JP2001167758A - Electrode for use in alkaline secondary battery, alkaline secondary battery, and method of fabricating electrode for use in alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode and a method of fabricating the electrode having a high capacity and utilization rate, as well as an alkaline secondary battery capable of exhibiting an excellent high-rate discharge characteristic. SOLUTION: The electrode 2 and the alkaline secondary battery including the electrode 2 are adopted. In the electrode, wherein at least electrode active substance powders are adhered to a sheet-shaped or porous conductive support. In the electrode active substance, a metallic nickel-containing conductive layer is coated on at least a portion of a surface of nickel hydroxide-based particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for an alkaline secondary battery, a method for producing the electrode, and an alkaline secondary battery provided with the electrode.

[0002]

2. Description of the Related Art With the development of portable electronic devices in recent years, it is desired to increase the capacity of secondary batteries used as power sources for these electronic devices. On the other hand, secondary batteries are also used for power supplies that require large currents, such as power tools,
In that case, improvement of the high rate discharge characteristics is desired.

By the way, for example, in an alkaline secondary battery using nickel hydroxide for the positive electrode and cadmium or a hydrogen storage alloy for the negative electrode, the charge and discharge capacity of the negative electrode is larger than that of the positive electrode. Designed. Therefore, the battery capacity of the alkaline secondary battery is determined by the charge and discharge capacity of the positive electrode. Therefore, in order to increase the capacity of the battery, it is necessary to increase the capacity of the positive electrode.

The positive electrode of a recent alkaline secondary battery is a so-called paste electrode, which is a paste containing nickel hydroxide powder as an electrode active material and a cobalt compound powder such as cobalt hydroxide or cobalt monoxide. It is manufactured by filling a porous metal body that is a current collector. The porous metal body is formed, for example, by forming a metal film of Ni or the like on a skeleton of a urethane foam and burning and removing the urethane foam to have a three-dimensional skeleton structure (sponge structure). The nickel hydroxide powder and the cobalt compound powder are filled and held in the voids of the three-dimensional skeletal structure. The cobalt compound is oxidized during the first charge of the battery to become conductive cobalt oxyhydroxide,
Deposits on the surface of nickel hydroxide.

When the cobalt oxyhydroxide precipitates on the surface of the insulating nickel hydroxide particles in a discharged state, a conductive network is formed between the nickel hydroxide powders or between the nickel hydroxide powder and the skeleton of the porous metal body. Thus, conductivity is imparted to the nickel hydroxide, and the internal resistance of the positive electrode during discharge is reduced.

Also, a hydrazine reduction catalyst is previously applied to the surface of the granular nickel hydroxide, and the nickel hydroxide is introduced into a neutral hydrazine aqueous solution and reduced to form 5 to 30% by weight of metallic nickel. There is also known a method in which the resulting material is used as a positive electrode active material (Japanese Unexamined Patent Application Publication No.
1-233110).

[0007]

However, cobalt oxyhydroxide is a semiconductor and has insufficient conductivity. In an alkaline secondary battery having such a positive electrode, the internal resistance of the positive electrode is increased. There has been a problem that the utilization rate is lowered and high-rate discharge characteristics cannot be obtained as desired. Further, the addition of cobalt oxyhydroxide has a problem that the amount of nickel hydroxide relatively decreases, and the charge / discharge capacity of the battery decreases.

Further, using a neutral hydrazine aqueous solution,
When the metal nickel phase was reduced on the surface of the electrode active material, it was difficult to uniformly form the metal nickel on the surface of the nickel hydroxide. In particular, when the content of metallic nickel is less than 5% by weight, it is difficult to coat metallic nickel evenly on the surface of nickel hydroxide, and there has been a problem that sufficient conductivity cannot be imparted to nickel hydroxide. In order to impart sufficient conductivity to nickel hydroxide, it is said that it is necessary to deposit 5% by weight or more of metal nickel. In this case, however, the amount of nickel hydroxide as an active material is reduced, There is a problem that the charge / discharge capacity of the battery is reduced.

The present invention has been made in view of the above circumstances, and provides an electrode capable of exhibiting excellent high-rate discharge characteristics, a method of manufacturing the electrode, and an alkaline secondary battery using the same. The purpose is to do.

[0010]

In order to achieve the above object, the present invention employs the following constitution. The electrode for an alkaline secondary battery of the present invention comprises at least a powder of an electrode active material fixed to a conductive support, and the electrode active material has at least one surface of particles mainly composed of nickel hydroxide. A conductive layer containing a metal nickel phase is formed on the portion, and the content of the metal nickel phase in the electrode active material is less than 5% by weight. Further, the electrode for an alkaline secondary battery of the present invention is configured by solidifying and molding at least a powder of an electrode active material, and the electrode active material has a metal on at least a part of the surface of particles mainly composed of nickel hydroxide. A conductive layer containing a nickel phase is coated and formed, and the content of the metal nickel phase in the electrode active material is less than 5% by weight.

The conductive layer is preferably obtained by reducing nickel hydroxide with hydrazine in an aqueous alkali metal hydroxide solution having a pH of 11.9 or more. The content of the metallic nickel phase in the electrode active material was 0.6% by weight.
And more preferably less than 5% by weight, more preferably 1.9% by weight or more and 4.9% by weight or less,
Most preferably, it is not less than 2.6% by weight and not more than 4.9% by weight.

