JP3499923B2 - Hydrogen storage alloy electrode for metal-hydride alkaline storage batteries and hydrogen storage alloy particles for metal-hydride alkaline storage batteries - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a hydrogen storage alloy electrode for a metal-hydride alkaline storage battery.

[0002]

2. Description of the Related Art In recent years,
Metal-hydride alkaline storage batteries using a hydrogen storage alloy electrode as a negative electrode are lighter than conventional storage batteries such as nickel-cadmium storage batteries and lead storage batteries, and have the potential for higher capacity. Has been done.

As a hydrogen storage alloy for hydrogen storage alloy electrodes, LaNi ₅ , LaNi ₄ Co and LaNi ₄ C are used.
In addition to u, LaNi _4.8 Fe _0.2, and the like, various rare earth-based hydrogen storage alloys have been proposed, such as those in which La in these alloys is replaced with Mm (Misch metal).

However, in the metal-hydride alkaline storage battery using these hydrogen storage alloys as they are as an electrode material, the hydrogen storage alloys are not easily corroded due to the poor corrosion resistance of the hydrogen storage alloys. Since the surface is oxidized and deteriorated, there is a problem that the battery life is generally short.

In order to prevent oxidative deterioration of the hydrogen storage alloy and prolong battery life, the surface of the hydrogen storage alloy is coated with an electroless nickel plating film (phosphorus content in the plating film: 8% by weight). Has been previously proposed (Japanese Patent Laid-Open No. Sho 61-61).
No. 163569).

However, when the surface of the particles of the hydrogen storage alloy is coated with such an electroless nickel plating film having a low phosphorus content, the plating film is an unporous and dense film having high crystallinity, so that activation is activated. Cracks are less likely to occur during the treatment, and the activation treatment requires a long time. Further, when the surface of the particles of the hydrogen storage alloy is covered with the dense nickel film in this manner, the absorption of oxygen gas generated during overcharge is delayed, and the internal pressure of the battery rises. Furthermore, the hydrogen storage alloy is oxidized by the generated oxygen gas, so that the battery life is not significantly extended.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a long battery life,
Another object of the present invention is to provide a hydrogen storage alloy electrode for obtaining an alkaline storage battery in which the internal pressure of the battery is unlikely to rise and the activation treatment can be completed in a short time.

[0008]

A hydrogen storage alloy electrode for a metal-hydride alkaline storage battery according to the present invention (hereinafter, referred to as "the electrode of the present invention") for achieving the above object is provided.
A hydrogen storage alloy electrode using a hydrogen storage alloy having an electroless nickel plating layer formed on a particle surface as an electrode material, wherein the electroless nickel plating layer is a porous coating film containing 11 to 14% by weight of phosphorus. The hydrogen storage alloy particles for a metal-hydride alkaline storage battery according to the present invention are porous films containing 11 to 14% by weight of phosphorus.
A certain electroless nickel plating layer is formed on the particle surface.

The phosphorus content of the electroless nickel plating layer in the present invention is regulated to 11 to 14% by weight for the following reason. That is, when the phosphorus content is less than 11% by weight, the crystallinity of the plating film is too high and the film becomes an unporous and dense film, which requires a long time for initial activation. Therefore, those having an electroless nickel plating layer having a phosphorus content of about 8 to 10% by weight, which is a general decorative plating, are excluded from the present invention. On the other hand, when the phosphorus content exceeds 14% by weight, the plating film becomes brittle and easily peels off from the hydrogen storage alloy, so that the effect of preventing oxidative deterioration of the hydrogen storage alloy due to electroless nickel plating decreases.

The electroless nickel plating can be carried out, for example, using a conventionally known electroless nickel plating bath using sodium hypophosphite as a reducing agent. However, as in the present invention, the electroless nickel plating having a considerably high phosphorus content is used. In order to form a nickel plating layer on the surface of particles of a hydrogen storage alloy,
It is necessary to increase the amount of sodium hypophosphite added to the plating bath, as compared with ordinary electroless nickel plating.

[0011]

Since the nickel plating layer containing a specific amount of phosphorus is formed on the surface of the particles of the hydrogen storage alloy, the hydrogen storage alloy is less likely to be oxidized and deteriorated even if the charge / discharge cycle is repeated. In addition, the nickel plating layer is a porous film having a high phosphorus content of 11 to 14% by weight as compared with ordinary electroless nickel plating, that is, a low crystallinity,
The gas absorption characteristics are excellent, and the reaction (charge / discharge reaction) between the electrolytic solution and the hydrogen storage alloy is not easily hindered. For this reason,
The activation process can be completed in a short time, and the internal pressure of the battery is less likely to rise during overcharge.

[0012]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible.

[Preparation of Hydrogen Storage Alloy Electrode] A hydrogen storage alloy (MmNi _3.2 Co _1.0 Al _0.6 Mn _0.2 ) was electrolessly nickel-plated using the plating bath shown in Table 1 and electroless with different phosphorus contents on the particle surface. Fifteen types of hydrogen storage alloys having nickel plated layers were prepared. Table 2 shows the phosphorus content of the electroless nickel plating layer of each hydrogen storage alloy.
The phosphorus content is ICP (Inductively Coupled Plasma Ato)
mic Emission Spectrometry).

[0014]

[Table 1]

[0015]

[Table 2]

Next, PEO (polyethylene oxide) as a binder was added to 100 parts by weight of each of the above hydrogen storage alloys.
1.0 part by weight and a small amount of water were added and mixed uniformly to prepare a paste. The paste was evenly applied to both sides of a nickel-plated punching metal (current collector) and dried,
It rolled and produced the hydrogen storage alloy electrode.

[Assembly of Nickel-Hydride Alkaline Storage Battery] The hydrogen storage alloy electrode as a negative electrode and a known sintered nickel electrode as a positive electrode are wound around an alkali-resistant separator to form a spiral electrode body. This swirl electrode body was inserted into a battery can, and a 30 wt% potassium hydroxide aqueous solution was poured into the battery can and sealed to obtain a capacity of 1000 mA.
h Cylindrical sealed nickel-hydride alkaline storage battery A
Assembled O. For comparison, a nickel-hydride alkaline storage battery X was similarly assembled separately using a hydrogen storage alloy that was not electrolessly nickel-plated.

[Charge / Discharge Cycle Test] After charging each nickel-hydride alkaline storage battery at 0.1 C for 15 hours,
The battery was discharged at 0.1 C until the battery voltage became 1 V, and the discharge capacity of each was measured. The results are shown in Table 2 and FIG. 1 above. FIG. 1 shows the charge / discharge cycle immediately after battery assembly of each storage battery, that is, the discharge capacity of the first cycle, the vertical axis shows the discharge capacity (mAh) of the first cycle, and the horizontal axis shows the hydrogen absorption used for each storage battery. It is the graph which took and showed the phosphorus content rate (%) of the electroless nickel plating layer of an alloy.

As shown in Table 2 and FIG. 1, when the phosphorus content of the electroless nickel plating layer is 11 to 14% by weight,
The discharge capacity immediately after the battery was assembled was large at 630 to 660 mAh, but when the phosphorus content ratio was outside this range, the discharge capacity was small. When the phosphorus content is as low as less than 11% by weight, the discharge capacity becomes small because the dense electroless nickel film with high crystallinity was formed so as to cover the particle surface of the hydrogen storage alloy. This is because the contact between the alloy and the electrolytic solution was insufficient and a smooth charge / discharge reaction was not performed.

Next, each nickel-hydride alkaline storage battery was further charged and discharged 10 times under the same conditions as above to activate the negative electrode.

After the activation treatment, each of these nickel-hydride alkaline storage batteries was subjected to a charge / discharge cycle test in which one cycle includes a process of charging at 1C for 1.2 hours and then discharging at 1C to 1V, and each storage battery was tested. I checked the battery life. The battery life was evaluated by the number of cycles (cycles) up to that point, when the time at which the capacity decreased to 60% or less of the capacity at the first cycle at 1 C charge / discharge was determined to be the life of the storage battery. The results are shown in Table 2 above and FIG. FIG. 2 shows the battery life of each storage battery, the battery life (times) on the vertical axis, and the phosphorus content (%) of the electroless nickel plating layer of the hydrogen storage alloy used on each storage battery on the horizontal axis. It is the graph shown.

As shown in Table 2 and FIG. 2, when the phosphorus content of the electroless nickel plating layer is 11 to 14% by weight,
The battery life is as long as 800 to 860 times, but when the phosphorus content rate is out of this range, the battery life is shortened. When the phosphorus content is as low as less than 11% by weight, the battery life is shortened because the contact between the hydrogen storage alloy and the electrolyte was insufficient and a smooth charge / discharge reaction was not performed. Is generated, and the hydrogen storage alloy reacts with this oxygen gas and is oxidized and deteriorated. Further, when the phosphorus content is higher than 14% by weight, the battery life is shortened because a part of the electroless nickel plating film is peeled off from the hydrogen storage alloy and the corrosion resistance of the hydrogen storage alloy is lowered. Is.

[Battery internal pressure test during overcharge] Nickel
A hydride alkaline storage battery was charged at 1 C for 120%, and the battery internal pressure of each storage battery was measured. The results are shown in Table 2 and FIG.
Shown in. Fig. 3 shows the battery internal pressure of each storage battery after 120% charging at 1C, the vertical axis shows the battery internal pressure (atmospheric pressure), and the horizontal axis shows the phosphorus of the electroless nickel plating layer of the hydrogen storage alloy used for each storage battery. It is the graph which took and showed the content rate (weight%).

As shown in Table 2 and FIG. 3, when the phosphorus content is 11 to 14% by weight, the battery internal pressure after overcharge is 4.
It is as low as 0 to 6.5 atm. It is considered that this is because a porous plating film having a higher phosphorus content, that is, a lower crystallinity, works more effectively as a gas absorption catalyst. On the contrary, when the phosphorus content exceeds 14% by weight, the internal pressure of the battery becomes high because the plating coating becomes brittle because the phosphorus content is too high and a part of the electroless nickel plating coating is a hydrogen storage alloy. It is considered that the catalytic action of the plating film on the absorption of oxygen gas was reduced as a result.

In the above-mentioned embodiment, the electrode of the present invention is nickel-plated.
Although the case where it is used as the negative electrode of a hydride alkaline storage battery has been described as an example, the electrode of the present invention can be widely used as a negative electrode of a metal-hydride alkaline storage battery.

[0026]

EFFECTS OF THE INVENTION Since the nickel plating layer containing a specific amount of phosphorus is formed on the surface of the particles of the hydrogen storage alloy, the hydrogen storage alloy is less likely to undergo oxidative deterioration even after repeated charge / discharge cycles, and this nickel plating layer Is a porous film having a high phosphorus content and low crystallinity, so that the charge / discharge reaction is not easily hindered and the internal pressure of the battery is unlikely to rise even when overcharged. Therefore, by using the electrode of the present invention as the negative electrode of a metal-hydride alkaline storage battery, the battery life is long, the internal pressure of the battery is unlikely to rise, and the activation treatment can be completed in a short time. It will be possible to obtain.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the phosphorus content of an electroless nickel plating layer and the discharge capacity immediately after battery assembly.

FIG. 2 is a graph showing the relationship between the phosphorus content of the electroless nickel plating layer and the battery life.

FIG. 3 is a graph showing the relationship between the phosphorus content of the electroless nickel plating layer and the battery internal pressure after overcharging.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kozo Nogami 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 within Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-61-163569 (JP, A) JP 61-64069 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/24 H01M 4/38 H01M 10/30

Claims (2)

(57) [Claims] 1. A hydrogen storage alloy electrode using a hydrogen storage alloy having an electroless nickel plating layer formed on the particle surface as an electrode material, wherein the electroless nickel plating layer contains 11 to 14% by weight of phosphorus. Hydrogen storage alloy electrode for a metal-hydride alkaline storage battery, which is characterized by a different coating . 2. A porous material containing 11 to 14% by weight of phosphorus.
Hydrogen storage alloy particles for a metal-hydride alkaline storage battery , in which an electroless nickel plating layer that is a simple coating is formed on the particle surface.