WO2018216374A1

WO2018216374A1 - Positive electrode for nickel metal hydride batteries

Info

Publication number: WO2018216374A1
Application number: PCT/JP2018/014893
Authority: WO
Inventors: 祐樹杉本; 厚志南形
Original assignee: 株式会社豊田自動織機
Priority date: 2017-05-23
Filing date: 2018-04-09
Publication date: 2018-11-29
Also published as: JP2018198147A

Abstract

The present invention addresses the problem of providing a collector coating type positive electrode for nickel metal hydride batteries, which has excellent electrical conductivity. A positive electrode for nickel metal hydride batteries, which comprises a collector and a positive electrode active material layer that is formed on the collector, and wherein the positive electrode active material layer contains positive electrode active material particles and nickel particles that have smaller diameters than the positive electrode active material particles.

Description

Nickel metal hydride battery positive electrode

The present invention relates to a positive electrode used in a nickel metal hydride battery.

The nickel metal hydride battery is a secondary battery including a positive electrode having a nickel oxide compound as a positive electrode active material, a negative electrode having a hydrogen storage alloy as a negative electrode active material, and an electrolyte solution made of an alkali metal aqueous solution.

Various studies have been conducted to improve the performance of nickel metal hydride batteries. Since nickel oxide compounds, which are positive electrode active materials for nickel metal hydride batteries, are relatively inferior in conductivity, a three-dimensional structure current collector with excellent conductivity is used for nickel metal hydride batteries as a technology that focuses on the positive electrode. Technology has been proposed.

Patent Document 1 discloses a positive electrode plate for a nickel metal hydride battery, in which a porous foamed nickel substrate is filled with a paste-like kneaded material containing a nickel oxide compound as a main component and is pressure-formed after drying. Yes. Patent Document 1 discloses that the foamed nickel substrate is obtained by performing nickel plating on a plate-shaped foam core, and then removing the foam core by heating or the like.

In this type of nickel metal hydride battery positive electrode plate, a nickel oxide compound is filled in the pores of a current collector having excellent conductivity and is closely integrated with the current collector. That is, in this type of positive electrode plate for nickel metal hydride batteries, the current collector itself is three-dimensionally distributed in the thickness direction of the positive electrode to form a conductive path for the positive electrode active material. For this reason, it is thought that this kind of positive electrode plate for nickel metal hydride batteries imparts excellent conductivity to the positive electrode.

JP 2001-35500 A

By the way, when using current collectors, such as metal foil, like the electrode of a general lithium ion secondary battery instead of the above-mentioned foam nickel substrate, the slurry containing nickel oxide compound particles is used as the current collector. It is assumed that a positive electrode active material layer is formed by coating on the top. Hereinafter, as necessary, this type of electrode manufacturing mode is referred to as a current collector coating type, and the nickel oxide compound particles are referred to as positive electrode active material particles.
In the current collector-coated positive electrode, it is assumed that many positive electrode active material particles are largely separated from the current collector in the thickness direction of the positive electrode, and the conductivity of the positive electrode active material layer as a whole is impaired. For this reason, in order to give sufficient electrical conductivity to the current collector-coated positive electrode, a positive electrode having a composition different from that of a conventional positive electrode plate for nickel metal hydride batteries using a foamed nickel substrate as a current collector. It is necessary to design an active material layer.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a collector-coated positive electrode for nickel metal hydride batteries, which is excellent in conductivity.

The inventor of the present invention actually manufactured a current collector-coated positive electrode with various changes in the composition of the positive electrode active material layer, and improved the conductivity of the current collector-coated positive electrode. The composition of the layer was explored. The inventor considered that a conductive path can be formed between the positive electrode active material and the current collector by using the conductive assistant in combination with the nickel oxide compound having poor conductivity, that is, the positive electrode active material particles. However, in practice, carbon-based conductive assistants such as acetylene black and carbon black, which are general conductive assistants, are not suitable for the positive electrode of nickel metal hydride batteries.

