JPH11273681A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is excellent in the balance of performance. SOLUTION: This nonaqueous electrolyte secondary battery has a binder containing a fluororesin and fluore rubber, a negative electrode, and a positive electrode having a positive electrode mix layer containing at least a conduction assistant and containing the fluoro rubber by 1.5 to 2.3 wt.% of the positive electrode mix layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art An electrode of a non-aqueous electrolyte secondary battery is manufactured by supporting a positive electrode active material and a negative electrode active material on an aluminum foil, a copper foil, or the like, which is a current collector metal. However,
Since only the positive electrode active material or the negative electrode active material is brittle and easily breaks or peels off, a binder is added and the mixture is adhered and held in a layer on the current collector metal as a mixture. In addition, when the conductivity between the particles or the current collector metal cannot be ensured by using only the positive electrode active material and the negative electrode active material, a conductive auxiliary is added to the mixture. The electrode in which the mixture layer is formed on the current collector metal as described above is wound or bent via a separator when the battery element is formed, and stored in a battery container.

Conventional binders include PVDF and P
A fluororesin such as TFE and a binary or tertiary copolymer such as fluororubber are used alone. However, with PVDF alone, the electrode mixture layer becomes hard, so that the electrode is likely to be broken or the mixture layer to be peeled when wound as an electrode plate group. In order to reduce the degree of hardening,
Some use only fluororubber as a binder, but the fluorocarbon rubber alone softens the mixture layer, but has a large swelling property with respect to the electrolyte, swells the electrode plate, and lowers the charge / discharge performance. .

To solve the above problem, Japanese Patent Laid-Open No.
No. 2,259,890, the polyvinylidene fluoride (P
The examples disclose that an equivalent mixture of VDF) and an elastomer (NBR, fluorine-containing acrylic rubber, fluorosilicone rubber, fluoride-based rubber) can be used as a binder.

[0005]

However, in the non-aqueous electrolyte secondary battery, in addition to the above-mentioned problems, high-rate discharge performance, low-temperature performance and safety performance are also required to be improved. It is with. In particular, a nonaqueous electrolyte secondary battery has a very high energy efficiency per volume, and thus its use has been diversified. Therefore, there is a need for a non-aqueous electrolyte secondary battery that can withstand any use environment and has no variation in various characteristics. However, Japanese Patent Application Laid-Open No. 9-259
No. 890 does not disclose any high-rate discharge performance, low-temperature performance, and safety performance.

Accordingly, the present invention has been made in view of such circumstances, and has excellent charge / discharge characteristics without cracking or cracking during manufacturing, and also has excellent high-rate discharge performance, low-temperature performance, and safety performance. Another object of the present invention is to provide a non-aqueous electrolyte secondary battery with balanced performance.

[0007]

That is, in order to solve the above-mentioned problems, the nonaqueous electrolyte secondary battery of the present invention has been studied by focusing on the positive electrode mixture layer as a guideline for various characteristics, A positive electrode mixture layer containing at least a binder containing a rubber, a positive electrode, and a conductive additive, wherein the fluorine rubber content is 1.7 to 2.3 wt% per the positive electrode mixture layer.
And a positive electrode having a positive electrode mixture layer. Preferably, it is 1.7 to 2.1%, more preferably 1.9 to 2.1%.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.

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

In the figure, 1 is a non-aqueous electrolyte secondary battery, 2
Is an electrode group, 3 is a positive electrode plate, 4 is a negative electrode plate, 5 is a separator,
6 is a battery case, 7 is a case lid, 10 is a positive electrode terminal, 11
Is a positive electrode lead.

The structure of the nonaqueous electrolyte secondary battery 1 is as follows. A flat lithium secondary battery comprising a positive electrode plate 3, a negative electrode plate 4, a separator 5, and a flat electrode group 2 composed of a nonaqueous electrolyte is accommodated in a battery case 6. Battery. The battery case 6 has a thickness of 0.3 m
5 mm thick nickel plating on the surface of an iron main body having a size of 63.0 × 29.0 × 5.0 mm and a hole for injecting an electrolyte solution (not shown) at an upper side portion. Is provided. The positive electrode plate 3 is connected to a terminal 10 provided on the case lid 7 via a positive electrode lead 11.
The negative electrode plate 4 is electrically connected to the inner wall of the battery case 6 by contact.

The current collector of the positive electrode plate 3 is an aluminum foil having a thickness of 20 μm, and a lithium cobalt composite oxide is held as an active material on the current collector. The positive electrode plate is
6 parts by weight of polyvinylidene fluoride as a binder and 3 parts of acetylene black as a conductive agent were mixed with 91 parts of an active material, and N-methylpyrrolidone was added as appropriate to prepare a paste. And dried on both sides. However, an uncoated portion was left in a rectangular shape as a lead. Then, it was rolled to a thickness of 180 μm and cut to a width of 25 mm leaving a rectangular lead.

The negative electrode plate 4 is prepared by mixing 92 parts of graphite as an active material and 8 parts of polyvinylidene fluoride as a binder on both sides of a current collector made of a copper foil having a thickness of 14 μm,
Methylpyrrolidone was added, and a paste prepared was applied and dried. At this time, the surface of the current collector was exposed without coating only the outermost portion of the electrode group. And
It was manufactured by rolling to a thickness of 220 μm and cutting to a width of 27 mm.

