JPH10334911A - Alkaline storage battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for an alkaline storage battery superior the utilization factor of nickel hydroxide and having a stable characteristic by providing a film layer made of a cobalt composite oxide on the surface of powder grains mainly made of nickel hydroxide. SOLUTION: A cobalt composite oxide is expressed by the general expression Mx CoO2 , where M indicates at least one element among Li, Na, K, and 0<x<=1. In this manufacture, a powder made mainly of nickel hydroxide is mixed with an aqueous solution of compounds expressed by [Co(NH3 )6 ]CO3 and [Co(NH3 )6 ]2 (CO3 )3 . The mixed aqueous solution is heated and stirred at 70 deg.C or above, and a film layer made of a cobalt compound is provided on the surface of the powder made mainly of nickel hydroxide. The coated powder is heated at 90-150 deg.C together with alkali hydroxide, and the film layer make of the cobalt composite oxide is synthesized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline storage battery, and more particularly to an active material for a paste-type nickel positive electrode such as a nickel-cadmium storage battery, a nickel-hydrogen storage battery, and a nickel-zinc storage battery, and a method for producing the same.

[0002]

2. Description of the Related Art In an alkaline storage battery, zinc, iron, hydrogen and the like are used as a negative electrode in addition to cadmium. At present, cadmium electrodes are the main component, but nickel-hydrogen storage batteries that use a metal hydride that can increase the energy density, that is, a hydrogen-absorbing alloy for the negative electrode, have been developed and put into practical use. Have been.

On the other hand, although some air electrodes, silver oxide electrodes and the like have been taken up as the positive electrode, most of them are nickel electrodes mainly composed of nickel hydroxide. The form of the electrode was changed from a pocket type to a sintered type, and further to a paste type, and the characteristics were improved. The paste-type nickel electrode is obtained by adding a powder such as cobalt and cadmium to a nickel hydroxide active material powder, further adding a binder, water, etc. to a viscous paste state, and converting this into a viscous paste ( Core material). This nickel electrode has a feature that its energy density is higher than that of a sintered type.

[0004] However, the paste type nickel electrode has a lower utilization rate of nickel hydroxide than the sintered type, and in order to improve this, a metal oxide or cobalt hydroxide is added, and a high conductivity higher oxidation state is obtained. Of cobalt hydroxide. In Japanese Patent Application Laid-Open No. Hei 1-200555, in order to improve the utilization rate of nickel hydroxide, cobalt hydroxide is formed on the surface of particles of an active material mainly composed of nickel hydroxide, and heat treatment is performed in the presence of alkali. It is disclosed that cobalt oxides such as CoOOH and CoO in a highly oxidized state having high conductivity are formed on the surface of active material particles mainly composed of nickel hydroxide.

In addition, there has been proposed a method of forming a highly oxidized cobalt oxide having high conductivity on the surface of active material particles mainly composed of nickel hydroxide.

[0006]

However, when oxidizing metal cobalt or cobalt hydroxide powder, which is a cobalt compound, by the conventional method, it is difficult to completely oxidize the inside of the powder particles, and it is difficult to oxidize the powder to a higher oxidation state than divalent. However, since the valence of cobalt of the cobalt oxide is not stable, there is a problem that the utilization rate of nickel hydroxide and the discharge characteristics at a large current are not stable.

An object of the present invention is to provide a positive electrode active material for an alkaline storage battery which has excellent utilization of nickel hydroxide and has stable characteristics, and a method for producing the same.

[0008]

[MEANS FOR SOLVING THE PROBLEMS]
In the present invention, nickel hydroxide, which is a positive electrode active material, is mainly used.
The general formula [Co (NH)_Three)₆] CO_Three,
And [Co (NH_Three) ₆]_Two(CO_Three)_ThreeCompound indicated by
(Hexammine cobalt carbonate) as starting material
General formula M obtained by synthesis_XCoO_Two(X is 0 <x ≦ 1,
M is at least one element of Li, Na and K)
Coating layer made of the cobalt composite oxide shown
And features.

The production method is based on the general formula [Co (NH ₃ ) ₆ ] C
Adding a powder mainly composed of nickel hydroxide to an aqueous solution of a compound (hexamminecobalt carbonate) represented by O ₃ and [Co (NH ₃ ) ₆ ] ₂ (CO ₃ ) ₃ and mixing them;
A step of heating and stirring the mixed aqueous solution at 70 ° C. or higher to form a coating layer composed of a cobalt compound on the surface of the powder mainly composed of nickel hydroxide, and bringing the powder after the coating treatment to 90 to 150 ° C. with alkali hydroxide. heating to the general formula M _X C
synthesizing a coating layer made of a cobalt composite oxide represented by oO ₂ (x is 0 <x ≦ 1, M is at least one element of Li, Na and K).

