JP2000340223A - Hydrogen storage alloy for alkaline storage battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve both of the initial discharge capacity and charge/discharge cycle characteristics by sticking an yttrium compound of fine holes formed in the surfaces of hydrogen storage alloy particles capable of reversibly storing/ releasing hydrogen. SOLUTION: Yttrium chloride 0 wt.% (no addition)-5.0 wt.% which is an yttrium compound is included in hydrogen storage alloy particles 1 using the hydrogen storage alloy particles. The hydrogen storage alloy particles 1 have fine holes 2 and the yttrium compound 3 is deposited and stuck to the fine hole 2. Preferably, the hydrogen storage alloy particles have CaCu5 crystal structure and those expressed by a compositional formula: MmNixCoyMnzM1-z are illustrated here. In the formula, M is Al or Cu; (x) is the abundance ratio of Ni, 3.0<=x<=5.2; (y) is the abundance ratio of Co, 0<y<=1.2; (z) is the abundance ratio of Mn, 0.1<=z<=0.9, and 4.4<=x+y+z<=5. Corrosion in the alkaline electrolyte can be suppressed in this composition range and hydrogen storage quantity is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy used as a negative electrode material for an alkaline storage battery, and more particularly to a hydrogen storage alloy electrode having a large initial discharge capacity and excellent charge-discharge cycle characteristics. The present invention relates to an improvement of a hydrogen storage alloy powder as an electrode material for the purpose.

[0002]

2. Description of the Related Art In recent years, nickel-metal hydride storage batteries that are twice as high as nickel-cadmium storage batteries and have excellent environmental compatibility have attracted attention as new alkaline storage batteries. However, with the spread of various portable devices, this nickel-hydrogen storage battery is expected to have higher performance. Here, the hydrogen storage alloy used for the negative electrode of the nickel-hydrogen storage battery generally has a coating such as an oxide formed on its surface by natural oxidation or the like, and the hydrogen storage alloy is manufactured using such a hydrogen storage alloy. However, when this hydrogen storage alloy electrode is used as a negative electrode of a nickel-metal hydride storage battery, there are problems such that the activity of the hydrogen storage alloy in the initial stage is low and the battery capacity in the initial stage is low.

For this reason, in recent years, for example,
As disclosed in Japanese Patent No. 225975, a method has been proposed in which a hydrogen storage alloy is immersed in an acidic solution such as hydrochloric acid to remove an oxide film on the surface of the hydrogen storage alloy.

Here, when the hydrogen storage alloy is immersed in an acidic solution to remove an oxide film or the like on the surface of the hydrogen storage alloy, active metal nickel (Ni), metal cobalt ( Co) and other parts appear. However, there is a problem that the active sites on the surface are oxidized again, the initial activity of the hydrogen storage alloy is not sufficiently improved, and the initial discharge capacity is still low.

[0005] Further, by removing the oxide film by the above method, sites such as active metals Ni and Co appear on the surface,
Because the electrochemical contact resistance between the alloy powders is reduced,
Although the initial discharge capacity is improved, the oxidation resistance has not been improved in the charge / discharge alkaline electrolyte.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to improve the initial discharge capacity and charge / discharge cycle characteristics used in nickel-metal hydride storage batteries. An object of the present invention is to provide a hydrogen storage alloy used for a hydrogen storage alloy electrode for an alkaline storage battery, which has both improved characteristics.

[0007]

SUMMARY OF THE INVENTION The present invention is a hydrogen storage alloy for an alkaline storage battery in which an yttrium compound is adhered to micropores formed on the surfaces of hydrogen storage alloy particles. The hydrogen storage alloy particles have a CaCu ₅ type crystal structure, and have a composition formula of MmNi _x Co _y Mn _z M _1-z [where M is aluminum (A
l), at least one element selected from copper (Cu), x
Is the abundance ratio of nickel (Ni), and 3.0 ≦ x ≦ 5.2, y
Is the abundance ratio of cobalt (Co) and 0 <y ≦ 1.2, z is the abundance ratio of manganese (Mn) and is 0.1 ≦ z ≦ 0.9, and the sum of x, y and z is 4.4 ≦ x + y + z ≦ 5.
4] can be exemplified as a typical example. When the composition is used as a hydrogen storage alloy in an alkaline storage battery in this composition range, corrosion in an alkaline electrolyte is suppressed, and an increase in the amount of hydrogen storage can be remarkably aimed at.

By filling the conductive core with the hydrogen storage alloy, a hydrogen storage alloy electrode for an alkaline storage battery is formed. Using these electrodes, an alkaline storage battery is formed.

Further, the present invention provides a first step of preparing hydrogen storage alloy particles capable of reversibly storing and releasing hydrogen, and adding an yttrium compound to the alloy particles prepared in the first step. Second immersion in acidic solution
Step, washing the alloy particles after the second step with water,
A method for producing a hydrogen storage alloy for an alkaline storage battery in which a hydrogen storage alloy is formed by drying, wherein the alloy particles are formed by depositing an yttrium compound in fine pores on the surface thereof. Things.

Here, the particles of the hydrogen storage alloy are CaCu
_FiveHaving a type crystal structure and a composition formula of MmNi_xCo _yMn_zM_1-z[Where M is
At least selected from aluminum (Al) and copper (Cu)
A kind of element, x is the abundance ratio of nickel (Ni).
0 ≦ x ≦ 5.2, y is the abundance ratio of cobalt (Co)
<Y ≦ 1.2, z is the abundance ratio of manganese (Mn) and is 0.1
≦ z ≦ 0.9, and the total value of the x, y, and z is 4.4 ≦
x + y + z ≦ 5.4].

In the second step, at least one of yttrium chloride (YCl ₃ ) and yttrium hydroxide (Y (OH) ₃ ) is used as an yttrium compound in an amount of 0.03 to 1.0 weight per weight of the alloy particles. %.

Furthermore, in the second step, the acidic solution has a pH of 0.7 to 2.0.

On the other hand, the hydrogen absorbing alloy particles may be prepared by using the first step as a gas atomizing method.

By filling a conductive core with the hydrogen storage alloy obtained by the method for producing a hydrogen storage alloy for an alkaline storage battery, a hydrogen storage alloy electrode for an alkaline storage battery can be provided.

By the way, in the second step, the particles of the hydrogen storage alloy are immersed and treated in an acidic solution to which the yttrium compound is added, so that the oxide on the surface of the particles is dissolved and removed, and is further generated by the dissolution. The yttrium compound precipitates in the micropores. The deposition of the yttrium compound is preferentially performed on the micropores on the surface of the hydrogen storage alloy as compared with other sites. The amount of yttrium compound added to the alloy particles should be 0.
The reason for setting the amount to 03 to 1.0% by weight is that if the amount is less than 0.03% by weight, the amount of the precipitated yttrium compound is small, and if the amount is more than 1.0% by weight, the amount of the precipitated yttrium compound becomes excessive, which inhibits the electrochemical reaction on the alloy surface. is there.

Further, in the second step, a suitable initial pH of the acidic aqueous solution is in the range of 0.7 to 2.0. If the pH is lower than 0.7, the oxidation of the alloy particles occurs rapidly, and the inside of the hydrogen storage alloy is melted.
This is because if it is higher, the oxide film is not sufficiently removed. Examples of the acidic aqueous solution used in the second step include hydrochloric acid, nitric acid, and phosphoric acid.

Thus, the hydrogen storage alloy according to the present invention having the structure shown in FIG. 1 is obtained. FIG. 1 is an explanatory view schematically showing the state of the hydrogen storage alloy of the present invention. In FIG. 1, the hydrogen storage alloy 1 has fine pores 2, and the yttrium compound 3 is deposited and adhered to the fine pores 2.

