JP2615054B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a secondary battery which can be used for an electric power storage system, and more particularly to a secondary battery using a non-aqueous electrolyte which is stable against oxidation and reduction.

2. Description of the Related Art A battery using an electrolytic solution or a molten salt obtained by adding a salt stable to oxidation and reduction to an organic solvent as a nonaqueous electrolyte and using an alkali metal as a negative electrode active material is known. Such a battery is considered to be promising as a secondary battery for a power storage system or a vehicle because of its high open circuit voltage and high energy density.

However, in this type of secondary battery, there is a problem that when charge and discharge are repeated, dendritic metal crystals grow on the negative electrode and the capacity of the battery gradually decreases. On the contrary,
A method using an alloy of lithium and aluminum for the negative electrode (JP-A-52-5423) and a method of attaching a wood alloy to the surface of a lithium metal electrode (JP-A-60-167297) have been proposed. However, even with these methods, the generation of dendritic crystals could not be completely prevented.

Problems to be solved In the conventional electrode using an alkali metal as described above,
In addition to the inability to prevent dendritic crystal formation, the alkali metal easily reacts with water and has the danger of explosion, so that it must be handled in an atmosphere of an inert gas such as argon, which is inconvenient or disadvantageous.

Therefore, an object of the present invention is to provide a secondary battery that can be easily manufactured without generating dendritic metal crystals on the electrode, particularly without an inert gas atmosphere.

[Configuration of the invention]

Means for Solving the Problems The non-aqueous electrolyte secondary battery of the present invention, which can achieve the above-described object, has a diameter in a secondary battery in which electrodes are opposed via a non-aqueous electrolyte. Is 0.1 to 3 μm of graphitic carbon fiber whose carbon layer surface is 2 to 2 with respect to the fiber axis.
A material which is oriented in a conical or pyramid shape at an inclination angle of 45 ° is used as a negative electrode active material.

In the present invention, the graphitic carbon fiber used as the material for the electrode active material is obtained by gasifying hydrocarbon compounds such as aromatic hydrocarbons such as benzene, toluene and naphthalene and aliphatic hydrocarbons such as ethane, ethylene and propane. Graphitized carbon fibers obtained by mixing with a carrier gas such as hydrogen together with hydrogen or a sulfur compound such as mercaptan and pyrolyzing at a temperature of 1000 ° C. or more can be used.

For such graphitization, a method of heat-treating the carbon fiber at 2000 to 3000 ° C. in an inert gas atmosphere can be adopted.

The diameter of the graphitic carbon fibers thus obtained is 0.1 to
3 μm, whose carbon layer surface is oriented in a conical or pyramid shape at an inclination angle of 2 to 45 ° with respect to the fiber axis is used. It is desirable to confirm such properties in advance by an X-ray diffraction method or the like.

The electrode used in the secondary battery of the present invention can be obtained by mixing the above-mentioned graphitic carbon fibers, for example, using a fluororesin as a binder, and pressing and molding the same to have a desired shape. .

The secondary battery in which the electrode having the electrode active material as described above is combined with a non-aqueous electrolyte forms the intercalation compound by taking in the substance deposited during charging into the graphite layer and forming the intercalation compound during discharging. The substances that have been taken in between the layers are released as ions. Therefore, a metal or the like deposited on the negative electrode does not form a dendritic crystal.

Example A carbon fiber having a diameter of 0.5 to 1.5 μm and a length of 0.1 to 2 mm obtained by subjecting a mixed gas of benzene, hydrogen sulfide and hydrogen to gas phase pyrolysis at 1100 ° C. was heat-treated at 2400 ° C. and graphitized. X-ray diffraction showed that the thus obtained graphitic carbon fiber had a conical shape in which the crystal layer surface of carbon was inclined at about 10 ° with respect to the axis of the fiber.

1 part by weight of the tetrafluoroethylene resin powder was uniformly mixed with 5 parts by weight of the carbon fiber, and the mixture was compressed under heating to form a disk-shaped electrode.

Using such a set of electrodes, a battery as shown in FIG. 1 was assembled. 1 is a sealing plate, 2 is a negative electrode, 3 is a separator made of nonwoven fabric of polypropylene fiber, 4 is a positive electrode, 5 is a stainless steel case, and 6 is a gasket. In this battery, a 1 mol / polypropylene carbonate solution of lithium perchlorate was used as an electrolyte.

Scheme of the positive electrode in this cell ^{_{nC + ClO 4 - Cn · ClO}} 4 + e - a is also Scheme of the negative electrode nC ⁺ Li + + e ^- a Cn · Li.

The open circuit voltage of this battery is 4.5V and the charge and discharge cycle is 20
No deterioration of the electrode was observed even after 00 times.

Comparative Example A mixed gas of benzene and hydrogen was brought into contact with ultrafine metallic iron particles floating in an air stream at 1100 ° C., and vapor-phase pyrolyzed to obtain vapor-grown carbon fibers having a diameter of 0.05 to 0.3 μm. This 2
Heat treatment was performed at 500 ° C. to obtain a graphitic carbon fiber in which the crystal layer surface of carbon was parallel to the fiber axis and oriented in a ring shape.

Using this carbon fiber, a battery as shown in FIG. 1 was assembled in the same manner as in the example, and a charge / discharge cycle test was performed in the same manner as in the example. The initial battery capacity was 89% in the example.
% And the battery capacity after 90 cycles is 90% of the initial value.
Had dropped by.

〔The invention's effect〕

The non-aqueous electrolyte secondary battery of the present invention utilizes a special graphitic carbon fiber as an electrode active material, and does not require the use of an active material such as an alkali metal. There is no need to use an inert atmosphere, and workability is good. In addition, since the solid metal does not precipitate on the negative electrode due to charging, there is no deterioration due to the generation of dendritic metal crystals, and therefore, there is an advantage that the capacity of the battery is small and the life is long.

[Brief description of the drawings]

FIG. 1 is a sectional view of a nonaqueous electrolyte secondary battery of the present invention. 1 ... sealing plate, 2 ... negative electrode, 3 ... separator, 4 ...
Positive electrode, 5 ... case, 6 ... gasket.

Claims (1)

(57) [Claims] 1. A secondary battery having electrodes opposed to each other via a non-aqueous electrolyte, wherein the carbonaceous carbon fiber has a diameter of 0.1 to 3 μm and a carbon layer surface of 2 to 45 ° with respect to the fiber axis. A non-aqueous electrolyte secondary battery characterized in that a material having a conical or pyramidal orientation at an inclination angle is used as a negative electrode active material.