JPH11329480A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery excellent in high rate discharge characteristic and having a high capacity by providing a negative electrode comprising a hydrogen storage allay and a conductive substrate made of a nickel foil having a specified thickness, and providing a specified energy charging density. SOLUTION: The energy charging density of this alkaline secondary battery is 310 Wh/l or more, and a conductive substrate consists of a nickel foil having a thickness of 10-20 μm. An electrode group 5 formed by laminating a positive electrode 2, a separator 3 and a negative electrode 4 and spirally winding them is housed in a bottomed cylindrical vessel 1. The negative electrode 4 is arranged on the outermost circumference of the electrode group 5, and electrically made into contact with the vessel 1. A circular first sealing plate having a hole 6 in the center is arranged on the upper opening part of the vessel 1, and a ring-like insulating gasket 8 is arranged between the periphery of the sealing plate 7 and the upper opening part inner surface of the vessel 1, and the sealing plate 7 is airtightly fixed to the vessel 1 through the gasket 8 by caulking.

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 having an improved negative electrode using hydrogen as an active material.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery, which is an example of an alkaline secondary battery, has an electrode in which a separator is interposed between a paste-type positive electrode containing nickel hydroxide as an active material and a paste-type negative electrode containing a hydrogen storage alloy. The group is housed in a container together with an alkaline electrolyte, and has a closed structure. This nickel-metal hydride secondary battery is compatible in voltage with a nickel-cadmium secondary battery using a negative electrode containing a cadmium compound instead of the paste-type hydrogen storage alloy negative electrode, and has a higher capacity than a nickel-cadmium secondary battery. It has excellent characteristics. Further, nickel-metal hydride secondary batteries have been widely used as operating power supplies for various electronic devices such as portable telephones and portable imaging devices, and in recent years, higher capacity and longer life have been demanded.

To increase the capacity of a sealed nickel-metal hydride secondary battery, it is necessary to increase the capacity of a positive electrode, which is a capacity regulating electrode. However, since the space for accommodating the electrode group and the alkaline electrolyte is limited, when the positive electrode capacity is increased, the space for accommodating the alkaline electrolyte is insufficient, and a problem is liable to occur during overcharge. Invite. If the amount of alkaline electrolyte is reduced to prevent liquid leakage,
Discharge capacity and cycle life decrease.

[0004] In order to secure a space for accommodating an alkaline electrolyte, it is necessary to increase the volume energy density of the negative electrode to reduce the volume of the negative electrode. By the way, a paste type negative electrode is prepared by kneading a hydrogen storage alloy powder, a conductive material and a binder in the presence of water to prepare a paste, and then forming the paste into a porous structure such as a punched metal or a felt-like porous metal body. It is obtained by filling a conductive substrate, drying and pressing. As a technique for increasing the volume energy density of the negative electrode, it has been considered to reduce the thickness of the conductive substrate.

[0005]

However, when the thickness of the porous conductive substrate described above is reduced, the conductivity is reduced, and the discharge capacity when discharging with a large current is reduced. Further, since the strength of the conductive substrate is reduced, the substrate is easily broken at the time of pressure molding.

Therefore, it has been difficult to produce a nickel-hydrogen secondary battery having a high capacity with an energy density of 310 Wh / l or more and excellent high-rate discharge characteristics by the conventional technology.

An object of the present invention is to provide an alkaline secondary battery having excellent high-rate discharge characteristics and high capacity.

[0008]

An alkaline secondary battery according to the present invention is an alkaline secondary battery including a negative electrode including a hydrogen storage alloy and a conductive substrate, and the energy filling density of the secondary battery is 310 Wh. / L or more, and the conductive substrate is a nickel foil having a thickness of 10 to 20 µm.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (for example, a cylindrical alkaline secondary battery) according to the present invention will be described in detail with reference to FIG.

An electrode group 5 formed by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a cylindrical container 1 having a bottom. 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.

