Metallization film for positive electrode of a secondary battery, and method of manufacturing the same

Abstract

The present invention aims to obtain a metallized film that can be transported without increasing contact resistance or breaking even when a conductive thin film layer is formed on a resin surface, and a method for manufacturing the same. This can be achieved by a metallized film for a positive electrode of a secondary battery in which an aluminum metal film is formed on at least one surface of a resin film, and the specular reflectance of the metal film surface not in contact with the resin film at a wavelength of 555 nm is 30% or less.

Description

Technology Field

[0001] The present invention relates to a metallized film for a secondary battery and a method for manufacturing the same. Background Technology

[0002] In recent years, due to the miniaturization of electrical and electronic devices and environmental concerns, there is a demand for storage devices such as secondary batteries and capacitors in gasoline-free vehicles (hybrid cars, electric cars) to be smaller and lighter, while simultaneously possessing high power density capable of instantaneously charging and discharging large currents.

[0003] Generally, to improve gravimetric energy density, the battery mounted in a vehicle has a configuration in which the positive and negative electrodes are formed as sheets, and the sheet-shaped positive and negative electrodes are wound or stacked and housed within a case with a separator also formed as a sheet interposed therebetween. The sheet-shaped electrode plate has a structure in which a layer of a mixture containing an active material is formed on the surface of a metal foil serving as a current collector.

[0004] In addition, one method to obtain high power density is to reduce the resistance of various materials constituting the battery (internal resistance of the battery). In batteries, aluminum foil is often used as the current collector, but conventional aluminum foil current collectors have an oxide film, and it is said that the internal resistance increases due to the oxide film formed on the surface of the aluminum. When internal resistance increases, it causes a voltage drop when charging and discharging with a large current, and as a result, it causes a decrease in the output of the battery. Generally, a strong insulating natural oxide film with a thickness of 5 to 10 nm is formed on aluminum, but the aluminum surface has the characteristic of maintaining good conductivity. As reasons for this, there are theories that current flows from defects in the oxide film, and from the field of quantum mechanics, the tunneling effect theory, which states that good electronic conductivity occurs when an electronic conductor approaches an electrical insulator within about 10 nm or less, and although it is not very clear, it is thought that the aluminum oxide film itself strongly influences the internal resistance.

[0005] As a method to reduce the contact resistance between an electrode and an active material that suppresses the increase in internal resistance caused by an oxide film, there is a method of making the surface of a metal foil used in the electrode rough (e.g., Patent Document 1). It is not clear whether the number of defects increases by roughening the aluminum surface or whether the tunnel effect becomes easier to manifest by forming many protrusions, but it is an effective method for reducing contact resistance.

[0006] As a method to improve high power density while miniaturizing and reducing weight, thinning of electrode substrates is being pursued with the aim of improving volumetric energy density or gravimetric energy density. However, if the metal foil used in the electrode is simply thinned to meet these requirements, a problem of insufficient strength arises. Furthermore, if the surface roughness of the thinned metal foil is increased to reduce contact resistance, it also causes a decrease in the strength of the metal foil, which is undesirable. Therefore, as a new material to replace metal, it has been proposed to use a material having a configuration in which a conductive thin film layer, such as metal, is formed on the surface of a biaxially stretched polyester thin film with excellent mechanical properties and heat resistance and dimensional stability, as a current collector, to function as an electrode substrate (e.g., Patent Document 2). Prior art literature

[0007] Japanese Patent Publication No. 2008-160053 Japanese Patent Publication No. Hei 10-40919 The problem to be solved

[0008] However, in the case of a configuration in which a conductive thin film layer, such as metal, is formed on the surface of a resin film such as a polyester thin film, the total electrical resistance increases as the metal thickness becomes thinner than that of conventionally used metal foils. Furthermore, even if one attempts to sinter the metal surface to lower the contact resistance of the aluminum metal surface, the conductive thin film layer, such as metal, on the surface of the resin film is typically a deposited metal film formed by vacuum deposition or the like; since it is a thin metal film, it is extremely difficult to sinter it using etching or similar methods. If the surface of the polyester thin film itself is sintered, it becomes prone to breakage, making it difficult to transport during the manufacturing process.

[0009] Taking into account the facts described above, the present invention aims to provide a metallized film that can be transported without increasing contact resistance or breaking, even when a conductive thin film layer is formed on the surface of a resin. means of solving the problem

[0010] The inventors, taking the above problem into consideration, have carefully examined the matter and have arrived at obtaining a metallized film with low contact resistance and a method for manufacturing the same by controlling the surface shape of the deposited film using a vacuum deposition method.

[0011] That is, the present invention relates to a metallized film for a positive electrode of a secondary battery, wherein an aluminum metal film is formed on at least one surface of a resin film, and the specular reflectance at a wavelength of 555 nm on the surface of the metal film not in contact with the resin film is 30% or less.

[0012] A metallized film for a positive electrode of a secondary battery, wherein the ratio I

[0200] / I

[0111] of the peak intensity of the X-ray diffraction of the 111 plane and the peak intensity I

[0200] of the X-ray diffraction of the 200 plane of the aluminum of the metal film is 1.0 or greater.

[0013] The metallized film for the positive electrode of the secondary battery having a surface resistance of 0.15Ω / □ or less,

[0014] The metallized film for a positive electrode of a secondary battery having a surface roughness (Ra) of 0.6 nm or more and 2.0 nm or less of the resin film,

[0015] The present invention relates to a metallized film for a positive electrode of a secondary battery, wherein the surface roughness (Ra) of the metal film is 2.3 nm or more and 10.0 nm or less.

[0016] In addition, the present invention relates to a method for manufacturing a metallized film for a positive electrode of a secondary battery, comprising a process of forming a film by depositing the vaporized aluminum onto a resin film using a vacuum deposition method in which argon gas is introduced when aluminum, which is a deposition source, is heated by resistance heating, induction heating, or an electron beam to vaporize it.

[0017] In addition, the present invention relates to a method for manufacturing a metallized film for a positive electrode of a secondary battery, comprising a process of forming a film by depositing aluminum onto a resin film by sputtering, and then depositing aluminum by at least one selected from the group consisting of resistance heating, induction heating, and an electron beam without exposing to the atmosphere. Effects of the invention

[0018] According to the present invention, it is possible to obtain a metallized film that can be transported without increasing contact resistance or breaking even when a conductive thin film layer is formed on the surface of a resin, and a method for manufacturing the same. Brief explanation of the drawing

[0019] Figure 1 is a schematic cross-sectional view of the metallized film of the present invention. FIG. 2 is a schematic cross-sectional view of the metallized film of the present invention. Figure 3 is a schematic cross-sectional view of the metallized film of the present invention. Figure 4 is a scanning electron microscope (SEM) image of the surface of an aluminum metal film (film thickness 1.48 μm) when the crystal grains were grown large and dense using an induction heating deposition source with a carbon crucible. Figure 5 is an SEM image of the surface of an aluminum metal film (film thickness 0.53 μm) when the crystal grains were grown large and dense using an induction heating deposition source with a carbon crucible. Figure 6 is an SEM image of the surface of an aluminum metal film (film thickness 1.12 μm) grown using a boat heating method in which an aluminum metal wire is continuously supplied to a resistance heating boat. Figure 7 is an SEM image of the cross-section of an aluminum metal film (film thickness 1.48 μm) when the crystal grains were grown large and dense using an induction heating deposition source with a carbon crucible. (It is the same as Figure 3, but viewed from a different direction.) Specific details for implementing the invention

[0020] The present invention will be described in detail below.

[0021] Metallization film

[0022] The metallized film (4) of the present invention has an aluminum metal film (3) on one or both sides of a resin film (1) (Figs. 1, 2, 3).

[0023] Aluminum metal film

[0024] The aluminum metal film (3) according to the present invention is an assembly of aluminum metals having one or more layers of aluminum as the main component. The main component refers to a value exceeding 80 atomic percent when the entire layer is 100 atomic percent.

[0025] In the present invention, the thickness of the aluminum metal film (3) is preferably 0.7 μm or more and 3.0 μm or less, and more preferably 1.0 μm or more and 2.5 μm or less.

