JPH09102314A - Negative electrode for alkaline storage battery and battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for use in a high-capacity alkaline storage battery by using a fulleride containing at least one kind of metal selected from among Li, Na, K, Mg, and Ca and to provide an alkaline storage battery using the same. SOLUTION: A negative plate 1 uses a fulleride containing either one of these metals: Li, Na, K, Mg, and Ca. The fulleride is represented by a general formula Mx Cn. In the general formula Mx Cn, M represents at least one kind of metal selected from among Li, Na, K, Mg, and Ca, (x) represents a stoichiometric composition ratio (1<=x<=3), and (n) represents carbon atom (n=60). Or in the general formula Mx Cn, (x)=1 and (n)=82. A nickel hydroxide used in a positive plate 2 is 9 to 12μm in average particle diameter and contains 10wt.% cobalt oxide or hydroxide and 8 to 9wt.% zinc oxide or hydroxide as additives.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to increasing the capacity of a negative electrode for an alkaline storage battery and improving the performance of a battery using the same, in particular to improving the 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 a typical alkaline storage battery, a nickel-cadmium storage battery using nickel hydroxide as the positive electrode active material and cadmium as the negative electrode active material and a nickel-hydrogen storage battery using a hydrogen storage alloy negative electrode that can be expected to have high capacity density 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 typical AB ₅ alloy has a capacity density of 300 mA when used in an actual battery.
It has stopped at about h / g. Therefore, in order to obtain a battery with higher 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 with a high energy density.

[0005]

The present invention comprises Li, Na,
Provided is a negative electrode for a high capacity density alkaline storage battery using a fullerene compound containing at least one of K, Mg and Ca metals, and further, this negative electrode and a nickel hydroxide positive electrode,
A high-performance alkaline storage battery is provided by constructing a battery provided with an alkaline electrolyte.

Further, as the above fullerene compound,
The general formula MxCn (M is at least one metal selected from Li, Na, K, Mg, and Ca, x is a stoichiometric composition ratio, 1 ≦ x ≦ 3, and n is a carbon atom. , N
= 60) or the above general formula MxCn
Is characterized by using x = 1 and n = 82.

[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 Unspecified, about 1.5 eV in conduction band and valence band
This is because the band gap of Therefore, although the electron conductivity and charge transfer of fullerenes are inferior to those of graphite, if there is an electron donation from another atom in the conduction band in advance, charge transfer is easily carried out on fullerenes to hydrogen having a high electron affinity,
Hydrogen ions are easily absorbed. This is because, for example, a material called C ₈ K in which potassium is intercalated in graphite in advance easily donates electrons to hydrogen (charge transfer) because electrons from potassium are contained in the conduction band of graphite, so that occlusion occurs. Feasible Facts (Enoki et al. Carbon 143, 136 (19
90)).

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 structure like ions, it is difficult for occluded chemical species with a clear ionic radius to absorb by steric factors.

The present inventors pay attention to these matters, and consider that an element effective for giving electrons to the conduction band of fullerene is an alkali metal or alkaline earth metal having a low ionization potential, and doping them We thought that it would be expected that fullerene with improved electron conductivity and thereby increased electron density could easily absorb and release hydrogen. In the present invention, among the alkali metals or alkaline earth metals, it was noted that it is particularly suitable as an element to be doped with Li, Na, K, Mg, and Ca, which has a low ionization potential and is lightweight.

C₆₀As a general method of doping into
Is C₆₀Interstitials of crystalline solids with the atom as one atom
Position, ie C₆₀Method of doping metal atoms to the outside
And C ₆₀To enclose and enclose metal atoms in the hollow of
Have been reported. The former is C₆₀3 pieces of metal
The unit cell consisting of atoms can be doped as a solid crystal.
Yes, C in the latter₆₀One metal atom is added for each
It is possible to It is also a higher fullerene
C₈₂Is reported to have the property of containing metal atoms more easily
Have been.

[0011] The present inventors have found that Li, Na,
A t _1u orbital that forms a conduction band even if doped with K, Mg, and Ca (orbital that forms a regular icosahedral symmetry and forms a triple degenerate LUMO (lowest empty state) that occurs from 11 orbitals)
Electrons are introduced into the electron, and the electron density and electron conductivity are improved. As a result, hydrogen ions with high electron affinity easily exchange electrons (charge transfer) from this orbit, and occlude the fullerene in the negatively charged electronic state. I thought it would be done. The electrochemical action when the metal-containing fullerene compound thus obtained is used as the negative electrode of an alkaline storage battery can be 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 hydrogen atoms can be occluded in one C ₆₀ molecule in a metal-doped state, and when converted into discharge electric capacity density, it is about 1900.
Since it is possible to achieve mAh / g, theoretically higher capacity density can be achieved as compared with the hydrogen storage alloy negative electrode.

