JP5114875B2 - Alkaline storage battery, electrode composite material, and method for producing the same - Google Patents

Description

  The present invention relates to a composite material for an electrode made of a hydrogen storage alloy and used for an alkaline storage battery, and more particularly to a technique for improving the surface state of a hydrogen storage alloy powder.

  Nickel metal hydride storage batteries using a hydrogen storage alloy as a negative electrode active material are attracting attention as power sources for electric vehicles and the like because they have excellent output characteristics and high durability (lifetime characteristics and storage characteristics). In recent years, since lithium ion secondary batteries are also entering this application, it is necessary to further improve output characteristics and durability from the viewpoint of highlighting the advantages of nickel metal hydride storage batteries.

As a hydrogen storage alloy, a hydrogen storage alloy having a CaCu ₅ type crystal structure is mainly used. From the viewpoint of improving durability, for example, a part of Ni of MmNi ₅ (Mm is a mixture of light rare earth elements) is used. In many cases, substitution is performed with Co, Mn, Al, Cu or the like. In order to further enhance the durability of this hydrogen storage alloy, for example, a technique has been proposed in which fine particles of oxide having an average particle size of 1 μm or less are mixed with hydrogen storage alloy powder to suppress pulverization (see Patent Document 1). . In addition, a technique has been proposed in which the hydrogen storage alloy powder is coated with at least one of Sc and Group III metal element oxides or hydroxides to suppress oxidation and elution (see Patent Document 2).
JP 07-258703 A JP 09-031501 A

  By using the techniques of Patent Documents 1 and 2, it is possible to improve the life characteristics near room temperature. However, it has been difficult to improve the high temperature life characteristics that combine the storage characteristics and the life characteristics even with the techniques of Patent Documents 1 and 2. Specifically, in the technique of Patent Document 1, since the surface of the hydrogen storage alloy powder cannot be covered with highly durable fine particles, the hydrogen storage alloy deteriorates due to repeated charge and discharge at high temperatures. Moreover, in the technique of patent document 2, since the surface of the hydrogen storage alloy powder is completely covered, the hydrogen storage reaction through the Ni layer unevenly distributed on the surface is lowered, and the battery reaction becomes insufficient every time charging and discharging are repeated.

  The present invention is for solving the above-described problem, and an object of the present invention is to improve high-temperature life characteristics without reducing the reactivity of a battery in an alkaline storage battery using a hydrogen storage alloy as a negative electrode active material. .

  In view of the above-described problems, the composite material for an electrode of the present invention has a group III metal element and a group III metal element oxidized on the surface of the hydrogen storage alloy powder having a Ni content of 20 to 70% by weight in the entire composition. It is characterized in that particles having an average particle diameter of 50 nm or less, which are composed of at least one of a metal and a Group III metal element hydroxide, are arranged.

  Further, as a method for embodying the composite material for electrodes, a hydrogen storage alloy powder having a Ni content of 20 to 70% by weight in the total composition is immersed in an aqueous alkali solution containing sodium hydroxide and / or potassium hydroxide aqueous solution. In the first step, the hydrogen storage alloy powder is subjected to high-speed impact with at least one of a group III metal element, an oxide of a group III metal element and a hydroxide of a group III metal element, and the surface of the hydrogen storage alloy powder is averaged. And a second step of arranging particles having a particle size of 50 nm or less.

  The present inventors selected at least one of Group III metal elements, Group III metal element oxides and / or hydroxides having high corrosion resistance, and used them as particles having an average particle diameter of 50 nm or less in the hydrogen storage alloy powder. It has been found that the hydrogen storage reaction can be carried out smoothly while preventing the corrosion of the hydrogen storage alloy by disposing it on the surface. Although the effects of the present invention are being intensively analyzed, hydrogen ions (protons) are occluded through the grain boundaries by providing a large number of these grain boundaries by setting the average grain size of the above-described particles to 50 nm or less. It is thought that this is because the Ni layer that is unevenly distributed on the surface of the alloy is easily reached.

  In order to embody such a composite material for electrodes, in the first step, after sufficiently providing a Ni layer unevenly distributed on the surface of the hydrogen storage alloy powder containing a certain amount of Ni in the first step, It is necessary to arrange the particles having the above-described composition so that the average particle size is 50 nm or less.

