JPH08293304A - Manufacture of hydrogen storage alloy electrode for alkaline storage battery, and manufacture of alkaline storage battery - Google Patents

Abstract

PURPOSE: To manufacture a hydrogen storage alloy electrode capable of finishing the initial activation within a relatively short cycle with a small number of processes by filling a surface reformed alloy obtained by treating a hydrogen storage alloy containing a specified quantity of V or the like with alkali into a conductive base. CONSTITUTION: A hydrogen storage alloy containing 0.5-2.5 atomic % of at least one element selected from V, Ag, Sn, Zn, Pb, Cu and W is treated with alkali followed by drying to manufacture a surface reformed alloy. The hydrogen storage alloy has a CaCu5 type crystalline structure or a C14 or C15 type Laves phase crystalline structure. The surface reformed alloy is filled into a conductive base (foamed nickel porous body) to manufacture a hydrogen storage alloy electrode. Thus, a hydrogen storage alloy electrode capable of finishing the initial activation within a short recycle or omitting the initial activation is manufactured with a small number of processes.

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 hydrogen storage alloy electrode for an alkaline storage battery and a method for producing an alkaline storage battery.

[0002]

2. Description of the Related Art In recent years,
Alkaline storage batteries (metal / hydride alkaline storage batteries) that use a metal compound such as nickel hydroxide for the positive electrode and a hydrogen storage alloy that can store and release hydrogen electrochemically for the negative electrode have high energy density. From that,
It is attracting attention as a next-generation alkaline storage battery that replaces the nickel-cadmium storage battery.

Hydrogen storage alloys used in this battery include Mm-Ni type (Mm: misch metal), Ti-M.
n-based, Ti-Fe-based, Ti-Zr-based, Mg-Ni-based, Z
Various types such as r-Mn type have been proposed. These hydrogen storage alloys are produced by cooling and solidifying the molten alloy, but they are not produced in a completely non-oxidizing atmosphere because of the high equipment cost. Therefore, generally, an oxide film that causes a capacity decrease is present on the surface of the particles of the hydrogen storage alloy. Therefore, in order to obtain the original battery capacity, it was necessary to repeat charging and discharging for initial activation for several to several tens of cycles.

In order to reduce the number of charge / discharge cycles for initial activation, a surface modification treatment method has been proposed in which a hydrogen storage alloy is treated with hydrochloric acid to remove an oxide film existing on the surface of the particles (Japanese Patent Laid-Open No. Hei 10 (1999) -242977). No. 5-225975). But,
In the case of the hydrochloric acid treatment, a water washing process for removing the treatment liquid adhering to the hydrogen storage alloy must be provided as a post process.

On the other hand, the oxide film can be removed by an alkali treatment of immersing the hydrogen storage alloy in an alkaline aqueous solution. In this alkali treatment, there is no need to provide a washing step afterwards, so the surface modification treatment is performed with a small number of steps. There is an advantage that you can. However, it has a drawback that the effect of removing the oxide film is inferior to that of the hydrochloric acid treatment.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to obtain a hydrogen storage alloy electrode capable of completing initial activation in a relatively short cycle in a small number of steps. It is an object of the present invention to provide a method for producing a hydrogen storage alloy electrode for an alkaline storage battery capable of producing the same, and a method for producing an alkaline storage battery having a large initial discharge capacity with a reduced number of steps.

[0007]

A method for producing a hydrogen storage alloy electrode for an alkaline storage battery according to the present invention to achieve the above object is V, Ag, Sn, Zn, Pb, Cu and W.
0.5 at least one element selected from the group consisting of
A first step of subjecting a hydrogen storage alloy containing 0.5 to 2.5 atomic% to an alkali treatment and drying to produce a surface-modified treatment alloy;
A second step of filling the conductive substrate with the surface-modified alloy to produce a hydrogen storage alloy electrode.

Further, a method of manufacturing an alkaline storage battery according to the present invention to achieve the above object is V, Ag, Sn, Z.
A hydrogen storage alloy containing 0.5 to 2.5 atomic% of at least one element selected from the group consisting of n, Pb, Cu and W is alkali-treated and dried to produce a surface-modified alloy. A first step, a second step of filling the surface-modified alloy into a conductive substrate to produce a hydrogen storage alloy electrode, and a third step of producing an alkaline storage battery using the hydrogen storage alloy electrode as a negative electrode. With. In the following, the method for producing a hydrogen storage alloy electrode for an alkaline storage battery according to the present invention and the method for producing an alkaline storage battery according to the present invention will be collectively referred to as "the present method".

