JP5532841B2 - Lithium-ion battery packaging material - Google Patents

Description

  The present invention relates to a packaging material for a lithium ion battery.

  Conventionally, nickel-metal hydride and lead-acid batteries have been used as secondary batteries, but miniaturization of secondary batteries has become indispensable due to downsizing of portable devices and restrictions on installation space. In order to meet the demand for miniaturization, lithium ion batteries with high energy density have attracted attention and are being adopted. Conventionally, metal cans have been used as packaging materials for such lithium ion batteries, but multilayer films that are lightweight, have high heat dissipation properties, and can be handled at low cost have come to be used. Such a multilayer film generally contains an aluminum foil layer, which is called an aluminum laminate type lithium ion battery.

The electrolyte of the lithium ion battery is composed of an aprotic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and an electrolyte. In addition, lithium salts such as LiPF ₆ and LiBF ₄ are used as the lithium salt that is an electrolyte, but these salts generate hydrofluoric acid by hydrolysis reaction with moisture. The laminate strength may be reduced. Therefore, the penetration of moisture from the surface of the multilayer film is blocked by using an aluminum foil as a part of the multilayer film for the purpose of preventing moisture penetration. As shown in FIG. 1, such a multilayer film is generally formed by laminating a sealant layer 1 on one side of an aluminum foil layer 3 via an adhesive layer 2 and a base material via an adhesive layer 4 on the other side. The layer 5 is laminated. The adhesive layer 2 is roughly classified into two types: a dry laminate structure composed of an adhesive resin layer for dry laminate and a heat laminate structure composed of a thermoplastic material. Since the adhesive of the dry laminate product has a highly hydrolyzable bond such as an ester group or a urethane group, hydrolysis reaction with hydrofluoric acid is likely to occur. Therefore, for applications that require high reliability, a thermal laminate configuration is used.
As the base material layer 5, a nylon film has been used conventionally. However, the nylon film has no electrolyte solution resistance, and when the electrolyte solution adheres to the outside of the multilayer film, there is a problem that the nylon film is eroded by the electrolyte solution from the outside. In recent years, more energy has been demanded in thermal laminate configurations that require high reliability, and the use of a plurality of aluminum laminate type lithium ion batteries collectively as a single battery pack has increased. For this reason, in consideration of safety when one multilayer film is damaged, there is an increasing demand for the base material layer 5 to have electrolyte solution resistance.

Also, in order to increase the energy density, a method has been adopted in which this multilayer film is cold-molded to form recesses and more battery contents are accommodated. Nylon film with toughness and high impact strength has been used for the layer 5. However, since the nylon film has no electrolyte solution resistance, the base material layer 5 is required to have a material and a structure having both the electrolyte solution resistance and high moldability.
In addition, the following patent document 1 is mentioned as a prior art of the packaging material for lithium ion batteries. The multilayer film configuration described in Patent Document 1 is a biaxially stretched polyester film layer, a biaxially stretched nylon film layer, and a metal foil layer that are sequentially laminated by a dry laminate method from the outside, and is biaxially stretched with electrolyte resistance. It is described that a toughness and high impact strength can be maintained because a biaxially stretched nylon film is laminated while a polyester film is used as an outermost layer and electrolyte resistance is imparted to the outer side of the multilayer film. However, in recent years, a deeper molding depth has been demanded, and the above configuration alone has become insufficient.

JP 2002-56824 A

  Then, in view of the said problem, this invention aims at providing the electrolyte solution tolerance on the outer side, and providing the packaging material for lithium ion batteries which is excellent in a moldability.

Invention of claim 1 wherein at least a sealant layer, adhesive layer, aluminum foil layer, the adhesive layer, the packaging material for lithium ion batteries obtained by laminating a base layer in this order, the substrate layer, the polyamide resin Comprising a first substrate layer comprising a film comprising, a thermoplastic adhesive resin layer comprising a maleic anhydride modified polyolefin resin or a maleic anhydride modified styrene elastomer resin, and a second substrate layer comprising a film comprising a polyester resin. The base material layer is formed by coextrusion of three layers, and is a packaging material for a lithium ion battery.
According to a second aspect of the invention, it is a lithium ion battery packaging material according to claim 1, characterized in that the base layer is biaxially oriented.

