JPH1040912A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conductivity of an active substance for battery and increase the batter capacity by constituting the battery by the use of a battery active substance having a specific stricture in a compound causing intercalation as either a positive pole active substance or a negative pole active substance. SOLUTION: A battery active substance having minute conductive paths and constituted with vapor-phase growth carbon fibers constituted with preferably carbon network-like planes arranged in a cylindrical shape in a compound causing intercalation and laminated in the diamentral direction of the cylinder is used as either positive pole active substance or negative pole active substance. For example, as the positive pole active substance 3 for the positive pole (collector 1) of a Li-V secondary battery, compound causing intercalation (such as V2 O<5> ) 2 in which vapor-phase growth carbon fibers 4 are dispersed is used. The vapor-phase growth carbon fibers have preferably a diameter of 1 micrometers of less and a length 0.01-100 micrometers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery capable of achieving an increase in battery capacity by forming fine conductive paths in an active material.

[0002]

2. Description of the Related Art Conventionally, metal oxides and metal sulfides have been used as active materials for various batteries. For example, nickel-metal hydride batteries use fine metal oxide or metal sulfide powder that is heated and pressed to sinter, and manganese dry batteries and the like use metal oxide or metal sulfide. A material obtained by mixing a binder such as PTEF (polytetrafluoroethylene) and a conductive agent such as carbon black and hardening the mixture by heating and pressing is used. In recent years, the development of lithium secondary batteries using lithium or a lithium alloy as a negative electrode active material has been activated, and metal oxides and metal sulfides have been used as these positive electrode active materials.

However, most of metal oxides and metal sulfides used as conventional active materials for batteries have high resistance in which electricity (electrons) do not easily flow, and exchange of ions and electrons is performed smoothly. Therefore, there is a problem that the capacity of the active material is hardly sufficiently extracted. For example, FIG. 7 schematically shows an example of a discharge reaction in a positive electrode of a lithium-vanadium secondary battery. In the figure, reference numeral 11 denotes a current collector, 13 denotes a positive electrode active material (V ₂ O ₅ ), and 15 denotes a positive electrode active material. Indicates an electrolyte.

As described above, in the positive electrode, the electrolyte 1
The lithium ions (Li ⁺ ) in the positive electrode active material (V
₂ O ₅ ) 13, receives electrons (e ⁻ ) and receives Li
A reaction to produce V ₂ O ₅ occurs. However, since the electrons (e ⁻ ) hardly flow through the inside of the positive electrode active material 13, the lithium ions penetrating into the positive electrode active material 13 cause the current collector 1
There is a problem that electrons cannot be received until reaching the vicinity of the interface with No. 1, which causes a loss of battery capacity. In addition, during the charge, a reaction reverse to that at the time of discharge occurs, and lithium ions (Li ⁺ ) are desorbed from Li · V ₂ O ₅ generated in the positive electrode active material 13, but electrons (e ⁻ ) also generate electrons (e ⁻ ). The charging reaction slows down because it cannot move smoothly inside.

Therefore, generally, a conductive powder such as carbon black is added to the positive electrode active material 13 to improve the conductivity of the active material. However, also in this case, the substantially spherical conductive powder is only dispersed discontinuously in the positive electrode active material 13. Therefore, the conductivity cannot be sufficiently improved everywhere in the active material, and there has been dissatisfaction in that the battery capacity of the active material cannot be sufficiently drawn.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the conductivity of an active material for a battery so as to increase the capacity of the battery.

[0007]

In order to solve the above-mentioned problems, a battery according to the present invention is characterized in that a battery active material having fine conductive paths in a compound causing intercalation is used as a positive electrode active material or a negative electrode active material. It is characterized by being used for any of them. The battery has fine conductive paths in the intercalating compound. The compound causing the above intercalation is appropriately selected depending on the structure of the battery. For example, when forming a lithium secondary battery using lithium or a lithium alloy as the negative electrode active material, a compound capable of causing intercalation with lithium ions is used. The conductive path is made of vapor grown carbon fiber in which carbon mesh planes are arranged in a cylindrical shape and stacked in the diameter direction of the cylinder.

