JPH10149819A - Manufacture of paste type nickel electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a paste type nickel electrode having a high filling density of an active material and giving an excellent cycle life characteristic to a battery incorporating it. SOLUTION: The manufacturing method for this paste type nickel electrode contains the process that a low-viscosity active material mix paste mainly made of nickel hydroxide powder is filled in a current collector having a three- dimensional meshy structure and the process that a high-viscosity active material mix paste mainly made of nickel hydroxide powder is filled in the processed body then it is dried and rolled in sequence as essential processes. The nickel electrode can be manufactured while the active material mix is surely carried to the core section of the current collector, and the filling density of the active material can be increased.

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 paste-type nickel electrode, and more particularly, to a method for maintaining a high discharge density of a battery incorporating the active material with a high packing density. The present invention relates to a method for producing a paste-type nickel electrode that can be used.

[0002]

2. Description of the Related Art For example, a nickel-hydrogen secondary battery, which is being rapidly commercialized as a high-capacity battery, is a battery that operates using hydrogen as a negative electrode active material, and a powder of nickel hydroxide as a positive electrode active material. And a positive electrode, and a negative electrode is a hydrogen storage alloy electrode obtained by supporting a hydrogen storage alloy powder for electrochemically storing and releasing hydrogen on a current collector. And the negative electrode are housed in an outer can together with a predetermined alkaline electrolyte, and the battery is entirely sealed.

[0003] As the above-mentioned nickel electrode, a sintered nickel electrode and a non-sintered nickel electrode are manufactured. The latter can increase the packing density of the active material and provide a high capacity electrode. It is advantageous in that it is possible to reduce the manufacturing cost. This non-sintered nickel electrode is also called a paste nickel electrode,
Generally, it is manufactured as follows.

That is, first, nickel hydroxide powder having a predetermined particle size, a thickener, and if necessary, a conductive material powder, a binder, and distilled water or deionized water containing no harmful components for the battery reaction. Water is kneaded at a predetermined ratio to prepare a mixture paste. Here, the thickener functions as a surfactant for dissolving in water and coating the surface of the powder component in the mixture paste to achieve uniform dispersion thereof. For example, carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, Cellulose polymers such as ethyl cellulose and synthetic polymers such as ethylene glycol, polyethylene glycol, propylene glycol, polyvinyl alcohol, and sodium polyacrylate are widely used.

The conductive material powder enhances the current collecting ability of the manufactured nickel electrode. For example, nickel powder, carbonyl nickel powder, cobalt powder, cobalt oxide powder, cobalt hydroxide powder and the like are widely used. ing. The binder is a component for supporting the powder components such as the above-described nickel hydroxide powder and the conductive material powder on a current collector by binding them to each other.
Polytetrafluoroethylene (PTFE) powder, tetrafluoroethylene / hexafluoropropylene copolymer (FEP) powder. Tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) powder, polychlorotrifluoroethylene (PCTFE) powder, polyvinylidene fluoride (PVDF) powder, polyvinyl fluoride powder, ethylene / tetrafluoroethylene copolymer (ECTFE) Powder and the like are used.

[0006] The prepared mixture paste is then filled into the voids of a current collector made of a conductive material and having a three-dimensional network structure, for example, a nickel foam, and is simultaneously adhered in layers to the surface. Then, after a drying process is performed on the whole at a predetermined temperature, roll rolling is further performed, and finally, an electrode plate having a predetermined size and shape is formed by, for example, punching. Then, a current collecting tab is attached to a predetermined portion of the electrode plate by spot welding, for example, to produce a desired paste-type nickel electrode.

[0007] By the above-mentioned drying treatment, the current collector is filled and
The water component of the applied mixture paste is removed, and a dry mixture mainly composed of nickel hydroxide powder remains in the voids and the surface of the current collector. Therefore, in the dried mixture after the drying treatment, traces of the removal of the water component remain as voids, and the dried mixture has a porous structure as a whole. Then, by the next roll rolling treatment, the above-mentioned voids are crushed and the dry mixture is densified, and the binder powder is spread to bind the nickel hydroxide powder and the conductive material powder to each other to form a dry mixture. Is carried on the voids and the surface of the current collector.

[0008] If necessary, the entire mixture is heated to a desired temperature to melt the binder, whereby the mixture is firmly supported on the current collector.

[0009]

However, in order to increase the capacity of the nickel electrode, it is desirable to carry as much active material (nickel hydroxide powder) as possible on the current collector. For that purpose, it is necessary to prepare a mixture paste containing a large proportion of the active material (nickel hydroxide powder), and to completely fill the paste into the core of the current collector.

However, increasing the mixing ratio of the nickel hydroxide powder means relatively lowering the mixing ratio of the water component. Therefore, the viscosity of the obtained mixture paste becomes high, Fluidity worsens. Therefore, filling the current collector with the high-viscosity mixture paste is effective for increasing the capacity of the nickel electrode,
On the other hand, it can cause the following problems.

