JP2001307690A - Package material for sheet-type battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a package material for a sheet-type battery, that is composed of more simple layers, has a barrier function against the environment (temperature, humidity or the like) and resistance to an electrolyte, does not cause a short circuit, and that is more excellent in a heat-seal function or the like by airtightly sealing the whole sheet-type battery by thermal fusing- adhesion. SOLUTION: This package material is composed of at least three layers, by laminating in order an outermost protective resin layer, a barrier-metal layer and an innermost layer made of a copolymer of ethylene and acrylic-acid monomer having a melting point of 90 to 100 deg.C. The material may be composed of four layers, by further laminating an adhesive layer made of a copolymer of ethylene and acrylic-acid monomer having a melting point of 90 to 110 deg.C, between the outermost protective resin layer and the barrier-metal layer. This package material is effective, in particular, for a lithium-polymer secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved outer packaging material for enclosing a sheet-type battery, for example, a lithium polymer secondary battery.

[0002]

2. Description of the Related Art In recent years, demands for lighter and smaller electronic devices have become stronger, and companies have been required to respond to them. One of the countermeasures is a battery (power supply) at the heart of the device.
The development of it is being studied. Such batteries are generally referred to as sheet batteries, polymer batteries, flat thin batteries, and paper batteries, and various techniques relating to this are disclosed in general technical literature and patents. Many have been published in the application.

[0003] Among the sheet type batteries, a lithium (ion) secondary battery is a battery of great interest, and most of them have recently been devoted to the study of improvement of this battery. Investigation of the battery is, of course, carried out not only for the constituent material of the battery itself, but also for an outer wrapping material which wraps the battery body and tightly seals it. The outer packaging material is an extremely important element in terms of protection from an electrolyte solution or the like from the inside of the battery (internal element) and protection against an external environment (damage due to heat, humidity, drying and impact) (external element). I have. The secondary battery body uses a polymer gel electrolyte, for example. A positive electrode mixture layer made of lithium cobalt oxide and a negative electrode mixture layer made of carbon are first laminated on both sides of a separator centered on the separator. An aluminum foil is provided on the side of the positive electrode mixture layer and a copper foil is provided on the side of the negative electrode mixture layer in order to collect the generated positive and negative currents and lead them to the outside. .

The function required of the outer packaging material is not only the inner element and the outer element, but also a lead drawn out from both collector electrodes of the battery when the battery body is sealed by the outer packaging material. Must be fully sealed with wires in close contact. Furthermore, the adhesion layer (electric insulating layer) between the two collecting electrode surfaces and the outer packaging material must not contain defects such as pinholes and bubbles. This is because there is a high risk of short-circuiting even with a small defect.

[0005] Patent applications relating to the battery outer packaging material are disclosed in, for example, JP-A-59-180962 and JP-A-11-6.
No. 7168 and JP-A-11-86842. Japanese Patent Application Laid-Open No. 59-180962 discloses a three-layer jacket in which a flat power generating element is sequentially laminated from the outside on a heat-resistant film (for example, PET film), an aluminum foil (barrier metal layer), and an inner surface adhesive layer having a multilayer structure. It is characterized by being packaged with a packaging material. Here, the inner surface adhesive layer is formed between the heat-fusible resin on the aluminum foil side and the innermost surface heat-fusible resin (contact surface with the positive / negative electrode current collector). It shows that it consists of at least three layers with a heat-resistant film (for example, PET film) interposed therebetween, and the innermost heat-fusible resin is, for example, ethylene.
Examples include (meth) acrylic acid derivative copolymers, polyolefins graft-modified with unsaturated carboxylic acids, etc.
It also discloses that the polyolefin is excellent. The effect of this is that there is no electrical short circuit even if a pinhole is formed at the bonding interface even if it is resistant to the organic electrolyte.

Japanese Patent Application Laid-Open No. 11-67168 is characterized in that a short prevention layer is provided between a barrier metal layer and an adhesion layer in a conventional battery outer packaging material. That is, an electrical short circuit between the positive and negative electrode current collectors can be prevented. The outer wrapping material is basically made of a protective layer (for example, PET film), a barrier metal layer (aluminum foil), a short prevention layer (for example, PET film), an adhesion layer (for example, ionomer, cyclic polyolefin, EVA, etc.) from the outside. EMAA, EMA, etc.)
However, since this is not sufficient, an adhesion layer such as the ionomer is further provided between the protective layer and the barrier metal layer and between the barrier metal layer and the short prevention layer. It is good to have a further multilayer structure. In this publication, the ionomer resin is frequently used because it has excellent adhesion to the barrier metal layer and has the effect of preventing an electrical short circuit even if a pinhole is formed. is there.

