JP2001266859A - Hydrogen storage alloy electrode and nickel hydrogen secondary battery incorporating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy electrode using spherical particle powders of hydrogen storage alloy and offers a hydrogen storage alloy electrode of which the nickel hydrogen secondary battery incorporating the same has a large discharging characteristics and excellent cycle life properties. SOLUTION: The hydrogen storing alloy electrode comprises hydrogen storing alloy powders carried on the current collector substrate 1. The hydrogen storing alloy powder is a spherical particle powder of the average size of 20-80 μm and the current collector substrate 1 has several openings 2 protruding from the metal sinter sheet of a thickness of 60 μm or less, and the periphery of the openings adjoining to each other is made a notched portion 3 protruding in the opposing direction each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy electrode and a nickel-hydrogen secondary battery incorporating the same, and more particularly, to a hydrogen storage alloy electrode having a good ability to hold an electrode mixture applied thereto, Hydrogen-absorbing alloy electrode equipped with a current-collecting substrate capable of realizing high-density application of a chemical agent, and nickel-hydrogen alloys with excellent high-rate discharge characteristics and cycle life characteristics by incorporating the hydrogen-absorbing alloy electrode Next battery.

[0002]

2. Description of the Related Art A hydrogen storage alloy electrode incorporated as a negative electrode in a nickel-hydrogen secondary battery is generally manufactured as follows. First, a powder of a hydrogen storage alloy that electrochemically stores and releases hydrogen, a conductive material such as carbon black, and a binder such as carboxymethyl cellulose are kneaded with water to form a viscous mixture having a predetermined composition. A paste of an agent (hereinafter, referred to as an electrode mixture) is prepared.

[0003] Then, the mixture paste is directly applied to or filled in the current collecting substrate and dried, and further, for example, roll-rolled to adjust the thickness, and at the same time, the dried mixture is densified on the current collecting substrate. Carry it. In general, a Ni punching sheet in which openings having a predetermined diameter are formed at predetermined intervals, for example, in a staggered lattice pattern, is used as the current collecting substrate. In such a case, the aperture ratio is adjusted to a desired one by appropriately setting the diameter and the number of the above-mentioned openings, and the coating amount of the electrode mixture carried there, that is, the packing density is adjusted. This is because if the amount of the coating increases, the capacity of the obtained hydrogen storage alloy electrode increases, and the assembled battery can be made a high capacity battery.

Conventionally, as a powder of a hydrogen storage alloy, a powder obtained by mechanically pulverizing an alloy ingot has been used. The pulverized powder has a complicated shape, and the powders are supported on the current collecting substrate in surface contact with each other, so that the pulverized powder has an advantage of reducing electrical contact resistance. Since it is small, the packing density of the current collecting substrate is low, which is disadvantageous for increasing the capacity of the battery.

[0005] For these reasons, recently, a spherical powder or an egg-shaped spherical powder of a molten metal of a hydrogen storage alloy has been used by a known gas atomizing method or disk atomizing method. This is because the spherical powder has a higher bulk density than a powder obtained by mechanically pulverizing an alloy ingot, and if the same amount of powder is supported on a current collecting substrate, the capacity as a hydrogen storage alloy is not high.

However, in the case of this spherical powder, there is a problem that the contact between the powders is a point contact, so that the electrical contact resistance between the powders increases and the high-rate discharge characteristics deteriorate. Also, since the spherical powder has a small slip resistance between each other, the electrode mixture prepared using the same is simply applied to a current collecting substrate such as the punched metal sheet in which the openings are distributed and then rolled, for example. When rolling is performed, there is also a problem in that spherical powder in the mixture slips in the process, so that a high packing density cannot be realized eventually.

To solve such a problem, a high-rate discharge characteristic and a low-rate discharge characteristic are improved by supporting a mixed powder obtained by mixing a spherical powder and the above-mentioned mechanically pulverized powder on a punching sheet. A proposal has been made (see JP-A-7-109543). In addition, heat treatment is performed on the spherical or almost spherical hydrogen storage alloy powder to promote partial sintering, and if necessary, the powder is crushed to give a punching metal sheet having a bulk specific gravity of 3.3 or more. There is a proposal of a hydrogen storage alloy electrode in which discharge characteristics are improved by carrying the electrode (see Japanese Patent Application Laid-Open No. 8-45505).

