TW201312825A - Laminate for battery outer packaging, method for manufacturing the same, and secondary battery - Google Patents

Abstract

The disclosure relates to a laminate for battery outer packaging, which has an excellent electrolyte resistance even after a forming process. The laminate for battery outer packaging of the disclosure includes a metal plate, an acid-modified polypropylene layer disposed on the metal plate, and a polypropylene layer disposed on the acid-modified polypropylene layer. After selectively etching an amorphous portion of the polypropylene layer by using an electron beam, outer diameters of exposed spherulites are less than 1 μ m when a surface of the polypropylene layer is observed by a scanning electron microscope.

Description

Laminated body for battery exterior, method of manufacturing the same, and secondary battery

The present invention relates to a battery exterior body for electrolyte solution resistance, a method for producing the same, and a secondary battery including the above-described battery exterior laminate.

Secondary batteries such as nickel-cadmium batteries or nickel-hydrogen batteries and lithium ion batteries are widely used in electronic devices such as mobile phones or notebook personal computers, digital cameras, and portable music players. In particular, lithium ion batteries are excellent in energy density and output characteristics, and are therefore widely used in mobile phones and mobile devices that require miniaturization and light weight.

Further, in recent years, secondary batteries have also been used in large-scale equipment such as electric vehicles, hybrid vehicles, and batteries for solar cells. In the secondary batteries for such large-sized machines, in order to increase the output capacity, it is necessary to increase the capacity of the electrolytic solution, and accordingly, the size of the secondary battery is also increased. In the packaging member of such a large-sized secondary battery, the safety (firmness, durability, etc.) of the packaging member exceeding the small secondary battery is required.

As a material of such a packaging member, a laminate having a metal plate and a polypropylene layer formed on the surface of the metal plate has been proposed. The laminated body is formed into a predetermined shape from a state of a flat plate by extrusion processing or drawing processing, and is used as a packaging member.

When the laminate of the metal plate and the polypropylene layer is subjected to extrusion processing or drawing processing, cracks (cracks) may occur in the processed portion of the polypropylene layer. As a method of solving this problem, it is proposed to have a metal plate and A method of rapidly cooling the polypropylene layer after heat welding (for example, refer to Patent Document 1 and Patent Document 2). It is known that polypropylene crystallizes when the cooling rate after heat welding is slow. Further, cracks are generated by forming a laminate having a polypropylene layer having such a high degree of crystallization. On the other hand, when the laminated body after heat welding is rapidly cooled, crystallization of the polypropylene layer can be suppressed, and as a result, generation of cracks can be suppressed.

Patent Document 1 describes a laminate for a can (for example, an 18 L can or a spray can) including a metal plate, an acid-modified polypropylene layer, and a polypropylene layer. The laminate described in Patent Document 1 is produced by laminating an acid-modified polypropylene layer and a polypropylene layer on a metal plate, and after heat welding, at 20 ° C /sec or more (preferably 100 ° C / The speed of seconds or more is cooled to a temperature of 55 ° C or less (preferably 30 ° C or less). Thereby, the degree of crystallization of the acid-modified polypropylene layer and the polypropylene layer is suppressed to 55% or less.

Further, Patent Document 2 also discloses a laminate for a can including a metal plate, an acid-modified polypropylene layer, and a polypropylene layer. The laminate described in Patent Document 2 is produced by laminating an acid-modified polypropylene layer and a polypropylene layer on a metal plate, and after heat welding, cooling to a room temperature at a rate of 200 ° C /sec or more (room temperature). This indicates that the crystallization of the acid-modified polypropylene layer and the polypropylene layer is partially suppressed or not produced at all.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. 06-008368

Patent Document 2: Japanese Patent Publication No. 02-501642

The inventors of the present invention produced a battery case using the laminate produced by the methods described in Patent Document 1 and Patent Document 2. Specifically, first, a layered body was produced by laminating acid-modified polypropylene and polypropylene on a stainless steel plate having a thickness of 100 μm which was subjected to a chemical conversion treatment of chromate phosphate. Then, the obtained laminated body was stretch-molded to a depth of 8 mm by a sheet forming tester to produce a battery case. Then, a secondary battery (lithium ion battery) was produced using the battery case, and as a result, the battery case (laminate) of the produced secondary battery was inferior in electrolyte solution resistance, and the metal plate (stainless steel plate) was peeled off from the resin layer.

Therefore, the inventors of the present invention observed the resin side surface of the laminated body after the forming process by a microscope in order to confirm the peeling of the metal plate and the resin layer. As a result, it was found that although there was no large crack on the resin side surface of the laminated body after the forming process, fine cracks which may cause a decrease in electrolyte resistance were generated.

The present invention has been made in view of the above, and it is an object of the invention to provide a battery exterior laminate which has excellent electrolyte resistance even after molding, and a method for producing the same. Moreover, an object of the present invention is to provide a secondary battery including the above-described battery exterior laminate.

The present inventors have found that by not only reducing the degree of crystallization in the polypropylene layer, but also suppressing the generation and growth of spherulites in the polypropylene layer, it is possible to prevent the occurrence of fine cracks during the forming process, and further study The present invention has been completed.

In other words, the present invention relates to the following laminate for battery exterior.

