JP2005093289A - Hydrogen storage alloy for alkaline storage battery and alkaline storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the deterioration of a hydrogen storage alloy and obtain a sufficient cycle life in an alkaline storage battery using the alloy containing a rare-earth element, Mg, Ni and Al, with an intensity ratio I<SB>A</SB>/I<SB>B</SB>of the strongest peak intensity I<SB>A</SB>appearing within a range of 2θ=31° to 33° to the strongest peak intensity I<SB>B</SB>appearing within a range of 2θ=40° to 44° in an X-ray diffraction measurement using a Cu-Kα ray. <P>SOLUTION: For a negative electrode of the alkaline storage battery, the alloy is used, wherein a layer of an oxide or a hydroxide is formed on the surfaces of hydrogen storage alloy powder containing at least the rare-earth element, Mg, Ni and Al and the intensity ratio I<SB>A</SB>/I<SB>B</SB>between the strongest peak intensity I<SB>A</SB>appearing within the range of 2θ=31°to 33° and that I<SB>B</SB>appearing within the range of 2θ=40° to 44° in the X-ray diffraction measurement using the Cu-Kα ray, and a specific surface area X (m<SP>2</SP>/g) and an oxygen density Y(ppm) satisfies a condition of X<SP>2</SP>/Y ≤1.3×10<SP>-5</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a hydrogen storage alloy for an alkaline storage battery and an alkaline storage battery using this hydrogen storage alloy for an alkaline storage battery as a negative electrode. Intensity ratio between the strongest peak intensity (I _A ) appearing in the range of 2θ = 31 ° to 33 ° and the strongest peak intensity (I _B ) appearing in the range of 2θ = 40 ° to 44 ° in the X-ray diffraction measurement using the source In an alkaline storage battery using a hydrogen storage alloy having (I _A / I _B ) of 0.1 or more, the above-described hydrogen storage alloy is prevented from deteriorating and a sufficient cycle life is obtained. It has characteristics.

  Nickel-hydrogen storage batteries, which are a type of alkaline storage battery, are widely used in various portable devices and hybrid electric vehicles, and it is expected that the nickel-hydrogen storage battery will have higher performance.

In a nickel-hydrogen storage battery, as a hydrogen storage alloy used for the negative electrode, a rare earth-nickel hydrogen storage alloy having a CaCu ₅ type crystal as a main phase, or a Laves phase system containing Ti, Zr, V and Ni is used. A hydrogen storage alloy or the like is generally used.

  However, these hydrogen storage alloys do not necessarily have sufficient hydrogen storage capacity, and there is a problem that it is difficult to further increase the capacity of the nickel-hydrogen storage battery.

In recent years, a hydrogen storage alloy having a crystal structure other than the CaCu ₅ type in which the above-described rare earth-nickel hydrogen storage alloy contains Mg or the like to improve the hydrogen storage capability of the hydrogen storage alloy is used. (See, for example, Patent Document 1 and Patent Document 2).

However, the hydrogen storage alloy having the above crystal structure is more likely to be deteriorated by reacting with an alkaline electrolyte or the like than the rare earth-nickel-based hydrogen storage alloy having a CaCu ₅ type crystal as a main phase. There was a problem that the cycle life could not be obtained.
JP-A-11-339792 JP 2002-164045 A

The present invention includes at least a rare earth element, magnesium, nickel, and aluminum, and the strongest peak intensity (I _A ) that appears in a range of 2θ = 31 ° to 33 ° in an X-ray diffraction measurement using Cu—Kα rays as an X-ray source. When, as described above for the alkaline storage battery using the 2 [Theta] = 40 ° strongest peak intensity appearing in the range of ~44 ° _{(I B)} and the intensity ratio of _(I a / I _B) is hydrogen absorbing alloy is 0.1 or more It is an object to solve a problem.

  That is, the present invention suppresses the deterioration of the hydrogen storage alloy by reacting with an alkaline electrolyte or the like in an alkaline storage battery using the hydrogen storage alloy as described above, so that a sufficient cycle life can be obtained. It is a problem to make.

