JP2003249215A - Manufacturing method of positive active material for alkaline storage battery and alkaline storage battery using the positive active material obtained by the manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost and efficient manufacturing method of a positive active material for an alkaline storage battery which is superior in utilization rate and charge-discharge efficiency in high-temperature atmospheres and also superior in a filling characteristic in order to manufacture the alkaline storage battery having a high capacity and a superior charge-discharge characteristic even in a high-temperature application at a low price. <P>SOLUTION: Solid solution particles in which nickel hydroxide covered by cobalt hydroxide is the main component, at least one kind of particles of oxide of element selected from among yttrium, scandium, lanthanoid and calcium, and an alkaline aqueous solution are agitated and mixed, and after particles are mode wet by soaking the surface with the aqueous alkaline solution, a heat-treatment is carried out while continuing agitation and mixing under the existence of oxygen, and this is continued until the particles are dried. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode active material for an alkaline storage battery and an alkaline storage battery using the positive electrode active material obtained by the production method.

[0002]

2. Description of the Related Art In recent years, the demand for small secondary batteries has increased with the spread of portable devices. Among them, nickel-cadmium storage batteries using a positive electrode mainly composed of nickel hydroxide and an alkaline aqueous solution as an electrolytic solution. Alkaline storage batteries, such as nickel and hydrogen storage batteries, are in great demand as secondary batteries with high capacity, high reliability, and low cost.

There are roughly two types of positive electrodes for alkaline storage batteries: sintered type and non-sintered type. The former is a porosity of 80 obtained by sintering a core material such as punching metal and nickel powder.
% Nickel sintered substrate is impregnated with a nickel salt solution such as nickel nitrate aqueous solution and then with an alkaline aqueous solution to produce nickel hydroxide in the porous nickel sintered substrate. is there. Since it is difficult for the positive electrode to increase the porosity of the substrate any more, the amount of nickel hydroxide cannot be increased, and there is a limit to increase the capacity.

The latter non-sintered positive electrode is, for example, a three-dimensionally continuous foamed nickel substrate having a porosity of about 95%, as disclosed in Japanese Patent Laid-Open No. 50-36935.
A material that holds nickel hydroxide particles has been proposed and is currently widely used as a positive electrode for a high-capacity alkaline storage battery. In this non-sintered positive electrode, spherical nickel hydroxide particles having a large bulk density are used from the viewpoint of increasing the capacity. In addition, in order to improve discharge characteristics, charge acceptability, and life characteristics, it is common to use the above nickel hydroxide particles by partially dissolving a metal element such as cobalt, cadmium, or zinc.

Further, as a conductive agent to be held on a foamed nickel substrate together with such nickel hydroxide particles, a divalent cobalt oxide such as cobalt hydroxide or cobalt monoxide has been proposed (for example, Japanese Unexamined Patent Publication No. Hei 10 (1999) -242977). 7-7712
No. 9). These divalent cobalt oxides are electrochemically oxidized into β-cobalt oxyhydroxide having conductivity in the initial charge, and this functions as a conductive network connecting the nickel hydroxide particles and the substrate skeleton. Due to the presence of this conductive network, it is possible to significantly increase the utilization rate of the high-density filled active material in the non-sintered positive electrode, and to increase the capacity as compared with the sintered positive electrode.

However, even in the non-sintered positive electrode having the above structure and the alkaline storage battery using the same, the current collecting performance of the conductive network made of cobalt is not perfect, and the utilization rate of nickel hydroxide particles has an upper limit. It was Furthermore, in the above positive electrode, the battery is left in an over-discharged or short-circuited state,
When stored for a long period of time or at a high temperature, the capacity of the positive electrode is reduced due to subsequent charge and discharge. this is,
This is because the electrochemical cobalt oxidation reaction in the battery as described above cannot completely convert the divalent cobalt oxide into β-cobalt oxyhydroxide, which easily causes the functional deterioration of the conductive network. is there.

As a means for improving such imperfections of the conductive network due to cobalt, JP-A-8-1481
According to Japanese Patent Laid-Open No. 46-46, nickel hydroxide solid solution particles having a coating layer of cobalt hydroxide are subjected to heat treatment (oxidation) in the presence of an alkaline aqueous solution and oxygen (air) outside the battery, and a divalent compound having a disordered crystal structure is obtained. A method of modifying the coating layer of cobalt oxide having a high valence is disclosed. In this case, there is also an advantage that the amount of cobalt to be used can be reduced for the reason of improving the dispersibility of cobalt by preparing cobalt hydroxide-coated nickel hydroxide solid solution particles in advance. On the other hand, in Japanese Patent Laid-Open No. 9-73900, regarding the manufacturing method at this time, cobalt hydroxide-coated nickel hydroxide particles containing an alkaline aqueous solution are heated while being fluidized or dispersed in a fluidized granulator or the like. A method is disclosed. When this kind of processing is performed,
There is an advantage that troubles such as generation of particle aggregates due to aggregation can be reduced.

However, in the positive electrode active material for alkaline storage batteries described in the above publication, it is hard to say that the oxidation state of the cobalt species forming the coating layer is still perfect, and there is room for improvement. This is because the progress of oxidation of cobalt hydroxide in the presence of an alkali is greatly affected not only by the ambient temperature and the concentration of the alkaline aqueous solution to be coexisted, but also by the ambient water content and oxygen content. This is because it cannot be oxidized to a sufficiently higher state.

Here, when the cobalt hydroxide-coated nickel hydroxide particles are oxidized in the coexisting atmosphere of the alkaline aqueous solution, the following two processes are considered as the reaction mechanism of the cobalt hydroxide forming the coating layer. First, the formula in an aqueous alkaline solution of cobalt hydroxide are present in the coating layer surface _{1: Co (OH) 2 +} OH - → HCoO 2 - + H 2 O reaction by the cobalt complex ion (HCoO ₂ ^-) dissolved as Then, when this is exposed to oxygen, the formula 2: HCoO ₂ ⁻ + 1 / 2H ₂ O + 1 / 4O ₂ → CoOO
It is a process of being oxidized by the reaction of H + OH ⁻ and being deposited as high-order cobalt oxide on nickel hydroxide particles.

Secondly, in the atmosphere in which cobalt hydroxide coexists with alkali and oxygen, while generating water, the formula 3: Co (OH) ₂ + OH ⁻ → CoOOH + H ₂ O +
It is a process in which a higher order cobalt oxide is oxidized by solid-phase reaction (that is, without dissolution) like e ⁻ . In this case, oxygen is consumed by the reaction of formula 4: 1 / 4O ₂ + 1 / 2H ₂ O + e ⁻ → OH ⁻ .

Considering the above two processes in detail, first, the progress of the first process depends on the solubility of cobalt hydroxide in the alkaline aqueous solution (Equation 1). However, for example, even in a KOH aqueous solution having a concentration of 30% by weight, the solubility is only several hundred ppm even at about 60 ° C., and the dissolution rate is not so large. Therefore, it is necessary to raise the temperature of the atmosphere to increase the reaction rate. However, if the alkaline aqueous solution evaporates and dries up when the temperature is raised to a high temperature, the complex ions of Formula 1 cannot be generated and the reaction is stopped. On the other hand, in the oxidation reaction of the equation 2, it is important that the generated cobalt complex ions come into sufficient contact with oxygen (air), and when the temperature becomes high in an environment where the surrounding oxygen is deficient, the equation 5: HCoO ₂ ⁻ + 1 / Due to a side reaction of 6O ₂ → ⅓Co ₃ O ₄ + OH ^−, a low-order cobalt oxide (Co ₃ O ₄ , Co valence: 2.67) having poor conductivity is generated.

In the second process, when cobalt hydroxide is heated in the presence of alkali, higher order cobalt oxide is produced by the mechanism of equation 3. At this time, in the coexistence of oxygen, the reaction of formula 4 simultaneously occurs, and the reaction of formula 3 proceeds continuously. In order to make this reaction proceed smoothly, the reaction system should be heated to a high temperature, the OH ^- concentration should be increased (Equation 3), the O ₂ concentration should be increased (Equation 4), and the produced water should be removed from the reaction system. The point is to remove it appropriately. If the water is removed excessively (that is, too much is dried), the reaction of the formula 3 is stopped because OH ⁻ ions cannot be generated from the alkaline species. On the contrary, when the water removal is insufficient, the reaction of the formula 4 does not proceed sufficiently because the O ₂ concentration near the cobalt hydroxide is relatively decreased, and as a result, instead of the formula 3, the formula 6: Co ( ^{_{OH) 2 + 2 / 3OH -}} → 1 / 3Co 3 O 4 +
A side reaction of 4 / 3H ₂ O + 2 / 3e ⁻ produces a low-order cobalt oxide (Co ₃ O ₄ ) having poor conductivity.

