JPH0793139B2 - Hydrogen storage alloy electrode material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a material for a hydrogen storage alloy electrode, and more specifically, it is suitable for constructing a battery having excellent characteristics such as discharge capacity and cycle characteristics. The present invention relates to a material for forming a hydrogen storage alloy electrode used.

(Prior Art) In recent years, technological advances in the electronic industry have been remarkable, and demands for high energy density, safety and the like have also increased in battery technology. Nickel / hydride batteries have a large energy density per unit volume and, since they do not contain pollutants, they are attracting attention as batteries having excellent safety.

Hydrogen storage alloys used as negative electrode active materials for such batteries include rare-earth alloys based on LaNi ₅ , MmNi ₅ (Mm: misch metal), TiNi, Ti ₂ Ni, Ti _1-x Zr _x Ni Titanium-based materials such as ZrV _0.4 Ni _1.6 and Laves phase materials such as ZrV _0.4 Ni _1.6 are known.

As a method of molding these hydrogen storage alloys into electrodes,
For example, alloy powder crushed to several tens of microns, conductive material (nickel, copper, carbon, etc.) and binder (polytetrafluoroethylene, FEP, polyethylene, nylon, etc.) are mixed, and this mixture is used as a current collector porous Generally known are a method of pressure-bonding to a high-quality nickel plate and the like, a method of forming the above mixture into a paste with a water-soluble binder such as polyvinyl alcohol, filling the current collector, and pressing. A method is also known in which the above-mentioned alloy particles coated with a conductive material by plating or the like are mixed with a binder, and the mixture is pressed or filled into a current collector.

(Problems to be Solved by the Invention) However, in the above-described method, the binder used is insoluble or hardly soluble in the solvent, and the solid particles are mixed with the alloy particles and the conductive material, so that the high filling rate is achieved. Properties, uniform dispersibility, adhesion to the current collector, etc., and as a result, the obtained battery has unsatisfactory discharge capacity, cycle characteristics, and the like.

Further, when a water-soluble binder such as water-soluble polyvinyl alcohol is used, when the battery is constructed, these are dissolved in the electrolytic solution, which causes a problem that the discharge performance of the battery is deteriorated.

Further, JP-A-1-253159 discloses the use of a thermoplastic elastomer composed of a styrene-ethylene-butadiene-styrene copolymer as a binder, but also in a battery obtained by such a method. , Its discharge capacity, cycle characteristics, etc. are unsatisfactory.

Therefore, an object of the present invention is to provide a material for a hydrogen storage alloy electrode capable of forming a battery having excellent discharge capacity, cycle characteristics and the like.

(Means for Solving Problems) According to the present invention, (A) 100 parts by weight of hydrogen storage alloy powder, (B) 5 to 30 parts by weight of conductive material, and (C) elongation of 300% or more. In addition, it does not contain a structural unit having an ethylenically unsaturated bond, or the content of the structural unit (hereinafter referred to as “unsaturated unit”) is 20
There is provided a material for a hydrogen storage alloy electrode, which comprises 1 to 10 parts by weight of a thermoplastic polymer in an amount of not more than 10% by weight.

That is, the present invention is characterized by using a thermoplastic polymer such as (C) above as a binder, and by adopting such means, a battery excellent in discharge capacity, cycle characteristics, etc. can be obtained. It is possible to form.

