JPH10172550A - Alkaline battery with nickel positive electrode and its activating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the uneven distribution of CoOOH to uniformly distribute in a nickel positive electrode, and enhance discharge characteristics being subject to the influence of an activation state of a battery by containing amorphous CoOOH in the nickel positive electrode in an alkaline battery with the nickel positive electrode. SOLUTION: In an activated alkaline battery, the active material surface of a nickel positive electrode is uniformly covered with fine particles of amorphous CoOOH, fine conducting networks are formed, and high discharge characteristics are obtained. Smaller particle diameter of Co and CoO which are starting material is preferable from the standpoint of solubility to an electrolyte, For example, mean particle diameter of Co is preferable to be 10 micron or less, and that of CoO is preferable to be 8 micron or less. If the mean particle diameters exceed these values, dissolution to the electrolyte is made difficult, at least one of Co and CoO remains in the electrolyte, and sometimes it has bad effect on the discharge characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline battery having a nickel positive electrode, such as a nickel-cadmium battery, a nickel-zinc battery, and a nickel-metal hydride battery, and a method of activating the alkaline battery. More specifically, the present invention relates to an alkaline battery having a nickel positive electrode in which cobalt is added to an active material and having excellent capacity characteristics and high-rate discharge characteristics, and a method for activating the alkaline battery.

[0002]

2. Description of the Related Art Alkaline storage batteries have high reliability,
Because of their small size, light weight, and high capacity, they are widely used as various portable devices and industrial power supplies. As a positive electrode of the alkaline storage battery, a nickel electrode having an active material mainly composed of nickel hydroxide is used.

[0003] The nickel positive electrode is manufactured by filling an active material into an electrode substrate made of a porous metal such as foamed nickel. As a method of filling the active material, for example, Japanese Patent Application Laid-Open No. 5-151965 discloses a method of physically filling a porous electrode base material with an active material mainly containing nickel hydroxide together with a binder. I have. This method
It is generally called a paste filling method.

Incidentally, nickel hydroxide, which is the active material of the nickel positive electrode, does not become conductive in either the charged state or the discharged state. Therefore, a separate conductive skeleton is required. A method of filling nickel oxide powder has been developed. However, even in this case, the utilization rate of the active material is still low, and it is necessary to ensure the conductivity between the active material powders.

[0005] Therefore, together with the active material, metallic cobalt, cobalt oxide (CoO) or cobalt fluoride (CoF)
It has been found that it is desirable to include such a cobalt compound, and research has been advanced. Due to the presence of metal cobalt or a cobalt compound, cobalt hydroxide and CoOOH are generated when charge and discharge are repeated, and the electrical contact between the porous metal electrode base material and the active material is improved. The use efficiency of the active material is improved.

That is, in an electrode containing a cobalt compound,
At the time of initial charging, reactions of the following equations (1) and (2) occur,
At the time of discharge, the reaction represented by the following equation (3) occurs, so that a conductive network is formed by the generated CoOOH. _{^{CoO + OH - → HCoO 2 -}} (1) HCoO 2 - + H 2 O → Co (OH) 2 + OH - (2) Co (OH) 2 + OH - → CoOOH + H 2 O + e - (3) That is, immediately after assembling the alkaline batteries In this case, the nickel positive electrode is not activated, and an activation treatment for causing the above-described reaction is required to enable use as a secondary battery.

For example, at the time of assembling a nickel-metal hydride battery, both the positive electrode and the negative electrode are not activated.
Charge about 150% with a charging current of about 0.1C,
A method is generally used in which activation is performed by repeating charge and discharge for discharging to about 0.9 V with a discharge current of about several times. A method of storing and activating the assembled battery at a high temperature without charging the battery is also known.