[0008] The conductive path is preferably formed using vapor grown carbon fiber. This vapor-grown carbon fiber uses aromatic hydrocarbons such as toluene, benzene and naphthalene, and aliphatic hydrocarbon compounds such as propane, ethane and ethylene, preferably benzene or naphthalene as raw materials.
This raw material is gasified and a catalyst made of ultrafine metal at a reaction temperature of 900 to 1500 ° C. together with a carrier gas such as hydrogen, carbon dioxide, carbon monoxide, etc.
The carbon fibers obtained by contacting with 03 μm iron, nickel, iron-nickel alloy, etc., and thermally decomposing the carbon fibers are graphitized by heat treatment. The heat treatment for graphitization is performed, for example, at 1500 to 3500 ° C., preferably at 200 ° C.
The reaction is performed at a temperature of 0 to 3000 ° C. for 3 to 120 minutes, preferably 30 to 60 minutes, under an atmosphere of an inert gas such as argon. The vapor-grown carbon fiber obtained in this manner has a shape in which carbon mesh planes are arranged in a cylindrical shape and stacked in the diameter direction of the cylinder. The vapor-grown carbon fiber has a diameter of 1 μm or less and a length of 0.01 to 100 μm.
It is desirable that

If the vapor-grown carbon fiber has a diameter larger than 1 μm, the vapor-grown carbon fiber may be dispersed in a dispersion medium and used for molding an active material for a battery as described later. Is difficult to disperse uniformly in a dispersion medium or to apply the dispersion on a substrate. On the other hand, if the length of the vapor-grown carbon fiber is less than 0.01 μm, the effect of improving the conductivity of the battery active material cannot be sufficiently obtained, and
If it is longer than μm, the formability of the active material for a battery is deteriorated as in the case where the diameter is too large. Therefore, the diameter and length ranges are preferably used. Particularly, the vapor growth carbon fiber 4 having an aspect ratio (diameter: length) of diameter and length of 1: 1000 or more is preferable. The weight ratio of the compound causing intercalation to the vapor grown carbon fiber in the battery active material is desirably 100: 0.5 to 3.

If the amount of the vapor-grown carbon fibers contained in the battery active material is too small, the effect of improving the conductivity of the battery active material cannot be sufficiently obtained, and if the amount is too large, the molding of the battery active material will be insufficient. And the film strength of the battery active material may be insufficient. Therefore, the range of the weight ratio is desirable. The compound causing the intercalation is a metal oxide or a metal sulfide. For example, V ₂ O ₅ , TiS ₂ ,
Metal oxides or metal sulfides such as Mn ₂ O ₄ , CoO ₂ , MoS ₂ , and TiS are suitable. By using these, a relatively small battery having a large charge / discharge capacity can be obtained. In particular, V ₂ O ₅ is preferably used among the metal oxides and metal sulfides because it is inexpensive and has a large discharge capacity.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 schematically shows an example in which a positive electrode of a lithium-vanadium secondary battery is formed by using the battery active material of the present invention. In the positive electrode, a layer of a battery active material (hereinafter, also referred to as a positive electrode active material) 3 is formed on a current collector 1, and an electrolyte layer 5 is provided so as to be in contact with the battery active material 3. ing. The battery active material 3 contains a vapor-grown carbon fiber 4 in a compound (V ₂ O ₅ ) 2 causing intercalation.
Is becoming dispersed. The current collector 1 is formed using a material that electrically connects the positive electrode active material 3 and the negative electrode active material (not shown). As such a material, for example, stainless steel, NiAl, or the like is suitably used.

The electrolyte 5 is appropriately selected and used according to the structure of the battery, and may be a liquid electrolyte or a solid electrolyte. In the present embodiment, a substance that is chemically stable with respect to the positive electrode active material 3 and the negative electrode active material and that can move for lithium ions to electrochemically react with the positive electrode active material 3 is used. For example, a solid electrolyte using lithium ions as a conductor such as polyethylene oxide, propylene carbonate, 2 methyl tetrahydrofuran,
-Dimethoxyethane, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile,
One or more aprotic organic solvents selected from formamide, dimethylformamide, nitromethane,
10 ₄ , LiAlCl ₄ , LiBF ₄ , LiCl, LiP
An electrolyte solution or the like in which a lithium salt such as F ₆ or LiAsF ₆ is dissolved can be used.

