JPH10289714A - Nickel-hydrogen storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel-hydrogen storage battery, having enhanced capacity density and high positive electrode characteristics by improving a positive electrode active material. SOLUTION: A nickel-hydrogen storage battery consist of a positive electrode, a negative electrode, an 8-12 mol/l-aqueous solution of sodium hydroxide as an alkaline electrolyte and a separator. Nickel hydroxide as the principal active material of the positive electrode is formed by soluting 8-12 atomic %-Mn into its metal nickel. The nickel hydroxide under a charged state is of a hexagonal system or a tetragonal system having a diffraction peak on a (001) plane at around the 16-19 degrees of a diffraction angle, 2θ, at X-ray diffraction using CUKα as a radiation source. Its ordered arrangement has a NaCl-type structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen storage battery, in which a positive electrode active material is improved to increase its capacity density and to improve characteristics of a positive electrode.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices, there has been a demand for higher capacity alkaline storage batteries. In particular, nickel-hydrogen storage batteries are secondary batteries consisting of a positive electrode made of an active material mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy, and are rapidly becoming high-capacity and highly reliable secondary batteries. It is becoming popular.

The positive electrode for an alkaline storage battery is roughly classified into a sintered type and a non-sintered type. The sintered positive electrode is prepared by impregnating a nickel salt solution such as a nickel nitrate aqueous solution into a porous nickel sintered substrate having a porosity of about 80% obtained by sintering nickel powder, and then immersing the substrate in an alkaline aqueous solution. To produce a nickel hydroxide active material in a porous nickel sintered substrate. Since it is difficult to further increase the porosity of the substrate in this electrode, the amount of the filled active material cannot be increased, and there is a limit to increasing the capacity.

A non-sintered positive electrode is disclosed in, for example,
No. 0667 discloses a method in which three-dimensionally continuous sponge-like porous material made of nickel metal and having a porosity of 95% or more is filled with nickel hydroxide as an active material. It is currently widely used as the positive electrode of high capacity alkaline storage batteries.

In this non-sintered type positive electrode, it has been proposed that spherical nickel hydroxide be filled into the pores of a sponge-like nickel porous material from the viewpoint of increasing the capacity. This is because the pore size of the sponge-like nickel porous body is 20
0 to 500 μm, and the pores have a particle size of several μm
It is filled with spherical nickel hydroxide of several tens of μm. In this configuration, the nickel hydroxide in the vicinity of the skeleton of the porous nickel body maintains conductivity, so that the charge / discharge reaction proceeds smoothly, but the reaction of nickel hydroxide separated from the skeleton does not sufficiently proceed.

[0006] For this reason, the non-sintered positive electrode uses a conductive agent in addition to nickel hydroxide as an active material in order to improve the utilization of the filled nickel hydroxide. The conductive network is formed by making electrical connection between them. As the conductive agent, a cobalt compound such as cobalt hydroxide or cobalt monoxide, metallic cobalt, metallic nickel or the like is used. As a result, the non-sintered positive electrode can maintain conductivity even when the active material is filled at a high density, and can achieve high capacity.

[0007]

However, the spherical nickel hydroxide used as the active material of the non-sintered positive electrode is in a discharged state in which activated nickel hydroxide (β-Ni (O
H) ₂ ), and the average valence of nickel is 2.
It is monovalent. This active material becomes β-type nickel oxyhydroxide (β-NiOOH) in a charged state, and the average valence of nickel is said to be around 3.1.

[0008] Therefore, in charge and discharge, the utilization rate becomes 100% by almost one-electron reaction. (The utilization is a percentage of a value obtained by dividing a capacity actually measured by a capacity per theoretical unit weight of 289 mAh / g assuming a one-electron reaction.) As a result, when this active material is used, the capacity density of the positive electrode is about 650 mAh / cc. become.

[0009] It has also been confirmed that when a nickel-hydrogen storage battery is continuously overcharged at a low temperature, the nickel valence of the positive electrode becomes higher and rises to 3.67 valence.