That is, since the carbon-based conductive additive is oxidized at the positive electrode even under a relatively low voltage in a nickel metal hydride battery in which an alkali metal aqueous solution is present, it is difficult to maintain the function as a conductive additive. For this reason, a carbon-type conductive support agent is not suitable for the positive electrode of a nickel metal hydride battery. The inventor of the present invention has completed the present invention through further intensive studies based on the above findings.

The positive electrode for nickel metal hydride battery of the present invention is
A current collector, and a positive electrode active material layer formed on the current collector,
The positive electrode active material layer is a positive electrode for a nickel metal hydride battery having positive electrode active material particles and nickel particles having a smaller diameter than the positive electrode active material particles.

The positive electrode for nickel metal hydride batteries of the present invention is a current collector-coated positive electrode for nickel metal hydride batteries and has excellent conductivity.

It is explanatory drawing which represents typically arrangement | positioning of the positive electrode active material particle and nickel particle | grains of the positive electrode active material layer in the positive electrode for nickel metal hydride batteries of this invention.

Hereinafter, modes for carrying out the present invention will be described. Unless otherwise specified, the numerical range “a to b” described in this specification includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from these numerical ranges can be used as new upper and lower numerical values.

The positive electrode for nickel metal hydride batteries of the present invention is a current collector-coated positive electrode for nickel metal hydride batteries having a current collector and a positive electrode active material layer formed on the current collector. . In the positive electrode for a nickel metal hydride battery of the present invention, the positive electrode active material layer includes positive electrode active material particles and nickel particles having a smaller diameter than the positive electrode active material particles. Hereinafter, the positive electrode for nickel metal hydride batteries of the present invention is simply referred to as the positive electrode of the present invention as necessary.

As described above, since the positive electrode of the present invention is a current collector-coated positive electrode, many positive electrode active material particles are largely separated from the current collector in the thickness direction of the positive electrode. However, the positive electrode of the present invention includes nickel particles that can electrically connect the positive electrode active material particles and the current collector. The nickel particles are hardly oxidized even during charge / discharge of the nickel metal hydride battery, and can maintain the function as a conductive additive. That is, in the positive electrode of the present invention, the conductive path that connects the positive electrode active material particles and the current collector is stably formed by the nickel particles as the conductive auxiliary agent. For this reason, the positive electrode of this invention can exhibit the outstanding electroconductivity.

Depending on the type of metal, when nickel metal hydride batteries are charged and discharged in the presence of an aqueous alkali metal solution that is an electrolyte, deterioration such as corrosion occurs. However, the nickel selected as a conductive additive in the positive electrode of the present invention. Is hardly deteriorated even under such conditions. It can be said that the positive electrode of the present invention can also exhibit excellent conductivity by using such a conductive additive.

In the positive electrode of the present invention, nickel particles having a smaller diameter than the positive electrode active material particles are used. Nickel particles having a diameter smaller than that of the positive electrode active material particles are suitable for entering the gaps between the positive electrode active material particles, and therefore suitable for efficiently forming a conductive path between the positive electrode active material particles and the current collector. it is conceivable that. Also by this, the positive electrode of the present invention can exhibit excellent conductivity.
In this specification, “the nickel particles are smaller than the positive electrode active material particles” means “the average particle diameter of the nickel particles used as the positive electrode material is the average of the positive electrode active material particles also used as the positive electrode material”. It means that less than the particle size ", the average particle diameter means a value of D ₅₀ in the measurement using a conventional laser diffraction particle size distribution meter.

Meanwhile, the inventors of the present invention, among which seek a positive electrode for a nickel-metal hydride batteries of the collector coating type excellent conductivity, the average particle diameter of the average particle diameter R ₁ and the nickel particles of the positive electrode active material particle It has been found that there is an optimum range for the relationship with R _{2 in} order to improve conductivity. Hereinafter, the arrangement of the positive electrode active material particles and the nickel particles in the positive electrode active material layer on the basis of FIG. 1 illustrating schematically the relationship between the average particle diameter R ₂ of average particle diameter R ₁ and the nickel particles of the positive electrode active material particle Will be explained.

