JPH07335210A - Electrode for alkaline battery - Google Patents

Abstract

PURPOSE:To provide an electrode for an alkaline battery which is inexpensive and is excellent both in discharging property and life. CONSTITUTION:This is a sintered substance in the shape of three-dimensional sponge where nickel is applied and made of iron, by covering the framework of a porous resin core with paste having iron powder and a binder for its main ingredients, and next, heating it in nonoxidizing atmosphere to the temperature where the iron powder is sintered or over, and applying nickel to this, and charging an active material powder into it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline storage battery such as a nickel-cadmium battery, a nickel-zinc battery and a nickel-hydrogen battery, and an electrode used for the battery.

[0002]

2. Description of the Related Art Lead batteries and alkaline batteries are used as storage batteries used as various power sources. Of these, the alkaline storage battery has been widely used for various portable devices and the large alkaline battery for industrial purposes because it is expected to have high reliability and can be made compact and lightweight.

In this alkaline storage battery, as the positive electrode, an air electrode, a silver oxide electrode and the like are partially taken up, but most of them are nickel electrodes. The characteristics of the electrode have been improved from the pocket type to the sintered type, and it has become possible to further seal and expand the applications. In order to further increase the electrode capacity, nickel electrodes using a foam type or fiber type support have been widely used.

On the other hand, as the negative electrode, zinc, iron, hydrogen, etc. are targeted in addition to cadmium.

The most widespread is the cadmium electrode, and nickel-cadmium storage batteries have become the protagonist of secondary batteries from portable devices to industrial applications. The next most popular zinc is satisfactory in terms of electric potential, capacity and price, but since it is soluble in an alkaline electrolyte, it has a problem in life and has not been widely used. On the other hand, for the hydrogen storage alloy electrode, nickel-hydrogen storage batteries have been commercialized due to their characteristics of high capacity and low pollution, and demand for them is increasing mainly for their small size.

[0006] By the way, in the case of a sintered type substrate using general nickel powder, when the porosity is 85% or more, the strength is drastically reduced, so that there is a limit to the filling amount of the active material, that is, the increase in capacity. % Or higher, a foamed substrate or a fibrous substrate is taken up as a substrate instead of a sintered substrate and put to practical use. On the other hand, it has long been proposed to apply a nickel paste to a foamed resin and sinter this to obtain a highly porous sintered body. For example, in Japanese Patent Application No. 36-45195, nickel powder is made into a muddy state and impregnated into urethane foam to carbonize the resin in hydrogen, and then nickel is semi-molten to produce a porous body. Further, in Japanese Patent Application No. 48-55274, alumina powder, silica powder and the like are crushed by a ball mill, and then impregnated in urethane foam and baked in air to obtain a sintered body. In Japanese Patent Application No. 645-64529, polyether foam is used as a nickel hydroxide positive electrode by immersing it in a loose powder bed of mond nickel powder and heating it to form a support. Also, a non-woven fabric is exemplified instead of the foam.

Powder filling using core material-sintering, paste-
When the porosity of the substrate is 85% or more in the sintered body of the sintering method, the strength is significantly reduced, and thus there is a limit to the increase in capacity. Therefore, it has long been proposed to obtain a high-porosity sintered body by applying a nickel paste to a foamed resin and sintering it as a substrate having a higher porosity of 90% or more. However, it is more expensive than the paste type using a punching metal, a screen, an expanded metal, etc. as a support because the sintering operation is performed and the raw material nickel is expensive.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrode substrate for an alkaline battery, which has a higher capacity and is inexpensive, an electrode and a method for producing the same, and an alkaline battery.

[0009]

According to the present invention, the skeleton of a porous resin core is coated with a paste containing iron powder and a binder as main components, and the temperature is raised to a temperature at which the iron powder is sintered or higher. Heating in a non-oxidizing atmosphere to form a three-dimensional sponge-like sintered body, nickel-plated on this, and filled with active material powder to form a nickel-plated three-dimensional sponge-like sintered body of the active material. The present invention provides an electrode for an alkaline battery, which is obtained by filling

The thickness of nickel plating is not particularly limited, but is usually about 20 to 100 μm, preferably 20 to 50.
It is about μm.

