JP2001192757A - Hydrogen storage alloy, producing method therefor and hydrogen storage alloy electrode made of same alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydrogen storage alloy electrode excellent in service capacity, durability and initial activating characteristics. SOLUTION: This alloy is shown by the general formula of R2 (Ni7-x-y-zMnxAyBz)n and has a mixed crystal structure of two or more kinds in which the ratio of crystals having P63/mmc structure is 40 vol.% or more, where R is rare earth elements or misch metal; A is at least one or more kinds among Al, Cu, Co and Fe; and B is at least one or more kinds among Cr, Zn, Nb, Mo, Ag, In, Sn, Sb, Si, P and S, and 0.3<=x<=2.0, 0<y<=2.0, 0<z<=1.0 and 1.0<=n<=1.3 are satisfied. The hydrogen storage alloy for an electrode excellent in service capacity, durability to repeated charging and discharging and initial activating characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy capable of electrochemically absorbing and releasing hydrogen and particularly suitable as a material for a secondary battery, a method for producing the same, and an electrode using the alloy. It is.

[0002]

2. Description of the Related Art Hydrogen storage alloys are used for various purposes by utilizing their hydrogen absorption / desorption reactions, and as one of their applications, they are used as electrodes for batteries. Secondary battery using the electrode, and expands significantly demand in fields such as portable computers and mobile phones, now As the electrode material, AB ₅ type (mainly Mm (NiMnCoA
l) _5- system, P6 / mmm crystal structure) is mainly used. Furthermore, AB ₂ type alloy as having improved discharge capacity _{(ZrMn 2,} ZrV 2 system, _etc.), A 2 _{B 7} type alloy _{(Mm 2 (Ni · Mn)} 7 _system, P6 3 / mmc crystal structure) hydrogen Storage alloys have been developed and proposed.

[0003]

In the above application, the battery
There is also a strong demand for miniaturization, and excellent durability against hydrogen storage materials
And charge / discharge capacity are required, especially the discharge capacity is high,
In addition, a material whose discharge capacity is less reduced by repeated charge and discharge
Fees are requested. However, of the above material systems, AB₅
The system is expected to grow further in both capacity and durability in the future
It is difficult to improve the battery, especially when it comes to durability.
In the current situation where long service life is desired,
Absent. On the other hand, AB₂Alloy (ZrMn ₂, ZrV₂system
) Can be expected to have a larger capacity than the current alloy,
Because the initial activity is slow, before shipping the product as a battery,
Charge and discharge burden for activation is large and cost is high
I will. Also, A₂B₇System alloy (Mm₂(Ni ・ Mn)
₇System, P6₃/ Mmc) is a sufficiently excellent hydrogen storage and release
Output characteristics, but sufficient discharge capacity when used as an electrode
Insufficient quantity and sufficient durability
is not.

The present invention has been made in view of the above circumstances, and has a high charge / discharge capacity, a small decrease in discharge capacity due to repeated charge / discharge, excellent durability, and excellent hydrogen storage properties. An object of the present invention is to provide an alloy, a method for producing the alloy, and a battery electrode using the alloy.

[0005]

[MEANS FOR SOLVING THE PROBLEMS]
The first invention among the hydrogen storage alloys of the present invention has a general formula R ₂
(Ni_7-xyzMn_xA_yB_z)_nIndicated by
It is characterized by comprising two or more kinds of mixed crystal structures. R: Rare earth element or misch metal A: At least one of Al, Cu, Co, Fe B: Cr, Zn, Nb, Mo, Ag, In, Sn, S
at least one of b, Si, P and S 0.3 ≦ x ≦ 2.0, 0 <y ≦ 2.0, 0 <z ≦ 1.
0, 1.0 ≦ n ≦ 1.3

[0006] hydrogen storage alloy of the second invention, the hydrogen storage alloy of the first invention, wherein the crystalline ratio of P6 3 / _mmc structure is 40 vol% or more.

