JP2001345081A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having a high safety. SOLUTION: In the nonaqueous electrolyte secondary battery in which a power generation element having a positive electrode plate, an insulator and a negative electrode plate are housed in a bag-type single battery case composed of metal laminated resin film, an opening part whose area ranging from 1 mm2 to 100 mm2 installed at a place except a welded part of the bag-type single battery case is sealed by the resin film, and opening pressures of this opening part are made to be in the range from 1 kgf/cm2 to 20 kgf/cm2.

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 in which a power generating element is accommodated in a bag-shaped unit cell case.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has realized a reduction in size and weight of electronic devices one after another. Along with this, there is an increasing demand for batteries that are power sources to be further reduced in size, weight, and energy density.

Conventionally, aqueous secondary batteries such as lead batteries and nickel cadmium batteries have been the mainstream as secondary batteries for general use. However, although these aqueous batteries are excellent in reliability, they cannot be said to be sufficiently satisfactory in terms of battery weight and energy density.

Therefore, recently, non-aqueous electrolyte secondary batteries having a high battery voltage and a high energy density have begun to be used. As a typical nonaqueous electrolyte secondary battery, there is a lithium ion secondary battery using a substance capable of reversible intercalation of lithium ions as an electrode material.

[0005] This lithium ion secondary battery has a negative electrode plate in which the above-mentioned negative electrode material is held on a negative electrode current collector as a support, and a reversible electrochemical reaction with lithium ions such as a lithium cobalt composite oxide. A positive electrode plate, which holds the positive electrode active material to be supported on a positive electrode current collector as a support, and a separator, which holds an electrolytic solution and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between the two electrodes. ing.

[0006] Each of the positive electrode plate and the negative electrode plate, each formed into a thin sheet or foil, is sequentially laminated or spirally wound through a separator to form a power generating element. Then, the power generating element is housed in a battery container made of a metal can made of stainless steel, nickel-plated iron, aluminum, or the like. After the electrolyte is injected, the battery is assembled and sealed with a lid plate.

However, when a metal can battery container is used,
Although it is highly airtight and has excellent mechanical strength,
There are great restrictions on battery weight, battery container material and design.

As a solution to the above problem, there has been proposed a method of using a unit cell case made by laminating a metal foil with a resin film on the material of the unit cell case. By this method,
There is no leakage of electrolyte or intrusion of moisture or the like from the outside of the battery, and the battery can be reduced in weight.

[0009]

However, in a lithium ion secondary battery using such a metal-laminated resin film case, when gas is generated during overcharge or the like, the case expands and ruptures, so that the power generation element This causes the problem of smoke or ignition.

When gas is generated inside the battery due to overcharging or the like, the gas is discharged to the outside of the battery using a safety valve as disclosed in Japanese Patent Application Laid-Open No. H11-102673 to prevent expansion and rupture of the case. There is a mechanism to prevent it. However, depending on the size of the valve, the effect may not be obtained or a manufacturing defect may occur.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery having high safety.

[0012]

The present invention relates to a non-aqueous electrolyte secondary battery in which a power generating element having a positive electrode plate, a separator and a negative electrode plate is housed in a bag-shaped unit cell case made of a metal laminated resin film. An opening provided in a place other than the welded portion of the bag-shaped single cell case and having an area in the range of 1 mm ² to 100 mm ² is sealed with a resin film, and the opening pressure of this opening is 1 kgf / cm ² to 20 kgf / cm. It is characterized by being in the range of ² .

Further, the present invention is characterized in that, in the above nonaqueous electrolyte secondary battery, a resin film for sealing the opening is joined to the bag-shaped unit cell case by heat welding.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the appearance of a non-aqueous electrolyte secondary battery according to the present invention. In FIG. 1, 1 is a battery body, 2 is a bag-shaped unit cell case, 3 is a positive terminal, 4 is a negative terminal, 5, 6 and 7 are welded portions of the bag-shaped unit cell case,
Reference numeral 8 denotes a resin film that seals the opening of the bag-shaped unit cell case. The bag-shaped single cell case 2 is made of a metal laminated resin film.

In the present invention, the opening is provided at a place other than the welded part of the bag-shaped unit cell case. The area of the opening is in the range of 1 mm ² to 100 mm ² . And
This opening is sealed with a resin film, and the opening pressure of this opening is in the range of 1 kgf / cm ² to 20 kgf / cm ² .

Further, in the present invention, the resin film for sealing the opening is joined to the bag-shaped unit cell case by heat welding.

In a conventional non-aqueous electrolyte secondary battery, when overcharging or the like, the temperature of the battery increases and the mixture and the electrolyte are decomposed inside the battery, gas is generated, the internal pressure of the battery increases, and the case expands. And then burst. As a result, the power generating element may be deformed, causing smoke or ignition.