The term "three-dimensional sponge-like" means that the ratio of voids in the sintered body, that is, the porosity is about 90 to 96%, preferably about 94 to 96%. The average diameter of the voids is 100 to 300 μm, preferably about 150 to 250 μm, when converted into a circle. The voids are filled with the electrode active material.

Any known active material may be used as the active material to be filled in the nickel-plated electrode substrate of the present invention, and the active material is not particularly limited, and examples thereof include nickel hydroxide and a hydrogen storage alloy. Nickel hydroxide is preferably exemplified. The filling of these active materials is not particularly limited, but for example, the powder and an appropriate binder may be mixed to form a paste, and the above three-dimensional sintered body may be impregnated and filled. After this impregnation, it is dried.

In the present invention, the resin of the porous resin core is not particularly limited as long as it is decomposed and removed during sintering, but examples thereof include polyurethane and polystyrene. Here, the core resin has the porosity or porosity necessary for the porosity of the three-dimensional sponge-like sintered body made of iron to fall within the above range. The particle size of the iron substance powder is 1 to 10 μm
It is a degree. Examples of the binder which is the other main component include known binders and are not particularly limited, and examples thereof include carboxymethyl cellulose (CMC), carboxypropyl methyl cellulose, methyl cellulose, starch, polyvinyl alcohol (PVA) and the like. Of these, CMC and PVA are preferable. The binder can be used by dissolving it in a solvent such as water or alcohol. When the total paste is 100 parts by weight, the iron powder is 94 to 99.
About 1 part by weight and about 1 to 6 parts by weight of the binder are included. The same binder is used as needed when the electrode active material is filled.

In the present invention, "covering" the paste means a state in which the paste is attached to the surface of the porous resin core. The method for coating the paste is not particularly limited, but for example, the porous resin core may be immersed or impregnated in the paste under normal pressure or pressure, and then the core may be removed from the paste for coating. it can. With the paste in the present invention, the iron substance powder and the binder can be uniformly or almost evenly distributed in the porous resin core, and the iron substance powder and the binder on the surface of the core adhere. It means that it has a fluidity such that it does not flow out.

In the production method of the present invention, the temperature above which the powder of the iron substance is sintered varies depending on the particle size of the iron powder and is not particularly limited, but is usually 850 to 1150 ° C., preferably 950 to 1050. The temperature is ° C. Although not particularly limited, the sintering is performed in a non-oxidizing atmosphere such as nitrogen, hydrogen, decomposed ammonia, etc.

The sponge-like sintered body obtained by sintering means a state in which the porous resin core body is decomposed and removed during sintering, and iron remains.

[0017]

[Function] First, as a skeleton of the porous core body, a paste containing iron powder such as reduced iron, carbonyl iron, electrolytic iron and the like as a main component and a binder is coated, and then at a temperature not lower than the sintering temperature of the iron powder. A three-dimensional sponge-like sintered body is obtained by heating in a non-oxidizing atmosphere. This makes it possible to obtain a support having a high porosity, unlike the case where iron powder is simply sintered.

Although iron is inexpensive, it partially oxidizes, unlike nickel, when it reaches an oxygen generation potential in a caustic alkali solution. Therefore, this sintered body is plated with nickel to improve the electrolytic solution resistance and the oxidation resistance. That is, it has been found that there is no concern that the support will be oxidized, and that the support can be used as a support for an active material of a high capacity electrode. As the iron substance, it is not necessary to use high-purity powder as used for iron electrodes, and a sintered body having high strength is sufficient, and inexpensive reduced iron is used. In addition, although it is a little expensive, electrolytic iron, carbonyl iron, etc. may be used and the type is not limited. Nickel plating
Known electrolytic nickel plating with few pinholes is preferable.

