JP5407719B2 - Packaging materials for electrochemical cells - Google Patents

Description

  The present invention relates to a packaging material for electrochemical cells that exhibits stable sealing and insulating properties.

  The lithium ion battery is also referred to as a lithium secondary battery, and includes a liquid, gel-like, or polymer polymer electrolyte, and a positive electrode / negative electrode active material made of a polymer polymer. The configuration of the lithium ion battery is composed of a positive electrode current collector / positive electrode active material layer / electrolyte layer / negative electrode active material layer / negative electrode current collector and an outer package for packaging these, and a multilayer film is used as a packaging material for forming the outer package. It is done.

  FIG. 2 is a cross-sectional view showing the layer structure of a conventional electrochemical cell packaging material. As shown in FIG. 2, the conventional electrochemical cell packaging material 110 includes at least a base layer 111, a metal foil layer 112, The base material layer 111 and the metal foil layer 112 are bonded via an adhesive layer 113, and the polypropylene layer 115 and the metal foil layer 112 are bonded via an acid-modified polypropylene layer 114. .

  This packaging material is processed into a bag shape, and a pouch-type battery exterior body that houses the battery body inside, or an embossed type that presses the packaging material to form a recess and stores the battery body inside the recess. There is a battery case. In any of these types of battery outer bodies, the battery main body is housed, and the polypropylene layers 115 are stacked and heat-sealed, whereby the battery main body can be hermetically housed inside the battery outer body.

  However, conventionally, as described in Patent Document 1, the acid-modified polypropylene layer 114 is melted and pushed out of the exterior body by heat and pressure of heat sealing, and the electrode terminal and the metal foil layer 112 are short-circuited. The metal foil layer 112 and the polypropylene layer 115 are problematically peeled off.

JP 2007-134304 A

  Then, in view of the said problem, this invention aims at providing the packaging material for electrochemical cells which is excellent in sealing performance and insulation.

  In order to achieve the above object, according to a first configuration of the present invention, a polyolefin layer is formed in a packaging material for an electrochemical cell in which a metal foil layer, an acid-modified polyolefin layer, and a polyolefin layer are sequentially laminated. The MFR (230 ° C.) of the resin is 10 g / 10 min or more and 25 g / 10 min or less, and the MFR (230 ° C.) of the resin constituting the acid-modified polyolefin layer is 5 g / 10 min or more and 7 g / 10 min or less. It is characterized by that.

  According to this configuration, by setting the MFR (230 ° C.) of the acid-modified polyolefin layer in the range of 5 g / 10 minutes to 7 g / 10 minutes, the outflow of the acid-modified polyolefin layer melted by heat during heat sealing is suppressed, It is possible to prevent a decrease in insulating properties of the seal portion. Further, by setting the MFR (230 ° C.) of the resin constituting the polyolefin layer in the range of 10 g / 10 min to 25 g / 10 min, the polyolefin layer resin is melt-extruded to laminate the packaging material for electrochemical cells. In this case, the film formability of the polyolefin layer can be stabilized.

  The second configuration of the present invention is characterized in that, in the packaging material for an electrochemical cell, the MFR (230 ° C.) of the resin constituting the polyolefin layer is 10 g / 10 min or more and 15 g / 10 min or less.

  According to this configuration, by setting the MFR of the polyolefin layer in the range of 10 g / 10 min or more and 15 g / 10 min or less, the adhesive strength of the heat seal portion immediately after the heat seal is improved, so the seal portion is peeled immediately after the heat seal. Even when a force is applied, peeling can be prevented. Thereby, the sealing performance as a packaging material can be improved.

These are sectional drawings which show the layer structure of the packaging material for electrochemical cells of this invention. These are sectional drawings which show the layer structure of the conventional packaging material for electrochemical cells.

  The present invention is an electrochemical cell packaging material exhibiting stable sealing and insulating properties, and will be described in more detail with reference to the drawings. In addition, the part which is common in FIG. 2 of a prior art example is abbreviate | omitted.

