WO2020090175A1 - Nickel-metal hydride battery - Google Patents

Abstract

Provided is a novel nickel-metal hydride battery demonstrating excellent battery properties. This nickel-metal hydride battery is characterized in comprising: a negative electrode active substance having an oxygen concentration before charging/discharging of 1,000 ppm or greater, and an electrolyte solution constituted of an aqueous solution containing a tungstic acid or a salt thereof and an alkali metal hydroxide.

Description

Nickel metal hydride battery

The present invention relates to a nickel metal hydride battery.

A nickel metal hydride battery is a secondary battery including a positive electrode having a nickel oxide compound such as nickel hydroxide as a positive electrode active material, a negative electrode having a hydrogen storage alloy as a negative electrode active material, and an electrolytic solution containing an alkali metal aqueous solution. Is.

Regarding the negative electrode, various techniques have been proposed in order to improve the performance of the hydrogen storage alloy as the negative electrode active material. For example, in Patent Document 1, after a hydrogen storage alloy having a CaCu ₅ type crystal structure and made of an alloy containing a rare earth element and Ni, Co, Mn, and Al is immersed in an aqueous sodium hydroxide solution, Techniques for washing with water are described. Then, the same document describes that the hydrogen storage alloy is in a state as if it was coated with nickel by immersing the hydrogen storage alloy in an aqueous solution of sodium hydroxide.

A high-concentration potassium hydroxide aqueous solution, which has excellent ionic conductivity, is generally used as the alkali metal aqueous solution used as the electrolytic solution of the nickel metal hydride battery. For example, Example 1 of Patent Document 2 specifically describes a nickel metal hydride battery using an aqueous solution of 1 to 8 mol / L potassium hydroxide as an electrolytic solution.

It is also known to use an aqueous solution in which potassium hydroxide and lithium hydroxide are dissolved as an electrolytic solution for a nickel metal hydride battery, and further, an aqueous solution in which potassium hydroxide, sodium hydroxide and lithium hydroxide are dissolved is used as a nickel solution. It is also known to be used as an electrolytic solution for metal hydride batteries.

Example 2 of Patent Document 2 specifically describes a nickel metal hydride battery using an aqueous solution in which potassium hydroxide and lithium hydroxide are dissolved as an electrolytic solution. The example of Patent Document 3 specifically describes a nickel metal hydride battery using an aqueous solution in which potassium hydroxide, sodium hydroxide and lithium hydroxide are dissolved as an electrolytic solution. In the example of Patent Document 4, an aqueous solution obtained by mixing a 5.5 mol / L potassium hydroxide aqueous solution, a 0.5 mol / L sodium hydroxide aqueous solution, and a 0.4 to 1.8 mol / L lithium hydroxide aqueous solution. A nickel metal hydride battery using is used as an electrolytic solution is specifically described.

It is also known to use a high-concentration sodium hydroxide aqueous solution as an electrolytic solution of a nickel metal hydride battery, and further, an aqueous solution in which sodium hydroxide and lithium hydroxide are dissolved is used as an electrolytic solution of a nickel metal hydride battery. It is also known to be used. For example, in the example of Patent Document 5, an aqueous sodium hydroxide solution of 6 to 9 mol / L or sodium hydroxide at a concentration of 4.8 to 8.5 mol / L and lithium hydroxide of 0.5 A nickel metal hydride battery using an aqueous solution containing a concentration of up to 1.2 mol / L as an electrolyte is specifically described.

JP, 2002-256301, A JP-A-61-214370 JP-A-11-162460 JP, 2004-31292, A JP, 2007-250250, A

Now, the industry is eager for a nickel metal hydride battery that exhibits excellent characteristics.
The present invention has been made in view of such circumstances, and an object thereof is to provide a new nickel metal hydride battery that exhibits excellent battery characteristics.

The present inventor studied a negative electrode, and surprisingly found that a nickel metal hydride battery using a hydrogen storage alloy having a high oxygen content as a negative electrode active material is effective in reducing battery resistance.

The present inventor also examined the electrolytic solution at the same time as the negative electrode. Then, as a result of diligent study by the present inventors, a nickel metal hydride battery employing an electrolytic solution in which sodium tungstate is dissolved, and a hydrogen storage alloy having a high oxygen content as a negative electrode active material, has battery characteristics. It was found to be excellent.

Based on these findings, the present inventor has completed the present invention.

The nickel metal hydride battery of the present invention,
A negative electrode active material having an oxygen concentration of 1000 ppm or more before charge and discharge,
And an electrolytic solution comprising an aqueous solution containing tungstic acid or a salt thereof and an alkali metal hydroxide.

The nickel metal hydride battery of the present invention has excellent battery characteristics.

9 is a schematic cross-sectional view of a bipolar nickel metal hydride battery of Application Example 1. FIG.

A mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “ab” described in the present specification includes the lower limit a and the upper limit b in the range. The upper limit value and the lower limit value, and the numerical values listed in the examples can be arbitrarily combined to form the numerical value range. Further, a numerical value arbitrarily selected from these numerical ranges can be set as a new upper and lower numerical value.

The nickel metal hydride battery of the present invention,
A negative electrode active material having an oxygen concentration of 1000 ppm or more before charge / discharge (hereinafter, sometimes referred to as negative electrode active material of the present invention);
An electrolytic solution comprising an aqueous solution containing tungstic acid or a salt thereof and an alkali metal hydroxide (hereinafter, may be referred to as an electrolytic solution of the present invention).

First, the negative electrode active material of the present invention will be described. The negative electrode active material of the present invention is a material in which the surface of the hydrogen storage alloy is substantially oxidized.

The negative electrode active material of the present invention has an oxygen concentration of 1000 ppm or more before charge / discharge. The oxygen concentration range is preferably in the range of 1,000 to 90,000 ppm, more preferably in the range of 5,000 to 80,000 ppm, further preferably in the range of 10,000 to 60,000 ppm, particularly preferably in the range of 15,000 to 50,000 ppm, particularly preferably in the range of 18,000 to 45,000 ppm. The range is most preferable.

The oxygen concentration of the negative electrode active material may be such that the oxygen concentration before charging / discharging the nickel metal hydride battery including the negative electrode active material is within the above range. The oxygen concentration of the negative electrode active material may change during charge / discharge of the nickel metal hydride battery.
The oxygen concentration of the negative electrode active material of the present invention may be interpreted as a value "before battery production" or "at battery production", or "before electrode production" or "at electrode production".

The average particle diameter of the negative electrode active material of the present invention is preferably in the range of 1 to 40 μm, more preferably in the range of 3 to 30 μm, further preferably in the range of 4 to 20 μm, particularly preferably in the range of 5 to 15 μm. Most preferably, it is within the range of 5 to 12 μm.

The BET specific surface area of the negative electrode active material of the present invention, preferably 0.2 ~ 10.0m ² / g, more preferably ^{0.5 ~ 8.0m 2 / g, 1.0} ~ 6.0m 2 / g Is more preferable.

The saturation magnetization of the negative electrode active material of the present invention containing Ni is preferably 0.2 to 10 emu / g, more preferably 0.5 to 9 emu / g, still more preferably 1 to 8 emu / g. , 1.5 to 7 emu / g are particularly preferable.

The hydrogen storage alloy in the negative electrode active material is not limited as long as it is used as the negative electrode active material of a nickel metal hydride battery. A hydrogen storage alloy is basically an alloy of a metal A that easily reacts with hydrogen but has a poor hydrogen releasing ability, and a metal B that does not easily react with hydrogen but has a good hydrogen releasing ability. As A, a misch containing a Group 2 element such as Mg, a Group 3 element such as Sc or lanthanoid, a Group 4 element such as Ti or Zr, a Group 5 element such as V or Ta, or a plurality of rare earth elements Examples thereof include metal (hereinafter sometimes abbreviated as Mm) and Pd. 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 a hexagonal Mg ₂ Ni type crystal structure, a solid solution type showing a 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. It can be exemplified of a type and a ₅ B ₁₉ type. The hydrogen storage alloy may have one kind 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 AB type hydrogen storage alloys 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. CeNi ₃ can be exemplified as the AB ₃ type hydrogen storage alloy. 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 metals or elements.

