JP2012079481A - Packaging material for electrochemical cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packaging material for an electrochemical cell, in which adhesive strength of a heat seal part is maintained even under high temperature conditions to exhibit certain safety performance.SOLUTION: The packaging material for an electrochemical cell is configured by sequentially laminating at least a base material layer 111, a metal foil layer 112, an acid-modified polyolefin layer 114, and a polyolefin layer 115. The polyolefin layer 115 is configured by adding a propylene-based elastomer resin with a melting point higher than 150°C to a polypropylene resin.

Description

  The present invention relates to a packaging material for an electrochemical cell, and more particularly to a packaging material for an electrochemical cell that maintains the adhesive strength of a heat seal part even under high temperature conditions and exhibits a certain safety performance.

  2 is a perspective view of a conventional lithium ion battery, and FIG. 3 is a cross-sectional view taken along the line A-A ′ of the lithium ion battery of FIG. 2. The lithium ion battery 221 is also referred to as a lithium secondary battery, and includes a liquid, gel-like, or polymer polymer electrolyte, and a cathode / negative electrode active material made of a polymer polymer. The configuration of the lithium ion battery 221 includes a lithium ion battery main body 222 composed of a positive electrode current collector / positive electrode active material layer / electrolyte layer / negative electrode active material layer / negative electrode current collector, and a packaging container 220 for housing these. The packaging container 220 is formed of a packaging material for an electrochemical cell made of a multilayer film. Specifically, the packaging container 220 includes a lid portion 220a and a storage portion 220b. The lithium ion battery main body 222 is stored inside the storage portion 220b, and the lid portion 220a and the storage portion 220b are connected to a current collector. The peripheral portion 220s is thermally bonded while the metal terminal 224 is sandwiched. The packaging material for an electrochemical cell constituting the packaging container 220 is configured by sequentially laminating a base material layer 211, a metal foil layer 212, and a polyolefin layer 215, and the opposing polyolefin layers 215 are thermally bonded to each other at the peripheral portion 220s. ing.

  In general, the lithium ion battery 221 is assumed to be used in various environments. For example, when the lithium ion battery 221 is placed in a high temperature environment of 150 ° C. or higher, or the lithium ion battery 221 itself generates heat. In this case, gas is generated inside the lithium ion battery 221, the polyolefin layer 215 is melted, a part of the peripheral portion 220s is peeled off, and the lid portion 220a and the storage portion 220b may be separated and opened. At this time, if the inside of the lithium ion battery 221 placed in a high temperature environment near 150 ° C. opens, there is a risk that the organic solvent containing the electrolyte in the lithium ion battery 221 may ignite.

  For this reason, US UL (Underwriters Laboratories) standard “UL1642” or “UL2054” is standardized in the safety evaluation test of lithium ion batteries. In the evaluation test standard “UL1642”, the lithium ion battery needs to clear the 150 ° C. heating test.

JP 2007-134304 A

  In view of the above problems, an object of the present invention is to provide an electrochemical cell packaging material that maintains the adhesive strength of the heat seal part even under high temperature conditions and exhibits a certain safety performance.

  To achieve the above object, the present invention provides an electrochemical cell in which a base material layer, a metal foil layer having a chemical conversion treatment layer on at least one side, an acid-modified polyolefin layer, and a polyolefin layer are sequentially laminated. In the packaging material, the polyolefin layer is formed by adding a propylene-based elastomer resin having a melting point higher than 150 ° C. to the polypropylene resin.

  According to this configuration, the polyolefin layer is formed in a state where the propylene-based elastomer resin having a melting point higher than 150 ° C. is uniformly dispersed in the polyolefin resin. Further, even after heat sealing (for example, a sealing temperature of 190 ° C., a surface pressure of 1.0 MPa, a sealing time of 3.0 seconds), the high melting point propylene-based elastomer resin is kept in a uniformly dispersed state in the polyolefin resin at 150 ° C. It is possible to prevent the bonded portion between the polyolefin layers from being melted and softened under a high temperature environment in the vicinity. As a result, the polyolefin resin added with the propylene elastomer resin having a melting point higher than 150 ° C. compared to the polypropylene resin without the addition of the propylene elastomer resin with a melting point higher than 150 ° C. has an adhesive strength between the polyolefin layers in a high temperature environment. Is stable. Further, by using a resin having a melting point higher than 150 ° C. as the propylene-based elastomer resin, the adhesive strength after heat sealing is stabilized even in an environment near 150 ° C., and separation between polyolefin layers is prevented.

