JPH11250903A - Nickel hydrogen storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel hydrogen storage battery with excellent charging discharging cycle characteristics and excellent high-rate discharging characteristics at a low temperature in the nickel hydrogen storage battery having a negative electrode constituted with a hydrogen storage alloy made of a multi-element alloy. SOLUTION: In a nickel hydrogen battery having a positive electrode using nickel hydroxide as an active material, a negative electrode made of a hydrogen storage alloy, an electrolyte, and a separator, the hydrogen storage alloy is constituted with a multi-element alloy prepared by replacing part of Ni of MmNi5 alloy (Mm shows misch metal) with at least one of Co, Mn, Al, Cu, Mo and Cr, and cobalt oxide in which the atomic ratio of cobalt and oxygen is 1:0.9 to 1:0.99 is contained in the negative electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel hydrogen storage battery using a hydrogen storage alloy electrode capable of reversibly storing and releasing hydrogen and used as a power source for portable terminal equipment.

[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 molding an electrode mixture containing a hydrogen storage alloy powder, a conductive powder and a polytetrafluoroethylene powder into a sheet, and forming the mixture into a porous material serving as a conductive base material. Press-bonding to a conductive metal plate,
A paste of an electrode mixture is prepared by kneading a hydrogen storage alloy powder, a conductive powder, a binder such as carboxymethyl cellulose and polyacrylic acid soda, and water, and forming the paste on a conductive base. It is manufactured by a method of applying the material to a current collector such as punched metal.

[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 fill using 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, in recent nickel hydrogen storage batteries, as a hydrogen storage alloy as an active material,
In order to increase the capacity, a multi-element alloy in which a part of Ni of an MmNi ₅ alloy (Mm represents a metal of a metal) is substituted with Co, Mn, Al or the like is used. In this type of alloy, corrosion progresses due to the alkaline electrolyte during the charge / discharge cycle, the capacity is remarkably reduced, and it is difficult to obtain good cycle characteristics. In addition, corrosion caused by the alkaline electrolyte inhibits charge transfer on the surface of the hydrogen storage alloy, and in particular, deterioration of high-rate discharge characteristics at low temperatures may become a problem.

The present invention has been made in view of the above circumstances and provides a nickel hydrogen storage battery having a negative electrode using a hydrogen storage alloy made of a multiplexed alloy as described above, which has excellent charge / discharge cycle characteristics and a low temperature. It is an object of the present invention to provide a nickel hydrogen storage battery having excellent high-rate discharge characteristics.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, when constructing a negative electrode using a hydrogen storage alloy made of the above-mentioned multi-element alloy, The inventor of the present invention has found that by including a specific cobalt oxide as a conductive powder in the negative electrode, a nickel hydrogen storage battery having both excellent charge-discharge cycle characteristics and high-rate discharge characteristics at low temperatures can be obtained. It led to.

According to the present invention, there is provided a nickel hydrogen storage battery having a positive electrode comprising nickel hydroxide as an active material, a negative electrode comprising a hydrogen storage alloy, an electrolyte and a separator, wherein the hydrogen storage alloy is an MmNi ₅ alloy (Mm is a Represents)
Is partially Co, Mn, Al, Cu, Mo or C
r is replaced by a ternary alloy substituted with at least one of the above, and the atomic ratio of cobalt to oxygen in the negative electrode is 1: 0.
Nickel hydrogen storage battery containing cobalt oxide of 90 to 1: 0.99 (Claim 1), in particular, the specific surface area of the cobalt oxide measured by the BET adsorption method is 10
２０20 m ² / g, pore volume 0.015 to 0.030 cc /
g, the nickel hydrogen storage battery having the above-described configuration having an average pore radius of 20 to 40 ° (claim 2).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the hydrogen storage alloy used in the present invention, a part of Ni of an MmNi ₅ alloy (Mm represents a metal of a metal) is Co, Mn, Al, Cu, Mo or C
This is a ternary alloy substituted with at least one of r, and any of ternary or higher quaternary alloys such as ternary alloys can be used. Among them, a quinary alloy in which a part of Ni is replaced by Co, Mn and Al is particularly preferable since a high capacity alloy can be obtained.
The particle diameter of the hydrogen storage alloy is preferably 100 μm or less, more preferably 20 to 100 μm.