According to the configuration of claim 1 of the present invention, in the packaging material for a lithium ion battery in which at least a sealant layer, an adhesive layer, an aluminum foil layer, an adhesive layer, and a base material layer are laminated in this order , the first base material layer and the first base material layer Lithium ion that has a structure in which a thermoplastic adhesive resin layer is interposed between two base material layers and is formed by coextrusion of the base material layer to provide electrolyte resistance to the outside and is excellent in moldability A battery packaging material can be provided.

According to the configuration of claim 2 of the present invention, the base material layer is biaxially stretched, so that it is possible to provide a packaging material for a lithium ion battery that imparts electrolyte resistance to the outside and is excellent in moldability. .

It is sectional drawing of the multilayer film which comprises the conventional packaging material for lithium ion batteries. It is sectional drawing of one Embodiment of the multilayer film which comprises the packaging material for lithium ion batteries of this invention. It is sectional drawing of one Embodiment of the multilayer film which comprises the packaging material for lithium ion batteries of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
2 and 3 are cross-sectional views of the multilayer film constituting the packaging material for a lithium ion battery according to this embodiment. The multilayer film in FIG. 2 includes a sealant layer 1, an adhesive layer 2, an aluminum foil layer 3, an adhesive layer 4, and a base material layer 9 from the upper side. The base material layer 9 includes a first base material layer 6 and a second base material layer 8. 3 is composed of a sealant layer 1, an adhesive layer 2, an aluminum foil layer 3, an adhesive layer 4, and a base material layer 10 from the upper side. The base material layer 10 includes a first base material layer 6, a thermoplastic adhesive resin layer 7, and a second base material layer 8. A positive electrode, a separator, a negative electrode, and a tab are placed inside the multilayer film embossed, and then the multilayer film is overlaid so that the sealant layer 1 faces, and three sides are sealed. Then, electrolyte solution is inject | poured from one side which remained in the vacuum state, the remaining one side is sealed last, and the inside is sealed, A lithium ion battery is produced.

<Sealant layer 1>
Examples of the component constituting the sealant layer 1 include a polyolefin resin or an acid-modified polyolefin resin obtained by graft-modifying maleic anhydride or the like on a polyolefin resin. The polyolefin resin is preferably an acid-modified polyolefin resin obtained by graft-modifying maleic anhydride or the like on the resin. Examples of the polyolefin include low-density, medium-density, and high-density polyethylene; ethylene-α olefin copolymer; homo, Examples thereof include block or random polypropylene; propylene-α-olefin copolymer. These polyolefin resins may be used individually by 1 type, and may use 2 or more types together. The sealant layer 1 may be a single layer film or a multilayer film in which a plurality of layers are laminated. Depending on the function required, for example, a multilayer film in which a resin such as an ethylene-cycloolefin copolymer or polymethylpentene is interposed may be used in terms of imparting moisture resistance. Furthermore, the sealant layer 1 may contain various additives such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier. 10-100 micrometers is preferable and, as for the thickness of the sealant layer 1, 20-50 micrometers is more preferable.

<Adhesive layer 2>
Examples of the component constituting the adhesive layer 2 include a resin obtained by adding an acid-modified styrene elastomer resin to an acid-modified polyolefin resin. Based elastomer resins are preferred. The adhesive layer 2 is formed by extruding these resins with an extrusion device.

<Aluminum foil layer 3>
As a material of the aluminum foil layer 3, a general soft aluminum foil can be used, but an aluminum foil containing iron is preferably used for the purpose of imparting further pinhole resistance and extensibility during molding. 0.1-9.0 mass% is preferable in 100 mass% of aluminum foil, and, as for content of iron, 0.5-2.0 mass% is more preferable. If the lower limit value of the iron content is less than the above value, sufficient pinhole resistance and ductility cannot be imparted. On the other hand, if the upper limit value is more than the above value, flexibility is impaired. The thickness of the aluminum foil layer 3 is preferably 9 to 200 μm, more preferably 15 to 100 μm in consideration of barrier properties, pinhole resistance, and workability. If it is thinner than 9 μm, the pinhole resistance is poor, and if it exceeds 200 μm, the processing suitability is poor.