  Since the composite material for an electrode of the present invention has a high corrosion resistance while the layer provided on the surface of the hydrogen storage alloy powder serving as a nucleus does not inhibit the hydrogen storage reaction, the alkaline storage battery configured as a negative electrode active material has a high temperature. Even if charging / discharging is repeated, the decrease in capacity is small.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing the vicinity of the surface of the composite material for electrodes of the present invention. On the surface of the hydrogen storage alloy powder 1 serving as a nucleus, a Ni layer 2 serving as a starting point of the hydrogen storage reaction is unevenly distributed. On this hydrogen storage alloy powder 1, particles 3 having an average particle diameter of 50 nm or less and comprising at least one of a group III metal element, an oxide of a group III metal element and a hydroxide of a group III metal element are arranged. ing. Although there are grain boundaries 4 between the particles 3, in the present invention, since the particles 3 are fine, many grain boundaries 4 can be provided. The hydrogen storage reaction corresponding to the charging reaction of the alkaline storage battery is a reaction in which protons in the electrolyte are diffused into the hydrogen storage alloy powder 1 through the Ni layer 2, but in the present invention there are many grain boundaries 4. Since the particles 3 prevent the corrosion of the hydrogen storage alloy powder 1, the hydrogen storage reaction is performed smoothly.

  1st invention is related with the composite material for electrodes, and the group III metal element, the oxide of group III metal element, and III on the surface of the hydrogen storage alloy powder 1 whose Ni content is 20 to 70 weight% in the whole composition It is characterized in that particles having an average particle diameter of 50 nm or less, which are made of at least one of group metal element hydroxides, are arranged. The functions of the hydrogen storage alloy powder 1, the Ni layer 2, the particles 3 and the grain boundaries 4 which are constituent elements of the electrode composite material are as described above. In order to fully exhibit this function, it is necessary to use the hydrogen storage alloy powder 1 whose Ni content in the entire composition is 20 to 70% by weight, and to make the average particle size of the particles 3 50 nm or less.

When the Ni content in the total composition of the hydrogen storage alloy powder 1 is less than 20% by weight, the Ni layer 2 that becomes the starting point of the hydrogen storage reaction becomes poor, and the high-temperature life characteristics deteriorate. To provide many of the Ni layer 2, the composition ratio of the hydrogen storage alloy powder 1 (for example _{MmNi 5, MmNi x (X>} 5) to) nonstoichiometric composition was biased Ni occupancy site It is effective to do. However, if the composition ratio is excessively biased toward Ni-occupied sites and, as a result, the Ni content in the total composition exceeds 70 wt%, the deviation from the ideal composition becomes severe and the theoretical capacity of the hydrogen storage alloy powder 1 is increased. Significantly decreases, battery reactivity itself decreases, and apparently high temperature life characteristics deteriorate.

When the average particle diameter of the particles 3 exceeds 50 nm, the grain boundaries 4 are poor, the hydrogen storage capacity is remarkably lowered, the battery reactivity itself is deteriorated, and the high temperature life characteristics are apparently lowered. The average particle size of the particles 3 is, for example, observed with a scanning electron microscope (SEM) or a tunneling electron microscope (T
EM) observation can be confirmed at a magnification of 100,000 times or more. As for the lower limit of the average particle diameter of the particles 3, as shown in the examples described later, since the effect of the present invention is effective if it is a region in which TEM observation is possible (for example, equivalent to 1 nm), the grain boundary 4 As long as exists, it is considered to be infinitesimal.

  For the particles 3, an oxide / hydroxide or a mixed system thereof can be selected at the time when the particles 3 are arranged on the surface of the hydrogen storage alloy powder 1. However, when an alkaline storage battery is configured using the composite material for an electrode of the present invention as a negative electrode active material, the oxide is partially changed to a hydroxide by a high-concentration alkaline aqueous solution, so even when a pure oxide is selected, the battery It exists as a mixed system of oxide and hydroxide in the system.

  The second invention is characterized in that, in the first invention, yttrium and / or erbium is selected as the group III metal element. Since the particles 3 made of yttrium and erbium have a low reaction resistance, the high-temperature life characteristics can be further enhanced as compared with the case where other group III metal elements are selected (the reason is under intensive analysis).

  The third invention is characterized in that, in the first invention, the amount of the particles 3 arranged is 0.4 to 2 wt% with respect to the hydrogen storage alloy powder 1. When the amount of the particles 3 is less than 0.5 parts by weight, the total amount is insufficient, the corrosion resistance effect by the particles 3 is reduced, the corrosion of the hydrogen storage alloy powder 1 is slightly accelerated, and the high-temperature life characteristics are slightly deteriorated. On the other hand, when the amount of the particles 3 is more than 2 parts by weight, the total amount becomes excessive, the hydrogen storage reaction is slightly lowered, and apparently the high temperature life characteristics are slightly lowered.

A fourth invention is characterized in that, in the first invention, the crystal structure of the hydrogen storage alloy powder 1 is a CaCu ₅ type. In the present invention, hydrogen storage alloy powder 1 having various crystal structures can be selected, but those having a CaCu ₅ type (ie, AB ₅ type) crystal structure have high hydrogenation reactivity at room temperature and easy activation. It is preferable from the viewpoint.

The fifth invention is characterized in that, in the fourth invention, the composition of the hydrogen storage alloy powder 1 contains rare earth elements, Co, Mn, and Al. This composition can be simply expressed as Mm (NiCoMnAl) ₅ . The rare earth element represented by Mm is preferable from the viewpoint of being inexpensive. Co is preferable from the viewpoint of enhancing the corrosion resistance of the hydrogen storage alloy powder 1 itself. Mn and Al are preferable from the viewpoint of lowering the equilibrium pressure of the hydrogen storage alloy powder 1 so that the hydrogen storage reaction can be performed under normal pressure. Mm preferably contains 40 to 50% Ce and 20 to 40% La, and further contains Pr and Nd from the viewpoint of improving both corrosion resistance and hydrogen storage reaction. In addition, it is one of the preferable embodiments that a part of Mm is substituted with Nb or Zr.

  A sixth invention is characterized in that, in the fifth invention, the Co content in the composition of the hydrogen storage alloy powder 1 is 0.5 to 6 wt%. From the viewpoint of enhancing the corrosion resistance of the hydrogen storage alloy powder 1 by Co, the content is preferably 0.5% by weight or more. However, if the content exceeds 6% by weight, the theoretical capacity of the hydrogen storage alloy powder 1 is insufficient. Apparently, the high temperature life characteristics are slightly deteriorated.

Based on the contents of the fourth to sixth inventions, the composition of the hydrogen storage alloy powder 1 suitable for the present invention is, for example, La _0.8 Nb _0.2 Ni _2.5 Co _2.4 Al _0.1 , La _0.8 Nb _0.2 Zr _0.03 Ni _3.8 Co _0.7 Al _0.5 , MmNi _3.65 Co _0.75 Mn _0.4 Al _0.3 , MmNi _2.5 Co _0.7 Al _0.8 , Mm _0.85 Zr _0.15 Ni _1.0 Al _0.8 V _0.2 and the like.

The seventh invention is characterized in that, in the first invention, the average particle diameter is 5 to 30 μm. Since the particle 3 layer in the electrode composite material is extremely thin, the average particle size of the electrode composite material itself is set in the same range by setting the average particle size of the hydrogen-absorbing alloy powder 1 serving as a nucleus to 5 to 30 μm. be able to. When the average particle size of the electrode composite material is less than 5 μm, the surface area of the hydrogen storage alloy powder 1 becomes slightly excessive, and the amount of the particles 3 is relatively insufficient, so the corrosion resistance is slightly reduced and the high-temperature life characteristics are slightly reduced. To do. On the other hand, when the average particle diameter exceeds 30 μm, the surface area of the hydrogen storage alloy powder 1 is slightly too small, and the amount of the particles 3 is relatively excessive, so that the hydrogen storage reaction is slightly reduced, and apparently high temperature life characteristics are obtained. Slightly lower.

  An eighth invention relates to an alkaline storage battery characterized by using the electrode composite material described in the first to seventh inventions as a negative electrode active material. By using the above-described composite material for electrodes as a negative electrode active material, it is possible to provide an alkaline storage battery having excellent high-temperature life characteristics.

  The ninth invention relates to a method for producing a composite material for an electrode, wherein the hydrogen storage alloy powder 1 having a Ni content of 20 to 70% by weight in the total composition is converted into an alkaline aqueous solution containing sodium hydroxide and / or potassium hydroxide aqueous solution. In the first step of immersing, the hydrogen storage alloy powder 1 is subjected to high-speed impact with at least one of a group III metal element, an oxide of a group III metal element, and a hydroxide of a group III metal element, and the hydrogen storage alloy powder 1 And a second step of arranging particles 3 having an average particle diameter of 50 nm or less on the surface of the substrate.

  Before the particles 3 are arranged, the hydrogen storage alloy powder 1 is immersed in an alkaline aqueous solution as a first step, so that a large amount of Ni layer 2 made of Ni unevenly distributed in the composition is formed on the surface of the hydrogen storage alloy powder 1. It can be provided and function efficiently as a starting point of the hydrogen storage reaction. In addition, when the above-described oxide or hydroxide is subjected to high-speed impact on the hydrogen storage alloy powder 1, it can be arranged on the surface of the hydrogen storage alloy powder 1 as particles 3 having an average particle size of 50 nm or less.

