JP2003263980A - Pellet for positive electrode of alkali battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a positive electrode pellet for an alkali battery which has less silver content and which is superior in a characteristics of service capacity, conductivity and easiness for storage compared to a conventional silver oxide battery. <P>SOLUTION: The pellet for the positive electrode of the alkali battery which has a crystal of chemical compound consisting of Ag, Bi and O (Oxygen) or a crystal of chemical compound consisting of Ag, Bi, M (M indicates a transition metal) and O, and which is molded with fine particles consisting of a particle wherein the Bi disperses in a whole area of the particle. When a mole ratio of Ag/(Bi+M) or Ag/Bi when M is not contained, this pellet shows the mole ratio of Ag/Bi from 1 to 7, an oxygen content at 5% or more by weight, an electrical conductivity at 1×10<SP>-4</SP>s/cm or more and a molding density at 5 g/cm<SP>3</SP>or more. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode pellet for an alkaline battery.

[0002]

2. Description of the Related Art Conventionally, in clocks, measuring instruments, cameras, etc.
Oxidized as an alkaline battery (commonly called a button battery) to be installed
Silver batteries are widespread. Silver oxide batteries are oxidized as the positive electrode
Silver (Ag ₂O) as the active material, depending on the application
MnO₂, NiOOH, CoOOH, AgNiO₂, AgCoO₂, CaO, Mn
O 2, HgO 2, CdO 2, CdS 2, polytetrafluoroethylene,
Metallic silver, graphite, etc. are added. As the negative electrode active material
Zinc powder, an alkaline solution as an electrolyte, such as hydroxide
With potassium (NaOH) or sodium hydroxide (KOH)
It is generally composed. Silver is an expensive material
However, silver oxide batteries are not suitable for high capacity even when they are small.
It is considered to be an essential positive electrode material, and as a result, most button batteries
It is no exaggeration to say that they are composed of silver oxide batteries.
Yes.

Recently, there is an increasing need for further miniaturization, higher capacity and long-term reliability as a battery for a power source of electronic devices, watches and the like, and there is a demand for higher performance of alkaline batteries.
However, as miniaturization and higher capacity have progressed, the ratio of the positive electrode mixture material in the battery volume has increased, and naturally the cost ratio of the positive electrode body in one battery has increased.

Among the positive electrode bodies, silver oxide occupies the most cost. Therefore, there is a constant demand for reducing the silver content in the positive electrode pellets. At the same time, it is desirable that the conductivity of the positive electrode pellet is as high as possible. However, when silver oxide is used as the positive electrode active material, since the pellet has almost no conductivity as it is, for example, a part of the pellet is reduced to form metallic silver. And a method of adding a conductive agent such as graphite.

[0005]

However, in the method of precipitating a part of silver oxide as metallic silver, metallic silver does not function as an active material, so that even if the problem of internal resistance is solved, the discharge capacity is lowered. Become. Further, when a conductive agent such as graphite is added to reduce the internal resistance, not only graphite does not function as an active material, but also the specific gravity is extremely small, so that it occupies a considerable volume in the positive electrode mixture, Similarly, even if the problem of internal resistance is solved, the proportion of the positive electrode active material decreases, and the discharge capacity of the battery decreases. For this reason, there has been a demand for a positive electrode pellet having a high electric conductivity which does not depend on such a method.

As for long-term reliability, since the life of an actual battery is required to be 3 to 5 years or more, it is necessary for the positive electrode pellet to have little deterioration in battery characteristics due to storage.

Further, since the weighing work and the filling work are indispensable at the time of manufacturing the positive electrode pellets, the positive electrode active material powder which is a constituent material of the pellets is easy to handle, that is, the dust is less generated and the filling property is excellent. It was necessary to use active materials with characteristics.

[0008] Therefore, an object of the present invention is to provide a positive electrode pellet capable of satisfying such requirements.

[0009]

In order to solve such a problem, the present inventors have conducted various tests and studies, but Ag-Bi- (M) -O obtained by a method which should be called a wet oxidation method.
When a pellet for a positive electrode is prepared by using a powder made of a system compound (M represents at least one kind of transition metal, typically manganese, nickel or cobalt), cost, conductivity, battery characteristics, storability, etc. It turns out that various requirements can be met at the same time. More specifically, Ag-Bi- (M) -O obtained by reacting an inorganic acid salt of silver, bismuth, and M, an alkali hydroxide, and an oxidizing agent such as sodium peroxodisulfide in a water solvent. A powder of a system compound is used as the positive electrode active material. This powder is Ag, B
A crystal of a compound consisting of i and O (oxygen), or A
It is composed of particles having a crystal of a compound consisting of g, Bi, M and O and having Bi dispersed throughout the particle.