For example, since the mixture paste used has poor fluidity, when filling the current collector, the mixture paste does not always completely fill the voids of the current collector core.
The current collector core may remain as an unfilled air hole. Therefore, even after the roll rolling process, air holes may remain in the core of the current collector, and as a result, the packing density of the active material may be reduced.

Further, when the last punching is performed, the above-mentioned air holes may be exposed from the cut surface. In that case, at the exposed location, the active material:
Since it is carried in a coarse state compared to other places, it is easy to fall off. Therefore, in the course of the progress of the charge / discharge cycle, a situation may occur in which nickel hydroxide as an active material falls off, or the whole or a part of the mixture falls off from the current collector.

When such a situation occurs, not only does the capacity of the nickel electrode itself decrease, but if the amount of the nickel electrode drops, the nickel hydroxide powder causes a short-circuit phenomenon between the positive electrode and the negative electrode, and the cycle of the battery decreases. The service life is shortened. The present invention solves the above-described problem that has occurred when filling a high-viscosity mixture paste into a current collector having a three-dimensional network structure in order to increase the packing density of the active material. Until the mixture paste is completely filled, and the active material is filled with a high packing density, the capacity increases,
An object of the present invention is to provide a method of manufacturing a paste-type nickel electrode capable of improving cycle life characteristics of a battery incorporated therein.

[0014]

According to the present invention, a low-viscosity active material mixture paste mainly composed of nickel hydroxide powder is provided on a current collector having a three-dimensional network structure. Filling step; and filling the obtained treated body with a high-viscosity active material mixture paste mainly composed of nickel hydroxide powder, and then sequentially performing a drying treatment and a rolling treatment. A method for producing a paste-type nickel electrode is provided.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an operation of filling an active material mixture paste into a current collector having a three-dimensional network structure is performed in two steps, and a low viscosity mixture paste is used in the first filling operation. The present invention is characterized in that the following processing is performed on the obtained treated body using a mixture paste having a higher viscosity.

In the present invention, a current collector is first filled with a low-viscosity active material mixture paste. As the current collector to be used, any current collector having a three-dimensional network structure conventionally used as a current collector for a paste-type nickel electrode may be used, and specific examples thereof include a nickel foam.

The mixture paste used in the first filling operation has a low viscosity and thus has a high fluidity. Therefore, the mixture paste is smoothly filled up to the core of the current collector, and no air hole is formed in the core of the current collector after the filling operation. The viscosity of the mixture paste used at this time varies depending on the size of the voids in the network structure of the current collector and the distribution thereof, but the viscosity is 1.0 to 3.5 Pa · sec.
Is preferably within the range.

If the viscosity is lower than 1.0 Pa · sec, the fluidity is so good that it may flow down during the filling operation,
In addition, the time required for the drying process after filling, which will be described later, becomes longer, causing a decrease in productivity. Conversely, if the viscosity is higher than 3.5 Pa · sec, the filling property of the current collector becomes poor, and it is difficult to completely fill the core, and air holes may remain. In this case, the skeleton of the current collector is deformed.

Next, the resulting processed product is filled with a high-viscosity mixture paste. In addition, the processed body is one in which the low-viscosity mixture paste is filled up to the core of the current collector. The mixture paste used at this time has a large mixture ratio of the active material (nickel hydroxide powder), that is, a small mixture ratio of the water component, and has a higher viscosity than the mixture paste used in the first filling operation. Are preferred. This is because, in the drying process after filling described later, the generation of voids due to the removal of the water component is reduced, and the filling density is increased.

Specifically, the mixture paste used at this time has a viscosity higher than 3.5 Pa · sec. In the mixture paste filling operation performed in these two stages, the total amount of the low-viscosity mixture paste to be filled first and the amount of the high-viscosity mixture paste to be filled next is the target mixture paste filling amount. In short, it is only necessary to fill the core of the current collector, and the filling amount of the low-viscosity active material paste may be smaller than the amount of the high-viscosity active material paste subsequently filled. . In that case, it is preferable that the ratio of the former filling amount to the latter filling amount is 2 to 4 for the former.

In the course of the transition from the first filling operation to the next filling operation, a half of the treated body filled with the low-viscosity mixture paste is such that the mixture paste exhibits some fluidity. You may perform the drying process which becomes a dry state. Specifically, it is preferable to dry at a temperature of about 50 to 80 ° C. for about 10 seconds. In performing the first filling operation and the next filling operation, two kinds of mixture pastes having the same composition and low viscosity and high viscosity are separately prepared, and they are sequentially collected, for example, at room temperature. What is necessary is just to fill an electric body.