(A) Hydrogen storage alloy powder In the present invention, as the hydrogen storage alloy, LaNi ₅ , MmNi ₅
Rare earth based on (Mm: misch metal), TiN
i, Ti ₂ Ni, Ti _1-x Titanium such as Zr _x Ni, Lav such as ZrV _0.4 Ni _1.6
All known es phase systems and the like can be used, but rare earth system and Laves phase systems are particularly preferably used. That is, in a titanium-based alloy, a passive oxide that hinders the diffusion of hydrogen atoms is generated on the surface of the alloy particles during charging / discharging of the battery, and the battery characteristics tend to deteriorate. Further, in order to obtain a battery having characteristics such as long life and high capacity, among rare earth-based and Laves phase-based hydrogen storage alloys, La-Ni-based alloy or Mm-Ni (Mm: misch metal) -based alloy is particularly preferable. The Mm-Ni-based alloy is most preferable because it is preferable and the manufacturing cost can be reduced. Most suitable
As an example of the Mm-Ni-based alloy, MmNi _4.2 Al _0.8 , or MmNi _4.2-x Co _x Al _0.8 (0.5 ≦ x ≦ 1.
The hydrogen storage alloy used in the present invention has a particle size of 10 to 10
It is preferably in the range of 0 μm. This particle size is 10 μm
If it is less than, electrode destruction due to repeated charge and discharge reactions,
Deterioration such as surface oxidation is likely to occur, and if it exceeds 100 μm, the charge / discharge efficiency tends to be lowered.

(B) Conductive Material Examples of the conductive material used in the present invention include nickel, copper, carbon, etc., which may be mixed with other components in the form of particles or fibers, It is also possible to coat the surface of the hydrogen storage alloy with it. The method for coating the surface of the hydrogen storage alloy with these conductive materials is not particularly limited, but a typical method is, for example, electroless plating.

In the present invention, nickel and copper are suitable for improving the conductivity, but when the surface of the hydrogen storage alloy is coated, it is particularly preferable to use nickel to prevent oxidation. These conductive materials are 5 to 30 parts by weight, preferably 10 to 25 parts by weight per 100 parts by weight of the hydrogen storage alloy.
Used in parts by weight. If the amount used is less than 5 parts by weight, sufficient electron conductivity cannot be obtained, resulting in a decrease in charge / discharge efficiency. If the amount used is more than 30 parts by weight, the filling efficiency of the hydrogen storage alloy decreases. However, this causes the disadvantage that the discharge capacity is reduced.

(C) Thermoplastic Polymer In the present invention, a thermoplastic polymer having an elongation of 300% or more, that is, a rubber-like elastic body is used as the binder.
In this specification, the elongation means a value measured according to JIS K 6301, and also a value measured for a thermoplastic polymer to which various compounding agents are not added. JIS
Examples of the method for preparing the sample used for K 6301 include a method in which pellets of the thermoplastic polymer are placed in a mold and hot pressed at a temperature 20 to 30 ° C. higher than the melting point of the thermoplastic polymer. If a material having this elongation lower than 300% is used, it is not possible to absorb the change in the volume of the electrode due to the extraction / removal of ions during charge / discharge of the battery, and the electrode is easily broken.

Further, it is necessary that the above-mentioned thermoplastic polymer does not contain unsaturated units or the content of unsaturated units is within the range of 20% by weight or less. That is, as is clear from the results of Comparative Examples 3, 4 and 5 described below, when a styrene-butadiene-styrene copolymer having a large amount of unsaturated units in its constitutional unit is used,
The obtained battery has unsatisfactory discharge capacity and cycle characteristics. This is probably because hydrogen generated in the charge / discharge reaction causes an oxidation reaction in the saturated bond portion of the copolymer, which causes deterioration of the electrode and inhibition during the charge / discharge reaction.

Here, examples of the unsaturated unit include a repeating unit based on a diene in a diene (co) polymer such as a butadiene (co) polymer or an isoprene (co) polymer.

In such a thermoplastic polymer, the unsaturated unit is not included, or the content of the unsaturated unit is adjusted to a range of 20% by weight or less, but is not limited to, for example, Styrene-ethylene-butylene-styrene block copolymer (hereinafter referred to as "SEBS"), styrene-ethylene-propylene block copolymer (hereinafter referred to as "SEP"), provided that the elongation is 300% or more. ), Hydrogenated nitrile-butadiene copolymer, hydrogenated polybutadiene and the like,
These thermoplastic polymers can be used alone or in combination of two or more.

