JPH09199123A - Negative electrode active material for alkaline storage battery and battery with it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the battery capacity by using a Fullerence compound containing a specific metal for a negative electrode active material. SOLUTION: A Fullerence compound containing at least one kind of metal selected from Fe, Co, Ni, Cu is used for an active material. The electrochemical action when it is used as a negative electrode is as follows: When charging, hydrogen ions in an electrolyte form C-H bond via the charge shift on the Fullerence compound having an increased charge density, and hydrogen is stored. In discharging, the C-H bond is released via the charge shift by the electron releasing reaction from the Fullerence compound, and hydrogen ions are diffused in the electrolyte. When the contained metal is doped, one Fullerence molecule can store 60 hydrogen ions, and this negative electrode can theoretically have the capacity and density higher than those of a hydrogen storage alloy negative electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high capacity negative electrode for an alkaline storage battery and a high performance battery using the same, particularly to an improvement in capacity density.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for alkaline storage batteries that can be expected to have high reliability as power sources for various small portable devices. As typical alkaline storage batteries, nickel-cadmium storage batteries that use nickel hydroxide as the positive electrode active material and cadmium as the negative electrode active material, and nickel-hydrogen storage batteries that use a hydrogen storage alloy negative electrode that can be expected to have higher capacity are in practical use. Has been converted.

[0003]

DISCLOSURE OF THE INVENTION In order to further increase the capacity of alkaline storage batteries, researches for improving hydrogen storage alloy materials are being conducted. Of these materials, the capacity density when a typical AB5 alloy is used in an actual battery is about 3
It remains around 00 mAh / g. Therefore, in order to obtain a battery with high energy density, it is necessary to obtain a novel negative electrode material capable of electrochemically absorbing and desorbing hydrogen.

In order to solve such problems, the present invention pays attention to the characteristics of fullerenes capable of storing and releasing hydrogen, and by modifying them as a compound with a metal,
The object of the present invention is to find a novel negative electrode material useful for batteries, and to provide a high capacity density negative electrode and an alkaline storage battery using the same having a high energy density.

[0005]

The present invention is based on Fe, Co,
Provided is a high capacity density negative electrode for an alkaline storage battery using a fullerene compound containing at least one metal selected from the group consisting of Ni and Cu, and further including the negative electrode, a nickel hydroxide positive electrode, and an alkaline electrolyte. By constructing a battery, a high performance alkaline storage battery is provided.

Further, as the above fullerene compound,
The general formula MxCn (M is at least one metal selected from the group consisting of Fe, Co, Ni, and Cu, x is a stoichiometric composition ratio, 1 ≦ x ≦ 3, and n is the number of carbon atoms. , N = 60), or in the above general formula MxCn, x = 1 and n = 82 is used.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Fullerene C ₆₀ is already 1985.
It was successfully synthesized by Kuroto et al. The shape is almost the same as a soccer ball. Other fullerenes include those having a carbon number of C ₇₀ , C ₈₂ , or higher, and are composed of a 5-membered ring or a 6-membered ring. The electronic structure of these fullerenes, unlike ordinary semi-metallic graphite, shows semiconductor-like properties. The reason is the electronic structure, the outer and inner sphere different electron density states of pi-electric electron, tended to be lower in higher inside the outside, to further sigma orbital is mixed, in a simple SP ² hybrid orbital It is not possible to specify it, and the conduction band and valence band are approximately 1.9e.
This is because a V band gap is generated. Therefore,
Fullerene is inferior to graphite in electron conductivity and charge transfer, but if there is an electron donation from another atom in the conduction band in advance, hydrogen with a high electron affinity will easily transfer charge on fullerene and occlude hydrogen ions. It is easy to be done. This is, for example, C ₈ K obtained by pre-intercalating potassium with graphite.
The fact that the material contains electrons from potassium in the conduction band of graphite can easily donate electrons to hydrogen (charge transfer) and can occlude (Enoki et al. Carbon 143,1).
36 (1990)).

The storage of hydrogen is possible by forming C--H bonds mainly outside the soccer ball-shaped fullerene. Hydrogen ions having almost no ionic radius can absorb such hydrogen, but for example, Li
Due to the 2S orbital closed shell structure such as ⁺ ion, it is difficult for a species having a definite ionic radius to absorb due to a steric factor.

The present inventors pay attention to these matters, and consider that an element effective for giving electrons to the conduction band of fullerene is a 3d transition metal which tends to have localized d electrons, and dope these. Therefore, we thought that it is expected that the fullerene with improved electron conductivity can absorb and release hydrogen easily.

