JP3292204B2 - Nickel sintered electrode for alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for filling an active material into a substrate by impregnating a molten salt such as nickel nitrate on a sintered nickel powder substrate and then converting the substrate to a hydroxide with an aqueous sodium hydroxide solution. The present invention relates to a sintered nickel electrode.

[0002]

2. Description of the Related Art In a sintered nickel electrode, a porous body obtained by sintering nickel powder on a substrate such as a perforated steel plate is immersed in a molten salt impregnating liquid such as nickel nitrate to impregnate the porous substrate with a nickel salt. Then, it is manufactured by a series of operations of changing to nickel hydroxide in an alkaline solution such as an aqueous sodium hydroxide solution. These operations are repeated several times until a predetermined filling amount is obtained.

Generally, by adding cadmium nitrate to the above-mentioned nickel nitrate impregnating liquid, a small amount of cadmium is added in a solid solution state to nickel hydroxide which is a main active material. This is because a sintered nickel electrode filled only with nickel hydroxide causes large electrode swelling (increase in electrode thickness) when charged and discharged. However, when a small amount of cadmium is contained in a solid solution state, such a swelling occurs. This is because electrode swelling is suppressed. Since electrode swelling causes a short circuit or shortening of the life of the battery, it is indispensable to add a cadmium solid solution as a means for suppressing the swelling.

[0004] However, with the recent close-up of environmental problems, the content of harmful metal, cadmium, has been regarded as a problem. Particularly in nickel metal hydride batteries and nickel zinc batteries, it is of the utmost importance that they do not contain cadmium, and the development of new additive elements that replace cadmium is desired.

On the other hand, as the size and weight of portable electronic devices have been reduced, batteries having a high power density have been demanded. However, it is known that the upper limit of the active material utilization rate of the sintered nickel electrode is as low as about 80%, which is a problem in increasing the capacity of the battery. In addition, the surrounding atmosphere of the batteries used in these devices is often at a high temperature, and development of batteries having excellent high-temperature performance is also desired.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems, and does not contain harmful metal, cadmium, prevents electrode swelling, has excellent high-temperature performance, and has an active material. An object of the present invention is to provide a completely nickel-free sintered nickel electrode having a high utilization factor.

[0007]

Means for Solving the Problems The sintered nickel electrode of the present invention is characterized in that nickel hydroxide, which is a main active material, contains a Group 2 element (zinc, magnesium, barium) and cobalt in an amount of 2% by weight or more. It is characterized by being contained in a solid solution state and containing α-Co (OH) ₂ in a free state.

[0008]

The present inventors have found that the inclusion of the above-mentioned zinc, magnesium or barium in a solid solution state in nickel hydroxide has an effect of suppressing electrode swelling similarly to cadmium. The inhibitory effect increased in proportion to the content of these elements, and was found to be effective in the range of 2% by weight or more. In addition, the addition of these elements has the effect of preciously shifting the oxygen generation potential of the nickel electrode, and the addition of cobalt has the effect of shifting the oxidation potential negatively. Therefore, the oxygen overvoltage (the oxygen generation potential and the oxidation potential) of the nickel electrode is increased. Potential difference) increases, and the electrode becomes excellent in charging efficiency at high temperatures.

It has also been found that α-Co (OH) ₂ mixed with the nickel hydroxide particles in a free state has an effect of improving the utilization rate of the active material. When the electrode is immersed in an alkaline electrolyte, α-Co (OH) ₂ changes to active β-Co (OH) ₂ , which is rapidly dissolved to form HCo
O ₂ ^- after the formation of the complex ion, is dispersed evenly throughout and reprecipitated electrode as Co (OH) _2. That is, α-Co
(OH) ₂ is stable in the air and changes to β-Co (OH) ₂ which is active only when it comes into contact with an alkaline aqueous solution. On the other hand, β-Co (OH) ₂ is unstable in air, forms CoOH ₂ that is hardly soluble on the surface, and prevents rapid dissolution. Thus, α-Co (OH) ₂ is an active β-
Co a (OH) ₂ only be produced when in contact with the electrolyte solution, it has become possible to avoid the CoHO ₂ film formation was problem when using beta-Co (OH) ₂ to this . Thus, β uniformly dispersed throughout the electrode
-Co (OH) ₂ is a conductive CoOOH
It is considered that the active material utilization rate was improved by connecting the nickel hydroxide particles with conductive CoOOH.