As described above, in any process,
Control of water and oxygen (air) during processing is important. From the above point of view, in order to most efficiently proceed the oxidation of cobalt hydroxide-coated nickel hydroxide particles in an atmosphere coexisting with an alkali, it is necessary to have an appropriate amount of an alkaline aqueous solution on the surface so that the funicular state (in terms of chemical engineering, particles Particles that have a sufficient amount of liquid on their surface and have a breathable (wet state) must be treated under high temperature while controlling the amounts of water and oxygen well.

As a proposal for improving this problem, Japanese Unexamined Patent Publication No.
1-97008 discloses that the cobalt species forming the coating layer by controlling the oxidation conditions are oxidized to γ-cobalt oxyhydroxide having a higher valence than trivalent, and this active material. It has been disclosed that the utilization factor and over-discharge resistance of the positive electrode using the are significantly improved as compared with the case where the active material whose oxidation is insufficient is used. Where this γ-
Cobalt oxyhydroxide is an alkali cation (K
^It also has the feature of containing a large amount of ⁺ or Na ⁺ ).

By the way, in recent years, many proposals have been made to obtain higher performance cobalt-coated nickel hydroxide particles by modifying the cobalt coating layer by dispersing a different element other than cobalt into the cobalt coating layer. For example, JP-A-10
In JP-A-21909, by coating the surface of nickel hydroxide particles with a eutectic of yttrium hydroxide and cobalt hydroxide, it is possible to develop a high utilization ratio of the active material not only at the beginning of the charge / discharge cycle but also for a long time. It is disclosed.

Further, in Japanese Patent Laid-Open No. 11-260360, at least a part of the surface of the nickel hydroxide particles is covered with a cobalt compound layer containing ytterbium to improve the utilization factor and the charging efficiency in a high temperature atmosphere. It is disclosed that this can be done. In addition, Japanese Patent Laid-Open No. 2001-185
In Japanese Patent No. 137, the cobalt valence is determined by coating the surface of nickel hydroxide particles with a mixed crystal of different elements such as cobalt and yttrium, and then performing oxidation with an oxidizing agent or air oxidation in the presence of an alkaline aqueous solution. It is disclosed that a high-order nickel hydroxide having a nickel valence of 2.0 to 2.3 and having a mixed crystal coating layer having a valence of more than 3.0 is obtained, and that this positive electrode active material exhibits a high utilization rate. Has been done.

[0017]

DISCLOSURE OF THE INVENTION As a result of examination by the present inventors, JP-A-10-21909 and JP-A-1
In the cobalt hydroxide-coated nickel hydroxide particles disclosed in JP-A 1-260360, the eutectic or mixed crystal of the coating layer of cobalt hydroxide and a different element grows at a higher density than cobalt hydroxide alone. Is difficult to
It was revealed that the nickel hydroxide particles themselves coated with them also become bulky, and thus have a problem in filling property. In addition, the eutectic or mixed crystal of the coating layer of cobalt hydroxide and a different element becomes a low-order cobalt oxide (Co ₃ O ₄ ) which has poor electrical conductivity in the air as compared with cobalt hydroxide alone. It has been revealed that there is also a problem that it cannot be stored in the air for a long time because it is easily oxidized. That is, when the nickel hydroxide powder coated with them is stored in the air for a long period of time, the coating layer is easily oxidized to a lower cobalt oxide, and the generated lower cobalt oxide is relatively stable in an alkaline aqueous solution, Even in the electrochemical oxidation in the battery, it is difficult to oxidize into β-cobalt oxyhydroxide having high conductivity, the conductivity between the positive electrode active materials decreases, and the utilization rate decreases.

Further, in the cobalt-coated nickel hydroxide particles disclosed in Japanese Patent Laid-Open No. 2001-185137, the active material powder before oxidation treatment is as bulky as described above,
It has become clear that there is a problem that it is more difficult to control the oxidation conditions than in the past. It has also been clarified that the eutectic or mixed crystal of cobalt hydroxide and a different element contains a large amount of water of hydration, which also affects the difficulty of controlling the oxidation conditions. It is believed that Furthermore, since the coating layer of the active material powder before the oxidation treatment is likely to be oxidized in the air to the low-order cobalt oxide having poor conductivity in the same manner as described above, it cannot be stored for a long time in the air and the high-order cobalt oxide is immediately after the coating. It also had the inconvenience of handling that it had to oxidize even oxides.

[0019]

Means for Solving the Problems The present invention is to solve the above problems and provides a positive electrode active material for an alkaline storage battery, which is excellent in utilization rate and charging efficiency in a high temperature atmosphere, and is also low in cost. And an efficient manufacturing method is provided. Further, the present invention provides an alkaline storage battery using the positive electrode active material produced by this production method, which has high capacity and excellent charge / discharge characteristics even when used at high temperature.

In order to solve the above-mentioned problems, the production method of the present invention comprises a solid solution particle containing nickel hydroxide as a main component coated with cobalt hydroxide, and at least one selected from yttrium, scandium, lanthanoid and calcium. The first step of mixing the oxide particles and the alkaline aqueous solution with stirring to make wet particles whose surface is wet with the alkaline aqueous solution, and performing heat treatment while stirring and mixing the wet particles in the presence of oxygen until drying. And a second step of guiding.

In the above-mentioned first step, the cobalt hydroxide-coated nickel hydroxide particles become wet particles whose surface is uniformly wetted with the alkaline aqueous solution, and at the same time, the oxide particles of yttrium or the like are gelled by the alkaline aqueous solution. Change into a thing. In the subsequent second step, the cobalt hydroxide coating layer is oxidized to a higher cobalt oxide by the reaction of Formula 1, Formula 2 and Formula 3, while the gel-like hydroxide such as yttrium is coated in the coating layer. It spreads inside. Finally, the hydroxide such as yttrium diffused in the coating layer is dehydrated and uniformly dispersed as an oxide in the coating layer. That is, nickel hydroxide particles coated with a higher cobalt oxide in which an oxide such as yttrium is uniformly dispersed are produced.

In the manufacturing method of the present invention, the method disclosed in JP-A-10-21
909, Japanese Unexamined Patent Publication No. 11-260360, and Japanese Unexamined Patent Publication No. 2001-185137, a eutectic or mixed crystal of cobalt hydroxide and a different element, which is difficult to grow at high density. It does not include the process of making a coating layer. Since nickel hydroxide particles coated with a simple cobalt hydroxide capable of high-density growth and oxide particles such as yttrium are used, a high-order cobalt oxide containing different elements with high density and excellent filling properties can be obtained. Coated nickel hydroxide particles are obtained. Cobalt hydroxide-coated nickel hydroxide particles as a raw material can be stored for a long time before the oxidation treatment because it is relatively difficult to be oxidized even in air, and since the amount of hydration water contained is small, it is easy to control the oxidation conditions. Productivity is improved. Further, the existing cobalt hydroxide-coated nickel hydroxide particles can be used as they are, and it also has an advantage that an increase in active material production cost can be suppressed.

Here, in JP-A-11-73954, nickel hydroxide, a cobalt compound or metallic cobalt, a compound of a different element such as yttrium, and an alkaline aqueous solution are mixed, and the mixture is mixed in the presence of oxygen. A manufacturing method similar to the present invention of heat treatment is disclosed. However, the above-mentioned manufacturing method is to deposit the higher cobalt compound layer on the surfaces of both the nickel hydroxide particles and the different element compound particles, and the different element is not dispersed in the cobalt coating layer. It is fundamentally different from the manufacturing method of the invention. Further, the above-mentioned production method has a problem that it is very difficult to control the oxidation conditions because the cobalt compound powder is used.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The production method of the present invention comprises solid solution particles containing nickel hydroxide as a main component and coated with cobalt hydroxide, and at least one kind of oxide particles selected from yttrium, scandium, lanthanoids and calcium. And an alkaline aqueous solution by stirring and mixing to make wet particles whose surface is wet with the alkaline aqueous solution, and a second step of performing heat treatment while stirring and mixing the wet particles in the presence of oxygen, and leading to drying It is characterized by having and.