[0008] However, such an activation method has a problem that the obtained alkaline battery has insufficient high-current discharge characteristics and low-temperature discharge characteristics. Therefore, for example, Japanese Patent Application Laid-Open
No. 73902 discloses a method of activating a charged alkaline battery by storing it at a high temperature for a short time. According to this method, sufficient activation can be performed in a short time, and the discharge characteristics such as a large current discharge characteristic and a low temperature discharge characteristic that are affected by the activation state of the battery are improved.

[0009]

However, even with an alkaline battery treated by the conventional activation method, large current discharge characteristics, low temperature discharge characteristics, and the like are not yet sufficient, and further improvement in characteristics is required. For example, JP-A-7-73902
The method disclosed in the above publication mainly activates the negative electrode of a nickel-metal hydride (Ni-MH) battery, and there are almost no other documents relating to the activation of the positive electrode.

In an alkaline battery manufactured by a method of constructing a conductive network using CoOOH,
Due to the large uneven distribution of the generated CoOOH, there is a problem that when charging and discharging are performed with a large current, the utilization efficiency is extremely low and the output is low. The present invention has been made in view of such circumstances, and has as its object to suppress uneven distribution of CoOOH so as to uniformly exist in the nickel positive electrode and further improve discharge characteristics affected by the activation state of the battery. I do.

[0011]

According to a first aspect of the present invention, there is provided an alkaline battery having a nickel positive electrode, wherein the nickel positive electrode contains amorphous CoOOH. It is in. A feature of the method for activating an alkaline battery having a nickel positive electrode according to claim 2 is that an alkaline battery having a nickel positive electrode containing at least one of a metal cobalt (Co) powder and a cobalt monoxide (CoO) powder is provided. Inject electrolyte 4
An aging step of holding at a temperature lower than 0 ° C. for a predetermined time;
And a charging step of performing initial charging at a temperature of 60 ° C. at a current amount of 20 mA or less per 1 g of the positive electrode active material so as to have a charging amount of 100 to 110% of the rated capacity.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the activation method of the present invention, by containing at least one of Co and CoO, it is considered that a reaction represented by the following formula (1) occurs when these come into contact with the electrolytic solution in the aging step. . CoO (Co) + OH ⁻ → HCoO ₂ ⁻ (1) That is, at least one of Co and CoO is dissolved in the electrolytic solution by the reaction of the formula (1) to become HCoO ₂ ⁻ ions.
The HCoO ₂ ^- ions diffuse in the electrolyte and uniformly cover the active material surface. At this point, the HCoO ₂ ^- ion is in the equilibrium state of the equation (2).

HCoO ₂ ⁻ + H ₂ O = Co (OH) ₂ + OH ⁻ (2) The reactions of the formulas (1) and (2) are desirably performed at a temperature lower than 40 ° C. When the temperature becomes 40 ° C. or higher, an oxidation reaction of at least one of Co and CoO occurs, and Co ₃ O ₄
Are generated, which are hardly dissolved in the electrolytic solution and exist as impurities in the active material. Therefore, the amount of HCoO ₂ ^- ions and the amount of CoOOH are reduced, and the discharge characteristics of the alkaline battery are reduced.

The time of the aging step is determined according to the aging temperature. The lower the aging temperature, the longer the aging time. For example, if the aging temperature is about room temperature of about 20 ° C., the aging time needs about 10 hours or more. Then, in the charging step, at a temperature of 40 to 60 ° C., a charging amount of 100 mA to 110% of the rated capacity is obtained at a current amount of 20 mA per gram of the positive electrode active material (this corresponds to a charging current of 0.07 C). (This is 300 to 32 per gram of the positive electrode active material.)
By performing the initial charging (corresponding to the total amount of electricity of 0 mAh), a competitive reaction of the following equations (3) and (4) occurs.

Co (OH) ₂ + OH ⁻ → CoOOH + H ₂ O + e ⁻ (3) Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (4) Since the equilibrium reaction of the equation (2) slowly moves to the right, the above condition is satisfied. Then, the reaction of the formula (3) also proceeds slowly. Thereby, a very fine amorphous CoOO is formed on the surface of the active material.
H is uniformly formed, and conductivity between the active materials is ensured.

