JP2001060463A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-capacity alkaline secondary battery, and especially a nickel-hydrogen secondary battery, with high coefficient of use of an active material, excellent high-rate discharging characteristics and charging/discharging cycle life characteristics. SOLUTION: In this alkaline secondary battery, an electrode group made by disposing a separator between a positive electrode and a negative electrode is sealed in a battery can together with an alkaline electrolytic solution. An active material powder is carried by the positive electrode. The active material powder is mainly composed of nickel hydroxide, has a conductive layer formed on surfaces of a part or the whole of the powder particles, and has a specific surface area of 15 m2/g or less measured by a BET method. The liquid ratio of the alkaline electrolytic solution is 0.5 to 2.0 m3/Ah to the theoretical capacity (in Ah) of the positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery having a nickel electrode as a positive electrode, and more particularly, to a high utilization rate of a positive electrode active material, excellent high-rate discharge characteristics, and an injection amount of an alkaline electrolyte. The present invention relates to a high-capacity alkaline secondary battery having excellent charge-discharge cycle life characteristics even under a small number of circumstances, particularly a nickel-hydrogen secondary battery.

[0002]

2. Description of the Related Art As typical examples of alkaline secondary batteries, there are a nickel-hydrogen secondary battery and a nickel-cadmium secondary battery. In each of these batteries, a nickel electrode mainly containing nickel hydroxide as a positive electrode active material is incorporated as a positive electrode. There are known two types of nickel electrodes: a sintered type and a non-sintered type.

[0003] Among them, the non-sintered nickel electrode is generally manufactured as follows. That is, first, a powder of nickel hydroxide functioning as a positive electrode active material and a binder such as carboxymethylcellulose, methylcellulose, sodium polyacrylate, and polytetrafluoroethylene are kneaded with water to form a viscous positive electrode mixture. Is prepared. Then, the paste of the positive electrode mixture is applied to, for example, a foamed nickel substrate, a net-like sintered substrate of metal fibers, or a three-dimensional substrate in which the surface of a nonwoven fabric is nickel-plated,
Filled or coated on a current collector which is a two-dimensional substrate such as a nickel punched sheet or expanded nickel, further dried, and then subjected to pressure molding, and the dried positive electrode mixture is loaded and carried on the current collector Is done.

[0004] Since the non-sintered nickel electrode manufactured in this manner has a higher packing density of nickel hydroxide (active material) than that of the sintered type, it is necessary to provide a battery having a high discharge capacity. This is advantageous in that it can be performed. Then, by using the above-described nickel electrode as a positive electrode, an alkaline secondary battery is assembled as follows.

First, a power generating element is manufactured by interposing a separator having electrical insulation and liquid retaining properties between the above-mentioned nickel electrode and a predetermined negative electrode. Here, when the alkaline secondary battery for manufacturing is a nickel-cadmium secondary battery, a negative electrode carrying a negative electrode mixture containing a cadmium compound such as metal cadmium or cadmium hydroxide as a negative electrode active material is used. Further, when the alkaline secondary battery for production is a nickel-hydrogen secondary battery, a negative electrode carrying a negative electrode mixture containing a hydrogen storage alloy as a main component is used. Also,
As the separator, for example, a nonwoven fabric of polyamide fiber or a nonwoven fabric of polyolefin fiber such as polyethylene fiber or polypropylene fiber which has been subjected to a hydrophilic treatment is generally used.

Next, the above-mentioned power generating element, which also serves as a negative electrode terminal, is disposed in a bottomed battery can made of, for example, a nickel-plated steel plate, and is further injected with a predetermined amount of a predetermined alkaline electrolyte. As the alkaline electrolyte, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of lithium hydroxide, and an appropriate mixed aqueous solution thereof are usually used.

[0007] After the positive electrode terminal is provided in the opening of the battery can, the whole is sealed and the battery is assembled. Then
Prior to shipment, the assembled battery is subjected to an initial charge to activate nickel hydroxide as an active material. The initial charging at that time is usually performed under conditions that allow charging of 100% or more of the amount of electricity with respect to the theoretical capacity of the built-in nickel electrode.

