JPH0950805A - Nickel electrode for alkaline storage battery and active material for nickel electrode and its manufacturing method and alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an effect to suppress expansion of an electrode plate while effectively utilizing properties such as the high use efficiency of an active material and the excellent over-discharging property of an active material which is produced by forming higher valence cobalt oxide on the surface of nickel hydroxide particles by alkaline thermal treatment. SOLUTION: An aqueous solution of nickel sulfate is prepared and while the solution being stirred, a sodium hydroxide solution is gradually dropped to precipitate nickel hydroxide crystal. Then, while the aqueous solution in which the crystal is precipitated being stirred, a cobalt sulfate solution and a sodium hydroxide solution are dropped to deposit cobalt hydroxide on the surface of the nickel hydroxide crystal. The produced granular material is separated and taken out, washed with water, dried, and the granular material is treated by an alkaline thermal treatment in which the resultant granular material is impregnated with an aqueous solution of sodium hydroxide in a prescribed concentration by adding the solution while being stirred in a beaker and then the material is heated while being stirred further. A prescribed amount of a cobalt hydroxide powder on the market is then added to the granular material treated by alkaline thermal treatment to produce the active material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel electrode used in an alkaline storage battery, particularly a non-sintered nickel electrode, an active material thereof, and a method for producing them.

[0002]

2. Description of the Related Art A nickel electrode for an alkaline storage battery is constructed by holding an active material containing nickel hydroxide as a main component on a substrate. In addition to a sintered nickel electrode which has been widely used in the past, There is also known a non-sintered nickel electrode formed by filling a base material such as foamed nickel or the like with an active material or forming it into a paste and holding it on a punching metal or the like.

Such a nickel electrode is used as a positive electrode of an alkaline storage battery such as a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery. Since the alkaline storage battery is used as a power source for portable electronic equipment, etc. There is also a great demand for higher capacity and longer life. The non-sintered type electrode is advantageous in that the packing density of the active material can be made higher than that of the sintered type when considering the increase in the capacity of the battery. Studies have also been carried out to improve the utilization rate of the active materials.

Techniques for improving the utilization rate of the active material include adding cobalt or a cobalt compound to particles containing nickel hydroxide as a main component, precipitating and coating the cobalt compound on the surface of the particles, or adding particles to the particles. It is conventionally known that after coating with a cobalt compound, it is further oxidized with hydrogen peroxide solution. Thus, the nickel positive electrode plate filled with an active material containing cobalt or a cobalt compound, when incorporated into an alkaline storage battery, the cobalt species is once dissolved in the electrolytic solution, uniformly dispersed on the surface of nickel hydroxide,
By the first charge thereafter, the active material-active material and the active material-current collector are deposited in a connected form. This precipitate becomes cobalt oxyhydroxide, and the conductive network of this cobalt oxyhydroxide improves the conductivity between the active material and the active material and between the active material and the current collector, thereby increasing the utilization rate of the active material. It is expected to improve.

However, even if a positive electrode is filled with a nickel active material containing such a cobalt species to produce a battery, the cobalt compound enters into the nickel hydroxide particles at the time of overdischarge, and the effect of the cobalt compound is lost. As a result, there is a problem in terms of over-discharge characteristics that the improvement of the utilization rate does not continue. On the other hand, the present inventors have filed Japanese Patent Application No. 6-22
5104, the nickel hydroxide particles whose surface is coated with a cobalt compound are further heat-treated in an oxygen atmosphere in which an alkali coexists (hereinafter referred to as an alkali heat treatment).
It is possible to form a high-order cobalt oxide having a valence higher than 2 on the surface of the nickel hydroxide particles in advance, thereby enhancing the effect of improving conductivity, and at the same time, forming a crystal of the nickel hydroxide particles. Change the state,
It was shown that there is an effect of improving over-discharge characteristics.

On the other hand, when looking at extending the life of a battery,
In the case of the non-sintered nickel electrode, swelling of the electrode is more likely to occur than in the sintered electrode, which tends to affect the battery life.
It has been conventionally known that the production of γ-NiOOH in the positive electrode is the main cause of swelling of the positive electrode, and the production of γ-NiOOH is suppressed by adding solid solution of cobalt, zinc, cadmium, etc. A technique for preventing swelling of spores is also known.