[0010] Such an effect is obtained, for example, by β-Co (O
H) ₂ , it is known that the α-C
Compared to o (OH) ₂ , the dissolution rate is slow and the dispersibility is also non-uniform for the reasons described above, so that the effect of improving the utilization rate of the active material is small.

[0011]

EXAMPLE A porosity of about 8 obtained by sintering nickel powder.
A 0% nickel-sintered substrate is immersed in an impregnating solution obtained by adding zinc nitrate and cobalt in various ratios to a nickel nitrate aqueous solution having a specific gravity of 1.8 at 80 ° C. for 30 minutes, dried, and then dried at 80 ° C. and a specific gravity of 1.3. A series of steps of converting the active material into an active material in an aqueous sodium hydroxide solution was repeated to obtain a predetermined filling amount, thereby producing various electrodes.

Next, the electrode is immersed in an aqueous cobalt nitrate solution having a specific gravity of 1.2, dried and then immersed in a dilute aqueous alkaline solution having a pH of 10 to 12 to release α-Co (OH) ₂ in a free state.
Was produced to produce the electrode (A) of the present invention. Also, p
The same treatment with H14 more highly concentrated alkali aqueous solution, β-Co (OH) electrodes to generate ₂ in a free state (D) was also made work. As a comparison electrode (C), sintered electrodes filled with only the nickel hydroxide was also made work. Such various electrodes manufactured created in the, to face the cadmium negative electrode with the separator, the aqueous potassium hydroxide solution having a specific gravity 1.24 and electrolyte were evaluated for charge-discharge was performance in an open system.

The following table shows that a solid solution containing 5% by weight of zinc and 5% by weight of cobalt was added to nickel hydroxide, and α-
150% charging of the sintered type comparative electrode (B) not producing Co (OH) ₂ , the electrode (A) of the present invention, the comparative electrode (D), and the comparative electrode (C) at 0.1C. And 0.
The nickel oxidation value when discharging to 0 V (with reference to Hg / HgO) at 2C is shown.

[0014]

The active material utilization of the electrode of the present invention is improved to 90%, and the depth of discharge is the deepest. That is, α-Co
(OH) ₂ has the effect of increasing the discharge depth of nickel hydroxide, and the effect is larger than β-Co (OH) ₂ . In the comparative electrode (C), γ which is the cause of electrode swelling
Formation of -NiOOH was observed, and the oxidation value at the end of charging was high. In the electrode (A) of the present invention containing zinc and the electrode (B), generation of γ-NiOOH was not recognized, and electrode swelling was prevented. The electrode swells when the zinc content is 2
It was effectively prevented in the range of weight% or more.

FIG. 1 shows the charging efficiency in the temperature range of 5 ° C. to 45 ° C. for the electrode of the present invention (A) and the comparative electrode (C). It can be seen that the charging efficiency at a high temperature of the electrode (A) of the present invention is good. To improve charging efficiency at high temperatures,
It was necessary to add a solid solution of cobalt to nickel hydroxide in a range of 2% by weight or more.

[0017]

As described above, according to the present invention, it is possible to provide a high-capacity and completely non-polluting nickel-sintered electrode which prevents electrode swelling, has excellent charging efficiency at high temperatures, and has no pollution. The target value is extremely large.

[Brief description of the drawings]

FIG. 1 shows the charging efficiency of various nickel sintered electrodes when the charging temperature is changed.

[Explanation of symbols]

 A electrode of the present invention C reference electrode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/52 H01M 4/24-4/34

Claims (2)

(57) [Claims] In a nickel electrode in which a porous substrate obtained by sintering nickel powder is filled with an active material, nickel hydroxide, which is a main active material, contains a small amount of Group 2 elements other than cadmium.
Contains at least one element and cobalt in solid solution
Of the Group 2 element and cobalt contained in the solid solution state.
Content ratio is 2% by weight or more in each element ratio
, And the and, α-Co (OH) sintered type nickel electrode for an alkaline storage battery, characterized in that it contained ₂ at a free state. 2. The sintered nickel electrode for an alkaline storage battery according to claim 1, wherein said Group 2 element is zinc, magnesium or barium.