JP2735909B2 - Method for producing hydrogen storage alloy powder for secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for producing a hydrogen storage alloy powder used as a negative electrode of an alkaline secondary battery and a metal-coated powder thereof.

[Prior art]

The composition of the hydrogen storage alloy used as the negative electrode of the alkaline secondary battery has been proposed in various ways such as Fe-Ti type and Ti-Mn type, but it has a CaCu _5- type hexagonal structure represented by LaNi ₅ which is the most excellent in characteristics. Rare earth based alloys are mainly used. On the other hand, the hydrogen storage alloy is used in a powder state in order to make large use of the surface area of the hydrogen storage alloy when performing a specific hydrogen storage / desorption reaction. Rare earth metal-containing hydrogen-absorbing alloy powders can be produced by melting and alloying by arc melting or high-frequency melting, then casting, and then mechanically pulverizing or self-expanding due to volume expansion and contraction associated with hydrogen storage and desorption. There is a method of obtaining powder by utilizing disintegration. When the hydrogen-absorbing alloy powder thus obtained is used for a secondary battery electrode, the hydrogen-absorbing alloy powder itself becomes finer due to self-disintegration due to volume expansion and contraction accompanying the hydrogen-absorbing and desorbing reaction. Problems such as a decrease in the devolatilization function, a decrease in the thermal conductivity, and a decrease in the electrical conductivity become problems. As a countermeasure for this problem, there has been proposed a method of coating the hydrogen storage alloy powder with a metal having excellent electric conductivity and heat conductivity such as Cu. As a method for producing the metal-coated hydrogen storage alloy powder, a method is generally used in which a predetermined metal is coated on the hydrogen storage alloy powder pulverized after melting and casting as described above by electroless plating.

[Problems to be solved by the invention]

However, rare earth alloys basically have an economic disadvantage that their raw material costs are higher than other alloy systems in nature. Further, when alloying by an arc melting method or a high frequency melting method, a chemically active and expensive rare earth metal must be used as a raw material. Further, there is a problem in operation safety that an alloy extremely active against oxidation containing a rare earth metal must be pulverized even after melting and casting. In addition, when metal coating is performed on the hydrogen-absorbed alloy powder that has been mechanically pulverized by an electroless plating method, the rare-earth-based alloy requires an oxide film removal step on its surface. This is very disadvantageous in the mass production process because it is completely divided into the electroless plating process.

[Means for Solving the Problems]

In order to solve the above problems, in the method for producing a hydrogen storage alloy powder for a secondary battery according to the present invention, La, Ce, Nd, a hydrogen storage alloy powder containing Ni as a main component and at least one of misch metals. At the time of producing, La, Ce, Nd, at least one kind of powder among misch metal and Ni powder having a Fischer particle size of 3 to 10 μm were mixed and obtained at a temperature of 950 to 1000 ° C. by a reduction diffusion method. A hydrogen storage alloy powder is produced by washing the reduced diffusion product with water and disintegrating it in water. Further, in the method for producing a hydrogen storage alloy powder for a secondary battery of the present invention, when mixing at least one powder of La, Ce, Nd, and misch metal with Ni powder, anhydrous CaCl ₂ is used as a flux. Up to 15% can be added to promote underwater disintegration. Further, in the method for producing a hydrogen storage alloy powder for a secondary battery according to the present invention, at least one powder of La, Ce, Nd, and misch metal is mixed with a Ni powder having a Fischer particle diameter of 3 to 10 μm, and the resultant is subjected to reduction diffusion. The process can be shifted directly from the water washing step of washing the reduced diffusion reactant obtained at a temperature of 950 to 1000 ° C. to the electroless plating step to coat the hydrogen storage alloy powder with a metal.