According to the electrode for an alkaline secondary battery of the present invention, is the powder of the electrode active material having the particle surface coated with the conductive layer containing the metallic nickel phase fixed to the conductive support? Or this powder is solidified and molded,
Since the particles are electrically connected to each other via the conductive layer to form a conductive network exhibiting metal conductivity of a higher-order structure, the internal resistance of the electrode can be reduced, and the utilization rate of nickel hydroxide can be reduced. Can be improved. In addition, since the metallic nickel phase has better conductivity than conventional cobalt oxyhydroxide, the internal resistance of the positive electrode can be further reduced.
Further, since the content of the metallic nickel phase contained in the conductive layer is less than 5% by weight, the amount of nickel hydroxide is relatively improved,
The charge / discharge capacity per electrode can be increased.

Further, the present invention does not form a conductive network by forming cobalt oxyhydroxide as a semiconductor as in the prior art, but forms a conductive network by a conductive layer having metal conductivity. The conductivity between the electrode active materials is significantly improved, and the internal resistance of the electrode can be reduced.

Since the conductive layer mainly composed of the metallic nickel phase is formed by reducing nickel hydroxide, the conductive layer and the nickel hydroxide are in close contact with each other, and the conductive layer and the nickel hydroxide are And the internal resistance of the positive electrode is reduced.

Further, it is preferable that at least a part of the conductive layer of the electrode active material is porous.
Since the form of the conductive layer is porous, the electrolytic solution easily penetrates into the conductive layer and reaches the nickel hydroxide layer thereunder, so that the charge / discharge reaction proceeds smoothly. be able to.

Further, an alkaline secondary battery of the present invention is provided with the above-mentioned electrode for an alkaline secondary battery. According to such an alkaline secondary battery, an electrode having an electrode active material having a conductive layer is provided, and since a conductive network having a higher-order structure and exhibiting metal electric conduction is formed on this electrode, the electrode , The internal resistance is reduced, and excellent high-rate discharge characteristics can be exhibited.

According to the method for producing an electrode for an alkaline secondary battery of the present invention, an electrode active material comprising a conductive layer containing a metallic nickel phase is coated on at least a part of the surface of particles mainly composed of nickel hydroxide. A method for producing an electrode constituted by fixing powder to a sheet-shaped or porous conductive support, wherein the electrode active material is fixed to the conductive support when the electrode active material is fixed to the conductive support. By applying a compressive stress to the powder of (1), at least a part of the conductive layer is broken, so that at least a part of the nickel hydroxide is exposed on a surface of the electrode active material. Further, the method for producing an electrode for an alkaline secondary battery according to the present invention provides a method of producing an electrode for an electrode active material, wherein at least a part of the surface of particles mainly composed of nickel hydroxide is coated with a conductive layer containing a metallic nickel phase. Is a method for manufacturing an electrode configured by solidification molding, and when solidifying and molding the electrode active material, at least a part of the conductive layer is broken by applying a compressive stress to the powder of the electrode active material. Then, at least a part of the nickel hydroxide is exposed on the surface of the electrode active material.

According to the above-described method for manufacturing an electrode for an alkaline secondary battery, compressive stress is applied to the powder of the electrode active material to break at least a part of the conductive layer to expose nickel hydroxide. The electrolyte comes in direct contact with the nickel hydroxide, and the charge / discharge reaction can proceed smoothly.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an alkaline secondary battery 1 according to a first embodiment of the present invention. The alkaline secondary battery 1 is called a cylindrical type, and includes a sheet-shaped positive electrode 2 (electrode) according to the present invention, a sheet-shaped negative electrode 3, and a separator 4 disposed between the positive electrode 2 and the negative electrode 3. And an electrolyte mainly impregnated in the positive electrode 2, the negative electrode 3 and the separator 4, a cylindrical battery container 5, and a sealing member 6 for sealing the battery container 5. In the alkaline secondary battery 1, a positive electrode 2, a negative electrode 3, and a separator 4 are superposed, and are housed in a battery container 5 in a state where they are spirally wound.

The positive electrode 2 (electrode) according to the present invention comprises a powder of an electrode active material fixed to a conductive support.
As shown in FIG. 5, positive electrode layers 22 and 22 (electrode layers) each containing an electrode active material are laminated on both surfaces of a punching metal 21 which is a sheet-shaped conductive support.

The positive electrode layer 22 is made of a powder 23 of an electrode active material in which a conductive layer is coated on particles mainly composed of nickel hydroxide, and a material such as Teflon which binds the powders 23 of the electrode active material. And at least a conductive material such as Ni powder, graphite, or carbon black, if necessary.

In the positive electrode layer 22, FIGS.
As shown in (2), the powder 23 of the electrode active material is bound via a binder, and the conductive layers 24 on the surface are in contact with each other to form a conductive network having a higher-order structure and exhibiting metal electrical conductivity. . The positive electrode layer 22 and the conductive support 21 are electrically connected by laminating and fixing the positive electrode layer 22 on the conductive support 21.

The negative electrode 3 is formed by fixing powder of an electrode active material for a negative electrode to a sheet-shaped conductive support, and a negative electrode comprising an electrode active material for a negative electrode on both surfaces of the conductive support. It is configured by laminating electrode layers.