As shown in FIG. 1, the positive electrode active material particles 1 are present in the positive electrode active material layer in a relatively high density state. In order to form a conductive path between the current collector (not shown) and the positive electrode active material particles 1 while maintaining the positional relationship of the positive electrode active material particles 1, the average particle diameter R2 of the nickel particles ₂ is adjacent to each other. It is considered that the size is preferably such that it can enter the gap b between the matching positive electrode active material particles 1.

When the average particle diameter of the positive electrode active material particles 1 is R ₁ and the size of the gap between the adjacent positive electrode active material particles 1 is b,
The relationship of (R ₁ + b) ² = R ₁ ² + R ₁ ² is established. To organize this,
{B + (2 ^1/2 +1) R ₁ } {b− (2 ^1/2 −1) R ₁ } = 0
From R ₁ > 0, b> 0,
b = (2 ^1/2 −1) R ₁ Here, in order for the nickel particles 2 to enter the gaps between the adjacent positive electrode active material particles 1, the relationship between the average particle diameter R ₂ of the nickel particles ₂ and the gap size b needs to be R ₂ ≦ b. some reason, the preferred relationship between the average particle diameter R ₂ of average particle diameter R ₁ and the nickel particles 2 of the positive electrode active material particle 1,
It can be said that R ₂ ≦ (2 ^1/2 −1) R ₁ .

Hereafter, each element which comprises the positive electrode of this invention is demonstrated in detail.
The positive electrode of the present invention includes a current collector and a positive electrode active material layer formed on the current collector, and the positive electrode active material layer includes positive electrode active material particles and positive electrode active material particles. A nickel metal hydride battery positive electrode having a smaller diameter nickel particle.

The positive electrode of the present invention is a current collector-coated positive electrode, and the current collector in the positive electrode of the present invention is a current collector in a conventional nickel metal hydride battery, that is, a foil shape, unlike a foamed nickel substrate. It has a thin plate shape such as a sheet shape, a film shape, or a plate shape. The term “thin plate” as used herein refers to a range of 1 mm or less in thickness. More preferably, the thickness of the current collector is 100 μm or less, 50 μm or less, 20 μm or less, or 10 μm or less. There is no lower limit to the thickness of the current collector, but to be strong, a range of 0.5 μm or more and 1 μm or more can be mentioned.

Further, the current collector in the positive electrode of the present invention can also be expressed as a current collector having a low porosity. Examples of the porosity of the current collector in the positive electrode of the present invention include a range of 20% by volume or less, 10% by volume or less, 5% by volume or less, and 2% by volume or less. Further, as the current collector in the positive electrode of the present invention, one having no pores, that is, one having a porosity of 0% by volume can be used. As the porosity, a value measured by a mercury intrusion method or a gas adsorption method may be used.

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.

A positive electrode active material layer is formed on the surface of the current collector. The positive electrode active material layer may contain a binder and other additives in addition to the positive electrode active material particles as the positive electrode active material and the nickel particles as the conductive additive.

The positive electrode active material particles are particulate nickel oxide compounds. Specific examples of the nickel oxide compound 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. As a positive electrode active material particle, only 1 type of these may be used and 2 or more types may be used together.

The average particle diameter of the positive electrode active material particles is preferably in the range of 1 to 100 μm, more preferably in the range of 3 to 50 μm, still more preferably in the range of 5 to 30 μm, and particularly preferably in the range of 7 to 20 μm.
The surface of the positive electrode active material particles may be treated by a known method.