[Action]

LaNi ₅ which is a rare earth hydrogen storage alloy representative of the present invention
The production of the hydrogen storage alloy powder by applying to the alloy and the metal coating on the hydrogen storage alloy powder will be described in detail. Therefore, what follows is described by L
a, Ce, Nd, and misch metal group
e, Nd, and misch metal can be similarly considered. Since a metal oxide is used as a part of the raw material in the reduction diffusion method, La ₂ O ₃ powder is used as a La raw material when producing a hydrogen storage alloy powder composed of LaNi ₅ . in this way,
In the reduction diffusion method, a metal that is extremely active against oxidation, such as a rare earth metal, can be used as a chemically stable oxide. Therefore, it is safe in industrial production, and can use economical raw materials, and is economical. Note that there is no significant difference in the dimensions of the La ₂ O ₃ powder in relation to the effects of the present invention. Ni is made from Ni powder metal powder having a Fischer particle size of 3 to 10 μm as a raw material. When a Ni powder having a Fischer particle size larger than 10 μm is used, it is necessary to perform a diffusion reduction reaction at a temperature higher than 1000 ° C. in order to diffuse La into Ni and obtain a LaNi ₅ uniform structure. However, in this case, although a uniform phase of LaNi ₅ can be obtained as an alloy phase, the sintering reaction proceeds and the yield as a hydrogen storage alloy powder deteriorates. Conversely, when a Ni powder having a Fischer particle size of less than 3 μm is used, a sufficient reduction-diffusion reaction cannot be performed at a temperature of less than 950 ° C., and at a temperature of 950 ° C. or more, the reduction-diffusion reaction proceeds sufficiently. Since the particle diameter is small, sintering becomes easy, sintering proceeds even at a relatively low temperature, and the yield as an alloy powder deteriorates. Further, when the diffusion reduction reaction is performed at a temperature higher than 1000 ° C. or when Ni powder having a Fischer particle size of less than 3 μm is used, when the diffusion reduction reaction is performed at a temperature of 950 ° C. or more, Ca as a reducing agent and by-product It is not preferable because the Ca and O grades in the alloy powder are increased due to the generation of the sintered powder in which the CaO bites. For these reasons, in order to allow the reduction diffusion reaction to proceed promptly, Ni powder having a Fischer particle diameter of 3 to 10 μm is used, and the reduction diffusion reaction is performed at 950 to 1000 ° C. for 0.5 to 5 hours. Note that, as Ni powder, it is preferable to use carbonyl Ni powder which is inexpensive and has a uniform particle shape. The reducing agent is preferably Ca particles of about 4 mesh or less,
Large grains and small lumps are also effective. The addition amount of the reducing agent Ca is 1.2 times (1.2 times the reduction equivalent of La ₂ O ₃ ).
Unequivalent), unreduced La ₂ O ₃ remains, and conversely, when it becomes 1.4 equivalent or more, non-intermetallic compounds such as (Ca, La) ₂ Ni ₁₇ and (Ca, La) Ni ₃ are formed. Therefore, addition of 1.2 to 1.4 equivalents is preferable. Further, in order to suppress sintering during the reduction diffusion reaction and to promptly promote water disintegration in the washing step after the reduction diffusion treatment, it is effective to add anhydrous CaCl ₂ as a flux. If the amount of CaCl ₂ added is less than 5% of the weight of the raw material oxide, the effect is not obtained. Conversely, if it is more than 15%, non-purpose compounds such as LaOCl are generated and remain, so addition of 5 to 15% is necessary. And the addition of 10% is preferred. After sufficiently mixing these raw materials, reducing agent and flux, they are charged into a stainless steel reaction vessel, and subjected to a reduction diffusion reaction at 950 to 1000 ° C. for 0.5 to 5 hours in an argon gas atmosphere. The reaction product is the desired LaNi ₅ hydrogen storage alloy and a mixed mass of residual CaCl ₂ and by-product CaO. The mixed mass is poured into water to disintegrate, and the hydrogen storage alloy powder is separated into a slurry by water washing by repeating decantation and repulping washing. After the hydrogen storage alloy powder slurry thus obtained is over-refined, washed with water using alcohol, and then vacuum-dried to obtain a hydrogen storage alloy powder. This hydrogen storage alloy powder is represented by X
According to the line diffraction, it is an alloy powder composed of a CaCu _5- type hexagonal LaNi ₅ single phase and having a particle size of 74 mesh or less and a Fisher particle size of 25 to 35 μm. Further, this alloy powder can be sufficiently used as an alloy powder for an electrode of an alkaline secondary battery without going through a mechanical pulverizing step. Furthermore, even in the case of multi-element alloys, rare earth metals and misch metals use their oxides as raw materials, and other metals mainly use metal powders or alloy powders to obtain alloy powders that do not need to be crushed as described above. It is possible. The water for disintegrating the hydrogen storage alloy in water may be ordinary tap water, but pure water is preferred. As described above, according to the production method of the present invention, a hydrogen storage alloy powder having a particle size of at least 74 mesh or less can be produced based on a tiler without requiring a mechanical pulverization step. Next, when performing metal coating on this alloy powder, a continuous flow from the reduction diffusion treatment is established by directly transferring the hydrogen storage alloy powder slurry obtained after the water washing step of the reduction diffusion method to the electroless plating step. Therefore, it is possible to simplify a process advantageous for mass production. The plating method in the electroless plating step may be any of various established electroless plating methods, and is not particularly limited. When performing metal coating on the hydrogen storage alloy powder by the electroless plating method, design the weight of the coating metal component with respect to the weight of the hydrogen storage alloy powder to be coated, and use this as the weight coating rate to correspond to the coating metal film thickness. This is convenient for production management. Therefore, when the hydrogen storage alloy powder slurry is directly transferred to the electroless plating step as in the present invention, it is necessary to know the alloy weight in the hydrogen storage alloy powder slurry.
The weight of the alloy powder in the hydrogen storage alloy powder slurry can be easily obtained by the following method. The specific gravity of the hydrogen storage alloy powder in the hydrogen storage alloy powder slurry is A, the specific gravity of the solvent is B, the total weight of the hydrogen storage alloy powder slurry is M (g), and the total weight of the hydrogen storage alloy powder slurry is V (cm ³ ). At this time, the alloy weight m (g) in the hydrogen storage alloy powder slurry can be obtained by equation (1). m = {A / (AB)} × (MB × V) (1) In the formula (1), A is obtained in advance by using a Peckman-type specific gravity measuring device or the like for a dried product of the target alloy. B is pure water. M and V can be measured each time. When controlling the plating amount by the electroless plating method,
A method in which the reaction is stopped when a predetermined plating reaction is completed based on the plating reaction speed, a non-plated material is removed from the plating bath, or a plating metal component in the plating bath is set to a required amount and completely precipitated. However, when the object to be plated is a powder as in the present invention, it is desirable to completely precipitate the plating metal component. Since the hydrogen-absorbing alloy powder is not oxidized in the atmosphere, no special pretreatment is required. However, even when a pretreatment such as pickling is required, the steps can be easily added. Therefore, the method of the present invention is economical because the steps for producing the metal-coated hydrogen storage alloy powder are simplified.

