JP2000058060A - Paste for positive electrode, paste-type nickel hydroxide positive electrode and alkaline storage battery - Google Patents

Abstract

(57) [Summary] [Problem] Characteristics of positive electrode weight and the like at the start of coating and at the end of coating in a continuous coating method, using a paste for a positive electrode which is less likely to change over time in viscosity and the like and has excellent stability. A paste-type nickel hydroxide positive electrode having uniformity on the surface is obtained,
Using this positive electrode, an alkaline storage battery excellent in productivity with little variation in capacity is obtained. SOLUTION: A positive electrode paste containing nickel hydroxide as an active material contains poly-N-vinylacetamide, and the positive electrode paste is applied to a conductive substrate, dried, and dried. A nickel hydroxide positive electrode is prepared, and the paste-type nickel hydroxide positive electrode and the negative electrode are loaded into a battery together with a separator and an alkaline electrolyte interposed between the two electrodes to form an alkaline storage battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a paste for a positive electrode using nickel hydroxide as an active material, a paste-type nickel hydroxide positive electrode obtained by applying the paste to a conductive substrate and drying the paste.
Further, the present invention relates to an alkaline storage battery using the positive electrode.

[0002]

2. Description of the Related Art As is well known, a nickel cadmium battery having a positive electrode as a nickel hydroxide electrode and a negative electrode as a cadmium electrode, and a nickel hydrogen storage battery having a negative electrode as a hydrogen storage alloy electrode are well known. ing.

[0003] In such an alkaline storage battery, as a nickel hydroxide positive electrode, conventionally, nickel nitrate is impregnated into a microporous substrate obtained by sintering nickel powder into a perforated plate or the like.
A sintering type is known which is produced by repeating a process of changing into nickel hydroxide in an alkaline solution. However, such a sintered nickel hydroxide positive electrode requires a complicated operation when manufacturing a sintered substrate or impregnating the sintered substrate with an alkaline solution, resulting in high cost and poor mass productivity. There was.

For this reason, recently, a paste for a positive electrode has been prepared in which nickel hydroxide in powder form is used as an active material and dispersed in a solvent together with a binder and a thickener.
A paste-type nickel hydroxide positive electrode prepared by applying a paste to a conductive substrate, drying the roll, and then rolling as necessary is used.

In order to mass-produce this paste-type nickel hydroxide positive electrode industrially, a method is employed in which the paste for the positive electrode is continuously supplied to a coating step to continuously apply the paste without stopping the line. You. In this case, it takes a long time from the time of preparing the paste to the time of completing the application. Therefore, the paste for the positive electrode has a stable property with little change over time in components, composition, viscosity, etc. Sex is required. In particular, in the above-mentioned mass production method, the application step becomes a rate-determining stage due to the problem of the application speed, and it often takes several days from the time of preparing the paste to the time of application, so that long-term stability is required.

[0006]

However, the conventional paste for a positive electrode tends to decrease in viscosity with time after preparation, and thus the obtained nickel hydroxide hydroxide positive electrode has a problem in that the coating is started in continuous coating. The uniformity of characteristics such as the weight of the positive electrode is impaired between the time and the end of coating, and the paste stability is further deteriorated, especially when the filling rate of nickel hydroxide powder is increased to increase the capacity. Therefore, the uniformity is more likely to be impaired. As a result, in the alkaline storage battery assembled using the nickel hydroxide positive electrode, there is a problem that the capacity tends to vary and the yield is reduced.

[0007] In view of such circumstances, the present invention provides a positive electrode paste having excellent stability in which a change with time in viscosity or the like is unlikely to occur over a long period of time, and using this positive electrode paste. To obtain a paste-type nickel hydroxide positive electrode in which uniformity in characteristics such as the weight of the positive electrode is maintained between the start of coating and the end of continuous coating.
It is an object of the present invention to obtain an alkaline storage battery excellent in productivity with little variation in capacity using the nickel hydroxide positive electrode.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and as a result, have found that poly (N-vinylacetamide) is contained in a paste for a positive electrode containing nickel hydroxide as an active material. When it is included, a paste for the positive electrode having excellent stability in which a change with time in viscosity and the like is unlikely to occur over a long period of time can be obtained. A paste-type nickel hydroxide positive electrode that maintains uniformity in characteristics such as the weight of the positive electrode at the end of coating can be obtained, and by using this nickel hydroxide positive electrode, excellent productivity with little variation in capacity is obtained. Knowing that an alkaline storage battery could be obtained, the present invention was completed.

