JP2014182872A - Sheath material for batteries, and aluminum foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheath material for batteries which is superior in heat sealability, hard to cause the exfoliation, and capable of being preferably adapted to various kinds of electrolyte, and which has good electrolyte resistance, and suitably serves as a sheath material for various batteries including lithium ion batteries, especially sheet-like slim lithium ion batteries; and an aluminum foil for such a sheath material for batteries.SOLUTION: A sheath material for batteries comprises a sealant layer, an adhesion layer, and aluminum foil. The aluminum foil has an oxide surface film formed on a surface thereof by an electrolytic process. The oxide surface film has a barrier type oxide surface film layer, and a porous oxide surface film layer. The porous oxide surface film layer has a thickness of 20-500 nm, and small holes which are formed in a surface thereof and have a diameter of 25-120 nm.

Description

  The present invention relates to an outer packaging material for a battery such as a lithium ion battery, and is excellent in heat sealability, hardly peeled off, excellent in electrolytic solution resistance, can be suitably applied to various electrolytic solutions, and is a sheet-like thin lithium. The present invention relates to a battery exterior material suitable as an exterior material for various batteries such as an ion battery, and an aluminum foil used for the battery exterior material.

  Lithium-ion secondary batteries and portable storage batteries are used as a battery with positive and negative electrode materials, as well as an aprotic solvent with penetrating power such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. In addition, an electrolyte solution in which an electrolyte (lithium salt) is dissolved or a polymer gel impregnated with the electrolyte solution is enclosed in an exterior material.

  Here, as the exterior material, conventionally, a metal, particularly aluminum, pressed into an appropriate shape has been used. However, because of the advantage that the shape of the battery can be freely selected, CPP is applied to the surface of the aluminum foil. A so-called laminate type exterior material is also used in which a film having a film attached thereto is joined in a bag shape.

  However, LiPF6, LiBF4, etc. are used for the lithium salt of the electrolyte, and these generate hydrofluoric acid by hydrolysis reaction with moisture, which causes the corrosion of the metal surface and the decrease in the laminate strength between the layers of the multilayer film. become. There is a concern that the laminate type exterior material has a problem in that the adhesion strength between the aluminum foil and the film layer decreases due to permeation of the electrolytic solution, and the electrolytic solution leaks out. In addition, the exterior material having a structure in which multilayer films are bonded together by heat sealing may cause moisture to enter from the end face of the seal part of the heat-fusible film layer such as CPP serving as a sealant. There are concerns.

  On the other hand, lithium-ion batteries are being developed not only for miniaturization applications such as portable mobile devices, but also for applications such as automobiles, and especially for automotive applications, there is a need for higher safety performance than before. Yes. Accordingly, it is necessary to increase the interlayer adhesion strength between the aluminum foil, the adhesive, and the multilayer film, and to have an electrolyte resistance characteristic, even for a laminate type exterior material.

  As the most effective method for imparting these resistances, a method of subjecting an aluminum foil to a chemical conversion treatment is known, and an example of the chemical conversion treatment is a chromate treatment. For example, Patent Document 1 discloses many chromate treatments such as a coating type chromate treatment and a chromate treatment by an immersion method.

JP 2002-144479 A

  However, in the chromate treatment as described in Patent Document 1, a material using hexavalent chromium as a main component is designated as an environmentally hazardous substance, which is not environmentally preferable. For this reason, trivalent chromium has come to be used, but it is difficult to obtain the same resistance as hexavalent chromium, and the problem of being unfavorable from the environmental viewpoint as long as chromium is used has not been solved.

  As a result of intensive studies in view of the above circumstances, the present inventor did not use a ground treatment agent containing heavy metal salts such as chromium in order to adopt a treatment method that does not give an environmental load as a ground treatment of the exterior material. In addition, by performing electrolytic treatment on the surface of the aluminum foil and forming an extremely thin oxide film on the surface of the aluminum foil, the corrosion resistance can be improved and the adhesiveness with the adhesive layer can be dramatically improved. The present inventors have found that it is possible to provide an outer packaging material for a battery and an aluminum foil for an outer packaging material for a battery that have excellent electrolytic solution resistance and excellent adhesion during molding.

