JPH11176431A - Manufacture of paste-type nickel electrode, the paste type nickel electrode, and alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste-type nickel electrode of an improved utilization factor and high-temperature charge acceptability. SOLUTION: Powder comprising nickel hydroxide grains coated with β-cobalt hydroxide charged in a three-dimensional porous collector is thermally oxidized in air, and β-cobalt hydroxide coating becomes coating comprising cobalt oxyhydroxide and tricobalt tetraoxide. An alkaline secondary battery chargeable at high temperature in a short time is also provided by executing initial charge at 35 deg.C or higher to an alkaline secondary battery provided with a paste-type nickel electrode as a positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a paste-type nickel electrode, a paste-type nickel electrode, and an alkaline secondary battery.

[0002]

2. Description of the Related Art Conventionally, a paste-type nickel electrode has been used as a positive electrode of an alkaline secondary battery such as a nickel-cadmium battery, a nickel-hydride battery, a nickel-zinc battery, and a nickel-iron battery. It is known that a nickel compound is added with a cobalt compound in order to increase the utilization factor. The paste-type nickel electrode is manufactured as follows. That is, at least one of cobalt-based additives such as metal cobalt, cobalt hydroxide, and cobalt monoxide is added to spherical or elliptical nickel hydroxide powder containing cobalt or zinc as a solid solution, and the mixture is treated with carboxymethyl cellulose ( CMC) or the like and kneaded with an aqueous solution of a thickener to form a paste. The paste is filled into a three-dimensional porous current collector having three-dimensionally continuous fine pores such as foamed nickel or nickel felt, and dried and pressed. Manufactured. When this is used as a positive electrode of an alkaline secondary battery, the added cobalt additive reacts with hydroxyl ions in the alkaline electrolyte to form a water-soluble cobalt complex ion, diffuses, and is oxidized by charging. Deposited in the nickel electrode as conductive cobalt oxyhydroxide, forming a so-called cobalt conductive matrix to increase the conductivity between the active material nickel hydroxide particles and between the active material and the current collector, It is possible to improve the utilization rate of the information. In addition, in order to reliably obtain a cobalt conductive matrix in the nickel electrode, a powder composed of nickel hydroxide particles coated with cobalt hydroxide powder is poured into a high-temperature alkaline aqueous solution, and air is blown into the alkaline aqueous solution. A paste obtained by oxidizing cobalt hydroxide to cobalt oxyhydroxide together with a thickener aqueous solution is filled, dried and pressed to produce a paste-type nickel electrode. Furthermore, in recent years, alkaline secondary batteries have been built in devices as power sources for electronic devices, have been used as battery packs, and have been used in environments that are rapidly charged and easily exposed to heat. In high temperature charging, the nickel electrode has a reduced oxygen overvoltage and approaches the charging potential of the active material, so the charging reaction and the oxygen generation reaction compete to lower the charging efficiency, and as a result, the battery capacity that can be taken out decreases. The problem was that the electronic equipment could not be used as designed, but in order to solve this, oxygen generation such as ytterbium, erbium oxide, cadmium oxide and calcium fluoride, which had the effect of making the oxygen generation potential noble, was A paste type nickel electrode in which a suppressor is added to a nickel hydroxide active material, and a paste is formed together with an aqueous solution of a thickener, and this is filled in a three-dimensional porous current collector, was used as a positive electrode of an alkaline secondary battery. At times, there has been proposed a device capable of preventing a decrease in oxygen overvoltage even at high temperature charging.

[0003]

