JPH11121009A - Hydrogen storage alloy electrode and nickel hydrogen storage battery using the electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy electrode having no aggregation substance of nickel powder to be seen in the hydrogen storage alloy electrode with nickel added as conductive power. SOLUTION: This electrode is formed by having an electrode mixture containing hydrogen storage alloy powder, conductive powder, and a binding agent on a conductive base material. In the conductive powder, primary particles are spherical, the aggregation of the primary particles has a three dimensional chain structure, the diameter of the chain column is 0.5 μm or less, a crystal size measured by powder X-ray diffraction measurement is 300 Å or less, and nickel powder of an oxygen content of 0.5 to 1.5 wt.% is contained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy electrode using a hydrogen storage alloy powder capable of reversibly storing and releasing hydrogen, and a nickel hydrogen storage battery using the same.

[0002]

2. Description of the Related Art A nickel hydrogen storage battery operates using hydrogen as a negative electrode active material, and comprises a hydrogen storage alloy electrode formed by supporting a hydrogen storage alloy powder capable of reversibly storing and releasing hydrogen on a conductive base material. A negative electrode is used, and a nickel electrode formed by supporting a nickel hydroxide, which normally operates as a positive electrode active material, on a conductive base material is used as a positive electrode, and both positive and negative electrodes are arranged in an alkaline electrolyte via a separator. Is done.

[0003] A hydrogen storage alloy electrode used as a negative electrode is formed by sheet molding an electrode mixture containing a hydrogen storage alloy powder, a conductive powder and a polytetrafluoroethylene powder, and forming the mixture using a porous metal as a conductive base material. Press-bonding to a plate, hydrogen storage alloy powder, conductive powder, carboxymethyl cellulose
A paste-shaped electrode mixture is prepared by kneading a binder such as sodium polyacrylate and water with water, and applying it to a current collector such as punched metal, which is a conductive base material. It is manufactured by a method such as

[0004] Here, the above-mentioned conductive powder is used to enhance the conductivity of the hydrogen storage alloy to improve the current collecting ability as a negative electrode. For example, nickel powder, cobalt powder,
Copper powder, carbon powder and the like are used, and the use of nickel powder is being studied in particular. JP-A-3-179664
No. 7-114922, the diameter of 1 μm
The following nickel powder is used to prevent an increase in internal pressure and to improve cycle characteristics, and to use a nickel powder having an average particle size of 2 to 8 μm and a bulk density of 0.4 to 1.0 g / cm ³ , It has been proposed to improve the discharge characteristics. In Japanese Patent Application Laid-Open Nos. 7-65826 and 7-37583, nickel powder contains a different element, for example, carbon to prevent an increase in internal pressure, or uses an alloy powder composed of nickel and cobalt. It has been proposed to improve high rate discharge characteristics.

[0005]

However, the nickel powder has a chain structure branched in a three-dimensional direction like a conductive carbon black, and particles are easily aggregated. If the mixture is mixed with a binder or the like, the agglomeration of the nickel powder will not be sufficiently loosened, and the agglomerates will remain in the paste. The above-mentioned grains are attached, and this is flatly rolled by a subsequent rolling process. In a nickel hydrogen storage battery using the hydrogen storage alloy electrode in such a state as a negative electrode, the internal resistance increases and the discharge capacity at low temperatures tends to decrease. In addition, in order to obtain a stable initial characteristic, which is inferior in the initial capacity, particularly the initial rise characteristic, a long-time treatment is required in the subsequent activation step, and there is a problem that the production efficiency is reduced.

On the other hand, in order to eliminate the above-mentioned aggregates, it has been considered to add a large amount of a binder or a thickener, or to apply a paste to a mesh to remove particles. However, in the former, the paste thickens, making it difficult to support the conductive base material at a predetermined thickness, and reducing the amount of hydrogen storage alloy per unit volume, making it impossible to obtain a high capacity electrode. In the latter case, the manufacturing process of the electrode becomes complicated, and the production efficiency decreases.