[1] A laminate for a battery exterior comprising: a metal plate; an acid-modified polypropylene layer disposed on the metal plate; and a polypropylene layer disposed on the acid-modified polypropylene layer; After the amorphous portion of the polypropylene layer was selectively etched by an electron beam, when the surface of the polypropylene layer was observed by a scanning electron microscope, the outer diameter of the exposed spherulites was less than 1 μm.

[2] The laminate for battery exterior according to [1], wherein the thickness of the metal plate is in a range of 15 μm to 600 μm.

[3] The laminate for battery exterior according to [1] or [2], wherein the metal plate is a stainless steel plate.

Further, the present invention relates to the following method for producing a laminate for a battery exterior.

[4] A method for producing a laminate for a battery exterior, comprising the steps of: preparing a metal plate; disposing an acid-modified polypropylene layer on the metal plate; and disposing a polypropylene layer on the acid-modified polypropylene layer; Heating the metal plate, the acid-modified polypropylene layer and the polypropylene layer to a temperature equal to or higher than a melting point of the polypropylene layer; and cooling the polypropylene layer from a temperature of 120 ° C or higher at a rate of 100 ° C /sec or more Temperature below 20 °C.

Further, the present invention relates to the following secondary battery.

[5] A secondary battery comprising a molded article obtained by thermally welding a molded article of a battery exterior laminate according to any one of [1] to [3].

According to the present invention, it is possible to provide a laminated body for a battery exterior which does not cause fine cracks even after the forming process and which is excellent in electrolyte resistance. another Further, according to the present invention, it is possible to provide a secondary battery excellent in electrolyte resistance.

1. Battery assembly body

The laminate of the present invention is a laminate for a battery exterior which can be used for exterior mounting of various batteries such as a lithium ion battery, and includes: 1) a metal plate, 2) an acid-modified polypropylene layer disposed on the metal plate, and 3) A polypropylene layer disposed on the above acid-modified polypropylene layer.

Hereinafter, each element of the battery exterior laminate of the present invention will be described.

1) Metal plate

The type of the metal plate is not particularly limited, and may be appropriately selected depending on the weight, strength, processing depth, and the like required for the battery exterior material. Examples of the material of the metal plate include: cold-rolled steel plate, galvanized steel plate, Zn-Al alloy plated steel plate, Zn-Ai-Mg alloy plated steel plate, aluminized steel plate, stainless steel plate (can be Worthite iron system, ferrite iron) Any one of the system, the Ma Tian scattered iron system, aluminum plate, aluminum alloy plate, copper plate, and the like. The metal plate is preferably a variety of plated steel sheets or stainless steel sheets from the viewpoint of corrosion resistance.

The thickness of the metal plate is not particularly limited, and may be appropriately set depending on the weight, strength, processing depth, and the like required for the battery exterior material. The thickness of the metal plate is preferably in the range of 15 μm to 600 μm, and particularly preferably in the range of 20 μm to 400 μm in consideration of the strength and processing depth of the battery exterior material which is usually required. From the viewpoint of making the battery lightweight, the thickness of the metal plate used as the battery exterior material is preferably thin. However, if the thickness of the metal plate is as thin as less than 15 μm, the strength and workability of the laminate for battery exterior is obtained. Decline, and manufacturing costs rise. On the other hand, if the plate thickness is 600 μm, it is sufficient even when a deep extrusion process of about 50 mm is performed.

The metal plate can form a chemical conversion treatment film on the surface thereof from the viewpoint of improving corrosion resistance and adhesion to the acid-modified polypropylene layer.

The type of chemical conversion treatment is not particularly limited. Examples of the chemical conversion treatment include chromate treatment (chromic acid system), chromium-free treatment (decane system, organic titanium system, organic aluminum system, etc.), and phosphate treatment (chromium phosphate, zinc phosphate, etc.). The amount of deposition of the chemical conversion treatment film formed by the chemical conversion treatment is not particularly limited as long as it is effective for improving the corrosion resistance and the adhesion to the acid-modified polypropylene layer. For example, in the case of the chromate film, the amount of adhesion may be adjusted so that the amount of adhesion in terms of total Cr is 5 mg/m ² to 100 mg/m ² . Further, in the case of the chrome-free film, the amount of adhesion may be adjusted so as to be 10 mg/m ² to 500 mg/m ² in the Ti-Mo composite film, and in the fluoroacid film, The amount of adhesion may be adjusted so that the amount of adhesion in terms of fluorine or the amount of adhesion of the total metal element is in the range of 3 mg/m ² to 100 mg/m ² . Further, in the case of a phosphate film, the amount of adhesion may be adjusted so as to be 5 mg/m ² to 500 mg/m ² .

The chemical conversion treatment film can be formed by a known method. For example, the chemical conversion treatment liquid may be applied to the surface of the metal plate by a method such as a roll coating method, a spin coating method, or a spray method, and may be dried without washing with water. The drying temperature and the drying time are not particularly limited as long as the water can be evaporated. From the viewpoint of productivity, the drying temperature is preferably in the range of 60 ° C to 150 ° C in terms of reaching the sheet temperature (arrival sheet-temperature). The drying time is preferably in the range of 2 seconds to 10 seconds.

2) Acid modified polypropylene layer

The acid-modified polypropylene layer is located between the metal plate and the polypropylene layer, which enhances the adhesion between the metal plate and the polypropylene layer.

