JP7376970B2 - Exterior material for power storage devices - Google Patents

Description

The present invention relates to an exterior material for a power storage device.

As power storage devices, for example, secondary batteries such as lithium ion secondary batteries, nickel metal hydride batteries, and lead storage batteries, and electrochemical capacitors such as electric double layer capacitors are known. BACKGROUND ART Due to the miniaturization of portable devices and restrictions on installation space, there is a demand for further miniaturization of power storage devices, and lithium ion secondary batteries with high energy density are attracting attention. Traditionally, metal cans were used as the exterior material for lithium-ion secondary batteries, but recently multilayer films have come to be used, which are lightweight, have high heat dissipation properties, and can be manufactured at low cost. There is.

The electrolytic solution of a lithium ion secondary battery is composed of an aprotic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and an electrolyte. As the electrolyte, lithium salts such as LiPF ₆ and LiBF ₄ are used. These lithium salts generate hydrofluoric acid through a hydrolysis reaction with moisture. Hydrofluoric acid may cause corrosion of the metal surfaces of battery components or a decrease in the strength of the laminate between the layers of the multilayer film that is the exterior material.

Therefore, in the above-mentioned exterior material, an aluminum foil or the like is provided as a barrier layer inside the multilayer film to suppress the infiltration of moisture from the surface of the multilayer film. The above-mentioned exterior material is, for example, a multi-layered structure in which a heat-resistant base material layer, a first adhesive layer, a barrier layer, a corrosion prevention layer that prevents corrosion by hydrofluoric acid, a second adhesive layer, and a sealant layer are laminated in this order. film is known. A lithium ion secondary battery using an exterior material including aluminum foil as a barrier layer is also called an aluminum laminate type lithium ion secondary battery.

As a type of aluminum laminate type lithium ion secondary battery, there is one called an embossed type. Embossed type lithium ion secondary batteries require, for example, a process of forming a recess in a part of the exterior material by cold molding, and a process of accommodating battery elements (positive electrode, separator, negative electrode, electrolyte, etc.) in this recess. Then, the remaining part of the exterior material is folded back and the edges are heat-sealed.

By forming a deep recess in which the battery element is housed, it is possible to manufacture a lithium ion secondary battery with a large battery capacity. However, in recent years, there has been a demand for thinner portable devices such as smartphones. For this reason, there is a tendency to avoid increasing the battery thickness due to deep recesses, and instead use thin batteries with a large area to ensure battery capacity.

Under such circumstances, there is also a demand for thinner exterior materials for power storage devices. Conventionally, stretched films have been widely used as the base layer of exterior materials, and exterior materials have generally been made by laminating this and other layers or films via adhesives. From the perspective of reducing the thickness of the entire exterior material, Patent Document 1 proposes providing an epoxy resin layer with a thickness of 5 to 10 μm by applying an epoxy resin to the outer surface of the aluminum foil constituting the barrier layer. Disclosed.

Japanese Patent Application Publication No. 2001-176465

By the way, Patent Document 1 discloses that in order to improve the slipperiness between the inner surface of the laminated film (the surface of the heat-adhesive resin layer) and the male die, the inner surface of the laminated film is coated with a lubricant or the heat-adhesive resin layer is coated with a lubricant. It is disclosed that the friction coefficient of the inner surface should be maintained at 0.4 or less by adding a lubricant to the inner surface (see paragraph [0021] of Patent Document 1). However, simply reducing the friction coefficient of the inner surface of the laminated film to a predetermined value or less does not provide sufficient moldability of the laminated film, and there is room for improvement in that it is difficult to form recesses of a desired depth.

In view of the above circumstances, the present inventors developed a coating layer with a lubricant added thereto to replace the conventional base film such as stretched film, in order to improve the slipperiness not only on the inner surface but also on the outer surface of the exterior material. We considered applying a coating liquid to the outside of the barrier layer. As a result, it was found that although the use of a coating liquid containing a lubricant improved the moldability of the exterior material, there was a problem in that printing could not be done on the surface of the coating layer. Since various types of information are usually displayed on the outer surface of a power storage device, it is required to be able to print on the outermost layer of the exterior material (printability).

An object of the present invention is to provide a sufficiently thin exterior material for a power storage device that can achieve both excellent moldability and excellent printing properties of the outermost layer at a sufficiently high level.

