JPH0670903B2 - Nickel electrode for alkaline secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nickel electrode for an alkaline secondary battery. More specifically, nickel-cadmium secondary battery,
The present invention relates to a nickel electrode that is used as a positive electrode of an alkaline secondary battery such as a nickel-zinc secondary battery and has low cost and excellent characteristics.

[Conventional technology]

Conventionally, a nickel electrode for an alkaline secondary battery uses a porous nickel sintered body produced by sintering nickel powder as an electrode substrate, soaking it in a nickel nitrate solution, and then thermally decomposing it for activation. Manufactured by sintering as a material (eg SUFalk & AJSalkind “Alkaline Storag
e Batteries "John Wiley & Sons Inc. (1969)).

The electrode manufactured by this sintering method has good characteristics such as high rate discharge, but has a drawback of high cost. The reason is that a high-temperature reducing atmosphere furnace is required to make a nickel sintered body used as an electrode substrate, and the active material filling process needs to be repeated several times. There was a lot of cost.

Therefore, although it has not yet been put to practical use at present, while maintaining the characteristics of the sintered electrode, in order to obtain a low cost nickel electrode, an active material, a conductive auxiliary agent and a binder are mixed in appropriate amounts, A paste method of forming a paste and applying it to a current collector such as punching metal has been proposed and attracts attention. However, since a good binder has not been found, neither one having sufficient electrode strength nor one in which the active material does not fall off even when the charge / discharge cycle is repeated is not obtained.

[Problems to be solved by the invention]

As described above, although the sintering method is excellent in electrode performance, it has a problem in manufacturing and cost. On the other hand, the paste method has an advantage that it can be manufactured at low cost. There is a problem in that the active material comes off due to repeated charging and discharging cycles, and at present, no satisfactory method has been obtained by any of the methods.

[Means for solving problems]

The present invention solves the above-mentioned problems of the prior art,
Ethylene-propylene-ethylidene norbornel terpolymer (hereinafter referred to as sulfonated EPDM), which was sulfonated and then neutralized with a metal carboxylate as a binder, was used in a specific ratio, and the amount of the conductive additive to the active material was specified. By defining the range, it is possible to obtain a paste type nickel electrode having excellent electrode characteristics.

That is, the present invention provides a sulfone as a binder in a nickel electrode for an alkaline secondary battery, which is manufactured by applying or filling a paste-like compounding agent containing an active material, a conductive additive, and a binder to a porous electrode substrate. EPDM in nickel electrode
The present invention relates to a nickel electrode for an alkaline secondary battery, which is used in an amount of 10% by weight and a weight ratio of an active material to a conductive auxiliary agent is 70:30 to 40:60.

The above-mentioned sulfonated EPDV has a very excellent binding force, and exerts a strong binding action at a usage amount of 1 to 10% by weight in a nickel electrode similar to the conventional one, enhances the electrode strength, and repeats charge / discharge cycles. Also, prevent the active material from falling off.

However, since a strong film is formed on the surface of the active material, the electron conductivity of the electrode is lowered, and it is sufficient to add about 10 to 20% by weight of a conductive auxiliary agent such as nickel powder or cobalt powder as in the conventional case. Electronic conductivity is not exhibited. Therefore, by increasing the use ratio of the conductive auxiliary agent and increasing the conductive auxiliary agent to the active material in a weight ratio of 70:30 to 40:60 as described above, the conductivity is increased and the electrode characteristics are improved to be practical. The present invention provides a nickel electrode having good properties.

In completing the present invention, the present inventors initially focused on the excellent binding action of the above-mentioned sulfonated EPDM, and simply replaced the conventional binder with Teflon (trade name, fluorocarbon resin manufactured by DuPont). Although a nickel electrode was produced by using it, the electrode with strong electrode strength was obtained, but when it was incorporated into a battery, the internal resistance was high, the operating voltage during charging was high, and the charging efficiency was reduced. The electrode characteristics were not obtained.

Therefore, the inventors of the present invention have conducted further studies to investigate the cause, and the cause of the increase in internal resistance as described above is
Sulfonated EPDM has a large film forming ability and forms a strong film on the surface of the active material, which reduces the electron conductivity of the electrode.
It was found that sufficient addition of about 10 to 20% by weight does not provide sufficient electron conductivity, and provided an electrode that can be put to practical use by increasing the amount of the conductive additive as described above. Of.

Sulfonated EPDM used as a binder in the present invention
Has excellent alkali resistance, the binding effect of the active material is very large as described above, and also has rubber elasticity, so that the formed film has flexibility, and when it is used as a spiral electrode, It is particularly suitable for use as a binder and is an excellent binder.

If the amount of the sulfonated EPDM used is too large, electron conduction between the active material particles cannot be obtained, the heavy load discharge characteristics are impaired, and if it is too small, the binding effect is not sufficiently exhibited. Up to 10% by weight.