[0007] Japanese Patent Application Laid-Open No. 11-86842 discloses that when a sheet battery is sealed with a packaging material, maleic anhydride is preferably added to this portion in order to increase the adhesion to a battery terminal (lead wire) portion. It is characterized by applying a modified polypropylene. The use of the polypropylene also has the effect of covering the drawbacks of the use of ionomers, particularly the drawbacks of heat sealability at high temperatures and resistance to electrolytes (the absence of which would cause an electrical short circuit). It is also stated that there is.

[0008]

SUMMARY OF THE INVENTION According to the present invention, an outer wrapping material (outer wrapping material) disclosed in the above-mentioned publication, which has a larger number of layers laminated, has a smaller number of layers and is more effective. The main task is to find an outer packaging material for sheet batteries.
In addition, when the battery is heat-sealed, it is a serious task to find an outer packaging material which can be sealed at once with a higher adhesion to a lead wire drawn from a metal foil current collector. Is achieved. These objects are easily achieved by the following means.

[0009]

That is, the present invention provides a first aspect of the present invention.
The outermost protective resin layer, the barrier metal layer, and the innermost layer made of a copolymer of ethylene and an acrylic acid monomer having a melting point of 90 to 110 ° C. are sequentially laminated, as described in, and are at least three layers. It is achieved by the feature.

In accordance with the first aspect, claims 2 and 3 are also provided and achieved as more preferred inventions. Hereinafter, the present invention will be described in detail with embodiments.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the outermost protective resin layer (hereinafter simply referred to as the outermost layer) has a melting point of about 100 ° C. or more, has excellent impact resistance and chemical resistance, and has a slight flexibility. Sa1
It is preferably formed as a thin layer of a thermoplastic resin of about 0 to 50 μm. Specifically, films of PET (biaxially stretched polyethylene terephthalate), nylon 6 or 66, which are generally exemplified, may be mentioned. In addition, especially a single polymer of nylon 11 or 12, nylon 6/6
6, 6/10 or 6/12 binary copolymer, nylon 6
/ 66/610 or 6/66/610/12 3 yuan to 4
An original copolymer film can be mentioned. These polymer films have better adhesion to the barrier metal layer than the PET, nylon 6 or 66 film,
It is preferable because it is flexible, has excellent impact resistance, and has low hygroscopicity. Further, the ternary or quaternary copolymer film has a melting point of 110 to 150 ° C. and is soluble in alcohol, so that the adhesion to the barrier metal layer becomes more advantageous. still,
Examples of the polyester film include, besides PET, polybutylene terephthalate, polyethylene naphthalate, and other films such as polyparaxylylene.

The barrier metal layer is a layer (intermediate barrier layer) necessary for ensuring absolute barrier properties, and its thickness is preferably in the range of about 1000 to 40 μm. The metal forming the metal layer is aluminum, zinc, nickel or the like. The layer thickness is exemplified in a wide range. The thinner one is formed by a thin film forming means such as a vacuum evaporation method or a sputtering method, while the thicker one is formed by a rolling method. The thicker layer may be laminated by itself, but the thinner layer is difficult to perform the laminating operation as it is. Therefore, it is preferable to laminate the resin film on one or both sides of the above-mentioned resin film to form the barrier metal.

Next, the innermost layer which is in direct contact with and tightly sealed to the electrode plate (current collector) constituting the sheet-shaped battery will be described. What constitutes the layer has a melting point of 90 to 110 in particular.
° C, preferably 95 to 108 ° C, more preferably 98 to 108 ° C.
A copolymer of ethylene and an acrylic acid monomer at 106 ° C. (hereinafter referred to as EA polymer) is selected. The present invention has found the specific EA polymer, and combined it with the outermost layer and the barrier metal layer to form an outer packaging material. The requirements for the outer packaging material to be used can be solved at once. Therefore, a simple copolymer of ethylene (not specified) and an acrylic acid monomer, as well as other polymers, cannot solve the necessary conditions at once.