  FIG. 1 is a cross-sectional view showing a layer structure of a packaging material for an electrochemical cell which is an example of an embodiment of the present invention. As shown in FIG. 1, the packaging material 10 for an electrochemical cell according to this embodiment is an outermost layer. The base material layer 11, the innermost layer is the polypropylene layer 15, and the metal foil layer 12 is disposed therebetween. The polypropylene layer 15 and the metal foil layer 12 are bonded via the acid-modified polypropylene layer 14. Moreover, the base material layer 11 and the metal foil layer 12 are bonded via an adhesive layer 13. At this time, a chemical conversion treatment layer 12 a is provided on the surface of the metal foil layer 12. In addition, the packaging material 10 for electrochemical cells of the present invention includes the above-described layers and includes the case where different layers are interposed between the respective layers in the technical scope of the present invention. The polypropylene layer is an example of the “polyolefin layer” in the present invention, and the acid-modified polypropylene layer is an example of the “acid-modified polyolefin layer” in the present invention.

  Here, the acid-modified polypropylene layer 14 and the polypropylene layer 15 are formed by forming an acid-modified polypropylene layer 14 by melting and extruding an acid-modified polypropylene resin on one surface of the metal foil layer 12 on which the chemical conversion treatment layer 12a is formed. The polypropylene layer 15 can be laminated by melting and extruding a polypropylene resin from above the polypropylene layer 14.

  At this time, the acid-modified polypropylene layer 14 is a layer provided for stably bonding the metal foil layer 12 and the polypropylene layer 15, and the MFR (230 ° C.) of the resin constituting the acid-modified polypropylene layer 14 is 5 g / It is 10 minutes or more and 7 g / 10 minutes or less. The MFR is measured at 230 ° C. and a load of 2.16 kg according to ASTM D1238. By setting the MFR (230 ° C.) of the resin constituting the acid-modified polypropylene layer 14 in the range of 5 g / 10 min to 7 g / 10 min, the outflow of the acid-modified polypropylene that is melted by the heat at the time of heat sealing is suppressed, and the seal The insulation of the part can be improved. Further, when the MFR (230 ° C.) of the resin constituting the acid-modified polypropylene layer 14 is less than 5 g / 10 minutes, the film-forming property when the acid-modified polypropylene layer 14 is formed by melt extrusion of the acid-modified polypropylene resin is not good. It becomes stable. Further, when the MFR (230 ° C.) of the resin constituting the acid-modified polypropylene layer 14 is larger than 7 g / 10 minutes, the melted acid-modified polypropylene easily flows out due to the heat at the time of heat sealing, and the insulating property of the seal portion Decreases.

The acid-modified polypropylene used in this layer is
(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.

  Further, when a polyolefin other than polypropylene is used for the polypropylene layer 15, the acid-modified polypropylene layer 14 needs to be appropriately selected and used depending on the resin type, but as the acid-modified polyolefin other than the acid-modified polypropylene, an unsaturated carboxylic acid may be used. There are graft-modified polyolefin resins, copolymers of ethylene or propylene and acrylic acid, or methacrylic acid, or metal-crosslinked polyolefin resins, butene components, ethylene-propylene-butene copolymers, Crystalline ethylene-propylene copolymer, propylene-α-olefin copolymer and the like may be added by 5% or more. In the case of using any of these acid-modified polyolefins, the MFR (230 ° C.) of the acid-modified polyolefin resin is used to suppress the outflow of the acid-modified polyolefin resin that is melted by the heat at the time of heat sealing and to improve the insulation of the seal portion. ) Is preferably 5 g / 10 min or more and 7 g / 10 min or less.

  Moreover, MFR (230 degreeC) of resin which comprises the polypropylene layer 15 is 10 g / 10min or more and 25 g / 10min or less, and it is more preferable that they are 10 g / 10min or more and 15 g / 10min or less. The MFR is measured at 230 ° C. and a load of 2.16 kg according to ASTM D1238. By setting the MFR (230 ° C.) of the resin constituting the polypropylene layer 15 in the range of 10 g / 10 min or more and 15 g / 10 min or less, the adhesive strength of the heat seal part immediately after the heat seal is improved. Even when a force is applied to peel off the seal portion, peeling can be prevented. Thereby, the sealing performance as a packaging material can be improved. Further, when the MFR (230 ° C.) of the resin constituting the polypropylene layer 15 is smaller than 10 g / 10 minutes and larger than 25 g / 10 minutes, the film is formed when the polypropylene layer 15 is formed by melt extrusion of the polypropylene resin. Sex becomes unstable. Moreover, when MFR (230 degreeC) of resin which comprises the polypropylene layer 15 is larger than 15 g / 10min, the adhesive strength of the heat seal part immediately after heat sealing falls, and the adhesive strength after heat sealing may be improved. Can not.

  Polypropylene is preferably used, but linear low density polyethylene, medium density polyethylene single layer or multilayer, or linear low density polyethylene, medium density polyethylene blend resin may be single layer or multilayer. Polypropylene can be classified into random propylene, homopropylene, block propylene, and the like. Random polypropylene, homopolypropylene, and block polypropylene include low crystalline ethylene-butene copolymer and low crystalline propylene-butene. Copolymers, terpolymers composed of ternary copolymers of ethylene, butene and propylene, silica, zeolite, antiblocking agents (AB agents) such as acrylic resin beads, fatty acid amide slip agents, etc. may be added. . However, in the case of using any polyolefin, from the viewpoint of film formability, the MFR (230 ° C.) of the polyolefin resin is 10 g / 10 min or more and 25 g / 10 min or less. From the viewpoint of strength, it is more preferably 10 g / 10 min or more and 15 g / 10 min or less.

  The polypropylene layer 15 according to the present invention may be multilayered by combining the above-mentioned types of polypropylene layers as appropriate.

  Next, each other layer which comprises the packaging material 10 for electrochemical cells shown in FIG. 1 is demonstrated concretely. The base material layer 11 can use a stretched polyester film in addition to the stretched nylon film. Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymerized 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. Further, by laminating polyethylene terephthalate on the upper surface of the stretched nylon film, it is possible to prevent the electrolyte solution from adhering to the stretched nylon film and whitening. In addition, polyethylene terephthalate can barrier the stretched nylon film from water vapor and improve insulation.

  The adhesive layer 13 is a layer that bonds the base material layer 11 and the metal foil layer 13, and is, for example, a polyvinyl acetate adhesive, a homopolymer such as ethyl acrylate, butyl, 2-ethylhexyl ester, or the like. And polyacrylic acid ester adhesives composed of copolymers of methyl methacrylate, acrylonitrile, styrene, etc., cyanoacrylate adhesives, ethylene and vinyl acetate, ethyl acrylate, acrylic acid, methacrylic acid and other monomers Ethylene copolymer adhesive made of copolymer, cellulose adhesive, polyester adhesive, polyamide adhesive, polyimide adhesive, amino resin adhesive made of urea resin or melamine resin, phenol resin Adhesives, epoxy adhesives, polyurethane adhesives, reactive (meth) acrylic adhesives Chloroprene rubber, nitrile rubber, styrene - butadiene made of rubber or the like rubber adhesive, a silicone-based adhesive, an alkali metal silicate, inorganic adhesive or the like made of a low-melting glass.

  The metal foil layer 12 is a layer for preventing water vapor from entering the inside of the lithium ion battery from the outside, and the pinhole and processing suitability (pouching, cold press formability) of the metal foil layer alone are stabilized. For example, a film having a thickness of 15 μm or more, such as aluminum or nickel, or a film in which an inorganic compound such as silicon oxide or alumina is vapor-deposited is used. The metal foil to be configured is preferably aluminum having a thickness of 20 to 100 μm.

  Moreover, in order to improve the occurrence of pinholes and to make the outer body type of the lithium ion battery an embossed type, there is no occurrence of cracks or the like in cold press molding. It is desirable that the material has an iron content of 0.3 to 9.0% by weight, preferably 0.7 to 2.0% by weight.

  As a result, compared to 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 cold-pressing the packaging material. be able to. When the iron content is less than 0.3% by weight, effects such as prevention of pinholes and improvement of cold press formability are not recognized, and the iron content of aluminum is 9.0% by weight. In the case of exceeding, 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.

  That is, the annealing conditions may be appropriately selected in accordance with processability (pouching, cold press molding). For example, in order to prevent wrinkles and pinholes during cold press molding, soft aluminum annealed according to the degree of molding can be used.

  Moreover, by performing a chemical conversion treatment on the front and back surfaces of the aluminum that is the metal foil layer 12 to form the chemical conversion treatment layer 12a, the adhesive strength with the adhesive can be improved.

  The chemical conversion treatment layer 12a is formed on at least the surface of the metal foil layer 12 on the polypropylene layer 15 side. The chemical conversion treatment layer 12 a stably adheres the acid-modified polypropylene layer 14 and the metal foil layer 12, and can prevent delamination of the metal foil layer 12 and the polypropylene layer 15. Further, the chemical conversion treatment layer 12 a also has a function of preventing the corrosion of the metal foil layer 12.