The sulfonated EPDM has a sulfonation rate of 0.2 to 20.
Those having a mol% are particularly preferable because of the excellent properties described above, and examples of metal carboxylates for neutralization after sulfonation include zinc stearate, barium stearate, calcium stearate, zinc acetate, zinc laurate and the like. Is used.

In carrying out the present invention, nickel hydroxide or nickel oxyhydroxide is used as the active material. The paste-like compounding agent containing the active material as the main ingredient is usually the above active material,
Metallic powder such as nickel, cobalt, silver, or short fibers, carbon powder, short carbon fibers and other conductive aids,
Prepared by mixing sulfonated EPDM as a binder and a hexane-methyl alcohol mixed solution, the cobalt has an important role of contributing to the improvement of charge / discharge characteristics in addition to the action as a conductive additive. is doing. In addition to the above components, lithium paste, calcium hydroxide, cadmium hydroxide and the like may be added to the above paste-like compounding agent for the purpose of improving charging efficiency.

When preparing the above-mentioned paste-like compounding agent, the weight ratio of the active material to the conductive additive is 70:30 to 40:60. This is because if the amount of the conductive additive is less than the above range, electron conduction between the active material particles is not sufficiently performed, the conductivity of the positive electrode is reduced, the internal resistance is increased, and the charging efficiency is reduced. Also, if the amount of the conductive additive exceeds the above range, the amount of the active material is reduced, and the welding efficiency of the battery is reduced accordingly.

For the electrode substrate, for example, a metal foam such as a nickel foam, a sintered body of a metal fiber chop, a metal plain woven wire mesh such as a nickel plain woven wire mesh, or a resin fiber on which metal plating is applied The conductive porous substrate used is used.

〔Example〕

 Next, the present invention will be described in more detail with reference to examples.

Example 1 60 parts by weight of nickel hydroxide powder, 35 parts by weight of metallic nickel powder, and 5 parts by weight of metallic cobalt powder were mixed, and a concentration of 2% by weight of sulfonated EPDM (sulfonation rate: 5 mol%, stearin) was used as a binder. A hexane-methyl alcohol (volume ratio 95: 5) solution of zinc acid neutralized) was added to prepare a pasty compounding agent. The amount of binder in this electrode is 5% by weight. The weight ratio of the active material to the conductive additive is 60: 4.
It is 0. The paste-like compounding agent is slid into a porous electrode base (electrode base made of nickel foam having a thickness of 0.8 mm and a porosity of 80% by volume), and after drying, pressed to a thickness of about 0.5 mm. A nickel electrode was manufactured by molding.

Using the nickel electrode thus manufactured as a positive electrode and the cadmium electrode as a negative electrode, a cylindrical nickel-cadmium secondary battery having a structure as shown in FIG. 1 and having a diameter of 14.5 mm and a height of 50.0 mm (nominal) A capacity of 500 mAh) was produced.

In FIG. 1, reference numeral 1 denotes the nickel electrode manufactured as described above, which has a plate shape with a thickness of 0.5 mm, a width of 40 mm and a length of 65 mm. 2 is a separator made of polyamide nonwoven fabric, having an average thickness of 0.2 mm and having a width that is about 2 mm larger than the width of each electrode. Reference numeral 3 is a cadmium electrode as a negative electrode. The cadmium electrode 3 is composed of a paste type electrode plate in which cadmium oxide is applied to a core body using a water-soluble binder and has a thickness of about
It is 0.5 mm wide, 40 mm wide, and 85 mm long, and has a capacitance about 1.5 times the capacitance of nickel electrodes. The cadmium electrode 3 is superposed on the nickel electrode 1 with the separator 2 interposed therebetween, is spirally wound, and is housed in the outer can 9. 4 is a lead of the nickel electrode 1, 5
Is a lead of the cadmium electrode 3, 6 is a sealing plate made of metal, and this sealing plate 6 is composed of an upper part 6a and a lower part 6b, and the lower part 6b has one end of the lead 4 on the nickel electrode side. Are spot welded. Further, this battery has an explosion-proof valve 7 for ensuring safety when the internal pressure of the battery rises abnormally, and has a sealed structure with a crimp seal that crimps the insulating packing 8 and the outer can 9. An electrolytic solution consisting of an aqueous potassium hydroxide solution having a concentration of 30% by weight is enclosed therein.

Comparative Example 1 A nickel electrode was produced in the same manner as in Example 1 except that Teflon was used as the binder instead of the sulfonated EPDM.
Using this nickel electrode as a positive electrode, a nickel-cadmium secondary battery was produced in the same manner as in Example 1.

Comparative Example 2 A nickel electrode was manufactured by impregnating a nickel sintered body with nickel nitrate and heating it to thermally decompose the nickel nitrate.
A nickel-cadmium secondary battery was produced in the same manner as in Example 1 except that this nickel electrode was used as the positive electrode.