The exterior material for a power storage device according to the present invention (hereinafter simply referred to as "exterior material" in some cases) includes a coating layer having a surface with a water wetting contact angle in a range of 40 to 80 degrees, a barrier layer, and a sealant layer in this order from the outside to the inside. The "wetting contact angle of water" here refers to the relationship between the tangent and the surface of the coating layer when a tangent is drawn from the area where water and air come into contact to the curved surface of the water on the surface of the coating layer onto which 1 μg of water is dropped. means the angle formed by This water wetting contact angle can be measured according to the method (sessile drop method) described in JIS R3257:1999.

In the above-mentioned exterior material, a coating layer is used instead of a conventional base film such as a stretched film. Since the coating layer can be formed sufficiently thin, the entire exterior material can be made sufficiently thin. In addition, since the surface of the coating layer has a water wetting contact angle within a predetermined range (40 to 80 degrees), it achieves a sufficiently high level of both excellent moldability and excellent printability of the outermost layer. can do.

The coating layer preferably contains an inorganic or organic filler. By employing such a configuration, it is possible to achieve even higher levels of both excellent moldability and excellent printability of the outermost layer.

The coating layer preferably contains at least one resin selected from the group consisting of polyester resins, urethane resins, fluororesins, epoxy resins, amino resins, acrylic resins, phenol resins, and alkyd resins. By forming the coating layer with these resins, the coating layer can have sufficient electrolyte resistance.

Preferably, the barrier layer is made of a metal foil selected from the group consisting of aluminum foil, copper foil, and stainless steel foil. By employing these metal foils as a barrier layer, the exterior material can have sufficient stretchability.

The exterior material may further include an adhesive layer between the barrier layer and the sealant layer. From the viewpoint of ensuring excellent slipperiness on the inner surface side (sealant layer side) of the exterior material and achieving excellent moldability of the exterior material, the adhesive layer is preferably made of an acid-modified polyolefin resin.

According to the present invention, it is possible to achieve a sufficiently high level of both excellent moldability and excellent printability of the outermost layer, and a sufficiently thin exterior material for an electricity storage device is provided.

FIG. 1 is a cross-sectional view schematically showing an embodiment of the exterior material according to the present invention. FIG. 2(a) is a perspective view showing an embossed type exterior material obtained by processing the exterior material shown in FIG. 1, and FIG. 2(b) is a perspective view taken along line bb shown in FIG. 2(a). FIG. FIG. 3(a) is a perspective view showing a state in which the exterior material shown in FIG. 1 is prepared, and FIG. 3(b) is a perspective view showing a state in which the exterior material and battery element shown in FIG. 2(a) are prepared. Fig. 3(c) is a perspective view showing a state in which a part of the exterior material is folded back and the ends are melted, and Fig. 3(d) is a perspective view showing a state in which both sides of the folded part are folded upward. It is a diagram.

Embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be omitted.

<Exterior material for power storage devices>
FIG. 1 is a cross-sectional view schematically showing the exterior material according to this embodiment. The exterior material 10 shown in the figure is made of a multilayer film comprising at least a coating layer 13 as the outermost layer, a metal foil (barrier layer) 11 exhibiting a barrier function, and a sealant layer 16 as the innermost layer in this order. Become. More specifically, the exterior material 10 includes a coating layer 13, a first corrosion prevention layer 12a formed on the first surface 11a of the metal foil 11, a metal foil 11, and a second surface of the metal foil 11. The second corrosion prevention layer 12b, adhesive layer 15, and sealant layer 16 formed on layer 11b are laminated in this order from the outside to the inside. When forming a power storage device using the exterior material 10, the coating layer 13 becomes the outermost layer and the sealant layer 16 becomes the innermost layer, as described above.

[Metal foil]
As the metal foil 11, various metal foils made of aluminum, copper, copper alloy, stainless steel, nickel, iron, magnesium, titanium, etc. can be used. Therefore, aluminum foil, copper foil or stainless steel foil is preferable. Aluminum foil is more preferable in terms of cost. As the aluminum foil, a general soft aluminum foil can be used. Among these, aluminum foil containing iron is preferred because it has excellent pinhole resistance and spreadability during molding.

When the total mass of the aluminum foil containing iron is 100 parts by mass, the iron content of the aluminum foil is preferably 0.1 to 9.0 parts by mass, more preferably 0.5 to 2.0 parts by mass. be. When the iron content is 0.1 parts by mass or more, the exterior material 10 has excellent pinhole resistance and spreadability. If the iron content is 9.0 parts by mass or less, the exterior material 10 has excellent flexibility.

The thickness of the metal foil 11 is preferably 9 to 200 μm, more preferably 15 to 100 μm, from the viewpoint of barrier properties, pinhole resistance, workability, and the like.