In view of such circumstances, the present invention provides a hydrogen storage alloy electrode to which nickel powder is added as a conductive powder, wherein the electrode has no nickel powder agglomerates. It is an object of the present invention to obtain a nickel hydrogen storage battery which has excellent characteristics and does not cause a problem of reduction in production efficiency.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, as a conductive powder, primary particles are spherical and an aggregate of primary particles is three-dimensional. By using nickel powder having a chain structure and having the diameter of chain columns, crystallite size, and oxygen content set in specific ranges, the agglomerates unlike the conventional case are not observed. A hydrogen storage alloy electrode can be obtained, and by using this as a negative electrode, it is known that a nickel hydrogen storage battery having excellent low-temperature characteristics and initial characteristics and having no problem of lowering the production efficiency can be obtained, and the present invention is completed. Led to.

More specifically, the present invention provides a hydrogen storage alloy electrode comprising an electrode mixture containing a hydrogen storage alloy powder, a conductive powder, and a binder supported on a conductive substrate, wherein the conductive powder is The primary particles are spherical, the aggregate of the primary particles has a three-dimensional chain structure, and the diameter of the chain pillar is 0.5
When the crystal size is 300 μm or less, the crystal size measured by powder X-ray diffraction
Å or less, and the oxygen content is 0.5 to 1.5% by weight
A hydrogen storage alloy electrode containing nickel powder (claim 1) and a negative electrode comprising a nickel electrode, wherein the hydrogen storage alloy electrode having the above-described configuration is used as a negative electrode. (Claim 5).

Further, according to the present invention, in the above hydrogen storage alloy electrode, the nickel powder has a tap density of 0.2 to 0.8 g / g.
cc (claim 2), nickel powder having a BET specific surface area of 4 to 8 m ² / g (claim 3), and a binder containing styrene and 2-ethylhexyl acrylate as main components. Constitution which is a copolymer of a monomer mixture (Claim 4)
Are preferred embodiments.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy electrode of the present invention
As the hydrogen storage alloy powder, Mm (La, Ce, N
d, Pr) -Ni, Ti-Ni, Ti-NiZr
(Ti_2-xZr _xV_4-yNi_y)_1-zCr_zSystem (x = 0
１．５1.5, y = 0.6-3.5, z = 0.2 or less), T
Various alloys such as i-Mn system and Zr-Mn system are used.
You.

In the hydrogen storage alloy electrode of the present invention, nickel powder having spherical primary particles and an aggregate of primary particles having a three-dimensional chain structure is used as the conductive powder. This nickel powder can exhibit efficient conductivity even with a small amount of addition, because the conductive structure develops between the hydrogen storage alloys.

The diameter of the chain pillar of the nickel powder is 0.5 μm.
m, preferably 0.05 to 0.4 μm, and the crystallite size measured by powder X-ray diffraction measurement is 300 ° or less, preferably 1
It is preferably between 00 and 250 °. By setting such diameters and crystallite sizes, good results can be obtained in reducing aggregates during paste preparation and the like. On the other hand, if the diameter exceeds 0.5 μm or the crystallite size exceeds 300 °, the aggregates of the nickel powder increase, and the particles of the aggregates increase when the nickel powder is supported on the conductive substrate. This is likely to cause the inconvenience.

The crystallite size in the present invention means a size measured by a powder X-ray diffraction method. Specifically, first, a diffraction spectrum is measured at 2 degrees / minute to determine a metal nickel. The diffraction peak was measured at a rate of 0.2 ° / min (slit: 0.15), Kα1 and Kα2 rays were separated, and the spread of the crystallite size of the diffraction line profile was identified. Is assumed to be Cauchy type, and the spread due to distortion is assumed to be Gauss type.
It means the size as determined by the integral width method. Further, the diameter of the chain-shaped column referred to in the present invention is defined as a value obtained by lightly compressing nickel powder into a green compact, and measuring the flow rate of gas passing through the green compact with a fish-subsieved sizer (MPIF32) Mean value.

The above-mentioned nickel powder has an oxygen content of 0.5 to 1.5% by weight, preferably 0.8 to 1.5% by weight, more preferably 0.8 to 1.2% by weight. There should be. By setting such an oxygen content, a favorable result is obtained in the dispersibility in the binder, and a favorable result is also obtained in the conductivity with the hydrogen storage alloy. On the other hand, when the oxygen content is less than 0.5% by weight, the amount of oxygen in the nickel powder is too small, so that the dispersibility in the binder is reduced and aggregates are easily generated. On the other hand, when the oxygen content is more than 1.5% by weight, the nickel content is reduced, so that the conductivity with the hydrogen storage alloy is likely to be adversely affected.

