JPH10340721A - Production of positive electrode active material for alkaline secondary battery and paste-type nickel electrode and alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a positive active material, capable of improving the utilization factor of a paste type nickel electrode active material for alkaline secondary battery. SOLUTION: A cobalt-additive is added to an aqueous alkaline solution, from which dissolved oxygen is removed by blowing an inert gas, to prevent formation of tricobalt tetraoxide and produce a cobalt complex ion, then a nickel oxide active material powder is added to the aqueous alkaline solution to impregnate secondary nickel hydroxide powder, which is dispersed by blowing the inert gas, with a produced cobalt complex ion and then, blowing of the inert gas is stopped and in the resultant state, the cobalt complex ion is oxidized so as to produce cobalt oxyhydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material used in a nickel-cadmium battery, a nickel-hydride battery, a nickel-zinc battery, an alkaline secondary battery of a nickel-iron battery, and a paste-type nickel electrode. And an alkaline secondary battery.

[0002]

2. Description of the Related Art A conventional paste-type nickel electrode for an alkaline secondary battery uses a nickel-based powder such as metallic cobalt, cobalt hydroxide, or cobalt monoxide in order to increase the utilization rate of the nickel hydroxide active material. The one with the additives added is kneaded with an aqueous solution of a sizing agent such as carboxymethyl cellulose, and the paste is filled into a three-dimensional metal porous substrate such as foamed nickel or nickel felt, and dried and pressed. Are known. In an alkaline secondary battery using this paste-type nickel electrode plate as a positive electrode, the above-mentioned cobalt-based additive reacts with hydroxyl ions in the electrolyte to form a water-soluble cobalt complex ion (HCo
O ₂ ⁻ ) is formed, diffused, oxidized by charging and precipitated as conductive cobalt oxyhydroxide CoOOH in the nickel electrode, forming a so-called cobalt conductive matrix to form a conductive material between the nickel hydroxide active material particles. To increase the utilization rate. On the other hand, in order to increase the utilization rate of the nickel hydroxide active material of the paste nickel electrode in the same manner as described above, the active material was coated with cobalt oxyhydroxide before kneading the active material with a paste to form a paste. It is also known to manufacture such materials and to use them to manufacture paste-type nickel plates. (Japanese Patent Publication No. 8-35052). The manufacturing method is as follows. The nickel hydroxide active material powder and the additive of the cadmium compound are put in an alkaline aqueous solution and stirred, and K ₂ S ₂ O ₈ is added as an oxidizing agent.
And oxidizing the active material with the generated oxygen gas to produce a nickel active material coated with cobalt oxyhydroxide.

[0003]

