JP2981537B2 - Negative electrode for alkaline batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Lead-acid batteries and alkaline batteries are known as storage batteries used as various power sources. Among these, the alkaline storage battery has been widely used for various portable devices, and the large alkaline battery has been widely used for industrial use, for any reason that high reliability can be expected and small size and light weight can be achieved.

In this alkaline storage battery, as the positive electrode, an air electrode, a silver oxide electrode, and the like are partially used, but in most cases, the electrode is a nickel electrode. The characteristics of the electrodes have been improved from the pocket type to the sintered type, and the sealing has become possible and the use has been expanded. On the other hand, in addition to cadmium, zinc, iron, hydrogen and the like are targeted as the negative electrode.

[0004] The most widely used negative electrode is a cadmium electrode, and nickel-cadmium storage batteries play a leading role in secondary batteries from portable equipment to industrial use. Zinc, which is next popularized as a negative electrode, is satisfactory in terms of potential, capacity, and price, but has a problem in life due to its solubility, and has not yet been widely used. On the other hand, the hydrogen storage alloy electrode is characterized by high capacity and low pollution, and a nickel-hydrogen storage battery has been commercialized, and the demand is growing mainly in small size.

[0005] As a method of these negative electrodes, a sintered cadmium electrode and a hydrogen storage alloy electrode are mainly used, and a paste type is mainly used except for some of them. Although the paste type is inexpensive, its properties are slightly inferior to those of the sintered type and the foam type.

However, in the case of a general sintered support, if the porosity is 85% or more, the strength is greatly reduced. Therefore, the filling amount of the active material, that is, the increase in the capacity is limited.
A foamed substrate or a fibrous substrate has been taken up as a substrate with higher porosity instead of a sintered substrate as described above, and a part of the substrate has been put to practical use. However, it has long been proposed to apply a nickel paste to a foamed resin and sinter the nickel paste to obtain a sintered body having a high porosity. For example, Japanese Patent Application No. 36-4
In No. 5195, a porous body is manufactured by making nickel powder into a mud state, impregnating urethane foam, carbonizing the resin in hydrogen, and then making nickel in a semi-molten state. In Japanese Patent Application No. 48-55274, alumina powder, silica powder and the like are crushed by a ball mill, then impregnated in urethane foam and baked in air to obtain a sintered body. Japanese Patent Application No. 49-
In No. 64529, a polyether foam for a nickel hydroxide positive electrode is immersed in a loose powder bed of mond nickel powder and heated to form a support. A nonwoven fabric is also exemplified in place of the foam.

Powder filling using core material-sintering, paste-
In a sintered body of the sintering method, if the porosity of the substrate is set to 85% or more, the strength is greatly reduced, so that there is a limit to increasing the capacity. Therefore, it has long been proposed to obtain a highly porous sintered body by applying a nickel paste to a foamed resin and sintering it as a substrate with a higher porosity of 90% or more. However, the sintering operation and the high price of nickel as a raw material are more expensive than the paste type using a punching metal, screen, expanded metal or the like as a support.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a negative electrode for a higher capacity and less expensive alkaline battery and a method for producing the same.

[0009]

According to the present invention, a skeleton of a porous resin core is coated with a paste containing iron powder and a binder as main components, and then heated to a temperature higher than the temperature at which the iron powder is sintered. An object of the present invention is to provide a negative electrode for an alkaline battery, wherein the negative electrode is obtained by heating in a non-oxidizing powder to form a three-dimensional sponge-like sintered body, and filling it with a negative electrode active material.

In the present invention, the "three-dimensional sponge-like" means that the ratio of the voids of the sintered body, that is, the porosity is 90 to 90%.
96%, preferably about 94 to 96%. The average diameter of the void portion is 10 in terms of a circle.
It is about 0 to 300 μm, preferably about 150 to 250 μm. The space is filled with the negative electrode active material.

As the negative electrode active material to be filled in the three-dimensional sponge-like sintered body, any known negative electrode active material is used, and is not particularly limited. Examples thereof include cadmium, a hydrogen storage alloy, and zinc. It is a hydrogen storage alloy.

The filling of the negative electrode active material is not particularly limited. For example, the powder can be mixed with a suitable binder to form a paste, and the paste can be filled by impregnating the three-dimensional sintered body.

In the present invention, the resin of the porous resin core is not particularly limited as long as it is incinerated and removed at the time of sintering, and examples thereof include polyurethane and polystyrene.

[0014] The binder as the other main component includes known binders, and is not particularly limited. Examples thereof include carboxymethylcellulose (CMC), carboxypropylmethylcellulose, methylcellulose, starch, and polyvinyl alcohol (PVA). And preferably CMC and PVA. The binder can be used after being dissolved in a solvent such as water or alcohol. When the whole paste is 100 parts by weight, the iron powder is 94-99.
Parts by weight and 1 to 6 parts by weight of the binder are contained. The same binder may be used as needed when filling the negative electrode active material.

In the present invention, "coating" a paste means a state in which the paste adheres to the surface of a porous resin core. The method of coating the paste is not particularly limited. For example, coating may be performed by immersing or impregnating the porous resin core in the paste under normal pressure or pressure, and then removing the core from the paste. it can. In the present invention, the paste means that the iron powder and the binder can be uniformly or almost uniformly distributed on the porous resin core, and the iron powder and the binder on the surface of the core adhere to the paste and flow out. Means that the fluidity is not so high.