That is, it is considered that the agglomeration of the nickel powder has a three-dimensional structure, so that the dispersibility of the powder is deteriorated and particles are easily generated on the electrode. In the present invention, the use of the fine particles as described above is considered to increase the cohesive force of the particles,
By increasing the oxygen content as described above, the adsorption form of the binder is modified, the dispersibility of the nickel powder is improved even with a small amount of the binder, the nickel powder can be uniformly dispersed in the electrode, and the conductive property can be improved. The performance can be improved.

Further, the nickel powder of the present invention has a tap density of 0.2 to reduce the volume occupied in the electrode.
It is preferably 0.8 g / cc. Further, in order to obtain a favorable result due to the dispersibility and conductivity in the binder,
The BET specific surface area is preferably from ⁴ to 8 m ² / g. BE
When T specific surface area is less than 4m ² / g, dispersibility tends to decrease in the binder, and when it exceeds 8m ² / g, prevents miniaturization of the nickel powder, the surface is easily oxidized Natsute, conductive The effect decreases.

The oxygen content referred to in the present invention is defined as inert gas melting / infrared ray absorption method (TC436 manufactured by LECO).
Means a value measured at a heating rate of 10 ° C./min up to 2,500 ° C. The BET specific surface area referred to in the present invention means a value measured at 1 to 100 ° by a nitrogen adsorption method (Yuasa Ionics, Autosorb 1), a sample 1 g, a measurement time 127 minutes, and a value measured on the adsorption side. is there.

The nickel powder of the present invention can be obtained by a carbonyl nickel method, that is, a thermal decomposition method of tetracarbonyl nickel as shown by the following formula: Ni (CO) ₄ → Ni + 4CO. By appropriately adjusting the partial pressure of tetracarbonyl nickel and oxygen in the vessel, the synthesis temperature, and the like, the primary particles are spherical, the aggregate of the primary particles has a three-dimensional chain structure, and the chain columns are formed. Having a diameter, crystallite size and oxygen content within the above ranges, and preferably having a tap density and a BET specific surface area within the above ranges, can be easily synthesized.

In the present invention, the nickel powder used as the conductive powder is used in an amount of 1 to 20 parts by weight, preferably 3 to 10 parts by weight, based on 100 parts by weight of the hydrogen storage alloy powder. If the amount of the nickel powder is too small, sufficient conductivity with the hydrogen storage alloy powder cannot be obtained,
On the other hand, if the amount of the nickel powder is too large, the absolute amount of the hydrogen storage alloy powder decreases accordingly, which is not preferable.

In the hydrogen storage alloy electrode of the present invention, as the binder, for example, polytetrafluoroethylene,
Examples include sodium polyacrylate, polyvinyl alcohol, and a copolymer of styrene and an acrylic compound. Among these, copolymers of a monomer mixture containing styrene and 2-ethylhexyl acrylate as main components are:
It is particularly preferably used because it has a high affinity for the nickel powder used as the conductive powder and good dispersibility can be obtained even in a small amount. The amount of the binder used is usually 0.5 to 5 parts by weight based on 100 parts by weight of the hydrogen storage alloy powder.
It is preferred to use parts by weight.

In the present invention, usually, the above-mentioned hydrogen storage alloy powder, the above-mentioned nickel powder as a conductive powder and a binder are mixed and dispersed in the presence of water to prepare a paste-like electrode mixture. I do. The electrode mixture is supported on a conductive base material and cut into a predetermined size to obtain the hydrogen storage alloy electrode of the present invention. Here, since the above-mentioned nickel powder has the above-mentioned specific configuration, there is a conventional problem at the time of preparing a paste-like electrode mixture and further at the time of carrying this electrode mixture on a conductive base material. There is no particular concern about the formation of agglomerates of nickel powder as has been done.

In preparing the paste-like electrode mixture, a thickening agent such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or polyoxyethylene may be blended. Polyoxyethylene is particularly preferably used because of little increase in viscosity when pasted. The compounding amount of the thickener is usually preferably 1 to 5 parts by weight based on 100 parts by weight of the hydrogen storage alloy powder.