In the method of the present invention, V, Ag, Sn, Zn, Pb, C are used as the hydrogen storage alloy to be treated with alkali.
A material containing 0.5 to 2.5 atomic% of at least one element selected from the group consisting of u and W (hereinafter referred to as “additional element”) is used. However, when the hydrogen storage alloy contains Mm (mixture of rare earth elements), the atomic% is a value calculated with Mm as one atom. If the contents of these elements deviate from this range, the initial discharge capacity decreases and the number of charge / discharge cycles for initial activation increases.

Examples of the hydrogen storage alloy include alloys having a CaCu ₅ type crystal structure and those having a C14 type or C15 type Laves phase crystal structure.
These hydrogen storage alloys are generally obtained by cooling and solidifying a molten alloy, but in the present invention, as the hydrogen storage alloy to be alkali-treated, those containing an additional element are used. The hydrogen storage alloy containing the additional element is obtained by solidifying the molten alloy containing the additional element. By including these elements in the molten alloy, the additional elements can be uniformly contained in the entire alloy particles. On the other hand, the additive elements are concentrated on the surface of the alloy particles or the electrode surface, such as chemical plating, electrolytic plating, application of paste containing additive elements, and mixing of alloys containing additive elements with alloys to be alkali-treated. With such a method, surface modification (activation) by the subsequent alkali treatment is not sufficiently performed.

Conventionally known means can be used as the melting means for obtaining the molten alloy and the cooling means for solidifying the molten alloy. For example, an arc melting furnace, a high frequency induction melting furnace, or the like can be used as the melting means, and a normal cooling method or a rapid cooling method such as a roll method can be used as the cooling means. In addition, as the hydrogen storage alloy in the present invention, it is possible to use the one which is heat-treated (annealed) after being rapidly solidified. By heat treatment, the alloy structure is homogenized, and a hydrogen storage alloy that is hard to be pulverized even if the charge / discharge cycle is repeated can be obtained.

A specific example of the alloy having a CaCu ₅ type crystal structure is MmNi _x M ¹ _y M ² _z (wherein M ¹ is C
at least one element selected from o, Al and Mn,
M ² is at least one additive element selected from V, Ag, Sn, Zn, Pb and Cu, 3.0 ≦ x ≦ 5.2, 0
≦ y ≦ 1.7, 4.7 ≦ x + y ≦ 5.2, 0.5 / 10
0 ≦ z / (1 + x + y + z) ≦ 2.5 / 100)
But also C14 or C15 type Laves
s) Specific examples of alloys having a phase crystal structure include Ti
_1-a Zr _a Ni _p M ³ _q M ⁴ _r (wherein M ³ is Co, A
at least one element selected from 1, Mn, Mo, Cr and Fe, M ⁴ is V, Ag, Sn, Zn, Pb and C
at least one additional element selected from u, 0 ≦ a ≦
1, 1.0 ≦ p ≦ 2.0, 0.2 ≦ q ≦ 1.2, 1.8
≦ p + q ≦ 2.2, 0.5 / 100 ≦ z / (1 + p + q
+ R) ≦ 2.5 / 100), respectively.

[0013]

[Function] When a hydrogen storage alloy containing an additive element is treated with an alkali, the oxide film is removed, and at the same time, the additive element present on the surface of the particles of the hydrogen storage alloy is eluted into the alkali treatment liquid to provide a highly active alloy element. (For example, Ni) appears. Therefore, in the hydrogen storage alloy electrode obtained by the method of the present invention, initial activation can be completed in a short cycle, or initial activation can be omitted.

[0014]

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.

(Experiment 1) [Preparation of Hydrogen Storage Alloy] Mm, Ni, Co, Al, Mn
And additional element M (M is V, Ag, Sn, Zn, Pb, C
u or W) (both of which have a purity of 99.9% or more) in a molar ratio of 1.0: 3.1: 1.0: 0.3: 0.6: X (X =
0.01, 0.03, 0.05, 0.07, 0.10,
0.13, 0.15, 0.20), melted in an arc melting furnace in an argon gas atmosphere, then allowed to cool naturally and represented by the composition formula MmNi _3.1 CoAl _0.3 Mn _0.6 M _x. A lump (ingot) of a hydrogen storage alloy was produced.