These effects can be expected not only for alloy particles produced and pulverized by an arc furnace in an argon atmosphere and alloy particles produced by a roll quenching method but also for alloy particles produced by a gas atomizing method.
In particular, the particles of the hydrogen storage alloy formed by the gas atomization method have a smooth surface and a small number of fine pores, so that by performing immersion treatment with an acidic aqueous solution, the specific surface area of the alloy particles is increased, and the reaction area in the battery is increased. It can be said that it can be increased and is suitable.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail together with comparative examples. However, the present invention is not limited to the following embodiments, and the present invention is carried out by appropriately changing the scope of the present invention. It is possible. (Experiment 1) In Experiment 1, the effect of the presence or absence of yttrium and the content thereof on the battery characteristics when the hydrogen storage alloy particles were treated in an acidic aqueous solution was examined. The result will be described below. The description will be made in the order of preparation of alloy particles, preparation of each sample, assembly of an alkaline storage battery, evaluation conditions of characteristics, and detailed results. [Preparation of MmNi _3.1 Co _0.9 Mn _0.6 Al _0.4 alloy particles] Mm (Misch metal Mm is a mixture of rare earth elements, La: 25% by weight, Ce: 50% by weight, Pr: 7% by weight, Nd: 18% by weight %), N
i, Co, Mn, Al (each elemental material is a simple metal with a purity of 99.9%) mixed in a molar ratio of 1.0: 3.1: 0.9: 0.6: 0.4, and roll quenched in an argon atmosphere to form a composition Formula MmNi
An alloy represented by _3.1 Co _0.9 Mn _0.6 Al _0.4 was produced. This alloy was mechanically pulverized in air to obtain alloy particles adjusted to an average particle size of 80 μm. [Samples A1 to A10] Using the above alloy particles, yttrium chloride (YCl ₃ ), which is an yttrium compound, is contained in an amount of 0% by weight (no addition) to 5.0% by weight based on the alloy particles, and pH =
It was immersed in a hydrochloric acid aqueous solution adjusted to 1.0 for 30 minutes and stirred. Then, suction filtration, washing and drying, sample A1 ~ sample A10
And As a result, yttrium chloride precipitates and adheres as an yttrium compound in which yttrium hydroxide and yttrium oxide are mixed.

On the other hand, as a comparative example, as shown in Japanese Patent Application Laid-Open No. 5-225975, a treatment solution containing a hydrochloric acid aqueous solution prepared at 0.5 N (pH = 0.3) and maintained at 25 ° C. Inside, the alloy particles were immersed and stirred for 30 minutes.
Thereafter, suction filtration, washing with water and drying were performed to obtain Comparative Sample X. [Assembly of Alkaline Storage Battery] A paste was prepared by mixing 100 parts by weight of each of the hydrogen storage alloys prepared above and 20 parts by weight of an aqueous solution of 5% by weight of PEO (polyethylene oxide) as a binder. This paste was applied (filled) on both surfaces of a conductive core made of punched metal plated with nickel and dried at room temperature. Thereafter, the resultant was cut into a predetermined size to prepare a hydrogen storage alloy electrode for an alkaline storage battery.

Using this hydrogen storage alloy electrode as a negative electrode,
AA-size positive electrode-dominated alkaline storage battery (battery capacity 1000
mAh). A conventionally known sintered nickel electrode as a positive electrode, an alkali-resistant nonwoven fabric as a separator,
In addition, a 30% by weight aqueous solution of potassium hydroxide was used as an electrolyte.

FIG. 2 is a schematic sectional view of the assembled alkaline storage battery. The positive electrode 11 and the negative electrode 12, the separator 13, the positive electrode lead 14, the negative electrode lead 15, the positive external terminal 16, the negative electrode can 17,
It consists of a sealing lid 18 and the like.

The positive electrode 11 and the negative electrode 12 are accommodated in a negative electrode can 17 while being spirally wound through a separator 13. The positive electrode 11 is connected to a sealing lid 18 via a positive electrode lead 14, and Numeral 12 is connected to a negative electrode can 17 via a negative electrode lead 15. An insulating packing 20 is attached to the joint between the negative electrode can 17 and the sealing lid 18 to hermetically seal the battery. A coil spring 19 is provided between the positive electrode external terminal 16 and the sealing lid 18 so that when the battery internal pressure rises abnormally, the battery is compressed and the gas inside the battery can be released to the atmosphere. [Evaluation Conditions for Characteristics] The initial discharge capacity at room temperature of each battery was determined. The conditions at this time are as follows. That is,
After charging each battery at a current value of 0.2 C for 6 hours at room temperature,
The cycle of discharging to 1.0 V at a current of 0.2 C was repeated twice to complete the activation of the battery. Thereafter, after charging at 1.0 C for 1.2 hours, the battery was discharged to 1.0 V at a current of 1.0 C, and the capacity was defined as an initial discharge capacity (mAh).

Further, the charge / discharge cycle characteristics of each battery were determined. The condition at this time is that after the battery activation is completed, each battery is charged at room temperature at a current value of 1.5 C for 0.8 hours, and then charged at a current value of 1.5 C for 1.0 hour.
The cycle of discharging to V is repeated, and the number of cycles when the discharge capacity becomes 75% of the designed capacity (1000 mAh) is actually measured. [Detailed Results] The initial discharge capacity and the high rate discharge capacity of each battery using the samples A1 to A10 and the comparative data X were obtained. Table 1 shows the results.

[0025]

[Table 1]

Samples A1 to A10 which were immersed in a hydrochloric acid aqueous solution to which no yttrium chloride (YCl ₃ ) was added or which was added at 5.0% by weight or less, all had an initial discharge capacity,
The charge / discharge cycle characteristics have a value larger than that of the comparative sample X.

In particular, in each battery using samples A2 to A8 in which the content of yttrium chloride (YCl ₃ ) is 0.03% by weight to 1.0% by weight, the initial discharge capacity is from 937 mAh to 965 mAh, and the charge / discharge cycle characteristics are 789. It showed a high value of 829 cycles from the cycle. Therefore, the addition amount of yttrium chloride (YCl ₃ ) is preferably 0.03% by weight based on the weight of the hydrogen storage alloy.
It is understood that the range of about 1.0% by weight is preferable.

In Experiment 1, in step 2 which is a process for preparing a hydrogen storage alloy, an aqueous hydrochloric acid solution was used as the acidic aqueous solution. However, the same tendency is observed with nitric acid and phosphoric acid. Although yttrium chloride (YCl ₃ ) was used as the yttrium compound, the same tendency is observed when yttrium hydroxide (Y (OH) ₃ ), which is another yttrium compound, is used. (Experiment 2) In Experiment 2, the pH of the acidic solution used in the second step of producing the hydrogen storage alloy was changed to examine the relationship with the battery characteristics.

Using the alloy particles prepared in the above Experiment 1, yttrium chloride (YCl ₃ ) was added to the alloy particles in an amount of 0.2%.
It was immersed and stirred in a hydrochloric acid aqueous solution containing 5% by weight and adjusted to pH = 0.3-3.0 for 30 minutes, filtered by suction, washed with water and dried.
Then, it was washed with water and dried to obtain a hydrogen storage alloy, and samples B1 to B6
Was prepared. Then, in the same manner as in Experiment 1, Sample B1
-B6 was used to produce a battery.

Table 2 shows the measurement results of the initial discharge capacity and the measurement results of the charge / discharge cycle characteristics of the batteries using the samples B1 to B6. The conditions for producing the battery and the conditions for measuring the capacity were the same as those in Experiment 1 described above.

[0031]

[Table 2]

After adding 0.5% by weight of yttrium chloride (YCl ₃ ), treating with a hydrochloric acid aqueous solution having a pH of 0.3 to 3.0, washing with water and drying, the batteries using the samples B1 to B6 according to the present invention include: The initial discharge capacity was from 920 mAh to 965 mAh, and the charge / discharge cycle characteristics were from 759 to 829 cycles.

In the batteries using the samples B3 to B5 treated at pH = 0.7 to 2.0, the initial discharge capacity shows 962 to 965 mAh, and the charge / discharge cycle characteristics show 817 to 829 cycles.
It can be seen that the charge / discharge cycle characteristics are excellent. Therefore, it is understood that the pH of the acidic solution is particularly preferably 0.7 to 2.0.

In Experiment 2, a hydrochloric acid aqueous solution was used as the acidic aqueous solution in Step 2 which is a manufacturing process of the hydrogen storage alloy. A similar tendency is observed with nitric acid and phosphoric acid. Although yttrium chloride (YCl ₃ ) is used as the yttrium compound, other yttrium compound, yttrium hydroxide (Y (OH) ₃ ) can be used.

In the examples, the alloy particles prepared by the roll quenching method are shown, but the same effect can be obtained by the alloy particles produced by the gas atomizing method.