As the hydrogen storage alloy, an A ₂ B ₇ type hydrogen storage alloy containing a rare earth element, Mg and Ni is preferable.

In order to obtain the negative electrode active material of the present invention having a high oxygen concentration, it is preferable to positively oxidize the surface of the hydrogen storage alloy. Hereinafter, using an A ₂ B ₇ type hydrogen storage alloy containing a rare earth element, Mg and Ni as an example, the hydrogen storage alloy is treated by a suitable method (hereinafter referred to as a hydrogen storage alloy treatment method), The procedure for producing the negative electrode active material of the present invention will be described.

The treatment method of hydrogen storage alloy is
N-1) a step of treating the hydrogen storage alloy with an alkaline aqueous solution,
N-2) a step of oxidizing the surface of the hydrogen storage alloy after the step N-1),
Have.
Step N-1) is not an essential step for oxidizing the hydrogen storage alloy, but as will be described later, a more suitable negative electrode active material of the present invention can be obtained due to the steps.

The step N-1) preferably includes the following steps a) and b).
a) a step of treating an A ₂ B ₇ type hydrogen storage alloy containing a rare earth element, Mg and Ni with a first alkaline aqueous solution in which a hydroxide of an alkali metal is dissolved b) a), and then a first alkaline aqueous solution Process of separating the hydrogen storage alloy from the solution and treating with a second alkaline aqueous solution in which hydroxide of alkali metal is dissolved

First, a) a step of treating an A ₂ B ₇ type hydrogen storage alloy containing a rare earth element, Mg and Ni with a first alkaline aqueous solution in which a hydroxide of an alkali metal is dissolved (hereinafter, simply “a step”) That. ) Will be described.

The hydrogen storage alloy used in the step a) is an A ₂ B ₇ type hydrogen storage alloy containing a rare earth element, Mg and Ni. It is considered that the rare earth element and Mg belong to the metal A and Ni belongs to the metal B. Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Other metal elements may be present in the hydrogen storage alloy used in the step a), and Mn, Fe, Co, Cu, Zn, Al, Cr, Pt, Cu, Ag, and Ti may be used as the other metal elements. , Zr, V, and Ta can be exemplified. The hydrogen storage alloy used in step a) is preferably a hydrogen storage alloy containing 60 to 70% by mass of Ni.

It is preferable that the hydrogen storage alloy be in the form of powder that has been crushed and adjusted to have a certain particle size. The average particle diameter of the hydrogen storage alloy is preferably in the range of 1 to 40 μm, more preferably in the range of 3 to 30 μm, further preferably in the range of 4 to 20 μm, particularly preferably in the range of 5 to 15 μm, and preferably 5 to The range of 12 μm is most preferable.

When the hydrogen storage alloy is treated with the first alkaline aqueous solution in which the hydroxide of the alkali metal is dissolved in the step a), the rare earth element having high solubility in the alkaline aqueous solution is eluted from the surface of the hydrogen storage alloy. Here, since Ni has a low solubility in an alkaline aqueous solution, the Ni concentration on the surface of the hydrogen storage alloy becomes higher as compared with the inside of the hydrogen storage alloy. Hereinafter, in the hydrogen storage alloy, the portion where the Ni concentration is higher than the inside is referred to as the Ni concentrated layer. It is considered that the performance of the negative electrode active material is improved due to the presence of the Ni concentrated layer.

Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, with sodium hydroxide being preferred. When the sodium hydroxide aqueous solution is used as the first alkaline aqueous solution, the battery characteristics of the nickel metal hydride battery of the present invention are optimized as compared with the case where lithium hydroxide or potassium hydroxide is used as the first alkaline aqueous solution. There is.

A strong base is preferred as the first alkaline aqueous solution. Examples of the concentration of the alkali metal hydroxide in the first alkaline aqueous solution include 10 to 60% by mass, 20 to 55% by mass, 30 to 50% by mass, and 40 to 50% by mass.

The step a) is preferably performed by a method of immersing the hydrogen storage alloy in the first alkaline aqueous solution. In that case, it is preferable to carry out under stirring conditions and preferably under heating conditions. Examples of the heating temperature range include 50 to 150 ° C., 70 to 140 ° C., and 90 to 130 ° C. The heating time may be appropriately determined depending on the concentration of the first alkaline aqueous solution and the heating temperature, and examples thereof include 0.1 to 10 hours, 0.2 to 5 hours, and 0.5 to 3 hours.

Regarding the relationship between the amount of the hydrogen storage alloy and the amount of the first alkaline aqueous solution, the mass ratio is preferably 1: 0.5 to 1:10, more preferably 1: 0.7 to 1: 5, and 1: 0.9 to 1: 3 is more preferable. If the amount of the first alkaline aqueous solution is too small, the Ni concentrated layer may not be sufficiently formed on the surface of the hydrogen storage alloy. On the other hand, if the amount of the first alkaline aqueous solution is too large, it is disadvantageous in terms of cost. ..

Next, after the step b) a), the step of separating the hydrogen storage alloy from the first alkaline aqueous solution and treating with the second alkaline aqueous solution in which the hydroxide of the alkali metal is dissolved (hereinafter simply referred to as the “b) step”. ) Will be described.

The rare earth element eluted from the hydrogen storage alloy is present in the first alkaline aqueous solution at the time when the step a) is completed. Then, the rare earth element can adhere to the surface of the hydrogen storage alloy as a hydroxide of the rare earth element when the first alkaline aqueous solution and the hydrogen storage alloy are separated.
It can be said that the step b) is a step of removing the hydroxide of the rare earth element attached to the surface of the hydrogen storage alloy separated from the first alkaline aqueous solution with the second alkaline aqueous solution. Rare earth element hydroxides are deposited under neutral conditions, but are easily dissolved in a basic aqueous solution. The step b) utilizes this property.

As a method for separating the hydrogen storage alloy from the first alkaline aqueous solution, filtration or centrifugation is preferable, and suction filtration is particularly preferable. Examples of the method of treating the hydrogen storage alloy with the second aqueous alkali solution include a method of immersing the hydrogen storage alloy in the second aqueous alkali solution and a method of exposing the second alkaline solution to the hydrogen storage alloy. It is rational to select a method in which the second alkaline aqueous solution is exposed to the hydrogen storage alloy subsequent to or while performing the above-described filtration.

Examples of the alkali metal hydroxide dissolved in the second alkaline aqueous solution include lithium hydroxide, sodium hydroxide and potassium hydroxide, and of these, sodium hydroxide is preferable.

Further, under the condition that the relationship between the concentration C ₁ of the alkali metal hydroxide of the first alkaline aqueous solution and the concentration C ₂ of the alkali metal hydroxide of the second alkaline aqueous solution satisfies C ₁ > C ₂ b). It is preferred to perform the steps. Since the alkaline aqueous solution having a low concentration has a low viscosity, the work of step b) proceeds smoothly under the condition that C ₁ > C ₂ is satisfied. Examples of the alkali metal hydroxide concentration in the second alkaline aqueous solution are 0.01 to 10% by mass, 0.03 to 5% by mass, 0.05 to 1% by mass, and 0.1 to 0.5% by mass. it can.

From the viewpoint of manufacturing cost, etc., it is preferable to carry out step b) under lower temperature conditions than step a). Examples of the temperature range of step b) include 0 to 100 ° C., 10 to 70 ° C., and 20 to 50 ° C. The temperature of step b) may be defined as the temperature of the environment in which the hydrogen storage alloy is present, or as the temperature of the second alkaline aqueous solution.

