JP2001110454A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which is superior in rate characteristic and can suppress generation of gases. SOLUTION: Generation of gases can be suppressed and rate characteristic can be improved due to a positive electrode layer and a negative electrode layer, by having both of them contain specific conductive ceramic powders.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery.

[0002]

2. Description of the Related Art In recent years, the performance of portable electronic devices such as mobile phones and personal digital assistants largely depends on rechargeable batteries as well as on-board semiconductor elements and electronic circuits. At the same time, it is desired to realize light weight and compactness at the same time. Heretofore, lead batteries and nickel cadmium batteries have been used for these batteries, but it has been difficult to cope with a reduction in weight and size due to insufficient energy density.

[0003] Therefore, a nickel-metal hydride battery having an energy density approximately twice that of a nickel-cadmium battery has been developed, and then a lithium-ion battery having a higher energy density has been developed and has been spotlighted.

[0004]

Since these lithium ion secondary batteries are used in portable telephones or personal digital assistants, further improvement in safety is desired, especially when the batteries generate heat due to overcharge or the like. It is important to prevent thermal runaway. In addition, a battery having particularly good high-rate characteristics as a battery that can withstand rapid charging and discharging is also desired.

[0005] As means for preventing such thermal runaway, a method using an electronic circuit equipped with an overcharge prevention mechanism, a method using a mechanical current interrupt utilizing gas generation during overcharge, and the like have been proposed.

However, in these methods, the battery has an additional structure, which not only increases the cost of the battery but also imposes restrictions on the product design.

[0007]

According to the present invention, a ceramic particle having an electric resistance of 2 Ωcm or less is contained in a positive electrode or a negative electrode, so that the ceramic particles are adsorbed on the active material surface in the positive electrode or the negative electrode. In addition, the reaction area can be controlled. When the reaction area can be controlled, gas generation can be prevented, and since the conductive ceramic particles are used, the electric resistance of the battery can be reduced, so that the rate characteristics can be improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a lithium ion secondary battery according to the present invention will be described. The positive electrode has a structure in which a positive electrode layer is stacked on a current collector. The current collector is made of an aluminum foil or an aluminum net.

The negative electrode has a structure in which a negative electrode layer is laminated on a current collector, and the negative electrode layer is arranged to face the positive electrode layer of the positive electrode. The current collector is made of, for example, a copper foil or a copper net.

Hereinafter, the ceramic particles, the positive electrode layer, and the negative electrode layer will be described.

Examples of the ceramic particles include alumina, titania, zirconia, silica gel, and magnesia. These particles may be used alone or in combination of two or more. The primary particle size of these particles is
The thickness should be 0.005 μm or more and 10 μm or less. Further, the content is desirably 0.01 to 10 parts by weight based on 100 parts by weight of the positive or negative electrode active material.

The positive electrode layer comprises an active material, a conductive material, a non-aqueous electrolyte,
Contains polymers. Examples of the active material include various oxides such as lithium manganese composite oxide, manganese dioxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing cobalt nickel oxide, and amorphous vanadium pentoxide containing lithium. , Titanium disulfide, molybdenum disulfide, or the like can be used.

Examples of the conductive material include artificial graphite and carbon black such as acetylene black.

Further, the electrolytic solution is prepared by dissolving the electrolyte in a non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate,
Butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, and the like can be given. The non-aqueous solvents may be used alone or in combination of two or more.

Examples of the electrolyte contained in the nonaqueous electrolyte include lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium borofluoride (LiBF4), lithium arsenide hexafluoride (LiAsF6), Lithium salts such as lithium fluorometasulfonic acid (LiCF3SO3) and lithium bistrifluoromethylsulfonylimide [LiN (CF3SO2) 2].

As the polymer, for example, a copolymer of vinylidene fluoride-hexafluoropropylene (VDF-HFP) can be used. VDF contributes to the improvement of the mechanical strength in the skeleton of the copolymer, and HFP is incorporated as amorphous in the copolymer, and functions as a holding portion for the electrolyte and a lithium ion transmission portion.