The type of the acid-modified polypropylene is not particularly limited and may be appropriately selected from those skilled in the art. Examples of the acid-modified polypropylene include grafting with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic anhydride, itaconic acid, itaconic anhydride or an anhydride thereof. A modified polypropylene or a copolymer of propylene and acrylic acid or methacrylic acid. Among these, from the viewpoint of heat resistance, the acid-modified polypropylene is preferably a polypropylene obtained by graft-modifying an unsaturated carboxylic acid such as maleic anhydride-modified polypropylene.

The thickness of the acid-modified polypropylene layer is not particularly limited, but is preferably in the range of 10 μm to 100 μm. When the thickness of the acid-modified polypropylene layer is less than 10 μm, the adhesion to the metal plate may not be sufficiently ensured. On the other hand, even if the thickness of the acid-modified polypropylene layer exceeds 100 μm, the improvement in adhesion is not observed, and the manufacturing cost becomes high. Further, there is a possibility that the workability of the laminate for battery exterior is lowered.

3) Polypropylene layer

The polypropylene layer functions to seal the battery by isolating the inside of the battery from the outside air. That is, when a battery is fabricated using the laminate of the present invention, the inside of the battery and the outside air (especially water) are thermally welded by a polypropylene layer of one laminate to a polypropylene layer or a metal electrode of another laminate. Vapor is isolated and prevents electrolyte leakage. In addition, the polypropylene layer also bears It functions to enhance the corrosion resistance of the metal plate to the electrolyte.

The type of the polypropylene is not particularly limited and may be appropriately selected from those skilled in the art. Examples of the polypropylene include homopolypropylene. The thickness of the polypropylene layer is not particularly limited, but is preferably in the range of 10 μm to 100 μm. When the thickness of the polypropylene layer is less than 10 μm, there is a possibility that the battery cannot be thermally welded with sufficient strength when the battery is manufactured. On the other hand, even if the thickness of the polypropylene layer exceeds 100 μm, the strength of the heat fusion is not improved, and the manufacturing cost becomes high. Further, there is a possibility that the workability of the laminate for battery exterior is lowered.

The laminate for battery exterior of the present invention is characterized in that it contains almost no large spherulites in the polypropylene layer. More specifically, the battery assembly for a battery exterior of the present invention is characterized in that, when the amorphous portion of the polypropylene layer is selectively etched by an electron beam, the surface of the polypropylene layer is observed by a scanning electron microscope. The exposed spherulites have an outer diameter of less than 1 μm. For example, a battery of the present invention in which the metal is not vapor-deposited is irradiated with a 10 kV acceleration voltage and a probe current of 90 eV under a pressure of 30 Pa using a low-pressure scanning electron microscope (SEM). The laminate was scanned for 5 minutes, whereby the amorphous portion of the polypropylene layer was selectively etched. Thereafter, the surface of the etched polypropylene layer was observed at a magnification of 500 times, whereby the crystal portion was clearly observed. When the outer diameter of the spherulites in the polypropylene layer is measured as described above, in the laminate for battery exterior of the present invention, the outer diameter of the spherulites is less than 1 μm (see the example).

In the laminate described in Patent Document 1 and Patent Document 2, by reducing the degree of crystallization of the polypropylene layer, it is possible to suppress large cracks during molding. The production of marks. In addition, the degree of crystallization of these laminated bodies is measured by X-ray diffraction (refer to Patent Document 1). However, the inventors of the present invention have found that even when the degree of crystallization measured by X-ray diffraction is less than the lower limit of the measurement, fine cracks are generated during the molding process. In order to trace the result of the occurrence of fine cracks, the inventors of the present invention have repeatedly studied the following two points: 1) The case where the lower limit value is measured even when the degree of crystallization measured by X-ray diffraction is not full In the polypropylene layer, spherulites may also be present; and 2) when spherulites having a predetermined diameter or more are present in the polypropylene layer, fine cracks may occur between the spherulites during the forming process.

Further, the inventors of the present invention have found that as long as the generation and growth of spherulites in the polypropylene layer are suppressed, not only large cracks but also fine cracks are not generated after the forming process. More specifically, the inventors of the present invention have found that if the outer diameter of the spherulites in the polypropylene layer is less than 1 μm, fine cracks do not occur after the processing.

As described above, the laminate for battery exterior of the present invention has a very low degree of crystallization in the polypropylene layer and the outer diameter of the spherulites in the polypropylene layer is less than 1 μm, so that it does not cause a large amount during the forming process. The cracks do not produce fine cracks. Therefore, by using the laminated body for battery exterior of the present invention, it is possible to produce an exterior (battery case) of a battery excellent in electrolyte resistance.

The method for producing the laminate for battery exterior of the present invention is not particularly limited. For example, the laminate for battery exterior of the present invention can be produced by the following procedure.

2. Method for manufacturing laminated body for battery exterior

The method for producing a laminate for battery exterior of the present invention comprises: 1) a first step of preparing a metal plate, 2) a second step of laminating an acid-modified polypropylene layer, and 3) a third step of laminating a polypropylene layer, 4 The fourth step of heating the laminate, and 5) the fifth step of cooling the polypropylene layer.

1) Step 1

In the first step, the metal plate to be a substrate is prepared. As described above, the chemical conversion treatment film can also be formed on the surface of the metal plate.

2) Step 2

In the second step, an acid-modified polypropylene layer is laminated on the metal plate.