[0010] The present invention mainly comprises nickel hydroxide.
General formula M on the powder surface_Three[Co (CO_Three)_Three] (M is L
i, at least one element of Na, K)
Compound (tricarbonatocobaltate) as the starting material
Formula M obtained by synthesis _XCoO_Two(X is 0 <x ≦
1, M is at least one element of Li, Na, and K
A coating layer made of cobalt composite oxide
It is characterized in that

The other features of the present invention and the method of manufacturing the positive electrode will be described in detail in the following embodiments of the present invention.

[0012]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, a powdery material mainly composed of nickel hydroxide, which is a constituent material of a positive electrode, has a general formula [Co (NH ₃ ) ₆ ] CO ₃ and [Co
(NH _{3) 6] 2} (CO ₃₎ a compound represented by the ₃ general formula (Hexaamminecobalt carbonate) obtained by synthesizing a starting material M _X CoO ₂ (x is 0 <x ≦ 1, M is Li , N
a coating layer composed of a cobalt composite oxide represented by at least one of a and K).

Conventional cobalt hydroxide, cobalt oxide, metal cobalt, etc. are mixed with an alkali hydroxide powder or an aqueous solution of an alkali hydroxide, heated and oxidized with oxygen (in the atmosphere) to obtain a powder mainly composed of nickel hydroxide. The method of synthesizing a highly conductive cobalt oxide layer on the surface of the particles requires a long treatment time because the solubility of cobalt in an aqueous alkaline solution is extremely low. Unreacted regions tend to remain in the cobalt powder particles. For this reason, there is a problem that the utilization rate of the positive electrode active material mainly composed of nickel hydroxide obtained by this method and the discharge characteristics under a large current are not stable.

On the other hand, the general formula [Co (NH ₃ ) ₆ ]
The compound represented by CO ₃ and [Co (NH ₃ ) ₆ ] ₂ (CO ₃ ) ₃ (hexamminecobalt carbonate) is soluble in water, and is heated by heating the aqueous solution to 70 ° C. or more. It can be easily oxidized and decomposed. Thus, the powder particles mainly composed of nickel hydroxide are dispersed in the aqueous solution of hexaammine cobalt carbonate, and heated to 70 ° C. or more in this state to oxidize and decompose [Co (NH ₃ ) ₆ ] CO _3. Or [Co (NH ₃ ) ₆ ] ₂ (C
O ₃ ) ₃ can be decomposed to form a cobalt oxyhydroxide layer on the surface of the nickel hydroxide powder particles.

The cobalt oxyhydroxide layer is formed by decomposing an aqueous solution of a trivalent cobalt salt, so that there is no unreacted portion and the layer is uniform. However, since the conductivity of cobalt oxyhydroxide generated in this decomposition step is low, a high nickel hydroxide utilization rate cannot be obtained. Therefore, it is necessary to react cobalt oxyhydroxide with alkali hydroxide to obtain a compound having high conductivity. Formula M _X Co from previous study results from divalent cobalt compound
When synthesizing a cobalt composite oxide represented by O ₂ (x is 0 <x ≦ 1, M is at least one element of Li, Na, and K), it is found that oxidation of cobalt becomes a rule. Was. That is, cobalt-cobalt composite oxide of the general formula M _X CoO ₂ be mixed with alkali hydroxide under conditions which are not oxidized is not synthesized.

The cobalt oxyhydroxide synthesized in this embodiment is a very fine powder, and since cobalt is uniformly oxidized to trivalent, 9% together with alkali hydroxide.
By heating at 0 to 150 ° C., the general formula M _X CoO ₂
(X is 0 <x ≦ 1, M is at least one element of Li, Na, and K), and a cobalt composite oxide represented by the formula (1) can be uniformly and easily synthesized.

As described above, a layer represented by the general formula M _X CoO ₂ having high conductivity can be formed on the surface of the nickel hydroxide powder particles, and the nickel hydroxide utilization and discharge characteristics at a large current can be improved. It is possible to obtain a positive electrode active material mainly composed of nickel hydroxide, which is excellent and has stable characteristics.

According to a second aspect of the present invention, there is provided the method for producing a positive electrode active material according to the first aspect, wherein the general formula [Co (NH ₃ ) ₆ ] C
From the step of adding and mixing powder mainly composed of nickel hydroxide into an aqueous solution of a compound represented by O ₃ and [Co (NH ₃ ) ₆ ] ₂ (CO ₃ ) ₃ (hexammine cobalt carbonate), Coating of a cobalt composite oxide represented by the general formula M _X CoO ₂ (x is 0 <x ≦ 1, M is at least one element of Li, Na, and K) on the particle surface of a powder mainly composed of nickel The layers are combined.