  Specifically, prevention of delamination between the metal foil layer 12 and the polypropylene layer 15 during embossing by forming an acid-resistant film such as phosphate, chromate, fluoride, triazine thiol compound, The hydrogen fluoride generated by the reaction between the electrolyte and water in the lithium ion battery prevents the aluminum surface from being dissolved and corroded, especially the aluminum oxide present on the aluminum surface from being dissolved and corroded, and also adheres to the aluminum surface. Can be improved.

  The chemical conversion treatment layer 12a is made of metal by chromium-based chemical conversion treatment such as chromate chromate treatment, phosphoric acid chromate treatment, and coating-type chromate treatment, or non-chromium (coating-type) chemical conversion treatment such as zirconium, titanium, and zinc phosphate. Although it is formed on the surface of the foil layer 12, it is a coating-type chemical conversion treatment, particularly an aminated phenol polymer, in that continuous processing is possible and a water washing step is unnecessary and the processing cost can be reduced. Most preferably, the treatment is performed with a treatment solution containing a trivalent chromium compound and a phosphorus compound.

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 1]

Hereinafter, the operation and effect of the present invention will be specifically described with reference to examples. Example 1 evaluated the insulation of the packaging material for electrochemical cells. In this experiment, in order to confirm the insulation of the packaging material for electrochemical cells, an acid constituting the packaging material for electrochemical cells was used. A sample prepared by changing the MFR value of the modified polyolefin layer was used.
[Packaging sample preparation]

One side of aluminum (thickness 40 μm) is subjected to chemical conversion treatment, and acid-modified polypropylene (thickness 20 μm) is melt-extruded on the chemical conversion-treated surface, and polypropylene (thickness 15 μm) is melt-extruded from above to form an aluminum / chemical conversion treatment layer A packaging material composed of / acid-modified polypropylene / polypropylene was obtained.

Here, in each chemical conversion treatment, an aqueous solution composed of a phenol resin, a chromium fluoride compound, and phosphoric acid was used as a treatment solution, applied by a roll coating method, and baked under conditions where the film temperature was 180 ° C. or higher. The amount of chromium applied was 10 mg / m ² (dry weight).

  In addition, for an electrochemical cell obtained by using a resin having a melting point of 160 ° C. and MFR (230 ° C.) of 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min for acid-modified polypropylene. The packaging materials were Sample 1 to Sample 4, respectively. The polypropylenes of Samples 1 to 4 used resins having a melting point of 140 ° C. and MFR (230 ° C.) of 18 g / 10 min. Here, MFR is measured at 230 ° C. and a load of 2.16 kg in accordance with ASTM D1238. In addition, with acid-modified polypropylene having an MFR (230 ° C.) of 3 g / 10 minutes and 4 g / 10 minutes, film formation by melt extrusion was not stable. Samples 1 to 3 are electrochemical cell packaging materials according to the present invention.

[Evaluation of insulation]
The packaging material for electrochemical cells according to Sample 1 to Sample 4 produced by the above method is cut into 60 mm (MD direction) × 120 mm (TD direction) strips, and the strips are folded back in the TD direction to overlap the polypropylene side. Then, two opposite sides were heat-sealed with a width of 7 mm to create a bag having an opening on one side. At this time, the heat sealing was performed under conditions of a surface pressure of 1.0 MPa, a sealing temperature of 190 ° C., and a sealing time of 3.0 seconds. Next, the bag was folded back 180 ° in the MD direction so that a fold was formed in the TD direction on the heat seal portion, and this folding was repeated 20 times. Thereafter, the lithium ion battery main body was sealed from the opening, and the electrolyte was put and hermetically sealed. Next, a voltage of 100 V was applied for 5 seconds between the encapsulated electrolyte and aluminum constituting the packaging material, and the resistance value was measured. In this evaluation method, 100 pieces of the above-mentioned bags were prepared from the packaging materials for electrochemical cells according to Sample 1 to Sample 4, respectively, and the case where the resistance value showed ∞ was regarded as a non-defective product. .

