JP2000090937A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having excellent energy density per weight by providing a negative electrode formed with a layer using a carbon material capable of storing and releasing lithium on a metal foil collector, and using a copper foil having a specified thickness as a collector and containing a specified weight ratio of iron. SOLUTION: As a collector, a copper foil having a thickness at 12 μm or less and containing iron at 0.020 wt.% or more is used. A positive plate 1 is formed by using cobalt acid lithium as the active material, and mixing the conductive agent and the binder in the active material, coating on the aluminum foil with this mixture, and drying it. The positive plate 1 has positive electrode lead piece 4 at the end thereof. A negative plate 2 is formed by coating a copper foil with the mix mainly composed of the artificial graphite and mixed with the binder, and drying it, and has a negative electrode lead piece 5 at the end thereof. The positive plate 1 and the negative plate 2 are wound through a separator 3 interposed between them so as to form a plate group, and a lower insulating ring 6 is installed, and they are housed in a battery case 7, and the negative electrode lead piece 5 is welded. An upper insulating ring 8 is installed in an upper part of the plate group, and the electrolyte is filled therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a metal foil current collector used for its negative electrode.

[0002]

2. Description of the Related Art Conventionally, as a nonaqueous electrolyte secondary battery, a transition metal oxide, a sulfide, a chalcogen compound such as a selenium compound, for example, manganese dioxide, molybdenum disulfide, titanium selenide, or the like is used as a positive electrode active material. As a non-aqueous electrolyte, a so-called lithium secondary battery using an organic electrolyte comprising an organic solvent of a lithium salt as a non-aqueous electrolyte has been studied with a view to high voltage, high capacity and high energy density.

[0003] However, this lithium secondary battery is
As the positive electrode active material, an interlayer compound having excellent charge / discharge characteristics can be selected, but the charge / discharge characteristics of metallic lithium of the negative electrode are not always excellent, and it has been difficult to secure a long cycle life.

The lithium metal of the negative electrode of this battery is eluted as lithium ions into the organic electrolyte by discharging. Lithium ions eluted during charging are deposited as lithium metal on the surface of the negative electrode. However, some of the lithium ions do not deposit as smooth as before, but instead precipitate as dendritic or mossy active metal crystals. Such active metal crystals react with the organic solvent in the electrolyte, and their surfaces are covered with a passivation film to be inactivated and hardly contribute to the discharge. Therefore, the capacity of the negative electrode decreases with the charge / discharge cycle. Therefore, it was necessary to make the capacity of the negative electrode significantly larger than that of the positive electrode during the production of the battery. In addition, the active lithium metal crystal penetrates through the separator and comes into contact with the positive electrode, which easily causes an internal short circuit. Due to this internal short-circuit, the cell sometimes suddenly generates heat.

[0005] Therefore, a so-called lithium ion secondary battery using a substance that absorbs and releases lithium ions by charging and discharging as a negative electrode material has been proposed, actively researched and developed worldwide, and has already been put into practical use.

As long as the lithium ion secondary battery is not overcharged, active lithium metal crystals do not precipitate on the surface of the negative electrode during charging, so that an improvement in safety can be expected.

[0007] Since the lithium secondary battery has higher charge / discharge characteristics and cycle life than the above-mentioned lithium secondary battery, the demand has been rapidly growing in recent years. Since lithium is an active material, a lithium ion secondary battery can be said to be one type of lithium secondary battery, but is distinguished from a conventional lithium secondary battery using metal lithium as a negative electrode.

[0008] LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiM
In many systems, a composite oxide of lithium and a transition metal such as n ₂ O ₄ is used, and a carbon material such as graphite whose potential is similar to that of metallic lithium when charged is used as the negative electrode. There is also a low-voltage operation system in which a composite oxide of lithium and a transition metal is used for the negative electrode.

When charging and discharging a lithium ion secondary battery,
Since the positive electrode active material can reversibly repeat lithium ion deintercalation and intercalation, and the negative electrode can reversibly repeat lithium ion intercalation and deintercalation, the cycle life is extremely long. In addition, a battery having a high energy density is formed because of a high voltage and a high capacity.