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

[0013]

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 Li, Na, K, M of the present invention.
A negative electrode plate using a fullerene compound containing a metal of g or Ca, 2 a nickel hydroxide positive electrode plate, 3 a separator, 4 an insulating plate, 5 a battery case, 6 a positive electrode lead,
7 is a gasket, 8 is a positive electrode cap, 9 is a safety valve, 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 manufacturing mechanism is the arc discharge method. First, a carbon rod electrode having a diameter of 1 cm, which was formed by mixing carbonates of various metals as a dopant in advance and was placed in a glass container, was installed vertically. Then, the container is evacuated to a vacuum, helium gas (about 200 Torr) is introduced as a carrier gas, and a DC voltage of 23 V is applied to the electrodes.
Was applied, 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
For the metal-encapsulated type, that is, for x = 1, the fullerene compound with x = 3 was further irradiated with a YAG laser of 532 nm at 1200 ° C. under an argon gas atmosphere to obtain 1 One metal was included in each fullerene compound.

To the negative electrode plate 1, 5% by weight of polytetrafluoroethylene (PTFE) fluororesin dispersion was added so that the amount of this resin was 3 times that of the fullerene compound, and at the same time, the carbon material as a conductive material was added to the fullerene compound. 3% by weight was added to form a paste, and this paste was applied to a punching metal plate made of iron and having a thickness of 0.17 mm, a hole diameter of 1.8 mm, and an opening degree of 53%, which was plated with nickel, and passed through a slit of 0.6 mm. Smoothed. 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. Here, the same effect was obtained by using polyvinyl alcohol (PVA), polyethylene (PE), carboxymethyl cellulose (CMC), polystyrene (PS), methyl cellulose (MC), etc. as the binder. Further, a foam substrate as a core material, a metal fiber-based or carbon fiber-based three-dimensional structure,
The same effect can be obtained with a metal mesh, an expanded metal, or the like. To obtain the conductivity of the negative electrode plate 1, the specific conductivity is 10 with respect to the fullerene compound.
^It is necessary to add 5 wt% or more of graphite having a characteristic of ¹ s / cm or more. However, Li, Na, K, Mg, C
In the negative electrode using the fullerene compound containing any of the metals a, the electron conductivity of the crystalline solid was improved. In this case, therefore, the battery characteristics could be sufficiently obtained by adding 3% by weight to the fullerene compound. .

As the positive electrode plate 2, a porous foamed nickel substrate filled with nickel hydroxide containing 10% by weight of cobalt and having an average particle size of 10 μm, and a separator made of hydrophilic polypropylene nonwoven fabric was used. . As the electrolytic solution, 25 g / l of lithium hydroxide was dissolved in a potassium hydroxide aqueous solution having a specific gravity of 1.25 and used. Here, in the positive electrode plate 2,
In addition to cobalt, which has the function of giving electronic conductivity between nickel hydroxide particles, also in a positive electrode mixture containing 8 to 9% by weight of Zn oxide or hydroxide, which has the function of increasing the oxygen overvoltage during charging. Similar results are obtained. The average particle size of nickel hydroxide was 9 to 12 μm, which was the best as a result of studying the filling property and charge / discharge characteristics. As the separator, the effect can be obtained by using a polyolefin sulfonated polypropylene or an acrylic acid graft polymer in addition to the polypropylene non-woven fabric. As an electrolytic solution, the effect is obtained at a specific gravity of 1.2 to 1.3 at 20 ° C. operation, but when 1.25,
The charge / discharge characteristics were the best. Also, the same effect can be obtained by using sodium hydroxide as the alkaline electrolyte.

The positive electrode plate 2 is constructed so that the filling capacity of the positive electrode active material is in excess of the filling capacity of the negative electrode.
The battery was configured such 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 AB5 type hydrogen storage alloy containing misch metal and nickel as main components. . 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).

[0018]

[Table 1]

However, regarding the capacity, the discharge capacity density per weight of the hydrogen storage alloy used for 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 voltage of the comparative sample was 1.24V.