The filling operation can be performed in the following manner. That is, first, a high-viscosity mixture paste to be used in the subsequent filling operation is prepared, and the mixture paste is divided into, for example, two parts. Then, a predetermined amount of a thickener aqueous solution having a predetermined concentration is added to one of the proportioning agent pastes to obtain a desired low-viscosity paste, and this is used as a paste at the time of the first filling operation. ,
It may be used as it is for the next filling operation.

Further, at the time of the first filling operation, one of the above-mentioned fraction pastes is heated or the environmental temperature is raised to room temperature or higher, so that the fraction paste is used with a low viscosity. In the latter stage of the filling operation, the other dispersant paste may be cooled to the lower temperature or the ambient temperature may be lowered so that the dispersant paste has a high viscosity.

The mixture paste to be filled may be any paste as long as it has been conventionally used for a paste-type nickel electrode. The shape is preferably spherical, egg-shaped, or elliptical. In the present invention, after filling the mixture paste into the current collector,
For example, a water component contained in the mixture paste is removed by performing a drying process using hot air or an infrared heater.

At this time, if the drying treatment is carried out at a high temperature from the beginning, for example, the water component will boil or the air entrained during the filling operation will expand rapidly, and voids will be formed in the dry mixture. Or cracks may occur. Therefore, when performing the drying process, it is preferable to perform a process of sequentially increasing the drying temperature from room temperature to a high temperature of, for example, 250 ° C. Specifically, after filling the mixture paste, the mixture paste is left at room temperature for a desired time, and then dried at 30 ° C., 80 ° C., 150 ° C., and 250 ° C. for a desired time. It is preferred to do so.

By performing such a treatment, the water component in the inside and air entrained during the filling operation can be volatilized gradually before the surface of the filled mixture paste dries. After drying the mixture paste filled in this way, the whole is then roll-rolled to adjust the thickness, and the dried mixture is firmly supported on the current collector. The operating conditions for roll rolling at this time are not particularly limited, and may be performed under the same conditions as in the conventional case.

The rolled body thus obtained is subjected to, for example, punching and cutting into a predetermined size and shape to produce the desired paste-type nickel electrode.

[0028]

【Example】

Examples 1 to 5 (1) Production of paste-type nickel electrode Spherical nickel hydroxide powder 10 having a particle size of 5 to 50 μm
0 g of nickel powder 10 having a particle size of 10 to 50 μm.
g and 5 g of cobalt oxide powder having a particle size of 0.5 to 30 μm were mixed.

This mixed powder is mixed with P having a suspension concentration of 60% by weight.
1 g of TFE dispersion was added, and 30 g of a 2% by weight aqueous solution of carboxymethylcellulose (CMC) was further added. The whole was mixed to prepare 46 g of a high-viscosity mixture paste. Room temperature (20 ° C) of this mixture paste
Was 4.0 Pa · sec. The mixture paste to A _1.

[0030] Apart from this mixture paste A _1, except that the amount of concentration of 2 wt% CMC aqueous solution was the amount shown in Table 1 in the same manner as the mixture paste A _1, low viscosity the mixture paste a ₁ was prepared. The viscosity at room temperature of the mixture paste a ₁ are shown in Table 1. Then, each of the mixture paste a _1, was charged to room temperature (20 ° C.) spongy nickel plate of a porosity of 95% in the lower, further, by applying the mixture paste A ₁ described above to the surface and subsequently at room temperature After standing for 1 minute, the sample was placed in a thermostat and dried at 50 ° C. for 5 minutes, 150 ° C. for 5 minutes, and 250 ° C. for 1 minute.

And 4 ton / cm^TwoRolling with pressure
And then immersed in the PTFE dispersion.
Soak and dry at 120 ° C for 20 minutes.
n / cm ^TwoRolls at a pressure of 0.7mm to form a 0.7mm thick sheet
Was. Then, this sheet is punched and the thickness
The nickel electrode was 0.7 mm, 40 mm long and 40 mm wide.

For comparison, the following nickel electrodes were manufactured. First, without a coating of mixture paste A _1, In Table 1, except that the filled only mixture paste a ₁ of low viscosity used in the production of nickel electrode of Examples 1 to 5 Example A nickel electrode was manufactured in the same manner as in Examples 1 to 5, and this was used as Comparative Example 1.

Further, except that the mixture paste A ₁ is only filled it in the same manner as in Example 1-5 to prepare a nickel electrode, which was used as a comparative example 2. (2) Production of hydrogen storage alloy electrode Composition formula: MmNi _3.2 Co _1.0 Al _0.2 Mn _0.4 (However,
A hydrogen storage alloy represented by Mm (mish metal) was pulverized into an alloy powder having a particle size of 10 to 100 μm.