Such a hydrogen storage alloy is, for example, M
m (Mesh metal which is a mixture of rare earth elements including La, Ce, Nd, Pr, etc.), Ni, Co, Mn,
At least one metal element selected from Al, Cu, Mo or Cr is melted in a high-frequency melting furnace or the like to form an alloy melt, which is rotated for about 200
Rapidly solidifies at a cooling rate of 1,000 ° C./sec, evacuates in a pressure vessel, keeps it under hydrogen pressure, evacuates hydrogen, and heats it at 200 to 600 ° C. to completely alloy hydrogen. It can be synthesized by releasing from inside.

The conductive powder used in the present invention is a cobalt oxide having an atomic ratio of cobalt to oxygen of 1: 0.90 to 1: 0.99. By using a conductive powder, good results can be obtained not only in cycle characteristics but also in high-rate discharge characteristics at low temperatures. In addition, the atomic ratio of the above-mentioned cobalt and oxygen is determined by an inert gas melting-infrared absorption method (heating rate 6 ° C./sec, 3,
(Up to 000 ° C.).

In general, the cobalt oxide in the negative electrode is apt to change into a Co (III) compound having low electron conductivity in the battery, which dissolves and precipitates on the surface of the negative electrode to cause charge transfer on the surface of the hydrogen storage alloy. And degrades high-rate discharge characteristics especially at low temperatures. However, since the specific cobalt oxide of the present invention has a structure in which a large amount of cobalt is contained in this oxide, cobalt and cobalt oxide are preferentially oxidized in cobalt and cobalt oxide, and Oxidation is suppressed accordingly, and Co, which inhibits charge transfer in the battery,
(III) The production of the compound is reduced,
A large amount of a Co compound having electron conductivity, such as, for example, precipitates on the electrode surface and plays a role in protecting the hydrogen storage alloy from alkali corrosion.

The atomic ratio of oxygen is 0.99 with respect to cobalt 1.
In the larger cobalt oxide, the surface of the cobalt oxide changes to Co ₂ O ₃ , so that the amount of cobalt that plays a role as a conductive powder is reduced, the cobalt network is not sufficiently formed in the negative electrode, and the temperature is low. Discharge characteristics in the battery are apt to deteriorate. On the other hand, cobalt oxide in which the atomic ratio of oxygen is less than 0.90 with respect to cobalt 1 requires a long time to synthesize this oxide, which is disadvantageous in terms of productivity and cost, and also reduces CoOOH in the battery. change or consume more water in the electrolyte during the, Co ₂ is oxidized cobalt surface during high temperature storage
O ₃ easily changes, a sufficient utilization rate cannot be obtained, and the cycle characteristics tend to deteriorate.

The cobalt oxide used in the present invention can be prepared by various methods as long as the atomic ratio of cobalt to oxygen can be set in the range of 1: 0.90 to 1: 0.99.
As a typical example, cobalt carbonate is calcined in an argon gas atmosphere at 200 to 400 ° C. for 1 to 3 hours, and then 800 to 400 ° C. in an argon gas atmosphere containing hydrogen chloride gas.
After heating at 1,000 ° C. for 7 to 12 hours, a method of performing heat treatment at 600 to 800 ° C. for 1 to 3 hours in a vacuum atmosphere may be used.

The cobalt oxide thus prepared is
Specific surface area by BET adsorption method is 10 to 20 m ² / g, BE
The pore volume measured by the T adsorption method is 0.015 to 0.5.
030 cc / g and an average pore radius of 20 to 40 ° are preferred. By having such properties, the dispersion of the cobalt oxide in the negative electrode is improved, and the oxidation of the surface can be suppressed. The above-mentioned BET adsorption method is a nitrogen adsorption method (Yours Auto-Ionics, Autosop 1), 1 to 100 °, a sample 1 g, a measurement time 127
Minute, means the value measured on the adsorption side.

In the present invention, the above cobalt oxide is usually 10 parts by weight or less, preferably 0.1 to 5 parts by weight, more preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the hydrogen storage alloy. Used in the ratio of Since such a small amount of use can provide sufficient conductivity and exhibit the above-mentioned excellent effects, there is also an advantage that the filling capacity of the hydrogen storage alloy in the negative electrode can be increased.

In the present invention, the above-mentioned hydrogen storage alloy, a conductive powder of cobalt oxide, and a binder are mixed in the presence of water or a solvent to form a paste mixture. Is coated on a conductive substrate made of a porous metal such as an alkali-resistant metal such as a punching metal or a foamed metal, filled, dried, and then compression-molded to form a negative electrode made of a hydrogen storage alloy electrode. In addition to the cobalt oxide of the present invention, other conductive powders such as nickel powder and cobalt powder which are conventionally used can be contained in the paste-like mixture.

