JP2001167759A - NON-STOICHIOMETRIC Zr-Ni-BASED HYDROGEN STORAGE ALLOY FOR USE IN NEGATIVE ELECTRODE OF Ni/MH SECONDARY BATTERY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-stoichiometric Zr-Ni-based hydrogen storage alloy for use in a negative electrode for Ni/MH secondary battery having a large capacity and a high performance. SOLUTION: Zr-based hydrogen storage alloy represented by the following general formula 1: Zr1-XTiX(MnUVVCrYNi1-U-V-Y)Z where X, U, V, Y and Z each independently represent an atomic fraction of the respective alloying elements or the like, and are values satisfying the following relationship: 0<X<=0.4; 0.3<=U<=0.4; 0.1<=V<=0.2; 0.0<=Y<=0.2; 0.45<=U+V+Y<=0.65; and 1.6<=Z<=1.9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high capacity, high performance hydrogen storage alloy for a Ni / MH secondary battery.

[0002]

2. Description of the Related Art At present, the main research directions of Ni / MH secondary batteries are high capacity and high performance (high rate discharge characteristics, long life, etc.).
It is reported that the characteristics of such a battery are mainly influenced by the characteristics of the hydrogen storage alloy constituting the negative electrode. That is, the higher capacity and higher performance of the Ni / MH secondary battery correspond to the higher capacity of the hydrogen storage alloy negative electrode,
It can be said that this is directly linked to higher performance, and thus many researchers have set the performance improvement of the hydrogen storage alloy negative electrode material as a core field of research. In recent studies on the performance improvement of hydrogen storage alloy negative electrode materials, some researchers have reported excellent high rate discharge characteristics and cycle life of hydrogen storage alloys having a non-stoichiometric composition,
As a result, interest in non-stoichiometric alloys has been focused on as an electrode active material.

In general, the reaction principle of a Ni / MH secondary battery using a hydrogen storage alloy as an active material of a negative electrode is as follows. During battery discharge hydroxide ions of the hydrogen storage hydrogen atom KOH electrolyte in the alloy (OH ^-) combined with it in water, this time the electron moves to the cathode through an external circuit,
During charging, water is converted to hydrogen ions (H ⁺ ) and hydroxide ions (O
Hydroxide ions are decomposed by H ⁻ ) and remain in the electrolyte, and the hydrogen ions combine with electrons introduced from the outside and combine with the hydrogen storage alloy in the form of hydrogen atoms to store hydrogen in the alloy. This is to make use of the inherent reversible properties of hydrogen storage alloys, which are stable in alkaline solutions and rapidly absorb / release large amounts of hydrogen.

In order to use a hydrogen storage alloy as a negative electrode active material for a Ni / MH secondary battery, the following two types of conditions are required. First, the gas - solid reaction hydrogen absorption and desorption pressures were fit (typically out 0.01 atm at room temperature), large hydrogen theoretical discharge capacity of the storage capacitor (electrode hydrogen storage capacity (C _H wt%) The hydrogenation reaction characteristics such as the theoretical discharge capacity [(mAh / g) = 268 × C _H ] and the rapid hydrogenation reaction rate must be uniform.Second, during the electrochemical reaction between the KOH electrolyte and the alloy The charge transfer reaction associated with the decomposition and synthesis of hydrogen at the alloy-electrolyte interface must be easy, that is, only the hydrogen storage alloy whose surface has a catalytic function of the charge transfer reaction is Ni / M
It can be used as a negative electrode active material of an H secondary battery.

[0005] Currently, such hydrogen storage alloys meet the requirements conditions are known many, La-Nd-Ni-Co of AB ₅ type hexagonal structure as a typical
-Al [see: U.S. Pat. No. 4,488,817], M
m-Mn-Ni-Co-Al [Reference: Japanese Patent Publication Nos. 61-1132501, 61-214361]
As the AB ₂ type C14,15- hexagonal, BCC
Ti-V-Ni-Cr with polymorphic structure [see U.S. Patent No. 4,551,400], Zr-V-Ni with C14 structure
[Ref: J. of the Less-Common Metals, 172-1
74: 1219 (1991)].