In the first step, the cobalt hydroxide-coated nickel hydroxide particles become wet particles whose surface is uniformly wet with an alkaline aqueous solution, and at the same time, oxide particles such as yttrium are gelled hydroxide by the alkaline aqueous solution. Changes to. In the subsequent second step, the cobalt hydroxide coating layer is oxidized to a higher cobalt oxide by the reaction of Formula 1, Formula 2, and Formula 3, while the gel-state hydroxide such as yttrium is coated in the coating layer. It spreads inside. Finally, the hydroxide such as yttrium diffused in the coating layer is dehydrated and uniformly dispersed as an oxide in the coating layer. That is, nickel hydroxide particles coated with a higher cobalt oxide in which an oxide such as yttrium is uniformly dispersed are produced. The amount of the alkaline aqueous solution required to bring the particles into the funicular state varies depending on the physical properties of the particles, but those skilled in the art can easily select the amount.

The alkaline aqueous solution mixed in the first step is an aqueous sodium hydroxide solution and / or an aqueous potassium hydroxide solution, and the concentration thereof is preferably higher than 40% by weight. Since the oxidation reaction used in the present invention occurs near the boiling point of the alkaline aqueous solution, the evaporation rate of water in the alkaline aqueous solution is high. However, as the first process of the oxidation reaction of the present invention, cobalt hydroxide is dissolved in an alkaline aqueous solution to form a cobalt complex ion (Equation 1), and this complex ion further reacts with oxygen to form a higher cobalt. It becomes an oxide (Equation 2). Therefore, during the treatment, a certain amount of alkaline aqueous solution must be present on the surface of the particles at high temperature. In other words, even if the temperature is high, the reaction cannot be sufficiently promoted if the alkaline aqueous solution evaporates quickly. From this point of view, it can be said that the higher the concentration of the alkaline aqueous solution, the higher the boiling point and the slower the evaporation rate, and hence the more suitable the treatment is. Also, considering the second oxidation process, the higher the OH ⁻ concentration is, the better the oxidation proceeds (Equation 3). Therefore, the higher the concentration of the alkaline aqueous solution is, the better. From the above viewpoint, it is suitable that the concentration of the alkaline aqueous solution used is greater than 40% by weight.

The heating temperature in the second step is 90-
It is preferably 130 ° C. The rate of the oxidation reaction is greatly influenced by the temperature, but if the set temperature is lower than 90 ° C., the progress of the oxidation is slow and it takes several hours per batch. At the same time, particles are likely to adhere to the inner wall of the oxidation treatment device, which is not preferable. On the other hand, if the temperature exceeds 130 ° C., the reaction takes place too much and damages the nickel hydroxide particles inside the coating layer. From the above viewpoint, the heating set temperature is 90 to 130 ° C.
It is preferable that

Further, when microwave irradiation is used as the auxiliary heating means in the second step, the oxidation reaction can be more efficiently progressed. The same heating method oscillates the derivative (in this case, an alkaline aqueous solution) at the molecular level by irradiating the wet particles with microwaves to cause collision of molecules.
This is a method of heating by frictional heat. In the second step, by performing microwave irradiation as an auxiliary heating means, it is possible to quickly raise the temperature of the wet particles to a predetermined temperature without causing uneven heating. Further, since the heating of the particles by microwave irradiation occurs from the cobalt hydroxide coating layer portion on the surface of the particles which is wet with the alkaline aqueous solution, the oxidation efficiency of the coating layer portion is higher than that of other heating means, and the coating layer Cobalt hydroxide oxidizes to higher cobalt oxides having a valence of more than 3.

In the cobalt hydroxide-coated nickel hydroxide solid solution particles, the cobalt hydroxide coating amount is preferably 5 to 12% by weight based on the nickel hydroxide solid solution particles. The positive electrode utilization rate largely varies depending on the cobalt coating amount on the nickel hydroxide particles, but if the coating amount is less than 5% by weight, a sufficient conductive network cannot be formed, and the positive electrode utilization rate is significantly reduced. On the other hand, the coating amount is 1
If it exceeds 2% by weight, the positive electrode utilization rate will no longer increase, and the decrease in the positive electrode capacity due to the decrease in the amount of nickel hydroxide will be remarkable. From the above viewpoints, the coating amount of cobalt hydroxide is preferably 5 to 12% by weight based on the nickel hydroxide solid solution particles.

The cobalt hydroxide-coated nickel hydroxide solid solution particles preferably have an average particle size of 5 to 20 μm and a BET specific surface area of 5 to 15 m ² / g. If the average particle size is less than 5 μm, it becomes difficult to bring the particles into the funicular state by a predetermined aqueous alkaline solution, and the coating layer cannot be oxidized to higher cobalt oxide. Further, since the bulk density of particles is lowered, a high capacity positive electrode cannot be obtained. If the average particle size exceeds 20 μm, the particles are too large to be uniformly coated with cobalt hydroxide, so that a good conductive network cannot be formed and the utilization factor decreases. Also, regarding the BET specific surface area,
If it is too large or too small, the wettability of the particles changes greatly, so that it becomes difficult for the particles to reach a funicular state with a predetermined alkaline aqueous solution, and the coating layer cannot be oxidized to higher cobalt oxide. From the above viewpoint,
The cobalt hydroxide-coated nickel hydroxide solid solution particles preferably have an average particle size of 5 to 20 μm and a BET specific surface area of 5 to 15 m ² / g.

Yttrium mixed in the first step,
The amount of at least one kind of oxide particles selected from scandium, lanthanoid and calcium is 0.1 to 0.1% with respect to cobalt hydroxide-coated nickel hydroxide solid solution particles.
It is preferably 3.0% by weight. If the mixing amount of the oxide particles is less than 0.1% by weight, the effect of adding the oxide (improvement of charging efficiency in a high temperature atmosphere) cannot be confirmed. On the other hand, even if the mixing amount exceeds 3.0% by weight, the above-mentioned addition effect is not further improved, and the high rate discharge characteristic is deteriorated due to the increase of the low conductive compound (Y ₂ O ₃ etc.) near the cobalt coating layer. It becomes remarkable. From the above viewpoint, the mixing amount of the oxide particles is
0.1 to 3.0% by weight, and further 0.5 to 1.0% by weight, based on the solid solution particles of nickel hydroxide coated with cobalt hydroxide.
Is preferred.

Yttrium mixed in the first step,
At least one kind of oxide particles selected from scandium, lanthanoid and calcium has an average particle size of 0.2 to 8.0 μm and a BET specific surface area of 3 to.
It is preferably 60 m ² / g. The oxide particles may be a composite oxide containing a plurality of metals. Further, one type of oxide particles may be used alone, or a plurality of oxide particles may be used in combination. If the average particle size is out of the above range or the BET specific surface area exceeds 60 m ² / g, the wettability of the particles is greatly changed, and it becomes difficult to bring the particles into a funicular state by a predetermined alkaline aqueous solution. . As a result, it becomes difficult to oxidize the cobalt hydroxide coating layer or diffuse the oxide particles into the cobalt oxide coating layer. From this viewpoint, the oxide particles have an average particle size of 0.2 to 8.0 μm, and more preferably 1.0 to 4.0 μm.
m, and the BET specific surface area is preferably ³ to 60 m ² / g, more preferably 3 to 30 m ² / g.

In the cobalt hydroxide-coated nickel hydroxide solid solution particles, the internal nickel hydroxide particles contain at least one element selected from cobalt, zinc, cadmium, calcium, manganese, magnesium, aluminum, titanium, yttrium and lanthanoid. It is preferable to contain. By using the solid solution particles as the raw material powder, it is possible to obtain a positive electrode active material for an alkaline storage battery in which swelling during charging is suppressed and the capacity deterioration due to charge / discharge cycles is small.

A preferred non-sintered positive electrode for an alkaline storage battery, to which the positive electrode active material produced by the production method of the present invention is applied, is a conductive core coated with a paste containing the active material,
Examples include a paste-type positive electrode formed by drying. Specific examples of the conductive core at this time include a nickel foam, a felt-like metal fiber porous body, a corrugated plate-processed core material, a perforated core material with burrs, and a punching metal.

Specific examples of suitable alkaline storage batteries using the positive electrode active material produced by the production method of the present invention include nickel-hydrogen storage batteries, nickel-cadmium storage batteries, and nickel-zinc storage batteries.