Furthermore, a substantially spherical powder, which is obtained by temporarily sintering a fine alloy powder having a particle size of 1/10 or less of the surface of a spherical alloy base powder, is applied to a conductive substrate and filled therein. By doing so, it has been proposed to suppress slippage during rolling, increase the packing density, and improve the discharge characteristics (see Japanese Patent Application Laid-Open No. 10-199521).

Thus, the spherical powder of the hydrogen storage alloy is
Although the material has a high bulk density and is useful as a material for increasing the electrode capacity, it is difficult to realize high-density packing due to its small sliding resistance when actually supported on a current collecting substrate. As in the case of technology, it is customary to apply some treatment to the spherical powder.

[0010] However, such treatment increases the production cost of the hydrogen storage alloy powder, which is a material of the electrode, and is economically disadvantageous. The present invention solves the above-described problem when using a spherical powder of a hydrogen storage alloy, and by using a current collecting substrate having a form described below, the spherical powder can be used as it is without performing any processing. To provide a hydrogen-absorbing alloy electrode with a high-density application of an electrode mixture containing it, and a nickel-hydrogen secondary battery with excellent high-rate discharge characteristics and cycle life characteristics by incorporating it And

[0011]

In order to achieve the above object, according to the present invention, in a hydrogen storage alloy electrode in which a hydrogen storage alloy powder is supported on a current collecting substrate, the hydrogen storage alloy powder has an average The current collector substrate is a spherical powder having a particle size of 20 to 80 μm, and the current collecting substrate has a plurality of openings perforated in a metal sintered body sheet having a thickness of 60 μm or less. A hydrogen storage alloy electrode is provided, which has burr portions projecting in opposite directions.

Further, the present invention provides a nickel-hydrogen secondary battery incorporating the above-mentioned hydrogen storage alloy electrode.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A hydrogen storage alloy electrode of the present invention is prepared by kneading a spherical powder of a hydrogen storage alloy, a binder, and, if necessary, a conductive agent with water to prepare a paste of an electrode mixture. The paste is applied to a current collecting substrate described later, dried, and subsequently roll-rolled, for example.

The spherical powder is produced by applying, for example, a gas atomizing method or a disk atomizing method to a molten metal of a hydrogen absorbing alloy having a predetermined composition, and has an average particle size of 20 to 80 μm. Average particle size is 20μm
In the case where the particle size becomes smaller, the proportion of fine particles in the powder produced by the above-mentioned atomizing method is increased, and thus a nickel-hydrogen secondary electrode incorporating a hydrogen storage alloy electrode produced with such a spherical powder as a negative electrode is used. In the battery, the fine spherical powder is corroded at an early stage of the charge / discharge cycle, causing a reduction in capacity and a problem that the battery life is shortened.

On the other hand, if the average particle size is larger than 80 μm, the number of charge / discharge cycles required to start the assembled battery to a practically usable capacity increases, which is not practical. As the spherical powder to be used, those having an average particle diameter of 20 to 70 μm and a ratio of fine particles having a particle diameter of 10 μm or less and coarse particles having a particle diameter of 150 μm or more each being less than 5% by volume are preferable. In particular, those having an average particle diameter of 30 to 60 μm and a ratio of fine particles having a particle diameter of 10 μm or less and coarse particles having a particle diameter of 150 μm or more each being less than 3% by volume are more preferable.

The hydrogen absorbing alloy is represented by the general formula AB
a hydrogen storage alloy represented by x (where A is a rare earth element containing Y and at least one element selected from the elements consisting of Zr and Hf, and B is Ni, Co, Mn, F
e, Cr, Al, Si, Cu, and the molar ratio x is 4.
(A number in the range of 5 to 5.5). If the molar ratio is less than 4.5, the negative electrode may deteriorate, and if the molar ratio x exceeds 5.5, the hydrogen storage capacity of the negative electrode may decrease. The alloy represented by the general formula ABx is Ca, Mg, Pb, C
Inevitable impurities such as l, Zn, Mo, and C may be contained.

