JPH07320735A - Non-sintered nickel electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To enhance active material utilization factor by covering the surface of a solid solution particle with a cobalt hydroxide layer. CONSTITUTION:A nickel hydroxide particle or a solid solution particle, whose surface is covered with a cobalt hydroxide layer is used as an active material particle. The ratio of divalent cobalt to the total weight of divalent cobalt and trivalent cobalt in the cobalt hydroxide layer is specified to 75-95wt.%. The ratio of cobalt in the cobalt hydroxide layer to the weight of the active material particles is preferably 2-10wt.%. Since the surface of the nickel hydroxide particle or the solid solution particle mainly comprising nickel hydroxide is covered with the cobalt hydroxide layer containing a specified ratio of divalent cobalt, high conductive matrix of CoOOH is formed during charge, and inert CoHO2 is difficult to produce in an electrolyte. Active material utilization factor in the initial stage and after storage is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-sintered nickel electrode for alkaline storage batteries, which has a high utilization rate of active materials.

[0002]

BACKGROUND OF THE INVENTION A typical nickel electrode for an alkaline storage battery is a solution impregnated into pores of a sintered substrate obtained by sintering nickel powder on a perforated steel plate or the like. Sintered nickel electrode filled with an active material by the method, and an alkali-resistant metal fiber sintered body, or a porous substrate made of carbon fiber nonwoven fabric plated with a metal having excellent alkali resistance such as nickel, There is a non-sintered nickel electrode formed by filling a paste of nickel hydroxide powder.

The sintered nickel electrode has a high utilization ratio of the active material because the sintered substrate has good conductivity. However, since the bonding between the nickel particles of the sintered substrate is weak, the active material is likely to drop out of the sintered substrate when the sintered substrate having high porosity is used. Therefore, the practicable sintered substrates are limited to those having a porosity of about 80% or less. In addition, a cored bar such as a perforated steel plate for holding the nickel sintered body is required. For these reasons, the sintered nickel electrode has a problem that the packing density is low. Further, since the pores of the nickel sintered body are as small as 10 μm or less, it is necessary to repeatedly perform the solution impregnation operation when filling the active material, and there is a problem that the electrode plate production is complicated.

The non-sintered nickel electrode has been proposed to solve the above problems of the sintered nickel electrode. In this non-sintered nickel electrode, since the active material is once filled in the base material such as the alkali-resistant metal fiber sintered body having a large porosity and having no core metal, the nickel electrode having a large packing density can be obtained. Also, the production of the electrode plate is simple.

However, if the substrate is filled with only nickel hydroxide powder, the utilization factor of the active material is remarkably low due to the poor conductivity of the electrode plate, and a practical product cannot be obtained.

As an attempt to improve the utilization rate of the active material of such a non-sintered nickel electrode and put it into practical use, a method of adding and mixing divalent cobalt hydroxide powder as a conductive agent to nickel hydroxide powder. (Addition and mixing method) has been proposed (Japanese Patent Laid-Open No. 61-49374).

By the way, the cobalt hydroxide powder is apt to be unevenly distributed in the paste and is difficult to be uniformly mixed and dispersed with the nickel hydroxide powder. Therefore, in order to effectively improve the utilization rate of the active material, a large amount of cobalt hydroxide powder should be used. It is necessary to add and mix. However, when a large amount of cobalt hydroxide powder is added, the filling amount of nickel hydroxide powder, which is an active material, is inevitably decreased, so that the electrode plate capacity is reduced.

Therefore, in recent years, a method (coating method) of forming a coating layer of cobalt hydroxide on the surface of nickel hydroxide particles has been proposed as an alternative to the above-mentioned addition and mixing method (JP-A-62-237667). Publication, JP-A-6
No. 2-2324867, JP-A No. 62-222566, etc.). This coating method is intended to improve the utilization factor of the active material by forming a coating layer made of divalent cobalt hydroxide on the surface of nickel hydroxide particles to enhance the conductivity between the active material particles.

However, the active material powder produced by the above-mentioned conventional coating method is inactive because Co (OH) ₂ in the cobalt hydroxide layer covering the surface of the nickel hydroxide particles is oxidized in the strong alkaline electrolyte. It is easy to generate CoHO ₂ . That is, it has been difficult to obtain a nickel electrode having a sufficiently high active material utilization rate by the conventional coating method.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-sintered nickel electrode for an alkaline storage battery having a high utilization rate of an active material.

[0011]

The non-sintered nickel electrode for an alkaline storage battery according to the present invention (hereinafter, referred to as "the electrode of the present invention") for achieving the above object is a cobalt hydroxide layer having a surface. What is claimed is: 1. A non-sintered nickel electrode for an alkaline storage battery, comprising coated nickel hydroxide particles or solid solution particles containing nickel hydroxide as a main component, the active material particles comprising divalent Co and trivalent Co in the cobalt hydroxide layer. The ratio of divalent Co to the total amount of Co is 75 to 95% by weight.