As described above, the battery using the nickel electrode of Example 1 of the present invention as the positive electrode was designated as battery A, and the battery using the paste type nickel electrode of Comparative Example 1 using Teflon as the binder according to the conventional technique as the positive electrode was designated as battery A. B, a battery using the sintered nickel electrode of Comparative Example 2 as a positive electrode is referred to as battery C, and these batteries A,
The charge / discharge cycle characteristics of B and C were examined. The results are shown in FIG. The difference between the battery A and the batteries B and C is only the difference in the nickel electrode, and the others are the same.
The test conditions for the charge / discharge cycle characteristic test are the discharge current.
Charged for 7.5 hours at 100mA and charging current of 100mA, the cut voltage during charging / discharging is 1.6V during charging and 1.0V during discharging.

As shown in FIG. 2, the battery A using the nickel electrode of the present invention as the positive electrode has a large discharge capacity even if the number of charge / discharge cycles increases, and the battery using the sintered nickel electrode of Comparative Example 2 as the positive electrode. It had a charge / discharge cycle characteristic equivalent to that of C, and was far superior in charge / discharge cycle characteristic to Battery B using the paste type nickel electrode of Comparative Example 1 as a positive electrode.

As described above, the nickel electrode of the present invention has charge / discharge cycle characteristics comparable to those of the sintered nickel electrode, but in the production thereof, it can be produced by the paste method, and compared with the case of producing the sintered nickel electrode. Can simplify the manufacturing process,
Manufacturing cost can be significantly reduced.

Example 2 A nickel electrode was produced in the same manner as in Example 1 except that 70 parts by weight of nickel hydroxide powder, 25 parts by weight of metallic nickel powder and 5 parts by weight of metallic cobalt powder were used.

Example 3 A nickel electrode was produced in the same manner as in Example 1 except that 50 parts by weight of nickel hydroxide powder, 45 parts by weight of metallic nickel powder and 5 parts by weight of metallic cobalt powder were used.

Example 4 A nickel electrode was produced in the same manner as in Example 1 except that 40 parts by weight of nickel hydroxide powder, 55 parts by weight of metallic nickel powder and 5 parts by weight of metallic cobalt powder were used.

Comparative Example 3 A nickel electrode was produced in the same manner as in Example 1 except that 30 parts by weight of nickel hydroxide powder, 65 parts by weight of metallic nickel powder and 5 parts by weight of metallic cobalt powder were used.

Comparative Example 4 A nickel electrode was produced in the same manner as in Example 1 except that 80 parts by weight of nickel hydroxide powder, 15 parts by weight of metallic nickel powder and 5 parts by weight of metallic cobalt powder were used.

The nickel electrodes of Examples 2 to 4 and Comparative Examples 3 to 4
A nickel-cadmium secondary battery similar to that of Example 1 was manufactured by using each of the nickel electrodes described in 1 above as a positive electrode.

The battery and the battery using the nickel electrode of Example 1 as the positive electrode were subjected to the charge / discharge cycle test in the same manner as described above, and the discharge capacity when the charge / discharge cycle was once,
Table 1 shows the results of examining the retention rate of the discharge capacity when the number of charge / discharge cycles reached 500 (retention rate with respect to the discharge capacity when the number of charge / discharge cycles was 1).

As shown in Table 1, when the weight ratio of the conductive additive to the active material was more than 40:60, as shown in Comparative Example 3, although the retention rate was good when the number of cycles was large, When the discharge capacity that can be charged in the battery is reduced and the capacity efficiency of the battery is reduced, and conversely the ratio of the conductive additive to the active material is less than 70:30 by weight, as shown in Comparative Example 4. In addition, although the welding efficiency of the battery is improved, the retention rate becomes lower as the cycle is repeated.

The nickel electrode obtained by the present invention is not limited to the nickel-cadmium secondary battery illustrated in the examples,
For example, it can be applied to alkaline secondary batteries such as nickel-zinc secondary batteries and nickel-iron secondary batteries.

〔The invention's effect〕

As described above, in the present invention, by using the sulfonated EPDM as the binder, the electrode strength can be increased, the active material can be prevented from falling off, and the charge / discharge cycle characteristics can be improved. Further, the advantages of the paste-type electrode production can be fully utilized, and the nickel electrode having excellent characteristics can be produced with a simple method, economically, and in the production process.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a cylindrical nickel-cadmium secondary battery using the nickel electrode of the present invention, and FIG. 2 is a cylindrical nickel-cadmium secondary battery using the nickel electrode of the present invention and a conventional battery. It is a figure which shows the charging / discharging cycle characteristic of a cylindrical nickel-cadmium secondary battery using a nickel electrode. 1 ... Nickel electrode, 2 ... Separator, 3 ... Cadmium electrode

Claims (1)

[Claims] 1. A nickel electrode for an alkaline secondary battery, which is produced by applying or filling a paste-like compounding agent containing an active material, a conductive auxiliary agent, and a binder to a porous electrode substrate to produce sulfone as a binder. 1-10% by weight of ethylene-propylene-ethylidene norbornel terpolymer neutralized with a metal carboxylate in a nickel electrode was used, and the active material and the conductive additive were added at a weight ratio of 70: 30-40: 60. A nickel electrode for an alkaline secondary battery characterized by the above.