In the non-aqueous electrolyte secondary battery of the present invention,
Since the opening of the bag-shaped unit cell case is sealed with a resin film, the internal pressure of the battery increases due to overcharge
f / cm ² to 20 kgf / cm ² ,
Since this resin film is first broken and the internal pressure is released, expansion and rupture of the bag-shaped unit cell case made of the metal laminated resin film can be prevented. That is,
The resin film sealing the opening of the bag-shaped single cell case functions as a safety valve, and as a result, the safety of the non-aqueous electrolyte secondary battery can be greatly improved.

The bag-shaped single cell case used in the non-aqueous electrolyte secondary battery of the present invention is formed by laminating one or a plurality of metal-laminated resin films at their ends by a method such as heat welding. And Therefore, the welded portion of the bag-shaped unit cell case is twice as thick as the unwelded portion, and is a portion to which the internal pressure of the battery is not directly applied. Therefore, the opening of the present invention needs to be provided in a place other than the welded part of the bag-shaped unit cell case.

[0020] The opening provided in the bag-like unit cell case is not work is enabled as a safety valve in the case of less than 1 mm ^2, also is greater than 100 mm ^2, the sealing is difficult, such as leakage It may cause defective products. Therefore, the area of the opening needs to be in the range of 1 mm ² to 100 mm ² .

As the material of the resin film for closing the opening, any material may be used as long as it is a conventionally known thermoplastic polymer material such as polyethylene, polypropylene and polyethylene terephthalate.

Further, by joining the resin film for sealing the opening to the bag-shaped unit cell case by heat welding, the sealing method is simple and the sealing is secure.

When the resin film for sealing the opening is joined to the bag-shaped unit cell case, it may be joined from the inside of the bag-shaped unit cell case or from the outside.

As the metal material of the metal laminated resin film used for the bag-shaped unit cell case of the non-aqueous electrolyte secondary battery according to the present invention, aluminum, aluminum alloy, titanium foil and the like can be used. As the material of the resin portion of the metal laminated resin film, any material may be used as long as it is a thermoplastic polymer material such as polyethylene, polypropylene, and polyethylene terephthalate.

Further, the resin layer and the metal foil layer of the metal laminate resin film are not limited to one layer each, but may be two or more layers.

As the metal-laminated resin film, the metal-laminated resin film is heat-welded to form an envelope, two metal-laminated resin film sheets are heat-sealed at four sides, or one sheet is used. Any shape can be applied, such as a case where the power generation element is put into a cup-shaped product obtained by press-molding a metal-laminated resin film sheet by folding it in two and heat-welding the three sides.

Further, as a compound capable of inserting and extracting lithium as a cathode material, an inorganic compound is represented by a composition formula L
ixMO ₂ or LiyM ₂ O ₄ (where M is a transition metal, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), a composite oxide, an oxide having tunnel-like vacancies, and a metal having a layered structure Chalcogenides can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , L
i ₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ ,
TiO ₂ , TiS _{2 and the} like can be mentioned. Examples of the organic compound include a conductive polymer such as polyaniline. Furthermore, regardless of inorganic compounds or organic compounds,
The above various active materials may be used in combination.

The compound as the negative electrode material includes A
alloys of lithium with l, Si, Pb, Sn, Zn, Cd, etc., transition metal oxides such as LiFe ₂ O ₃ , WO ₂ , MoO ₂ , graphite, carbonaceous materials such as carbon, Li
Lithium nitride such as ₅ (Li ₃ N), or metallic lithium foil, or a mixture thereof may be used.

The electrolyte solvent used in the non-aqueous electrolyte secondary battery according to the present invention includes ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide. , 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran,
A polar solvent such as 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof may be used.

The lithium salts dissolved in the organic solvent include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAs
F ₆ , LiCF ₃ CO ₂ , LiCF ₃ SO ₃ , LiN (SO ₂
CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (CO
Salts such as CF ₃ ) ₂ and LiN (COCF ₂ CF ₃ ) ₂ or mixtures thereof may be used.

The separator of the non-aqueous electrolyte battery according to the present invention may be a material obtained by impregnating an electrolytic solution in an insulating microporous polyethylene membrane, a solid polymer electrolyte, or a solid polymer electrolyte containing an electrolytic solution. A gel electrolyte or the like can also be used. Further, an insulating microporous film and a solid polymer electrolyte may be used in combination. Further, when a porous solid polymer electrolyte membrane is used as the solid polymer electrolyte, the electrolyte contained in the polymer and the electrolyte contained in the pores may be different.

The power generating element according to the present invention may be either a positive electrode plate or a negative electrode plate formed into a thin sheet or foil, laminated in order, or spirally wound. Good.

[0033]

Embodiments of the present invention will be described below. In addition,
The following are merely examples, and do not limit the scope of the present invention.

EXAMPLE A non-aqueous electrolyte secondary battery according to the present invention was prepared in which an opening was provided in a bag-shaped unit cell case as shown in FIG. 1 and the opening was sealed with a resin film.

As the battery case, a metal laminated resin film having a thickness of 200 μm and having three layers of PET film / aluminum foil / polyethylene film from the outside was used.

The opening of the bag-shaped unit cell case has a thickness of 20
A μm polyethylene film was thermally welded to the bag-shaped unit cell case and sealed.