A particle size of 0.5 to 3 is added to 100 g of the alloy powder.
5 g of PTFE powder of 0 μm was mixed, 15 g of deionized water was added thereto, and the whole was kneaded to prepare a mixture paste for a negative electrode. This mixture paste was applied to a punched nickel plate (opening diameter 1.5 mm, opening ratio 38%, thickness 0.07
mm) on both sides. Then, after drying at a temperature of 80 ° C. for 60 minutes, it is roll-rolled at a pressure of 3 ton / cm ^{2 to} obtain a thickness.
A 0.35 mm hydrogen storage alloy electrode was used.

(3) Battery assembly FT-310 (trade name, polyolefin-based nonwoven fabric manufactured by Japan Vilene Co., Ltd.) was washed with water to remove the nonionic surfactant adhering to the surface, and then dried. The nonwoven fabric was immersed in hot concentrated sulfuric acid (temperature: 100 ° C.) having a concentration of 95% for 30 minutes to perform a sulfonation treatment on the surface. The treated nonwoven fabric was sufficiently washed with running water, dried at a temperature of 80 ° C. for 1 hour, immersed in a 1% aqueous sodium hydroxide solution for 5 minutes, and further washed with water.

Also, FT-773 (trade name, nonwoven fabric of polyamide resin manufactured by Japan Vilene Co., Ltd.) was washed with water,
The treated product of FT-310 is superimposed on both sides of this nonwoven fabric, and the temperature is 80 ° C. while applying a pressure of 3 kg / m ^{2 to} the whole.
Was subjected to a heat and pressure treatment for 1 hour to be integrated to obtain a separator. Between the nickel electrodes and the hydrogen storage alloy electrodes, the separator is interposed to form an electrode group, which is housed in a nickel-plated stainless steel can. NaOH, 1N LiOH and 7
An electrolyte composed of N KOH was injected and sealed, and an AA type nickel-hydrogen secondary battery with a rated capacity of 200 mAh was assembled.

(4) Investigation of battery characteristics For the assembled battery, at a temperature of about 20.degree.
A cycle life test was performed in which the battery was charged for 1.5 hours and discharged at 1 C, so that the battery voltage became 1 V. The discharge capacity was measured at the beginning of the cycle test and after the 500 cycle test, and the value was divided by the initial capacity to calculate the capacity retention (%).
The results are shown in Table 1.

In the above cycle life test, 5
At the end of the 00 cycle, the battery was disassembled, the nickel electrode was taken out, its weight was measured, and the amount of nickel hydroxide powder falling off was determined from the weight before being incorporated into the battery. Regarding the amount of nickel electrode falling off, the amount of nickel electrode falling off in Comparative Example 2 was 1
Are shown in Table 1 as relative values.

[0039]

[Table 1]

As is clear from comparison between Comparative Example 1 and Comparative Example 2, when the low-viscosity mixture paste a1 is _first filled,
Than when filled with mixture paste A ₁ of high viscosity from the beginning, dropping amount of the nickel hydroxide powder after the cycle life test is reduced. This is because the mixture paste a ₁ is a low viscosity, indicating that it is reliably filled up to the core of the sponge nickel plate.

[0041] Then, the nickel electrode of each embodiment, after the mixture paste a ₁ of the first low viscosity is filled, because further is mixture paste A ₁ of high viscosity is filled, after the cycle life test The amount of nickel hydroxide powder falling off is very small, and therefore, the capacity retention of the battery is also high. Example 6 Mixture paste A ₁ (viscosity at 20 ° C. 4.0 Pa · sec) was heated to about 50 ° C. At that time, the viscosity decreased to 2.4 Pa · sec. The mixture paste to a _2.

The temperature of the sponge-like nickel electrode was maintained at 50 ° C., and the mixture paste a ₂ was filled therein. Thereafter, the whole was cooled to 20 ° C., and the mixture paste A ₁ was applied thereto. Drying was performed in the same manner as in Examples 1 to 5 to obtain a nickel electrode. Example 1 using this nickel electrode
Batteries similar to those of Nos. 1 to 5 were assembled, and the same cycle life test was performed.

Comparative Example 2
Was 1/5. Battery capacity retention is 98%
Met.

[0044]

As is apparent from the above description, according to the method of the present invention, a nickel electrode can be manufactured in a state where the active material mixture is securely carried on the core of the current collector. The packing density of the active material can be increased. Therefore, the capacity of this nickel electrode is high, and the capacity retention rate of the battery in which it is incorporated is high.

Claims (1)

[Claims] 1. A step of filling a low-viscosity active material mixture paste mainly composed of nickel hydroxide powder into a current collector having a three-dimensional network structure; and adding nickel hydroxide powder to the obtained treated body. A process of filling a high-viscosity active material mixture paste, which is a main component, and subsequently performing a drying process and a rolling process sequentially, as an essential process.