The active material for a battery according to the present invention can be produced, for example, as follows. Here, a case where V ₂ O ₅ is used as a compound causing intercalation will be described as an example. First, an organic metal or metal polymer solution is prepared as a raw material of a compound causing intercalation. When V ₂ O ₅ is used as the compound causing the intercalation, alkoxy vanadium (VO (OC ₂ H ₅ ) ₅ ) can be preferably used. Then, the vapor-grown carbon fiber is dispersed in an appropriate dispersion medium such as xylene, and is preliminarily dispersed by ultrasonic waves. Then, alkoxy vanadium is added to the predispersion, and the mixture is uniformly mixed and dispersed. Alternatively, the vapor grown carbon fiber may be added to the metal polymer solution, mixed, and uniformly dispersed. Mixing and dispersion of the vapor-grown carbon fiber and the metal can be preferably performed using, for example, a three-roll mill, a kneader, a ball mill, or the like.

Next, the obtained dispersion is applied to an appropriate substrate. A current collector is generally used as the substrate. As a coating means, a spin coat, an applicator,
Coater, spraying, printing, dipping and the like can be preferably used. Further, the thickness of the coating film obtained by applying the dispersion, the thickness of the battery active material obtained after the firing step described below is preferably 0.5 to 2 μm, more preferably about 1.0 μm. It is set as follows. As the thickness of the active material for a battery increases, the amount of intercalating Li increases, and there is no problem in the principle of a battery if the thickness is larger than the above range. The number of layers to be superimposed increases extremely.

Subsequently, the applied dispersion liquid coating film is heated.
To dry the dispersion medium and the solvent in the dispersion. This heating
The step is preferably performed at a temperature of 50-150 ° C,
More preferably, it is performed at 120 ° C. for about 30 minutes. this
After that, baking is performed to convert the alkoxy vanadium in the coating film into an acid.
Vanadium (V _TwoO_Five)
Quality is obtained. This firing step is preferably performed in air.
Is 180 to 600 ° C, more preferably 350 to 400 ° C
For about 30 minutes.

In the lithium-vanadium secondary battery of the present embodiment, the cathode active material 3 is obtained by dispersing a vapor-grown carbon fiber 4 inside a compound (V ₂ O ₅ ) 2 which causes intercalation. This vapor-grown carbon fiber 4
Is a low-resistive fiber.
A fine conductive path is formed therein. Therefore, even if the compound 2 causing the intercalation has a high resistance that does not easily allow electrons to flow, the conductivity of the battery active material 3 is good, and the exchange of ions and electrons in the positive electrode active material 3 can be performed smoothly. Will be

For example, FIG. 1 schematically shows a discharge reaction at a positive electrode of a lithium-vanadium secondary battery. Electrons (e ⁻ ) are passed through a conductive path made of a vapor-grown carbon fiber 4 to a positive electrode. It is easy to move in the active material 3. Therefore, the lithium ions (Li ⁺ ) supplied from the electrolyte 5 at the time of discharging can receive the electrons (e ⁻ ) before reaching the interface between the positive electrode active material 3 and the current collector 1, and the discharging can be performed as compared with the related art. The reaction speeds up. Also, when charging, the electronic (e
^-) is to easily navigate through the positive electrode active material 3, desorption of lithium ions from the positive electrode active material 3 progresses faster, the battery capacity is increased. Furthermore, since the vapor-grown carbon fiber 4 is rich in bending stiffness, the effect of increasing the bending strength of the positive electrode active material 3 is obtained by including the same.