  Moreover, the present invention is characterized in that the propylene-based elastomer resin is mixed in an amount of 3% by weight to 30% by weight with respect to the polypropylene resin in the packaging container for electrochemical cells.

  According to this configuration, if the addition amount of the propylene-based elastomer resin is less than 3% by weight with respect to the polypropylene resin, the polyolefin layer after heat sealing is likely to crack, and if it is greater than 30% by weight, the polyolefin layer is softened. However, since the polyolefin layer is easily crushed by pressing during heat sealing, this can be prevented.

These are schematic sectional drawings which show the layer structure of the packaging material for batteries of this invention. FIG. 3 is a perspective view of a conventional lithium ion battery. FIG. 3 is a cross-sectional view taken along the line A-A ′ of the lithium ion battery in FIG. 2.

  The present invention is an electrochemical cell packaging container that exhibits a certain safety performance under high temperature conditions, and will be described in more detail with reference to the drawings. The description of the parts common to FIGS. 2 and 3 of the conventional example is omitted.

  FIG. 1 is a cross-sectional view showing a layer structure of an electrochemical cell packaging material as an example of an embodiment of the present invention. As shown in FIG. A layer 111, a metal foil layer 112, an acid-modified polyolefin layer 114, and a polyolefin layer 115 are sequentially laminated. Although not shown, a chemical conversion treatment layer is applied to both surfaces of the metal foil layer 112 to increase the interlayer adhesion strength between the metal foil layer 112 and the acid-modified polyolefin layer 114.

  The lamination method of the metal foil layer 112, the acid-modified polyolefin layer 114, and the polyolefin layer 115 is a method of laminating an acid-modified polyolefin film and a polyolefin film using a polyester-based known dry lamination adhesive, and a molten acid-modified layer. A method of extruding a polyolefin resin onto the surface of the metal foil layer 112 and sandwiching and laminating a melted acid-modified polyolefin resin between the metal foil layer 112 and the polyolefin film, and a method of laminating the melted acid-modified polyolefin resin and the polyolefin resin. The packaging material for electrochemical cells laminated by any method of co-extrusion on the surface and lamination is also included in the technical scope of the present invention.

  Here, the polyolefin layer 115 is composed of a polyolefin resin to which a propylene-based elastomer having a melting point higher than 150 ° C. is added, and compared with a polyolefin resin to which a propylene-based elastomer resin having a melting point higher than 150 ° C. is not added, The adhesive strength between the polyolefin layers 115 in an environment near 150 ° C. is stabilized. This is because the polyolefin layer 115 is formed in a state in which a propylene-based elastomer resin having a melting point higher than 150 ° C. is uniformly dispersed in the polyolefin resin, and heat seal (for example, seal temperature 190 ° C., surface pressure 1.0 MPa, seal time 3 This is because the high melting point propylene-based elastomer resin is kept in a state of being uniformly dispersed in the polyolefin resin even after 0.0 seconds). This prevents melt-softening of the bonded portion between the polyolefin layers even in a high temperature environment around 150 ° C.

  As a result, the peripheral heat seal portion of the electrochemical cell packaging container formed by heat sealing the polyolefin layers 115 at the peripheral portion of the electrochemical cell packaging material 110 opens in an environment near 150 ° C. hard. Moreover, even if gas is generated inside the packaging container and the internal pressure of the container rises, the packaging container is difficult to open easily.

  In addition, polypropylene can be divided into random propylene, homopropylene, block propylene, and other types, and a multilayer polypropylene resin layer made of each type of polypropylene includes a polypropylene film mixed with a propylene-based elastomer resin in the lamination. As a result, the physical properties such as durability, flexibility, and whitening resistance can be increased as the melting point of the polyolefin layer 115 increases.

  When the propylene-based elastomer resin is mixed in an amount of 3% by weight to 30% by weight with respect to the polypropylene resin, the physical properties of the polypropylene layer can be most improved. If the added amount of the propylene-based elastomer resin is less than 3% by weight with respect to the polypropylene resin, the polyolefin layer after heat sealing is likely to crack, and if it is greater than 30% by weight, the polyolefin layer softens and is heat sealed. The polyolefin layer is easily crushed by pressing.

