JPH0896832A - Alkaline secondary battery - Google Patents

Abstract

PURPOSE: To enhance charging efficiency at high temperature providing a positive electrode, a negative electrode, and a specific alkaline electrolyte. CONSTITUTION: A positive electrode 1 is prepared by filling paste containing nickel hydroxide powder, a conductor, a binder, and water in a current collector, drying the paste, pressing it, then cutting the paste coated current collector in a specified size. A negative electrode 2 is prepared by filling paste obtained by kneading a negative active material, a conductor, a binder, and water in a current collector, drying the paste, and forming it. A separator 3 is interposed between the positive electrode 1 and the negative electrode 2, and they are spirally wound, put into a cylindrical container 4 with a bottom and a circular sealing plate 6 having a hole 5 in the center is arranged in an upper opening of the container 4. An alkaline electrolyte containing 0.01-0.20wt.% boron is poured in the container 4 through the hole 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery provided with a positive electrode having a structure in which a current collector is filled with a paste containing nickel hydroxide powder as a main component, and more particularly to an alkaline secondary battery having an improved alkaline electrolyte. It relates to batteries.

[0002]

2. Description of the Related Art In an alkaline secondary battery, an electrode group made by interposing a separator made of synthetic resin fiber between a nickel positive electrode and a negative electrode is housed in a container together with an alkaline electrolyte made of potassium hydroxide, for example. It has a structure. The nickel positive electrode is prepared by kneading nickel hydroxide powder, a conductive agent such as cobalt oxide or cobalt hydroxide, a binder, and water to prepare a paste, and then forming the paste into, for example, a three-dimensional sponge form. It is manufactured by filling a current collector such as a metal porous body or a metal fiber mat.

When the secondary battery provided with the positive electrode is charged at a high temperature, the oxygen overvoltage of the positive electrode is lowered. Therefore, the charging reaction of the nickel hydroxide powder of the positive electrode represented by the following formula (1) and the following (2) The potential difference from the oxygen gas generation reaction as a side reaction shown in the formula becomes small. As a result, the two reactions compete with each other, so that there is a problem that the amount of NiOOH produced decreases and the charging efficiency of the positive electrode decreases.

Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1) 4OH ⁻ → 2H ₂ O + O ₂ + 4e ⁻ (2) Therefore, the nickel hydroxide powder contains several% of cadmium or zinc. The addition of lithium hydroxide to the alkaline electrolyte is performed. However, it is difficult to sufficiently improve the charging efficiency of the positive electrode in the high temperature state by these methods.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the conventional problems, and it is an object of the present invention to provide an alkaline secondary battery having a positive electrode with improved charging efficiency at high temperatures. is there.

[0006]

According to the present invention, a positive electrode having a structure in which a paste containing nickel hydroxide powder as a main component is filled in a current collector, a negative electrode, and an interposition between the positive electrode and the negative electrode. And an alkaline electrolytic solution in which boron or a boron compound is dissolved, and an alkaline secondary battery.

The alkaline secondary battery of the present invention will be described below with reference to FIG. The positive electrode 1 is spirally wound with the separator 3 interposed between the positive electrode 1 and the negative electrode 2, and is housed in a bottomed cylindrical container 4. The negative electrode 2 is arranged on the outermost periphery of the prepared electrode group and is in electrical contact with the container 4. The alkaline electrolyte is contained in the container 4. A circular sealing plate 6 having a hole 5 in the center is arranged in the upper opening of the container 4. The ring-shaped insulating gasket 7 is arranged between the peripheral edge of the sealing plate 6 and the inner surface of the upper opening of the container 4, and the sealing plate is attached to the container 4 by caulking to reduce the diameter of the upper opening inward. 6 is airtightly fixed via the gasket 7. One end of the positive electrode lead 8 is connected to the positive electrode 1, and the other end is the sealing plate 6.
Is attached to the underside of. Hat-shaped positive terminal 9
Is mounted on the sealing plate 6 so as to cover the hole 5. The rubber safety valve 10 is arranged so as to close the hole 5 in a space surrounded by the sealing plate 6 and the positive electrode terminal 9.

As the alkaline electrolyte in which boron or a boron compound is dissolved, for example, a potassium hydroxide solution, a mixed solution of potassium hydroxide with one or both of sodium hydroxide and lithium hydroxide added is used. it can. Above all, an alkaline electrolyte containing lithium hydroxide and sodium hydroxide is preferable because it can further improve the charging efficiency of the positive electrode in a high temperature state.

Examples of the boron compound include boric acid, potassium borate, sodium borate, and lithium borate. The boron concentration of the alkaline electrolyte in which boron or the boron compound is dissolved is preferably 0.01% by weight or more. If the concentration is less than 0.01% by weight, it may be difficult to improve the charging efficiency of the positive electrode 1 in a high temperature state. The preferred upper limit of the concentration is
It is 0.20% by weight. This is because when boron or a boron compound is added to the alkaline electrolyte in an excessive amount, the charging efficiency of the positive electrode 1 can be improved, but the boron or the boron compound adversely affects the charge and discharge of the secondary battery. This is because the utilization rate of the positive electrode 1 may decrease. More preferable boron concentration is 0.03% by weight
Is about 0.10% by weight.

For the positive electrode 1, a paste containing nickel hydroxide powder, a conductive agent, a binder, and water was prepared, the current collector was filled with the paste, and the paste was dried and pressure-molded. Then, it is manufactured by cutting into a desired size.

It is preferable that zinc or cobalt is coprecipitated with metallic nickel in the nickel hydroxide powder to be contained as a solid solution. The positive electrode containing such nickel hydroxide powder can further improve the charging efficiency in a high temperature state.

Examples of the conductive agent include cobalt compounds such as cobalt monoxide, dicobalt trioxide, and cobalt hydroxide. Examples of the binder include polytetrafluoroethylene, carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polyvinyl alcohol.

The current collector has a sponge-like, fibrous-like, or felt-like porous structure made of, for example, an alkali-resistant metal such as nickel or stainless steel, or an alkali-resistant nickel-plated resin. Can be mentioned.

The negative electrode 2 is prepared by adding a conductive material to a negative electrode active material, kneading it with a binder and water to prepare a paste, filling the current collector with the paste, drying it, and then molding it. Manufactured.

Examples of the negative electrode active material include cadmium compounds such as metal cadmium and cadmium hydroxide, and hydrogen storage alloys. Above all, the hydrogen storage alloy is preferable because it can improve the capacity of the secondary battery as compared with the case where the cadmium compound is used. The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in the electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ and MmNi ₅ (Mm is La,
Ce, Pr, Nd, Sm, etc. means a misch metal which is a mixture of lanthanum-based elements), LnNi ₅ (L
n; lanthanum-enriched misch metal), and some of these Nis are Al, Mn, Co, Ti, Cu, Zn, Z
multi-element system substituted with elements such as r, Cr, B,
Alternatively, TiNi-based and TiFe-based materials can be used. Above all, the general formula LnNi _x Mn _y A _z (However, A
Is at least one metal selected from Al and Co, and the atomic ratios x, y, and z have a total value of 4.8 ≦ x + y + z ≦ 5.
4) is preferable because it has a desired hydrogen equilibrium pressure and can improve the charge / discharge cycle life of the secondary battery. More preferred formula _{LmNi w Co x Mn y Al z} ( where atomic ratios w, x, y, z are each 3.1 ≦ w ≦ 4.8,0.2
≤x≤0.8, 0.2≤y≤0.8, 0.2≤z≤0.
8, the sum of these values is 5.1 ≦ w + x + y + z ≦ 5.
4) is a hydrogen storage alloy. Such a hydrogen storage alloy can significantly improve the charge / discharge cycle life.

Examples of the conductive material include carbon black. The same binder as the positive electrode 1 can be used as the binder. Examples of the current collector include two-dimensional substrates such as punched metal, expanded metal, perforated rigid plate and nickel net, and three-dimensional substrates such as felt-like metal porous bodies and sponge-like metal porous bodies. You can

Examples of the separator 3 include a nonwoven fabric made of polyamide fiber and a nonwoven fabric made of polyolefin fiber such as polyethylene and polypropylene to which a hydrophilic functional group is added.

[0018]

According to the alkaline secondary battery of the present invention, a positive electrode having a structure in which a current collector is filled with a paste containing nickel hydroxide powder as a main component, and an alkaline electrolyte in which boron or a boron compound is dissolved are provided. By being provided, boron is adsorbed on the nickel hydroxide powder. As a result, since the oxygen overvoltage of the positive electrode in a high temperature state can be increased, the oxygen gas generation reaction represented by the above-mentioned formula (2) is suppressed, and the nickel hydroxide powder represented by the above-mentioned formula (1) is charged. Since the reaction occurs preferentially, the production amount of NiOOH can be increased and the charging efficiency of the positive electrode can be improved.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. Examples 1 to 4 First, 0.3% by weight of carboxymethyl cellulose and 1.0% by weight of polytetrafluoroethylene were added to a mixture of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide. 45% by weight of water was added and kneaded to prepare a paste. Each of the pastes was filled in a nickel-plated fiber substrate having a porosity of 95% as a current collector, dried, and then roller pressed to form a positive electrode.

In addition, LaNi _4.0 Co _0.4 Mn _0.3 Al
_To 95 parts by weight of hydrogen storage alloy powder having a composition of _0.3 , 3 parts by weight of polytetrafluoroethylene powder, 1 part by weight of carbon powder, and 1 part by weight of carboxymethyl cellulose as a binder are added and mixed with 50 parts by weight of water. To prepare a paste. The paste was applied to a nickel net, dried, and then pressure-molded to prepare a hydrogen storage alloy negative electrode.

On the other hand, potassium borate was dissolved in 8N potassium hydroxide aqueous solution to obtain a boron concentration of 0.01% by weight.
An alkaline electrolyte containing 0.05% by weight, 0.10% by weight, and 0,20% by weight was prepared.

Next, a separator made of a non-woven fabric made of olefin resin, which has been subjected to a hydrophilic treatment, is interposed between each of the positive electrodes and the negative electrodes and spirally wound to prepare an electrode group, which is then formed into a bottomed cylindrical container. Stowed. By pouring the alkaline electrolyte into the container and closing the opening of the container, the structure shown in FIG. 1 is provided and the capacity is 1100 mAh.
An A size cylindrical nickel-hydrogen secondary battery was assembled. Comparative Example 1 AA having the same structure as that of Examples 1 to 4 except that an alkaline electrolyte consisting of only 8N potassium hydroxide aqueous solution was used and having the structure shown in FIG. 1 and having a capacity of 1100 mAh.
A size nickel-hydrogen secondary battery was assembled.

100 of each of the obtained secondary batteries of Examples 1 to 4 and Comparative Example 1 were prepared and aged at 45 ° C. for 24 hours. Each of the batteries was charged at 25 ° C. with a current of 0.1 C to a depth of 150%, and then a charge / discharge cycle of discharging with a current of 1 C was repeated 20 times to stabilize the discharge capacity. For each type of battery, 10 batteries having substantially the same discharge capacity at the 20th cycle were selected. After charging the selected batteries at a high temperature of 45 ° C with a current of 0.1 C to a depth of 150%, then at 25 ° C for 1
It was discharged with a current of C. From the measured discharge capacity, the discharge capacity ratio (the discharge capacity at the time of 20th cycle capacity selection is set to 100) was obtained, and the charging efficiency was obtained when 0.1 C charging was performed at 45 ° C., and the result is shown in FIG. Show.

As is apparent from FIG. 2, the secondary batteries of Examples 1 to 4 provided with the alkaline electrolyte in which potassium borate was dissolved had a high charging efficiency of over 75 at a high temperature of 45 ° C. Recognize. On the other hand, the secondary battery of Comparative Example 1 provided with the alkaline electrolyte containing no potassium borate was
It can be seen that the charging efficiency in the high temperature state is extremely low at 69. Example 5 Boric acid was dissolved in an 8N potassium hydroxide aqueous solution in place of the potassium borate to prepare an alkaline electrolyte having a boron concentration of 0.07% by weight. Using the alkaline electrolyte and the same positive electrode, negative electrode and separator as in Examples 1 to 4, an AA size nickel-hydrogen secondary battery having the structure shown in FIG. 1 was assembled.

The obtained secondary battery of Example 5 was manufactured by the same method as in Examples 1 to 4 at a high temperature of 45 ° C.
When the charging efficiency at the time of 1C charging was obtained, it was as high as 83. Comparative Example 2 A positive electrode containing nickel hydroxide powder co-precipitated with 3 to 5% by weight of zinc as an active material and containing no manganese compound, and an alkali containing 1N lithium hydroxide and 7N potassium hydroxide. Examples 1 to 4 except that an electrolytic solution was used
An AA size nickel-hydrogen secondary battery having the structure shown in FIG.

With respect to the obtained secondary battery of Comparative Example 2, the same procedure as in Examples 1 to 4 was carried out at a high temperature of 45 ° C.
When the charging efficiency when 1C charging was performed, it was as low as 69.

[0027]

As described in detail above, according to the alkaline secondary battery of the present invention, remarkable effects such as improvement of charging efficiency of the positive electrode in a high temperature state can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing an alkaline secondary battery according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a boron conversion amount of potassium borate and a charging efficiency of a positive electrode in a high temperature state in an example of the present invention.

[Explanation of symbols]

1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 4 ... Container, 6 ...
Seal plate, 7 ... Insulation gasket.

Claims (1)

[Claims] 1. A positive electrode having a structure in which a current collector is filled with a paste containing nickel hydroxide powder as a main component, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and boron or boron. An alkaline secondary battery comprising an alkaline electrolyte in which a compound is dissolved.