JP3301879B2 - Hydrogen storage alloy electrode for sealed metal-hydride alkaline storage batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen-absorbing alloy electrode for a sealed metal-hydride alkaline storage battery, and more particularly to a sealed battery having a long charge-discharge cycle life and a small rise in battery internal pressure during overcharge. The present invention relates to an improvement in a hydrogen storage alloy for the purpose of providing a hydrogen storage alloy electrode capable of obtaining a type alkaline storage battery.

[0002]

2. Description of the Related Art In recent years,
A sealed metal / hydride alkaline storage battery that uses a metal compound such as nickel hydroxide for the positive electrode and a hydrogen storage alloy that can repeatedly store and release hydrogen in the negative electrode has an energy density per unit weight and unit volume. And high capacity can be achieved, it is attracting attention as a next-generation alkaline storage battery that replaces the nickel-cadmium storage battery.

As a hydrogen storage alloy used for this type of battery, an Mm-Ni-based hydrogen storage alloy is well known.
The battery characteristics largely depend on the characteristics of the Mm-Ni-based hydrogen storage alloy used. Because of this, M
Conventionally, attempts have been made to improve battery characteristics by replacing m or Ni with various elements.

For example, with respect to Mm, in order to improve various characteristics such as a discharge capacity, a temperature characteristic, and a charge / discharge cycle life, it has been proposed that a part of the Mm be replaced with another element to be multi-dimensional.

[0005] Further, Ni is partially replaced with Co in order to suppress the change in volume during charging and discharging of the alloy to prevent the alloy from falling off from the electrode and thereby improve the charging and discharging cycle life.
Alternatively, it has been proposed to replace a part of the alloy with Mn or Al in order to increase the hydrogen storage capacity (capacity) by substituting with Cu or lowering the hydrogen equilibrium pressure of the alloy.

However, despite the improvement of the hydrogen storage alloy as described above, in the conventional metal-hydride alkaline storage battery, when overcharged, the oxygen gas absorption reaction at the negative electrode (hydrogen storage alloy electrode) is rapidly performed. For this reason, there is a problem that the internal pressure of the battery increases.

The present invention has been made to solve this problem, and an object of the present invention is to provide a sealed metal-hydride alkaline storage battery in which the internal pressure of the battery hardly increases during overcharge. To provide a hydrogen storage alloy electrode.

[0008]

In order to achieve the above object, the hydrogen storage alloy electrode for a sealed metal-hydride alkaline storage battery according to the present invention (electrode of the present invention) is based on 1 mol of Mm (mish metal). To the molten metal of the Mm-Ni-based hydrogen storage alloy component containing 0.2 to 0.9 mol of Co,
After the addition of WNi ₃ , the Mm− having a CaCu ₅ type crystal structure containing W as a second phase, obtained by cooling and solidifying.
A Ni-based hydrogen storage alloy is used as a hydrogen storage material.

As a battery using a hydrogen storage alloy containing a second phase as a hydrogen storage material for a negative electrode, WM ₃ (M is N
Mm-N having a CaCu ₅ type crystal structure containing a second phase consisting of one or two elements selected from i and Co)
Japanese Patent Application Laid-Open No. 3-4677 discloses an i-type hydrogen storage alloy.
Have been proposed previously in No. 0, cells of this publication disclosure has been proposed to improve the load characteristics at low temperature, increase in the internal pressure of the battery in the second phase consisting of WM ₃ shown here Is not much suppressed.

In the present invention, the Mm—Ni-based hydrogen storage alloy having the CaCu ₅ type crystal structure is regulated to contain 0.2 to 0.9 mol of Co to 1 mol of Mm. When the Co content is less than 0.2 mol, the internal pressure of the battery is relatively hard to increase, but the corrosion resistance of the hydrogen storage alloy is reduced, so that the charge / discharge cycle life is shortened.
On the other hand, if the Co content exceeds 0.9 moles, increase in the internal pressure of the battery during overcharge because so is WM ₃ inferior in oxygen gas reduction ability to increase precipitated as the second phase sufficiently as compared with W This is because it becomes difficult to suppress them.

The Mm-Ni-based hydrogen storage alloy according to the present invention preferably contains the second phase [W (tungsten)] in a ratio of 0.01 to 0.15 mol per 1 mol of Mm. When the content of W is less than 0.01 mol,
Oxygen gas is not absorbed at a sufficient rate, making it difficult to sufficiently suppress the rise in battery internal pressure during overcharge. On the other hand, when the W content exceeds 0.15 mol, W is charged and discharged. The capacity is reduced because it is not involved.

In the present invention, WNi ₃ is added without adding W to the molten alloy. If W is added, W will form a solid solution in the mother phase, and will be added as the second phase. This is because precipitation is difficult.

[0013]

The hydrogen storage alloy having the second phase composed of W functions as a catalyst for promoting the oxygen gas absorption reaction (reaction in which the stored hydrogen reacts with oxygen to produce water) at the negative electrode. Therefore, by using the electrode of the present invention as a negative electrode of a metal-hydride alkaline storage battery, an increase in battery internal pressure during overcharge is suppressed.

[0014]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

(Experiment 1) [Preparation of hydrogen storage alloy] Mm (lanthanum content: 25% by weight), Ni, Co, Mn, Al (all of which have a purity of 99.9% or more) and WNi ₃ , which are alloy components, are weighed. Mix,
After melting in an arc melting furnace in an argon atmosphere,
By cooling and solidifying with a water-cooled mold, Mm-Ni-based hydrogen storage alloy blocks having CaCu ₅ type crystal structures of various compositions differing only in the W content were produced.

The cross sections of these Mm-Ni-based hydrogen storage alloy ingots were examined by EPMA and X-ray diffraction to confirm that a second phase composed of W was formed.

[Preparation of hydrogen storage alloy electrode] Each Mm-Ni
The hydrogen-absorbing alloy lump is mechanically pulverized under an inert gas (Ar gas) atmosphere into a powder having an average particle size of about 70 μm, and sieved to a maximum particle size of less than 150 μm (in the following Examples or Comparative Examples). Similarly, the maximum particle size was adjusted to less than 150 μm by the same operation.) Next, 90 parts by weight of this powder and 10 parts by weight of a 0.5% by weight aqueous solution of polyethylene oxide were kneaded to prepare a slurry,
The slurry was applied to a punching metal and dried to produce a hydrogen storage alloy electrode.

[Preparation of Battery] An AA size (AA) type sealed positive nickel-hydride alkaline battery (battery capacity: 1000 m) was used with each hydrogen storage alloy electrode as a negative electrode.
(Ah ± 10 mAh) A1 to A4 and B1 were prepared. A conventionally known sintered nickel electrode was used as the positive electrode, a nonwoven fabric made of polyamide was used as the separator, and a 30% by weight aqueous solution of potassium hydroxide was used as the alkaline electrolyte.

Table 1 shows the composition of the hydrogen storage alloy used for the batteries A1 to A4 and the battery B1.

[0020]

[Table 1]

<Battery internal pressure test after overcharge> Each battery was charged at 100 mA for 10 hours at room temperature (about 25 ° C.) for 10 hours and then discharged to 100 V at 1.0 mA twice to activate. Processed.

Next, a hole was made in the bottom of the outer can of each battery, and a pressure sensor was mounted.
In A), charging (150% charging) corresponding to 1.5 times (1500 mAh) of the battery capacity was performed, and the internal pressure of the battery (kg / cm ² ) after overcharging was measured. The results are shown in Table 1 above.

<Charge / Discharge Cycle Test> After activating each battery under the same conditions as above, the battery was subjected to 1500 mA (1.
After charging at 5C) until the battery voltage became 10 mV lower than the maximum voltage, a charge / discharge cycle test was performed in which the cycle of discharging to 1.0 V at 1500 mA was one cycle, and the charge / discharge cycle life of each battery was examined. The charge / discharge cycle life was determined as the number of cycles (times) until the discharge capacity was reduced to 50% or less of the initial capacity. The results are shown in Table 1 above.

As shown in Table 1, in the batteries A1 to A4, since the second phase promoted the oxygen gas absorption reaction and suppressed the oxidative deterioration of the alloy, the hydrogen storage alloy having no second phase was hydrogenated. The internal pressure of the battery at the time of overcharge is lower and the charge / discharge cycle life is longer than that of the battery B1 used as the storage material. Among the batteries A1 to A4, since the characteristics of the batteries A1 to A3 are excellent, it is understood that the molar ratio of W to 1 mol of Mm is preferably 0.01 mol or more.

(Experiment 2) Mm-Ni-based hydrogen storage alloys having CaCu ₅ type crystal structures of various compositions shown in Table 2 which differ from each other only in the W content were prepared.
Except that a Ni-based hydrogen storage alloy was used, an AA-size positive electrode-dominant sealed nickel-hydride alkaline battery (battery capacity: 1000 mAh ± 10
mAh) A5-A8 and B2 were prepared.

[0026]

[Table 2]

Next, the internal pressure of the battery after overcharge and the charge / discharge cycle life of each battery were examined under the same conditions as in Experiment 1. The results are shown in Table 2 above.

As shown in Table 2, Mm-Ni containing 0.4 mol of Co with respect to 1 mol of Mm (misch metal).
In the case of a system hydrogen storage alloy, as in Experiment 1, by using a material having a second phase composed of W as a hydrogen storage material, a battery having a low internal pressure during overcharge and a long charge / discharge cycle life can be obtained. It can be seen that it is obtained.

(Experiment 3) Mm-Ni-based hydrogen storage alloys having CaCu ₅ type crystal structures of various compositions shown in Table 3 were prepared, which differ only in the W content.
5 parts by weight of polytetrafluoroethylene powder was added to 100 parts by weight of the Ni-based hydrogen storage alloy, kneaded, and rolled to prepare a paste. A predetermined amount of the paste was wrapped in a nickel mesh and pressed to produce a disk-shaped test electrode.

[0030]

[Table 3]

Next, a test cell was assembled using these test electrodes as negative electrodes and cylindrical sintered nickel electrodes having a sufficiently large capacity with respect to the negative electrodes as positive electrodes.

FIG. 1 is a schematic perspective view of the assembled test cell C. The illustrated test cell C has a disk-shaped test electrode 2, a cylindrical sintered nickel electrode 3, and an insulating closed container. 4
Etc.

The sintered nickel electrode 3 is held by a positive electrode lead 5 connected to the upper surface 6 of the closed container 4, and the test electrode 2 is positioned substantially vertically in the center of the cylinder of the sintered nickel electrode 3. As shown in the figure, the negative electrode 7 is held by a negative electrode lead 7 connected to the upper surface 6 of the closed container 4.

Each end of the positive electrode lead 5 and the negative electrode lead 7 penetrates the upper surface 6 of the closed container 4 and
a and the negative electrode terminal 7a.

The test electrode 2 and the sintered nickel electrode 3 are immersed in an alkaline electrolyte (30% by weight aqueous solution of potassium hydroxide; not shown) contained in a closed container 4, and a space above the alkaline electrolyte is provided. The portion is filled with nitrogen gas so that a predetermined pressure (5 atm) is applied to the test electrode 2.

In the center of the upper surface 6 of the closed container 4,
In order to prevent the internal pressure of the sealed container 4 from rising above a predetermined pressure, a relief pipe 10 having a pressure gauge 8 and a relief valve 9 is mounted.

For these test cells, a current of 50 mA
/ G for 8 hours and rest for 1 hour, then current 100m
The charge / discharge cycle in which the step of discharging to 1.0 V at A / g was defined as one cycle was repeated five times, and the maximum discharge capacity in the five cycles was determined as the discharge capacity of these batteries. The results are shown in Table 3 above.

As shown in Table 3, as the W content increases, the discharge capacity decreases, and particularly when the content ratio of W to 1 mol of Mm exceeds 0.15 mol, the discharge capacity significantly decreases. . From this and the experiment 1, in order to suppress the increase in the internal pressure of the battery at the time of overcharging without substantially lowering the discharge capacity, the content of W is set to 0.01 to 0.15 mol with respect to 1 mol of Mm. Is preferable.

(Experiment 4) W was set to 0.0 with respect to 1 mol of Mm.
5 contains a molar ratio of, was prepared and then the Mm-Ni-based hydrogen storage alloy having a CaCu ₅ type crystal structure of various compositions only content shown in different table 4 mutually Co in the same manner as in Experiment 1. As a comparative alloy, a Mm-Ni-based hydrogen storage alloy having a CaCu ₅ type crystal structure containing no W and containing 0.2 mol of Co with respect to 1 mol of Mm in the same manner as in Experiment 1 was used. Produced. Each of these Mm-N
AA-size positive electrode-dominant sealed nickel-hydride alkaline battery (battery capacity: 100) was prepared in the same manner as in Experiment 1 except that an i-type hydrogen storage alloy was used as a hydrogen storage material.
0 mAh ± 10 mAh) A9 to A14 and B3 were prepared.

[0040]

[Table 4]

Next, each battery was subjected to a battery internal pressure test and a charge / discharge cycle test after overcharging under the same conditions as in Experiment 1. The results are shown in Table 4 above. Note that Table 4 also shows the results of Battery A6 produced in Experiment 2 transcribed from Table 2.

As can be seen from Table 4, when the Co content is in the range of 0.2 to 0.9 mol per 1 mol of Mm, the increase in the internal pressure of the battery at the time of overcharging is small and the charge / discharge cycle life is long. Is obtained.

(Experiment 5) In the same manner as in Experiment 1, except that a hydrogen storage alloy having a non-stoichiometric composition shown in Table 5 was used as the hydrogen storage material, an AA-size positive electrode-dominated closed type nickel / hydride was used. Alkaline battery (battery capacity: 1000 mA
h ± 10 mAh) A9 to A14 and B3 were prepared.

[0044]

[Table 5]

Next, each battery was subjected to a battery internal pressure test after overcharge and a charge / discharge cycle test under the same conditions as in Experiment 1. The results are shown in Table 5 above. Table 5 also shows the results of Battery A6 produced in Experiment 2 transcribed from Table 2 for reference.

In Table 5, the reason why the charge / discharge cycle life of the battery A14 is shorter than that of the batteries A6, A12 and A13 is as follows.
This is because the content of Co is small, so that the corrosion resistance of the alloy itself is low, and the battery internal pressure after overcharging of the batteries A9 to A11 is higher than that of the batteries A6, A12, and A13.
This is because WCo _{3, which} is inferior in catalytic ability to promote the oxygen gas absorption reaction as compared with W, was produced in a large amount as the second phase due to the excessive content of W.

As can be seen from Table 5, the hydrogen storage alloy having a non-stoichiometric composition also has a small increase in the internal pressure of the battery during overcharge by using an alloy having a second phase composed of W as the hydrogen storage material for the negative electrode. Further, it can be seen that a battery having a long charge / discharge cycle life can be obtained.

In the above embodiment, the molten alloy is cooled and solidified by a water-cooled mold. However, the present invention is not particularly limited to cooling means, and other cooling means such as a roll method and an atomizing method can be used. It is.

[0049]

Since the hydrogen storage alloy to be used has the second phase for promoting the oxygen gas absorption reaction, the electrode of the present invention quickly absorbs the oxygen gas generated during overcharge. Therefore, by using the electrode of the present invention as a negative electrode of a metal-hydrogen alkaline storage battery, it is possible to obtain a battery in which the internal pressure of the battery during the overcharge is small.

[Brief description of the drawings]

FIG. 1 is a perspective view of a test cell assembled in an example.

[Explanation of symbols]

 C Test cell 2 Test electrode 3 Sintered nickel electrode 4 Closed vessel

──────────────────────────────────────────────────続 き Continuing on the front page (72) Yasushi Kuroda 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Kozo Nogami 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi City, Osaka Prefecture Inside Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5, Keihanhondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. (56) References JP-A-5-151967 (JP, A) JP-A-6-231763 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/38 H01M 4/24 H01M 10/30

Claims (2)

(57) [Claims] (1) C per mole of Mm (misch metal)
Ca is obtained by adding WNi ₃ to a molten metal of an Mm-Ni-based hydrogen storage alloy component containing 0.2 to 0.9 mol of o, cooling and solidifying, and containing W as a second phase.
A hydrogen storage alloy electrode for a sealed metal-hydride alkaline storage battery, wherein an Mm-Ni-based hydrogen storage alloy having a _5- type crystal structure is used as a hydrogen storage material. 2. The method according to claim 1, wherein the Mm-Ni-based hydrogen storage alloy comprises:
The hydrogen storage alloy electrode for a sealed metal-hydride alkaline storage battery according to claim 1, which is contained in a proportion of 0.01 to 0.15 mol per mol of mol.