【Example】

Hereinafter, the present invention will be described specifically with reference to examples. In the following,% is% by weight, μm representing particle size is based on Fisher method, and mesh is based on Tyler. (Example 1) La ₂ O ₃ having a particle size of 10 μm (purity 99.99%) as a raw material: 11
2.4G, Carbonyl Ni powder of 5μm particle size (purity 99.7%): 2
03.6 g and Ca particles having a particle size of 4 mesh or less (purity: 99%): 49.7
g (1.2 times the reduction equivalent) and 11.2 g of anhydrous CaCl ₂ are sufficiently mixed, charged into a stainless steel reaction vessel, and subjected to a reduction-diffusion reaction at 970 ° C. for 4.5 hours in an argon gas atmosphere to perform a reaction. The container was air-cooled to room temperature, and the reaction product was taken out, poured into pure water and collapsed. After that, decantation and revalve were repeated until pH <9, and residual Ca,
By-product CaO was removed, and after that, washing with water and washing with water was performed, followed by vacuum drying to obtain a hydrogen storage alloy powder. The hydrogen-absorbing alloy powder, La: 31.4%, remainder Ni and inevitable impurities (Ca: 0.43%, O: 0.06%, C: 0.01%) consists, a CaCu ₅ type hexagonal According to X-ray diffraction It was a LaNi ₅ alloy powder having a particle size of 39 μm with a mesh of 74 mesh or less. The hydrogen storage properties of this hydrogen storage alloy powder are, for example,
As shown in the figure, the hydrogen storage / desorption equilibrium pressure (hereinafter, referred to as plateau pressure) at 60 ° C. was 0.5 to 0.8 MPa, and the maximum hydrogen storage / desorption amount in the plateau pressure portion was 1.15%. When the hydrogen storage alloy powder was used as a secondary battery electrode without pulverization, the initial capacity was 297 mA · h / g, and the hydrogen storage alloy powder had a sufficient initial capacity. (Example 2) Among the conditions of Example 1, the amount of added Ca particles was changed to 58.0 g (1.4 times the reduction equivalent), and the other conditions were the same as in Example 1. The obtained hydrogen storage alloy powder was La: 31.5%, and the balance was Ni
And inevitable impurities (Ca: 0.53%, O: 0.07%, C: 0.02%)
According to X-ray diffraction, it has a CaCu type ₅ hexagonal crystal,
It was a LaNi ₅ alloy powder having a mesh size of 31 μm or less. Regarding the hydrogen storage properties of this alloy powder, for example, the plateau pressure at 60 ° C. was 0.5 to 0.8 MPa, and the maximum hydrogen storage and desorption amount in the plateau portion was 1.15%. When the hydrogen storage alloy powder was used as a secondary battery electrode without pulverization, the initial capacity was 295 mA · h / g, indicating that the hydrogen storage alloy powder had a sufficient initial capacity. (Example 3) Of the conditions of Example 2, the reduction diffusion time was changed to 1.5 hours, and the other conditions were the same. The obtained hydrogen storage alloy powder was La: 31.5%, and the balance was Ni
And inevitable impurities (Ca: 0.53%, O: 0.07%, C: 0.02%)
According to X-ray diffraction, it has a CaCu type ₅ hexagonal crystal,
Mesh or less was LaNi ₅ alloy powder particle size 30 [mu] m. Regarding the hydrogen storage properties of this alloy powder, for example, the plateau pressure at 60 ° C. was 0.5 to 0.8 MPa, and the maximum hydrogen storage and desorption amount in the plateau portion was 1.15%. Further, when the hydrogen storage alloy powder was used as a secondary battery electrode without pulverization, the initial capacity was 295 mA · h / g, and the hydrogen storage alloy powder had a sufficient initial capacity. (Example 4) Of the conditions of Example 2, Ni powder was changed to carbonyl Ni powder (purity 99.7%) having a particle size of 8.8 µm, and the other conditions were the same. The obtained hydrogen storage alloy powder was La: 31.5%, and the balance was Ni
