to have an average particle size of 75 μm.
m. 3% by weight based on 10 g of the powder
2.5 g of an aqueous solution of polyvinyl alcohol (having a degree of saponification of 98 mol% and an average degree of polymerization of 2,000) was added and mixed to obtain a paste. The obtained paste is formed into a porous nickel foam having a porosity of 94 to 96% (dimensions 30 × 40 × thickness 1.2 m).
m) was uniformly filled, dried, and then press-molded to produce a negative electrode.

[0018]

[Table 1]

On the other hand, a sintered nickel produced according to a known method was used as a nickel oxide positive electrode. An open-type nickel-hydrogen storage battery was constructed using a polyolefin (PP) nonwoven fabric as a separator, combining the above electrode with the above-mentioned negative electrode, and using an aqueous solution of 6 molar potassium hydroxide as an electrolytic solution.

Each of the obtained batteries is charged at a constant temperature of 20 ° C. with a charging current of 30 mA / g for 15 hours, left for 30 minutes, and continued until the battery voltage reaches 0.8 V at a discharging current of 60 mA / g. After repeating this cycle 15 times, 5
The same cycle was repeated 10 times at 0 ° C., and when the temperature was returned to 20 ° C. again, the amount of discharge was 2
The recovery rate with respect to the discharge capacity at 0 ° C. was measured and defined as “post-high-temperature recovery rate”. After repeating a cycle of charging at a constant current of 20 ° C. at a charging current of 30 mA / g for 15 hours, leaving the battery for 30 minutes, and continuing at a discharging current of 60 mA / g until the battery voltage becomes 0.8 V, 300 times. Was measured, and the maximum discharge capacity in the initial to 30 cycles was defined as the initial capacity, and the ratio of the capacity to this was measured as the "discharge capacity retention ratio". Using a battery prepared in the same manner, the battery was charged at 20 ° C. at a current of 60 mA / g for 7.5 hours, and then charged at various currents (300 mA / g, 900 mA / g).
To discharge the battery voltage to 0.8 V, and change the capacity ratio to the initial capacity by the discharge rate (“300 mA / g discharge rate”, “9
00 mA / g discharge rate "). Table 2 shows the above results.

[0021]

[Table 2]

Comparative Examples 1 to 8 Each element was weighed so as to have the composition shown in Table 1, and alloys and negative electrodes were produced in the same manner as in the examples. An open nickel-hydrogen storage battery was constructed in the same manner as in the example. The characteristics were examined in the same manner as in the examples. Table 2 shows the above results.

As shown in Comparative Example 3 in Table 2, when a negative electrode containing 55% by weight of La with respect to 45% by weight of Ce was used, the recovery rate of the battery after high temperature was 100%, and the recovery rate after high temperature was about 100%. It has been proved that a high-capacity battery can be obtained, but the high-rate discharge characteristics are insufficient.

In Table 2, Example 1 was compared to Comparative Example 3.
As shown in Tables 1 to 5, it can be seen that the high-rate discharge characteristics were improved when Ti was present. In addition, in Comparative Examples 1, 2, 4 to 8 as compared with Examples 1 to 5, it can be seen that the discharge capacity is small and the life is short.

[0025]

When the hydrogen storage alloy of the present invention is used as a negative electrode of an alkaline storage battery, it can be used as an electrode having a high temperature history and a high capacity. Therefore, according to the electrode using the hydrogen storage alloy of the present invention, not only can it be used at a low temperature, but even after experiencing a high temperature, deterioration of the electrode is small, so that the capacity change of the battery is small. Further, it is possible to provide a battery capable of maintaining a high capacity for a long period of time. Further, it is possible to provide a battery having excellent high-rate discharge characteristics and capable of coping with rapid charging.

Claims (4)

[Claims] 1. A LaNi ₅ -based hydrogen storage alloy represented by the following general formula (1). R (Ni) _xyz (M ¹ ) _y (M ² ) _z (M ³ ) _w (1) (where R is a rare earth element containing at least 41 to 50% by weight of Ce and 50 to 59% by weight of La) A mixture of elements, M ¹ represents Mn and / or Al, M ² represents Co,
M represents at least one or more selected from Fe and Cu;
³ represents Si and / or Ti, x, y, and z are atomic ratios with respect to R, and 4.83 ≦ x ≦ 5.27, 0.3 ≦
It is a number that satisfies y ≦ 1.0 and 0.4 ≦ z ≦ 1.0.
w is the atomic ratio to R, and R, Ni, M ¹ , M ²
When the total amount of 100 wt%, 0.01 is M ³
It is a number set to be 1% by weight. ) 2. A LaNi ₅ -based hydrogen storage alloy represented by the following general formula (2). R (Ni) _x-y1-y2-z (Mn) _y1 (Al) _y2 (M ² ) _z (M ³ ) _w (2) (where R is at least 41 to 50% by weight of Ce and La Is a mixture of rare earth elements containing 50 to 59% by weight, M ² represents at least one or more selected from Co, Fe, and Cu; M ³ represents Si and / or Ti;
3. x, y1, y2, and z are atomic ratios to R;
83 ≦ x ≦ 5.27, 0.1 ≦ y1 ≦ 0.5, 0.1 ≦
It is a number that satisfies y2 ≦ 0.6 and 0.4 ≦ z ≦ 1.0. w is the atomic ratio to R, and R, Ni, Mn,
Al, when the total amount of M ² to 100 wt%, a number M ³ is set to be 0.01 to 1 wt%. ) 3. The hydrogen storage alloy according to claim 1, wherein R is a rare earth mixture of La and Ce. 4. The LaN according to claim 1, wherein
electrodes formed by using a i ₅ based hydrogen storage alloy.