However, when the average valence of nickel exceeds about 3.5, the nickel hydroxide becomes γ-type nickel oxyhydroxide (γ-NiOOH). γ-NiOOH is Cu
A substance having a (003) plane diffraction peak at a diffraction angle 2θ of about 12 degrees (λ = 1.5405) in X-ray diffraction using Kα as a source. Cations, anions and water are present between the nickel-nickel metal plane layers. Are inserted, β-NiOO
The crystals are more likely to expand than H (density 4.68 g / cm ³ ).

Γ-NiOOH (density 3.79 g /
cm ³ ) is α-3Ni (OH) ₂ .2H ₂ when discharging.
O (density 2.82 g / cm ³ ). At this time, the density change is large, and thus the active material repeatedly expands and contracts. Therefore, the spherical nickel hydroxide loses its spherical shape, and the charged γ-NiOOH is accumulated without being discharged, so that the positive electrode swells and absorbs the electrolytic solution in the battery.

As a result, the amount of the electrolytic solution held by the separator is reduced and the electrolyte is leaked, so that the internal resistance of the battery is increased and the battery cannot be discharged. This phenomenon has been known for a long time even when a sintered positive electrode is used. Particularly in a sealed battery, the battery characteristics deteriorate due to swelling of the positive electrode.

An object of the present invention is to provide a nickel-hydrogen storage battery that improves the positive electrode active material, improves the capacity density thereof, and improves the characteristics of the positive electrode.

[0014]

In order to achieve the above object, a nickel-hydrogen storage battery according to the present invention comprises a positive electrode mainly composed of nickel hydroxide as an active material, a negative electrode mainly composed of a hydrogen storage alloy, and an alkaline battery. Consisting of an electrolyte and a separator,
Nickel hydroxide, which is the main active material of the positive electrode, has at least one kind of transition metal dissolved therein, and its crystalline structure in a charged state has a diffraction angle 2θ in X-ray diffraction using CuKα as a source. It is a hexagonal system or a tetragonal system having a (001) plane diffraction peak at around 16 to 19 degrees, and has a regular arrangement of a NaCl type structure.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION According to the first aspect of the present invention, the positive electrode active material has the crystal structure described above, and in a charged state, the average valence of nickel is 3.5, which is higher than β-NiOOH. Since the valence becomes valence, the number of reactive electrons increases, the capacity density of the active material improves, and the characteristics of the positive electrode can be improved.

According to a second aspect of the present invention, the transition metal dissolved in nickel hydroxide is at least one of Mn, Al, Cr and Co, and the transition metal in a charged state is specified. The crystal structure is a hexagonal system or a tetragonal system having a (00l) plane diffraction peak at a diffraction angle 2θ of around 16 to 19 degrees in X-ray diffraction using a CuKα radiation source, and an ordered structure is a NaCl type structure. Is preferred. An appropriate amount of the specified transition metal solid solution is 2 to 20 atomic% based on the metal nickel of the nickel hydroxide. if,
If this amount is less than 2 atomic%, the amount of solid solution in nickel hydroxide is not sufficient, and the above-mentioned diffraction peak cannot be obtained. Conversely, if the amount of solid solution is large, the amount of nickel hydroxide itself, which is the active material, is relatively reduced, and the amount of the active material filled in the positive electrode is reduced, so that the capacity of the positive electrode is reduced.

[0017]

EXAMPLES As a positive electrode plate, an average particle size of 15 as an active material was used.
μm spherical nickel hydroxide powder, 100 atomic parts of solid solution of Mn with respect to the metallic nickel, 100 parts by weight, 0.5 parts by weight of polytetrafluoroethylene as a binder, and hydroxide as a conductive agent 10 parts by weight of cobalt and an appropriate amount of water as a dispersion medium were added to form a paste, which was filled into the pores of the sponge-like nickel porous body and dried,
It was produced by rolling with a roll press. The dimensions of the positive electrode plate were 35 mm in width, 120 mm in length, and 0.78 mm in thickness. Theoretical capacity of this positive electrode (calculated as 289 mAh / g assuming that nickel hydroxide is a one-electron reaction)
Was 1600 mAh.