[0036]

EXAMPLES Examples of the present invention will be described in detail below. Example 1 (i) Preparation of Raw Material Powder Cobalt hydroxide-coated nickel hydroxide solid solution particles used as a raw material were synthesized by the following well-known method. First, an aqueous solution containing nickel sulfate as a main component and cobalt sulfate and zinc sulfate in a predetermined amount is stirred while gradually adding dropwise an aqueous sodium hydroxide solution while adjusting the solution pH with an aqueous ammonia solution to form a spherical water solution. A method of precipitating nickel oxide solid solution particles was used. The precipitated nickel hydroxide solid solution particles were washed with water and dried, then put into a cobalt sulfate aqueous solution, sodium hydroxide aqueous solution was gradually added, and stirring was continued while adjusting the pH to 12 at 35 ° C. Cobalt hydroxide was deposited on the surface of the solid solution particles. Here, the coating amount of cobalt hydroxide was adjusted so that the ratio with respect to the nickel hydroxide solid solution particles was 7.0% by weight. The prepared cobalt hydroxide-coated nickel hydroxide solid solution particles were washed with water and then vacuum dried.
Hereinafter this is referred to as powder A. The powder A has an average particle size of 10.4 μm and a BET specific surface area of 10.6 m ² /
The tap density was 2.1 g / cm ³ .

(Ii) First Step The powder A and the yttrium oxide powder are put into an oxidation treatment apparatus having a stirring and mixing function and a heating function, and a concentration of 45 is obtained.
Stirring and mixing were performed while adding an appropriate amount of an aqueous solution of sodium hydroxide of wt% dropwise. Here, the yttrium oxide powder is
Average particle size 3.8 μm, BET specific surface area 3.2 m ² /
1.0 g by weight based on the powder A was used. In the first step, the powder A became wet particles whose surface was almost uniformly wet.

(Iii) Second step While the stirring and mixing are continued, the inside of the oxidation treatment apparatus is set to 1
The mixture was heated to 10 ° C., and thereafter, heating and stirring and mixing were continued until the wet particles were almost completely dried while controlling the temperature to be constant at 110 ° C. The cobalt oxide-coated nickel hydroxide solid solution particles thus obtained were washed with water and then dried. Hereinafter, this is referred to as powder B. The powder B thus obtained has an average particle size of 10.3 μm, BE
T specific surface area of 10.2 m ² / g, tap density of 2.2 g
/ Cm ³ . Moreover, it was confirmed by observation with a transmission electron microscope (TEM) that yttrium was contained in the cobalt oxide coating layer.

Comparative Example 1 In the first step, the same first and second steps as in Example 1 were carried out except that yttrium oxide powder was not added, and the powder A was subjected to an oxidation treatment and then washed with water. It was dried. Hereinafter, this is referred to as powder C. The powder C had an average particle size of 10.3 μm, a BET specific surface area of 9.7 m ² / g and a tap density of 2.2 g / cm ³ .

Comparative Example 2 The nickel hydroxide solid solution particles obtained in Example 1 were put into a mixed aqueous solution of cobalt nitrate and yttrium nitrate, an aqueous sodium hydroxide solution was gradually added, and pH = 12 was maintained at 35 ° C. The mixed crystal of cobalt hydroxide and yttrium hydroxide was deposited on the surface of the nickel hydroxide solid solution particles while adjusting the temperature as described above. Here, the coating amount of cobalt hydroxide was adjusted so that the ratio with respect to the nickel hydroxide solid solution particles was 7.0% by weight. Further, the coating amount of yttrium hydroxide was adjusted so that the ratio with respect to the nickel hydroxide solid solution particles would be 1.0% by weight in terms of Y ₂ O ₃ . The produced yttrium mixed crystal cobalt hydroxide-coated nickel hydroxide solid solution particles were washed with water and then vacuum dried. Hereinafter, this is referred to as powder D. The powder D has an average particle size of 11.0.
μm, the BET specific surface area was 14.2 m ² / g, and the tap density was 1.8 g / cm ³ .

In the first step, the powder D was used in place of the powder A, and the same first and second steps as in Example 1 were performed except that the yttrium oxide powder was not added, and the powder D was subjected to the oxidation treatment. After that, it was washed with water and dried. Hereinafter, this is referred to as powder E. The powder E has an average particle size of 1
The surface area was 0.8 μm, the BET specific surface area was 12.8 m ² / g, and the tap density was 2.0 g / cm ³ . Moreover, it was confirmed by observation with a transmission electron microscope (TEM) that yttrium was contained in the cobalt oxide coating layer.

Comparative Example 3 Nickel hydroxide solid solution particles and cobalt hydroxide powder obtained in Example 1 (average particle size 0.1 μm)
m), yttrium oxide powder (average particle size 1.0 μm) was put into an oxidation treatment apparatus, the first step and the second step similar to those in Example 1 were performed, and after the oxidation treatment, washing and drying were performed. went. Here, the input amounts of the cobalt hydroxide powder and the yttrium oxide powder were adjusted to be 7.0% by weight and 1.0% by weight, respectively, with respect to the nickel hydroxide solid solution particles. Hereinafter, this is referred to as powder F. This powder F has an average particle size of 11.0 μm and a BET specific surface area of 1
It was 5.3 m ² / g and the tap density was 1.9 g / cm ³ .

[Physical Properties of Active Material] Powder A thus obtained
The average cobalt valence of F was calculated by iodine reduction titration. Here, the average nickel valence of each powder was assumed to be 2.0. Further, with respect to the powders B, C, E, and F, each powder was pressure-molded at a pressure of ² t / cm ² to prepare pellets, and the powder conductivity was measured by an AC 4-terminal method. The above results are shown in Table 1.

[0044]

[Table 1]

Powder B has almost the same BET specific surface area and tap density as powder C, whereas powders E and F have BE.
The T specific surface area is large and the tap density tends to be small. Since the mixed crystal of cobalt hydroxide and yttrium hydroxide is bulkier than cobalt hydroxide alone, powder D is powder A
The BET specific surface area is large and the tap density is small as compared with. It is considered that the powder E has a larger BET specific surface area and a smaller tap density than the powder C, reflecting the physical properties of the raw material powder even after the oxidation treatment. With respect to the powder F, since the method is a method in which fine powder of cobalt hydroxide is mechanically mixed and bonded to the surface of nickel hydroxide, the surface of the coating layer becomes rough and free cobalt oxide fine particles are also present. Further, it is considered that the BET specific surface area is large and the tap density is small. On the other hand, powder B
Is produced from powder A, which is the same raw material powder as powder C, so that the active material powder has a small BET specific surface area, a large tap density, and excellent filling properties.

Further, the powder B has a higher average cobalt valence and powder conductivity than the powder C, while the powders E and F both tend to have a low valence and a low conductivity. is there.
The mixed crystal of cobalt hydroxide and yttrium hydroxide, which is the coating layer of powder D, contains a large amount of water of hydration. During the oxidation treatment, this hydration water is dehydrated to generate water in the vicinity of the cobalt hydroxide coating layer, and the O ₂ concentration is lowered, so that the reaction of the formula 4 is inhibited and the reaction of the formula 3 becomes difficult to proceed. As a result, it is considered that the oxidation of the cobalt hydroxide coating layer is suppressed, and the powder E has lower cobalt average valence and powder conductivity than the powder C. Further, since the powder F is a bulky fine powder of cobalt hydroxide, a large amount of aqueous sodium hydroxide solution is required to bring the mixture of particles into a wet state. Therefore, it is considered that the cobalt hydroxide particles containing a large amount of water are oxidized and the reaction of the formula 3 is more difficult to proceed than in the case of the powder E.
As a result, due to the side reaction of Formula 6, Co _{3 having} poor conductivity is used.
It is considered that O ₄ is generated and the average cobalt valence and the powder conductivity are lower than those of the powder E.

On the other hand, since the powder B is produced from the powder A which is the same raw material powder as the powder C, the powder B can be easily treated under substantially the same oxidizing conditions as the powder C. The amount of yttrium oxide powder mixed in requires a slightly larger amount of sodium hydroxide aqueous solution to obtain a wet state.
The average cobalt valence and the powder conductivity do not decrease as in the above case, and the active material powder is superior to the powder C in both the cobalt average valence and the powder conductivity. It is considered that this is because the oxidation process proceeds by the following mechanism. First, in the first step, the powder A becomes wet particles whose surface is uniformly wetted with an aqueous sodium hydroxide solution, and at the same time, the yttrium oxide powder is changed into a gel-form yttrium hydroxide by the aqueous sodium hydroxide solution. In the following second step,
The cobalt hydroxide coating layer is oxidized to higher cobalt oxide by the reactions of the formulas 1, 2 and 3, and at the same time, the gel-form yttrium hydroxide diffuses into the coating layer. The gel-form yttrium hydroxide diffused in the coating layer is dehydrated and converted to yttrium oxide, at which time water is generated in the vicinity of the coating layer, but the coating layer has already been oxidized to higher cobalt oxides, which has a bad effect. I will not receive it. Rather, since the gel-form yttrium hydroxide diffused in the higher-order cobalt oxide coating layer contains sodium, the coating layer has a higher order (γ-described in JP-A No. 11-97008).
It is speculated that even CoOOH) may be oxidized.

[Characteristics of nickel-hydrogen storage battery]
Carboxymethyl cellulose (CMC) was added as a thickener in an amount of 0.1% by weight, and polytetrafluoroethylene (PTFE) was added in an amount of 0.2% by weight as a binder, and an appropriate amount of pure water was mixed and dispersed to obtain an active material slurry. This active material slurry was filled in a foamed nickel porous substrate having a thickness of 1.3 mm, dried in a drier at 80 ° C., and then rolled by a roll press to a thickness of about 0.7 mm, and further, a predetermined size. It was cut into pieces and a nickel positive electrode was produced.

This positive electrode and a negative electrode mainly composed of a hydrogen storage alloy, a polypropylene nonwoven fabric separator subjected to a hydrophilic treatment, a two-component alkali having a potassium hydroxide concentration of 7.0 normal and a lithium hydroxide concentration of 1.0 normal. AA-sized nickel-hydrogen storage battery B was produced by a known method using the electrolytic solution.

Further, in the same manner as the battery B except that the powders E and F were used instead of the powder B, the batteries E and
F was produced. Further, a battery C was prepared in the same manner as the battery B, except that the powder C was used and 1.0% by weight of Y ₂ O ₃ was added to the powder C. Here, these four types of batteries have different packing properties of the powders used, so that the packing densities of the positive electrodes differ, and the battery capacities vary. The theoretical capacity of each battery based on the one-electron reaction of nickel is 1500 mAh for batteries B and C and 140 mA for batteries E and F.
It was 0 mAh.

These four types of batteries were charged at a constant temperature of 20 ° C. at a charge rate of 0.1 CmA for 15 hours, and then discharged at a discharge rate of 0.2 CmA until the battery voltage reached 1.0 V. The discharge capacity at the fifth cycle was measured by repeating the cycle, and was defined as the discharge capacity C ₁ .

Next, the battery was charged at a constant temperature of 50 ° C. at a charge rate of 0.1 CmA for 15 hours, and after 3 hours of rest, 2
The discharge capacity was measured when the battery was discharged at a constant temperature of 0 ° C. at a discharge rate of 0.2 CmA until the battery voltage became 1.0 V, and the discharge capacity was defined as C ₂ . The active material utilization rate defined by the following equation was obtained as an index showing the ratio of the active material that contributed to the discharge with respect to the theoretical capacity. Further, as an index showing charging efficiency at high temperature, 50 ° C. charging efficiency defined by the following equation was obtained. Active material utilization rate (%) = {discharge capacity C ₁ / theoretical capacity} × 1
00 50 ° C charging efficiency (%) = {discharge capacity C ₂ / discharge capacity C ₁ }
× 100

Further, the battery was charged at a constant temperature of 20 ° C. and a charge rate of 0.1 CmA for 15 hours, and then discharged at a discharge rate of 0.
After discharging at 2 CmA until the battery voltage became 1.0 V, the battery was immediately disassembled to collect each discharged positive electrode powder. Iodine reduction titration was performed on each of the collected positive electrode powders, and the average nickel valence of each positive electrode powder after discharge was calculated. Here, the average valence of nickel was calculated assuming that the average valence of cobalt of each powder is the value in Table 1.

The results of the above charge / discharge test are shown in Table 2 as the utilization factor, the charging efficiency at 50 ° C. and the average valence of nickel after discharging. Further, the discharge curve of each battery at a constant temperature of 20 ° C. is shown in FIG.

[0055]

[Table 2]

The battery B showed a higher utilization factor and a 50 ° C. charging efficiency than the battery C. From Table 1, it is suggested that powder B has extremely excellent average cobalt valence and powder conductivity, and thus a very good conductive network is formed in the positive electrode, indicating high utilization. . In fact, the nickel valence of the positive electrode powder after discharge is lower than that of the battery C, which means that the powder B can be discharged deeper. In addition, since yttrium, which has an effect of increasing the oxygen generation overvoltage at the time of charging, is uniformly dispersed in the cobalt coating layer, the charging efficiency at 50 ° C. is higher than that of the battery C in which yttrium oxide powder is simply added. It is supposed to do.

The temperature of the battery E is 50 ° C. higher than that of the battery C.
The charging efficiency shows an excellent value, but the utilization rate at room temperature is only slightly improved. As shown in Table 1, powder E has a slightly lower average cobalt valence and powder conductivity than powder C, and the nickel valence of the positive electrode powder after discharge is almost the same as that of battery C. The conductive network in the positive electrode is considered to be almost the same as or slightly inferior to Battery C. It is speculated that the slight improvement in the utilization factor is due to the improvement in the charge acceptance due to the yttrium in the coating layer even at room temperature. However, as described above, since the powder E has poor filling properties,
The positive electrode packing density was reduced compared to Battery C, resulting in
As shown in, the discharge capacity becomes small. 5
It is considered that the improvement of the 0 ° C. charging efficiency is due to the presence of yttrium in the cobalt coating layer with good dispersibility, as described above.

The utilization factor of the battery F is lower than that of the battery C. From Table 1, the powder F has a lower average cobalt valence and a lower powder conductivity than the powder C, and is considered to be a positive electrode that is difficult to discharge. The nickel valence of the positive electrode powder after discharging also showed a higher value than that of the battery C, suggesting that the battery was not sufficiently discharged. Further, as described above, since the powder F has poor filling property, as a result, the battery capacity of the battery F becomes extremely small as shown in FIG. The 50 ° C. charging efficiency is the same as that of the battery C because the yttrium oxide powder exists between the particles of the positive electrode active material as in the battery C.

Example 2 The powder A described in Example 1 was left in the atmosphere for 1 month. Powder A after left for 1 month is
A slight brownish discoloration occurred. Hereinafter, this is referred to as powder G. This powder G has an average particle size of 10.3μ.
m, BET specific surface area was 10.3 m ² / g, and tap density was 2.2 g / cm ³ . Next, the powder G was subjected to an oxidation treatment in the same manner as in the first step and the second step described in Example 1, followed by washing with water and drying. Hereinafter, this is referred to as powder H. The powder H thus obtained had an average particle size of 10.3 μm, a BET specific surface area of 9.8 m ² / g, and a tap density of 2.2 g / cm ³ . Moreover, it was confirmed by observation with a transmission electron microscope (TEM) that yttrium was contained in the cobalt oxide coating layer.

Comparative Example 4 The powder D described in Comparative Example 2 was used in a large amount.
It was left in the air for one month. Powder D after left for 1 month is
It turned dark brown. Hereinafter this is referred to as powder I. Na
The powder I has an average particle size of 11.1 μm and a BET ratio table.
Area is 13.8m²/ G, tap density is 1.8g / cm³
Met. Next, using this powder I, yttrium oxide
All described in Example 1 except that no powder was added.
Oxidation treatment was performed in the same manner as the first step and the second step.
Then, it was washed with water and dried. Hereinafter, this is referred to as powder J
It The powder J thus obtained has an average particle size of 11.0 μ.
m, BET specific surface area 12.9 m ²/ G, tap density
1.9 g / cm³Met. Also, its cobalt oxide
It is confirmed that the coating layer contains yttrium by transmission electron
It was confirmed by observation with a microscope (TEM).

[Physical Properties of Active Material] With respect to the powders G to J, the average cobalt valence was calculated by the same method as described in Example 1. Further, with respect to the powders H and J, the powder conductivity was measured by the same method as described in Example 1. The above results are shown in Table 3.

[0062]

[Table 3]

Powder G obtained by leaving powder A in the air for one month
Regarding, the average cobalt valence was almost no higher than that before the standing, and the powder H obtained by the oxidation treatment of the powder H also had the same cobalt average valence and the same powder B as the powder B obtained by the oxidation treatment of the powder A without standing. The value of conductivity is shown. This means that in the production method of the present invention, the cobalt hydroxide coating layer of the powder A to be used is relatively difficult to be oxidized even when stored in the air for a long period of time. This means that it is possible to obtain an active material powder having excellent number and powder conductivity.