[Preparation of Hydrogen Storage Alloy Electrode] A lump of each hydrogen storage alloy is mechanically crushed in air to obtain an average particle size of 80.
A hydrogen storage alloy powder having a size of μm was used. The hydrogen-absorbing alloy powder was immersed in a 30 wt% potassium hydroxide aqueous solution heated at 80 ° C for 2 hours for alkali treatment, and then the treatment liquid was suction-filtered, and the residue was dried to obtain an alkali-added alkali-treated alloy. A powder was made. Further, alloy powder (comparative alloy powder) was prepared as shown in the following (1) and (2).

(1) Preparation of additive-free alkali-treated alloy powder 30 wt% potassium hydroxide obtained by heating hydrogen storage alloy powder (average particle size 80 μm) represented by the composition formula MmNi _3.1 CoAl _0.3 Mn _0.6 to 80 ° C. After being immersed in the aqueous solution for 2 hours for alkali treatment, the treatment liquid was suction-filtered and the residue was dried to produce an additive-free alkali-treated alloy powder.

(2) Preparation of additive-free acid-treated alloy powder A hydrogen storage alloy powder (average particle size 80 μm) represented by the composition formula MmNi _3.1 CoAl _0.3 Mn _0.6 was dipped in 0.5N hydrochloric acid at room temperature for 30 minutes. After acid treatment with acid, the treatment liquid was suction-filtered, and the filtered material was washed with water and dried to prepare an additive-free acid-treated alloy powder.

Next, additive-free untreated alloy powder (additive-free alloy powder that was neither alkali-treated nor acid-treated) or the above-mentioned treated alloy powder (added-alkali-treated alloy powder, additive-free alkali-treated alloy powder or additive-free acid-treated) Alloy powder) 0.5
g and 0.1 g of PTFE (polytetrafluoroethylene) as a binder were filled in a foamed nickel porous body (conductive substrate) and pressure-molded at a molding pressure of 1.2 ton / cm ^2. A disk-shaped hydrogen storage alloy electrode having a diameter of 20 mm was produced.

[Assembly of Test Cell] Each hydrogen storage alloy electrode was used as a test electrode, a cylindrical sintered nickel electrode having a sufficiently large electrochemical capacity as compared with this test electrode was used as a counter electrode, and a plate-shaped electrode was used. A test cell was assembled using the sintered nickel electrode as a reference electrode. As the alkaline electrolyte, a 30 wt% potassium hydroxide aqueous solution was used.

FIG. 1 is a perspective view schematically showing the assembled test cell C. The test cell C shown in the drawing is a disc-shaped test electrode 2, a cylindrical sintered nickel electrode (counter electrode) 3, and a plate. It is composed of a sintered nickel electrode (reference electrode) 1, an insulating closed container (made of polypropylene) 4, and the like.

The sintered nickel electrode 3 has an upper surface 6 of a closed container 4.
Is held by a conductive tab 5 connected to the test electrode 2, and the test electrode 2 is connected to the upper surface 6 of the hermetically sealed container 4 such that the test electrode 2 is positioned vertically in the approximate center of the cylinder of the sintered nickel electrode 3. It is held by the tab 7.

The other ends of the conductive tab 5 and the conductive tab 7 penetrate the upper surface 6 of the closed container 4 and are exposed to the outside, and are connected to the external terminals 5a and 7a, respectively.

The test electrode 2 and the sintered nickel electrode 3 are immersed in an alkaline electrolyte (not shown) contained in a closed container 4, and the space above the alkaline electrolyte is filled with nitrogen gas. The internal pressure of the test cell is 5 kgf / cm ²
Is kept at.

At the center of the upper surface 6 of the closed container 4, a relief pipe 10 having a pressure gauge 8 for measuring the internal pressure of the closed container 4 and a relief valve 9 as a safety valve is mounted.

[Charge / Discharge Test] Each test cell was tested at room temperature for 5 minutes.
After charging for 8 hours at 0mA / g and resting for 1 hour, 50m
Discharge up to 0.9V at A / g and hydrogen storage alloy powder 1g
Initial discharge capacity per 1st cycle discharge capacity (m
Ah / g) was determined. The results are shown in Table 1.