The amount of the positive electrode active material particles is preferably 75 to 99% by mass, more preferably 80 to 97% by mass, and 82 to 95% by mass with respect to the total mass of the positive electrode active material layer. Is more preferable. The preferable range of the amount of the positive electrode active material particles mentioned here can be regarded as a preferable blending amount of the positive electrode active material particles with respect to the material of the positive electrode active material layer. In this case, the solid content of the positive electrode active material layer may be 100% by mass. Similarly, the preferable range of the amount of each substance in the positive electrode, the negative electrode, the electrolytic solution, the nickel metal hydride battery and the like can be regarded as the blending amount of each substance.

The nickel particles are metallic nickel in the form of particles. The average particle diameter of the nickel particles may be smaller than the average particle diameter of the positive electrode active material particles, and the range of the average particle diameter of the nickel particles is not particularly limited, but is preferably 0.5 μm or more, and is 1 μm or more. Is more preferable. Further, as described above, the relationship between the average particle diameter _{R 2} of average particle diameter _{R 1} and the nickel particles of the positive electrode active material _{^{particles, R 2 ≦ (2 1/2 -1}} ) preferably is _{R 1.}
The surface of the nickel particles may also be treated by a known method.

The amount of nickel particles is preferably 0.3% by mass to 15% by mass, more preferably 0.5% by mass to 10% by mass with respect to the total mass of the positive electrode active material layer. % To 10% by mass is more preferable, 3% to 8% by mass is more preferable, 3% to 7% by mass is still more preferable, and 3% to 6% by mass is preferable. Is particularly preferred.

The positive electrode active material layer in the positive electrode of the present invention may contain a conductive additive other than nickel particles. The conductive aid other than the nickel particles is referred to as a second conductive aid as necessary. The second conductive additive may be added to the positive electrode active material layer in a powder state. Alternatively, the surface of the positive electrode active material particles may be coated with the second conductive auxiliary agent, and an integrated product of the second conductive auxiliary agent and the positive electrode active material particles may be used for the positive electrode. Specific examples of the second conductive assistant include metals such as cobalt and copper, metal oxides such as cobalt oxide, and metal hydroxides such as cobalt hydroxide. Among these, metallic cobalt forms a coating layer of a cobalt compound having excellent conductivity on the surface of the positive electrode active material particles in a nickel metal hydride battery. For this reason, metallic cobalt is particularly preferably used as the second conductive additive. In addition, when a coat layer is formed on the surface of the positive electrode active material particles by the second conductive additive, the average particle size of the positive electrode active material particles before coating can be regarded as the average particle size of the positive electrode active material particles. . This is because even when the treatment is performed, there is almost no change in the average particle diameter of the positive electrode active material particles before and after the treatment.
Although there is no particular limitation on the average particle size of the second conductive additive, the average particle size is preferably smaller than the average particle size of the positive electrode active material particles in the same manner as the nickel particles.

The amount of the second conductive auxiliary agent is preferably 0.5 to 7% by mass, more preferably 1 to 5% by mass, with respect to the total mass of the positive electrode active material layer. More preferably, it is 4.5 mass%.

Examples of the additive include Y ₂ O ₃ , Li ₂ WO ₄ , Na ₂ WO ₄ , and K ₂ WO ₄ . These additives are preferably contained in a total amount of 0.05 to 5% by mass, more preferably 0.1 to 4% by mass, based on the total mass of the positive electrode active material layer. More preferably, it is contained at 2 to 3% by mass. These additives can suppress the generation of oxygen in the nickel metal hydride battery.

The binder plays a role of connecting the positive electrode active material and the like to the surface of the current collector. As a binder, what is used as a binder for electrodes of a nickel metal hydride battery may be used, and it is not particularly limited. 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 positive electrode active material layer, the binder is preferably contained in an amount of 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, based on the mass of the entire positive electrode active material layer. It is preferably contained at 1 to 7% by 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.

In order to form the positive electrode active material layer on the surface of the current collector, a conventionally known 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 may be used. Specifically, positive electrode active material particles, nickel particles, a solvent, and if necessary, a binder, a second conductive auxiliary agent, and other additives are mixed to form a slurry, and then the slurry is collected. After applying to the body surface, it is 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.