In this regard, JP-A-3-78965 discloses a nickel electrode active material in which a layer of cobalt oxyhydroxide is formed on the surface of nickel hydroxide to which zinc, cadmium and cobalt are added as a solid solution. . In this active material, addition of a solid solution enhances the hydrogen bonding between the layers of the active material, and the cobalt oxyhydroxide layer has a function of blocking the permeation of cations and water molecules from the outside into the active material. The generation of
It has been shown that the increase of the internal pore volume and the swelling of the electrode are prevented, which contributes to the longer life of the battery.

[0008]

By the way, also in the nickel active material on the surface of which the higher order cobalt oxide is formed by the above-mentioned alkali heat treatment, similarly, the higher order cobalt oxide has cations or water from the outside. It can be expected that the effect of suppressing the swelling of the electrode having a function of preventing the permeation of the molecule into the active material can be expected, and it is also considered that the combined use of the addition of the solid solution can enhance the effect of suppressing the electrode swelling. At present, there is a demand for a material having a high effect of suppressing electrode swelling.

In view of the above situation, the present invention provides the active material utilization rate and the over-discharge characteristics of the active material in which the higher order cobalt oxide formed by the above-mentioned alkali heat treatment is formed on the surface of the nickel hydroxide particles. This is done for the purpose of further improving the effect of suppressing swelling of the electrode plate while taking advantage of the excellent property. That is, an object of the present invention is to provide a nickel electrode and an active material for a nickel electrode, which have excellent utilization factor and overdischarge characteristics of the active material and have low electrode plate swelling property, and a method for producing the same.

[0010]

In order to solve the above-mentioned problems, a nickel electrode for an alkaline storage battery according to claim 1,
Higher order cobalt oxide particles having a valence higher than 2 are formed by heat-treating particles containing nickel hydroxide as a main component and a cobalt compound on the surface in the presence of alkali and oxygen. It is characterized in that the nickel hydroxide granules arranged on the surface and the cobalt compound having a valence of 2 or less added to the nickel hydroxide granules are held by a holder.

The nickel electrode active material according to claim 2 is formed by heat-treating particles having a cobalt compound on the surface of particles containing nickel hydroxide as a main component in the presence of an alkali and oxygen. And nickel hydroxide granules in which a higher-order cobalt oxide having a valence higher than divalent is arranged on the particle surface, and a cobalt compound having a valence of 2 or less added to the nickel hydroxide granules, It is characterized by consisting of.

The invention according to claim 3 is the same as the invention according to claim 2, wherein the active material for a nickel electrode is a nickel hydroxide granular material in which a higher-order cobalt oxide is arranged on the particle surface, It is characterized by being a mixture with a cobalt compound having a valence of 2 or less. Further, in the invention described in claim 4, in contrast to the invention described in claim 3, the content of the cobalt compound disposed on the surface of the nickel hydroxide granules is 1 weight with respect to the weight of the nickel hydroxide granules. % To 15% by weight.

Further, the invention of claim 5 is different from the invention of claim 3 in that the content of the cobalt compound having a valence of 2 or less is 0.5% by weight based on the weight of the active material. ~ 7
It is characterized in that it is wt%. Further, in the method for producing an active material for a nickel electrode according to claim 6, an alkali which heat-treats a granular material in which a cobalt compound is arranged on the surface of particles containing nickel hydroxide as a main component in the presence of alkali and oxygen. It is characterized by comprising a heat treatment step and a cobalt compound addition step of adding a cobalt compound having a valence of 2 or less to the product of the alkali heat treatment step.

According to a seventh aspect of the present invention, there is provided a method for producing a nickel electrode for an alkaline storage battery, wherein a granular material having a cobalt compound on the surface of particles containing nickel hydroxide as a main component is treated in an oxygen atmosphere in which an alkali coexists. 2 in the product of the alkali heat treatment process and the alkali heat treatment process
It is characterized by including a cobalt compound addition step of adding a cobalt compound having a valence of not more than a valence and a filling step of filling the substrate with the product of the cobalt compound addition step.