Therefore _, according to the present invention, Ag, Bi
And a crystal of a compound consisting of O (oxygen), or Ag,
A pellet for a positive electrode of an alkaline battery formed by using a powder made of particles having a compound crystal made of Bi, M (M represents a transition metal) and O and having Bi dispersed throughout the particle. provide. A positive electrode pellet of an alkaline battery formed by using a powder made of such particles is A
The molar ratio of g / (Bi + M) is 1 to 7 (calculated as M = 0 when M is not contained), and the molar ratio of Bi / M is 0.1.
And a composition having an oxygen content of 5% by weight or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A pellet for a positive electrode according to the present invention comprises
A crystal of a compound consisting of Ag, Bi and O, or A
It is characterized in that it is formed by using a powder having particles of a compound having g, Bi, M and O and having Bi dispersed throughout the particle. M is one or more elements selected from the transition elements, and is added for the purpose of keeping the open circuit voltage, which is a battery characteristic, low.
n, Ni or Co are preferred.

The term "molding" as used herein means that the powder is compacted into pellets having a shape suitable for a positive electrode of a battery, and one pellet is usually molded in this manner. For each battery, one pellet is loaded for the positive electrode.

This positive electrode pellet is preferably NO ₃
The content is less than 0.1% by weight, the total content of alkali metals and alkaline earth metals is less than 2% by weight, and C
The O ₃ content is 0.5% by weight or less, whereby a positive electrode pellet with less deterioration of battery characteristics during storage is obtained. The term "storability" as used herein means both the degree of deterioration of the battery characteristics when the positive electrode pellets themselves are stored and the degree of deterioration of the battery characteristics when the positive electrode pellets are incorporated into a battery.

Further, the positive electrode pellets preferably have an electric conductivity of 1 × 10 ^-4 S / cm or more and a density of 5 g.
/ cm ³ or more. Further, this positive electrode pellet may have a Mn content similar to that of a normal silver oxide battery, depending on the application.
O ₂ , NiOOH, CoOOH, AgNiO ₂ , AgCo
It may contain at least one additive selected from the group consisting of O ₂ , CaO, MnO, HgO, CdO, CdS, polytetrafluoroethylene, metallic silver and graphite.

Particles having a crystal of a compound composed of Ag, Bi and O, or having a crystal of a compound composed of Ag, Bi, M and O and having Bi dispersed throughout the particle (A
In order to obtain a powder composed of particles of a g-Bi- (M) -O-based compound), a method of wet-oxidizing a water-soluble salt of Ag, Bi, or M as described below, that is, (1) A step of reacting a salt of silver, bismuth, or a transition metal with an alkali in water to obtain a neutralized starch (hereinafter referred to as a neutralization step) (2) An oxidizing agent is added to the obtained suspension of the neutralized starch. Step of oxidizing the starch (hereinafter referred to as oxidation step) (3) Step of solid-liquid separating the obtained oxidized starch (hereinafter referred to as separation step) (4) Step of washing and drying the separated starch (5) Drying It can be manufactured by going through a process of crushing an object to obtain a powder.

Each step will be described below individually. (1) Neutralization step: Silver nitrate, bismuth, and transition metal salts such as silver nitrate, bismuth nitrate and nickel nitrate can be typically used. A strong alkali (eg, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc.) is used as the alkali. The neutralization treatment includes a method of adding an aqueous solution of silver, bismuth and a salt of a transition metal to an alkaline aqueous solution, a method of mixing an alkaline aqueous solution with an aqueous solution of a salt of silver, bismuth and a transition metal, a method of adding a salt of silver, bismuth and a transition metal. Any method of adding an alkaline aqueous solution to the aqueous solution may be used, but a method of adding an aqueous solution of a salt of silver, bismuth, or a transition metal to the alkaline aqueous solution is particularly effective.
Further, the higher the alkalinity, the easier the reaction proceeds. The reaction temperature is not particularly limited, but is preferably in the range of room temperature to 110 ° C. As for the stirring, it is sufficient that the stirring strength is such that the neutralization reaction proceeds uniformly.