As described above, since the positive electrode of the present invention is a collector-coated positive electrode, the present invention can also be regarded as an invention relating to a method for manufacturing a positive electrode.
In this case, the method for producing the positive electrode of the present invention is as follows.
Producing a positive electrode active material layer slurry comprising positive electrode active material particles, nickel particles having a smaller diameter than the positive electrode active material particles, and a solvent; and
It can be expressed as a method for producing a positive electrode for a nickel metal hydride battery having a step of applying the slurry to the surface of the current collector and drying the slurry.

Next, the battery components that can constitute the nickel metal hydride battery of the present invention together with the positive electrode of the present invention will be described. The nickel metal hydride battery of the present invention includes the positive electrode of the present invention, and may further include a negative electrode, an electrolytic solution, and, if necessary, a separator.

The negative electrode includes a current collector and a negative electrode active material layer formed on the surface of the current collector. The negative electrode active material layer includes a negative electrode active material, and includes a negative electrode additive, a binder, and a conductive additive as necessary. What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode about a collector. What is necessary is just to employ | adopt suitably the thing demonstrated with the positive electrode about a binder.

What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode as a conductive support agent. 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 2% by mass.

The negative electrode active material is not limited as long as it is used as a negative electrode active material of a nickel metal hydride battery, that is, a hydrogen storage alloy. 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 surface of the negative electrode active material may be treated by a known method. The negative electrode active material is preferably in a powder state, and the average particle diameter 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.

In the negative electrode active material layer, the negative electrode active material is preferably contained in an amount of 85 to 99.5% by mass, and more preferably 90 to 99% 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 examples of the negative electrode additive include fluorides of rare earth elements such as CeF ₃ and YF ₃ , bismuth compounds such as Bi ₂ O ₃ and BiF _3, and indium compounds such as In ₂ O ₃ and InF ₃ .

As a method for forming the negative electrode active material layer on the surface of the current collector, a method similar to the method for forming the positive electrode active material layer described above can be employed.

The electrolytic solution is an aqueous solution in which an alkali metal hydroxide is dissolved. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. The electrolytic solution may contain one kind of alkali metal hydroxide or may contain a plurality of kinds of alkali metal hydroxides. The concentration of the alkali metal hydroxide in the electrolytic solution is preferably 2 to 10 mol / L, more preferably 3 to 9 mol / L, still more preferably 4 to 8 mol / L.

When only lithium hydroxide is used as the alkali metal hydroxide in the electrolyte, the concentration of lithium hydroxide is preferably 1.5 to 5 mol / L, more preferably 2 to 5 mol / L, and more preferably 3 to 5 mol / L. L is more preferable. When only sodium hydroxide is used as the alkali metal hydroxide in the electrolyte, the concentration of sodium hydroxide is preferably 1.5 to 15 mol / L, more preferably 3 to 10 mol / L, and 4 to 8 mol / L. L is more preferable. When only potassium hydroxide is used as the alkali metal hydroxide in the electrolyte, the concentration of potassium hydroxide is preferably 1.5 to 15 mol / L, more preferably 3 to 10 mol / L, and more preferably 4 to 8 mol / L. L is more preferable.

The electrolyte solution may be added with a known additive employed in an electrolyte for nickel metal hydride batteries.

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.

A specific method for producing the nickel metal hydride battery of the present invention will be described. A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like, the electrolytic solution of the present invention is added to the electrode body to obtain a nickel metal hydride Use batteries.

The shape of the nickel metal hydride battery of the present invention 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.

The nickel metal hydride battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy generated by a nickel metal hydride battery for all or a part of its power source. For example, the vehicle may be an electric vehicle or a hybrid vehicle. When a nickel metal hydride battery is mounted on a vehicle, a plurality of nickel metal hydride batteries may be connected in series to form an assembled battery. Examples of the device on which the nickel metal hydride battery is mounted include various home electric appliances, office devices, industrial devices, and the like driven by batteries, such as personal computers and portable communication devices, in addition to vehicles. Furthermore, the nickel metal hydride battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power for power sources such as ships, and / or power supply sources for auxiliary equipment, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

As mentioned above, although embodiment of this invention was described, 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.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples.