The present invention has been made to achieve the above object, and comprises the following (1) to (4).
(1) A battery exterior material comprising a sealant layer, an adhesive layer, and an aluminum foil, wherein the aluminum foil has an oxide film formed by electrolytic treatment on the surface, and the oxide film is a barrier type oxidation A battery layer comprising a coating layer and a porous oxide coating layer, wherein the porous oxide coating layer has a thickness of 20 to 500 nm, and a small hole having a diameter of 25 to 120 nm is formed on the surface. Exterior material.
(2) The battery packaging material according to claim 1, wherein the barrier-type oxide film layer has a thickness of 3 to 30 nm.
(3) The battery packaging material according to claim 1 or 2, wherein the aluminum foil is subjected to alternating current electrolysis in an alkaline aqueous electrolytic solution.
(4) The aluminum foil for battery outer packaging materials according to any one of claims 1 to 3.

  The exterior material of the present invention and the aluminum foil for an exterior material for a battery are environmentally friendly, and as an exterior material for a secondary battery such as a lithium ion battery, are excellent in heat sealability, hardly peeled off, and have anti-electrolytic properties. It can be suitably used as an exterior material for a sheet-like thin lithium ion battery.

Hereinafter, the present invention will be described in detail for each element.
<Aluminum foil>
The packaging material for a secondary battery of the present invention is an electrolytic treatment and an oxide film is provided on the surface of the aluminum foil. Here, the aluminum foil on which the oxide film is formed is an aluminum alloy foil, particularly a soft aluminum foil because of its high tensile strength and elongation rate, as a base material layer that blocks moisture, gas, oxygen and the like from entering the battery. Can be produced by a known method. For example, it is preferable to use a JIS standard 8000 series alloy or 1000 series alloy. In addition, the said alloy is an example of the alloy used, and this invention is not limited to an alloy composition.

  The thickness of the aluminum foil of the present invention is preferably 9 to 200 μm, and more preferably 15 to 100 μm, taking into consideration barrier properties, pinhole resistance, and workability when being molded as an exterior material. preferable. If the thickness is less than 9 μm, the aluminum foil is likely to break during press molding, and even if it does not break, pinholes etc. are likely to occur. Oxygen and moisture may be transmitted, and if it exceeds 200 μm, There is no improvement in the breakage and prevention of pinhole occurrence, and simply increasing the total thickness of the exterior material and increasing the weight may not achieve weight reduction, which may increase costs. .

<Aluminum oxide film layer>
The aluminum foil of the present invention has an oxide film formed on the surface by electrolytic treatment, and this oxide film has a structure of a barrier type oxide film and a porous oxide film from the foil side. Thus, the oxide film layer is composed of two layers of the porous oxide film layer and the barrier type oxide film layer, whereby the adhesion and workability to the adhesive layer are ensured by the porous oxide film layer, and the barrier Because the entire oxide film layer and the aluminum foil substrate are firmly bonded together by the mold oxide film layer, by using it as a battery exterior material, it has excellent heat-sealability, hardly peels off, and has excellent electrolyte solution characteristics. Can be granted.

<Barrier type oxide film layer>
The thickness of the barrier oxide film layer of the present invention is preferably 3 to 30 nm. If the thickness is less than 3 nm, sufficient bonding force cannot be imparted to the bonding between the porous oxide film layer and the aluminum substrate as an intervening layer, and particularly the bonding force in a harsh environment such as high temperature and high humidity becomes insufficient, which will be described later. Adhesion between the adhesive layer and the entire oxide film layer may not be ensured. Moreover, since the film is too thin, the corrosion resistance is inferior and the electrolytic solution resistance may not be secured. On the other hand, if the thickness exceeds 30 nm, the barrier-type oxide film layer is likely to be broken when the aluminum foil is molded, and problems such as peeling of the adhesive layer after the molding process may occur.

<Porous oxide film layer>
In the present invention, the thickness of the porous oxide film layer needs to be 20 to 500 nm. If the thickness is less than 20 nm, the thickness is not sufficient, and the porous oxide film layer is destroyed and the adhesive layer is peeled off when the aluminum foil is deformed. On the other hand, when it exceeds 500 nm, the porous oxide film layer itself is easily broken, and the adhesive layer is peeled in the same manner.