In the present invention, it is noted that among the 3d transition metals that tend to have localized d-electrons, Fe, Co, Ni and Cu, which tend to have localized electrons, are suitable as doping elements. And examined.

C₆₀As a general method of doping into
Is C₆₀Lattice of a crystalline solid with the atom as an atom
Between positions, that is, C₆₀Method of doping metal atoms to the outside
And C₆₀To enclose and enclose metal atoms in the hollow of
Have been reported. The former is C ₆₀3 original metal pieces
Can be doped as a solid crystal
And in the latter C₆₀Doping one metal atom per one
It is possible to C, which is a higher fullerene
₈₂Has been reported to be more likely to contain metal atoms.
Have been.

[0012] The present inventors have found that Fe, C
A t _1u orbital in which a d electron forms a conduction band even if doped with o, Ni, or Cu (an orbital that forms a regular icosahedral symmetry and forms a triple degenerate LUMO (lowest empty state) generated from 11 orbitals) ), The electron density and electron conductivity are improved. As a result, hydrogen ions with a high electron affinity easily exchange electrons from this orbit (charge transfer) and are occluded by fullerenes in the negatively charged electronic state. I thought it was something. The electrochemical action when the metal-containing fullerene compound thus obtained is used as the negative electrode of an alkaline storage battery is explained as follows.

First, at the time of charging, hydrogen ions in the electrolytic solution form C—H bonds on the metal-containing fullerene compound having an increased charge density by charge transfer, and the hydrogen ions are occluded. During discharge, C—H bonds are broken due to charge transfer due to a deelectron reaction from the fullerene compound, and hydrogen ions diffuse into the electrolytic solution. In this case, up to 60 hydrogens can be stored in one C ₆₀ molecule in the metal-doped state,
Converting this to the discharge capacitance density, about 1900 mAh
/ G is possible, and the capacity density can be theoretically increased as compared with the hydrogen storage alloy negative electrode.

As described above, by using a metal-doped fullerene compound as the negative electrode active material, it is possible to provide a high capacity alkaline storage battery.

[0015]

EXAMPLE FIG. 1 is a schematic configuration diagram of a nickel-carbon storage battery using a fullerene compound in one example of the present invention. In FIG. 1, 1 is Fe, Co, Ni of the present invention,
A negative electrode plate using a fullerene compound containing any metal of Cu, 2 a nickel hydroxide positive electrode plate, 3 a separator, 4 an insulating plate, 5 a battery case, 6 a positive electrode lead,
Reference numeral 7 is an insulating gasket, 8 is a positive electrode cap, 9 is a safety valve, and 10 is a sealing plate.

A method for producing the fullerene compound used for the negative electrode in the examples of the present invention will be described. The basic mechanism is the arc discharge method.
A carbon rod electrode, which was formed by mixing carbonates of various metals as dopants in advance, was placed vertically. Then, the inside of the container was evacuated to a vacuum, helium gas (about 200 Torr) was introduced as a carrier gas, a DC voltage of 22 V was applied to the electrodes, and an electric current of about 40 mA was applied to generate arc discharge. When the discharge reaction is performed, a carbon-containing carbon deposit grows on the tip of the counter electrode. As a result of analyzing this deposit,
The yield of the fullerene compound was 18%. A fullerene compound having a purity of about 90% was fractionated from this carbon material using octadecyl silica or the like, and this was used as a negative electrode material for evaluation. Solid crystalline fullerene compound, ie X
= 3 was obtained by the above method, but for the metal-encapsulated type, that is, X = 1, a fullerene compound of X = 3 was further added under an argon gas atmosphere.
A 532 nm YAG laser was irradiated at 00 ° C. to encapsulate one metal per one fullerene compound.

For the negative electrode plate 1, a paste was prepared by adding 5% by weight of a fluororesin dispersion so that the weight of this resin was 3 times that of the fullerene compound, and then this paste was formed to a thickness of 0.17 mm and a pore diameter of 1 It is applied to a punching metal plate made of iron with a diameter of 8 mm and an opening degree of 53% and plated with nickel, and smoothed through a slit of 0.6 mm.
Then, it was dried at 120 ° C. for 1 hour, and this electrode was passed through a roller press to adjust the thickness to 0.5 mm.
The negative electrode lead plate was attached by spot welding. For the positive electrode plate 2, a porous foamed nickel substrate filled with nickel hydroxide was used, and for the separator, a hydrophilic polypropylene non-woven fabric was used. The electrolyte used was a 25 g / l lithium hydroxide solution dissolved in a potassium hydroxide aqueous solution having a specific gravity of 1.25.