[0018] the negative electrode plate, and the AB ₅ type hydrogen absorbing alloy powder 100 parts by weight, and the carbon powder 1 part by weight, polytetrafluoroethylene 1 part by weight, a paste by adding an appropriate amount of water, which punched metal And then rolled. The dimensions of the negative electrode plate were 35 mm in width, 145 mm in length, and 0.39 mm in thickness. The theoretical capacity of this negative electrode (the amount of electricity per unit weight of the hydrogen storage alloy is 280 m
(Calculated as Ah / g) was 2900 mAh.

A positive electrode plate, a negative electrode plate, and a separator made of a polypropylene nonwoven fabric are disposed between the two, and the whole is spirally wound to form an electrode plate group, which is inserted into a battery case. Sodium hydroxide 1 as alkaline electrolyte
After injecting a predetermined amount of 0 mol / l aqueous solution, it is sealed with a sealing plate also serving as a positive electrode terminal, and is 4 / 5A in size, with a nominal capacity of 1
A 600 mAh nickel-hydrogen storage battery A was configured.

A battery having the same configuration as the battery B of the comparative example except that nickel hydroxide not containing Mn as a solid solution was used instead of the positive electrode plate active material prepared above.
And

Each of the batteries A and B was charged at 160 mA to 1
After charging for 5 hours and allowing to stand for 1 hour, two charge / discharge cycles were performed at 320 mA until the terminal voltage reached 1 V.

After aging for 3 days in a temperature atmosphere of 45 ° C.,
After charging for 18 hours with a current of 60 mA and leaving for 1 hour,
Discharge was performed at 320 mA until the terminal voltage reached 1 V. The active material utilization rate of the positive electrode obtained from the discharge capacity at this time (percentage when the actual discharge capacity / the positive electrode theoretical capacity is 289 mAh)
The battery A was 130% and the battery B was 100%.

For confirmation, the batteries A and B in the charged state were respectively disassembled, the positive electrode plate was taken out, and analyzed by X-ray diffraction using CuKα as an active material (wavelength λ is 1.5405). . The diffraction angle 2θ was determined by this analysis. As a result, a diffraction peak of the (00l) plane was confirmed in the positive electrode plate of the battery A where 2θ was close to 16 degrees, but the positive electrode plate of the battery B had the same No diffraction peak could be confirmed.

Thus, in the battery B of the comparative example, when the positive electrode active material was in a charged state, it became β-NiOOH, and the average valence of nickel was 3.1. Is 100%.

In the battery A of the embodiment, when the positive electrode active material is in a charged state, it is in a higher nickel oxidation state and has an average valence of 3.5.
Since the number of reaction electrons increases, the number of reactive electrons increases as compared with the comparative example, and the capacity density of nickel hydroxide itself improves. Therefore, the utilization rate of the positive electrode active material was 130%, which was 30% less than that of the comparative example.
% Improved.

In the embodiment of the present invention, nickel hydroxide, which is a positive electrode active material, is obtained by dissolving Mn at 10 atomic% with respect to the metallic nickel. When the content is in the range of 20 atomic%, almost the same effect as that of the embodiment is obtained, and the most preferable range is 8 to 12 atomic%.

Further, in the embodiment of the present invention, Mn is used as a solid solution metal in nickel hydroxide which is a positive electrode active material. In addition, any one of transition metals of Al, Cr and Co is used. Even in this case, substantially the same effects as in the embodiment can be obtained. At this time, the solid solution amount of each metal is 5% for Al with respect to metallic nickel of nickel hydroxide as an active material.
Preferred results were ％ 15 at%, 5-20 at% for Cr, and 15-20 at% for Co.

Further, as a solid solution metal in nickel hydroxide which is a positive electrode active material, not only a single metal as described above but also any one of a combination of Mn and Al, Mn and Cr, and Mn and Co is used. In the state, almost the same effects as those of the embodiment can be obtained. The amount of each solid solution at the time of this combined use is Mn and Mn if Al and Mn are relative to metallic nickel of nickel hydroxide.
5-10 atomic% and Al 5-10 atomic%, Mn and Cr, Mn 5-10 atomic% and Cr 5-10 atomic%, Mn and C
If o, Mn is preferably 5 to 10 atomic% and Co is preferably 2 to 5 atomic%.