In order to solve the above problems, the hydrogen storage alloy for alkaline storage batteries according to the present invention is a hydrogen storage alloy for alkaline storage batteries used for the negative electrode of alkaline storage batteries, and includes at least a rare earth element, magnesium, nickel, and aluminum. , the strongest peak intensity and the strongest peak intensity appearing in the range of 2θ = 31 ° ~33 ° in X-ray diffraction measurement of the Cu-K [alpha line and X-ray source _{(I a),} appears in the range of 2θ = 40 ° ~44 ° with (I _B) and the intensity ratio of _(I a _/ I _B) to form a layer of oxide or hydroxide on the surface of the hydrogen-absorbing alloy powder is 0.1 or more, the specific surface area of the hydrogen-absorbing alloy powder Is X (m ² / g) and the oxygen concentration is Y (ppm), the condition of X ² /Y≦1.3×10 ⁻⁵ is satisfied.

  In the present invention, in the alkaline storage battery including the positive electrode, the negative electrode using the hydrogen storage alloy, and the alkaline electrolyte, the hydrogen storage alloy for the alkaline storage battery is used as the hydrogen storage alloy in the negative electrode. did.

  Here, in the alkaline storage battery using the hydrogen storage alloy as described above, a dense oxide or hydroxide layer having a small surface area is provided on the surface of the hydrogen storage alloy powder, and the hydrogen storage alloy powder. By reducing the specific surface X, the activity and deterioration of the hydrogen storage alloy are suppressed, and the amount of oxide or hydroxide per unit area on the surface of the hydrogen storage alloy powder, that is, oxygen per unit area It has been found that by increasing the amount, the reactive sites on the surface of the hydrogen storage alloy are sufficiently covered with the oxide or hydroxide layer, and the activity and deterioration of the hydrogen storage alloy are suppressed.

  Here, when the surface area of the hydrogen storage alloy powder is S, the amount of oxygen on the surface of the hydrogen storage alloy powder is q, and the mass of the hydrogen storage alloy powder is W, the specific surface area X of the hydrogen storage alloy powder is X = In S / W, the oxygen amount O per unit area on the surface of the hydrogen storage alloy powder is represented by O = q / S, and increasing the oxygen amount O per unit area on the surface of the hydrogen storage alloy powder is: It means that the inverse 1 / (q / S) of O = q / S is made small.

  Therefore, when reducing the specific surface X of the hydrogen storage alloy powder as described above and increasing the amount of oxygen per unit area on the surface of the hydrogen storage alloy powder, the specific surface area X = S / W and the above O The product (S / W) × [1 / (q / S)] of the inverse of 1 / (q / S) is reduced.

And when this equation (S / W) × [1 / (q / S)] is transformed,
(S / W) × [1 / (q / S)] = (S / W) / (q / S) = (S / W) ² / (q / W)
It becomes.

Here, in the above hydrogen storage alloy powder, the amount of oxygen in the inside thereof can be ignored. Therefore, the oxygen amount q on the surface of the hydrogen storage alloy powder is almost equal to the oxygen amount of the entire hydrogen storage alloy powder. Therefore, q / W is the oxygen concentration Y of the hydrogen storage alloy powder, and it is preferable to reduce the value of X ² / Y as described above.

When the value of X ² / Y is 1.3 × 10 ⁻⁵ or less, a dense oxide or hydroxide layer is formed on the surface of the hydrogen storage alloy powder, and the oxide or hydroxide The oxygen concentration on the surface of the hydrogen-absorbing alloy powder on which the product layer is formed becomes high, and the surface of the hydrogen-absorbing alloy powder is sufficiently covered with the oxide or hydroxide layer. It is considered that the deterioration due to reaction with an alkaline electrolyte or the like is suppressed.

As described above, in the present invention, in an alkaline storage battery including a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, the hydrogen storage alloy in the negative electrode includes at least a rare earth element, magnesium, nickel, and aluminum. wherein the door, and Cu-K [alpha line X-ray source and X-ray diffraction strongest peak intensity appearing in the range of 2θ = 31 ° ~33 ° in the measurement _{(I a),} appears in the range of 2θ = 40 ° ~44 ° since the strongest peak intensity (I _B) and the intensity ratio of _(I a _/ I _B) is to use a hydrogen absorbing alloy is 0.1 or more, the rare earth as a main phase crystal type ₅ CaCu - hydrogen nickel Compared to the case of using an occlusion alloy, a high capacity alkaline storage battery can be obtained.

In the present invention, an oxide or hydroxide layer is formed on the surface of the hydrogen storage alloy powder, the specific surface area of the hydrogen storage alloy powder is X (m ² / g), and the oxygen concentration is Y. (Ppm), since the condition of X ² /Y≦1.3×10 ⁻⁵ is satisfied, the hydrogen storage alloy is prevented from being deteriorated by reacting with an alkaline electrolyte or the like. Become.

  As a result, in the present invention, an alkaline storage battery having a high capacity and a sufficient cycle life can be obtained.

  Hereinafter, an example of producing a hydrogen storage alloy for an alkaline storage battery will be described, and in the alkaline storage battery according to an embodiment of the present invention using a hydrogen storage alloy for an alkaline storage battery that satisfies the conditions of the present invention, the cycle life is improved. It is clarified by giving a comparative example. In addition, the hydrogen storage alloy for alkaline storage batteries and alkaline storage battery in this invention are not specifically limited to what was shown in the following Example, It can implement by changing suitably in the range which does not change the summary.

(Manufacture of hydrogen storage alloys A to F for alkaline storage batteries)
In producing the hydrogen storage alloys A to F for alkaline storage batteries, the rare earth elements La, Pr, and Nd, Mg, Ni, and Al have an alloy composition of (La _0.2 Pr _0.4 Nd _0.4 ) _0.83 Mg _0.17 Ni _3.1 After mixing so that Al becomes _0.2 , it melt | dissolved in argon atmosphere, this was cooled, and the ingot of the hydrogen storage alloy was produced.

The hydrogen storage alloy ingot was heat treated at 1000 ° C. to be homogenized, and then mechanically pulverized in an inert atmosphere, and classified to obtain a volume average particle diameter of 65 μm as described above ( La was obtained _{0.2 Pr 0.4 Nd 0.4) 0.83 Mg} 0.17 Ni 3.1 hydrogen-absorbing alloy powder having a composition consisting of Al _0.2.

Here, with respect to the hydrogen storage alloy powder thus produced, an X-ray diffraction measurement apparatus (RIGAKU RINT2000 system) using Cu—Kα rays as an X-ray source is used, a scanning speed of 2 ° / min, and a scanning step of 0.02 °. , subjected to X-ray diffraction measurement in the range of the scanning range 20 ° to 80 °, the strongest peak intensity _{(I a)} which appears in the range of 2θ = 31 ° ~33 °, appears in the range of 2θ = 40 ° ~44 ° strongest and measuring the peak intensity _{(I B),} these intensity ratio _(I a / I _B) result of obtaining, intensity ratio _I a / _{I B} is 0.53, the crystal structure different from the CaCu ₅ type Had.

  For the hydrogen storage alloys A to E for alkaline storage batteries, the hydrogen storage alloy powder is immersed in a 30 wt% potassium hydroxide aqueous solution for oxidation treatment, while for the hydrogen storage alloys F for alkaline storage batteries, The hydrogen storage alloy powder was used as it was.

  Here, when the above hydrogen storage powder is immersed in a 30 wt% potassium hydroxide aqueous solution and oxidized, in the hydrogen storage alloy A for alkaline storage batteries, a stirring blade provided at the center of the immersion tank is used at 60 rpm at 60 rpm. Stirring is performed for 60 minutes at 50 rpm for the hydrogen storage alloy B for alkaline storage batteries, 60 minutes for 60 minutes for the hydrogen storage alloy C for alkaline storage batteries, and 80 minutes at 40 rpm for the hydrogen storage alloy D for alkaline storage batteries. In the hydrogen storage alloy E for alkaline storage batteries, stirring was performed at 50 rpm for 80 minutes.

