JP3124458B2 - Metal oxide / hydrogen storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide / hydrogen storage battery using a hydrogen storage alloy which electrochemically stores and releases hydrogen as an active material for a negative electrode.

[0002]

2. Description of the Related Art Nickel-cadmium storage batteries, nickel-hydrogen storage batteries, and the like are widely used as alkaline storage batteries for various portable power supplies. this house,
A metal oxide / hydrogen storage battery represented by a nickel / hydrogen storage battery is expected to have a higher capacity density, and has recently been rapidly spreading as a small sealed storage battery. As the hydrogen storage alloy that plays an important role in the metal oxide / hydrogen storage battery, an improved MmNi ₅ (Mm: misch metal) alloy, a ZrMn ₂ alloy, or the like is mainly used. As the electrolytic solution, a solution mainly containing an aqueous solution of potassium hydroxide is used. With the development of portable devices in recent years, there is a demand for longer life and higher reliability of metal oxide / hydrogen storage batteries.

[0003]

In the conventional metal oxide / hydrogen storage battery, the most easily dissolved element among the elements contained in the hydrogen storage alloy is selectively contained in the electrolyte as the battery is charged or discharged or stored at a high temperature. For example, the performance of the hydrogen storage alloy is remarkably deteriorated due to elution into the battery, and the characteristics of the battery are deteriorated. Therefore, there are problems in the cycle life characteristics and the high-temperature storage characteristics of the battery. In order to solve these problems, JP-A-4-31045, JP-A-4-63240, JP-A-4-666
Various alloy compositions have been proposed in, for example, Japanese Patent Publication No. 36-36. However, these compositions have insufficient effects on cycle life characteristics and high-temperature storage characteristics. Also, Japanese Patent Application Laid-Open No. 6-124705 proposes surface treatment methods, but these methods are not ideal because they involve problems such as an increase in manufacturing cost and a complicated manufacturing process. The improved method of Japanese Patent Application Laid-Open No. 6-215765 proposed for the same purpose as the present invention has a great effect, but ZrMn _0.6 V _0.2 Cr which is a C15 type Laves phase of an intermetallic compound. _0.1 Ni
_It is not always satisfactory for some hydrogen storage alloys such as _1.2 . It is an object of the present invention to provide a metal oxide / hydrogen storage battery having excellent cycle life characteristics and high-temperature storage characteristics easily and inexpensively using a hydrogen storage alloy belonging to the Laves phase of an intermetallic compound for a negative electrode. .

[0004]

The metal oxide-hydrogen storage battery of the present invention comprises a positive electrode mainly composed of a metal oxide, and a hydrogen storage alloy which electrochemically stores and releases hydrogen as an active material as a main constituent material. A negative electrode, a separator, and an alkaline electrolyte, wherein the negative electrode is selected from the group consisting of Ln ₂ O ₃ and Ln (OH) ₃ (where Ln is a lanthanoid element and is not included in the hydrogen storage alloy) At least one
0.1 to 10% by weight of seed powder based on hydrogen storage alloy
Including. The average particle size of the Ln ₂ O ₃ and Ln (OH) ₃ powders is preferably 30 μm or less.

A metal oxide-hydrogen storage battery according to the present invention has a positive electrode mainly composed of a metal oxide, a negative electrode mainly composed of a hydrogen storage alloy electrochemically absorbing and releasing hydrogen as an active material, and a separator. And an alkaline electrolyte,
At least one selected from the group consisting of Ln ₂ O ₃ and Ln (OH) ₃ is dissolved in the alkaline electrolyte. The amount of the lanthanoid compound to be dissolved in the alkaline solution is 10 to 1 of the saturated solubility at 45 ° C.
00% is preferred.

The hydrogen storage alloy used for the negative electrode is represented by the general formula AB
_x (where A is Zr, Ti, Hf, Ta, Ca, Mg,
Mo, Al, Si and at least one element selected from the group consisting of rare earth elements, B is Ni, Mg, Ca, T
i, Hf, V, Nb, Cr, Mo, Mn, Fe, Co,
At least one element selected from the group consisting of Pd, Cu, Ag, Zn, Cd, Al, Si and rare earth elements;
1.5 <x <2.5) A metal oxide / hydrogen storage battery represented by 1.5 <x <2.5, wherein the main alloy phase belongs to the Laves phase of the intermetallic compound, and its crystal structure is a hexagonal C ₁₄ type lattice constant. Is a =
4.8-5.2 angstroms, c = 7.9-8.3
It is preferable that the lattice constant is a = 6.9 to 7.3 angstroms in Angstroms and cubic C ₁₅ type.