The alkaline storage battery according to claim 8 is
Higher order cobalt oxide particles having a valence higher than 2 are formed by heat-treating particles containing nickel hydroxide as a main component and a cobalt compound on the surface in the presence of alkali and oxygen. A nickel electrode provided with nickel hydroxide granules arranged on the surface and a cobalt compound having a valence of 2 or less added to the nickel hydroxide granules; and having a concentration of 7 normal to 8.5 normal It is characterized by comprising an alkaline electrolyte containing a hydroxide of an alkali metal and a negative electrode provided with an MmNi ₅ type hydrogen storage alloy.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention conducted research on utilization rate of an active material, over-discharge characteristics, and electrode swelling property in a nickel positive electrode in an alkaline storage battery. When the following cobalt oxide is an active material formed on the surface of nickel hydroxide particles, it has been found that the characteristics of the active material in terms of utilization rate and overdischarge characteristics are excellent as described above. The present invention has been found out that the effect of suppressing swelling of the positive electrode is added by adding a cobalt compound having a valence of 2 or less, such as cobalt hydroxide powder, to the active material.

Here, although high-order cobalt oxide is already present on the surface of the nickel hydroxide particles, 2
The effect of suppressing the swelling of the positive electrode by further adding a cobalt compound having a valence of less than is not well understood, but the effect of suppressing the swelling of the positive electrode by adding a cobalt compound having a valence of 2 or less It has been confirmed by experiments as will be described later that the above phenomenon occurs and that this positive electrode swelling suppression effect is greater than that obtained by increasing the cobalt content on the surface of the nickel hydroxide particles.

The effect of adding the cobalt compound having a valence of 2 or less is the same even when a small amount of the cobalt compound or the like is solid-dissolved in the nickel hydroxide particles. Hereinafter, an example of the present invention, an experiment conducted together with a comparative example, and an effect derived from the result will be described. (Embodiment) FIG. 1 is a diagram showing a manufacturing process of a nickel active material and a nickel positive electrode according to an embodiment of the present invention, and also schematically shows the state of nickel particles in each process.

Based on this figure, a method for producing a nickel active material and a nickel positive electrode, and features of the nickel active material and the nickel positive electrode will be described. [Preparation of Nickel Active Material] A mixed aqueous solution of nickel sulfate, zinc sulfate, and cobalt sulfate was adjusted so that zinc was 0.02 and cobalt was 0.02 with respect to nickel in a molar ratio, and while stirring this, A sodium hydroxide solution is gradually added dropwise to stabilize the pH at 13 to 14 during the reaction to precipitate nickel hydroxide crystals. Traces of zinc and cobalt are solid-dissolved in the precipitated nickel hydroxide crystals.

Next, while stirring the aqueous solution in which the nickel hydroxide crystals are deposited, a cobalt sulfate aqueous solution having a specific gravity of 1.30 and a 25 wt% sodium hydroxide aqueous solution are dropped to maintain the pH at 9 to 10. As a result, particles of nickel hydroxide crystals as nuclei and cobalt hydroxide precipitated on the surface thereof are produced. Here, the amount of cobalt hydroxide to be deposited on the surface of nickel hydroxide, that is, the content of cobalt hydroxide in the formed particles, is maintained by maintaining the concentration of the dropped cobalt sulfate aqueous solution and the pH at 9 to 10. By adjusting the aging time, the addition amount can be adjusted to a predetermined value.

The granules thus produced are separated, washed with water and dried. Then, while stirring the separated granules in a beaker, an aqueous solution of sodium hydroxide having a predetermined concentration is added and impregnated into the beaker, and further heated for 0.5 hours at a predetermined temperature while stirring, thereby performing an alkali heat treatment step. I do. The amount of the alkaline aqueous solution to be impregnated is, for example, 4
In the case of 0 wt% sodium hydroxide, a solution prepared by dissolving 5 parts by weight of sodium hydroxide in 7.5 parts by weight of water with respect to 95 parts by weight of the granular material is used, and when changing the alkali concentration,
Change the amount of sodium hydroxide dissolved.

In this alkaline heat treatment step, the cobalt hydroxide attached to the surface is made higher-order, and the produced granules have nickel hydroxide particles as nuclei and higher-order water having a valence higher than two. Cobalt oxide is particles arranged on the surface. Further, as described later, it is considered that the state of the nickel hydroxide crystal is also changed in favor of the overdischarge characteristic.

For the alkali-heat treated granules,
An active material is produced by adding and mixing a predetermined amount of commercially available cobalt hydroxide powder. The active materials A, B1 to B4, C1 to C4, D1 to D4, E1 to
E4 was produced. Tables 1 to 5 below show, for each of the produced active materials, the surface cobalt content of the granular material subjected to the alkali heat treatment before the addition of cobalt hydroxide, the sodium hydroxide concentration and the heat treatment temperature at the time of the alkali heat treatment, The amount of cobalt powder added (that is, the amount of cobalt added separately) is shown.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5] The characteristics of each active material are as follows. Active material A has a surface cobalt content of 7 wt%, an additional cobalt content of 3 wt%,
The concentration of sodium hydroxide aqueous solution during alkaline heat treatment is 2
The heat treatment temperature is 5 wt% and the heat treatment temperature is 80 ° C.

The active materials B0, B1, B2, B3, B4 and B5 are
Same as the active material A, but with a surface cobalt content of 0.
It was changed to 5%, 1%, 3%, 7%, 15%, 16%. In addition, active materials C0, C1, C2, C3, C4,
C5 is the same as the active material A, but the amount of attached cobalt is changed to 0.3%, 0.5%, 2%, 5%, 7% and 8%.

Further, the active materials D0, D1, D2, D3, D4,
D5, D6, and D7 are the same as the active material A, but the concentration of the aqueous sodium hydroxide solution is 8%, 10%, 12%, 15
%, 25%, 35%, 40%, 45%. In addition, active materials E0, E1, E2, E3, E4, E5,
E6 is the same as the active material A, but the heat treatment temperature is 40
℃, 50 ℃, 70 ℃, 80 ℃, 120 ℃, 150 ℃, 1
It was changed to 60 ° C.

The surface cobalt contents shown in Tables 1 to 5 were measured by the following method. Since nickel hydroxide and cobalt oxide are easily dissolved in hydrochloric acid, the alkali-heat-treated granular material before adding cobalt hydroxide is dissolved in hydrochloric acid water, and the ratio of Ni and Co in this solution is analyzed by ICP. This granular material was regarded as being formed of nickel hydroxide and cobalt hydroxide, and was measured.
Based on the ratio of Co and Co, wt% of cobalt hydroxide with respect to the weight of the entire granular material is calculated, and this value is taken as the surface cobalt content.

The values of the amount of cobalt added as shown in Tables 1 to 5 indicate the weight of the added cobalt hydroxide powder with respect to the weight of the produced active material. The active material A
Regarding the granular material subjected to the alkali heat treatment before the addition of cobalt hydroxide, the analysis regarding the higher order was performed as follows. When the crystal structures of the alkali-heat-treated granules and the cobalt hydroxide crystal standard product were compared by X-ray diffraction analysis, the alkali-heat-treated granules showed that the cobalt hydroxide crystal crystals were larger than those of the cobalt hydroxide crystal standard product. The X-ray diffraction peak had disappeared. It is considered that this is because most of the cobalt hydroxide on the surface of the granular material subjected to the alkali heat treatment was changed to trivalent cobalt oxide.

Further, while the divalent cobalt oxide is soluble in nitric acid, the trivalent cobalt oxide is difficult to dissolve in nitric acid, and the average oxidation number of the higher-order cobalt oxide is calculated as follows. Was measured as follows. First, a predetermined amount of alkali-heat-treated granular material is washed with a hydrochloric acid solution, and the amount of cobalt eluted in this washing solution is measured by ICP to obtain a divalent cobalt content.

Next, the same amount of the granular material that has been subjected to the alkali heat treatment is washed with a nitric acid solution, and the amount of cobalt eluted in this washing liquid is measured by ICP to obtain the total cobalt content. The difference between the total cobalt content and the divalent cobalt content is the trivalent cobalt content. The average oxidation number was calculated from the divalent cobalt content and the trivalent cobalt content thus obtained.

The average oxidation number of the active material A which had been subjected to the alkali heat treatment before the addition of cobalt hydroxide was measured by this method was 2.9. Further, almost the same values were obtained for the other active materials. The average oxidation number of the cobalt hydroxide crystal standard product was 2.0 as measured by the same measurement method. From this, it is judged that most of the cobalt hydroxide on the surface of the particles has been converted to the trivalent cobalt oxide by the alkali heat treatment.