  The first step can be realized, for example, by adding the above-described alkaline aqueous solution to a metal container capable of raising the temperature and adding the hydrogen storage alloy powder 1 after sufficiently raising the temperature. Here, it is preferable that the alkaline aqueous solution is 80 ° C. or higher and the alkali salt (KOH, NaOH) concentration is 30 to 48% by weight because the Ni layer 2 can be provided quickly.

  The second step can be realized by using a hybridization system NHS-3 (trade name) manufactured by Nara Machinery Co., Ltd., etc., but the optimum conditions (rotation speed, processing time, etc.) of this apparatus are possible. ) Varies depending on the particle size and hardness of the hydrogen storage alloy powder 1 to be used. Therefore, care must be taken so that the hydrogen storage alloy powder 1 is not pulverized.

  It is desirable to provide a water washing step between the first step and the second step. Washing with water until the pH of the washing water containing the hydrogen storage alloy powder 1 becomes 9 or less is preferable because impurities (such as rare earth element hydroxide) remaining on the surface of the hydrogen storage alloy powder 1 can be eliminated. Moreover, it is desirable to oxidize the hydrogen storage alloy powder 1 after washing with water by mixing with an oxidizing agent in water. By oxidizing the dispersion containing the hydrogen storage alloy powder 1 to a pH of 7 or higher to remove a trace amount of hydrogen remaining in the hydrogen storage alloy powder 1 after washing with water, reaction with oxygen in the air is avoided. Is preferable. As an example of oxidation, there is a method in which hydrogen peroxide solution is stirred and introduced into water having a pH of 7 or higher in which alloy powder is dispersed. Hydrogen peroxide at the time of charging is preferably 0.005 to 1 part by weight based on 100 parts by weight of the hydrogen storage alloy powder 1.

  According to a tenth aspect, in the ninth aspect, a wet process for mixing the hydrogen storage alloy powder 1 with water is provided as a pre-process of the first process. By providing the wetting step, the hydrogen storage alloy powder 1 can be brought into contact with the alkaline aqueous solution in a wet state, so that excessive oxidation of the hydrogen storage alloy powder 1 caused by rapid contact with the high concentration alkaline aqueous solution is avoided. It is preferable from a viewpoint that can be made. In particular, when the hydrogen storage alloy powder 1 is obtained by dry pulverizing coarse particles of the hydrogen storage alloy, or when the hydrogen storage alloy powder 1 having a desired particle size is obtained directly by an atomizing method or the like, the wet storage step is first performed. Thus, it is preferably introduced into the first step.

  The eleventh invention is characterized in that, in the tenth invention, the hydrogen storage alloy powder 1 is pulverized in the wetting step so as to have an average particle diameter of 5 to 30 μm. As shown in claim 7, the average particle diameter of the composite material for an electrode of the present invention is 5 to 30 μm, but it is efficient if the average particle diameter is pulverized in the above-mentioned wet process. . In addition, as a wet process which can grind | pulverize the hydrogen storage alloy powder 1, wet ball mill grinding | pulverization etc. are mentioned.

  Next, an alkaline storage battery using the electrode composite material of the present invention as a negative electrode active material will be described.

  As the positive electrode, a known sintered nickel positive electrode can be used.

  Using the composite material for an electrode of the present invention, a conductive agent, a thickener, and a binder are added to prepare an alkaline storage battery negative electrode. The conductive agent used for the negative electrode is not particularly limited as long as it is a material having electronic conductivity. For example, graphite such as natural graphite (such as flake graphite), artificial graphite, expanded graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber Conductive fibers such as metal fibers, metal powders such as copper, and organic conductive materials such as polyphenylene derivatives may be used. Among them, artificial graphite, ketjen black, and carbon fiber are preferable, but these materials may be mixed and used. Further, these materials may be mechanically coated on the electrode material. The addition amount of the said electrically conductive agent is not specifically limited, For example, the range of 1-50 weight part is preferable with respect to 100 weight part of electrode materials, and the range of 1-30 weight part is more preferable.

  As the thickener used for the negative electrode, those capable of imparting viscosity to the electrode mixture paste can be used. Examples include carboxymethylcellulose (hereinafter abbreviated as CMC) and modified products thereof, polyvinyl alcohol, methylcellulose, polyethylene oxide, and the like.