Next, the current collecting substrate in the hydrogen storage alloy electrode of the present invention will be described. FIG. 1 is a partial perspective view showing an example of the current collecting substrate of the present invention, and FIG. 2 is a cross-sectional view taken along line II-II of FIG. The current collecting substrate 1 is made of a metal powder sintered body sheet manufactured by a powder rolling method. Specifically, metal powder (for example, Ni powder) having a predetermined particle size is supplied between a pair of rolling rolls while adjusting a supply amount, and a green compact sheet having a predetermined thickness is continuously manufactured by the rolling rolls. The green compact sheet is further heated to a predetermined temperature (for example, 700 to 1000).
C.), which is a sheet manufactured by introducing into a firing furnace in an atmosphere of an inert gas such as Ar and sintering the metal powder. The sheet after sintering may be further subjected to hot rolling with a pair of rolling rolls.

According to the powder rolling method, it is possible to produce a sheet having a density close to the theoretical density, and thus a dense and flexible sheet, by using a small-scale and simple facility and performing only one rolling-sintering step. Therefore, the manufacturing cost is reduced. The current collector substrate of the present invention is obtained by machining the entire surface of a metal powder sintered body sheet manufactured by the above-described powder rolling method to form an opening 2 and a burr portion 3 described later. In that case, the thickness (t) of the current collecting substrate of the present invention is 60 μm or less, because the powder rolling method cannot produce a very thick sheet. Preferably 25 to
40 μm.

A plurality of openings 2 are formed in the current collecting substrate 1, and the peripheral edge of each opening 2 is a burr 3. The burrs 3 of the openings adjacent to each other are formed so as to protrude in opposite directions. A paste-like electrode mixture is applied to both surfaces or one surface of the current collecting substrate 1, then dried, and further formed by, for example, roll rolling to adjust the whole to a predetermined thickness. An alloy electrode is manufactured.

In this process, the electrode mixture is filled into the opening 2 and the burr portion 3 is crushed in the thickness direction during molding, so that the electrode mixture is held on the current collecting substrate.
The opening 2 having such a function is preferably formed in a zigzag pattern on the entire surface of the current collecting substrate 1.
In addition, the shape of the opening 2 in plan view is not particularly limited, and examples thereof include a square shape as shown in the figure, a polygonal shape similar thereto, a circular shape, an elliptical shape, and the like. In this case, if the opening 2 is too small, the state of application of the electrode mixture becomes insufficient and the ability to hold the electrode mixture becomes difficult. If the opening 2 is too large, the strength of the current collecting substrate 1 decreases and the electrode (Group) may be damaged at the time of manufacture, and the electrode mixture may easily fall off or peel off. For example, when the opening 2 has a rectangular shape, the length of one side is 0.03 to 1.0.
It is preferred to be within the range of 0 mm. If the distance between the adjacent openings is too long, the ability to hold the coated electrode mixture is also reduced. If the distance is too short, the strength of the current collecting substrate is reduced and the formation of the burr portion 3 is difficult. Therefore, it is preferable to set the interval to about 0.3 to 1.5 mm.

If the height (h) of the burr portion 3 is too high, the opening 2 is inevitably enlarged, and the strength of the current collecting substrate is reduced. For this reason, it is preferable that the height (h) of the burr portion 3 is set in the range of 0.05 to 2.0 mm. In this current collecting substrate, the aperture ratio of the opening 2 in such an embodiment is preferably set to 10 to 40%. This is because an appropriate coating amount of the electrode mixture can be secured.

The electrode mixture is applied to the current collecting substrate, dried, and then roll-rolled to adjust the thickness, thereby producing the hydrogen storage alloy electrode of the present invention. The nickel-hydrogen secondary battery of the present invention comprises a negative electrode of the above-mentioned hydrogen storage alloy electrode, a positive electrode of a known nickel electrode, and a separator disposed therebetween to form an electrode group. It is housed in a battery can together with the liquid, and is manufactured by closing the opening of the battery can.