[0007]

In a power generating element comprising a positive electrode mainly composed of a metal oxide, a negative electrode mainly composed of a hydrogen storage alloy which electrochemically stores and releases hydrogen, a separator and an alkaline electrolyte, Ln is contained in the negative electrode material. ₂ O ₃ and Ln (OH) ₃
By mixing at least one selected from the group consisting of 0.1 to 10% by weight with respect to the hydrogen storage alloy, the mixed lanthanoid oxide and hydroxide are eluted into the electrolyte and come into contact with the surface of the hydrogen storage alloy. This increases the apparent Ln metal ion concentration near the alloy and prevents elution of alloy elements. This suppresses the deterioration of the hydrogen storage alloy. Further, by setting the average particle size of the Ln ₂ O ₃ and Ln (OH) ₃ powders to 30 μm or less, the cycle life is extended by 10% or more.

[0008] Ln ₂ O ₃ and L
By dissolving at least one powder selected from n (OH) ₃ , the deterioration of the hydrogen storage alloy is suppressed by the same action as in the case of mixing with the hydrogen storage alloy. In particular, the Ln ₂ O ₃ and Ln
The cycle life is improved by dissolving at least one selected from (OH) ₃ at 10 to 100% of the saturated solubility at 45 ° C.

[0009]

The present invention will be described below in more detail with reference to examples. Example 1 As a hydrogen storage alloy, ZrMn _0.6 V _0.2 C whose main alloy phase is a C15-type Laves phase of an intermetallic compound
r _0.1 Ni _1.2 was used. The alloy was produced by arc melting, mechanically pulverized, and then sieved to an average particle size of about 20 μm. In addition, L which is an example of Ln ₂ O ₃ and Ln (OH) ₃
a ₂ O ₃ powder (average particle size: about 5 μm) was mixed, and water and carboxymethylcellulose as a binder were further mixed to form a paste, which was filled into a foamed nickel porous body having a porosity of 95%. At this time, the mixing amount of La ₂ O ₃ was 2% by weight based on the hydrogen storage alloy. This is vacuum-dried at 120 ° C., press-molded to a thickness of 0.33 mm, and then
The negative electrode was cut into 9 mm and 97 mm in length. A well-known foamed nickel electrode was selected as the positive electrode, and had a width of 39 mm, a length of 77 mm, and a thickness of 0.70 mm, and a lead plate was attached thereto. A polypropylene nonwoven fabric provided with hydrophilicity was used for the separator. The above-described negative electrode, positive electrode and separator were combined into a three-layer spiral shape and stored in an AA-sized cylindrical battery case. 2.2 cc of an electrolyte obtained by dissolving 40 g / l of lithium hydroxide in an aqueous solution of potassium hydroxide having a specific gravity of 1.30 was poured into the container, and the container was closed to obtain a sealed battery. This is called battery A.

Next, a battery using the same negative electrode as the battery A, using the same negative electrode as the battery A, except that the above-mentioned La ₂ O ₃ powder was not mixed with the negative electrode, and using the following electrolyte solution: Was made. After dissolving 40 g / l of lithium hydroxide in an aqueous solution of potassium hydroxide having a specific gravity of 1.30, 10 g / l of La ₂ O ₃ (average particle size of about 5 μm) was added while heating and maintaining the solution at 45 ° C. Stir for 2 hours. La ₂ O ₃
Is sufficiently large relative to the liquid volume, La ₂ O ₃ is not completely dissolved, and the supernatant is a saturated solution of La ₂ O ₃ . 2.2 cc of the supernatant was poured into a battery case as an electrolyte and sealed to form a sealed battery. This is called battery B. As a comparative example, a battery manufactured by a conventional manufacturing method was also manufactured. However, batteries A and B of the above example were used except that La ₂ O ₃ was not mixed or dissolved in the negative electrode and the electrolytic solution.
The same configuration was used. This is designated as battery Z of the comparative example.

These batteries A, B and Z had a capacity of about 1300 mAh when discharged at a 5-hour rate. These batteries were evaluated by a charge / discharge cycle test under the following conditions.
The charging was performed at a rate of 1 hour for 1.5 hours, and the discharging was performed at a rate of 2 hours up to a final voltage of 1.0 V. The ambient temperature was set to 45 ° C. in order to clarify the evaluation results based on the fact that generally the higher the temperature than the room temperature, the faster the deterioration rate of the alloy. The cycle life of the battery was defined as the number of cycles until the discharge capacity reached 60% of the initial value. These results are shown in FIG. The life of the battery Z of the comparative example is about 300 cycles, whereas the battery A of the example is about 450 cycles and the battery B is about 4 cycles.
00 cycles.

