JP3272151B2 - Non-sintered nickel electrode for alkaline storage battery and method for producing the same - Google Patents

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 an alkaline storage battery having a high active material utilization rate and a method for producing the same.

[0002]

2. Description of the Related Art A typical example of a nickel electrode for an alkaline storage battery is solution impregnation in pores of a sintered substrate obtained by sintering nickel powder into a perforated steel plate or the like. A sintered nickel electrode filled with an active material by a method, and an alkali-resistant metal fiber sintered body, or a porous substrate made of a carbon fiber nonwoven fabric plated with a metal having excellent alkali resistance such as nickel, There is a non-sintered nickel electrode filled with a paste of nickel hydroxide powder.

[0003] In the sintered nickel electrode, the utilization of the active material is high because the conductivity of the sintered substrate is good. However, since the bond between the nickel particles of the sintered substrate is weak, the active material easily falls off the sintered substrate when a sintered substrate having a high porosity is used. Therefore, practically usable sintered substrates are limited to those having a porosity of about 80% or less. In addition, a core metal 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. Also, the pores of the nickel sintered body are 10 μm
Due to the small size described below, it is necessary to repeat the solution impregnation operation when filling the active material, and there is also a problem that the production of the electrode plate is complicated.

[0004] The non-sintered nickel electrode has been proposed to solve the above-mentioned problems of the sintered nickel electrode. In this non-sintered nickel electrode, a base such as a sintered body having a high porosity and a high porosity without a metal core is filled once with an active material, so that a nickel electrode having a high packing density can be obtained. Also, the production of the electrode plate is simple.

[0005] However, if only the nickel hydroxide powder is filled in the substrate, the conductivity of the electrode plate is poor and the utilization rate of the active material is extremely low.

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

By the way, cobalt hydroxide tends to be unevenly distributed in the paste and is difficult to be uniformly mixed and dispersed with the nickel hydroxide powder.
It is necessary to add a large amount of cobalt hydroxide. However, when a large amount of cobalt hydroxide is added, the filling amount of nickel hydroxide, which is an active material, must be reduced, so that the electrode plate capacity decreases.

Therefore, in recent years, a method (single-coating method) for forming a coating layer (single 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 (particular coating method). JP-A-62-234867, JP-A-62-237667, JP-A-62-22566
No. 6). In this single coating method, the active material utilization rate is increased by forming a coating layer of α-Co (OH) ₂ or β-Co (OH) _{2 on} the surface of nickel hydroxide particles to increase the conductivity between the active material particles. The aim is to improve the quality. α
—Co (OH) ₂ or β-Co (OH) ₂ is oxidized during charging to form a conductive matrix made of CoOOH.

Incidentally, α-Co (OH) ₂ is converted to β-C
Since a dense conductive matrix is formed as compared with o (OH) ₂ , it is preferable as a coating layer for increasing the conductivity of the active material powder. However, the present inventors have studied and found that α
-Co (OH) ₂ is unstable and almost changes to β-Co (OH) ₂ when immersed in an electrolytic solution (high concentration alkaline solution). It was found that it was difficult to form a non-sintered nickel electrode having a sufficiently high active material utilization rate.

The present invention has been made based on such findings, and it is an object of the present invention to provide a non-sintered nickel for an alkaline storage battery having an extremely high active material utilization rate due to the high conductivity of an electrode plate. An object of the present invention is to provide a pole and a method of manufacturing the pole.

[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 has a cobalt hydroxide layer having a surface. In the non-sintered nickel electrode for an alkaline storage battery using the coated nickel hydroxide particles or solid solution particles containing nickel hydroxide as a main component as an active material, the cobalt hydroxide layer is mainly composed of α-Co (OH) ₂ . And an outer layer mainly composed of β-Co (OH) ₂ .

The inner layer mainly composed of α-Co (OH) ₂ is:
a layer containing α-Co (OH) ₂ as a main component,
It may be a layer substantially composed of only α-Co (OH) ₂ . On the other hand, the inner layer mainly composed of β-Co (OH) ₂
a layer containing β-Co (OH) ₂ as a main component,
It may be a layer consisting essentially of β-Co (OH) ₂ .