According to a third aspect of the present invention, the surface of the powder mainly composed of nickel hydroxide has the general formula M ₃ [Co (CO ₃ ) ₃ ] (M
Is a general formula M _X CoO ₂ (x is 0 <x ≦ 1, obtained from a compound (tricarbonatocobaltate) represented by at least one element of Li, Na and K).
M is provided with a coating layer made of a cobalt composite oxide represented by at least one element of Li, Na and K).

The general formula M ₃ [Co (CO ₃ ) ₃ ] (M is L
The compound (tricarbonatocobaltate) represented by at least one of i, Na, and K) is soluble in water and is easily decomposed by heating the aqueous solution to 60 ° C. or higher. be able to. From this, the powder particles mainly composed of nickel hydroxide are dispersed in the aqueous solution of tricarbonatocobaltate and heated to 60 ° C. or more,
The tricarbonatocobaltate can be decomposed to form a cobalt oxyhydroxide layer on the surface of the nickel hydroxide powder particles. The cobalt oxyhydroxide layer is uniform because there is no unreacted portion because the trivalent cobalt salt is decomposed and formed.

Further, since this cobalt oxyhydroxide is a very fine powder, and cobalt is uniformly oxidized trivalently, the cobalt oxyhydroxide is mixed with an alkali hydroxide at 90 to 15%.
Formula by heating at 0 ℃ M _X CoO ₂ (x is 0 <
x ≦ 1, M is at least one element of Li, Na, and K), and a cobalt composite oxide represented by the following formula (1) can be uniformly and easily synthesized.

According to a fourth aspect of the present invention, there is provided the positive electrode according to the third aspect.
A method for producing an active material, comprising the general formula M _Three[Co (C
O_Three)_Three] (M is at least one of Li, Na and K
Element) does not contain alkali bicarbonate
Alkali hydrogen carbonate
Formula M in an aqueous solution of_Three[Co (CO_Three)_Three] (M
Is at least one element of Li, Na and K)
Dissolve the compound to be used, and add nickel hydroxide
And mixing and dispersing the powder,
Heat the solution to 60 ° C or higher and stir the nickel hydroxide powder.
Providing a coating layer made of a cobalt compound on the surface,
The powder after the coating treatment is mixed with an alkali hydroxide in an amount of 90 to
Heat to 150 ° C to obtain general formula M_XCoO_Two(X is 0 <x ≦
1, M is at least one element of Li, Na, and K
Synthesis of a coating layer of cobalt composite oxide
And a process.

A fifth aspect of the present invention also provides a method for producing a positive electrode active material according to the _{third aspect} , which comprises a general formula M ₃ [Co (CO ₃ ) ₃ ].
(M is at least one element of Li, Na and K)
Is dissolved in an aqueous alkali hydrogen carbonate solution,
A powder mainly composed of nickel hydroxide is added thereto and dispersed,
Mixing, and further adding alkali hydroxide gradually to this solution and heating to 90 to 150 ° C. to obtain a compound of the general formula M ₃ [C
o (CO _{3) 3]} (M is Li, Na, at least one element of K) with decomposition of the compound represented by the general formula _{M X CoO 2 (x 0 <} x ≦ 1, M is (At least one element of Li, Na, and K).

According to a sixth aspect of the present invention, a cobalt salt is added to an aqueous solution of alkali hydrogen carbonate or alkali carbonate (where the alkali is at least one of Li, Na, K and ammonia) in which a powder mainly composed of nickel hydroxide is dispersed or mixed. Mixing a mixed aqueous solution of urea and an oxidizing agent;
Heating and stirring at 0 ° C. or higher to form a coating layer made of a cobalt compound on the surface of the nickel hydroxide powder; and drying the powder provided with the coating layer together with alkali hydroxide at 90 to 150 ° C.
And heated to (the x 0 <x ≦ 1, M is Li, Na, at least one element of K) formula M _X CoO ₂ step of synthesizing a coating layer of cobalt composite oxide represented by It consists of:

By dropping and mixing a mixed solution of a cobalt salt and an oxidizing agent in an aqueous alkali hydrogencarbonate solution, cobalt ions and alkali ions, carbonate ions, anions constituting the cobalt salt or other various anions (for example, , Chlorine, sulfuric acid, acetic acid, nitric acid, oxalic acid, etc.) to form various water-soluble cobalt complexes. Soluble cobalt complex for these water to decompose by heating, further, the general formula M _X CoO ₂ having a high conductivity by thermal reaction of these decomposition products alkali hydroxide
(X is 0 <x ≦ 1, M is at least one element of Li, Na, and K).

As described above, it is possible to form a highly conductive general formula M _x CoO ₂ layer on the surface of nickel hydroxide powder particles, and to have excellent nickel hydroxide utilization and discharge characteristics at high currents. In addition, a positive electrode active material having stable characteristics can be obtained.

According to a seventh aspect of the present invention, in the same manner as in the production method of the sixth aspect, an alkali hydrogen carbonate or an alkali carbonate in which a powder mainly containing nickel hydroxide is dispersed or mixed (the alkali is Li, Na, K, ammonia at least one) step of mixing the mixed aqueous solution of a cobalt salt with an oxidizing agent to an aqueous solution, and heated by adding an alkali hydroxide to the mixed aqueous solution 90 to 150 ° C., the general formula M _X CoO ₂ (x of Is 0
(X ≦ 1, M is at least one element of Li, Na, and K).

[0028] The invention of claim 8 is that the powder mainly composed of nickel hydroxide and the cobalt hydroxide powder or the cobalt oxide powder are heated in the coexistence of alkali hydroxide, carbon dioxide, oxidizing agent and water, and the general formula M _This is to synthesize and mix a cobalt composite oxide powder represented by _X CoO ₂ (x is 0 <x ≦ 1, M is at least one element of Li, Na and K).

By introducing carbon dioxide gas under these treatment conditions, the solubility of cobalt hydroxide and cobalt oxide can be improved, so that the reaction time can be significantly shortened and the oxidation of cobalt can be reduced. The reaction area can be greatly reduced.

Therefore, it is possible to improve the utilization rate of nickel hydroxide and the discharge characteristics at a large current, and to stabilize the characteristics.

According to a ninth aspect of the present invention, there is provided the method according to the eighth aspect, wherein the general formula M _X CoO ₂ (x is 0 <x ≦ 1, M is at least one element of Li, Na, and K) ) Covers the surface of the powder mainly composed of nickel hydroxide.

According to a tenth aspect of the present invention, in the positive electrode active material according to the first or third aspect, the cobalt composite oxide is added in an amount of 2 to 30% by weight based on nickel hydroxide which is a positive electrode active material for an alkaline storage battery. It is. By mixing in this range, excellent effects can be exerted without significantly reducing the active material.

[0033]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 A positive electrode active material for an alkaline storage battery was prepared in the following procedure. Nickel hydroxide, which is a eutectic of cobalt hydroxide and zinc hydroxide, was used as nickel hydroxide, which is a main component of the active material. Hereinafter, this nickel hydroxide is simply referred to as nickel hydroxide.

First, cobalt hydroxide powder was dispersed and mixed in aqueous ammonia, and carbon dioxide gas was passed through the mixed aqueous solution to dissolve the cobalt hydroxide to prepare an aqueous cobalt complex solution. Cobalt hydroxide dissolved in divalent Hexaamminecobalt Carbonate _{[Co (NH 3) 6]} CO 3, it is oxidized by oxygen in the atmosphere trivalent Hexaamminecobalt Carbonate [Co (NH _{3) 6] 2} (CO ₃ ) ₃ Here, cobalt hydroxide was used as cobalt, but similar results can be obtained by dissolving cobalt carbonate in aqueous ammonia.

In the first step, nickel hydroxide powder particles are added to the aqueous cobalt complex solution so that the cobalt in the aqueous cobalt complex solution becomes 10 in terms of cobalt hydroxide with respect to the weight of 100 nickel hydroxide powder. It was added, dispersed and mixed.

In the second step, the mixed aqueous solution is heated at 90 ° C.
For 1 hour to form a cobalt compound layer on the surface of the nickel hydroxide particles. Divalent hexaammine cobalt carbonate [Co (NH ₃ ) ₆ ] CO ₃ changes to trivalent in this step. The above-mentioned cobalt compounds are mainly cobalt oxyhydroxide, hexaammine cobalt carbonate [Co (N
H ₃ ) ₆ ] CO ₃ .

In the third step, the nickel hydroxide powder having the cobalt compound layer formed thereon is recovered, put into a 30% by weight aqueous sodium hydroxide solution, heated and stirred at 110 ° C. for 1 hour, washed with water and dried. A positive electrode active material was prepared.

The influence of the treatment amount was examined by setting the weight of the nickel hydroxide treated to 100 g, 1 kg, and 10 kg by the above-mentioned production method.

[0040] The Hexaamminecobalt carbonate in the third step is completely decomposed, further, is oxidized by reaction with sodium hydroxide, changing the cobalt composite oxide of Na _0.6 CoO _2. Further, cobalt oxyhydroxide was further oxidized and reacted with sodium hydroxide to be converted to a cobalt composite oxide of Na _0.6 CoO ₂ .

Further, the mixed nickel hydroxide is also slightly oxidized in this step, but a higher-order oxidized compound such as cobalt is hardly formed, and the result of X-ray analysis shows that the diffraction pattern of β-type nickel hydroxide is Indicated.

In the second step, an aqueous solution of sodium hydroxide is gradually added to the aqueous solution mixed in the first step while stirring without recovering the nickel hydroxide powder on which the cobalt compound layer has been formed. The same effect as in the above-described method could be obtained by reacting with sodium oxide.

A battery was prepared using the positive electrode active material prepared above, and its characteristics were evaluated.

The method for preparing the battery, the test method, and the results are described.

2% by weight of zinc oxide powder was added to the positive electrode active material prepared by the above-mentioned manufacturing method, mixed and stirred sufficiently, and further water was added to form a paste. The average pore size of the core material was 150 μm, and the porosity was 95%. %, And filled into a foamed nickel sheet having a thickness of 1.0 mm. This was dried at 90 ° C. and then pressed by a roller press, and the surface was coated with a fluororesin powder to form an electrode. These electrodes are 3.5 cm wide, 11 cm long and 0.7-0.8 mm thick.
And the lead was attached to a predetermined position to obtain the positive electrode plate 1. The capacity was about 1500 mAh.

The negative electrode material has the general formula MmNi _3.55 Co
A hydrogen storage alloy of _0.75 Mn _0.4 Al _0.3 was used. Particle size 53
An alloy powder of μm or less was put into a 31% KOH alkaline solution at 80 ° C. for 1 hour to perform a surface activation treatment on the alloy to remove alkali-soluble components.

A predetermined amount of a dilute aqueous solution of carboxymethylcellulose was added to the alloy sample powder subjected to the above-mentioned treatment, mixed and stirred to form a paste, which was then subjected to an average pore size of 150 μm.
m, a porosity of 95%, and a foamed nickel sheet having a thickness of 1.0 mm. This was dried at 90 ° C. and then pressed by a roller press, and the surface was coated with a fluororesin powder to form an electrode. These electrodes are 3.5 c wide.
m, length 14.5 cm, thickness about 0.4 mm.

The positive electrode plate 1, the negative electrode plate 2, and the separator 3 made of a polypropylene nonwoven fabric having hydrophilicity were combined, spirally wound, and housed in a battery case 4 of 4/5 A size. An electrolytic solution obtained by dissolving 30 g / l of lithium hydroxide in an aqueous solution of potassium hydroxide having a specific gravity of 1.3 was 2.3.
After injecting 5 ml, the opening of the case was sealed with a sealing plate 5 and FIG.
The sealed battery shown in the following was prepared. In FIG. 1, reference numeral 6 denotes a positive electrode terminal cap that presses the safety valve 7 between the sealing plate 5 and
8 is an insulating gasket, 9 is a positive electrode lead.

The battery thus prepared was charged to 150% at 20 ° C. at a rate of 0.1 C (10 hours, for example, a battery of 1500 mAh has a current of 150 mA).
At C, the battery was discharged to a final voltage of 1.0 V. After the discharge, the battery was left at 45 ° C. for 5 days.

After standing, the battery was subjected to 10 to 20 charge / discharge cycles of 45 ° C., 120% charge at 0.2 C and discharge at 0.2 C to 1.0 V to form a test battery.

The following test was performed on this test battery.

(1) Nickel hydroxide utilization rate;
At a charging current of 0.1 C (0.15 A) at a temperature of 150 ° C.
%, And after one hour of rest, the discharge capacity at the time of discharging to 1.0 V at 0.2 C is measured, and the theoretical capacity of nickel hydroxide in the positive electrode (when the nickel valence of nickel hydroxide changes by 1) The amount of nickel hydroxide was calculated from the following (Equation 1).

[0053]

Formula 1: Nickel hydroxide utilization rate = (discharge capacity / theoretical capacity) × 100 (2) 1 C (1.5 A) charge / discharge test at 20 ° C .; In 3A), the cut-off voltage is 1.
After discharging to 0 V, the charging current was 1% and 120% (1.2%).
Time) The battery was charged, and after one hour of rest, the discharge capacity at the time of discharging to 1.0 V at 1 C was measured. The nickel hydroxide utilization rate was determined by (Equation 1) and was defined as the nickel hydroxide utilization rate at the time of 1C discharge.

(3) Overdischarge characteristic test in a high temperature state;
Was stored at 45 ° C. for 2 months with an external load, and the discharge capacity was measured in a 20 ° C., 1C charge / discharge test after overdischarge.
The nickel hydroxide utilization rate was determined from (Equation 1), and was defined as the nickel hydroxide utilization rate at the time of 1C discharge after overdischarge.

(Comparative Example) For comparison, a cobalt hydroxide powder 10 was mixed with a nickel hydroxide powder weight of 100, and 1.5 liter of a 40% by weight aqueous sodium hydroxide solution was mixed with the mixed powder.

Next, the mixture was passed through air at 110 ° C. while mixing.
Was heated. After the treatment, the product was washed with water and dried to prepare a positive electrode active material. The processing time was 110 ° C. for 1 hour.

The weight of nickel hydroxide was 100 g, 1 kg,
A positive electrode active material was prepared by changing the treatment amount of nickel hydroxide to 10 kg.

Using the positive electrode active material thus prepared, a test battery similar to the above was prepared, and the same measurement was performed. The results are shown in (Table 1).

In the comparative example, the nickel hydroxide utilization rate at the time of 0.2 C discharge and the nickel hydroxide utilization rate at the time of 1 C discharge were reduced due to the increase in the treatment amount of nickel hydroxide. The positive electrode active material produced by the production method had a high nickel hydroxide utilization rate, and showed a stable nickel hydroxide utilization rate even when the amount of nickel hydroxide treated was large.
Further, no decrease in the nickel hydroxide utilization rate during 1C discharge after high-temperature overdischarge was observed.

[0060]

[Table 1]

Example 2 First, the general formula Na ₃ [Co
(CO ₃ ) ₃ ] to produce a sodium tricarbonatocobaltate compound.

An aqueous solution of hydrogen peroxide was mixed with an aqueous solution of cobalt nitrate cooled to about 0 ° C. to obtain a mixed solution. While sufficiently stirring this mixed solution in an aqueous solution containing sodium bicarbonate cooled to about 0 ° C. (powder is required because the amount of sodium bicarbonate is equal to or more than the dissolution amount of sodium bicarbonate), Was gradually added. The precipitate formed was filtered by suction, washed with a small amount of cold water, washed with ethanol and ether, and dried in a desiccator containing phosphorus pentoxide to prepare sodium tricarbonatocobaltate. Here, cobalt nitrate is used as cobalt, but the same effect can be obtained by using a water-soluble cobalt salt such as cobalt sulfate, cobalt chloride, or cobalt acetate.

As a first step, the above-mentioned predetermined amounts of sodium tricarbonatocobaltate and nickel hydroxide powder are added to an aqueous solution in which sodium hydrogencarbonate is dissolved. An amount of sodium tricarbonatocobaltate having an amount of 10 in terms of cobalt was added and mixed with stirring to obtain a mixed solution.

In the second step, the mixed aqueous solution is heated to 90 ° C.
For 1 hour to form a cobalt compound layer on the surface of the nickel hydroxide particles. In this step, sodium tricarbonatocobaltate was decomposed to form a layer mainly composed of cobalt oxyhydroxide on the surface of the nickel hydroxide particles.

In the third step, the nickel hydroxide powder on which the above-mentioned cobalt oxyhydroxide layer was formed was recovered, put into a 10% by weight aqueous solution of lithium hydroxide, and heated at 100 ° C. for 1 hour.
After heating and stirring for an hour, the product was washed with water and dried to prepare a positive electrode active material. Note that lithium hydroxide was used in an amount twice as much as that of cobalt.

According to the above-described method, the weight of nickel hydroxide was reduced to 1
The effect of the treatment amount was examined at 00 g, 1 kg, and 10 kg.

In the third step, cobalt oxyhydroxide is LiC
It was changed to oO ₂ cobalt composite oxide. Although the mixed nickel hydroxide is slightly oxidized in this step, almost no higher-order oxidized compound such as cobalt is formed similarly to Example 1, and the result of X-ray analysis shows the diffraction pattern of β-type nickel hydroxide. showed that.

In the second step, the lithium hydroxide aqueous solution was gradually added to the aqueous solution mixed in the first step while stirring without recovering the nickel hydroxide powder on which the cobalt compound layer was formed, and further heated. The same effect as in the above method could be obtained even when the reaction was carried out with lithium hydroxide.

Using the positive electrode active material prepared above, a battery similar to that of Example 1 was prepared, and the same measurement as that of Example 1 was performed. The results are also shown in (Table 1).

Although the nickel hydroxide utilization rate was slightly lower than that of Example 1 using sodium hydroxide, the nickel hydroxide utilization rate was high and stable even when the treatment amount of nickel hydroxide was increased. . This drop in utilization was due to
Compared to Na _0.6 CoO ₂ considered to be due electric resistance of LiCoO ₂ is large.

After the high temperature overdischarge, the nickel hydroxide utilization at the time of 1C discharge also showed a high value.

Example 3 An aqueous solution of cobalt sulfate was mixed with an aqueous solution of hydrogen peroxide to prepare a mixed solution of cobalt salts.

As a first step, nickel hydroxide is dispersed and mixed in an aqueous solution in which ammonium hydrogen carbonate is dissolved, and the above-mentioned cobalt salt mixed solution is gradually dropped and mixed into this solution with sufficient stirring to obtain a cobalt complex and water. A mixed solution of nickel oxide powder was used. In this step, a number of water-soluble cobalt complexes were produced, but the complex compounds could not be identified.