However, according to the above-mentioned prior art, the cobalt compound such as cobalt hydroxide or cobalt monoxide has no conductivity per se,
Prior to the first charge, the conductivity between the nickel hydroxide active material particles and between the active material particles and the current collector is poor, so that the polarization at the time of the first charge is increased, and there is a concern that gas may be adversely affected. Therefore, a long charging time with a small current is required to secure a specified charging amount. In addition, metallic cobalt has a similar problem because it forms an oxide film on its surface. Therefore, in order to obtain a predetermined cobalt conductive matrix due to low reactivity with the electrolyte, the cobalt-based additive mixed in the conventional paste-type nickel electrode plate is an expensive cobalt-based additive. A large amount of addition was required, and the initial charging conditions had to be mild, and it was inevitable that the initial charging would take a long time. On the other hand, in the latter conventional technique, it is difficult to cover the surface of the primary particles constituting the secondary aggregate with the nickel oxyhydroxide without penetrating into the secondary aggregate of the generated nickel oxyhydroxide. Yes, therefore, in charging an alkaline secondary battery using a paste-type nickel electrode plate containing the same, the generation of conductive cobalt complex ions generated between active material particles is reduced, and as a result, the utilization rate of the active material is reduced. Is low. Therefore, it is desired to develop a method for producing a positive electrode active material which solves the above-mentioned problems in the method for producing a positive electrode active material and provides a paste-type nickel electrode having an improved active material utilization rate.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for producing a positive electrode active material for an alkaline secondary battery which has solved the above-mentioned problems. A) A cobalt-based additive as at least one kind of additive. Is added to an aqueous alkali solution, and a reaction solution containing a cobalt complex ion (HCoO ₂ ⁻ ) is prepared by stirring and reacting while blowing an inert gas into the aqueous alkali solution. After charging the powder and stirring while blowing in an inert gas to disperse the nickel hydroxide particles, the blowing of the inert gas is stopped, and an oxidizing agent is added to the dispersion to oxidize the cobalt complex ions. It is characterized by forming cobalt oxyhydroxide (CoOOH). In this case, as an additive, an additive for suppressing the expansion of the nickel electrode and / or a raw material for increasing the oxygen overvoltage is further added to the aqueous alkali solution, and the following is performed in the same manner as in the production of the above-described positive electrode active material. It consists in producing a positive electrode active material. Further, the present invention resides in a paste-type nickel formed using the positive electrode active material manufactured by the above-described manufacturing method. Further, the present invention resides in an alkaline secondary battery comprising the above-mentioned paste-type nickel as a positive electrode.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail. Metal cobalt and cobalt hydroxide, at least one selected from cobalt-based additives comprising a cobalt compound such as cobalt monoxide, the powder is blown with an inert gas such as argon, nitrogen and the like, lithium hydroxide and the like A predetermined amount is poured into an alkaline aqueous solution, the whole is stirred by bubbling, and the reaction is carried out while continuing to blow an inert gas to obtain a cobalt complex ion (HCo
A reaction solution in which O ₂ ⁻ ) has been prepared is prepared. This reaction may be carried out without heating the reaction solution, or may be carried out at 30 to 80 ° C. under a suitable high temperature. In this reaction, since the surface of the alkaline aqueous solution is covered with an inert gas, the above-mentioned reaction is performed in a state where air oxidation is prevented and there is almost no dissolved oxygen in the alkaline aqueous solution. Cobalt tetroxide Co _{3 with} inert additive
The cobalt additive used without O ₄ can be formed into the cobalt complex toon without waste.

[0006] Next, a predetermined amount of nickel hydroxide active material powder is charged into the reaction solution, and the powder is dispersed by bubbling with an inert gas and stirring is continued for a predetermined time.
A small amount of a water-soluble oxidizing agent is added, and stirring is continued, or air or oxygen is bubbled in to oxidize the cobalt complex ion, and the conductive cobalt oxyhydroxide (CoO
OH). Next, the reaction solution is subjected to solid-liquid separation by filtration or the like, and the solid content is washed with water, so that oxyhydroxide is contained in the nickel hydroxide active material composed of primary particles and secondary particles (aggregates of primary particles). The positive electrode active material of the present invention is obtained in which cobalt fine particles are mixed and the primary and secondary particles of the nickel hydroxide are coated.

In particular, according to the present invention, since the inert gas is blown to react with the aqueous alkali solution under an inert atmosphere as described above, the formation of cobalt complex ions is carried out smoothly and smoothly. Ions easily penetrate into the secondary particles of nickel hydroxide well stirred and dispersed under the bubbling of inert gas, i.e., the gaps between the myriad of primary particles that make up the secondary particle aggregates within the aggregates of primary particles I'm sick. In this state, after the blowing of the inert gas was stopped, it was oxidized with an oxidizing agent, so that it became conductive cobalt oxyhydroxide. Thus, it was covered with countless primary particles in the aggregate. Therefore, secondary particles with improved conductivity can be obtained. Thus, in the conventional manufacturing method, the conductivity inside the agglomerate of nickel hydroxide particles is improved as compared with the positive electrode active material in which almost no cobalt oxyhydroxide is generated. Active material can be manufactured. By using this, the conventional problems can be solved and a paste-type nickel electrode with improved utilization can be manufactured.