On the other hand, in the powder I which has been left in the air for one month, the average cobalt valence is higher than that before the powder is left, and the cobalt hydroxide coating layer is oxidized by the long-term storage. I understand. The mixed crystal of cobalt hydroxide and yttrium hydroxide, which is the coating layer, is easily oxidized in the air, and the lower cobalt oxide (Co
_It is thought that this is because it was oxidized to ₃ O ₄ ). In addition, in the powder J obtained by oxidizing the powder I, both the average cobalt valence and the powder conductivity were lower than those of the powder E in which the powder D was oxidized without being left. The low-conductivity low-order cobalt oxide (Co ₃ O ₄ ) generated in the cobalt coating layer after being left for a long time is relatively stable even in an alkaline atmosphere and is not oxidized to the high-conductivity high-order cobalt oxide. it is conceivable that.

[Characteristics of nickel-hydrogen storage battery] Powder H, J
Using, the AA size nickel-hydrogen storage battery was produced by the same method as described in Example 1. Hereinafter, powders H and J
These batteries corresponding to are referred to as batteries H and J, respectively. Since the packing properties of the powders H and J are different, the packing densities of the positive electrodes are different, and the theoretical capacity of each battery based on the one-electron reaction of nickel is 1500 mA for the battery H.
h, the battery J became 1400 mAh.

These batteries were charged at a constant temperature of 20 ° C. at a charge rate of 0.1 CmA for 15 hours and then discharged at a discharge rate of 0.2 CmA until the battery voltage reached 1.0 V. This cycle was repeated 5 times. The discharge capacity at the 5th cycle was measured, and the utilization rate was calculated in the same manner as in Example 1. Immediately after the end of discharge, each battery was disassembled to collect the positive electrode powder after discharge. The collected positive electrode powder was subjected to iodine reduction titration to calculate the average nickel valence of the positive electrode powder after discharge. Here, the average nickel valence of each powder was calculated assuming that the average cobalt valence of each powder is the value in Table 3.

The results of the above charge / discharge test are shown in Table 4 as the utilization ratio and the average valence of nickel after discharge. The discharge curve of each battery is shown in FIG. In addition, in Table 4 and FIG. 2, the results of the batteries B and E prepared by using the powders B and E that were subjected to the oxidation treatment without leaving the raw material powder are also shown.

[0068]

[Table 4]

The battery H exhibited an excellent utilization rate almost equal to that of the battery B. Also, the nickel valence of the positive electrode powder after discharge shows a low value as in the case of the battery B, indicating that deep discharge is possible. From Table 3, it is considered that the powder H has the same high cobalt average valence and powder conductivity as the powder B, and it is considered that an extremely good conductive network is formed in the positive electrode.

Regarding Battery J, it was confirmed that the utilization factor was remarkably reduced as compared with Battery E. The nickel valence of the positive electrode powder after discharge is also higher than that of the battery E, suggesting that the battery was not sufficiently discharged. From Table 3, powder J has lower cobalt average valence and powder conductivity than powder E, and it is considered that the powder J is a positive electrode that is difficult to discharge.

From the above results, the yttrium-dispersed cobalt oxide-coated nickel hydroxide powder having excellent utilization factor and charging efficiency under high temperature atmosphere and capable of high density filling can be efficiently produced by the production method of the present invention. It became clear that it was possible. Further, it has been clarified that the raw material powder used in the production method of the present invention is relatively hard to be oxidized even in the air, so that even if the raw material powder after long-term storage is used, an excellent active material powder can be obtained.

Example 3 All steps were the same as the first step and the second step described in Example 1 except that the concentration of the mixed sodium hydroxide aqueous solution was changed to 35, 40, 45 and 48% by weight. To produce an oxidation-treated powder. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. The results are shown in Table 5. In addition, a nickel-hydrogen storage battery was prepared by using each oxidation-treated powder in the same manner as in Example 1, and the charge / discharge evaluation was performed. FIG. 3 shows the relationship between the sodium hydroxide aqueous solution concentration and the active material utilization rate.

[0073]

[Table 5]

From Table 5, when the concentration of the aqueous sodium hydroxide solution mixed in the first step is made higher than 40% by weight, both the cobalt average valence and the powder conductivity show high values, and the coating layer is high. It can be seen that even the subcobalt oxide is oxidized. Further, it can be seen from FIG. 3 that the utilization rate also shows a high value when the concentration of the aqueous sodium hydroxide solution is made higher than 40% by weight, corresponding to the result.

This result is estimated as follows. As one of the oxidation reaction processes, as shown in Formula 1 and Formula 2, cobalt hydroxide is dissolved in an aqueous sodium hydroxide solution to form a cobalt complex ion, and this complex ion reacts with oxygen to form a higher cobalt oxidation. It is a reaction that becomes a thing. Therefore, a certain amount of sodium hydroxide aqueous solution must be present on the surface of the coating layer at high temperature during the oxidation treatment. However, since the oxidation treatment is performed near the boiling point of the sodium hydroxide aqueous solution, the reaction cannot be sufficiently advanced if the concentration of the sodium hydroxide aqueous solution is low and the evaporation thereof is fast. On the contrary, the higher the concentration of the sodium hydroxide aqueous solution, the higher the boiling point and the slower the evaporation rate thereof, and therefore, it can be said that it is suitable for the oxidation treatment. Also, when considering the second process of the oxidation reaction represented by Formula 3, the higher the OH ⁻ concentration is, the more the oxidation is promoted. Therefore, the higher the concentration of the sodium hydroxide aqueous solution is, the higher the oxidation treatment is. Considered to be suitable for.

From the examination results of this example, when the concentration of the aqueous sodium hydroxide solution was set to be higher than 40% by weight,
It was found that the coating layer was sufficiently oxidized to higher-order cobalt oxide, resulting in high utilization rate. From the above, it has been clarified that the concentration of the sodium hydroxide aqueous solution used for the oxidation treatment in the production method of the present invention is preferably greater than 40% by weight.

Example 4 All steps were the same as the first and second steps described in Example 1 except that the heating temperature in the second step was changed to 70, 90, 110, 130 and 140 ° C. Oxidized powder was prepared. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. The results are shown in Table 6.
Shown in. In addition, a nickel-hydrogen storage battery was prepared by using each oxidation-treated powder in the same manner as in Example 1, and the charge / discharge evaluation was performed. FIG. 4 shows the relationship between the oxidation treatment temperature and the active material utilization rate.

[0078]

[Table 6]

From Table 6, in any case where the oxidation treatment was carried out in the temperature range of 70 to 140 ° C., good cobalt average valence and powder conductivity were shown, and the coating layer was a higher cobalt oxide. You can see that it has been oxidized up to. However, as shown in FIG. 4, the utilization rate of the powder oxidized at 140 ° C. was significantly reduced. Even if the powder was oxidized at 140 ° C., the average cobalt valence and powder conductivity values were good, so this decrease was not due to the cobalt oxide coating layer, and the treatment temperature was too high and the inside of the coating layer was too high. It is considered that the nickel hydroxide particles in 1. were damaged. When the oxidation treatment is performed at 70 ° C., the average valence of cobalt,
Although it was possible to obtain a powder having good powder conductivity and utilization rate, it became clear that the oxidation treatment requires several hours. This is because the rate of the oxidation reaction is affected by the treatment temperature, and the lower the treatment temperature, the slower the progress of the oxidation reaction. From the above, it became clear that the heating temperature during the oxidation treatment in the production method of the present invention is suitably 90 to 130 ° C.

Example 5 In the second step, an oxidation-treated powder was produced in the same manner as the first step and the second step described in Example 1 except that microwave irradiation was performed as an auxiliary heating means. Hereinafter, this is referred to as powder K. With respect to this powder K, the average cobalt valence and the powder conductivity were measured in the same manner as in Example 1. Furthermore, powder K
Using the above, a nickel-hydrogen storage battery was prepared in the same manner as described in Example 1, and the charge / discharge evaluation was performed. The above results are shown in Table 7 in comparison with the value of powder B.

[0081]

[Table 7]

From Table 7, it can be seen that the powder K has improved cobalt average valence, powder conductivity, and utilization rate as compared with the powder B. It is considered that since the heating by microwave irradiation occurs from the cobalt hydroxide coating layer portion of the particle surface which is wet with the sodium hydroxide aqueous solution, the oxidation reaction of the coating layer proceeds more efficiently. In addition, by performing microwave irradiation, it is possible to quickly raise the temperature to a predetermined temperature with almost no heating unevenness, and it is possible to shorten the oxidation treatment time. From the above, the second
It has become clear that it is more preferable to use microwave irradiation as an auxiliary heating means in the process.