A carbon fiber obtained by baking and carbonizing a polyester fiber generally used as a carbon fiber generally has a diameter of about 80 μm, whereas the carbon fiber used in the present embodiment has a diameter of about 80 μm. Since the phase-grown carbon fiber 4 has a small diameter of 10 μm or less, the vapor-grown carbon fiber 4 can be uniformly dispersed in a dispersion medium or a metal polymer solution when producing an active material for a battery. Therefore, a coating liquid containing the compound 2 and in which the vapor-grown carbon fibers 4 are uniformly dispersed can be obtained, and by using this, the battery active material 3 in which the vapor-grown carbon fibers 4 are uniformly dispersed can be obtained. .

In the above description, the battery active material of the present invention is used as the positive electrode active material of a lithium-vanadium secondary battery. The battery capacity can be similarly increased. Further, the configuration, shape, and the like of the battery can be appropriately changed, and the battery active material of the present invention can be widely applied to various batteries.

FIG. 3 is a sectional view showing an example in which a coin-type lithium-vanadium secondary battery is constructed using the battery active material of the present invention as a positive electrode active material. In the figure, reference numeral 21 denotes a positive electrode current collector, 22 denotes a positive electrode active material, 23 denotes a negative electrode current collector,
Reference numeral 4 denotes a negative electrode active material, 25 denotes a separator, and 26 denotes a gasket. In this coin-type battery, the rising portion 23a of a disc-shaped negative electrode current collector 23 having a rising portion 23a on the periphery is inserted into an annular gasket 26, and the negative electrode current collector inside the gasket 26 is formed. Negative electrode active material 24, separator 25, and positive electrode active material 2
5 are sequentially stacked. Also, the upper surface of the gasket 26,
A positive electrode current collector 21 is arranged and caulked so as to cover the side surface and the upper surface of the positive electrode active material 22. The positive electrode current collector 21 and the negative electrode current collector 23 are made of stainless steel. The positive electrode active material 22 is made of a battery active material in which vapor-grown carbon fibers are dispersed inside V ₂ O _5.
Is made of lithium or a lithium alloy. The separator 25 is made of a thin film made of porous polypropylene or the like, and the gasket 26 is made of Teflon or the like which is excellent in stability to an electrolyte and insulation. The separator 25 and the gasket 26 are impregnated with an electrolyte solution.

FIG. 4 is a sectional view showing an example in which a paper-type (thin) lithium-vanadium secondary battery is constructed using the battery active material of the present invention as a positive electrode active material. In the figure, reference numeral 31 denotes a positive electrode current collector, 32 denotes a positive electrode active material, 33 denotes a negative electrode current collector, 34 denotes a negative electrode active material, 35 denotes an electrolyte layer, and 36 denotes a sealing member. In this paper-type battery, a positive electrode active material 32 formed on one surface of a positive electrode current collector 31 and a negative electrode active material 34 formed on one surface of a negative electrode current collector 33 include:
They are laminated with the electrolyte layer 35 interposed therebetween, and their peripheral edges are sealed with a sealing member 36. The positive electrode current collector 31 and the negative electrode current collector 33 are made of stainless steel. The positive electrode active material 32 is made of a battery active material in which vapor-grown carbon fibers are dispersed inside V ₂ O ₅ , and the negative electrode active material 34 is made of lithium or a lithium alloy. The electrolyte layer 35 is made of a solid electrolyte such as polyethylene oxide, and the sealing member 36 is made of a resin such as polypropylene and Teflon.

In the paper-type battery having such a configuration, for example, a layer of a positive electrode active material 32 made of the battery active material of the present invention is formed on a positive electrode current collector 31, while a negative electrode After forming the layer of the active material 34, the solid electrolyte 35 is laminated on the positive electrode active material 32, the negative electrode active material 34 is laminated thereon, and the positive electrode active material 32, the solid electrolyte 35, and the negative electrode active material layer 34 are formed. It is manufactured by sealing the periphery with a sealing member 36.

