JPH10106585A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the lowering of discharging capacity, and improve the charging and discharging cycle characteristic by forming a carbon film on a surface of an aluminum collector, and forming an active material layer on this carbon film. SOLUTION: Carbon powder at 95 pts.wt. and the solution, which is obtained by dissolving polyvinylidene fluoride at 5 pts.wt. in N-methyl-2-pyrolidone, are kneaded so as to adjust the slurry, and this slurry is applied on a surface of an aluminum foil by a doctor blade method, and the coated aluminum foil is dried, rolled so as to manufacture an aluminum collector having a carbon film on a surface thereof. The carbon film of the aluminum collector is coated with the slurry, which is obtained by kneading the positive electrode active material powder at 90 pts.wt. acetylene black at 6 pts.wt. and the N-methyl-2- pyrolidone solution, which includes polyvinylidene fluoride at 4 pts.wt. for adjustment. Thereafter, it is dried, and formed into a disc at 20mm of diameter by the molding pressure 2t/cm<2> , and heated at 100 deg.C for two hours so as to form a positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using an aluminum current collector as a positive electrode current collector, and more particularly, to an aluminum current collector for improving the charge / discharge cycle characteristics thereof. It relates to the improvement of electric bodies.

[0002]

2. Description of the Related Art In recent years,
BACKGROUND ART Non-aqueous electrolyte secondary batteries such as lithium secondary batteries have attracted attention because they can achieve higher voltages and higher capacities than conventional alkaline secondary batteries. This is because in the case of a non-aqueous electrolyte secondary battery that does not use an alkaline electrolyte, it is not necessary to consider the decomposition voltage of water when designing the battery.

The positive electrode of a non-aqueous electrolyte secondary battery is
Generally, active materials (LiCoO ₂ , LiNiO ₂ , LiM
n ₂ O _4, etc.) and a conductive agent (acetylene black, etc. artificial graphite) and the like N- methyl-2-pyrrolidone solution of the binder solution (polyvinylidene fluoride) and applying a slurry formed by kneading the collector of Then, after drying, the active material layer is formed on the current collector. As a material for the positive electrode current collector, aluminum that is hardly soluble in an organic solvent (a non-aqueous electrolyte) even at a high potential is known as a suitable material.

However, the conventional non-aqueous electrolyte secondary battery using the above-mentioned positive electrode has a problem that the discharge capacity is remarkably reduced as the charge-discharge cycle proceeds.

[0005] Japanese Patent Application Laid-Open No. 6-140045 discloses that the surface of an aluminum current collector of a positive electrode is roughened to enhance current collection, thereby suppressing a decrease in discharge capacity accompanying the progress of a charge / discharge cycle. Have been reported.

However, the decrease in the discharge capacity of a nonaqueous electrolyte secondary battery using an aluminum current collector as the positive electrode current collector with the progress of the charge / discharge cycle is due to passivation of the surface of the aluminum current collector. However, because of the large size, the above-described method based on surface roughening has not been able to significantly improve the charge / discharge cycle characteristics.

The present invention has been made in view of the above circumstances, and since the surface of the aluminum current collector of the positive electrode is hardly passivated, the decrease in the discharge capacity with the progress of the charge / discharge cycle is small. An object of the present invention is to provide a nonaqueous electrolyte secondary battery having extremely excellent charge / discharge cycle characteristics.

[0008]

Means for Solving the Problems A non-aqueous electrolyte secondary battery (battery of the present invention) according to the present invention for achieving the above object, comprises:
A positive electrode is formed by forming a carbon film on the surface of an aluminum current collector and forming an active material layer on the carbon film.

[0009] As the carbon forming the carbon film, in order to improve the charge-discharge cycle characteristics, surface spacing d ₀₀₂ of the lattice plane (002) plane preferably has the following 3.37 Å. The average particle diameter of carbon forming the carbon film is preferably 1 to 5 μm, and the thickness of the carbon film is preferably 1 to 10 μm.

As a method for forming a carbon film, a carbon powder and a binder solution (N-methyl-2 of polyvinylidene fluoride) are used.
-Pyrrolidone solution) is applied to an aluminum current collector, followed by drying, but other methods such as vapor deposition may be used.

The present invention relates to an improvement in a positive electrode current collector of a non-aqueous electrolyte secondary battery. The present invention is suitable for application to, for example, a lithium secondary battery. In this case, as the positive electrode active material, the negative electrode material and the non-aqueous electrolyte, conventionally known ones shown below can be used without any particular limitation.

As a specific example of the positive electrode active material, a general formula: L
_{i x MO y (0 <x} ≦ 1.3; 1.8 ≦ y ≦ 2.2; M
Is a composite oxide of lithium and a transition element represented by at least one transition element selected from Co, Ni and Mn.

Examples of the negative electrode material include a substance capable of electrochemically storing and releasing lithium ions and lithium metal. Specific examples of the substance capable of electrochemically occluding and releasing lithium ions include carbon materials such as graphite, coke, and fired organic materials;
Lithium alloys such as aluminum alloys, lithium-lead alloys, lithium-tin alloys; SnO ₂ , SnO, TiO ₂ , N
A metal oxide having a potential such as b ₂ O ₃ which is lower than that of the positive electrode active material may be used.

Specific examples of the solvent of the non-aqueous electrolyte include ethylene carbonate (EC) and vinylene carbonate (V
C), cyclic carbonates such as propylene carbonate (PC), and dimethyl carbonate (DMC);
Diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DE
E) and a mixed solvent with a low boiling point solvent such as ethoxymethoxyethane (EME). Specific examples of the solute of the non-aqueous electrolyte include LiPF ₆ , LiClO ₄ , and LiC
F ₃ SO ₃ . It is also possible to use a solid electrolyte instead of the non-aqueous electrolyte.

