JP3454606B2 - Method for producing positive electrode active material for alkaline storage battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material for an alkaline storage battery containing a nickel hydroxide active material as a main component.

[0002]

2. Description of the Related Art In recent years, word processors, mobile phones, personal computers,
Portable electronic devices such as video cameras are
Increasingly smaller and lighter. Further, as for batteries used in these electronic devices, higher performance batteries are required in order to further improve convenience.

Conventionally, as a positive electrode used in an alkaline storage battery, a substrate obtained by applying a slurry containing nickel powder as a main component to a punching metal or the like and then sintering the substrate is impregnated with an active material. So-called sintered nickel positive electrodes are known. However, the electrode of this system is weak in strength when the substrate has high porosity, and nickel powder comes off, so that the practical limit of the porosity of the substrate is 80%. Since a core body such as punching metal is required, the packing density of the active material is small, which is disadvantageous in achieving high energy density.

Further, the pores of the sintered substrate are as small as 10 μm or less, and the method of filling the active material has a drawback that it is limited to the solution impregnation method and the electrodeposition impregnation method which require complicated steps.

As an attempt to improve these drawbacks, for example, a non-sintering type in which a nickel hydroxide active material powder is directly filled with a binder in a metallic porous body such as nickel foam having a porosity of about 95% and having no core body Nickel positive electrodes have been proposed.

As a means for improving the utilization rate of nickel hydroxide, which is one of the active materials for such a non-sintered nickel positive electrode, a method of coating the surface of nickel hydroxide particles with cobalt hydroxide or the like has been proposed. There is. As such a coating method, in Japanese Patent Laid-Open No. 6-187984, a part or all of the surface of nickel hydroxide mother particles, which is a main constituent material of the positive electrode active material, is treated with a metal by a mechanochemical reaction.
It is disclosed that a coating treatment with a child particle material made of at least one of a metal oxide and carbon is performed.

When a nickel hydroxide active material whose surface is coated with cobalt hydroxide is used as the positive electrode of a sealed alkaline storage battery, the cobalt hydroxide is oxidized at the time of the first charge and becomes highly conductive cobalt oxyhydroxide. Become.

However, since the state of cobalt hydroxide having low conductivity is present at the start of charging, the current density distribution becomes uneven in the case of a flat electrode, and the oxidation reaction from cobalt hydroxide on the surface to cobalt oxyhydroxide occurs. Since the (higher order) does not proceed uniformly, the function of the surface cobalt was not sufficiently exerted, and the utilization rate improved to some extent as compared with the uncoated product, but it was not sufficient. Even when metallic cobalt having high conductivity is used as a starting material, a similar phenomenon occurs when metallic cobalt is converted into cobalt oxyhydroxide by passing through cobalt hydroxide. Furthermore, during over-discharging, cobalt in cobalt hydroxide that is not highly ordered moves and diffuses easily into nickel hydroxide, which is the base particle, so the surface cobalt concentration decreases, and as the utilization rate decreases, over-discharging There was a problem that the charge / discharge cycle characteristics afterwards deteriorated.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a method for producing a positive electrode active material for an alkaline storage battery, which can improve charge / discharge cycle characteristics after overdischarge. It is an object of the present invention.

[0010]

The method for producing a positive electrode active material for an alkaline storage battery according to the present invention comprises nickel hydroxide as a main component.
The particles to be heated and the particles containing at least cobalt at high temperature.
Mechanically wet mix with Lucari aqueous solution
Of particles containing nickel hydroxide as a main component by a reaction
Particles containing cobalt on at least part of the surface
It is characterized in that it is physically covered with.

[0011]

The mechanochemical reaction in the present invention refers to a reaction in which mechanical energy applied to a substance by means such as compression, shearing, rubbing or stretching causes a chemical change of the substance.

[0013]

By coating a part or all of the surface of the nickel hydroxide particles, which is the positive electrode material, with the particles containing at least cobalt by the mechanochemical reaction, the binding force between the nickel hydroxide particles and the particles containing at least cobalt is increased. Become extremely strong.

If the cobalt compound coated on the surface of the nickel hydroxide particles is heated in the presence of an aqueous alkaline solution before being incorporated into the battery, the cobalt compound on the surface is efficiently converted into highly conductive cobalt oxyhydroxide. As a result, the utilization rate is improved.

Further, there is almost no unordered cobalt hydroxide, and the enhanced cobalt oxyhydroxide is unlikely to change to cobalt hydroxide during discharge, so that cobalt is less likely to diffuse into nickel hydroxide. Therefore, it is possible to prevent deterioration of charge-discharge cycle characteristics after over-discharge.

Further, when a zinc compound, a cadmium compound and a nickel compound are present together with the cobalt compound in the surface coating layer, these are partially solid-dissolved at the boundary portion in contact with the cobalt compound during heating in the presence of an alkaline aqueous solution. However, since cobalt added to the surface of the active material is less likely to diffuse into nickel hydroxide, it is possible to effectively prevent deterioration of charge / discharge cycle characteristics after overdischarge.

[0017]

Example ( Reference Example 1) [Preparation of nickel hydroxide active material] Mixing nickel sulfate, zinc sulfate, and cobalt sulfate in a molar ratio of 1 nickel to 0.02 zinc and 0.05 cobalt. While stirring the aqueous solution, gradually add ammonia water and an aqueous sodium hydroxide solution to adjust the pH during the reaction.
The amount of ammonia water and the aqueous sodium hydroxide solution added was controlled so that the ratio became 11, and nickel hydroxide was deposited. Next, this precipitate was collected, washed with water and dried to prepare nickel hydroxide particles.

Next, in a stainless steel pot having an internal volume of 1 liter, 95 parts by weight of the nickel hydroxide particles and 5 parts by weight of cobalt particles, or 5 parts by weight of cobalt hydroxide particles were added as active material particles of 1 kg. Then, 1 kg of stainless steel balls were charged, the inside was replaced with an inert gas, and then sealed. By rotating this pot at a rotation speed of 1500 rpm for 1 hour, a nickel hydroxide active material A1 having a surface coated with cobalt particles or a nickel hydroxide active material A2 having a surface coated with cobalt hydroxide particles was produced. [Alkaline heat treatment] Next, a 25 wt% sodium hydroxide aqueous solution was dropped onto the active materials A1 and A2 to obtain nickel active material particles impregnated with the sodium hydroxide aqueous solution. Heated for hours. Then washed with water this active material, followed by drying to produce a reference example active material B1, B2. [Preparation of Electrode] 100 parts by weight of each active material prepared as described above and 50 parts by weight of a 0.2 wt% aqueous solution of hydroxypropyl cellulose were mixed to prepare an active material slurry. This active material slurry was filled in foamed nickel having a thickness of about 1.6 mm and a porosity of 95%, dried and rolled to produce a nickel positive electrode having a thickness of about 0.6 mm. [Preparation of test cell] Preparation of open-type simple cell The positive electrode and a known sintered cadmium electrode having a sufficiently larger capacity than the positive electrode were sandwiched between acrylic plates via a separator made of nonwoven fabric, and pressed. About 25
An open type simple cell was prepared by immersing in an aqueous solution of potassium hydroxide of weight%. Production of Sealed Battery A commercially available metal element was weighed so as to be MmNi3.4Co0.8Al0.2Mn0.6 and melted in a high frequency melting furnace, and then this molten metal was poured into a mold to produce a hydrogen storage alloy ingot. Next, this ingot was roughly crushed in advance, and then mechanically crushed in an inert gas atmosphere until the average particle size became about 150 μm.

Polyethylene oxide as a binder and an appropriate amount of water were added to this alloy powder and mixed to form a slurry. This slurry was applied on both sides of a collector made of punching metal, dried, and pressed to prepare a negative electrode having a thickness of about 0.4 mm.

The positive electrode and the negative electrode made of a hydrogen storage alloy were wound around a separator made of a non-woven fabric to prepare an electrode group. This electrode group was inserted into a battery can, 2.0 g of a KOH aqueous solution of 7 to 8.5 N was injected, and the opening was immediately closed to produce a nickel-hydrogen storage battery having a nominal capacity of 1200 mAh. [Battery test conditions] Measurement of discharge capacity per unit amount of active material The open type simple cell prepared as described above was used to measure 120
The battery was charged at a current value of mA for 24 hours, discharged at a current value of 400 mA until the battery voltage reached 1.0 V, and the discharge capacity was measured. Then, the discharge capacity per unit active material amount is obtained,
The results are shown in Table 1 below. Measurement of over-discharge characteristics Using the sealed battery prepared as described above, 120 mA
The battery was activated by repeating the cycle of charging for 16 hours at a current value of 16 hours and then discharging at a current value of 240 mA until 1.0 V was reached.

Charging is performed at a current value of 1200 mA, and when the voltage drop amount (-ΔV) after the charging voltage reaches the maximum value reaches 10 mV, the charging is stopped and the battery is stopped for 1 hour.

Discharge is performed at a current value of 1200 mA, the discharge is terminated when the battery voltage reaches 1.0 V, and the discharge capacity X is measured.

After the end of the discharge, the discharge is further forced at 60 mA for 16 hours.

The above steps 1 to 6 are repeated 6 times.

At this time, the discharge capacity X1 in the first cycle
To the discharge capacity X6 in the final cycle (X6 / X
1) was obtained, and this value was used as the overdischarge characteristic, and the results are shown in Table 1 below.

The above measurement results are shown as an index with the value of the active material A1 as 100.

[0027]

[Table 1]

As is clear from Table 1, the active materials B1 and B2 of the reference example have a higher unit active material capacity than the comparative active materials A1 and A2 which are not subjected to the alkali heat treatment, and in particular, the overdischarge characteristics are remarkable. It turns out that it is excellent. The alkali heat treatment further improved the electric capacity and the over-discharge characteristics because the alkali heat treatment changed the compound to a higher-order cobalt compound having a valence of more than 2 and excellent in conductivity, and almost no cobalt hydroxide was not formed. It is considered that this is because the cobalt added to the surface of the active material is not easily diffused into the nickel hydroxide particles, and the effect of adding the cobalt is exhibited even after overdischarge.

Reference Example 2 In Reference Example 2, the surface coating substance was examined.

The active material used here was prepared according to [Preparation of active material] in Reference Example 1 above. That is, Table 2 below
Except that a mixing ratio shown in was prepared in Reference Example active material B3~B8 in the same manner as in Reference Example 1.

[0031]

[Table 2]

Then, an open simple cell and a sealed battery were prepared in the same manner as in Reference Example 1, and the unit active material capacity and overdischarge characteristics were measured under the same conditions as the test conditions of the battery. The results are shown in Table 3.

The above measurement results are shown as an index with the value of the active material A1 as 100.

[0034]

[Table 3]

As is clear from Table 3, the surface coating substance is a cobalt compound and at least one selected from the group of cadmium compounds, zinc compounds and nickel compounds.
It can be seen that if the component system is subjected to alkali heat treatment, the over-discharge characteristics are dramatically improved.

This is because a zinc compound, a cadmium compound or a nickel compound was simultaneously present in the surface coating layer together with the cobalt compound, and these were partially solid-dissolved at the boundary portion in contact with the cobalt compound during the alkali heat treatment, It is considered that this is because the cobalt added to the surface of the active material is less likely to diffuse into nickel hydroxide, and therefore the effect of improving the conductivity of the surface of the active material by cobalt oxyhydroxide is sufficiently exerted even after overdischarge.

Example In this example, a manufacturing method different from that of Reference Example 1 was examined.

[0038] each active material were the same active material composition as the active material B1~B8 of Reference Example 1 and Reference Example 2.

