WO2018123579A1 - Method for producing negative electrode material - Google Patents

Abstract

The present invention provides a technique which is able to improve the electrical conductivity of a negative electrode material that comprises hydrogen storage alloy particles. A method for producing a negative electrode material, which comprises: a plating solution preparation step wherein a plating solution containing a nickel salt, a hetero element-containing organic compound and an aqueous solvent is obtained; and a plating step wherein a hydrogen storage alloy particle dispersion liquid, which contains an aqueous solvent and hydrogen storage alloy particles, the plating solution and a reducing agent are mixed with each other, thereby obtaining a negative electrode material wherein a plating layer containing nickel is formed on the hydrogen storage alloy particles.

Description

Method for producing negative electrode material

The present invention relates to a method for producing a negative electrode material having a hydrogen storage alloy.

A technique using a hydrogen storage alloy as a negative electrode active material for nickel metal hydride batteries is known. Further, a technique for forming a metal layer on the surface of the hydrogen storage alloy particles is known for the purpose of improving the conductivity and durability of the hydrogen storage alloy particles and suppressing the oxidation of the surface of the hydrogen storage alloy particles.
For example, Patent Document 1 introduces a negative electrode material in which a metal layer is provided on the surface of hydrogen storage alloy particles. In paragraph [0008] of Patent Document 1, it is described that by providing the metal layer, the area of the hydrogen storage alloy exposed on the surface of the negative electrode material is reduced, and oxidation of the surface of the hydrogen storage alloy particles is suppressed. ing. Further, paragraph [0009] of Patent Document 1 describes that the surface of the hydrogen storage alloy particles is stabilized by the metal layer, thereby suppressing the oxidation of the surface of the hydrogen storage alloy particles.
In Patent Document 1, as a method of forming the metal layer, a compound serving as a material of the metal layer is dissolved in an acidic solution, and the hydrogen storage alloy particles are immersed in an acidic solution containing the metal, A method of depositing metal on the surface of hydrogen storage alloy particles (see paragraph [0018]) is disclosed. As another method for forming the metal layer, a mixture of hydrogen storage alloy particles and metal powder is heated to form a metal layer in which a part of the surface of the hydrogen storage alloy particles and the metal powder are in solid solution. (See paragraph [0021]).

JP 2000-40509 A

In recent years, further improvement in battery characteristics has been desired, and further improvements in various characteristics have been desired for the negative electrode material in order to contribute to the improvement in battery characteristics. As the negative electrode material having hydrogen storage alloy particles, a material having excellent conductivity is particularly desired.
This invention is made | formed in view of this situation, and makes it a subject to provide the technique which can improve the electroconductivity of the negative electrode material which has a hydrogen storage alloy particle.

The method for producing the negative electrode material of the present invention is as follows.
A plating solution preparation step for obtaining a plating solution containing a nickel salt, a heteroelement-containing organic compound and an aqueous solvent;
A negative electrode material in which a nickel-containing plating layer is formed on the hydrogen storage alloy particles by mixing a hydrogen storage alloy particle dispersion containing an aqueous solvent and hydrogen storage alloy particles, the plating solution, and a reducing agent. And a plating step to obtain

According to the method for producing a negative electrode material of the present invention, a negative electrode material having excellent conductivity can be produced.

It is the surface analysis result of the negative electrode material of Example 1 measured by XPS. It is the surface analysis result of the negative electrode material of the comparative example 2 measured by XPS. 2 is a SEM image of a negative electrode material of Example 1. 4 is a SEM image of a negative electrode material of Example 3. 6 is a SEM image of a negative electrode material of Comparative Example 2. It is the result of the cycle test of the nickel metal hydride battery of Example 1 and Comparative Example 1. 3 is an X-ray diffraction chart of a negative electrode material of Example 2. FIG. 3 is an X-ray diffraction chart of a negative electrode material of Comparative Example 1. It is the surface analysis result of the negative electrode material of Example 4 measured by XPS. 3 is a surface analysis result of the negative electrode material of Example 1-A measured by XPS. It is the surface analysis result of the negative electrode material of Example 5 and Example 1 measured by XPS. It is a surface analysis result of the negative electrode material of Example 6 measured by XPS. It is the surface analysis result of the negative electrode material of Comparative Example 1-A measured by XPS. It is a surface analysis result of the negative electrode material of Example 11 measured by XPS. It is a surface analysis result of the negative electrode material of Example 11 measured by XPS. It is the figure which compared the charging curve of the nickel metal hydride battery of Example 10 and Example 11. FIG. It is the figure which compared the charging curve of the nickel metal hydride battery of Example 11 and Example 12. It is a surface analysis result of the negative electrode material of Example 12 measured by XPS. It is a surface analysis result of the negative electrode material of Example 12 measured by XPS. It is the surface analysis result of the negative electrode material of Example 14 measured by XPS. It is the surface analysis result of the negative electrode material of Example 14 measured by XPS. 10 is a SEM image of a negative electrode material of Example 12. 16 is a SEM image of a negative electrode material of Example 14. 6 is a charge / discharge curve representing the relationship between voltage and charge time or discharge time of nickel metal hydride batteries of Example 10 and Examples 12 to 14. FIG. It is a charging / discharging curve showing the relationship between the voltage and charging time or discharging time of the nickel metal hydride batteries of Example 10, Example 15 and Example 16. It is a surface analysis result of the negative electrode material of Example 17 measured by XPS. It is a surface analysis result of the negative electrode material of Example 17 measured by XPS. It is a surface analysis result of the negative electrode material of Example 18 measured by XPS. It is a surface analysis result of the negative electrode material of Example 18 measured by XPS. It is a charging / discharging curve showing the relationship between the voltage and charging time or discharging time of the nickel metal hydride batteries of Example 10, Example 17 and Example 18. 10 is a SEM image of a negative electrode material of Example 19. 10 is a SEM image of a negative electrode material of Example 20. It is the surface analysis result of the negative electrode material of Example 20 measured by XPS. It is the surface analysis result of the negative electrode material of Comparative Example 1-B measured by XPS.

Hereinafter, the method for producing the negative electrode material of the present invention will be described in detail. Hereinafter, the manufacturing method of the negative electrode material of the present invention may be referred to as the manufacturing method of the present invention or simply the manufacturing method as necessary.

Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y. And a new numerical value range can be comprised by combining these arbitrarily including those upper limit values and lower limit values and numerical values listed in the embodiments. Furthermore, numerical values arbitrarily selected from any one of the numerical ranges described above can be used as the upper and lower numerical values of the new numerical range.

As described above, the production method of the present invention is a method of producing a negative electrode material having a plating layer on hydrogen storage alloy particles, and the negative electrode material of the present invention has a plating layer on hydrogen storage alloy particles. Unlike the conventional manufacturing method introduced in Patent Document 1, the manufacturing method of the present invention is a method of forming a metal layer by electroless plating using a reducing agent.

The manufacturing method of the present invention includes a plating solution preparation step and a plating step.
The plating solution preparation step is a step of obtaining a plating solution containing a nickel salt, a hetero element-containing organic compound, and an aqueous solvent. The plating solution may further contain a metal salt. The said metal salt means the salt of metals other than nickel. Hereinafter, unless otherwise specified, the term “metal” used herein refers to a metal contained in the metal salt.

As described above, the plating solution contains a nickel salt, a heteroelement-containing organic compound, an aqueous solvent, and, if necessary, a metal salt. Hereinafter, description will be made assuming that the plating solution contains a nickel salt and a metal salt.
Nickel contained in the nickel salt and metal contained in the metal salt are main materials constituting the plating layer. The aqueous solvent is a solvent that dissolves nickel salts, metal salts, and the like. That is, nickel and metal are considered to exist as ions in the plating solution. The hetero element-containing organic compound is considered to function as a complexing agent that forms a complex with the nickel ions and metal ions in the plating solution. That is, according to the production method of the present invention, nickel and metal are considered to exist as stable complexes in the plating solution.

The plating step includes mixing a hydrogen storage alloy particle dispersion containing an aqueous solvent and hydrogen storage alloy particles, the above plating solution, and a reducing agent, and a plating layer containing nickel and metal on the hydrogen storage alloy particles. This is a step of obtaining a negative electrode material in which is formed.

In the plating step, the above plating solution, the hydrogen storage alloy particle dispersion, and the reducing agent are mixed. Then, nickel ions and metal ions in the plating solution are reduced by electrons supplied from the reducing agent to become zero-valent metal, and are deposited on the surfaces of the hydrogen storage alloy particles. And the said nickel and metal which precipitated on the surface of the hydrogen storage alloy particle comprise the plating layer on a hydrogen storage alloy particle.

As described above, nickel ions and metal ions are complexed in the plating solution, and the nickel ions and metal ions are considered to be dissolved in a stable state. According to the production method of the present invention, it is considered that a uniform plating layer can be obtained by stably dissolving nickel ions and metal ions in this manner until immediately before being subjected to the plating step.

By the way, in the electroless plating method that does not use a complexing agent, it is considered that a part of nickel ions and metal ions in the plating solution is precipitated as a hydroxide. When the plating solution in such a state is used in the plating process, there is a possibility that a uniform plating layer cannot be obtained. In addition, a plating layer containing a large amount of nickel hydroxide and metal hydroxide may be obtained. In these cases, it may be difficult to sufficiently increase the conductivity of the negative electrode material composed of the hydrogen storage alloy particles and the plating layer.

According to the production method of the present invention, as described above, the hetero-element-containing organic compound, that is, the complexing agent, is mixed with the nickel salt and, if necessary, the metal salt in the plating solution, thereby suppressing nickel and metal hydroxylation. It is considered that the proportion of nickel hydroxide and metal hydroxide in the plating layer can be reduced. As a result, according to the production method of the present invention, a negative electrode material having excellent conductivity can be obtained.
In addition, as an aspect of the negative electrode material of the present invention, a material whose surface has a mesh shape can be exemplified. The negative electrode material whose surface has a mesh shape has a larger specific surface area than the negative electrode material whose surface has a smooth shape, and it is considered that the battery reaction proceeds smoothly.

The plating solution preparation step in the method for producing a negative electrode material of the present invention is a step of obtaining a plating solution containing a nickel salt, a hetero element-containing organic compound, an aqueous solvent, and, if necessary, a metal salt.

Examples of the nickel salt used for the plating solution include nickel sulfate, nickel nitrate, nickel chloride, nickel acetate, nickel sulfamate and the like.

The metal salt used in the plating solution may be a salt of various metals that can be used for electroless plating. In view of the possibility of plating and the oxidation resistance of the metal, the metals include Cu, Sn, Zn, Co, Au, Ag, Pt, Pd, Rh, Ru, In, Bi, or Cd is preferable. In terms of conductivity, the preferred order is generally Ag, Cu, Au, Rh, Co, Zn, Ru, Pt, Pd, Cd, In, Sn, and Bi. In terms of spreadability, Au, Ag, Cu, Sn, Cd, In, Zn, Pt and Pd are preferable.
Examples of metal salts include sulfates, nitrates, chlorides and the like of these metals. More specifically, examples of the metal salt include cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt acetate, cobalt sulfamate, copper sulfate, copper nitrate, copper chloride, silver sulfate, silver nitrate, hexachloride platinum acid, potassium gold cyanide. And gold sodium sulfite. As a metal salt, only 1 type may be used and multiple types may be used together.
As will be described later, it is considered that the negative electrode material of the present invention whose surface has a mesh shape is formed by heating the negative electrode material after electroless plating. In order to obtain a negative electrode material having a network shape by the heating, it is considered that the plating layer preferably contains at least one selected from a nickel indium alloy, a nickel bismuth alloy, a nickel tin alloy, and a nickel cadmium alloy.
And in this case, as a metal salt used in the plating solution, indium sulfate, indium nitrate, indium chloride, indium acetate, indium sulfamate, bismuth sulfate, bismuth nitrate, bismuth chloride, bismuth acetate, stannous sulfate, stannous chloride, Examples thereof include stannous acetate, cadmium sulfate, cadmium nitrate, cadmium chloride, cadmium acetate, and cadmium sulfamate.

The ratio of the nickel salt to the metal salt to be mixed in the plating solution is not particularly limited, but the mass ratio is preferably in the range of nickel salt: metal salt = 1: 99 to 99: 1, and nickel salt: metal salt. = 20: 80 to 80:20 is more preferable, and nickel salt: metal salt = 30: 70 to 70:30 is more preferable.
Hereinafter, if necessary, nickel and metal are collectively referred to as plating metal. The salt of the plating metal is called a plating metal salt. Examples of the concentration of the plating metal salt in the plating solution include a range of 2 to 500 g / L.

The plating solution further contains a heteroelement-containing organic compound. As described above, the heterometal-containing organic compound forms a complex with the plating metal ion in the plating solution.
The hetero element in the hetero element-containing organic compound means N, O, P or S. Examples of hetero element-containing organic compounds include amino groups, amide groups, imide groups, imino groups, cyano groups, azo groups, hydroxyl groups, alkoxy groups, carboxyl groups, ester groups, ether groups, carbonyl groups, which can be coordinated to metal ions, Phosphoric acid group, phosphoric acid ester group, phosphonic acid group, phosphonic acid ester group, phosphinic acid group, phosphinic acid ester group, phosphenic acid group, phosphenic acid ester group, phosphinic acid group, phosphinic acid ester group, thiol group, Examples include organic compounds having a sulfide group, a sulfinyl group, a sulfonyl group, a sulfonic acid group, a thiocarboxyl group, a thioester group, or a thiocarbonyl group.
In particular, the hetero element-containing organic compound is preferably a chelate compound having a plurality of the above groups and capable of coordinating to a metal ion at a plurality of locations.
Alternatively, the hetero element-containing organic compound preferably has any of a carboxyl group, an amino group, a hydroxyl group, a ketone group, and an imide group.