As the solid solution particles containing nickel hydroxide as a main component, zinc hydroxide, cobalt hydroxide, cadmium hydroxide, calcium hydroxide, barium hydroxide, manganese hydroxide or the like may be used alone or in combination with nickel hydroxide. Examples of co-precipitated seeds are given.

Divalent and trivalent Co in the cobalt hydroxide layer
The ratio of divalent Co in the cobalt hydroxide layer is regulated to 75 to 95% by weight with respect to the total amount of, and when the ratio is less than 75% by weight, Co which is inactive in the cobalt hydroxide layer is
There are many trivalent cobalt compounds (CoHO ₂ ), and when the ratio exceeds 95% by weight, the cobalt hydroxide layer is oxidized in a high-concentration alkali and is inactive Co trivalent cobalt compound (CoHO ₂ ). This is because a nickel electrode that exhibits a high utilization factor of the active material cannot be obtained in any case.

The ratio of Co in the cobalt hydroxide layer to the weight of the active material particles is preferably 2 to 10% by weight. This is because when the ratio of Co in the cobalt hydroxide layer is as low as less than 2% by weight, the conductivity cannot be sufficiently increased due to insufficient coating, so that the active material utilization rate cannot be significantly improved. On the other hand, if the ratio exceeds 10% by weight,
This is because the filling amount of nickel hydroxide, which is an active material, is forced to decrease, resulting in a decrease in capacity.

[0015]

The nickel hydroxide particles or the solid solution particles containing nickel hydroxide as the main component in the electrode of the present invention have the surface thereof covered with a cobalt hydroxide layer containing divalent Co in a predetermined ratio. A good conductive matrix (CoOOH) is formed, and inactive CoHO ₂ is less likely to be generated in the electrolytic solution. Therefore, the utilization rate of the active material is improved both in the initial stage and after standing.

[0016]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

(Preliminary Experiment) [Preliminary Experiment 1: Relationship between Mixing Time and Ratio of Bivalent Co in Cobalt Hydroxide Powder] 50.6 g of cobalt sulfate was mixed solvent of ethyl alcohol and water at a weight ratio of 1: 9. (25 °
In 1000 ml of cobalt solution dissolved in C), a mixed solvent of ethyl alcohol and water in a weight ratio of 1: 9 (25 ° C)
An alkali solution in which 1 mol / liter of sodium hydroxide was dissolved was added dropwise to the solution while measuring the pH of the solution until the pH reached 12. Then 10 minutes, 30 minutes, 3 hours, 6 hours, 8
After stirring and mixing for 10 hours, 12 hours, 14 hours, or 15 hours, the mixture is filtered, washed with water, and dried in vacuum. Cobalt hydroxide powder a, b, c, d, e, f, g, h, i was made. This manufacturing method is referred to as a manufacturing method (1). In addition,
Glass electrode p with automatic temperature compensation function for pH measurement
An H meter was used (the same was used for pH measurement below).

Further, 50.6 g of cobalt sulfate was added to water (25
1 mol / liter of sodium hydroxide aqueous solution was added dropwise to 1000 ml of cobalt aqueous solution dissolved in (° C.) Until the pH of the solution reached 12. Then 10 minutes, 3 hours, 6
After stirring for 9 hours, 12 hours or 15 hours,
It was filtered, washed with water, and vacuum dried to prepare cobalt hydroxide powders j, k, l, m, n, o in order. This manufacturing method is referred to as a manufacturing method (2).

The amount of Co (A) in the solution obtained by dissolving a certain amount of each cobalt hydroxide powder in concentrated hydrochloric acid was quantified by the atomic absorption method (step 1). In this step 1,
Since both Co (OH) _{2 and} Co trivalent compounds are soluble in concentrated hydrochloric acid, the Co amount (A) is the total Co amount, that is, divalent Co.
And the total amount of trivalent Co. Also, the same amount of C
The solution obtained by dissolving o (OH) ₂ powder in concentrated nitric acid was filtered, and the amount of divalent Co (B) in the filtrate was quantified by atomic absorption spectrometry (step 2). In this step 2, Co
(OH) ₂ is soluble in concentrated nitric acid, but the Co3 valent compound is not dissolved in concentrated nitric acid and remains on the filter paper. Therefore, the ratio of divalent Co in each cobalt hydroxide powder was calculated by the following formula. The results are shown in Fig. 1.