In the case of the above-mentioned nickel electrode, increasing the conductivity between the active materials (nickel hydroxide) and between the active material and the current collector improves the utilization rate of the active material. It is important in that. In order to realize such a problem, the following countermeasures have been conventionally taken.

First, at the time of preparing a paste of a positive electrode mixture, a predetermined amount of particles of metal cobalt, a cobalt compound such as cobalt hydroxide, cobalt trioxide, cobalt tetroxide, cobalt monoxide, or a mixture thereof is added to a conductive material. , And mixed with a powder of nickel hydroxide at a predetermined ratio to produce a mixed powder, which is used as an active material.

When the nickel electrode carrying the active material powder produced as described above is incorporated as a positive electrode of an alkaline secondary battery, the metal cobalt and the cobalt compound contained in the active material powder are all Once dissolved in the alkaline electrolyte as complex ions, which cover the surface of the nickel hydroxide powder, and when the battery is first charged, these complex ions are oxidized before nickel hydroxide and become conductive. It is converted into a higher oxide of cobalt mainly composed of cobalt oxyhydroxide, which precipitates between the nickel hydroxide powder, which is the active material, and between the active material layer and the current collector. Is formed. As a result, the conductivity between the active materials and between the active material and the current collector is improved, and the utilization rate of the active material is improved.

A method of treating the mixed powder produced as described above with a hot alkaline aqueous solution is also known. Specifically, the mixed powder is immersed in an alkaline aqueous solution, and the alkaline aqueous solution is attached to or impregnated with the mixed powder, then the whole is filtered, and the collected material is heated at a predetermined temperature. According to this method, a part of the metal cobalt or the cobalt compound contained in the mixed powder is dissolved in the hot alkaline aqueous solution as a cobalt complex ion,
By uniformly covering the surface of the powder mainly composed of nickel hydroxide, it changes into an active material powder having the above-mentioned precursor of the conductive matrix.

Therefore, in order to increase the utilization rate of the active material, it is considered advantageous to increase the content of the conductive matrix by increasing the content of metallic cobalt or a cobalt compound in the active material powder. Can be
However, when the content of the metal cobalt or the cobalt compound in the mixed powder is increased in order to increase the utilization rate of the active material, not only the production cost as the nickel electrode is increased, but also the nickel hydroxide powder functioning as the positive electrode active material. Is reduced, which is disadvantageous for increasing the capacity of the battery.

In view of the above, it is preferable that the active material is such that even if the content of metallic cobalt or the cobalt compound is a minimum amount, the active material and the cobalt compound can exert their effects. become. In the case of a battery in which a nickel electrode having a high content of metallic cobalt or a cobalt compound is incorporated, at the time of overdischarge, the cobalt compound penetrates into the crystal structure of the nickel hydroxide powder. There is also a problem that the function and effect inherent to the cobalt compound, that is, the formation of the conductive matrix does not proceed, and it is difficult to continuously improve the utilization rate of the active material.

In the case of the above-mentioned method of treating with a hot alkaline aqueous solution, the cobalt complex ion once dissolved in the hot alkaline aqueous solution is reprecipitated in the cooling process of the hot alkaline aqueous solution,
At that time, the adjacent powders are mutually bonded to form a particle mass. Therefore, since the obtained processed material is an aggregate of the particle mass, when a positive electrode mixture paste is prepared using this processed material, the distribution of the nickel hydroxide powder as the positive electrode active material in the paste is determined. Is in a non-uniform state, and a problem arises in that effective utilization as an active material is not realized.

As still another method for increasing the utilization rate of the active material, for example, a powder containing nickel hydroxide as a main component is put into an aqueous alkaline solution controlled at pH 11 to 13,
For example, by gradually adding an aqueous solution of cobalt sulfate, a cobalt compound such as cobalt hydroxide to be produced is applied to the surface of the powder, and the surface is covered with the conductive matrix precursor described above. There is also a method of using powder as an active material.

According to this method, the surface of the nickel hydroxide powder can be coated with a small amount of the cobalt compound, but there is a problem that the formation amount of the above-mentioned conductive matrix is correspondingly reduced. By the way, recently, with the development of portable electronic devices, nickel-hydrogen rechargeable batteries and nickel-cadmium rechargeable batteries used as driving power sources have high capacity. ,
There has been a strong demand for a capacity not to be reduced even after standing, to exhibit a large current discharge characteristic from an initial stage, and to exhibit excellent discharge characteristics even in a low temperature environment.

In this case, it is known that it is effective to increase the content of metallic cobalt or a cobalt compound in the nickel electrode, which is the positive electrode, in order to enhance the large current discharge characteristics. However, these methods
All of these methods are countermeasures against the increase in the capacity of the battery as described above, and cannot be said to be a method of improving the large-current discharge characteristics without sacrificing the increase in the capacity.

On the other hand, JP-A-8-195218 and JP-A-8-236145 disclose that the metal cobalt or the cobalt compound contained in the nickel electrode is kept at a high temperature until it is completely oxidized to cobalt oxyhydroxide. Discloses a method of performing initial charging. According to this method, the metal cobalt and the cobalt compound contained in the nickel electrode can contribute to the formation of the conductive matrix without waste, so that the content of the metal cobalt and the cobalt compound is reduced while increasing the capacity of the battery. Since the formed conductive matrix is stronger than the conductive matrix formed at the time of the first charge at room temperature,
The effect is obtained that the capacity is not easily reduced after standing.

However, this method has a problem that the environment at the time of the first charge must be set to a high-temperature atmosphere, and the required time for the first charge becomes longer, so that the manufacturing cost as a whole increases. On the other hand, in order to realize a higher capacity of the battery, it is important to increase the amount of the active material powder carried by the positive electrode, as well as the above-described measure for increasing the utilization rate of the active material. Conceivable. This is because the theoretical capacity as the positive electrode increases.

However, when the amount of the active material powder supported on the positive electrode is increased, the capacity of the battery can is constant, so that the amount of the alkaline electrolyte injected into the battery can is reduced. The amount of the alkaline electrolyte per unit active material that regulates the battery reaction is reduced. In such a state, for example, when the specific surface area of the active material powder is large, not all of the surface of the active material is involved in the battery reaction, and a part of the surface contributes to the battery reaction. As a result, the overall battery reaction becomes non-uniform,
Eventually, it is difficult to achieve a high capacity.

[0021]

SUMMARY OF THE INVENTION According to the present invention, the content of metallic cobalt or a cobalt compound is as small as possible,
In addition, the conductive matrix formed at the time of the first charge is also strong, and incorporates a positive electrode (nickel electrode) having an active material powder having a high utilization rate, and has excellent high-rate discharge characteristics and excellent charge-discharge cycle life characteristics. To provide a high capacity alkaline secondary battery.

[0022]

In order to achieve the above object, according to the present invention, an electrode group having a separator disposed between a positive electrode and a negative electrode is placed in a battery can together with an alkaline electrolyte. In the enclosed alkaline secondary battery,
In the positive electrode, a conductive layer is formed on part or all of the surface of a powder mainly composed of nickel hydroxide;
An active material powder having a specific surface area of 15 m ² / g or less as measured by the ET method is supported, and at the same time, the ratio of the alkaline electrolyte to the theoretical capacity (unit: Ah) of the positive electrode is 0.5. To 2.0 cm ³ / Ah is provided.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION In the battery of the present invention, first, as the active material powder to be supported on the positive electrode, a powder mainly composed of nickel hydroxide whose surface is coated with a conductive layer described later is used. . Therefore, at the time of manufacturing a positive electrode using this active material powder, the conductive matrix has already been partially or entirely formed on the positive electrode, as in the case of the above-described conventional prior art. In addition, it is not always necessary to generate a conductive matrix by initial charging.

In the battery of the present invention, the specific surface area of the active material powder is defined as 15 as the specific surface area measured by the BET method.
m ² / g and regulations below, and, by regulating the liquid ratio of the alkaline electrolyte to liquid injection within the range shown above, effectively allowed use the entire surface of the active material powder as a place for the battery reaction, have been active The utilization rate of the substance is increased, and the high rate discharge characteristics are enhanced.