That is, the present invention relates to a paste for a positive electrode comprising nickel hydroxide as an active material, wherein the paste for a positive electrode contains poly-N-vinylacetamide. is there. Further, the present invention relates to a paste-type nickel hydroxide positive electrode obtained by applying the paste for a positive electrode having the above-mentioned structure to a conductive substrate and drying the paste. -An alkaline storage battery comprising a nickel hydroxide nickel positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte (Claim 3). It is related to.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the reason why poly N-vinylacetamide gives a favorable result on the stability of the paste for positive electrode is considered as follows. Nickel hydroxide acts as a catalyst that promotes the oxidative decomposition of organic substances such as binders and thickeners in the paste because the surface is active,
The molecular weight of the organic substance is reduced to lower the viscosity, and the decomposition product is irreversibly adsorbed on the surface of the nickel hydroxide to promote the reduction in the viscosity. When poly-N-vinylacetamide is contained in the paste, it is preferentially adsorbed on the surface of the nickel hydroxide to form an organic layer, and the organic layer forms a binder or a thickener in the paste. It is considered that the stability of the paste is highly improved because the organic layer itself has excellent oxidation resistance and is less likely to be oxidatively decomposed.

The poly-N-vinylacetamide used in the present invention has a weight average molecular weight of 10,000-1.
0,000,000, preferably 50,000-50,000.
It is preferably 00,000. Weight average molecular weight of 10,
When the molecular weight is not less than 000, a high adsorption effect on the surface of the nickel hydroxide is obtained, and the weight average molecular weight is 10, 000.
By setting the content to not more than 1,000,000, an extremely thick paste can be suppressed, and a paste excellent in continuous coating properties can be obtained even when a nickel hydroxide positive electrode thinned for high capacity is used. be able to.

The amount of such poly N-vinylacetamide to be used is usually 0.05 to 6 parts by weight, preferably 0.2 to 3 parts by weight, more preferably 0.1 to 100 parts by weight of nickel hydroxide. The content is preferably 4 to 2 parts by weight. 0.0
When the amount is 5 parts by weight or more, the adsorption layer of poly-N-vinylacetamide can sufficiently cover the surface of the nickel hydroxide, suppresses the oxidative decomposition of a binder and a thickener, and has a viscosity even after being left for a long time. The decrease can be reduced and the filling rate of nickel hydroxide, which is an active material, can be improved by adjusting the content to 5 parts by weight or less.

In the present invention, a paste for a positive electrode is prepared by using nickel hydroxide as an active material, containing the above-mentioned ratio of polyN-vinylacetamide, and forming a paste by a conventional method. I do. As the active material nickel hydroxide, a conventionally known nickel hydroxide can be used. Among these, high capacity is possible, but the surface is active and the binder is easily oxidized and decomposed. Nickel hydroxide containing zinc or cobalt as a solid solution is particularly suitable for the present invention. As the solvent used for preparing the paste, for example, water or an alcoholic solvent such as methanol, ethanol, or isopropanol is used. These may be used alone or in combination of two or more.

In the paste for the positive electrode, if necessary,
Conventionally used binders and thickeners may be blended. Examples of the binder include polytetrafluoroethylene and polyethylene, and examples of the thickener include methylcellulose, hydroxypropylcellulose, carboxymethylcellulose, polyacrylamide, polyvinylpyrrolidone, and polyethylene oxide. Can be Considering the oxidative decomposition and the filling rate of the nickel hydroxide, these binders and thickeners are preferably used in an amount of usually 0.01 to 4 parts by weight based on 100 parts by weight of the nickel hydroxide.

The above-mentioned paste for a positive electrode may contain a conventional conductive agent. As this conductive agent, cobalt oxide is most preferable. The conductive agent is
In order to increase the conductivity of the nickel hydroxide to improve the current collecting ability as a positive electrode, and also to improve the chargeability of the nickel hydroxide, a fine particle state is used. It is easy for the pastes to aggregate, difficult to prepare a uniform paste, and easily thickened. But,
Considering this point, cobalt oxide improves the adsorption form of the binder and forms a conductive network on the surface of the nickel hydroxide by the charge / discharge reaction. It has the effect of further reducing direct contact with the nickel surface and further suppressing oxidative decomposition.

In the present invention, the paste for a positive electrode prepared as described above is applied to a conductive substrate and dried, and then, if necessary, subjected to a press treatment to form a paste-type hydroxide. A nickel positive electrode is manufactured. As the above-mentioned conductive base material, an alkali-resistant metal porous body such as a punching metal or a foamed metal, or a metal plate such as a nickel plate is used. In the coating process, a continuous coating method is adopted for mass production.However, due to the long-term stability of the paste, a stable coating amount can be secured from the start of coating to the end of coating. As a result, the obtained paste-type nickel hydroxide positive electrode has uniformity in terms of characteristics such as weight.