Specific examples of chelate compounds include polyamine compounds such as ethylenediamine and diethylenetriamine, glycine, alanine, cysteine, glutamine, arginine, asparagine, aspartic acid, serine, ethylenediaminetetraacetic acid and other amino acids, malonic acid, succinic acid, glutaric acid, maleic acid. Acids, dicarboxylic acids such as phthalic acid, glycolic acid, lactic acid, tartronic acid, glyceric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, γ-hydroxybutyric acid, malic acid, tartaric acid, citramalic acid, citric acid, isocitric acid, leucine Examples include hydroxycarboxylic acids such as acids, mevalonic acid, pantoic acid, quinic acid, shikimic acid, salicylic acid, gentisic acid, orthoric acid, mandelic acid, benzylic acid, and 2-hydroxy-2-phenylpropionic acid. That.

These hetero element-containing organic compounds may be used alone or in combination.
The concentration of the heteroelement-containing organic compound in the plating solution may be an amount that can form a complex with the plating metal in the plating solution, and can be appropriately set according to the type and amount of the plating metal. The compounding amount of the heteroelement-containing organic compound in the plating solution is preferably stoichiometrically an amount capable of forming a complex with more than half of the plating metal, and forms a complex with more than 2/3 of the plating metal. It is more preferable that the amount be capable of forming a complex with the total amount of the plating metal. The hetero element-containing organic compound is particularly preferably blended in an amount that is at least an amount capable of forming a complex with the total amount of the plating metal, that is, an excess amount.

The aqueous solvent used in the plating solution may be water as a main component, and may contain a solvent other than water as necessary. Examples of the solvent other than water include methanol, ethanol, propanol, acetone, acetylacetone, methyl ethyl ketone, ethyl acetate, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, acetonitrile, and cyclohexanone. These solvents may be used alone or in combination with water.

Prior to the plating step, a treatment step of forming catalyst nuclei as active points for the growth of the plating layer on the surface of the hydrogen storage alloy particles may be performed. Furthermore, the surface of the hydrogen storage alloy particles may be modified by treating the hydrogen storage alloy particles with a surfactant or a basic aqueous solution before the treatment step. The treatment process may be performed according to a regular method.

As a specific treatment step, for example, a step of bringing hydrogen storage alloy particles into contact with a Pd-containing solution and attaching Pd to the surface of the hydrogen storage alloy particles can be mentioned.

An example of a more specific processing process will be described. First, the hydrogen storage alloy particles and the tin chloride hydrochloric acid aqueous solution are mixed to remove the oxide film on the surface of the hydrogen storage alloy particles and adsorb divalent tin ions on the surface of the hydrogen storage alloy particles. The hydrogen storage alloy particles are separated by filtration. Next, the hydrogen storage alloy particles are mixed with a palladium chloride / hydrochloric acid aqueous solution, thereby adhering zero-valent Pd to the hydrogen storage alloy particles. The phenomenon here is due to the progress of the reaction Sn (II) + Pd (II) → Pd (0) + Sn (IV) on the surface of the hydrogen storage alloy particles. It is considered that catalyst nuclei can be formed on the surface of the hydrogen storage alloy particles by the above-described method.

Further, as another example of the treatment step, there can be mentioned a method of bringing hydrogen storage alloy particles into contact with an aqueous solution containing Pd (II) and Sn (II) such as palladium chloride and tin chloride. Even with this method, zero-valent Pd can be adhered to the surface of the hydrogen storage alloy particles. In the treatment step, a strong acid aqueous solution such as concentrated hydrochloric acid may be used instead of the tin chloride aqueous solution.

As the tin chloride aqueous solution, a commercial product such as a brand name Pink Schumer manufactured by Nippon Kanisen Co., Ltd. may be used, or an aqueous solution in which tin chloride is dissolved in hydrochloric acid may be used. Moreover, as palladium chloride aqueous solution, commercial items, such as brand name Red Schumer made by Nippon Kanisen Co., Ltd., may be used, or an aqueous solution in which palladium chloride is dissolved in water may be used. The above-mentioned complexing agent and other additives such as a pH adjusting agent and a buffering agent may be added to the palladium chloride aqueous solution.
After the treatment step, a washing step of washing the hydrogen storage alloy particles with water or an acid aqueous solution may be added.

The plating step includes mixing a hydrogen storage alloy particle dispersion containing an aqueous solvent and hydrogen storage alloy particles, the above plating solution, and a reducing agent, and a plating layer containing nickel and metal on the hydrogen storage alloy particles. This is a step of obtaining a negative electrode material in which is formed.

What is necessary is just to use what was demonstrated in the column of the above-mentioned plating solution as an aqueous solvent of a hydrogen storage alloy particle dispersion. The aqueous solvent for the hydrogen storage alloy particle dispersion may be different from the aqueous solvent for the plating solution, but it is preferable to use the same one.

Hydrogen storage alloy particles refer to particulate hydrogen storage alloys. The hydrogen storage alloy is not limited as long as it is used as a negative electrode active material of a nickel metal hydride battery. The hydrogen storage alloy is basically an alloy of metal A, which easily reacts with hydrogen, but is inferior in hydrogen releasing ability, and metal B, which does not easily react with hydrogen but has excellent hydrogen releasing ability. A includes a group 2 element such as Mg, a group 3 element such as Sc and a lanthanoid, a group 4 element such as Ti and Zr, a group 5 element such as V and Ta, and a misch containing a plurality of rare earth elements. Examples thereof include metal (hereinafter sometimes abbreviated as Mm), Pd, and the like. Examples of B include Fe, Co, Ni, Cr, Pt, Cu, Ag, Mn, Zn, and Al.

Specific hydrogen-absorbing alloy, AB ₅ type showing a hexagonal CaCu ₅ type crystal structure, hexagonal MgZn ₂ type or AB ₂ type showing a cubic MgCu ₂ type crystal structure, AB type indicating the cubic CsCl-type crystal structure , A ₂ B type showing hexagonal Mg ₂ Ni type crystal structure, solid solution type showing body-centered cubic crystal structure, and AB ₃ type and A ₂ B _{7 in which} AB ₅ type and AB ₂ type crystal structures are combined Examples include molds and A ₅ B ₁₉ types. The hydrogen storage alloy may have one of the above crystal structures, or may have a plurality of the above crystal structures.

Examples of the AB ₅ type hydrogen storage alloy include LaNi ₅ , CaCu ₅ , and MmNi ₅ . Examples of the AB ₂ type hydrogen storage alloy include MgZn ₂ , ZrNi ₂ , and ZrCr ₂ . Examples of the AB type hydrogen storage alloy include TiFe and TiCo. Examples of the A ₂ B type hydrogen storage alloy include Mg ₂ Ni and Mg ₂ Cu. Examples of the solid solution type hydrogen storage alloy include Ti—V, V—Nb, and Ti—Cr. An example of the AB ₃ type hydrogen storage alloy is CeNi ₃ . Ce ₂ Ni ₇ can be exemplified as the A ₂ B ₇ type hydrogen storage alloy. Examples of the A ₅ B ₁₉ type hydrogen storage alloy include Ce ₅ Co ₁₉ and Pr ₅ Co ₁₉ . In each of the above crystal structures, some of the metals may be replaced with one or more other types of metals or elements.

The hydrogen storage alloy particles need only be particles composed of the above-mentioned hydrogen storage alloy, and the shape thereof is not particularly limited. However, in consideration of the use as a negative electrode active material, it is preferably sufficiently small. Specifically, the average particle size of the hydrogen storage alloy particles is preferably within the range of 1 to 100 μm, more preferably within the range of 3 to 50 μm, and even more preferably within the range of 5 to 30 μm. Furthermore, the average particle diameter of the hydrogen storage alloy particles is preferably 27 μm or less, more preferably 20 μm or less, further preferably 15 μm or less, and particularly preferably 10 μm or less.
In addition, when only saying an average particle diameter in this specification, D50 in the case of measuring a sample with a general laser diffraction type particle size distribution measuring device is meant.

The reducing agent used in the plating process plays a role of reducing nickel ions and metal ions. Examples of the reducing agent include formaldehyde, glyoxylic acid, hypophosphorous acid, sodium hypophosphite, sodium borohydride, potassium borohydride, ascorbic acid, thiourea, hydroquinone, dimethylaminoborane, and hydrazine. In the plating step, one type of reducing agent may be used, or a plurality of types of reducing agents may be used. When hypophosphorous acid or sodium hypophosphite is used as the reducing agent, P is included in the metal film. When sodium borohydride, potassium borohydride, or dimethylaminoborane is used as the reducing agent, B is included in the metal film.
Examples of the concentration of the reducing agent in the mixed solution of the plating solution, the hydrogen storage alloy particle dispersion, and the reducing agent include a range of 1 to 200 g / L. Hereinafter, the mixed solution of the plating solution, the hydrogen storage alloy particle dispersion, and the reducing agent is referred to as a plating mixed solution as necessary.

It is preferable to further add an organic compound dispersant to the plating mixture. As described above, nickel ions and metal ions in the plating mixture are reduced by the reducing agent, and nickel and metal are deposited on the surface of the hydrogen storage alloy. By adding an organic compound dispersant to the plating mixture, it is considered that nickel and metal deposited on the surface of the hydrogen storage alloy particles are covered with a coating layer using the organic compound dispersant as a raw material. And since nickel and a metal precipitate while being covered with the said coating layer, it becomes difficult for nickel and a metal to grow coarsely, Therefore It is thought that nickel and a metal exist in a plating layer as a comparatively small particle | grain. That is, in this case, the plating layer is considered to be composed of an aggregate of composite particles in which nickel and metal forming small particles are each covered with a coating layer.
If nickel and metal grow coarsely, a sufficient amount of electrolyte may not be supplied to the hydrogen storage alloy. However, as described above, a plating layer having a large specific surface area obtained by adding an organic compound-based dispersant to a plating mixture is porous and has excellent infusion performance of an electrolytic solution. Therefore, a negative electrode material having the plating layer is used. This is considered to improve the battery characteristics of the nickel metal hydride battery.
Further, by adding an organic compound-based dispersant to the plating mixed solution, adhesion or adhesion between the negative electrode materials due to the plating layer can be suppressed, and there is an advantage that the negative electrode material after the plating step can be easily crushed.

The organic compound dispersant may be a polymer that is generally used as a dispersant or a monomer that can form the polymer, but is preferably water-soluble or hydrophilic. This is because an aqueous solvent is used for the plating solution and the hydrogen storage alloy particle dispersion contained in the plating mixture. As the organic compound dispersant, a water-soluble polymer or a water-soluble monomer is particularly preferable.
Examples of the polymer include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, diacetyl cellulose, sodium alginate, polyacrylic acid, sodium polyacrylate, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyhydroxyalkyl. (Meth) acrylate, styrene-maleic acid copolymer, non-crosslinked polyacrylamide and the like. As already described, monomers capable of constituting these polymers are also preferably used.

The organic compound dispersant is preferably added in an amount of 0.1 to 200 parts by mass, more preferably 1 to 150 parts by mass, when the plating metal salt is 100 parts by mass. More preferably, the amount is 10 to 100 parts by mass, and particularly preferably 25 to 75 parts by mass.

Other additives may be added to the plating mixture. Examples of the additive include a pH adjusting agent and a buffering agent. These may be added to the plating mixed solution in the plating step, or may be added to the plating solution in the plating solution preparation step, or may be added to the hydrogen storage alloy particle dispersion.

The pH of the plating mixture is usually adjusted to an appropriate value within the range of 4 to 14 according to the type of metal salt and reducing agent. For example, in a plating mixed solution using nickel salt and sodium hypophosphite, the pH is preferably in the range of 4-9. Preferable ranges of the pH of the plating mixed solution include 4 to 6, 4 to 5, 4.1 to 4.8, 4.2 to 4.5, and 4.3 to 4.4.

Examples of pH adjusters include sodium carbonate, sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, ammonium chloride, sulfuric acid, and hydrochloric acid.

It is preferable that there is no or moderate pH fluctuation of the plating mixture. The buffer is used for the purpose of suppressing rapid pH fluctuation of the plating mixture. Examples of the buffer include hydroxyacetic acid, lactic acid, gluconic acid, tartaric acid, malic acid, succinic acid, malonic acid, citric acid and other weak acids, and salts thereof.

Other additives that can be added to the plating mixture include bismuth nitrate, iodic acid, polyethylene glycol, and various surfactants.

As a raw material of the plating mixed solution, a known material may be adopted, or a commercially available product may be purchased and used. Alternatively, hydrogen storage alloy particles or the like may be added to a commercially available electroless plating aqueous solution. As a commercially available aqueous solution for electroless plating, trade names Blue Schumer, S-680, SE-680, SD-200, S-300, S-760, S-762, SE-660, SE-manufactured by Nippon Kanigen Co., Ltd. 666, S-500, SE-650, SFK-63, S-810, SEK-670, S-795, SEK-797, canibolone SKB-230, and SFB-26.

In the plating step, a method of dropping the plating solution to the hydrogen storage alloy particle dispersion is preferable. In order to allow the plating reaction to proceed uniformly, the plating process is preferably performed under stirring conditions.

The plating temperature in the plating step is preferably 50 to 95 ° C, more preferably 60 to 95 ° C. The higher the temperature, the faster the plating reaction proceeds. The thickness of the plating layer in the negative electrode material of the present invention varies depending on the amount, concentration, and plating reaction time of the plating solution.

The production method of the present invention may include a step of washing the negative electrode material obtained by the plating step and a drying step. Furthermore, it is preferable to have a heating step for heating the negative electrode material. As will be described later, the conductivity of the negative electrode material is improved through the heating step. The reason for this is not clear, but it is likely that the state or structure of the hydrogen storage alloy particles changes upon heating.

The temperature of the heating process is over 200 ° C and less than 500 ° C, 250 ° C or more and less than 500 ° C, 300 ° C or more and less than 500 ° C, over 300 ° C and less than 500 ° C, 320 ° C or more and 450 ° C or less, 350 ° C or more and 420 ° C or less. Can be mentioned.
By performing the heating step in the above temperature range, the function of the hydrogen storage alloy as a negative electrode active material for nickel metal hydride batteries is not impaired, and the conductivity of the negative electrode material can be sufficiently improved. In particular, when at least one selected from A ₂ B ₇ type, A ₅ B ₁₉ type, and AB ₃ type is selected as the hydrogen storage alloy, the effect of the heating step is remarkable. Since all of these hydrogen storage alloys have a crystal structure in which AB ₅ type and AB ₂ type crystal structures are combined, it is considered that the same effect can be obtained by heating in the same temperature range.

More specifically, the at least one hydrogen storage alloy selected from the A ₂ B ₇ type, A ₅ B ₁₉ type, and AB ₃ type is preferably a rare earth-Mg—Ni-based hydrogen storage alloy. The rare earth-Mg—Ni-based hydrogen storage alloy may be an alloy containing rare earth elements, Mg and Ni, and the composition ratio and other elements that can be contained are not particularly limited. Further, part or all of the rare earth element may be substituted with at least one of Ca, Sr, Sc, Y, Ti, Zr and Hf. As the rare earth-Mg—Ni-based hydrogen storage alloy, for example, one represented by the following general formula (1) can be selected.

General formula (1): Ln _1-x Mg _x Ni _yz T _z (where Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, At least one element selected from Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf, T is Mn, Co, Ti, V, Nb, W, Ta, Cr, Mo, Fe, Al , Ga, Zn, Sn, In, Cu, Si, Li, P, S, and B, x, y, and z are 0 <x <0.3 and 2.8, respectively. ≦ y ≦ 3.8 and 0 ≦ z ≦ 0.5 are satisfied.)

Moreover, it is considered that a negative electrode material having a mesh part can be produced by a heating process. In other words, depending on the type of metal salt, the plating layer after the plating step is considered to be composed of a plated metal having a fine particle shape. By heating the negative electrode material, such particles are melted, adjacent particles are joined and integrated to grow into a mesh shape, and eventually become a mesh portion.

In order to suppress melting of the hydrogen storage alloy at this time, the heating temperature of the negative electrode material is not less than the melting point of the metal and / or nickel metal alloy in which nickel and metal are alloyed and not more than the melting point of the hydrogen storage alloy. preferable. Furthermore, the heating temperature of the negative electrode material is more preferably higher than the melting point of the metal and nickel metal alloy and lower than the melting point of the hydrogen storage alloy.

In order to produce a negative electrode material having a mesh portion, the melting point of the metal and / or nickel metal alloy is preferably equal to or lower than the melting point of the hydrogen storage alloy, and the melting point of the metal and nickel metal alloy is equal to or lower than the melting point of the hydrogen storage alloy. More preferably. In other words, from the viewpoint of producing a negative electrode material having a mesh portion, as a metal salt of the plating solution, the melting point of the metal, and the melting point of the nickel metal alloy when alloyed with nickel is less than the melting point of the hydrogen storage alloy. More preferably, the metal salt is selected.

The melting point of the hydrogen storage alloy varies depending on the composition of the hydrogen storage alloy, and the hydrogen storage alloy having a small average particle diameter is more easily melted than the hydrogen storage alloy having a large average particle diameter. However, when the melting points of the metal and nickel metal alloy are relatively low, it is considered that a plating layer having a network shape can be formed on the hydrogen storage alloy particles having various compositions and average particle diameters.
Specifically, the melting point of the metal and the nickel metal alloy is preferably less than 450 ° C., preferably 430 ° C. or less, and particularly preferably 420 ° C. or less. There is no preferred lower limit for the melting point of the metal and nickel metal alloy in this case, but if it is to be strong, it is preferably 100 ° C. or higher, more preferably 200 ° C. or higher in view of handleability. More preferably, the temperature is higher than or equal to ° C. In consideration of suppressing the melting of the hydrogen storage alloy, the average particle diameter of the hydrogen storage alloy particles is preferably 8 μm or more, more preferably 10 μm or more, and still more preferably 20 μm or more. In this case, there is no preferred upper limit for the average particle size of the hydrogen storage alloy particles, but it is preferably 100 μm or less in view of the ease of battery reaction.

From the viewpoint of producing a negative electrode material having a mesh portion, it is preferable to select a metal having a low melting point so that a sufficiently low melting point is obtained when it is combined with nickel having a melting point of 1455 ° C. to form a nickel metal alloy. . As the metal, for example, a metal having a melting point of 350 ° C. or lower is preferably selected. Specific examples include indium having a melting point of 157 ° C., bismuth having a melting point of 271 ° C., tin having a melting point of 232 ° C., and cadmium having a melting point of 321 ° C. That is, when the negative electrode material of the present invention has a mesh part, the nickel metal alloy constituting the plating layer is preferably at least one selected from a nickel indium alloy, a nickel bismuth alloy, a nickel tin alloy, and a nickel cadmium alloy. It can be said.

The manufacturing method of the present invention may include a low oxygen gas exposure step after the heating step.
The low oxygen gas exposure step is a step of exposing the negative electrode material after the heating step to low oxygen gas. By performing the low oxygen gas exposure step, oxidation of the negative electrode material surface can be suppressed.
Low oxygen gas refers to a gas having a lower oxygen content than air. Preferably, the oxygen gas content of the low oxygen gas is more than 0% and not more than 10% by mass ratio. Furthermore, the oxygen gas content of the low oxygen gas is preferably 0.01% or more and 7% or less, more preferably 0.01% or more and 5% or less in terms of mass ratio, and 0.01% or more. It is more preferably 3% or less, still more preferably 0.01% or more and 2% or less, and particularly preferably 0.01% or more and 1% or less. The gas other than the oxygen gas contained in the low oxygen gas is preferably an inert gas such as argon gas.

In the low oxygen gas exposure step, the time for exposing the negative electrode material to the low oxygen gas is not particularly limited, but is preferably 3 minutes or more, more preferably 5 minutes or more, and further preferably 10 minutes or more. It is preferably 15 minutes or longer. In the low oxygen gas exposure step, the negative electrode material may be exposed to the low oxygen gas while still standing, but the negative electrode material may be exposed to the low oxygen gas while stirring or during the low oxygen gas exposure step. It is preferable to stir the negative electrode material one or more times.

In the negative electrode material of the present invention, the plating layer preferably covers the whole of the hydrogen storage alloy particles, and preferably covers the entire surface. The plating layer may have a mesh shape as described above, but may have a shape other than the mesh shape, such as a smooth shape.

In consideration of using the hydrogen storage alloy particles as a negative electrode active material for a nickel metal hydride battery, the thickness of the plating layer is preferably 500 nm or less from the viewpoint of smoothly storing and releasing hydrogen ions. The thickness range of the plating layer is preferably 2 to 500 nm, more preferably 2 to 400 nm, and even more preferably 2 to 300 nm.

The plated layer may be crystalline, but may contain amorphous, and all of the plated layer may be amorphous. The plating layer is assumed to have a function of protecting the hydrogen storage alloy particles in addition to a function of imparting conductivity to the negative electrode material. In other words, a hydrogen storage alloy that expands and contracts with charge and discharge may cause cracks and the like with long-term use, but by covering the hydrogen storage alloy particles with a plating layer, the hydrogen storage alloy particles Can be protected. If a metal having spreading properties is used as the plating metal, the plating layer can follow the expansion and contraction of the hydrogen storage alloy particles, so that it is considered to exhibit an excellent protective function. In particular, suitable spreadability can be expected in the amorphous portion of the plating layer.

Also, the plating layer may contain P and / or B. P and / or B originates from the manufacturing method and is contained in the plating layer. Due to the presence of P and / or B, the physical properties such as the hardness of the plating layer may suitably change. The proportion of the element in the plating layer is preferably 1 to 15% by mass, and more preferably 2 to 13% by mass. Note that the plating layer may contain impurities derived from the manufacturing method or the like.

The plating layer in the negative electrode material of the present invention contains nickel contained in the plating solution. When the plating solution contains a metal other than nickel, the plating layer may contain the metal in addition to nickel. The plating layer may contain nickel hydroxide, nickel oxide, metallic nickel, etc. as nickel, but preferably contains a lot of metallic nickel having excellent conductivity.
Specifically, in the XPS spectrum of the surface of the negative electrode material, when the peak intensity derived from metallic nickel is larger than the peak intensity derived from nickel hydroxide, the negative electrode material of the present invention has very excellent conductivity. It is considered to be granted.

In the negative electrode material of the present invention, as described above, a part of the surface of the hydrogen storage alloy particles may be covered with the plating layer, but it is preferable that the entire surface of the hydrogen storage alloy particle is covered with the plating layer. Here, as described above, hydrogen storage alloys such as A ₂ B ₇ type, A ₅ B ₁₉ type, and AB ₃ type contain rare earth metals. The plating layer contains at least nickel which is a transition metal. Therefore, the existing ratio of the rare earth metal and the transition metal can take different values between the surface of the hydrogen storage alloy particles and the surface of the plating layer, that is, the surface of the negative electrode material.
More specifically, the ratio B / A between the mass A of the rare earth metal and the mass B of the transition metal is used as the abundance ratio of the rare earth metal and the transition metal, and the ratio B / A is on the surface of the negative electrode material. If the value is larger than the surface of the hydrogen storage alloy particles, it can be considered that at least a part of the surface of the hydrogen storage alloy particles is covered with the plating layer. Further, if the ratio B / A is a large value, it can be considered that many portions of the surface of the hydrogen storage alloy particles are covered with the plating layer.
B / A in the negative electrode material of the present invention is preferably 5 times or more, more preferably 10 times or more, and further preferably 20 times or more of B / A on the surface of the hydrogen storage alloy particles. 30 times or more is particularly preferable.

As described later, the plating layer in the negative electrode material of the present invention is preferably composed of an aggregate of particles and has a large specific surface area. Specifically, the value obtained by dividing the BET specific surface area of the negative electrode material of the present invention by the BET specific surface area of the hydrogen storage alloy particles is preferably 3 or more, more preferably 5 or more, and 10 or more. Is more preferable, and 20 or more is particularly preferable.

When the negative electrode material of the present invention is a negative electrode material having a mesh shape on the surface, the mesh portion on the surface of the negative electrode material (sometimes referred to as a mesh portion in the present specification) has a linear shape or a strip shape. A plurality of ridges are partially integrated with each other. The mesh portion in the negative electrode material of the present invention is considered to have a relatively high strength due to such a structure.
Further, it is considered that the mesh part is mainly composed of a plating layer. That is, in the negative electrode material of the present invention having a mesh portion, the plating layer is considered to form a three-dimensional conductive path that is firmly connected by forming a mesh shape. Such a conductive path is considered to improve the conductivity of the negative electrode material.

The negative electrode material of the present invention can be used as a negative electrode material for nickel metal hydride batteries. The nickel metal hydride battery includes a positive electrode, a negative electrode, an electrolytic solution, and a separator. Hereinafter, the nickel metal hydride battery will be described.

The positive electrode includes a current collector and a positive electrode active material layer formed on the surface of the current collector. The negative electrode includes a current collector and a negative electrode active material layer formed on the surface of the current collector. Hereinafter, although it demonstrates from the structure of a positive electrode, about the thing which overlaps with the structure of a negative electrode, it demonstrates without attaching | limiting with a positive electrode.

A current collector refers to a chemically inert electronic conductor that keeps a current flowing through an electrode during discharge or charging of a nickel metal hydride battery. The material of the current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. The current collector material is at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Examples of such a metal material can be given. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector. As a material for the current collector, nickel or a metal material plated with nickel is preferable.

The current collector can take the form of foil, sheet, film, wire, rod, mesh, sponge or the like. When the current collector is in the form of foil, sheet, or film, the thickness is preferably in the range of 1 μm to 100 μm, and the so-called punching metal-like one having a large number of holes or a cut What is called an expanded metal shape which spread | stretched the metal plate and made it mesh shape is preferable.

The positive electrode active material layer contains a positive electrode active material and, if necessary, contains a positive electrode additive, a binder and a conductive additive.

The positive electrode active material is not limited as long as it is used as the positive electrode active material of the nickel metal hydride battery. Specific examples of the positive electrode active material include nickel hydroxide and nickel hydroxide doped with metal. Examples of the metal doped into nickel hydroxide include Group 2 elements such as magnesium and calcium, Group 9 elements such as cobalt, rhodium and iridium, and Group 12 elements such as zinc and cadmium.

The surface of the positive electrode active material may be treated by a known method. The positive electrode active material is preferably in a powder state, and the average particle size thereof is preferably in the range of 1 to 100 μm, more preferably in the range of 3 to 50 μm, and still more preferably in the range of 5 to 30 μm.

The positive electrode active material layer preferably contains the positive electrode active material in an amount of 75 to 99% by mass, more preferably 80 to 97% by mass, and more preferably 82 to 95% by mass with respect to the total mass of the positive electrode active material layer. More preferably, it is contained in mass%.

The positive electrode additive is added to the positive electrode in order to improve the battery characteristics of the nickel metal hydride battery. The positive electrode additive is not limited as long as it is used as a positive electrode additive for nickel metal hydride batteries. Specific positive electrode additives include niobium compounds such as Nb ₂ O ₅ , tungsten compounds such as WO ₂ , WO ₃ , Li ₂ WO ₄ , Na ₂ WO ₄ and K ₂ WO _4, and ytterbium compounds such as Yb ₂ O ₃ . And titanium compounds such as TiO ₂ , yttrium compounds such as Y ₂ O ₃ , zinc compounds such as ZnO, calcium compounds such as CaO, Ca (OH) ₂ and CaF ₂ , and other rare earth oxides.

In the positive electrode active material layer, the positive electrode additive is preferably contained in an amount of 0.1 to 10% by mass, more preferably 0.5 to 5% by mass with respect to the mass of the entire positive electrode active material layer. .

The binder plays a role of connecting an active material or the like to the surface of the current collector. The binder is not limited as long as it is used as a binder for electrodes of nickel metal hydride batteries. Specific binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, polyolefin resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, carboxymethylcellulose, methylcellulose and hydroxypropyl. Cellulose derivatives such as cellulose, copolymers such as styrene butadiene rubber, and polyacrylic acid, polyacrylic acid ester, polymethacrylic acid and polymethacrylic acid ester containing (meth) acrylic acid derivatives as monomer units ( An example is a (meth) acrylic resin.

In the active material layer, the binder is preferably contained in an amount of 0.1 to 15% by mass, more preferably 1 to 10% by mass, with respect to the mass of the entire active material layer. More preferably, it is contained in mass%. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

Conductive aid is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be added to the active material layer in a powder state, or may be used in a state where the surfaces of the active material particles are coated. The conductive auxiliary agent may be an electronic conductor that is chemically inert. Specific conductive materials include metals such as cobalt, nickel, copper, metal oxides such as cobalt oxide, metal hydroxides such as cobalt hydroxide, carbon monoxide complexes such as carbonyl nickel, carbon black, and the like. Examples thereof include carbon materials such as graphite and carbon fiber.

The active material layer preferably contains 0.1 to 20% by mass of a conductive additive with respect to the total mass of the active material layer. In the positive electrode active material layer, the conductive additive is preferably contained in an amount of 1 to 15% by mass, more preferably 3 to 12% by mass, with respect to the total mass of the positive electrode active material layer. More preferably, it is contained in mass%. The negative electrode active material layer preferably contains 0.1 to 5% by mass, more preferably 0.2 to 3% by mass of the conductive auxiliary agent with respect to the total mass of the negative electrode active material layer. More preferably, the content is 0.3 to 1% by mass. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered.

The negative electrode active material layer includes a negative electrode material and, if necessary, a negative electrode additive, a binder, and a conductive additive. As described above, the negative electrode material is composed of hydrogen storage alloy particles, which are negative electrode active materials, and a plating layer. The binder and the conductive aid are as described above.

In the negative electrode active material layer, the negative electrode material is preferably contained in an amount of 85 to 99% by mass, more preferably 90 to 98% by mass with respect to the mass of the entire negative electrode active material layer.

The negative electrode additive is added to the negative electrode in order to improve the battery characteristics of the nickel metal hydride battery. The negative electrode additive is not limited as long as it is used as a negative electrode additive for nickel metal hydride batteries. Specific negative electrode additives include rare earth fluorides such as CeF ₃ and YF ₃ , bismuth compounds such as Bi ₂ O ₃ and BiF ₃ , indium compounds such as In ₂ O ₃ and InF ₃ , and positive electrode additives Can be mentioned as examples.

In the negative electrode active material layer, the negative electrode additive is preferably contained in an amount of 0.1 to 10% by mass, more preferably 0.5 to 5% by mass with respect to the total mass of the negative electrode active material layer. .

In order to form an active material layer on the surface of the current collector, a current collecting method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. An active material may be applied to the surface of the body. Specifically, an active material, a solvent, and if necessary, a binder, a conductive additive and an additive are mixed to form a slurry, and the slurry is applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

The separator separates the positive electrode and the negative electrode, and provides a storage space and a passage for the electrolyte while preventing a short circuit due to contact between the two electrodes. As the separator, a known separator may be employed, such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile and other synthetic resins, cellulose, amylose and other polysaccharides, fibroin. And porous materials, nonwoven fabrics, woven fabrics, and the like using one or more electrical insulating materials such as natural polymers such as keratin, lignin, and suberin, and ceramics. The separator may have a multilayer structure.

The separator is preferably subjected to a hydrophilic treatment on the surface. Examples of the hydrophilic treatment include sulfonation treatment, corona treatment, fluorine gas treatment, and plasma treatment.

The electrolytic solution may be a strong base aqueous solution generally used as an electrolytic solution for nickel metal hydride batteries. Specific examples of the strong base aqueous solution include a potassium hydroxide aqueous solution, a sodium hydroxide aqueous solution, and a lithium hydroxide aqueous solution. As the electrolytic solution, only one kind of strong base aqueous solution may be used, or plural kinds of strong base aqueous solutions may be mixed and used.
Moreover, the well-known additive employ | adopted as the electrolyte solution for nickel metal hydride batteries may be added to electrolyte solution.

As a manufacturing method of the nickel metal hydride battery, a separator is interposed between the positive electrode and the negative electrode as necessary to form an electrode body, from the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside. After the connection using a current collecting lead or the like, the electrolyte solution of the present invention may be added to the electrode body to form a nickel metal hydride battery.
The shape of the nickel metal hydride battery is not particularly limited, and various shapes such as a square shape, a cylindrical shape, a coin shape, and a laminate shape can be adopted.

As mentioned above, although the manufacturing method of this invention and the negative electrode material of this invention were demonstrated, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

Example 1
<Plating solution preparation process>
A plating solution was prepared using nickel sulfate as a nickel salt, cobalt sulfate as a metal salt, malonic acid which is a dicarboxylic acid as a hetero element-containing organic compound, and water as an aqueous solvent.
First, 1.5 g of NiSO ₄ .6H ₂ O, 1.5 g of CoSO ₄ .7H ₂ O, and 1.5 g of dicarboxylic acid were measured, and 75 g of distilled water was added. This was heated to 90 ° C. to form a solution, and NaOH was added to maintain the solution at 80 ° C. so that the pH was 4 to 5, thereby obtaining a plating solution.

<Plating process>
1.0 g of sodium borohydride was weighed out as a reducing agent, and distilled water was added to 100 ml to obtain a reducing agent solution.
As hydrogen storage alloy particles, particles of A ₂ B ₇ type hydrogen storage alloy represented by (Nd _0.88 Zr _0.01 Mg _0.11 ) _1.0 (Ni _0.95 Al _0.05 ) _3.5 Was used. The average particle diameter of the hydrogen storage alloy particles was 25 μm.
60 g of the above hydrogen storage alloy particles were added to a 1 L glass reaction tank, and distilled water was added so that the amount of the liquid in the reaction tank was 400 ml to obtain a slurry-like hydrogen storage alloy particle dispersion.

The hydrogen storage alloy particle dispersion in the reaction vessel was stirred using a paddle type stirring blade. A plating solution and a reducing agent solution were dropped into the reaction vessel. This plating mixture was stirred for about 1 hour. By this step, a negative electrode material having a plating layer formed on the surface of the hydrogen storage alloy was obtained.

Thereafter, the negative electrode material was immediately filtered off, and the solid content thus filtered, that is, the negative electrode material was washed with pure water. The washed negative electrode material was vacuum dried, and the dried negative electrode material was crushed in the air using a mortar.

<Heating process>
After the above-described plating step, the vacuum-dried negative electrode material was placed in a heating furnace and heated from room temperature to 350 ° C. in an argon atmosphere. The negative electrode material after the heating step was used as the negative electrode material of Example 1.

(Example 2)
A negative electrode material of Example 2 was obtained in the same manner as in Example 1 except that the heating step was not performed. In the method of Example 2, the powder after the plating process was used as the negative electrode material of Example 2.

(Comparative Example 1)
The same hydrogen storage alloy particles having an average particle diameter of 25 μm as those used in Example 1 were used as the negative electrode material of Comparative Example 1.

(Comparative Example 2)
A negative electrode material of Comparative Example 2 was obtained in the same manner as in Example 1 except that no heteroelement-containing organic compound was blended in the plating solution.
Incidentally, the plating solution in the manufacturing method of Comparative Example _2, heating NiSO 4 · _6H 2 O and 1.5g and CoSO ₄ · 7H ₂ O 1.5g of measured out, those of distilled water was added 75g of a 90 ° C. Then, NaOH is added so that the pH is 5 while keeping the solution at 80 ° C.

(Comparative Example 3)
A negative electrode material of Comparative Example 3 was obtained in the same manner as Comparative Example 2, except that the heating step was not performed.

(Evaluation 1 conductivity)
The powder resistance of each of the negative electrode materials of Example 1 and Example 2 and the negative electrode materials of Comparative Examples 1 to 3 was measured. As a measuring device, a powder resistance measuring device manufactured by Mitsubishi Chemical Analytech Co., Ltd. was used. Table 1 shows the results of the conductivity evaluation.

As shown in Table 1, the powder resistance of the negative electrode material of Example 1 and Example 2 is lower than the powder resistance of the negative electrode material of Comparative Example 1. This is considered to be due to the presence or absence of the plating layer, and it is considered that excellent conductivity was imparted to the negative electrode material of Example 1 and the negative electrode material of Example 2 by having the plating layer.

The powder resistance of the negative electrode material of Example 1 is significantly lower than that of the negative electrode material of Comparative Example 2. This is considered due to the presence or absence of complexation of the plating metal in the plating solution. From this result, it is understood that a plating layer having excellent conductivity can be obtained by forming a plating layer with a complexed plating metal.

Also, the powder resistance of the negative electrode material of Example 1 is lower than that of the negative electrode material of Example 2. This is considered due to the presence or absence of the heating step. It can be seen that heating after forming the plating layer can further reduce the powder resistance of the negative electrode material and further improve the conductivity of the negative electrode material.

Further, when the negative electrode material of Comparative Example 2 in which the plating layer was formed without complexing and the negative electrode material of Comparative Example 3 were compared, the negative electrode material of Comparative Example 2 in which the heating process was performed was compared without performing the heating process. Compared to the negative electrode material of Example 3, the powder resistance is low. Further, the negative electrode material of Comparative Example 3 in which the plating layer was not formed and the heating step was not performed had a powder resistance comparable to that of the negative electrode material of Comparative Example 1 without the plating layer. From this result, it can be seen that it is difficult to improve conductivity simply by forming a plating layer, and that a plating layer having excellent conductivity can be obtained only by forming a plating layer through complexation of plating metal. Furthermore, it turns out that the electroconductivity of negative electrode material improves by performing a heating process for a certain reason.

(Evaluation 2 Surface analysis)
The negative electrode material of Example 1 and the negative electrode material of Comparative Example 2 were subjected to surface analysis using X-ray Photoelectron Spectroscopy (XPS). ULVAC-PHI PH15000 VersaProbeII was used as the apparatus. A monochromatic AlKα ray (15 kV, 10 mA) was used as the X-ray source. The surface analysis results of the negative electrode material of Example 1 and the negative electrode material of Comparative Example 2 measured by XPS are shown in FIGS.

As shown in FIGS. 1 and 2, in the XPS spectrum of the negative electrode material of Example 1 and the XPS spectrum of the negative electrode material of Comparative Example 2, peaks were observed in the binding energy regions of 870 eV, 856 eV, and 853 eV. Among these, it is considered that the bonding groups having the bonding energy of 870 eV and 853 eV are derived from metallic nickel. On the other hand, the bonding group having a binding energy of 856 eV is considered to be derived from nickel hydroxide. In the XPS spectrum of the negative electrode material of Comparative Example 2, the peak intensity of 856 eV derived from nickel hydroxide is larger than the peak intensity of 870 eV and 853 eV derived from metallic nickel. On the other hand, in the XPS spectrum of the negative electrode material of Example 1, the peak intensity of 853 eV derived from metallic nickel is larger than the peak intensity of 856 eV derived from nickel hydroxide. From this result, it can be considered that a lot of nickel hydroxide is present on the surface of the negative electrode material of Comparative Example 2 whereas a large amount of metallic nickel is present on the surface of the negative electrode material of Example 1. This result suggests that nickel hydroxide was suppressed in the production method of Example 1, and that nickel complexation was effective in suppressing nickel hydroxide.

As described above, in the XPS spectrum of the negative electrode material of Example 1 and the XPS spectrum of the negative electrode material of Comparative Example 2, a peak was observed in the binding energy region of 870 eV. The peak is considered to be a peak of CoNi, and is very strong in the XPS spectrum of the negative electrode material of Example 1. For this reason, in the negative electrode material of Example 1, it can be said that the nickel cobalt alloy which nickel and cobalt alloyed is formed.

(Evaluation 2-A Surface analysis)
The surface composition of the negative electrode material of Example 1 and the negative electrode material of Comparative Example 1 was analyzed. Specifically, the composition from the surface to a depth of 5 nm was measured by XPS in a measurement area having a predetermined area at an arbitrary position on the surface of the negative electrode material. Based on the measurement result, the mass (A) of the rare earth metal and the mass (B) of the transition metal in the predetermined volume of the region were calculated, and the B / A value obtained by dividing B by A was calculated. The B / A can be said to be an abundance ratio of the rare earth metal and the transition metal.

B / A in the negative electrode material of Example 1 was 127.5, and B / A in the negative electrode material of Comparative Example 1 was 3.7. That is, the B / A in the negative electrode material of Example 1 was approximately 34 times the B / A in the negative electrode material of Comparative Example 1.
In other words, the B / A on the surface of the negative electrode material of Example 1 was 127.5, and the B / A on the surface of the hydrogen storage alloy particles as the material was 3.7. That is, the B / A on the surface of the negative electrode material of Example 1 was approximately 34 times the B / A on the surface of the hydrogen storage alloy particles.
From this result, it can be said that B / A on the surface of the negative electrode material of the present invention is larger than B / A on the surface of the hydrogen storage alloy particles. Although rare earth elements are contained in the hydrogen storage alloy particles but are not substantially contained in the plating layer, it can be said that the higher the B / A, the higher the surface coverage of the hydrogen storage alloy particles by the plating layer. The B / A on the surface of the negative electrode material of the present invention is preferably 5 times or more, more preferably 10 times or more, more preferably 20 times or more of the B / A on the surface of the hydrogen storage alloy particles. More preferably, it is particularly preferably 30 times or more.

Furthermore, B / A on the surface of the negative electrode material of the present invention is preferably 10 or more and 1000 or less, more preferably 50 or more and 1000 or less, still more preferably 70 or more and 1000 or less, and 100 or more. It can be said that it is especially preferable that it is 1000 or less.

(Example 3)
In the plating step, 0.03 g of polyvinyl pyrrolidone as an organic compound dispersant was added to the slurry-like hydrogen storage alloy particle dispersion, and the negative electrode material after plating, washing and drying was crushed in the atmosphere. A negative electrode material of Example 3 was obtained in the same manner as in Example 1 except that it was omitted.
In addition, according to the manufacturing method of Example 1, the negative electrode material aggregated during filtration in the plating step, but the aggregation does not occur in the manufacturing method of Example 3, and the negative electrode material after washing and drying does not crush. But it was easy to understand.

(Evaluation 3 SEM observation)
The surfaces of the negative electrode material of Example 1, the negative electrode material of Example 3, and the negative electrode material of Comparative Example 2 were observed using a scanning electron microscope (SEM). The SEM image of the negative electrode material of Example 1 is shown in FIG. 3, the SEM image of the negative electrode material of Example 3 is shown in FIG. 4, and the SEM image of the negative electrode material of Comparative Example 2 is shown in FIG.

As shown in FIGS. 3 and 4, aggregates of particles were observed on both the surface of the negative electrode material of Example 1 and the surface of the negative electrode material of Example 3. On the other hand, as shown in FIG. 5, fine irregularities that were difficult to say as particles were observed on the surface of the negative electrode material of Comparative Example 2. Since the surface of the negative electrode material of Example 1, Example 3, and Comparative Example 2 is composed of a plating layer, it is considered that the particles and irregularities are composed of a plating layer. That is, it can be said that the negative electrode material of Example 1 and Example 3 has a plating layer composed of an aggregate of particles, whereas the negative electrode material of Comparative Example 2 has a plating layer having fine irregularities.
The difference between the manufacturing method of Example 1 and Example 3 and the manufacturing method of Comparative Example 2 is the presence or absence of complexation of the plating metal in the plating solution. Therefore, it is considered that the difference in surface shape is caused by the presence or absence of complexation of the plating metal. From this result, it is confirmed that by plating the plating metal in the plating solution, the plating metal, that is, nickel and metal precipitate in a granular form, and a plating layer composed of an aggregate of particles can be obtained.

The average particle size of the particles present on the surface of the negative electrode material of Example 3 is 10 nm, and the particle size is the average particle size of the particles present on the surface of the negative electrode material of Example 1. It was smaller than 10 nm to 20 nm. From this result, it can be seen that, in addition to complexation of the plating metal, a plating layer composed of an aggregate of finer particles can be obtained by performing the plating step in the presence of an organic compound dispersant. Furthermore, since the negative electrode material having the plating layer hardly aggregates and does not require crushing, the negative electrode material can be easily prepared according to the manufacturing method of Example 3, that is, the manufacturing method in which the plating process is performed in the presence of the organic compound dispersant. It can be seen that it can be manufactured.

(Evaluation 3-A BET specific surface area)
The specific surface area of the negative electrode material of Example 1 and the negative electrode material of Comparative Example 1 was measured by the BET method.

The negative electrode material of Example 1 has a BET specific surface area of 4.085 m ² / g, the negative electrode material of Comparative Example 1 has a BET specific surface area of 0.173 m ² / g, and the negative electrode material of Example 1 has a BET specific surface area. Was 24 divided by the BET specific surface area of the negative electrode material of Comparative Example 1.
In other words, the negative electrode material of Example 1 has a BET specific surface area of 4.085 m ² / g, and the hydrogen storage alloy particles of the material has a BET specific surface area of 0.173 m ² / g. A value obtained by dividing the BET specific surface area of the material by the BET specific surface area of the hydrogen storage alloy particles as the material was 24.

Incidentally, since the plating layer constituting the surface of the negative electrode material of the present invention is composed of an aggregate of particles as shown in FIG. 3, for example, the specific surface area is large. Therefore, the BET specific surface area of the negative electrode material of the present invention having such a plating layer is larger than the BET specific surface area of the hydrogen storage alloy particles as the material. That is, it can be said that the value obtained by dividing the BET specific surface area of the negative electrode material of the present invention by the BET specific surface area of the hydrogen storage alloy particles exceeds 1.

Further, considering the result of the above evaluation 3-A, the value obtained by dividing the BET specific surface area of the negative electrode material of the present invention by the BET specific surface area of the hydrogen storage alloy particles is preferably 3 or more, and more preferably 5 or more. More preferably, it is more preferably 10 or more, and particularly preferably 20 or more. There is no particular upper limit to the value obtained by dividing the BET specific surface area of the negative electrode material of the present invention by the BET specific surface area of the hydrogen storage alloy particles.
Further, the BET specific surface area of the negative electrode material of the present invention is preferably 1 to 10 m ² / g, more preferably 1.5 to 8 m ² / g, and 2 to 6 m ² / g. More preferred is 3 to 5 m ² / g.

(Nickel metal hydride battery)
Using the negative electrode materials of Example 1, Example 3, and Comparative Example 1, nickel metal hydride batteries were produced as follows.

<Positive electrode>
83.3 parts by mass of nickel hydroxide powder as a positive electrode active material, 5 parts by mass of cobalt powder as a conductive additive, 5 parts by mass of an acrylic resin emulsion (Johncrill PDX7341, BASF) as a binder, A slurry was prepared by mixing 0.7 parts by mass of carboxymethyl cellulose as a binder, 1 part by mass of Y ₂ O ₃ as a positive electrode additive, and an appropriate amount of ion-exchanged water. A nickel foil having a thickness of 10 μm was prepared as a positive electrode current collector. The slurry was applied in a film form on the surface of the nickel foil using a doctor blade. The nickel foil coated with the slurry was dried to remove water, and then the nickel foil was pressed to obtain a bonded product. The obtained joined product was dried by heating at 70 ° C. for 1 hour with a dryer to produce a positive electrode in which a positive electrode active material layer was formed on a current collector.

<Negative electrode>
As the negative electrode material, the negative electrode material of Example 1, Example 3, or Comparative Example 1 was used. 96.9 parts by mass of the negative electrode material, 0.4 parts by mass of carbon black as the conductive auxiliary agent, 2 parts by mass of the acrylic resin emulsion (Johncrill PDX7341, BASF) as the binder, and as the binder A slurry was produced by mixing 0.7 part by mass of carboxymethyl cellulose and an appropriate amount of ion-exchanged water. A nickel foil having a thickness of 10 μm was prepared as a negative electrode current collector. The slurry was applied in a film form on the surface of the nickel foil using a doctor blade. The nickel foil coated with the slurry was dried to remove water, and then the nickel foil was pressed to obtain a bonded product. The obtained joined product was dried by heating at 70 ° C. for 1 hour with a dryer to produce a negative electrode having a negative electrode active material layer formed on a current collector.

<Electrolyte>
An aqueous solution in which the concentration of potassium hydroxide is 5.5 mol / L, the concentration of sodium hydroxide is 0.5 mol / L, and the concentration of lithium hydroxide is 0.5 mol / L is prepared. It was.
<Battery>
A 120 μm-thick polypropylene fiber nonwoven fabric subjected to sulfonation treatment was prepared as a separator. A separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. Each of the nickel metal hydride batteries of Example 1, Example 3, and Comparative Example 1 was prepared by placing an electrode plate group in a resin case, injecting an electrolyte, and sealing the case. Manufactured.

(Evaluation 4 Battery characteristics)
About each nickel metal hydride battery of Example 1, Example 3, and Comparative Example 1, it adjusted to the state of SOC60% used as voltage 1.39V, it was made to discharge by constant output to voltage 0.8V at 25 degreeC, and this The discharge time was measured. The measurement was also performed at 0 ° C. From the obtained results, a constant output (W) at which the discharge time from 1.39 V to 0.8 V was 10 seconds was calculated for each nickel metal hydride battery. Furthermore, the said fixed output value in the nickel metal hydride battery of the comparative example 1 in each temperature was made into 100%, respectively, and the percentage of the said fixed output value of Example 1 and Example 3 in the applicable temperature was computed. The results are shown in Table 2.
Note that SOC is an abbreviation for State of Charge, and SOC 60% is a charge capacity corresponding to 60% when the theoretical capacity of the positive electrode active material is SOC 100%.

As shown in Table 2, the nickel metal hydride batteries of Example 1 and Example 3 having a plating layer obtained by complexing a plating metal are compared with the nickel metal hydride battery of Comparative Example 1 having no plating layer. Excellent output value at 25 ° C and 0 ° C. In particular, according to the nickel metal hydride batteries of Example 1 and Example 3, a large output can be obtained even at a low temperature of 0 ° C. This is considered to be due to the improved conductivity of the negative electrode by the plating layer.
Further, comparing Example 3 using an organic compound dispersant in Example 1 with no organic compound dispersant in the plating layer forming step, the nickel metal hydride battery of Example 3 is the same as that of Example 1. Compared to nickel metal hydride batteries, the output value is even better. From this result, it can be seen that a negative electrode material capable of further improving the output characteristics of the nickel metal hydride battery can be obtained by using an organic compound dispersant when forming the plating layer. As shown in FIG. 3 and FIG. 4, since the surface shape of the plating layer varies depending on the presence or absence of the organic compound dispersant, the difference in the output characteristics is also related to the surface shape of the plating layer. Can be considered. That is, it is considered that the plating layer made of an aggregate of particles contributes to improvement of output characteristics.

(Evaluation 4-A Battery characteristics)
Each nickel metal hydride battery of Example 1 and Comparative Example 1 was charged and discharged at 40 ° C., 2 C, SOC 0% to SOC 150% for 37 cycles.
In each cycle, (discharge capacity when SOC was 0%) / (charge capacity when SOC was 150%) × 100 was calculated and used as capacity utilization rate (%). The result of Evaluation 4-A is shown in FIG.

As shown in FIG. 6, the capacity utilization of the nickel metal hydride battery of Example 1 from the first cycle to the 37th cycle was almost unchanged, whereas the nickel metal hydride battery of Comparative Example 1 The capacity utilization rate dropped significantly after 20 cycles. From this result, the capacity utilization rate in the nickel metal hydride battery is greatly improved by the presence of the plating layer, that is, the negative electrode material of the present invention having the plating layer contributes to the improvement of the durability of the nickel metal hydride battery. I understand that.

(Reference Example 1)
A negative electrode material of Reference Example 1 was obtained in the same manner as Comparative Example 2 except that the heating temperature in the heating step was 200 ° C.

(Reference Example 2)
A negative electrode material of Reference Example 2 was obtained in the same manner as Reference Example 1 except that the heating temperature in the heating step was 350 ° C.

(Reference Example 3)
A negative electrode material of Reference Example 3 was obtained in the same manner as Reference Example 1 except that the heating temperature in the heating step was 450 ° C.

(Reference Example 4)
A negative electrode material of Reference Example 4 was obtained in the same manner as Reference Example 1 except that the heating temperature in the heating step was 600 ° C.

(Evaluation 5 conductivity)
Similar to Evaluation 1, the powder resistance of the negative electrode materials of Reference Examples 1 to 4 was measured. The results are shown in Table 3.

(Evaluation 6: Battery characteristics)
Using the negative electrode materials of Reference Examples 1 to 4, nickel metal hydride batteries of Reference Examples 1 to 4 were obtained in the same manner as the nickel metal hydride battery of Example 1. Using the nickel metal hydride batteries of Reference Examples 1 to 4 and the nickel metal hydride battery of Comparative Example 1, the battery characteristics of each nickel metal hydride battery were evaluated.
The nickel metal hydride batteries of Reference Examples 1 to 4 and Comparative Example 1 were charged to a voltage of 1.5 V at 25 ° C. and 0.5 C, and then discharged to 0.8 V at 10 C. The discharge capacity at this time was 10 C discharge capacity. Based on the theoretical capacity of each nickel metal hydride battery and the 10C discharge capacity of each nickel metal hydride battery, the 10C discharge efficiency (%) of each nickel metal hydride battery was calculated using the following formula.
10C discharge efficiency (%) = 100 × (10C discharge capacity) / (theoretical capacity)

For each of the nickel metal hydride batteries of Reference Examples 1 to 4 and Comparative Example 1, after the above test, a charge / discharge cycle of voltage 1.5V-0.8V at 25 ° C. and 1C was repeated to increase the cycle life. It was measured. For each nickel metal hydride battery, the charge / discharge cycle was terminated when the discharge capacity reached zero. The number of cycles at the end of the charge / discharge cycle was defined as the cycle life of each nickel metal hydride battery.
Table 3 shows the results.

As shown in Table 3, the powder resistances of the negative electrode materials of Reference Examples 2 to 4 in which the heating temperatures in the heating process are 350 ° C., 450 ° C., and 600 ° C., respectively, are 200 ° C. in the heating process. All were low compared with the powder resistance of the negative electrode material of the reference example 1. This result suggests that the conductivity of the negative electrode material can be improved by heating the negative electrode material at a temperature exceeding 200 ° C. in the heating step. Moreover, since the powder resistance of the negative electrode material of Reference Example 2 having a heating temperature of 350 ° C. is lower than the powder resistance of the negative electrode materials of Reference Example 3 and Reference Example 4, the heating temperature of the negative electrode material is around 350 ° C. It is suggested that this is preferable.
The nickel metal hydride battery of Reference Example 2 was also superior to the batteries of Comparative Example 1, Reference Example 3 and Reference Example 4 in terms of 10C discharge efficiency and cycle life. This suggests that excellent battery characteristics can be imparted to the nickel metal hydride battery by the negative electrode material subjected to the heating process at a suitable temperature.

(Evaluation 7 X-ray diffraction)
The X-ray diffraction of the negative electrode material of Example 2 and the negative electrode material of Comparative Example 1 was measured with a powder X-ray diffractometer using CuKα rays. An X-ray diffraction chart of the negative electrode material of Example 2 is shown in FIG. 7, and an X-ray diffraction chart of the negative electrode material of Comparative Example 1 is shown in FIG.
The X-ray diffraction chart of the negative electrode material of Example 2 shown in FIG. 7 has a peak around 44.6 ° and a peak around 51.879 ° compared to the X-ray diffraction chart of the negative electrode material of Comparative Example 1 shown in FIG. The peak is getting stronger. It is considered that the peak near 44.6 ° is derived from the (111) crystal plane of Ni, and the peak near 51.879 ° is derived from the (200) crystal plane of Ni. Since these strong peaks are observed in the X-ray diffraction chart of the negative electrode material of Example 2, it is confirmed that crystalline Ni metal exists on the surface of the negative electrode material of Example 2.

Example 4
A negative electrode material of Example 4 was obtained in the same manner as the production method of Example 3, except that the negative electrode material was heated at 400 ° C. in the heating step. That is, in the manufacturing method of Example 4, as in the manufacturing method of Example 3, since the aggregation of the negative electrode material did not occur during the filtration after the plating process, the step of crushing the dried negative electrode material in the atmosphere was performed. I don't have it.

Example 1-A
A negative electrode material of Example 1-A was obtained in the same manner as in Example 1. Similar to the manufacturing method of Example 1, the manufacturing method of Example 1-A includes a step of crushing the dried negative electrode material in the air using a mortar after the plating step.

(Evaluation 8 Surface analysis)
The negative electrode material of Example 4 and the negative electrode material of Example 1-A were subjected to surface analysis using XPS in the same manner as in Evaluation 2 Surface Analysis. 9 and 10 show the surface analysis results of the negative electrode material of Example 4 and the negative electrode material of Example 1-A measured by XPS.

As shown in FIGS. 9 and 10, in the XPS spectrum of the negative electrode material of Example 4, the ratio of the peak intensity of 853 eV to the peak intensity of 856 eV is larger than the XPS spectrum of the negative electrode material of Example 1-A. As described above, the peak at 856 eV is considered to be derived from nickel hydroxide, and the peak at 853 eV is considered to be derived from metallic nickel. Therefore, this result suggests that the ratio of metallic nickel to nickel hydroxide is higher on the surface of the negative electrode material of Example 4 than on the surface of the negative electrode material of Example 1-A. In the manufacturing method of Example 1-A, it is considered that the negative electrode material was crushed in the air after the plating and before the heating step, so that the negative electrode material was exposed to the air and the surface of the negative electrode material was oxidized. On the other hand, in the manufacturing method of Example 4, since the above-mentioned crushing in the atmosphere was not performed, it was considered that the negative electrode material was not exposed to the atmosphere and the oxidation of the negative electrode material surface could be suppressed.

(Evaluation 9 conductivity)
Similar to Evaluation 1 and Evaluation 5, the powder resistance of the negative electrode materials of Example 4 and Example 1-A was measured. The results are shown in Table 4.

As shown in Table 4, the negative electrode material of Example 4 obtained by performing the plating step in the presence of the organic compound dispersant and without exposing to air after filtration was plated in the absence of the organic compound dispersant. Compared with the negative electrode material of Example 1-A obtained by performing the process and exposing to air after filtration, the powder resistance was remarkably reduced and the conductivity was excellent. This is presumably due to the presence of a large amount of metallic nickel on the surface of the negative electrode material of Example 4 as described above.

(Example 5)
Except that vacuum drying after plating and pulverization in the atmosphere were omitted, that the heating temperature in the heating step was 300 ° C., and that the drying step was performed before the heating step, the same as in Example 1. The negative electrode material of Example 5 was obtained by the method.
Specifically, in Example 5, the negative electrode material filtered and washed in the plating step is directly put into a heating furnace, and the negative electrode material is preheated in a heating furnace under vacuum at 60 ° C. for 5 hours to obtain moisture, etc. After performing the drying process which evaporates the volatile component of this, it heated up to 300 degreeC in argon atmosphere similarly to Example 1, and the heating process was performed.
In Example 5, it can be said that substantially vacuum drying was performed in the heating furnace.

(Evaluation 10 Surface analysis)
The negative electrode material of Example 5 was subjected to surface analysis using XPS in the same manner as in Evaluation 2 above. The result of Evaluation 10 is shown in FIG. 11 along with the result of Example 1 in Evaluation 2.

(Evaluation 11 Conductivity)
For the negative electrode material of Example 5, the powder resistance was measured in the same manner as in Evaluation 1 above. The results are shown in Table 5.

As shown in FIG. 11, the ratio of the peak intensity of 853 eV derived from metallic nickel to the peak intensity of 856 eV derived from nickel hydroxide is the same as that of the negative electrode material of Example 1 in the XPS spectrum of the negative electrode material of Example 5. It was much larger than the XPS spectrum. This result suggests that the ratio of metallic nickel to nickel hydroxide is higher on the surface of the negative electrode material of Example 5 than on the surface of the negative electrode material of Example 1. In the manufacturing method of Example 5, it is considered that the oxidation of the negative electrode material surface was suppressed by omitting the disintegration of the negative electrode material in the air before the heating step after plating.
In addition, as shown in Table 5, the negative electrode material of Example 5 that avoided atmospheric exposure as much as possible had lower powder resistance than the negative electrode material of Example 1 that was crushed while being exposed to the air after filtration. . From this result, it is possible to obtain a negative electrode material having a large amount of metallic nickel on the surface and excellent in conductivity by eliminating the disintegration of the negative electrode material in the air after the heating process after plating and avoiding exposure of the negative electrode material to the atmosphere as much as possible. It can be said.

(Example 6)
A negative electrode material of Example 6 was obtained in the same manner as in Example 1 except that the low oxygen gas exposure process was performed after the heating process.
Specifically, low oxygen gas in which argon gas and oxygen gas were mixed at a mass ratio of 99: 1 was circulated for 15 minutes in a heating furnace that was naturally cooled to room temperature after the heating step. In the low oxygen gas exposure step, the negative electrode material after the heating step was exposed to low oxygen gas to oxidize the negative electrode material under mild conditions. In addition, in the manufacturing method of the negative electrode material of Example 6, similarly to Example 1, the negative electrode material before plating and before the heating step was crushed in the atmosphere.

(Evaluation 12 Surface analysis)
The negative electrode material of Example 6 was subjected to surface analysis using XPS in the same manner as in Evaluation 2 above. The result of evaluation 12 is shown in FIG.

(Evaluation 13 Conductivity)
For the negative electrode material of Example 6, the powder resistance was measured in the same manner as in Evaluation 1 above. The results are shown in Table 6.

As shown in FIG. 12, the ratio of the peak intensity of 853 eV derived from metallic nickel to the peak intensity of 856 eV derived from nickel hydroxide is the same as that of the negative electrode material of Example 1 in the XPS spectrum of the negative electrode material of Example 6. It was much larger than the XPS spectrum. This result suggests that the ratio of metallic nickel to nickel hydroxide is higher on the surface of the negative electrode material of Example 6 than on the surface of the negative electrode material of Example 1. In the manufacturing method of Example 6, the negative electrode material was crushed in the air before the post-plating heating step, but it was considered that the oxidation of the negative electrode material surface was suppressed by performing the low oxygen gas exposure step thereafter.
In addition, as shown in Table 6, the negative electrode material of Example 6 that was subjected to the low oxygen gas exposure step after the heating step was crushed while being exposed to the air after filtration, and the low oxygen gas exposure step was not performed Compared with the negative electrode material of No. 1, the powder resistance was lowered. In addition, the negative electrode material of Example 6 had a lower powder resistance than the negative electrode material of Example 5 that avoided exposure to the atmosphere as much as possible and did not perform the low oxygen gas exposure step.
From this result, it can be seen that the conductivity of the negative electrode material can be further improved by performing the low oxygen gas exposure step after heating.

(Example 7)
Except for the heating temperature in the heating step, negative electrode materials of Examples 7-1 to 7-4 were obtained in the same manner as in Example 3.
Specifically, the heating temperatures in Example 7-1, Example 7-2, and Example 7-3 were 300 ° C., 250 ° C., and 200 ° C., respectively. In Example 7-4, the heating step was not performed.

(Evaluation 14 Conductivity)
For the negative electrode materials of Examples 7-1 to 7-4 and Example 3, the powder resistance was measured in the same manner as in Evaluation 1 above. The results are shown in Table 7.

As shown in Table 7, the powder resistance of the negative electrode material of Example 7-3 in which the heating temperature was 200 ° C. was comparable to the powder resistance of the negative electrode material of Example 7-4 that was not subjected to the heating step. In the heating temperature range of 250 ° C. to 350 ° C., the powder resistance decreased as the heating temperature increased. From this result, when performing a heating process, it can be said that it is preferable that heating temperature is a temperature exceeding 200 degreeC, it is more preferable that it is 250 degreeC or more, and it is still more preferable that it is 300 degreeC or more.

(Example 8)
Example 3 except that in the plating step, the amounts of the hydrogen storage alloy particles and the plating solution were adjusted so that the sum of the mass of nickel and the mass of cobalt relative to 100 parts by mass of the hydrogen storage alloy particles was 1 part by mass. A negative electrode material of Example 8 was obtained in the same manner as described above.
Example 9
Example 8 except that the sum of the mass of nickel and the mass of cobalt with respect to 100 parts by mass of the hydrogen storage alloy particles was 0.5 parts by mass, and that the heating temperature in the heating step was 300 ° C. The negative electrode material of Example 9 was obtained by the method.

(Evaluation 15 SEM observation)
The cross section of the negative electrode material of Example 8 and Example 9 was observed using SEM. Based on the SEM images, the plating thicknesses of the negative electrode materials of Examples 8 and 9 were measured. The results are shown in Table 8.
(Evaluation 16 Battery characteristics)
Using the negative electrode material of Example 8 and Example 9, nickel metal hydride batteries of Examples 8 and 9 were obtained in the same manner as the nickel metal hydride battery of Example 1. About the nickel metal hydride battery of the said Example 8 and Example 9, and the nickel metal hydride battery of the comparative example 1, battery characteristics were evaluated similarly to said evaluation 4. The results are shown in Table 8.

(Evaluation 17 DC-IR)
Using the nickel metal hydride batteries of Comparative Example 1, Example 8 and Example 9, the internal direct current resistance (DC-IR) was measured by the following method.
The nickel metal hydride batteries of Comparative Example 1, Example 8 and Example 9 were discharged at 25 ° C. to 1 V at a 0.33 C rate, then charged to SOC 61% at a 0.33 C rate, and further 0.1 C Was discharged to SOC 60%. Thereafter, the battery was further discharged at a 1C rate for 10 seconds, and the amount of change in voltage during discharge for 10 seconds at the 1C rate was measured.

The resistance value (DC-IR) was calculated by dividing the voltage change amount by the current value according to Ohm's law. The amount of change in voltage of each battery during 0.1 second discharge was also measured in the same manner, and the result was DC-IR at 25 ° C., SOC 60%, 0.1 second. Then, for each DC-IR in the nickel metal hydride batteries of Example 8 and Example 9, the percentage when the DC-IR in the nickel metal hydride battery of Comparative Example 1 was taken as 100% was calculated.
The results are shown in Table 8.

As shown in Table 8, the negative electrode material of Example 8 and Example 9 having a plating layer is less in internal resistance and the output of the nickel metal hydride battery than the negative electrode material of Comparative Example 1 having no plating layer. Greatly contributes to improvement.
In addition, when Example 8 and Example 9 are compared, by reducing the thickness of the plating layer, the internal resistance of the nickel metal hydride battery can be further reduced, and the output of the nickel metal hydride battery can be further improved. It is guessed.

The thickness of the plating layer is considered to be affected by the film formation rate in the reaction system of the plating process. The film formation rate is determined by, for example, the concentration of the plating solution in the reaction system of the plating process, specifically, the value obtained by dividing the sum of the mass of nickel and the mass of cobalt in the reaction system by the mass of the hydrogen storage alloy particles. Can be adjusted. As in Example 9, the plating layer thickness can be reduced by setting the concentration of the plating solution in the reaction system low.

(Example 10)
In the plating solution preparation step, the negative electrode material of Example 10 was prepared in the same manner as in Example 3 except that only nickel sulfate was used as the plating metal salt and the heating temperature in the heating step was 300 ° C. Obtained.
Specifically, in the negative electrode material manufacturing method of Example 10, in the plating solution preparation step, 3.0 g of NiSO ₄ .6H ₂ O and 1.5 g of malonic acid were measured and 75 g of distilled water was added. . This was heated to 90 ° C. to form a solution, and NaOH was added to maintain the solution at 80 ° C. so that the pH was 4 to 5, thereby obtaining a plating solution.

(Example 11)
In the plating solution preparation process, except that nickel sulfate hexahydrate and dicopper (II) carbonate dihydroxide were used as the plating metal salt so that the molar ratio of nickel to copper was 95: 5. In the same manner as in Example 10, the negative electrode material of Example 11 was obtained.

(Example 12)
In the plating solution preparation process, except that nickel sulfate hexahydrate and dicopper (II) carbonate dihydroxide were used as the plating metal salt so that the molar ratio of nickel to copper was 3: 1. In the same manner as in Example 10, the negative electrode material of Example 12 was obtained.

(Comparative Example 1-A)
A negative electrode material of Comparative Example 1-A was obtained in the same manner as in Comparative Example 1.

(Evaluation 18 Surface analysis)
The negative electrode materials of Example 11, Example 12, and Comparative Example 1-A were subjected to surface analysis using XPS in the same manner as in Evaluation 2 above. The results of Evaluation 18 are shown in FIGS. 13 shows the surface analysis results of the negative electrode material of Comparative Example 1-A, and FIGS. 14 and 15 show the surface analysis results of the negative electrode material of Example 11. The XPS spectrum shown in FIGS. 13 and 14 shows a peak mainly derived from nickel, and the XPS spectrum shown in FIG. 15 shows a peak mainly derived from copper.

As shown in FIG. 13, in the XPS spectrum of the negative electrode material of Comparative Example 1-A, that is, the negative electrode material before plating, the peak intensity of 856 eV derived from nickel hydroxide is higher than the peak intensity of 853 eV derived from metallic nickel. It was big. As shown in FIG. 14, in the XPS spectrum of the negative electrode material of Example 11, the peak intensity of 853 eV derived from metallic nickel was much larger than the peak intensity of 856 eV derived from nickel hydroxide. Although details will be described later, the XPS spectrum of the negative electrode material of Example 12 was almost the same as the XPS spectrum of the negative electrode material of Example 11.
From this result, it can be seen that the negative electrode material having a large amount of metallic nickel on the surface can also be manufactured in the negative electrode material manufacturing methods of Example 11 and Example 12 using copper as the metal for the plating solution.

Further, as shown in FIG. 15, on the surface of the negative electrode material of Example 11, the peak intensity of 953 eV derived from metallic copper and the peak intensity of 933 eV are compared with the peak intensity around 940 to 945 derived from copper oxide. It was remarkably big. The same was true for the XPS spectrum of the negative electrode material of Example 12.
From this result, it can be estimated that the ratio of metallic copper to copper oxide is large on the surfaces of the negative electrode materials of Examples 11 and 12.

(Evaluation 19 Conductivity)
For the negative electrode materials of Example 11, Example 12, and Comparative Example 1-A, the powder resistance was measured in the same manner as in Evaluation 1 above. The results are shown in Table 9.

As shown in Table 9, the powder resistance of the negative electrode material of Example 11 and the negative electrode material of Example 12 using nickel and copper as the plating metal is larger than the powder resistance of the negative electrode material of Comparative Example 1-A. It was low. From this result, it is understood that a negative electrode material having low powder resistance and excellent conductivity can be obtained even when copper is used instead of cobalt as the metal for the plating solution.

(Evaluation 20 Battery characteristics)
Using the negative electrode materials of Examples 10 to 12, nickel metal hydride batteries of Examples 10 to 12 were obtained in the same manner as the nickel metal hydride batteries of Example 1.
The nickel metal hydride batteries of Examples 10 to 12 were charged to SOC 100% at 25 ° C. and 0.1 C. The relationship between the voltage and the charging time at this time is shown in FIGS. 16 is a diagram comparing the charge curves of the nickel metal hydride batteries of Example 10 and Example 11, and FIG. 17 is a comparison of the charge curves of the nickel metal hydride batteries of Example 11 and Example 12. FIG.

As shown in FIGS. 16 and 17, the voltage of the nickel metal hydride batteries of Examples 10 to 12 when the SOC is 100% is about 1.45 to 1.5 V, and these nickel metal hydride batteries are It can be said that the battery is fully charged at a low voltage. This result suggests that the charging resistance of the nickel metal hydride batteries of Examples 10 to 12 is low.

Also, as shown in FIG. 16, the nickel metal hydride battery of Example 11 was fully charged at a lower voltage than the nickel metal hydride battery of Example 10. For this reason, when nickel and copper are included in the plating layer, it can be said that the charging resistance is further reduced as compared with the case where only nickel is included in the plating layer. That is, it is thought that the electroconductivity of a plating layer improves more by using nickel and copper together as a plating metal.

Furthermore, as shown in FIG. 17, the nickel metal hydride battery of Example 12 was fully charged at a lower voltage than the nickel metal hydride battery of Example 11. For this reason, when forming a plating layer containing nickel and copper as the plating metal, the molar ratio of nickel to copper in the plating solution is 3: 1 rather than 95: 5, considering the conductivity of the plating layer. It can be said that it is preferable. Furthermore, as a preferable range of the molar ratio of nickel and copper in the plating solution based on the result, 99: 1 to 30:70, 95: 5 to 50:50, 90:10 to 65:35, 80 : The range of 20 to 70:30 may be mentioned.

Note that copper hardly dissolves in a strong alkaline electrolyte in a nickel metal hydride battery. For this reason, there is also an advantage that durability of the plating layer can be improved by using nickel and copper together as the plating metal.

(Example 13)
A negative electrode material of Example 13 was obtained in the same manner as in Example 12 except that the heating temperature in the heating step was 250 ° C.
(Example 14)
A negative electrode material of Example 14 was obtained in the same manner as in Example 12 except that the heating temperature in the heating step was 350 ° C.

(Evaluation 21 Surface analysis)
About the negative electrode material of Example 12 and Example 14, the surface analysis using XPS was performed similarly to said evaluation 2. The results of evaluation 21 are shown in FIGS. 18 and 19 show the surface analysis results of the negative electrode material of Example 12, and FIGS. 20 and 21 show the surface analysis results of the negative electrode material of Example 14. The XPS spectra shown in FIGS. 18 and 20 show peaks mainly derived from nickel, and the XPS spectra shown in FIGS. 19 and 21 show peaks mainly derived from copper.

As shown in FIG.18 and FIG.20, also about the negative electrode material of Example 12 whose heating temperature in the heating process was 300 degreeC, also about the negative electrode material of Example 14 whose said heating temperature was 350 degreeC, metallic nickel The peak intensity in the vicinity of 853 eV derived from No. 1 was much larger than the peak intensity in the vicinity of 856 eV derived from the nickel hydroxide. From these results, it can be seen that even when copper is used as the plating metal in the production method of the present invention, negative electrode materials having a large amount of metallic nickel on the surface can be produced at various temperatures.

As shown in FIGS. 19 and 21, also on the surface of the negative electrode material of Example 12 and the negative electrode material of Example 14, the peak intensity around 953 eV and the peak intensity around 933 eV derived from metallic copper are copper oxide. The peak intensity around 940 to 945 derived from the product was remarkably large. From this result, according to the manufacturing method of the present invention, even when the temperature condition of the heating process is changed, when copper is used as the plating metal, the negative electrode material has a high ratio of metallic copper to copper oxide on the surface of the negative electrode material. It can be seen that can be manufactured.

(Evaluation 22 Surface observation)
About the negative electrode material of Example 12 and Example 14, the surface was observed by SEM. The SEM image of the surface of the negative electrode material of Example 12 is shown in FIG. 22, and the SEM image of the surface of the negative electrode material of Example 14 is shown in FIG.
As shown in FIGS. 22 and 23, aggregates of particles similar to those observed in FIGS. 3 and 4 were observed on the surfaces of the negative electrode materials of Examples 12 and 14. From this result, even when copper is used as the plating metal in the manufacturing method of the present invention, a plating layer composed of an aggregate of particles is formed on the surface of the negative electrode material, as in the case of using cobalt as the plating metal. You can see that
In addition, particles having a larger particle diameter were observed on the surface of the negative electrode material of Example 14 shown in FIG. 23 than on the surface of the negative electrode material of Example 12 shown in FIG. Since the difference between the manufacturing method of Example 12 and the manufacturing method of Example 14 is the heating temperature in the heating step, the heating temperature is set to 350 ° C., which is compared with the case where the heating temperature is set to 300 ° C. It is considered that the particles constituting the layer grow. Furthermore, it is estimated that the crystallinity of the plating layer is improved by setting the heating temperature to 350 ° C.

(Evaluation 23 Battery characteristics)
Using the negative electrode materials of Example 10 and Examples 12 to 14, nickel metal hydride batteries of Example 10 and Examples 12 to 14 were obtained in the same manner as the nickel metal hydride battery of Example 1. .
The nickel metal hydride batteries of Example 10 and Examples 12 to 14 were charged to 100% SOC at 25 ° C. and 0.1 C, and then discharged to 1 V at 0.2 C. The relationship between the voltage and the charging time or discharging time at this time is shown in FIG.

As shown in FIG. 24, all of the nickel metal hydride batteries were charged and discharged well. In particular, the nickel metal hydride battery of Example 14 having a heating temperature of 350 ° C. was fully charged at the lowest potential and Since the discharge was performed at the highest potential, it can be said that the negative electrode material of Example 14 shows excellent performance as a negative electrode material for nickel metal hydride batteries. From this result, it can be seen that the heating temperature in the heating step is preferably 350 ° C. in the manufacturing method of the present invention using nickel and copper as the plating metal.

(Evaluation 24 Conductivity)
About the negative electrode material of Example 13 and Example 14, powder resistance was measured similarly to said evaluation 1. The results are shown in Table 10. In Table 10, the powder resistance of the negative electrode material of Example 12 according to Evaluation 19 is also shown.

As shown in Table 10, the powder resistance is low in the order of Example 13, Example 12, and Example 14, and in the method for producing the negative electrode material of Examples 12 to 14, the heating temperature in the heating step is high. It can be seen that a negative electrode material having better conductivity can be produced.
Considering the result of evaluation 22, when the heating temperature is 350 ° C., the particles constituting the plating layer grow or the crystallinity of the particles is higher than when the heating temperature is 300 ° C. As a result, it is speculated that excellent conductivity was imparted to the plating layer.

(Evaluation 25 DC-IR)
For the nickel metal hydride batteries of Example 10, Example 14, and Example 13, the DC-IR was measured for 60% SOC and 10 seconds under the same conditions as in Evaluation 17 under two conditions of 25 ° C. and 0 ° C. The results are shown in Table 11.

As shown in Table 11, the discharge resistance of the nickel metal hydride battery of Example 14 was lower than that of the nickel metal hydride battery of Example 10 and the nickel metal hydride battery of Example 13. From this result, nickel metal hydride battery that not only nickel but also nickel and copper were used together as the plating metal for the negative electrode material, and that the heating temperature in the heating process was 350 ° C. higher than 250 ° C. It is presumed that this works favorably for reducing DC resistance.

(Example 15)
In the plating step, the same as Example 11 except that nickel sulfate hexahydrate and ruthenium nitrate (III) nitrate solution were used as the plating metal salt so that the molar ratio of nickel to ruthenium was 70:30. The negative electrode material of Example 15 was obtained by the method described above.

(Example 16)
In the plating process, except that nickel sulfate hexahydrate and ruthenium nitrate (III) nitrate solution were used as plating metal salts so that the molar ratio of nickel to ruthenium was 97.5: 2.5. In the same manner as in Example 15, the negative electrode material of Example 16 was obtained.

(Evaluation 26 Battery Characteristics)
Using the negative electrode material of Example 15 and Example 16, the nickel metal hydride battery of Example 15 and Example 16 was obtained in the same manner as the nickel metal hydride battery of Example 1.
About the nickel metal hydride battery of Example 15 and Example 16, it charged to SOC100% at 25 degreeC and 0.1 C, and discharged to 1V at 0.2 C after that. The relationship between the voltage at this time and the charging time or discharging time is shown in FIG. 25 together with the result of Example 10 in Evaluation 23.

As shown in FIG. 25, the nickel metal hydride battery of Example 15 and the nickel metal hydride battery of Example 16 are fully charged at a lower potential than the nickel metal hydride battery of Example 10, and Discharged at a high potential. For this reason, compared with the negative electrode material of Example 10 which contains only nickel as a plating metal, the negative electrode material of Example 15 which contains nickel and ruthenium as a plating metal and the negative electrode material of Example 16 are for nickel metal hydride batteries. It can be said that it exhibits excellent performance as a negative electrode material.

Also, compared with the nickel metal hydride battery of Example 16 using a negative electrode material in which the molar ratio of nickel to ruthenium is 97.5: 2.5, the negative electrode material in which the molar ratio of nickel to ruthenium is 70:30 The nickel metal hydride battery of Example 15 using was fully charged at a lower potential and discharged at a higher potential. For this reason, when ruthenium is contained in the plated metal, it can be said that the higher the content of ruthenium, the better the performance as a negative electrode material for nickel metal hydride batteries. Considering the result of evaluation 26, the molar ratio of nickel to ruthenium in the plating solution is preferably in the range of 99: 1 to 50:50, more preferably in the range of 98: 2 to 60:40. The range of 97: 3 to 65:35 is more preferable.

(Example 17)
A negative electrode material of Example 17 was obtained in the same manner as in Example 15 except that the heating temperature in the heating step was 350 ° C.

(Example 18)
A negative electrode material of Example 18 was obtained in the same manner as in Example 17, except that the heating temperature in the heating step was 400 ° C.

(Evaluation 27 DC-IR)
Using the negative electrode material of Example 17, Example 18 and Example 14, the nickel metal hydride battery of Example 17, Example 18 and Example 14 was obtained in the same manner as the nickel metal hydride battery of Example 1. .
For the nickel metal hydride batteries of Example 17, Example 18 and Example 14, and the nickel metal hydride battery of Example 10, as in Evaluation 17, 0.1 second, 1 second, 5 seconds, and 10 DC-IR at 25 ° C. and SOC 60% was measured under four conditions for 2 seconds. The results are shown in Table 12.

As shown in Table 12, the nickel metal hydride batteries of Example 17 and Example 18 using nickel and ruthenium as the plating metal are only the nickel metal hydride batteries of Example 10 using only nickel as the plating metal. In comparison with the nickel metal hydride battery of Example 14 using nickel and copper as the plating metal, the DC resistance was reduced. For this reason, it is presumed that the combined use of nickel and ruthenium as the plating metal is advantageous for reducing the DC resistance.

Ruthenium, like copper, is unlikely to elute into a strong alkaline electrolyte in nickel metal hydride batteries. For this reason, it is possible to improve the durability of the plating layer by using nickel and ruthenium as the plating metal in the same manner as when using nickel and copper as the plating metal.

(Evaluation 28 Surface analysis)
About the negative electrode material of Example 17 and Example 18, the surface analysis using XPS was performed similarly to said evaluation 2. The results of Evaluation 28 are shown in FIGS. 26 and 27 show the surface analysis results of the negative electrode material of Example 17, and FIGS. 28 and 29 show the surface analysis results of the negative electrode material of Example 18. The XPS spectra shown in FIGS. 26 and 28 mainly show peaks derived from nickel, and the XPS spectra shown in FIGS. 27 and 29 show peaks mainly derived from ruthenium.

As shown in FIGS. 26 and 28, in the XPS spectrum of the negative electrode material of Example 17 and the XPS spectrum of the negative electrode material of Example 18, the peak intensity of 853 eV derived from metallic nickel is derived from nickel hydroxide. It was much larger than the peak intensity of 856 eV.
From this result, it is possible to produce a negative electrode material in which a large amount of nickel metal is present on the surface even in the negative electrode material production methods of Example 17 and Example 18 in which nickel and ruthenium are used in combination as the metal for the plating solution. Recognize.

Further, as shown in FIGS. 27 and 29, in the XPS spectrum of the negative electrode material of Example 17 and the XPS spectrum of the negative electrode material of Example 18, the peak intensity of 280.1 eV derived from metal ruthenium is higher than that of ruthenium oxide. It was much larger than the peak intensity of 280.8 eV derived.
From this result, it can be presumed that the ratio of the metal ruthenium to the ruthenium oxide is large on the surface of the negative electrode material of Example 17 and Example 18.

(Evaluation 29 conductivity)
About the negative electrode material of Example 17 and Example 18, powder resistance was measured similarly to said evaluation 1. The results are shown in Table 13 together with the powder resistance of the negative electrode material of Comparative Example 1-A.

As shown in Table 13, the powder resistance of the negative electrode material of Example 17 and the negative electrode material of Example 18 in which nickel and ruthenium are used in combination as plating metals is that of Comparative Example 1-A using only nickel as the plating metal. It was lower than the powder resistance of the negative electrode material. From this result, it is understood that a negative electrode material having low powder resistance and excellent conductivity can be obtained even when ruthenium is used instead of cobalt or copper as the metal for the plating solution.

(Evaluation 30 Battery characteristics)
About the nickel metal hydride battery of Example 17 and Example 18, it charged to SOC100% at 25 degreeC and 0.1C. The relationship between the voltage and the charging time or discharging time at this time is shown in FIG. 30 together with the result of Example 10 in Evaluation 23.

As shown in FIG. 30, the nickel metal hydride battery of Example 17 and the nickel metal hydride battery of Example 18 were fully charged at a lower potential than the nickel metal hydride battery of Example 10. For this reason, the negative electrode material of Example 17 and the negative electrode material of Example 18 containing nickel and ruthenium as the plating metal are compared with the negative electrode material of Example 10 containing only nickel as the plating metal for the nickel metal hydride battery. It can be said that it exhibits excellent performance as a negative electrode material.

In addition, the nickel metal hydride battery of Example 18 using a negative electrode material having a heating temperature of 400 ° C. is still lower than the nickel metal hydride battery of Example 17 using a negative electrode material having a heating temperature of 350 ° C. Fully charged with potential. For this reason, when nickel and ruthenium are used together as plating metals in the method for producing a negative electrode material of the present invention, it is considered that a higher heating temperature is preferable in order to realize charging at a lower potential. Considering the result of evaluation 30, when nickel and ruthenium are used in combination as the plating metal, the preferable range of the heating temperature in the heating step is 250 ° C. to 500 ° C., 300 ° C. to 500 ° C., 350 ° C. to 500 ° C. , 350 ° C. or higher, 480 ° C. or lower, 360 ° C. or higher and 450 ° C. or lower.

(Example 19)
The negative electrode material of Example 19 has A ₂ B ₇ type hydrogen storage alloy particles and a plating layer containing nickel and indium and formed on the hydrogen storage alloy particles.
The method for producing the negative electrode material of Example 19 was that indium sulfate was used as the metal salt, the average particle diameter of the hydrogen storage alloy particles was 25 μm, the heating temperature was 400 ° C., and nickel and indium Except that the nickel salt and the metal salt were blended so that the molar ratio was 0.5: 0.25, the production method of the negative electrode material of Example 1 was the same.

In the plating solution preparation step of the negative electrode material manufacturing method of Example 19, 1.5 g of NiSO ₄ .6H ₂ O, 1.5 g of In ₂ (SO ₄ ) ₃ .9H ₂ O, and 1.5 g of dicarboxylic acid Weighed and added 75 g of distilled water. This was heated to 90 ° C. to form a solution, and NaOH was added to maintain the solution at 80 ° C. so that the pH was 4 to 5, thereby obtaining a plating solution.
Moreover, in the heating process of the negative electrode material manufacturing method of Example 19, after the plating process, the vacuum dried negative electrode material was heated from room temperature to 400 ° C. in an argon atmosphere and baked. The fired negative electrode material was used as the negative electrode material of Example 19.

(Example 20)
A negative electrode material of Example 20 was obtained in the same manner as in Example 19, except that the negative electrode material was heated from room temperature to 350 ° C. and fired in the heating step.
(Comparative Example 1-B)
A negative electrode material of Comparative Example 1-B was obtained in the same manner as Comparative Example 1 and Comparative Example 1-A.

(Evaluation 31 Conductivity)
For the negative electrode materials of Example 19, Example 20, and Comparative Example 1-B, the powder resistance was measured in the same manner as in Evaluation 1. Table 14 shows the results of the electrical conductivity evaluation.

As shown in Table 14, the powder resistance of the negative electrode material of Example 19 and the negative electrode material of Example 20 is lower than the powder resistance of the negative electrode material of Comparative Example 1-B. Since the negative electrode material of Example 19 and the negative electrode material of Example 20 have a plating layer, this result is considered to be due to the presence or absence of the plating layer. In Example 19 and Example 20, since the plating solution containing nickel sulfate and indium sulfate is used, the negative electrode material of Example 19 and the negative electrode material of Example 20 are considered to contain nickel and indium. It is done. Therefore, from the results of the conductivity evaluation shown in Table 14, it can be said that excellent conductivity can be imparted to the negative electrode material even when a plating layer containing nickel and indium is provided instead of the plating layer containing nickel and cobalt. Can do.

Further, comparing the powder resistance of the negative electrode material of Example 19 and the negative electrode material of Example 20, the heating temperature in the heating step of the negative electrode material of Example 19 that was 400 ° C. in the heating step was 350 ° C. Compared with the negative electrode material of Example 20 that was, the powder resistance was remarkably reduced.
From this result, it can be said that when a plating layer containing nickel and indium is provided, heating the negative electrode material at a temperature exceeding 350 ° C. greatly contributes to improvement in conductivity.

(Evaluation 32 SEM observation)
About the negative electrode material of Example 19, and the negative electrode material of Example 20, the surface was observed similarly to evaluation 3 SEM observation. An SEM image of the negative electrode material of Example 19 is shown in FIG. 31, and an SEM image of the negative electrode material of Example 20 is shown in FIG.

As shown in FIG. 31, the surface of the negative electrode material of Example 19 has a mesh shape, and as shown in FIG. 32, the surface of the negative electrode material of Example 20 has fine irregularities formed of particle aggregates. It was. From this result, it is suggested that the plating layer containing nickel and indium is actually melted at 400 ° C., does not melt at 350 ° C. or less, and the molten plating layer has a mesh shape.

Further, in view of the above-described evaluation 31 conductivity results, the negative electrode material of Example 19 having a mesh shape on the surface is more conductive than the negative electrode material of Example 20 having a fine irregular surface and no mesh shape on the surface. It can be said that it is excellent.

(Evaluation 33 Surface analysis)
The negative electrode material of Example 20 and the negative electrode material of Comparative Example 1-B were subjected to surface analysis in the same manner as in Evaluation 2, Surface Analysis. The surface analysis results of the negative electrode material of Example 20 and the negative electrode material of Comparative Example 1-B measured by XPS are shown in FIG. 33 and FIG.

As shown in FIGS. 33 and 34, in the XPS spectrum of the negative electrode material of Example 20 and the XPS spectrum of the negative electrode material of Comparative Example 1-B, the binding energy region of 856 eV derived from nickel hydroxide, and the metallic nickel Peaks were observed in both of the derived 853 eV binding energy region. In the XPS spectrum of the negative electrode material of Comparative Example 1-B shown in FIG. 34, the peak intensity of 856 eV derived from nickel hydroxide is much higher than the peak intensity of 853 eV derived from metallic nickel. In contrast, in the XPS spectrum of the negative electrode material of Example 20 shown in FIG. 33, the peak intensity of 853 eV derived from metallic nickel is larger than the peak intensity of 856 eV derived from nickel hydroxide. From this result, it is considered that a lot of nickel hydroxide is present on the surface of the negative electrode material of Comparative Example 1-B, whereas a lot of nickel metal is present on the surface of the negative electrode material of Example 20.

Further, from the results of FIG. 34, nickel is also present on the surface of the negative electrode material of Comparative Example 1-B having no plating layer, the nickel is considered to be included in the hydrogen storage alloy, and the nickel It turns out that many are hydroxides. This result further suggests that the metallic nickel confirmed on the surface of the negative electrode material of Example 20 was not originally contained in the hydrogen storage alloy but originated from the plating layer.

Further, in the XPS spectrum of the negative electrode material of Example 20 shown in FIG. 33, a peak of 870 eV is confirmed, whereas in the XPS spectrum of the negative electrode material of Comparative Example 1-B shown in FIG. 34, the peak of 870 eV is Not confirmed. The peak at 870 eV is considered to be derived from metallic nickel and a nickel indium compound (specifically, InNi or InNi ₃ ). Therefore, this result means that the plating layer contains Ni and In. Further, this result suggests that the plating layer contains a nickel indium alloy, and the nickel indium alloy is mainly composed of a mesh shape.

Claims (15)

A plating solution preparation step for obtaining a plating solution containing a nickel salt, a heteroelement-containing organic compound and an aqueous solvent;
A negative electrode material in which a nickel-containing plating layer is formed on the hydrogen storage alloy particles by mixing a hydrogen storage alloy particle dispersion containing an aqueous solvent and hydrogen storage alloy particles, the plating solution, and a reducing agent. And a plating step for obtaining a negative electrode material. The plating solution in the plating solution preparation step further contains a metal salt,
The method for manufacturing a negative electrode material according to claim 1, wherein the plating layer includes nickel and a metal. The manufacturing method of the negative electrode material of Claim 1 or 2 which has a heating process which heats the negative electrode material obtained at the said plating process at the temperature of 250 degreeC or more and 450 degrees C or less. The method for producing a negative electrode material according to claim 3, further comprising a low oxygen gas exposure step of exposing the negative electrode material to a low oxygen gas after the heating step. The method for producing a negative electrode material according to any one of claims 1 to 4, wherein an organic compound dispersant is further added in the plating step. The method for producing a negative electrode material according to claim 5, wherein the organic compound dispersant is a water-soluble polymer or a water-soluble monomer. The production of a negative electrode material according to any one of claims 1 to 6, wherein the hydrogen storage alloy particles include a hydrogen storage alloy selected from A ₂ B ₇ type, A ₅ B ₁₉ type, and AB ₃ type. Method. Hydrogen storage alloy particles, and a plating layer formed on the hydrogen storage alloy particles,
The plating layer includes nickel;
A negative electrode material for a nickel metal hydride battery, wherein the peak intensity derived from metallic nickel is larger than the peak intensity derived from nickel hydroxide in the surface XPS spectrum. The value obtained by dividing the BET specific surface area of the negative electrode material for nickel metal hydride batteries having the hydrogen storage alloy particles and the plating layer by the BET specific surface area of the hydrogen storage alloy particles is 3 or more. The negative electrode material for nickel metal hydride batteries described in 1. The ratio B / A between the mass A of the rare earth metal and the mass B of the transition metal on the surface of the negative electrode material for nickel metal hydride batteries having the hydrogen storage alloy particles and the plating layer is:
The negative electrode material for nickel metal hydride batteries according to claim 8 or 9, which is 20 times or more of the ratio B / A on the surface of the hydrogen storage alloy particles. 11. The negative electrode material for a nickel metal hydride battery according to claim 8, wherein the plating layer contains at least one selected from a nickel indium alloy, a nickel bismuth alloy, a nickel tin alloy, and a nickel cadmium alloy. 12. The negative electrode material for a nickel metal hydride battery according to claim 8, wherein the surface has a mesh shape. 13. The negative electrode material for a nickel metal hydride battery according to claim 8, wherein the hydrogen storage alloy particles include a hydrogen storage alloy selected from A ₂ B ₇ type, A ₅ B ₁₉ type, and AB ₃ type. A nickel metal hydride battery negative electrode comprising the nickel metal hydride battery negative electrode material according to any one of claims 8 to 13. 15. A nickel metal hydride battery having the negative electrode for nickel metal hydride battery according to claim 14.

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