[0019]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

280 cc of a 3% aqueous solution of carboxymethyl cellulose was added to a commercially available reduced iron powder having an apparent specific gravity of 2.5 g / cc and an average particle diameter of 1 to 3 μm, and a thickness of 1.5 mm,
A polyurethane foam having an average pore diameter of 0.3 mm and a porosity of 97% is impregnated and attached as a support. Except for the paste that is basically attached to the foam through the roller. This is dried at 90 ° C. and then sintered in hydrogen at 1150 ° C. for 30 minutes. During this time, the foam and carboxymethyl cellulose are decomposed and removed. The obtained iron sintered body had a thickness of 1.4 mm, an average particle size of 0.25 mm, and a porosity of 95%. A nickel watt bath is used for this iron-made sintered body,
Electrolytic plating with an average plating thickness of 60 μm was performed, washed with water and dried.

An example of producing a nickel electrode using the nickel-plated iron sintered body obtained above as a support is described in detail below.

To a mixture of 75 parts of commercially available spherical nickel hydroxide powder, 3 parts of cobalt, and 4 parts of cobalt oxide powder, 2% by weight aqueous solution of polyvinyl alcohol was added and the mixture was pressed and filled as a paste. Smooth the surface, then 1 at 120 ℃
Dried for hours. The obtained electrode was adjusted to a thickness of 0.75 mm by passing through an embossed roller press three times. The paste-type nickel electrode thus obtained was cut into a width of 33 mm and a length of 180 mm, and a lead plate was attached by spot welding. The nominal capacity is 2.7 Ah.

Hydrogen storage alloy LaNi known as a counter electrode
MmNi _3.7 Mn _0.4 Al _0.3 Co _0.6 which is a kind of ₅ was used. Filling known foamed nickel, thickness 0.5m
m, width 33 mm, length 220 mm, and the lead plate was attached by spot welding. Further, a hydrophilic non-woven polypropylene fabric was used as a separator to construct a sealed nickel-hydrogen storage battery. Specific gravity of 1.28 as electrolyte
30 g / l of lithium hydroxide was dissolved in the caustic potash aqueous solution. The battery was a Sub C type. This battery is designated as A.

A battery prepared by filling the same nickel hydroxide as in Example 2 into a known foam type nickel as a nickel electrode and using it was added as B.

Battery performance test After completion of formation, each battery (A and B) has a discharge current of 1 A, a final voltage of 0.95 V, and a final voltage of 10 A, an average discharge voltage and a capacity at a final voltage of 0.85 V. Was charged at a constant current of 120%, and the life characteristics were examined under conditions of 1.2 A and a final voltage of 0.9 V. The test results are collectively shown in Table 1.

[0026]

Table 1 Battery 1A discharge 10A discharge 700 cycles V Ah V Ah Capacity retention rate (%) A 1.24 2.67 1.15 2.23 91 B 1.24 2.67 1.15 2.23 91 Above As is clear from the results in Table 1, the discharge characteristics are not different from those of the nickel foam support. In addition, when a nickel electrode as in this example is used with iron as a support, oxygen is generated in the positive electrode during overcharge, and there is a concern that iron may be oxidized, but nickel plating does not cause such a phenomenon at all.
Life was no problem.

[0027]

According to the present invention, an electrode for an alkaline battery which is inexpensive and has excellent discharge characteristics and life can be obtained.

Claims (4)

[Claims] 1. A skeleton of a porous resin core is coated with a paste containing iron powder and a binder as main components, and then heated in a non-oxidizing atmosphere at a temperature at which the iron powder is sintered or higher. To form a three-dimensional sponge-like sintered body, which is plated with nickel,
An electrode for an alkaline battery, which is obtained by filling a nickel-plated iron-made three-dimensional sponge-like sintered body filled with an active material powder with an active material. 2. The electrode for an alkaline battery according to claim 1, wherein the porous resin is polyurethane or polystyrene. 3. The electrode for an alkaline battery according to claim 1, wherein the iron is any one of reduced iron, carbonyl iron and electrolytic iron. 4. The electrode for an alkaline battery according to claim 1, wherein the active material is nickel hydroxide.