The negative electrode layer contains at least a powder of an electrode active material for a negative electrode and a binder made of, for example, Teflon, which binds the powder of the electrode active material. A conductive auxiliary material such as powder, graphite, and carbon black may be included. As the electrode active material for the negative electrode, for example, a hydrogen storage alloy, cadmium hydroxide, or the like can be used. Further, a punching metal can be used for the conductive support as in the case of the positive electrode.

The electrolyte is prepared by dissolving any one of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide and lithium hydroxide or a mixture thereof in water, and adding alkaline earth metal ions as necessary. It was done.
For the separator 4, a nonwoven fabric made of, for example, a polyamide resin or polypropylene can be used.

The electrode active material of the positive electrode 2 is obtained by covering at least a part of the surface of particles mainly composed of nickel hydroxide, which is a positive electrode active material, with a conductive layer 24. The shape of particles mainly composed of nickel hydroxide is spherical, plate-like,
Any shape such as a lump may be used, but a spherical shape is preferable because the density of the electrode active material itself can be increased.

The particles have an average particle size of 5 μm.
(5 × 10 ⁻⁶ m) to 500 μm (5 × 10 ⁻⁴ m), preferably 10 μm (1 × 10 ⁻⁵ m) to 100 μm (1 × 1
^0-4 m). Average particle size is 5μ
m (5 × 10 ⁻⁶ m) or less, the weight ratio of the conductive layer / nickel hydroxide increases when the conductive layer 24 is formed,
It is not preferable because the content of nickel hydroxide in the electrode active material is reduced and the electric capacity per unit weight of the electrode active material is reduced. The average particle size is 500 μm (5 ×
If it exceeds 10 ^-4 m), the utilization of nickel hydroxide decreases, which is not preferred.

It is preferable that the particles contain one or more elements of Zn, Al, Co, and Ca in addition to nickel hydroxide. These elements are preferably dissolved in the crystals of nickel hydroxide. Z
n and Co have the effect of lowering the crystallinity of nickel hydroxide and improving the charge / discharge characteristics of nickel hydroxide.
Ca has an effect of preventing a capacity decrease at a high temperature,
Co also has the effect of improving the conductivity of nickel hydroxide. The addition amounts of these elements are as follows: 1 to 6% by weight of Zn, 0.2 to 2% by weight of Al,
Is preferably 1 to 6% by weight and Ca is preferably 1 to 5% by weight.

The conductive layer 24 is made of nickel hydroxide of pH = 1.
It is produced by reduction with hydrazine in an aqueous solution of 1.9 or more alkali metal hydroxide, and preferably contains at least a metallic nickel phase. This metallic nickel phase is a reduction product of nickel hydroxide. In addition,
The conductive layer 24 may contain an unreduced nickel hydroxide phase in addition to the metal nickel phase. The conductive layer 24 is preferably porous because it allows the electrolyte to penetrate the conductive layer and reach the nickel hydroxide, thereby facilitating the charge / discharge reaction.

The thickness of the conductive layer 24 is 0.05 μm (5 ×
It is preferably in the range of 10 ⁻⁸ m) to 5 μm (5 × 10 ⁻⁶ m). The thickness of the conductive layer 24 is 0.05 μm (5 × 1
When the thickness is less than 0 ^-8 m), the conductive layer becomes thin, and the formation of a conductive network becomes insufficient, so that the internal resistance of the positive electrode 2 may not be reduced.
If the thickness exceeds 5 μm (5 × 10 ⁻⁶ m), the electrolyte may not be able to permeate the nickel hydroxide, which is not preferable.

The content of the metallic nickel phase in the electrode active material is preferably less than 5% by weight, more preferably 0.6% by weight or more and less than 5% by weight.
The content is more preferably from 9% by weight to 4.9% by weight, and most preferably from 2.6% by weight to 4.9% by weight. When the content of the metallic nickel phase is 5% by weight or more, the amount of nickel hydroxide as an active material relatively decreases,
It is not preferable because the charge / discharge capacity of the alkaline secondary battery decreases.

Next, a method for producing the positive electrode used in the alkaline secondary battery of the present invention will be described. (Method for Producing Electrode Active Material) First, a powder composed of particles mainly composed of nickel hydroxide is prepared. This powder is supplied simultaneously with a nickel salt aqueous solution and a sodium hydroxide aqueous solution in which ammonia water has been previously mixed into a reaction vessel under stirring to continuously produce nickel hydroxide and wash it.
It can be obtained by drying. Also, nickel hydroxide has Z
In the case where n, Al, Co, Ca, etc. are to be dissolved, these dissolved elements are dissolved in a nickel salt aqueous solution in advance, and these are taken into the crystal at the same time as the precipitation of nickel hydroxide to form a solid solution. .

Next, the obtained powder is put into an aqueous solution of an alkali metal hydroxide adjusted to pH = 11.9 or more, a reducing agent is further added, and this is heated to reduce the particle surface. As a result, nickel hydroxide is reduced, and a conductive layer containing a metallic nickel phase is deposited on the surface of the particles.