The method of disposing the acid-modified polypropylene layer on the metal plate is not particularly limited, and can be appropriately selected from known methods. For example, an acid-modified polypropylene film (layering method) may be laminated on a metal plate, or an acid-modified polypropylene resin composition (coating method) may be applied to a metal plate. Examples of the lamination method include a thermal lamination method, a sandwich lamination method, and the like. Further, as the acid-modified polypropylene film, a commercially available acid-modified polypropylene film can be used, and it can also be produced by using a T-die extruder or the like. Further, the acid-modified polypropylene film may be an unstretched acid-modified polypropylene film, or may be a uniaxially or biaxially stretched acid-modified polypropylene film. On the other hand, examples of the coating method include a method in which a resin composition is melted and then coated by a T-die extruder, a bar coater, a roll coater, or the like, and the metal plate is immersed in the molten metal. In the method of the resin composition, the resin composition is dissolved in a solvent, and then applied by a bar coater, a roll coater, a spin coater or the like.

3) Step 3

In the third step, a polypropylene layer is laminated on the acid-modified polypropylene layer.

The method of disposing the polypropylene layer on the acid-modified polypropylene layer is not particularly limited, and can be appropriately selected from known methods. For example, a polypropylene film (layering method) may be laminated on the acid-modified polypropylene layer, or a polypropylene resin composition (coating method) may be applied to the acid-modified polypropylene layer. As the polypropylene film, a commercially available polypropylene film can be used, and it can also be produced by using a T-die extruder or the like. Further, the polypropylene film may be an unstretched polypropylene film or a uniaxially or biaxially stretched polypropylene film. On the other hand, examples of the coating method include a method in which a resin composition is melted and then coated by a T-die extruder, a bar coater, a roll coater, or the like, and an acid-modified polypropylene is formed. A method in which a metal plate of a layer is immersed in a molten resin composition, a resin composition is dissolved in a solvent, and then coated by a bar coater, a roll coater, a spin coater or the like.

The third step can be performed after the second step or simultaneously with the second step. That is, after the acid-modified polypropylene layer is placed on the metal plate, the polypropylene layer is disposed on the disposed acid-modified polypropylene layer. Further, an acid-modified polypropylene layer and a polypropylene layer may be simultaneously disposed on the metal plate.

4) Step 4

In the fourth step, the laminate obtained by the first step to the third step is heated to a temperature equal to or higher than the melting point of the polypropylene (and the acid-modified polypropylene) constituting the polypropylene layer. Thereby, the adhesion between the layers of the laminate can be improved.

The method of heating the laminate is not particularly limited. Examples of the method of heating the laminate include a method of putting the laminate into an oven, and the like. Further, the temperature of the heated laminate is not particularly limited as long as it is equal to or higher than the melting point of the polypropylene and the acid-modified polypropylene. For example, the heating temperature is preferably 165 ° C ~ 190 ° C In the range. When the heating temperature is less than 165 ° C, there is a possibility that the polypropylene and the acid-modified polypropylene are not sufficiently melted, and the adhesion between the layers cannot be sufficiently improved. On the other hand, when the heating temperature exceeds 190 ° C, there is a possibility that the polypropylene and the acid-modified polypropylene are thermally decomposed.

5) Step 5

In the fifth step, the polypropylene layer heated in the fourth step is cooled (rapidly cooled) to a temperature of 20 ° C or lower at a temperature of 120 ° C or higher at a rate of 100 ° C /sec or more. Usually, in the fifth step, the entire laminate heated in the fourth step is cooled from a temperature of 120 ° C or higher to a temperature of 20 ° C or lower at a rate of 100 ° C /sec or more, not just a polypropylene layer. . Thereby, spherulites having a size larger than a predetermined diameter are hardly generated in the polypropylene layer, and the laminated body heated by cooling can be cooled.

The method of cooling the laminate is not particularly limited. Examples of the method of cooling the laminate include a method of submerging the layered body in water, a method of blowing a cooling gas, a method of spraying the cooling water, a method of contacting the cooling roll, and the like.

The cooling start temperature is not particularly limited as long as it is 120 ° C or higher, but is preferably in the range of 120 ° C to 190 ° C. When the cooling start temperature is a temperature less than 120 ° C, crystallization occurs in the polypropylene layer. On the other hand, when the temperature is rapidly cooled from a temperature exceeding 190 ° C, there is a possibility that a cooling strain caused by heat shrinkage occurs on the metal plate, and the flatness of the surface of the polypropylene layer is remarkably deteriorated. Further, there is a possibility that the outermost layer of the polypropylene layer is oxidized, and the strength of heat fusion of the laminates for the battery exterior is lowered.

The cooling rate from the cooling start temperature to the cooling end temperature is not particularly limited as long as it is 100 ° C /sec or more. By setting the cooling rate At 100 ° C / sec or more, crystallization in the polypropylene layer can be suppressed.

The production method of the present invention is characterized in that the cooling end temperature is 20 ° C or lower. It is considered that crystallization of the polypropylene layer does not proceed as long as the polypropylene layer is cooled to a temperature lower than the melting point of the polypropylene. However, in practice, it takes time until the entire polypropylene layer reaches the heat balance. Therefore, even if the polypropylene layer is cooled to a temperature lower than the melting point of the polypropylene, fine crystals may be formed in the polypropylene layer. By setting the cooling end temperature to 20° C. or less, generation and growth of spherulites in the polypropylene layer can be suppressed, and as a result, the outer diameter of the spherulites in the polypropylene layer can be made less than 1 μm (refer to Example 1). ).