In the second step, the mixed aqueous solution of the cobalt complex and the nickel hydroxide powder was heated and stirred at 90 ° C. for 1 hour to form a cobalt compound layer on the surface of the nickel hydroxide particles.

In the third step, the nickel hydroxide powder on which the above-mentioned cobalt compound layer was formed was recovered, put into a 10% by weight aqueous solution of lithium hydroxide, heated and stirred at 100 ° C. for 1 hour, washed with water and dried. Thus, a positive electrode active material was prepared.

The influence of the treatment amount was examined by setting the weight of nickel hydroxide to 100 g, 1 kg, and 10 kg by the above-mentioned preparation method.

In the third step, cobalt oxyhydroxide is converted to LiC
It is changed to oO ₂ cobalt composite oxide. Although the mixed nickel hydroxide is slightly oxidized in this step, almost no higher-order oxidized compound such as cobalt is formed similarly to Example 1, and the result of X-ray analysis shows the diffraction pattern of β-type nickel hydroxide. showed that.

In the second step, the lithium hydroxide aqueous solution was gradually added to the aqueous solution mixed in the first step while stirring without recovering the nickel hydroxide powder on which the cobalt compound layer was formed, and further heated. The same effect as in the above method could be obtained even when the reaction was carried out with lithium hydroxide.

Using the positive electrode active material prepared as described above, a battery similar to that of Example 1 was prepared. The results of the same measurements as in Example 1 are shown in (Table 1).

The same results as in Example 2 can be obtained.
Even when the treatment amount of nickel hydroxide was large, the nickel hydroxide utilization rate was high and stable.

After the high-temperature overdischarge, the nickel hydroxide utilization at the time of 1C discharge also showed a high value.

Example 4 10 kg of nickel hydroxide powder
Was used, and cobalt hydroxide powder 10 was mixed with nickel hydroxide powder weight 100, and 1.5 liter of a 40% by weight aqueous sodium hydroxide solution was mixed with the mixed powder.

Next, a heat treatment was performed at 110 ° C. for 1 hour through air mixed with carbon dioxide gas while mixing. After the treatment, the product was washed with water and dried to prepare a positive electrode active material.

A positive electrode active material was prepared by changing the mixing ratio of air and carbon dioxide gas during the heat treatment, and the effect was examined.

Using the positive electrode active material thus prepared, a test battery similar to that of Example 1 was prepared, and the same measurement as in Example 1 was performed. The result is shown in FIG. The concentration of carbon dioxide in the air was 0.03%. By increasing the concentration of carbon dioxide during the nickel hydroxide treatment, it is possible to increase the utilization rate of nickel hydroxide during 0.2C discharge and 1C discharge, and to increase nickel hydroxide during 1C discharge after high-temperature overdischarge. The utilization rate could be improved. This is probably because the addition of carbon dioxide produced a water-soluble cobalt complex as an intermediate product.

However, as is apparent from FIG. 2, when the carbon dioxide concentration was higher than 5% by volume, the nickel hydroxide utilization decreased. This is considered to be because sodium hydroxide and carbon dioxide reacted, and the effect of sodium hydroxide treatment, that is, the reactivity with cobalt hydroxide was reduced.

Thus, the concentration of carbon dioxide is 0.1 to
10% by volume is an appropriate amount. In the above embodiments, the nickel-hydrogen storage battery using the hydrogen storage alloy as the negative electrode has been described. However, the same effect can be obtained in an alkaline storage battery using cadmium or zinc as the negative electrode.

[0088]

According to the present invention, it is possible to obtain a positive electrode active material which is excellent in the utilization rate of nickel hydroxide and the discharge characteristics under a large current and has stable characteristics.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a cylindrical battery according to the present invention.

FIG. 2 is a diagram showing the relationship between the concentration of carbon dioxide in the processing gas for the positive electrode active material and the utilization rate of nickel hydroxide

[Explanation of symbols]

 Reference Signs List 1 positive electrode plate 2 negative electrode plate 3 separator 4 battery case 5 sealing plate 6 positive electrode terminal cap 7 safety valve 8 insulating gasket 9 positive electrode lead body

Claims (10)