Examples of the binder include polytetrafluoroethylene, sodium polyacrylate, polyvinyl alcohol, and a copolymer of styrene and an acrylic compound. Among them, copolymers of a monomer mixture containing styrene and 2-ethylhexyl acrylate as main components as the above-mentioned copolymers have a high affinity for the cobalt oxide and are good even in a small amount. It is particularly preferably used because of its excellent dispersibility. It is preferable that 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.

A thickener such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, or polyoxyethylene may be blended with the above binder. Polyoxyethylene is particularly preferably used because of little increase in viscosity when pasted. The compounding amount of these thickeners is usually preferably 1 to 5 parts by weight based on 100 parts by weight of the hydrogen storage alloy.

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 electrolytic solution. Here, the above separation
As the substrate, a nonwoven fabric made of polyolefin-based fibers provided with a hydrophilic group is used. In addition, an alkaline electrolyte such as an aqueous solution of potassium hydroxide is used as the electrolyte.

[0022]

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

The cobalt oxides A to C used as the conductive powder in Examples 1 to 3 and the cobalt oxides D and E used in Comparative Examples 2 and 3 were all cobalt carbonates in the reaction vessel. Is a cobalt oxide synthesized by appropriately adjusting the treatment temperature, time, etc., and the atomic ratio of cobalt to oxygen, specific surface area by BET adsorption method, pore volume, and average pore radius are shown in Table 1 below. It is configured.

[0024]

Example 1 Metal Mm (La, Ce, Nd, Pr), N
i, Co, Mn, Al and Mo (all with a purity of 99.
Mm (La: 0.32 atomic%, Ce: 0.48 atomic%, Nd: 0.15 atomic%, P
r: 0.04 atomic%), Ni: 3.55 atomic%, Co:
The hydrogen storage alloy is heated and melted in a high frequency melting furnace so as to have a composition of 0.75 at%, Mn: 0.4 at%, Al: 0.3 at%, and Mo: 0.04 at%. I got
This hydrogen storage alloy is evacuated to 10 ⁻³ Torr in a pressure vessel, and then kept at a hydrogen pressure of 14 kg / cm ² for 24 hours, evacuated of hydrogen, and further heated at 400 ° C. to completely remove hydrogen. By releasing, a hydrogen storage alloy powder of 20 to 100 μm was obtained.

To 100 parts of the hydrogen-absorbing alloy powder, 0.2 part of cobalt oxide A, 4 parts of carbonyl Ni powder, and 20 parts of a polyethylene oxide aqueous solution (solid content: 6% by weight) as a thickener were added. Aqueous dispersion of a copolymer of styrene and 2-ethylhexyl acrylate (styrene unit 35 mol%, 2-ethylhexyl acrylate unit 65 mol%) (solids concentration 42.5% by weight) 1 Then, 0.7 part was added and mixed and dispersed to prepare a paste mixture. This paste-form mixture was applied to a punched metal in which Ni plating was applied to iron, filled and dried, and then compression-molded. After that, it is cut to a predetermined size and the negative electrode sheet is cut.
And

The positive electrode was prepared by dry-mixing 2 parts of nickel powder with 100 parts of nickel hydroxide powder, and then 10 parts of cobalt powder, 5 parts of carboxymethyl cellulose aqueous solution (solid content concentration 5% by weight), and polytetrafluorocarbon. 5 parts of an ethylene dispersant solution (solid content: 60% by weight) was mixed to obtain a paste mixture. This paste-form mixture is applied to a nickel foam base material, filled and dried at 80 ° C. for 2 hours.
It was compression molded at 1 ton / cm ² . Then, it was washed with warm water of 80 ° C. for 2 hours, dried at 80 ° C. for 1 hour, and compression-molded. Thereafter, the sheet was cut into a predetermined size to obtain a positive electrode sheet.

Next, the above-mentioned negative electrode sheet and positive electrode sheet are wound through a separator made of nylon non-woven fabric, placed in a AAA-size electrode can, and placed in an electrolytic solution (30% by weight KOH).
An alkaline aqueous solution in which 17 g of LiOH was dissolved in 1 liter of the aqueous solution was injected. The positive electrode tab was spot-welded to the sealing body with the reversible valve provided with the resin packing, and the outermost peripheral portion of the negative electrode was brought into contact with the side surface of the can, followed by sealing. Then
This was stored at 60 ° C. for 17 hours, and 0.25 C (138 m
After charging for 6 hours at A), 1.0 charge at 0.2 C (110 mA)
Discharged to V. This charge / discharge cycle was repeated until the discharge capacity became constant, thereby producing a nickel hydrogen storage battery.