First, the above-mentioned active material powder will be described in detail. This active material powder can be manufactured as follows. First, as a starting material, a powder mainly composed of nickel hydroxide, metallic cobalt, cobalt hydroxide,
A mixed powder comprising a cobalt compound powder such as cobalt trioxide, cobalt tetroxide, cobalt monoxide, or a mixture of two or more thereof is prepared. As a starting material, a powder mainly composed of nickel hydroxide is charged into an alkaline aqueous solution controlled at pH 11 to 13, and, for example, an aqueous solution of cobalt sulfate is gradually added thereto to oxidize the surface of the powder. Powders coated with a cobalt compound such as cobalt can also be used.

In this case, the content of metallic cobalt or a cobalt compound in the powder is preferably set in the range of 0.5 to 20% by weight based on the weight of the whole powder. If the amount is less than 0.5% by weight, the formation of the conductive matrix at the time of the first charge of the battery in which the positive electrode supporting the obtained active material is incorporated becomes insufficient, and the utilization rate of the active material is high. On the other hand, if the content is more than 20% by weight, the relative proportion of the nickel hydroxide powder in the active material decreases, and the discharge capacity of the battery decreases.

Next, the above-mentioned powder is charged into a mixing and stirring vessel to form a mixing / stirring system. While stirring the charged powder, an alkaline aqueous solution is sprayed or dropped on the powder to uniformly mix the two. Mix. And at the same time,
The stirring system is heated in the presence of oxygen. Examples of the aqueous alkali solution used at this time include an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, a mixed aqueous solution thereof, and a mixed aqueous solution of lithium hydroxide.

In the process of mixing and stirring the above-mentioned powder and the aqueous alkali solution, a part of the cobalt compound contained in the powder is dissolved as a complex ion in the aqueous alkaline solution, and the cobalt compound is coated on the surface of the powder. It is distributed between the powders to form the precursor of the conductive matrix described above. At this time, the concentration of the alkaline aqueous solution is preferably set in a range of 1 to 14N. When the concentration is lower than 1N, the solubility of the metal cobalt or the cobalt compound contained in the powder becomes low, and the formation of the precursor of the conductive matrix does not proceed sufficiently. Because it is not so high, and when the concentration is higher than 14N,
This is because the viscosity of the alkaline aqueous solution becomes high and it becomes difficult to sufficiently wet the powder, and thus it becomes impossible to sufficiently dissolve the cobalt metal and the cobalt compound.

When the mixing / stirring system is heated in the presence of oxygen (specifically, in the air), the precursor of the conductive matrix is oxidized to cover the surface of the powder. A conductive layer composed of a higher oxide of cobalt is formed. Here, the heating means is not particularly limited, for example, external heating of the mixing / stirring system, a method of blowing hot air directly to the mixing / stirring system, and further mixing / stirring of microwaves from a magnetron. Examples of the method include irradiating the system.

Of these heating means, microwave irradiation is useful in improving the utilization of the active material. That is, the microwave vibrates the water molecules in which the powder is incorporated in the mixing / stirring system, thereby uniformly heating the powder. Therefore, the precursor of the conductive matrix formed on the surface of the powder is also oxidized while being heated uniformly, and as a result, the higher oxide of cobalt, which is a conductive layer, is formed on the surface of the powder. Is uniformly formed. In addition, this microwave irradiation may cause defects in the crystal structure of the nickel hydroxide powder or change the state of the pores depending on the input energy, and may change the surface of the nickel hydroxide powder after the treatment. It is thought that it may also act to increase the activity.

Such a heat treatment by microwave may be performed for about 20 minutes with respect to the mixing / stirring system. In this process, since the powder is constantly stirred and always uniformly heated by the microwave, the situation such as the reprecipitation of the cobalt complex ion accompanying the cooling of the alkaline aqueous solution does not occur. As a result, caking between the adjacent nickel hydroxide powders is suppressed, and no particle agglomerates are generated in the obtained processed product.

