JPH10188956A - Now-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having excellent safety and high cycle life performance by specifying specific surface area of a negative electrode mix layer, which includes carbonaceous material. SOLUTION: Specific surface area of a negative electrode mix layer to be formed in both surfaces of a collector of a negative electrode plate 3 is set at 0.6m<2> /g or more and at 1.4m<2> /g or less. In the case this specific surface area is formed at a value less than the lower limit value, electrical deposition of metal lithium or the like is generated in a surface of a negative electrode at the time of low-temperature charge, and discharging capacity is lowered. In the case where the specific surface area exceeds an upper limit value, when a short-circuit is generated between a positive electrode (a positive electrode terminal 9 and a positive electrode plate 2) and a negative electrode (a cover plate 7, a battery case 5 and a negative electrode plate 3) for some cause, abnormal chemical reaction of the negative electrode mix layer is generated by heating, a phenomenon as a trouble on the safety such as abnormal heating and ignition is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as portable radio telephones, portable personal computers, and portable video cameras have been miniaturized, non-aqueous electrolyte secondary batteries having high energy density and excellent lightness have been developed. Batteries have been put into practical use.

Recently, a positive electrode in which a positive electrode mixture layer containing a LiCo-based compound is laminated on the surface of a current collector, and a negative electrode in which a negative electrode mixture layer containing a carbonaceous material such as coke is laminated on the surface of the current collector Non-aqueous electrolyte secondary batteries having the following have been proposed.

[0004]

However, it has been pointed out that the above non-aqueous electrolyte secondary battery is inferior in safety to the conventional aqueous secondary battery. For example, if the user stores or holds the non-aqueous electrolyte secondary battery in a state where the positive electrode and the negative electrode of the battery are short-circuited by mistake, the internal temperature of the battery increases due to the generation of Joule heat. When the temperature inside the battery rises and reaches around a specific temperature, a surface reaction occurs between the carbonaceous material and the surrounding electrolyte, which may cause rapid heat generation. This heat generation further raises the temperature inside the battery, causing an abnormal reaction in the electrolyte or the positive electrode, and the battery cannot function. Since the nonaqueous electrolyte secondary battery is expected to be used in various environments, it is required to have high safety in various usage forms.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent cycle life and excellent safety.

[0006]

Means for Solving the Problems and Effects of the Invention The present inventors have intensively studied to improve the safety performance of the nonaqueous electrolyte secondary battery. As a result, when the specific surface area of the mixture layer of the negative electrode exceeds 1.4 m ² / g, an abnormal chemical reaction occurs in the mixture layer due to heat generation due to a short circuit between the positive electrode and the negative electrode, which causes a safety problem. Found that it led to a failure.
It has also been found that when the specific surface area of the mixture layer of the negative electrode is smaller than 0.6 m ² / g, a problem that electrodeposition occurs on the surface of the negative electrode during low-temperature charging occurs. Then, the following invention was devised.

[0007] In a non-aqueous electrolyte secondary battery having a negative electrode mixture layer is formed containing a carbonaceous material in the collector, the specific surface area of the mixture layer is 0.6 m ² / g or more 1.4 m ² / g or less. Here, the mixture layer refers to a layer in which a carbonaceous material is mixed with a binder or the like on the surface of the current collector, and the mixture is held in a layer on the surface of the current collector. The specific surface area of the mixture layer was determined by using a BET multipoint method.
The negative electrode swells as the charge and discharge cycle of the battery is repeated. Therefore, the specific surface area of the mixture layer used here is a value substantially at the time of production before swelling.

If the specific surface area of the mixture layer is less than 0.6 m ² / g, electrodeposition occurs on the negative electrode surface as the number of charge / discharge cycles increases, and the discharge capacity decreases rapidly. Also,
When the specific surface area of the mixture layer becomes larger than 1.4 m ² / g,
When the positive electrode and the negative electrode are erroneously short-circuited, abnormal heat generation occurs inside the battery, which may cause smoke or ignition. Therefore, by setting the specific surface area of the mixture layer of the negative electrode within the above range, a non-aqueous electrolyte secondary battery having excellent safety and a high cycle life can be obtained.

[0009]

FIG. 1 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery according to the present invention. In FIG. 1, an electrode group 1 includes a positive electrode plate 2 and a negative electrode plate 3 stacked with a separator 4 interposed therebetween.
It is formed by winding an elliptical spiral around a winding core 6 made of a polyethylene resin plate. The electrode group 1 is inserted into a nickel-plated rectangular battery case 5. The battery case 5 has a thickness of 0.3 mm and an inner dimension of 3
It is formed in a size of 3.1 mm × 46.5 mm × 7.5 mm.

The positive electrode plate 2 is formed by holding a positive electrode mixture layer mainly composed of lithium cobalt composite oxide (LiCoO ₂ ) on both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm. This positive electrode plate 2 is prepared by appropriately adding N-methylpyrrolidone (NMP) to polyvinylidene fluoride as a binder and acetylene black as a conductive agent to a lithium-cobalt composite oxide, mixing them into a paste, and mixing the resultant with an aluminum foil. It is formed by applying it to both sides, drying it, rolling it to a thickness of 180 μm, and cutting it to a width of 54 mm leaving a rectangular lead.