The reducing agent used here is hydrazine, hydrazine
Mixture of drazine and ammonia, ratio including hydrogen
Relatively unstable hydrogen compounds, lower oxides, lower oxyacid salts,
It must be one of the low-oxidation organic compounds
It is particularly preferable to use an aqueous solution containing hydrazine.
Is preferred. The amount of hydrazine added is alkali metal water.
1000 ml of oxide solution (1 × 10^-3m^Three2) for
g (2 × 10^-3kg) to 20 g (2 × 10^-2kg)
It is preferable to set it as an enclosure. The amount of hydrazine added is 2g
(2 × 10^-3kg), metal nickel is sufficiently precipitated
It is not preferable because it can not be
Is 20 g (2 × 10 ^-2kg), nickel metal
The amount of precipitation becomes excessive, the conductive layer is formed thick and the electrolyte
Is difficult to penetrate to nickel hydroxide,
No.

Particles containing nickel hydroxide as a main component are represented by p
When heated in an alkali metal hydroxide solution adjusted to H = 11.9 or higher, the surface of the nickel hydroxide slightly dissolves, and nickel complex ions (HNiO ₂ ⁻ ) are dissolved in the alkali metal hydroxide solution. Elute. This nickel complex ion (HNiO ₂ ⁻ ) is reduced by a reducing agent on the surface of the nickel hydroxide to become a metallic nickel phase, and a uniform conductive layer is generated. This reaction is represented by the following reaction formula. That is, Ni (OH) ₂ → HNiO ₂ ⁻ + H ⁺ (1) 2HNiO ₂ ⁻ + N ₂ H ₄ + 6H ⁺ + 4OH ⁻ → 2Ni + N ₂ + 8H ₂ O (2)

The above formula (1) is a dissolution reaction of nickel hydroxide, and the formula (2) is a reducing agent (hydrazine (N
₂ H ₄ )) to reduce the nickel complex ion (HNiO ₂ ⁻ ). Therefore, according to this manufacturing method, the nickel complex ion (HNiO ₂ ⁻ ) once dissolved is reduced on the surface of the nickel hydroxide to precipitate a metallic nickel phase, so that the conductive layer is uniformly deposited on the surface of the nickel hydroxide. be able to. Also, since the conductive layer is uniformly and thinly deposited on the nickel hydroxide surface, even if the amount of the conductive layer formed is reduced,
Sufficient conductivity can be imparted to nickel hydroxide. If the pH of the aqueous alkali metal hydroxide solution is less than 11.9,
Nickel complex ion (H
The amount of NiO ₂ ⁻ ) to be dissolved becomes small, and it takes a long time to form a metallic nickel phase, which is not preferable.

The heating is preferably performed until a metallic nickel phase is precipitated on the surface of the electrode active material. Specifically, the heating temperature is set to 313 K (40 ° C.) to 378 K (105 ° C.).
323K (50 ° C.) to 353K
(80 ° C.) is more preferable. Heating temperature is 31
When the temperature is less than 3K, the amount of nickel complex ion (HNiO ²⁻ ) dissolved in the alkali metal hydroxide solution decreases,
It is not preferable because it takes a long time to form the metallic nickel phase. When the heating temperature exceeds 378 K, the alkali metal hydroxide solution boils, a pressure vessel is required, and the reducing agent may be decomposed by itself. It is not preferable.
After the heating, washing and drying are performed to obtain the electrode active material of the present invention.

(Method of Manufacturing Positive Electrode) Next, the electrode active material obtained as described above, a binder such as Teflon powder,
If necessary, a conductive aid such as Ni powder or graphite powder is mixed, and this mixture is added to a dispersion medium such as water or ethylene glycol to form a paste. Next, this paste is applied to both surfaces of a conductive support such as a punching metal. After this,
The paste is heated and dried to volatilize the dispersion medium. Then, the dried paste is pressed against the conductive support while being compressed by a roll press or the like. The compression of the paste is preferably performed until at least a part of the conductive layer of the electrode active material is broken and the nickel hydroxide is exposed on the particle surface of the electrode active material. When the nickel hydroxide is exposed on the surface of the particles of the electrode active material, the electrolytic solution comes into direct contact with the nickel hydroxide, and the charge / discharge reaction can proceed smoothly.

The rolling reduction applied during compression is 0.05
It is preferably in the range of 0.6 to 0.6. Reduction rate is 0.0
If it is less than 5, the conductive layer may not be broken, so that it is not preferable. If it exceeds 0.6, the conductive support may be damaged, which is not preferable.
In general, the rolling reduction refers to a reduction rate when a material or the like is compressed and its thickness is reduced to reduce its cross-sectional area or thickness. Here, the thickness of the positive electrode before compression is defined as t age,
When the thickness after compression is t ′, (tt−t) × 10
0 / t (%). Thus, a positive electrode as shown in FIG. 2 is obtained.

According to the positive electrode 2 for an alkaline secondary battery described above, the powder 23 of the electrode active material having the particle surface coated with the conductive layer 24 is pressed and held on the punching metal 21, and the particles are electrically conductive. Since the conductive network is electrically connected via the layer 24 and has a higher-order structure and exhibits metal electrical conductivity, the internal resistance of the positive electrode 2 can be reduced, and the utilization rate of nickel hydroxide is improved. Can be done. Further, the cathode 2 of the present invention does not form a conductive network by forming cobalt oxyhydroxide as a semiconductor as in the related art, but forms a conductive network by a conductive layer containing metallic nickel. The conductivity between the active materials is significantly improved, and the internal resistance of the positive electrode 2 can be reduced.