The paste-like electrode mixture is supported on the conductive substrate by a method in which the above-mentioned electrode mixture is applied to the conductive substrate, dried and then rolled. As the conductive substrate, for example, an alkali-resistant metal porous body such as a punched metal or a foamed metal is used. In particular, punching metal is preferable because it has inferior current collection performance as compared with foamed metal having a three-dimensional structure, so that the effect when nickel powder, which is a conductive powder, is used is better exhibited.

A nickel hydrogen storage battery according to the present invention is characterized in that a hydrogen storage alloy electrode having the above structure is used as a negative electrode with respect to a positive electrode comprising a nickel electrode. The nickel electrode is usually prepared by mixing and dispersing nickel hydroxide powder, a conductive additive and a binder in the presence of water to form a paste, filling the paste into an alkali-resistant porous metal body, After drying and rolling, it is manufactured by cutting to a predetermined size.

The nickel hydrogen storage battery of the present invention comprises, for example, a positive electrode comprising the above-mentioned nickel electrode and a negative electrode comprising the above-mentioned hydrogen-absorbing alloy electrode laminated via a separator.
It can be manufactured by inserting this into a battery can and then injecting an alkaline electrolyte. Here, as the above separator, a non-woven fabric made of polyolefin fibers having a hydrophilic group is used. In addition, as the alkaline electrolyte, an aqueous solution of potassium hydroxide or the like is used.

The nickel hydrogen storage battery thus manufactured can exhibit stable initial characteristics by performing the activation treatment at 60 to 70 ° C. In addition, the activation process can be performed in a very short time as compared with the conventional method, and a nickel hydrogen storage battery having excellent low-temperature characteristics and initial characteristics can be manufactured with good productivity.

[0028]

Next, an embodiment of the present invention will be described in more detail. In the following, “parts” means “parts by weight”.

The nickel powders A to C used as conductive powders in Examples 1 to 3 and the nickel powders D and E used as conductive powders in Comparative Examples 1 and 2 were all prepared by the carbonyl nickel method. The primary particles are spherical, and the aggregate of primary particles is a nickel powder having a three-dimensional chain structure, which is synthesized by appropriately adjusting the partial pressure of tetracarbonyl nickel and oxygen in the reaction vessel, the synthesis temperature, and the like. Hot,
The diameter of the chain pillar, the crystal size, the oxygen content, the tap density, and the BET specific surface area as determined by powder X-ray diffraction measurement were configured as shown in Table 1 below.

[0030]

Example 1 Hydrogen storage alloy powder (MmNi _3.48 Co _0.75 Mn _0.4 Al
_0.3 ) 2 parts of nickel powder A as a conductive powder was dry-blended with 100 parts. In this mixture, a polyoxyethylene aqueous solution (solid concentration: 6% by weight) was used as a thickener.
20 parts of a copolymer of a monomer mixture containing styrene and 2-ethylhexyl acrylate as the main components (35 mol% of styrene unit, 65 mol of 2-ethylhexyl acrylate unit) %) (Solid content concentration: 42.5% by weight), and mixed and dispersed.

The paste-like electrode mixture prepared as described above was applied to a punching metal as a conductive base material, rolled, and then cut into a predetermined size to produce a hydrogen storage alloy electrode. No nickel powder particles were observed in the paste-like electrode mixture, confirming that the dispersibility was good. The electrode mixture is applied to the conductive substrate, rolled, cut into a predetermined size, and then placed on the electrode surface (coated surface).
Was visually observed, and no agglomerate of nickel powder was observed.

Example 2 A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that nickel powder B2 was used instead of nickel powder A2 as the conductive powder. No nickel powder particles were observed in the prepared paste-like electrode mixture, confirming that the dispersibility was good. The electrode mixture was coated on a conductive substrate, rolled, cut into a predetermined size, and then visually observed on the electrode surface (coated surface). As a result, no aggregate of nickel powder was observed. .

Example 3 A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that nickel powder C2 was used instead of nickel powder A2 as the conductive powder. No nickel powder particles were observed in the prepared paste-like electrode mixture, confirming that the dispersibility was good. The electrode mixture was coated on a conductive substrate, rolled, cut into a predetermined size, and then visually observed on the electrode surface (coated surface). As a result, no aggregate of nickel powder was observed. .