However, these lithium ion secondary batteries use an organic electrolyte having a relatively low electric conductivity, similarly to a conventional lithium secondary battery. Therefore, a thin positive electrode and a negative electrode in which an active material layer or a mixed layer of an active material and a conductive material is thinly formed on a metal foil of a current collector are manufactured. For example, an aluminum foil of about 20 μm is used as a positive electrode current collector, and a copper foil of approximately the same thickness is used as a negative electrode current collector. The positive electrode and the negative electrode are opposed to each other via a thin microporous polyolefin resin membrane separator to form an electrode group, and by increasing the facing area between the positive electrode and the negative electrode, practical high-rate charge / discharge characteristics are secured. , Expanding its suitability for many applications.

[0011]

Recently, lithium ion secondary batteries have been required to have higher energy density and lighter weight. That is, an improvement in energy density per weight of the battery is required. Among them, the copper foil used as the negative electrode current collector is a good conductor, but has a large specific gravity, and is a constituent material for reducing the energy density per unit weight of the battery. In order to solve this problem, it is possible in principle to reduce the thickness of the copper foil. However, when the thickness is extremely reduced, practical use is difficult due to a problem of mechanical strength.

The present invention provides a non-aqueous electrolyte secondary battery having an excellent energy density per weight by using a copper foil having a mechanical strength that does not cause any practical problem even when the thickness of the copper foil is extremely thin. Is what you do.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-aqueous electrolyte secondary battery in which a lithium-containing transition metal oxide is used for a positive electrode and a carbon material capable of occluding and releasing lithium is used for a negative electrode. It is configured using the copper foil containing iron described above. As a result, the thickness of the copper foil becomes 12 μm
Even in the case of the following, it is possible to maintain mechanical strength that has no problem in practical use, and it is possible to improve the energy density per weight of the battery.

In the non-aqueous electrolyte secondary battery according to the present invention, in which the positive electrode plate and the negative electrode plate are spirally wound together with the separator and housed therein, the amount of iron contained in the copper foil is 0.02.
It is preferable that the content is 0 wt% or more. If the amount of iron contained is less than 0 wt%, the mechanical strength of the copper foil decreases when the thickness of the copper foil is reduced to 12 μm or less, so that the copper foil withstands actual use. You can't do that.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of a prototype cylindrical battery to demonstrate the effects of the present invention. The dimensions of this battery are 18 mm in diameter and 65 mm in total height.

Example 1 In FIG. 1, a positive electrode plate 1 was prepared by mixing lithium cobalt oxide (LiCoO ₂ ) as an active material, acetylene black as a conductive agent at 3% by weight, and then polytetrafluoroethylene as a binder. A mixture prepared by mixing 7% by weight of an aqueous dispersion of ethylene fluoride resin was applied to both sides of a core material made of aluminum foil having a thickness of 20 μm, dried and rolled, and then cut into a predetermined size. Things. The positive electrode lead piece 4 is spot-welded to the end.

The negative electrode plate 2 is composed mainly of artificial graphite (average particle size: 25 μm) capable of occluding and releasing lithium, and after mixing styrene-butadiene rubber of 3% by weight with respect to the active material as a binder, carboxylate is added. The mixture which was suspended in an aqueous solution of methylcellulose to form a paste was prepared by adding 0.020 wt% of iron.
% On both sides of a core material made of copper foil with a thickness of 12 μm,
After drying, it is rolled using a roll press and cut into a predetermined size. A negative electrode lead piece 5 is spot-welded to an end of the negative electrode plate.

The separator 3 was formed by cutting a porous film made of polypropylene more widely than the positive electrode plate 1 and the negative electrode plate 2.

The whole of the positive electrode plate 1 and the negative electrode plate 2 was spirally wound with a separator interposed therebetween to form an electrode plate group.

Next, the lower insulating ring 6 was attached to the lower side of the electrode plate group, housed in a battery case 7 having a diameter of 18 mm and a height of 65 mm, and the negative electrode lead piece 5 was spot-welded to the battery case 7. Further, an upper insulating ring 8 was attached to the upper side of the electrode plate group, a groove was formed in the upper part of the battery case 7, and then a non-aqueous electrolyte was injected.