Further, since the metal nickel phase contained in the electrode active material is less than 5% by weight of the whole, the amount of nickel hydroxide is relatively improved, and the charge / discharge capacity of the alkaline secondary battery is increased. Can be. Further, since the metallic nickel phase has better conductivity than conventional cobalt oxyhydroxide, the internal resistance of the positive electrode 2 can be further reduced.

Since the conductive layer 24 is porous, the electrolyte can penetrate the conductive layer 24 and reach the nickel hydroxide under the conductive layer. The reaction can proceed smoothly.

Further, the positive electrode 2 for the alkaline secondary battery described above is used.
According to the manufacturing method of (1), the electrode active material is compressed until the conductive layer 24 is broken and the nickel hydroxide is exposed, so that the electrolytic solution comes into direct contact with the nickel hydroxide, and the charge / discharge reaction proceeds smoothly. be able to.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 shows another positive electrode 32 suitable for use in an alkaline secondary battery according to the second embodiment of the present invention. The positive electrode 32 (electrode) is formed by fixing powder of an electrode active material to a porous conductive support, and as shown in FIG. It is formed by filling a positive electrode layer 34 (electrode layer) containing a substance. As the conductive support 33, for example, a porous sheet such as a nickel porous body, an expanded metal, and a wire mesh can be suitably used.

The positive electrode layer 34 includes at least a powder of an electrode active material mainly composed of nickel hydroxide, which is a positive electrode active material, and a binder made of, for example, Teflon for binding the powder of the electrode active material. It may contain a conductive auxiliary material such as Ni powder, graphite, or carbon black, if necessary.

The electrode active material of the positive electrode 32 is formed by coating a conductive layer containing a metallic nickel phase on at least a part of the surface of particles mainly composed of nickel hydroxide as the positive electrode active material. This is the same as the electrode active material described in the embodiment.

The porous conductive support 33 has a form in which a large number of pores are partitioned into a mesh-like metal skeleton. For example, a metal nickel film is formed on a urethane foam skeleton to form a urethane foam. Was manufactured by incineration removal.

The porous conductive support 33 may be obtained by forming a metal film on a fiber such as a nonwoven fabric and burning off the nonwoven fabric.

As shown in FIG. 4, the positive electrode layer 34 is formed by binding powder of an electrode active material via a binder, and the conductive layers are brought into contact with each other to form a higher-order metal-electrode. A conductive network showing conduction is formed. The positive electrode layer 34 is filled in the pores of the porous conductive support 33 and is in contact with the metal skeleton of the conductive support 33, whereby the positive electrode layer 34 and the conductive support 33
Are electrically connected.

Next, this positive electrode is manufactured in substantially the same manner as the positive electrode of the first embodiment described above. First, an electrode active material, a binder such as Teflon powder, and N
i powder, graphite powder, and other conductive additives, and this mixture is added to a dispersion medium such as water or ethylene glycol to form a paste. The electrode active material is manufactured in substantially the same manner as the electrode active material of the first embodiment described above. Next, this paste is applied and filled on a porous conductive support by a roll filling method or the like, and these are heated and dried to volatilize the dispersion medium. Then, the conductive support containing the dried paste is pressed (compressed) by a roll press or the like, and the paste is brought into close contact with the metal skeleton of the conductive support. This compression is preferably performed until the conductive layer of the electrode active material is broken and the underlying nickel hydroxide is exposed on the particle surface of the electrode active material. When the nickel hydroxide is exposed on the surface of the particles of the electrode active material, the electrolytic solution comes into direct contact with the nickel hydroxide, and the charge / discharge reaction can proceed smoothly.

The rolling reduction applied during compression is 0.05
It is preferably in the range of 0.6 to 0.6. Reduction rate is 0.0
If it is less than 5, the conductive layer may not be broken, so that it is not preferable. If it exceeds 0.6, the conductive support may be damaged, which is not preferable.
Thus, the positive electrode 32 as shown in FIG. 4 is obtained.

According to the above-described positive electrode 32, substantially the same effects as in the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows an alkaline secondary battery 41 according to a third embodiment of the present invention. The alkaline secondary battery 41 is called a button type, and includes a columnar positive electrode 42 (electrode) according to the present invention, a columnar negative electrode 43, and a separator 44 disposed between the positive electrode 42 and the negative electrode 43.
And an electrolyte mainly impregnated in the positive electrode 42, the negative electrode 43, and the separator 44, a cylindrical battery container 45 also serving as a positive electrode terminal, and a sealing member 46 also serving as a negative electrode terminal for closing the battery container 45. It is configured. In the alkaline secondary battery 41, a positive electrode 42, a separator 44 and a negative electrode 43 are sequentially stored in a battery container 45, and the battery container 45 is sealed by a sealing member 46. With this configuration, the positive electrode 42 contacts the battery container 45 that is a positive electrode terminal, and the negative electrode 43 is a sealing member 4 that is a negative electrode terminal.
Touch 6.