However, the cobalt-based additive causes the following problems. That is, in the case of cobalt hydroxide, the conductivity itself is poor, and since this is interposed between the nickel hydroxide active material particles and between the active material particles and the current collector, the polarization at the time of the first charge increases, Since adverse effects due to gas generation are feared, a long charging time with a small current is required in order to obtain a specified charge amount in the nickel electrode. In addition, since cobalt hydroxide has low reactivity with an alkaline electrolyte, in order to obtain a predetermined cobalt conductive matrix, a large amount of expensive cobalt hydroxide must be added or the charging conditions for initial charging must be moderated. In addition, there was an inconvenience of requiring a long charging time. Also,
In the case of cobalt oxide, the paste is poorly conductive because the surface is oxidized and a large amount of inactive cobalt tetroxide is formed in the air or in a paste containing dissolved oxygen or in the drying process of the electrode plate manufacturing process. Formulas tend to be nickel electrodes.
Since metal cobalt is also easily oxidized, it causes the same disadvantages as the above-mentioned cobalt-based additive, and when a large amount is added in order to obtain the effect of addition, the content of nickel hydroxide is reduced accordingly, There is a disadvantage that the battery capacity is reduced. Heating a powder composed of nickel hydroxide particles coated with cobalt hydroxide in an aqueous alkaline solution requires washing with water, and the cobalt complex ions eluted during the treatment are oxidized, and the desired good conductor oxywater Since the cobalt oxide is changed into a large amount of cobalt trioxide, there is a disadvantage that the conductivity of the nickel electrode is reduced and the paste cannot be maintained as a stable and good paste type electrode plate. On the other hand, there is a problem of disposal of the treated alkaline aqueous solution, and the cost tends to be high. Also, the use of the various antioxidants described above added to improve high temperature charge acceptance,
There is a problem in that the addition of such a substance hinders an increase in capacity, and also causes agglomeration of CMC of a CMC thickener aqueous solution used during paste preparation.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, improves the utilization factor, reduces the amount of cobalt to be added, increases the capacity, and enables the first charge to be performed efficiently. Further, the present invention provides a method for producing a paste-type nickel electrode having improved high-temperature charge acceptability without adding an oxidation generation inhibitor, and a paste of powder comprising nickel hydroxide particles coated with β-cobalt hydroxide. Is heated in air to oxidize a part or all of the coated β-cobalt hydroxide to cobalt oxyhydroxide and cobalt tetroxide. It is characterized by. Furthermore, the present invention provides a paste-type nickel electrode which is stable at room temperature without being oxidized and can be stored for a long period of time. The active material comprises nickel hydroxide coated with cobalt oxyhydroxide and cobalt tetroxide. Thus, a paste-type nickel electrode composed of a three-dimensional current collector filled with is obtained. Further, the present invention provides an alkaline secondary battery capable of performing high-temperature charging in a short time. The alkaline secondary battery having the paste-type nickel electrode of the present invention obtained as described above as a positive electrode is heated at 35 ° C. The first charge is performed at the above temperature.

[0005]

According to the present invention, as the first step, for example, a commercially available powder comprising nickel hydroxide particles coated with spherical or ovoid β-cobalt hydroxide is used,
This is kneaded with a thickener aqueous solution to prepare a paste, filled in a three-dimensional porous current collector such as a foamed nickel current collector, dried,
Apply pressure. Instead of using commercially available powders of nickel hydroxide particles coated with β-cobalt hydroxide, put nickel hydroxide powder into an aqueous solution of cobalt such as cobalt sulfate and add sodium hydroxide to this while stirring. By doing so, cobalt hydroxide is produced, and the product obtained by coating the surface of the nickel hydroxide particles with the produced cobalt hydroxide is obtained as a precipitate, which is obtained by filtering, washing and drying. You may make it.

After the paste-type nickel electrode is manufactured as described above, as a second step, the paste-type nickel electrode is placed in a heating furnace and heated in air, and preferably at a temperature of 140 to 200 ° C. for a desired time, preferably After heating for 15 to 20 minutes, the coating material, cobalt hydroxide β-Co (OH) _2, was partially or entirely replaced with cobalt oxyhydroxide CoOO having relatively high crystallinity.
Oxidation treatment is performed on H and cobalt trioxide Co ₃ O ₄ . By this oxidation treatment, a large amount of cobalt oxyhydroxide and a moderately small amount of cobalt tetroxide are generated. Thus, the paste-type nickel electrode of the present invention was manufactured. As a result of analyzing the oxide formed on the surface of the nickel hydroxide particles of the paste-type nickel electrode manufactured as described above, FIG.
As is clear from the X-ray diffraction pattern shown in FIG. 3, cobalt oxyhydroxide CoOOH (or CO 2
HO ₂ ) and cobalt tetroxide Co ₃ O ₄ . Incidentally, the illustrated example of the oxidized product shows that a part of the cobalt hydroxide is not oxidized and a part remains. Thus, since the surface of the nickel hydroxide particles is already oxidized, it is stable at room temperature and can be obtained as a paste-type nickel electrode capable of maintaining battery characteristics such as good conductivity even after long-term storage.

