JPH10284070A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an internal pressure rise when overcharging and discharging excessively by improving conductive material for a negative material. SOLUTION: A positive electrode 2, a negative electrode 4 on which negative electrode material containing hydrogen occluded alloy and conductive material is carried, a separator 3 inserted between the positive electrodes and electrolyte are provided, and the conductive material is composed of both active carbon and carbon black.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an alkaline secondary battery.

[0002]

2. Description of the Related Art In recent years, an alkaline secondary battery provided with a negative electrode including a hydrogen storage alloy that stores and releases hydrogen has attracted attention. This secondary battery has a high energy density, has a high volumetric efficiency, can operate safely, and has high reliability in characteristics.

In the nickel-hydrogen secondary battery, the capacity of the negative electrode is made larger than the capacity of the positive electrode. This is to avoid a pressure increase in the battery during overcharge and overdischarge. That is, at the time of charging, the positive electrode is first set to the charging end state, and at the time of overcharging, oxygen is generated from the positively charged positive electrode, and the oxygen gas is rapidly reduced on the hydrogen storage alloy surface of the negative electrode to form By returning to, the internal pressure rise in the battery at the time of overdischarge is avoided. Therefore, one of the characteristics required for the negative electrode is that the oxygen gas reduction rate and the hydrogen gas oxidation rate on its surface are sufficiently high.

[0004] The negative electrode has a structure in which a negative electrode material containing a hydrogen storage alloy and a conductive material is supported on a conductive substrate such as a punched metal. Conventionally, carbon black such as acetylene black has been used as the conductive material. Carbon black is
In addition to having the effect of improving the conduction between the hydrogen storage alloy and the conduction between the hydrogen storage alloy and the conductive substrate, it has the effect of improving the gas reaction rate of the hydrogen storage alloy.

However, if the capacity is increased for the purpose of improving the charge / discharge cycle life of the alkaline secondary battery, the amount of gas generated during overcharging / discharging increases. In the negative electrode, it is difficult to always sufficiently increase the gas absorption capacity. Alkaline secondary batteries have a problem that, when the internal pressure increases, the discharge capacity decreases and the charge / discharge cycle life decreases.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an alkaline secondary battery capable of suppressing a rise in internal pressure during overcharge and overdischarge by improving the conductive material of the negative electrode. It is.

[0007]

An alkaline secondary battery according to the present invention comprises a positive electrode, a negative electrode having a conductive substrate carrying a negative electrode material containing a hydrogen storage alloy and a conductive material, and a positive electrode and a negative electrode interposed between the positive and negative electrodes. Comprising a separator and an electrolytic solution,
The conductive material comprises both activated carbon and carbon black.

The activated carbon is blended in the negative electrode in an amount of 0.05 to 1 part by weight with respect to 100 parts by weight of the hydrogen storage alloy, and the carbon black is mixed in the negative electrode with respect to 100 parts by weight of the hydrogen storage alloy. It is preferable that 0.05 to 3 parts by weight be blended. The activated carbon has a specific surface area of 1
It is preferably at least 000 m ² / g.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (cylindrical nickel-metal hydride secondary battery) according to the present invention will be described with reference to FIG. An electrode group 5 produced by stacking the positive electrode 2, the separator 3, and the negative electrode 4 and winding them in a spiral shape is accommodated in the bottomed cylindrical container 1. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular first sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 1. The ring-shaped insulating gasket 8 is
Is arranged between the periphery of the container and the inner surface of the upper opening of the container 1,
The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking to reduce the diameter of the upper opening inward. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. Rubber safety valve 1
1 is arranged so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 so that a protrusion of the positive electrode terminal 10 is provided on the holding plate 1.
2 so as to protrude from the holes. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described. 1) Positive electrode 2 The positive electrode 2 is prepared by kneading a nickel compound as an active material, a conductive material and a polymer binder together with water to prepare a paste, filling the paste into a conductive substrate, drying, and drying the paste. It is produced by performing pressure molding accordingly.

Examples of the nickel compound include nickel hydroxide, nickel oxide and nickel oxide in which nickel hydroxide, zinc and cobalt are coprecipitated.
Particularly, nickel hydroxide in which zinc and cobalt are coprecipitated is preferable.