In the present invention, among these thermoplastic polymers, solubility in a solvent, kneadability with a solid electrolyte powder, adhesiveness with an electrode active material, strength of the obtained solid electrolyte sheet, etc., SEBS and SEP Is preferably used. Such thermoplastic polymer elastics are commercially available, for example SE
As BS, Kraton G-1650, G-1652, G-1657X, G-1660
Kraton G-170 as SEP such as X, G-1726 (manufactured by Shell)
Commercially available products such as 1X and G-1702X (manufactured by Shell) can be preferably used.

The thermoplastic polymer is used in an amount of 1 to 10 parts by weight, preferably 1.5 to 5 parts by weight, based on 100 parts by weight of the hydrogen storage alloy. If the amount used is less than 1 part by weight, the adhesion to the current collector will deteriorate and the charge / discharge characteristics will deteriorate. If it is used in excess of 10 parts by weight, the conductivity will decrease and the charge / discharge efficiency will decrease. Causes an inconvenience that

Further, in the present invention, other thermoplastic polymer may be used in combination with the above-mentioned thermoplastic polymer within a range satisfying the elongation and the content of the unsaturated unit. Examples of such other thermoplastic polymers include 1,4-polybutadiene, natural rubber, polyisoprene, SBR, NBR, EPDM, EPM, urethane rubber, polyester rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, phosphazene rubber. ,
1,2-polybutadiene, styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-
Styrene block copolymer (SIS), a mixture thereof and the like can be exemplified. From the viewpoint of high packing of hydrogen storage alloy powder and strength of the obtained mixture sheet, SB
S, SIS and mixtures thereof are preferred.

Preparation of Material for Hydrogen Storage Alloy Electrode The material for hydrogen storage alloy electrode of the present invention is a solution prepared by dissolving the above-mentioned thermoplastic polymer in a suitable solvent, hydrogen storage alloy powder and conductive material (or coated with conductive material). (Hydrogen storage alloy) is easily prepared by mixing with a ball mill or the like.

Examples of the solvent used for preparing the thermoplastic polymer solution include n-hexane, n-heptane, n-octane, cyclohexane, benzene, toluene, xylene, and the like.
Examples of the organic solvent include ethyl acetate and trichlene.

Preparation of Electrode The hydrogen storage alloy electrode material thus prepared is molded, for example, through a blade coater and the solvent is dried and removed to obtain a molded sheet. Two or more molded sheets obtained here are used to form through holes. After sandwiching the metal plate (collector) which it has, it can be thermocompression-bonded by a hot press etc., and the said molded sheet and a metal plate can be integrated, and it can be set as a hydrogen storage alloy electrode.
Of course, the electrode can be obtained by directly coating the metal plate for the hydrogen storage alloy electrode on the metal plate, removing the solvent by evaporation, and then molding by means such as hot pressing.

As the metal plate having a through hole, for example, a nickel wire mesh, a stainless wire mesh, a punching board obtained by plating iron or stainless with nickel, or the like can be used. Further, in order to increase the contact area between the surface of these metal plates and the molded sheet to improve the adhesion between them,
It is desirable to previously polish the surface of the metal plate with sandpaper or the like.

The obtained hydrogen storage alloy electrode is effectively used, for example, as an electrode of an alkaline secondary battery.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

(Example) Example 1-3 hydrogen-absorbing alloy, with MmNi _3.5 Co _0.7 Al _0.8, after this was less of powder 100 mesh and mechanical grinding, Part 2
Electroless nickel plating was performed so that the content of the electroless nickel would be 0% by weight.

On the other hand, SEBS (elongation: 500%, unsaturated unit: 1% by weight or less) was dissolved in toluene to prepare a 5% by weight SEBS solution.