Next, when the paste-type nickel electrode is immersed in an alkaline electrolyte, the above-mentioned cobalt oxyhydroxide having high crystallinity comes into contact with the electrolyte and becomes apparent from the X-ray diffraction pattern shown in FIG. Further, it was found that the diffraction peak changed to cobalt oxyhydroxide having a low crystallinity and a low broad crystallinity. This change proceeds more smoothly as the heating temperature is higher. Also, this low crystallinity cobalt oxyhydroxide,
It was found to have high conductivity. Thus, when the nickel electrode is used as a positive electrode, an alkaline electrolyte is injected, and an alkaline secondary battery is manufactured, the above reaction causes the surface of the nickel hydroxide particles to have high conductivity and low crystallinity of cobalt oxyhydroxide. A film of is generated, the conductivity between the nickel hydroxide active material particles and between the active material particles and the current collector is improved,
The utilization rate of the active material can be improved. Therefore,
Even if the addition amount of cobalt hydroxide is smaller than the conventional addition amount, the same utilization as the conventional one can be obtained, and the addition amount of the nickel hydroxide active material can be increased by the reduced amount. If the addition amount is the same as the conventional one, the utilization factor is improved. Thus, the resource saving of the added cobalt amount and the increase of the capacity are brought about. On the other hand, cobalt trioxide is formed competitively from cobalt hydroxide together with cobalt oxyhydroxide by the above-described heat oxidation treatment at a high temperature, and it is considered that the production amount is determined by the oxygen partial pressure, temperature, and time. . Conventionally, the formation of cobalt trioxide as an inert substance has been avoided, but surprisingly, even if it is formed on the surface of nickel hydroxide active material particles, if a large amount of CoOOH coexists, sufficient conductivity is obtained. It has been found that the properties can be ensured and the effect of further increasing the oxygen overvoltage is brought about. Accordingly, it is possible to improve the charge acceptability of the positive electrode at a high temperature and to increase the oxidation number of nickel, so that it is possible to omit the addition of the oxygen gas generation inhibitor as in the related art. Thus, the heat oxidation treatment of the above-mentioned cobalt hydroxide coating can be performed only by installing an electric furnace after the paste filling, drying, and rolling steps in the conventional paste-type nickel electrode production. The poles can be manufactured easily and efficiently, and
Air is blown into an alkaline aqueous solution that heats conventional cobalt hydroxide-coated nickel hydroxide powder, and the strong alkaline waste liquid seen when oxidized is not discharged.This eliminates the need for wastewater treatment, reduces manufacturing costs, and reduces environmental impact. Advantageous without problems.

[0008]