[Coating layer]
The coating layer 13 provides heat resistance in the sealing process when manufacturing the electricity storage device and/or electrolyte resistance that does not deteriorate even if the electrolyte is attached, and prevents pinholes that may occur during processing or distribution. Plays a role in suppressing outbreaks. The coating layer 13 is formed through a process of coating a coating liquid containing resin, and is preferably formed directly on the first corrosion prevention layer 12a without using an adhesive layer.

When 1 μg of water is dropped on the surface of the coating layer 13, when a tangent is drawn to the curved surface of the water from the area where the coating layer, water, and air come into contact, the relationship between this tangent and the surface of the coating layer 13 is The angle (wetting contact angle) is preferably 40 degrees to 80 degrees (see JIS R3257:1999). More preferably, this angle is between 50 degrees and 70 degrees. If the wetting contact angle is 40 degrees or more, the affinity with the mold surface during molding will be reduced, promoting the flow of the exterior material into the molding area, and improving moldability. When the angle is 80 degrees or less, repelling of ink during printing on the coating layer 13 is sufficiently suppressed, resulting in excellent printing performance. The wetting contact angle can be adjusted by the type of main resin constituting the coating layer, and the type and content of additives such as fillers.

For the coating layer 13, various resins such as polyester, urethane, fluorine, epoxy, amino, acrylic, phenol, alkyd, or polyvinyl alcohol can be used. , epoxy resin, and acrylic resin are preferred. Polyester resins and urethane resins are more preferred from the viewpoint of followability during stretching to the metal foil 11.

Polyester resins include solvent-soluble types and water-dispersible types. Examples of the solvent-soluble type include those obtained by replacing a part of polyalcohol such as ethylene glycol with cyclohexanedimethanol or neopentyl glycol. From the viewpoint of solvent solubility, the polyester resin is more preferably an amorphous polyester obtained by replacing a part of ethylene glycol with cyclohexanedimethanol in polyethylene terephthalate obtained by dehydration condensation of terephthalic acid and ethylene glycol. Amorphous polyester resins can be used alone or in combination. As a water-dispersed type, for example, a polyester with a chemical structure obtained by polycondensation of a carboxylic acid component consisting of a polyhydric carboxylic acid compound of divalent or higher valence and an alcohol component consisting of a polyhydric alcohol compound of divalent or higher valence, and a sulfonic acid Examples include coating liquids in which hydrophilic polar groups such as metal bases, carboxyl groups, and phosphoric acid groups are introduced and dispersed in water.

Examples of urethane resins include two-component curing type and water dispersion type. Two-component curing types include, for example, acrylic polyols, polyester polyols, polyether polyols, etc. that have a hydroxyl group in the molecule as the main ingredient, and TDI (toluene diisocyanate) and MDI (diphenylmethane diisocyanate) that have an NCO partial structure in the molecule. Examples include coating liquids to which isocyanates such as XDI (xylylene diisocyanate), IPDI (isophorone diisocyanate), and HDI (hexamethylene diisocyanate) are added as a curing agent. After coating, the solvent is dried, and in order to promote the reaction between the hydroxyl group and the isocyanate, an aging treatment is performed at, for example, 60° C. for 5 days to form a coating film. Examples of water-dispersible types include polyol components such as polyether diol, polyester diol, and polycarbonate diol that have a hydroxyl group in the molecule, and TDI, MDI, XDI, IPDI, and HDI systems that have an NCO partial structure in the molecule. Examples include coating liquids in which hydrophilic groups are introduced (self-emulsifying type) into the reaction products with isocyanates such as, and dispersed in water.

The coating layer 13 preferably contains an inorganic or organic filler. By containing the filler in the coating layer 13, it is possible to achieve even higher levels of both excellent moldability and excellent printability of the outermost layer.

Inorganic fillers include oxides such as silica, silica zirconia, silica titania, aluminosilicate glass, barium glass, quartz and alumina; hydroxides such as calcium hydroxide; carbonates such as calcium carbonate; and barium sulfate. talc, mica, and silicates such as wollastonite. Among these, silica and calcium carbonate are preferred because they are spherical in shape and easily provide slipperiness. Among these, one type may be used alone, or two or more types may be used in combination.