As the binder used for the negative electrode, any of a thermoplastic resin and a thermosetting resin may be used as long as the electrode mixture can maintain the state of being bound to the current collector. For example, styrene-butadiene copolymer rubber (hereinafter abbreviated as SBR), polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer , Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene , Vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-he Sa hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer, ethylene - acrylic acid copolymer Na ⁺ ion crosslinking body, an ethylene - Methacrylic acid copolymer, ethylene-methacrylic acid copolymer Na ⁺ ion crosslinked product, ethylene-methyl acrylate copolymer, ethylene-methyl acrylate copolymer Na ⁺ ion crosslinked product, ethylene-methyl methacrylate copolymer Ethylene-methyl methacrylate copolymer Na ⁺ ion cross-linked body can be used alone or in combination.

  As the separator, a polypropylene nonwoven fabric separator or the like can be used.

  As the electrolytic solution, an electrolytic solution in which 40 g / L lithium hydroxide is dissolved in a potassium hydroxide aqueous solution having a specific gravity of 1.30 can be used.

By combining the above components, the alkaline storage battery of the present invention can be configured.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, a following example does not limit this invention.

(Example 1-1)
(I) Preparation of hydrogen storage alloy powder A mixture of simple substances of Mm, Ni and Mn in a predetermined ratio was melted in a high-frequency melting furnace, and hydrogen having a composition of MmNi _1.5 Mn _3.5 (Ni in the composition was 20% by weight) An ingot of a storage alloy was produced. The ingot was heated in an argon atmosphere at 1060 ° C. for 10 hours, and then pulverized into coarse particles. The obtained coarse particles were pulverized using a wet ball mill and then sieved with a sieve having a mesh size of 75 μm in a wet state to obtain a hydrogen storage alloy powder having an average particle size of 20 μm.

(Ii) First Step The above-described hydrogen storage alloy powder was brought into contact with an alkaline aqueous solution at 100 ° C. containing 40% by weight of sodium hydroxide for 50 minutes. After this step, the hydrogen storage alloy powder was washed with warm water until the pH became 9 or less, dried after dehydration.

(Iii) Second Step After charging 800 g of the hydrogen storage alloy powder passed through the first step into the sample introduction part of the hybridization system NHS-3 type (trade name) manufactured by Nara Machinery Co., Ltd., purity 4N The yttrium oxide powder was put into the sample feeding section, and the rotor was rotated at 5000 rpm (rpm is the number of revolutions per minute) for 10 minutes. As a result of analyzing the arrangement amount of yttrium oxide in the thus obtained electrode composite material by ICP analysis (specified in JiS K0116), it was 1% by weight with respect to the hydrogen storage alloy powder. Further, as a result of SEM observation of the shape of this yttrium oxide, it was particulate as shown schematically in FIG. 1, and the average particle diameter of the yttrium oxide particles was 30 nm.

(Iv) Production of negative electrode 0.15 part by weight of carboxymethyl cellulose (CMC, degree of etherification 0.7, degree of polymerization 1600), carbon black (AB) 0.3 weight with respect to 100 parts by weight of the above-mentioned composite material for electrodes And 0.7 parts by weight of a styrene butadiene copolymer (SBR) were added, and water was further added and kneaded to obtain a paste. This paste was applied to both surfaces of a core material made of nickel-plated iron punching metal (thickness 60 μm, hole diameter 1 mm, hole area ratio 42%). The coating film of the paste was pressed with a roller together with the core material after drying. Thus, a negative electrode having a thickness of 0.4 mm, a width of 35 mm, and a capacity of 2200 mAh was obtained. In addition, the exposed part of the core material was provided in the one end part along the longitudinal direction of a negative electrode.

(V) Production of Nickel Metal Hydride Battery Using a sintered nickel positive electrode with a capacity of 1500 mAh having an exposed part of a core material with a width of 35 mm at one end along the longitudinal direction, a nickel metal hydride battery with a nominal capacity of 1500 mAh in a 4/5 A size is produced. did. Specifically, the positive electrode and the negative electrode were wound through a separator (thickness: 100 μm) made of a sulfonated polypropylene nonwoven fabric to produce a cylindrical electrode plate group. In the electrode plate group, the exposed portion of the positive electrode core material that does not carry the positive electrode mixture and the exposed portion of the negative electrode core material that does not carry the negative electrode mixture were exposed on the opposite end surfaces. A positive electrode current collector plate was welded to the end face of the electrode plate group from which the positive electrode core material was exposed. While the negative electrode current collector plate was welded to the end face of the electrode plate group where the negative electrode core material was exposed, the sealing plate and the positive electrode current collector plate were made conductive through the positive electrode lead. The electrode plate group was accommodated in a battery case made of a cylindrical bottomed can with the negative electrode current collector plate facing downward, and the negative electrode lead connected to the negative electrode current collector plate was welded to the bottom of the battery case. Furthermore, after injecting an electrolytic solution in which lithium hydroxide was dissolved at a concentration of 40 g / L into a potassium hydroxide aqueous solution having a specific gravity of 1.3, the opening of the battery case was sealed with a sealing plate having a gasket on the periphery, A nickel metal hydride storage battery was produced. This is Example 1-1.