[0023]

EXAMPLES Specific examples will be described below. By using the battery active material of the present invention as a positive electrode active material, a paper-type lithium-vanadium secondary battery as shown in FIG. 4 was produced. A positive electrode active material was manufactured as follows. First, 0.5 g of a vapor-grown carbon fiber having a diameter of 0.1 μm and a length of 10 to 100 μm is prepared, added to 10 g of xylene, and subjected to ultrasonic waves (frequency of 28 kHz, output of 100 W).
Preliminary dispersion for 0 minutes was performed. To this, 1 g of alkoxy vanadium (VO (OC ₂ H ₅ ) ₅ ) was added and mixed using a three-roll mill. In this mixing, the dispersion
It was rolled to make a paste. FIG. 5 is a transmission electron micrograph of the dispersion thus obtained. As shown in this figure, the vapor grown carbon fibers were almost uniformly dispersed. Next, the obtained dispersion was set to a thickness of 35 μm.
Was applied with an applicator on a stainless steel foil. The thickness of the coating film of this dispersion was about 20 μm. Thereafter, the coating film was dried by heating at 120 ° C. for 30 minutes, and further baked in air at a temperature of 350 ° C. for 30 minutes.
A cathode active material having a thickness of about 1 μm, in which vapor-grown carbon fibers were dispersed inside vanadium oxide (V ₂ O ₅ ), was obtained.

On the other hand, a negative electrode active material was manufactured. That is,
A lithium layer was formed on a stainless steel foil having a thickness of 35 μm by a sputtering method. The thickness of this lithium layer is 1 μm
Thus, the same planar shape as that of the positive electrode active material layer was obtained. 10 μm thick polyethylene oxide on the positive electrode active material
m of the solid electrolyte was laminated thereon, and the negative electrode active material was laminated thereon. Then, the peripheral portion between the two stainless steel foils was sealed with polypropylene.

(Comparative Example) A paper-type lithium-vanadium secondary battery was manufactured in the same manner as in the above example except that the vapor grown carbon fiber was not used.

The relationship between the voltage (V) and the capacity density (mAh / g) when a constant current of 10 μA / cm ^{2 was} applied to the secondary batteries obtained in the above Examples and Comparative Examples was examined. The results are shown in FIG. In FIG. 6, the vertical axis represents voltage (V), and the horizontal axis represents capacity density (mAh / g). As is clear from FIG. 6, the discharge starting voltage of the secondary battery according to the present example is 3.9 V, which is obtained as a value larger than 3.6 V of the comparative example, and the capacity density is 1 to less than that of the comparative example. The value was 20% larger. From this, it was recognized that the battery capacity was increased by dispersing the vapor-grown carbon fibers in the positive electrode active material.

[0027]

As described above, according to the battery of the present invention, fine conductive paths are formed in the compound causing intercalation, so that the conductivity of the battery active material is improved and the battery capacity is improved. Is achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a discharge reaction in a positive electrode using the battery active material of the present invention.

FIG. 2 is a perspective view showing an example of a vapor-grown carbon fiber used in the present invention.

FIG. 3 is a sectional view showing an example of a coin-type battery according to the present invention.

FIG. 4 is a sectional view showing an example of a paper-type battery according to the present invention.

FIG. 5 is a transmission electron micrograph showing the shape of a vapor-grown carbon fiber in an example of a coating solution used for producing the battery active material of the present invention.

FIG. 6 is a graph showing a relationship between voltage and capacity density of batteries according to an example and a comparative example.

FIG. 7 is an explanatory view schematically showing a discharge reaction in a positive electrode using a conventional battery active material.

[Explanation of symbols]

 2 Compound causing intercalation 3 Active material for battery 4 Vapor-grown carbon fiber

Claims (5)

[Claims] 1. A battery comprising a battery active material having a fine conductive path in a compound causing intercalation, as either a positive electrode active material or a negative electrode active material. 2. The conductive path of the active material for a battery according to claim 1, wherein the carbon mesh plane is formed of vapor-grown carbon fibers arranged in a cylindrical shape in a cylindrical shape and stacked in the diameter direction of the cylindrical shape. battery. 3. The battery according to claim 2, wherein the vapor-grown carbon fiber has a diameter of 1 μm or less and a length of 0.01 to 100 μm. 4. The battery according to claim 1, wherein the ratio of the compound causing intercalation to the vapor-grown carbon fiber in the active material for a battery is one.
00: 0.5-3. 5. The battery according to claim 1, wherein the compound causing the intercalation is a metal oxide or a metal sulfide.