[0006] Of these alloys, AB ₅ type of La-Ni
The system negative electrode is an alkaline electrolyte, and the charge / discharge cycle greatly reduces the electrode capacity [J. of the Less-Common
Metals, 161: 193 (1990) and 155: 119
(1989)]. Such development is referred to as degeneration. J. G. US Patent No. 4,488, Willems et al.
No. 817 can improve the cycle life by substituting a small amount of the Ni element with Co and Al and substituting the La element with a small amount of Nd among the alloy composition elements, but has a disadvantage that the capacity is reduced. .

Further, T.S. US Patent No. 4,9 by Gamo et al.
No. 46,646 discloses a Zr-based hydrogen storage alloy containing 30 atomic% or more of Zr and 40 atomic% or more of Ni, but has a limit that a discharge capacity is limited to 300 to 370 mAh / g.

Further, K. US Patent No. 4,84 by Hong
9, 205; A. U.S. Pat. Nos. 4,728,586 and 4,551,400 to Fechenko et al. Also describe a Ti-Zr-VN with a capacity of 300-380 mAh / g.
Only a hydrogen storage alloy of i-Cu-Mn-M (M = Al, Co, Fe, etc.) is disclosed.

[0009]

[Problems to be Solved by the Invention] The N
Hydrogen storage alloy for i / MH secondary battery is Mm-Ni AB
_FiveType (A = element with high affinity for hydrogen, La, Ce, P
rare earth metals such as r, Nd, B = Ni, Mn, C
o, Fe, transition elements such as Al) and Zr-Ni, Ti
-Ni-based AB_TwoThere is a type, AB_FiveEnergy for type
-The disadvantage of low storage density is AB_TwoFor various types, various performance
It has the problem of falling. In the future, high capacity and high performance N
AB for i / MH secondary battery development_FiveHigher water than
AB with element storage capacity_TwoCapacity of hydrogen storage alloy
Research for excellent electrode life must be preceded
No.

An object of the present invention is to develop a high capacity, high performance AB ₂ type hydrogen storage alloy by providing a novel Zr-based hydrogen storage alloy having a non-stoichiometric composition. I do.

[0011]

The Zr according to the present invention will now be described.
The system based hydrogen storage alloy will be described more specifically.

The Zrr-based hydrogen storage alloy of the present invention is represented by the following general formula (I).

Zr _1-x T _x (Mn _U V _V Cr _Y Ni _1-UVY ) _Z (I) In the above formula, X, U, V, Y and Z are each an atomic fraction of an alloy composition element or the like. , 0 <X ≦ 0.4, 0.3 ≦ U ≦
0.4, 0.1 ≦ V ≦ 0.2, 0.0 ≦ Y ≦ 0.2,
0.45 ≦ U + V + Y ≦ 0.65, 1.6 ≦ Z ≦ 1.9
Is a value that satisfies

Zr in the hydrogen storage alloy of the present invention is a basic alloy composition element, and its optimum composition ratio is at least 0.6 and less than 1 in atomic fraction in consideration of the composition of Ti as a substitution metal element. is there.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Ti in a hydrogen storage alloy according to the present invention is an element which increases the discharge capacity ratio, and its optimum composition ratio is more than 0 and 0.4 or less in atomic fraction. . If the composition ratio deviates, the discharge capacity becomes 30.
At 0 mAh / g, it decreases, and the life of the electrode is shortened, which is not desirable. Of the compositions in the alloy, Z
The reason for substituting Ti for r is as follows. Generally, an alloy having a non-stoichiometric composition has a tendency that the equilibrium hydrogen pressure of the alloy as a whole is lower because the affinity of the alloy element at the A site for hydrogen is higher than that of the element at the B site. Therefore, to increase the reversible hydrogen storage capacity by having a suitable hydrogen equilibrium pressure, the hydrogen affinity is reduced in place of Zr, but other crystallographic properties replace the Ti by replacing the Ti. It is intended to increase the reversible hydrogen storage capacity.

In the present invention, the optimum composition ratio of Mn in the hydrogen storage alloy is 0.3 or more and 0.4 or less. If the Mn content is less than 0.3, the discharge efficiency (current density Dependency) rapidly decreases and exceeds 0.4, which is undesirable because the charging efficiency is reduced and the catalyst function is reduced.