<Adhesive layer 4>
The adhesive layer 4 is preferably a two-component curable polyurethane adhesive using a polyester polyol, a polyether polyol, or an acrylic polyol as a main agent and an aromatic or aliphatic isocyanate as a curing agent. By performing the aging after coating at 40 ° C. for 4 days or longer, the reaction between the OH group and the NCO group proceeds and the films on both sides are firmly bonded. In general, the molar ratio [NCO / OH] of the curing agent NCO to OH of the main agent is preferably about 1 to 10, more preferably 2 to 5. The thicknesses of the adhesive layers 2 and 4 are preferably 1 to 10 μm, more preferably 3 to 7 μm in consideration of adhesive strength, followability, workability, and the like.

<First base material layer 6>
As the first base material layer 6, it is preferable to use a resin layer that improves molding processability at the time of manufacturing a lithium ion battery. As such a resin layer, for example, a polyamide film containing a polyamide-based resin, a stretched polyester film, or an unstretched film can be used. A polyamide film, particularly a biaxially stretched polyamide film is preferred from the viewpoint of improving moldability and heat resistance.

<Thermoplastic adhesive resin layer 7>
Examples of components constituting the thermoplastic adhesive resin layer 7 include resins obtained by adding an acid-modified styrene-based elastomer resin to an acid-modified polyolefin resin, and maleic anhydride-modified polyolefin resin grafted with maleic acid, maleic anhydride An acid-modified styrene elastomer resin is preferred.

<Second base material layer 8>
The second base material layer 8 is preferably a resin layer that provides electrolyte solution resistance outside the lithium ion battery packaging material. As such a resin layer, for example, a film containing a polyester resin, specifically, a stretched or unstretched film of a polyester film can be used. A biaxially stretched polyester film is preferable from the viewpoint of improving chemical resistance and moldability.

<Method for producing packaging material for lithium ion battery>
Next, although the manufacturing method of the packaging material for lithium ion batteries of this invention shown in FIG. 2 and FIG. 3 is described, it is not limited to this.

(Forming process of base material layers 9 and 10)
The base material layer 9 or 10 is formed. As a molding method of the base material layer 9, an extrusion molding technique is used. Pellets made of polyester resin and pellets made of polyamide resin are heated and melted, and two layers are coextruded from a T die to form a composite film. The base material layer 10 is molded by interposing a thermoplastic adhesive resin layer between a polyester resin and a polyamide resin, and coextruding three layers to form a composite film. Biaxially stretched films are prepared from these films by a sequential biaxial stretching method using a tenter method.

(Bonding process of base material layers 9 and 10 and aluminum foil layer 3)
The aluminum foil layer 3 and the base material layer 9 or 10 are bonded together. As a method of bonding, a dry laminating method is used, and both are bonded with a polyurethane-based adhesive mainly composed of polyester polyol, polyether polyol, and acrylic polyol, and the base layer 9 or 10 / adhesive layer 4 / aluminum. A laminate composed of the foil layer 3 is prepared.

(Lamination process of sealant layer 1)
A sealant layer 1 is laminated on the laminate. As a lamination method, the adhesive layer 2 is extruded and laminated on the laminate, and the sealant layer 1 is further laminated to produce a packaging material for a lithium ion battery.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to the following example. Here, materials used in the examples are shown below.