[Table 1]

As shown in Table 1 above, as a result of comparing Sample 1 to Sample 4, it was found that Sample 1 to Sample 3 showed good insulation. From the above, it was found that when the MFR (230 ° C.) of the acid-modified polypropylene is 5 g / 10 min or more and 7 g / 10 min or less, stable insulation is exhibited after heat sealing. Further, it was found that when the MFR (230 ° C.) of the acid-modified polypropylene is smaller than 5 g / 10 minutes, the film formation by melt extrusion is not stable.
[Example 2]

Example 2 evaluated the adhesive strength of the heat seal part immediately after heat sealing of the packaging material for electrochemical cells. In this experiment, the adhesive strength of the heat seal part immediately after heat sealing of the packaging material for electrochemical cells was evaluated. In order to confirm the above, a sample prepared by changing the MFR value of the polyolefin layer constituting the packaging material for an electrochemical cell was used.
[Packaging sample preparation]

  One side of aluminum (thickness 40 μm) is subjected to chemical conversion treatment, acid-modified polypropylene (thickness 23 μm) is melt-extruded on the chemical conversion-treated surface, and polypropylene (thickness 23 μm) is melt-extruded from above to form an aluminum / chemical conversion treatment layer. A packaging material composed of / acid-modified polypropylene / polypropylene was obtained.

Here, in each chemical conversion treatment, an aqueous solution composed of a phenol resin, a chromium fluoride compound, and phosphoric acid was used as a treatment solution, applied by a roll coating method, and baked under conditions where the film temperature was 180 ° C. or higher. The amount of chromium applied was 10 mg / m ² (dry weight).

  Moreover, the melting point is 140 ° C. for polypropylene, and the MFR (230 ° C.) is 11 g / 10 min, 15 g / 10 min, 18 g / 10 min. Sample 7 was obtained. Further, the acid-modified polypropylenes of Sample 5 to Sample 7 were resins having a melting point of 160 ° C. and MFR (230 ° C.) of 5 g / 10 min. Here, MFR is measured at 230 ° C. and a load of 2.16 kg in accordance with ASTM D1238. In addition, with polypropylene having MFR (230 ° C.) of 7 g / 10 minutes, 9 g / 10 minutes, and 27 g / 10 minutes, film formation by melt extrusion was not stable. In addition, polypropylenes having MFR (230 ° C.) of 20 g / 10 minutes and 25 g / 10 minutes and polypropylenes of Sample 5 to Sample 7 were stable by melt extrusion. Sample 5 and sample 6 are electrochemical cell packaging materials according to the present invention.

[Evaluation of adhesive strength of heat seal part immediately after heat seal]
The electrochemical cell packaging material according to Sample 5 to Sample 7 prepared by the above method is cut to produce two 25 mm × 250 mm strips, and the polypropylene side is stacked on a hot tack tester (made by Theller). Two samples are set together and heat sealed (sealing temperature 170 ° C., surface pressure 3.8 MPa, sealing time 2.0 seconds). Immediately after heat sealing, the sealing portion is pulled off at a pulling speed of 2000 mm / min, and then taken off. The intensity of time was measured. Table 2 shows the strength at the start of measurement as the adhesive strength of the heat seal portion immediately after heat sealing. The unit is N / 25 mm width.

[Table 2]

  As shown in Table 2 above, as a result of comparing samples 5 to 7, it was found that in samples 5 and 6, the adhesive strength of the heat seal part immediately after heat sealing showed a good value. From the above, it was found that when the MFR (230 ° C.) of polypropylene is 10 g / 10 min or more and 15 g / 10 min or less, the adhesive strength of the heat seal part immediately after the heat seal is high. Further, it was found that when the MFR (230 ° C.) of polypropylene is smaller than 10 g / 10 minutes and larger than 25 g / 10, film formation by melt extrusion is not stable.

10, 110 Electrochemical cell packaging material 11, 111 Base layer 12, 112 Metal foil layer 12a Chemical conversion layer 13, 113 Adhesive layer 14, 114 Acid-modified polypropylene layer 15, 115 Polypropylene layer

Claims (2)

In the packaging material for electrochemical cells in which the metal foil layer, the acid-modified polyolefin layer, and the polyolefin layer are sequentially laminated,
The MFR (230 ° C.) of the resin constituting the polyolefin layer is 10 g / 10 min or more and 25 g / 10 min or less,
A packaging material for electrochemical cells, wherein the resin constituting the acid-modified polyolefin layer has an MFR (230 ° C) of 5 g / 10 min to 7 g / 10 min.   2. The packaging material for an electrochemical cell according to claim 1, wherein the resin constituting the polyolefin layer has an MFR (230 ° C.) of 10 g / 10 min or more and 15 g / 10 min or less.

Images