[0027]

[Table 1]

Table 1 shows the alloy composition used in the test cell, the treatment method, each additive element M (vanadium V, silver Ag, tin S).
It shows the added amount x (atomic%) of n, zinc Zn, lead Pb, copper Cu, and tungsten W), and the initial discharge capacity (mAh / g) corresponding to these. First, the alloy MmNi
The initial discharge capacity of the test cell using _3.1 CoAl _0.3 Mn _0.6 as untreated was 197 mAh / g, and the alloy M
The initial discharge capacity of the test cell using mNi _3.1 CoAl _0.3 Mn _0.6 treated with alkali is 248 mAh /
g. On the other hand, the alloy MmNi _3.1 CoAl _0.3 Mn
The initial discharge capacity of each test cell of _0.6 M _x was used after alkali treatment is 255~285mAh / g. From these results, it can be seen that the alkali-treated alloy containing the additive element M has a large discharge capacity in a wide range of the additive amount x.

Next, the alloy MmNi _3.1 CoAl _0.3 Mn
The initial discharge capacity of the test cell using the acid-treated _0.6 is 264 mAh / g. On the other hand, the alloy MmNi _3.1
CoAl _0.3 Mn _0.6 M _x with an addition amount x of 0.03
To 0.15, that is, the added atomic% is 0.50
The initial discharge capacity of each test cell using an alkaline treatment in the range of 2.50 is 269 to 285 mA.
h / g (produced by the method according to the present invention). Therefore, the test cell using the alkali-treated alloy in which the added atomic% of the specific additional element M is in the range of 0.5 to 2.5 has a high capacity from the first cycle of charging and discharging, It can be seen that the discharge capacity is large. When the added amount x is less than 0.03, that is, the added atomic% is less than 0.50, or when the added amount exceeds 0.15, that is, when the added atomic% exceeds 2.50, Even if the alloy MmNi _3.1 CoAl _0.3 Mn _0.6 M _x treated with alkali was used, the initial discharge capacity of each test cell was 267 mAh / g or less, and the initial discharge capacity of the test cell using the acid-treated alloy was Is equivalent to

(Experiment 2) [Preparation of hydrogen storage alloy] Mm, Ni, Co, Al, Mn
And additional element M (M is V, Ag, Sn, Zn, Pb, C
u or W) (both of which have a purity of 99.9% or more) in a molar ratio
Mixed with 1.0: 3.1: 1.0: 0.3: 0.6: 0.1
And melt in an arc melting furnace in an argon gas atmosphere.
After cooling, let it cool naturally, and the composition formula is MmNi._3.1CoAl_0.3
Mn_0.6M _0.1A lump of hydrogen storage alloy represented by
Was produced.

[Production of Hydrogen Storage Alloy Electrode] A lump of each hydrogen storage alloy is mechanically crushed in air to obtain an average particle size of 80.
A hydrogen storage alloy powder having a size of μm was used. The hydrogen-absorbing alloy powder was treated with alkali in the same manner as in Experiment 1, the treatment liquid was suction-filtered, and the residue was dried to prepare an added alkali-treated alloy powder.

Next, non-added untreated alloy powder (non-added alloy powder that was neither alkali-treated nor acid-treated) or each treated alloy powder [added alkali-treated alloy powder, non-added alkali-treated alloy powder (prepared in Experiment 1 Same as additive alkali treated alloy powder) or additive-free acid treated alloy powder (Experiment 1
The same as the additive-free acid-treated alloy powder produced in [1]] 100
Parts by weight and 20 parts by weight of a 5% by weight aqueous solution of PEO (polyethylene oxide) as a binder are mixed to prepare a paste, and the paste is applied to both surfaces of a nickel-plated core made of punching metal. After being deposited and dried at room temperature, it was cut into a predetermined size to prepare a hydrogen storage alloy electrode.

[Assembly of Alkaline Storage Battery] AA size (AA type) positive electrode-dominated alkaline storage battery (battery capacity: 1000 mAh)
1-A7 and B1-B3 were produced. A conventionally known sintered nickel electrode was used as the positive electrode, an alkali resistant non-woven fabric was used as the separator, and a 30 wt% potassium hydroxide aqueous solution was used as the alkaline electrolyte.

FIG. 2 is a schematic cross-sectional view of the assembled alkaline storage battery A (same for other batteries). The illustrated alkaline storage battery A has a positive electrode 11 and a negative electrode (hydrogen storage alloy electrode) 1
2. A separator 13 for separating the two electrodes, a positive electrode lead 14, a negative electrode lead 15, a positive electrode external terminal 16, a negative electrode can 17 into which an alkaline electrolyte is injected, a sealing lid 18, and the like.