Regarding the relationship between the amount of the hydrogen storage alloy and the amount of the second alkaline aqueous solution, the mass ratio is preferably 1: 0.5 to 1:50, more preferably 1: 1 to 1:30, and 1: 1.5 to 1:10. More preferable. If the amount of the second alkaline aqueous solution is too small, the hydroxide of the rare earth element may be insufficiently removed. On the other hand, if the amount of the second alkaline aqueous solution is too large, the cost is disadvantageous.

In the step b), the hydrogen storage alloy may be washed with water subsequently to the treatment with the second alkaline aqueous solution. The second alkaline aqueous solution adhering to the surface of the hydrogen storage alloy can be removed by washing with water. Regarding the relationship between the hydrogen storage alloy and the amount of water at the time of washing with water, the mass ratio is preferably 1: 1 to 1:50, more preferably 1: 2 to 1:30, and further preferably 1: 3 to 1:10. preferable.

Next, N-2) the step of oxidizing the surface of the hydrogen storage alloy after the step N-1) (hereinafter simply referred to as “N-2) step”. ) Will be described.

The N-2) step may be a method of exposing the hydrogen storage alloy to the air and oxidizing it with oxygen in the air, or a method of contacting the hydrogen storage alloy with an oxide such as hydrogen peroxide to oxidize it. .. However, in any method, in order to suppress excessive heat generation of the hydrogen storage alloy, it is preferable to carry out the cooling operation of the hydrogen storage alloy. Specifically, the hydrogen storage alloy may be exposed to water while cooling the hydrogen storage alloy, or the hydrogen storage alloy may be placed in water or stored in an aqueous solution of an oxide such as hydrogen peroxide. It is preferable to carry out after the alloy is arranged. The hydrogen-absorbing alloy, which may be carried out after the treatment with the second alkaline aqueous solution in the step b), may be washed in water under the atmosphere to be the step N-2).

The preferred negative electrode active material of the present invention produced through the steps N-1) and N-2) contains a hydrogen storage alloy in which the surface Ni concentration is increased as compared with the internal Ni concentration. The internal Ni concentration has the same meaning as the Ni concentration in the hydrogen storage alloy before the treatment used in step N-1). It can also be said that the preferable negative electrode active material of the present invention has a Ni concentrated layer on the surface.

The thickness of the Ni concentrated layer may be, for example, 5 to 200 nm, 10 to 150 nm, or 30 to 100 nm. The thickness of the Ni concentrated layer can be confirmed by observing the cross section of the particles of the negative electrode active material of the present invention with various electron microscopes.

In the method for treating a hydrogen storage alloy, first, in the step a) of the step N-1), a rare earth element which is easily dissolved in an alkaline aqueous solution is eluted, so that the surface of the hydrogen storage alloy after the step a) is Ni. A concentrated layer is formed. Next, in step b), since the hydroxide of the rare earth element attached to the surface of the hydrogen storage alloy is removed with the second alkaline aqueous solution, the Ni concentration on the surface of the hydrogen storage alloy after step b) is further increased. It can be said that.

Actually, when the present inventor measured the surface of the hydrogen storage alloy after the step b) by X-ray photoelectron spectroscopy, the Ni ratio was significantly higher than that of the hydrogen storage alloy before the treatment used in the step a). It was confirmed that it was getting higher. Therefore, the following can be grasped as one preferable embodiment of the negative electrode active material of the present invention.

One embodiment of the negative electrode active material of the present invention contains La, Mg and Ni, contains an A ₂ B ₇ type hydrogen storage alloy containing 60 to 70% by mass of Ni, and has an internal Ni / La element ratio. The value of the Ni / La element ratio on the surface is 1.3 or more.
Here, the internal Ni / La element ratio means the Ni / La element ratio inside the hydrogen storage alloy, for example, in the center of the particles of the negative electrode active material of the present invention, and also the internal Ni / La element ratio Is synonymous with the Ni / La element ratio in the hydrogen storage alloy before the treatment used in step a).

The values of the surface Ni / La element ratio with respect to the internal Ni / La element ratio can be in the range of 1.3 to 2, 1.31 to 1.5, 1.34 to 1.4. The larger the value of the surface Ni / La element ratio with respect to the internal Ni / La element ratio, the better the removal of the rare earth element from the surface.

Next, the electrolytic solution of the present invention will be described. The electrolytic solution of the present invention is an aqueous solution containing tungstic acid or its salt and an alkali metal hydroxide. Here, tungstic acid is a hydrate of tungsten trioxide.

As the tungstic acid salt, alkali metal salts such as lithium salt and sodium salt are preferable.

As the electrolytic solution, one type of tungstic acid and its salt may be used, or a plurality of types may be used in combination. The concentration of tungstic acid and its salt in the electrolytic solution is preferably 0.001 to 0.5 mol / L, more preferably 0.005 to 0.4 mol / L, and further preferably 0.01 to 0.3 mol / L. 0.015 to 0.2 mol / L is particularly preferable.

Examples of the alkali metal hydroxide contained in the electrolytic solution of the present invention include lithium hydroxide, sodium hydroxide and potassium hydroxide. The electrolytic solution may contain one kind of alkali metal hydroxide or a plurality of kinds of alkali metal hydroxide. Particularly, those containing hydroxides of three kinds of alkali metals such as lithium hydroxide, sodium hydroxide and potassium hydroxide are preferable.
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, and further preferably 4 to 8 mol / L.

The well-known additive used for the nickel metal hydride battery electrolyte may be added to the electrolyte.

Next, a specific configuration of the nickel metal hydride battery of the present invention will be described. The nickel metal hydride battery of the present invention specifically comprises a negative electrode active material layer containing the negative electrode active material of the present invention, an electrolytic solution of the present invention, a positive electrode active material layer containing a positive electrode active material, and a separator. To do.

Here, the nickel metal hydride battery of the present invention may be a normal nickel metal hydride battery including a positive electrode having the positive electrode active material layer and a negative electrode having the negative electrode active material layer, or It may be a bipolar nickel metal hydride battery in which the positive electrode active material layer is provided on one surface of the current collector foil and the bipolar electrode having the negative electrode active material layer is provided on the other surface.

The following will describe the positive electrode and the negative electrode, but the description of the positive electrode and the negative electrode will be appropriately incorporated with respect to the description of the bipolar electrode.

Explain the positive electrode. It should be noted that those having the same structure as the negative electrode will be described without being limited to the positive electrode.

The positive electrode includes a current collector and a positive electrode active material layer formed on the surface of the current collector.
The positive electrode active material layer contains a positive electrode active material and, if necessary, a positive electrode additive, a binder and a conductive auxiliary agent.

As the positive electrode active material, a material known as a positive electrode active material for nickel metal hydride batteries may be appropriately adopted, but it is preferable to form a layer of cobalt oxyhydroxide around the positive electrode active material in advance. Furthermore, it is preferable that a layer of cobalt oxyhydroxide is formed in advance around the positive electrode active material and that the layer of cobalt oxyhydroxide is doped with an alkali metal, particularly lithium.

Hereinafter, a particularly preferable positive electrode active material (hereinafter referred to as the positive electrode active material of the present invention) will be described. The positive electrode active material of the present invention includes a cobalt oxyhydroxide layer containing lithium and cobalt oxyhydroxide, and a positive electrode active material body coated with the cobalt oxyhydroxide layer (herein, simply referred to as “positive electrode active material”). That is.) Is included.