  Here, the propylene-based elastomer resin according to the present invention is a copolymer composed of a structural unit derived from propylene and a structural unit derived from an α-olefin having 2 to 20 carbon atoms (excluding propylene). 50 mol% or more of units (herein, the total of the structural units derived from propylene and the structural units derived from α-olefins having 2 to 20 carbon atoms is 100 mol%), specifically the propylene system according to the present invention Examples of the α-olefin having 2 to 20 carbon atoms (excluding propylene) constituting the elastomer resin include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1 -Decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene and the like.

  Further, the propylene-based elastomer resin according to the present invention is a copolymer comprising a structural unit derived from propylene and a structural unit derived from an α-olefin having 2 to 20 carbon atoms (excluding propylene). More preferably, the copolymer is composed of a structural unit derived from ethylene, a structural unit derived from ethylene, and a structural unit derived from an α-olefin having 4 to 10 carbon atoms.

  The propylene-derived structural unit is 50 mol% or more and 99 mol when the total of the propylene-derived structural unit and the structural unit derived from an α-olefin having 2 to 20 carbon atoms (excluding propylene) is 100 mol%. %, Preferably 60 mol% or more and 99 mol% or less.

  As described above, the propylene-based elastomer resin according to the present invention is not particularly limited as long as it satisfies the above physical properties. For example, a commercially available one may be used. Examples of commercially available products include “Notio (registered trademark)” manufactured by Mitsui Chemicals, Inc., but are not limited thereto.

  As the acid-modified polyolefin layer 114, acid-modified polypropylene is preferably used in order to stably bond the aluminum foil layer 112 and the polyolefin layer 115. In addition, it is necessary to select and use appropriately depending on the resin type used for the polyolefin layer 115. When using an acid-modified polyolefin resin other than acid-modified polypropylene, a polyolefin resin graft-modified with an unsaturated carboxylic acid, ethylene or propylene and acrylic acid, Or, there is a copolymer with methacrylic acid, or a metal-crosslinked polyolefin resin, and the like, butene component, ethylene-propylene-butene copolymer, amorphous ethylene-propylene copolymer, propylene-α as necessary. -You may add 5% or more of olefin copolymers.

When using acid-modified polypropylene,
(1) A homotype having a bigat softening point of 115 ° C or higher and a melting point of 150 ° C or higher,
(2) A copolymer of ethylene-propylene having a bigat softening point of 105 ° C or higher and a melting point of 130 ° C or higher (random copolymer type)
(3) A simple substance or a blended product obtained by acid-modified polymerization using an unsaturated carboxylic acid having a melting point of 110 ° C. or higher can be used.

  The metal foil layer 112 is a layer for preventing water vapor from entering the inside of the lithium ion battery 121 from the outside, and stabilizes pinholes and processability (pouching, embossing formability) of the metal foil layer alone. In order to have pinhole resistance, aluminum having a thickness of 15 μm or more is used.

  In addition, when the generation of pinholes is improved and the type of the outer package of the lithium ion battery is an embossed type, the material of aluminum used as the metal foil layer 112 is selected in order to prevent the occurrence of cracks in the embossing molding. It is desirable that the iron content is 0.3 to 9.0% by weight, preferably 0.7 to 2.0% by weight.

  As a result, compared with aluminum that does not contain iron, aluminum has good spreadability, and the occurrence of pinholes due to bending as an exterior body is reduced, and the side wall can be easily formed when embossing the packaging material. it can. In addition, when the iron content is less than 0.3% by weight, effects such as prevention of pinholes and improvement of embossing formability are not observed, and the iron content of aluminum exceeds 9.0% by weight. In this case, the flexibility as aluminum is hindered, and the bag-making property as a packaging material is deteriorated.

  In addition, aluminum produced by cold rolling changes its flexibility, waist strength and hardness under annealing (so-called annealing treatment) conditions, but the aluminum used in the present invention is harder than the non-annealed hard-treated product. Aluminum which tends to be soft with some or complete annealing is preferred.

  Stretched polyester or nylon film can be used for the base material layer 111, and examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, and polycarbonate. Examples of nylon include polyamide resin, that is, nylon 6, nylon 6,6, a copolymer of nylon 6 and nylon 6,6, nylon 6,10, polymetaxylylene adipamide (MXD6), and the like.

  In addition, the base material layer 111 can be laminated with films of different materials in addition to a polyester film or a nylon film in order to improve pinhole resistance and insulation when used as a battery outer package.