The optimum composition ratio of V in the hydrogen storage alloy according to the present invention is set to an atomic ratio of 0.1 or more and 0.2 or less, so that Cr, which is an element for improving electrode life and hydrogen storage capacity, is optimized. The composition ratio is set to 0.2 or less. Said C
r is for improving the degeneration and the discharge capacity of the alloy electrode in which Ti has been substituted, and has a property of having a high affinity for hydrogen and preventing the dissolution of V. In the hydrogen storage alloy of the present invention, Ni is an element that imparts a catalytic function in the KOH electrolyte of the obtained alloy, and its optimum composition ratio is set to be 0.35 or more and 0.55 or less in atomic fraction. Is desirable.

The hydrogen storage alloy of the present invention which satisfies the above-mentioned various conditions has a high discharge capacity of 370 to 425 mAh / g, and has a current density dependence of 400 mA / g based on the discharge capacity at 25 mA / g. Has more than 80%.

Process for producing hydrogen storage alloy of the present invention, gas
An experimental method for measuring the hydrogenation reaction characteristics in a solid state reaction and the characteristics of a hydrogen storage alloy in an alkaline electrolyte is as follows.

First, the amount of each element is determined by the atomic ratio so as to match each composition of the hydrogen storage alloy, and quantitatively determined so that the total weight becomes about 5 g. Next, arc melting is performed in an argon atmosphere. At this time, in order to improve the homogeneity of the sample, a process of solidifying the melted sample, turning the sample over, and re-dissolving the sample is repeated four times or more.

The specimen obtained in the above process is pulverized to 100-2
After injecting only the 00 mesh specimen into the reaction tube, it is connected to a Sievert's type high-pressure hydrogen device, and the activation treatment is performed by maintaining the inside of the reaction tube at about 10 ^-2 Torr for about 30 minutes and then without heat treatment. About 20 atm of hydrogen. In this case, hydrogen absorption is completed almost within one hour.

When the hydrogen absorption is completed by the above process, the inside of the reaction tube is maintained at a vacuum to release all the hydrogen in the specimen, and the hydrogen absorption / desorption process is completed within a few minutes. So that On the other hand, after the activation process, the hydrogen injection device including the reaction tube is always maintained at a constant temperature by using an automatic temperature controller, and then hydrogen absorption is performed at a predetermined temperature.
Equilibrium hydrogen pressure curve (PCT) depending on the hydrogen composition at the time of release
Curve) to obtain the thermodynamic properties of the alloy from this curve. In the PCT curve, the X axis indicates the number of moles of hydrogen atoms with respect to the alloy ball, and the Y axis indicates the hydrogen partial pressure.

Next, in order to examine the characteristics of the hydrogen storage alloy in the alkaline electrolyte, first, Zr-Ti-
Mn-V-Cr-Ni system (α = 0.0, 0.2, 0.
4, 0.6) The alloy is manufactured by arc melting under an argon atmosphere. The alloy produced by the above process is mechanically pulverized from the air, and the PCT curve is measured using an automatic PCT curve measuring device to measure the thermodynamic properties of the alloy. XRD analysis is then performed to determine the structural analysis and lattice constant of the manufactured alloy. In the crushed alloy
A 400 mesh size powder is mixed with 300 wt% Ni powder and then cold pressed at a pressure of 10,000 kg / cm ² to produce pellets, and a half battery test is performed using the produced pellets. In the present invention, the charge / discharge current density was 100 mA / g, and the charge / discharge was cut off at −0.75 V (vs. Hg / HgO) during charging and discharging for 6 hours. After the electrodes are sufficiently activated, the discharge capacity, current density dependence, and electrode life are measured.

The above objects and other features and advantages of the present invention will be apparent from the following description of preferred embodiments of the present invention with reference to the accompanying drawings.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings by way of examples, but the scope of the present invention is not limited to these examples.

In the embodiment of the present invention, Zr _{1 -x} Ti _x (Mn
_0.2 V _0.2 Ni _0.5 ) _1.8 as a base alloy, and changing the atomic fraction of Ti at 0.0, _0.2 , 0.4 and 0.6 to obtain T
Changes in various physical properties due to i-substitution were observed and the results were shown in FIG.
4 to FIG.

Further, Zr _0.7 Ti _0.3 (Mn _0.2 V _0.2)
FIG. 5 and FIG. 6 show the change in physical properties due to the substitution of Cr with Cr _Y Ni _0.6-Y ) _1.8 as a basic alloy.