(2) Oxidation step: The oxidation step can be carried out simultaneously with the neutralization step, but it is preferable to carry out the neutralization step and the oxidation step separately. Further, it is preferable to insert a temperature raising step between these steps. As the oxidizing agent, a common oxidizing agent (for example, KMnO ₄ , NaOCl, H ₂ O ₂ , K ₂ S _{2 is used).
O 8, Na 2 S 2 O} 8, ozone, etc.) can be used. In the oxidation treatment, the liquid temperature is 50 ° C or higher, preferably 7
It is desirable to add an oxidizer while stirring at 0 ° C or higher. The liquid temperature is preferably 110 ° C. or lower because the decomposition of the oxidant proceeds as the liquid temperature rises. The amount of the oxidizing agent to be added may be sufficient to increase the valence of silver, bismuth, and the transition metal, and is equal to or more than this valence change, preferably about twice the equivalent.

(3) After the separation step: It is preferable to insert a step of aging the oxidized starch before solid-liquid separation of the suspension of the oxidized starch. This step is a treatment for holding the suspension after the oxidation treatment for about 10 to 120 minutes at that temperature, and is intended to make the oxidized precipitate uniform. After the oxidized precipitate was filtered off from the liquid, it was washed and washed with Ag-Bi- (M)-.
A cake of O-based compound is obtained. It is preferable to wash with pure water. Drying is performed at 50 to 200 ° C. If the temperature exceeds 200 ° C, the produced compound may decompose. The obtained dried product can be crushed into a powder by a crusher.

The thus obtained Ag-Bi-
The main peak group of the X-ray pattern (using a copper target, wavelength = 1.5405 angstrom) of the powder composed of the particles of the (M) -O compound is the X-ray diffraction database (ICD).
D0) does not match any of the compounds of AgO or A
The main peak group of g ₂ O does not appear either. Therefore, the compound as AgO or Ag ₂ O is not substantially present in this powder, or if it is present, it is as an impurity, and the amount of this impurity is the total amount of both AgO and Ag ₂ O. At most 1% by weight or less, preferably 0.5% by weight
Below, the amount is more preferably below the calibration limit in X-ray diffraction. When this powder is molded into a positive electrode pellet, it can have high conductivity, and can be used at a utilization rate close to 100% under high molding density.

Further, in order to improve this powder to one having a property of excellent dustability and excellent flowability and filling property, spray formation is performed on the oxidation product obtained through the above-mentioned oxidation step. The average particle size is 10 using the granulation method or crushing granulation method.
If it is a powder or granular product consisting of particles of μm or more, preferably 50 μm or more, the repose angle is 50 degrees or less and the fluidity is improved, so that a powder or granular product with less dust generation and excellent filling property can be obtained, If the powder product is molded into a positive electrode pellet, its molding workability becomes good. Furthermore, this powder product has a bulk density of 1.0 or more to 6.3 g / cm ³ and a tap density of
It becomes 1.5 to 6.3 g / cm ³ , and as a secondary effect, the formability of pellets can be further improved.

[0021]

Example 1 In the above neutralization step, silver nitrate and bismuth nitrate were weighed so that the molar ratio was Ag / Bi = 3. 10 times the molar amount of both NaOH
The silver nitrate and bismuth nitrate were added to an aqueous solution (1.5 liters) in which was dissolved and stirred to form a neutralized precipitate in the solution. The temperature of the obtained suspension of neutralized starch was raised to 90 ° C., and sodium peroxodisulfide (Na ₂ S ₂ O ₈ ) as an oxidant was added to the total amount of Ag and Bi in a molar ratio with stirring. Was added to the suspension in an amount of 2 times, and subjected to oxidation treatment. After completion of oxidation, after aging by holding at a temperature of 90 ° C. for 30 minutes,
The precipitate was separated by filtration, washed with water and dried at 100 ° C, and the dried product was crushed with a crusher to obtain a powder.

The obtained powder was molded by the following method to prepare a positive electrode pellet, and the discharge capacity thereof was determined.
It was shown to.