As described above, as the solid solution metal in nickel hydroxide, a combined use state in which Al, Cr and Co are combined around Mn is shown, but any one of Mn, Al, Cr and Co is used. The same effect as in the embodiment can be obtained even in the combined state in which the main body is combined. When used together, the total amount of the solid solution metal is preferably in the range of 2 to 20 atomic% based on the metal nickel of nickel hydroxide as the active material.

As the alkaline electrolyte, an aqueous solution of sodium hydroxide 10 mol / l was used in the above,
It is not limited to this concentration but 8 to 12 mol / l
Within this range, substantially the same effects as in the embodiment can be obtained.

The above-mentioned alkaline electrolyte is a single aqueous solution of sodium hydroxide. However, the present invention is not limited to this. A single aqueous solution of potassium hydroxide or a mixed aqueous solution thereof, and further, lithium hydroxide, rubidium hydroxide and Even when a mixed aqueous solution to which at least one of cesium hydroxide is added is used, substantially the same effects as in the embodiment can be obtained.

[0032]

As described above, in the battery of the present invention, nickel hydroxide, which is the main active material of the positive electrode, has at least one kind of transition metal in solid solution, and the charged state is CuK.
16 to 1 of diffraction angle 2θ in X-ray diffraction using α as a source
It is a hexagonal or tetragonal system having a (00l) plane diffraction peak at around 9 degrees and has a regular arrangement of a NaCl type structure, so that the average valence of nickel is 3.5 in a charged state. Since the valence becomes higher, the number of reactive electrons increases, the capacity density of the active material improves, and the characteristics of the positive electrode can be improved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Yuasa 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A positive electrode mainly composed of nickel hydroxide as an active material, a negative electrode mainly composed of a hydrogen storage alloy, an alkaline electrolyte, and a separator. And a solid solution of at least one of transition metals, and in a charged state, has a (001) plane diffraction peak near 16 to 19 degrees of diffraction angle 2θ in X-ray diffraction using CuKα as a radiation source. A nickel-hydrogen storage battery having a crystal system or a tetragonal system and having a regular arrangement having a NaCl type structure. 2. The transition metal used is at least one of Mn, Al, Cr and Co, and its solid solution amount is 2 to 20 at% with respect to metallic nickel of nickel hydroxide. Nickel-hydrogen storage battery. 3. A positive electrode mainly composed of nickel hydroxide as an active material, a negative electrode mainly composed of a hydrogen storage alloy, an alkaline electrolyte, and a separator. , Mn is 8 with respect to the metallic nickel.
~ 12 at.% Solid solution and charged state is CuKα
Of diffraction angle 2θ in X-ray diffraction using
A nickel-metal hydride storage battery having a hexagonal or tetragonal system having a diffraction peak of the (00l) plane in the vicinity of a degree and having a NaCl-type structure in a regular arrangement. 4. The nickel-hydrogen storage battery according to claim 1, wherein the alkaline electrolyte is a single aqueous solution of sodium hydroxide or potassium hydroxide or a mixed aqueous solution. 5. The alkaline electrolyte is a single aqueous solution of sodium hydroxide or potassium hydroxide, or a mixed aqueous solution obtained by adding at least one of rubidium hydroxide, cesium hydroxide and lithium hydroxide to a mixed aqueous solution. The nickel-hydrogen storage battery according to any one of claims 1 to 3. 6. A positive electrode mainly composed of nickel hydroxide as an active material, a negative electrode mainly composed of a hydrogen storage alloy, an alkaline electrolyte comprising 8 to 12 mol / l aqueous solution of sodium hydroxide, and a separator, Nickel hydroxide, which is the main active material of the positive electrode, has Mn of 8 with respect to the metallic nickel.
~ 12 at.% Solid solution and charged state is CuKα
Of diffraction angle 2θ in X-ray diffraction using
A nickel-metal hydride storage battery having a hexagonal or tetragonal system having a diffraction peak of the (00l) plane in the vicinity of a degree and having a NaCl-type structure in a regular arrangement.