And inevitable impurities (Ca: 0.61%, O: 0.12%, C: 0.02%)
According to X-ray diffraction, it has a CaCu type ₅ hexagonal crystal,
Mesh or less was LaNi ₅ alloy powder particle size 34 .mu.m. The hydrogen storage properties of this hydrogen storage alloy powder are, for example, 60
The plateau pressure at 0.5 ° C. was 0.5 to 0.8 MPa, and the maximum amount of desorbed and desorbed hydrogen in the plateau was 1.15%. When the hydrogen storage alloy powder was used as a secondary battery electrode without pulverization, the initial capacity was 295 mA · h / g, indicating that the hydrogen storage alloy powder had a sufficient initial capacity. (Comparative Example 1) Among the conditions of Example 2, the Ni powder was changed to carbonyl Ni powder having a particle size of 2.8 μm (purity: 99.7%), and the other conditions were the same. The obtained hydrogen storage alloy powder had a La content of 28.5% and a balance of Ni
And inevitable impurities (Ca: 3.16%, O: 65%, C: 0.13%), and had a mesh size of 74 mesh or less. In addition to the CaCu type ₅ hexagonal crystal, several X-ray diffraction peaks were observed. The hydrogen storage properties of the hydrogen storage alloy powder were, for example, a plateau pressure at 60 ° C. of 0.5 to 0.8 MPa, and a maximum hydrogen storage and desorption amount of the plateau portion was 0.77%. When the hydrogen storage alloy powder was used as a secondary battery electrode without pulverization, the initial capacity was 102 mA · h / g, and the initial capacity was insufficient hydrogen storage alloy powder. As can be seen from this comparative example, when Ni powder having a particle size of 3 μm or less is used, the grades of Ca, O, and C are increased due to the progress of sintering, and a phase other than LaNi ₅ is generated, and sufficient performance is obtained. Absent. (Comparative Example 2) Under the conditions of Example 2, Ni powder was added to Ni powder having a particle size of 15.6 μm (purity: 99.8%), and the amount of added Ca particles was 58.0 g (reduction equivalent of 1.4).
Times), and the others were manufactured under the same conditions. The obtained hydrogen storage alloy powder was La: 27.2%, and the balance was Ni
And inevitable impurities (Ca: 0.62%, O: 0.82%, C: 0.03%), 12 mesh of 74 mesh or more, and several X-ray diffraction peaks were observed in addition to the CaCu _5- type hexagonal crystal. The hydrogen storage properties of the hydrogen storage alloy powder, for example, the plateau pressure at 60 ° C. was 0.5 to 0.8 MPa, and the maximum amount of hydrogen storage and desorption at the plateau pressure portion was 0.68%. Was used as a secondary battery electrode without pulverization, the initial capacity was 100 mA · h / g, and the initial capacity was insufficient hydrogen storage alloy powder. In the use of the above Ni powder, it is necessary to increase the reduction diffusion temperature in order to sufficiently promote the diffusion reaction.
Since the grades of O and C became high, and phases other than LaNi ₅ were generated, La which could not be sufficiently diffused remained in the hydrogen storage alloy powder as La ₂ O ₃ , and sufficient performance was obtained. Absent. (Example 5) La ₂ O ₃ : 70 g as in Example 1, and Ni powder: 189.3 g as in Example 1
And atomized Al powder with a particle size of 80 μm (purity 99.6%): 9.7
g, Nd ₂ O ₃ having a particle size of 8 μm (purity: 99.9%): 48.2 g, the amount of Ca particles added to 61.0 g (1.4 times the reduction equivalent), and anhydrous CaCl ₂ : 11.8 g
g was used and the other conditions were the same as in Example 1. The hydrogen storage alloy powder obtained here has La: 19.4%, Nd: 1