[Claims] 1. A structure comprising a positive electrode, a negative electrode, and an alkaline electrolyte.
The alkaline storage battery is formed, and the positive electrode is a nickel hydroxide
It has an active material mainly composed of Kel, and the particle surface of the active material is
Coated with a cobalt composite oxide, said composite oxide
Is represented by the general formula [Co (NH_Three)₆] CO_Three, And [Co
(NH_Three)₆]_Two(CO_Three)_ThreeCompound represented by (hexa
(Mn cobalt carbonate) as a starting material.
General formula M _XCoO_Two(X is 0 <x ≦ 1, M is Li, N
a) at least one element of K)
Is an alkaline storage battery. 2. Nickel hydroxide is added to an aqueous solution of a compound represented by the general formulas [Co (NH ₃ ) ₆ ] CO ₃ and [Co (NH ₃ ) ₆ ] ₂ (CO ₃ ) ₃ (hexamminecobalt carbonate). A step of adding and mixing the main powder, a step of heating and stirring the mixed aqueous solution at 70 ° C. or more to form a coating layer made of a cobalt compound on the surface of the powder mainly composed of nickel hydroxide, and 90-150 with alkali
Step of synthesizing a coating layer of a cobalt composite oxide represented by the general formula M _x CoO ₂ (x is 0 <x ≦ 1, M is at least one element of Li, Na, and K) by heating to ° C. A method for producing a positive electrode for an alkaline storage battery, comprising: 3. An alkaline storage battery comprising a positive electrode, a negative electrode, and an alkaline electrolyte, wherein the positive electrode comprises an active material mainly composed of nickel hydroxide, and the surface of the active material particles is a cobalt composite oxide. And the composite oxide is represented by the general formula M ₃ [Co (CO ₃ ) ₃ ] (M is Li, Na,
K, at least a compound represented by one) (commonly obtained by combining tricarbocyanine isocyanatomethyl cobalt salt) as the starting active material formula M _X CoO ₂ (x is 0 <x ≦ 1, M of the L
or at least one element of i, Na and K). 4. The general formula M ₃ [Co (CO ₃ ) ₃ ] (M is L
dissolving a compound represented by at least one element selected from i, Na, and K) in an aqueous alkali hydrogen carbonate solution, adding a powder mainly composed of nickel hydroxide thereto, and mixing;
A step of heating and stirring the mixed aqueous solution to 60 ° C. or higher to form a coating layer made of a cobalt compound on the surface of the powder mainly composed of nickel hydroxide;
Was heated to 0 to 150 ° C. general formula M _X CoO ₂ (x is 0 <x
≦ 1, M is at least one element selected from the group consisting of Li, Na, and K) and a step of synthesizing a cobalt composite oxide coating layer represented by the following formula: 5. The general formula M ₃ [Co (CO ₃ ) ₃ ] (M is L
dissolving a compound represented by at least one element selected from i, Na, and K) in an aqueous alkali hydrogen carbonate solution, adding a powder mainly composed of nickel hydroxide thereto, and mixing;
An alkali hydroxide is further added to this mixed solution,
It was heated to 0.99 ° C., the general formula M _X CoO ₂ (x is 0 <x ≦
1. a method of producing a positive electrode for an alkaline storage battery, the method comprising: synthesizing a cobalt composite oxide coating layer represented by the following formula: 6. A mixture of a cobalt salt and an oxidizing agent in an aqueous solution of alkali hydrogen carbonate or alkali carbonate (alkali is at least one of Li, Na, K and ammonia) in which a powder mainly composed of nickel hydroxide is dispersed or mixed. Mixing the aqueous solution, heating and stirring the mixed aqueous solution at 60 ° C. or higher to form a coating layer made of a cobalt compound on the surface of the powder mainly composed of nickel hydroxide, formula M _X CoO ₂ (x is heated to 90 to 150 ° C. with alkali oxide is 0 <x ≦ 1, M is Li, N
a step of synthesizing a cobalt composite oxide coating layer represented by at least one of a and K). 7. A mixture of a cobalt salt and an oxidizing agent in an aqueous solution of alkali hydrogen carbonate or alkali carbonate (alkali is at least one of Li, Na, K and ammonia) in which a powder mainly composed of nickel hydroxide is dispersed or mixed. and mixing the aqueous solution, by adding an alkali hydroxide to the aqueous mixture was heated to 90 to 150 ° C., the general formula M _X CoO ₂ (x
Is a step of synthesizing a cobalt composite oxide coating layer represented by the following formula: 0 <x ≦ 1, M is at least one element of Li, Na, and K). 8. A powder mainly composed of nickel hydroxide and a cobalt hydroxide powder or a cobalt oxide powder are heated in the presence of alkali hydroxide, carbon dioxide, an oxidizing agent and water to obtain a compound of the general formula M _X CoO ₂ (x: 0 <x ≦ 1, M is at least one element selected from the group consisting of Li, Na, and K). 9. A cobalt composite oxide powder represented by the general formula: M _X CoO ₂ (x is 0 <x ≦ 1, M is at least one element of Li, Na and K) is mainly nickel hydroxide. The method for producing a positive electrode for an alkaline storage battery according to claim 8, wherein the powder surface is coated. 10. The addition amount of the cobalt composite oxide is 2 to nickel hydroxide which is a positive electrode active material for an alkaline storage battery.
The alkaline storage battery according to claim 1, wherein the content of the alkaline storage battery is about 30% by weight.