(Example 1-2)
A nickel-metal hydride storage battery produced in the same manner as in Example 1-1, except that the composition of the hydrogen storage alloy powder was MmNi ₅ (Ni in the composition was 70% by weight) is referred to as Example 1-2.

(Example 1-3)
Example 1-3 is a nickel-metal hydride storage battery produced in the same manner as in Example 1-1 except that the composition of the hydrogen storage alloy powder is MmNi _3.7 Mn _1.3 (Ni in the composition is 50% by weight).

(Examples 1-4 to 6)
The number of rotations of the hybridization system in the second step was 8000, 6000, and 3000 rpm, and the average particle diameter of the yttrium oxide particles was 1 nm (Example 1-4), 10 nm (Example 1-5), and 50 nm (Example). A nickel-metal hydride storage battery was produced in the same manner as in Example 1-3 except that 1-6). In addition, the average particle diameter of the yttrium oxide of Example 1-4 was confirmed by TEM observation.

(Comparative Example 1-1)
A nickel hydride storage battery produced in the same manner as in Example 1-1 except that the composition of the hydrogen storage alloy powder was changed to MmNi _1.4 Mn _3.6 (Ni in the composition was 18% by weight) is referred to as Comparative Example 1-1.

(Comparative Example 1-2)
A nickel hydride storage battery produced in the same manner as in Example 1-1 except that the composition of the hydrogen storage alloy powder was MmNi _5.1 (Ni in the composition was 73% by weight) is referred to as Comparative Example 1-2.

(Comparative Example 1-3)
A nickel-metal hydride storage battery produced in the same manner as in Example 1-3, except that the rotation speed of the hybridization system in the second step was 2500 rpm and the average particle size of the yttrium oxide particles was 60 nm, Comparative Example 1- 3.

  Each of the above examples and comparative examples were evaluated by the following methods. The results are shown in (Table 1).

(High temperature life characteristics)
The nickel metal hydride storage batteries of each Example and Comparative Example were charged at a 10 hour rate (150 mA) for 15 hours in a 40 ° C. environment, and discharged at a 5 hour rate (300 mA) until the battery voltage reached 1.0V. This charge / discharge cycle was repeated 100 times. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the second cycle was obtained as a percentage as the capacity maintenance rate, and is shown in (Table 1).

水素吸蔵合金粉末の全組成中のＮｉ含有量が２０重量％を下回った比較例１−１は、水素吸蔵反応の起点となるＮｉ層が乏しくなった影響で高温寿命特性が低下した。逆に組成比をＮｉ過剰にして全組成中のＮｉ含有量が７０重量％を上回った比較例１−２は、水素吸蔵合金粉末１の理論容量が著しく低下し、電池反応性そのものが低下して見かけ上高温寿命特性が低下した。また酸化イットリウム粒子の平均粒径が５０ｎｍを超えた比較例１−３は、粒子間の粒界が乏しくなって水素吸蔵能力が著しく低下し、電池反応性そのものが悪化して見かけ上高温寿命特性が低下した。

In Comparative Example 1-1 in which the Ni content in the total composition of the hydrogen storage alloy powder was less than 20% by weight, the high temperature life characteristics were deteriorated due to the influence of the Ni layer that became the starting point of the hydrogen storage reaction. Conversely, in Comparative Example 1-2, in which the composition ratio was excessively Ni and the Ni content in the total composition exceeded 70% by weight, the theoretical capacity of the hydrogen storage alloy powder 1 was significantly reduced, and the battery reactivity itself was lowered. Apparently the high temperature life characteristics deteriorated. In Comparative Example 1-3 in which the average particle size of the yttrium oxide particles exceeded 50 nm, the intergranular grain boundary was poor, the hydrogen storage capacity was remarkably lowered, and the battery reactivity itself was deteriorated, resulting in apparent high temperature life characteristics. Decreased.

  In contrast to these comparative examples, Examples 1-1 to 6 in which the Ni content in the total composition of the hydrogen storage alloy powder and the average particle diameter of the yttrium oxide particles were optimized showed relatively good high-temperature life characteristics. . In particular, Example 1-6, in which the average particle diameter of yttrium oxide was 1 nm, showed good high-temperature life characteristics due to the presence of many grain boundaries between particles.