The positive electrode 11 and the negative electrode 12 are housed in the negative electrode can 17 in a spirally wound state with the separator 13 in between, and the positive electrode 11 is attached to the sealing lid 18 via the positive electrode lead 14 and also to the negative electrode 12. Is connected to a negative electrode can 17 via a negative electrode lead 15, and chemical energy generated inside the battery A can be taken out as electric energy to the outside. An insulating packing 20 is attached to the joint between the negative electrode can 17 and the sealing lid 18 to seal the battery.

A coil spring 19 is provided between the positive electrode external terminal 16 and the sealing lid 18 so as to be compressed when the internal pressure of the battery rises abnormally so that the gas inside the battery can be released to the atmosphere. It has become.

[Charge / Discharge Test] Each battery was charged at room temperature with a current of 0.2 C for 6 hours and then with a current of 0.2 C at 1.0 V.
The initial discharge capacity (first cycle discharge capacity) (mAh) was determined. The results are shown in Table 2.

[0038]

[Table 2]

Table 2 shows the composition, treatment method and initial discharge capacity (mAh) of each hydrogen storage alloy used in the alkaline storage batteries A1 to A7 and the comparative batteries B1 to B3 produced by the method according to the present invention. As shown in Table 2, the alkaline storage batteries A1 to A7 have an initial discharge capacity of about 800 mAh.
And has a much larger initial discharge capacity than the comparative batteries B1 to B3. The reason why the initial discharge capacities of the alkaline storage batteries A1 to A7 are so large is that the alloy in which the addition atomic% of the specific addition element M is in the range of 0.5 to 2.5 is used for the alkali treatment. . Comparative battery B
No. 1 is a battery using the alloy MmNi _3.1 CoAl _0.3 Mn _0.6 without treatment, and Comparative battery B 2 is the alloy Mm.
It is a battery using an alkaline-treated Ni _3.1 CoAl _0.3 Mn _0.6 , and the comparative battery B3 is an alloy Mm.
This is a battery that uses Ni _3.1 CoAl _0.3 Mn _0.6 treated with an acid.

According to the method for producing an alkaline storage battery of the present invention, it goes without saying that an alkaline storage battery having a large initial discharge capacity can be obtained, but the battery manufacturing process can be shortened as compared with the case of acid treatment. is there. The reason is that in the case of acid treatment, if acid such as hydrochloric acid, which is generally used in acid treatment, remains in the battery, it corrodes battery components and reduces battery performance. This is because the step of removing an acid such as hydrochloric acid needs to be provided before the battery assembly step, whereas this step is not necessary when the alkali treatment is performed.

[0041]

EFFECTS OF THE INVENTION According to the method for producing a hydrogen storage alloy electrode for an alkaline storage battery according to the present invention, hydrogen which can finish initial activation in a short cycle or omit initial activation. An occlusion alloy electrode can be obtained in a small number of steps. Further, according to the method for producing an alkaline storage battery of the present invention, it is possible to obtain an alkaline storage battery having a large initial discharge capacity with a small number of steps.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of the alkaline storage battery assembled in the example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Watanabe 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Shin Shin Fujitani 2-chome, Keihan-hondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Ikuro Yonezu 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. V, Ag, Sn, Zn, Pb, Cu and W
0.5 at least one element selected from the group consisting of
A first step of subjecting a hydrogen storage alloy containing 0.5 to 2.5 atomic% to an alkali treatment and drying to produce a surface-modified treatment alloy;
A second step of producing a hydrogen storage alloy electrode by filling the surface-modified alloy in a conductive substrate, and a method of producing a hydrogen storage alloy electrode for an alkaline storage battery. 2. The method for producing a hydrogen storage alloy electrode for an alkaline storage battery according to claim 1, wherein the hydrogen storage alloy has a CaCu ₅ type crystal structure or a C14 type or C15 type Laves phase crystal structure. 3. V, Ag, Sn, Zn, Pb, Cu and W
0.5 at least one element selected from the group consisting of
A first step of subjecting a hydrogen storage alloy containing 0.5 to 2.5 atomic% to an alkali treatment and drying to produce a surface-modified treatment alloy;
Alkaline storage battery comprising a second step of filling the conductive substrate with the surface-modified alloy to produce a hydrogen storage alloy electrode, and a third step of producing an alkaline storage battery using the hydrogen storage alloy electrode as a negative electrode. Of manufacturing. 4. The method for producing an alkaline storage battery according to claim 3, wherein the hydrogen storage alloy has a CaCu ₅ type crystal structure or a C14 type or C15 type Laves phase crystal structure.