The heat treatment temperature at this time is preferably set in the range of 60 to 160 ° C. When the temperature is lower than 60 ° C., the amount of metal cobalt or a cobalt compound contained in the mixing / stirring system dissolved in the aqueous alkali solution is reduced, and the formation of the above-described conductive matrix becomes insufficient. The utilization rate of the substance is not so high
If the temperature is higher than 60 ° C., the nickel hydroxide powder itself starts to undergo a structural change and deteriorates as an active material.

It is preferable to operate the magnetron which oscillates the microwave so that the output is in the range of 0.5 to 12 kW per 1 kg of the powder system in the mixer. If the operation is performed in a state where the output is lower than 0.5 kW, the energy input from the microwave to the powder system is too small, and the powder system is sufficiently uniformly heated in the above temperature range. This is because difficulties arise, and a sufficient effect cannot be obtained in terms of characteristics even if the output is higher than 12 kW.

A heating / cooling jacket having a heating / cooling jacket disposed outside the mixing / stirring apparatus is used. Hot water is fed into the jacket, the apparatus itself is brought to a high temperature state, and the powder is further microwaved. The system may be heat treated. Further, the above-described heat treatment may be performed while flowing high-concentration oxygen inside the apparatus. In this way, an active material powder is obtained in which a conductive layer made of a higher oxide of cobalt is formed by coating the surface of the powder mainly composed of nickel hydroxide functioning as an active material.

In the present invention, the specific surface area of the active material powder is 15 m ^{2 as} measured by the BET method.
/ G or less. This specific surface area is 15
When it is larger than m ² / g, the amount of the alkaline electrolyte injected per unit volume of the active material powder (liquid ratio) must be increased, and therefore, the active material that can be accommodated in a battery having a constant capacity. This is because the powder is reduced in weight, which makes it difficult to increase the capacity of the battery.

The specific surface area can be determined, for example, by using a powder having a specific surface area as a powder mainly composed of nickel hydroxide as a starting material, or by using a pH value, temperature, It can also be adjusted by appropriately setting stirring conditions and the like. The alkaline secondary battery of the present invention is assembled as follows.

First, a positive electrode mixture is prepared using the active material powder produced as described above as a main component, and the positive electrode mixture is supported on a current collector to produce a positive electrode. After the power generation element is manufactured with the separator interposed therebetween, the power generation element is housed in the battery can. Here, the positive electrode mixture is produced by kneading the above-mentioned active material powder and the above-mentioned binder with water, as in the conventional case. When the battery to be manufactured is a nickel-hydrogen secondary battery, a negative electrode having a negative electrode mixture mainly composed of a powder of a hydrogen storage alloy supported on a current collector is used as the negative electrode. When the target battery is a nickel-cadmium secondary battery, a battery using a cadmium compound such as metal cadmium or cadmium hydroxide as a negative electrode active material is used.

Next, after a predetermined alkaline electrolyte is poured into the battery can, the battery can is sealed and a battery precursor is assembled according to a conventional method. At this time, in the present invention, the amount of the alkaline electrolyte to be injected is defined as follows. That is, the liquid ratio to the theoretical capacity (unit: Ah) of the positive electrode in the incorporated power generating element is 0.5 to 0.5.
It is defined as the injection volume of 2.0 cm ³ / Ah.

If the amount of the solution exceeds 2.0 cm ³ / Ah, the increase in the capacity of the battery is hindered. The smaller the liquid ratio is, the more advantageous it is for increasing the capacity of the battery.
If it is less than 5 cm ³ / Ah, the utilization rate of the active material is reduced, and the high-rate discharge characteristics of the battery and the discharge characteristics after being left are lowered.

Preferably, the liquid ratio is 0.8 to 1.5 cm ³ / A.
Make the injection volume to be h. Next, initial charging is performed on the obtained battery precursor. In this initial charging, it is not always necessary to adopt a condition that supplies an amount of electricity of 100% or more with respect to the theoretical capacity of the positive electrode as in the conventional case. Rather, it is more preferable that the initial charge be such that the amount of electricity supplied is 100% or less of the theoretical capacity of the positive electrode. This is for the following reasons.