If the temperature in the charging step is lower than 40 ° C., the reaction of the formula (3) becomes difficult to occur, and as a result, at least one of Co and CoO remains to adversely affect discharge characteristics. If the temperature exceeds 60 ° C., the anode may be oxidized and deteriorated. When the amount of current exceeds 20 mA per 1 g of the positive electrode active material, the reaction of the formula (3) proceeds rapidly, and the crystalline CoOOH of large particles precipitates non-uniformly. And the discharge characteristics are degraded.

The lower limit of the current is not particularly limited. However, the smaller the current, the longer the charging time and the lower the productivity. When the charged amount is less than 100% of the rated capacity, the reaction of the formula (3) does not sufficiently proceed, and the generation of CoOOH is small,
Is exceeded, the reaction of the formula (3) proceeds rapidly, and crystalline CoOOH of large particles precipitates non-uniformly, so that the conductivity between the active materials is considered to be non-uniform, and the discharge characteristics deteriorate. Particularly preferred is a range of 103 to 110% of the rated capacity.

Therefore, in the alkaline battery activated by the activation method of the present invention, a dense conductive network is formed since the surface of the active material of the nickel positive electrode is uniformly covered with fine particles of amorphous CoOOH. Shows high discharge characteristics. The smaller the particle size of the starting materials Co and CoO, the better the smaller the particle size in consideration of the solubility in the electrolytic solution. For example, the average particle size of Co is preferably 10 μm or less, and the average particle size of CoO is preferably 8 μm or less. If the particle size is larger than this, it becomes difficult to dissolve in the electrolytic solution, and at least one of Co and CoO remains as Co ₃ O _{4 in} the electrolytic solution, which may adversely affect the discharge characteristics.

The total amount of at least one of Co and CoO, including both, is 15% of the positive electrode active material amount.
% By weight or less. If the content is more than 15% by weight, the battery capacity is relatively reduced, which is not preferable. Note that at least one of Co and CoO may be included as a starting material, and it is preferable to include both Co and CoO. As a result, although the mechanism is unknown, Co
_Since the production of ₃ O ₄ is suppressed, Co and CoO become HCoO ₂ ^- ions smoothly, and the reaction of the formula (3) is promoted. As a result, a large amount of amorphous CoOOH is produced with a small amount of Co and CoO. . Therefore, Co added in comparison with the conventional method
By reducing the amount, a nickel positive electrode having the same performance as that of the related art can be obtained, the cost can be reduced, and the battery capacity can be increased by relatively increasing the amount of the active material.

The present invention can be applied to various alkaline batteries such as a nickel-hydrogen (Ni-MH) battery, a nickel-cadmium battery, and a nickel-zinc battery, and is particularly suitable for activating a nickel-metal hydride battery. For example, nickel monoxide (Ni
O), nickel oxide such as nickel dioxide (NiO ₂ ), and nickel hydroxide such as nickel hydroxide [Ni (OH) ₂ ] are used as the active material. Further, as the nickel positive electrode, one produced by any of a sintering method, a paste method and the like can be used.

Further, the negative electrode active material of the nickel-metal hydride battery
For example, AB_TwoSystem, AB_FiveSystem, AB system, A_TwoB system
And other hydrogen storage alloys. A is T
i, Zr, Mn, V, etc., and B is V, Ni, Cr,
Co, Fe, Mn, etc., and as a hydrogen storage alloy,
For example, Ti₁₆Zr₁₆V_{twenty two}Ni₃₉Cr₇, Ti₁₆Zr₁₆V
_{twenty two}Ni₃₂Cr₇Co₇, Ti_FifteenZr_FifteenV_20.6Ni₃₀Cr
_6.6Co_6.6Mn_3.6Al_2.7, Ti_FifteenZr_FifteenV_{twenty one}Ni
₃₁Cr₆Co₆Fe₆, Ti_FifteenZr_{twenty one}V_FifteenNi ₃₁Cr₆
Co₆Fe₆And the like.