  The porous oxide film layer of the present invention has small holes extending in the depth direction from the surface thereof, contributes to the formation of an adhesive layer described later, and firmly bonds the aluminum foil and the adhesive layer by an anchor effect. In the present invention, the diameter of the small holes formed on the surface needs to be 25 to 120 nm, and the definition of this diameter is different from the case of forming other oxide films, and not only the aluminum foil but also the oxidation during the forming process. The film itself is also deformed according to the processing deformation, and good moldability is imparted. When the diameter of the small holes is less than 25 nm, the adhesive layer is not sufficiently taken into the small holes, and sufficient adhesion cannot be obtained. On the other hand, if the diameter of the small holes exceeds 120 nm, the entire porous oxide film layer becomes brittle and easily breaks, and the adhesive layer peels off.

<Method for forming oxide film on aluminum foil>
In the present invention, as a method for forming the oxide film on the aluminum foil, a method in which the aluminum foil is subjected to alternating current electrolysis treatment in an electrolytic solution of an alkaline aqueous solution can be suitably employed. A method including the steps (a) and (b).
(A) A step of carrying out an alternating current electrolytic treatment under the conditions of pH 9 to 13 and an alkaline aqueous solution having a liquid temperature of 35 to 80 ° C. as an electrolytic solution and a frequency of 20 to 100 Hz, a current density of 4 to 50 A / dm 2 and an electrolysis time of 5 to 60 seconds.
(B) A step of immersing the aluminum foil in the electrolytic solution for 3 to 60 seconds.

  Here, in the step (a), one side of the aluminum foil is placed instead of the electrode so as to face the counter electrode, and an alternating current electrolysis treatment is performed in the alkaline electrolyte. By optimizing the conditions combined with the step (b) described later, electrolytic treatment is performed to form a porous oxide film layer having a thickness of 20 to 500 nm on the outer surface of the aluminum, and a barrier type oxide film having a thickness of 3 to 30 nm on the aluminum substrate side. Each layer is formed. In addition, although the above is a case where an oxide film is formed only on one surface of the aluminum foil, an oxide film may be provided on both surfaces of the aluminum foil in the present invention. In order to form a porous oxide film layer and a barrier-type oxide film layer on the treated surface and the other surface, for example, a counter electrode may be disposed on the other surface side and electrolytic treatment may be performed in the same manner as described above. If an untreated aluminum foil is sandwiched between electrodes when performing AC electrolytic treatment, a film can be simultaneously formed on both surfaces, which is industrially advantageous because the number of steps can be reduced.

  In the AC electrolytic treatment step (a), an electrode such as a graphite electrode is used as the other electrode, but it is not particularly limited. In addition, alkaline aqueous solutions used as electrolytic solutions include phosphates such as sodium phosphate, potassium hydrogen phosphate, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate; alkalis such as sodium hydroxide and potassium hydroxide. A metal hydroxide, an ammonium hydroxide solution, or an aqueous solution of a mixture thereof can be used. Since it is necessary to keep the pH of the electrolytic solution in a specific range as will be described later, it is preferable to use an alkaline aqueous solution containing a phosphate-based substance that can be expected to have a buffer effect. Moreover, although the density | concentration of an alkali component is adjusted so that pH of electrolyte solution may become a desired value, it is 1 * 10 <-4> -1 mol / liter normally. In addition, you may add surfactant to these alkaline aqueous solution for the improvement of the removal capability with respect to a soil component.

  The pH of the electrolytic solution is recommended to be 9 to 13, and more preferably 9.5 to 12. When the pH is less than 9, the porous structure of the porous oxide film layer may be incomplete, and when the pH exceeds 13, the porous oxide film layer is difficult to grow and has a desired thickness. In addition, the formation of a barrier-type oxide film layer may be hindered.

  In the step (a), it is recommended that the electrolytic solution temperature be 35 to 80 ° C, and more preferably 40 to 70 ° C. When the electrolytic solution temperature is less than 35 ° C., the porous structure of the porous oxide film layer may be incomplete, and when it exceeds 80 ° C., growth of both the porous oxide film layer and the barrier oxide film layer is inhibited. There is a case.

  In alkaline AC electrolysis, the thickness of the entire oxide film including the porous oxide film layer and the barrier oxide film layer is controlled by the quantity of electricity, that is, the product of the current density and the electrolysis time. As the number increases, the thickness of the entire oxide film increases. It is recommended that the electrolytic conditions of the porous oxide film layer and the barrier oxide film layer be adjusted as follows.

  Furthermore, it is recommended that the frequency be 20-100 Hz. If it is less than 20 Hz, the formation of the porous structure of the porous oxide film layer does not proceed and a dense structure may be obtained. On the other hand, if it exceeds 100 Hz, the formation of the entire oxide film becomes extremely slow, and both the porous oxide film layer and the barrier type oxide film layer require a very long time to obtain a predetermined thickness, which is industrially disadvantageous. It may become.

  The current density is preferably 4 to 50 A / dm2. When the current density is less than 4 A / dm 2, only the barrier type oxide film layer is preferentially formed, and therefore the porous oxide film layer may not be obtained. On the other hand, if it exceeds 50 A / dm 2, it becomes difficult to control the thickness of the porous oxide film layer and the barrier oxide film layer, and a desired film cannot be obtained.

  In the step (a), the electrolytic treatment time is preferably 5 to 60 seconds. If the treatment time is less than 5 seconds, the formation of the porous oxide film layer and the barrier type oxide film layer is too rapid, so that neither oxide film layer is sufficiently formed, and the oxide film is composed of amorphous aluminum oxide. It may become. On the other hand, if it exceeds 60 seconds, the porous oxide film layer and the barrier oxide film layer may become too thick or redissolved, and the productivity may decrease.

  Next, in the step (b), it is preferable to continue immersing the treated aluminum foil in the electrolytic solution used in the step (a) for 3 to 60 seconds. Thereby, the diameter of the small hole of a porous oxide-film layer can be controlled appropriately. According to the knowledge of the present inventors, the diameter of the small holes obtained by the AC electrolytic treatment using the above electrolytic solution and electrolytic conditions is often about 5 to 20 nm. If it is kept immersed in the solution for 3 to 60 seconds, a desired small hole having a diameter of 25 to 120 nm is obtained. If the immersion time is less than 3 seconds, the diameter of the small holes remains small, whereas if the time exceeds 60 seconds, the diameter of the small holes may become too large.

  Incidentally, as a method for artificially forming an oxide film layer in the prior art, direct current anodizing treatment (so-called alumite treatment or anodizing treatment) can be mentioned. This is a technique in which an acidic electrolytic solution is mainly used, and direct current electrolysis is performed using an aluminum material to be treated as an anode. Is extremely difficult. That is, the thickness of the oxide film layer in the prior art anodic oxidation treatment is several μm or more, and the order is completely different. It is difficult to control thin film thicknesses such as the porous oxide film layer (20 nm to 500 nm) and the barrier oxide film layer (3 to 30 nm) in the present invention. In addition, it is almost impossible to form a barrier-type oxide film layer at the interface between the aluminum foil substrate and the porous oxide film.

  Moreover, the form of the film | membrane produced | generated by the electrolytic condition may differ from the oxide film formed in the aluminum material surface by performing the anodizing process of a prior art. Films formed by direct current electrolysis are roughly divided into two types: barrier type oxide films and porous type oxide films. Among them, the porous oxide film has a hexagonal cell structure having a hexagonal shape, and has a hole in the center thereof. Usually, a treatment for closing the hole is performed to improve the corrosion resistance of the oxide film. This is called sealing treatment, so that an aluminum material with an oxide film formed is immersed in boiling water or a water bath solution of nickel acetate or cobalt acetate, or an aluminum material with an oxide film formed in a pressurized steam environment is retained. In this way, the oxide film is hydrated to form a hydroxide, which closes the pore wall. However, this method can obstruct the achievement of the requirements of the present invention because the method closes the hole in the oxide film generated by the anodizing treatment. That is, since the upper portion of the porous oxide film generated by using the electrolytic treatment of the present invention is covered with hydroxide, the adhesive cannot be taken into the porous oxide film layer, and the adhesion is improved. It becomes difficult.

<Battery exterior material>
The battery outer packaging material of the present invention can be composed of a laminated structure consisting of a sealant layer / adhesive layer / oxide film layer / aluminum foil layer from the side in contact with the electrolyte solution, with the predetermined oxide film layer interposed therebetween. The sealant layer and the adhesive layer only have to be bonded to the aluminum foil, and the configuration is not particularly limited. For example, sealant layer / adhesive layer / oxide film layer / aluminum foil layer / oxide film layer / adhesion layer / A laminated structure of base layers may be used.

<Sealant layer (electrolyte contact side film layer)>
A polyolefin film layer can be used as the sealant layer, and the polyolefin film is laminated by pressure bonding by a known method. Here, as the polyolefin-based film, a known film can be used, but it is recommended that the film contains at least an acid-modified polyolefin. The acid-modified polyolefin film may be used alone, or the acid-modified polyolefin film and other films may be used. It may be a two-layer structure film in which a polyolefin film is bonded by coextrusion. Further, it may be a two-layer structure film in which an acid-modified polyolefin film and a polyamide film or a polyester film are bonded. The structure as the film layer is not particularly limited, and may be a three-layer structure or a four-layer structure as desired. As the acid-modified polyolefin film in the polyolefin-based film, the same type as the acid-modified polyolefin in the organosol is used. Therefore, when maleic anhydride-modified polypropylene is used as the acid-modified polyolefin in the organosol, maleic anhydride-modified polypropylene can be used as the acid-modified polyolefin film in the polyolefin film.

  The method of laminating the sealant layer is not particularly limited. For example, when performing hot melt lamination, an adhesive layer of an aluminum foil in which an adhesive layer is formed on an oxide film in advance and an acid-modified polyolefin of a polyolefin film. Lamination is completed by abutting the film surface or a treatment surface on which the polyolefin-type film is appropriately activated and press-bonding. This lamination can generally be performed under heating, and the heating condition is performed at about 160 to 240 ° C. The lamination conditions are a pressure of 0.5 to 2 kg / cm <2> and a time of about 0.5 to 3 seconds, but these conditions are not particularly limited.

  Moreover, the thickness of the polyolefin film as the sealant layer is not particularly limited, but usually a thickness of 5 μm or more is necessary, and a preferable thickness is 10 to 100 μm. If the thickness is too thin, the thermal conductivity is too high during heat sealing, the film may melt, and defects may occur in the heat sealing portion. If the thickness is too thick, the heat conductivity is low when the laminate is hot melted, so that heat is hardly transmitted to the entire aluminum foil, and the adhesive is not sufficiently melted.

<Adhesive layer>
The battery exterior material of the present invention is provided with an adhesive layer between the sealant layer and the oxide film. By providing this adhesive layer, it is possible to firmly adhere to the excellent oxide film and stably hold the sealant layer. The adhesive layer can be formed by applying an organosol having an acid-modified polyolefin as a solid content as an adhesive.

  Here, the acid-modified polyolefin is obtained by adding a dicarboxylic acid to the side chain of polyethylene or polypropylene, and is generally preferably obtained by adding maleic acid or maleic anhydride to the side chain of polypropylene. . An organosol having an acid-modified polyolefin as a solid content refers to a colloid solution in which an acid-modified polyolefin is colloidally dispersed in an organic liquid. As the organic liquid, a hydrocarbon-based liquid is used, and toluene can be mainly used. Moreover, about 5-50 mass% can be used for solid content concentration of organosol. After the organosol is applied to the surface of the porous oxide film layer, the organosol is introduced into a drying step and dried. Drying conditions are a temperature of 150 to 220 ° C. and a time of about 5 to 40 seconds. By this drying step, the organosol is solidified and becomes an adhesive layer. In the organosol, since the acid-modified polyolefin is dispersed in a colloidal form, it is applied relatively uniformly on the surface of the porous oxide film layer, and a uniform adhesive layer is obtained. By providing the adhesive layer on the surface of the porous oxide film layer, it becomes possible to adhere a film having no adhesiveness.

<Opposite surface of aluminum foil>
The battery exterior material of the present invention may be bonded to a substrate layer film described later on the surface opposite to the surface on which the sealant layer is provided, and this substrate layer film is made of an aluminum foil by a known adhesive or method. Can be glued to.

<Adhesive for base layer film>
As the adhesive used for the base layer film, for example, a two-component curable urethane adhesive, a polyether urethane adhesive, a polyester adhesive, a polyester polyol adhesive, a polyester polyurethane polyol adhesive, or the like was used. Methods such as dry lamination, coextrusion, extrusion coating, thermal lamination using an anchor coating agent, and the like can be adopted, but the dry lamination method is particularly preferable. In particular, it is preferable to laminate by a dry laminating method using an adhesive containing a urethane resin, and more preferably, laminating by an dry laminating method using an adhesive containing an epoxy-containing urethane resin. In addition, although the thickness of the contact bonding layer formed with an adhesive material is not restrict | limited in particular, Usually, it is preferable that it is 1-10 micrometers, and it is more preferable that it is especially 3-7 micrometers. If the thickness is too thin, the adhesive layer cannot follow the surface irregularities of the layer to be coated, resulting in uneven formation of the layer and possible adhesion failure during bonding. If it is too thick, it takes time to dry the adhesive layer, and excess adhesive may protrude from the end of the laminate during lamination. Also, simply increasing the total thickness of the aluminum foil and film and increasing the weight may increase the cost.