Example 6 The coating amount of cobalt hydroxide in the raw material powder was set to 3, 5 with respect to the nickel hydroxide solid solution particles.
Oxidation-treated powder was produced in the same manner as in the first step and the second step described in Example 1 except that the content was changed to 7, 12, and 14% by weight. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. The results are shown in Table 8. In addition, a nickel-hydrogen storage battery was prepared by using each oxidation-treated powder in the same manner as in Example 1, and the charge / discharge evaluation was performed. Figure 5
Shows the relationship between the cobalt hydroxide coating amount and the active material utilization rate.

[0084]

[Table 8]

From Table 8 and FIG. 5, cobalt hydroxide was 5
It can be seen that when the raw material powder coated in an amount of not less than wt% is used, the average cobalt valence, the powder conductivity, and the utilization rate show good values. With the powder having a coating amount of 3% by weight, the powder conductivity and the utilization rate are remarkably reduced, but it is considered that this reduction is because the coating amount is too small to form a sufficient conductive network. Further, the utilization rate gradually increases when the coating amount is in the range of 5 to 12% by weight, but when the coating amount exceeds 12% by weight, the utilization rate does not increase anymore, but rather, the positive electrode capacity decreases due to the reduction of the nickel hydroxide amount. It will be noticeable. Further, a problem that a part of the cobalt oxide, which is the coating layer, peels off and adheres to the inner wall of the oxidation treatment device has occurred. From the above, the cobalt hydroxide coating amount of the raw material powder used in the production method of the present invention is 5 to 1 with respect to the nickel hydroxide solid solution particles.
It has been found that 2% by weight is suitable.

Example 7 The average particle size of the raw material powder was 3,
Oxidation-treated powder was produced in the same manner as in the first step and the second step described in Example 1, except that the powder was changed to 5, 10, 20, and 24 μm. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. The results are shown in Table 9. Also,
A nickel-hydrogen storage battery was produced in the same manner as in Example 1 using each of the oxidation-treated powders, and charge / discharge evaluation was performed. FIG. 6 shows the relationship between the average particle size of the raw material powder and the active material utilization rate.

[0087]

[Table 9]

From Table 9 and FIG. 6, when the raw material powder having an average particle size of 5 to 20 μm was used for the oxidation treatment,
It can be seen that the average cobalt valence, the powder conductivity, and the utilization rate show good values. On the other hand, in the case of using the raw material powder having an average particle diameter of 3 μm or 24 μm, it was confirmed that both the powder conductivity and the utilization rate decreased. Generally, when the average particle size is small, the specific surface area tends to be large. Even when the average particle size is 3 μm, the specific surface area is large. Is difficult. Therefore, it is considered that the oxidation of the coating layer hardly progressed during the oxidation treatment, the average cobalt valence and the powder conductivity decreased, and the utilization factor also decreased. Further, in this case, there is also a problem that the bulk density of the powder is lowered and thus the filling property is also lowered. When the average particle size is 24 μm, it is considered that the particles are too large to be uniformly coated with cobalt hydroxide, so that a good conductive network cannot be formed, the powder conductivity is lowered, and the utilization factor is also lowered. .

Next, the BET specific surface area of the raw material powder was set to 3,
Oxidized powder was produced in the same manner as in the first step and the second step described in Example 1, except that the powder was changed to 5, 10, 15, and 18 m ² / g. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. The results are shown in Table 10. In addition, a nickel-hydrogen storage battery was prepared by using each oxidation-treated powder in the same manner as in Example 1, and the charge / discharge evaluation was performed. FIG. 7 shows the relationship between the BET specific surface area of the raw material powder and the active material utilization rate.

[0090]

[Table 10]

From Table 10 and FIG. 7, 5 to 15 m ² / g
It can be seen that when the oxidation treatment is performed using the raw material powder having the BET specific surface area, the cobalt average valence, the powder conductivity, and the utilization rate show good values. On the other hand, when the raw material powder having a BET specific surface area of 3 m ² / g or 18 m ² / g is used, the average cobalt valence, the powder conductivity and the utilization rate decrease. It is considered that this result is because when the specific surface area of the raw material powder is too large or too small, the wettability of the particles is greatly changed, so that the oxidation of the cobalt hydroxide coating layer is suppressed as described above. Furthermore, BET specific surface area is 18m
^{When 2} / g of the raw material powder was used, a phenomenon was also observed in which part of the cobalt oxide, which was the coating layer, peeled off and adhered to the inner wall of the oxidation treatment device. From the above, the raw material powder used in the production method of the present invention has an average particle size of 5 to 20 μm.
It has been clarified that those having m and BET specific surface area of 5 to 15 m ² / g are suitable.

Example 8 The yttrium oxide powder mixed amount in the first step was 0.05, 0.
Oxidized powder was produced in the same manner as in the first step and the second step described in Example 1, except that the content was changed to 1, 0.5, 1.0, 3.0, and 5.0% by weight. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. The results are shown in Table 1.
Shown in 1. In addition, a nickel-hydrogen storage battery was prepared by using each oxidation-treated powder in the same manner as in Example 1, and the charge / discharge evaluation was performed. Fig. 8 shows the amount of yttrium oxide mixed and 5
The relationship of 0 degreeC charge efficiency is shown.

[0093]

[Table 11]

From FIG. 8, the yttrium oxide powder was added to 0.1
It can be seen that when the mixture is mixed in an amount of not less than wt% and the oxidation treatment is performed, good high temperature charging efficiency is exhibited. 0.05% by weight
In case (2), the high temperature charging efficiency was the same as that in the case where yttrium oxide powder was not mixed (in the case of battery C), and the effect of adding yttrium oxide could not be confirmed. The mixing amount is 0.
In the range of 1 to 3.0% by weight, the high temperature charging efficiency gradually improves, but when it exceeds 3.0% by weight, no further improvement can be seen. Rather, when 5.0% by weight is added,
There has been a problem that the high rate discharge characteristics are significantly deteriorated. From Table 11, it is confirmed that the powder conductivity is reduced in the powder obtained by mixing 5.0% by weight of yttrium oxide powder and subjected to the oxidation treatment. Therefore, yttrium oxide having low conductivity is increased in the cobalt coating layer. Therefore, it is considered that the powder conductivity was lowered and the high rate discharge characteristics were also lowered. From the above, it was revealed that the suitable amount of yttrium oxide used in the production method of the present invention was 0.1 to 3.0% by weight with respect to the powder A.

Example 9 The average particle size of the yttrium oxide powder mixed in the first step is 0.1, 0.2, 1.
Oxidation-treated powder was produced in the same manner as in the first step and the second step described in Example 1, except that the powder was changed to 0, 4.0, 8.0, and 16.0 μm. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. The results are shown in Table 12. In addition, a nickel-hydrogen storage battery was prepared by using each oxidation-treated powder in the same manner as in Example 1, and the charge / discharge evaluation was performed. FIG. 9 shows the relationship between the average particle size of the yttrium oxide powder and the active material utilization rate.

[0096]

[Table 12]

From Table 12 and FIG. 9, 0.2 to 8.0 μ
When yttrium oxide powder having an average particle size of m is used for the oxidation treatment, the average cobalt valence, the powder conductivity,
It can be seen that the utilization rate shows good values. On the other hand, when yttrium oxide powder having an average particle diameter of 0.1 μm or 16.0 μm was used, both the powder conductivity and the utilization rate were confirmed to be lowered. When the average particle size is 0.1 μm, the yttrium oxide powder becomes very bulky, and a large amount of aqueous sodium hydroxide solution is required to convert it into yttrium hydroxide in the form of gel. Therefore, excess water exists near the cobalt hydroxide coating layer during the oxidation treatment, and the O ₂ concentration decreases, so that the reaction of formula 4 is inhibited and the reaction of formula 3 becomes difficult to proceed. As a result, it is considered that the oxidation of the cobalt hydroxide coating layer is suppressed, the average cobalt valence and the powder conductivity become low, and the utilization rate also decreases. On the other hand, when the average particle size is 16.0 μm, the particle size is too large, and it is considered that the yttrium hydroxide gel is unlikely to change. As a result, it is considered that yttrium does not sufficiently diffuse into the cobalt oxide coating layer and adheres to the surface of the coating layer as yttrium oxide having low conductivity, so that the powder conductivity decreases and the utilization rate also decreases.

Next, the BET specific surface areas of the yttrium oxide powders mixed in the first step are set to 3, 10, 30, 60,
Oxidation-treated powder was produced in the same manner as in the first step and the second step described in Example 1, except that the powder was changed to 90 m ² / g. Example 1 of these oxidized powders
The average cobalt valence and the powder conductivity were measured by the same method as described in 1. The results are shown in Table 13. In addition, using each oxidation-treated powder in the same manner as described in Example 1, nickel.
A hydrogen storage battery was produced and evaluated for charge and discharge. FIG. 10 shows the relationship between the BET specific surface area of yttrium oxide powder and the active material utilization rate.