The EA polymer is, for example, a copolymer selected by copolymerizing ethylene with acrylic acid or methyl (ethyl) methacrylate, or methyl (ethyl) acrylate or methyl (ethyl) methyl (ethyl) methacrylate. Among them, acrylic acid represented by the former two is more preferable than acrylic acid ester represented by the latter two. When the ester is used, it is preferably used as the third component in the form of a terpolymer. Since the polymer is basically determined by the reaction molar ratio and the molecular weight, an EA polymer having a melting point of 90 to 110 ° C. is particularly selected and used. Note that acrylamide is also included in the acrylic acid-based monomer, and this may be used as the third component.

The specific reason why the EA polymer having the above melting point range is used is as follows. In other words, when the melting point is lower than 90 ° C., the level of the sheet-shaped battery can be satisfied with the resistance to the positive / negative electrode mixture layer (electrolyte layer) and the barrier property against the environment (for example, about 90 ° C., under an atmosphere of RH 50% or more). No improvement is made, and even if the EA polymer adheres to the electrode current collector surface of the battery, it tends to become a contact surface with a pinhole (a cause of short circuit). On the other hand, if the melting point exceeds 110 ° C., the surface of the metal foil current collector and the portion of the lead wire (particularly, the connection portion) drawn from the current collector will not be sufficiently adhered.

Preferably, the thickness of the innermost layer is larger than the thickness of the electrode current collector of the sheet-like battery and the thickness of the lead wire drawn from the current collector. This is of course sufficient expression of the electrical insulation function, but if the innermost layer is thinner, especially when the entire battery is wrapped in an outer wrapping material and the entire periphery is sealed by heat sealing, The edge portion of the current collector and the connection root portion of the lead wire break through the innermost layer and come into contact with the barrier metal layer, thereby causing a risk of short circuit. Furthermore, even if the heat seal is sufficient, there is a risk that fine pinholes are easily formed in the innermost layer. For this reason, the layer thickness is preferably designed to be about 1.2 to 3 times the thickness of the electrode current collector or the lead wire.

The adhesion between the barrier metal layer and the innermost layer of the (EA polymer) does not require the use of an adhesive since the EA polymer itself has good adhesiveness. However, especially with respect to the connection root of the lead wire, complete sealing is feared. Therefore, for complete wiping of the lead wire, it is preferable to seal at least this part with an adhesive. This adhesive is more preferably made of a low melting point copolymer of ethylene and an acrylic acid monomer having a melting point of about 60 to 80 ° C.

The adhesion between the outermost layer and the barrier metal layer is as follows:
Except for copolymers of two or more nylons in the above examples,
For other polymers, it is preferable to adhere closely with an adhesive. In this case, the adhesive is appropriately selected and used, and among them, it is more preferable to use the EA polymer used as the innermost layer. The thickness of the adhesive layer is 10 to 3
It may be as thin as about 0 μm. In this case, a copolymer of two or more nylons does not require the use of the adhesive. This is because the copolymer itself has a strong adhesive force and is easily heat-fused. This tendency is 3
More effective than the original nylon copolymer.
In addition, although there is an ionomer among general adhesives and is often used, in the present invention, since there is a high risk of metal ions binding to the electrolyte flowing out, it is assumed that a general adhesive is used. It is better to avoid using it.

The means for producing the outer packaging material may be, for example,
A solvent solution of the EA polymer is coated and dried and adhered and laminated on one side of a metal foil having a thickness so as to have an effective thickness (1.2 to 3 times) as the innermost layer. Is extruded and laminated with the metal foil while being melt-extruded at the above thickness. Next, this layer is laminated on the opposite surface as an outermost layer with a thickness of about 10 to 50 μm made of the thermoplastic resin exemplified above. Here, the outermost layer is formed by coating with a solvent solution of the resin, by extrusion lamination, or by heating the resin, which has been formed into a film having a predetermined thickness, through a heating roller. Melt adhesion to Here, when the adhesive is interposed, it is preferable that the adhesive is previously laminated on the metal foil or the film.