Next, examples of the present invention will be described in detail along with comparative examples and conventional examples. Preparation of Various Nickel Hydroxides The surface of commercially available nickel hydroxide particles was coated with 4% β-cobalt hydroxide in terms of metallic cobalt, and had a spherical shape, and 1.5% Co and 5.0% Zn were dissolved. A powder composed of nickel hydroxide was prepared. Hereinafter, this is referred to as nickel hydroxide a. A powder having a spherical shape and comprising nickel hydroxide particles in which 1.5% of Co and 5.0% of Zn were dissolved was prepared. Hereinafter, this is referred to as nickel hydroxide b.
30 powders of nickel hydroxide consisting of the above commercially available particles
% Aqueous NaOH and stirred, the alkali aqueous solution was heated and maintained at 60 ° C., and allowed to react for 1 hour while blowing air thereinto, followed by filtration, washing and drying to coat the surface with cobalt oxyhydroxide. A nickel hydroxide powder was obtained. Hereinafter, this is referred to as nickel hydroxide c. Production of paste-type nickel electrode using nickel hydroxide a 1.2% by weight based on 100 parts by weight of the above-mentioned cobalt hydroxide a
38 parts by weight of a CMC aqueous solution is charged and stirred to prepare an active material paste, which is filled into a long nickel foam substrate, dried and pressed to produce a paste-type nickel electrode, cut into prescribed prescribed dimensions, and cut into many pieces. Sheets were manufactured. Among the paste-type nickel electrodes thus manufactured, an unheated paste-type nickel electrode that cannot be put in a thermostat is prepared as paste-type nickel electrode A, and the remaining paste-type nickel electrode is put in a thermostat and heated at 170 ° C. 5 minutes each in the air at constant temperature,
Heat-treated pieces with different heating times for 15 minutes and 30 minutes were taken out, allowed to cool, and returned to room temperature to produce a paste-type nickel electrode. The paste-type nickel electrodes of the present invention obtained by performing the heat oxidation treatment for 5 minutes, 15 minutes, and 30 minutes, respectively, are referred to as nickel electrodes B, C, and D, respectively. The thickness and filling amount of these nickel plates were substantially the same. Production of paste-type nickel electrode using nickel hydroxide b 94 parts by weight of nickel hydroxide b and cobalt hydroxide 6
A 1.2% CMC aqueous solution was added to the mixed powder in an amount corresponding to 36% by weight based on the mixed powder, and mixed and stirred to prepare an active material paste. This was filled in a long nickel foam substrate, dried and pressed, and then cut into the same dimensions as above to produce a number of conventional paste-type nickel electrodes. This is called nickel electrode E. The thickness and filling amount of this electrode plate were substantially the same as above. Production of paste-type nickel electrode using nickel hydroxide c 1.2% based on 100 parts by weight of the above nickel hydroxide c
36 parts by weight of a CMC aqueous solution was charged and stirred to prepare an active material paste. This was filled in a long nickel foam substrate, dried and pressed, and then cut into the same dimensions as above to produce a conventional paste-type nickel electrode. This is called nickel electrode F.

Half battery test Next, the nickel electrodes A, B, C, D, E, and
F is fixed with a holder which is applied to a constant pressurization, and is used as a working electrode. A reference electrode of Hg / HgO, nickel foam is used as a counter electrode, and an alkaline electrolyte having a specific gravity of 1.30 and containing KOH as a main component is injected into the battery case. To form a half-cell. After injecting the electrolytic solution, the battery was left at 45 ° C. for 5 hours, and then initially charged at 45 ° C. with a current of 0.2 C. FIG. 3 shows the potential change during the first hour of the first charge. In FIG. 3, as is apparent from the charge curves of the nickel electrodes A to D, the longer the heating and oxidizing treatment time, the smaller the polarization at the beginning of the first charge, and changes from +2 valence of cobalt to +2 valence.
It can be seen that the plateau region oxidized to trivalence becomes shorter.
This is presumably because the longer the heat treatment time, the smaller the amount of +2 valent cobalt hydroxide. That is, it is conceivable that the amount changed to cobalt oxyhydroxide by the heat oxidation treatment increases. The nickel pole E is the nickel pole D
This is because polarization is slightly larger than that of nickel electrode D because there is almost no plateau region where cobalt is oxidized from +2 valence to +3 valence, as in nickel electrode D. This confirms that cobalt oxide was oxidized to cobalt oxyhydroxide. The nickel electrode F has a larger polarization than the unheated nickel electrode A. This is thought to be due to the difference in the presence or absence of the coating with cobalt hydroxide.

Capacity Test Next, each half-cell was heated to 25 ° C. and a current of 0.2 C was used for 7.
The battery was charged for 5 hours and discharged at a potential of 0.1 V with respect to the Hg / HgO reference electrode at a current of 0.2 C, and the capacity at the third cycle was measured. At this time, in order to conveniently determine the ease of generation of oxygen, the difference ΔE (mV) between the maximum charging potential and the average charging potential was determined by arithmetic mean. In addition, the theoretical capacity of the discharge based on the one-electron reaction of pure nickel hydroxide is 10
The utilization rate (%) was determined as 0%. The results are shown in Table 1 below.
Shown in