As a concrete manufacturing method, 1 kg of particles and 1 kg of stainless steel balls were put into a stainless steel pot having an internal volume of 1 liter at the same ratio as in Reference Examples 1 and 2, and the particles were wet to such an extent. After adding a 25 wt% sodium hydroxide aqueous solution, the mixture was sealed. Although the inside is air, a part or all of it may be replaced with oxygen gas. By rotating this pot at a rotation speed of 1500 rpm for 2 hours at 80 ° C., nickel hydroxide active materials C1 to C8 of the present invention were produced, the surface of which was coated with particles containing at least cobalt and heat-treated in the presence of an alkaline aqueous solution. .

Next, an open simple cell and a sealed battery were prepared in the same manner as in Reference Example 1, and the unit active material capacity and overdischarge characteristics were measured under the same conditions as the test conditions of the battery, The results are shown in Table 4.

The above measurement results are shown as an index with the value of the active material A1 being 100.

[0042]

[Table 4]

From Table 4, it is clear that the same effect as in Reference Example 1 can be obtained.

Reference Example 3 In Reference Example 3 , the weight ratio of the cobalt compound used for coating the surface of the active material to the weight of all particles and the battery characteristics were examined.

Each active material was prepared according to [Preparation of active material] in Reference Example 1 above. That is, the weight ratio of cobalt hydroxide to the weight of all particles is changed by adjusting the amount of cobalt hydroxide used for coating the surface of the active material.

The specific weight ratio of each cobalt hydroxide is 0% by weight, 0.1% by weight, 0.5% by weight, 1.0
% By weight, 3.0% by weight, 5.0% by weight, 10.0% by weight, 15.0% by weight, 20.0% by weight, 25.0% by weight
And active materials D1, D2, D3, D4, D5,
Called D6, D7, D8, D9, D10.

Next, an open type simple cell was prepared in the same manner as in Reference Example 1, and the unit active material capacity was measured under the same conditions as the test conditions of the battery, and the results are shown in Table 5.

The weight ratio of cobalt hydroxide is 10.0.
It is shown as an index with the weight%, that is, the value of D7 as 100.

[0049]

[Table 5]

As is apparent from Table 5, when the cobalt hydroxide content is less than 1% by weight and when the cobalt hydroxide content is 1%,
When it exceeded 5% by weight, the capacity of the active material was greatly reduced.

It is considered that the reason is that if the amount is less than 1% by weight, the amount of the cobalt compound is insufficient and a good conductive network cannot be formed. On the other hand, when it exceeds 15% by weight, it is considered that the negative effect (decrease in energy density) due to the relative decrease in the nickel hydroxide content in the active material particles exceeds the conductivity improving effect. .

From these results, it is understood that the amount of cobalt compound is preferably in the range of 1 to 15% by weight based on all particles.

It was confirmed that similar results were obtained in the manufacturing method of the example .

Reference Example 4 In Reference Example 4 , the heating temperature during the alkaline heat treatment and the battery characteristics were examined. Each active material was prepared according to [Preparation of Active Material] in Reference Example 1. That is, an active material having the same active material composition as the active material B2 of Reference Example 1 was prepared by changing only the heating temperature.

Specific heating temperatures during the alkali heat treatment are 30 ° C., 40 ° C., 60 ° C., 80 ° C., 100 ° C., 1
20 ° C. and the active materials E1, E2, E3, E4,
Called E5 and E6.

Next, an open type simple cell was prepared in the same manner as in Reference Example 1, and the unit active material capacity was measured under the same conditions as the battery test conditions, and the results are shown in Table 6.

The heating temperature during the alkali heat treatment is 80
It is indicated by an index with the value of ° C, that is, E4 being 100.

[0058]

[Table 6]

As is apparent from Table 6, the heating temperature is 40
If the temperature is lower than 100 ° C. or higher than 100 ° C., the active material capacity is largely decreased. Therefore, it is preferable that the heating temperature in the alkaline heat treatment is in the range of 40 ° C. or higher and 100 ° C. or lower.

Here, good results were obtained at a heating temperature of 40 ° C. to 100 ° C. When the temperature was within this range, the higher order of cobalt proceeded smoothly, and the higher order cobalt compound was obtained. It is probable that the microstructure of the surface coating layer was disturbed by the thermal action during the formation of the, and a coating layer having an appropriate porosity was formed. This is because, when the coating layer has an appropriate pore size, the coating layer does not hinder the contact between the nickel hydroxide particles and the electrolytic solution, so that the electrochemical reaction can be carried out smoothly.

On the other hand, when the heating temperature is lowered, the solubility of cobalt hydroxide in the alkaline solution is lowered, and the thermal action on the coating layer is reduced. On the other hand, it is considered that when the heating temperature exceeds 100 ° C., the thermal action adversely affects the nickel hydroxide particles themselves.

It was confirmed that similar results were obtained in the manufacturing method of the example .

Reference Example 5 In Reference Example 5 , the alkaline concentration and the battery characteristics were examined. Each active material was prepared according to [Preparation of Active Material] in Reference Example 1. That is, an active material having the same active material composition as the active material B2 of Reference Example 1 was prepared by changing only the alkali concentration.

Specific alkali concentrations are 12% by weight, 15% by weight, 25% by weight, 35% by weight, 40% by weight and 45% by weight, respectively, and the active materials G1, G2 and G respectively.
3, G4, G5, G6.

Next, an open type simple cell was prepared in the same manner as in Reference Example 1, the unit active material capacity was measured under the same conditions as the test conditions of the battery, and the results are shown in Table 7.

The alkali concentration is 25% by weight, that is, G3
The value is shown as an index.

[0067]

[Table 7]

As is apparent from Table 7, when the alkali concentration is less than 15% by weight or exceeds 45% by weight, the capacity of the active material is largely decreased. This is because the alkali concentration is 15
When the content is less than 10% by weight, the solubility of cobalt hydroxide in an alkaline solution is lowered, so that the higher order reaction of cobalt hydroxide does not proceed smoothly, while the alkali concentration is 40% or less.
It is considered that when the content exceeds 5% by weight, the solution viscosity remarkably increases, and it becomes difficult for the alkali to permeate into the coating layer, so that the higher order reaction becomes non-uniform.

From the above, the alkali concentration to be added is 15% by weight or more and 40% in the presence of an aqueous alkaline solution.
It is preferable to carry out in the range of not more than wt%.

It was confirmed that similar results were obtained in the manufacturing method of the example .

[0071]

As described above, according to the manufacturing method of the present invention,
Since the diffusion of surface cobalt into the nickel hydroxide particles can be effectively suppressed, the charge / discharge cycle characteristics after overdischarge can be improved, and its industrial value is extremely large.

Continuation of the front page (56) Reference JP-A-6-188794 (JP, A) JP-A-1-281670 (JP, A) JP-A-1-200555 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) H01M 4/00-4/62

Claims (5)

(57) [Claims] 1. Particles containing nickel hydroxide as a main component,
Mechanically wet mixing with particles containing at least cobalt in a high temperature alkaline aqueous solution, and physically or partially covering all or part of the surface of the particles containing nickel hydroxide as a main component with particles containing at least cobalt by a mechanochemical reaction. A method for producing a positive electrode active material for an alkaline storage battery, comprising: 2. A particle material for coating the particles containing nickel hydroxide as a main component together with cobalt, cadmium,
Zinc, method for producing a positive electrode active material for an alkaline storage battery according to claim 1 Symbol mounting, characterized in that it contains more than at least one selected from the group of nickel. Content according to claim 3, wherein the cobalt cathode active method for producing a material for an alkaline storage battery according to claim 1 Symbol mounting, characterized in that all particles is 15 wt% or less 1 wt% or more. 4. A process for producing a positive electrode active material for an alkaline storage battery according to claim 1, wherein the temperature during wet mixing in the presence of an alkaline aqueous solution coexistence is 100 ° C. or less than 40 ° C.. 5. The preparation of the positive electrode active material for an alkaline storage battery according to claim 1, wherein the alkali concentration of the aqueous solution during wet mixing in the presence of an alkaline aqueous solution coexistence is 15% by weight to 40% by weight Method.