[0020]

EXAMPLES The present invention will be described in more detail with reference to Examples together with Comparative Examples. Here, the sheet battery used in the test has the following structure. ● Positive electrode plate: Disperse lithium cobalt oxide, carbon black and polyvinylidene fluoride in N-methylpyrrolidone, apply it to one side of aluminum foil (thickness 35μm), dry it, and press it hot to make it full thickness It was adjusted to 50 μm. And cut this into 50mm square, and the thickness of this center is 40mm.
A strip of aluminum foil of 4 μm × 90 μm is welded and drawn out as a lead wire. Negative electrode plate: Graphite carbon and polyvinylidene fluoride were dispersed in N-methylpyrrolidone, applied to one surface of a copper foil (thickness: 35 μm), dried, and heated and pressed to adjust the total thickness to 50 μm. Then, this is cut into a 50 mm square, and a 4 × 90 mm thick copper strip is welded to the center thereof and drawn out as a lead wire. ● Electrolyte solution ··· LiBF4 dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and γ-butyl lactone. ● Separator: A foamed film (60 μm) of a copolymer of ethylene / 6-fluoropropylene cut into 55 mm square. Using each of the above members, the electrolyte is first heated and impregnated on both surfaces of the saparator. Then, the positive electrode plate is laminated on one side, and the negative electrode plate is laminated on the other side, and heat-pressed to form a sheet battery (both lead wires are exposed to the left and right as connection terminals by about 35 mm).

(Example 1) An outer packaging material having three layers was manufactured according to the following specifications. ◎ First, an alcohol-soluble ternary copolymer nylon consisting of 6/66/610 for the outermost layer (melting point about 140 to 14)
3 ° C.) Extruded chips with a T-die extruder to a thickness of 35 μm
◎ 30 μm aluminum foil for the barrier metal layer ◎ Melting point 104 ° C. (MFR = 1.5 for the innermost layer)
g / 10 minutes) of a copolymer of ethylene and methyl methacrylic acid was extruded with a T-die extruder to produce a 55 μm thick film (EA film 1).

The above members were laminated as follows to obtain an outer packaging material. In other words, the aluminum foil (both sides are previously degreased and cleaned)
On one side, a water-containing ethyl alcohol is uniformly applied, and the AN film is pasted in a wet state. After a while, the EA film 1 is pasted on the other side, and the whole is mirror-finished. And pressed at 110 ° C. by heating and pressing.

(Example 2) An outer packaging material having four layers was manufactured according to the following specifications. ◎ Nylon 12 for the outermost layer (melting point: about 175 ° C)
The chip was extruded with a T-die extruder and extruded into a 15 μm-thick film (12 films). ◎ 30 μm aluminum foil for the barrier metal layer. ◎ 98 ° C. melting point (MFR = 2.7 g / 1 for the innermost layer).
0 min) by extruding a copolymer of ethylene and methyl methacrylic acid with a T-die extruder, a 55 μm-thick film (EA film 2), ◎ and a melting point of 97 ° C. for an adhesive layer (MFR = 2.5 g)
/ 10 min) by extruding a copolymer of ethylene and methyl methacrylic acid with a T-die extruder to produce a film (EA film S) having a thickness of 20 μm.

The above members were laminated as follows to obtain an outer packaging material. In other words, the aluminum foil (both sides are previously degreased and cleaned)
First, an EA film S for the adhesive layer is placed on one side of
After laminating the two films sequentially, they were sandwiched between the stainless steel plates and heated to 120 ° C. Then, the EA film 2 was adhered to the opposite surface, sandwiched again by a stainless steel plate, and the whole was heated and pressed similarly.

(Example 3) The operation and effect of the outer packaging material of the present invention can be easily understood from the detailed description of the above-mentioned example as a non-conventional one, but it is confirmed and shown in the following test for reference. I will.

First, the outer wrapping material obtained in Example 1 was folded in double with the innermost layer facing inside, and heat-sealed on two sides at 150 ° C. for 5 seconds to form a bag. About 1/3 of the bag volume was charged with the above-mentioned electrolytic solution, and the remaining one side was heat-sealed in the same manner, and the electrolytic solution was sealed (T sample 1).

Then, the T sample 1 was heated at 60 ° C./RH7
The bag was left in an atmosphere of 5% (high-temperature humidification test) and 60 ° C./RH 15% (high-temperature low-humidity test) for 40 days, and the presence or absence of a change in the weight of the entire bag was checked. As a result, in the high-temperature humidification test, a very small increase of + 0.05% by weight was obtained, and in the high-temperature and low-humidity test, a very small decrease of -0.03% by weight was obtained. Finally, the bag was broken and the inner layer was observed with a magnifying microscope. No swelling or erosion of the inner surface layer was observed at all, and no scratch was caused even when this layer surface was rubbed with a nail, and the adhesion to the barrier metal layer was complete.