The negative electrode layer is made of a carbon-based material that stores lithium ions, conductive ceramic particles, a non-aqueous electrolyte, and a polymer.

Examples of the carbon-based material include those obtained by firing an organic polymer compound (for example, phenol resin, polyacrylonitrile, cellulose, etc.), those obtained by firing coke and pitch, and those obtained by artificial production. Examples include graphite and natural graphite. The nonaqueous electrolyte, the polymer, and the conductive ceramic are the same as those described for the positive electrode layer.

The method for attaching the ceramic particles to the surface of the active material is not particularly limited.

[0020]

Embodiments of the present invention will be described below in detail.

Example 1 A positive electrode layer was formed as follows. A polymer solution of vinylidene fluoride-hexafluoropropylene (VDF-HFP) was prepared by dissolving 10% by weight of the polymer in acetone.

Next, the lithium-containing cobalt oxide was added to 70
% Of acetylene black, and 20% by weight of the above-mentioned polymer solution. This mixed solution was formed into a film by a doctor blade, allowed to stand at room temperature, and naturally dried to form a sheet-shaped positive electrode having a thickness of 100 μm.

The negative electrode layer was prepared as follows. Vinylidene fluoride-hexafluoropropylene (VDF-HF
The polymer (P) was dissolved in acetone at 10% by weight to prepare a polymer solution.

Next, 75 weight of graphite carbon was used.
%, Conductive titania with a primary particle size of 5 μm (powder electric resistance 5
(0 mΩcm) at a ratio of 5% by weight. The mixture of carbon and titania and the polymer solution described above
It was mixed so that it might become weight%. This mixed solution was formed into a film by a doctor blade, allowed to stand at room temperature, and naturally dried to form a 150-μm-thick sheet negative electrode.

Next, the sheet electrolyte layer is interposed between the positive electrode and the negative electrode, and lithium hexafluorophosphate (LiPF6) is added to ethylene carbonate (EC).
The lithium ion secondary battery described above is obtained by immersing the sheet-like material in a dissolved electrolytic solution for 20 minutes to impregnate the sheet-like positive electrode layer, the sheet-like negative electrode layer, and the sheet-like polymer electrolyte layer with the electrolytic solution. Manufactured.

Example 2 In the positive electrode layer, a polymer solution of vinylidene fluoride-hexafluoropropylene (VDF-HFP) was prepared by dissolving 10% by weight of the polymer in acetone.

Next, 65% by weight of lithium-containing cobalt oxide and 5% by weight of conductive titania (powder electric resistance: 50 mΩcm) having a primary particle diameter of 5 μm were dry-mixed, and 10% by weight of acetylene black was further mixed. The above-mentioned polymer solution was mixed so as to be 20% by weight. This mixed solution was formed into a film by a doctor blade, allowed to stand at room temperature, and naturally dried to form a sheet-shaped positive electrode having a thickness of 100 μm.

A lithium ion secondary battery was prepared in the same manner as in Example 1 except for the positive electrode layer described above.

Comparative Example 1 A polymer solution was prepared by dissolving 10% by weight of vinylidene fluoride-hexafluoropropylene (VDF-HFP) polymer in acetone in the positive electrode layer.

Next, 80% by weight of graphite carbon
And the polymer solution described above were mixed so as to be 20% by weight. This mixed solution was formed into a film by a doctor blade, allowed to stand at room temperature, and naturally dried to form a 150-μm-thick sheet negative electrode.

A lithium ion secondary battery was prepared in the same manner as in Example 1 except for the positive electrode layer described above.

Comparative Example 2 A polymer solution was prepared by dissolving a polymer of vinylidene fluoride-hexafluoropropylene (VDF-HFP) at 10% by weight in acetone in the negative electrode layer.

Next, 70% by weight of graphite carbon
%, And dry mixing of conductive titania having a primary particle diameter of 20 μm was performed at a ratio of 10% by weight. A mixture of carbon and titania and the above-described polymer solution were mixed so as to be 20% by weight. This mixed solution was formed into a film by a doctor blade, allowed to stand at room temperature, and naturally dried to form a 150-μm-thick sheet negative electrode.