A method for producing a hydrogen storage alloy according to a third aspect of the present invention comprises:
A method for producing a hydrogen storage alloy according to the first or second invention, comprising a quenching step of quenching the alloy material at a cooling rate of 10 ² to 10 ⁷ ° C / sec.

[0008] A method for producing a hydrogen storage alloy according to a fourth aspect of the present invention comprises:
A method for producing a hydrogen storage alloy according to the first or second invention, wherein the hydrogen storage alloy material is subjected to a homogenization heat treatment at a temperature of 400 ° C. to 1100 ° C. in a vacuum or an inert gas atmosphere. It is characterized by having a process.

A method for producing a hydrogen storage alloy according to a fifth aspect of the present invention comprises:
As a post-step of the quenching step of the third invention, 400 ° C. to 11
The method is characterized by including a step of performing a homogenizing heat treatment in a vacuum at 00 ° C. or in an inert gas atmosphere.

[0010] A hydrogen storage alloy electrode according to a sixth aspect of the invention is characterized in that it is made of the hydrogen storage alloy according to the first or second aspect of the invention. A hydrogen storage alloy electrode according to a seventh aspect is characterized in that the electrode is made of a hydrogen storage alloy obtained by any one of the third to fifth manufacturing methods.

The reasons for limiting the compositional elements, quantity ratios and the like of the hydrogen storage alloy of the present invention will be described below. In the present invention, as the component represented by R in the general formula, one or more rare earth elements, or both, can be used in addition to the misch metal in which a plurality of rare earth elements are mixed. As a misch metal, for example, La: 25-
35 wt.%, Ce: 40 to 50 wt.%, Nd: 5 to 20 wt.%, Pr: 2 to 10 wt.%, Other rare earth metals and 1 to 5 wt.% Of other metals.

Mn ratio x (0.3 ≦ x ≦ 2.0) In the present invention, Mn is one of the basic components together with R and Ni. By containing Mn, a hydrogen dissociation pressure that can be used as an active material for a battery negative electrode can be obtained, and as a result, a sufficient discharge capacity can be obtained. In order to obtain this hydrogen dissociation pressure, the amount ratio x of Mn needs to be 0.3 or more. If the amount ratio is less than 0.3, a hydrogen dissociation pressure that can be used as an active material for a battery negative electrode can be obtained. Can not. On the other hand, when the amount of Mn is excessively larger than the amount ratio of 2.0, the elution into the electrolyte solution in the battery becomes intense, and when the battery is a sealed battery, it adversely affects the positive electrode or precipitates on the separator, As a result, battery life is reduced. Therefore, Mn
Is in the range of 0.3 to 2.0. For the same reason, it is desirable to set the lower limit of the quantitative ratio to 0.4 and the upper limit to 1.5.

Amount ratio y of group A (0 <y ≦ 2.0) Al, Cu, Co, and Fe constituting group A act to suppress a decrease in discharge capacity due to repeated charging and discharging, thereby improving durability. Therefore, one or more kinds are added. However, when the content exceeds 2.0, the discharge capacity is significantly reduced, so the upper limit is set to 2.0. In order to obtain the above effect sufficiently, the lower limit of the quantity ratio y is preferably set to 0.1, and the upper limit is preferably set to 1.6 for the same reason as described above. More preferably, the lower limit is 0.15 and the upper limit is 1.4.

Amount ratio z of group B (0 <z ≦ 1.0) Cr, Zn, Nb, Mo, Ag, In,
Sn, Sb, Si, P, and S have an effect of further suppressing a decrease in discharge capacity due to repeated charging and discharging and improving durability, and one or more of them are added. However, if the content exceeds 1.0, the discharge capacity is significantly reduced, so the upper limit is set to 1.0. In order to obtain the above effect sufficiently, the lower limit of the quantity ratio z is preferably set to 0.03, and the upper limit is preferably set to 0.8 for the same reason as described above. More preferably, the lower limit is 0.05 and the upper limit is 0.5.

N coefficient (1.0 ≦ n ≦ 1.3) In order to obtain a mixed crystal structure, it is necessary to set the value of n within the above-mentioned range. As a result, a desired effect cannot be obtained, or an unsuitable phase is generated as an active material for an electrode negative electrode.