[Production of Nickel Positive Electrode] A positive electrode was produced as follows using each nickel active material thus produced. 100 parts by weight of each active material and 50 parts by weight of a 0.2 wt% hydroxypropylcellulose aqueous solution were mixed to prepare an active material slurry liquid. This active material slurry liquid was filled in nickel foam having a porosity of 95% and a thickness of 1.6 mm, dried, and then rolled to a thickness of 0.60 mm to give a nominal capacity of 120.
A 0 mAh positive electrode was prepared. The weight of each active material to be filled in the positive electrode was common, and the weight of the active material to be filled was calculated from the nominal capacity by regarding the active material as nickel hydroxide.

Comparative Example Active material X1, X2, X of Comparative Example
3, X4 and X5 were manufactured as follows. Active material X1: Precipitated nickel hydroxide crystals were collected in the same manner as in the above example, and cobalt hydroxide powder was added thereto in an amount of 7 w.
The active material X1 was obtained by adding and mixing t%. Active material X2: Similar to the active material A of the above-mentioned example, cobalt hydroxide was deposited on the surface of the nickel hydroxide particles, and the granular material obtained by performing the alkali heat treatment was used as the active material X2.

Active material X3: Same as active material X2, but active material X3 having a cobalt content of 10 wt% on the surface
It was 3. Active material X4: Similar to the active material A of the above-mentioned example, a granular material in which cobalt hydroxide was deposited on the surface of nickel hydroxide particles was taken out and subjected to oxidation treatment with hydrogen peroxide solution. The active material X4 was used.

Active material X5: To the active material X4, 3 wt% of cobalt hydroxide powder was added and mixed to obtain an active material X5. In Table 1 above, each active material X produced in this way
Also for 1, X2, X3, X4, and X5, the content of surface cobalt in the granular material, the manufacturing conditions when each active material was manufactured, and the amount of attached cobalt are described.

Each nickel active material X thus prepared
Using 1, X2, X3, X4, and X5, a positive electrode was produced in the same manner as in the above-mentioned example. (Experiment) Using each of the positive electrodes of Example 1 and Comparative Example produced as described above, an alkaline storage battery was produced as follows.

First, a common negative electrode is manufactured as follows. Misch metal (Mm), nickel, cobalt, aluminum, manganese 1.0: 3.6: 0.6: 0.
The mixture is mixed at a ratio of 2: 0.6, and this mixture is made into a molten alloy in a high frequency induction furnace in an argon gas atmosphere. Then, this molten alloy is cooled and the composition formula Mm _1.0 Ni _3.6 Co _0.6 Al
An ingot represented by _0.2 Mn _0.6 is produced. This ingot is crushed to produce a hydrogen storage alloy having an average particle size of about 100 μm.

A binder such as polyethylene oxide and an appropriate amount of water are added to the hydrogen storage alloy and mixed to prepare a hydrogen storage alloy paste, which is applied to both sides of the punching metal.
After drying, a negative electrode is formed by rolling to a thickness of 0.4 mm. Then, using each positive electrode and the common negative electrode, a cylindrical sealed nickel-hydrogen storage battery (AA size) was manufactured.

In this alkaline storage battery, an electrode group formed by stacking a positive electrode using non-sintered nickel as an active material and a negative electrode containing a hydrogen storage alloy via a separator and spirally winding the electrode group has a cylindrical exterior. It was housed in a can and impregnated with an alkaline electrolyte to prepare the device. As the alkaline electrolyte, 7 to
An 8.5 KOH aqueous solution was used, and a nylon non-woven fabric was used as the separator.

The theoretical capacity of the battery is defined by the positive electrode, and the capacity of the negative electrode is set to be larger than that and about 1.5 times. Using the positive electrode and the battery thus produced, the following unipolar test and battery performance test were performed. * Monopole test (1) Measurement of electrode plate utilization For each nickel electrode for each test, a simple open cell was made using a nickel electrode as the counter electrode and about 25 wt% KOH aqueous solution, and charged at 120 mA for 24 hours. To do. Next, the nickel plate is discharged at 400 mA until the discharge end voltage becomes −0.8 V, and the discharge capacity is measured. Then, the ratio of the measured discharge capacity value to the nominal capacity (1200 mAh) of the electrode is taken as the utilization rate of the active material.

(2) Measurement of electrode plate swelling With respect to the nickel electrode for each test, an open type simple cell was prepared using a nickel electrode as a counter electrode and an aqueous solution of about 25 wt% KOH, and charged at 120 mA for 24 hours. . Then, the active material of the nickel electrode in this charged state is dropped and taken out, and the intensity ratio is measured by X-ray diffraction to obtain the ratio of γ-NiOOH / β-NiOOH, which is taken as the value of the electrode plate swelling property. did.