(Examples 2-1 to 5)
The composition of the hydrogen storage alloy powder is MmNi _4.1 Mn _0.4 Al _0.3 Co _0.4 (Ni in the composition is 55 wt%, Co is 5 wt%), and the group III is formed on the surface of the hydrogen storage alloy powder described above in the second step. Examples of metal element oxides include yttrium oxide (Example 2-1), erbium oxide (Example 2-2), thulium oxide (Example 2-3), yttrium oxide (Example 2-4), and lutetium oxide (implementation). Example 2-5) was arranged under the same conditions as in Example 1-1 (average particle diameter 30 nm, arrangement amount 1 wt%). Otherwise, a nickel-metal hydride storage battery was produced in the same manner as in Example 1-1.

(Examples 2-6 to 10)
The number of rotations of the hybridization system in the second step was set to 8000, 6000, and 3000 rpm, and the amount of yttrium oxide particles arranged was 0.3 wt% with respect to the hydrogen storage alloy powder (Example 2-6), 0.4 Except for the weight% (Example 2-7), 0.5 wt% (Example 2-8), 2 wt% (Example 2-9) and 2.2 wt% (Example 2-10). Produced the nickel-metal hydride storage battery similarly to Example 2-1.

(Examples 2-11 to 14)
The composition of the hydrogen storage alloy powder is MmNi _4.28 Mn _0.4 Al _0.3 Co _0.02 (Example 2-11, Ni in the composition is 59% by weight, Co is 0.3%), MmNi _4.27 Mn _0.4 Al _0.3 Co _0.03 (Example) 2-12, Ni in composition is 60% by weight, Co is 0.5%), MmNi _3.86 Mn _0.4 A
l _0.3 Co _0.44 (Example 2-13, Ni in composition is 53 wt%, Co is 6%) and MmNi _3.78 Mn _0.4 Al _0.3 Co _0.52 (Example 2-14, Ni in composition is 52 wt%, A nickel-metal hydride storage battery was produced in the same manner as in Example 2-1, except that Co was 7%.

(Examples 2-15 to 19)
The coarse particles of the hydrogen storage alloy were pulverized by a wet ball mill for 60 minutes, 50 minutes, 40 minutes, 25 minutes and 15 minutes, and the average particle size of the hydrogen storage alloy powder was 3 μm (Example 2-15), 5 μm (Example 2-15) Example 2-16) Nickel metal hydride storage battery as in Example 2-1, except that it was set to 10 μm (Example 2-17), 30 μm (Example 2-18) and 35 μm (Example 2-19) Was made. About each of these Examples, the high temperature life characteristic was evaluated by the same method as Example 1. The results are shown in (Table 2).

ＩＩＩ族金属元素の酸化物として酸化イットリウムおよび酸化エルビウムを用いた実施例２−１および２−２は、他のＩＩＩ族金属元素の酸化物を用いた実施例２−３〜５と比較して、より良好な高温寿命特性を示した。この理由として、酸化イットリウム粒子および酸化エルビウム粒子は反応抵抗が低いため、電池反応が活発化したことが挙げられる。

Examples 2-1 and 2-2 using yttrium oxide and erbium oxide as oxides of Group III metal elements are compared with Examples 2-3 to 5 using other Group III metal element oxides. It showed better high-temperature life characteristics. This is because the battery reaction is activated because the reaction resistance of yttrium oxide particles and erbium oxide particles is low.

  In Example 2-6, in which the amount of yttrium oxide particles disposed was less than 0.4 wt% with respect to the hydrogen storage alloy powder, the total amount was insufficient and the corrosion resistance was reduced, and the corrosion of the hydrogen storage alloy powder was somewhat Due to the advance, the high-temperature life characteristics slightly decreased. Conversely, in Example 2-10 in which the arrangement amount of yttrium oxide particles exceeded 2% by weight, the total amount thereof was excessive, the hydrogen storage reaction was slightly reduced, and apparently the high-temperature life characteristics were slightly deteriorated. From the above results, it can be seen that the preferable range of the amount of group III metal element oxide particles is 0.4 to 2% by weight with respect to the hydrogen storage alloy powder.

In Example 2-11 in which the Co content in the composition of the hydrogen storage alloy powder was less than 0.5% by weight, the high temperature life characteristics were slightly deteriorated due to the slightly insufficient corrosion resistance of the hydrogen storage alloy powder 1 itself. On the other hand, in Example 2-14 in which the Co content exceeded 6% by weight, the high-temperature life characteristics apparently slightly decreased due to the lack of the theoretical capacity of the hydrogen storage alloy powder. From the above results, it can be seen that the preferable range of the Co content in the hydrogen storage alloy powder composition is 0.5 to 6% by weight.

