JPH08250115A - Alkaline secondary battery - Google Patents

Abstract

PURPOSE: To provide a highly long-lived and downsized alkaline secondary battery having excellent charge and discharge characteristic. CONSTITUTION: This alkaline secondary battery has a positive electrode 1a, a negative electrode 1c and an alkaline electrolyte. The negative electrode 1c is formed of a metal containing 5.0g/cm<3> or more of a hydrogen storage alloy represented by the formula LmNiw Cox Mny Alz (wherein Lm represents at least one element selected from rare earth elements including La, and the values of atomic ratios w, x, y, z are 3.90<=w<=4.50, 0.50<=x<=1.20, 0.28<=y<=0.50, 0.28<=z<=0.50, 5.10<=w+x+y+x+z<=5.50), and the ratio of capacity to the positive electrode 1a is set to 1.0-1.5 times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sealed alkaline secondary battery in which a metal oxide is used as a positive electrode active material and hydrogen is used as a negative electrode active material.

[0002]

2. Description of the Related Art With the rapid spread of small cordless devices, there is an increasing demand for secondary batteries having a high capacity. As a secondary battery that meets such demands, a secondary battery in which an electrode made of a hydrogen storage alloy is used as a negative electrode, a metal oxide is used as a positive electrode, and an alkaline aqueous solution is used as an electrolytic solution is drawing attention. That is, in the secondary battery having the above structure, when the hydrogen storage alloy is used as the negative electrode and electrolysis is performed in the alkaline aqueous solution, the hydrogen storage alloy itself forming the negative electrode stores the generated hydrogen. Further, when discharging is performed using a suitable positive electrode such as a nickel electrode as a counter electrode, the stored hydrogen is released, and the released hydrogen is oxidized to generate water again. That is, the reaction reversibly occurs in response to charge and discharge. When the hydrogen storage alloy is used as a negative electrode, compared with a conventional typical secondary battery, that is, when cadmium is used as a negative electrode material,
The energy density per unit weight or unit volume can be increased. Therefore, it is possible to increase the capacity of the secondary battery, and on the other hand, there is little risk of environmental pollution, and in combination with good battery characteristics, it is becoming popular as a powerful portable power source.

The hydrogen storage alloy forming the main material of the negative electrode is an alloy formed of a rare earth element represented by LaNi ₅ and another metal element, or a mixed system of a lanthanum element instead of the rare earth element. Examples of the alloy include a mischmetal (hereinafter, referred to as Mm) and a metal element, or an alloy formed of Mm and a plurality of kinds of metal elements.

[0004]

However, the above-mentioned conventional alkaline secondary battery, for example, nickel-hydrogen secondary battery, has the following problems. First, (a) by repeating charging / discharging (as the charging / discharging cycle progresses), the hydrogen-absorbing alloy powder forming the negative electrode tends to become finer, causing so-called deterioration. That is, the alkaline secondary battery has a problem that the charge / discharge cycle life is easily reduced and the charge / discharge cycle life varies greatly.

Further, (b) in a nickel-hydrogen secondary battery in which the capacity is regulated by the positive electrode in order to maintain the charge / discharge performance, particularly stable performance during overcharge, the capacity of the negative electrode is different from that of the positive electrode.
It is necessary to select and set to 1.5 to 2.5 times. That is, due to the deterioration of the negative electrode containing the hydrogen storage alloy as a main component,
Since the ability to absorb and release hydrogen in the negative electrode decreases, the capacity ratio of the negative electrode is set to 1.5 to 2.5 times the capacity of the positive electrode as a reserve for charging and discharging, including the amount of capacity decrease. Therefore, the volume of the negative electrode housed and mounted in the secondary battery is significantly increased compared to the volume of the positive electrode,
As a result, downsizing of the secondary battery or increasing the capacity of the secondary battery is hindered.

The inventors of the present invention have made earnest studies on the problem of deterioration of the hydrogen storage alloy contained in the secondary battery as the negative electrode. As a result, the amount of Co component in the hydrogen storage alloy, the amount of hydrogen storage alloy contained in the negative electrode, It was also found that the capacity ratio of the negative electrode to the capacity of the positive electrode is correlated with the cycle life of the secondary battery.

The present invention has been made based on the above findings, and an object of the present invention is to provide an alkaline secondary battery having excellent charge / discharge characteristics and having a long life and a small size.

[0008]

The alkaline secondary battery according to the present invention is an alkaline secondary battery comprising a positive electrode, a negative electrode and an alkaline electrolyte, the negative electrode having the formula: LmN
_{i w Co x Mn y Al z} ( However, Lm represents at least one element selected from rare earth elements including La, atomic ratio w, x, y, z values are 3.90 ≦ w ≦ 4.50, 0.50 ≦ x ≤1.2
0, 0.28 ≦ y ≦ 0.50, 0.28 ≦ x ≦ 0.50, 5.10 ≦ w + x
+ Y + z ≦ 5.50) hydrogen storage alloy 5.0g / cm ³
It is characterized in that it is composed of the above-described metal system and that the capacity ratio to the positive electrode is set to 1.0 to 1.5 times.

In the alkaline secondary battery according to the present invention,
The hydrogen storage alloy constituting the main material of the negative electrode, as described above, wherein shown by _{LmNi w Co x Mn y Al z} . Here, the atomic ratio w, x, y, z of Ni, Co, Mn, Al is 3.90.
≤w≤4.50, 0.50≤x≤1.20, 0.28≤y≤0.50, 0.28≤
It is selected in the range of x ≦ 0.50 and 5.10 ≦ w + x + y + z ≦ 5.50. In particular, the atomic ratio x of Co is important for suppressing the deterioration of the constituent hydrogen-absorbing alloy, that is, the reduction of hydrogen absorption / desorption ability as the charge / discharge cycle progresses.
If it is less than 1, the effect is scarcely recognized, and if it exceeds 1.20, on the contrary, the hydrogen storage amount is reduced, so that it is selected within the above range.

Further, in the present invention, the negative electrode containing the hydrogen storage alloy as a main component must contain the hydrogen storage alloy at a density of at least 5.0 g / cm ³ . That is, if the content density is less than 5.0 g / cm ^3, it is not possible to ensure sufficient contact between the hydrogen-absorbing alloy powders constituting the negative electrode as the main component, and sufficient conductivity between the hydrogen-absorbing alloy powders and the conductive core. Is. That is, as described above, most of the hydrogen storage alloy powder in the negative electrode is effective for the battery reaction, because mutual contact of the hydrogen storage alloy powder is easily ensured, and the conductive core also exhibits good conductivity. Therefore, even if the capacity tends to slightly decrease with an increase in the composition ratio of Co atoms exhibiting the function of suppressing the deterioration,
Sufficient electrode capacity can be obtained.

Further, in the present invention, the capacity of the negative electrode containing the hydrogen storage alloy as a main component is set to 1.0 to 1.5 times the capacity of the positive electrode. The reason is Co
Since the addition of hydrogen chloride suppresses the decrease in hydrogen absorption / desorption capacity k as the battery cycle progresses, it is sufficient to set the capacity ratio of the negative electrode to 1.0 to 1.5 times the capacity of the positive electrode.

[0012]

According to the alkaline secondary battery of the present invention, the negative electrode containing the hydrogen storage alloy as the main component is accompanied by the progress of the charging / discharging cycle due to the Co atoms having the predetermined component ratio (atomic ratio) forming the hydrogen storage alloy. Effectively suppress the decrease of hydrogen absorption / desorption ability. On the other hand, in a negative electrode containing a hydrogen storage alloy as a main component, the battery reaction is effectively promoted due to good contact between the hydrogen storage alloy powders and the like, while increasing the capacity while suppressing the size increase of the alkaline secondary battery. It can be planned.

[0013]

Embodiments of the present invention will be described below with reference to FIG.

This example is for a nickel-hydrogen secondary battery with a theoretical capacity of 1200 mAh.

First, the formula, LmNi _4.4-x Co _x Mn _0.3
Hydrogen storage alloy powders represented by Al _0.3 (where x is 0.2, 0.5, 0.8, 1.2 or 1.6) were manufactured and annealed at 1000 ° C. for 10 hours in an inert atmosphere. Next, each of the hydrogen-absorbing alloy powders is screened, particles of 25 to 75 μm are taken out, and polytetrafluoroethylene as a binder is added to each of the hydrogen-absorbing alloy particles.
Six kinds of pastes were kneaded and prepared by adding sodium polyacrylate and carboxymethyl cellulose, carbon black as a conductive agent, and water. Then, the paste was applied to a punched metal, dried, pressed, and cut to prepare a hydrogen storage alloy electrode. In the paste coating / filling step, the paste coating / filling amount is adjusted to adjust the content density of the hydrogen storage alloy in the hydrogen storage alloy electrode to 4.0 g / cm ³ , 5.0 g / cm ³ , 6.0, respectively. g
There are 3 types of / cm ³ .

On the other hand, a paste containing nickel hydroxide and cobalt oxide was prepared, and the paste was filled / dried / pressed on a nickel-plated fiber substrate and cut to prepare a non-sintered nickel positive electrode.

An electrode group was prepared by winding and winding a laminate of the non-sintered nickel positive electrode, a 0.20 mm thick polyamide separator and a hydrogen storage alloy electrode (negative electrode). This electrode group is loaded into an AA size container, and potassium hydroxide (KOH
) After injecting 7N and lithium hydroxide (LiOH) 1N electrolyte solution and sealing it, 15 types of secondary batteries including a comparative example and a positive electrode capacity of 1200 mAh and a negative electrode capacity of 2000 mAh were assembled.

FIG. 1 is a partially cutaway sectional view showing the structure of the secondary battery. Reference numeral 1 denotes a positive electrode 1a having an external lead wire, a separator 1b, and a negative electrode 1c containing hydrogen storage alloy as a main component. An electrode group formed by winding, 2 is the electrode group 1
Is a cylindrical outer case (container) that also serves as a negative electrode terminal. Further, 3 is a sealing body which is fitted / installed in the opening of the cylindrical outer case 2 via a shield packing 4 to seal liquid tightly, and the sealing body 3 is a positive electrode terminal 3a, It has an insulating plate 3b and a safety valve 3c to constitute another structure. Further, 5 is in contact with the end face portion of the electrode group 1 in the cylindrical outer case 2 liquid-tightly sealed by the sealing body 3,
An internal insulating plate that insulates and fixes the electrode group 1, and a conductor portion 6 that electrically connects the external lead wire of the positive electrode 1a and the positive electrode terminal 3a of the sealing body 3. Regarding each of the assembled secondary batteries, at a high temperature of 45 ° C, charge: 1200mA, 90 minutes, discharge: 1200m
A, under the condition of accelerated cycle test with cut-off voltage of 1 V,
The cycle life was measured by repeating the charge and discharge and measuring the number of cycles required for the discharge capacity to become 900 mAh or less.

The results of the cycle life test are shown as the Co atom ratio in the hydrogen storage alloy, the hydrogen storage alloy density in the negative electrode, the first cycle capacity (initial capacity), the capacity ratio (negative electrode capacity mAh /
It is shown in Table 1 together with the positive electrode capacity mAh).

[0020]

[Table 1] As can be seen from Table 1 above, in the case of the nickel-hydrogen secondary battery according to the present invention, not only the initial capacity is high and the battery characteristics are excellent, but also the cycle life is long, and the capacity of the positive electrode and the negative electrode is large. The ratio is as low as 1.0 to 1.5, so it has an excellent function as a portable power supply.

Although an example of a nickel-hydrogen secondary battery with a theoretical capacity of 1200 mAh has been described above, the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention. For example, the positive electrode active material may be a metal oxide or hydroxide other than nickel hydroxide to which nickel hydroxide or cobalt oxide is added.

[0022]

As described above, according to the present invention,
It is possible to further improve the practicability of an alkaline secondary battery including a negative electrode containing a hydrogen storage alloy as a main component and using hydrogen as an active material of a negative electrode while using a metal oxide as a positive electrode active material. In other words, while many expectations and interests have been received in the past, the problem of charge / discharge cycle life, which has been regarded as a problem in practical use, and the problem of improving battery capacity while ensuring compactness have been resolved and improved. It can be said that it will greatly contribute to the promotion of practical use of alkaline secondary batteries.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view showing a structural example of a tubular alkaline secondary battery according to the present invention.

[Explanation of symbols]

1 …… Battery group 1a …… Positive electrode 1b …… Separator 1c …… Negative electrode 2 …… Cylindrical outer case 3 …… Encapsulation body 3a ……
Electrode terminal 3b …… Insulation plate 3c …… Safety valve
4 …… Seal packing 5 …… Internal insulating plate 6
……conductor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuta Takeno 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Co., Ltd.

Claims (1)

[Claims] 1. A positive electrode, an alkaline secondary battery comprising comprises a negative electrode and an alkaline electrolyte, the negative electrode wherein the _{LmNi w Co x Mn y Al z} ( where a rare earth element and Lm, including La Value of at least one element selected and atomic ratio w, x, y, z is 3.90 ≦ w ≦
4.50, 0.50 ≤ x ≤ 1.20, 0.28 ≤ y ≤ 0.50, 0.28 ≤ x ≤ 0.
50, 5.10 ≦ w + x + y + z ≦ 5.50) composed of a metal system containing 5.0 g / cm ³ or more of a hydrogen storage alloy and having a capacity ratio of 1.0 to 1.5 times the positive electrode. And alkaline secondary battery.