As the conductive material, for example, at least one selected from a cobalt compound and metallic cobalt is used. As the cobalt compound,
For example, cobalt hydroxide [Co (O hydrogen storage alloy) ₂ ],
Cobalt monoxide (CoO) and the like can be mentioned. In particular, it is preferable to use cobalt hydroxide, cobalt monoxide, or a mixture thereof as the conductive material.

Examples of the polymer binder include hydrophobic polymers such as polytetrafluoroethylene, polyethylene and polypropylene; cellulosic materials such as carboxymethylcellulose, methylcellulose and hydroxypropylmethylcellulose; acrylic acid such as sodium polyacrylate Esters; hydrophilic polymers such as polyvinyl alcohol and polyethylene oxide; and rubber-based polymers such as latex.

Examples of the conductive substrate include a mesh-like, sponge-like, fibrous, or felt-like porous metal body formed of nickel, stainless steel, or nickel-plated metal.

2) Negative Electrode 4 The negative electrode 4 has a structure in which a negative electrode material containing a hydrogen storage alloy and a conductive material composed of activated carbon and carbon black is supported on a conductive substrate. The negative electrode 4 having such a structure is prepared by kneading, for example, a hydrogen storage alloy powder, the conductive material composed of activated carbon and carbon black, and a polymer binder together with water to prepare a paste. , Dried and, if necessary, pressure-formed.

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. . As this hydrogen storage alloy,
For example, LaNi ₅ , MmNi ₅ (Mm; La, Ce, P
a misch metal composed of a mixture of lanthanum-based elements such as r, Nd, and Sm), LmNi ₅ (Lm; lanthanum-enriched misch metal), or a part of these Nis as A
l, Mn, Co, Ti, Cu, Zn, Zr, Cr, a multi-element system substituted with elements such as B, or TiN
i-based, TiFe-based, ZrNi-based, and MgNi-based ones. Above all, a rare earth hydrogen storage alloy is preferable. In particular, the general formula LmNi _x Mn _y A _z (where
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 ≦
The negative electrode containing the rare earth-based hydrogen storage alloy represented by 5.4) is suitable because it can suppress the pulverization accompanying the progress of the charge / discharge cycle and can improve the charge / discharge cycle life of the secondary battery. It is.

Carbon black, which is one of the components constituting the conductive material, has the function of improving the conductivity between the hydrogen storage alloy and the conductivity between the hydrogen storage alloy and the conductive substrate. It has the effect of improving the reaction rate. As such carbon black, for example, acetylene black, Ketchan black, furnace black and the like can be used.

Activated carbon, which is the other component of the conductive material, has a lower gas conductivity than that of the carbon black, but has a high gas absorption capacity and a reduction rate of oxygen gas of the hydrogen storage alloy and the hydrogen absorption rate. It has the effect of improving the gas oxidation rate. Such activated carbon preferably has a specific surface area of 1000 m ² / g or more. When the specific surface area of the activated carbon is less than 1000 m ² / g, it is difficult to sufficiently improve the gas absorption performance because the gas absorption reaction area on the activated carbon surface is small. More preferably, the specific surface area of the activated carbon is 1500 m ² / g or more.

The activated carbon is incorporated in the negative electrode in an amount of 0.05 to 1 part by weight based on 100 parts by weight of the hydrogen storage alloy, and the carbon black is contained in the negative electrode in an amount of 0 to 100 parts by weight of the hydrogen storage alloy. It is preferable to mix 0.05 to 3 parts by weight. This is for the following reason. If the compounding ratio of the activated carbon to 100 parts by weight of the hydrogen storage alloy is less than 0.05 parts by weight, it becomes difficult to sufficiently enhance the gas absorption performance of the negative electrode. On the other hand, when the mixing ratio of the activated carbon to 100 parts by weight of the hydrogen storage alloy exceeds 1 part by weight, the mixing ratio of the conductive material in the negative electrode becomes too large, and the amount of the hydrogen storage alloy per unit volume of the negative electrode decreases. There is a possibility that the discharge capacity of the secondary battery provided with the leverage negative electrode may decrease. Further, when the mixing ratio of the carbon black in the negative electrode is less than 0.05 part by weight with respect to 100 parts by weight of the hydrogen storage alloy, the conduction between the hydrogen storage alloy and the conduction between the hydrogen storage alloy and the conductive substrate are insufficient. Therefore, the discharge capacity of the secondary battery including the negative electrode may be reduced. On the other hand, if the compounding ratio of the carbon black in the negative electrode exceeds 3 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy, the compounding ratio of the conductive material in the negative electrode becomes too large, and the hydrogen storage per unit volume of the negative electrode increases. There is a possibility that the discharge capacity of a secondary battery provided with this negative electrode will decrease due to a decrease in the amount of alloy. In particular, the activated carbon is contained in the anode in an amount of 0.05 to 100 parts by weight of the hydrogen storage alloy.
0.5 parts by weight, and the carbon black is contained in the negative electrode in an amount of 0.05 parts by weight based on 100 parts by weight of the hydrogen storage alloy.
More preferably, it is blended in an amount of up to 1.5 parts by weight.