Then, electroless nickel-plated hydrogen storage alloy powder was added to SEBS so that the weight of SEBS was 1.5, 5 and 7.5 parts by weight with respect to 100 parts by weight of hydrogen storage alloy.
In addition to the solution, it mixed using the homogenizer and prepared the material for electrodes.

The obtained electrode material was formed into a film by using a doctor blade and then air-dried to obtain a molded sheet. Also 50 as a current collector
Using a nickel metal mesh of mesh, the metal mesh was sandwiched between the two molding sheets, and thermocompression bonding was performed under the conditions of 150 ° C. and 300 kg / cm ² f to prepare a hydrogen storage alloy electrode.

The evaluation of the hydrogen storage alloy electrode was performed as follows.
That is, the hydrogen storage alloy electrode was used as the negative electrode, and the positive electrode was sintered nickel, nylon non-woven fabric, and electrolyte (5M KOH, 1M
LiOH) is used to construct a battery, and under the conditions of negative electrode regulation, 25mA
Charging and discharging were repeated at a current density of / cm ² , and the cycle characteristics were examined. The results are shown in Table 1.

Comparative Examples 1 and 2 A hydrogen storage alloy electrode was prepared and evaluated in the same manner as in Examples 1 to 3 except that SEBS was used in amounts of 0.5 and 15 parts by weight, respectively. The evaluation results are shown in Table 1.

Examples 4 and 5, using the same hydrogen storage alloy powder as in Examples 1 to 3, 20% by weight of copper powder having a particle size of 100 mesh or less as a conductive material was added to this powder, and further this mixed powder was carried out. Examples 1-3
In the same manner as in, the SEBS weight was adjusted to 1.5 and 5 parts by weight, respectively, to prepare a material for electrodes by adding it to a toluene solution of SEBS.

With respect to this electrode material, hydrogen storage alloy electrodes were prepared in the same manner as in Examples 1 to 3 and evaluated. The evaluation results are shown in Table 2.

Comparative Examples 3 and 4 SBS as a binder (elongation: 800%, polybutadiene content:
A hydrogen storage alloy electrode was prepared and evaluated in the same manner as in Examples 4 and 5 except that 60% by weight and an unsaturated unit: 60% by weight) were used. The evaluation results are shown in Table 2.

Example 6 A binder was prepared and evaluated in the same manner as in Example 1 except that the weight mixing ratio of SEBS and SBS was 85:15 as the binder. (Stretch: 5
70%, unsaturated unit: 9% by weight) The evaluation results are shown in Table 3.

Comparative Example 5 It was prepared and evaluated in the same manner as in Example 1 except that the weight mixing ratio of SEBS and SBS as the binder was 40:60. (Stretch: 6
80%, unsaturated unit: 36% by weight) Table 3 shows the evaluation results.

Comparative Example 6 A hydrogen storage alloy electrode was prepared and evaluated in the same manner as in Examples 1 to 3 except that the hydrogen storage alloy powder was not subjected to electroless nickel plating. The evaluation results are shown in Table 1.

Comparative Example 7 In Example 5, the amount of copper powder used was changed to 20% by weight,
A hydrogen storage alloy electrode was prepared and evaluated in the same manner as in Example 5 except that the content was changed to 3% by weight. The evaluation results are shown in Table 2.

(Effects of the Invention) According to the material for a hydrogen storage alloy electrode of the present invention, a hydrogen storage alloy electrode having a high hydrogen storage alloy filling efficiency is obtained, and a battery configured using the electrode has a discharge capacity and a cycle. The characteristics are extremely excellent.

Claims (1)

[Claims] 1. A structural unit having (A) 100 parts by weight of a hydrogen storage alloy powder, (B) 5 to 30 parts by weight of a conductive material, and (C) an elongation of 300% or more and an ethylenically unsaturated bond. 1 to 10 parts by weight of a thermoplastic polymer which does not contain or the content of the constituent unit is in the range of 20% by weight or less, and a material for a hydrogen storage alloy electrode.