The solid solution particles containing nickel hydroxide as a main component include, in addition to nickel hydroxide, zinc hydroxide, cobalt hydroxide, cadmium hydroxide, calcium hydroxide, barium hydroxide, manganese hydroxide or the like. Examples include those coprecipitated with more than one species.

Further, the method for producing a non-sintered nickel electrode for an alkaline storage battery according to the present invention (hereinafter referred to as the "method of the present invention") is characterized in that nickel hydroxide particles or solid solution particles containing nickel hydroxide as a main component. Is immersed in an aqueous solution of a cobalt compound, an alkaline aqueous solution is added until the pH of the solution becomes 9 to 10, and the mixture is stirred and mixed to precipitate α-Co (OH) ₂ on the surface of the nickel hydroxide particles or the solid solution particles. Let me
Α on the surface of the nickel hydroxide particles or the solid solution particles.
Step 1 of preparing an active material intermediate on which a coating layer mainly composed of -Co (OH) ₂ is formed, and immersing the active material intermediate in an aqueous solution of a cobalt compound, and changing the pH of the aqueous solution to 11 to 11 with an alkaline aqueous solution. 12 and stirred and mixed to precipitate β-Co (OH) ₂ on the surface of the particles of the active material intermediate, and β-Co (O ₂ ) on the surface of the particles of the active material intermediate.
H) Step 2 of preparing an active material on which a coating layer mainly composed of ₂ is formed, and Step 3 of filling the conductive material into a conductive substrate.

When the pH of the solution is in the range of 9 to 10, the reaction between the cobalt compound and the aqueous alkali solution mainly causes α-Co.
(OH) ₂ precipitates on the surface of the nickel hydroxide particles or solid solution particles. Further, in the range of pH of the liquid of 11 to 12,
Β-Co (OH) ₂ is mainly precipitated by the reaction between the cobalt compound and the aqueous alkali solution.

Examples of the cobalt compound in the method of the present invention include water-soluble cobalt salts such as cobalt nitrate, cobalt hydrochloride, and cobalt sulfate. Examples of the alkaline aqueous solution include sodium hydroxide, potassium hydroxide and lithium hydroxide. An aqueous solution is exemplified.

[0017]

In the electrode of the present invention, the unstable α-Co (O
H) ₂ is mainly composed of β-Co (O
Since H is protected by the outer layer mainly composed of H) ₂ , α-Co (OH) ₂ in the inner layer hardly changes to β-Co (OH) ₂ when an alkaline electrolyte is injected. Therefore, a relatively dense conductive matrix of CoOOH is formed in the electrode plate during charging, and the conductivity of the nickel electrode is improved.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

(Example) A nickel liquid obtained by mixing aqueous solutions of nickel nitrate, zinc nitrate and cobalt nitrate so that the weight ratio of nickel nitrate: zinc nitrate: cobalt nitrate was 95: 2: 3, An aqueous alkali solution obtained by mixing a 5% by weight aqueous sodium hydroxide solution and a 20% by weight aqueous ammonia solution at a weight ratio of 5: 1 was simultaneously added to a water tank filled with water, and the resulting coprecipitate was filtered. , Washed, dried,
A solid solution powder containing nickel hydroxide as a main component was prepared.

The solid solution powder is immersed in an aqueous solution of cobalt nitrate, and the pH of the solution is measured until the pH reaches 9 while measuring the pH of the solution.
An aqueous solution of sodium hydroxide is added dropwise, and the mixture is reacted for 1 hour while stirring and mixing. Then, the mixture is filtered, washed with water, and dried under vacuum to coat the surface of the nickel hydroxide particles mainly with α-Co (OH) _2. An active material intermediate on which a layer was formed was prepared (Step 1). For the pH measurement, a glass electrode pH meter equipped with an automatic temperature compensation function was used (pH in the following).
The same was used in the measurement. ).

Next, the above active material intermediate is immersed in an aqueous solution of cobalt nitrate, a 1N aqueous solution of sodium hydroxide is added dropwise to the solution while measuring the pH of the solution until the pH reaches 11, and the mixture is reacted for 1 hour while stirring and mixing. , Filtration, washing with water, and vacuum drying, the surface of the nickel hydroxide particles is coated with β-Co (O
H) An active material having a coating layer mainly composed of ₂ was prepared (step 2).

A slurry is prepared by kneading 90 parts by weight of the active material thus obtained with 20 parts by weight of a 1% by weight aqueous solution of methylcellulose, and the slurry is filled in a nickel foam to prepare an electrode A (electrode of the present invention). Fabricated (step 3).

(Comparative Example) A solid solution powder prepared in the same manner as in the example was immersed in an aqueous solution of cobalt nitrate, and the pH of the solution was measured, and the pH of the solution was adjusted to pH 9, 10, 11, 12 or 13 until the pH reached 9, 10, 11, 12 or 13. Then, the mixture was reacted for 1 hour with stirring and mixing, filtered, washed with water, and dried under vacuum to prepare five types of active materials having a cobalt hydroxide layer formed on the surface of solid solution particles.

X-ray diffraction measurements were performed on the cobalt hydroxide layers of these five types of active materials under the following conditions. X-ray diffraction patterns are shown in FIGS. From FIG. 1, pH = the 9,10 α-Co (OH) ₂ is, from FIG. 2, pH = the 11,12 β-Co (OH) ₂ is also from FIG. 3, a pH = 13 in an inert It can be seen that CoHO ₂ is mainly produced.

<Measurement conditions> Anti-cathode Cu Tube voltage 40 kV Tube current 100 mA Filter Ni Scanning speed 2.00 ° / min Divergence slit 1 °

Next, the electrode B1 (pH = 9) and the electrode B1 (pH = 9) were sequentially used in the same manner as in the example except that these active materials were used.
B2 (pH = 10), B3 (pH = 11), B4 (pH
= 12) and B5 (pH = 13) (single coat method). The solid solution powder 8 produced in the same manner as in the example
One part by weight was kneaded with 9 parts by weight of cobalt hydroxide and 20 parts by weight of a 1% by weight aqueous solution of methylcellulose to prepare a slurry, and this slurry was filled in a nickel foam to prepare an electrode B6 (addition mixing method).

[Preparation of Test Cell] Electrodes A and B1 to B6
Is used as a test electrode, a hydrogen storage alloy electrode having a sufficiently large electrochemical capacity as compared with the test electrode is used as a counter electrode, and these are laminated via a separator (polyamide nonwoven fabric) to form a laminate. The electrode body was put in a polyethylene bag, pressurized with a pressing force of 40 kgf to produce an electrode body, and an electrolyte (aqueous KOH solution having a specific gravity of 1.23) was injected into the separator, and the test cell (open-type monopolar cell) Was prepared. As a hydrogen storage alloy electrode, MmNi _3.2 Co
_A slurry was prepared by kneading 90 parts by weight of _1.0 Mn _0.6 Al _0.2 with a 1% by weight aqueous solution of polyvinyl alcohol, and this slurry was applied to a punching metal having a porosity of 40% and dried.

[Active Material Utilization Rate of Each Electrode] Each test cell was charged at a current of 0.1 C for 15 hours, then discharged at a current of 1/3 C to 1.0 V, and the capacity of each test cell was measured. ,
The active material utilization of the test electrode used for each test cell was calculated from the following equation. Table 1 shows the results.

Active material utilization (%) = discharge capacity of test cell (mAh) × 100 / {weight of active material (g) × theoretical capacity per unit weight of active material (mAh / g)}

[0030]

[Table 1]

As shown in Table 1, the electrode A and the electrodes B1 to B5 by the coating method were replaced with the electrode B by the addition and mixing method.
The active material utilization rate is higher than that of No. 6, and in particular, the electrode A (the present invention electrode) produced by the two-coat method has a significantly higher active material utilization rate than the electrodes B1 to B5 produced by the single-coat method. The reason why the active material utilization rate of the electrode B6 is low is that cobalt hydroxide tends to be unevenly distributed in the paste and is difficult to be uniformly mixed and dispersed with the nickel hydroxide powder. The active material utilization of the electrode A is particularly high because α-Co (OH) ₂ present in a large amount in the inner layer.
So that if protected by an outer layer composed mainly of β-Co (OH) _2, liquid hardly varies β-Co (OH) ₂ to touch the electrolysis, the conductive matrix comprised of dense CoOOH by charge formation Because it is done.

The electrodes B1 to B prepared by the single coating method
Among pH 5, pH at which a large amount of α-Co (OH) ₂ is formed =
The electrodes B1 and B2 produced in 9 or 10 were made of β-Co (O
H) The active material utilization rate is higher than that of the electrodes B3 and B4 produced at pH = 11 or 12 where a large amount of ₂ is produced.

In the above embodiment, the pH of step 1 is 9 and the pH of step 2 is 1 as the method of the present invention.
Although the case where it is set to 1 has been described as an example, the pH in each step may be within the range regulated by the present invention.
Even when H was 12, it was confirmed that an electrode having a high active material utilization rate similar to that of the electrode A could be obtained.

In the above embodiment, a case where a solid solution particle obtained by coprecipitating nickel hydroxide, zinc hydroxide and cobalt hydroxide and coated with a cobalt hydroxide layer is used as an active material is taken as an example. As described above, when the nickel hydroxide particles or other solid solution particles containing nickel hydroxide as a main component coated with a cobalt hydroxide layer having a two-layer structure regulated by the present invention is used as an active material. It was also confirmed that a nickel electrode having a high active material utilization was obtained.

[0035]

According to the present invention, the electrode is α-Co (OH)._TwoWealth
The inner layer is β-Co (OH)_TwoProtected by a rich outer layer
Α-Co (OH) in the inner layer_TwoIs β-Co
(OH) _TwoThe conductive material is difficult to change
A trick is formed. For this reason, the electrode of the present invention
High quality utilization.

Further, according to the method of the present invention, it is possible to produce the electrode of the present invention having a high active material utilization rate.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of an active material prepared at pH = 9 or 10 in Examples.

FIG. 2 is an X-ray diffraction diagram of an active material prepared at pH = 11 or 12 in Examples.

FIG. 3 is an X-ray diffraction diagram of an active material prepared at pH = 13 in Examples.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Kozo Nogami 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-1-272050 (JP, A) (58 ) Surveyed field (Int.Cl. ⁷ , DB name) H01M 4/32 H01M 4/26 H01M 4/52

Claims (3)

(57) [Claims] 1. A non-sintered nickel electrode for an alkaline storage battery comprising nickel hydroxide particles whose surface is coated with a cobalt hydroxide layer or solid solution particles mainly composed of nickel hydroxide as an active material. The layer is made of α-Co (O
Inner layer and, β-Co (OH) non-sintered nickel electrode for an alkaline storage battery, characterized in that forming a two-layer structure of ₂ mainly outer layer to H) ₂ mainly. 2. A method of immersing nickel hydroxide particles or solid solution particles containing nickel hydroxide as a main component in an aqueous solution of a cobalt compound, adding an aqueous alkali solution until the pH of the solution becomes 9 to 10, stirring and mixing, Depositing α-Co (OH) ₂ on the surface of the nickel hydroxide particles or the solid solution particles,
Α on the surface of the nickel hydroxide particles or the solid solution particles.
Step 1 of preparing an active material intermediate on which a coating layer mainly composed of -Co (OH) ₂ is formed; and dipping the active material intermediate in an aqueous solution of a cobalt compound;
An alkaline aqueous solution is added until the pH of the liquid becomes 11 to 12, and the mixture is stirred and mixed.
depositing o (OH) ₂ to form an active material in which a coating layer mainly composed of β-Co (OH) ₂ is formed on the surface of the particles of the active material intermediate; And filling the non-sinterable substrate with a non-sintered nickel electrode for an alkaline storage battery. 3. An alkaline storage battery active material comprising nickel hydroxide particles or solid solution particles mainly composed of nickel hydroxide, the surface of which is coated with a cobalt hydroxide layer, wherein the cobalt hydroxide layer has an α- Co (OH) and an inner layer mainly _2, beta-Co (OH) active material for an alkaline storage battery, characterized in that forming a two-layer structure of ₂ mainly outer layer.