The negative electrode plate 3 has a negative electrode mixture layer containing graphite (graphite) on both surfaces of a current collector made of copper foil having a thickness of 14 μm. The negative electrode plate 3 is prepared by appropriately adding a binder such as polyvinylidene fluoride and N-methylpyrrolidone (NMP) to a graphite, mixing the resulting mixture into a paste, applying the paste to both surfaces of a copper foil, and drying. And a thickness of 220
After being rolled to μm, leaving a rectangular lead, width 56 mm
It is formed by cutting into pieces.

The separator 4 is formed of, for example, a polyethylene microporous film having a thickness of 25 μm and a width of 58 mm as a porous polyolefin material.

In the battery case 5, as an organic electrolyte,
A mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate containing 1 mol / l (liter) of LiPF ₆ is filled. The volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate is 2: 1: 2.

A cover plate 7 is attached to the upper opening of the battery case 5. A positive electrode terminal 9 made of aluminum rivets is attached to the center of the cover plate 7 by caulking via an insulating packing 8 made of polypropylene. A current-collecting washer 10 is attached to the lower end of the positive electrode terminal 9, and the current-collecting washer 10 is made of stainless steel (SUS3).
17JH) and is connected to one end of the positive electrode plate 2 via a positive electrode lead 11 made of 17JH). A lead cover 13 made of a polypropylene resin is provided below the cover plate 7.

The cover plate 7 is made of a negative electrode lead 1 made of nickel.
2 is connected to one end of the negative electrode plate 3 by resistance welding. Thereby, the cover plate 7 and the battery case 5 become negative electrode terminals. Further, a hole 14 is formed in the cover plate 7, and a safety valve 15 is attached so as to cover the hole 14. The lid plate 7 and the battery case 5 are sealed by laser welding.

In the non-aqueous electrolyte secondary battery having the above structure, the specific surface area of the negative electrode mixture layer formed on both surfaces of the current collector of the negative electrode plate 3 is 0.6 m ² / g or more and 1.4 m ² / g. It is formed as follows. When the specific surface area is smaller than 0.6 m ² / g, lithium metal is deposited on the surface of the negative electrode during low-temperature charging, and the discharge capacity decreases. If the specific surface area is larger than 1.4 m ² / g, a short circuit occurs between the positive electrode (positive electrode terminal 9 or positive electrode plate 2) and the negative electrode (cover plate 7, battery case 5 or negative electrode plate 3) for some reason. When this occurs, heat generation may cause an abnormal chemical reaction in the negative electrode mixture layer, which may cause a problem such as abnormal heat generation or ignition that poses a safety problem.

[0017]

EXAMPLE Here, a non-aqueous electrolyte secondary battery having various values of the specific surface area of the negative electrode mixture layer of the negative electrode plate 3 was produced with respect to the non-aqueous electrolyte secondary battery having the above structure, and a performance test was performed. Was done. Table 1 shows the value of the specific surface area of the negative electrode mixture layer of the nonaqueous electrolyte secondary battery used in the test.

[0018]

[Table 1]

The specific surface area of the negative electrode plate 3 taken out of the battery after repeating the charge / discharge cycle and vacuum-dried was measured using an automatic specific surface area measuring device Gemini 2360 manufactured by Shimadzu Corporation. It is measured according to the BET multipoint method.

First, the non-aqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were fully charged by low-current low-voltage charging to 4.1 V at 0.5 C current for 3 hours. State. Then, a nail having a diameter of 2.5 mm was pierced into each non-aqueous electrolyte secondary battery, and an internal short circuit was forcibly generated, and the state change of the battery was observed. Table 2 shows the results of the nail penetration test.

[0021]

[Table 2]

As can be seen from the results of Comparative Example 2 in Table 2,
When the specific surface area of the mixture layer of the negative electrode was 1.46 m ² / g, smoking from the battery was confirmed.

Next, a cycle life test was conducted in which charge and discharge cycles for charging and discharging after charging under the same conditions as described above were repeated. The result is shown in FIG. Comparative Example 1 of FIG.
According to the result, when the specific surface area is 0.53 m ² / g,
A phenomenon in which the discharge capacity sharply decreased was observed. Further, in this case, it was found that metallic lithium was electrodeposited on the surface of the negative electrode plate 3, thereby decreasing the discharge capacity of the nonaqueous electrolyte secondary battery.

According to the results of the above test, by setting the specific surface area of the mixture layer of the negative electrode in the range of 0.6 m ² / g or more and 1.4 m ² / g or less, the discharge capacity does not decrease and It can be seen that a non-aqueous electrolyte secondary battery excellent in safety without any trouble due to abnormal heat generation can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a diagram showing the results of a cycle life test of a nonaqueous electrolyte secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode part 2 Positive electrode plate 3 Negative electrode plate 4 Separator 5 Battery case

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Murai 1st ino-babacho, Nishi-no-Sho, Kichijo-in, Minami-ku, Kyoto Inside (72) Inventor Shigeo Komatsu Ino-no-Shi, Nishino-sho, Kichijo-in, Minami-ku, Kyoto 1 Babacho Inside Nihon Battery Co., Ltd.

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery having a negative electrode in which a current collector contains a mixture layer containing a carbonaceous material, wherein the specific surface area of the mixture layer is 0.6 m ² / g or more. 4m ²
/ G or less.