The surface of the inorganic filler is vinyltriethoxysilane, vinyl-tris(β-methoxyethoxy)silane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, β- (3,4-epoxycyclohexyl)-ethyltrimethoxysilane, γ-glycidoxypropyl-trimethoxysilane, N-β-(aminoethyl)-γ-aminopropyl-trimethoxysilane, γ-ureidopropyl-triethoxy It may be treated with a silane coupling agent such as silane, γ-chloropropyltrimethoxysilane, and vinyltrimethoxysilane. Since the surface of the inorganic filler is treated with a silane coupling agent, it is easy to obtain adhesive strength with the main component of the coating liquid for forming the coating layer 13 (the above-mentioned resin).

Examples of the organic filler include acrylic resin, benzoguanamine resin, and melamine resin. The shape of these fillers is preferably spherical from the viewpoint of slipperiness. Among these, one type may be used alone, or two or more types may be used in combination.

The particle size of the inorganic or organic filler is preferably 1.0 μm to 10.0 μm from the viewpoint of slipperiness. Further, the amount of the inorganic or organic filler added is preferably 0.5 to 5.0 parts by mass based on 100 parts by mass of the coating layer 13 in order to impart sufficient slipperiness to the coating layer 13. and more preferably 1.0 to 3.0 parts by mass.

The thickness of the coating layer 13 is preferably 3 to 30 μm, more preferably 5 to 20 μm, from the viewpoint of maintaining insulation and stretchability. By directly forming the coating layer 13 on the first corrosion prevention layer 12a formed on the first surface 11a of the metal foil 11, and by setting the thickness of the coating layer 13 to, for example, 20 μm or less, the conventional It is also easy to make it thinner than the exterior material.

[Corrosion prevention layer]
The first corrosion prevention layer 12a and the second corrosion prevention layer 12b (hereinafter referred to as "corrosion prevention layer") suppress corrosion of the metal foil 11 caused by electrolyte or hydrofluoric acid generated by reaction between the electrolyte and water. play a role. The anti-corrosion layer also serves to enhance the adhesion between the coating layer 13 and the metal foil 11, as well as between the metal foil 11 and the adhesive layer 15.

Examples of the corrosion prevention layer include a coating film formed with a coating type or dipping type acid-resistant corrosion prevention treatment agent, or a layer of metal oxide derived from the metal constituting the metal foil 11. Such a coating film or layer has an excellent corrosion prevention effect against acids. Examples of coating films include coatings formed by ceriazole treatment with corrosion inhibitors made of cerium oxide, phosphates, and various thermosetting resins, and coatings formed using chromates, phosphates, fluorides, and various thermosetting resins. Examples include coating films formed by chromate treatment with a corrosion prevention treatment agent made of resin. Note that the coating film is not limited to those described above as long as it can provide sufficient corrosion resistance of the metal foil 11. For example, a coating film formed by phosphate treatment, boehmite treatment, etc. may be used. On the other hand, examples of the metal oxide layer derived from the metal constituting the metal foil 11 include layers depending on the metal foil 11 used. For example, when aluminum foil is used as the metal foil 11, the aluminum oxide layer functions as a corrosion prevention layer. These corrosion-inhibiting layers can be used as a single layer or in combination of multiple layers. Moreover, the first corrosion prevention layer 12a and the second corrosion prevention layer 12b may have the same structure or may have different structures. Additives such as silane coupling agents may be added to the corrosion prevention layer.

The thickness of the corrosion prevention layer is preferably 10 nm to 5 μm, more preferably 20 to 500 nm, from the viewpoint of corrosion prevention function and anchor function.

[Adhesive layer]
The adhesive layer 15 is a layer that adheres the metal foil 11 on which the second corrosion prevention layer 12b is formed and the sealant layer 16. The exterior material 10 can be roughly divided into two types, a thermal lamination structure and a dry lamination structure, depending on the adhesive component forming the adhesive layer 15.

In the case of a thermally laminated structure, the adhesive component forming the adhesive layer 15 is preferably an acid-modified polyolefin resin obtained by graft-modifying a polyolefin resin with an acid such as maleic anhydride. Since the acid-modified polyolefin resin is a non-polar polyolefin resin with a polar group introduced into a part thereof, for example, a non-polar layer formed of a polyolefin resin film or the like is used as the sealant layer 16, Further, when a polar layer is used as the second corrosion prevention layer 12b, it is possible to firmly adhere to both of these layers. Further, by using an acid-modified polyolefin resin, resistance to contents such as electrolyte is improved, and even if hydrofluoric acid is generated inside the battery, it is easy to prevent a decrease in adhesion strength due to deterioration of the adhesive layer 15. Note that the acid-modified polyolefin resin used for the adhesive layer 15 may be one type or two or more types.

Examples of the polyolefin resin used in the acid-modified polyolefin resin include low density, medium density or high density polyethylene; ethylene-α olefin copolymer; homo, block or random polypropylene; propylene-α olefin copolymer, etc. Can be mentioned. Furthermore, copolymers obtained by copolymerizing the above-mentioned materials with polar molecules such as acrylic acid and methacrylic acid, and polymers such as crosslinked polyolefins can also be used. In addition, examples of the acid that modifies the polyolefin resin include carboxylic acids, acid anhydrides, and the like, and maleic anhydride is preferable.

In the case of a thermally laminated structure, the adhesive layer 15 can be formed by extruding the adhesive component using an extrusion device.

In the case of a dry laminate structure, the adhesive component of the adhesive layer 15 is, for example, a base agent such as polyester polyol, polyether polyol, acrylic polyol, etc., and a bifunctional or higher functional aromatic or aliphatic isocyanate compound acting as a curing agent. Examples include two-component curing polyurethane adhesives. However, since the polyurethane adhesive has highly hydrolyzable bonding parts such as ester groups and urethane groups, a thermal lamination structure is preferable for applications requiring higher reliability.

The adhesive layer 15 having a dry laminate structure can be formed by applying an adhesive component onto the second anti-corrosion layer 12b and then drying it. If a polyurethane adhesive is used, aging at 40°C for 4 days or more after coating will allow the reaction between the hydroxyl groups of the main ingredient and the isocyanate groups of the curing agent to proceed, resulting in strong adhesion. becomes.

When the adhesive layer 15 has a dry laminate configuration, the lubricant contained in the sealant layer 16 or the lubricant applied on the sealant layer 16 tends to be trapped in the adhesive layer 15, and the slipperiness of the sealant layer 16 tends to decrease. Therefore, from the viewpoint of maintaining the slipperiness of the sealant layer 16, it is preferable that the adhesive layer 15 is formed from an acid-modified polyolefin resin using an extrusion device and then laminated by thermal lamination.

The thickness of the adhesive layer 15 is preferably 2 to 50 μm, more preferably 3 to 20 μm from the viewpoint of adhesion, trackability, processability, etc.

[Sealant layer]
The sealant layer 16 is a layer that provides sealing properties by heat sealing in the exterior material 10. Examples of the sealant layer 16 include a resin film made of a polyolefin resin or an acid-modified polyolefin resin obtained by graft-modifying a polyolefin resin using an acid such as maleic anhydride.

Examples of the polyolefin resin include low density, medium density or high density polyethylene; ethylene-α olefin copolymer; homo, block or random polypropylene; propylene-α olefin copolymer. These polyolefin resins may be used alone or in combination of two or more. Examples of the acid that modifies the polyolefin resin include the same acids as those mentioned in the description of the adhesive layer 15.

The sealant layer 16 may be a single layer film or a multilayer film, and may be selected depending on the required function. For example, in terms of imparting moisture resistance, a multilayer film in which a resin such as ethylene-cyclic olefin copolymer or polymethylpentene is interposed can be used. The sealant layer 16 may contain various additives such as a flame retardant, a lubricant, an anti-blocking agent, an antioxidant, a light stabilizer, and a tackifier.

The thickness of the sealant layer 16 is preferably 5 to 50 μm, more preferably 10 to 30 μm from the viewpoint of ensuring insulation.

The exterior material 10 may be one in which the sealant layer 16 is laminated by dry lamination, but from the viewpoint of the slipperiness of the sealant layer 16, the adhesive layer 15 may be made of acid-modified polyolefin resin and sandwich lamination or coextrusion method may be used. , the sealant layer 16 is preferably laminated.

<Manufacturing method of exterior material>
Hereinafter, a method for manufacturing the exterior material 10 of this embodiment will be described. Specifically, the manufacturing method includes a method having the following steps 1 to 3, but the following content is just an example, and the manufacturing method of the exterior material 10 is not limited to the following content.

Step 1: A step of forming a first corrosion prevention layer 12a and a second corrosion prevention layer 12b on both sides (first surface 11a and second surface 11b) of metal foil 11.
Step 2: A step of forming a coating layer 13 on the first corrosion prevention layer 12a formed on the first surface 11a of the metal foil 11 using a coating layer raw material (resin material).
Step 3: A step of bonding the sealant layer 16 onto the second corrosion prevention layer 12b formed on the second surface 11b of the metal foil 11 via the adhesive layer 15.

(Step 1)
For example, a corrosion prevention treatment agent is applied to both sides of the metal foil 11 and dried to form a first corrosion prevention layer 12a and a second corrosion prevention layer 12b. Examples of the corrosion-inhibiting agent include the above-mentioned corrosion-inhibiting agent for ceriazole treatment, corrosion-inhibiting agent for chromate treatment, and the like. The method of applying the corrosion prevention treatment agent is not particularly limited, and various methods such as gravure coating, reverse coating, roll coating, and bar coating can be employed. Alternatively, by oxidizing the surface of the metal foil 11, layers of metal oxide derived from the metal constituting the metal foil 11 (the first corrosion prevention layer 12a and the second corrosion prevention layer) are formed on both sides of the metal foil 11. 12b). Note that one surface of the metal foil 11 may be treated with a corrosion-preventing treatment agent, and the other surface may be oxidized.

(Step 2)
A coating layer raw material (resin material) that will become the coating layer 13 is applied onto the first corrosion prevention layer 12a formed on the first surface 11a of the metal foil 11, and is dried to form the coating layer. form 13. The coating method is not particularly limited, and various methods such as gravure coating, reverse coating, roll coating, and bar coating can be employed. After coating, curing can be accelerated by aging treatment at 60° C. for 7 days, for example.

(Step 3)
Forming an adhesive layer 15 on the second corrosion prevention layer 12b of a laminate in which the coating layer 13, the first corrosion prevention layer 12a, the metal foil 11, and the second corrosion prevention layer 12b are laminated in this order, The laminate and the resin film forming the sealant layer 16 are bonded together. At this time, the adhesive layer 15 and the sealant layer 16 can also be laminated into a laminate by co-extruding them.

Through steps 1 to 3 described above, the exterior material 10 is obtained. Note that the process order of the method for manufacturing the exterior material 10 is not limited to a method in which steps 1 to 3 are performed sequentially. For example, step 2 may be performed after step 3.

[Method for manufacturing electricity storage device]
Next, a method for manufacturing a power storage device using the exterior material 10 will be described with reference to FIGS. 2 and 3. Here, an example will be described in which the embossed type exterior material 30 shown in FIG. 2(a) is used to manufacture the electricity storage device 40 (one-side molded battery) shown in FIG. 3(d). The power storage device may be a double-sided molded battery manufactured by using two exterior materials such as the embossed exterior material 30 and bonding these exterior materials together while adjusting the alignment. .

The power storage device 40 can be manufactured, for example, by the following steps S21 to S25 (see FIGS. 3(a) to 3(d)).
Step S21: A step of preparing the exterior material 10, the battery element 1 including the electrode, and the lead 2 extending from the electrode.
Step S22: Step of forming a recess 32 for arranging the battery element 1 on one side of the exterior material 10 (see FIG. 2).
Step S23: The battery element 1 is placed in the molding area (recess 32) of the embossed type exterior material 30, and the embossed type exterior material 30 is folded back and stacked so that the lid 34 covers the recess 32. A process of pressurizing and heat-sealing one side of the embossed type exterior material 30 so as to sandwich the existing leads 2.
Step S24: Leave one side other than the side that holds the lead 2, press and heat seal the other sides, then inject the electrolyte from the remaining side, and press and heat seal the remaining side in a vacuum state. The process of doing.
Step S25: A step of cutting the edges of the pressurized and heat-sealed edges other than the edges that sandwich the lead 2 and bending them toward the molding area (recess 32).

(Step S21)
In step S21, an exterior material 10, a battery element 1 including an electrode, and a lead 2 extending from the electrode are prepared. The exterior material 10 is prepared based on the embodiment described above. There are no particular limitations on the battery element 1 and leads 2, and known battery elements 1 and leads 2 can be used.

(Step S22)
In step S22, a recess 32 for arranging the battery element 1 is formed on the sealant layer 16 side of the exterior material 10. The planar shape of the recess 32 is a shape that matches the shape of the battery element 1, for example, a rectangular shape in plan view. The recess 32 is formed, for example, by pressing a pressing member having a rectangular pressure surface against a portion of the exterior material 10 in the thickness direction thereof. Further, the position to be pressed, that is, the recess 32, is formed at a position that is biased toward one end of the exterior material 10 in the longitudinal direction from the center of the exterior material 10 cut out into a rectangle. Thereby, after the molding process, the other end side where the recess 32 is not formed can be folded back to form a lid (lid portion 34).