Since the aluminum current collector of the battery of the present invention having a carbon film formed on the surface is hardly passivated, the current collecting ability is not easily reduced even after repeated charging and discharging. In addition, since the current collecting ability of the aluminum current collector is made uniform by forming the carbon film, the charge / discharge reaction is performed uniformly over the entire active material layer.
That is, a part of the positive electrode active material is unlikely to be deteriorated by overcharging and overdischarging before others. For this reason,
The battery of the present invention is excellent in charge / discharge cycle characteristics.

[0016]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples and can be carried out by appropriately changing the scope of the invention without changing its gist. It is something.

[Preparation of positive electrode current collector] A slurry was prepared by kneading 95 parts by weight of carbon powder and a solution of 5 parts by weight of polyvinylidene fluoride in N-methyl-2-pyrrolidone to prepare a slurry. 30 thickness by blade method
One side of a μm aluminum foil was applied, dried and rolled to produce an aluminum current collector having a carbon film on the surface.

[Preparation of Positive Electrode] An N-methyl-2-pyrrolidone solution containing 90 parts by weight of a positive electrode active material powder, 6 parts by weight of acetylene black as a conductive agent, and 4 parts by weight of polyvinylidene fluoride as a binder was used. A slurry was prepared by kneading, and the slurry was applied on the carbon film of the aluminum current collector by a doctor blade method, dried, and formed into a disk having a diameter of 20 mm at a molding pressure of 2 ton / cm ^2. ,
Heat treatment was performed at 100 ° C. for 2 hours to produce a positive electrode.

[Preparation of Negative Electrode] A disk having a diameter of 20 mm was punched from a rolled sheet of metallic lithium to prepare a negative electrode.

[Preparation of Nonaqueous Electrolyte] LiClO ₄ was dissolved in a mixed solvent having a volume ratio of 1: 1 at 1 mol / L to prepare a nonaqueous electrolyte.

[Assembly of Battery] A flat lithium secondary battery (battery size: 24.0 mm in diameter, 3.0 mm in thickness) was assembled using the above positive electrode, negative electrode and non-aqueous electrolyte. A microporous film made of polypropylene was used for the separator, and this was impregnated with a non-aqueous electrolyte.

The type of the positive electrode active material, the carbon lattice plane (00
2) plane spacing d ₀₀₂ (Å), thickness of carbon film (μm),
Tables 1 and 2 show the average particle size (μm) of carbon and the type of the mixed solvent. In these tables, batteries A1 to A30 are batteries of the present invention. Batteries B1 to B7 are comparative batteries,
This is a battery using an aluminum foil as it is as a positive electrode current collector without forming a carbon film. In particular, the battery B7 is a battery corresponding to the conventional battery disclosed in JP-A-6-140045, and the surface roughness of the aluminum current collector used is J.
It is 40S in IS B0601 (1995) standard display.

[0023]

[Table 1]

[0024]

[Table 2]

[Charge / discharge cycle test]
After charging to 4.3 V at 1 mA, a charge / discharge cycle test was performed in which the process of discharging to 3 V at 2.0 V was defined as one cycle, and the discharge capacity at the first cycle (mA)
h), the capacity deterioration rate (%) of the discharge capacity at the 100th cycle (mAh) was determined. The results are shown in Tables 1 and 2 above. 1, the present invention battery A20～A25, based on the results of A1, the relationship between the lattice plane (002) plane face spacing d ₀₀₂ and 100 cycle capacity deterioration rate of carbon that forms a carbon film, vertical axis Is the capacity deterioration rate (%), and the horizontal axis is the surface distance d.
₀₀₂ is a graph showing each of them.

Capacity degradation rate (%) = {(discharge capacity at first cycle−discharge capacity at 100th cycle) / discharge capacity at first cycle} × 100

As shown in Tables 1 and 2, the battery A of the present invention
1 to A30 generally have lower capacity deterioration rates than the comparative batteries B1 to B7. In particular, batteries A1 to A6 and batteries B1 to B6
From the comparison, it can be seen that the capacity deterioration rate is greatly reduced by forming the carbon film on the surface of the aluminum current collector.

The batteries A7 to A11 of the present invention and the battery A1 of the present invention
From the comparison of 2 to A15, the thickness of the carbon film is generally 1 to 10
It can be seen that μm is preferable. In addition, the battery A20 of the present invention
A23 and batteries A24, A25, and A1 show that the carbon forming the carbon film is preferably one having a lattice spacing (002) plane spacing d ₀₀₂ of 3.37 ° or less (see FIG. 1).

[0029]

The positive electrode current collector of the battery of the present invention having a carbon film formed on the surface is hardly passivated, so that the current collecting property is hardly reduced even after repeated charging and discharging. In addition, since the current collection by the aluminum current collector is uniformly performed by forming the carbon film, the charge and discharge reaction is uniformly performed over the entire active material layer. For this reason, the battery of the present invention is excellent in charge / discharge cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a spacing _d002 between lattice planes (002) of carbon forming a carbon film and a capacity deterioration rate.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode in which a carbon film is formed on a surface of an aluminum current collector and an active material layer is formed on the carbon film. 2. A lattice plane of carbon forming a carbon film.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a surface distance d ₀₀₂ between the surfaces is 3.37 ° or less.