[Raw materials]
<Base material layer>
The layer structure of the composite film used for the base material layer is shown below.
A-1: Nylon / polyethylene terephthalate A-2: Nylon / thermoplastic adhesive resin / polyethylene terephthalate A-3: Nylon / adhesive / polyethylene terephthalate A-4: Nylon <Adhesive layer 4>
B-1: Polyurethane adhesive (thickness 4 μm)
<Aluminum foil layer 3>
C-1: Soft aluminum foil 8079 material (thickness 40 μm)
<Adhesive layer 2>
D-1: Maleic anhydride-modified polypropylene (thickness 20 μm) -based adhesive <Sealant layer 1>
E-1: Unstretched polypropylene film (thickness 25 μm) inner surface corona treatment

[Production and evaluation method of packaging materials for lithium ion batteries]
<Creation of packaging material 1>
Using a method of extrusion molding, a pellet made of nylon resin (Ny) and a pellet made of polyethylene terephthalate resin (PET) were heated and melted, and two layers were coextruded from a T die to form a Ny / PET composite film. A biaxially stretched film was prepared from this composite film by a sequential biaxial stretching method using a tenter method, and used as a base material layer 9. Thereafter, the base material layer 9 was laminated on the aluminum foil layer 3 by a dry laminating method using a polyurethane adhesive (A525 / A50, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.). Thereafter, aging was performed at 60 ° C. for 6 days. Next, the acid-modified polypropylene was extruded using an extrusion apparatus, and the other surface of the aluminum foil layer 3 on which the base material layer 9 was laminated and the sealant layer 1 were sandwich-laminated. Thereafter, the laminate was thermocompression bonded at 160 ° C. under the conditions of 4 kg / cm ² and 2 m / min to prepare a packaging material for a lithium ion battery.
<Creation of packaging material 2>
Nylon / thermoplastic adhesive resin layer / PET by extruding nylon resin pellets, acid-modified polypropylene resin pellets, polyethylene terephthalate resin pellets by heating and melting, and co-extruding 3 layers from a T-die. A composite film was formed. A biaxially stretched film was prepared from this composite film by a sequential biaxial stretching method using a tenter method, and used as a base material layer 10. Thereafter, the base material layer 10 was laminated on the aluminum foil layer 3 by a dry laminating method using a polyurethane-based adhesive (A525 / A50, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.). Thereafter, aging was performed at 60 ° C. for 6 days. Next, the acid-modified polypropylene was extruded using an extrusion apparatus, and the other surface on which the base material layer 10 of the aluminum foil layer 3 was laminated and the sealant layer 1 were subjected to sandwich lamination. Thereafter, the laminate was thermocompression bonded at 160 ° C. under the conditions of 4 kg / cm ² and 2 m / min to prepare a packaging material for a lithium ion battery.
<Creation of packaging material 3>
A biaxially stretched Ny film was laminated as the first base layer 6 on the aluminum foil layer 3 by a dry laminating method using a polyurethane-based adhesive (A525 / A50, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.). Thereafter, biaxial stretching as the second base material layer 8 is further performed on the first base material layer 6 by a dry laminating method using a polyurethane adhesive (manufactured by Mitsui Chemicals Polyurethane Co., Ltd., A525 / A50). A PET film was laminated and aged at 60 ° C. for 6 days. Next, acid-modified polypropylene was extruded using an extrusion apparatus, and the other surface of the aluminum foil layer 3 on which the base material layer 6 and the base material layer 8 were laminated was sandwiched with the sealant layer 1. Thereafter, the laminate was thermocompression bonded at 160 ° C. under the conditions of 4 kg / cm ² and 2 m / min to prepare a packaging material for a lithium ion battery.
<Creation of packaging material 4>
A biaxially stretched Ny film was laminated as the base material layer 5 on the aluminum foil layer 3 by a dry laminating method using a polyurethane-based adhesive (A525 / A50, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.). Thereafter, aging was performed at 60 ° C. for 6 days, and then the acid-modified polypropylene was extruded using an extrusion apparatus, and the other surface on which the base material layer 5 of the aluminum foil layer 3 was laminated and the sealant layer 1 were sandwich-laminated. Thereafter, the laminate was thermocompression bonded at 160 ° C. under the conditions of 4 kg / cm ² and 2 m / min to prepare a packaging material for a lithium ion battery.