  In Example 2-15 in which the average particle size of the composite material for electrodes is less than 5 μm, the surface area of the hydrogen storage alloy powder is slightly excessive, and the amount of yttrium oxide particles is relatively insufficient, so the corrosion resistance is slightly reduced. The high temperature life characteristics were slightly degraded. On the contrary, in Example 2-19 in which the average particle size exceeds 30 μm, the surface area of the hydrogen storage alloy powder is slightly too small, and the amount of yttrium oxide particles is relatively excessive, so the hydrogen storage reaction is slightly reduced, and apparently The high temperature life characteristics were slightly degraded. From the above results, it can be seen that the preferable range of the average particle diameter is 5 to 30 μm.

  In addition, when a part of the nickel metal hydride storage battery of each example was decomposed before evaluating the high-temperature life characteristics, it became clear that some of the group III metal element oxide particles were converted from oxide to hydroxide. . From this, it can be seen that the effect of the Group III metal element compound arranged on the surface of the hydrogen storage alloy powder is the same regardless of whether it is an oxide or a hydroxide.

(Examples 3-1 to 5)
The composition of the hydrogen storage alloy powder is MmNi _4.1 Mn _0.4 Al _0.3 Co _0.4 (Ni in the composition is 55 wt%, Co is 5 wt%), and the group III is formed on the surface of the hydrogen storage alloy powder described above in the second step. Examples of yttrium (Example 3-1), erbium (Example 3-2), thulium (Example 3-3), yttrium (Example 3-4) and lutetium (Example 3-5) as metal elements Arrangement was performed under the same conditions as in 1-1 (average particle diameter 30 nm, arrangement amount 1 wt%). Otherwise, a nickel-metal hydride storage battery was produced in the same manner as in Example 1-1. About each of these Examples, the high temperature life characteristic was evaluated by the same method as Example 1. The results are shown in (Table 3).

酸化物や水酸化物に代えてＩＩＩ族金属元素を用いた場合でも、効果は同様であることがわかる。なお理由は不明であるが、イットリウムおよびエルビウム以外の金属元素を用いても、実施例２に見られたような顕著な差は見られなかった。

It can be seen that the effect is the same even when a group III metal element is used instead of the oxide or hydroxide. Although the reason is unknown, no significant difference as seen in Example 2 was found even when metal elements other than yttrium and erbium were used.

  By utilizing the present invention, the high-temperature life characteristics of alkaline storage batteries can be greatly improved, so that it can be used as a power source for all devices and in the field of power sources for hybrid vehicles used in harsh environments. It can be expected to bring about a great effect.

Schematic sectional view showing the vicinity of the surface of the composite material for electrodes of the present invention

Explanation of symbols

1 Hydrogen storage alloy powder 2 Ni layer 3 Particles 4 Grain boundary

Claims (8)

An electrode composite material having an average particle size of 5 to 30 μm used for an alkaline storage battery,
On the surface where the Ni layer of the hydrogen storage alloy powder having a Ni content of 20 to 70% by weight in the total composition is unevenly distributed, a group III metal element, an oxide of a group III metal element, and a hydroxide of a group III metal element An electrode composite material comprising 0.4 to 2% by weight of at least one particle having an average particle diameter of 50 nm or less with respect to the hydrogen storage alloy powder . 2. The electrode composite material according to claim 1, wherein yttrium and / or erbium is selected as the group III metal element. 2. The composite material for an electrode according to claim 1, wherein the crystal structure of the hydrogen storage alloy powder is CaCu ₅ type. The composite material for an electrode according to claim 3, wherein the composition of the hydrogen storage alloy powder contains rare earth elements, Co, Mn, and Al. The composite material for an electrode according to claim 4, wherein the Co content in the composition of the hydrogen storage alloy powder is 0.5 to 6% by weight. Alkaline storage battery characterized by using the claims 1-5 electrode composite material described as a negative electrode active material. A method for producing a composite material for an electrode used in an alkaline storage battery,
A first step of immersing a hydrogen storage alloy powder having an average particle size of 5 to 30 μm having an Ni content of 20 to 70% by weight in the total composition in an aqueous alkali solution containing sodium hydroxide and / or potassium hydroxide aqueous solution; The hydrogen storage alloy powder is subjected to high-speed impact with at least one of a group III metal element, an oxide of a group III metal element and a hydroxide of a group III metal element, and an average particle size of 50 nm is formed on the surface of the hydrogen storage alloy powder. The manufacturing method of the composite material for electrodes characterized by providing the 2nd process of arrange | positioning the following particles 0.4 to 2weight% . 8. The method for producing a composite material for an electrode according to claim 7 , wherein a wet process of mixing the hydrogen storage alloy powder with water is provided as a pre-process of the first process.

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