In the present invention, the temperature at which the sintering of the iron powder is carried out depends on the size of the particles of the iron powder and is not particularly limited. For example, about 850 to 1150 ° C., preferably about 950 to 1050 ° C. It is. The sintering is performed in a non-oxidizing atmosphere, that is, in an inert gas such as nitrogen, or in a reducing gas such as hydrogen gas or decomposed ammonia gas.

[0017]

First, as a skeleton of a porous core, 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. Is heated in a non-oxidizing atmosphere to form a three-dimensional sponge-like iron sintered body.

Although iron is inexpensive, it partially oxidizes, unlike nickel, when it reaches an oxygen generation potential in caustic alkali of an electrolytic solution. However, since the capacity of the negative electrode is generally larger than the capacity of the positive electrode in a storage battery, the negative electrode does not overdischarge, and thus does not reach the oxygen generation potential. In other words, it has been found that there is no concern that the support is oxidized, and that a three-dimensional sponge-like sintered body made of iron can be used as the support for the high-capacity negative electrode. In addition, as iron, high-purity powder is not required as in the case of an iron negative electrode, and a sintered body having high strength may be used, and inexpensive reduced iron is used. In addition, although slightly expensive, electrolytic iron or carbonyl iron may be used, and the type is not limited. In this case, the iron does not discharge unless the electrolyte has high purity and the electrolyte does not contain sulfide.

[0019]

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

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 was added to carboxymethyl cellulose 3
280 cc of a 2.5% aqueous solution is added and impregnated with a polyurethane foam having a thickness of 1.5 mm, an average pore diameter of 0.3 mm, and a porosity of 97% as a support and adhered thereto. Except for the paste that is basically adhered to the foam through the roller. After drying at 90 ° C., it is sintered at 1150 ° C. for 30 minutes in hydrogen. During this time, the foam and carboxymethyl cellulose are decomposed and removed. The obtained iron sintered body had a thickness of 1.
4 mm, average pore size 0.25 mm in voids, porosity 95
%Met.

A method for producing a hydrogen storage alloy electrode using the iron sintered body obtained above as a support will be described in detail below.

MmNi _3.7 Mn which is a kind of LaNi _5
0.4 Al _0.3 Co _0.6 is crushed and passed through a 300 mesh. A 2% by weight aqueous solution of carboxymethylcellulose is added to this powder to form a paste. This paste is filled in a sintered body. The surface was smoothed and then dried at 120 ° C. for 1 hour. The obtained electrode was passed through an embossed roller press three times to adjust the thickness to 0.5 mm. The paste-type hydrogen storage alloy electrode obtained in this manner was
The sheet was cut into a size of 3 mm and a length of 220 mm, and a lead plate was attached by spot welding. A sealed nickel-hydrogen storage battery was formed using a known foamed nickel electrode having a nominal capacity of 2.7 Ah as a counter electrode and a polypropylene nonwoven fabric separator subjected to hydrophilic treatment. As an electrolytic solution, 30 g / l of lithium hydroxide was dissolved and used in an aqueous caustic potassium solution having a specific gravity of 1.28. The battery was a SubC type. This battery is designated as A.

A battery B was used as a negative electrode in which a known foaming nickel was filled with the same hydrogen storage alloy as in Example 2.

A battery obtained using a hydrogen-absorbing alloy electrode obtained by coating a known punching metal obtained by plating nickel with iron on a paste using a fluororesin as a binder is referred to as C. did.

Battery performance test After completion of the formation, the average discharge voltage, capacity and 5 hour rate of each battery (A, B and C) at a discharge voltage of 1A at a cut-off voltage of 0.95V and at a discharge voltage of 10A at a cut-off voltage of 0.85V The battery was charged at a constant current of 120% of the capacity, and the life characteristics under conditions of 1.5 A and a final voltage of 0.9 V were examined. Table 1 summarizes these test results.
Shown in

[0026]

Table 1 Battery 1A discharge 10A discharge 700 cycles V Ah V Ah Capacity retention (%) A 1.24 2.67 1.15 2.23 88 B 1.24 2.67 1.15 2.23 88 C 1.23 2.67 1.13 2.20 82 As is clear from the results in Table 1 above, the discharge characteristics of the battery using the negative electrode of the present invention did not differ at all from the case of the nickel foamed support. It was superior to C, which is a support having a three-dimensional structure.

In a sealed battery using iron as a support as in the present invention, oxygen from the positive electrode causes an oxidizing atmosphere at the time of overcharge, and there is a concern that iron may be oxidized. It was found that the hydrogen in the hydrogen storage alloy prevented oxidation of iron and corrosion by the electrolyte.

[0028]

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

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 4/24-4/26 H01M 4/80 B22F 5/00

Claims (3)

(57) [Claims] 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 to a temperature at which the iron powder sinters. After obtaining a three-dimensional sponge-like sintered body by the above, the obtained three-dimensional sponge-like sintered body is filled with a hydrogen storage alloy as a negative electrode active material.
Ri, the porosity of the sintered body is 90 to 96%, the average diameter of the void portions of the sintered body (circular equivalent) is 100~300μm dense
Hydrogen storage alloy negative electrode for closed alkaline batteries. 2. The hydrogen for a sealed alkaline battery according to claim 1, wherein the porous resin is polyurethane or polystyrene.
Storage alloy negative electrode. 3. The hydrogen storage device for a sealed alkaline battery according to claim 1, wherein the iron is any one of reduced iron, carbonyl iron, and electrolytic iron.
Storage alloy negative electrode.