The initial charge is performed to activate the positive and negative electrodes. Particularly, for a positive electrode containing a cobalt component, the cobalt component is oxidized to form a conductive material composed of a higher oxide of cobalt. It is an indispensable treatment for forming a conductive matrix and oxidizing nickel hydroxide to convert it to nickel oxyhydroxide. for that reason,
In view of the oxidation of the cobalt component, it was necessary to supply a sufficient amount of electricity at the time of the first charge, which was higher than the theoretical capacity of the positive electrode. Further, it has been considered that it is preferable to perform the initial charging at a low rate in order to completely realize the oxidation of the cobalt component before the nickel hydroxide.

However, in the case of the positive electrode incorporated in the battery of the present invention, at the time of assembling the battery precursor, the positive electrode already partially or entirely has a conductive matrix composed of a higher oxide of cobalt. It is not always necessary to generate a conductive matrix by initial charging as in the conventional case, that is, since it has already been activated to some extent before the initial charging, The required quantity of electricity is sufficient even if it is 100% or less of the theoretical capacity of the positive electrode.

In addition, it is not necessary to perform initial charging at a low current in order to oxidize the cobalt component prior to nickel hydroxide, and a charging rate of 0.5 C or more is sufficient.

[0044]

EXAMPLES Examples 1-4 and Comparative Examples 1-3 1-3. Production of Active Material Powder Cobalt hydroxide particles (conductive material) having an average particle size of 1 μm were added to a certain amount of nickel hydroxide powder having an average particle size of 10 μm.
0% by weight was mixed to prepare various mixed powders as raw materials of the active material powder. The concentration of the aqueous solution is 8N.
Sodium hydroxide aqueous solution was selected.

The mixed powder is charged into the inlet of the fluidized-granulation apparatus and stirred, and an aqueous sodium hydroxide solution is sprayed in such an amount that the powder and granules can be infiltrated, and the whole is stirred and mixed. At the same time, the magnetron was operated at 4.0 kW, irradiated with microwaves, and heat-treated at about 100 ° C. for 20 minutes to produce various active material powders. In addition,
At this time, the specific surface area of the obtained active material powder was changed as shown in Table 1 by using nickel hydroxide powder having different specific surface areas. Also, N in Table 1
The active material powder of o.5 is the starting material itself of the active material powder of No.3.

2. Production of electrodes The following nickel electrodes were produced using these active material powders. First, 0.2 part by weight of carboxymethylcellulose, 1.0 part by weight of PTFE dispersion (specific gravity 1.5, solid content 60% by weight) and 35 parts by weight of water were mixed and kneaded with 100 parts by weight of each active material powder. Then, a positive electrode mixture paste was prepared.

This paste is made to have a porosity of 95% and a thickness of 1.
A 7 mm nickel-plated porous sheet was filled, dried, and roll-rolled to form a nickel electrode. At this time, the filling amount of the active material powder is such that the theoretical capacity as a nickel electrode is 12
It was adjusted to be 00 mAh. On the other hand, a negative electrode was manufactured as follows.

First, commercially available misch metal, Ni, C
o, Mn, Al in a weight ratio of 4.0: 0.4: 0.3: 0.3.
It was mixed so that the ratio of the melt was cooled After dissolving the mixture in a high-frequency melting furnace, composition: MmNi _4.0
An ingot of a hydrogen-absorbing alloy of Co _0.4 Mn _0.3 Al _0.3 (Mm is a misch metal) was manufactured, crushed and classified to obtain an alloy powder having a particle size of 50 μm or less.

Based on 95 parts by weight of the alloy powder, 1.0 part by weight of carboxymethyl cellulose, 3.0 parts by weight of PTFE dispersion (specific gravity 1.5, solid content 60% by weight),
1.0 part by weight of carbon black and 50.0 parts by weight of water were blended to prepare a negative electrode mixture paste. This paste was applied to a punched nickel sheet having an aperture ratio of 45%, dried, and roll-rolled to form a hydrogen storage alloy electrode (negative electrode).