The positive electrode active material coated with the cobalt oxyhydroxide layer is not limited as long as it is used as a positive electrode active material of a nickel metal hydride battery. Specific examples of the positive electrode active material include nickel hydroxide and nickel hydroxide doped with a metal. Examples of the metal with which nickel hydroxide is doped 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 method of forming a cobalt oxyhydroxide layer containing lithium and cobalt oxyhydroxide on the positive electrode active material body is the following steps P-1) and P-2).

P-1) A step of forming a cobalt hydroxide layer on the surface of the positive electrode active material P-2) The positive electrode active material on which the cobalt hydroxide layer is formed is heated to change the cobalt hydroxide layer to a cobalt oxyhydroxide layer. A step of further converting the cobalt hydroxide layer or the cobalt oxyhydroxide layer with lithium.

Examples of P-1) include the following P-1-1) or P-1-2).
P-1-1) A step of producing a dispersion liquid in which the positive electrode active material is dispersed in an aqueous cobalt salt solution, and then making the pH of the dispersion liquid alkaline and precipitating cobalt hydroxide on the surface of the positive electrode active material P- 1-2) A step of producing a dispersion liquid in which the positive electrode active material is dispersed in an alkaline aqueous solution, and then adding a cobalt salt aqueous solution to the dispersion liquid to deposit cobalt hydroxide on the surface of the positive electrode active material.

Examples of cobalt salts include cobalt sulfate, cobalt nitrate, and cobalt chloride.

Examples of the heating temperature in the step P-2) include 70 to 230 ° C and 80 to 200 ° C. The atmosphere in step P-2) is an oxygen-containing atmosphere. From the viewpoint of cost, it is preferable to carry out the step P-2) in the presence of air.

In the step P-2), lithium may be doped in the cobalt hydroxide layer before heating, or in the cobalt hydroxide layer or cobalt oxyhydroxide layer during heating.

In the step P-2), as a method of doping lithium, a method of spraying a lithium salt aqueous solution on the positive electrode active material is preferable. By heating while spraying the lithium salt aqueous solution on the positive electrode active material, or by heating after spraying the lithium salt aqueous solution on the positive electrode active material, the cobalt oxyhydroxide layer on the surface of the positive electrode active material (or, Lithium is doped with respect to the cobalt hydroxide layer before conversion into the cobalt oxyhydroxide layer).
As the heating temperature in the method of doping lithium, it is rational to carry out at the same temperature as the heating temperature at the time of converting the cobalt hydroxide layer into the cobalt oxyhydroxide layer in the step P-2).

Examples of the lithium salt include lithium hydroxide, lithium sulfate, lithium nitrate, lithium chloride, lithium acetate, lithium trifluoromethanesulfonate, and lithium bis (trifluoromethanesulfonyl) imide.

In step P-2), not only lithium but also another alkali metal may be doped. Examples of other alkali metals include sodium and potassium.
As another alkali metal doping method, a method of spraying an alkali metal aqueous solution is preferable as in the method of doping lithium.

The reason why the positive electrode active material of the present invention exhibits excellent conductivity is considered as follows.

First, in the case where a cobalt oxyhydroxide layer is formed on the positive electrode active material without being doped with an alkali metal such as lithium, the cobalt oxyhydroxide layer contains β-CoOOH, which is less conductive than CoOOH, and has conductivity. It is considered that Co ₃ O ₄ having poor properties is formed. In Co ₃ O ₄ , cobalt exists in both divalent and trivalent states.

Next, when a cobalt oxyhydroxide layer is formed on the positive electrode active material by using a method of doping an alkali metal other than lithium, the cobalt oxyhydroxide layer contains γ-CoOOH having excellent conductivity among CoOOH. However, it is considered that Co ₃ O ₄ having poor conductivity is also formed.

However, when the cobalt oxyhydroxide layer is formed on the positive electrode active material by using the method of doping lithium, even if Co ₃ O ₄ having poor conductivity is formed, it is at least Co due to the presence of lithium. It is considered that a part of ₃ O ₄ is converted into LiCoO ₂ having excellent conductivity. Then, when a cobalt oxyhydroxide layer is formed on the positive electrode active material by using the method of doping lithium, the cobalt oxyhydroxide layer contains a large amount of γ-CoOOH having excellent conductivity among CoOOH, Although LiCoO ₂ having relatively high conductivity also exists, the proportion of Co ₃ O ₄ having poor conductivity is considered to be extremely low.

The resistivity of γ-CoOOH is approximately 2 Ω · cm, the resistivity of LiCoO ₂ is approximately 1 × 10 ² Ω · cm, the resistivity of Co ₃ O ₄ is approximately 1 × 10 ⁶ Ω · cm, and β is The resistivity of —CoOOH is approximately 1 × 10 ⁸ Ω · cm.

Cobalt of γ-CoOOH and LiCoO ₂ which are excellent in conductivity are both trivalent. Considering that cobalt of cobalt hydroxide as a raw material is divalent, and that Co ₃ O ₄ has both divalent and trivalent cobalt, the oxyhydroxide of the positive electrode active material of the present invention is considered. It can be said that the higher the valence of cobalt in the cobalt layer, the better.

The valence of cobalt in the cobalt oxyhydroxide layer of the positive electrode active material of the present invention is preferably 2.9 to 3.2, more preferably 2.95 to 3.1, and even more preferably 2.98 to 3.07. preferable.
The valence of cobalt here is a value obtained by measuring the valence of cobalt in the cobalt oxyhydroxide layer existing on the surface of the positive electrode active material of the present invention by an iodometry method.

The content of cobalt in the positive electrode active material of the present invention is preferably 1 to 10% by mass, more preferably 2 to 7% by mass, and further preferably 3 to 7% by mass.
The content of lithium in the positive electrode active material of the present invention is preferably 0.01 to 0.3% by mass, more preferably 0.04 to 0.2% by mass, and further preferably 0.07 to 0.1% by mass. ..
The content of the alkali metal other than lithium in the positive electrode active material of the present invention is preferably 0.01 to 1% by mass, more preferably 0.1 to 0.6% by mass, and 0.2 to 0.5% by mass. More preferable.

The positive electrode active material of the present invention is preferably in a powder state, and its average particle size is preferably in the range of 3 to 40 μm, more preferably in the range of 5 to 30 μm, and further preferably in the range of 7 to 20 μm. In the present specification, the average particle diameter means a value of D ₅₀ in the measurement using a conventional laser diffraction particle size distribution analyzer.

The BET specific surface area of the positive electrode active material of the present invention, preferably 5 ~ ^30m 2 / g, more preferably from 10 ~ ^20m 2 / g, more preferably 12 ~ ^18m 2 / g.

The resistivity of the positive electrode active material of the present invention is preferably 0.1 to 7 Ω · cm, more preferably 0.1 to 5 Ω · cm, and even more preferably 0.1 to 4 Ω · cm.

Current collector refers to a chemically inert electronic conductor that keeps current flowing through the electrodes during discharging 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 capable of withstanding a voltage suitable for the active material used. The material for the current collector 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. Metal materials such as The current collector may be covered with a known protective layer. You may use what collected the surface of the collector by a well-known method as a collector. As the material of the current collector, nickel or a metal material plated with nickel is preferable.

The current collector can be in the form of foil, sheet, film, wire, rod, mesh, sponge, etc. When the current collector is in the form of foil, sheet or film, its thickness is preferably in the range of 1 μm to 100 μm.

Since the positive electrode active material of the present invention has excellent conductivity, it may be rational to employ a foil-shaped current collector. For the same reason, it can be said that the positive electrode active material of the present invention is suitable for a bipolar electrode using a collector foil.

The positive electrode active material layer contains a positive electrode active material, and if necessary, a positive electrode additive, a binder, and a conductive additive.
The amount of one positive electrode active material layer present on the current collector of the positive electrode is preferably 20 mg / cm ² or more, more preferably 25 to 50 mg / cm ² , and even more preferably 27 to 40 mg / cm ² .
The density of the positive electrode active material layer, 2.5 g / cm ³ or more, more preferably 2.6 ~ 3.2g / cm ^3, more preferably 2.7 ~ 3.1g / cm ^3, 2.8 It is particularly preferably from 3.0 g / cm ³ .