[0016] As mixed crystal organization in the mixed crystal structure present invention, mainly _P6 3 / mmc structure _(structure constituting the A 2 _{B 7} type alloy) and P6 / mmm consist structure (structure constituting the AB ₅ type alloy) Is desirable. Both structures have excellent hydrogen absorption and desorption characteristics, but when viewed as a single structure, the following characteristics generally differ depending on their composition (constituent elements), but are superior. It can be said that. - high rate charge and discharge characteristics: _P6 3 / mmc <alloy component elution resistance to P6 / _{mmm-electrolyte: P6 3 / mmc> P6 /} mmm · hydrogen absorption and release during耐微powder _resistance: P6 3 / mmc > P6 / mmm Note that the eluted element has an adverse effect on the positive electrode,
For example, the battery may be deposited on the separator, thereby shortening the battery life. Further, when the alloy is pulverized, the specific surface area of the alloy increases, so that the elution amount further increases. P6 /
mmm structure, has the-prone nature elution of the alloy components, P6 3 / _mmc is on the originally hard elution and excellent in耐微powdering performance, in the mixed crystal of both tissue, P6 ₃ / to mmc matrix within the structure becomes crystals dispersed condition of P6 / mmm structure, combines the advantages of both,
That is, the material is excellent in macro-pulverization resistance. When this is used as an electrode for a battery, the total elution amount of components is reduced, and characteristics with excellent durability (a decrease in discharge capacity due to repeated charging / discharging is small) are obtained. Moreover,
For the charge-discharge characteristics, the presence of P6 / mmm _structure, and that significantly better compared to the P6 3 / mmc single phase. Therefore, the mixed crystal structure alloy exhibits excellent characteristics as an active material for an electrode as compared with each single-phase alloy.

Incidentally, in order to obtain the above-mentioned characteristics, P6₃/
The crystals of the P6 / mmm structure are dispersed in the parent phase of the mmc structure.
Needs to be assured of the situation,
P6 ₃The crystal ratio of the / mmc structure is 40% by volume or more.
It is desirable. On the other hand, P6₃/ Mmc crystal ratio
If the amount is too large, the effect of improving the charge / discharge characteristics is reduced.
Therefore, it is desirable to set the upper limit to 80% by volume. Also on
The remainder in the crystal ratio is substantially a P6 / mmm structure.
It is desirable to have. Here, “substantially” means both structures
In addition to the above, a small amount of other structural crystals can be mixed as impurities.
Means that the amount is as small as possible
Is desirable, and specifically, it is desirable to be 10% by volume or less.
New The phases other than both structures are AB₃, Ni
It is.

Rapid cooling step (cooling rate: 10 ² to 10 ⁷ ° C /
Second) In the production of the above alloy, 10
That it provides a rapid cooling step of cooling at a cooling rate of ² to 10 ⁷ ° C. / sec desirable. By the rapid cooling described above, a mixed crystal (for example, P
( ₃ / mmc structure and P6 / mmm structure or two or more types of structures) can be finer and more uniformly distributed, so that the properties of the obtained alloy are homogenized and the durability is improved. Is further improved. In order to ensure these effects, it is necessary to set the cooling rate to 10 ² ° C / sec or more. On the other hand, if it exceeds 10 ⁷ ° C. / sec, and amorphous, crystalline order can not be obtained, defining the range. For the same reason, the lower limit is 10 ⁴ ° C / sec and the upper limit is 10 ⁶ ° C.
/ Sec is more desirable.

Homogenization treatment (400 to 1100 ° C.) After that, the melted alloy is usually subjected to a uniform heat treatment in a vacuum atmosphere or an inert gas atmosphere and cooled. Examples of the inert gas atmosphere include a nitrogen gas atmosphere and an argon gas atmosphere, but the present invention is not limited to the type of the inert gas. Further, the degree of vacuum in a vacuum atmosphere is not particularly limited. For example, 10 ⁻³ To
A degree of vacuum of rr or less can be mentioned. The heating temperature at the time of the homogeneous heating is 400 to 1100 ° C. This is 40
If the temperature is lower than 0 ° C., sufficient homogenization is not achieved, while 1
If the temperature exceeds 100 ° C., the alloy may be re-melted, or if the quenching treatment is performed, the structure may grow too much and the effect of the quenching treatment may be lost.