As can be seen from Table 1, Li, Na,
Batteries using a fullerene compound containing K, Mg, and Ca in the negative electrode are superior to fullerene in which voltage and capacity are not added with metal, and have a higher capacity density than when a hydrogen storage alloy is used in the negative electrode. Has been obtained. 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 nobler than that of the metal hydride. This is because the fullerene has a band gap of 1.5 eV as described above. This is because the Fermi level exists in the electrode and the electrode potential is placed at a low energy level. However, when a metal is added, electrons are donated to the t _1u orbit, so that the Fermi level rises, the electrode potential is placed at a position higher in energy level, and the potential shifts to the base direction, which increases the battery voltage. It is considered to be a thing. In addition, the reason why full capacity is not obtained in fullerene to which a metal element is not added is that the above-mentioned band gap exists, so overvoltage is large due to charge transfer or reduction in electron conductivity,
It is considered that the discharge end voltage was reached early because the negative electrode potential operated at a noble potential.

In the table, the mark * indicates the case of x = 1. At this time, n is 82, and one metal atom is included in C82, and when x = 3, n = 60 and C6
It was confirmed that 0 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. In such a case, x shows a value of 1 or more and less than 3. In the case where n = 60, the same level of battery characteristics as the battery of the example was obtained even in the battery using the sample in which the fullerene compounds showing various x values in such a range were mixed as the negative electrode material. Is 1
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 also applicable to Li, Na, K, Mg and Ca.
Even when another fullerene compound having the above is used for the negative electrode, the same effect can be expected.

[0022]

As described above, according to the present invention, Li, Na,
By using a fullerene compound containing at least one metal selected from K, Mg, and Ca 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 the 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 Negative electrode using a fullerene compound 2 Nickel hydroxide positive electrode 3 Separator 4 Insulating plate 5 Battery case 6 Positive electrode lead 7 Gasket 8 Positive electrode cap 9 Safety valve 10 Sealing plate

Claims (10)

[Claims] 1. A negative electrode for an alkaline storage battery, comprising a fullerene compound containing at least one metal selected from the group consisting of Li, Na, K, Mg and Ca. 2. A fullerene compound is represented by the general formula MxCn (M
Is at least one metal selected from Li, Na, K, Mg, and Ca, x is a stoichiometric composition ratio, 1 ≦ x ≦ 3, n is the number of carbon atoms, and n = 60) The negative electrode for an alkaline storage battery according to claim 1, which is a fullerene compound represented by: 3. A fullerene compound is represented by the general formula MxCn (M
Is at least one metal selected from Li, Na, K, Mg, and Ca, x is a stoichiometric composition ratio, x = 1, n is the number of carbon atoms, and n = 82). 2. The negative electrode for an alkaline storage battery according to claim 1, which is a fullerene compound. 4. A positive electrode using nickel hydroxide and Li, N
An alkaline storage battery, comprising: a negative electrode using a fullerene compound containing at least one of a metal group consisting of a, K, Mg, and Ca, and an alkaline electrolyte. 5. A negative electrode using a fullerene compound containing at least one metal selected from the group consisting of Li, Na, K, Mg and Ca, wherein the conductive agent is contained in an amount of 3% by weight based on the fullerene compound. The alkaline storage battery according to claim 4. 6. A positive electrode containing nickel hydroxide having an average particle diameter of 9 to 12 μm, containing 10 wt% of cobalt oxide or hydroxide and 8 to 9 wt% of zinc oxide or hydroxide as additives. The alkaline storage battery according to claim 4, wherein: 7. An alkaline electrolyte is an aqueous solution of potassium hydroxide or sodium hydroxide containing lithium hydroxide as an additive, and an electrolyte having a specific gravity of 1.2 to 1.3 at 20 ° C. is used. 5. The alkaline storage battery according to claim 4. 8. A negative electrode having a fullerene compound containing at least one metal selected from the group consisting of Li, Na, K, Mg and Ca, wherein the binder is polyvinyl alcohol, polyethylene, polytetrafluoroethylene, The alkaline storage battery according to claim 4, wherein any one of carboxymethyl cellulose, polystyrene, and methyl cellulose is used. 9. A three-dimensional structure in which a core material is a foamed substrate, a metal fiber or a carbon fiber, in the constitution of a negative electrode using a fullerene compound containing at least one kind of metal group consisting of Li, Na, K, Mg and Ca. The alkaline storage battery according to claim 4, wherein any one of a structure, a metal mesh, a punching metal, and an expanded metal is used. 10. The alkaline storage battery according to claim 4, wherein the separator is a polypropylene non-woven fabric, a non-woven fabric subjected to a polyolefin sulfonation treatment, or an acrylic acid graft polymer.