JP2003242973A - Positive active material for battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve storage stability in powder state or in battery state of positive active material of Ag-Bi-(M)-O system (M is a transition metal). <P>SOLUTION: This is a positive active material for an alkaline battery that has a crystal of a compound made of Ag, Bi, and O (oxygen) or a crystal of a compound made of Ag, Bi, M (M expresses a transition metal), and O, and that is a powder made of particles in which Bi is dispersed in all areas inside the particles, and the content of NO<SB>3</SB>, alkali metal and alkaline earth metal, CO<SB>3</SB>or the like is controlled to a prescribed level or less. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode active material for alkaline batteries.

[0002]

2. Description of the Related Art Conventionally, silver oxide batteries have been widely used as alkaline batteries (commonly called button batteries) mounted on watches, measuring instruments, cameras and the like. A silver oxide battery is generally constructed by using silver oxide (Ag ₂ O) as a positive electrode active material, zinc powder as a negative electrode active material, and an alkaline solution such as an aqueous solution of KOH or NaOH as an electrolytic solution.

The silver oxide battery has a small size and a high capacity, and has a reliability such that there is no problem in use even after 3 years have passed in a normal use environment. Therefore, silver is an expensive material, but it is no exaggeration to say that most of the button batteries are silver oxide batteries.

The positive electrode active material may be called a positive electrode active material or an anode active material, and the negative electrode active material may also be called a negative electrode active material or a negative electrode active material.

As mentioned above, silver is an expensive substance. Therefore, the inventors of the present invention, as a cost reduction measure of the positive electrode active material for a battery made of silver oxide, in Japanese Patent Application No. 2001-285788 and Japanese Patent Application No. 2001-274194 require Ag, Bi and O (oxygen). Or a crystal of a compound consisting of Ag, Bi, M (M is Ni, Co or M
The invention of a positive electrode active material for a battery, which is composed of particles having a crystal of a compound consisting of a transition metal such as n) and O and having Bi dispersed throughout the particle, was proposed. This positive electrode active material is economical because a high discharge capacity can be obtained even if the content of Ag is low. In addition, Japanese Patent Application No. 2001-388900
In the No. 1 issue, an invention was proposed to further improve the powder characteristics of the positive electrode active material.

[0006]

[Problems to be Solved by the Invention] Japanese Patent Application No. 2001-285
Although the positive electrode active material proposed in Japanese Patent Application No. 788 and Japanese Patent Application No. 2001-274194 has a small amount of Ag and is low in cost, it has been found from subsequent investigations that this positive electrode active material, in some cases, shows battery characteristics, especially in batteries during storage. It was found that the characteristics changed. Therefore, the object of the present invention is to solve this problem,
It is to improve the storage stability of the Ag-Bi- (M) -O-based positive electrode active material proposed above.

[0007]

According to the present invention, Ag, Bi and O are used as a positive electrode active material for solving the above problems.
Crystal of compound consisting of (oxygen) or Ag, Bi, M
(M represents a transition metal) and O is a powder comprising particles of a compound having O and a Bi dispersed throughout the particle, and the NO ₃ content in the powder is 0.1. The positive electrode active material for a battery is 1% by weight or less, and the total content of alkali metal and alkaline earth metal in this powder is 2% by weight.
The following positive electrode active materials for batteries, and further C in this powder
Provided is a positive electrode active material for a battery having an O ₃ content of 0.5% by weight or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Ag proposed in Japanese Patent Application Nos. 2001-285788 and 2001-274194
The -Bi- (M) -O-based positive electrode active material experienced a change in battery characteristics during storage at some time, which may be due to impurities in the positive electrode active material. all right. Here, “storage” includes (1) storage of positive electrode active material and (2) storage of battery. The case (1) corresponds to the time from the production of the positive electrode active material to the production of the battery, and the case (2) means the time from the production of the battery to the actual use. If deterioration occurs during storage in (1), the discharge capacity will decrease, and (2)
When deterioration occurs during storage, the discharge capacity not only decreases,
In the worst case, the battery may explode or leak during storage.

According to the investigation by the present inventors, it has been clarified that there is a causal relationship between certain impurities in the positive electrode active material and storage characteristics, and if a certain allowable limit value is set according to the impurities, It has been found that the storage stability is improved.