Example 2 Nickel was prepared in the same manner as in Example 1 except that 0.5 parts of cobalt oxide B was used in place of 0.2 parts of cobalt oxide A in producing the negative electrode sheet. A hydrogen storage battery was manufactured.

Example 3 A nickel sheet was prepared in the same manner as in Example 1, except that 1.0 part of cobalt oxide C was used in place of 0.2 part of cobalt oxide A in producing the negative electrode sheet. A hydrogen storage battery was manufactured.

Comparative Example 1 A nickel hydrogen storage battery was produced in the same manner as in Example 1 except that cobalt oxide A was not used in producing a negative electrode sheet.

Comparative Example 2 Nickel was prepared in the same manner as in Example 1 except that 0.5 parts of cobalt oxide D was used in place of 0.2 parts of cobalt oxide A in producing a negative electrode sheet. A hydrogen storage battery was manufactured.

Comparative Example 3 Nickel was prepared in the same manner as in Example 1 except that 0.5 parts of cobalt oxide E was used in place of 0.2 parts of cobalt oxide A in producing the negative electrode sheet. A hydrogen storage battery was manufactured.

The nickel hydrogen storage batteries of Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated for charge / discharge cycle characteristics and high-rate discharge characteristics at low temperatures by the following methods.

<Charge / Discharge Cycle Characteristics>
Charge 0.6A (-ΔV = 5mV), Discharge 0.6A (1V
Charge / discharge in the cycle of (Cut), discharge capacity is 300mA
The number of cycles until deterioration to h was evaluated. The results were as shown in FIG.

<High Rate Discharge Characteristics at Low Temperature> Each battery was charged at 145 mA at 25 ° C. for 6 hours and then charged at −10.
C. for 5 hours, discharge at 550 mA, and discharge capacity (mA) until the battery voltage becomes 1.0 V.
h) was measured, whereby the high-rate discharge characteristics at low temperatures were evaluated. The results were as shown in Table 2 below.

[0037]

As is clear from FIG. 1 and Table 2, each nickel of Examples 1 to 3 in which a specific cobalt oxide having an atomic ratio of cobalt to oxygen within the range of the present invention was used as the conductive powder. It can be seen that the hydrogen storage battery has excellent charge-discharge cycle characteristics and also has excellent high-rate discharge characteristics at low temperatures.

On the other hand, both nickel hydrogen storage batteries of Comparative Examples 2 and 3 using cobalt oxide having an atomic ratio of cobalt and oxygen outside the range of the present invention as the conductive powder were as follows:
Compared with the nickel hydrogen storage battery of Comparative Example 1 in which no cobalt oxide was used, the charge-discharge cycle characteristics were somewhat improved, but were not sufficient, and the effect of improving the high-rate discharge characteristics at low temperatures was low. In 3, it is rather lower.

[0040]

As described above, according to the present invention, a cobalt oxide having an atomic ratio of cobalt and oxygen in a specific range is contained in a negative electrode using a hydrogen storage alloy powder made of a ternary alloy as a conductive powder. With this configuration, it is possible to provide a nickel hydrogen storage battery having excellent charge / discharge cycle characteristics and discharge characteristics at low temperatures.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing charge / discharge cycle characteristics of the nickel hydrogen storage batteries of Examples 1 to 3 and the nickel hydrogen storage batteries of Comparative Examples 1 to 3.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Ryu Nagai 1-1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd.

Claims (2)

[Claims] 1. A nickel hydrogen storage battery having a positive electrode using nickel hydroxide as an active material, a negative electrode made of a hydrogen storage alloy, an electrolyte and a separator, wherein the hydrogen storage alloy is M
mNi ₅ alloy (Mm represents a metal mesh) is composed of a ternary alloy in which part of Ni is replaced by at least one of Co, Mn, Al, Cu, Mo or Cr, and cobalt and oxygen are contained in the negative electrode. The atomic ratio is 1: 0.90
1: A nickel hydrogen storage battery containing 0.99 cobalt oxide. 2. The cobalt oxide in the negative electrode, wherein BE
Specific surface area by T adsorption method is 10 to 20 m ² / g, pore volume is 0.015 to 0.030 cc / g, average pore radius is 20
2. The nickel-metal hydride storage battery according to claim 1, wherein the angle is about 40 [deg.].