The above homogenization treatment is completed by heating and cooling at the above temperature. When this cooling rate or the homogenization treatment is not performed, a mixed crystal structure alloy having a desired crystal structure ratio can be obtained by controlling the cooling rate of the rapid cooling treatment. In other words, the slower the cooling
/ Ratio of mmm structure _increases, the proportion of P6 3 / mmc structure is reduced. Therefore, by appropriately controlling the cooling rate, the P6 ₃ / mmc structure and the P6 / m
A mixed crystal structure with a mixed mm structure is obtained. It should be noted that a preferable cooling rate cannot be univocally defined because it varies depending on the composition of the alloy, the cooling method, and the like. The manufacturing process desirably includes one of the quenching process and the homogenizing process.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The alloy of the present invention can be produced by a conventional method as a material having a quantitative ratio within the range of the present invention.
The present invention is not particularly limited as to the method. For example, after weighing each metal powder so as to have a desired quantitative ratio, it is stored in a water-cooled copper crucible of an arc type vacuum melting apparatus, and is arc melted in a high purity Ar gas atmosphere. It is desirable that the above-mentioned material goes through the above-mentioned quenching step and homogenizing step according to the production method of the present invention. The quenching method in the quenching step is not particularly limited, and an appropriate method such as a roll method can be adopted so as to obtain the above-mentioned cooling rate conditions. In the homogenization treatment, heat treatment is performed according to the above heating conditions. The heating method is not particularly limited, and for example, heating can be performed using a heating furnace such as a batch furnace or a continuous furnace.

The alloy obtained through the above manufacturing process and the like is made of P
6 ₃ / mmc in structure and P6 / mmm structure becomes a mixed crystal structure consisting mainly. As described above, the ratio of the mixed crystal can be controlled by the cooling rate in the cooling process in the homogenization heat treatment. The cooling rate can be changed by the type of the refrigerant, the selection of the cooling method, and the like. The above alloy is usually pulverized to about several tens of μm in the air or in an inert atmosphere, in some cases, in a wet atmosphere after the homogenization treatment, but it can be used as a solid or as a molded powder. . The alloy is suitable as a material for a secondary battery, and is incorporated in a battery as an electrode. The method of assembling into the battery and the structure of the battery are not particularly limited, and a conventional method or a known structure can be adopted. Further, the alloy of the present invention can be used for other applications, and can be used for various applications utilizing the absorption and release of hydrogen.

[0023]

(Embodiment 1) An embodiment of the present invention will be described below. Each elemental material was measured so as to have a quantitative ratio shown in Table 1, melted with an argon arc to melt the alloy material, and further shifted to the following manufacturing process. (1) Homogenization treatment Some materials were subjected to a homogenization heat treatment at 850 ° C. for 12 hours in an argon atmosphere. The cooling rate at this time is about 2 ° C. / min on average, resulting alloy with respect to inventive material comprises mainly _,, P6 3 / mmc and P6 / mmm, and P
6 ₃ / mmc about 50 vol%, P6 / mmm it was confirmed that the mixed crystal is about 50% by volume. On the other hand, comparative materials 18 and 19 _is P6 3 / mmc single phase, comparative materials 20
Is approximately P6 / mmm single phase, comparative materials 21 and 22 as well as the invention material _P6 3 / mmc and the P6 / mmm was mixed crystal it is about 50% by volume, respectively. In addition, these crystal structure ratios were measured by X-ray diffraction. (2) Rapid cooling treatment Some of the other materials were redissolved in an argon atmosphere after the above-described argon arc melting, and rapidly solidified by a single roll method to form flakes. The single roll used in the method is made of Cu, and the pouring nozzle (injection nozzle) is made of quartz. The cooling rate during the rapid cooling was 10 ⁵ ° C / sec. The obtained alloy was subjected to P6
It was confirmed that ₃ / mmc was about 50% by volume and P6 / mmm was about 50% by volume. (3) Quenching + Homogenization A part of the material subjected to the quenching was vacuum-sealed in a quartz tube and subjected to a homogenization heat treatment at 800 ° C. for 5 hours. The cooling rate at this time was 50 ° C./min on average, and it was confirmed that the obtained alloy was a mixed crystal having the same ratio as described above.