[0036]

As described above in detail, according to the hydrogen storage alloy and the method for producing the same according to the present invention, the initial activity of the alloy is improved and the charge / discharge cycle characteristics are also improved. By forming an electrode using this alloy and using it for a negative electrode of a nickel-metal hydride storage battery, the initial discharge capacity is increased and the charge / discharge cycle characteristics are improved, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a hydrogen storage alloy of the present invention.

FIG. 2 is a schematic sectional view of an alkaline storage battery.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Hydrogen storage alloy particle 2 Micropore 3 Yttrium compound 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode lead 15 Negative electrode lead 16 Positive external terminal 17 Negative can 18 Sealing lid 19 Coil spring 20 Packing

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/26 H01M 4/26 J // H01M 10/30 10/30 Z (72) Inventor Yoshihiro Masuda Osaka 2-5-5 Keihanhondori, Moriguchi-shi, Sanyo Electric Co., Ltd. (72) Kikuko Kato 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Higashiyama Nobuyuki 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Mamoru Kimoto 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Yasuhiko Ito 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 4K017 AA04 BA03 BB07 BB12 CA07 DA09 EB08 4K018 BA05 BC24 BC28 BD07 KA38 5H003 AA02 AA04 BA01 BA02 BB02 BB04 BB07 BC01 BC05 BC06 BD04 BD06 5H016 AA05 BB09 EE01 5H028 AA02 EE01 FF04

Claims (10)

[Claims] 1. A hydrogen storage alloy for an alkaline storage battery in which an yttrium compound is attached to micropores formed on the surface of hydrogen storage alloy particles capable of reversibly storing and releasing hydrogen. Wherein said hydrogen absorbing alloy particles have a CaCu ₅ type crystal structure, a composition formula _{MmNi x Co y Mn z M 1} -z [ wherein M is selected from aluminum (Al), copper (Cu) X is an abundance ratio of nickel (Ni), and 3.0 ≦ x
≦ 5.2, y is the abundance ratio of cobalt (Co), and 0 <y ≦
1.2, z is the abundance ratio of manganese (Mn), and 0.1 ≦ z ≦
0.9, and the total value of the x, y, and z is 4.4 ≦ x + y +
2. The hydrogen storage alloy according to claim 1, wherein z ≦ 5.4]. 3. A hydrogen storage alloy electrode for an alkaline storage battery, wherein the conductive core is filled with the hydrogen storage alloy for an alkaline storage battery according to claim 1. 4. An alkaline storage battery using the hydrogen storage alloy electrode for an alkaline storage battery according to claim 3. 5. A first step of preparing hydrogen storage alloy particles capable of reversibly storing and releasing hydrogen, and placing the alloy particles prepared in the first step in an acidic solution containing an yttrium compound. A second step of immersing; and a method of manufacturing a hydrogen storage alloy for an alkaline storage battery in which a hydrogen storage alloy is formed by washing and drying the alloy particles after the second step, wherein the alloy particles have a surface thereof. A method for producing a hydrogen storage alloy for an alkaline storage battery, characterized in that an yttrium compound is precipitated in the fine pores of (1). Wherein particles of the hydrogen absorbing alloy has a CaCu ₅ type crystal structure, a composition formula _{MmNi x Co y Mn z M 1} -z [ wherein M is selected from aluminum (Al), copper (Cu) X is the abundance ratio of nickel (Ni), and 3.0 ≦
x ≦ 5.2, y is the abundance ratio of cobalt (Co), and 0 <y
≦ 1.2, z is the abundance ratio of manganese (Mn) and 0.1 ≦ z
≦ 0.9, and the sum of the x, y, and z is 4.4 ≦ x + y
+ Z ≦ 5.4], wherein the method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 5 is provided. 7. In the second step, at least one of yttrium chloride (YCl ₃ ) and yttrium hydroxide (Y (OH) ₃ ) is used as an yttrium compound in an amount of 0.03 to 1.0 weight based on the weight of the alloy particles. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 5, wherein 8. In the second step, an acidic solution is used.
The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 5, wherein the pH is 0.7 to 2.0. 9. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 5, wherein said first step is a gas atomization method. 10. A hydrogen storage alloy for an alkaline storage battery, characterized in that a conductive core is filled with the hydrogen storage alloy obtained by the method for producing a hydrogen storage alloy for an alkaline storage battery according to any one of claims 5 to 9. Manufacturing method of electrode.