* Battery performance test (1) Measurement of capacity per unit active material The battery for each test is charged at 120 mA for 16 hours. Next, it discharges at 240 mA until the discharge end voltage becomes 1.0 V, and the discharge capacity is measured. Then, the weight of nickel hydroxide corresponding to the theoretical capacity (1200 ÷ 289)
The measured discharge capacity for (g)) is taken as the capacity per unit active material.

(2) Over-discharge characteristics The battery for each test was 1200 mA at room temperature.
When the voltage drop amount (-ΔV) shows 10 mV after the charging voltage shows the maximum value, the charging is finished,
After resting for 1 hour, discharging is performed at 1200 mA, and when the discharge voltage reaches 1 V, the discharging is finished.

Here, the discharge capacity is measured during the discharge. Then, forced discharge is further performed at 60 mA for 16 hours. This cycle of-is repeated for 10 cycles, and the cycle of-is repeated for 5 cycles, and the discharge capacity is measured at the time of discharging at the fifth cycle. The ratio of the discharge capacity measured last (before forced discharge) to the discharge capacity measured first (before forced discharge) is taken as the value of the overdischarge characteristic.

[Test Results and Discussion] Table 1 shows the capacity per unit active material, the overdischarge characteristics, and the degree of electrode plate swelling suppression for the active material A of the example and the active materials X1 to X5 of the comparative example. Has been done. In addition, the capacity per unit active material and the numerical value of the over-discharge characteristic shown in Table 1 are shown as an index with the value for the active material X1 as a reference value 100. In addition, the numerical value of the electrode plate swelling inhibition degree is indicated by an index in which the reciprocal of the electrode plate swelling is based on the value for the active material X1 as the reference value 100 (that is, the larger the value, the less the electrode plate swells. ).

In the active material A and the active material X2, the capacity per unit active material and the overdischarge characteristics are higher than those of the active materials X1, X4 and X5. This is because the active material A and the active material X2 have a higher-order cobalt hydroxide layer formed on the surface of the nickel hydroxide crystal nuclei. In contrast to the formation of a conductive network, in the active material X1, the cobalt hydroxide as an attachment is present, but since a higher-order cobalt hydroxide layer is not formed, it is used in a battery. Formation of conductive network is weak, and active materials X4, X5
Although the cobalt oxyhydroxide layer is formed by hydrogen peroxide solution, it is considered that the formation of the conductive network when used in a battery is weaker than in the case of the alkali heat treatment.

In addition, the active materials X4 and X5 have lower over-discharge characteristics than the active materials A and X2 because they have been subjected to a higher-order treatment with hydrogen peroxide solution, which is the case with alkaline heat treatment. It is considered that this is due to the fact that it does not change the state of the crystal particles of nickel hydroxide. Also in Table 1,
The active material A is the active material X2, X3 with respect to the electrode plate swelling suppression degree.
And higher than the active material X4 (less swelling). This indicates that the separately added cobalt hydroxide has an action of suppressing swelling of the positive electrode.

Here, the active material A and the active material X3 both have a total cobalt content of about 10 wt%.
Has a greater degree of inhibition of electrode plate swelling than the active material X3. This indicates that the separately added cobalt hydroxide in the active material A has a suppressing effect more than the suppressing effect of the electrode plate swelling due to the mere increase of the cobalt content. In addition, active material A
The degree of inhibition of electrode plate swelling is higher than that of the active materials X1 and X5. This is similar to the point that cobalt hydroxide is added, but when nickel hydroxide is covered with a higher-order cobalt oxide layer subjected to alkali heat treatment as in the active material A, , The effect of suppressing the swelling of the electrode plate is greater than that of the case where it is not covered with the cobalt oxide layer or the case where it is covered with the cobalt oxyhydroxide layer by the hydrogen peroxide solution.

As described above, the granular material in which the higher order cobalt oxide is formed on the surface of the nickel hydroxide particles by the alkali heat treatment has a good utilization factor of the active material and the overdischarge characteristics. It can be seen that the effect of suppressing swelling of the positive electrode is added by further adding cobalt hydroxide. Table 2 shows the active materials B0, B1, B2, B of the examples.
The results of capacity per unit active material and over-discharge characteristics are shown for 3, B4 and B5. The values of the capacity per unit active material and overdischarge characteristics in Table 2 are the same as those of the active material A and the active material B.
The value for 3 is shown as an index with a reference value of 100.