The alloy having undergone any of the above steps (1) to (3) is pulverized to a particle size of 400 to 500 mesh, and
In an aqueous KOH solution, perform surface treatment at 80 ° C for 1 hour.
After further washing with water, it was dried. This alloy powder and C
u powder and alloy powder: Cu powder = 1: 4 (weight ratio), and the mixed powder was pressed into a pellet. The pellet was used as a negative electrode, and Ni hydroxide was used as a counter electrode.
A test cell was manufactured using an Hg / HgO electrode as an electrode and a reference electrode, and a 6M KOH aqueous solution as an electrolyte.

Using the test cell, a charge / discharge test was repeatedly performed under the following charge / discharge conditions. Charge / 100 mA / g × 4 hours (per weight of hydrogen storage alloy) Discharge / 50 mA / g, final voltage -0.6 V (potential of test electrode with respect to reference electrode) * g of mA / g is hydrogen storage alloy in test electrode Weight Initial maximum discharge capacity (mA)
h / g) was measured and is shown in Table 1 as a discharge capacity. Further, the discharge capacity at 200 cycles of repeated charge / discharge was compared with the maximum discharge capacity, and the ratio (%) is shown in Table 1 as durability.

[0026]

[Table 1]

As is clear from the table, the material of the present invention greatly exceeds the discharge capacity of 250 mAh / g, which is practically necessary, and the durability is also practically required, 70.
%, And it was clear that both the discharge capacity and the durability were excellent. On the other hand, Fe and group A, free of B group _element, the comparative material 18 consisting of P6 3 / mmc single phase, was insufficient initial capacity, durability both. The comparative materials 19 and 20 have a quantitative ratio n defined in the present invention.
Made but is intended to be outside the scope of the invention, n <Comparative material 19 consisting of a 1.0 _P6 3 / mmc single phase, initial capacity is also insufficient durability, n> 1.3 The comparative material 20 has good capacity but has insufficient durability. Furthermore, the comparative materials 21 and 22 which do not contain Fe and the elements of Groups A and B have satisfactory capacities but are inferior in durability.

(Example 2) A comparative test was conducted on the initial activation characteristics of AB- ₂ type alloys shown in Table 1 and Table 2. In addition, AB type ₂ alloy is the invention material N
o. It was manufactured by the same manufacturing method as in Example 1. With respect to these test materials, test cells were manufactured in the same manner as in Example 1, and the same charge / discharge was repeated. At that time, the number of cycles until reaching the maximum discharge capacity was measured. As a result, as shown in Table 2, the present invention has reached the maximum discharge capacity in an early stage as compared with the AB ₂ type alloys, it has excellent initial activity characteristics are revealed.

[0029]

[Table 2]

[0030] (Embodiment 3) _Next, P6 3 / mmc _{(A 2}
And electrodes pellets were mixed in 1,: B ₇ type) single-phase alloy powder and P6 / mmm (AB ₅ type) and a single-phase alloy powder 1
Mixing the two alloys in the same ratio, and _dissolved, P6 3 / mm
An electrode manufactured from an alloy (invention material) in which the c structure and the P6 / mmm structure were mixed crystals at a ratio of 1: 1 was prepared. These components have substantially the same quantitative ratio as a whole. Using these electrodes, a test cell was manufactured in the same manner as in Example 1, and a charge / discharge test was performed under the same conditions. Table 3 shows the results. As is clear from Table 3, in the case where the alloy was simply mixed, the discharge capacity and the charge / discharge characteristics were significantly inferior to those of the inventive material, and it was found that the capacity and the durability were greatly improved by the mixed crystal structure.