[Production Method of Positive Electrode Pellets] As shown in FIG. 1, a steel die 2 having a cylindrical cavity 1 having an inner diameter of 11.3 mm and a height of 30 mm, and an outer diameter of 11.3 mm and a height of 10 mm. The first steel punch 3 and the second steel punch 4 having an outer diameter of 11.3 mm and a height of 40 mm are used. In the molding, as shown in FIG. 2, the first punch 3 is set on the bottom of the cavity 1 of the die 2, and 1.0 g of the powder is loaded in the cavity 1 above the first punch 3. Then, the powder 5 in the cavity 1 is molded by the second punch 4 at a pressure of 4 t / cm ² to obtain a positive electrode pellet. [Battery evaluation method] The positive electrode pellets as a positive electrode,
Zn plate 0.5g as negative electrode, Zn saturated KO as electrolyte
H40% is used, and the separator is cellophane 2
Create an electrode cell. The battery created in this way is
After leaving it in a thermostat at 5 ° C. for 1 hour, it was discharged at a discharge rate of 0.01 C, and the discharge capacity at the end of 1.4 V was obtained.

Example 2 By the same method as in Example 1, silver nitrate, bismuth nitrate, and nickel nitrate were changed by changing the Ag: Bi: Ni molar ratio to the values shown in Table 1. Weigh each dissolved aqueous solution at a temperature of 50 ° C (Ag + Bi + Ni)
A neutralized precipitate was obtained by adding to an aqueous solution (1.5 liters) in which sodium hydroxide was dissolved in a molar ratio of 10 times with respect to the above (1.5 liter) with stirring.
The temperature of the suspension of each neutralized starch was raised to 90 ° C., and sodium peroxodifluide (Na ₂ S ₂ O ₈ ) was used as an oxidizer in a molar ratio twice as much as (Ag + Bi + Ni) Then, the precipitate was filtered, washed with water and dried at 100 ° C., and the dried product was crushed with a crusher to obtain a powder. A positive electrode pellet was prepared from the powder by the method described above, and the discharge capacity was measured. The measured values of discharge capacity are shown in Table 1.

Further, cobalt nitrate or manganese nitrate is used instead of nickel nitrate, and Ag: Bi: Co or Ag: Bi: Mn is used.
Example 1 was repeated except that the compounding ratios of silver nitrate, bismuth nitrate, and cobalt nitrate or manganese nitrate were changed so that the molar ratio of the above became the value of Table 2, and the powder obtained was prepared as described above. Table 2 shows the discharge capacity of the positive electrode pellets.
It was shown to. The discharge capacity of the silver oxide positive electrode pellets measured under the same conditions is 210 mAh / g. Compared with this, Table 1 and Table 2
It can be seen from the results that the discharge capacity is high despite the low Ag content.

[0026]

[Table 1]

[0027]

[Table 2]

Example 3 Except that the mixing ratios of silver nitrate, bismuth nitrate and nickel nitrate used in the neutralization step were changed so that the molar ratio of Ag: Bi: Ni became the value shown in Table 3.
Example 1 was repeated to obtain each Ag-Bi-Ni-O-based powder. A positive electrode pellet was prepared from the powder by the above method, and the conductivity of the pellet was determined by the following method. The results are shown in Table 3.

[Method of Measuring Conductivity] A jig similar to the jig shown in FIG. 1 was used except that the material was different. That is, FIG.
As shown in, a die 7 made of vinyl chloride having a circular cavity 6 with an inner diameter of 11.3 mm and a height of 30 mm, a steel first punch 8 with an outer diameter of 11.3 mm and a height of 10 mm, and an outer diameter of 11.3 mm with a high height. A 40 mm thick steel second punch 9 is used to set the first punch 8 at the bottom of the cavity 6, and then the positive electrode pellet 10 is set on the first punch 8. Then, a pressure of 4 t / cm ² is applied to the pellet 10 by the second punch 9. At that time, aluminum foils 11 and 12 are attached to both end surfaces of the first punch 8 and the second punch 9, respectively.

Next, the height (thickness) under the pressure is measured, and the aluminum foils 11 and 12 attached to both ends of the first punch 8 and the second punch 9 are molded under this pressure. Measure the electrical resistance between them. Then, from the measured thickness, resistance value and cross-sectional area (area calculated from punch diameter) of the green compact, conductivity is calculated by the following equation. The electrical resistance between the aluminum foils 11 and 12 in the absence of the positive electrode pellet is measured as a blank, and the blank value is corrected by subtracting it from each measured value.
Table 3 also shows the conductivity of the silver oxide pellets measured by the same method. It can be seen that the positive electrode pellets obtained in this example showed sufficient conductivity. Conductivity = height (thickness) / (electrical resistance x cross-sectional area)

[0031]

[Table 3]

[Example 4] Except that the compounding ratios of silver nitrate, bismuth nitrate and nickel nitrate used in the neutralization step were changed so that the molar ratio of Ag: Bi: Ni became the value shown in Table 4. Example 1 was repeated to obtain each Ag-Bi-Ni-O-based powder. A positive electrode pellet was prepared from the powder by the method described above, and the result of obtaining the molding density from the weight and size of the pellet is shown in Table 4.