3. Battery assembly First, a polyolefin-based nonwoven fabric subjected to hydrophilic treatment is disposed as a separator between a nickel electrode using each active material powder and the hydrogen storage alloy electrode, and the whole is spirally wound to form an electrode group ( Power generation element). This electrode group was accommodated in a battery can, and an aqueous solution of potassium hydroxide having a concentration of 8.5 N was injected so as to have a liquid ratio shown in Table 1, and then a sealing plate was arranged to form a sealed cylindrical nickel-hydrogen secondary battery. A battery (AA size) was assembled.

[0051]

[Table 1]

4. Evaluation (1) First, regarding the battery of Example 3 and the battery of Comparative Example 1,
The capacity per unit active material and high rate discharge characteristics were measured according to the following specifications. Capacity measurement per unit active material: 360 for each battery
The battery was charged for 5 hours at mA and then discharged at 240 mA until the discharge end voltage reached 1.0 V, and the discharge capacity at that time was measured.

Then, the value obtained by dividing the measured value by the total weight of the positive electrode mixture in the nickel electrode is defined as the capacity per unit active material (mAh / g). Measurement of high rate discharge characteristics: Each battery is charged at 360 mA for 5 hours, and then at 2400 mA, the discharge end voltage is 1.0 V
Discharge (2C discharge) until is reached, and measure the discharge capacity at that time.

The battery was charged at 360 mA for 5 hours, and then charged for 3 hours.
Discharge at 600 mA until the discharge end voltage reaches 1.0 V (3 C discharge), and measure the discharge capacity at that time. The above results are shown in Table 2 as relative values where the measurement result of the battery of Comparative Example 1 is 100.

[0055]

[Table 2]

(2) A charge / discharge cycle test was performed on each of the batteries shown in Table 2 in accordance with the following specifications, and when the initial capacity of each battery was 100%, the number of cycles until the capacity reached 80% was determined. Was. Charge / discharge cycle test: Charging was performed at 1 C for 72 minutes (−dV = 10
mV). Discharge up to 1.0V at 1C.

Table 3 shows the results.

[0058]

[Table 3]

(3) The following is clear from the above results. As is clear from Table 2, the battery of Example 3 and Comparative Example 1
The battery of the above is excellent in both the capacity per unit active material and the high-rate discharge characteristics, although the batteries have the same liquid ratio except that the active material powder used is different. Active material powder No. 3 and active material powder No. 5 both have the same specific surface area of 15 m ² / g.
No. 3 is obtained by subjecting the active material powder No. 5 to a thermal alkali treatment by microwave irradiation. The surface of the nickel hydroxide powder has a conductive layer made of a higher oxide of cobalt formed thereon. Taking this into consideration, the above measurement results prove the usefulness of using an active material powder having a conductive layer formed on the surface of a nickel hydride powder by microwave irradiation.

As is clear from Tables 1 and 3, when the specific surface area of the active material powder used is larger than 15 m ² / g, the charge-discharge cycle life characteristics are significantly reduced (Comparative Examples 2 and 3).

[0061]

As is apparent from the above description, the alkaline secondary battery of the present invention has a high utilization rate of the active material, has excellent high-rate discharge characteristics, and has excellent charge-discharge cycle life characteristics. It is useful as a high-capacity battery with a long service life.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA02 AA04 BB04 BC01 BC05 BD03 BD05 5H016 AA01 AA02 CC09 EE05 HH01 HH06 HH15 5H028 AA01 AA06 BB15 CC10 EE05 EE10 HH00 HH01 HH02

Claims (2)

[Claims] 1. An alkaline secondary battery in which an electrode group comprising a separator disposed between a positive electrode and a negative electrode is enclosed in a battery can together with an alkaline electrolyte, wherein the positive electrode comprises nickel hydroxide. A conductive layer is formed on part or all of the surface of the powder mainly composed of
An active material powder having a specific surface area of 15 m ² / g or less as measured by the ET method is supported, and at the same time, the ratio of the alkaline electrolyte to the theoretical capacity (unit: Ah) of the positive electrode is 0.5. An alkaline secondary battery having a density of about 2.0 cm ³ / Ah. 2. The alkaline secondary battery according to claim 1, wherein said conductive layer is made of a higher oxide of cobalt.