In the past, the heated laminate is cooled to 55 ° C (preferably 30 ° C) or less (see Patent Document 1) or room temperature (see Patent Document 2). As described above, the inventors of the present invention have found that even if the degree of crystallization of the polypropylene layer is less than the lower limit of measurement by X-ray diffraction, fine cracks may occur during the forming process. Further, the inventors of the present invention have found that if the outer diameter of the produced spherulites is less than 1 μm, not only large cracks but also fine cracks are not generated after the forming process. In other words, it is considered that crystallization does not proceed as long as it is cooled to 55 ° C (preferably 30 ° C) or lower than the melting point of the polypropylene layer. However, in practice, since it takes time until the entire polypropylene layer completely reaches the heat balance, it is considered that fine spherulites which cannot be measured by X-ray diffraction grow. In addition, as a result of repeated efforts by the inventors of the present invention, it has been found that when the cooling start temperature is 120° C. or higher, the cooling rate is 100° C./sec or more, and the cooling end temperature is 20° C. or lower, the ball is used. The outer diameter of the crystal becomes less than 1 μm.

1A to 1C are self-baking after heat treatment at a plate temperature of 180 ° C. The laminate (polypropylene layer) was taken out from the box and slowly cooled at a rate of 6 ° C / sec to 25 ° C as room temperature. Fig. 1A is a graph showing the results of X-ray diffraction of a polypropylene layer. Fig. 1B is an SEM image of the surface (after etching) of the polypropylene layer before the forming of the laminate. Fig. 1C is a photograph obtained by microscopy of a surface of a polypropylene layer obtained by drawing a laminate into a depth of 8 mm by a sheet forming tester.

As shown in FIG. 1A, in the X-ray diffraction spectrum of the polypropylene layer when the laminate was slowly cooled, crystallized peaks of α crystals (2θ=14, 17) were observed. Further, as shown in FIG. 1B, large spherulites (outer diameter of 20 μm or more) were confirmed in the polypropylene layer. Further, as shown in Fig. 1C, many large cracks were generated in the polypropylene layer after the forming process.

2A to 2C are results when the laminate (polypropylene layer) is cooled (rapidly cooled) from a temperature of 160 ° C to a temperature of 30 ° C at a rate of 100 ° C /sec or more. 2A is a graph showing the results of X-ray diffraction of a polypropylene layer. 2B is an SEM image of the surface (after etching) of the polypropylene layer before the forming of the laminate. 2C is a photograph obtained by microscopy of the surface of the polypropylene layer after the laminate is formed.

As shown in FIG. 2A, in the X-ray diffraction spectrum of the polypropylene layer when the laminate was rapidly cooled to a temperature of 30 ° C, no crystal crystallization peak of α crystal was observed. However, as shown in FIG. 2B, fine spherulites (outer diameter of 1 μm or more) were confirmed in the polypropylene layer. Further, as shown in Fig. 2C, many fine cracks were generated in the polypropylene layer after the forming process.

3A to 3C are temperatures at which the laminate (polypropylene layer) is cooled (quickly cooled) from a temperature of 160 ° C to a temperature of 20 ° C at a rate of 100 ° C /sec or more. The result of the time. Fig. 3A is a graph showing the results of X-ray diffraction of a polypropylene layer. Fig. 3B is an SEM image of the surface (after etching) of the polypropylene layer before the forming of the laminate. Fig. 3C is a photograph of a surface of a polypropylene layer obtained by molding a laminated body by a microscope.

As shown in FIG. 3A, in the X-ray diffraction spectrum of the polypropylene layer when the laminate was rapidly cooled to a temperature of 20 ° C, no crystal crystallization peak of α crystal was observed. Further, as shown in Fig. 3B, fine spherulites were not observed in the polypropylene layer. Further, as shown in Fig. 3C, no fine cracks were observed in the polypropylene layer after the forming process.

In the fifth step, the mechanism is such that the cooling rate is 100° C./sec or more and the cooling end temperature is 20° C. or less, and the outer diameter of the spherulites is less than 1 μm. as follows.

In the fifth step, the polypropylene layer is cooled while being formed and dissolved by the nucleus which becomes the spherulite group. When the temperature is rapidly cooled to 20 ° C or lower at a rate of 100 ° C /sec or more as in the present invention, a plurality of fine nuclei are formed, and the fine nuclei are frozen and fixed. When a plurality of fine nuclei are formed in the polypropylene layer as described above, the growth of each nuclei is hindered by the adjacent nuclei, and thus it is impossible to grow to the extent that it can be observed by SEM (outer diameter is 1 μm or more). . On the other hand, when it is only cooled to about 30 ° C at a rate of 100 ° C / sec, it is considered that the number of nuclei generated in the polypropylene layer is smaller than when it is cooled to 20 ° C or lower. The core grows into spherulites before reaching thermal equilibrium and freezing. Therefore, each core grows to the extent that it can be observed by SEM.

As described above, the method for producing a laminate for battery exterior of the present invention can be A laminate for a battery exterior of the present invention which does not cause spherulites having an outer diameter of 1 μm or more in the polypropylene layer and which does not crystallize the polypropylene layer is produced.

3. Secondary battery

The laminate of the present invention can be preferably used as an exterior material (box) of a secondary battery. The shape of the secondary battery is not particularly limited, and is, for example, a rectangular parallelepiped or a cylindrical shape. The type of the secondary battery is also not particularly limited, and examples thereof include a nickel-cadmium battery, a nickel-hydrogen battery, and a lithium ion battery.