[0008] As the nickel hydroxide active material as a raw material, a material containing a solid solution such as cobalt, zinc, or calcium in its particles can also be used.

[0009] In addition to improving the utilization of the paste-type nickel electrode, an expansion inhibitor such as zinc and an oxygen overvoltage increasing agent such as calcium and yttrium are used in the present invention to suppress expansion or increase oxygen overvoltage. In the above-mentioned production method, a zinc-based additive or a calcium-based additive, or both additives are added to the aqueous alkali solution, and the mixture is stirred while blowing an inert gas and reacted under an inert atmosphere. Each of the complex ions is satisfactorily generated, and then the generated complex ions are stirred and dispersed in an inert atmosphere by blowing in an inert gas to allow the nickel hydroxide active material to penetrate into the secondary particles. The blowing of the inert gas is stopped, and the inert gas is oxidized by an oxidizing agent to coat not only the primary particles of the nickel hydroxide active material in and out of the secondary particles but also the sub-particles. Positive electrode active material results in swelling suppression effect or / and oxygen overvoltage rise effect of the hydroxide and / or mixed nickel electrode plate in the form of compounds such as calcium hydroxide can be produced.

[0010]

Next, embodiments of the present invention will be described in detail. Example 1 Step A) Preparation of Alkaline Aqueous Solution Containing Cobalt Complex Ion 10 g of cobalt oxide was weighed as a conductive agent, and argon was bubbled beforehand in a processing vessel to remove dissolved oxygen.
It was charged into 100 cc of a 0% aqueous sodium hydroxide solution. The solution was maintained at 80 ° C. for 2 hours while bubbling argon, and then filtered in argon at 80 ° C. to remove unreacted cobalt oxide. The resulting reaction solution was a blue solution. This reaction solution was used as treatment solution A. B) Alkaline containing cobalt complex ion and calcium ion
Preparation of aqueous solution 10 g of cobalt oxide and 10 g of calcium hydroxide as raw materials for the oxygen overvoltage additive were weighed, and charged in a treatment vessel into 100 cc of a 30% aqueous sodium hydroxide solution from which dissolved oxygen was removed by bubbling argon beforehand. While maintaining the solution temperature at 80 ° C. for 2 hours while bubbling argon,
The mixture was filtered at 80 ° C. in argon to remove unreacted cobalt oxide. The obtained reaction liquid was used as treatment liquid B. C) Cobalt complex ion and zincate (hydrochlorite) ion
Preparation of an alkaline aqueous solution containing 10 g of cobalt oxide and 1 g of zinc oxide as raw materials for an electrode plate expansion inhibitor, and in a treatment vessel, 100 cc of a 30% aqueous sodium hydroxide solution from which dissolved oxygen was removed by bubbling argon beforehand. I put it in. The solution was maintained at 80 ° C. for 2 hours while bubbling argon, and then filtered at 80 ° C. in argon to remove unreacted cobalt oxide. The obtained reaction liquid was used as treatment liquid C. Second Step Production of Positive Electrode Active Material While the above-mentioned treatment solution A was kept at 80 ° C., 5% of zinc having a spherical or elliptical shape and 1% of cobalt were dissolved in a reaction vessel bubbled with argon. The obtained nickel hydroxide active material powder was charged and held for 2 hours. These particles are secondary particles in which many primary particles have grown from the center.
Then, bubbling of argon was stopped, and 200 ml of 10% hydrogen peroxide solution was added dropwise over 5 hours while stirring the solution. Then, after stirring with a stirrer in the air for 5 hours,
After filtration, washing with water and drying, a positive electrode active material A of the present invention was obtained.
In addition, the same operation was performed on the processing liquids B and C to obtain the positive electrode active materials B and C. Second step (change of oxidizing agent) Next, while the processing solution A was kept at 80 ° C, a spherical or elliptical nickel hydroxide active material powder was charged into a reaction vessel bubbled with argon. The powder was dispersed and reacted by stirring with bubbling of the active gas and kept for 2 hours. Next, bubbling of argon was stopped, oxygen was blown in as an oxidizing agent, and bubbling was performed for 5 hours.
The oxidation reaction was sufficiently performed. Oxygen flow rate is 10cc / mi
n. Next, bubbling of oxygen was stopped, and the mixture was stirred in air for 5 hours, filtered, washed with water and dried to obtain a positive electrode active material D.