1. Zr _1-x Ti _x (Mn _0.2 V _0.2 Ni
_0.5 ) _1.8 (X = 0.0, 0.2, 0.4, 0.6) Analysis of alloy properties In the present invention, Zr () having a relatively large hydrogen storage capacity and an appropriate equilibrium pressure is used. Mn _0.2 V _0.2 Ni
_0.5 ) _1.8 alloy is selected as the base alloy and Ti
The thermodynamic and discharge characteristics of the hydrogen storage alloy with increasing non-stoichiometric ratio were investigated.

FIG. 1 shows the result of measuring the discharge capacity of the alloy electrode due to the increase of Ti, and it can be seen that the maximum development according to the amount of Ti is shown.

FIG. 2 shows the PCT characteristics of the alloy as the Ti content increases. The hydrogen equilibrium pressure increases as the atomic fraction of Ti increases and the overall hydrogen storage capacity increases. Is found to decrease. However, as shown in FIG. 3, the increase in the amount of Ti improves the current density dependency of the alloy electrode, and thus shows the above-described discharge capacity tendency. However, as shown in FIG. 4, it can be seen that the life of the alloy electrode is gradually reduced as the Ti is replaced. This is because the porosity increases, the penetration of oxygen and the dissolution in the electrolyte such as V increase, and the thickness of the oxide film formed eventually increases.

2. Zr _0.7 Ti _0.3 (Mn _0.2 V _0.2 C
r _Y Ni _0.6-Y ) _1.8 Characteristic analysis of alloy FIG. 5 shows Zr _0.7
Shows the change in the P-C-T curve at 30 ° C. by Cr substituted for _{Ti 0.3 (Mn 0.2 V 0.2 Cr} Y Ni 0.6-Y) 1.8 alloy. As can be seen from the curve, it can be seen that the more the Cr is replaced, the greater the hydrogen storage capacity of the alloy. In order to improve the degeneration and the discharge capacity of the Ti-substituted alloy electrode, instead of Ni, Cr was substituted instead of Ni, which has a high affinity for hydrogen and can prevent the dissolution of V. It can be seen that as the Cr is replaced, the hydrogen storage capacity of the alloy increases. In addition, as shown in FIG. 6, the discharge capacity of the electrode for the above-described alloy is found to be considerably increased while the Cr is replaced.

3. Zr _0.65 Ti _0.35 (Mn _0.3 V
_0.14 Cr _0.11 Ni _0.45 ) _1.76 Characteristic analysis of alloy FIGS. 7 and 8 show that the stoichiometric ratio of the alloy and the substitution amounts of Ti and Cr have been optimized through the conventional alloy design process. Zr _0.65
Ti _0.35 (Mn _0.3 V _0.14 Cr _0.11 Ni _0.45 ) _1.8
1 shows a PCT curve and a discharge curve at 30 ° C. of an alloy. According to this, the alloy has a reversible hydrogen storage capacity (0.01 atm to 1 atm) of about 1.6 wt%, and a discharge capacity of 425 mAh / g, which is about 45% higher than the alloy commercialized. It can be confirmed that the battery has a very high discharge capacity.

FIGS. 9 and 10 show a change in discharge capacity according to a discharge current density and a change in discharge capacity according to the number of charge / discharge cycles for the alloy. According to this, it can be confirmed that other various performances such as electrode life and current density dependence are almost equal to or excellent in performance with existing commercial alloys.

[0034]

The present invention relates to the development of a high-performance, high-capacity hydrogen storage alloy for a Ni / MH secondary battery, and more particularly to an existing commercially available hydrogen storage alloy containing a Co element (Mm-Ni). System) can be substituted. Therefore, the present invention can further increase the specific gravity of the Ni / MH secondary battery in the secondary battery market by improving the performance and energy density of the existing Ni / MH secondary battery, and also increase the capacity and the high capacity. Performance secondary batteries can drive the development of electric vehicles where key performance factors.

Although the present invention has been described in detail with reference to the embodiments, the present invention is not limited to the embodiments, and any person having ordinary knowledge in the technical field to which the present invention belongs can apply the idea and spirit of the present invention. The invention could be modified or changed without departing.

[Brief description of the drawings]

FIG. 1 Zr _x Ti _1-x (Mn _0.2 V _0.2 Ni _0.5 ) _1.8
4 is a graph showing a discharge curve (discharge current density: 50 mA / g) at 30 ° C. for an alloy (X = 0.0, 0.2, 0.4, 0.6).

FIG. 2 Zr _x Ti _1-x (Mn _0.2 V _0.2 Ni _0.5 ) _1.8
(X = 0.0, 0.2, 0.4, 0.6) The graph which showed the PCT curve at 30 degreeC with respect to an alloy.

FIG. 3 Zr _x Ti _1-x (Mn _0.2 V _0.2 Ni _0.5 ) _1.8
6 is a graph showing a change in discharge capacity according to a discharge current density at 30 ° C. for an (X = 0.0, 0.2, 0.4, 0.6) alloy.

FIG. 4 Zr _x Ti _1-x (Mn _0.2 V _0.2 Ni _0.5 ) _1.8
6 is a graph showing a change in discharge capacity according to the number of charge / discharge cycles at 30 ° C. for an alloy (X = 0.0, 0.2, 0.4, 0.6).

FIG. 5: Zr _0.7 Ti _0.3 (Mn _0.2 V _0.2 Cr _Y Ni
_0.6-Y ) _1.8 P at 30 ° C by Cr substitution for alloy
-The graph which showed the CT curve.

FIG. 6: Zr _0.7 Ti _0.3 (Mn _0.2 V _0.2 Cr _Y Ni
_0.6-Y ) A graph showing a discharge curve (discharge current density: 50 mA / g) at 30 ° C. of the _1.8 alloy by substitution with Cr.

FIG. 7: Zr _0.65 Ti _0.35 (Mn _0.3 V _0.14 Cr
_0.11 Ni _0.45 ) _{PC at} 30 ° C. for _1.76 alloy
-Graph showing a T curve.

FIG. 8: Zr _0.65 Ti _0.35 (Mn _0.3 V _0.14 Cr
_0.11 Ni _0.45 ) Graph showing a discharge curve (discharge current density: 50 mA / g) at 30 ° C. for the _1.76 alloy.

FIG. 9: Zr _0.65 Ti _0.35 (Mn _0.3 V _0.14 Cr)
_0.11 Ni _0.45 ) Graph showing the change in discharge capacity with respect to the discharge current density at 30 ° C. for _1.76 alloy.

FIG. 10: Zr _0.65 Ti _0.35 (Mn _0.3 V _0.14 Cr
_FIG . 10 is a graph showing a change in discharge capacity according to the number of charge / discharge cycles at 30 ° C. for a _0.11 Ni _0.45 ) _1.76 alloy.

Continuing on the front page (72) Inventor Kuk Jin Jiang South Korea, Daejeon Gwangyokshi, Yu Song-k, Guk Son-Dong, 373-1 Collia Advanced Institute of Science and Technology (72) Inventor The Sun・ U.S. Republic of Korea, Daejeon Kung-Yukshi, U-Sung-Ku, Kgu-Song-Don, 373-1 Collia Advanced Institute of Science and Technology (72) Inventor San Min-Lee -Ku, Kseong-Dong, 373-1 Korea Advanced Institute of Science and Technology (72) Inventor Ho Lee, Republic of Korea, Daejon Kwangyokshi, Yu-Sung-Ku, Kseong-Dong, 373-1 Korea Advanced Institute Of science AND TECHNOLOGY (72) Inventor Sung Hoe Kim Kim, Republic of Korea, Daejeon Kyun-yukshi, Yu Song-k, Kuseong-dong, 373-1 Collia Advanced Institute of Science and Technology

Claims (1)

[Claims] 1. A Zr-based hydrogen storage alloy represented by the following general formula: Zr _1-x T _x (Mn _U V _V Cr _Y Ni _1-UVY ) _Z (I) In the above formula, X, U, V, Y and Z are each 0% < X ≦ 0.4, 0.3 ≦ U ≦
0.4, 0.1 ≦ V ≦ 0.2, 0.0 ≦ Y ≦ 0.2,
0.45 ≦ U + V + Y ≦ 0.65, 1.6 ≦ Z ≦ 1.9
Is a value that satisfies