[0099]

[Table 13]

From Table 13 and FIG. 10, 3 to 60 m ² /
It can be seen that when the yttrium oxide powder having a BET specific surface area of g is used for the oxidation treatment, the cobalt average valence, the powder conductivity, and the utilization rate show good values. BE
When yttrium oxide powder having a T specific surface area of 90 m ² / g is used, the average cobalt valence, the powder conductivity, and the utilization rate decrease. This result indicates that the yttrium oxide powder has an excessively large specific surface area, and therefore a large amount of sodium hydroxide aqueous solution is required to convert it to gel yttrium hydroxide, and the oxidation of the cobalt hydroxide coating layer is suppressed as described above. It is thought to be a tame. From the above, the yttrium oxide powder used in the production method of the present invention has an average particle size of 0.2 to 8.0 μm and a BET specific surface area of 3 to 60.
It has been found that a value of m ² / g is suitable.

Example 10 In the first step, scandium oxide, erbium oxide, ytterbium oxide, lutetium oxide and calcium oxide having the same average particle diameter and BET specific surface area were used instead of the yttrium oxide powder. Oxidation-treated powder was produced in the same manner as in the first step and the second step described in Example 1. The cobalt average valence and the powder conductivity of these oxidation-treated powders were measured by the same method as described in Example 1. In addition, a nickel-hydrogen storage battery was prepared by using each oxidation-treated powder in the same manner as in Example 1, and the charge / discharge evaluation was performed. The above results are shown in Table 14 in comparison with the values of the powder B using yttrium oxide.

[0102]

[Table 14]

From Table 14, it is found that, in each case where scandium oxide, erbium oxide, ytterbium oxide, lutetium oxide or calcium oxide was used for the oxidation treatment instead of the yttrium oxide powder, the average cobalt valence and the powder conductivity were determined. It can be seen that the utilization rate shows good values. The result is that instead of yttrium oxide powder,
Even if oxidation treatment is performed using scandium oxide, erbium oxide, ytterbium oxide, lutetium oxide, or calcium oxide, a higher-order cobalt oxide having a good coating layer with the same reaction mechanism as in the case of powder B described in Example 1 It is thought to be the result of being oxidized.

From the above, the oxide powder used in the production method of the present invention is not limited to yttrium oxide powder, and the same applies to the case of using oxide powder selected from scandium, lanthanoid and calcium. It became clear that the effect of.

In this embodiment, only the sodium hydroxide aqueous solution is described as the alkaline aqueous solution used at the time of the oxidation treatment, but the present invention is not limited to this, and the potassium hydroxide aqueous solution or the sodium hydroxide and hydroxide is used. It was confirmed that the same effect can be obtained by using a binary aqueous solution of potassium. Further, in this example, only the solid solution particles of cobalt and zinc were described as the raw material powder used for the oxidation treatment, but the type of the solid solution element is not limited to this, and cobalt, zinc, cadmium, and calcium. It has been confirmed that the same effect can be obtained with all nickel hydroxide particles containing at least one element selected from manganese, magnesium, aluminum, titanium, yttrium and lanthanoid.

[0106]

As described above, according to the production method of the present invention, a positive electrode active material for an alkaline storage battery, which is excellent in utilization rate and charging efficiency in a high temperature atmosphere and is excellent in filling property, is efficiently provided. It is possible to Further, in the production method of the present invention, since the existing raw material powder can be used as it is, an increase in the active material production cost can be suppressed, and the raw material powder can be stored for a long period of time, so that the productivity can be improved. As a result, it becomes possible to manufacture an alkaline storage battery having a high capacity and excellent charge / discharge characteristics even when used at high temperature at a low price.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between discharge capacities of batteries B, C, E and F and battery voltage.

FIG. 2 is a diagram showing the relationship between the discharge capacities of batteries B, E, H and J and the battery voltage.

FIG. 3 is a diagram showing the relationship between the concentration of the sodium hydroxide aqueous solution used in the first step and the active material utilization rate.

FIG. 4 is a diagram showing a relationship between a heating temperature and an active material utilization rate in a second step.

FIG. 5 is a diagram showing the relationship between the amount of cobalt hydroxide coating nickel hydroxide and the utilization factor of the active material.

FIG. 6 is a diagram showing a relationship between an average particle diameter of raw material powder and an active material utilization rate.

FIG. 7 is a diagram showing a relationship between a BET specific surface area of raw material powder and an active material utilization rate.

FIG. 8 is a graph showing the relationship between the amount of yttrium oxide powder mixed and the charging efficiency at 50 ° C. used in the first step.

FIG. 9 is a diagram showing the relationship between the average particle size of the yttrium oxide powder used in the first step and the active material utilization rate.

FIG. 10: B of yttrium oxide powder used in the first step
It is a figure which shows the relationship between ET specific surface area and an active material utilization rate.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoichi Izumi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 5H028 AA02 AA06 BB03 BB05 BB06                       BB15 EE05 HH01 HH05 HH08                 5H050 AA05 AA08 AA19 BA13 BA14                       CA04 CB14 CB16 DA02 DA10                       EA12 FA17 FA18 GA02 GA10                       GA22 GA27 HA01 HA05 HA07                       HA14

Claims (11)

[Claims] 1. Solid solution particles containing nickel hydroxide as a main component coated with cobalt hydroxide, at least one kind of oxide particles selected from yttrium, scandium, lanthanoid and calcium, and an alkaline aqueous solution are mixed by stirring. A positive electrode active material for an alkaline storage battery comprising a first step of forming wet particles whose surface is wet with an alkaline aqueous solution, and a second step of performing heat treatment while stirring and mixing the wet particles in the presence of oxygen and leading to drying. Production method. 2. The alkali aqueous solution mixed in the first step is an aqueous sodium hydroxide solution and / or an aqueous potassium hydroxide solution, and the concentration thereof is higher than 40% by weight. A method for producing a positive electrode active material for an alkaline storage battery. 3. The heating temperature in the second step is 90 to
It is 130 degreeC, The manufacturing method of the positive electrode active material for alkaline storage batteries of Claim 1 or 2 characterized by the above-mentioned. 4. A microwave irradiation is used as an auxiliary heating means in the second step.
4. The method for producing a positive electrode active material for an alkaline storage battery according to any one of 3 above. 5. In the solid solution particles containing nickel hydroxide as a main component and coated with cobalt hydroxide, the coating amount of the cobalt hydroxide is 5 to 12 relative to the solid solution particles containing nickel hydroxide as a main component. It is weight%, The manufacturing method of the positive electrode active material for alkaline storage batteries in any one of Claims 1-4 characterized by the above-mentioned. 6. The solid solution particles containing nickel hydroxide coated with cobalt hydroxide as a main component have an average particle size of 5 to 20 μm and a BET specific surface area of 5 to 15.
The method for producing a positive electrode active material for an alkaline storage battery according to claim 1, characterized in that the m ² / g. 7. A solid solution containing nickel hydroxide as a main component, wherein the amount of at least one oxide particle selected from yttrium, scandium, lanthanoid and calcium mixed in the first step is cobalt hydroxide-coated nickel hydroxide as a main component. It is 0.1-3.0 weight% with respect to a particle | grain, The manufacturing method of the positive electrode active material for alkaline storage batteries in any one of Claims 1-6 characterized by the above-mentioned. 8. The average particle size of at least one oxide particle selected from yttrium, scandium, lanthanoid and calcium mixed in the first step is 0.2 to 8.0 μm, and the BET specific surface area is Is 3
-60 m < ² > / g, The manufacturing method of the positive electrode active material for alkaline storage batteries in any one of Claims 1-7 characterized by the above-mentioned. 9. The solid solution particles containing nickel hydroxide as a main component coated with cobalt hydroxide are at least one selected from cobalt, zinc, cadmium, calcium, manganese, magnesium, aluminum, titanium, yttrium and lanthanoids. The method for producing a positive electrode active material for an alkaline storage battery according to claim 1, further comprising: 10. A positive electrode active material for an alkaline storage battery manufactured by the manufacturing method according to claim 1. 11. A positive electrode containing the positive electrode active material for an alkaline storage battery according to claim 10 as a main component, a negative electrode containing a hydrogen storage alloy or cadmium oxide as a main component, a separator, an alkaline electrolyte, and a battery containing these components. An alkaline storage battery consisting of a case.