An alkaline aqueous solution is used as the electrolytic solution of the nickel-metal hydride battery. For example, an aqueous solution of sodium hydroxide, potassium hydroxide, lithium hydroxide or the like can be used.

[0023]

The present invention will be specifically described below with reference to examples and comparative examples. (Example 1) <Assembly of Ni-MH battery> 1.6% by weight of Zn and Co
1.5% by weight and an average particle size of 10 μm and a maximum particle size of 30 μm
100 parts by weight of nickel hydroxide powder having an average particle size of 8
2 parts by weight of metal cobalt powder having a particle size of 5.3 μm
m CoO powder, 5 parts by weight in terms of metal Co, 1.5 parts by weight of CMC (carboxymethylcellulose) as a binder, and an appropriate amount of pure water were mixed.
The mixture was dispersed for 8 hours to prepare a paste.

Next, a foamed nickel electrode base material having a three-dimensional network structure ("Celmet", manufactured by Sumitomo Electric Industries, Ltd., thickness 1.
6 mm and a porosity of 95%), and the above paste was filled using a spatula. The filling amount of the paste is 0.75 g per 1 cm ³ of the foamed nickel electrode base material. And 60
After heating to ８０80 ° C. and drying it sufficiently, it was rolled and cut into predetermined dimensions to produce a positive electrode plate.

On the other hand, Mm Ni _3.55 Co _0.75 Mn _0.4 Al
_0.3 hydrogen storage alloy is mechanically pulverized and sieved with a micro sieve to obtain an average particle size of 55 μm and a maximum particle size of 75 μm.
m MH powder was prepared. 100 parts by weight of this MH powder, 0.5 parts by weight of CMC, 0.5 parts by weight of carbon powder having an average particle diameter of 2 μm as a conductive additive, and appropriate amounts of ethanol and water were mixed, and further mixed with a ball mill. A paste was prepared by dispersing for a time. Then, the foamed nickel electrode base material was filled in the same manner as the positive electrode, and dried, rolled and cut in the same manner to produce a negative electrode plate.

The obtained positive electrode plate and negative electrode plate are wound around a separator made of non-woven fabric made of polypropylene / polyethylene which has been subjected to a hydrophilic treatment, and this is housed in a cylindrical battery can. Then, KOH: NaOH = 7: A predetermined amount of an alkaline electrolyte prepared to a concentration of 6 mol / L at a ratio of 3 was injected, a battery cover was provided, and a AA-size, 1200 mAh cylindrical sealed Ni-MH was used.
The battery was assembled. This battery uses a negative electrode /
The positive electrode was 1.2, and the rated capacity per gram of the positive electrode active material was 289 mA / g.

<Aging Step> The obtained sealed battery in an inactive state is first left at room temperature (25 ° C.) for 10 to 24 hours.
The electrolyte was sufficiently permeated into the positive electrode and the negative electrode. <Charging process> After that, the temperature is 60 ° C and the charging current is 0.07C
(20 mA per gram of positive electrode active material) and rated capacity of 10
The battery was charged to 3% (298 mA per 1 g of the positive electrode active material) and discharged at 1 / 5C.

<Test> After charging the activated battery at 1 / 5C for 5.5 hours, the discharge current was reduced to 1 / 5C, 1C,
The discharge capacity at the time of discharging at 3C and 6C, respectively, was measured, and the results are shown in Table 1. As can be seen from Table 1, this battery shows stable discharge characteristics regardless of the magnitude of the discharge current.

When the battery after activation was disassembled and the surface of the positive electrode was observed under a microscope, it was observed that fine particles of several nm to several tens nm were uniformly attached to the surface of the positive electrode active material. When the positive electrode surface was analyzed by infrared spectroscopy, the presence of CoOOH and Co ₃ O ₄ was confirmed. When the particles on the surface of the positive electrode active material were analyzed by X-ray diffraction, a peak of Co ₃ O ₄ was observed as shown in FIG. 1, but no peak of CoOOH was observed. That is, the particles uniformly adhered to the surface of the positive electrode active material do not contain crystalline CoOOH, and CoOOH exists as amorphous.

(Example 2) The same inactive battery as in Example 1 was used, and the temperature in the charging step was set to 40 ° C.
And a charging current of 0.06C (17 g / g of the positive electrode active material).
Activation was performed in the same manner as in Example 1 except that mA) was used. Then, the discharge capacity and the form of CoOOH were measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 3 A positive electrode plate manufactured in the same manner as in Example 1 was used except that the addition amount of Co powder was 4 parts by weight and the addition amount of CoO powder was 10 parts by weight. An inactive battery was produced in the same manner. The charging current was set to 0.05 C (14 mA / g of the positive electrode active material), and 105% of the rated capacity (3% / g of the positive electrode active material).
Activated in the same manner as in Example 1 except that the battery was charged so as to have a discharge capacity and CoOO.
Table 1 shows the measurement results of the form of H.

Example 4 The same procedure as in Example 1 was carried out except that the addition amount of Co powder was 10 parts by weight, and the addition amount was 4 parts by weight using CoO powder having an average particle size of 8 μm. An inactive battery was manufactured in the same manner as in Example 1 using the positive electrode plate. The charging current was set to 0.05 C (14 mA per 1 g of the positive electrode active material), and the rated capacity was set to 10
Activation was performed in the same manner as in Example 1 except that the battery was charged to 5% (corresponding to 303 mA per 1 g of the positive electrode active material), and the discharge capacity and the form of CoOOH were measured in the same manner as shown in Table 1.

Example 5 Example 1 was performed without using Co powder.
An inactive battery was produced in the same manner as in Example 1, except that 7 parts by weight of the CoO powder used in Example 1 was added. Then, activation was performed in the same manner as in Example 1 except that the temperature in the charging step was set to 50 ° C., and the results of similarly measuring the discharge capacity and the form of CoOOH are shown in Table 1.

Example 6 Instead of Co powder and CoO powder, 8 parts by weight of a commercially available cobalt oxide having an average particle size of 3.8 μm (main component is CoO and partially contains metal Co) was added. A non-active battery was manufactured in the same manner as in Example 1 except that a positive electrode plate manufactured in the same manner as in Example 1 was used.
Then, activation was performed in the same manner as in Example 1 except that the temperature in the charging step was set to 50 ° C., and discharge capacity and CoOOH
Table 1 shows the results obtained by measuring the morphology.

Example 7 A positive electrode plate manufactured in the same manner as in Example 1 except that the addition amount of the Co powder was 3 parts by weight and the addition amount of the CoO powder was 6 parts by weight was used. An inactive battery was produced in the same manner as described above. The charging current was set to 0.01 C (3 mA / g of the positive electrode active material), and 110% of the rated capacity (3 g / g of the positive electrode active material).
(Equivalent to 18 mA), and activated in the same manner as in Example 1.
Table 1 shows the measurement results of the form of H.

Comparative Example 1 An inactive battery similar to that of Example 1 was used and activated in the same manner as in Example 1 except that the temperature in the charging step was set at 20 ° C. And Example 1
Similarly, the discharge capacity and the form of CoOOH were measured, and the results are shown in Table 1. (Comparative Example 2) Using the same inactive battery as in Example 1, except that the temperature in the charging step was 40 ° C and the charging current was 0.1 C (29 mA per 1 g of the positive electrode active material). Activation was carried out as in Example 1. Then, the discharge capacity and the form of CoOOH were measured in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 3 Instead of Co powder and CoO powder, cobalt hydroxide (Co (OH) having an average particle size of 6 μm was used.
An inactive battery was produced in the same manner as in Example 1 except that 8 parts by weight of ₂ ) was added, using a positive electrode plate produced in the same manner as in Example 1. Then, activation was performed in the same manner as in Example 1, and the results of measuring the discharge capacity and the form of CoOOH in the same manner are shown in Table 1.

(Reference Example) A positive electrode plate manufactured in the same manner as in Example 1 was used except that Co powder having an average particle size of 15 μm and CoO powder having an average particle size of 10 μm were used. An active battery was made. Then, activation was performed in the same manner as in Example 1 except that the temperature in the charging step was set to 40 ° C., and the results of similarly measuring the discharge capacity and the form of CoOOH are shown in Table 1.

(Evaluation)

[0040]

[Table 1]

As is clear from Table 1, the Ni of each embodiment was
It can be seen that the −MH battery shows a stable discharge capacity even when the discharge current fluctuates greatly, and is extremely excellent in discharge characteristics. However, in each comparative example, as the discharge current increased, the discharge capacity was greatly reduced, and the discharge characteristics were inferior. FIG. 2 shows an X-ray diffraction chart of the particles attached to the surface of the positive electrode active material of Comparative Example 3. These particles contain crystalline CoOOH, which is completely different from the chart of the embodiment shown in FIG. In other words, the difference between the embodiment and the comparative example in terms of phenomenon is that CoO
Due to the difference between whether OH is amorphous or crystalline and whether the distribution of CoOOH is uniform or non-uniform, amorphous CoOOH is present in a uniform distribution as in the example. It is clear that it is giving favorable results.

In Comparative Example 1, the temperature in the charging step was as low as 20 ° C. In Comparative Example 2, the charging current in the charging step was as large as 0.1 C (29 mA / g of the positive electrode active material). The fact that the substance is cobalt hydroxide is different from the example, and it is clear that when the composition deviates from the constitution of the present invention, amorphous CoOOH is not formed and the discharge characteristics are deteriorated.

Further, as shown in the reference example, when the particle size of the starting material is as large as 10 to 15 μm, an insoluble portion is present in the electrolyte during the aging step, which becomes Co ₃ O _4. It will be present as non-uniform crystalline particles. This does not have a favorable effect on the characteristics, but rather degrades the discharge characteristics. Therefore, it is desirable that the particle diameter is as small as 10 μm or less as shown in each embodiment.

[0044]

That is, according to the alkaline battery having a nickel positive electrode of the present invention, a uniform conductive network is formed by amorphous CoOOH, so that even when the discharge current is large, a stable discharge capacity is exhibited and the discharge characteristic is maintained. Is excellent. In addition, since the utilization rate of the active material is improved, high output and high capacity are obtained.

According to the activation method of the present invention, an alkaline battery having the above-described excellent characteristics can be easily and reliably formed. Furthermore, when the battery was activated by a conventional method, an aging and aging period for dispersing the cobalt compound as cobalt hydroxide after adding the electrolytic solution was required for several days, but this period can be shortened. Productivity is improved, and CoO
Since the efficiency of forming OH is improved, the amount of cobalt used can be reduced, and the cost can be reduced.
Further, since the amount of the active material relatively increases, the battery capacity increases.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart of particles attached to the active material surface of a positive electrode of an alkaline battery of Example 1.

FIG. 2 is an X-ray diffraction chart of particles attached to an active material surface of a positive electrode of an alkaline battery of Comparative Example 3.

Claims (2)

[Claims] 1. An alkaline battery having a nickel positive electrode, wherein the nickel positive electrode contains amorphous CoOOH. 2. An electrolytic solution is injected into an inactive alkaline battery having a nickel positive electrode containing at least one of metal cobalt (Co) powder and cobalt monoxide (CoO) powder, and the electrolyte is charged at 40 ° C.
An aging step in which the temperature is maintained at a temperature of less than 40 ° C. for a predetermined time;
a method of activating an alkaline battery having a nickel positive electrode, comprising: performing a charging step of performing initial charging so as to obtain a charging amount of 100 to 110% of a rated capacity at a current amount of mA or less.