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 further preferably 85 to 95%, based on the total mass of the positive electrode active material layer. More preferably, it is contained by 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 , ytterbium compounds such as Yb ₂ O ₃ . , 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.

The positive electrode active material layer preferably contains the positive electrode additive in an amount of 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, based on the total mass of the positive electrode active material layer. ..

The binding agent plays a role in binding active materials and 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 polyvinylidene fluoride, fluoro resins such as polytetrafluoroethylene and fluororubber, polyolefin resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, carboxymethyl cellulose, methyl cellulose 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 a (meth) acrylic acid derivative as a monomer unit ( An example is a (meth) acrylic resin.

The active material layer preferably contains the binder in an amount of 0.1 to 15% by mass, and more preferably 0.3 to 10% by mass, based on the total mass of the active material layer. It is more preferable that the content is 0.5 to 7% by mass. This is because if the amount of the binder is too small, the moldability of the electrode is lowered, and if the amount of the binder is too large, the energy density of the electrode becomes low.

Conductivity aid is added to enhance the conductivity of the electrode. Therefore, the conductive additive may be optionally added when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. Specific examples of the conductive aid include metals such as cobalt, nickel and copper, metal oxides such as cobalt oxide, metal hydroxides such as cobalt hydroxide, carbon materials such as carbon black, graphite and carbon fiber. Is exemplified.

The active material layer preferably contains the conductive additive in an amount of 0.1 to 20 mass% with respect to the total mass of the active material layer. The positive electrode active material layer preferably contains the conductive additive in an amount of 1 to 15% by mass, more preferably 3 to 12% by mass, and more preferably 5 to 10% by mass based on the total mass of the positive electrode active material layer. More preferably, it is contained by mass%. The negative electrode active material layer preferably contains the conductive additive in an amount of 0.1 to 5% by mass, and more preferably 0.2 to 3% by mass, based on the total mass of the negative electrode active material layer. , 0.3 to 1 mass% is more preferable. This is because if the amount of the conductive additive is too small, an efficient conductive path cannot be formed, and if the amount of the conductive additive is too large, the moldability of the active material layer deteriorates and the energy density of the electrode decreases.

The negative electrode of the present invention comprises the negative electrode active material of the present invention. The negative electrode of the present invention 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 contains the negative electrode active material of the present invention and, if necessary, a negative electrode additive, a binder and a conductive auxiliary agent. The binder and the conductive aid are as described above.

The negative electrode active material layer preferably contains the negative electrode active material in an amount of 85 to 99% by mass, more preferably 90 to 98% by mass, based on the total mass of the 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 of a nickel metal hydride battery. Specific negative electrode additives include rare earth element 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. The compounds exemplified as can be mentioned.

The negative electrode active material layer preferably contains the negative electrode additive in an amount of 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, based on the total mass of the negative electrode active material layer. ..

To form an 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 is used. The active material may be applied to the surface of the body. Specifically, an active material, a solvent, and, if necessary, a binder, a conductive auxiliary agent, 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. The dried product may be compressed to increase the electrode density.

The separator separates the positive electrode from the negative electrode to prevent a short circuit due to contact between both electrodes, while providing a storage space and passage for the electrolytic solution. Any known separator may be used as the separator, such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, synthetic resin such as polyacrylonitrile, polysaccharides such as cellulose and amylose, and fibroin. Examples include natural polymers such as keratin, lignin, and suberin, and porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as ceramics. Further, the separator may have a multi-layer structure.

The surface of the separator is preferably hydrophilized. Examples of the hydrophilic treatment include sulfonation treatment, corona treatment, fluorine gas treatment, and plasma treatment.

One aspect of a specific method for producing the nickel metal hydride battery of the present invention will be described.
The separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. After connecting the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal that communicate with the outside by using a current collecting lead or the like, the electrolytic solution of the present invention is added to the electrode body to form 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 prismatic type, a cylindrical type, a coin type and a laminated type can be adopted.

The nickel metal hydride battery of the present invention may be mounted on a vehicle. The vehicle may be any vehicle that uses electric energy from a nickel metal hydride battery for all or part of its power source, and may be, for example, 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. In addition to vehicles, examples of devices equipped with nickel metal hydride batteries include personal computers, portable communication devices, and other battery-powered home appliances, office equipment, and industrial equipment. Further, the nickel metal hydride battery of the present invention is a power storage device and power smoothing device for wind power generation, solar power generation, hydroelectric power generation and other power systems, power supply for ships and / or power supply for auxiliary machinery, aircraft, Power supply source for spacecraft and / or auxiliary machinery, auxiliary power source for vehicles that do not use electricity as power source, mobile home robot power source, system backup power source, uninterruptible power source power source, It may be used for a power storage device that temporarily stores electric power required for charging in an electric vehicle charging station or the like.

The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Without departing from the scope of the present invention, various modifications and improvements that can be made by those skilled in the art can be implemented.

[Examples] Hereinafter, the present invention will be described more specifically by showing Examples and Comparative Examples. The present invention is not limited to these examples.

(Production Example 1: Production of negative electrode active material)
As a rare earth-Mg-Ni system hydrogen storage alloy, an A ₂ B ₇ type hydrogen storage alloy represented by (La, Sm, Mg, Zr) _1.0 (Ni, Al) _3.6 was prepared. In the A ₂ B ₇ type hydrogen storage alloy, the Ni content was 62 mass%.

(Fine crushing process of negative electrode active material)
Coarse powder of hydrogen storage alloy and polyvinyl alcohol were mixed in distilled water so that the concentration of hydrogen storage alloy was 10% by mass, and mixed by a mixer to obtain a mixture. The content of polyvinyl alcohol was 0.5% by mass based on the hydrogen storage alloy. This mixture was transferred to a bead mill in the atmosphere, mixed in the bead mill, and then discharged from the bead mill. As beads for the bead mill, those made of zirconia were used.
The mixture discharged from the bead mill was transported to the mixer via the circulation pipe and then returned to the bead mill again. That is, the hydrogen storage alloy and water were circulated between the bead mill and the mixer, and the hydrogen storage alloy was repeatedly crushed by the bead mill.
The crushed product obtained through the above steps was filtered to obtain a crushed filtered product of Production Example 1 containing the hydrogen storage alloy powder and a small amount of water. The crushed and filtered product of Production Example 1 was subjected to the following alkali treatment step.
The average particle diameter (D ₅₀ ) of the hydrogen storage alloy powder in the pulverized and filtered product of Production Example 1 was 7 μm.

(Negative electrode active material alkaline treatment step: N-1) step a) step As the first alkaline aqueous solution, an aqueous sodium hydroxide solution containing 40% by mass of sodium hydroxide was prepared. Under stirring conditions, 50 parts by mass of the crushed and filtered product of Production Example 1 was added to 50 parts by mass of the first alkaline aqueous solution to form a suspension. The suspension was heated to 90 ° C. and held for 1 hour, then cooled to room temperature.

Step b) As the second alkaline aqueous solution, an aqueous sodium hydroxide solution containing 0.4% by mass of sodium hydroxide was prepared. The suspension after step a) was suction-filtered to separate the hydrogen storage alloy from the first alkaline aqueous solution. While continuing the suction filtration, 50 parts by mass of the second alkaline aqueous solution was poured over the hydrogen storage alloy to wash the hydrogen storage alloy.

N-2) Step With the suction filtration of step b) being continued, 300 parts by mass of water was poured over the hydrogen storage alloy to wash the hydrogen storage alloy with water.