Examples of the polymer binder include those similar to those used for the positive electrode 2. Examples of the conductive substrate include those having a two-dimensional structure such as a punched metal, an expanded metal, a perforated rigid plate, and a wire mesh, and a three-dimensional structure such as a foamed metal and an Amejo sintered metal fiber.

3) Separator 3 The separator 3 is made of, for example, an olefin-based nonwoven fabric such as a nonwoven fabric made of polyethylene fiber, a nonwoven fabric made of ethylene-vinyl alcohol copolymer fiber, or a nonwoven fabric made of polypropylene fiber, or an olefin such as a nonwoven fabric made of polypropylene fiber. Examples thereof include nonwoven fabrics made of a nonwoven fabric made of a base fiber and hydrophilic functional groups, and nonwoven fabrics made of polyamide fibers such as nylon 6,6. In order to impart a hydrophilic functional group to the olefin fiber nonwoven fabric, for example, corona discharge treatment, sulfonation treatment, graft copolymerization, or application of a surfactant or a hydrophilic resin can be employed.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH.

The alkaline secondary battery according to the present invention described above includes a negative electrode in which a conductive substrate carries a negative electrode material containing a hydrogen storage alloy and a conductive material composed of both activated carbon and carbon black. Since carbon black in such a conductive material has an effect of improving conduction between the hydrogen storage alloy and conduction between the hydrogen storage alloy and the conductive substrate, a high-capacity negative electrode can be realized. In addition, the carbon black has an effect of improving the oxygen gas reduction rate and the hydrogen gas oxidation rate of the hydrogen storage alloy and the gas reaction rate, and activated carbon blended with the carbon black has a high gas absorption capacity, so that the In addition, a negative electrode with improved gas absorption performance during overdischarge can be realized. Therefore, since the secondary battery of the present invention has a negative electrode having a high capacity and excellent gas absorption performance during overcharge and overdischarge, the internal pressure rise during overcharge and overdischarge can be suppressed, and the charge / discharge cycle life is reduced. Be improved.

Further, the amount of the activated carbon is defined in the range of 0.05 to 1 part by weight based on 100 parts by weight of the hydrogen storage alloy, and the amount of the carbon black is set in the negative electrode. By defining the activated carbon having a specific surface area of 1000 m ² / g or more as the activated carbon, the gas at the time of overcharging and overdischarging is further increased by using the activated carbon having a specific surface area of 1000 m ² / g or more. An alkaline secondary battery having a negative electrode with excellent absorption performance and an improved charge / discharge cycle life can be realized.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. (Examples 1 to 10 and Comparative Examples 1 to 3) <Preparation of Paste Type Negative Electrode> LmNi _4.0 Co _0.4 Mn _0.3 using a commercially available lanthanum-enriched misch metal Lm and Ni, Co, Mn, and Al by a high frequency furnace. Al
_A hydrogen storage alloy having a composition of _0.3 was prepared. The hydrogen storage alloy was mechanically pulverized and passed through a 200-mesh sieve. To 100 g of the obtained hydrogen storage alloy powder, 0.5 g of sodium polyacrylate, 0.05 g of carboxymethylcellulose (CMC) as a polymer binder, and a dispersion of polytetrafluoroethylene (specific gravity 1.
5, solid content 60 wt%) 1.6 ml, activated carbon having a blending amount and specific surface area shown in Table 1 below, carbon black (specific surface area: about 800 m ² / g), and 60 ml of water are added and kneaded. Thus, 13 kinds of pastes were prepared. These pastes were applied to a punched metal as a conductive substrate, dried, pressed, and cut to produce 13 types of paste-type negative electrodes.

<Preparation of Paste-Type Positive Electrode> To a mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder, 0.3 parts by weight of carboxymethylcellulose, A paste was prepared by adding 0.5 parts by weight of a dispersion of fluoroethylene (specific gravity: 1.5, solid content: 60% by weight) in terms of solid content, adding 45 parts by weight of pure water thereto, and kneading. Subsequently, after this paste was filled in a nickel-plated fiber substrate, the paste was further applied to both surfaces thereof, dried, and rolled by roller pressing to produce a paste-type positive electrode.

Next, a nonwoven fabric made of polypropylene fiber is interposed between the negative electrode and the positive electrode, and spirally wound to form
Three types of electrode groups were produced. After each such electrode group is housed in a cylindrical container having a bottom, an electrolytic solution composed of 8N KOH is injected into the container, and the container is sealed or the like, thereby having the above-described structure shown in FIG. Thirteen types of cylindrical nickel-metal hydride secondary batteries (capacity: 1400 mAh) were assembled.

The obtained Examples 1 to 10 and Comparative Examples 1 to
The 100 secondary batteries of No. 3 were charged at 150% at 1 C, paused for 10 minutes, discharged at 1 C, and repeated charge / discharge cycles of 1 V cut. In such a charge / discharge cycle test, at the time of 20 cycles, 50 cycles, and 1 cycle
The number of operating safety flights and the number of cycles required for the capacity to fall below 1000 mAh in each of the 00 cycles were examined. The results are shown in Table 1 below.

[0029]

[Table 1]

As is apparent from Table 1, the secondary batteries of Examples 1 to 10 provided with the negative electrodes containing the conductive material composed of both activated carbon and carbon black exhibited gas reaction rates during overcharge and overdischarge. It can be seen that the internal pressure of the battery can be reduced and the capacity is high due to the improvement effect of the battery. In particular, activated carbon having a specific surface area of at least 1000 m ² / g is blended in an amount of 0.05 to 1 part by weight with respect to 100 parts by weight of the hydrogen storage alloy, and the carbon black is mixed with the hydrogen storage alloy 10
The secondary batteries of Examples 1 to 8 including the negative electrode mixed with 0.05 to 3 parts by weight with respect to 0 part by weight can further reduce the internal pressure of the battery and achieve higher capacity. Recognize.

On the other hand, the secondary batteries of Comparative Examples 1 and 2 provided with the negative electrodes containing a conductive material consisting of only carbon black were caused by slow gas reaction rates during overcharge and overdischarge. It can be seen that the internal pressure of the battery rises. On the other hand, it can be seen that Comparative Example 3 including the negative electrode containing a conductive material composed of only activated carbon has an effect of improving the gas reaction rate during overcharge and overdischarge, but cannot increase the capacity.

[0032]

As described above, according to the present invention, by improving the conductive material of the negative electrode, it is possible to increase the capacity and improve the gas absorption performance at the time of overcharge and overdischarge, and to improve the charge / discharge cycle life. Can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view of a nickel-metal hydride secondary battery as an example of a nickel-metal hydride secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket, 11 ... Safety valve.

Claims (3)

[Claims] A negative electrode having a conductive substrate supporting a negative electrode material containing a hydrogen storage alloy and a conductive material; a separator interposed between the positive and negative electrodes; and an electrolytic solution. An alkaline secondary battery, wherein the conductive material comprises both activated carbon and carbon black. 2. The activated carbon is blended in the negative electrode in an amount of 0.05 to 1 part by weight based on 100 parts by weight of the hydrogen storage alloy, and the carbon black is contained in the negative electrode in an amount of 100 parts by weight of the hydrogen storage alloy. 2. The alkaline secondary battery according to claim 1, wherein the content of the alkaline secondary battery is 0.05 to 3 parts by weight. 3. The activated carbon has a specific surface area of 1000 m ^2.
2 / g or more.