[0033]

[Table 4]

Example 5 In the above-mentioned neutralization step,
An aqueous solution in which silver nitrate, bismuth nitrate and nickel nitrate were weighed and dissolved so that the molar ratios were Ag / (Bi + Ni) = 3 and Bi / Ni = 1, at a liquid temperature of 50 ° C, (Ag + Bi + Ni) Against 1
Zero volume of sodium hydroxide solution (1.5 liters)
Under stirring to give a neutralized precipitate. The temperature of this neutralized starch suspension was raised to 90 ° C., and sodium peroxodisulfide (Na ₂ S ₂ O ₈ ) as an oxidant was added to the theoretical valence change equivalent of 2 to oxidize metal ions in the liquid. A double amount was added to the suspension for oxidation treatment. After completion of the oxidation, aging was carried out by maintaining the temperature at 90 ° C. for 30 minutes, the precipitate was filtered off and washed with pure water until the electric conductivity of the filtrate was 0.4 mS / m.

The obtained cake was dried at 100 ° C. for 12 hours and then pulverized to obtain a powder of Ag-Bi-Ni-O compound, and the positive electrode pellet was prepared by the above method.

A battery was prepared using this positive electrode pellet,
Discharge was started 1 hour after the battery was assembled, and the discharge capacity was determined. Further, in order to evaluate the storability of the battery, the discharge capacity of a battery stored at a temperature of 60 ° C. for 7 days after the battery assembly was determined, and the maintenance ratio of the discharge capacity before and after the storage was determined. The results are shown in Table 5.

Example 6 The electric conductivity of the washing filtrate is 10 mS.
Example 5 was repeated except that the washing was performed until it became / m. Table 5 also shows the evaluation results of the impurity content of the obtained positive electrode pellet and the battery storability.

[Comparative Example 1] The electric conductivity of the washing filtrate is 900 m.
Example 5 was repeated except that the washing was performed until the S / m was reached. Table 5 also shows the evaluation results of the impurity content of the obtained positive electrode pellet and the battery storability.

[0039]

[Table 5]

Example 7 After the completion of oxidation, the temperature was raised to 90 ° C. for 30 hours.
The same treatment as in Example 5 was performed until the aging was carried out for holding for 1 minute. The obtained slurry was separated by filtration, washed with an aqueous solution of NaOH = 5% in an amount four times the volume of the slurry, and then with pure water until the electric conductivity of the washing filtrate reached 20 mS / m. The obtained cake was dried at 100 ° C. for 12 hours and then pulverized to obtain a powder of Ag-Bi-Ni-O compound, and the positive electrode pellet was prepared by the method described above.

A battery was prepared using this positive electrode pellet,
Discharge was started 1 hour after the battery was assembled, and the discharge capacity was determined. Furthermore, in order to evaluate the storability of the positive electrode pellets, the positive electrode pellets were stored in a thermo-hygrostat at a temperature of 60 ° C and a humidity of 80% for 30 days.
The discharge capacity was similarly determined for those left for a day, and the capacity retention rate was determined from the discharge capacities of the two as described above. The results are shown in Table 6.

Example 8 Example 7 was repeated except that a 5% KOH aqueous solution was used as the cleaning solution. Table 6 shows the results of the impurity content and the pellet storability of the obtained positive electrode pellets.

Example 9 After washing with 5% NaOH aqueous solution,
When washing with pure water, the electric conductivity of the washing filtrate is 0.
Example 7 was repeated except that the washing was carried out to 5 S / m. Table 6 shows the results of the impurity content and the pellet storability of the obtained positive electrode pellets.

Comparative Example 2 Example 7 was repeated except that the washing was carried out with a 5% NaOH aqueous solution and the washing with pure water was omitted. Table 6 shows the results of the impurity content and the pellet storability of the obtained positive electrode pellets.

[Comparative Example 3] Example 8 was repeated except that washing with a 5% KOH aqueous solution was performed and washing with pure water was omitted. Table 6 shows the results of the impurity content and the pellet storability of the obtained positive electrode pellets.

[0046]

[Table 6]

From the results shown in Table 6, it can be seen that the storage performance of the pellets deteriorates when the amount of impurities of strong alkali such as Na and K increases. Therefore, the total content of these strong alkali metals must be at least 2% by weight or less.

Example 10 Example 6 was repeated except that sodium hydroxide after filtering off sodium carbonate was used as the sodium hydroxide aqueous solution used in the neutralization step.
Here, the sodium hydroxide after the sodium carbonate is filtered is the sodium hydroxide aqueous solution after the sodium carbonate produced by absorbing the carbonic acid in the atmosphere during the storage of sodium hydroxide is filtered off as a white precipitate. is there.

The CO ₃ content in the obtained positive electrode pellets was measured, and a battery was prepared using this positive electrode pellet, and the open circuit voltage was measured 1 hour after the battery was assembled. The results are shown in Table 7.

Example 11 Example 10 was repeated except that the neutralization step and the oxidation step were carried out under a CO ₂ -free air atmosphere, and the drying step was carried out in vacuum. The CO ₃ content in the obtained positive electrode pellets was measured, a battery was prepared using the positive electrode pellets, and the open circuit voltage after 1 hour of battery assembly was measured. The results are shown in Table 7.

Comparative Example 4 As an alkaline aqueous solution used in the neutralization step, 9 times the molar amount of sodium hydroxide and 1 times the molar amount of sodium carbonate were dissolved with respect to (Ag + Bi + Ni). Example 6 was repeated except that the prepared aqueous solution (1.5 liters) was used. The CO ₃ content in the obtained positive electrode pellets was measured, and a battery was prepared using this powder,
The open circuit voltage was measured 1 hour after the battery was assembled. The results are shown in Table 7.

[0052]

[Table 7]

From the results of Table 7, CO ₃ in the positive electrode pellets
It can be seen that the higher the content, the higher the open circuit voltage of the battery. If this open circuit voltage exceeds 1.65 V, gas generation may occur due to decomposition of the electrolytic solution. Therefore, the amount of CO ₃ in the positive electrode pellet needs to be 0.5% by weight or less.

Example 12 In the above-mentioned neutralization step, the molar ratio Ag / (Bi + Ni) = 3, the molar ratio Bi / Ni = 1.
Aqueous solution in which silver nitrate, bismuth nitrate and nickel nitrate are weighed and dissolved so that the temperature becomes 50 ° C (Ag + Bi + N
A 10-fold amount of sodium hydroxide aqueous solution (1.5 liter) with respect to i) was added with stirring to obtain a neutralized precipitate. The temperature of this neutralized starch suspension was raised to 90 ° C., and sodium peroxodisulfide (Na ₂ S ₂ O ₈ ) was added as an oxidant in an amount twice the valence change to oxidize the suspension. Processed. After completion of the oxidation, aging was carried out by maintaining the temperature at 90 ° C. for 30 minutes, the precipitate was filtered off, washed with water and dried at 100 ° C., and the dried product was crushed with a crusher to obtain a powder. . This powder is called [intermediate powder].

A sample for measurement was sampled from the obtained intermediate powder, and its bulk density, tap density, angle of repose, particle size and specific surface area were measured, and the results are shown in Table 8. The fluidity, the degree of dust generation, and the packing property of this intermediate powder were evaluated as follows, and the results are also shown in Table 8.

[Measurement of bulk density]: diameter 15 mm, height 160 mm
The test tube was filled with the powder, and it was determined from the measured values of the filling weight and the filling volume. [Measurement of tap density]: The same test tube used for measurement of bulk density was filled with powder, and the filling weight and the filled powder were 100%.
It was determined from the measured value of the filling volume after tapping 0 times. [Evaluation of flowability]: Good flowability (○) if the angle of repose is 40 degrees or less, acceptable (△) if the repose angle is more than 40 degrees and less than 50 degrees,
A rating of 50 degrees or more was judged as unacceptable (x) and a three-level evaluation was performed. [Measurement of angle of repose]: It is a funnel for chemical experiments and has a caliber of 60.
mm, nozzle length 65 mm, nozzle inner diameter 6 mm, fix the funnel at a position where the tip of the nozzle is 75 mm above the horizontal base,
100 g of the powder is put into the hopper of the funnel, and the angle from the horizontal of the deposit is measured when all of them are conical on the horizontal table.

[Measurement of particle size]: By a laser diffraction method (particle size measuring device manufactured by Shimadzu Corporation). [Measurement of specific surface area]: BET method (manufactured by Kantachrome Co., Ltd.) was used. [Evaluation of dust generation]: 25 powder in a 100 cc transparent plastic container
Add g, let it infiltrate 10 times, and visually observe the particles floating in the upper part of the container when left standing for 10 seconds.Good (○) if no suspended matter is observed, and those that become cloudy with suspended matter It was rated as bad (×), and some particles were found to float, but those that were not noticeable were evaluated as acceptable (Δ), and three-level evaluation was performed. [Evaluation of packing property]: Good packing property for bulk density of 2.0 g / cm ³ or more (○), exceeding 1.0 g / cm ³ to 2.0 g / c
Those having a packing capacity of less than m ³ were evaluated as having a good packing property (Δ), and those having a packing density of 1.0 g / cm ³ or less were evaluated as having a poor packing property (x), and three-level evaluation was performed.

As can be seen from the results in Table 8, the fluidity of the intermediate powder and the evaluation of dust generation were not always good.

Next, the intermediate powder was heated to a hot air temperature of 200 ° C. using a spray dryer FOC-16 manufactured by Okawara Koki Co., Ltd.
Spray granulation was performed. The obtained granulated product is called [granulated powder]. Electron micrographs (SEM images) of the granulated powder showed that most of them consisted of spherical particles of about 65 μm. A sample for measurement was sampled from the granulated powder, and its bulk density, tap density, angle of repose, particle size and specific surface area were measured, and the fluidity of the granulated powder, the degree of dust generation, and the packing property were evaluated. The results are also shown in Table 8. As can be seen from the results in Table 8, the granulated powder had a high bulk density and a low angle of repose, resulting in good fluidity and no generation of dust.

Example 13 Example until an intermediate powder was obtained
Repeated 12 times. The obtained intermediate powder was compacted using a roller compactor of WP160 manufactured by Turbo Industry Co., Ltd., and this molded product was manufactured by Nippon Granulator Co., Ltd. GRN-
It was crushed using 1531 to obtain granulated powder. The molding pressure of the roller compactor was 1.0 t / cm. Also, crushing with a granulator is performed in three stages, the groove pitch of the first stage of the roll is 2 mm (roll clearance 0.35 mm), and the groove pitch of the second stage of the roll is 1.2 mm (roll clearance 0.11
mm) and the groove pitch of the third stage of the roll was 0.6 mm (roll clearance 0.11 mm).

A sample for measurement was sampled from this granulated powder, and the bulk density, tap density, angle of repose, particle size and specific surface area were measured, and the fluidity of the granulated powder, the degree of dust generation, and the packing property were evaluated. went. The results are also shown in Table 8.

Further, the granulated powder was sieved with a sieve of 50 μm to remove particles of 50 μm or less. Sampling a sample for measurement from the obtained powder on the sieve (referred to as sized powder 1),
The bulk density, tap density, angle of repose, particle size and specific surface area were measured, and the fluidity of the sized powder, the degree of dust generation, and the packing property were evaluated. The results are also shown in Table 8.

Next, the granulated powder was sieved to remove particles having a size of 100 μm or less using a sieve having a mesh size of 100 μm. A sample for measurement is sampled from the obtained powder on the sieve (referred to as sized powder 2), and its bulk density, tap density, angle of repose, particle size and specific surface area are measured, and the fluidity of the sized powder and dust are measured. Degree of occurrence,
The packing property was evaluated. The results are also shown in Table 8.

As can be seen from the results in Table 8, the sized powder has a higher bulk density and tap density, a lower specific surface area, and has good evaluation of fluidity, dust generation and packing property. Was given.

[Comparative Example 5] In the neutralization step described above,
Ag / (Bi + Ni) molar ratio = 3, Bi / Ni molar ratio = 1.0
An aqueous solution in which silver nitrate, bismuth nitrate and nickel nitrate are weighed and dissolved so that the temperature becomes 50 ° C and (Ag + Bi +
An aqueous solution of sodium hydroxide 10 times the amount of Ni) (1.5
Liter) under stirring to give a neutralized precipitate. The temperature of this neutralized starch suspension was raised to 90 ° C., and sodium peroxodisulfide (Na ₂ S ₂ O ₈ ) was added as an oxidant in an amount twice the valence change to oxidize the suspension. Processed. After completion of the oxidation, aging was carried out by maintaining the temperature at 90 ° C. for 30 minutes, the precipitate was filtered off, washed with water and dried at 100 ° C., and the dried product was crushed with a crusher to obtain a powder. .

A sample for measurement was sampled from this powder, and its bulk density, tap density, angle of repose, particle size and specific surface area were measured, and the fluidity of the sized powder, the degree of dust generation,
The packing property was evaluated. The results are also shown in Table 8.

[0067]

[Table 8]

[0068]

As described above, according to the present invention, by using the powder of the Ag-Bi- (M) -O type compound synthesized by the wet oxidation method, the discharge can be performed even if the silver content is small. Provided is a positive electrode pellet for an alkaline battery, which has excellent capacity, conductivity, and storage characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing a dimensional shape of a jig used for measuring a molding density.

FIG. 2 is a schematic cross-sectional view showing a state in which a molding density is measured using the jig shown in FIG.

FIG. 3 is a schematic cross-sectional view showing a state in which the conductivity of a positive electrode pellet is measured.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshikazu Omoto             1-8-2 Marunouchi, Chiyoda-ku, Tokyo             Within Wa Mining Co., Ltd. (72) Inventor Masayuki Nishina             1-8-2 Marunouchi, Chiyoda-ku, Tokyo             Within Wa Mining Co., Ltd. F-term (reference) 5H024 AA04 AA14 BB07 CC03 DD17                       EE01 EE03 EE06 EE07 EE09                       FF07 HH00 HH01 HH04 HH08                       HH13                 5H050 AA08 AA09 AA12 AA19 BA04                       CA02 CB13 DA09 EA01 EA05                       EA09 EA12 EA24 GA10 HA01                       HA02 HA05 HA07 HA08 HA17

Claims (14)

[Claims] 1. A crystal of a compound composed of Ag, Bi and O (oxygen), or a crystal of a compound composed of Ag, Bi, M (M represents a transition metal) and O, and Bi is distributed throughout the particle. A positive electrode pellet for an alkaline battery, which is formed by using a powder composed of dispersed particles. 2. A molar ratio of Ag / (Bi + M) in the powder,
Alternatively, when M is not contained, the molar ratio Ag / Bi is 1
The positive electrode pellet according to claim 1, wherein the positive electrode pellet has an oxygen content of 7 or more and an oxygen content of 5% by weight or more. 3. The positive electrode pellet according to claim 1, which has an electric conductivity of 1 × 10 ⁻⁴ S / cm or more. 4. The positive electrode pellet according to claim 1, which has a density of 5 g / cm ³ or more. 5. The positive electrode pellet according to claim 1, wherein the NO ₃ content is 0.1% by weight or less. 6. The pellet for a positive electrode according to claim 1, wherein the total content of the alkali metal and the alkaline earth metal is 2% by weight or less. 7. The pellet for a positive electrode according to claim 1, which has a CO ₃ content of 0.5% by weight or less. 8. The positive electrode pellet according to claim 1, wherein the NO ₃ content, the alkali metal and alkaline earth metal content, and the total CO ₃ content are 2% by weight or less. 9. The positive electrode pellet according to claim 1, wherein the powder has a repose angle of less than 50 degrees. 10. The powder has an average particle size of 10 μm or more and 5 m.
The pellet for a positive electrode according to any one of claims 1 to 8, which is composed of particles of m or less and has an angle of repose of less than 50. 11. The powder has a bulk density of more than 1.0 to 6.3 g / c.
positive electrode pellets according to any one of claims 1 to 10 and a tap density in m ³ is of 1.5 beyond ~6.3 g / cm ^3. 12. The positive electrode pellet according to claim 1, wherein the powder has a specific surface area measured by BET method of 0.1 to 30 m ² / g. 13. MnO ₂ , NiOOH, CoOOH,
AgNiO ₂ , AgCoO ₂ , CaO, MnO, HgO,
The pellet for a positive electrode according to any one of claims 1 or 4 to 12, containing at least one additive selected from the group consisting of CdO, CdS, polytetrafluoroethylene, metallic silver and graphite. 14. An alkaline battery comprising a negative electrode active material, a positive electrode active material and an electrolyte, wherein the positive electrode pellet according to any one of claims 1 to 13 is used as the positive electrode active material.