The battery in a discharged state is stored at 65 ° C.
The change in open circuit voltage was investigated. Here, the final voltage is 1.0
The battery discharged to V was allowed to stand at 65 ° C., and the number of days until the open circuit voltage became 0.5 V was defined as the number of days that can be stored at 65 ° C. The result is shown in FIG. The battery Z of the comparative example had a storable period of about 20 days, while the battery A of the example had a storage time of 40 days and the battery B had a storage time of about 35 days. After completion of the storage test, the battery was disassembled, and the negative electrode of the hydrogen storage alloy was observed with an electron microscope. In the battery Z of the comparative example, the surface of the hydrogen storage alloy powder was rough, and it was apparent that the surface was corroded by the alkaline electrolyte inside the battery. On the other hand, in the batteries A and B of the examples, the surfaces were kept relatively smooth, and it was confirmed that the present invention was effective in preventing the deterioration of the alloy negative electrode.

Example 2 Next, the optimum value of the amount of La ₂ O ₃ mixed with the hydrogen storage alloy was examined. A battery was manufactured in the same configuration as the battery A of Example 1 except that the mixing amount of the La ₂ O ₃ powder having an average particle size of 5 μm was changed in the range of 0.01 to 30% by weight based on the anode hydrogen storage alloy. . These batteries were evaluated by a charge / discharge cycle test under the above conditions. The results are shown in FIG. When the amount of La ₂ O ₃ mixed in the hydrogen storage alloy was in the range of 0.1 to 10% by weight with respect to the negative electrode hydrogen storage alloy, the cycle life was improved by 10% or more with respect to the battery Z of the comparative example. However, when the content was less than 0.1% by weight, no sufficient effect was obtained, and when the content was more than 10% by weight, the capacity density of the negative electrode was lowered, and conversely, the life was extremely reduced.

Next, La ₂ O ₃ mixed with the hydrogen storage alloy
The optimal value of the particle size was investigated. A battery having the same configuration as that of the battery A of Example 1 except that the particle size of the La ₂ O ₃ powder was changed in the range of 0.1 to 50 μm was produced, and evaluated by the charge / discharge cycle test under the above conditions. FIG. 4 shows the results. When the average particle size was 30 μm or less, the cycle life was improved by 10% or more with respect to the battery Z of the comparative example. However, when the particle size was larger than this, no improvement in life was observed. This is thought to be because if the particle size is too large, the rate of elution into the electrolytic solution becomes extremely slow. In this example, a powder having an average particle size of less than 0.1 μm was not used, but it is clear that La ₂ O ₃ exerts a life improving effect.

Example 3 Next, L dissolved in an electrolytic solution
The optimum value of the concentration of a ₂ O ₃ was examined. In the same configuration as the battery B of Example 1, a battery in which the amount of La ₂ O ₃ dissolved in the electrolytic solution was changed by the following method was evaluated by a charge / discharge cycle test under the above conditions. The electrolyte of the battery A of Example 1 obtained by dissolving 40 g / l of lithium hydroxide in an aqueous solution of potassium hydroxide having a specific gravity of 1.30 is referred to as an electrolyte a. While heating and maintaining the electrolyte a at 45 ° C., 10 g / l of La ₂ O ₃ powder having an average particle size of about 5 μm was mixed therein, and the mixture was stirred for 2 hours and obtained as a supernatant liquid. A saturated solution of La ₂ O ₃ equal to the electrolyte solution of B is referred to as an electrolyte solution b. By preparing these electrolyte solutions a and b in a predetermined amount, La ₂ O ₃ is added to the solution at a saturation amount of 45 ° C. of 1 to 4.
An electrolytic solution dissolved in a range of 100% was obtained. However, these operations were performed while maintaining the temperature at 45 ° C.

Using the solution thus obtained as an electrolyte, a battery was prepared in the same manner as for battery B, and evaluated by a charge / discharge cycle test. The result is shown in FIG. The amount of La ₂ O ₃ dissolved in the electrolyte is 10% of the saturated amount at 45 ° C.
If it did, the life was hardly improved. Since La ₂ O ₃ is hardly dissolved in the alkaline aqueous solution, it is considered that the effect is hardly exhibited when the concentration further decreases. From the above results, the concentration of La ₂ O _{3 in the} alkaline electrolyte was 10% of the saturated solubility at 45 ° C.
-100% is desirable, and in this range, the cycle life is improved by 10% or more.

The Ln ₂ 0 ₃ were dissolved in a mixed or alkaline electrolyte and the hydrogen absorbing alloy in the above (however, Ln
Although a lanthanide element, with La ₂ O ₃ as an example of the hydrogen to the storage alloy are not included elements),
La (OH) ₃ , Ce ₂ O ₃ , Ce (OH) ₃ , Pr ₂ O ₃ ,
Almost the same effect was obtained when other lanthanoid oxides or hydroxides such as Pr (OH) ₃ , Nd ₂ O ₃ and Nd (OH) ₃ were used.