[0011]

[Table 1]

As is apparent from Table 1, the value of ΔE is larger as the heat treatment time is longer, as shown by the nickel electrodes A, B, C, and D, and a nickel electrode with less oxygen generation can be obtained. . The nickel hydroxide utilization rate is such that the heat-oxidized nickel electrodes B, C, and D are different from the other nickel electrodes A, E, and F.
It can be seen that it is improved as compared with. The maximum utilization rate of the nickel electrode C was 15 minutes when the heat oxidation treatment time was 15 minutes.
This means that the ratio of cobalt oxyhydroxide, which improves the conductivity generated by oxidation of the cobalt hydroxide film by heating oxidation treatment at 170 ° C. for 15 minutes, and cobalt tetroxide, which increases the oxygen overvoltage, is optimal. It is presumed that it becomes.

Next, in order to investigate the influence of the environmental temperature at the time of the first charge, half-cells are manufactured using nickel electrodes A to F having the same configuration as above, and the initial charge temperature of each half-cell is set at 25 ° C. A capacity test was performed at 35 ° C., 45 ° C., and 55 ° C. under the same conditions as described above. The results are shown in Tables 2 and 3 below.

[0014]

[Table 2]

[0015]

[Table 3]

As is apparent from Tables 2 and 3, 25 ° C.
Even when the temperature changes to 35 ° C., 45 ° C., and 55 ° C., at each temperature, the nickel electrodes B, C, and D manufactured according to the present invention are compared with the nickel electrodes A, E, and F at each temperature. However, it was recognized that the utilization rate improved in all cases. Further, the nickel electrodes B, C, and D have improved utilization rates and ΔE values with an increase in the initial charging temperature.
, The temperature was significantly improved at 45 ° C. or higher, and the increase became saturated at 55 ° C. Further, regarding the ΔE value, it was recognized that the nickel electrode D was most improved.

Due to a change in the temperature of the heat oxidation treatment in the thermostatic oven
Influence Next, each nickel electrode A was put into a thermostat, and the temperature was set to 120.
After heating at a temperature of 140 ° C., 140 ° C., 170 ° C., 200 ° C., and 220 ° C. for 15 minutes, the product was taken out, allowed to cool, and returned to room temperature to produce a paste-type nickel electrode. These are called nickel electrodes G, H, C, I, and J, respectively. A half-cell was prepared in the same manner as described above using the respective nickel electrodes as positive electrodes, and the initial charge was performed at the initial charge temperature of 45 ° C. in the same manner as described above. The results are shown in Table 4 below.

[0018]

[Table 4]

As is evident from Table 4, it was recognized that the ΔE value and the utilization factor were significantly improved when the heat treatment temperature was particularly 140 ° C. or higher. Further, ΔE reached its maximum value at 200 ° C., and showed a saturated value without any further improvement above that. As for the utilization factor, the heat treatment at 170 ° C. showed the maximum value. Also,
When increasing from 120 ° C. to 140 ° C., both ΔE and utilization improved significantly. From this, it is estimated that the decomposition point of β-cobalt hydroxide was exceeded at 140 ° C. or higher.

From the above results, the paste-type nickel electrode of the present invention produced by heating and oxidizing a nickel electrode filled with nickel hydroxide coated with β-cobalt hydroxide in air was used as a positive electrode. It can be seen that, at the time of the first charge, by increasing the temperature at the time of the first charge, a nickel electrode having both a larger ΔE and a higher utilization factor can be obtained. Further, the oxidation state which determines the ratio of cobalt oxyhydroxide to cobalt tetroxide or the remaining cobalt hydroxide is not limited because it is determined by temperature × time, but in industrial production, the temperature is from 140 ° C. to 200 ° C. , 5 minutes to 30 minutes
Within minutes, a highly efficient and economically excellent paste-type nickel electrode can be manufactured, and an excellent alkaline storage battery can be obtained by performing initial charging at 35 ° C. or more, and optimally at or near 45 ° C. I understand.