The separator 5 has a thickness of 25 μm and a width of 29 m.
m is a microporous polyethylene membrane. The electrolyte is LiPF
It is a mixed solution of ethylene carbonate: diethyl carbonate = 2: 3 (volume ratio) containing ₆ at 1 mol / l. Then, the electrode group 2 is housed in the battery case 6 and the positive electrode lead 11
And the terminal 10 were connected, and the lid 7 was sealed to the battery case 6 by laser welding. Next, a predetermined amount (3 ml) of the electrolytic solution was
The injection hole was sealed by vacuum injection from the electrolyte injection hole.

As described above, a conventional battery A having a designed capacity of 600 mAh was manufactured.

The batteries B to G according to the present embodiment were manufactured in the same manner as described above. However, a fluorine rubber (here, a terpolymer of vinylidene fluoride / hexafluoropropylene / tetrafluoroethylene was used) was added as a binder. At this time, the amount of addition is 1.4, 1.5, 1.7, 2.0, 2, or 2, based on the amount of the positive electrode mixture layer (here, the total amount of the active material, the binder, and the conduction aid). .1,2.
3, 2.6, 3.0, 3.5, 5.0 wt% (BK)
It was made to become. Also, the amount of polyvinylidene fluoride was reduced by the amount of the fluororubber added.

[Test] In these batteries, at 25 ° C.
The battery was charged at a constant current and a constant voltage up to 4.1 V with a current of 1 C for 3 hours to obtain a fully charged state. And it discharged to 2.75V at 1C, and performed the cycle test. Next, charge as well,
A low-temperature discharge test at −10 ° C. was performed. Further, after the same charge, a high-rate discharge test at 2C was performed. These test results are shown in FIG. Here, the vertical axis is the capacity ratio (%),
This is the capacity ratio (%) with respect to the initial discharge at 25 ° C. to 2.75 V at 1 C, and the horizontal axis shows the amount of fluorine rubber added (wt%) in the total amount (dry weight) of the positive electrode mixture.

FIG. 2 shows that when the fluorine rubber content is in the range of 1.4 to 2.3 wt%, the cycle characteristics, the low temperature characteristics, the high rate performance, and the balance among them are also excellent.

In addition, at 25 ° C. and 1 C current for 3 hours,
The battery was charged at a constant current and a constant voltage up to 4.2 V, and a nail made of steel having a diameter of 2.5 mm was inserted into each battery to forcibly cause an internal short circuit. As a result, only in the cases of 0% and 1.4%, the operation of the safety valve was recognized.

Accordingly, it is shown that when the content of the fluororubber is in the range of 1.5 to 2.3 wt%, the cycle characteristics, the low temperature characteristics, the high rate performance, and the safety are excellent, and the balance among them is also excellent. Was.

The fluororesin according to the present invention includes, in addition to the above-mentioned polyvinylidene fluoride, polytetrafluoroethylene, a tetrafluoroethylene / hexafluoropropylene binary copolymer, and a tetrafluoroethylene / perfluoroalkylvinyl ether binary. Copolymer,
Polychlorotrifluoroethylene, polyvinyl fluoride,
Examples include an ethylene / tetrafluoroethylene binary copolymer and an ethylene / chlorotrifluoroethylene binary copolymer. Examples of the fluororubber include vinylidene fluoride / hexafluoropropylene / tetrafluoroethylene terpolymer, vinylidene fluoride / hexafluoropropylene binary copolymer, and vinylidene fluoride / chlorofluoropropylene copolymer. Copolymer, propylene / tetrafluoroethylene binary copolymer, vinylidene fluoride / pentafluoropropylene binary copolymer, vinylidene fluoride / pentafluoropropylene / tetrafluoroethylene terpolymer, vinylidene fluoride / Perfluoromethyl vinyl ether / tetrafluoroethylene terpolymer and the like. (However, these classifications are based on the description of the fluororesin handbook of the first edition of November 1990.) Further, in the above embodiment, an active material as a positive electrode mixture,
Although the case where the binder and the conductive assistant are added is shown, this mixture is not necessarily limited to these, and other materials can be added as needed. Further, the positive electrode active material electrode group is not limited to the wound type in which the positive electrode and the negative electrode are wound as described above, but may be any type such as a laminated type.

[0022]

As is apparent from the above description, according to the battery of the present invention, the present invention has excellent charge-discharge characteristics without cracking or cracking during production, and has high-rate discharge performance and low-temperature performance. It is also possible to provide a nonaqueous electrolyte secondary battery with excellent performance and excellent safety performance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a diagram showing a relationship between a capacity ratio and a fluorine content according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Positive electrode plate 4 Negative electrode plate 5 Separator 6 Battery case 7 Case lid 10 Positive electrode terminal 11 Positive electrode lead

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiro Nakamitsu 5 Kichijoin Nitta Ichidantancho, Minami-ku, Kyoto City Inside S-Melcotec Co., Ltd. (72) Inventor Minoru Mizutani Minami-ku, Kyoto No. 1 Ino Babacho, Nohon Battery

Claims (1)

[Claims] A positive electrode mixture layer containing a binder containing a fluororesin and a fluororubber, a positive electrode active material, and a conductive auxiliary, wherein the content of the fluororubber is in the range of the positive electrode mixture layer. ,
A nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode mixture layer of 1.5 to 2.3 wt%.