Ratio of divalent Co in cobalt hydroxide powder (% by weight) = divalent Co amount (B) × 100 / total Co amount (A)

FIG. 1 shows the ratio of divalent Co in the cobalt hydroxide powder at various mixing times, the ratio of divalent Co (%) on the vertical axis, and the mixing time (h) on the horizontal axis. As shown in the same drawing, the ratio of divalent Co decreases as the mixing time becomes longer in any of the manufacturing method (1) and the manufacturing method (2). The method 2) cannot obtain a divalent Co content of 75% by weight or more. From this, inert trivalent cobalt (C
It can be seen that it is necessary to use the production method (1) in order to obtain an active material powder having a low content of oHO ₂ ) and excellent conductivity.

[Preliminary experiment 2: 2 after immersion in alkaline electrolyte
Ratio of valence Co] 1 g of each of cobalt hydroxide powders a, b, c, d, e, f, g, h, and i prepared by the preparation method is added to electrolyte solution 5
After dipping in 0 ml for 30 minutes, filtering, washing with water, and vacuum drying, the divalent Co ratio of each cobalt hydroxide powder after dipping in the alkaline electrolyte was determined in the same manner as in Preliminary Experiment 1.
The results are shown in Figure 2.

In FIG. 2, the vertical axis indicates 2 after immersion in alkaline electrolyte.
2 is a graph showing the ratio (weight%) of valent Co and the ratio (weight%) of divalent Co before immersion in the alkaline electrolyte on the horizontal axis. As shown in FIG. When the ratio of the divalent Co in (1) exceeds 95% by weight, the ratio of the divalent Co after the immersion in the alkaline electrolyte is drastically reduced. From this fact, in order to obtain an active material powder having a small amount of trivalent cobalt (CoHO ₂ ) that is inactive after immersion in an alkaline electrolyte and having excellent conductivity, divalent Co before immersion in an alkaline electrolyte is required.
It can be seen that the ratio must be 95% by weight or less.

(Examples and Comparative Examples) [Preparation of Active Material Powder] 50.6 g of cobalt sulfate was mixed with ethyl alcohol and water at a weight ratio of 1: 9 (25 ° C.).
After adding 100 g of nickel hydroxide to 1000 ml of a cobalt solution dissolved in C), an alkali was prepared by dissolving 1 mol / liter of sodium hydroxide in a mixed solvent (25 ° C.) of ethyl alcohol and water in a weight ratio of 1: 9. Liquid, p of liquid
While measuring H, the solution was added dropwise until the pH reached 12. Then, after stirring and mixing for 10 minutes, 30 minutes, 3 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours or 15 hours,
After filtering, washing with water, and vacuum drying, the active material powder A,
B, C, D, E, F, G, H and I were produced. This manufacturing method is called a manufacturing method.

Further, 50.6 g of cobalt sulfate was added to water (25
After adding 100 g of nickel hydroxide to 1000 ml of an aqueous cobalt solution dissolved in ° C), a 1 mol / liter aqueous sodium hydroxide solution was added dropwise until the pH of the liquid reached 12. After that, 10 minutes, 3 hours, 6 hours, 9 hours,
After stirring and mixing for 12 hours or 15 hours, the mixture is filtered, washed with water, dried in vacuum, and the active material powders J, K, L, M, and
N and O were produced. This manufacturing method is called a manufacturing method. This production method is a production method according to the method disclosed in JP-A-62-234867.

[Preparation of Nickel Electrode] 80 parts by weight of each active material powder and 20 parts by weight of a 1% by weight methylcellulose aqueous solution were kneaded to prepare a paste, and this paste was nickel-plated metal foam (porosity 95%; average). Particle size 200μ
m) was filled in a porous body (alkali resistant substrate), dried and molded to prepare a nickel electrode.

[Assembly of Alkaline Storage Battery] Each nickel electrode is used as a positive electrode, a known paste type cadmium electrode having a sufficiently large electrochemical capacity with respect to each nickel electrode is used as a negative electrode, a polyamide nonwoven fabric is used as a separator, and water is used as an electrolytic solution. AA-sized nickel-cadmium storage batteries A, B and C were prepared by using strong alkaline aqueous solutions (specific gravity = 1.285) containing potassium oxide, sodium hydroxide and lithium hydroxide in a weight ratio of 8: 1: 1. , D, E,
F, G, H, I and J, K, L, M, N, O (theoretical capacity: 700 mAh) were assembled. The code of each storage battery is
The symbol of the active material powder used is shown.

[Charge / Discharge Cycle Test] Each nickel-cadmium storage battery was subjected to a charge / discharge cycle test in which one cycle includes a process of charging to a depth of 160% at 0.1C and then discharging to 1.0V at 1C. The battery capacity at the cycle was calculated to calculate the active material utilization rate. The result is shown in Figure 3.
Shown in. The active material utilization rate was calculated from the following formula.