  Then, each hydrogen storage compound powder oxidized in this way was washed with water and dried to obtain hydrogen storage alloys A to E for alkaline storage batteries.

  Here, the hydrogen storage alloys A to E for alkaline storage batteries oxidized as described above are examined by a transmission electron microscope (TEM-EDX) equipped with X-ray photoelectron spectroscopy (ESCA) and an energy dispersive electron beam microanalyzer. As a result, an oxide or hydroxide layer containing rare earth elements, magnesium, nickel, and aluminum is formed on the surface of the hydrogen storage powder, and most of the oxygen exists on the surface of the hydrogen storage powder. I confirmed.

Next, for the hydrogen storage alloys A to F for alkaline storage batteries, the specific surface area X (m ² / g) is measured by the BET method, and the oxygen concentration Y (ppm) is determined by the melting method in an inert gas. Then, X ² / Y value was calculated, and the result is shown in Table 1 below.

As a result, the hydrogen storage alloys A to D for alkaline storage batteries satisfied the condition of X ² /Y≦1.3×10 ⁻⁵ of the present invention, but the hydrogen storage alloys E and F for alkaline storage batteries satisfy this condition. Did not meet.

(Alkaline storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2)
In producing the alkaline storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2, as the hydrogen storage alloy in the negative electrode, in Example 1, the above-described hydrogen storage alloy A for alkaline storage batteries was used, and in Example 2, the above-described alkaline storage battery was used. The hydrogen storage alloy B, the hydrogen storage alloy C for alkaline storage batteries in Example 3, the hydrogen storage alloy D for alkaline storage batteries in Example 4, and the hydrogen storage alloy E for alkaline storage batteries in Comparative Example 1 were used. In Comparative Example 2, the above hydrogen storage alloy F for alkaline storage batteries was used.

  Next, a paste was prepared by mixing 0.5 parts by weight of polyethylene oxide, 0.5 parts by weight of polyvinylpyrrolidone, and 20 parts by weight of water with respect to 100 parts by weight of each of the above hydrogen storage alloy powders. The paste was uniformly applied to both surfaces of a nickel-plated punching metal conductive core, dried and pressed, and then cut to a predetermined size to form a hydrogen storage alloy electrode used for the negative electrode. Produced.

  On the other hand, in preparing the positive electrode, nickel hydroxide powder containing 2.5 wt% zinc and 1.0 wt% cobalt was put into a cobalt sulfate aqueous solution, and 1 mol of sodium hydroxide aqueous solution was stirred while stirring the powder. Was gradually added dropwise to react until the pH reached 11, and then the precipitate was filtered, washed with water, and dried under vacuum to obtain nickel hydroxide having a surface coated with 5 wt% cobalt hydroxide. . The nickel hydroxide thus coated with cobalt hydroxide is impregnated with a 25 wt% sodium hydroxide aqueous solution added at a weight ratio of 1:10 and heated at 85 ° C. with stirring for 8 hours. After the treatment, this was washed with water and dried to obtain a positive electrode material in which the surface of the nickel hydroxide was coated with sodium-containing cobalt oxide.

  Then, 95 parts by weight of the positive electrode material, 3 parts by weight of zinc oxide, and 2 parts by weight of cobalt hydroxide were mixed with 50 parts by weight of 0.2 wt% hydroxypropylcellulose aqueous solution. A slurry was prepared by mixing, and the slurry was filled in a nickel foam, dried and pressed, and then cut into a predetermined size to produce a positive electrode composed of a non-sintered nickel electrode.

  In addition, a nonwoven fabric made of polypropylene was used as the separator, and an alkaline electrolyte having a specific gravity of 1.30 containing KOH, NaOH, and LiOH in a weight ratio of 15: 2: 1 was used as the alkaline electrolyte.

  In Examples 1 to 4 and Comparative Examples 1 and 2, a cylindrical alkaline storage battery as shown in FIG. 1 having a design capacity of 1900 mAh was produced.

  Here, in producing each of these alkaline storage batteries, as shown in FIG. 1, a separator 3 is interposed between the positive electrode 1 and the negative electrode 2, and these are spirally wound and accommodated in the battery can 4. At the same time, after 2.4 g of the above alkaline electrolyte was injected into the battery can 4, the battery can 4 and the positive electrode lid 6 were sealed with an insulating packing 8, and the positive electrode 1 was connected with the positive electrode lead 5. Then, the negative electrode 2 was connected to the battery can 4 via the negative electrode lead 7 and the battery can 4 and the positive electrode cover 6 were electrically separated by the insulating packing 8. In addition, when a coil spring 10 is provided between the positive electrode lid 6 and the positive electrode external terminal 9 and the internal pressure of the battery rises abnormally, the coil spring 10 is compressed and the gas inside the battery is brought into the atmosphere. To be released.

  Next, each of the alkaline storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2 manufactured as described above was charged with a current of 190 mA for 16 hours, and allowed to stand for 1 hour, and then with a current of 380 mA. The batteries were discharged until the battery voltage reached 1.0 V, and these were left for 1 hour to activate each alkaline storage battery.

Then, after each of the alkaline storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2 thus activated, and then each of the alkaline storage batteries described above, the battery voltage reached a maximum value with a current of 1900 mA, respectively. Charge the battery until it drops to 10 mV and let it stand for 1 hour. Then, discharge the battery at a current of 1900 mA until the battery voltage reaches 1.0 V and leave it for 1 hour. a capacitor Q _1, and 100 th cycle discharge capacity Q _100, 200 to measure a discharge capacity Q ₂₀₀ of cycle, the capacity maintenance rate at the 100th cycle by the following formula R ₁₀₀ (%) 200 cycle capacity The maintenance rate R ₂₀₀ (%) was calculated, and the results are shown in Table 2 below.

Capacity maintenance rate R ₁₀₀ (%) = (Q ₁₀₀ / Q ₁ ) × 100
Capacity maintenance rate R ₂₀₀ (%) = (Q ₂₀₀ / Q ₁ ) × 100

As a result, implementation using the hydrogen storage alloys A to D for alkaline storage batteries in which the specific surface area X (m ² / g) and the oxygen concentration Y (ppm) satisfy the condition of X ² /Y≦1.3×10 ^−5. Each alkaline storage battery of Examples 1-4 is compared with each alkaline storage battery of Comparative Examples 1 and 2 using hydrogen storage alloys E and F for alkaline storage batteries that do not satisfy the condition of X ² /Y≦1.3×10 ^−5. Thus, the capacity maintenance ratio R _{200 at} the 200th cycle was greatly improved.

It is a schematic sectional drawing of the alkaline storage battery produced in Examples 1-4 and Comparative Examples 1 and 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery can 5 Positive electrode lead 6 Positive electrode lid 7 Negative electrode lead 8 Insulation packing 9 Positive electrode external terminal 10 Coil spring

Claims (2)

A hydrogen storage alloy for an alkaline storage battery used for a negative electrode of an alkaline storage battery, comprising at least a rare earth element, magnesium, nickel, and aluminum, and 2θ = 31 ° to 33 in an X-ray diffraction measurement using a Cu—Kα ray as an X-ray source. The intensity ratio (I _A / I _B ) between the strongest peak intensity (I _A ) appearing in the range of ° and the strongest peak intensity (I _B ) appearing in the range of 2θ = 40 ° to 44 ° is 0.1 or more. When an oxide or hydroxide layer is formed on the surface of the hydrogen storage alloy powder, the specific surface area of the hydrogen storage alloy powder is X (m ² / g), and the oxygen concentration is Y (ppm). A hydrogen storage alloy for alkaline storage batteries characterized by satisfying the condition of X ² /Y≦1.3×10 ⁻⁵ . An alkaline storage battery comprising a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, wherein the hydrogen storage alloy for an alkaline storage battery according to claim 1 is used as the hydrogen storage alloy of the negative electrode. Alkaline storage battery.

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