JPS5983348A - Manufacture of nickel positive electrode - Google Patents

Abstract

PURPOSE:To manufacture a nickel positive electrode which improves chargedischarge performance of a battery by anodically electrolyzing a weakly alkaline active material mixed paste containing nickel hydroxide, metallic cobalt, and metallic nickel at a specified potential. CONSTITUTION:A past-like active material mixture containing nickel hydroxide, metallic nickel powder, and metallic cobalt powder is made in weak alkali, and they are anodically electrolyzed at a potential which is lower than the oxidation potential of nickel hydroxide but higher than the oxidation potential of metallic cobalt. The positive active material mixture paste obtained by electrochemically oxidizing metallic cobalt is filled in a sponge-like nickel substrate to form a nickel positive electrode. A nickel-cadmium storage battery is assembled by using this nickel positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a nickel positive electrode for use in alkaline storage batteries such as nickel-cadmium '4ta and nickel-zinc storage batteries.

Conventional nickel positive electrodes used in alkaline storage batteries are made by depositing nickel hydroxide, which serves as a stop active material, on a porous sintered nickel substrate by means such as electrolytic deposition or chemical impregnation. Alternatively, a sintered type nickel positive electrode filled with cobalt hydroxide or the like or a pocket type nickel positive electrode has been suggested.

The process of filling the active material of a sintered nickel positive electrode, such as the chemical impregnation method, requires many steps such as an impregnation process, an alkali treatment frame, a water washing process, and a drying process. In order to obtain this, it is necessary to repeat these steps several times, which is generally very complicated. The limit of the porosity of the sintered nickel substrate that holds the shredded electrode active material is about 80 modulus, and therefore the capacitance density of the electron microscope has a corresponding limit.

In addition, although the manufacturing method of the pocket-type positive electrode in which the electrode active material is held in a metal container is simple, the utilization rate of the active material or the large current discharge characteristics are inferior to the sintered type, and its structure is Due to these problems, it is difficult to make the battery thinner or to apply it to smaller batteries in order to improve discharge characteristics.

Due to the above-mentioned problems, recently a method of directly filling a sponge-like metallic nickel substrate with a porosity of about 96 coefficients with a paste-like active material mixture mainly composed of nickel hydroxide, and a method of directly filling a paste-like active material mixture mainly consisting of nickel hydroxide, and a method of filling a similar active material mixture A method of applying nickel to a conductive support such as a perforated metal plate using roll pressure has been proposed. These positive electrodes are much easier to manufacture than conventional sintered positive electrodes, have a high capacitance density, and are thinner.
It is attracting attention because it is suitable for miniaturization and its charge/discharge characteristics are on the same level as sintered positive electrodes.

The sintered positive electrode uses so-called chemical conversion, in which charging and discharging are performed in an alkaline electrolyte to activate the positive electrode active material, or to remove inorganic salts such as nitrate radicals that penetrate into the board during -fW and board manufacturing. The process is adopted.

On the other hand, nickel positive (1r
Then, after manufacturing the electrode plate, it is difficult to perform chemical formation using the same method as for the sintered positive electrode. This is because the retention state of the active material of this positive electrode on the substrate is weaker than that of a sintered positive electrode, and if chemical formation is performed in the same manner as the sintered positive electrode, the active material in the positive electrode can be removed from the alkaline electrolyte. This is because the result will be that it will fall off.

As mentioned earlier, the base 1 set positive electrode has many advantages over the sintered positive electrode, but due to the reasons mentioned above, it is difficult to chemically form the impact plate, so it is difficult to activate the active material. Conventionally, this was done by repeating charging and discharging after battery construction. However, the state of the positive electrode active material before activation after battery construction is unstable4, and changes depending on the period from battery construction to charging/discharging or the ambient temperature, which has a large effect on later battery characteristics. . Furthermore, charging to activate the positive electrode active material after battery construction requires a long period of time with a small current, which poses problems in terms of man-hours, such as difficulty in manufacturing control.

OBJECTS OF THE INVENTION The present invention aims to solve the above-mentioned problem of activating the active material of the positive electrode using the base 1 and to improve its characteristics.

Structure of the Invention The present invention is characterized in that a paste-like active material mixture containing nickel hydroxide, metallic nickel powder, and metallic cobalt powder is made weakly alkaline and subjected to positive electrolysis to electrochemically oxidize metallic cobalt. The present invention will be explained in detail below.