<Base material layer film>
It is preferable to manufacture the base material layer film which is the arbitrary structure of this invention as a kind, for example from a film extending | stretching polyester or a nylon film. Examples of the polyester resin here 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. When the film is used as a lithium ion battery, a film having insulating properties is basically preferable.

  The base film of the present invention can be further laminated in order to improve pinhole resistance and insulation when used as a battery exterior material. When the base film is used as a component of the exterior material, the base film includes at least one resin layer of two or more layers, and the thickness of each layer is 6 μm or more, preferably 12 to 25 μm. If the thickness is small, the barrier property of water vapor and other gases may be inferior, and the puncture resistance due to external pressurization may be inferior. If it is too thick, simply increasing the total thickness of the exterior material and increasing the weight may increase costs.

<Corona treatment>
In the present invention, in the configuration of the exterior material other than the aluminum foil and the oxide film, in order to improve the mutual adhesion of each layer of the exterior material, a desired surface treatment can be performed in advance on each layer as necessary. . As the surface treatment method, for example, corona treatment, ozone treatment, low-temperature plasma treatment using oxygen gas or nitrogen gas, glow discharge treatment, oxidation treatment using chemicals, etc. are optionally performed. Thereby, the adhesiveness between each layer improves.

  The laminated structure of the exterior material of the present invention may be a sealant layer / adhesive layer / oxide film layer / aluminum foil layer from the side in contact with the electrolytic solution, and optionally a sealant layer / adhesive layer / oxide film layer / aluminum foil. Layer / oxide film layer / adhesion layer / base material layer film. The sealant layer ensures sealing performance against the electrolytic solution and suppression of water vapor permeation from the cross-sectional direction. The oxide film layer ensures adhesion with the adhesive layer and electrolyte solution characteristics. The aluminum foil ensures the barrier property to prevent moisture, gas, oxygen and the like from entering the inside of the battery and the moldability and rigidity of the exterior material itself. Although a base material layer film is arbitrary structures in this invention, the metal foil protection from the outside, piercing property, and heat resistance are ensured. And an adhesive bond layer contributes to the adhesive improvement of each layer. Such a laminated structure is a general structure except for the oxide film layer of the present invention, but by providing the oxide film of the predetermined structure of the present invention on the surface of the aluminum foil, the aluminum foil and the adhesive layer are adhered to each other. It is possible to contribute to further improving the formability of the entire exterior material of the sealant layer / adhesive layer / oxide film layer / aluminum foil layer and improving the electrolytic solution resistance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to the following Example.

  An aluminum foil (8000 series alloy) having a thickness of 40 μm was prepared. A working electrode having this aluminum foil as an electrode was used, and a graphite electrode was used as a counter electrode. One side of the aluminum foil was made to face the counter electrode, and both electrodes were arranged so that a porous oxide film layer on the surface side and a barrier type oxide film layer on the substrate side were formed on the surface layer on the one side facing the aluminum foil. An alkaline aqueous solution mainly composed of sodium pyrophosphate was used as the electrolytic solution. The concentration of these alkali components was 0.5 mol / liter, and the pH was adjusted with hydrochloric acid and a sodium hydroxide aqueous solution (both concentrations were 0.1 mol / liter). Under the electrolysis conditions shown in Table 1, alternating current electrolysis was performed to form a porous oxide film layer and a barrier oxide film layer.

  The aluminum foil produced as described above was examined by SEM and TEM. Specifically, the thickness of the porous oxide film layer and the barrier-type oxide film layer, and the diameter of the small holes in the porous oxide film layer were measured by TEM observation of a thin sample prepared by an ultramicrotome, and an observation field (1 μm × The average value of the measurement results at 10 arbitrary points in 1 μm) was recorded. The survey results are shown in Table 1.