3.4%, Al: 3.25%, the balance being Ni and unavoidable impurities (Ca: 0.2
7%, O: 0.05%, C: 0.01%), having a CaCu type ₅ hexagonal crystal, La mesh of 74 mesh or less and a particle size of 38 μm La _0.6 Nd _0.4
Ni _4.5 Al _0.5 . The hydrogen storage properties of this hydrogen storage alloy powder are, for example, the plateau pressure at 60 ° C. is 0.5 to 0.8 MPa.
a, and the maximum amount of desorbable and desorbable hydrogen in the plateau is 1.15
%Met. The initial capacity of this hydrogen storage alloy powder when used as a secondary battery electrode without grinding was 280 m.
It was A · h / g, and was a hydrogen storage alloy powder having a sufficient initial capacity. (Example 6) As a raw material, misch metal oxide powder (rare earth purity)
98% La ₂ O ₃ : 26%, CeO 2: 55%, Pr ₅ O ₁₁ : 5%, Nd ₂ O ₃ : 12
%, Sm ₂ O ₃ : 0.8%, other <0.1%): 84.6 g, particle size 5 μm
Carbonyl Ni powder (purity 99.7%): 100.6g, particle size 80μ
m atomized Al content powder (purity 99.6%): 10.6g and 300
Using 20.2 g of Co powder (purity 99.9%) of mesh or less, changing the addition amount of Ca particles to 56.0 g (1.4 times the reduction equivalent) and anhydrous CaCl ₂ : 8.5 g, and reducing the diffusion temperature to 1000 ° C. Except for having changed to, the same conditions as in Example 1 were used. The obtained hydrogen storage alloy powder had La: 9.3% and Ce: 18.9.
%, Pr: 1.7%, Nd: 4.5%, Sm: 0.4%, Co: 10.2%, Al: 5.
3%, the remainder is Ni and unavoidable impurities (Ca: 0.29%, O: 0.06
%, C: 0.01%), a MmNi _3.5 Co _0.7 Al _0.8 hydrogen storage alloy powder having CaCu type ₅ hexagonal crystal, 74 mesh or less, and a particle size of 34 μm. The hydrogen storage properties of this hydrogen storage alloy powder are, for example, the plateau pressure at 60 ° C. is 0.5 to 0.8 MPa.
a, and the maximum amount of hydrogen that can be stored and desorbed in the plateau pressure section is 1.1.
5%. When the hydrogen storage alloy powder was used as a secondary battery electrode without pulverization, the initial capacity was 23.
The hydrogen storage alloy powder was 0 mA · h / g and had a sufficient initial capacity. (Example 7) Cu coating was performed using an alloy slurry manufactured under exactly the same conditions as in Example 4. That is, the weight coating ratio of Cu required for coating the hydrogen storage alloy powder having a particle size of 34 μm and a specific gravity of 8.4 produced in Example 4 with Cu having a thickness of 1 μm is 8.
6%. The amount of the alloy in the hydrogen-absorbing alloy powder slurry was determined by the formula (1) to be 75.6 g. Therefore, the required amount of Cu was 7.1 g. Electroless Cu used here
Plating _{bath, CuSO 4 · 5H 2 O:} 50g /, sodium ethylenediaminetetraacetate: 150g /, αα ^- Jibirijiru: 0.01 g / l,
Polyethylene glycol: Cu composed of 0.1 g / bath composition: 1
It was a 2.5 g / use Cu electroless plating solution. The required amount of Cu is 7.1
g, prepare this plating solution 0.57, add the alloy slurry, and perform the plating reaction with aqueous sodium hydroxide solution at pH = 1.
The reaction was controlled at 0.5 and the bath temperature was 65 ° C. by adding formalin. After the completion of the plating reaction, the substrate was washed with pure water, washed with water and washed with water, and dried under vacuum. Observation of the cross section of the particles with a metallurgical microscope showed that C with a thickness of 0.5 to 1 μm
u A film was formed. When this Cu-coated LaNi ₅ hydrogen storage alloy powder was used as a secondary battery electrode, the initial capacity was 29
The hydrogen storage alloy powder was 1 mA · h / g and had a sufficient initial capacity. It was confirmed that the Cu-coated LaNi ₅ hydrogen storage alloy powder had a longer life than that without the Cu coating. The above results are shown in Tables 1, 2 and 3.