Example 1
(Positive electrode)
89.3 parts by mass of nickel hydroxide powder having an average particle diameter of 15 μm as positive electrode active material particles, 5 parts by mass of metallic nickel powder having an average particle diameter of 5 μm as nickel particles, and 3 parts by mass of cobalt powder as a second conductive additive , Acrylic resin emulsion (Joncrill PDX7341, BASF) as a binder, 2 parts by mass as a solid content, 0.7 parts by mass of carboxymethyl cellulose as a binder, and an appropriate amount of ion-exchanged water, A slurry was produced. A nickel foil without pores 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 the positive electrode of Example 1 in which the positive electrode active material layer was formed on the current collector.

In the positive electrode of Example 1, since the average particle diameter R ₁ of the positive electrode active material particles was 15 μm and the average particle diameter R ₂ of the nickel particles was 5 μm, R ₁ and R ₂ were R ₂ ≦ (2 ^{1 /} 2-1) The relationship of R ₁ was satisfied.

(battery)
As a negative electrode active material, 97.8 parts by mass of an A ₂ B ₇ type hydrogen storage alloy, 0.4 parts by mass of carbon black as a conductive additive, and an acrylic resin emulsion (Joncrill PDX7341, BASF) as a binder. A slurry was prepared by mixing 1.5 parts by mass as a solid content, 0.7 parts by mass of carboxymethyl cellulose as a binder, and an appropriate amount of ion-exchanged water. A nickel foil without pores having a thickness of 10 μm was prepared as a current collector for a negative electrode. 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.

As a separator, a nonwoven fabric made of polypropylene fiber having a thickness of 100 μm was prepared.
As an electrolytic solution, an aqueous solution containing potassium hydroxide, sodium hydroxide, and lithium hydroxide in desired amounts was prepared.

A separator was sandwiched between the negative electrode and the positive electrode of Example 1 to form an electrode plate group. The nickel metal hydride battery of Example 1 was manufactured by arranging the electrode plate group in a resin casing, injecting the above electrolyte, and sealing the casing.

(Example 2)
As in Example 1, except that 84.3 parts by mass of nickel hydroxide powder having an average particle diameter of 15 μm was used as positive electrode active material particles and 10 parts by mass of metal nickel powder having an average particle diameter of 5 μm was used as nickel particles. The positive electrode of Example 2 was manufactured. Using the positive electrode of Example 2, a nickel metal hydride battery of Example 2 was produced in the same manner as in Example 1.
In the positive electrode of Example 2, similarly to the positive electrode of Example 1, the average particle diameter R ₁ of the positive electrode active material particles is 15 [mu] m, since the average particle diameter R ₂ of the nickel particles was 5 [mu] m, R ₁ and R ₂ satisfied the relationship of R ₂ ≦ (2 ^1/2 −1) R ₁ .

(Example 3)
As in Example 1, except that 89.3 parts by mass of nickel hydroxide powder having an average particle diameter of 15 μm was used as the positive electrode active material particles, and 5 parts by mass of metal nickel powder having an average particle diameter of 10 μm was used as the nickel particles. The positive electrode of Example 3 was manufactured. Using the positive electrode of this Example 3, a nickel metal hydride battery of Example 3 was produced in the same manner as in Example 1.
Note that in the positive electrode of Example 3, the average particle diameter _{R 1} of the positive electrode active material particles is 15 [mu] m, since the average particle diameter _{R 2} of the nickel particles was 10 [mu] m, _{R 1} and _{R 2,} _{R 2} ≦ (2 ^{1 /} 2-1) The relationship of R ₁ was not satisfied.