[0026] For electrode applications, it is desirable for electrical resistance to be as low as possible. Regarding surface resistance, it is desirable for the metal film surface resistance to be 0.15 Ω / □ or less, and even more desirable for it to be 0.05 Ω / □ or less. On the other hand, since thinning is necessary to improve energy density, simply making the metal film thick is not desirable. Considering the electrical resistance of the electrode, the thickness of the aluminum metal film is preferably 0.7 µm or more, and if it is 1.0 µm or more, the resistance becomes lower, which can reduce the increase in internal resistance. Meanwhile, since it is necessary to thin the electrode substrate for the purpose of improving volumetric energy density, it is desirable for it to be 3.0 µm or less, and even more desirable for it to be 2.5 µm or less.

[0027] The aluminum metal film (3) according to the present invention has the characteristic of being able to lower contact resistance by controlling the crystal growth of the metal film so that the surface roughness increases during film formation by vacuum deposition.

[0028] When an aluminum metal film (3) of a metallized film (4) is placed facing upward on a 10mm thick NR sponge rubber, and two gold-plated copper plates with dimensions of 25mm × 25mm are placed with a 500g weight on each plate at a distance of 1mm, and the resistance value between the two copper plates is taken as the contact resistance value, it is preferable that the contact resistance value be 15mΩ or less and more preferable that it be 10mΩ or less in order to reduce the increase in internal resistance. Here, the contact resistance value is a value that includes the contact resistance of the two electrode areas of 25mm × 25mm and the film resistance (surface resistance) between the two electrodes. Therefore, the ratio of the contact resistance value to the surface resistance value [contact resistance value] / [surface resistance value] can show a value with little influence from the surface resistance, and the ratio of the surface resistance value [contact resistance value] / [surface resistance value] is preferably 0.35 or less and more preferable that it be 0.25 or less.

[0029] As a feature of the surface of the aluminum metal film (3) that controls the crystal growth of the metal film to lower contact resistance, it is preferable that the specular reflectance of the surface of the aluminum metal film (3) that is not in contact with the resin film has a wavelength of 555 nm of 30% or less, and more preferable that it has a specular reflectance of 20% or less. This is effective in lowering contact resistance because the specular reflectance of visible light at 555 nm is reduced as the surface of the aluminum metal film is finely harmonized.

[0030] As a surface feature of the aluminum metal film (3) that controls the crystal growth of the metal film to lower contact resistance, it is preferable that the surface roughness (Ra) of the surface of the aluminum metal film (3) that is not in contact with the resin film (1) is 2.3 nm or more and 10.0 nm or less, and more preferable that it is 5.0 nm or more and 10.0 nm or less. Since contact resistance tends to decrease when the aluminum surface is sufficiently harmonized and a certain size is secured in the height of the convex and concave parts, it is preferable that the surface roughness (Ra) be larger. However, if the surface roughness (Ra) is excessively large, it causes the metal film to break when the thin aluminum metal film (3) is transported or folded, so it is preferable that it be 10.0 nm or less.

[0031] As a feature of the surface of an aluminum metal film (3) that controls the crystal growth of the metal film to lower contact resistance, it is preferable that the ratio I

[0111] of the peak intensity of the X-ray diffraction of the 111 plane of aluminum and the peak intensity I

[0200] of the X-ray diffraction of the 200 plane of the aluminum metal film (3) is 1.0 or higher, and more preferable that it is 2.0 or higher.

[0032] For reference, since aluminum is cubic, when aluminum is in powder form, the crystal orientation is random, so the peak intensity of the X-ray diffraction of the 111 plane is the greatest, and the intensity ratio I

[0200] / I

[0111] becomes less than 1.0. On the other hand, rolled aluminum foil becomes denser due to the rolling process and the crystal orientation becomes the same, so the peak intensity of the X-ray diffraction of the diagonal 111 plane I

[0111] is weaker, and the intensity ratio I

[0200] / I

[0111] becomes greater than 1.0. The larger the intensity ratio I

[0200] / I

[0111] , the denser the crystal orientation of the aluminum metal film (3) becomes, so the film resistance (surface resistance) is reduced, and the contact resistance of the contact surface is also reduced. The metal particles of the aluminum metal film produced by the conventional vacuum deposition method are columnar crystal films with large gaps, the peak intensity of X-ray diffraction on the 111 plane is the largest, and the intensity ratio I

[0200] / I

[0111] is less than 1.0.

[0033] By raising the surface temperature of the substrate (resin film; hereinafter, the resin film may be referred to as the substrate) during deposition, the columnar crystals become larger and denser, the crystals become symmetrical in the 200-plane direction, and the intensity ratio I

[0200] / I

[0111] becomes greater than 1.0.

[0034] However, if the substrate is a resin film, it melts and breaks when the substrate temperature is raised. Therefore, if it is manufactured without research, the substrate temperature cannot be raised, and the metal particles of the aluminum metal film produced by vacuum deposition become a columnar crystal film with large gaps, and the strength ratio I

[0200] / I

[0111] becomes less than 1.0.

[0035] In the present invention, even if the substrate is a resin film, it is successful to form appropriate irregularities on the surface of the aluminum metal film by growing large and dense columnar crystals of the aluminum metal film by introducing argon gas while raising the surface temperature of the substrate and increasing the crystal grain size. By forcibly cooling the resin film from the back side and increasing the heat generation of the deposition source, it is possible to raise the temperature only near the surface of the resin film exposed to the deposition source, thereby making the columnar crystals large and dense.

[0036] In the case of a general vacuum deposition method for aluminum, the boat heating method involves continuously supplying aluminum metal wire to a resistance heating boat, but when an aluminum metal film is formed in this way, the strength ratio I

[0200] / I

[0111] becomes less than 1.0.

[0037] Therefore, it is desirable to deposit the film in a short time by maximizing the heat output of the deposition source so that the substrate surface temperature rises easily. By using a deposition source with a high heat output, such as an induction heating method using a carbon crucible or a method heating by an electron beam, the heat output of the deposition source can be increased, allowing the crystal grains to grow large and dense. However, since the resin film would melt due to the heat if left as is, it is desirable to grow the columnar crystals of the aluminum metal film large and dense by forcibly cooling the resin film from the back side to a temperature just before it melts. In addition, by introducing argon gas during deposition, it becomes possible to form additional irregularities on the surface of the aluminum metal film.

[0038] Figures 4 and 5 are SEM images of the surface of an aluminum metal film when the surface roughness (Ra) of the resin film (polyethylene terephthalate (PET) film) is 1.6 nm, and the crystal grains are grown large and densely using an induction heating deposition source with a carbon crucible that generates a large amount of heat. Figure 4 is an SEM image of the surface of an aluminum metal film with a thickness of 1.48 μm, and Figure 5 is an SEM image of the surface of an aluminum metal film with a thickness of 0.53 μm. From Figures 4 and 5, it can be determined that appropriate irregularities could be formed on the surface of the aluminum metal film by increasing the crystal grain size. At this time, the surface roughness (Ra) was 8.3 nm in Figure 4 and 2.7 nm in Figure 5.

[0039] Figure 7 is a cross-sectional SEM image of the aluminum metal film of Figure 4, and it can be determined that the aluminum metal film is a columnar crystal and that the convex portion of the irregularities on the surface of the aluminum metal film corresponds to a single columnar crystal. Based on this, it is inferred that the larger the size of the convex portion of the irregularities on the surface of the aluminum metal film, the larger and denser the columnar crystals are. When comparing Figure 4 and Figure 5, it is inferred that the growth of the columnar crystals is greater in Figure 4, where the deposition time is longer and the heat content is greater in order to increase the film thickness.

[0040] Meanwhile, Fig. 6 is an SEM image of the surface of an aluminum metal film grown using a boat heating method in which an aluminum metal wire is continuously supplied to a general resistance heating boat. Fig. 6 is an SEM image of the surface of an aluminum metal film with a thickness of 1.12 μm, and the surface roughness (Ra) at this time was 2.2 nm. Since no distinct irregularities can be observed on the surface of the aluminum metal film in Fig. 6, it is presumed that the columnar crystals are not significantly grown and are not densely grown.

[0041] In addition, in order to make the metal film with large grains and a dense structure, it is necessary to expose it to a deposition source, which is a heat source, for a certain amount of time, and consequently, it is necessary to extend the deposition time. Therefore, it is desirable for the aluminum metal film thickness to be 0.7㎛ or more, and even more desirable if it is 1.0㎛ or more.

[0042] Method for manufacturing aluminum metal film

[0043] As a method for forming an aluminum metal film (3), a vacuum deposition method is preferred, which allows a metal film to be formed on a thin resin film without using an adhesive for the purpose of producing a thin electrode. Vacuum deposition methods include induction heating deposition, resistance heating deposition, laser beam deposition, and electron beam deposition, but among them, electron beam deposition, laser beam deposition, and induction heating deposition, which have a large amount of heat from the deposition source, are suitable for use. The amount of heat from the deposition source needs to be large enough to form large and dense crystal grains of the aluminum metal film (3), so the surface temperature of the substrate needs to be sufficiently high; however, since it is difficult to measure this, it is determined whether the amount of heat is sufficient by confirming that the aluminum metal film (3) after deposition has the required physical properties.

[0044] It is preferable that the aluminum metal film (3) has a specular reflectance of 30% or less at a wavelength of 555 nm on the surface of the metal film that is not in contact with the resin film, and that the ratio I

[0200] / I

[0111] of the peak intensity of the X-ray diffraction of the 111 plane of aluminum and the peak intensity I

[0200] of the X-ray diffraction of the 200 plane is 1.0 or more and 10 or less, and also that the surface roughness (Ra) of the surface of the metal film is 2.3 nm or more and 10.0 nm or less. However, if the heat output of the deposition source is raised to the required amount of heat, there is a possibility that the temperature of the resin film will rise and melt due to the management of the cooling function of the conventional vacuum deposition method, so it is necessary to perform deposition while managing the cooling function so that the film can be uniformly cooled so that the temperature does not rise excessively during deposition. Specifically, it is necessary to uniformly cool from the back side of the deposition surface using a cooling mechanism consisting of a metal plate or a metal roll that has been sufficiently cooled by a refrigerant. To achieve uniform cooling, it is essential to ensure that the resin film and the cooling mechanism are in close contact without creating any gaps between them.

[0045] For example, if there is a scratch on the metal roll of the cooling mechanism, the scratched area becomes a gap, and the resin film cannot be cooled in the scratched area, causing it to melt. For example, if foreign matter enters the resin film and the metal roll of the cooling mechanism, the resin film cannot be cooled due to the foreign matter and melts. If the heat output of the deposition source is increased to the required amount of heat, scratches on the metal roll or the inclusion of foreign matter, which are permissible in the conventional vacuum deposition method, become a problem, so it is necessary to manage scratches on the metal roll and the inclusion of foreign matter more strictly. By increasing the heat output of the deposition source and strengthening the management of the cooling function, it becomes possible to grow the crystal grains of the aluminum metal film (3) significantly and form them densely, leading to a reduction in internal resistance including contact resistance. In particular, in the case of electron beam deposition and laser beam deposition methods, it is more desirable to use an alumina crucible, which has better heat retention than a carbon crucible, as the deposition crucible, so that the heat output of the deposition source can be increased even more.

[0046] Suzy Film

[0047] The resin film (1) used in the present invention is preferably formed by molding a polymer, such as a synthetic resin, into a thin film. Examples of resin films suitable for use in the present invention include polyester films, polyethylene terephthalate films or polyethylene naphthalate films among polyester films, or polyimide films, polyphenylene sulfide films, and polypropylene films. Among these, polyethylene terephthalate films are more preferably used. These resin films may be used alone or as composites. Additionally, it may be used if a resin or adhesive is coated on the surface of the resin film.

[0048] The thickness of the resin film (1) is preferably 1 μm or more and 20 μm or less, and is more preferably 3 μm or more and 10 μm or less. For thinning of the electrode substrate, it is more preferable for the thickness of the resin film to be thin, preferably 20 μm or less, and more preferably 10 μm or less. However, if it is too thin, there is a possibility of reducing the yield due to breakage during the manufacturing process, so it is preferable for it to be 1 μm or more, and more preferably 3 μm or more.

[0049] It is preferable that the surface roughness (Ra) of the resin film is 0.6 nm or more and 2.0 nm or less. If the surface roughness of the resin film is 0.6 nm or less, it may stick together when the resin film is wound into a roll, making transport difficult. It is preferable that the surface roughness of the resin film be 0.6 nm or more, and more preferable that it be 1.0 nm or more. On the other hand, since it is preferable for the surface irregularities of the aluminum metal film to be large, it is undesirable to increase the surface roughness (Ra) of the resin film so that it becomes prone to breakage during transport. Since it is desirable for the resin film to form the minimum irregularities necessary for transport and to be as smooth as possible, it is preferable that the surface roughness (Ra) be 2.0 nm or less, and more preferable that it be 1.5 nm or less.

[0050] Anchor layer

[0051] An anchor layer (2) may be present between the resin film and the aluminum metal film (3) of the metallization film (4) of the present invention. By forming the anchor layer (2), an improvement in the adhesion between the resin film and the aluminum metal film can be expected. As for the anchor layer (2), it is preferable to form a metal layer on the resin film by a sputtering method. Since the thickness of the anchor layer can be reduced using the sputtering method, it is optimal for applications requiring thinner capacitors.

[0052] As for the anchor layer (2), it is preferable that the anchor layer (2) be a metal layer comprising one or more selected from the group consisting of aluminum, nickel, titanium, nichrome, and chromium, but it is even more preferable that the anchor layer (2) be an aluminum metal layer formed by sputtering. At this time, it is important to ensure that the surface of the metal selected as the anchor layer (2), such as aluminum, nickel, titanium, chromium, and nichrome, is not oxidized, and that a copper layer is formed thereon. Specifically, after forming the metal layer as the anchor layer (2) by sputtering, it is important to form the aluminum metal film (3) while maintaining a vacuum without opening it to the atmosphere. If the surface of the metal selected as the anchor layer (2), such as aluminum, nickel, titanium, chromium, and nichrome, is oxidized, a stable metal oxide film is formed, making it difficult to form a metal bond with the interface with the aluminum metal film (3) formed thereon, so that adhesion is not secured, and the aluminum metal film (3) may peel off from the anchor layer (2). Therefore, it is important not to oxidize aluminum, nickel, titanium, chromium, nichrome, etc., selected as the anchor layer (2). When the anchor layer (2) is an aluminum metal layer formed by sputtering, if an aluminum metal film (3) is vacuum deposited thereon, the columnar crystals grow larger and denser, thereby further suppressing the contact resistance of the aluminum metal film, which is desirable.

[0053] The thickness of the anchor layer (2) is preferably 3 nm or more and 40 nm or less, and more preferably 5 nm or more and 20 nm or less. If the thickness is less than 3 nm, sufficient adhesion may not be obtained. On the other hand, since the effect of improving adhesion does not increase even if the anchor layer is made larger than 40 nm, it is preferable that it be 40 nm or less, and when the anchor layer is produced by a sputtering method with a slow film formation speed, it is more preferable to make the anchor layer 20 nm or less to improve productivity.

[0054] (Example)

[0055] The present invention will be described below based on examples. Furthermore, the present invention is not limited to these examples, and modifications and changes to these examples are possible based on the spirit of the present invention, and such modifications are not excluded from the scope of the invention.

[0056] (Magneron sputtering)

[0057] A resin film is installed inside a batch-type vacuum deposition apparatus (Alvacze EBH-800), a 50mm × 550mm target is used, and a vacuum attainment of 5×10 is achieved in an argon gas atmosphere. -1 The DC power was adjusted to Pa or less and continuously applied for a time until a predetermined metal film thickness was reached.

[0058] Alternatively, install a resin film inside a roll-type vacuum deposition apparatus (Alvacze EWC-060), use a 70mm × 550mm target, and achieve a vacuum attainment of 1×10 in an argon gas atmosphere. -2 A metal layer was formed by adjusting the value to Pa or lower and applying a pulse power supply.

[0059] In addition, unless otherwise specified, sputtering and vacuum deposition were performed continuously, and contact with the atmosphere was prevented between the anchor layer and the aluminum metal film.

[0060] (Vacuum deposition)

[0061] After installing a resin film inside a batch-type vacuum deposition apparatus (Alvacze EBH-800) and stacking an amount of aluminum to the target thickness on the deposition boat, a vacuum reach of 9.0×10 -3 After vacuuming until the temperature was below Pa, the deposition boat was heated to perform vacuum deposition, thereby forming an aluminum metal film.

[0062] Alternatively, a resin film was placed in a roll-type vacuum deposition apparatus (Alvac EWC-060), and vacuum deposition was performed by heating an aluminum ingot using an induction heating deposition method employing a carbon crucible at a conveying speed and output conditions such that the aluminum film thickness becomes a predetermined value, thereby forming an aluminum metal film.

[0063] Alternatively, a resin film was installed in a roll-type vacuum deposition apparatus (Alvacze EWC-060), and vacuum deposition was performed by introducing an aluminum wire into a deposition boat heated by a resistance heater at a conveying speed at which the aluminum film thickness becomes a predetermined value, thereby forming an aluminum metal film.

[0064] (Regarding the introduction of argon gas)

[0065] The argon gas introduced during magnetron sputtering is used. Since sputtering and vacuum deposition were not performed simultaneously in the batch vacuum deposition apparatus (Alvacze EBH-800), argon gas was not introduced during vacuum deposition.

[0066] In the roll-type vacuum deposition apparatus (Alvacze EWC-060), sputtering and vacuum deposition are processed continuously; therefore, sputtering and vacuum deposition are performed simultaneously within the same deposition chamber, and argon gas is always introduced into the deposition source for vacuum deposition.

[0067] (XRD (X-ray diffraction) measurement method)

[0068] Measurements were taken using X-ray diffraction (RIGAKU SmartLab 9kW). The measurement conditions were X-ray tube voltage and current: 45kV-200mA, scanning speed: 2° / min, incident slit: 1.0mm, and receiving slit: 1.0mm. The peak intensity of the X-ray diffraction of plane 111 I

[0111] and the peak intensity of the X-ray diffraction of plane 200 I

[0200] obtained from the measurement results were calculated, and the ratio I

[0200] / I

[0111] was calculated and compared.

[0069] (Spectrophotometer absolute reflectance)

[0070] An absolute reflectance measuring device ASR-3105 (angle of incidence 5°) was attached to the large sample chamber unit MPC-603A of the UV-3600i Plus spectrophotometer manufactured by Shimadzu Seisakusho Co., Ltd., and the reflectance of the measurement sample was measured using the aluminum mirror attached to the absolute reflectance measuring device as a reference. The reflectance data at 555 nm of visible light was taken as the representative value.

[0071] (Contact resistance measurement)

[0072] A metallization film was placed on a 10mm thick NR sponge rubber (NRS-06 manufactured by Waki ​​Sangyo Co., Ltd.) with the metal film facing upward, and two gold-plated copper plates measuring 25mm × 25mm were placed with a 500g weight on each plate at a distance of 1mm. The resistance between the two copper plates was measured using a resistance meter RM3544 manufactured by Hioki Denki Co., Ltd. and recorded as the contact resistance.

[0073] (Surface resistance measurement)

[0074] The metallized film was cut to a size of approximately 300 mm × approximately 80 mm, and the surface resistance at three points was measured using the 4-terminal method with a simple low-resistivity meter ("Loresta" (registered trademark) EP MCP-T360 manufactured by Mitsubishi Chemical Analytic Tech Co., Ltd.), and the average value was adopted as the surface resistance value.

[0075] (Aluminum metal film thickness)

[0076] The metallization film was cut to a size of approximately 30 mm × approximately 30 mm, 10 sheets were stacked and their thickness measured with a micrometer, and the thickness of the metallization film per sheet was calculated. Then, the thickness of the aluminum metal film was calculated from the difference between the thickness of the metallization film calculated from the thickness of the undeposited resin film, which was also stacked and measured with a micrometer, and the thickness of the aluminum metal film.