More specifically, a method for forming the recess 32 includes molding using a mold (deep drawing molding). The molding method uses a female mold and a male mold arranged to have a gap equal to or greater than the thickness of the exterior material 10, and presses the male mold together with the exterior material 10 into the female mold. can be mentioned. By adjusting the amount of depression of the male mold, the depth of the recess 32 (deep drawing amount) can be adjusted to a desired amount. By forming the recesses 32 in the exterior material 10, an embossed type exterior material 30 is obtained (see FIG. 2).

(Step S23)
In step S23, the battery element 1 composed of a positive electrode, a separator, a negative electrode, etc. is placed within the molding area (recess 32) of the embossed type exterior material 30. Further, the leads 2 extending from the battery element 1 and joined to the positive electrode and the negative electrode are pulled out from the molding area (recess 32). Thereafter, the embossed type exterior material 30 is folded back at approximately the center in the longitudinal direction, and is stacked so that the sealant layers 16 are on the inside, and one side of the embossed type exterior material 30 that sandwiches the lead 2 is heat-sealed under pressure. Ru. Pressure heat fusion is controlled by three conditions: temperature, pressure, and time, and is set appropriately. The temperature of the pressure heat fusion is preferably higher than the temperature at which the sealant layer 16 is melted.

The thickness of the sealant layer 16 before heat sealing is preferably 40% or more and 80% or less of the thickness of the lead 2. When the thickness of the sealant layer 16 is at least the above lower limit, the heat-sealing resin tends to be able to sufficiently fill the ends of the leads 2, and when it is at most the above upper limit, the thickness at the end of the sheathing material 10 tends to be can be moderately suppressed, and the amount of moisture infiltrating from the end of the exterior material 10 can be reduced.

(Step S24)
In step S24, one side other than the side holding the lead 2 is left, and the other sides are pressurized and heat fused. After that, electrolyte is injected from the remaining side, and the remaining side is heat-sealed under pressure in a vacuum state. The conditions for pressure heat fusion are the same as in step S23.

(Step S25)
The edges of the peripheral pressurized and heat-sealed edges other than the edges that sandwich the leads 2 are cut, and the sealant layer 16 protruding from the edges is removed. Thereafter, the peripheral pressurized heat-sealed portion is folded back toward the recess 32 to form a folded portion 42, thereby obtaining the electricity storage device 40. Note that specific examples of power storage devices include secondary batteries such as lithium ion secondary batteries, nickel hydride batteries, and lead acid batteries, and electrochemical capacitors such as electric double layer capacitors.

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited by the following description.

[Materials used]
The materials used for producing the exterior materials of Examples , Reference Examples , and Comparative Examples are shown below.

(Coating layer)
Fifteen types of coating liquids (A-1 to A-15) shown in Table 1 were used. Each coating liquid was prepared by mixing a base resin and a slipperiness imparting additive. The "additive addition amount" shown in Table 1 is based on the mass (100 parts by mass) of the main resin. "Particle size" is the value of the particle size of the filler (slidability imparting additive) measured using a particle size distribution measuring device using a laser diffraction method. "Wetting contact angle" is a value measured by measuring the wetting contact angle of water on the coating layer after aging treatment at 60°C for 7 days according to the method described in JIS R3257:1999 (sessile drop method). .

(Coating layer side corrosion prevention layer: first corrosion prevention layer)
Corrosion prevention layer B-1: Cerium oxide layer (layer thickness 100 nm)
Corrosion prevention layer B-2: chromium oxide layer (layer thickness 100 nm)
Corrosion prevention layer B-3: Aluminum oxide layer (layer thickness 100 nm)

(metal foil)
Metal foil C-1: Soft aluminum foil 8021 material (manufactured by Toyo Aluminum Co., Ltd., thickness 30 μm)
Metal foil C-2: Copper foil (manufactured by JX Nippon Mining Co., Ltd., thickness 30 μm)
Metal foil C-3: Stainless steel foil (manufactured by Nippon Kinzoku Co., Ltd., thickness 30 μm)

(Sealant layer side corrosion prevention layer: second corrosion prevention layer)
Corrosion prevention layer D-1: Cerium oxide layer (layer thickness 100 nm)

(Adhesive layer)
Adhesive resin E-1: Polypropylene resin graft-modified with maleic anhydride (trade name "ADMER", manufactured by Mitsui Chemicals, layer thickness 10 μm)

(Sealant layer)
Heat-fusion resin F-1: Polypropylene resin (trade name "Prime Polypro", manufactured by Prime Polymer Co., Ltd., layer thickness 20 μm)