When the laminate of the present invention is used as a cartridge for a secondary battery, it is preferred that the laminates of the present invention are bonded to each other and sealed. At this time, the laminated bodies which are formed by molding may be bonded to each other, or only one laminated body may be subjected to forming processing. The method of forming the laminated body of the present invention is not particularly limited, and can be appropriately selected from known methods such as press working, shrinking processing, and extrusion processing. As a method of bonding the laminate of the present invention, a method in which the laminates of the present invention are combined with each other and then adhered by heat welding is preferred.

When a secondary battery is produced by using the laminated body of the present invention, a battery element such as a positive electrode, a negative electrode, a separator, or the like, or an electrolyte solution is housed in a cartridge obtained by molding the laminated body of the present invention, and by Heat it to adhere.

As described above, the secondary battery of the present invention is excellent in electrolyte resistance because it uses a battery case (layered body) which does not cause large cracks and does not cause fine cracks.

Hereinafter, the invention will be described in detail with reference to examples, but the invention is not limited to the examples.

Instance [Example 1]

In Example 1, the results of investigating the relationship between the cooling end temperature and the generation of spherulites in the polypropylene layer are shown.

1. Production of laminate for battery exterior

The surface of the stainless steel plate (SUS304: thickness: 0.1 mm) was subjected to degreasing and then dried, and then a commercially available coating was applied by a roll coater so that the total Cr conversion amount was 25 mg/m ² . Type chromate chromate treatment solution (ZMR1320; Nihon Parkerizing Co., Ltd.). The steel sheet coated with the chromate treatment liquid was heated for 10 seconds so that the plate temperature reached 120 ° C to form a chemical conversion treatment film.

Then, a maleic anhydride-modified polypropylene film having a surface layer thickness of 30 μm on a stainless steel sheet subjected to chemical conversion treatment (QE-060; Mitsui Chemicals Tohcello Co., Ltd., melting point: 139 ° C), and a film thickness of A 30 μm non-stretch polypropylene film (CP-S; Mitsui Chemicals Tohcello Co., Ltd., melting point 163 ° C) was then subjected to heat crimping using a heated laminating roll heated to 140 °C. Thereafter, the stainless steel plate, the acid-modified polypropylene film, and the polypropylene film were heat-welded by heating for 50 seconds so that the plate temperature reached 180 °C.

After the heat welding, it was left to cool to a cooling start temperature of 160 ° C (cooling rate: 6 ° C / sec). Then, each of the laminates is submerged in warm water or cold water in a water tank controlled to a predetermined cooling end temperature, and the polypropylene layer is changed from 160 ° C to 80 ° C and 70 ° C at a cooling rate of 100 ° C /sec or more. 60 ° C, 50 ° C, 40 ° C, 35 ° C, 30 ° C, 25 ° C, 20 ° C or 15 ° C. The temperature of the polypropylene layer is measured at intervals of 0.01 seconds. The data logger (Memory HiLogger 8430; Hioki Electric Co., Ltd.) was used for measurement. Each of the laminates was produced by spot welding a thermocouple to a center of a stainless steel sheet which was subjected to chemical conversion, and then layering acid-modified polypropylene and polypropylene.

2. Determination of crystallized peaks by X-ray diffraction

For each of the laminates, the crystallization peak of the polypropylene layer was measured using an X-ray diffraction apparatus (Rint Ultima III; Rigaku Co., Ltd.) to confirm the presence or absence of α crystal. The X-ray diffraction apparatus is measured using a copper tube ball, and the rated tube voltage-tube current is set to 20 kV to 60 kV to 2 mA to 60 mA, and the measurement range is set to 5° ≦ 2θ ≦ 35°.

3. Determination of the outer diameter of spherulites using low vacuum SEM

Using a low-vacuum SEM (S-3700N; Hitachi High-Tech Fielding Co., Ltd.), a 5-minute scan was performed at a pressure of 30 Pa with an acceleration voltage of 10 kV and a probe current of 90 eV, thereby selectively etching each The amorphous portion of the polypropylene layer of the laminate (metal is not vapor-deposited). Thereafter, the surface of the etched polypropylene layer was observed at a magnification of 500 times for each layered body.

Further, when spherulites were observed in each of the laminates, the average outer diameter of the spherulites was measured. The average outer diameter of the spherulites is calculated as the average value of the outer diameters of the ten spherulites randomly selected from one field of view of the SEM image.

4. Evaluation of cracks after forming

For each laminate, a thin plate forming tester (Model 1420-20; ERICHSEN Co., Ltd.) was used, and the punch was pressed against the side of the polypropylene layer to perform deep extrusion processing, and the crack in the polypropylene layer at the corner of the concave portion was observed. Produce condition. The conditions for deep extrusion processing are as follows.

Blank: 80 mm square

Bead height: 1.5 mm

Bead width: 3 mm

Stretch height: 8 mm

Stretching speed: 280 mm/min

Punch: 40×40×Rc10

Mold: 42×42×Rc11

Blank holder: 30 kN

5. Evaluation results

4A and 4B are graphs showing the results of X-ray diffraction of the polypropylene layer of each laminate. As shown in FIG. 4A and FIG. 4B, when the cooling end temperature was 35 ° C or more, the crystallized peak of the α crystal (2θ=14, 17) (arrow) was observed.