The alkaline storage battery of the present invention is characterized in that a paste-type nickel hydroxide positive electrode having the above structure is used for a negative electrode using cadmium or a hydrogen storage alloy as an active material. Due to the uniformity in the characteristics described above, it is possible to provide an alkaline storage battery excellent in productivity (yield) with little variation in capacity.

This alkaline storage battery comprises, for example, a paste-type nickel hydroxide positive electrode having the above-described structure and the above-described negative electrode,
It is manufactured by laminating through a separator, inserting this into a battery can, and then injecting an alkaline electrolyte. As the separator, a material obtained by imparting a hydrophilic group to a nonwoven fabric made of polyolefin fiber or polyamide fiber is preferably used. Also, as the alkaline electrolyte,
An aqueous solution of potassium hydroxide in which an electrolyte such as a lithium salt is dissolved is preferably used.

[0019]

EXAMPLES Examples of the present invention will be described below in more detail. However, the present invention is not limited to only these examples, and it goes without saying that the present invention can be appropriately changed without departing from the spirit of the present invention. In the following examples, “parts” means “parts by weight”.

EXAMPLE 1 8 parts of cobalt oxide and 2 parts of nickel powder were dry-mixed with 100 parts of nickel hydroxide (2% by weight of zinc, 1% by weight of solid solution of cobalt) and mixed with 10% by weight of poly N-vinyl. Acetamide aqueous solution 10 parts, concentration as binder 60% by weight
4 parts of a polytetrafluoroethylene aqueous dispersion of
A paste for a positive electrode was prepared.

Example 2 The procedure of Example 1 was repeated, except that the number of used poly N-vinylacetamide aqueous solution was changed from 10 parts to 20 parts.
A paste for a positive electrode was prepared.

Example 3 A paste for a positive electrode was prepared in the same manner as in Example 1 except that the number of used poly N-vinylacetamide aqueous solution was changed from 10 parts to 4 parts.

Comparative Example 1 A positive electrode paint was prepared in the same manner as in Example 1 except that the use of the aqueous solution of poly (N-vinylacetamide) was omitted, and the number of parts used in the aqueous dispersion of polytetrafluoroethylene was changed from 4 parts to 6 parts. -Prepared a strike.

Comparative Example 2 Instead of 10 parts of an aqueous solution of poly (N-vinylacetamide),
A paste for a positive electrode was prepared in the same manner as in Example 1 except that 10 parts of a 10% by weight aqueous solution of polyvinyl alcohol was used.

The stability of each of the positive electrode pastes of Examples 1 to 3 and Comparative Examples 1 and 2 was examined as follows. That is, 100 g of each paste was collected in a beaker, and the temperature was 20 ° C.
For 2 days, and the change in viscosity was monitored with a B-type viscometer. These results were as shown in FIG.
In FIG. 1, curve-1a is the result of Example 1, curve-2a is the result of Example 2, curve-3a is the result of Example 3, curve-1b is the result of Comparative Example 1, and curve-2b is the result of Example 1. It is the result of Comparative Example 2.

As is apparent from FIG. 1, the poly-N of the present invention
-Each of the pastes for positive electrodes of Examples 1 to 3 containing vinylacetamide was used after active standing for a long time despite the use of active nickel hydroxide in which zinc and cobalt were dissolved as an active material. It can be seen that there is almost no decrease in viscosity, and the stability is excellent. On the other hand, poly N-
The pastes for both positive electrodes of Comparative Examples 1 and 2, which did not contain vinylacetamide, began to decrease in viscosity immediately after preparation, and were very poor in stability.

Next, using the respective pastes for positive electrodes of Examples 1 to 3 and Comparative Examples 1 and 2, the following method was used.
A paste-type nickel hydroxide positive electrode was prepared and evaluated for uniformity. The results were as shown in Table 1.

<Preparation of paste-type nickel hydroxide nickel cathode and its evaluation> A three-dimensional porous foam core material having a thickness of 1.29 mm, a width of 135 mm, and a length of 240 m was used as a conductive base material. Then, a paste for a positive electrode was coated on the substrate by a continuous coating method, dried at 70 ° C., and pressed to a total thickness of 500 μm to obtain a sheet. The application start portion and the application end portion of this sheet-like material are each set to a width of 36.
mm, cut into 48 mm length to produce 1,000 paste-type nickel hydroxide positive electrodes for each, measure the weight,
The average value and variation were examined.

[0029]

As is clear from the above Table 1, the paste-type nickel hydroxide positive electrode produced by the continuous coating method using the paste for the positive electrode of Examples 1 to 3 of the present invention was applied. There is no change in the weight between the time and the end of the application, and the variation is almost the same. It can be seen that a uniform positive electrode can be produced even by the continuous application method. On the other hand, the paste-type nickel hydroxide positive electrode produced using the paste for the positive electrode of Comparative Examples 1 and 2 has a considerable difference in weight between the start and end of coating, and the coating end. In some cases, the variation in weight is large, and it is understood that a problem is likely to occur in the yield of the positive electrode, and it is difficult to perform stable continuous coating.

Next, each of the 1,000 pieces produced by the above method was used.
A nickel hydrogen storage battery was fabricated using the zero paste nickel hydroxide positive electrode by the following method, and the uniformity was evaluated. The results were as shown in Table 2.

<Preparation of Nickel Hydrogen Storage Battery and Its Evaluation>
100 parts of the hydrogen storage alloy MmNi _5, styrene and 2-ethylhexyl acrylate les as a binder - a monomer mixture mainly composed of bets copolymer (emulsion polymerization product) 1.7 parts and,
20 parts of a polyoxyethylene aqueous solution was added as a thickener and mixed well to obtain a paste. This paste is applied to punched metal, which is a conductive porous substrate, and after drying,
After compression molding, it was cut into a predetermined size to obtain a negative electrode.

Each of the paste-type nickel hydroxide positive electrodes comprising the negative electrode and the coating start portion or the coating end portion was
Wound through a nylon non-woven separator
Into an electrode can of the same size, and add an alkaline electrolyte (1 liter of LiOH to 1 liter of 30% by weight aqueous solution of potassium hydroxide).
7 g and an aqueous solution in which 33 g of zinc oxide were dissolved), and then sealed, stored at 60 ° C. for 17 hours, charged at 295 mA for 2.5 hours, and discharged at 380 mA. This charge / discharge cycle was repeated until the discharge capacity became constant, thereby producing a nickel hydrogen storage battery. The battery was fully charged at 145 mA, and after a 1-hour pause, was discharged at 100 mA until the battery voltage reached 1 V to determine the standard capacity. The average value and variation of 1,000 batteries were evaluated.

[0034]

As is clear from Table 2 above, each nickel hydrogen storage battery using the paste type nickel hydroxide positive electrode prepared by the continuous coating method from the positive electrode pastes of Examples 1 to 3 of the present invention is shown in FIG. It can be seen that there is little variation in the battery capacity between the start of coating and the end of coating in the continuous coating method, stable production is possible, and the yield of the battery can be greatly improved. On the other hand, Comparative Examples 1 and 2
Nickel hydrogen storage batteries using a paste-type nickel hydroxide positive electrode manufactured by a continuous coating method from the positive electrode paste described above have large variations in the above battery capacity, making stable production difficult and increasing the battery yield. It can be seen that it decreases.

[0036]

As described above, in the present invention, the paste for the positive electrode containing nickel hydroxide as an active material is contained in the paste for the positive electrode.
By using vinylacetamide,
A paste for the positive electrode with excellent long-term stability can be obtained, and a paste-type nickel hydroxide positive electrode that maintains uniformity even in the continuous coating method, and has excellent productivity with less variation in capacity. An alkaline storage battery can be obtained.

[Brief description of the drawings]

FIG. 1 is a positive electrode paste of Examples 1 to 3 and Comparative Examples 1 and 2.
FIG. 5 is a characteristic diagram showing a change in viscosity over time for the positive electrode paste.

[Explanation of symbols]

 1a Characteristic curve of positive electrode paste of Example 1 2a Characteristic curve of positive electrode paste of Example 2 3a Characteristic curve of positive electrode paste of Example 3 1b Characteristic curve of positive electrode paste of Comparative Example 1 Characteristic curve 2b Characteristic curve of paste for positive electrode of Comparative Example 2

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA08 BA01 BA03 BB04 BB11 5H016 AA03 BB02 BB06 BB09 EE05 EE09 5H028 AA01 AA05 BB03 BB05 BB06 CC08 EE05 EE06

Claims (3)

[Claims] 1. A paste for a positive electrode comprising nickel hydroxide as an active material, the paste for a positive electrode comprising poly-N-vinylacetamide. 2. A paste-type nickel hydroxide positive electrode obtained by applying the paste for a positive electrode according to claim 1 to a conductive substrate and drying the paste. 3. A paste-type nickel hydroxide positive electrode according to claim 2, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. An alkaline storage battery, characterized in that: