JP2008210554A - Negative electrode for alkaline storage battery, and alkaline storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a negative electrode used for an alkaline storage battery and make it possible to obtain an alkaline storage battery which has high capacity and is excellent in discharge charactaristic especially at low temperatures, and excellent in cycle life. <P>SOLUTION: In negative electrode of an alkaline battery, hydrogen storage alloy which is expressed as a general formula Ln<SB>1-x</SB>Mg<SB>x</SB>Ni<SB>y-a-b</SB>Al<SB>a</SB>M<SB>b</SB>(in the formula, Ln is an element of one kind selected at least from rare-earth element including Y and Zr, M is an element of at least one kind selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, and Ti, x, y, a, and b satisfy conditions of 0.05≤x≤0.25, 3.1≤y≤3.6, 0.01≤a+b≤0.30) and in which Vickers hardness by JIS Z2244 is 650 Hv or less, and a rubber based binder are made to be contained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an alkaline storage battery comprising a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, and an alkaline storage battery negative electrode used for the negative electrode of the alkaline storage battery. It is characterized by an improved alkaline storage battery with high capacity, discharge characteristics, particularly low temperature discharge characteristics, and excellent cycle life.

  Conventionally, nickel-cadmium storage batteries have been widely used as alkaline storage batteries, but in recent years they have a higher capacity than nickel-cadmium storage batteries and are superior in environmental safety because they do not use cadmium. Therefore, nickel-hydrogen storage batteries using a hydrogen storage alloy for the negative electrode have come to attract attention.

  In recent years, alkaline storage batteries composed of such nickel / hydrogen storage batteries have come to be used in various portable devices, and it is expected that the capacity of these alkaline storage batteries will be further increased.

Here, in such an alkaline storage battery, as a hydrogen storage alloy used for the negative electrode, a rare earth-nickel hydrogen storage alloy having a CaCu ₅ type lattice crystal as a main phase or a Laves type AB ₂ lattice crystal is generally used. In general, a hydrogen storage alloy having a main phase of is used.

  However, the hydrogen storage alloy described above does not necessarily have sufficient hydrogen storage capacity, and it has been difficult to further increase the capacity of the alkaline storage battery.

Therefore, in recent years, in order to improve the hydrogen storage capacity in the rare earth-nickel hydrogen storage alloy, Mg or the like is contained in the rare earth-nickel hydrogen storage alloy, and Ce ₂ Ni other than CaCu ₅ type is used. It has been proposed to use a hydrogen storage alloy having a crystal structure such as ₇ type or CeNi ₃ type (see, for example, Patent Document 1).

  However, the hydrogen storage alloys as described above are generally prone to cracking, resulting in poor corrosion resistance, and the cycle life of the alkaline storage battery is not sufficient. In particular, there is a problem that the discharge characteristics at a low temperature are greatly deteriorated.

  In the past, it has been proposed to use a hydrogen storage alloy having a Vickers hardness of 700 Hv or less to suppress cracking of the hydrogen storage alloy during charge and discharge to improve the cycle life of the alkaline storage battery (for example, Patent Document 2).

However, even when such a hydrogen storage alloy is used, a negative electrode material containing this hydrogen storage alloy is applied to a conductive support such as a punching metal, and is rolled with a roller mill or the like to produce a negative electrode for an alkaline storage battery. When doing so, there was a problem that the above-mentioned hydrogen storage alloy cracked. In particular, in order to increase the battery capacity of the alkaline storage battery, for example, as proposed in Patent Document 3, when the negative electrode material is filled so that the filling density is 4.8 g / cm ³ or more, Since rolling is performed at a strong pressure, many cracks occur in the hydrogen storage alloy, the cycle life of the alkaline storage battery is reduced, the internal resistance of the negative electrode for the alkaline storage battery is increased, and the discharge characteristics, particularly at low temperatures, are large. There was a problem of lowering.

  Further, conventionally, when a slurry containing a hydrogen storage alloy is applied to a conductive support, a water-soluble polymer and a rubber-based resin are used as a binder, and the hydrogen storage alloy falls off the conductive support. In order to prevent this, there has also been proposed one in which the filling density of the hydrogen storage alloy is increased (see, for example, Patent Document 4).

However, the above-described one increases the adhesion of the hydrogen storage alloy to the conductive support with the rubber resin, while reducing the amount of the rubber resin with the water-soluble polymer to increase the filling amount of the hydrogen storage alloy. In order to suppress the occurrence of cracks in the hydrogen storage alloy during rolling, there is no suggestion of what kind of hydrogen storage alloy is used, and the cracks in the hydrogen storage alloy are sufficiently suppressed. In addition, the cycle life of the alkaline storage battery and the discharge characteristics, particularly the discharge characteristics at a low temperature cannot be sufficiently improved.
JP 2002-69554 A JP-A-11-323469 JP 2000-133254 A Japanese Patent Laid-Open No. 7-45278

  This invention makes it a subject to solve the above problems in the negative electrode for alkaline storage batteries using a hydrogen storage alloy, and the alkaline storage battery using such a negative electrode for alkaline storage batteries. An object of the present invention is to improve the negative electrode so that an alkaline storage battery having a high capacity, discharge characteristics, particularly discharge characteristics at low temperatures, and excellent cycle life can be obtained.

In order to solve the above-described problems, the alkaline storage battery negative electrode according to the present invention is selected from the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is selected from rare earth elements including Y and Zr). At least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, and Ti. And x, y, a, and b satisfy the conditions of 0.05 ≦ x ≦ 0.25, 3.1 ≦ y ≦ 3.6, and 0.01 ≦ a + b ≦ 0.30). And a hydrogen storage alloy having a Vickers hardness of 650 Hv or less according to JISZ2244 and a rubber-based binder.

When a negative electrode material containing the hydrogen storage alloy and the rubber binder is applied to a conductive support and rolled to produce a negative electrode for an alkaline storage battery, a high-capacity alkaline storage battery is obtained. Therefore, the packing density of the negative electrode material is preferably set to 5.7 g / cm ³ or more.

  In the alkaline storage battery negative electrode, it is necessary to use a rubber-based binder that has an appropriate rubber elasticity and does not adversely affect the hydrogen storage alloy. For example, styrene-butadiene rubber can be used.

  In the alkaline storage battery negative electrode, it is preferable to contain carbon in addition to the hydrogen storage alloy and the rubber-based binder. Thus, when carbon is contained in the negative electrode for an alkaline storage battery, when the negative electrode material is applied to the conductive support and rolled as described above, the carbon functions as a cushioning material and cracks into the hydrogen storage alloy. Is suppressed from occurring. In addition, the carbon contained in this manner facilitates uniform distribution of the alkaline electrolyte in the negative electrode for alkaline storage batteries, and carbon also functions as a conductive agent. Therefore, the charge / discharge reaction is uniform throughout the negative electrode for alkaline storage batteries. And the occurrence of cracks in the hydrogen storage alloy is further suppressed. If the amount of carbon in the negative electrode for an alkaline storage battery is too large, the amount of hydrogen storage alloy to be filled decreases and the battery capacity decreases, so the amount of carbon added to the above hydrogen storage alloy It is preferable to make it 4 wt% or less.

  And in the alkaline storage battery in this invention, the above negative electrodes for alkaline storage batteries were used for the negative electrode.

Hydrogen storage alloy represented by the general used in a negative electrode for alkaline storage battery formula _{Ln 1-x Mg x Ni yab} Co a M b of the present invention is adapted to similar crystal structure Ce ₂ Ni ₇ type or to Since it has a high hydrogen storage capacity, an alkaline storage battery with a high battery capacity can be obtained.

Further, when a hydrogen storage alloy having a Vickers hardness of 650 Hv or less according to JISZ2244 is used as in the negative electrode for an alkaline storage battery according to the present invention, the hydrogen storage alloy is soft and sticky, so that cracking hardly occurs. When a rubber-based binder is used, the rubber-based binder has flexibility, so that a negative electrode material containing a hydrogen storage alloy and a rubber-based binder is applied to the conductive support as described above. When the negative electrode for alkaline storage battery is produced by rolling, the rubber-based binder functions as a cushioning material, and the generation of cracks in the hydrogen storage alloy is further suppressed. Corrosion resistance is improved and an increase in internal resistance is prevented. In particular, in order to obtain an alkaline storage battery having a high battery capacity, even when the negative electrode material is rolled at a strong pressure such that the packing density of the negative electrode material is 5.7 g / cm ³ or more, the above-described hydrogen storage alloy is sufficiently cracked. It will be suppressed.

  As a result, when the above-described negative electrode for an alkaline storage battery is used for the alkaline storage battery, an alkaline storage battery having a high capacity, excellent discharge characteristics, particularly low temperature discharge characteristics, and excellent cycle life can be obtained.

  Hereinafter, the negative electrode for an alkaline storage battery according to an embodiment of the present invention and the alkaline storage battery using the negative electrode for an alkaline storage battery will be specifically described, a comparative example will be given, and the negative electrode for an alkaline storage battery according to an embodiment of the present invention will be used. In the conventional alkaline storage battery, it is clarified that cracking of the hydrogen storage alloy is suppressed, and an alkaline storage battery having excellent discharge characteristics, particularly low temperature discharge characteristics and cycle life can be obtained. In addition, the negative electrode for alkaline storage batteries and alkaline storage battery in this invention are not limited to what was shown to the following Example, In the range which does not change the summary, it can implement suitably.

(Example 1)
In Example 1, when producing an alkaline storage battery, a negative electrode and a positive electrode produced as described below were used.

[Production of negative electrode]
In producing the negative electrode, after mixing rare earth elements La, Pr, and Nd, Mg, Ni, and Al so as to have a predetermined alloy composition, this was melted at 1500 ° C. in an induction melting furnace. This was cooled to obtain a hydrogen storage alloy ingot. The hydrogen storage alloy ingot was heat treated in an argon atmosphere at a temperature 60 ° C. lower than the liquefaction start temperature for 10 hours to be homogenized. As a result of analyzing the composition of the hydrogen storage alloy by high frequency plasma spectroscopy (ICP), the composition of the hydrogen storage alloy was La _0.17 Pr _0.33 Nd _0.33 Mg _0.17 Ni _3.10 Al _0.20 . Further, as a result of measuring the Vickers hardness of the hydrogen storage alloy ingot after the heat treatment as described above according to JISZ2244, the hydrogen storage alloy had a Vickers hardness of 610 Hv.

  Next, the hydrogen storage alloy ingot homogenized by heat treatment as described above was mechanically pulverized in an inert atmosphere and classified to obtain a hydrogen storage alloy powder having the above composition. . As a result of measuring the particle size distribution of the hydrogen storage alloy powder using a laser diffraction / scattering particle size distribution measuring device, the average particle size at a weight integral of 50% was 65 μm.

And, 100 parts by weight of the above hydrogen storage alloy powder, 1 part by weight of styrene-butadiene rubber (SBR) as a rubber-based binder, 0.2 part by weight of sodium polyacrylate, and 0.1 part of carboxymethylcellulose. 2 parts by weight, 1 part by weight of nickel powder flakes of conductive powder, 1 part by weight of carbon black and 50 parts by weight of water were added and kneaded to prepare a paste of negative electrode material. And this paste was apply | coated uniformly on both surfaces of the electroconductive support body which consists of punching metal, this was dried and pressed, Then, it cut | disconnected to the predetermined dimension and produced the negative electrode. In this negative electrode, the packing density of the negative electrode material was 5.7 g / cm ³ .

[Production of positive electrode]
In preparing the positive electrode, nickel hydroxide powder containing 2.5% by weight of zinc and 1.0% by weight of cobalt was charged 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 cause the reaction to pH 11, and the precipitate was filtered, washed with water and dried in vacuo to obtain nickel hydroxide having a surface coated with 5% by weight of cobalt hydroxide. .

  The nickel hydroxide thus coated with cobalt hydroxide was impregnated with a 25% by weight aqueous sodium hydroxide solution in a weight ratio of 1:10, and this was stirred for 8 hours at 85 ° C. Then, this was washed with water and dried at 65 ° C. to obtain a positive electrode active material in which the nickel hydroxide surface was coated with sodium-containing cobalt oxide. In addition, the valence of cobalt in said cobalt oxide was 3.05.

Next, 95 parts by weight of the positive electrode active material, 3 parts by weight of zinc oxide, and 2 parts by weight of cobalt hydroxide were mixed with 50 parts by weight of a 0.2% by weight hydroxypropylcellulose aqueous solution. These were mixed to prepare a slurry of the positive electrode material. Then, this slurry is filled in a nickel foam having a basis weight of about 600 g / m ² , dried and pressed, and then cut to a predetermined size to produce a positive electrode made of a non-sintered nickel electrode. did.

Then, with using the positive electrode and the negative electrode fabricated as described above, as a separator, using a nonwoven fabric made of polypropylene, and as the alkaline electrolyte, and the KOH and NaOH and LiOH · H ₂ O 8: 0.5 An alkaline aqueous battery with a design capacity of 1500 mAh as shown in FIG. 1 was assembled using an alkaline aqueous solution that was included at a weight ratio of 1: 1 and the sum of these was 30% by weight.

  Here, in assembling the alkaline storage battery, 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. The positive electrode 1 is connected to the positive electrode lid 6 via the positive electrode lead 5, the negative electrode 2 is connected to the battery can 4 via the negative electrode lead 7, and an alkaline electrolyte is injected into the battery can 4. Sealing was performed between the battery can 4 and the positive electrode lid 6 via an insulating packing 8, and the battery can 4 and the positive electrode lid 6 were electrically separated by the insulating packing 8. Further, a closing plate 11 urged by a coil spring 10 is provided between the positive electrode cover 6 and the positive electrode external terminal 9 so as to close the gas discharge port 6a provided in the positive electrode cover 6, and the battery When the internal pressure of the battery rises abnormally, the coil spring 10 is compressed so that the gas inside the battery is released into the atmosphere.

(Example 2)
In Example 2, in the production of the negative electrode in Example 1, rare earth elements Nd, Mg, Ni, and Al were mixed so as to have a predetermined alloy composition, and the same as in Example 1 above. Then, after obtaining an ingot of a hydrogen storage alloy having a composition of Nd _0.90 Mg _0.10 Ni _3.30 Al _0.20 , the ingot was heat-treated, and then the ingot was mechanically pulverized and classified in an inert atmosphere. Thus, a hydrogen storage alloy powder having the above composition was obtained. In addition, as a result of measuring the Vickers hardness of the ingot of the hydrogen storage alloy after the heat treatment according to JISZ2244, the Vickers hardness of the hydrogen storage alloy was 570 Hv. Further, as a result of measuring the particle size distribution of the above-mentioned hydrogen storage alloy powder using a laser diffraction / scattering particle size distribution measuring apparatus, the average particle size when the weight integral was 50% was 65 μm.

Then, except for using a powder of the above Nd _0.90 Mg _0.10 Ni _3.30 hydrogen storage alloy became the composition of Al _0.20, as in the case of Example 1 above to obtain an alkali storage battery of Example 2.

(Comparative Example 1)
In Comparative Example 1, in preparation of the negative electrode in Example 1, rare earth elements La, Pr, and Nd, Mg, Ni, and Al were mixed so as to have a predetermined alloy composition. In the same manner as above, after obtaining an ingot of a hydrogen storage alloy having a composition of La _0.50 Pr _0.15 Nd _0.15 Mg _0.20 Ni _3.30 Al _0.10 , the ingot was heat-treated, and then the ingot was heated in an inert atmosphere. Mechanically pulverized and classified to obtain a hydrogen storage alloy powder having the above composition. In addition, as a result of measuring the Vickers hardness of the hydrogen storage alloy ingot after the heat treatment according to JISZ2244, the hydrogen storage alloy had a Vickers hardness of 670 Hv. Further, as a result of measuring the particle size distribution of the above-mentioned hydrogen storage alloy powder using a laser diffraction / scattering type particle size distribution measuring apparatus, the average particle size when the weight integral was 50% was 65 μm.

The alkaline storage battery of Comparative Example 1 was obtained in the same manner as in Example 1 except that the hydrogen storage alloy powder having the composition of La _0.50 Pr _0.15 Nd _0.15 Mg _0.20 Ni _3.30 Al _0.10 was used. Obtained.

  Next, the alkaline storage batteries of Examples 1 and 2 and Comparative Example 1 obtained as described above were each left in a temperature atmosphere of 45 ° C. for 10 hours, and then each of the alkaline storage batteries described above was subjected to 16 mA at a current of 150 mA. After charging for a period of time, discharging was performed at a current of 1500 mA until the battery voltage reached 1.0 V, and this was regarded as one cycle, and charging / discharging for 3 cycles was performed to activate each alkaline storage battery.

  And after dismantling each alkaline storage battery of Examples 1 and 2 and Comparative Example 1 activated as described above, the hydrogen storage alloy particles were taken out from the respective negative electrodes, washed with water, and dried under reduced pressure. About each said hydrogen storage alloy particle, the particle size distribution was measured with the laser diffraction and scattering type particle size distribution measuring apparatus as mentioned above, and the average particle diameter in 50% of weight integral was calculated | required. Then, assuming that the average particle size of the hydrogen storage alloy particles in Example 1 was 100, the alloy particle size of each hydrogen storage alloy particle was calculated.

  In addition, the alkaline storage batteries of Examples 1 and 2 and Comparative Example 1 activated as described above were reduced by 10 mV after the battery voltage reached the maximum value at a current of 1500 mA in a temperature environment of 25 ° C. The battery is charged for 20 minutes and then discharged for 20 minutes, and then discharged at a current of 1500 mA until the battery voltage reaches 1.0 V, paused for 10 minutes, and this is repeated as charge and discharge. , The number of cycles until 70% of the initial discharge capacity was obtained. And the cycle life of each alkaline storage battery was calculated by setting the number of cycles in the alkaline storage battery of Example 1 to 100, and the results are shown in Table 1 below.

  In addition, the alkaline storage batteries of Examples 1 and 2 and Comparative Example 1 activated as described above were reduced by 10 mV after the battery voltage reached the maximum value at a current of 1500 mA in a temperature environment of 25 ° C. Each of the alkaline storage batteries is discharged until the battery voltage reaches 1.0 V at a current of 1500 mA in a temperature environment of −10 ° C. The discharge capacity at low temperature was determined. And the discharge capacity in the alkaline storage battery of Example 1 was set to 100, the low temperature discharge characteristic of each alkaline storage battery was calculated, and the result is shown in Table 1 below.

  As a result, the alkaline storage battery of Examples 1 and 2 using a rubber binder and a hydrogen storage alloy having a Vickers hardness of 650 Hv or less for the negative electrode uses a hydrogen storage alloy having a Vickers hardness of over 650 Hv. Compared with the alkaline storage battery of Comparative Example 1, the alloy particle size of the hydrogen storage alloy particles after activation of the alkaline storage battery was increased, and the cracks of the hydrogen storage alloy particles were reduced.

  Moreover, in the alkaline storage batteries of Examples 1 and 2, the charge / discharge cycle life and low-temperature discharge characteristics were also improved as compared with the alkaline storage battery of Comparative Example 1.

It is a schematic sectional drawing of the alkaline storage battery produced in Examples 1, 2 and Comparative Example 1 of the present 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 cover 6a Gas discharge port 7 Negative electrode lead 8 Insulation packing 9 Positive electrode external terminal 10 Coil spring 11 Closure board

Claims (4)

Formula _{Ln 1-x Mg x Ni yab} Al a M b ( wherein, at least one element Ln is selected from the rare earth element and Zr containing Y, M is V, Nb, Ta, Cr, Mo, It is at least one element selected from Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, and Ti, and x, y, a, and b are 0.05 ≦ x ≦ 0.25, 3.1 ≦ y ≦ 3.6, 0.01 ≦ a + b ≦ 0.30), a hydrogen storage alloy having a Vickers hardness of 650 Hv or less according to JISZ2244, and a rubber system A negative electrode for an alkaline storage battery, comprising a binder. 2. The negative electrode for an alkaline storage battery according to claim 1, wherein the negative electrode material containing the hydrogen storage alloy and the rubber-based binder is applied to a conductive support and rolled, and the packing density of the negative electrode material is 5.7 g. A negative electrode for an alkaline storage battery, wherein the negative electrode is / cm ³ or more.   3. The negative electrode for an alkaline storage battery according to claim 1 or 2, wherein the rubber-based binder is styrene-butadiene rubber.   In the alkaline storage battery provided with the positive electrode, the negative electrode using a hydrogen storage alloy, and alkaline electrolyte, the negative electrode for alkaline storage batteries of any one of said Claims 1-3 was used for the negative electrode. An alkaline storage battery characterized by that.

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