The positive electrode mixture was prepared by mixing 90 parts by weight of LiCoO _{2 as} an active material, 5 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder, and mixing N-methyl-2-pyrrolidone. Was added and dispersed to prepare a slurry. This slurry was uniformly applied to an aluminum current collector having a thickness of 30 μm, dried, then compressed by a roll press, and cut into a desired size to produce a positive electrode plate.

The negative electrode mixture was prepared by mixing 90 parts by weight of flaky graphite and 10 parts by weight of polyvinylidene fluoride, adding N-methyl-2-pyrrolidone as needed, and dispersing the mixture to prepare a slurry. The slurry was uniformly applied to a copper current collector having a thickness of 20 μm, dried, compressed by a roll press, and cut into a desired size to produce a negative electrode plate.

As the separator, a microporous polyethylene film having a thickness of 25 μm was used. The electrolytes include ethylene carbonate (EC) and methyl ethyl carbonate (M
A mixture obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solution of EC) having a volume ratio of 50:50 was used.

In this embodiment, the shape of the opening provided in the bag-shaped unit cell case was circular, and this opening was sealed with a resin film having a diameter 6 mm larger than the opening. Therefore, the width of the welded portion of the resin film was 3 mm.

Thus, the area of the opening is 1 mm ²
The size is 40mm wide and 6mm ^high within the range of ~ 100mm2.
A non-aqueous electrolyte secondary battery having a thickness of 0 mm and a thickness of 5 mm, cells 1 to 7, were produced.

The nominal voltage of the cells 1 to 7 is 3.6.
V and the internal resistance was 50 mΩ. The battery was charged at a constant current / constant voltage of 500 mA / 4.1 V for 3 hours at an ambient temperature of 25 ° C., and discharged at 500 mA to 2.75 V. The discharge capacity was 500 mAh. Using these batteries, an overcharge test was performed at a constant current / constant voltage of 1 A / 15 V.

[Comparative Example] As the cell 8, the same battery as in Example 1 was produced except that no opening was provided in the bag-shaped unit cell case. Further, the same as in Example 1, cell 1 area of the opening is a cell 9,150Mm ² is 0.5 mm ²
A cell 11 having a size of 0 and ²⁰⁰ mm ² was produced. And
The cells 8 to 11 were also subjected to an overcharge test under the same conditions as in Example 1. The test number of each cell is 100
It was made into pieces.

Table 1 summarizes the contents and test results (indicated by the number of batteries) of the cells 1 to 7 of the examples and the cells 8 to 11 of the comparative examples.

[0045]

[Table 1]

From Table 1, it can be seen that, at the stage of manufacturing the battery,
The area of the opening provided in the cell case is 100 mm^TwoOver
In the case of cell 10 or cell 11 obtained, generation of defective products due to liquid leakage
It turned out that life would occur. In addition, there is no opening
8mm and opening area is 1mm ^TwoIf cell 9 is less than
In the charging test (1A / 15V, constant current / constant voltage)
It has been found that fuming and igniting batteries are produced.

In the embodiment, the shape of the opening provided in the bag-shaped unit cell case is circular. However, even in the case of various shapes other than the circle, for example, a square, a rectangle, a polygon, and an ellipse. The same effect can be obtained.

[0048]

According to the nonaqueous electrolyte secondary battery, overcharging is provided by providing an opening at a place other than the welded portion of the metal-laminated resin film case of the bag-shaped unit cell case, and closing the opening with a resin film. Thus, a gas generated inside the battery is discharged to the outside of the battery to prevent expansion and rupture of the case, thereby providing a highly safe non-aqueous electrolyte secondary battery.

[Brief description of the drawings]

FIG. 1 is a view showing the appearance of a non-aqueous electrolyte secondary battery according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery main body 2 Bag-shaped cell case 3 Positive electrode terminal 4 Negative electrode terminal 5, 6, 7 Welding part of bag-shaped cell case 8 Resin film to seal opening of bag-shaped cell case

Continued on the front page F-term (reference) 5H011 AA13 CC10 DD13 FF02 GG09 HH13 KK00 KK04 5H024 AA02 AA03 AA12 BB01 BB14 CC04 EE09 HH00 HH15 HH17 5H029 AJ12 AL02 AL03 AM03 AM04 AM05 AM07 AM16 BJ04 DJ12JJJJJJJJJJJJJJJJJJJJJJ12J02

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery in which a power generating element having a positive electrode plate, a separator, and a negative electrode plate is housed in a bag-shaped unit cell case made of a metal laminated resin film, wherein the bag-shaped unit cell case is welded. The opening provided in a place other than the area and having an area of 1 mm ² to 100 mm ² is sealed with a resin film, and the opening pressure of the opening is 1 kgf / cm ^2.
A non-aqueous electrolyte secondary battery in the range of 1 to 20 kgf / cm ² . 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a resin film for sealing the opening is joined to the bag-shaped unit cell case by heat welding.