[0023]

EXAMPLES (1) Production of current collector substrate A Ni powder sintered body sheet was produced as follows by a powder rolling method using an apparatus schematically shown in FIG. First, an endless track is drawn between the rolls 4a and 4b, and the running speed is set to 1.0.
A doctor blade disposed on the downstream side by continuously supplying Ni powder 7 having an average particle size of 0.5 μm contained in a hopper 6 on a belt conveyor 5 rotating at m / min and transporting it downstream. 8, a powder layer having a thickness of 300 μm is passed through a pair of rolling rolls 9, 9, and a pressure of 3 × 1 is applied from above and below.
And rolled in the 0 ⁶ MPa was in the dust layer.

Then, it was introduced into a baking furnace 10 in an Ar atmosphere and heated at a temperature of 950 ° C. for 5 minutes to form a sintered body sheet 1 which was peeled off from the belt conveyor 5 and continuously wound up. The thickness of the obtained sintered body sheet 1 is 30 on average.
μm. Then, a rectangular opening 2 and a burr portion 3 each having a side length of 1.0 mm and a height of 1.0 mm are formed on the sintered body sheet 1, and the interval between the openings is 0.5 mm.
Thus, a current collecting substrate having an aperture ratio of 30% was manufactured. This is referred to as a current collecting substrate A.

For comparison, a Ni punching sheet having a thickness of 0.06 mm and a diameter of 1.0 mm, and having an opening ratio of 30% and formed in a houndstooth check pattern at intervals of 3.0 mm was prepared. This is referred to as a current collecting substrate B. (2) Production of hydrogen storage alloy electrode Composition: Spherical powder having particle size characteristics shown in Table 1 by applying a disk atomization method to a hydrogen storage alloy of MmNi _4.0 Co _0.4 Mn _0.4 Al _0.3 (Mm is a misch metal). Was manufactured.

With respect to 100 parts by weight of these spherical powders, 0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethyl cellulose, and a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60% by weight) 1.0 parts by weight (in terms of solid content), carbon black
After mixing 5 parts by weight and 30 parts by weight of water, the mixture was kneaded to prepare a negative electrode mixture paste.

This paste is applied to the above-mentioned current collecting substrate.
Heat treatment was performed and roll rolling was performed to produce a hydrogen storage alloy electrode having a thickness of 0.35 mm. For each of the obtained hydrogen storage alloy electrodes, the following formula: packing density = {(electrode weight−substrate weight) × 100 / 102.12}
/ Packing density of the supported spherical powder based on the electrode volume (g / m
l) was calculated. The results are shown in Table 1.

(3) Battery assembly First, 100 parts by weight of a mixed powder composed of 90% by weight of nickel hydroxide particles having an average particle size of 10 μm and 10% by weight of cobalt monoxide particles having an average particle size of 2 μm was added to 0 parts by weight of carboxymethyl cellulose. 0.3 parts by weight, 0.5 parts by weight (in terms of solids) of polytetrafluoroethylene dispersion (specific gravity 0.15, solids content 60% by weight), and 45 parts by weight of water, and then kneaded, followed by kneading and mixing. I made it.

This paste was filled in a foamed nickel substrate having a porosity of 96%, dried at a temperature of 100 ° C. for 10 minutes, and then roll-rolled at a pressure of 9 × 10 ⁶ MPa to a thickness of about 0.7 mm. Of nickel electrode. The theoretical capacities of these nickel electrodes are all adjusted to be about 3550 mAh. A nonwoven fabric made of polypropylene fiber which has been subjected to a hydrophilic treatment by graft polymerization is arranged between the hydrogen storage alloy electrode and the nickel electrode, and then spirally wound to form an electrode group. 0
145 liters) and a specific gravity of 1.30 consisting of a 7N aqueous solution of potassium hydroxide and a 1N aqueous solution of lithium hydroxide.
The electrolyte solution was injected and sealed, and a 4/3 A size (3500 mAh nominal capacity) cylindrical nickel-metal hydride secondary battery was assembled.