Active material utilization rate (%) = discharge capacity (mAh) of battery at 10th cycle × 100 / {weight of active material (g)
× Theoretical capacity per unit weight of active material powder (mAh /
g)}

FIG. 3 shows the active material utilization rate at the 10th cycle of each nickel-cadmium storage battery, the active material utilization rate on the vertical axis, and the active material powder used on the horizontal axis, which is divalent before dipping in the alkaline electrolyte. It is the graph which took and showed the ratio of Co. In addition, the active material utilization rate on the vertical axis is the active material utilization rate of the nickel-cadmium storage battery E using the active material powder in which the ratio of divalent Co in the cobalt hydroxide layer before immersion in the alkaline electrolyte is 80% by weight. It is shown by an index of 100. From the figure, it is understood that the ratio of divalent Co in the cobalt hydroxide layer needs to be 75 to 95% by weight in order to obtain a nickel-cadmium storage battery having a high active material utilization rate.

[Relationship between Battery Capacity and Ratio of Co in Cobalt Hydroxide Layer to Weight of Active Material Particles] Manufacturing method or Co (O) with respect to Ni (OH) ₂ powder in the manufacturing method
H) ₂ powder was mixed in various amounts to prepare active material powders having different ratios of Co in the cobalt hydroxide layer to the weight of the active material particles. The mixing time was 8 hours in all cases.

Next, a nickel-cadmium storage battery was prepared in the same manner as in the previous example except that these active material powders were used, and a charge / discharge cycle test was conducted under the same conditions as above, and the 10th cycle of each storage battery was tested. The battery capacity was determined, and the relationship between the battery capacity and the ratio of Co in the cobalt hydroxide layer to the weight of the active material particles was investigated. The results are shown in Fig. 4.

FIG. 4 is a graph in which the vertical axis represents the battery capacity, and the horizontal axis represents the ratio (% by weight) of Co in the cobalt hydroxide layer to the weight (100% by weight) of the active material particles. . The battery capacity on the vertical axis is an index of battery capacity as 100 when the ratio of Co in the cobalt hydroxide layer to the weight of the active material particles is 10% by weight.
From the figure, it is understood that the ratio of Co in the cobalt hydroxide layer to the weight of the active material particles is preferably 2 to 10% by weight in order to obtain a high capacity alkaline storage battery.

In the above embodiments, the case where the active material particles in which the surface of the nickel hydroxide particles is coated with the cobalt hydroxide layer is used has been described as an example, but the surface of the solid solution particles containing nickel hydroxide as the main component is used. It was confirmed that the same excellent effect can be obtained even when the active material particles having the cobalt hydroxide layer are used.

[0035]

INDUSTRIAL APPLICABILITY The non-sintered nickel electrode according to the present invention forms a good conductive matrix (CoOOH) by charging and hardly produces inactive CoHO ₂ in the electrolytic solution. High utilization rate. Therefore, by using the electrode of the present invention as the positive electrode, it is possible to obtain an alkaline storage battery having a large battery capacity.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the mixing time when preparing an active material powder and the ratio of divalent Co in the cobalt hydroxide powder.

FIG. 2 is a graph showing the relationship between the ratio of divalent Co in the cobalt hydroxide powder before immersion in the alkaline electrolyte and the ratio of divalent Co in the cobalt hydroxide powder after immersion in the alkaline electrolyte.

FIG. 3 is a graph showing the relationship between the ratio of divalent Co before immersion in an alkaline electrolyte in a cobalt hydroxide layer and the active material utilization rate at the 10th cycle.

FIG. 4 is a graph showing the relationship between the ratio of Co in the cobalt hydroxide layer to the weight of active material particles and the battery capacity.

Front page continuation (72) Inventor Katsuhiko Niiyama 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan-hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A non-sintered nickel electrode for an alkaline storage battery, which comprises nickel hydroxide particles whose surface is coated with a cobalt hydroxide layer or solid solution particles containing nickel hydroxide as a main component as active material particles, said non-sintered nickel electrode comprising: Divalent Co in cobalt hydroxide layer
And the ratio of divalent Co to the total amount of trivalent Co is 75 to 9
A non-sintered nickel electrode for an alkaline storage battery, which is 5% by weight. 2. The non-sintered nickel electrode for an alkaline storage battery according to claim 1, wherein the ratio of Co in the cobalt hydroxide layer to the weight of the active material particles is 2 to 10% by weight. 3. An active material for an alkaline storage battery, comprising nickel hydroxide particles whose surface is coated with a cobalt hydroxide layer or solid solution particles containing nickel hydroxide as a main component, wherein the divalent cobalt hydroxide layer is a divalent compound. The active material for alkaline storage batteries, wherein the ratio of divalent Co to the total amount of Co and trivalent Co is 75 to 95% by weight. 4. The ratio of Co in the cobalt hydroxide layer to the weight of the nickel hydroxide particles or the solid solution particles whose surfaces are coated with the cobalt hydroxide layer is 2 to 10% by weight.
The active material for alkaline storage batteries according to claim 3.