That is, in the manufacturing process of the positive electrode active material, a predetermined amount or more of an alkali metal salt caused by NaOH or KOH used in the neutralization step or an alkaline earth metal salt mixed from treated water or raw materials remains. It was found that the positive electrode active material deteriorates when stored in a high temperature and high humidity state, resulting in a decrease in discharge capacity. It was also found that when the amount of NO ₃ in the positive electrode active material is large, it self-discharges when the battery is stored at a high temperature, resulting in a decrease in battery capacity. Not always clear for existence form of NO _{3 but,} Ag-N
Conditions such as O ₃ , Bi (NO ₃ ) _3, Ni (NO ₃ ) _2, NaNO _3, KNO ₃ are considered. Furthermore, if the residual amount of CO ₃ is large,
It was also revealed that the open circuit voltage becomes higher. The open circuit voltage is one of the important indexes for evaluating the reliability of an unused battery, and the open circuit voltage when Zn is used for the negative electrode is 1.
If the voltage exceeds 65 V, oxygen is generated due to the decomposition of the aqueous electrolytic solution, which may cause the battery to expand or even burst. In addition, high open circuit voltage causes deterioration of the battery member separator, which causes self-discharge. Ag ₂ as a CO ₃ salt
CO _3, Na ₂ CO _3, but like K ₂ CO ₃ are considered, it is highly likely that a high Ag ₂ CO ₃ of these discharge potential.

Impurities that cause such deterioration during storage are
It is desirable that the content be as low as possible, but it may be contained inevitably in the production of the positive electrode active material. Therefore although the present inventors have conducted various tests to determine the tolerable amount of each of these impurities in the context of storage stability, NO ₃
The content should be 0.1 wt% or less, the total amount of alkali metal and alkaline earth metal should be 2 wt% or less, and the CO ₃ content should be 0.5 wt% or less. I found it necessary to be. It is also important that the total amount of these impurities is 2% by weight or less. In order to reduce the amount of impurities as described above, an Ag-Bi- (M) -O-based compound is synthesized, and the electrical conductivity of the washing filtrate is controlled when the compound is filtered and washed. It has been found that, when the electric conductivity is a predetermined value or more, it is effective to reduce the concentration of CO ₃ in the alkali used when the compound is formed by the wet method as much as possible.

The peculiarities of the manufacturing method of the positive electrode active material, the accompanying route of impurities and the means for reducing the impurity quality will be described below.

The powder for the positive electrode active material for an alkaline battery according to the present invention is basically a particle composed of Ag, Bi, (M) and O, which has a compound crystal in the particle and is a particle. There is a feature that Bi is dispersed in the entire area. M is one or more elements selected from transition elements, for example N
i, Co, Mn, etc., which are added for the purpose of keeping the open circuit voltage, which is a battery characteristic, low. This positive electrode active material particle powder preferably has a composition in which the molar ratio Ag / (Bi + M) is 1 or more and 7 or less and the oxygen content is 5% by weight or more. The amount is preferably 75% by weight
It is the following.

The Ag-Bi- (M) -O type compound according to the present invention can be obtained by a wet method which sequentially undergoes the following steps. (1) A step of reacting each salt of silver, bismuth, and transition metal with an alkali in water to obtain a neutralized precipitate (referred to as a neutralization step),
(2) a step of adding an oxidizing agent to the obtained suspension of neutralized starch to oxidize the starch (oxidation step), (3) solid-liquid separation of the suspension of the oxidized starch, Process for collecting things (separation process), (4)
Washing and drying the filtered precipitate, (5) Crushing the dried product into powder.

(1) Neutralization step: As salts of silver, bismuth and transition metals, silver nitrate, bismuth nitrate, nickel nitrate and the like can be typically used. As the alkali, a strong alkali (eg, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc.) is used. At this time, if CO ₃ is present in the alkali salt, silver carbonate is produced, and its amount is large. If this happens, the open circuit voltage of the positive electrode active material of the final product will rise. That is, it was found that the CO ₃ content of the alkali salt used adversely affects the storage stability of the positive electrode active material.

[0016] In the alkali salt in the air, so easy to produce a carbonate absorbs CO _2, it is necessary to use those stored in a state not in contact with the atmosphere as possible. Further, since CO ₂ in the atmosphere is entrained during the neutralization reaction, it is desirable that the atmosphere in the reaction tank is also a decarbonated air or nitrogen gas atmosphere.