[0031]

[Table 3]

[0032]

As described above, according to the hydrogen storage alloy of the present invention, the general formula R ₂ (Ni _{7 -xyz} Mn _x)
A _y B _z ) _n , where R: rare earth element or misch metal A: at least one of Al, Cu, Co, Fe B: Cr, Zn, Nb, Mo, Ag, In, Sn, S
at least one of b, Si, P, and S 0.3 ≦ x ≦ 2.0, 0 <y ≦ 2.0, 0 <z ≦ 1.
Since 0, 1.0 ≦ n ≦ 1.3 and two or more mixed crystal structures, high discharge capacity and excellent durability can be obtained, and characteristics suitable as an electrode material for a secondary battery can be obtained. An electrode using this material can constitute a secondary battery having excellent characteristics. In the above, if a mixed crystal structure is assumed crystal ratio of P6 3 _/ mmc structure is 40 vol% or more, improvement in discharge capacity and durability is assumed reliable and sufficient. Excellent initial activation characteristics.

Further, regarding the production of the above-mentioned hydrogen storage alloy, 1
If a quenching step of quenching at a cooling rate of 0 ² to 10 ⁷ ° C / sec is provided, a fine and uniform mixed crystal structure can be obtained, and the above characteristics can be homogenized, and the durability is particularly improved.

Further, regarding the production of the above-mentioned hydrogen storage alloy, the temperature may be 400 ° C. to 1100 ° C. in a vacuum or in an inert gas atmosphere.
If the homogenization heat treatment is performed at a temperature of ℃, the characteristics can be homogenized, and the ratio in the mixed crystal can be controlled by the cooling rate in the cooling process at that time, so that the desired discharge capacity and durability characteristics can be obtained. Obtainable.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C22F 1/00 661 C22F 1/00 661C 691 691B 692 692A (72) Inventor Toshimitsu Goto 4th Chazu-cho, Muroran-shi, Hokkaido Co., Ltd. Japan Steel Works (72) Inventor Hideaki Ito 4 Chazu-cho, Muroran, Hokkaido Japan Steel Works Co., Ltd. F-term (reference) 5H050 AA07 AA08 BA14 CB17 DA03 FA19 GA01 GA02 GA27 HA00 HA02 HA14 HA20

Claims (7)

[Claims] 1. A compound of the general formula R ₂ (Ni _7-xyz Mn _x
A _y B _z ) A hydrogen storage alloy represented by _{n and} having a mixed crystal structure of two or more types, provided that R: a rare earth element or a misch metal A: at least one type of Al, Cu, Co, and Fe B: Cr, Zn, Nb, Mo, Ag, In, Sn, S
at least one of b, Si, P and S 0.3 ≦ x ≦ 2.0, 0 <y ≦ 2.0, 0 <z ≦ 1.0, 1.0 ≦ n ≦ 1.3 Wherein P6 3 / _mmc crystal ratio of structure is characterized in that 40% by volume or more claim 1, wherein the hydrogen storage alloy 3. The method for producing a hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy material is 10 ²
The method of manufacturing a hydrogen-absorbing alloy characterized by having a rapid cooling step of quenching at a cooling rate of to 10 ⁷ ° C. / sec 4. The method for producing a hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy material is heated to 400 ° C. to 1100 ° C. in a vacuum or in an inert gas atmosphere.
A method for producing a hydrogen storage alloy, comprising a step of performing a homogenizing heat treatment at a temperature of 50 ° C. 5. A method for producing a hydrogen storage alloy, comprising a step of performing a homogenizing heat treatment in a vacuum at 400 ° C. to 1100 ° C. or in an inert gas atmosphere as a post-step of the quenching step according to claim 3. Method 6. A hydrogen storage alloy electrode comprising the hydrogen storage alloy according to claim 1 or 2. 7. A hydrogen storage alloy electrode comprising a hydrogen storage alloy obtained by the method according to claim 3. Description: