JP2010212117A - Negative electrode for alkaline storage battery, and alkaline storage battery - Google Patents

Abstract

[PROBLEMS] In particular, in an alkaline storage battery using an alkaline storage battery negative electrode using Mg-Ni-rare earth-based hydrogen storage alloy, the binder of the negative electrode for alkaline storage battery is improved, and high-rate discharge characteristics and low-temperature discharge characteristics are improved. It is an object of the present invention to obtain an alkaline storage battery that is excellent in resistance and cycle characteristics.
In a negative electrode for an alkaline storage battery using a hydrogen storage alloy and a styrene-butadiene copolymer emulsion as a binder, the particle size of the styrene-butadiene copolymer in the emulsion is 180 nm or more. More preferably, the particle size of the styrene-butadiene copolymer in the emulsion is from 180 nm to 300 nm.
[Selection] Figure 1

Description

  The present invention relates to a negative electrode for an alkaline storage battery and an alkaline storage battery, and is particularly characterized in that an alkaline storage battery excellent in high rate discharge characteristics, low temperature discharge characteristics and cycle characteristics is obtained.

  Conventionally, nickel cadmium storage batteries have been generally used as alkaline storage batteries. However, in recent years, nickel-metal hydride storage batteries using a hydrogen storage alloy for the negative electrode are attracting attention because they have a higher capacity than nickel-cadmium storage batteries and are superior in environmental safety because they do not use cadmium. Became.

  Such nickel-metal hydride storage batteries are used in various portable devices and hybrid electric vehicles, and it is expected that the nickel-metal hydride storage batteries have higher performance.

  The hydrogen storage alloy electrode used as the negative electrode of nickel metal hydride storage batteries is a paste prepared by mixing hydrogen storage alloy powder, conductive agent, binder, thickener, etc. with water, and applying it to a core such as punching metal, followed by drying. It is obtained by rolling and fixing the hydrogen storage alloy to the core.

  In the nickel-metal hydride storage battery, since the hydrogen storage alloy powder expands and contracts by repeating charge and discharge, the hydrogen storage alloy powder peels from the hydrogen storage alloy electrode. Therefore, the capacity of the negative electrode is reduced and the discharge characteristics are reduced.

  In order to solve the above problem, for example, a styrene-butadiene copolymer having a glass transition temperature of -18 ° C. or lower that is soft and has high adhesiveness and a fiberized fluororesin are used as a binder for the negative electrode. In the following Patent Document 1, it is proposed to suppress the dropping of the hydrogen storage alloy powder.

  However, if the fiberized fluororesin and styrene-butadiene copolymer cover the hydrogen storage alloy, the interface between the hydrogen storage alloy and the electrolyte will decrease, hindering the charge / discharge reaction, increasing the electrode's reaction resistance and causing discharge. Characteristics are degraded.

On the other hand, as a hydrogen storage alloy used for the negative electrode for alkaline storage batteries, LaNi ₅ type hydrogen storage alloy, which is a rare earth-nickel intermetallic compound having a main crystal structure of CaCu ₅ type crystal, or Ti, Zr, V and Ni is used. A hydrogen storage alloy having a Laves phase contained as a constituent element as a main phase is used. There are many rare earth-nickel-based intermetallic compounds other than LaNi ₅ and Mg-Ni-rare earth-based hydrogen storage alloys having a composition in which a part of the rare earth elements of the rare earth-nickel alloy is replaced with Mg are The following Patent Document 2 proposes to store a large amount of hydrogen gas.

  The Mg-Ni-rare earth hydrogen storage alloy as described above is prone to cracking, and the new surface with high reactivity contributes to the charge / discharge reaction. Cracks did not occur, charge / discharge reaction was not sufficient, and high rate discharge characteristics, low temperature discharge characteristics, and cycle characteristics were not sufficient.

JP 2000-331685 A JP 2002-69554 A

  An object of the present invention is to solve the above-mentioned problems in an alkaline storage battery using a negative electrode for an alkaline storage battery provided with a hydrogen storage alloy, and in particular, an Mg-Ni-rare earth hydrogen storage alloy is used. In the alkaline storage battery using the negative electrode for alkaline storage battery, the above negative electrode for alkaline storage battery is improved so that an alkaline storage battery excellent in high rate discharge characteristics, low temperature discharge characteristics, and in cycle characteristics can be obtained. It is to be an issue.

  In order to solve the above-described problems, the alkaline storage battery negative electrode of the present invention uses a styrene-butadiene copolymer emulsion as a binder in the alkaline storage battery negative electrode, and the styrene-butadiene in the emulsion. The particle diameter of the copolymer was 180 nm or more.

  Here, the glass transition temperature of the styrene-butadiene copolymer is preferably -48 ° C or lower. This is because even if the nickel-hydrogen storage battery is charged and discharged at an extremely low temperature of −20 ° C., the binder is soft and maintains adhesiveness, so that the hydrogen storage alloy particles of the alkaline storage battery negative electrode do not fall off. This is because an alkaline storage battery negative electrode having excellent low-temperature discharge characteristics can be obtained.

  Also, at room temperature, if the glass transition temperature is too low, it is too soft and the strength is reduced. On the other hand, when an emulsion having a styrene-butadiene copolymer particle size of 180 nm or more is used as the binder, Since a large amount of styrene-butadiene copolymer is present in the vicinity of the alloy particles, the core such as punching metal, and the hydrogen storage alloy in contact with each other, dropping of the hydrogen storage alloy particles of the negative electrode for an alkaline storage battery is suppressed.

  If the particle size of the styrene-butadiene copolymer exceeds 300 nm, the styrene-butadiene copolymer aggregates, making it difficult to produce an emulsion. If it is increased, the number of particles of styrene-butadiene copolymer will decrease, and there will be places where there is no styrene-butadiene copolymer near the contact point between the hydrogen storage alloy particles. It is considered a thing.

  For this reason, the particle diameter of the styrene-butadiene copolymer is particularly preferably in the range of 180 nm to 300 nm.

  The addition amount of the styrene styrene-butadiene copolymer is preferably in the range of 0.25 to 1.00 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder. This is because if the amount is less than 0.25 parts by weight, sufficient binding force cannot be obtained, and if it exceeds 1.00 parts by weight, sufficient high rate discharge characteristics and low temperature discharge characteristics cannot be obtained.

In the negative electrode for alkaline storage battery of the present invention, the type of the hydrogen storage alloy used is not particularly limited, but the crystal structure such as Ce ₂ Ni ₇ type or CeNi ₃ type that causes cracks that contribute to the charge / discharge reaction as described above It is effective when using a Mg-Ni-rare earth-based hydrogen storage alloy having, for example, the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is a rare earth element containing Y and Zr And at least one element selected from Ti, M is selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B Particularly effective when using a hydrogen storage alloy that is at least one element and satisfies the following conditions: 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9. There is.

The average particle diameter corresponding to 50% by weight of the hydrogen storage alloy is preferably in the range of 25 to 150 μm. If it is less than 25 μm, the effect of the present invention due to the difference in particle diameter of the styrene-butadiene copolymer is small, and sufficient cycle life characteristics cannot be obtained. On the other hand, if the thickness exceeds 150 μm, sufficient high rate discharge characteristics and low temperature discharge characteristics cannot be obtained.
Moreover, in the alkaline storage battery of this invention, in the alkaline storage battery comprising a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, the negative electrode for an alkaline storage battery as described above is used for the negative electrode.

  In the present invention, an emulsion of styrene-butadiene copolymer is used as the binder, and an emulsion having a particle diameter of 180 nm or more of the styrene-butadiene copolymer in the emulsion is used. This is because when the particle size of the styrene-butadiene copolymer is less than 180 nm, the styrene-butadiene copolymer is widely dispersed in the negative electrode for an alkaline storage battery, and the contact between the hydrogen storage alloy particles and the core or the hydrogen storage alloy particles Since there are many other than the vicinity of the contact between them, the interface between the hydrogen storage alloy contributing to the charge / discharge reaction and the electrolytic solution decreases, and the reaction resistance of the negative electrode for alkaline storage batteries increases.

  When the particle diameter of the styrene-butadiene copolymer is 180 nm or more, a large amount of the styrene-butadiene copolymer is present at the contact point between the hydrogen storage alloy particles and the core or between the hydrogen storage alloy particles. Therefore, the mechanical strength of the negative electrode for alkaline storage batteries is increased. In addition, since such a styrene-butadiene copolymer is not widely dispersed, the interface between the hydrogen storage alloy contributing to the charge / discharge reaction and the electrolyte increases, and the charge / discharge reactivity of the negative electrode for alkaline storage batteries is improved. .

  However, if the particle size of the styrene-butadiene copolymer exceeds 300 nm, the styrene-butadiene copolymer aggregates, making it difficult to produce an emulsion. If it is increased, the number of particles of styrene-butadiene copolymer will decrease, and there will be places where there is no styrene-butadiene copolymer near the contact point between the hydrogen storage alloy particles. Therefore, it is preferably 300 nm or less.

  1 to 3 show schematic diagrams comparing the negative electrodes of Examples and Comparative Examples of the present invention. Here, 10 is a hydrogen storage alloy, 11 is a styrene-butadiene copolymer particle having a particle diameter of 180 nm (Example), 12 is a styrene-butadiene copolymer particle having a particle diameter of 120 nm (Comparative Example), and 13 is a particle. Styrene-butadiene copolymer particles having a diameter exceeding 300 nm (comparative example) and 14 are cores such as punching metal.

  From this figure, when the addition amount of the styrene-butadiene copolymer as the binder is the same, one particle having a particle diameter of 180 nm corresponds to approximately 3.4 particles having a particle diameter of 120 nm. Therefore, the particle size of 180 nm does not exist more than the contact point between the hydrogen storage alloy particles and the core or near the contact point between the hydrogen storage alloy particles than the particle size of 120 nm, and contributes to the charge / discharge reaction. Since the decrease in the interface between the hydrogen storage alloy and the electrolyte is suppressed, discharge performance such as high rate discharge characteristics and low temperature discharge characteristics is improved.

  However, as described above, when it exceeds 300 nm, the styrene-butadiene copolymer aggregates, making it difficult to produce an emulsion, and the number of particles of the styrene-butadiene copolymer is reduced. Since there are places where styrene-butadiene copolymer does not exist in the vicinity of the contact points between the storage alloy particles, the amount of the hydrogen storage alloy particles falling off from the negative electrode plate increases. Therefore, the particle diameter of the styrene-butadiene copolymer is particularly preferably in the range of 180 nm to 300 nm.

In particular, the hydrogen storage alloy in the negative electrode for alkaline storage batteries is prone to cracks that contribute to the charge / discharge reaction. The general formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is a rare earth element including Y and Zr And at least one element selected from Ti, M is selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B When using a hydrogen storage alloy that is at least one element and satisfies the following conditions: 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9. Since the surface of the hydrogen storage alloy that is not covered with the styrene-butadiene copolymer increases, cracks that contribute to the charge / discharge reaction occur uniformly, and the charge / discharge reaction occurs efficiently, resulting in high-rate discharge characteristics and low-temperature discharge characteristics. An alkaline storage battery having excellent cycle characteristics is obtained.

It is a schematic diagram of the Example of this invention. It is a schematic diagram of the comparative example of this invention. It is a schematic diagram of the comparative example of this invention.

  Embodiments of an alkaline storage battery negative electrode and an alkaline storage battery including the alkaline storage battery negative electrode according to the present invention will be specifically described. 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 embodiment, It can implement by changing suitably in the range which does not change the summary.

  The negative electrode for alkaline storage battery according to the present invention and the alkaline storage battery provided with the negative electrode for alkaline storage battery will be specifically described with reference to examples, and the negative electrode for alkaline storage battery according to this example and the negative electrode for alkaline storage battery are provided. In the alkaline storage battery, it will be clarified by giving a comparative example that the high rate discharge characteristic and the low temperature discharge characteristic are particularly improved.

Example 1
[Production of negative electrode]
Nd, Mg, Ni, and Al were mixed so as to have a predetermined alloy composition, and an ingot of a hydrogen storage alloy was produced using an induction melting furnace. The ingot was homogenized by heat treatment, and pulverized so that the average particle diameter corresponding to 50% of the weight integral was 65 μm in an inert atmosphere to obtain an alloy powder. As a result of analyzing the composition of this hydrogen storage alloy by high frequency plasma spectroscopy (ICP), the composition was La _0.64 Sm _0.16 Mg _0.20 Ni _3.40 Al _0.10 .

  With respect to 100 parts by weight of the hydrogen storage alloy powder, 0.5 parts by weight of a styrene-butadiene copolymer having a particle size of 180 nm, 0.2 parts by weight of sodium polyacrylate, and 0.2 parts by weight of carboxymethylcellulose are added, and ketjen black 1 part by weight and 50 parts by weight of water were kneaded to prepare a paste. This paste was uniformly applied to both surfaces of a conductive core made of punching metal, dried and pressed, and then cut into predetermined dimensions to obtain a negative electrode of Example 1. The styrene-butadiene copolymer used was an emulsion having a glass transition temperature of −48 ° C. or lower.

(Comparative Example 1)
In Comparative Example 1, a negative electrode of Comparative Example 1 was obtained in the same manner as in Example 1 except that a styrene-butadiene copolymer having a particle size of 120 nm was used.
[Production of positive electrode]
Add nickel hydroxide powder containing 2.5% by weight of zinc and 1.0% by weight of cobalt to cobalt sulfate aqueous solution, and gradually drop 1 mol of sodium hydroxide aqueous solution with stirring to adjust the pH during the reaction to 11. ) The reaction was continued with stirring, and then the precipitate was filtered off, washed with water, dried in vacuo, and then the surface of the nickel hydroxide particles was coated with 5% by weight of cobalt hydroxide. This was impregnated with a 25% by weight aqueous solution of sodium hydroxide so that the mass ratio was 1:10, heat-treated at 85 ° C. with stirring for 8 hours, washed with water, and dried at 65 ° C. Then, a nickel positive electrode active material powder coated with a high-order cobalt oxide was produced. The nickel positive electrode active material powder thus obtained was composed of 95% by weight, zinc oxide 3% by weight, and cobalt hydroxide 2% by weight. A positive electrode active material slurry was prepared by adding and mixing 50% by weight of a 0.2% by weight aqueous solution of hydroxypropylcellulose as a binder with respect to the weight of the mixed powder. This is filled in pores of foamed nickel with a basis weight of about 600 g / m ² , porosity of 95% and thickness of about 2 mm, dried, and adjusted so that the active material density is about 2.9 g / cm ³ -void. After rolling, it was cut into a predetermined size to obtain a non-sintered nickel positive electrode.

[Production of battery]
For the negative electrode of Example 1 obtained as described above, the non-sintered nickel positive electrode produced as described above was obtained by subjecting a polypropylene nonwoven fabric separator to fluorination treatment with fluorinated gas and sulfurous acid gas. It is wound through a polypropylene non-woven fabric separator having a sulfone group, and an electrode body is produced. This is inserted into a cylindrical can in which nickel is plated on iron, KOH / NaOH / LiOH weight mixing ratio 15: 2: 1, specific gravity A 1.30 electrolyte was injected and sealed to obtain an AA size nickel metal hydride storage battery with a design capacity of 2500 mAh. The battery thus produced is referred to as Example Battery A.

  Then, Comparative Example Battery X was produced in the same manner as Example Battery A except that the negative electrode of Comparative Example 1 was used.

Each of the nickel hydride storage batteries of Example Battery A and Comparative Example Battery X produced as described above was charged for 16 hours at a current of 250 mAh, and then discharged at a current of 250 mAh until the battery voltage reached 1.0 V. Was activated by charging and discharging for 3 cycles.
[High rate discharge characteristics]
After each of the alkaline batteries of Example Battery A and Comparative Example Battery X activated as described above reached a maximum value at a current of 2500 mA, the battery was charged until it decreased by 10 mV, and left for 60 minutes, Discharge at a current of 7500 mA, determine the discharge capacity until the battery voltage reaches 1.0 V, determine the discharge capacity in Comparative Example Battery X as the high rate discharge characteristic index 100, determine the high rate discharge characteristics in Example Battery A, and the result Is shown in Table 1 below.
[Low temperature discharge characteristics]
After each of the alkaline storage batteries of Example Battery A and Comparative Example Battery X activated as described above reached a maximum value at a current of 2500 mA, the battery was charged until it decreased by 10 mV, and the ambient temperature was −20 ° C. The battery was discharged at a current of 2500 mA at an ambient temperature of −20 ° C. for 60 minutes, and the discharge capacity until the battery voltage reached 1.0 V was obtained. The low temperature discharge characteristics in Example Battery A were determined, and the results are shown in Table 1 below.
[Cycle characteristics]
After each of the nickel hydride storage batteries of Example Battery A and Comparative Example Battery X activated as described above reached a maximum value at a current of 2500 mA, the battery was charged until it decreased by 10 mV and left for 30 minutes. The battery is discharged at a current of 2500 mA until the battery voltage reaches 1.0 V and left for 30 minutes, and this is repeated as one cycle until the discharge capacity reaches 70% of the initial capacity for each nickel metal hydride battery. The cycle number was obtained, the cycle number in Comparative Example Battery X was taken as the cycle life index 100, the cycle life characteristics in Example Battery A were obtained, and the results are shown in Table 1 below.

  As is clear from the results of Table 1 above, Example Battery A using a styrene-butadiene copolymer having a particle size of 180 nm is compared with a battery using a styrene-butadiene copolymer having a particle size of 120 nm. As a result, the high rate discharge characteristics and the low temperature discharge characteristics are remarkably improved and the cycle characteristics are also improved as compared with the example battery X.

  This is because when the particle size of the styrene-butadiene copolymer is 180 nm, there will be a lot of contact between the hydrogen storage alloy particles and the core or between the hydrogen storage alloy particles. Increase the mechanical strength of the negative electrode. Furthermore, since such a styrene-butadiene copolymer does not disperse too widely compared to a styrene-butadiene copolymer having a particle size of 120 nm, the hydrogen storage alloy that contributes to the charge / discharge reaction and the electrolytic solution It is considered that the reduction of the interface is suppressed and the high rate discharge characteristics and the low temperature discharge characteristics are remarkably improved.

In the above-described examples and comparative examples, the hydrogen storage alloy is selected from the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (wherein Ln is selected from rare earth elements including Y, Zr, and Ti). At least one element, M is at least one element selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9.), But the particle size of styrene-butadiene copolymer was used. It is considered that the same effect can be obtained even when another hydrogen storage alloy is used when the material having a thickness of 180 nm or more is used. However, the hydrogen storage alloy used in the above examples and the like is less pulverized than the conventional CuCu ₅ type hydrogen storage alloy, but has the property of being prone to cracking. When a styrene-butadiene copolymer is used, a further effect can be obtained.

DESCRIPTION OF SYMBOLS 10 Hydrogen storage alloy 11 Styrene-butadiene copolymer particle | grains with a particle diameter of 180 nm 12 Styrene-butadiene copolymer particle | grains with a particle diameter of 120 nm 13 Styrene-butadiene copolymer particle | grains with a particle diameter exceeding 300 nm 14 Core

Claims (5)

  An alkaline storage battery negative electrode using a hydrogen storage alloy and a styrene-butadiene copolymer emulsion as a binder, wherein the particle size of the styrene-butadiene copolymer in the emulsion is from 180 nm to 300 nm. Negative electrode for storage battery.   The negative electrode for an alkaline storage battery according to claim 1, wherein the styrene-butadiene copolymer has a glass transition temperature of -48 ° C or lower.   3. The negative electrode for an alkaline storage battery according to claim 1, wherein an average particle size of the hydrogen storage alloy is 25 μm or more and 150 μm or less. The hydrogen storage alloy has the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is at least one element selected from rare earth elements including Zr, Ti, Y, M is V, Nb And at least one element selected from Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30 The condition of 0 ≦ b ≦ 0.50 and 2.8 ≦ y ≦ 3.9 is satisfied.) The negative electrode for an alkaline storage battery according to any one of claims 1 to 3. An alkaline storage battery comprising a positive electrode, a negative electrode using a hydrogen storage alloy and an alkaline electrolyte, wherein the negative electrode for an alkaline storage battery according to any one of claims 1 to 4 is used as the negative electrode. Alkaline storage battery.

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