JPH07111160A - Secondary battery - Google Patents

Abstract

PURPOSE:To retard the drop in discharge capacity attendant on the progress of charge/discharge cycles by using a clad metal having an aluminium layer on the inside as a positive case. CONSTITUTION:A battery case (positive case) 1 also serving as a positive terminal is manufactured by blanking and forming a clad plate of a 5mum aluminium plate and a 200mum stainless steel plate with a press. A battery is sealed by climping inward the opening edge of the case 1 against the inner circumference of a sealing plate 2 also serving as a negative terminal through a gasket 4. The organic electrolyte secondary battery using the clad material having the aluminium layer on the inside as the battery case 1 material has higher discharge capacity retainability in repeated charge/discharge cycle compared with conventional batteries.

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 having a high energy density and a high safety as a power source for driving electronic equipment or a memory holding power source.

[0002]

2. Description of the Related Art With the rapid miniaturization and weight reduction of electronic equipment, the development of a secondary battery that is smaller, lighter in weight and high in energy density, and that can be repeatedly charged and discharged with respect to the power source battery The demand is increasing. Non-aqueous electrolyte secondary batteries are the most promising secondary batteries that meet these requirements.

Various positive electrode active materials for non-aqueous electrolyte secondary batteries such as titanium disulfide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide have been investigated. ing. Among them, lithium cobalt composite oxide (Li
xCoO ₂ ) and spinel type lithium manganese oxide (Lix
Since Mn ₂ O ₄ ) charges and discharges at an extremely noble potential of 4 V (Li / Li ⁺ ) or more, a battery having a high discharge voltage can be realized by using it as a positive electrode.

As a negative electrode active material for a non-aqueous electrolyte secondary battery, various materials such as metallic lithium, Li-Al alloys capable of inserting and extracting lithium, and carbon materials have been studied. Among them, carbon materials are particularly preferable. Has the advantage that a battery with high safety and long cycle life can be obtained.

However, a lithium cobalt composite oxide (Li _X CoO ₂ ) or spinel type lithium manganese oxide (LixMn ₂ O ₄ ) which operates at high voltage is used for the positive electrode, and stainless steel (SUS304) steel is used as the material for the positive electrode can. The discharge capacity of the 2020 type coin battery that used was drastically reduced after repeated charging and discharging. It is considered that this is because the positive electrode can was oxidized by the positive electrode having a noble potential.

Therefore, there has been a demand for the development of a positive electrode can having further improved oxidation resistance.

[0007]

The present invention relates to a positive electrode made of a substance which absorbs and releases lithium ions, and a secondary battery which uses a negative electrode and an ionic conductor containing lithium ions as an electrolyte. It is intended to solve the above-mentioned problems by using the clad metal contained in 1.

[0008]

The non-aqueous electrolyte secondary battery of the present invention has an effect of excellent discharge capacity retention characteristics after repeated charge / discharge cycles as compared with the conventional non-aqueous electrolyte secondary battery. It is considered that this is because the oxidation of the positive electrode can was suppressed by the material of the new case used for the non-aqueous electrolyte secondary battery of the present invention.

[0009]

EXAMPLES The present invention will be described below with reference to preferred examples.

First, a lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was synthesized as follows. Basic cobalt carbonate was pyrolyzed in air at a temperature of 650 ° C. for 24 hours to synthesize cobalt trioxide (Co ₃ O ₄ ). Lithium carbonate and this cobalt trisodium oxide were mixed at a lithium: cobalt atomic ratio of 1: 1 at a temperature of 700 ° C. for 16
Pyrolyzed in air for hours.

Then, a positive electrode plate was prototyped as follows. 6.5 parts by weight of polyvinylidene fluoride, 10 parts by weight of graphite (SFG6 manufactured by Lonza), 1.5 parts by weight of Ketjenblack and N as a solvent are added to 82 parts by weight of the lithium cobalt composite oxide obtained by the above method. An appropriate amount of -methyl-2-pyrrolidone was added and kneaded well to prepare a positive electrode mixture paste. This paste was evenly applied to a 100 mesh aluminum wire mesh (wire diameter 0.1 mm), dried with hot air at a temperature of 85 ° C. for 10 hours, then baked at a temperature of 250 ° C. for 30 minutes, punched into a disk with a diameter of 16 mm, and lithium cobalt. A composite oxide electrode was prototyped. The theoretical capacity of this electrode is
0.5 mol of lithium is occluded per mol of (LiCoO ₂ ).
If released, it is about 18 mAh.

A negative electrode plate was manufactured as follows. A negative electrode mixture paste was prepared by adding 8 parts by weight of polyvinylidene fluoride and N-methyl-2-pyrrolidone as a solvent in appropriate amounts to 92 parts by weight of carbon powder (pyrolytic carbon) and kneading the mixture well. This paste is 100 mesh copper wire mesh (wire diameter 0.1m
m) and evenly dry with hot air at 85 ℃ for 10 hours,
Then, after baking at 250 ℃ for 30 minutes, the diameter is 16mm
A negative electrode plate was manufactured by punching into a circular plate. The charge / discharge capacity of this electrode is about 18 mAh.

