JP2019073757A - Hydrogen storing alloy particle - Google Patents

Abstract

To provide a hydrogen storing alloy particle excellent in discharge characteristic when electric current density is enhanced.SOLUTION: There is provided a hydrogen storing alloy particle containing Ti, Cr, V, and 5 at.% to 10 at.% of Ni, having a base phase having a body-centered cubic structure mainly containing Ti, Cr and V and having lattice constant of 3.05±0.05Å, and a grain boundary phase mainly containing Ti and Ni and existing between base phases, in which average cross section area of the base phase is 5 μmor less and area ratio of the grain boundary phase in a particle surface of 30% or more.SELECTED DRAWING: Figure 1

Description

  The present application discloses hydrogen storage alloy particles.

Hydrogen storage alloys are used as electrode materials for alkaline batteries. For example, in Patent Document 1, a parent phase comprising a Ti-V based solid solution and having a body-centered cubic structure and a Ti-Ni based alloy are present in a three-dimensional network shape in the parent phase and the parent phase is A predetermined hydrogen storage alloy is disclosed that includes a second phase that is divided into a small matrix phase, and the average cross-sectional area of the small matrix phase is 30 μm ² or less, specifically 10-15 μm ² or so, and high. A hydrogen storage alloy electrode excellent in rate discharge characteristics and charge / discharge cycle characteristics is obtained.

JP 2002-003975 A

  According to a new finding of the present inventor, when a hydrogen storage alloy as disclosed in Patent Document 1 is applied to the electrode of a battery, the discharge characteristic is reduced when the current density is increased, and the output of the battery is reduced. There is a problem of

The present application is a hydrogen storage alloy particle containing Ti, Cr, V, and Ni at 5 at% or more and 10 at% or less, as one means for solving the above-mentioned problems, wherein Ti, Cr and V are main components A matrix phase having a body-centered cubic structure with a constant of 3.05 ± 0.05 Å, and a grain boundary phase consisting mainly of Ti and Ni and existing between the matrix phases, and the average breakage of the matrix phase Disclosed is a hydrogen storage alloy particle having an area of 5 μm ² or less and an area ratio of the grain boundary phase occupying on the particle surface of 30% or more.

“Ti, Cr and V as main components” means that the proportion (at%) of the total amount of Ti, Cr and V in the total amount of elements contained in the matrix is the largest.
The term “mainly composed of Ti and Ni” means that the proportion (at%) of the total amount of Ti and Ni out of the total amount of elements contained in the grain boundary phase is the largest.
The “average cross-sectional area of the matrix” is obtained by obtaining a cross-sectional SEM image of the hydrogen storage alloy particle, and measuring the area of the region (crystal grain) surrounded by the grain boundary phase in the cross-sectional SEM image to determine the average value. Can be identified. For example, ten or more regions (crystal grains) surrounded by the grain boundary phase in the cross-sectional SEM image are extracted, and each area is measured to obtain an average value thereof.
The “area ratio of the grain boundary phase occupied on the particle surface” can be identified by measuring the ratio of the area detected as white when the reflection electron image of the surface of the hydrogen storage alloy particle is converted to two gradations. . For example, a backscattered electron image is obtained on the surface of a hydrogen storage alloy particle, and in the backscattered electron image, an area of 10 μm × 10 μm is selected, and two gradations are performed by image processing software. The area ratio of the grain boundary phase occupying the region is determined as x100), the area ratio is similarly determined for 10 or more locations on the particle surface, and the area ratio as a whole is specified.

The hydrogen storage alloy particles of the present disclosure have a small average cross-sectional area of 5 μm ² or less of the matrix phase and a large area ratio of the grain boundary phase contributing to the discharge reaction to the particle surface of 30% or more. When applied, the discharge capacity hardly decreases even if the current density is high, and the output is high.

FIG. 2 is a schematic view for explaining a hydrogen storage alloy particle 10; It is the schematic for demonstrating the mechanism of discharge characteristic improvement. It is a reflection electron image which shows the surface state (state of a parent phase, a grain boundary phase) of hydrogen storage alloy particles concerning comparative examples 1 and 2 and an example. (A) is Comparative Example 1, (B) is Comparative Example 2, and (C) is an Example. It is a reflection electron image which shows the surface state (state of a parent phase, a grain boundary phase) of hydrogen storage alloy particles concerning an example. The bright white part corresponds to the grain boundary phase, and the dim part adjacent to the grain boundary phase corresponds to the parent phase. It is a figure which shows the relationship of current density and discharge capacity about the electrode using the hydrogen storage alloy particle which concerns on the comparative examples 1 and 2 and an Example.