The active materials B0, B1, B2, B3, and B4 have higher unit active material capacities than the active material B5. In addition, the active materials B1, B2, B3, B4, and B5 have higher over-discharge characteristics than the active material B0. This is because when the surface cobalt content is less than 1 wt%, a sufficient conductive network cannot be ensured, so the over-discharge characteristics deteriorate, and when it exceeds 15 wt%, the proportion of nickel hydroxide in the active material is high. It is considered that the decrease in the value of the value affected the decrease in the capacity per unit active material.

From this, as the surface cobalt content,
It can be seen that the range of 1 to 15 wt% is good. Table 3
Shows the results of the capacity per unit active material and the electrode plate swelling property for the active materials C0, C1, C2, C3, C4 and C5 of the examples. The capacity per unit active material in Table 3 is shown as an index with the value for the active material C2 as a reference value of 100, and the electrode plate swelling inhibition degree is the reciprocal of the electrode plate swelling property, and the value for the active material C2 is shown. It is shown as an index with a standard value of 100 (that is, the larger the value, the less swelling of the electrode plate).

The active materials C0, C1, C2, C3, and C4 have a higher capacity of the unit active material than the active material C5. In addition, the active materials C1, C2, C3, C4, and C5 have a higher electrode plate swelling suppression value than the active material C0. This is because if the amount of attached cobalt is less than 0.5 wt%,
When the electrode plate swelling suppression effect cannot be sufficiently ensured and exceeds 7 wt%, it is considered that the decrease in the proportion of nickel hydroxide in the active material has affected the decrease in the capacity per unit active material.

From this, the amount of the additional cobalt was 0.
It can be seen that the range of 5 to 7 wt% is good. Table 4 shows the active materials D0, D1, D2, D3, D4, D5, D of the examples.
The results of the capacity per unit active material are shown for D6 and D7. In addition, the numerical value of the capacity per unit active material in Table 4 is shown as an index with the reference value 100 being the value for the same active material D4 as the active material A.

The capacities of the active materials D1, D2, D3, D4, D5 and D6 are higher than the capacities of the active materials D0 and D7. This is because when the concentration of the alkaline aqueous solution is less than 10 wt% during the alkali heat treatment, the alkaline aqueous solution has a weak ability to dissolve cobalt hydroxide, so that the action of producing higher-order cobalt hydroxide is weak and exceeds 40 wt%. In this case, it is considered that the alkaline aqueous solution has a high viscosity and a low permeability to the granular material, and thus the action of producing higher-order cobalt hydroxide is weak.

From this, it can be seen that the concentration of sodium hydroxide to be impregnated is appropriately in the range of 10 wt% to 40 wt%. Table 5 shows the active materials E0, E1, and
The results of the capacity per unit active material are shown for E2, E3, E4, E5 and E6. In addition, the numerical value of the capacity per unit active material in Table 4 is shown as an index with the reference value 100 being the value for the same active material E3 as the active material A.

The capacities of the active materials E1, E2, E3, E4, E5 are higher than the capacities of the active materials E0, E6.
This is because when the temperature is less than 50 ° C. during the alkali heat treatment, the alkaline aqueous solution has a weak ability to dissolve cobalt hydroxide and a weak effect of producing higher-order cobalt hydroxide.
It is considered that when the temperature exceeds 50 ° C., the structure of nickel hydroxide itself is changed and the performance as an active material is deteriorated.

From this, the heat treatment temperature is from 50 ° C to
It turns out that the range of 150 ° C. is suitable. In the above experiment, an example of performing the test by filling the active material in foamed nickel was shown, but the same result is obtained when the paste type electrode in which the active material is held in punching metal is manufactured and tested. Is considered to be obtained.

Further, in the above-mentioned embodiment, an example in which the alkali heat treatment is carried out by using the granular material in which cobalt hydroxide is deposited on the surface of the nickel hydroxide crystal in which a trace amount of zinc and cobalt are solid-dissolved is shown. The same can be done when the nickel hydroxide crystal contains cadmium or the like. Further, in general, if it is a granular material in which a cobalt compound is arranged on the surface of particles containing nickel hydroxide as a main component, it can be carried out by similarly subjecting to alkali heat treatment.