(4) Evaluation of battery characteristics First, each battery was tested at 0.1 ° C. for 15 minutes at a temperature of 20 ° C.
The battery was charged for a period of time, and further discharged for 5 cycles at 0.2 CmA until the voltage became 1 V, thereby performing an initial activation process. Next, the battery was charged at 1 CmA at a temperature of 20 ° C. for 90 minutes, and then charged at a temperature of 0.2.
Discharge was performed at 2 CmA until the voltage reached 1 V, and the capacity at this time was defined as the initial capacity.

After charging at 1 ° C. for 90 minutes at a temperature of 20 ° C., discharging at 10 ° C. at a temperature of 0 ° C., and measuring the capacity at that time (high-rate discharge capacity). After that, at a temperature of 45 ° C, the battery is charged at 3 CmA for 90 minutes, and then charged at 3 CmA.
The charge / discharge cycle until the final voltage became 1 V was repeated, and the number of cycles when the battery capacity showed 2500 mAh with respect to the initial capacity was measured. Table 1 summarizes the above results.
It was shown to.

[0032]

[Table 1]

The following is clear from Table 1. (1) Even when the current collecting substrates are the same, when the average particle size of the spherical powder is larger than 80 μm (Comparative Example 1), the high-rate discharge characteristics are significantly reduced as compared with the examples, and the average particle size is reduced. Is 20
In the case of smaller than μm (Comparative Example 2), a significant decrease in cycle life characteristics is observed.

(2) The spherical powder has an average particle diameter of 20.
In the case where the current collecting substrate is a punched metal sheet similar to the conventional one, even in the range of up to 80 μm (Comparative Example 4)
In both cases, both the high rate discharge characteristics and the cycle life are significantly reduced. (3) From the above, when the hydrogen storage alloy electrode is manufactured using the spherical powder of the hydrogen storage alloy, the average particle diameter of the spherical powder is set in the range of 20 to 80 μm as in the example. In addition, it is clear that the use of the current collector substrate defined in the present invention is useful.

[0035]

As is apparent from the above description, the hydrogen storage alloy electrode of the present invention can enhance the high-rate discharge characteristics and cycle life characteristics of a nickel-hydrogen secondary battery incorporating it as a negative electrode.

[Brief description of the drawings]

FIG. 1 is a partial perspective view showing an example of a current collecting substrate used in a hydrogen storage alloy electrode of the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a schematic view showing a line example of a powder rolling method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Current collection board (sintered metal powder sheet) 2 Opening 3 Burr part 4a, 4b Roll 5 Belt conveyor 6 Hopper 7 Metal powder (Ni powder) 8 Doctor blade 9 Rolling roll 10 Firing furnace

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 10/30 H01M 10/30 Z (72) Inventor Masayoshi Hiruma 3-4-1 Minamishinagawa, Shinagawa-ku, Tokyo No. Toshiba Battery Co., Ltd. CC27 DD08 EE04 HH03 5H028 BB04 EE01 EE05 HH05 5H050 AA02 AA07 BA14 CA03 CB17 DA04 FA10 FA14 FA17 GA03 GA06 HA04 HA05

Claims (4)

[Claims] 1. A hydrogen storage alloy electrode in which a hydrogen storage alloy powder is supported on a current collecting substrate, wherein the hydrogen storage alloy powder is a spherical powder having an average particle diameter of 20 to 80 μm, and the current collecting substrate is A plurality of openings formed in a sintered metal sheet having a thickness of 60 μm or less, and peripheral portions of the openings adjacent to each other are burr portions projecting in opposite directions to each other. Storage alloy electrode. 2. The hydrogen storage alloy electrode according to claim 1, wherein said spherical powder is produced by an atomizing method. 3. The hydrogen storage alloy electrode according to claim 1, wherein the metal sintered body sheet is manufactured by a powder rolling method. 4. A nickel-hydrogen secondary battery comprising the hydrogen storage alloy electrode according to claim 1 incorporated therein.