Production of Paste Nickel Electrode To 100 parts by weight of each of the above-mentioned positive electrode active materials A to D of the present invention, 35 parts by weight of a 1% CMC aqueous solution is added and stirred to form a paste, which is filled in a foamed nickel substrate. After drying, pressing and cutting, paste-type nickel plates A to D of the present invention were manufactured. The cut dimensions and the filling amount of nickel hydroxide were almost the same.

For comparison, 1% by weight was added to 100 parts by weight of the positive electrode active material consisting of nickel hydroxide powder having the same spherical or elliptical shape as above without the above-mentioned coating treatment.
35 parts by weight of the CMC aqueous solution was added, stirred to form a paste, filled in a foamed nickel substrate, dried, pressed and cut to produce a paste-type nickel electrode plate E of the present invention. The cut dimensions and the filling amount of nickel hydroxide were almost the same as above. For comparison, paste-type nickel plates F and G were produced by the conventional method as described below. Conventional Example 1 That is, 1% was added to 95 parts by weight of nickel hydroxide powder in which 5% of zinc and 1% of cobalt were dissolved, and 5 parts by weight of cobalt hydroxide.
A CMC aqueous solution was added in an amount corresponding to 35% of the total powder weight, and mixed and stirred to prepare a conventional positive electrode active material paste. This paste is filled into a foamed nickel substrate, dried, pressed and cut to form a paste-type nickel electrode plate F.
Was manufactured. The cut size and the filling amount were almost the same as those of the above-mentioned paste-type nickel electrodes A to E. Conventional Example 2 1% CM was added to 90 parts by weight of nickel hydroxide powder in which 5% of zinc and 1% of cobalt were dissolved in solid solution and 10 parts by weight of cobalt hydroxide.
C aqueous solution was added in an amount corresponding to 35% of the total powder weight, and mixed and stirred to prepare a conventional positive electrode active material paste. This paste was filled into a foamed nickel substrate, dried, pressed, and cut to produce a paste-type nickel electrode plate G. The cut size and the filling amount were almost the same as those of the above-mentioned paste-type nickel electrodes A to F.

[0013] The nickel electrode plate A~G produced in manufacturing the above method of alkaline secondary battery as each positive electrode, a commercially available AB ₅ hydrogen storage alloy, as for example, hydrogen storage _{alloy, MmNi 3.4 Co 0.8 Al 0.3 Mn} 0.4 (Mm
An electrode plate mainly composed of a misch metal) is used as a negative electrode, and a group of electrode plates comprising a hydrophilic polyolefin nonwoven fabric separator interposed between these electrode plates is housed in a battery can, and the KOH
An alkaline electrolyte having a specific gravity of 1.30 mainly composed of
AA size nickel-metal hydride batteries corresponding to a nominal capacity of 1200 mAh were manufactured by sealing the lid, and batteries A to G were respectively obtained.

