JPH0574462A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolyte secondary battery excellent in an overdischarge resistant characteristic and safety. CONSTITUTION:In a nonaqueous electrolyte secondary battery which uses lithium-containing composite oxides of transition metals as positive electrode material and a carbonaceous material as negative electrode material, a negative electrode plate 2 which uses nickel, titanium, and stainless steel as core materials is heat treated at temperatures above 180 deg.C. Thereby a very thin oxide film is formed on the surface of the core materials and so elusion of the core materials is prevented even if the electric potential of the negative electrode is raised by an overdischarging device, and thus the capacity of the battery is recovered simply by recharging. The ceiling temperature of the heat treatment is restricted depending on the thermal properties of the core materials and of a binding agent used.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
In particular, it relates to the improvement of the over-discharge resistance.

In recent years, with the remarkable portable and intelligent use of cordless information / communication devices such as mobile phones and camcorders, a non-aqueous electrolyte secondary battery having a small size, a light weight and a high energy density has been used as a power source for driving the cordless information / communication devices. Is getting attention. More recently, there is a tendency to attach particular importance to its safety.

[0003]

2. Description of the Related Art Conventionally, oxides of transition metals and sulfur have been used as positive electrode materials.
Compound such as manganese dioxide (MnO) ₂), Molybdenum disulfide
Buden (MoS₂), Etc., with metallic lithium as the negative electrode material
The battery system used for each has been proposed. But charging
When lithium is deposited, the non-aqueous electrolyte composition and charging
It is mainly needle-shaped due to the influence of the situation, etc.
Is removed from the negative electrode or penetrates the separator
It may come into contact with the pole and cause an internal short circuit or fire.
It is said that there is a problem with safety.

Therefore, a battery system using a compound that electrochemically inserts / extracts lithium into / from the positive and negative electrode materials has been proposed. In this case, the positive electrode material is a lithium-containing composite oxide of a transition metal, that is, LiMO having a layered structure.
₂ (M is a transition metal such as cobalt, nickel, iron)
However, as a negative electrode material, a carbon material having a layered structure is also considered promising because it reversibly inserts / extracts lithium.

[0005]

As described above, by using a lithium-containing composite oxide of a transition metal as a positive electrode material and a carbon material as a negative electrode material, a non-aqueous liquid having a small size and a high energy density and high energy density can be obtained. It is assumed that an electrolyte secondary battery can be provided.

However, some problems still remain in this battery. One of them is improvement in over-discharge resistance.

The potential at which the carbon material inserts / extracts lithium differs depending on the physical properties of the carbon material, particularly the degree of development of the layered structure (interlayer distance, layer overlap), and is about 0.1 V to about 0 relative to lithium. It is 0.8V.

Therefore, it is necessary to use, as the core material, a material such as nickel, titanium, or stainless steel which hardly causes an interaction such as occluding / releasing lithium within this potential range.

However, at the time of over-discharging, the potential of the negative electrode rises above the melting potential of the core material, so that the phenomenon that the core material melts and deposits on the positive electrode is seen, and at the same time, the current collecting property of the negative electrode is remarkable. However, there was a problem that the capacity hardly recovered even after re-charging after the decrease and over-discharge.

[0010]

In order to solve these problems, the present invention is to heat-treat a negative electrode plate using a core material of nickel, titanium or stainless steel.
Preferably, the heat treatment is performed at 180 ° C. or higher.

[0011]

According to the present invention, a very thin oxide film can be formed on the surface of the core material. Even if the potential of the negative electrode rises above the dissolution potential of the core material after being left to overdischarge due to this oxide film, the core material does not dissolve and deposit on the positive electrode. Therefore, the capacity is quickly restored by recharging, and the over-discharge resistance can be improved.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross section of the configuration of the cylindrical non-aqueous electrolyte secondary battery of the present invention.

The positive electrode plate 1 is made of carbon lithium (LiCO ₃ )
And cobalt trioxide (Co ₃ O ₄ ) were mixed and fired at 900 ° C. in air lithium cobalt oxide (LiCo
O ₂ ) as an active material, 3% by weight of acetylene black as a conductive agent and 4% by weight of graphite were mixed, and then 7% by weight of an aqueous dispersion of poly (tetrafluoroethylene) was kneaded as a binder to prepare a paste form. The mixture was prepared by applying aluminum foil to the core material, applying the mixture on both sides, drying and rolling. Further, the positive electrode lead plate 4 is spot-welded to the end portion thereof.

The negative electrode plate 2 was prepared by kneading mesophase pitch in an argon atmosphere at 2800 ° C. with spherical graphite as an active material and kneading 5% by weight of an aqueous dispersion of polytetrafluoroethylene as a binder. It was prepared by the following manufacturing method using a paste-form mixture. Further, the negative electrode lead plate 5 is spot-welded to the end portion thereof.