5 and 6 are SEM images before processing of the polypropylene layer of each laminate and photographs obtained by a microscope after processing. As shown in FIG. 5 and FIG. 6, when the cooling completion temperature was 35 to 80 ° C, spherulites (outer diameter of 1 μm or more) were confirmed in the SEM image, and cracks occurred after the processing. In addition, when the cooling end temperature is 30 ° C, no crystal crystallization peak of α crystal is observed by X-ray diffraction, but spherulites (outer diameter of 1 μm or more) can be confirmed in the SEM image, and processed. After the crack occurred. When the cooling completion temperature was 25 ° C, fine spherulites (outer diameter of 1 μm or more) were observed in the SEM image, but almost no cracks occurred after the processing. On the other hand, when the cooling end temperature is 20 ° C or less, it is impossible to observe in the SEM image. To the spherulites, in addition, no cracks were formed after processing.

Fig. 7 is a graph showing the cooling end temperature and the average outer diameter of the spherulites in the polypropylene layer. The upper end of the error bar in the figure indicates the maximum value of the measured outer diameter, and the lower end indicates the minimum value of the measured outer diameter. As shown in Fig. 7, when the cooling end temperature is 25 ° C or more, spherulites having an outer diameter of 1 μm or more are generated. In addition, the higher the cooling end temperature becomes, the larger the average outer diameter of the spherulites becomes. On the other hand, when the cooling end temperature was 20 ° C or lower, spherulites of a size which can be observed in the SEM image were not produced.

[Example 2]

In the example 2, the relationship between the cooling start temperature and the generation of spherulites in the polypropylene layer, and the electrolyte solution resistance of the battery exterior laminate of the present invention were examined.

1. Production of laminate for battery exterior

In the same manner as in Example 1, the surface of the stainless steel plate (SUS304: thickness: 0.1 mm) was degreased and then dried, and then coated by a roll coater so that the total Cr conversion amount was 25 mg/m ² . Coated phosphoric acid chromate treatment solution (ZMR1320; Nihon Parkerizing Co., Ltd.) commercially available. The steel sheet coated with the chromate treatment liquid was heated for 10 seconds so that the plate temperature reached 120 ° C to form a chemical conversion treatment film.

Then, a maleic anhydride modified polypropylene film (QE-060; Mitsui Chemicals Tohcello Co., Ltd.) having a surface layer thickness of 30 μm in a stainless steel sheet which has been chemically processed, and a film thickness of 30 μm without extension A polypropylene film (CP-S; Mitsui Chemicals Tohcello Co., Ltd.) was then heated and crimped using a heated laminating roll heated to 140 °C. After that, The plate temperature was heated to 180 ° C for 50 seconds, and the stainless steel plate, the acid-modified polypropylene film, and the polypropylene film were heat welded.

After heat welding, place and cool to a cooling start temperature (100 ° C ~ 180 ° C) (6 ° C / sec). Then, each of the laminates was cooled under the conditions shown in Table 1. When the cooling method is submerged in water, each of the laminates is submerged in warm water or cold water in a water tank controlled to a predetermined cooling end temperature to be cooled. Further, when the cooling start temperature was 180 ° C, each of the laminates was submerged in water and cooled shortly after being taken out from the oven. When the cooling method is a spray gun, the cooling rate is changed by adjusting the temperature and the discharge amount of the cooling water. The temperature of the polypropylene layer was measured in the same manner as in Example 1.

2. Determination of spherulites using a scanning electron microscope (SEM)

The outer diameter of the spherulites in the polypropylene layer was measured in the same procedure as in Example 1.

3. Evaluation of cracks after processing

Whether or not cracks were generated in the polypropylene layer of the processed laminate after the same procedure as in Example 1 was evaluated.

4. Electrolyte resistance test

Each of the laminates subjected to deep extrusion processing in the same manner as in Example 1 was placed in a sealed container. The electrolytic solution was injected into the concave portion of each laminated body (having a polypropylene layer) so as to have a depth of 5 mm, and then allowed to stand in a heating furnace at 85 ° C for 28 days. The electrolyte solution is added to a mixture (1:1) of ethylene carbonate and diethylene carbonate so that lithium hexafluorophosphate (LiPF ₆ ) is 1 mol/L. preparation. Thereafter, the inside of the concave portion of each laminate is washed with ethanol and dried.

Then, a cellophane tape was attached to the surface of the polypropylene layer at the corner inside the concave portion of each laminated body, and then the cellophane tape was peeled off, and the resin layer (polypropylene layer and acid-modified polypropylene layer) was evaluated. Closed state. The adhesion state of the resin layer is evaluated as "○" when the resin layer is not peeled off after the peeling of the cellophane tape, and the peeling of the resin layer after peeling of the cellophane tape is set to "△", and the cellophane tape is attached. When the front resin layer has been peeled off, it is set to "x".

5. Evaluation results

The cooling conditions of each laminate and the results of the respective evaluation tests are shown in Table 2.

Fig. 8A is an SEM image of a polypropylene layer of a laminate (Comparative Example) of No. 10. 8B is an SEM image of a polypropylene layer of the laminate (Comparative Example) of No. 11. 8C is an SEM image of a polypropylene layer of the laminate (Comparative Example) of No. 14.