Initial Charging Characteristics Test Each of the above-mentioned batteries A to G was sealed with a cover, left to stand for 5 hours, and then charged with a current of 0.2 C to a nominal capacity of 150%.
% Of electricity was charged. The voltage change of the batteries A to G at the initial stage of the first charge was measured. The result is shown in FIG. As apparent from the voltage change curves A to G at the initial stage of the initial charge shown in FIG. 1, the batteries A to D of the present invention did not show a large polarization at the initial stage of the initial charge, and only the nickel oxide plateau immediately after the energization. Was observed. On the other hand, in the battery E, a large polarization was recognized at the beginning. In addition, in the batteries F and G, an oxide plateau of cobalt hydroxide appeared at an early stage, and thereafter, a plateau of nickel oxide was observed. From these results,
It is considered that the batteries A to D according to the present invention had good conductivity between the nickel hydroxide particles and small polarization because the conductive cobalt oxyhydroxide matrix was formed in the nickel hydroxide secondary particles. With this low polarization, it seems that larger currents are possible. Battery E was considered to have a very large polarization immediately after energization due to the absence of cobalt oxyhydroxide. Also, batteries F and G
It is considered that, since the added gobalt hydroxide is divalent, the oxidation of nickel hydroxide progressed after the oxidation reaction proceeded in the initial stage.

Capacity Test After the batteries A to G were initially charged, each was left at 20 ° C. for 1 hour, then discharged at a current of 0.2 C to a battery voltage of 1.0 V, and further discharged at 20 ° C. under a voltage of 0.1 V. Charging at 2 C for 7.5 hours and discharging at 0.2 C to a battery voltage of 1.0 V were performed three cycles to activate the battery. This third cycle was defined as the battery capacity. Table 1 below shows the battery capacity obtained in the capacity test and the utilization rate of nickel hydroxide. The utilization rate was a value based on a one-electron reaction of nickel hydroxide as 100%.

[0016]

[Table 1]

In the batteries A to D according to the present invention, since the ratio of nickel hydroxide in the nickel electrode was higher than that of the conventional batteries F and G, a large battery capacity was obtained with the same filling amount. Batteries A, B, and D using nickel electrodes to which zinc was not added
Of the battery C using the nickel electrode to which zinc was not added, a higher utilization factor was obtained.

Each of the charge acceptance test batteries A to G under a high temperature was charged at a temperature of 50 ° C. and 0.2 C for 7.5 hours, and then left at 20 ° C. for 16 hours. The battery was discharged to a battery voltage of 1.0 V at 0.2 C and the capacity was measured. The results are shown in Table 2 below.

[0019]

[Table 1]

As is clear from Table 2, although the capacity was generally reduced as compared with the charging at room temperature, the battery A according to the present invention was used.
~ D can obtain higher capacity and utilization rate than batteries E, F and G even when charged at high temperature. In particular, the battery B using the treatment liquid B and using the nickel electrode containing the positive electrode active material containing a coprecipitate such as cobalt oxyhydroxide and calcium hydroxide in the second step has an effect of increasing the oxygen overvoltage. It has been recognized that particularly high temperature charging provides a particularly high capacity compared to other batteries.

Each of the capacity recovering batteries A to G after storage at the low battery voltage was charged at 0.2 C for 7.5 hours, discharged at 0.2 C to 1.0 V, and the capacity was measured. In the connected state, it was left in an atmosphere of 60 ° C. for 24 hours. Next, charge and discharge under the same conditions as the previous cycle,
The capacity was measured, and the ratio to the capacity before standing was determined to be the capacity recovery rate. The results are shown in Table 3 below.

[0022]

[Table 3]

As is clear from Table 3, the batteries A to D according to the present invention exhibit a higher capacity recovery rate than the batteries F and G manufactured by the conventional method. This is because a sufficient amount of the cobalt conductive matrix is formed by treating in an alkaline electrolyte containing a cobalt complex ion while blowing an inert gas, thereby improving durability against a reducing atmosphere at the nickel electrode. Presumed to have. Battery E showed a capacity recovery rate of 100%, presumably because the capacity recovery rate did not change because cobalt was not contained in the nickel electrode.