50 parts by mass of 5% by mass hydrogen peroxide solution was added to the total amount of the filtered material obtained in the preceding paragraph, and the mixture was stirred for 20 minutes. After that, suction filtration was performed, 300 parts by mass of water was poured over the hydrogen storage alloy, and the hydrogen storage alloy was washed with water. This filtered hydrogen storage alloy was used as the negative electrode active material of Production Example 1.

(Production Example 2)
A negative electrode active material of Production Example 2 was produced in substantially the same manner as in Production Example 1 except that N-1) step and N-2) step were not performed.
Although the negative electrode active material of Production Example 2 was not oxidized with hydrogen peroxide in step N-2), it was oxidized to a certain extent because it was exposed to the atmosphere.

(Production Example 3)
A negative electrode active material of Production Example 3 was produced in substantially the same manner as in Production Example 1 except that the pulverization conditions were relaxed and that the oxidation with hydrogen peroxide in the N-2) step was not performed.
The average particle diameter (D ₅₀ ) of the hydrogen storage alloy powder of Production Example 3 was 15 μm.
Although the negative electrode active material of Production Example 3 was not oxidized with hydrogen peroxide in the step N-2), it was oxidized to a certain extent because it was exposed to the atmosphere in the step b) in the step N-1). ing.

(Production Example 4)
A negative electrode active material of Production Example 4 was produced in substantially the same manner as in Production Example 1 except that in step a) of step N-1), the suspension was heated to 90 ° C. and held for 3 hours.
The hydrogen storage alloy powder of Production Example 4 had an average particle size (D ₅₀ ) of 9 μm.

(Comparative Production Example 1)
A negative electrode active material of Comparative Production Example 1 was produced in substantially the same manner as in Production Example 1 except that the pulverization conditions were relaxed and that N-1) step and N-2) step were not performed.
The average particle diameter (D ₅₀ ) of the hydrogen storage alloy powder of Comparative Production Example 1 was 15 μm.

(Evaluation example 1: Physical properties of negative electrode active material)
With respect to the negative electrode active materials of Production Example 1, Production Example 2, Production Example 3, Production Example 4 and Comparative Production Example 1, measurement of oxygen concentration, measurement of BET specific surface area, and measurement of saturation magnetization were performed.
The oxygen concentration was measured using an oxygen / nitrogen / hydrogen analyzer (inert gas melting method). The BET specific surface area was measured using a general BET specific surface area measuring device. The measurement of the saturation magnetization was performed using a vibrating sample magnetometer.
The above results are shown in Table 1.

(Example 1)
(Production of positive electrode active material)
Nickel sulfate, cobalt sulfate and zinc sulfate were weighed so that the molar ratio of nickel, cobalt and zinc was 94.5: 4.5: 1.1, and these were added to an aqueous sodium hydroxide solution containing ammonium ions. , A mixed aqueous solution was prepared. A sodium hydroxide aqueous solution was gradually added to the mixed aqueous solution with stirring to adjust the pH of the mixed aqueous solution to 13-14. Thereby, precursor particles containing nickel hydroxide as a main component and cobalt and zinc as a solid solution were produced. The obtained precursor particles (main body of the positive electrode active material) were washed with water and then dried.

Step P-1) The obtained precursor particles were put into an aqueous ammonia solution to form a suspension. Aqueous cobalt sulfate solution was added to the suspension while maintaining the pH of the suspension at 9-10. As a result, cobalt hydroxide was deposited on the surface of the precursor particles, and thus particles having a layer of cobalt hydroxide were obtained.

P-2) Step The particles provided with the layer of cobalt hydroxide obtained in the preceding paragraph are sprayed with an aqueous solution of sodium hydroxide and an aqueous solution of lithium hydroxide while convection is carried out in high temperature air containing oxygen to perform heat treatment. gave. As a result, the cobalt hydroxide on the surface of the particles becomes highly conductive cobalt oxyhydroxide, and sodium and lithium are incorporated into the cobalt oxyhydroxide layer to form a cobalt oxyhydroxide containing sodium and lithium. A layer is formed.
Then, the particles having the cobalt oxyhydroxide layer were collected by filtration, washed with water, and then dried at 60 ° C. Thus, the positive electrode active material of Example 1 coated with the cobalt oxyhydroxide layer containing sodium and lithium was produced.

(Battery manufacturing process)
The nickel metal hydride battery of Example 1 was manufactured as follows.

94.3 parts by mass of the positive electrode active material of Example 1, 1 part by mass of cobalt powder as a conduction aid, 3.5 parts by mass of an acrylic resin emulsion as a solid component as a binder, and carboxymethylcellulose as a binder. 0.7 parts by mass, 0.5 parts by mass of Y ₂ O ₃ as a positive electrode additive, and an appropriate amount of ion-exchanged water were mixed to prepare a slurry. A nickel foil having a thickness of 20 μm was prepared as a current collector for the positive electrode. The above-mentioned slurry was applied in a film form on the surface of this nickel foil. The nickel foil coated with the slurry was dried to remove water, and then the nickel foil was pressed to manufacture a positive electrode having a positive electrode active material layer formed on a current collector.
The amount of the positive electrode active material layer present on the current collector of the positive electrode was 28 mg / cm ² , and the density of the positive electrode active material layer was 2.9 g / cm ³ .

97.8 parts by mass of the negative electrode active material of Production Example 1, 1.5 parts by mass of an acrylic resin emulsion as a solid component as a binder, 0.7 parts by mass of carboxymethyl cellulose as a binder, and an appropriate amount of ions. Exchanged water was mixed to produce a slurry. A nickel foil with a thickness of 20 μm was prepared as a negative electrode current collector. The above-mentioned slurry was applied in a film form on the surface of this nickel foil. The nickel foil coated with the slurry was dried to remove water, and then the nickel foil was pressed to manufacture a negative electrode having a negative electrode active material layer formed on a current collector.

As the electrolytic solution, the concentration of potassium hydroxide was 5.4 mol / L, the concentration of sodium hydroxide was 0.8 mol / L, the concentration of lithium hydroxide was 0.5 mol / L, and Na ₂ WO _{4 was used.} An aqueous solution having a concentration of 0.16 mol / L was prepared. This was used as the electrolytic solution of Example 1.

As a separator, a sulfonation-treated nonwoven fabric made of polyolefin fiber having a thickness of 104 μm was prepared.

▽ A separator was sandwiched between the positive and negative electrodes to form an electrode plate group. A nickel metal hydride battery of Example 1 was manufactured by disposing the electrode plate group in a resin casing, further injecting the electrolytic solution, and sealing the casing.

(Example 2)
As the electrolytic solution, the concentration of potassium hydroxide was 5.4 mol / L, the concentration of sodium hydroxide was 0.8 mol / L, the concentration of lithium hydroxide was 0.5 mol / L, and Na ₂ WO _{4 was used.} An aqueous solution having a concentration of 0.02 mol / L was prepared. This was used as the electrolytic solution of Example 2.
A nickel metal hydride battery of Example 2 was manufactured in the same manner as in Example 1 except that the electrolytic solution of Example 2 was used.

(Example 3)
Generally performed except that the molar ratio of nickel, cobalt and zinc was slightly changed in the production of the positive electrode active material main body, and that the sodium hydroxide aqueous solution and the lithium hydroxide aqueous solution were not sprayed in the step P-2). The positive electrode active material of Example 3 was manufactured in the same manner as in Example 1.
A nickel metal hydride battery of Example 3 was manufactured in the same manner as in Example 1 except that the positive electrode active material of Example 3 was used and the electrolytic solution of Example 2 was used.

