JPH06342655A - Electrode and battery provided therewith - Google Patents

Abstract

PURPOSE:To provide an electrode and a battery, in which the discharging capacity per unit volume is large and the initial voltage drop is restricted while stable discharging voltage can be maintained. CONSTITUTION:Graphite fluoride and fluorene fluoride are contained in an electrode. The fluorene fluoride is indicated by am expression CxFy where C is a carbon atom forming a fluorene frame, F is a fluorine atom connected to the carbon atom, (x) is integer from 28 to 1000, and (y) is 0.01x-1.8x. The fluorene fluoride is provided by fluorinating fluorene such as 35 C60, C70, C76, C78, C82, C84, C90, C96, C102, C106, C110 by a fluoride gas. In a battery provided with the electrode serving as a positive electrode, even when the fluorene fluoride is of small amount, the voltage drop at the early stage of discharging is drastically restricted. The battery is provided with, for example, a negative electrode containing alkali metal serving as an active material, and with a nonaqueous electrolyte.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode that can be used in, for example, a lithium battery, and a battery including the electrode.

[0002]

2. Description of the Related Art Fullerenes, which are also called carbon clusters, are special carbon allotropes having a three-dimensional structure different from the graphite structure and having a void portion in the center. Among the fullerenes, C ₆₀ is composed of 60 carbon atoms and has a football-like structure, and the mass number found in the soot generated by laser irradiation of graphite by Kroto et al. 720 substances. Also, 1991
In April 2013, Hebard et al. Reported that C ₆₀ doped with potassium exhibited superconductivity at an absolute temperature of 18 ° K. As described above, since fullerenes have special structures and properties, development of new fullerene derivatives and their uses is expected.

On the other hand, a battery using a light metal such as lithium or magnesium as an active material has been attracting attention because of its high energy density. For example, in a lithium battery using lithium as a negative electrode active material, sulfur dioxide, fluorinated graphite, copper sulfide, manganese dioxide, etc. are used as a positive electrode active material, and an organic solvent or an inorganic nonaqueous solvent having a high dielectric constant is used as an electrolytic solution. Various types of batteries have been developed.

Among these, the battery using fluorinated graphite as the positive electrode active material is particularly excellent in terms of storability as well as obtaining a relatively stable discharge voltage. However, this battery has a problem that the discharge voltage is lower than that in the middle stage of discharge because the overvoltage is large at the initial stage of discharge.

As a method of solving this problem, a method of discharging the battery to some extent before use has been proposed. However, this method wastes the discharge capacity. Further, as another method, a method has been proposed in which fluorinated graphite in which a part of fluorine is released by γ-ray irradiation is used as a positive electrode active material. However, this method cannot be said to be industrially advantageous because the process becomes complicated.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electrode which has a large discharge capacity per unit volume, a small overvoltage and can maintain a stable discharge voltage, and a battery using this electrode. To do.

[0007]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, when fluorinated graphite and a fluorinated fullerene obtained by fluorinating fullerene are used in combination as an electrode active material, The inventors have found that the voltage drop at the initial stage of discharge, which is observed when only fluorinated graphite is used as the active material, can be remarkably suppressed and the present invention has been completed.

That is, the present invention relates to a fluorinated graphite and a formula
C _x F _y (wherein, C represents the carbon atoms constituting the fullerene skeleton, F is a fluorine atom bonded to the carbon atoms, x is an integer of 28-1,000, y is 0.01X～1.
8x) and at least one fluorinated fullerene.

The present invention also provides a battery including the electrode.

The fluorinated graphite is prepared by a conventional method, for example,
It can be obtained by reacting graphite and fluorine gas at a temperature of about 250 to 650 ° C. Fluorinated graphite F
/ C is, for example, about 0.45 to 1.30.

The fluorinated fullerene contains carbon atoms having 1 to 3 fluorine atoms bonded by a covalent bond. The carbon atoms that make up the fullerene skeleton include
Usually, one fluorine atom is bonded, but at the site where the fullerene skeleton is partially missing, two or three fluorine atoms may be bonded to the carbon atom.

In the above formula, preferred x is 60 to 11
It is about 0. Particularly preferred x is 60, 70, 76,
78, 82, 84, 90, 96, 102, 106, 11
0 and the like are included. The F / C atomic ratio in the fluorinated fullerene is, for example, 0.01 to 1.8, preferably about 0.5 to 1.8. Even if a fluorinated fullerene having a small F / C atomic ratio, for example, about 0.01 to 0.5 is used, the voltage drop problem characteristic of a battery using fluorinated graphite as a positive electrode active material can be solved. it can.

The fluorinated fullerene is usually a white to yellowish white or brown solid, has excellent water repellency, and is stable in air. The structure of fullerene fluoride is
Elemental analysis, mass spectrum, nuclear magnetic resonance spectrum, X
It can be analyzed by analysis means such as line diffraction and Raman absorption spectrum.