Further, 1 mol / l of perchloric acid was added to a solvent prepared by mixing propylene carbonate (hereinafter referred to as PC) and dimethyl carbonate (hereinafter referred to as DMC) at a volume ratio of 7: 3 in the electrolytic solution. Organic electrolyte in which lithium oxide (LiClO ₄ ) is dissolved (below LiClO ₄ (1M) / PC + DMC (1: 1)
Will be used). The electrolyte was used by injecting only about 200 microliters in total into the positive and negative electrode plates and the separator.

FIG. 1 is a vertical sectional view of a battery. In this figure, 1 is a case that also functions as a positive electrode terminal and is formed by punching a clad steel plate of aluminum with a thickness of 5 μm and stainless steel (SUS304) with a thickness of 200 μm by a press, and 2 is a thickness of 25.
It is a sealing plate that also functions as a negative electrode terminal made by punching out a 0 μm stainless steel (SUSU304) steel plate, and the negative electrode 3 is in contact with the inner wall thereof. 5 is a separator made of polypropylene impregnated with an organic electrolytic solution, 6 is a positive electrode, and the opening end of the case 1 also serving as a positive electrode terminal is swaged inward, and the inner periphery of the sealing plate 2 also serving as a negative electrode terminal is inserted through a gasket 4. It is closed and sealed by tightening.

The organic electrolyte secondary battery of the present invention using the above positive electrode plate, negative electrode plate, electrolytic solution and positive electrode can is referred to as (A). A conventional battery having the same structure as the organic electrolyte battery (A) of the present invention is referred to as (A) except that a 25 μm thick stainless steel (SUS304) steel plate is used as the material of the positive electrode can.

Next, these batteries were charged at a constant current of 2.0 mA until the terminal voltage reached 4.2 V, and then at the same constant current of 2.0 mA, the terminal voltage became 2.7 V. Charge-discharge cycle life test (temperature 45
℃).

The results of the cycle test are shown in FIG. The battery (A) of the present invention shows no significant decrease in discharge capacity until the number of charge / discharge cycles reaches 100 times. However, in the conventional battery (A) for comparison, the discharge capacity significantly decreases with the progress of the charge / discharge cycle.

As described above, the organic electrolyte secondary battery of the present invention using the clad material having the aluminum layer inside as the material of the positive electrode can has repeated charge / discharge cycles more than the conventional organic electrolyte secondary battery. In this case, the retention characteristic of the discharge capacity was significantly improved.

In the above embodiment, the case where the clad material of aluminum and stainless steel (SUS304) is used is explained. However, instead of SUSU304, SUS316, SUSU430, iron, chromium,
Similar results can be obtained by using various materials such as nickel and copper. Further, aluminum-stainless-nickel or the like having nickel or the like plated on the upper surface of the above stainless steel or the like can also be effectively used.

In the above examples, the case where the lithium cobalt composite oxide is used as the positive electrode active material has been described. However, titanium disulfide, manganese dioxide, spinel type lithium manganese oxide (LixMn ₂ O ₄ ), vanadium pentoxide and Various materials such as molybdenum trioxide can be used. Although a carbon material was used as the negative electrode, the negative electrode active material is basically not limited when using the positive electrode of the present invention, and the negative electrode active material used in the conventional non-aqueous electrolyte secondary battery, for example, pure Lithium, a lithium alloy, or the like can be used.

Further, the electrolytic solution which is a lithium ion conductive substance and the solid ionic conductor are basically not limited, and those used in the conventional organic electrolytic solution secondary battery can be used. Examples of the organic solvent include cyclic esters such as ethylene carbonate which is an aprotic solvent and ethers such as tetrahydrofuran and dioxolane. These can be used alone or in a mixture of two or more kinds. As the solid ionic conductor, any substance having lithium ion conductivity can be used. A typical example thereof is polyethylene oxide.

Also, the supporting electrolyte dissolved in such a non-aqueous solvent or solid ionic conductor is not basically limited. For example, LiAsF ₆ , LiClO ₄ , Li
One or more of BF ₄ , LiPF ₆ and LiCF ₃ SO ₃ can be used.

Although the batteries according to the above-mentioned embodiments are all button type batteries, the same effect can be obtained by applying the present invention to cylindrical, prismatic or paper type batteries.

[0024]

As described above, in the non-aqueous electrolyte secondary battery of the present invention, the decrease in discharge capacity with the progress of charge / discharge cycles is small.

[Brief description of drawings]

FIG. 1 is a diagram showing an internal structure of a button battery which is an example of a non-aqueous electrolyte secondary battery.

FIG. 2 is a diagram showing cycles and discharge capacities of test batteries.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Negative Electrode 4 Gasket 5 Separator 6 Positive Electrode

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode made of a substance which absorbs and releases lithium ions, a negative electrode, and an electrolyte made of an ion conductor containing lithium ions, wherein an aluminum layer is used as a positive electrode case inside. A non-aqueous electrolyte secondary battery using the clad metal as defined in 1.