In the layered product (comparative example) of No. 9 having a cooling completion temperature of 30 ° C, the crystallized peak of the α crystal by X-ray diffraction was not confirmed (see 30 ° C of FIG. 4A ). However, spherulites having an average particle diameter of 1 μm (see 30 ° C in Fig. 6) were confirmed from the SEM image, and fine cracks were generated after the processing. Therefore, the laminated body of No. 9 has a slightly poor electrolyte solution resistance.

Laminated body of No. 10 at a cooling rate of less than 100 ° C / sec (Comparative Example) In the layered product (comparative example) of No. 11, the crystallization peak of the α crystal which was X-ray-diffracted was confirmed. Further, spherulites having an average particle diameter of 5 μm and 10 μm were observed from the SEM image (see FIGS. 8A and 8B), and fine cracks were generated after the processing. Therefore, the laminated body of No. 10 and the laminated body of No. 11 are slightly inferior in electrolyte solution resistance.

In the layered product (comparative example) of No. 12 in which the cooling start temperature was less than 120 ° C (100 ° C), the crystallized peak of the α crystal by X-ray diffraction was observed. Further, spherulites having an average particle diameter of 2 μm were confirmed from the SEM image, and fine cracks were generated after the processing. Therefore, the laminated body of No. 12 has a slightly poor electrolyte solution resistance.

In the layered product (comparative example) of No. 13 having a cooling rate of 83 ° C / sec and a cooling end temperature of 80 ° C, a crystallized peak of the α crystal by X-ray diffraction was observed. Further, spherulites having an average particle diameter of 20 μm were confirmed from the SEM image, and cracks were generated after the processing. Therefore, the laminated body of No. 13 is inferior in electrolyte solution resistance.

In the laminate of No. 14 (Comparative Example) having a cooling rate of 6 ° C / sec, a crystallized peak of α crystals which were X-ray-diffracted was observed. Further, spherulites having an average particle diameter of 35 μm were confirmed from the SEM image (see FIG. 8C), and cracks were generated after the processing. Therefore, the laminated body of No. 14 is inferior in electrolyte solution resistance.

On the other hand, in the laminate (example) of No. 1 to No. 8, the crystallized peak of the α crystal which was X-ray-diffracted was not observed, and no spherulites were observed in the SEM image. In addition, no cracks were formed after processing. Therefore, the laminated body of No. 1 to No. 8 has good electrolyte solution resistance.

According to the above results, the laminate for battery exterior of the present invention is excellent in electrolyte solution resistance even after molding.

The present application claims priority based on Japanese Patent Application No. 2011-196095, filed on Sep. 8, 2011. The contents described in the specification and drawings of the application are all incorporated in the specification of the present application.

[Industrial availability]

Since the laminated body of the present invention is excellent in electrolytic solution resistance, it is useful as a battery exterior material.

1A is a graph of X-ray diffraction of a polypropylene layer when a laminate is slowly cooled, FIG. 1B is an SEM image of a polypropylene layer when the laminate is slowly cooled, and FIG. 1C is a processing when the laminate is slowly cooled. A photo taken by a microscope.

2A is a graph showing X-ray diffraction of a polypropylene layer when the laminate is rapidly cooled to 30° C. FIG. 2B is an SEM image of the polypropylene layer when the laminate is rapidly cooled to 30° C. FIG. 2C is FIG. A photograph obtained by a microscope of a processed portion of a polypropylene layer when the laminate was rapidly cooled to 30 °C.

Fig. 3A is a graph showing X-ray diffraction of a polypropylene layer when the laminate is rapidly cooled to 20 ° C, and Fig. 3B is an SEM image of the polypropylene layer when the laminate is rapidly cooled to 20 ° C, and Fig. 3C is A photograph obtained by a microscope in a processed portion of a polypropylene layer when the laminate was rapidly cooled to 20 °C.

4A and 4B are X-ray diffraction of the polypropylene layer of each laminate. Chart.

Fig. 5 is a SEM image of a polypropylene layer of each laminate and a photograph of a processed portion obtained by a microscope.

Fig. 6 is a SEM image of a polypropylene layer of each laminate and a photograph of a processed portion obtained by a microscope.

Fig. 7 is a graph showing the relationship between the cooling end temperature and the average outer diameter of the spherulites.

8A to 8C are SEM images of a polypropylene layer of a laminate of a comparative example.

Claims (5)

A laminate for a battery exterior comprising: a metal plate; an acid-modified polypropylene layer disposed on the metal plate; and a polypropylene layer disposed on the acid-modified polypropylene layer; After the amorphous portion of the polypropylene layer was selectively etched, the outer diameter of the exposed spherulites was less than 1 μm when the surface of the polypropylene layer was observed by a scanning electron microscope. The laminated body for a battery exterior according to the first aspect of the invention, wherein the metal plate has a thickness of 15 μm to 600 μm. The laminate for battery exterior according to the first aspect of the invention, wherein the metal plate is a stainless steel plate. A method for producing a laminate for a battery exterior, comprising: a step of preparing a metal plate; a step of disposing an acid-modified polypropylene layer on the metal plate; and a step of disposing a polypropylene layer on the acid-modified polypropylene layer a step of heating the metal plate, the acid-modified polypropylene layer, and the polypropylene layer to a temperature equal to or higher than a melting point of the polypropylene layer; and, at a rate of 100 ° C/sec or more, the polypropylene layer from 120 ° C or higher The step of cooling the temperature to a temperature below 20 °C. A secondary battery comprising a case in which a molded article of a battery exterior laminate according to the first aspect of the invention is thermally welded.