The cycle life test batteries A to G were each charged at 1 C (−ΔV = 10 m
V), the battery was discharged at 1 C, and a charge / discharge cycle life test was performed up to a battery voltage of 1 V. The result is shown in FIG. FIG.
As is clear from the above, in the batteries A to D according to the present invention, a significantly higher discharge capacity was obtained as compared with the batteries E, F, and G, and a remarkable improvement in cycle life was also recognized. This is considered to be because the reversibility is good because A to D surely form a conductive matrix. In particular, battery C was prepared from a solution containing zincate ion [Zn (OH) ₄ ] ^2−. To produce an active material using Zn,
It is considered that the nickel electrode was more effectively inhibited from expanding than the solid solution such as F or G because it was mixed as O, Zn (OH) ₂ or the like.

When a positive electrode active material is produced by using ytterbium in addition to the above-described calcium oxidation and through the above first and second steps, oxides and hydroxides of ytterbium are mixed in the active material. Thus, the effect of increasing the oxygen overvoltage can be obtained. According to the above method, the above additives can be mixed in the active material, thereby suppressing the expansion of the nickel electrode and increasing the oxygen overvoltage of the battery.

[0026]

As described above, according to the present invention, the cobalt-based additive is introduced into the aqueous alkali solution while bubbling with an inert gas, and the whole is agitated by bubbling under the inert atmosphere. Since the reaction can be carried out, it is possible to improve the production efficiency of the cobalt complex ion satisfactorily. Next, the nickel hydroxide active material was injected under the blowing of the inert gas, so that the cobalt complex ion was well dispersed. Secondary particles of nickel hydroxide, that is, can be allowed to penetrate into the agglomerate, in this state, the blowing of the inert gas is stopped, and an oxidizing agent is acted on this to form cobalt oxyhydroxide. It is possible to produce a positive electrode active material having good conductivity, in which cobalt hydroxide is satisfactorily mixed and interposed and coated between primary particles constituting the same. The positive electrode active material manufactured in this way is filled into a porous substrate in the form of a paste, dried, and pressed to improve the active material utilization of the paste-type nickel electrode plate manufactured. Thus, an alkaline secondary battery manufactured using the paste-type nickel electrode plate of the present invention as a positive electrode has improved battery characteristics such as battery capacity, discharge characteristics, and cycle life characteristics. In addition, in the production of the positive electrode active material, in addition to the cobalt-based additive, as an additive, a raw material of an electrode plate expansion inhibitor or an oxygen overvoltage increasing agent is added, and when the same treatment is performed as described above, the final It can be mixed with the nickel hydroxide active material as an additive composed of the oxides, hydroxides, etc., thereby producing a positive electrode active material that simultaneously brings about the respective additive effects. A paste-type nickel electrode plate and a battery having these effects can be provided.

[Brief description of the drawings]

FIG. 1 is a comparison graph of battery voltage characteristics at the initial stage of first charge.

FIG. 2 is a comparison graph of cycle life characteristics of a battery.

[Explanation of symbols]

AD Battery of the present invention E, F, G Comparative battery

[Table 2]

Claims (4)

[Claims] 1. a) As at least one additive, at least one of a cobalt-based additive is added to an aqueous alkali solution, and the mixture is stirred and reacted while blowing an inert gas into the aqueous alkali solution to form a cobalt complex ion (HCoO ₂ ^−). B) Next, nickel hydroxide powder is added thereto, and the mixture is stirred while blowing in inert gas to disperse the nickel hydroxide particles. Then, the blowing of inert gas is stopped. And adding an oxidizing agent to the dispersion to oxidize the cobalt complex ions to form cobalt oxyhydroxide (CoOOH). 2. An additive for suppressing the expansion of a nickel electrode and / or a raw material for an additive for increasing an oxygen overvoltage is further added and dissolved in an aqueous alkali solution as an additive.
The method for producing a positive electrode active material for an alkaline secondary battery according to claim 1, wherein an oxidizing agent is caused to act on the oxidizing agent. 3. A paste-type nickel electrode comprising the positive electrode active material obtained by the method according to claim 1 or 2. 4. An alkaline secondary battery comprising the paste-type nickel electrode according to claim 3 as a positive electrode.