Such fluorinated fullerenes are, for example,
It can be obtained by reacting fullerene with fluorine under reduced pressure, normal pressure or increased pressure.

The fullerene used in the reaction includes C ₆₀ ,
C ₇₀ , C ₇₆ , C ₇₈ , C ₈₂ , C ₈₄ , C ₉₀ , C ₉₆ , C ₁₀₂ ,
Examples include C ₁₀₆ , C ₁₁₀ , C ₂₄₀ , C _{540 and the} like. Preferred fullerenes are composed of x = 60 to 110 carbon atoms.

The form of the fullerene may be spherical, egg-shaped, rugby ball-shaped or the like as long as it has a three-dimensional shape and has a void in the central portion, and carbon atoms constituting the vertices or faces of the three-dimensional structure. It may have a basket-like shape in which is partially missing. In addition, carbon number of 1 by-product in the production of fullerene
It may be an incomplete basket of 00 or more. These fullerenes can be used alone or as a mixture of two or more kinds.

In the above reaction, the fluorine pressure is generally in the range of 0.07 to 1.5 atm.
Fluorine gas may be used as it is, nitrogen, helium,
It may be diluted with an inert gas such as argon or neon before use.

The amount of fluorine used is, for example, 0.1 to 1000 mol, preferably 1 to 1 mol, relative to 1 mol of fullerene.
It is about 100 mol. The reaction temperature is, for example, 0 to 350.
C., preferably room temperature to about 300.degree.

The F / C atomic ratio of the resulting fluorinated fullerene can be adjusted by the reaction temperature, the reaction time, the amount of fluorine used, and the like.

The fluorinated fullerene thus obtained usually has a form corresponding to the fullerene used as the raw material.

A feature of the present invention is that the combined use of fluorinated graphite and fluorinated fullerene reduces overvoltage and suppresses initial voltage drop.

The addition amount of the fullerene fluoride in the electrode of the present invention can be appropriately selected within the range where the effect of suppressing the voltage drop is exhibited. Generally, since the voltage drop is significantly suppressed by adding a small amount of fluorinated fullerenes, a large amount of fluorinated fullerenes is not required. For example, the addition amount of the fluorinated fullerene is 0.1 to 50 parts by weight, preferably 0.3 to 10 parts by weight, and more preferably 1 to 8 parts by weight with respect to 100 parts by weight of fluorinated graphite. . If the amount of the fluorinated fullerene added is less than 0.1 parts by weight, the effect of suppressing the voltage drop is difficult to obtain, and if it exceeds 50 parts by weight, the moldability is likely to decrease, which is not preferable in terms of economy. .

The electrode of the present invention may contain a substance other than the fluorinated graphite and the fullerene fluoride. For example, a caking material or a conductive material may be contained in order to improve moldability and conductivity. Examples of the binder include thermoplastic resins such as polyvinyl acetate, acrylic resin, polyvinyl chloride, polystyrene, polyethylene, polyamide, polyester, and fluororesin such as polytetrafluoroethylene; amino resin, phenol resin, epoxy resin, Thermosetting resin such as urethane resin may, for example, be mentioned. Examples of the conductive material include carbon black such as acetylene black, graphite, metal and the like. The content of each of the binder material and the conductive material is, for example, 10 to 1000 parts by weight, preferably 20 parts by weight, relative to 100 parts by weight of the active material.
It is about 300 parts by weight.

The electrode of the present invention is prepared, for example, by mixing a positive electrode active material containing fluorinated graphite and fluorinated fullerene with an additive such as the conductive material, if necessary, and molding the mixture by a conventional method. Can be easily obtained.

The battery of the present invention comprises the above electrode.
As such a battery, for example, the electrode is a positive electrode,
Examples thereof include a primary battery provided with a negative electrode and a non-aqueous electrolyte.

The negative electrode may be formed of only the negative electrode active material, or may be formed by supporting the negative electrode active material on a negative electrode material such as a carbon material. Examples of the negative electrode active material include alkali metals or alkaline earth metals such as lithium, sodium and magnesium. Preferred negative electrode active materials include alkali metals such as lithium and sodium. A particularly preferred negative electrode active material is lithium.

As the electrolytic solution, various organic solvents having a high dielectric constant are used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane,
Examples thereof include aprotic solvents such as sulfolane, 1,2-dimethoxyethane, dimethyl sulfoxide, acetonitrile, N, N-dimethylformamide, and diethylene glycol dimethyl ether.

As the electrolytic solution, LiClO ₄ , LiBF ₄ , LiClF may be added to one or more of the above solvents.
₄ , LiAsF ₆ , LiSbF ₆ , LiAlO ₄ , Li
AlCl ₄ , LiPF ₆ , LiCl, LiBr, LiI
A solution in which a salt that produces an anion that is difficult to solvate is dissolved is often used.