The separator 3 is formed by cutting a porous film made of polypropylene wider than the positive and negative electrode plates.

An electrode group was constructed by spirally winding the whole with a separator interposed between the positive and negative plates.

Next, the upper and lower parts of the electrode plate group are heated with warm air to heat-shrink the separator 3. The lower insulating ring 6 is attached to the lower side of the electrode plate group, is housed in the case 7, and the negative electrode lead plate 5 is spot-welded to the case 7. Further, an upper insulating ring 8 is attached to the upper side of the electrode plate group, a groove is formed in the upper portion of the case 7, and then a nonaqueous electrolytic solution is injected. The non-aqueous electrolytic solution was prepared by mixing ethylene carbonate (EC) and diethylene carbonate (DEC) at a volume ratio of 1: 1 and dissolving lithium perchlorate (LiClO ₄ ) at 1 mol / l. After spot welding the assembled sealing plate 9 having a gasket incorporated therein and the positive electrode lead plate 4, the assembled sealing plate 9 is mounted on the case 7 and caulked.

The overdischarge characteristic was evaluated by the following method. First, a battery was constructed and a constant current charge / discharge of 100 mA at 20 ° C. was repeated for 5 cycles. The upper limit voltage during charging is 4.
The lower limit voltage during discharge was 1 V and 3.0 V. Then, the battery was placed in a discharged state and further subjected to constant resistance discharge of 100Ω, and left for 2 weeks in a state where the battery voltage was 0V. Then, 100 mA constant current charging / discharging was performed again, and the capacity recovery characteristics were compared.

(Example 1) The negative electrode plate 2 was subjected to various temperatures at various temperatures.
A nickel foil, titanium foil, or stainless steel foil that had been heat treated for a period of time was used, and the above mixture was applied to both sides, dried and rolled. FIG. 2 shows the capacity recovery rate of a battery using these negative electrode plates after being left over-discharged.

(Example 2) The negative electrode plate 2 uses a nickel foil, a titanium foil, and a stainless steel foil as a core material, and after coating the above mixture on both surfaces thereof, drying and rolling, it is carried out at various temperatures for 5 hours. It was heat treated. FIG. 3 shows the capacity recovery rate of a battery using these negative electrode plates after being left over-discharged.

As is apparent from FIGS. 2 and 3, when a negative electrode plate heat-treated at at least 180 ° C. is used,
A 70% or more capacity recovery was observed even after standing for over-discharge.

Even if the potential of the negative electrode rises due to over-discharge, a very thin oxide film is formed on the surface of nickel, titanium or stainless steel used for the core material by heat treatment at at least 180 ° C. or higher. Therefore, it is considered that the core material is not melted.

Here, when the heat treatment is performed at 320 ° C. or higher in Example 1, the oxide film formed on the surface of the core material grows, so that the current collecting property and the adhesion property to the mixture are deteriorated. Therefore, when the carbon material expands due to recharging, the negative electrode plate collapses (the mixture is peeled or dropped from the core material), and the capacity recovery rate decreases. That is, the upper limit temperature of the heat treatment is limited by the physical properties of the core material used, particularly the thermal properties.

When heat-treated at 280 ° C. or higher in Example 2, the binding property is partially lost because polytetrafluoroethylene is used as the binding agent. Therefore, when the carbon material expands due to recharging, the negative electrode plate collapses (the mixture is peeled or dropped from the core material), and the capacity recovery rate decreases. That is, the upper limit temperature of the heat treatment is limited by the physical properties of the binder used, particularly the thermal properties.

[0025]

As described above, according to the present invention, in a non-aqueous electrolyte secondary battery using a lithium-containing composite oxide of a transition metal as a positive electrode material and a carbon material as a negative electrode material, nickel is used as a core material. By heat-treating a negative electrode plate made of titanium, titanium or stainless steel at 180 ° C. or higher, the over-discharge resistance can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of the configuration of a cylindrical non-aqueous electrolyte secondary battery.

FIG. 2 is a diagram showing overdischarge characteristics of Example 1.

FIG. 3 is a diagram showing overdischarge characteristics of Example 2.

[Explanation of symbols]

 1 Positive Electrode Plate 2 Negative Electrode Plate 3 Separator 4 Positive Electrode Lead Plate 5 Negative Electrode Lead Plate 6 Lower Insulation Ring 7 Case 8 Upper Insulation Plate 9 Assembly Seal Plate

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery using a lithium-containing composite oxide of a transition metal as a positive electrode material and a carbon material as a negative electrode material, wherein a negative electrode plate heat-treated at 180 ° C. or higher is used. Non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode plate uses, as a core material, any one of nickel, titanium, and stainless steel heat-treated at 180 ° C. or higher. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode plate is made of nickel, titanium or stainless steel as a core material and is coated with a carbon material and then heat-treated at a temperature of at least 180 ° C. or higher.