Further, in the above-mentioned embodiment, the example of using the sodium hydroxide aqueous solution as the alkali aqueous solution at the time of the alkali heat treatment is shown, but the same can be carried out by using the potassium hydroxide aqueous solution or the like. Further, the same operation can be performed by adding a small amount of lithium hydroxide to the alkaline aqueous solution. In addition, in the above-mentioned examples, an example in which cobalt hydroxide is used as the cobalt compound having a valence of 2 or less is shown.
It is considered that a similar effect can be obtained even if a cobalt compound having a valency or less is used.

Further, in the above embodiment, an example of adding and mixing cobalt hydroxide powder was shown, but the form of addition is not limited to powder mixing, and for example, alkali heat treatment may be performed to perform higher cobalt oxidation. It is considered that the same effect can be obtained when cobalt hydroxide is further deposited on the surface of the granular material on which the physical layer is formed.

[0065]

According to the nickel active material of the present invention described above, the active material utilization ratio of the active material in which a higher order cobalt oxide having a valence higher than 2 is formed on the surface of nickel hydroxide particles by the alkali heat treatment It is possible to improve the suppression of electrode plate swelling by further adding a divalent or lower valent cobalt compound while making the most of the characteristics of high and excellent over-discharge characteristics.

Therefore, this is a valuable technique for realizing high capacity and long life of the alkaline storage battery.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a nickel active material and a nickel positive electrode according to an embodiment of the present invention.

Claims (8)

[Claims] 1. A high-order particle having a valence of more than 2 formed by heat-treating particles having a cobalt compound on the surface of particles containing nickel hydroxide as a main component in the presence of alkali and oxygen. Nickel hydroxide granules in which cobalt oxide is arranged on the particle surface, and a cobalt compound having a valence of 2 or less and added to the nickel hydroxide granules are held by a holder. Nickel electrode for alkaline storage battery. 2. A high-order particle having a valence of more than two, which is formed by heat-treating particles having a cobalt compound on the surface of particles containing nickel hydroxide as a main component in the presence of alkali and oxygen. A nickel electrode active material comprising: a nickel hydroxide granular material in which cobalt oxide is arranged on a particle surface; and a cobalt compound having a valence of 2 or less added to the nickel hydroxide granular material. material. 3. The nickel electrode active material is a mixture of nickel hydroxide granules in which the higher order cobalt oxide is arranged on the particle surface and a cobalt compound having a valence of 2 or less. The active material for a nickel electrode according to claim 2, wherein 4. The content of the cobalt compound disposed on the surface of the nickel hydroxide granules is 1% by weight to 15% by weight based on the weight of the nickel hydroxide granules. 3. The active material for a nickel electrode according to 3. 5. The content of the cobalt compound having a valence of 2 or less is 0.5% by weight to 7% by weight based on the weight of the active material.
The active material for a nickel electrode according to claim 3, wherein the active material is in a weight percentage. 6. An alkali heat treatment step of heat-treating a granular material having a cobalt compound on the surface of particles containing nickel hydroxide as a main component in the presence of alkali and oxygen, and a product of the alkali heat treatment step. A cobalt compound addition step of adding a cobalt compound having a valence of 2 or less, and a method for producing an active material for a nickel electrode, comprising: 7. An alkali heat treatment step of heat-treating a granular material having a cobalt compound on the surface of particles containing nickel hydroxide as a main component in an oxygen atmosphere in which an alkali coexists, and a product of the alkali heat treatment step. And a cobalt compound addition step of adding a cobalt compound having a valence of 2 or less, and a filling step of filling the substrate with the product of the cobalt compound addition step. Method. 8. A high-order particle having a valence of more than two, which is formed by heat-treating particles having a cobalt compound on the surface of particles containing nickel hydroxide as a main component in the presence of alkali and oxygen. 7. Nickel electrode comprising nickel hydroxide granules in which cobalt oxide is arranged on the particle surface and a cobalt compound having a valence of 2 or less and added to the nickel hydroxide granules; An alkaline storage battery comprising: an alkaline electrolyte containing an alkali metal hydroxide having a concentration of ₅ N or less; and a negative electrode including an MmNi ₅ -based hydrogen storage alloy.