The neutralization treatment itself is carried out by adding an aqueous solution of a salt of silver, bismuth or a transition metal to an alkaline aqueous solution, mixing an aqueous solution of an alkali with an aqueous solution of a salt of silver, bismuth or a transition metal, silver, bismuth or transition. A method of adding an alkaline aqueous solution to an aqueous solution of a metal salt 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. 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 stirring, it is sufficient that the stirring strength is such that the neutralization reaction proceeds uniformly.

(2) Oxidation step: The oxidation step can be performed simultaneously with the neutralization step, but it is preferable to perform the neutralization step and the oxidation step separately. Further, it is preferable to insert a temperature raising step between these steps. As the oxidant, an ordinary oxidant (for example, KMnO ₄ , NaOCl, H ₂ O ₂ ,
K ₂ S ₂ O _8, Na ₂ S ₂ O ₈ , ozone, etc.) can be used. In the oxidation treatment, it is desirable that the liquid temperature is 50 ° C. or higher, preferably 70 ° C. or higher, and the oxidizing agent is added under stirring. 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 added may be sufficient to increase the valence of silver, bismuth and 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 is filtered off from the liquid, it is washed to obtain a cake of Ag-Bi- (M) -O compound. It is preferable to wash with pure water. NO _{3 after} cleaning
It has been found that the residual capacity may cause a decrease in discharge capacity during battery storage. It is considered that this is because the redox reaction of NO ₃ occurs in the battery and accelerates the self-discharge of the positive electrode. Therefore, it is desirable that the amount of NO _{3 in} the compound after washing be 0.1% or less.

In order to reduce the residual NO ₃ after washing, it is advantageous to wash with a diluted alkaline aqueous solution and then with pure water. However, if the washing with pure water is insufficient at this time, the alkaline salt will remain in the active material, and this time the alkaline salt will cause deterioration during powder storage. For this reason, it is preferable to perform sufficient washing with pure water so that the residual amount of alkali metal is 2% or less. It is thought that the reason why deterioration occurs during powder storage when the alkaline salt remains is that the unevenly distributed alkaline salt is dissolved by the moisture in the atmosphere and the surface of the powder becomes in a high pH state. .

The high pH on the powder surface may occur not only when the alkali metal but also when the alkaline earth metal remains. Therefore, in the present invention, it is preferable to regulate the content of the alkali metal and the alkaline earth metal that bring about a high pH on the powder surface, and the total amount of these is preferably 2% by weight or less. The content of alkali metal and alkaline earth metal can be known by measuring the electric conductivity of the washing filtrate. Actually, the electric conductivity of the washing filtrate is 20 mS / m
The content of the alkali metal and the alkaline earth metal in the powder can be reduced to 2% by weight or less, preferably 0.1% by weight or less, by washing with pure water until the amount becomes 1 mS / m or less. it can.

The cleaning powder is then dried at a temperature of 50 to 250 ° C. Since the compound may be decomposed when dried at a temperature exceeding 200 ° C, it is actually preferable to dry at a temperature of 50 to 200 ° C. The obtained dried product can be made into a fluid powder by crushing it with a crusher.

[0024]

EXAMPLES The present invention will be further described below with reference to examples. In each of the examples, with respect to the relationship between the amount of impurities in the positive electrode active material and the battery characteristics, battery storability, powder storability and open circuit voltage were evaluated by the following test methods.

[Battery storability]: The prepared battery was stored at 60 ° C. for 7 days, the discharge capacity was measured, and the capacity retention rate (%) was calculated from the percentage of the discharge capacity before storage. Was used as an index. The higher the capacity retention rate, the better the battery storability.

[Powder storability]: Capacity retention rate (percentage of discharge capacity after storage for 30 days in a thermo-hygrostat having a temperature of 60 ° C. and a humidity of 80% and a discharge capacity before storage) ( %)
Was used as the index. The higher the capacity retention rate (%), the better the storage property of the electric powder.

[Open circuit voltage]: The test battery was a beaker type battery. When making the positive electrode, use an active material, PTFE (polytetrafluoroethylene), and carbon.
The mixture mixed at a ratio of 0.8: 0.1: 0.1 is passed through a rolling mill to form a sheet with a thickness of 0.2 mm.
A 5 mm disk-shaped desk was cut out and attached to a Ni mesh as a current collector with a pressure of 2 t, and this was used as a positive electrode. The weight of the active material in the positive electrode was 0.15 mg. The negative electrode uses a Zn plate of w × h × t = 20 mm × 10 mm × 1 mm, and the reference electrode is w × h × t = 5 mm × 20 mm ×
A 1 mm Zn plate was used. 40% as an electrolyte
100 cc of KOH solution was used. The open circuit voltage was measured by measuring the voltage after the above battery was prepared and left in an incubator at 25 ° C. for 1 hour. The discharge was performed at a discharge rate of 0.05 C, and the discharge capacity at the end of 1.4 V was obtained.

Example 1 In the above-mentioned neutralization step,
An aqueous solution prepared by weighing and dissolving silver nitrate, bismuth nitrate and nickel nitrate so that the molar ratio of Ag / (Bi + Ni) was 3 and the molar ratio of Bi / Ni was 1 was obtained at a liquid temperature of 50 ° C. with respect to (Ag + Bi + Ni). Then, the mixture was added to an aqueous solution (1.5 liters) in which sodium hydroxide was dissolved at a molar ratio of 10 times under stirring to obtain a neutralized precipitate. 9 suspensions of this neutralizing substance
The temperature was raised to 0 ° C, and sodium peroxodisulfide (Na ₂ S ₂ O ₈ ) was added as an oxidizer in an amount twice the theoretical valence change equivalent required to further oxidize metal ions in the liquid. The solution was added to the solution for oxidation treatment. After the oxidation process is completed, increase the temperature to 90 ° C for 3
After aging for 0 minute, the precipitate was filtered off and washed with pure water. The washing with pure water was carried out until the electric conductivity of the washing filtrate became 0.4 mS / m.

The cake thus obtained was dried at 100 ° C. for 12 hours and then pulverized to obtain a powder containing an Ag-Bi-Ni-O compound. The analysis value of the impurity content of this powder is shown in Table 1.
It was shown to. A battery was prepared by using this powder as an active material as described above, and discharge was started 1 hour after the battery was assembled, and the discharge capacity was determined. Furthermore, in order to evaluate the battery storability, the discharge capacity of the battery that was stored at a temperature of 60 ° C for 7 days after assembly was obtained, and the capacity retention rate (%) was calculated from the discharge capacity of both as described above. However, as shown in Table 1, the capacity retention rate was 91%.

Example 2 The electric conductivity of the washing filtrate is 10
Example 1 was repeated except that the washing was performed until the mS / m was reached. Table 1 also shows the content of impurities in the obtained powder and the result of the evaluation of the battery storability.

[Comparative Example 1] The electric conductivity of the washing filtrate was 90.
Example 1 was repeated except that the washing was performed until it reached 0 mS / m. Table 1 also shows the content of impurities in the obtained powder and the result of the evaluation of the battery storability.

[0032]

[Table 1]

From the results shown in Table 1, it can be seen that when the residual amount of NO _{3 in} the powder is increased, the battery storability is deteriorated. Therefore, the amount of NO ₃ in the powder needs to be at least 0.1% by weight or less.

Example 3 The same process as in Example 1 was carried out until the aging was carried out by holding the temperature at 90 ° C. for 30 minutes after the completion of the oxidation process. The resulting slurry is filtered off,
First, washing was performed with an aqueous solution of NaOH = 5%, which was 4 times the volume of the slurry, and then with pure water until the electric conductivity of the washing filtrate became 20 mS / m. The obtained cake was dried at 100 ° C. for 12 hours and then crushed to obtain Ag-Bi.
A powder made of a -Ni-O compound was obtained.

The analytical values of the impurity content of this powder are shown in Table 2. A battery was prepared by using this powder as an active material as described above, and discharge was started 1 hour after the battery was assembled, and the discharge capacity was determined. Furthermore, in order to evaluate the powder storability, the discharge capacity was similarly determined for the powder left in a thermo-hygrostat at a temperature of 60 ° C. and a humidity of 80% for 30 days. When the capacity retention ratio (%) was calculated from the above, as shown in Table 2,
The capacity retention rate, which is an index of powder storability, was 95%.

[Example 4] 5% Na used as a cleaning solution
Example 3 was repeated except that the aqueous OH solution was replaced with a 5% aqueous KOH solution. The impurity content of the obtained powder and the results of the powder storability evaluation are also shown in Table 2.

Example 5 Example 3 was repeated except that the washing filtrate was washed with 5% NaOH aqueous solution and then with pure water until the electric conductivity of the washing filtrate became 0.5 mS / m. Was repeated. The impurity content of the obtained powder and the results of the powder storability evaluation are also shown in Table 2.

Comparative Example 2 Example 3 was repeated except that cleaning with a 5% NaOH aqueous solution was carried out and cleaning with pure water was omitted.
Was repeated. The impurity content of the obtained powder and the results of the powder storability evaluation are also shown in Table 2.

Comparative Example 3 Example 3 was repeated except that cleaning with a 5% KOH aqueous solution was carried out and cleaning with pure water was omitted. The impurity content of the obtained powder and the results of the powder storability evaluation are also shown in Table 2.

[0040]

[Table 2]

From the results shown in Table 2, it can be seen that the powder storability deteriorates when the residual amount of the strong alkaline impurities 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 6 Example 2 was repeated except that the sodium hydroxide aqueous solution used in the neutralization step was the sodium hydroxide aqueous solution after filtering off sodium carbonate. Here, the sodium hydroxide aqueous solution after filtering the sodium carbonate means the sodium hydroxide aqueous solution after filtering the sodium carbonate produced by absorbing the carbonic acid in the atmosphere during the storage of sodium hydroxide as a white precipitate. Is.

[0043] as well as measuring the CO ₃ content in the obtained _powder, the powder used for creating a cell, to measure the open circuit voltage of 1 hour after the battery assembly. The results are shown in Table 3.
It was shown to.

Example 7 Example 6 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. With measuring the CO ₃ content in the obtained _powder, to create a battery by using this powder was measured open circuit voltage of 1 hour after the battery assembly. The results are shown in Table 3.

[Comparative Example 4] As an alkaline aqueous solution used in the neutralization step, an aqueous solution in which 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) (1 Example 2 was repeated except that 0.5 liter) was used. CO in the obtained powder
₃ as well as determine the _content, to create a battery by using this powder was measured open circuit voltage of 1 hour after the battery assembly. The results are shown in Table 3.

[0046]

[Table 3]

From the results in Table 3, it can be seen that the open circuit voltage of the battery increases as the amount of CO _{3 in} the powder increases. Therefore, the amount of CO ₃ in the powder needs to be 0.5% by weight or less.

[0048]

As described above, according to the present invention,
A that has the same battery characteristics as silver oxide even if the amount of Ag is reduced
A g-Bi- (M) -O-based positive electrode active material having excellent powder storability and battery storability can be obtained. Therefore, it is possible to provide a positive electrode active material for an alkaline battery that is inexpensive and has good battery characteristics.

   ─────────────────────────────────────────────────── ─── 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 FF07                       FF38 HH01                 5H050 AA09 BA04 CA02 CB13 FA17                       GA10 HA01 HA02

Claims (7)

[Claims] 1. A crystal of a compound consisting of Ag, Bi and O (oxygen), or a crystal of a compound consisting of Ag, Bi, M (M represents a transition metal) and O, and Bi is distributed throughout the particle. A positive electrode active material for a battery, which is a powder composed of dispersed particles and in which the NO ₃ content is 0.1% by weight or less. 2. A crystal of a compound consisting of Ag, Bi and O (oxygen), or a crystal of a compound consisting of Ag, Bi, M (M represents a transition metal) and O, and Bi is distributed throughout the particle. A positive electrode active material for a battery, which is a powder composed of dispersed particles and in which the total content of alkali metals and alkaline earth metals is 2% by weight or less. 3. A crystal of a compound consisting of Ag, Bi and O (oxygen), or a crystal of a compound consisting of Ag, Bi, M (M represents a transition metal) and O, and Bi is distributed throughout the particle. A positive electrode active material for a battery, which is a powder composed of dispersed particles and has a CO ₃ content of 0.5% by weight or less. 4. A crystal of a compound consisting of Ag, Bi and O (oxygen), or a crystal of a compound consisting of Ag, Bi, M (M represents a transition metal) and O, and Bi is distributed throughout the particle. For a battery consisting of dispersed particles, the total content of NO ₃ content, alkali metal and alkaline earth metal content and CO ₃ content of which is 2% by weight or less Positive electrode active material. 5. The battery according to claim 1, wherein the powder particles have a composition in which a molar ratio Ag / (Bi + M) is 1 or more and 7 or less and an oxygen content is 5% by weight or more. Positive electrode active material. 6. The positive electrode active material for a battery according to claim 1, wherein the Ag content in the powder particles is 75% by weight or less. 7. An alkaline battery comprising a negative electrode active material, a positive electrode active material and an electrolyte, wherein the positive electrode active material according to any one of claims 1 to 6 is used as the positive electrode active material.