(Preparation of exterior material)
A corrosion prevention layer D-1 was formed on one side of the metal foil C-1, C-2 or C-3 by direct gravure coating. Next, the corrosion prevention layer B-1, B-2 or B-3 is directly gravure coated on the other side of the metal foil C-1, C-2 or C-3 on which the corrosion prevention layer D-1 is not formed. It was formed by engineering. In the Examples and Reference Examples , raw material A- for the coating layer was applied to the surface of the metal foil C-1, C-2 or C-3 on which the corrosion prevention layer B -1, B -2 or B -3 was formed, respectively. 1 (Example 1) to A-7 (Example 11) and coating layer raw materials A-8 (Reference Example 12) to A-12 ( Reference Example 16) were coated to form a coating layer. was formed (see Table 2). On the other hand, in the comparative examples, raw materials for coating layers A-13 (comparative example 1) to A-15 (comparative example 3) were applied to the surface on which the corrosion prevention layer B-1 was formed on the metal foil C-1. to form a coating layer (see Table 2).

Next, adhesive resin E-1 and heat-sealing resin F-1 were co-extruded and bonded onto the corrosion prevention layer D-1 side of the obtained laminates of Examples , Reference Examples , and Comparative Examples using an extrusion device. layer and a sealant layer. Exterior materials of each example , reference example, and comparative example were produced through the above steps.

[Various evaluations]
Various evaluations were performed according to the following methods. The evaluation results are shown in Table 2.

[Evaluation of printability]
A barcode was printed on the surface of the coating layer of the exterior material obtained in each example using an inkjet printer, and the printing performance was evaluated using a barcode reader. Evaluation was performed according to the following criteria.
"A": No ink repellency, barcode readable.
"B": There are some ink repellents, but the barcode can be read.
"C": Ink is repelled, barcode cannot be read.

[Evaluation of moldability]
The exterior material obtained in each example was cut into a blank shape of 150 mm x 190 mm, and cold molded while changing the molding depth in a molding environment with a room temperature of 23 °C and a dew point temperature of -35 °C, and moldability was evaluated. . The punch used had a shape of 100 mm x 150 mm, a punch corner R (RCP) of 1.5 mm, a punch shoulder R (RP) of 0.75 mm, and a die shoulder R (RD) of 0.75 mm. The evaluation criteria were as follows.
"A": Deep drawing molding to a molding depth of 3 mm or more is possible without causing breakage or cracks.
"B": Deep drawing molding with a molding depth of 2 mm or more and less than 3 mm is possible without causing breakage or cracks.
"C": Fractures and cracks occur during deep drawing with a molding depth of less than 2 mm.

In Examples 1 to 11 and Reference Examples 12 to 16, it was possible to achieve sufficiently high levels of both excellent moldability and excellent printability of the outermost layer.

DESCRIPTION OF SYMBOLS 10... Exterior material for electricity storage devices, 11... Metal foil (barrier layer), 12a... First corrosion prevention layer, 12b... Second corrosion prevention layer, 13... Coating layer, 15... Adhesive layer, 16... Sealant layer .

Claims (4)

An exterior material for a power storage device made of a multilayer film,
a coating layer having a surface with a water wetting contact angle in the range of 50 to 70 degrees;
a first corrosion prevention treatment layer;
a barrier layer;
a second anti-corrosion treatment layer;
a sealant layer;
in this order, and the coating layer is formed directly on the first corrosion prevention treatment layer,
The wetting contact angle of the water is defined as the angle between the tangent and the surface of the coating layer when a tangent is drawn from the area where water and air come into contact with the curved surface of the water on the surface of the coating layer onto which 1 μg of water is dropped. is the angle formed by the surface,
The coating layer contains an inorganic or organic filler,
An exterior material for an electricity storage device, wherein the content of the filler is 0.5 to 5.0 parts by mass based on 100 parts by mass of the coating layer. The electricity storage device according to claim 1 , wherein the coating layer contains at least one resin selected from the group consisting of polyester resin, urethane resin, fluororesin, epoxy resin, amino resin, acrylic resin, phenol resin, and alkyd resin. Exterior material for devices. The exterior material for a power storage device according to claim 1 or 2 , wherein the barrier layer is made of a metal foil selected from the group consisting of aluminum foil, copper foil, and stainless steel foil. further comprising an adhesive layer between the barrier layer and the sealant layer,
The exterior material for a power storage device according to any one of claims 1 to 3 , wherein the adhesive layer is made of an acid-modified polyolefin resin.

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