The positive electrode 42 (electrode) is formed by compressing at least a powder of the electrode active material and solidifying and forming the same into a columnar shape. The powder of the electrode active material and, for example, Teflon for binding the powder of the electrode active material are used. And a binder such as Ni powder, graphite, or carbon black, if necessary.

The electrode active material according to the present invention contained in the positive electrode 42 has a structure in which a conductive layer containing a metallic nickel phase is coated on part or all of the surface of particles mainly composed of nickel hydroxide, which is a positive electrode active material. This is the same as the electrode active material described in the first embodiment.

The positive electrode 42 is formed by binding powder of an electrode active material via a binder, and the conductive layers are brought into contact with each other to form a conductive network having a higher-order structure and exhibiting metal electrical conductivity. . Then, the positive electrode 42 contacts the battery case 45 also serving as the positive electrode terminal, and the positive electrode 42 and the positive electrode terminal are electrically connected.

The negative electrode 43 contains at least a powder of an electrode active material for the negative electrode and a binder made of, for example, Teflon, which binds the powder of the electrode active material. , Graphite, carbon black and the like. As the electrode active material for the negative electrode, for example, a hydrogen storage alloy, cadmium hydroxide, or the like can be used.

The electrolyte is prepared by dissolving any of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide and lithium hydroxide or a mixture thereof in water, and adding alkaline earth metal ions as necessary. It is. Further, as the separator 44, a nonwoven fabric made of, for example, a polyamide resin, polypropylene, or the like can be used.

Next, the positive electrode 42 is manufactured as follows. First, an electrode active material, a binder such as Teflon powder, and a conductive additive such as graphite powder are mixed to form a mixture. The electrode active material is manufactured in substantially the same manner as the electrode active material of the first embodiment described above. Next, this mixture is filled into a mold having, for example, a cylindrical cavity,
The mixture is compressed by applying pressure to a mold by a press machine or the like, and the mixture is solidified and formed into a cylindrical shape. When compressing the mixture,
It is preferable to perform the process until the conductive layer of the electrode active material is broken and a part of the nickel hydroxide is exposed on the particle surface of the electrode active material. When the nickel hydroxide is exposed, the electrolytic solution comes into direct contact with the nickel hydroxide, and the charge / discharge reaction can proceed smoothly.

The pressure applied during compression is 5 × 10 ⁶
It is preferable to be in the range of 5 × 10 ⁷ Pa. In less than 5 × 10 ⁶ Pa pressure, unpreferably possibility that it can not be broken conductive layer, 5 × 10 ⁷ Pa
Exceeding the range is not preferred because the positive electrode may be chipped or cracked. Thus, a positive electrode as shown in FIG. 5 is obtained.

In the positive electrode 42, substantially the same effects as those of the positive electrode of the first embodiment can be obtained.

[0062]

EXAMPLE First, a nickel salt aqueous solution containing 3% by weight of zinc and 5% by weight of cobalt was prepared. Next, the nickel salt aqueous solution and the sodium hydroxide aqueous solution premixed with ammonia water are simultaneously supplied into a stirred reaction tank,
Nickel hydroxide was continuously produced. The precipitated nickel hydroxide is dried and has a particle size of 10 μm (1 × 10 ⁻⁵ m) or more.
A 300 μm (5 × 10 ⁻⁵ m) granular nickel hydroxide powder was obtained.

Next, 100 g (0.1 kg) of nickel hydroxide powder was added to 1000 ml of 10N (pH = 15).
(1 × 10 ⁻³ m ³ ) aqueous sodium hydroxide solution, and 2 g (2 × 10 ⁻³ kg) to 20 g with further stirring
(2 × 10 ^-2 kg) of hydrazine monohydrate (hereinafter referred to as hydrazine), and heated at 70 ° C. (343 K) for 1 hour (3600 seconds) to reduce the surface of the nickel hydroxide particles. Reduction was performed to form a conductive layer. Examples 11 to 15 having a conductive layer were obtained by further washing with water and drying.
Was prepared. Table 1 shows the amount of hydrazine added when producing the nickel hydroxide powder of each example.

After attaching a hydrazine decomposition catalyst (Pd) to the surface of the nickel hydroxide powder, 1000 ml
(1 × 10 ⁻³ m ³ ) of water and further 31 g (3.1 × 3
10 ^{- 2} kg) hydrazine was charged in, 37 ° C. (310
K) for 65 minutes (3900 seconds) to reduce the nickel hydroxide surface to form a metallic nickel phase, thereby producing a nickel hydroxide powder of Comparative Example 11. Further, a nickel hydroxide powder without any reduction treatment was used as Comparative Example 12.

[0065]

[Table 1]

The obtained nickel hydroxide powder was subjected to morphological observation using a scanning electron microscope (SEM), X-ray diffraction measurement, and oxygen analysis using EPMA (electron probe for micro-analysis). .
6 and 7 show the results of SEM observation, FIG. 10 shows the results of X-ray diffraction measurement, and Table 2 shows the results of oxygen by the EPMA method. 8 and 9 show the results of SEM observation of the nickel hydroxide powder of Comparative Example 12.