Use of Nickel Hydroxide for Alkaline Secondary Battery
Comparative Test The above nickel electrode A rate, B, C, D, E, and the respective positive electrode F, commercially available AB ₅ hydrogen storage alloy, for example AmNi _3.4
An electrode group formed by laminating a hydrogen absorbing alloy electrode made of Co _0.8 Al _0.3 Mm _0.4 as a negative electrode through a hydrophilic polyolefin nonwoven fabric separator is housed in a battery case.
1.9 cc of an alkaline electrolyte having a specific gravity of 1.30 mainly composed of
AA size nickel-hydride batteries corresponding to 00 mAh were each manufactured. Each of the batteries is a battery A, B, C, D,
They are called E and F. Next, each of the batteries A to F was sealed immediately after injecting the above-mentioned electrolyte solution, left at 45 ° C. for 5 hours, and initially charged with a current of 0.2 C to an amount of electricity of 150% of the nominal capacity. . Then, after standing at 25 ° C for 16 hours,
Discharge was performed at a current of 0.2 C to 1 V. Next, the same charge and discharge are repeated for three cycles to perform initial activation.
The capacity of each battery at the time of the discharge in the third cycle was measured, and the utilization rate of nickel hydroxide was calculated from the capacity of each battery. The results are shown in Table 5 below.

[0022]

[Table 5]

As is clear from Table 5, the utilization rate of nickel hydroxide in each battery was the same as that in the test using the half-cell, and the battery B using the paste-type nickel electrodes B, C, and D of the present invention was used. , C, and D, an improvement in the utilization rate was observed.

Next, in order to evaluate the high-temperature charge acceptability of each of the batteries A to F, charging was performed at 40 ° C.
Performed at 50 ° C. and 60 ° C. with a current of 0.2 C for 7.5 hours, allowed to stand at room temperature for 1 hour, performed with a current of 0.2 C up to 1 V, measured the capacity, and measured the capacity at the cycle of Table 5 above. The ratio when the discharge capacity was set to 100% was calculated. The results are shown in Table 6 below.

[0025]

[Table 6]

As is clear from Table 6, a battery using a nickel electrode having a large ΔE in the half-cell test described above has a larger value.
It was recognized that the high-temperature charge acceptability was high, the oxygen generation reaction during the charging reaction was suppressed, the reaction of oxidizing nickel hydroxide was promoted, and the charging efficiency at high temperatures was increased.

[0027]

As described above, according to the present invention, a three-dimensional porous current collector filled with powder composed of nickel hydroxide particles coated with β-cobalt hydroxide is heated and oxidized in air at a high temperature. As a result, a paste-type nickel electrode having an improved utilization rate in which a part or the whole of the coating of β-cobalt hydroxide is changed to an oxide coating composed of cobalt oxyhydroxide and cobalt tetroxide is obtained. When constituting an alkaline secondary battery using the paste-type nickel electrode as a positive electrode,
A battery having a high capacity and a large ΔE can be obtained. In particular, when the initial charge is performed at 35 ° C. or higher, an alkaline secondary battery having excellent high-temperature charge acceptability can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing an X-ray diffraction pattern of β-cobalt hydroxide and its oxide obtained by a heat oxidation treatment method of the present invention.

FIG. 2 is a diagram showing an X-ray diffraction pattern of an oxidized product of β-cobalt hydroxide shown in FIG. 1 and a reaction of the oxidized product with an electrolytic solution.

FIG. 3 is a diagram showing the relationship between the charging time of each half-cell using each paste-type nickel electrode obtained by different manufacturing methods and the potential of the electrode.

Claims (3)

[Claims] 1. A three-dimensional porous current collector filled with a paste of powder composed of nickel hydroxide particles coated with β-cobalt hydroxide, and heated in air to form the coated β-water. A method for producing a paste-type nickel electrode, comprising oxidizing a part or all of cobalt oxide to cobalt oxyhydroxide and cobalt trioxide. 2. A paste-type nickel electrode comprising a three-dimensional current collector filled with an active material comprising nickel hydroxide particles coated with cobalt oxyhydroxide and cobalt tetroxide. 3. An alkaline secondary battery comprising the paste-type nickel electrode according to claim 2 as a positive electrode and an initial charge at 35 ° C. or higher.