A lithium ion secondary battery was prepared in the same manner as in (Example 1) except for the above-mentioned negative electrode layer.

Comparative Example 3 A polymer solution was prepared by dissolving 10% by weight of vinylidene fluoride-hexafluoropropylene (VDF-HFP) polymer in acetone in the negative electrode layer.

Next, 50 weight of graphite carbon was added.
%, And conductive titania having a primary particle diameter of 5 μm was dry-blended at a ratio of 30% by weight. A mixture of carbon and titania and the above-described polymer solution were mixed so as to be 20% by weight. This mixed solution was formed into a film by a doctor blade, allowed to stand at room temperature, and naturally dried to form a 150-μm-thick sheet negative electrode.

A lithium ion secondary battery was prepared in the same manner as in (Example 1) except for the above-mentioned negative electrode layer.

Comparative Example 4 A polymer solution was prepared by dissolving 10% by weight of vinylidene fluoride-hexafluoropropylene (VDF-HFP) polymer in acetone in the negative electrode layer.

Next, 99.99 g of graphite carbon was added.
0.005% by weight of conductive titania having a primary particle diameter of 5 μm.
Dry mixing was performed at a ratio of 5% by weight. A mixture of carbon and titania and the above-described polymer solution were mixed so as to be 20% by weight. This mixed solution was formed into a film by a doctor blade, allowed to stand at room temperature, and naturally dried to form a 150-μm-thick sheet negative electrode.

A lithium ion secondary battery was prepared in the same manner as in (Example 1) except for the above-mentioned negative electrode layer.

In the battery prepared as described above, after measuring the electric resistance and the volume, it was measured at 0.2 C (100 mA).
After charging in the constant current mode, the battery was charged in the constant voltage mode of 4.2V. Next, 0.2C (100mA) 1C (5
(00 mA) and 2 C (1000 mA), and discharge was performed for each, and the capacity was confirmed at a discharge voltage of 3 V. Here, the volume change rate was calculated assuming that the volume before charging was 0%.

[0042]

[Table 1]

As shown in Table 1, in Examples 1 and 2, conductive titania is adsorbed on the surface of the positive electrode or negative electrode active material, and gas generation can be suppressed by reducing the reaction area. Also, from Comparative Example 2, 20 μm
When the conductive titania is used, the reaction area is excessively reduced, and the high-rate characteristic is particularly deteriorated. As compared with Comparative Example 3, when more than 10 parts by weight of conductive titania is added to 100 parts by weight of the active material, the reaction area of the active material is reduced and the rate characteristics are deteriorated. Further, it can be seen that no effect is obtained when the amount of conductive titania added is too small.

[0044]

As described above, according to the present invention, the positive electrode layer and the negative electrode layer contain conductive ceramic particles having a primary particle diameter of 0.005 μm or more and 10 μm or less and an electric resistance of 2 Ωcm or less, thereby producing gas. The present invention relates to a lithium ion secondary battery having excellent suppression and rate characteristics.

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Claims (4)

[Claims] 1. A lithium battery having a structure in which an electrolyte is disposed between a negative electrode and a positive electrode, wherein a lithium ion secondary battery containing at least one or more ceramic particles having a powder electric resistance of 2 Ωcm or less in the positive electrode or the negative electrode. battery. 2. The lithium ion secondary battery according to claim 1, wherein the negative electrode or the positive electrode contains an active material to which ceramic particles having a powder electric resistance of 2 Ωcm or less are adhered. 3. The ceramic particles having a primary particle size of 0.1.
2. The lithium ion secondary battery according to claim 1, wherein the thickness is not less than 005 μm and not more than 10 μm. 4. The lithium ion secondary battery according to claim 1, wherein 0.01 to 10 parts by weight of ceramic particles are added to 100 parts by weight of the active material in the negative electrode or the positive electrode.