【The invention's effect】

According to the present invention, a hydrogen storage alloy powder having a particle size of at least 74 mesh or less can be produced based on a tiler without requiring a mechanical pulverization step. The present invention has the basic characteristics as a rare earth metal-based hydrogen storage alloy having a CaCu _5- type hexagonal structure in the production of a hydrogen storage alloy powder, and is an inexpensive and safe oxide to handle rare earth components in the production process. Can be used to produce multi-component alloys, and when used as a hydrogen storage alloy powder for secondary battery electrodes, completely eliminates the pulverization process of rare earth alloys that are extremely active against oxidation. Also, if necessary, it is possible to continue the process up to the metal coating process by electroless plating to prevent the alloy powder from pulverization, improve electrical conductivity, and improve thermal conductivity. This is a method for producing a hydrogen storage alloy powder and a metal-coated hydrogen storage alloy powder, and their industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing the hydrogen storage amount and the hydrogen equilibrium pressure of the LaNi alloy powder produced in Example 1 at a constant temperature.

Claims (3)

(57) [Claims] 1. A method for producing a hydrogen storage alloy powder for a secondary battery comprising at least one of La, Ce, Nd, and Misch metal and Ni as a main component, wherein at least one of La, Ce, Nd, and Mish metal is provided. One type of powder is mixed with Ni powder having a Fischer particle size of 3 to 10 μm,
A method for producing a hydrogen storage alloy powder for a secondary battery, comprising washing a reduced diffusion reaction product obtained at a temperature of 0 to 1000 ° C. with water. 2. The method according to claim 1, wherein when mixing at least one powder of La, Ce, Nd and misch metal with the Ni powder, 5 to 15% of anhydrous CaCl ₂ is added as a flux. A method for producing a hydrogen storage alloy powder for a secondary battery according to the above. 3. The method according to claim 1, wherein the step of coating the hydrogen storage alloy powder obtained by the method according to claim 1 directly shifts from a washing step of washing the reduced diffusion reactant to an electroless plating step. A method for producing a coated hydrogen storage alloy powder.