The positive electrode plate 2 was constructed so that the filling amount of the positive electrode active material was in excess of the filling capacity of the negative electrode, and the battery was constructed so that the battery characteristics were regulated by the characteristics of the negative electrode. As a comparative example, a nickel-hydrogen storage battery was prepared by the same construction method as that of the example, using a negative electrode constructed in the same manner as above using an AB ₅ type hydrogen storage alloy containing misch metal and nickel as main components. did. The batteries of these examples and the batteries of comparative examples were subjected to constant current charging at 0.17 A for 11 hours, and then constant current discharging to 0.5 V at 0.5 A. The results are shown in (Table 1).

[0019]

[Table 1]

However, regarding the capacity, the discharge capacity density per weight of the hydrogen storage alloy using the negative electrode of the comparative sample is 1
The relative value of the discharge capacity density per weight of the fullerene compound when 00 was shown. The average discharge voltage was 1.
It was 24V.

As can be seen from Table 1, Fe, Co,
The battery using a fullerene compound containing Ni and Cu for the negative electrode is superior in voltage and capacity to the fullerene containing no metal, and has a higher capacity density than the case using a hydrogen storage alloy for the negative electrode. Has been. These reasons are considered as follows. First, the reason why the voltage is low in the fullerene to which the metal element is not added is that the negative electrode potential is a nobler potential than the metal hydride, which is the fullerene band of 1.9 eV as described above. This is because the Fermi level exists between the gaps, and the electrode potential is placed at a low energy level. But,
When a metal is added, electrons are donated to the t _1u orbit, so the Fermi level rises, the electrode potential is placed at a position higher in energy level, and the battery voltage becomes higher because the potential shifts to the base direction. thinking.

In addition, fullerene to which a metal element is not added does not have a sufficient capacity, because the above-mentioned band gap exists, so that overvoltage is large due to charge transfer or deterioration of electronic conductivity, and the negative electrode potential is noble. It is considered that the discharge end voltage was reached early due to the fact that it operated at a potential.

In the table, when x = 1, n at this time is 82, and one metal atom is included in C ₈₂ ,
When x = 3, n = 60, and it was confirmed that C ₆₀ and the metal were crystalline solids having periodicity. In addition to the above examples, when n = 60, metal defects may be unevenly distributed in the crystal, and in such a case, X has a value of 1 or more and less than 3. The same level of battery characteristics as that of the battery of the example was obtained even in the battery using the sample in which the fullerene compounds exhibiting various X values in such a range were mixed as the negative electrode material. It was confirmed that the effect of the present invention can be exhibited when ≦ X ≦ 3. In addition to the above-mentioned C ₆₀ and C _82- based fullerene compounds, the present invention is expected to have similar effects even when other fullerene compounds containing Fe, Co, Ni and Cu are used for the negative electrode. it can.

[0024]

As described above, according to the present invention, Fe, Co, N
By using a fullerene compound containing at least one metal of i or Cu for a negative electrode for an alkaline storage battery, a negative electrode having a high capacity and the battery can be provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a nickel-hydrogen storage battery using a fullerene compound negative electrode according to an embodiment of the present invention.

[Explanation of symbols]

 1 Hydrogen Storage Electrode (Fullerene Compound) 2 Nickel Hydroxide Electrode 3 Separator 4 Insulating Plate 5 Battery Case 6 Positive Electrode Lead 7 Insulating Gasket 8 Positive Cap 9 Safety Valve 10 Sealing Plate

Claims (4)

[Claims] 1. A negative electrode active material for an alkaline storage battery, wherein a fullerene compound containing at least one metal selected from the group consisting of Fe, Co, Ni and Cu is used as the active material. 2. A fullerene compound is represented by the general formula MxCn (M
Is at least one metal selected from the group consisting of Fe, Co, Ni and Cu, x is a stoichiometric composition ratio, and 1 ≦ x
≦ 3, n represents the number of carbon atoms, and is a fullerene compound represented by n = 60).
The negative electrode active material for an alkaline storage battery according to the above. 3. A fullerene compound, a general formula MxCn (M is at least one metal selected from the group consisting of Fe, Co, Ni and Cu, x is a stoichiometric composition ratio, x = 1, and n Represents the number of carbon atoms and is a fullerene compound represented by n = 82), The negative electrode active material for alkaline storage batteries according to claim 1. 4. A positive electrode using nickel hydroxide and Fe, C
An alkaline storage battery comprising a negative electrode using a fullerene compound containing at least one metal selected from the group consisting of o, Ni, and Cu, and an alkaline electrolyte.