(Example 4)
As the electrolytic solution, the concentration of potassium hydroxide was 5.4 mol / L, the concentration of sodium hydroxide was 0.8 mol / L, the concentration of lithium hydroxide was 0.5 mol / L, and Na ₂ WO _{4 was used.} An aqueous solution having a concentration of 0.01 mol / L was prepared. This was used as the electrolytic solution of Example 4.
A nickel metal hydride battery of Example 4 was produced in the same manner as in Example 1 except that the negative electrode active material of Production Example 4 and the electrolytic solution of Example 4 were used.

(Example 5)
A nickel metal hydride battery of Example 5 was manufactured in the same manner as in Example 4 except that the electrolytic solution of Example 2 was used.

(Example 6)
In the production of the electrolytic solution, the electrolytic solution of Example 6 was produced in the same manner as in Example 4 except that the concentration of Na ₂ WO ₄ was 0.03 mol / L.
A nickel metal hydride battery of Example 6 was manufactured in the same manner as in Example 4 except that the electrolytic solution of Example 6 was used.

(Example 7)
In the production of the electrolytic solution, the electrolytic solution of Example 7 was produced in the same manner as in Example 4 except that the concentration of Na ₂ WO ₄ was 0.04 mol / L.
A nickel metal hydride battery of Example 7 was manufactured in the same manner as in Example 4 except that the electrolytic solution of Example 7 was used.

(Example 8)
In the production of the electrolytic solution, the electrolytic solution of Example 8 was produced in the same manner as in Example 4, except that the concentration of Na ₂ WO ₄ was 0.05 mol / L.
A nickel metal hydride battery of Example 8 was produced in the same manner as in Example 4 except that the electrolytic solution of Example 8 was used.

(Example 9)
In the production of the electrolytic solution, the electrolytic solution of Example 9 was produced in the same manner as in Example 4 except that the concentration of Na ₂ WO ₄ was 0.06 mol / L.
A nickel metal hydride battery of Example 9 was manufactured in the same manner as in Example 4 except that the electrolytic solution of Example 9 was used.

(Example 10)
As the electrolytic solution, the concentration of potassium hydroxide is 5.4 mol / L, the concentration of sodium hydroxide is 0.8 mol / L, the concentration of lithium hydroxide is 0.5 mol / L, and the concentration of WO ₃ is Was prepared to be 0.01 mol / L. This was used as the electrolytic solution of Example 10.
A nickel metal hydride battery of Example 10 was manufactured in the same manner as in Example 4 except that the electrolytic solution of Example 10 was used.

(Example 11)
A positive electrode active material of Example 11 was manufactured in substantially the same manner as in Example 1 except that the lithium hydroxide aqueous solution was not sprayed in the step P-2) in the manufacture of the positive electrode active material main body.
A nickel metal hydride battery of Example 11 was manufactured in the same manner as in Example 4 except that the positive electrode active material of Example 11 was used.

(Comparative Example 1)
A nickel metal hydride battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the negative electrode active material of Comparative Production Example 1 and the electrolytic solution of Example 2 were used.

(Comparative example 2)
As an electrolytic solution, an aqueous solution having a potassium hydroxide concentration of 5.4 mol / L, a sodium hydroxide concentration of 0.8 mol / L, and a lithium hydroxide concentration of 0.5 mol / L was prepared. This was used as the electrolytic solution of Comparative Example 2.
A nickel metal hydride battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the negative electrode active material of Comparative Production Example 1 and the electrolytic solution of Comparative Example 2 were used.

(Comparative example 3)
A nickel metal hydride battery of Comparative Example 3 was manufactured in the same manner as in Example 4 except that the electrolytic solution of Comparative Example 2 was used.

(Evaluation example 2: Physical properties of positive electrode active material)
For the positive electrode active materials of Example 1, Example 3 and Example 11, analysis of lithium and sodium contents, measurement of average particle size, measurement of BET specific surface area, measurement of valence of cobalt, and measurement of resistivity. I went.

When the analysis of the lithium and sodium contents was performed by the atomic absorption method using the solution in which each positive electrode active material was dissolved, the lithium content in the positive electrode active material of Example 1 was about 0.1 mass%, The sodium content was about 0.3% by mass.
No lithium was detected from the positive electrode active materials of Example 3 and Example 11. A small amount of sodium was detected in the positive electrode active material of Example 3. Moreover, the sodium content in the positive electrode active material of Example 11 was about the same as that of the positive electrode active material of Example 1.

The average particle diameter (D ₅₀ ) was measured using a general laser diffraction particle size distribution analyzer. The BET specific surface area was measured using a general BET specific surface area measuring device. The valence of cobalt was measured by the iodometry method. The resistivity was measured using a powder resistivity measuring system (Mitsubishi Analytech Co., Ltd.) at 20 kN under conditions of 25 ° C. and relative humidity of 40 to 50% with respect to 2.0 g of the powder of the positive electrode active material. It was measured after applying a load.
The above results are shown in Table 2.

It can be seen from Table 2 that the valence of cobalt in the positive electrode active material is high and the resistivity of the positive electrode active material is low due to the presence of lithium.

(Evaluation example 3)
The nickel metal hydride batteries of Examples 1 to 3 and Comparative Examples 1 to 2 were charged to 1.5 V at a 0.1 C rate at a temperature of 25 ° C., and then charged to 0.1 C. The discharge was performed to 0.8 V at a rate. Then, the charge / discharge efficiency of each nickel metal hydride battery was calculated using the following formula.
Charge / discharge efficiency (%) = 100 × (discharge capacity) / (charge capacity)

Further, the nickel metal hydride batteries of Examples 1 to 3 and Comparative Examples 1 and 2 adjusted to SOC (State of Charge) 60% were discharged at a 1C rate for 5 seconds under a condition of 25 ° C. .. The discharge resistance was calculated based on Ohm's law from the amount of voltage change before and after discharge and the current value during discharge.

Table 3 shows the results of the above charge / discharge efficiency and discharge resistance.
The nickel metal hydride battery of Example 2 employs the positive electrode active material of Example 1 in which the layer of cobalt oxyhydroxide coating the positive electrode active material body is doped with lithium, and the nickel metal hydride battery of Example 3 is used. The hydride battery employs the positive electrode active material of Example 3 in which the layer of cobalt oxyhydroxide covering the body of the positive electrode active material is not doped with lithium.

From the results of Table 3, it can be said that the nickel metal hydride batteries of Examples are excellent in terms of charge / discharge efficiency and discharge resistance. From the results of Example 2 and Comparative Example 1, it can be seen that the charge / discharge efficiency and discharge resistance are optimized when the oxygen concentration of the negative electrode active material before charge / discharge is increased. Further, the results of Comparative Example 1 and Comparative Example 2 show that the presence of sodium tungstate in the electrolytic solution optimizes the charge / discharge efficiency.
It can be said that the nickel metal hydride battery of the present invention including both the negative electrode active material of the present invention and the electrolytic solution of the present invention has been proved to have excellent battery characteristics.

(Evaluation example 4)
The nickel metal hydride batteries of Examples 4 to 9 and Comparative Example 3 were charged from SOC 0% to SOC 100% at a rate of 1 / 3C at a temperature of 65 ° C., and then 1 / 3C. The discharge was performed at a rate of 100% SOC to 0% SOC. Then, the charge / discharge efficiency of each nickel metal hydride battery was calculated using the following formula.
Charge / discharge efficiency (%) = 100 × (discharge capacity) / (charge capacity)

Further, the nickel metal hydride batteries of Examples 4 to 9 and Comparative Example 3 adjusted to SOC (State of Charge) 60% were discharged at a 1C rate for 5 seconds under a condition of 25 ° C. The discharge resistance was calculated based on Ohm's law from the amount of voltage change before and after discharge and the current value during discharge. ‥

From the results of Example 1 and Example 2 in Table 3, Examples 4 to 9 and Comparative Example 3 in Table 4, it can be seen that the charge / discharge efficiency is optimized when the content of sodium tungstate is increased.