The shape of the battery may be any shape such as a cylindrical shape, a square shape or a button shape. The battery of the present invention can be used in a wide variety of applications such as a power source for various electronic devices.

[0030]

EFFECTS OF THE INVENTION Since the electrodes and batteries of the present invention contain fluorinated graphite and fullerene fluoride as active materials, the discharge capacity per unit volume is large, and the overvoltage is small and the voltage drop at the initial stage of discharge is remarkable. Since it is suppressed, a stable discharge voltage can be maintained.

[0031]

EXAMPLES The present invention will be described in more detail based on the following examples.

Example 1 Fullerene having a C ₇₀ content of 20% by weight or less (C ₆₀ / C
_{The 70} mixture (manufactured by MER, USA) was evacuated at 200 ° C. for about 10 hours to remove the organic solvent contained as an impurity.

0.04 g of this fullerene was charged into a reactor made of nickel, the system was evacuated and filled with argon gas. Then, at room temperature, a fluorine gas was passed at 2 cc / min and reacted for 4 hours. As a result, 0.08 g of fluorinated fullerene was obtained. As a result of elemental analysis, the composition formula was C ₆₀ F ₄₁ . The crystals of the obtained fullerene fluoride were analyzed by the X-ray diffraction method. The measurement conditions and measurement results are shown below.

Measurement conditions Tube: Cu, Tube voltage: 50 KV, Tube current: 80 mA, Goniometer: Wide-angle goniometer, Sampling width: 0.
010 °, scanning speed: 5.000 ° / min, divergence slit: 1 °, scattering slit: 1 °, light receiving slit: 0.
30 mm, attachment: standard sample holder, filter: Ni measurement result Peak No. 1: 2θ = 8.950, surface spacing 9.87
235, intensity value 4388, half width 1.178, I / I
₀ = 100 Peak No. 2: 2θ = 14.770, surface spacing 5.9
9273, strength value 3668, I / I ₀ = 84 100 parts by weight of fluorinated graphite (F / C = 1.01) were mixed with 5 parts by weight of the fluorinated fullerene obtained above. To this, 105 parts by weight of acetylene black and 105 parts by weight of polyethylene were added and mixed. About 30 mg of the obtained mixture was sandwiched between filter papers and molded into disc-shaped pellets having a diameter of 0.9 cm. Next, carbon fibers were wound around the edge portion of the disk-shaped pellet and fused with polyethylene to obtain continuity to obtain a positive electrode.

On the other hand, the negative electrode was obtained by connecting a lead wire to a lithium plate having a diameter of 1 cm.

As an electrolytic solution, propylene carbonate in which lithium perchlorate having a concentration of 1 mol / liter was dissolved was used.

A primary battery was prepared from the positive electrode, the negative electrode and the electrolytic solution thus obtained, and the apparatus as shown in FIG.
It was discharged at a current density of 0.5 mA / cm ² . The above operations were all performed under an argon atmosphere except for the production of the positive electrode. Lithium was used for the electrode of the reference electrode.

As a result, no voltage drop was observed at the initial stage of discharge. The open circuit voltage was 3.3V, the discharge potential was 2.1V, and the discharge capacity utilization rate was 98%.

Comparative Example A positive electrode using only fluorinated graphite as an active material was prepared in the same manner as in Example 1 except that fluorinated fullerene was not used. Further, a primary battery was prepared in the same manner as in Example 1 except that this positive electrode was used, and a discharge experiment was conducted.

As a result, a voltage drop of 0.1 V was observed at the initial stage of discharge. The open circuit voltage was 3.3 V and the discharge capacity utilization rate was 98%.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an experimental apparatus used in Examples.

[Explanation of symbols]

 1, 2 ... Negative electrode 3 ... Positive electrode 4 ... Reference electrode 5 ... Electrolyte solution 6 ... Constant current generator 7 ... Voltage follower 8 ... Recorder

Claims (4)

[Claims] 1. A fluorinated graphite and a formula C _x F _y (wherein C
Is a carbon atom constituting the fullerene skeleton, F is a fluorine atom bonded to the carbon atom, and x is 28 to 100.
An integer of 0, y is 0.01x to 1.8x) and an electrode containing at least one kind of fluorinated fullerene. 2. x is 60, 70, 76, 78, 82, 8
The electrode of claim 1, comprising at least one fluorinated fullerene that is 4, 90, 96, 102, 106 or 110. 3. A battery comprising the electrode according to claim 1 or 2. 4. A battery comprising a positive electrode, a negative electrode containing an alkali metal as an active material, and a non-aqueous electrolyte,
The battery according to claim 3, wherein the electrode according to claim 1 or 2 is used as the positive electrode.