Comparative Example 1 A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that nickel powder A2 was used instead of nickel powder A2 as the conductive powder. In the prepared paste-like electrode mixture, particles of nickel powder having a diameter of about 3 mm were observed. In addition, this electrode mixture is applied to a conductive substrate, rolled,
After cutting to a predetermined size, the electrode surface (coating surface) was visually observed. As a result, aggregates of nickel powder having a diameter of about 3 mm were also observed.

Comparative Example 2 A hydrogen storage alloy electrode was manufactured in the same manner as in Example 1, except that nickel powder E2 was used instead of nickel powder A2 as the conductive powder. In the prepared paste-like electrode mixture, particles of nickel powder having a diameter of about 3 mm were observed. In addition, this electrode mixture is applied to a conductive substrate, rolled,
After cutting to a predetermined size, the electrode surface (coating surface) was visually observed. As a result, aggregates of nickel powder having a diameter of about 3 mm were also observed.

The number of times of the activation treatment was measured for each of the hydrogen storage alloy electrodes of Examples 1 to 3 and Comparative Examples 1 and 2. The activation treatment was performed at 70 ° C. for 6 hours.
The number of times of the activation treatment is the number of charge / discharge cycles required for the manufactured electrode to exhibit the maximum capacity, and the quality of the initial startup characteristics when a nickel hydrogen storage battery is manufactured using this hydrogen storage alloy electrode. It is an index to judge.

In practice, each of the above-mentioned hydrogen storage alloy electrodes is combined with a known nickel electrode, wound through a separator, inserted into a cylindrical container, and injected with a potassium hydroxide electrolyte. Then, the battery was sealed to produce a AAA type nickel hydrogen storage battery. After charging the battery at 175 mA at 25 ° C. for 6 hours as a discharge characteristic at a low temperature,
The battery was held for 5 hours in a constant temperature bath at −20 ° C., discharged at 700 mA, and evaluated by the discharge capacity until the battery voltage became 1.0 V. The discharge capacity at this low temperature and the number of times of the activation treatment were as shown in Table 2 below.

[0039]

As is clear from the results in Table 2, the hydrogen storage alloy electrodes of Examples 1 to 3 require one to two times of activation treatment as compared with the hydrogen storage alloy electrodes of Comparative Examples 1 and 2. The processing time is very short, the initial characteristics are excellent,
It can also be seen that a nickel hydrogen storage battery having excellent low-temperature characteristics can be manufactured with good productivity.

[0041]

As described above, according to the present invention, as the conductive powder, the primary particles are spherical, and the aggregate of the primary particles is nickel powder having a three-dimensional chain structure. By using the nickel powder with the diameter, crystallite size and oxygen content set to specific ranges, it is possible to provide a hydrogen-absorbing alloy electrode in which agglomerates are not seen as in the related art, and by using this as a negative electrode, Excellent low temperature characteristics and initial characteristics,
In addition, it is possible to provide a nickel hydrogen storage battery free from the problem of a reduction in production efficiency.

Claims (5)

[Claims] 1. A hydrogen storage alloy electrode comprising an electrode mixture containing a hydrogen storage alloy powder, a conductive powder, and a binder supported on a conductive substrate, wherein the conductive particles have a primary particle having a spherical shape. The aggregate of the primary particles has a three-dimensional chain structure, the diameter of the chain pillar is 0.5 μm or less, the crystal size by powder X-ray diffraction measurement is 300 ° or less, and the oxygen content is A hydrogen-absorbing alloy electrode comprising 0.5 to 1.5% by weight of nickel powder. 2. The nickel powder having a tap density of 0.2 to 0.1.
The hydrogen storage alloy electrode according to claim 1, which is 8 g / cc. 3. The nickel powder has a BET specific surface area of 4 to 8 m.
The hydrogen storage alloy electrode according to claim 1, wherein the hydrogen storage alloy electrode is ² / g. 4. The hydrogen storage alloy electrode according to claim 1, wherein the binder is a copolymer of a monomer mixture containing styrene and 2-ethylhexyl acrylate as main components. 5. A nickel hydrogen storage battery comprising a hydrogen storage alloy electrode according to claim 1 as a negative electrode and a positive electrode comprising a nickel electrode.