<Electrolytic solution evaluation>
Several drops of the electrolytic solution were dropped on the base material layer side of the obtained packaging material for lithium ion batteries, and the surface of the base material layer was observed in a state where the electrolyte solution was wiped off by being left overnight.
○: No erosion (no change in surface condition)
×: Erosion <Formability evaluation>
The obtained lithium ion battery packaging material was cut into a blank shape of 150 mm × 190 mm, and the molding depth at which breakage and cracks did not occur was evaluated. The punch shape was 100 mm × 150 mm, the punch corner R (R _CP ) was 1.5 mm, the punch shoulder R (R _P ) was 0.75 mm, and the die shoulder R (R _D ) was 0.75 mm.
(Double-circle): It can shape | mold without a fracture | rupture and a crack by the shaping | molding depth of 7 mm or more.
○: Molding is possible at a molding depth of 5 mm or more and less than 7 mm without causing breakage or cracks.
X: Breaking and cracking occur at a molding depth of 5 mm or less.

[Examples 1 and 2 and Comparative Examples 1 and 2]
In Examples 1 and 2 and Comparative Examples 1 and 2, a packaging material for a lithium ion battery was prepared by creating packaging materials 1 to 4 and evaluated. The results are shown in Table 1. Example 1 is a reference example.

Example 1 uses a two-layer coextruded Ny / PET composite film as the base material layer, has an electrolyte solution resistance outside the packaging material, and could be molded without breaking or cracking even at a molding depth of 6.5 mm. .
Example 2 uses a three-layer coextruded Ny / thermoplastic adhesive resin / PET composite film as the base material layer, and has an electrolyte solution resistance outside the packaging material, and does not break or crack even at a molding depth of 8 mm. I was able to mold it.
Comparative Example 1 uses a Ny / adhesive / PET composite film laminated on a base material layer by a dry laminating method, and the electrolyte solution resistance on the outside of the packaging material was obtained, but breakage occurred even at a molding depth of 5 mm. .
In Comparative Example 2, a Ny film was used for the base material layer, the electrolyte solution resistance outside the packaging material was not obtained, and the fracture occurred at a molding depth of 7 mm.

  In summary, it can be said that when the outermost layer is made of PET, electrolyte resistance can be obtained. In addition, when a Ny / thermoplastic adhesive resin / PET composite film molded by three-layer coextrusion is used for the base material layer, it can be said that breakage and cracking hardly occur even if the molding depth is increased. From the above, it can be said that laminating Ny and PET compensates for the weaknesses of both films and improves electrolyte resistance and moldability. However, if an adhesive for dry laminating is used for laminating Ny and PET, the adhesive is buffered. It becomes a layer, and it is thought that the relationship between both films will be interrupted. In addition, it is considered that in the two-layer extrusion of Ny and PET, the adhesive strength is lowered and the effect of lamination is reduced. It is preferable to increase the adhesive strength by interposing a thermoplastic adhesive resin layer that is not as soft as an adhesive between Ny and PET. Thus, according to the present invention, a packaging material for a lithium ion battery that can impart electrolyte resistance to the outside of the packaging material and is less prone to breakage and cracking even when the molding depth is increased, and has excellent moldability. Can be provided.

DESCRIPTION OF SYMBOLS 1 ... Sealant layer 2 ... Adhesive layer 3 ... Aluminum foil layer 4 ... Adhesive layer 5 ... Base material layer 6 ... First base material layer 7 ... Thermoplastic resin layer 8 ... Second base material layer 9, 10 ... Base material layer

Claims (2)

In a lithium ion battery packaging material in which at least a sealant layer, an adhesive layer, an aluminum foil layer, an adhesive layer, and a base material layer are laminated in this order, the base material layer is a first base material made of a film containing a polyamide-based resin. Layer, a thermoplastic adhesive resin layer made of maleic anhydride-modified polyolefin resin or maleic anhydride-modified styrene elastomer resin, and a second base material layer made of a film containing a polyester resin, the base material layer comprising three layers A packaging material for a lithium ion battery, which is formed by coextrusion. Lithium ion battery packaging material according to claim 1, characterized in that the base layer is biaxially oriented.

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