The electrolyte is ethylene carbonate (EC)
And ethyl methyl carbonate (EMC) in a volume ratio of 1:
3 and mixed with 1 mol / l of lithium hexafluorophosphate (LiPF ₆ ). After spot welding the assembled sealing plate 9 in which the gasket is incorporated and the positive electrode lead piece 4 in advance, the assembled sealing plate 9 is attached to the battery case 7.
To make the battery A of the present invention.

(Example 2) As a negative electrode current collector, iron was used in an amount of 0.1.
A battery was formed in the same manner as in (Example 1) except that a 8 μm-thick copper foil containing 020 wt% was used, and a battery B of the present invention was obtained.

(Example 3) As a negative electrode current collector,
A battery was formed in the same manner as in (Example 1) except that a 12-μm-thick copper foil containing 30 wt% was used, and a battery C of the present invention was obtained.

(Comparative Example 1) As a negative electrode current collector, iron was added in an amount of 0.1%.
A battery was formed in the same manner as in Example 1 except that a 14 μm-thick copper foil containing 018 wt% was used, and a battery D of Comparative Example was obtained.

(Comparative Example 2) As a negative electrode current collector, iron was added in an amount of 0.1%.
A battery was formed in the same manner as in Example 1 except that a 14 μm-thick copper foil containing 010 wt% was used, and a battery E of Comparative Example was obtained.

Comparative Example 3 A negative electrode paste prepared in the same manner as in Example 1 was applied to a negative electrode current collector made of a copper foil having a thickness of 12 μm and containing 0.018 wt% of iron, dried, and then rolled. Although rolled by pressing, the copper foil broke during rolling.

The tensile strength of the copper foil used in Examples 1 to 3 and Comparative Examples 1 and 2 was measured according to JIS-C6511.

The batteries A, B, and C of the present invention and the battery D of the comparative example
Was charged at 20 ° C. with a charging voltage of 4.2 V, a charging time of 2 hours, and a constant voltage / constant current charging of a limited current of 1100 mA, and was performed at 320
At Ah, a constant current discharge test was performed until the discharge end voltage reached 3.0 V.

Table 1 shows the amount of iron contained in the copper foil, the energy density per weight, and the tensile strength of the copper foil.

[0030]

[Table 1]

From Table 1, the effects of the present invention are clear when the energy densities per weight of the batteries A, B, and C of the present invention are compared with those of the batteries D and E of the comparative examples. 0.018 for copper foil
Batteries A, B, and C using a copper foil containing iron of not less than wt% as the negative electrode current collector have mechanical strength that can withstand actual use even when the thickness of the copper foil is 12 μm or less. The thickness can be reduced, and the energy density per unit weight of the battery can be improved. On the other hand, the copper foil used in Comparative Example 3 does not have mechanical strength enough to withstand rolling, and thus is not practically usable.

[0032]

As described above, since the nonaqueous electrolyte secondary battery of the present invention is formed using a copper foil containing 0.020 wt% or more of iron, the thickness of the copper foil is reduced to 12 μm or less. Energy density per unit weight of the battery can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical battery of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode plate 2 negative electrode plate 3 separator 4 positive electrode lead piece 5 negative electrode lead piece 6 lower insulating ring 7 battery case 8 upper insulating ring 9 assembly sealing plate

Continuation of front page (72) Inventor Hideshi Koshina 1006 Kadoma, Kadoma, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. AK03 AL06 AM01 AM02 AM03 AM04 AM05 AM06 BJ02 BJ14 CJ02 CJ03 CJ04 CJ05 CJ07 CJ08 DJ07 EJ01 HJ01 HJ04

Claims (1)

[Claims] 1. A negative electrode having a layer made of a carbon material capable of inserting and extracting lithium on a metal foil current collector, wherein the current collector has a thickness of 12 μm or less and an iron content of 0.020.
A non-aqueous electrolyte secondary battery using a copper foil containing not less than wt%.