The present invention can be applied to a case where an alloy other than the alloy used in the above embodiment is used for the negative electrode. In particular, the hydrogen storage alloy is represented by the general formula AB _x (where A
Are Zr, Ti, Hf, Ta, Ca, Mg, Mo, Al,
At least one element selected from the group consisting of Si and rare earth elements, B is Ni, Mg, Ca, Ti, Hf, V,
Nb, Cr, Mo, Mn, Fe, Co, Pd, Cu, A
g, Zn, Cd, Al, Si and at least one element selected from the group consisting of rare earth elements, 1.5 <x <2.
5), wherein the main alloy phase belongs to the Laves phase of the intermetallic compound, the crystal structure of which is hexagonal C ₁₄ type, and the lattice constant is a
= 4.8-5.2 angstroms, c = 7.9-8.0.
Excellent properties were exhibited when the lattice constant was 3 Å or at least one of a = 6.9 to 7.3 Å in the cubic C ₁₅ type. In addition, LaN
i _5, MmNi ₅ (Mm is a mixture of rare earth elements) alloys such as, that the present invention is the alloy containing lanthanoid elements as its component had no effect.

[0019]

According to the present invention, a metal oxide / hydrogen excellent in cycle life characteristics and high-temperature storage characteristics is obtained by suppressing the elution of the constituent elements in the hydrogen storage alloy and preventing the deterioration of the hydrogen storage alloy. A storage battery can be obtained inexpensively and easily.

[Brief description of the drawings]

FIG. 1 is a cycle life characteristic diagram showing a change in discharge capacity of a battery according to an example of the present invention and a battery of a comparative example during a charge / discharge cycle.

FIG. 2 is a high-temperature storage characteristic diagram showing a change in open circuit voltage when left at 65 ° C. in a discharged state.

FIG. 3 is a characteristic diagram showing the relationship between the amount of La ₂ O ₃ mixed into a negative electrode and the cycle life.

FIG. 4 is a characteristic diagram showing a relationship between an average particle diameter of La ₂ O ₃ and a cycle life.

FIG. 5 is a characteristic diagram showing the relationship between the concentration of La ₂ O _{3 in} an alkaline electrolyte and the cycle life.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Moriwaki 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-62-80963 (JP, A) 187983 (JP, A) JP-A-62-249364 (JP, A) JP-A-57-111964 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4 / 26 H01M 4/38 H01M 10/24-10/30 H01M 10/34

Claims (5)

(57) [Claims] 1. A negative electrode comprising: a positive electrode mainly composed of a metal oxide; a negative electrode mainly composed of a hydrogen storage alloy electrochemically absorbing and releasing hydrogen as an active material; a separator; and an alkaline electrolyte. At least one type of powder selected from the group consisting of Ln ₂ O ₃ and Ln (OH) ₃ (where Ln is a lanthanoid element and is not included in the hydrogen storage alloy). 0.1 to 10
A metal oxide / hydrogen storage battery characterized by containing by weight. 2. The metal oxide-hydrogen storage battery according to claim 1, wherein the average particle diameter of the powder of Ln ₂ O ₃ and Ln (OH) ₃ is 30 μm or less. 3. A method according to claim 1, further comprising a positive electrode mainly composed of a metal oxide, a negative electrode mainly composed of a hydrogen storage alloy electrochemically absorbing and releasing hydrogen as an active material, a separator and an alkaline electrolyte. The electrolyte is Ln ₂ O ₃ and Ln (O
H) ₃ (where, Ln is a lanthanoid element and is not included in the hydrogen storage alloy) at least one selected from the group consisting of dissolved metal oxide / hydrogen storage batteries . 4. The amount of the lanthanoid compound dissolved in the alkaline solution is 10% of the saturated solubility at 45 ° C.
The metal oxide-hydrogen storage battery according to claim 3, wherein the content of the battery is from 100% to 100%. 5. The method according to claim 1, wherein the hydrogen storage alloy has the general formula AB _x (where A is Zr, Ti, Hf, Ta, Ca, Mg, Mo,
At least one element selected from the group consisting of Al, Si and rare earth elements, B is Ni, Mg, Ca, Ti, H
f, V, Nb, Cr, Mo, Mn, Fe, Co, Pd,
At least one element selected from the group consisting of Cu, Ag, Zn, Cd, Al, Si and rare earth elements, 1.5 <
represented by x <2.5), the main alloy phase belongs to Laves (Laves) phase of the intermetallic compound, the lattice constants C ₁₄ type crystal structure is hexagonal system a = 4.8-5.2 Å, c = 7.9 to 8.3 Å, and cubic claim 1 or 3 metal oxide according lattice constant C ₁₅ type is at least one of a = 6.9 to 7.3 Å・ Hydrogen storage battery.