On the other hand, the following test was also performed on the four-layered outer packaging material obtained in Example 2. First, two sides of the folded outer packaging material cut about 15 mm larger than the size of the sheet battery are heat-sealed at 150 ° C. for 5 seconds to be processed into a bag shape, and the sheet is then placed therein. After inserting the battery, the remaining 1
The side was heat-sealed at 150 ° C for 5 seconds to seal the whole. At this time, the heat seal width was about 3 mm, and the two lead wires were substantially exposed at about 15 mm. Then, the encased sheet battery was subjected to a high-temperature humidification test and a high-temperature low-humidity test under the same conditions as described above to check for a change in weight. The result was +0.04 in the high-temperature humidification test.
% By weight, and a very small decrease of -0.02% by weight in the high temperature and low humidity test.

(Comparative Example 1) First, in Example 2,
Four members are laminated under the same conditions except that a copolymer of ethylene and methyl methacrylic acid having a melting point of 86 ° C. and an MFR of 5.6 g / 10 min is used instead of the EA film 2 for the innermost layer used here. Thus, a four-layer outer packaging material was obtained. However, the film thickness of the copolymer was 70 μm.

Then, using the outer packaging material, a bag was formed in the same manner as in Example 3, and an electrolytic solution was put into the bag.
The whole was heat-sealed and subjected to a high-temperature humidification test and a high-temperature low-humidity test in the same manner as described above to check for a change in weight. The result was +0.7 in the high temperature humidification test.
8% by weight, and -0.64% by weight in the high temperature and low humidity test. Further, when the bag was broken and the inner layer was observed with a magnifying microscope in the same manner as in Example 3, the inner layer changed to a plasticized state, and when this layer surface was rubbed with a nail, scratches were formed and adhesion was weak. It can be seen that there is a large difference in the electrolytic solution and the environmental barrier properties as compared with the above-mentioned examples.

Comparative Example 2 First, in Example 2,
Four members are laminated under the same conditions except that a copolymer of ethylene and methyl methacrylic acid having a melting point of 115 ° C. and an MFR of 0.8 g / 10 min is used instead of the EA film 2 for the innermost layer used here. Thus, a four-layer outer packaging material was obtained. However, the film thickness of the copolymer was 57 μm, and the heat sealing was performed at 140 ° C.

Using the outer packaging material, a bag was formed in the same manner as in Example 3, and an electrolytic solution was put into the bag.
The whole was heat-sealed and subjected to a high-temperature humidification test and a high-temperature low-humidity test in the same manner as described above to check for any change in weight. The result was +0.1 in the high-temperature humidification test.
8% by weight, and -0.15% by weight in the high temperature and low humidity test. When the bag was broken and the inner layer was observed with a magnifying microscope in the same manner as in Example 3, no swelling or erosion of the inner layer was observed. However, the interlayer adhesion with the aluminum foil was poor, and it was partially peeled off when rubbed with a nail.

[0033]

Since the present invention is configured as described above, the following effects can be obtained.

A multi-layered screen shown in the prior art
As compared with the battery outer packaging material, the desired outer packaging material can be obtained with a smaller number of layers, and the productivity can be greatly improved.

As for the performance, not only the sheet battery body was sufficiently protected against impact, but also the barrier property against the environment (dry, humid environment) and the resistance against the electrolytic solution were further improved. This is particularly due to the innermost layer, which is due to the resistance to the electrolyte and the strong and dense adhesion (there is no pinhole and no electrical short-circuit due to it).

The outer packaging material is also excellent in heat sealability, so that not only the sheet battery body but also the lead wire, which is a problem, in particular, the connection root part is sufficiently sealed, and at the same time, the heat seal is achieved. Started to work.

Although the present outer packaging material is used for various types of sheet batteries, it is particularly effective for lithium polymer secondary batteries due to the above-described effects.

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Claims (3)

[Claims] 1. An outermost protective resin layer, a barrier metal layer, and a melting point of 9
An outer packaging material for a sheet-shaped battery, comprising at least three layers in which an innermost layer made of a copolymer of ethylene and an acrylic acid monomer at 0 to 110 ° C is sequentially laminated. 2. The method according to claim 1, wherein an adhesive layer of a copolymer of ethylene and an acrylic acid monomer having a melting point of 90 to 110 ° C. is laminated between the outermost protective resin layer and the barrier metal layer. An outer packaging material for a sheet-shaped battery. 3. An outer packaging material for a sheet-shaped battery according to claim 1, wherein said sheet-shaped battery is a lithium polymer secondary battery.