[0067]

[Table 2]

Also, a dispersion of Teflon was added to the nickel hydroxide powders of Examples 11 to 15 and Comparative Examples 11 and 12 to form a paste, which was then applied to a punched metal sheet. And at 150 ° C. (423 K) for 4 hours (14400
Second) 0.7m thick by pressing after drying
m (7 × 10 ⁻⁴ m) nickel electrode was manufactured. In addition,
As for the nickel hydroxide of Comparative Example 12, after mixing 10% by weight of CoO, a Teflon dispersion liquid was added to form a paste, and a nickel electrode was produced using this paste.

Next, Mm _1.0 Ni _4.5 Co _0.5 (however,
Mm is an abbreviation for misch metal). A paste is prepared by adding a Teflon dispersion liquid to a hydrogen-absorbing alloy powder having a composition of (Mm metal) and applying the paste to a punching metal sheet. 14400 seconds) By pressing after drying,
A hydrogen electrode having a thickness of 0.6 mm (6 × 10 ⁻⁴ m) was manufactured.

Next, a polyimide separator is sandwiched between the nickel electrode and the hydrogen electrode, spirally wound and stored in a cylindrical battery container, and sealed after adding an alkaline electrolyte. AA type (AA size) of Examples 11 to 15 and Comparative Examples 11 and 12
Was manufactured.

The obtained battery was charged and discharged.
The discharge capacity at the cycle and the 100th cycle was measured. The charging was performed under the condition of charging at a current density of 0.1 C to a capacity of 110% of the theoretical battery capacity, and the discharging was performed under the condition of discharging to a current density of 0.2 C and a discharge end voltage of 0.9 V. Table 1 shows the results. The discharge current density of the batteries of Example 11 and Comparative Example 12 was 0.2 to 3C.
, And the discharge capacity was measured. The result is shown in FIG.

As shown in FIGS. 6 and 7, it can be seen that a porous layer is uniformly formed on the surface of the nickel hydroxide particles of Example 11. On the other hand, FIG.
As shown in FIG. 9, such a porous layer is not seen on the surface of the nickel hydroxide particles (Comparative Example 12) before reduction with hydrazine.

FIG. 10 shows the result of X-ray diffraction measurement of Example 11. The diffraction pattern of metallic nickel is confirmed in addition to the diffraction pattern of nickel hydroxide. This allows
By reducing the surface of the nickel hydroxide particles with hydrazine, it can be confirmed that a metallic nickel phase is deposited on the surface.

Further, Table 2 shows the conductive layer portion on the surface of the electrode active material particles (nickel hydroxide particles) and the nickel hydroxide portion inside in Examples 11 to 15 and Comparative Examples 11 and 12 respectively. The result of oxygen analysis by EPMA is shown. As is clear from Table 2, in the table, it is found that the oxygen content of the conductive layer portion on the surface is lower than the oxygen content of the internal nickel hydroxide portion. Thereby, in the nickel hydroxide of Examples 11 to 15, the surface of the nickel hydroxide particles is reduced by hydrazine, whereby the oxygen content on the particle surface is reduced, and finally, the metallic nickel phase is precipitated. Is evident.

FIG. 11 shows the result of measuring the reduction rate of nickel hydroxide by measuring the magnetic susceptibility.
Since metallic nickel is a magnetic material, it is possible to estimate the amount of metallic nickel in the electrode active material by measuring the magnetic susceptibility of the electrode active material. The vertical axis in FIG. 11 indicates the content of metallic nickel precipitated on the surface of the nickel hydroxide particles.
As shown in FIG. 11, it can be seen that the higher the amount of hydrazine added, the higher the content of metallic nickel.

The content of metallic nickel in the nickel hydroxide of Example 11 was 4.2% by weight, and the electrical resistance of this nickel hydroxide was measured while applying a pressure of 8.0 × 10 ⁶ Pa. And 5 × 10 ² Ω · m.

From the above, it is clear that the porous layer observed in FIGS. 6 and 7 is a conductive layer having a low oxygen content and containing a metallic nickel phase. Also, by adjusting the amount of hydrazine added,
It can be seen that the amount of precipitation of the metallic nickel phase can be adjusted.

Next, as apparent from Table 1, Example 11
It can be seen that the discharge capacity at 0.2 C of the batteries of Nos. To 15 was higher than the discharge capacity of the battery of Comparative Example 11. This is because the conductive layer containing less than 5% by weight of the metallic nickel phase is uniformly formed on the nickel hydroxide of the batteries of Examples 11 to 15, so that the amount of nickel hydroxide filled in the battery is reduced. It is considered that the discharge capacity increased relatively and the discharge capacity increased.

Further, in the battery of Comparative Example 12, since the conventional conductive network was formed of cobalt oxyhydroxide, which is a semiconductor, the resistance was high, the utilization rate of nickel hydroxide was low, and the discharge capacity was low. Is considered to be smaller than the batteries of Examples 11 to 15.

As shown in FIG. 12, the battery of Example 11 has a small decrease in the discharge capacity even when the discharge current density is increased, and is capable of high-rate discharge. It can be seen that the discharge capacity sharply decreases as the current density increases. Thus, the battery of Example 11
It can be seen that the battery has better high-rate discharge characteristics than the battery of Comparative Example 12. This is probably because the internal resistance of the nickel electrode of the battery of Example 11 was small, so that the utilization rate of nickel hydroxide was high, and the discharge capacity was high even at a high discharge current density.

[0081]

As described in detail above, the electrode for an alkaline secondary battery of the present invention is obtained by coating the surface of the particles mainly composed of nickel hydroxide with the conductive layer containing the metallic nickel phase. The powder of the electrode active material is fixed to the conductive support, or the powder of the electrode active material is formed by solidification, and the particles are electrically connected via the conductive layer. Since a conductive network having a higher-order structure and exhibiting metal electric conduction is formed, the internal resistance of the electrode can be reduced, and the utilization rate of nickel hydroxide can be improved. The electrode of the present invention does not form a conductive network by forming cobalt oxyhydroxide, which is a semiconductor, after the electrode active material is fixed to the conductive support as in the related art. At the time of being fixed to the conductive support, a conductive network showing metal electric conduction is formed, so that a stable conductive network having a large conductivity can always be formed, and the internal resistance of the electrode can be further reduced. .

Further, the conductive layer of the electrode active material contains a metal nickel phase, and since the conductivity of the metal nickel phase is superior to that of the conventional cobalt oxyhydroxide, the internal resistance of the electrode can be further reduced. . Further, since the form of the conductive layer is porous, it is possible to make the electrolytic solution permeate the conductive layer and reach the nickel hydroxide under the conductive layer, thereby facilitating the charge / discharge reaction.

In the method for manufacturing an electrode for an alkaline secondary battery according to the present invention, a part of the nickel hydroxide is exposed by compressing the electrode active material and breaking the conductive layer, so that the electrolytic solution is It comes into direct contact with nickel hydroxide, and the charge / discharge reaction can proceed smoothly.

[Brief description of the drawings]

FIG. 1 shows an alkali 2 according to a first embodiment of the present invention.
It is a perspective sectional view showing a secondary battery.

FIG. 2 is a schematic sectional view of a positive electrode of the alkaline secondary battery shown in FIG.

FIG. 3 is an enlarged schematic view showing a main part of the positive electrode shown in FIG.

FIG. 4 is a schematic sectional view of a positive electrode according to a second embodiment of the present invention.

FIG. 5 shows an alkali 2 according to a third embodiment of the present invention.
It is sectional drawing which shows a secondary battery.

FIG. 6 is an SEM of the nickel hydroxide powder of Example 11.
It is a photograph.

FIG. 7 is a further enlarged photograph of the SEM photograph shown in FIG.

FIG. 8 is an SEM of the nickel hydroxide powder of Comparative Example 12.
It is a photograph.

9 is a further enlarged photograph of the SEM photograph shown in FIG.

10 is a view showing a result of an X-ray diffraction measurement of the nickel hydroxide powder of Example 11. FIG.

FIG. 11 is a graph showing the relationship between the amount of hydrazine introduced and the content of metallic nickel.

FIG. 12 is a graph showing the relationship between discharge current density and discharge capacity.

[Description of Signs] 1 Alkaline secondary battery 2 Positive electrode (electrode) 3 Negative electrode 4 Separator 21 Punched metal (conductive support) 22 Positive electrode layer 23 Powder of electrode active material 24 Conductive layer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Ichisuke Sato 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materials Corporation Materials Technology Laboratory F-term (reference) 5H003 AA01 BA04 BA05 BB04 BB14 BC01 BC04 BC05 BD04 5H016 AA02 AA05 BB04 BB05 BB08 CC03 EE01 EE05 HH01 5H028 BB04 EE01 EE05 EE10 HH01

Claims (6)

[Claims] 1. An electrode in which at least a powder of an electrode active material is fixed to a conductive support, wherein the electrode active material has a metal nickel phase on at least a part of the surface of particles mainly composed of nickel hydroxide. An electrode for an alkaline secondary battery, wherein a conductive layer containing the metal nickel phase is coated and the content of the metal nickel phase in the electrode active material is less than 5% by weight. 2. An electrode formed by solidifying and molding a powder of an electrode active material, wherein the electrode active material is a conductive layer containing a metal nickel phase on at least a part of the surface of particles mainly composed of nickel hydroxide. And a content of the metal nickel phase in the electrode active material is less than 5% by weight. 3. The electrode for an alkaline secondary battery according to claim 1, wherein at least a part of the conductive layer of the electrode active material is porous. 4. An alkaline secondary battery comprising the electrode for an alkaline secondary battery according to any one of claims 1 to 3. 5. A sheet-like or porous conductive material comprising a powder of an electrode active material in which at least a part of the surface of particles mainly composed of nickel hydroxide is coated with a conductive layer containing a metallic nickel phase. A method of manufacturing an electrode configured to be fixed to a support, wherein the electrode active material is fixed to the conductive support,
Applying a compressive stress to the powder of the electrode active material to break at least a portion of the conductive layer, thereby exposing at least a portion of the nickel hydroxide to the surface of the electrode active material. A method for manufacturing an electrode for a secondary battery. 6. An electrode is produced by solidifying and molding an electrode active material powder in which at least a part of the surface of particles mainly composed of nickel hydroxide is coated with a conductive layer containing a metallic nickel phase. When solidifying and molding the electrode active material, at least a portion of the conductive layer is broken by applying a compressive stress to the powder of the electrode active material, and at least a portion of the nickel hydroxide is formed. A method for manufacturing an electrode for an alkaline secondary battery, wherein the electrode is exposed on a surface of an electrode active material.