Hereinafter, the negative electrode 4, the positive electrode 2, the separator 3
And the alkaline electrolyte will be described in detail.

(1) Negative Electrode 4 The negative electrode 4 has a structure in which a paste containing a hydrogen storage alloy is applied to a conductive substrate.
It is a nickel foil of 0 to 20 μm.

The negative electrode 4 is prepared, for example, by adding a conductive material to a hydrogen storage alloy powder, kneading it with a binder and water to prepare a paste, applying the paste to a conductive substrate, and drying the paste. It is manufactured by press molding.

The hydrogen storage alloy is not particularly limited, and may be any alloy capable of storing hydrogen electrochemically generated in an electrolytic solution and easily releasing the stored hydrogen during discharge. For example, LaNi ₅ , MmNi
₅ (Mm is misch metal), LmNi ₅ (Lm is La
At least one element selected from the group consisting of rare earth elements containing Al, Mn, Co, Ti, and C.
Examples thereof include a multi-element-based material substituted with an element such as u, Zn, Zr, Cr, and B, or a TiNi-based or TiFe-based material. Among them, the general formula LmNi _w Co _x Al
_y Mn _z (where, Lm is at least one selected from rare earth elements including La, atomic ratio w is 3.30 ≦ w
≦ 4.50, atomic ratio x is 0.50 ≦ x ≦ 1.10, atomic ratio y is 0.20 ≦ y ≦ 0.50, and atomic ratio z is 0.05 ≦
A rare earth-nickel-based hydrogen storage alloy having a composition represented by z ≦ 0.20 and a total value of atomic ratios w, x, y, and z is 4.90 ≦ w + x + y + z ≦ 5.50) is preferable.
The rare earth-nickel-based hydrogen storage alloy represented by the above general formula has a small elution of Mn, so that the cycle life can be extended and the cost is low. The atomic ratio w, x,
More preferable values of y and z are 3.80 ≦ w ≦
4.20, 0.70 ≦ x ≦ 0.90, 0.30 ≦ y ≦
0.40, 0.08 ≦ z ≦ 0.13, and the total value is 5.00 ≦ w + x + y + z ≦ 5.20.

The reason why the thickness of the nickel foil serving as the conductive substrate is specified in the above range is as follows. When the thickness is less than 10 μm, the strength of the conductive substrate is reduced, and the substrate is easily broken at the time of pressure molding. On the other hand, if the thickness exceeds 20 μm, the volume efficiency of the negative electrode is reduced, so that in an alkaline secondary battery having an energy filling density of 310 Wh / l or more, liquid leakage or deterioration of charge / discharge characteristics is caused.

Examples of the conductive material include carbon black and graphite.

Examples of the binder include polyacrylates such as sodium polyacrylate and potassium polyacrylate, fluorine resins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CM).
C) and the like.

(2) Positive Electrode 2 The positive electrode 2 is formed of a positive electrode material containing nickel hydroxide powder and a binder carried on a current collector.

As the nickel hydroxide powder, for example, non-eutectic nickel hydroxide powder or nickel hydroxide powder in which a metal such as zinc, cobalt, bismuth or copper is eutectic can be used. The latter positive electrode containing nickel hydroxide powder can further improve the charging efficiency in a high temperature state.

The nickel hydroxide powder has a peak half-value width of the (101) plane determined by an X-ray powder diffraction method of 0.8 ° / 2θ.
(Cu-Kα) or more is preferable. A more preferable value of the half width of the peak is 0.9 to 1.0 ° / 2θ (C
u-Kα).

Examples of the binder include polytetrafluoroethylene, carboxymethylcellulose, methylcellulose, polyacrylate, and polyvinyl alcohol.

Examples of the current collector include those having a sponge-like, fibrous, felt-like, or net-like porous structure made of a metal such as nickel or stainless steel, or a resin plated with nickel. it can.

The positive electrode is prepared by, for example, preparing a paste containing nickel hydroxide powder, a conductive additive, a binder, and water, filling the paste into a current collector, drying and pressing the paste. It is made.

As the conductive assistant, for example, at least one selected from metallic cobalt and a cobalt compound can be used. As the cobalt compound, dicobalt trioxide (Co ₂ O ₃ ), cobalt monoxide (Co
O), cobalt hydroxide {Co (OH) ₂ } and the like.

(3) Separator 3 Examples of the separator 3 include a nonwoven fabric made of a polyamide fiber and a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group.

(4) Alkaline Electrolyte As the alkaline electrolyte, for example, an aqueous solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH)
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

The secondary battery has an energy filling density of 3
10 Wh / l or more. This energy filling density C
(Wh / l) (volume energy density) is defined by the following equation.

C = (C _T × Z) / V (1) where C _T (Ah) is the theoretical capacity of the secondary battery, and Z (V)
Represents the voltage of the secondary battery, and V (l) represents the volume of the secondary battery (the internal volume of the container).

As described in detail above, the alkaline secondary battery according to the present invention includes a negative electrode including a hydrogen storage alloy and a conductive substrate, has an energy filling density of 310 Wh / l or more, and the conductive substrate has It is a nickel foil having a thickness of 10 to 20 μm. Such a conductive substrate has the same thickness and can improve strength and conductivity as compared with a substrate having a porous structure (for example, punched metal).
By applying a paste containing the hydrogen storage alloy to the conductive substrate, drying and applying pressure molding, the substrate was excellent in conductivity and volume efficiency was improved without causing breakage of the substrate during pressure molding. A negative electrode can be obtained. By constructing an alkaline secondary battery having an energy filling density of 310 Wh / l or more using this negative electrode, a space for accommodating an alkaline electrolyte can be secured without impairing large-current discharge characteristics. High capacity can be achieved while maintaining the life and the large current discharge characteristics.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Paste-Type Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 parts of carboxymethyl cellulose with respect to the nickel hydroxide powder. A paste was prepared by adding 0.5 parts by weight of a solid dispersion and 60 parts by weight of a polytetrafluoroethylene dispersion (solid content: 60% by weight), adding 45 parts by weight of water thereto, and kneading. This paste was filled into a nickel-plated metal porous body as a conductive substrate, dried, and then roll-pressed to form a positive electrode.

<Preparation of Paste Type Negative Electrode> Commercially available lanthanum-enriched misch metal Lm, Ni, Co, Mn and A
LmNi _4.0 Co _0.4
A hydrogen storage alloy having a composition of Mn _0.3 Al _0.3 was produced. The obtained hydrogen storage alloy was mechanically pulverized,
Passed through a mesh sieve.

To 100 parts by weight of the obtained hydrogen storage alloy powder, 0.5 parts by weight of sodium polyacrylate, 0.125 parts by weight of carboxymethyl cellulose (CMC), and a dispersion of polytetrafluoroethylene (solid content: 6%)
0% by weight) and 1.0 part by weight of carbon black as a conductive material in terms of solid content, and mixed with 50 parts by weight of water to prepare a paste. This paste was applied to a nickel foil having a thickness of 10 μm as a conductive substrate, dried, and then subjected to pressure molding to produce a paste-type negative electrode.

Next, a separator made of a polyolefin nonwoven fabric subjected to a hydrophilic treatment was interposed between the negative electrode and the positive electrode and spirally wound to form an electrode group.
After storing such an electrode group in a bottomed cylindrical container, 7N
The structure shown in FIG. 1 described above is accommodated by accommodating an alkaline electrolyte composed of KOH and 1N LiOH, and performing sealing and the like. The theoretical capacity is 4500 mAh (the energy filling density is 310 Wh / l or more), A 3 A size cylindrical nickel-metal hydride secondary battery was assembled.

Example 2 A cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the thickness of the nickel foil serving as the conductive substrate for the negative electrode was changed to 15 μm.

Example 3 A cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the thickness of the nickel foil as the conductive substrate for the negative electrode was changed to 20 μm.

(Comparative Example 1) <Preparation of Paste Type Negative Electrode> A paste similar to that described in Example 1 was punched metal (a nickel-plated steel plate was used as a material, and had a thickness of 60 μm and a basis weight). Amount is 345 g / m ² and the aperture ratio is 40%)
After drying, a paste-type negative electrode was produced by pressure molding.

Then, a separator similar to that described in Example 1 was interposed between the negative electrode and the positive electrode similar to that described in Example 1, and spirally wound to form an electrode group. After storing such an electrode group in a bottomed cylindrical container,
An alkaline electrolyte having the same composition as that described in Example 1 is accommodated therein, and the structure shown in FIG. 1 is provided by sealing and the like, and the theoretical capacity is 3000 mAh (the energy filling density is less than 310 Wh / l). Thus, a 4/3 A size cylindrical nickel-metal hydride secondary battery was assembled.

Comparative Example 2 A negative electrode paste similar to that described in Example 1 was applied to a nickel foil having a thickness of 5 μm.
After being dried and subjected to pressure molding, the nickel foil was broken, and a negative electrode could not be produced.

Comparative Example 3 A cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the thickness of the nickel foil serving as the negative electrode conductive substrate was 30 μm.

After activating the obtained secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 3, the batteries were charged with a current of 0.2 C for 90 minutes and a final voltage of 1 with a current of 0.2 C. 0.0V
The charge / discharge cycle of discharging the battery until the discharge was repeated, the discharge capacity at the sixth cycle was measured, and the results are shown in Table 1 below. Further, the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 3 were charged at a current of 0.2 C for 90 minutes, and charged at each rate (1
C, 2C, 3C, 5C), the discharge capacity when discharging to a final voltage of 1.0 V was measured, and the discharge capacity ratio at each rate (2C, 3C, 5C) to the discharge capacity at 1C was calculated (1C The discharge capacity at 100% is assumed to be 100%), and the results are also shown in Table 1 below.

Further, for each of the 100 secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 3, 150
%, The number of leaked liquids was measured, and the results are shown in Table 2 below.

[0043]

[Table 1]

[0044]

[Table 2]

As is clear from Table 1, the secondary batteries of Examples 1 to 3 provided with a negative electrode containing a nickel foil having a thickness of 10 to 20 μm as a conductive substrate have a thickness of 60 μm as a conductive substrate. Comparative Example 1 with a negative electrode containing punched metal
The discharge capacity is higher than that of the secondary battery of Comparative Example 3, and the thickness of the nickel foil exceeds 20 μm.
It can be seen that the capacity when discharged at a high rate of C or higher is high.
In addition, the secondary batteries of Examples 1 to 3 had no number of liquids that leaked during overcharging, whereas the nickel foil had a thickness of 20%.
In the secondary battery of Comparative Example 3 exceeding μm, the number of leaked liquids during overcharge was as large as five.

In the above-described embodiment, the separator is interposed between the negative electrode and the positive electrode and spirally wound and accommodated in a cylindrical container having a bottom. It is not limited to a simple structure. For example, the present invention can be similarly applied to a square nickel-metal hydride secondary battery in which a separator is interposed between a negative electrode and a positive electrode, and a laminate obtained by laminating a plurality of the separators is housed in a bottomed rectangular cylindrical container.

[0047]

According to the alkaline secondary battery of the present invention, it is possible to increase the volumetric efficiency of the negative electrode while maintaining the high rate discharge characteristics, and to achieve a remarkable effect such as achieving a high capacity. Play.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an alkaline 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.

Claims (1)

[Claims] 1. An alkaline secondary battery including a negative electrode including a hydrogen storage alloy and a conductive substrate, wherein the secondary battery has an energy filling density of 310 Wh / l or more, and the conductive substrate has a thickness of not less than 310 Wh / l. 10-20μ
m alkaline nickel battery.