(Evaluation example 5)
The nickel metal hydride batteries of Example 4 and Example 10 were charged at a temperature of 60 ° C. from SOC 0% to SOC 100% and then at a rate of 1 / 3C SOC 100. The discharge was performed from 0% to SOC 0%. Then, the charge / discharge efficiency of each nickel metal hydride battery was calculated using the following formula.
Charge / discharge efficiency (%) = 100 × (discharge capacity) / (charge capacity)

Further, the nickel metal hydride batteries of Example 4 and Example 10 adjusted to SOC (State of Charge) 60% were discharged at a 1C rate for 5 seconds under a condition of 25 ° C. The discharge resistance was calculated based on Ohm's law from the amount of voltage change before and after discharge and the current value during discharge. ‥

It can be seen from Table 5 that similar effects can be obtained when tungstic acid is used instead of the tungstic acid salt.

(Evaluation example 6)
The nickel metal hydride battery of Example 11 adjusted to SOC (State of Charge) 60% was discharged at a 1C rate for 5 seconds at 25 ° C. The discharge resistance was calculated based on Ohm's law from the amount of voltage change before and after discharge and the current value during discharge.
As a result, the discharge resistance of the nickel metal hydride battery of Example 11 was 0.14Ω.

(Application example 1)
FIG. 1 shows a schematic cross-sectional view of the bipolar nickel metal hydride battery of Application Example 1 observed from the thickness side of the electrode.

The bipolar nickel metal hydride battery 1 of application example 1 is
A positive electrode 2 having a positive electrode active material layer 21 formed on one surface of a collector foil 20;
A negative electrode 3 having a negative electrode active material layer 31 formed on one surface of a collector foil 30,
A bipolar electrode 4 having a positive electrode active material layer 41 formed on one surface of the current collector foil 40 and a negative electrode active material layer 42 formed on the other surface;
And a separator 5 made of polyolefin that has been subjected to a hydrophilic treatment.

The collector foil 20 of the positive electrode 2 is made of nickel and is a rectangular foil having a thickness of 20 μm. A positive electrode active material layer 21 containing a positive electrode active material, a conductive auxiliary agent, a binder, and an additive is formed on the upper surface of the current collector foil 20. The periphery of the current collector foil 20 is fixed by an outer frame 7 made of synthetic resin, and a seal portion 6 made of fluorine-containing resin is arranged inside the outer frame 7. The seal portion 6 is bonded to the upper surface and the lower surface of the current collector foil 20.

The separator 5 is arranged on the upper surface of the positive electrode active material layer 21 of the positive electrode 2. The separator 5 is impregnated with the electrolytic solution of the present invention. The area of the surface of the separator 5 is larger than the area of the surface of the positive electrode active material layer 21 in contact therewith.

On the upper surface of the separator 5 arranged on the upper surface of the positive electrode active material layer 21 of the positive electrode 2, the bipolar electrode 4 is arranged in the direction in which the negative electrode active material layer 42 faces.

In the bipolar electrode 4, the positive electrode active material layer 41 is formed on the upper surface of the current collector foil 40 and the negative electrode active material layer 42 is formed on the lower surface. The current collector foil 40 is the same as the current collector foil 20 of the positive electrode 2, and the positive electrode active material layer 41 is also the same as the positive electrode active material layer 21 of the positive electrode 2. The negative electrode active material layer 42 of the bipolar electrode 4 contains the negative electrode active material and the binder of the present invention.

The periphery of the current collector foil 40 is fixed by an outer frame 7 made of synthetic resin, and a seal portion 6 made of fluorine-containing resin is arranged inside the outer frame 7. The seal portion 6 is bonded to the upper surface and the lower surface of the collector foil 40, and the seal portion 6 on the upper surface of the collector foil 40 is further bonded to the lower surface of the collector foil 40 of the other bipolar electrode 4 on the upper side. The seal portion 6 on the lower surface of the collector foil 40 is also bonded to the upper surface of the collector foil 20 of the positive electrode 2. That is, the positive electrode active material layer 21, the separator 5, the electrolytic solution, and the negative electrode active material layer 42 are sealed by the seal portion 6.

On the upper surface of the bipolar electrode 4 laminated on the positive electrode 2 via the separator 5, a plurality of bipolar electrodes 4 are laminated via the separator 5.
The separator 5 is arranged on the upper surface of the positive electrode active material layer 41 of the uppermost bipolar electrode 4, and the negative electrode 3 is arranged on the upper surface of the separator 5 in a direction facing the negative electrode active material layer 31.

The negative electrode 3 has a negative electrode active material layer 31 formed on the lower surface of the current collector foil 30. The collector foil 30 is similar to the collector foil 20 of the positive electrode 2 and the collector foil 40 of the bipolar electrode 4, and the negative electrode active material layer 31 is also similar to the negative electrode active material layer 42 of the bipolar electrode 4. is there. The periphery of the current collector foil 30 is fixed by an outer frame 7 made of synthetic resin, and a seal portion 6 made of fluorine-containing resin is arranged inside the outer frame 7. The seal portion 6 is bonded to the upper surface and the lower surface of the collector foil 30, and the seal portion 6 on the lower surface of the collector foil 30 is also bonded to the upper surface of the collector foil 40 of the bipolar electrode 4.

A cooling unit 8 is arranged above and below the battery module composed of the positive electrode 2, the bipolar electrode 4, the negative electrode 3 and the separator 5 in the thickness direction. The cooling unit 8 is a rectangular plate made of aluminum and has a plurality of through holes 80 capable of air cooling.

Outside the cooling unit 8, a module positive electrode 22 and a module negative electrode 32, which conduct electricity with the outside, are arranged respectively. The module positive electrode 22 and the module negative electrode 32 are rectangular plates made of metal.
The restraints 9 are arranged outside the module positive electrode 22 and the module negative electrode 32, respectively. The restraint 9 is a rectangular plate made of synthetic resin. The two restraints 9 are fastened with a plurality of bolts and nuts (not shown), and pressurize and restrain the battery module in the thickness direction of the electrodes. The separator 5 is compressed by the pressure applied by the two restraints 9.

DESCRIPTION OF SYMBOLS 1 Bipolar nickel metal hydride battery 2 Positive electrode 3 Negative electrode 4 Bipolar electrode 5 Separator 6 Seal part 7 Outer frame 8 Cooling 9 Restraint tool 20 Current collecting foil (positive electrode current collecting foil)
21 positive electrode active material layer 22 module positive electrode 30 current collector foil (negative electrode current collector foil)
31 negative electrode active material layer 32 module negative electrode 40 collector foil (bipolar electrode collector foil)
41 Positive Electrode Active Material Layer 42 Negative Electrode Active Material Layer 80 Through Hole

Claims (4)

1. A negative electrode active material having an oxygen concentration of 1000 ppm or more before charge and discharge,
   A nickel metal hydride battery, comprising: an electrolyte containing an aqueous solution containing tungstic acid or a salt thereof and an alkali metal hydroxide.
2. The nickel metal hydride battery according to claim 1, wherein the negative electrode active material contains an A ₂ B ₇ type hydrogen storage alloy containing a rare earth element, Mg and Ni.
3. The nickel metal hydride battery according to claim 1 or 2, wherein the concentration of tungstic acid and its salt in the electrolytic solution is in the range of 0.001 to 0.5 mol / L.
4. A method for manufacturing a nickel metal hydride battery according to any one of claims 1 to 3,
   A method of manufacturing, comprising the steps of N-1) and N-2) below, which comprises manufacturing a negative electrode active material having an oxygen concentration of 1000 ppm or more.
   N-1) a step of treating the hydrogen storage alloy with an alkaline aqueous solution N-2) a step of oxidizing the surface of the hydrogen storage alloy after the step N-1)

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