Example 4
As in Example 1, except that 84.3 parts by mass of nickel hydroxide powder having an average particle diameter of 15 μm was used as the positive electrode active material particles and 10 parts by mass of metal nickel powder having an average particle diameter of 10 μm was used as the nickel particles. The positive electrode of Example 4 was manufactured. Using the positive electrode of Example 4, a nickel metal hydride battery of Example 4 was produced in the same manner as in Example 1.
In the positive electrode of Example 4, similar to the positive electrode of Example 3, the average particle diameter R ₁ of the positive electrode active material particles is 15 [mu] m, since the average particle diameter R ₂ of the nickel particles was 10 [mu] m, R ₁ and R ₂ did not satisfy the relationship of R ₂ ≦ (2 ^1/2 −1) R ₁ .

(Comparative Example 1)
A positive electrode of Comparative Example 1 was produced in the same manner as in Example 1 except that 94.3 parts by mass of nickel hydroxide powder having an average particle diameter of 15 μm was used as the positive electrode active material particles and no nickel particles were used. Using the positive electrode of Comparative Example 1, a nickel metal hydride battery of Comparative Example 1 was produced in the same manner as in Example 1.

(Evaluation test)
The nickel metal hydride batteries of Examples 1 to 4 and Comparative Example 1 were adjusted to 50% SOC and then discharged at a 1C rate for 5 seconds at a temperature of 0 ° C., and the voltage change for 5 seconds. Was measured. A value obtained by dividing the potential difference before and after the discharge by the current value was defined as a DC resistance value (Ω).

The same tests were performed on the nickel metal hydride batteries of Examples 2 to 4 and Comparative Example 1. The results are shown in Table 1.

As shown in Table 1, each of the nickel metal hydride batteries of Examples 1 to 4 including nickel particles in the positive electrode active material layer is more direct current than the nickel metal hydride battery of Comparative Example 1 that does not include nickel particles. Resistance value is low. From these results, it can be said that the positive electrodes of Examples 1 to 4 are excellent in conductivity.

Further, the nickel metal hydride battery of Example 1 and the nickel metal hydride battery of Example 2 in which the average particle diameter of the nickel particles is small and satisfying the relationship of R ₂ ≦ (2 ^1/2 −1) R ₁ are: Compared to the nickel metal hydride battery of Example 3 and the nickel metal hydride battery of Example 4 that do not satisfy the relationship of R ₂ ≦ (2 ^1/2 −1) R ₁ , the DC resistance value is low. From this result, nickel particles having an average particle diameter satisfying the relationship of R ₂ ≦ (2 ^1/2 −1) R ₁ can be used to further improve the conductivity of the positive electrode, and the nickel metal hydride battery It can be proved that the DC resistance value can be lowered.

Furthermore, in the nickel metal hydride battery of Example 1 and the nickel metal hydride battery of Example 2 that satisfy the relationship of R ₂ ≦ (2 ^1/2 −1) R ₁ , the amount of nickel particles is 5% by mass. There was no change in the DC resistance value in either case or 10% by mass. From this, it can be said that the amount of nickel particles is 5 mass% or less.

1: positive electrode active material particles 2: nickel particles b: gaps between adjacent positive electrode active material particles R ₁ : average particle size of positive electrode active material particles R ₂ : average particle size of nickel particles

Claims

A current collector, and a positive electrode active material layer formed on the current collector,
The positive electrode active material layer is a positive electrode for a nickel metal hydride battery, having positive electrode active material particles and nickel particles having a smaller diameter than the positive electrode active material particles.
2. The nickel metal according to claim 1 , wherein a relationship between an average particle diameter R 1 of the positive electrode active material particles and an average particle diameter R 2 of the nickel particles satisfies R 2 ≦ (2 1/2 −1) R 1. Positive electrode for hydride battery.
The nickel metal hydride battery positive electrode according to claim 1 or 2, wherein the amount of the nickel particles in the positive electrode active material layer is in the range of 0.5 mass% to 10 mass%.
A nickel metal hydride battery comprising the positive electrode for a nickel metal hydride battery according to any one of claims 1 to 3.