The present invention is not limited to the above-described embodiments, and various modifications are possible. Embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the present invention. Included in the technical scope.
[Example]

  In this example, the seal strength in a high temperature environment when a propylene-based elastomer resin is mixed with the polypropylene layer constituting the polyolefin layer is evaluated.

  First, a chemical conversion treatment is performed on both surfaces of aluminum, and a stretched nylon film is bonded to one chemical conversion treatment surface by a dry laminating method via a two-component curable polyurethane adhesive, and then melted on the other chemical conversion treatment surface. A modified polypropylene resin (hereinafter abbreviated as PPa) and a molten polypropylene resin (hereinafter abbreviated as PP) are coextruded and laminated, and a stretched nylon film (thickness: 25 μm) / aluminum (thickness: 40 μm) / PPa A packaging material for an electrochemical cell consisting of (thickness: 23 μm) / PP (thickness: 23 μm) was obtained.

  At this time, in the packaging material for an electrochemical cell according to the first aspect of the present invention, 20 wt% of propylene-based elastomer resin is added to PPa with respect to PPa, and the added propylene-based elastomer resin has a melting point of 157 ° C. 2060 (Mitsui Chemicals, Notio (registered trademark)) was used. In addition, 30% by weight of propylene-based elastomer resin is added to PP with respect to PPa, and PN-2060 (Mitsui Chemicals, Notio (registered trademark)) having a melting point of 157 ° C. is added to the added propylene-based elastomer resin. Was used.

  In addition, in the packaging material for an electrochemical cell according to Comparative Example 1, 20 wt% of propylene-based elastomer resin is added to PPa with respect to PPa, and PN-2060 having a melting point of 157 ° C. is added to the added propylene-based elastomer resin. (Mitsui Chemicals, Notio (registered trademark)) was used. In addition, 20% by weight of propylene-based elastomer resin is added to PP with respect to PPa, and the added propylene-based elastomer resin has a melting point of 140 ° C. PN-2070 (manufactured by Mitsui Chemicals, Notio (registered trademark)). Was used.

  Next, the packaging material for an electrochemical cell according to the present invention 1 and Comparative Example 1 produced by the above method is cut into two pieces of 150 mm × 60 mm strips, and the PP side is overlapped to heat seal (seal temperature 190 ° C. Surface pressure 1.0 MPa, sealing time 3.0 seconds). Next, the packaging material for electrochemical cells was cut to a width of 15 mm in a direction perpendicularly intersecting with the folded fold, and the cut sample was stored in a 145 ° C. environment, and then a tension machine (manufactured by Shimadzu Corporation, AGS- 50D (trade name)), the seal portions of the two strips were separated at a speed of 300 mm / min, and the strength at the time of taking was measured as the seal strength. The results are shown in Table 1. The unit is N / 15 mm width. As shown in Table 1, as compared with Comparative Example 1, the packaging material according to the present invention 1 maintains a high seal strength even in an environment at 145 ° C.

  As shown in Table 1, as compared with Comparative Example 1, the packaging material according to the present invention 1 was able to maintain a high sealing strength even in an environment where the adhesive strength after heat sealing was 145 ° C. From this result, a packaging container for an electrochemical cell formed by heat-sealing polyolefin layers constituted by adding a propylene-based elastomer resin having a melting point higher than 150 ° C. to a polypropylene resin is an environment near 150 ° C. It was also confirmed that the peripheral heat seal part was difficult to open.

110 Packaging material for electrochemical cells 111, 211 Base material layer 112, 212 Metal foil layer 114 Acid-modified polyolefin layer 115, 215 Polyolefin layer
220 Packaging container for electrochemical cells (packaging container)
220s peripheral edge
220a lid
220b storage section
221 Lithium ion battery
222 Lithium ion battery body
224 Metal terminal

Claims (2)

In a packaging material for an electrochemical cell in which a base material layer, a metal foil layer provided with a chemical conversion treatment layer on at least one side, an acid-modified polyolefin layer, and a polyolefin layer are sequentially laminated,
A packaging material for battery chemical cells, wherein the polyolefin layer is constituted by adding a propylene-based elastomer resin having a melting point higher than 150 ° C. to a polypropylene resin.   The packaging material for an electrochemical cell according to claim 1, wherein the propylene-based elastomer resin is mixed in an amount of 3 wt% to 30 wt% with respect to the polypropylene resin.

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