  Next, an adhesive made of modified polyolefin is further uniformly applied to the oxide film layer obtained above with a bar coater, and dried and baked at 200 ° C. for 20 seconds. The basis weight is 1.0 ± 0.00. An adhesive layer of 5 g / m 2 was formed. This adhesive layer was subjected to corona treatment to form a corona-treated surface of a CPP film having a thickness of 60 μm, and bonded to the adhesive layer side, and hot melt lamination was performed at a temperature of 110 ° C. and 1 m / min. As described above, a battery exterior material (hereinafter referred to as a sample) was laminated in the order of (heat sealing layer) / CPP film / modified polyolefin adhesive layer / oxide film layer / aluminum foil.

The characteristics of the test pieces thus prepared were evaluated by the following tests (a) to (c).
(A) Heat seal strength The sample was cut into 200 mm × 10 mm, the CPP surface was overlapped with an area of 100 mm × 10 mm, and the range of 10 mm × 15 mm was heat sealed with a heat sealer manufactured by Yasuda Seiki Seisakusho. Sealing conditions were a temperature of 180 ° C., a pressure of 2.4 kg / G pressure, and a time of 2 seconds. After heat sealing, the sealing strength was measured with a tensile tester at a peeling speed of 50 mm / min and a peeling angle of 180 °. After the measurement, the retort pouch was classified according to the JAS standard value (Article 10) of the sealing strength of the retort pouch.
○: 15.3 N / cm or more ×: less than 15.3 N / cm ○ was accepted and x was rejected.

(B) Peeling mode evaluation The peeled surface of the sample after heat seal strength measurement was visually confirmed and classified according to the following criteria.
○: Film / film cohesive failure ×: Adhesive layer / aluminum foil interface peeling ○ was accepted and x was rejected.

(C) Electrolytic solution property test Two quadrilateral pieces 90 mm long and 50 mm wide are cut from the sample, and the two quadrilateral pieces are laminated so that the heat sealing layers are in contact with each other. Was sealed with a width of 5 mm to prepare a quadrilateral bag. The heat sealing conditions were a temperature of 200 ° C., a pressure of 2 kg / cm 2 and a time of 1 sec. As an electrolyte, 0.27 ml of 1 mol / L LiPF6 / EC: EMC (3: 7) is prepared. In the glove box (dew point −80 ° C. or lower), an electrolyte solution was injected from the mouth of the bag. Finally, the bag mouth was heat sealed under the same conditions as the previous conditions to obtain a quadrilateral bag. After holding at 85 ° C. for 1 day, 3 days, and 7 days, the sample is disassembled, washed with pure water, and the appearance of the sample taken out is confirmed. Based on the presence or absence of peeling, the adhesion of the film and the aluminum foil and the corrosion resistance of the ground treatment are evaluated.
○: No peeling after 7 days.
X: Peeling after 7 days.
○ was accepted and x was rejected.

The evaluation results are shown in Table 2.

  As shown in Table 2, since Examples 1 to 23 satisfied the specified requirements of the present invention, the heat seal strength, the peeling mode evaluation, and the electrolytic solution resistance were all good.

On the other hand, in Comparative Example 1, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 2, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 3, the heat seal strength, the peeling mode evaluation, and the electrolytic solution characteristics failed.
In Comparative Example 4, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 5, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 6, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 7, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 8, the heat seal strength, the peeling mode evaluation, and the electrolytic solution characteristics failed.
In Comparative Example 9, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 10, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 11, the heat seal strength and the peeling mode evaluation failed.
In Comparative Example 12, the heat seal strength and the peeling mode evaluation failed.

Claims (4)

  A battery exterior material comprising a sealant layer, an adhesive layer, and an aluminum foil, wherein the aluminum foil has an oxide film formed on the surface by electrolytic treatment, and the oxide film is a barrier-type oxide film layer, What is claimed is: 1. A battery exterior material comprising a porous oxide film layer, wherein the porous oxide film layer has a thickness of 20 to 500 nm, and small pores having a diameter of 25 to 120 nm are formed on the surface.   2. The battery packaging material according to claim 1, wherein the barrier oxide film layer has a thickness of 3 to 30 nm.   3. The battery packaging material according to claim 1, wherein the aluminum foil is subjected to alternating current electrolysis in an alkaline aqueous electrolytic solution.   The aluminum foil for battery exterior materials of any one of Claims 1-3.