1. Hydrogen storage alloy particle The hydrogen storage alloy particle 10 shown in FIG. 1 is a hydrogen storage alloy particle containing Ti, Cr, V, and Ni at 5 at% or more and 10 at% or less, and contains Ti, Cr, and V as main components. A matrix phase 1 having a body-centered cubic structure with a constant of 3.05 ± 0.05 Å, and a grain boundary phase 2 containing Ti and Ni as main components and existing between the matrix phases 1 are provided. Moreover, in the hydrogen storage alloy particle 10 of the present disclosure, the average cross-sectional area of the matrix phase 1 is 5 μm ² or less, and the area ratio of the grain boundary phase 2 occupied on the particle surface is 30% or more.

1.1. Mother phase Mother phase 1 has a body-centered cubic structure mainly composed of Ti, Cr and V and having a lattice constant of 3.05 ± 0.05 Å. The matrix phase 1 is basically composed of a TiCrV alloy, but may contain elements other than Ti, Cr, and V for the purpose of increasing the hydrogen storage capacity. For example, La may be included. However, if the amount of elements other than Ti, Cr, and V is too large, the proportion of the matrix phase of the body-centered legislation having high hydrogen storage capacity may decrease, which may lead to a decrease in capacity. Therefore, 20 at% or less is preferable and, as for the quantity of elements other than Ti, Cr, and V, 10 at% or less is more preferable. In other words, when the whole component contained in matrix phase 1 is 100 at%, the total amount of Ti, Cr and V contained in matrix phase 1 is preferably 80 at% or more in total, and is 90 at% or more Is more preferred. The amounts of Ti, Cr and V contained in the matrix phase 1 are not particularly limited. For example, when the whole component contained in the mother phase 1 is 100 at%, the amount of Ti contained in the mother phase 1 is preferably 15 at% or more and 40 at% or less, and more preferably 20 at% or more and 35 at% or less Is preferred. The amount of Cr is preferably 10 at% or more and 50 at% or less, and more preferably 20 at% or more and 40 at% or less. The amount of V is preferably 10 at% or more and 70 at% or less, and more preferably 30 at% or more and 60 at% or less.

According to the knowledge of the present inventor, when the battery electrode is configured using the hydrogen storage alloy 10, the matrix phase 1 contributes to the capacity but hardly has the discharge reaction activity, and in the surface exposed portion of the grain boundary phase 2 described later It is considered that a discharge reaction is taking place. Therefore, for example, as shown in FIG. 2A, when the parent phase is large in the hydrogen storage alloy particle, the surface exposed portion of the grain boundary phase is sparse, and the effective reaction area is limited, which is a bottleneck. It is considered that the discharge characteristics at high current density are degraded. On the other hand, as shown in FIG. 2 (B), as in the hydrogen storage alloy particles 10 of the present disclosure, by reducing the average cross-sectional area of the matrix phase 1 and 5 [mu] m ² or less, a surface exposed portion of the grain boundary phase 2 ( The area ratio to the surface relatively increases, the area of the interface between parent phase 1 and grain boundary phase 2 in the whole particle also increases, hydrogen diffusion becomes advantageous, and the discharge capacity becomes high even if the current density is high. It is hard to lower and an electrode with high output is obtained. In particular, according to the findings of the inventor of the present invention, the grain boundary phase 2 described later is difficult to grow to a certain size (width) or more (the spread of Ni from the grain boundary is usually 0.5 μm or less). In order to increase the area ratio of the grain boundary phase 2, it is extremely effective to reduce the size of the matrix phase 1.

1.2. Grain Boundary Phase The grain boundary phase 2 is a phase mainly composed of Ti and Ni, and exists between the above-mentioned parent phases 1. Grain boundary phase 2 contains more Ni than parent phase 1. The solid solution alloy system has high capacity and low charge and discharge characteristics as a single substance, but the charge and discharge characteristics can be improved by introducing the grain boundary phase 2 containing Ti and Ni as main components. The amount of Ti contained in the grain boundary phase 2 is preferably 70 at% or more and 30 at% or less, and the amount of Ni is 70 at% or more and 30 at% or less, when the whole component contained in the grain boundary phase 2 is 100 at%. Is preferred. Furthermore, when the whole component contained in the grain boundary phase 2 is 100 at%, the total amount of Ti and Ni contained in the grain boundary phase 2 is preferably 80 at% or more in total, and 90 at% or more More preferable.

  According to the knowledge of the inventor, if the area ratio of the grain boundary phase 2 occupied on the particle surface in the hydrogen storage alloy particle 10 is 30% or more, the current density is high when the particle is applied as an electrode material of a battery. Also, the discharge capacity does not easily decrease and the output becomes high.

1.3. Others The size of the hydrogen storage alloy particles 10 as a whole is not particularly limited. From the viewpoint of further enhancing input / output characteristics when applied as an electrode of a battery, the particle diameter of the hydrogen storage alloy particle 10 is preferably 50 μm or less.

  The hydrogen storage alloy particles 10 of the present disclosure include Ti, Cr, V, and 5 at% or more and 10 at% or less of Ni as the entire composition. According to the knowledge of the present inventor, when the amount of Ni contained in the hydrogen storage alloy particle 10 is less than 5 at%, Ni is solid-solved, the above-mentioned grain boundary phase 2 is difficult to be formed, and the charge / discharge characteristics deteriorate. On the other hand, when the amount of Ni contained in the hydrogen storage alloy particle 10 is more than 10 at% (for example, when the amount of Ni is 12 at% as disclosed in Patent Document 1), particles having a small contribution to the capacity There is a risk that the number of interphases increases more than necessary, and the merit of the solid solution alloy, which is an advantage of high capacity, may not be obtained.

  On the other hand, the content of Ti, Cr and V in the entire hydrogen storage alloy particle 10 is not particularly limited. For example, it is preferable to set Ti to 20 at% or more and 35 at% or less, Cr to 5 at% or more and 40 at% or less, and V at 25 at% or more and 70 at% or less. According to the knowledge of the present inventor, in the hydrogen storage alloy particle 10, as the amount of Cr contained in the matrix phase 1 increases, the durability of the particle is improved. In this respect, the amount of Cr in the matrix phase 1 is more preferably 10 at% or more, further preferably 20 at% or more.

  As described above, according to the hydrogen storage alloy particle 10 of the present disclosure, in the hydrogen storage alloy particle having high capacity but having a problem in output, the alloy structure is miniaturized to make the matrix 1 small, and the surface The output characteristics can be improved by increasing the proportion of the grain boundary phase 2 which becomes the reaction active point. Moreover, durability can also be improved by including Cr essentially.

2. Method of Producing Hydrogen Storage Alloy Particles In producing the hydrogen storage alloy particles 10 of the present disclosure, a hydrogen storage alloy having the small mother phase 1 described above can be produced, for example, through a quenching method. Specifically, the hydrogen storage alloy particles having the above-mentioned alloy composition can be maintained at a cooling speed of 1000 K / sec or more from the temperature at which the molten state or body-centered cubic structure can be maintained by the quenching method such as gas atomizing method, roll quenching method, water cooling method By rapidly cooling at the same temperature, a hydrogen storage alloy having a small parent phase 1 can be obtained (see, for example, FIG. 3 (B)). In addition, a grain boundary phase is naturally formed around such a small mother phase 1, but in order to make the area ratio of the grain boundary phase to the particle surface 30% or more, from the grain boundary phase to the periphery It is preferable to diffuse Ni to expand the grain boundary phase. For example, the grain boundary phase can be expanded by further performing heat treatment on the particles obtained by the above-mentioned quenching method (see, for example, FIG. 3C). The heat treatment conditions at this time are not particularly limited. For example, the heat treatment atmosphere can be a vacuum atmosphere, the heat treatment temperature can be about 500 ° C., and the heat treatment time can be about 2 hours. Thus, the hydrogen storage alloy particles 10 of the present disclosure can be easily manufactured, preferably through rapid cooling and subsequent heat treatment.

3. Applications The hydrogen storage alloy particles 10 of the present disclosure are applicable as an electrode material of a battery. In this case, the electrode can be the same as the conventional one except that the hydrogen storage alloy particle 10 is applied. For example, the electrode may contain, in addition to the hydrogen storage alloy particles 10, a conductive additive, a binder, and the like. The method of manufacturing the electrode including the hydrogen storage alloy particle 10 itself is obvious to those skilled in the art having reference to the present application. For example, after a paste containing hydrogen storage alloy particles 10 is applied to a substrate (for example, a porous conductive member) and dried, an electrode containing hydrogen storage alloy particles 10 can be manufactured by optionally pressing or the like. is there.

In particular, the hydrogen storage alloy particles 10 of the present disclosure are preferably applied as a negative electrode material (negative electrode active material) of an alkaline storage battery. The alkaline storage battery may be, for example, a nickel hydrogen battery, an air battery, or any other form. When the alkaline storage battery is a nickel hydrogen battery, for example, nickel hydroxide (Ni (OH) ₂ ) can be used for the positive electrode. On the other hand, when the alkaline storage battery is an air battery, for example, an oxide having a perovskite structure such as LaNiO ₃ can be used as the positive electrode.

  The electrolyte layer is disposed between the positive electrode and the negative electrode, and includes an aqueous alkaline solution. As alkaline aqueous solution, potassium hydroxide (KOH) aqueous solution is mentioned, for example. The concentration of the aqueous solution is not particularly limited, and can be, for example, 6 mol / L. The electrolyte layer may be made only of the electrolytic solution, or may be one in which the electrolytic solution is impregnated in the separator. As the separator, for example, a non-woven separator made of polyethylene / polypropylene can be used.

  When manufacturing an alkaline storage battery, the negative electrode containing the hydrogen storage alloy particle 10 can be manufactured by the method mentioned above, for example. On the other hand, for the positive electrode, for example, a paste-like composition prepared by kneading nickel hydroxide, cobalt oxide, and a binder so as to have a predetermined weight ratio and then kneading them is porous conductive It can be manufactured by a method such as pressing it at a predetermined pressure after being applied to a sexing member and subsequently dried. After that, an alkaline aqueous solution adjusted to a predetermined concentration is placed in a container, and an alkaline storage battery can be manufactured by further arranging a positive electrode and a negative electrode in a container containing the alkaline aqueous solution. .

1. Preparation of Hydrogen Storage Alloy Particles 1.1. Comparative Example 1
The preparation amount was adjusted so that the alloy composition was Ti: Cr: V: Ni = 26: 8: 56: 10 in atomic ratio, and Ti26Cr8V56Ni10 alloy particles according to Comparative Example 1 were obtained by the arc melting method. By acquiring a cross-sectional SEM image of the obtained particles, extracting 10 regions (crystal grains) surrounded by the grain boundary phase in the cross-sectional SEM image, measuring each area to obtain an average value thereof, The average cross-sectional area of the mother phase was identified. In addition, a backscattered electron image is acquired for the surface of the obtained particle, and in the backscattered electron image, an area of 10 μm × 10 μm is selected, and two gradations are performed by image processing software. The area ratio of the grain boundary phase in the region is determined as x 100), the area ratio is similarly calculated for each of ten locations on the particle surface, and the average value is calculated. "Rate" was identified. The reflected-electron image of the particle | grain which concerns on the comparative example 1 to FIG. 3 (A) is shown.

In the Ti26Cr8V56Ni10 alloy particles according to Comparative Example 1, the average cross-sectional area of the matrix phase was 275 μm ² , and the area ratio of the grain boundary phase occupied on the particle surface was 16%.

1.2. Comparative example 2
The preparation amount was adjusted so that the alloy composition was Ti: Cr: V: Ni = 26: 8: 56: 10 in atomic ratio, and Ti26Cr8V56Ni10 alloy particles according to Comparative Example 2 were obtained by gas atomization. By acquiring a cross-sectional SEM image of the obtained particles, extracting 10 regions (crystal grains) surrounded by the grain boundary phase in the cross-sectional SEM image, measuring each area to obtain an average value thereof, The average cross-sectional area of the mother phase was identified. In addition, a backscattered electron image is acquired for the surface of the obtained particle, and in the backscattered electron image, an area of 10 μm × 10 μm is selected, and two gradations are performed by image processing software. The area ratio of the grain boundary phase in the region is determined as x 100), the area ratio is similarly calculated for each of ten locations on the particle surface, and the average value is calculated. "Rate" was identified. The reflected-electron image of the particle | grain which concerns on the comparative example 2 in FIG. 3 (B) is shown.

In the Ti26Cr8V56Ni10 alloy particles according to Comparative Example 2, the average cross-sectional area of the parent phase was 5.8 μm ² , and the area ratio of the grain boundary phase occupied on the particle surface was 15%.

1.3. Example Ti26Cr8V56Ni10 alloy particles according to Comparative Example 2 were heat-treated at 500 ° C. for 2 hours under vacuum to obtain Ti26Cr8V56Ni10 alloy particles according to Example. By acquiring a cross-sectional SEM image of the obtained particles, extracting 10 regions (crystal grains) surrounded by the grain boundary phase in the cross-sectional SEM image, measuring each area to obtain an average value thereof, The average cross-sectional area of the mother phase was identified. In addition, a backscattered electron image is acquired for the surface of the obtained particle, and in the backscattered electron image, an area of 10 μm × 10 μm is selected, and two gradations are performed by image processing software. The area ratio of the grain boundary phase in the region is determined as x 100), the area ratio is similarly calculated for each of ten locations on the particle surface, and the average value is calculated. "Rate" was identified. The reflected-electron image of the particle | grain which concerns on FIG.3 (C) and FIG. 4 concerning an Example is shown.

The average cross-sectional area of the parent phase of the Ti26Cr8V56Ni10 alloy particle according to the example was 4.6 μm ² , and the area ratio of the grain boundary phase occupied on the particle surface was 34%. As shown in FIGS. 3 and 4, in the particles according to the example, the parent phase is smaller and the grain boundary phase is larger than the particles according to comparative examples 1 and 2 (the width is expanded). I understand that).

2. Evaluation as an electrode material The Ti26Cr8V56Ni10 alloy particles prepared as described above are used as an active material, kneaded with a conductive additive (Ni powder) and a binder, coated on foamed Ni, dried and roll pressed, and evaluated. Hydrogen storage alloy electrode was obtained. The hydrogen storage alloy electrode manufactured as described above was used as a negative electrode, the Ni (OH) ₂ electrode was used as a counter electrode, and 6 M-KOH was used as an electrolytic solution to manufacture a battery for evaluation.

The discharge rate characteristics of the produced battery were evaluated under the following charge and discharge conditions. The results are shown in FIG.
Charge / discharge conditions: temperature 25 ° C., CC charge / discharge charge: 10 mA / cm ² , 7.5 h cut Discharge: 5 to 100 mA / cm ² , working electrode − 0.5 V vs Hg / HgO cut

  As shown in FIG. 5, when the hydrogen storage alloy particles according to the example are applied as an electrode material of a battery, the current density is higher than when the hydrogen storage alloy particles according to comparative examples 1 and 2 are applied as an electrode material of a battery It was found that the discharge capacity was hard to decrease even if the value of. In the examples, the high rate discharge characteristics are greatly improved because of the effect of the refinement of the matrix phase seen in Comparative Example 2 (the increase in the grain boundary phase (reaction active portion) exposed to the surface, and the matrix phase and the grain boundary In addition to the increase in the area of the interface with the phase), the heat treatment diffuses Ni on the surface to expand the grain boundary phase, and the area ratio of the grain boundary phase occupied on the surface increases. It is considered to be due to the increase.

However, according to the findings of the present inventor, heat treatment may also promote grain growth of the matrix phase (a reduction factor of discharge characteristics), and heat treatment conditions may be set based on the balance of Ni diffusion amount and grain growth of the matrix phase. preferable. By setting the heat treatment conditions optimally, in the hydrogen storage alloy particles containing Ti, Cr, V and Ni of 5 at% or more and 10 at% or less, the average cross-sectional area of the parent phase is 5 μm ² or less, and The area ratio of the grain boundary phase can be 30% or more.

  The hydrogen storage alloy particles of the present disclosure can be used, for example, as an electrode material for batteries, preferably as a negative electrode material (negative electrode active material) of an alkaline storage battery.

1 mother phase 2 grain boundary phase 10 hydrogen storage alloy particles

Claims (1)

A hydrogen storage alloy particle comprising Ti, Cr, V, and 5 at% to 10 at% Ni,
A parent phase having a body-centered cubic structure having Ti, Cr and V as main components and a lattice constant of 3.05 ± 0.05 Å, and a grain boundary phase containing Ti and Ni as main components and existing between the parent phases , And
The average cross-sectional area of the matrix phase is 5 μm ² or less,
The area ratio of the grain boundary phase occupied on the particle surface is 30% or more
Hydrogen storage alloy particles.