In an active material mixture consisting of nickel hydroxide, metal disokel, and metal cobalt, nickel hydroxide is an active material with iE ability, metal nickel is mainly a conductive material, and gold 1-metal cobal 1- is activated by interaction with metal nickel. It contributes to the charging and discharging of the substance nickel hydroxide, and works to improve the utilization rate of the so-called active material.

When a battery such as a nickel-cadmium storage battery is purchased and charged using a positive electrode in which the above positive electrode active material mixture is made into a paste and filled in a bond-shaped metal nickel substrate, etc., the metal cobalt is electrochemically oxidized. Then, the nickel hydroxide of the positive electrode active material is oxidized, that is, charged.

The utilization rate of nickel hydroxide as a positive electrode active material varies depending on its crystal form in its charged or discharged state. When the crystal form of nickel oxyhydroxide in a charged state is γ type, the utilization rate is low, and when the crystal form is β type, the utilization rate is high. γ of nickel oxyhydroxide present in the positive electrode in the charged state,
The ratio of the crystal form of β is the ratio of metallic cobalt in the 1F garden,
It is greatly influenced by the metal nickel ratio. That is, the larger the cobalt ratio and metal nickel ratio added for the purpose of improving the utilization rate of the positive electrode active material, the higher the ratio of β-type nickel oxyhydroxide, and the higher the utilization rate of the positive electrode active material.

As stated earlier (・ζ), metallic cobalt is oxidized during the initial charging stage and becomes stable cobalt oxide that does not contribute to charging and discharging after n1. Even if cobalt oxide is added, it does not contribute to improving the utilization rate of the positive electrode active material.

From the above, in order to improve the utilization rate of nickel hydroxide as a Seisho active material, nickel hydroxide must be used.

By electrochemically oxidizing metallic cobalt in a state where the three components of metallic nickel and metallic cobalt coexist,
It seems to be effective to change the crystal form of nickel hydroxide to one with a higher utilization rate.

However, as mentioned earlier, the state of the three components of nickel hydroxide, metallic cobalt, and metallic nickel before charging is unstable, and if the charging current for activation is large, as shown in Figure 1, The final utilization rate of nickel hydroxide decreases to the open end. Figure 1 shows the relationship between the charging current and the active material utilization rate when charging an amount of electricity equivalent to 160 times the battery capacity with a current of 0.05 C to 1 C. This seems to be because metallic cobalt, which contributes to the direction of the utilization rate, is eluted into the alkali by charging with a large current, or is changed into a higher-order oxide which does not affect the utilization rate of the active material. Therefore, charging for activating the positive electrode active material is
It has to be done with a small current.

Conventionally, the initial charge after battery configuration to activate the positive electrode active material was performed with a current equivalent to 0.05 G - 0.1 G.
The charging time required 16 to 30 hours, and there was a problem in terms of shortening the battery manufacturing time.

Electrochemical cobalt oxidation for active material activation
For example, positive electrolysis may be carried out in an alkaline electrolyte after forming the electrode plates, but as mentioned later, in such chemical formation, The active material falls off from the electrode plate severely and is difficult.

Therefore, the present inventors investigated the possibility of activation of the active material by chemical conversion during paste production of the positive electrode active material mixture. As mentioned above, the formation of a positive electrode active material mixture consisting of nickel hydroxide, metallic cobalt, and metallic nickel is achieved by gradually electrochemically oxidizing the Friday cobalt in the presence of the three components. be done.

This seems to be the same whether the positive electrode active material is in the state of an electrode plate in a battery or in the state of a paste before forming grooves on the plate. Therefore, activation of the positive electrode active material should be achieved by electrochemically oxidizing the metallic cobalt in the positive (1T active material base).

Figure 2 shows the electrolyzer. 1 is a power supply for paste electrolysis,
2 is a metal container that also serves as a negative electrode, 3 is a positive electrode,
4 is a porous electrolytic diaphragm that isolates the paste 6 and the negative electrode 2. Further, 6 is an aqueous solution flowing out from the paste 6 through the diaphragm 4 . When the paste 5 is made weakly alkaline to facilitate electrolysis and electrolysis is performed, components in the paste are electrochemically oxidized. The oxidation sequence starts with the metal cobalt in the paste, which is most susceptible to oxidation, followed by the oxidation of nickel hydroxide.

1"("+γ plate must be in a discharge state, that is, in a state where nickel hydroxide is not oxidized during battery construction. Therefore, during paste formation, only the metal cobal 1- is oxidized, and the nickel hydroxide is not oxidized. Nickel oxide must be in a state that does not undergo oxidation.

Therefore, when forming the paste, it is necessary that the potential on the positive side, that is, on the paste side, be below the oxidation potential of cobalt hydroxide on the oxidation potential plate of cobalt. To carry out such electrolysis, ideally constant potential electrolysis with a constant potential on the paste side is required, but in simple terms,
This can be done using constant voltage electrolysis, where the voltage between the positive and negative poles is kept constant.

The present inventors performed constant voltage and constant current electrolysis of the positive electrode base based on the principle similar to that described above, and attempted to activate the positive active material in the positive electrode base. Only metallic cobalt is electrochemically oxidized, and the positive electrode active material produced in this way is activated in the same way as when activated in a battery, and the utilization rate of nickel hydroxide as an electrode active material is also low. I found it to be very expensive.

Description of examples The positive electrode active material mixture is nickel hydroxide.

Metallic cobalt and metallic nickel in a weight ratio of 1o○:6:
Using a mixture of 18 parts, water and carboxymethyl cellulose were added and kneaded to form a paste.

The electrolytic cell shown in FIG. 2 was used.

The pH of the paste was slightly alkaline at 7 to 8, but the total pH was adjusted to 9 to 10 by adding an aqueous sodium hydroxide solution to facilitate electrolysis. The electrodes 2 and 3 of the electrolytic cell were made of metal nickel, and the diaphragm 4 was made of nylon nonwoven fabric.

Electrolysis was carried out in an atmosphere of 20°C. As mentioned earlier, electrolytic oxidation of metallic cobalt cannot be carried out with a large current, and the potential of the Branne electrode cannot be lower than the oxidation potential of nickel hydroxide. Because it was necessary, electrolysis was carried out at constant voltage (r) and constant current. In this type of electrolysis, the current is constant at the beginning, and as the oxidation of the metal cobal 1- gradually progresses, the electrolytic voltage increases, and continues to become a constant voltage 1! The remaining metal core 1- is all oxidized as +'il. The constant current part is the current value (
o, 1G), pace l-I 6 per CG
The voltage was 0 mA, and the constant voltage part was set to be 1.4 µF or less on a ca/cao basis so that the potential of the positive glue was below the oxidation potential of nickel hydroxide.

As a result of electrolysis under the following conditions, the amount was determined in about 2 hours.
Electrolysis progresses in the torrent flow, enters constant voltage electrolysis, and electrolysis? The li current gradually decreased and the current reached O after about 2 hours.

The paste electrolyzed as described above was heated to a porosity of 96%.
filled into a sponge-like nickel substrate, processed into a positive electrode, and
A sealed nickel-cadmium storage battery equivalent to 600 mAh was placed in the trench bottom. The battery manufactured in this way has a temperature of 100% or less when the battery is left after construction, as seen in batteries manufactured by conventional methods, because the active material is activated and stable. There was no phenomenon in which the battery characteristics varied depending on the period, and the utilization rate of the positive electrode active material nickel hydroxide was at the same level as when the active material was activated within the battery.

In addition, as mentioned above, batteries made using the conventional method could not be charged with a large current at the initial stage due to a decline in the utilization of active materials, etc., whereas the battery according to the present invention could not be charged at a large current at the initial stage. Even with current charging, no decrease in the active material utilization rate was observed, and the battery exhibited excellent characteristics.

Effects of the Invention As described above, according to the present invention, a large amount of positive electrode active material can be activated at once in a paste state, which is extremely efficient compared to conventional activation within a battery. becomes.

In addition, the battery has many advantages, such as being more stable after construction than conventional batteries and being able to charge with a large current from the beginning.

[Brief explanation of the drawing]

Figure 1 shows the closed type Ninokel-Cadmira 1. Figure 2, which shows the relationship between the initial charging current value of a battery and the utilization rate of a nickel hydroxide active material, is a schematic diagram of an electrolysis device using a heavy-walled active material. 1... Power supply for electrolysis, 2... Metal container that also serves as a negative terminal, 3... Positive opposition, 4... Electrolytic diaphragm. 5 ・Positive active material base I-0

Claims (1)

[Claims] Production of a nickel positive electrode comprising the step of positively electrolyzing a weakly alkaline active material mixture paste containing nickel hydroxide, metallic cobalt, and metallic nickel at a potential below the oxidation potential of nickel hydroxide and above the oxidation potential of metallic cobal 1- Law.