[0077] (Surface roughness)

[0078] Surface roughness (Ra) was measured using a scanning white interference microscope manufactured by Hitachi High-Tech Science Co., Ltd. The measurement conditions were set to measurement mode "wave," light source 530 White, and objective lens 50x. Using the included analysis software, the values ​​calculated under the conditions of surface correction 4th order, enhancement "complete," and Gaussian filter "cutoff 2㎛" were used.

[0079] (In-depth evaluation)

[0080] A paper adhesive tape (NITTO, No. 720) with a width of 18 mm was bonded to the surface of an aluminum metal film, and then, when the paper adhesive tape (NITTO, No. 720) was peeled off, it was determined whether the deposited film peeled off from the resin film. If the deposited film peeled off from the resin film, it was marked × (Fail), and if it did not peel off, it was marked ○ (Pass), serving as a criterion for determining whether it could be used as a metallization film for the positive electrode of a secondary battery.

[0081] (Example 1)

[0082] A biaxially oriented polyethylene terephthalate film (manufactured by SKC Co., Ltd., Type: SC42) with a thickness of 11.5 μm was used as the resin film. The surface roughness of this resin film was 1.6 nm. The resin film was installed on a roll disc of this resin film inside a roll-type vacuum deposition apparatus (Alvac EWC-060), and aluminum was deposited by sputtering to a thickness of 5 nm by applying a pulsed power source. As a condition, a sputtering output of 2.0 kW was adopted using a pulsed power source. Subsequently, an aluminum metal film was vacuum deposited to a thickness of 1.48 μm by vacuum deposition by heating the aluminum ingot using an induction heating deposition method employing a carbon crucible.

[0083] For the metallized film produced in this way, the ratio of the peak intensity of the X-ray diffraction of the 111th plane of aluminum I

[0111] to the peak intensity of the X-ray diffraction of the 200th plane I

[0200] / I

[0111] was 4.3, the specular reflectance at a wavelength of 555 nm of the aluminum metal film surface not in contact with the resin film was 3.4%, and the surface roughness was 8.3 nm.

[0084] The surface resistance of the aluminum metal film surface not in contact with the resin film of this metal film was 0.037Ω / □, the contact resistance was 8.63mΩ, and the ratio of the contact resistance to the surface resistance [contact resistance / surface resistance] was 0.24.

[0085] The contact resistance value was 15 mΩ or less, and the contact resistance was sufficiently small and the judgment was passed.

[0086] (Examples 2–5)

[0087] A metallized film was prepared and evaluated in the same manner as in Example 1, except that the thickness of the aluminum metal film was as specified in Table 1. The results are shown in Table 1.

[0088] (Example 6)

[0089] A biaxially oriented polyethylene terephthalate film with a thickness of 11.5 μm (manufactured by SKC, Type: SC42) was used as the resin film. The surface roughness of this resin film was 1.6 nm. The resin film was installed on a roll disc inside a roll-type vacuum deposition apparatus (Alvac EWC-060), and while introducing argon gas, a vacuum attainment of 1 × 10⁻⁶ -2 After adjusting to Pa or lower, vacuum deposition was performed by inserting an aluminum wire into a deposition boat heated by a resistance heater, and an aluminum metal film was vacuum deposited to a thickness of 1.04 μm and evaluated. The results are shown in Table 1.

[0090] (Example 7)

[0091] A biaxially oriented polyethylene terephthalate film (manufactured by SKC, Type: SC42) with a thickness of 11.5 μm was used as the resin film. The surface roughness of this resin film was 1.6 nm. The resin film was installed on a roll disc inside a roll-type vacuum deposition apparatus (ALVAC EWC-060), and aluminum was deposited by sputtering to a thickness of 5 nm by applying a pulsed power source. As a condition, a sputtering output of 2.0 kW using a pulsed power source was adopted. Subsequently, vacuum deposition was performed by inserting an aluminum wire into a deposition boat heated by a resistance heater to vacuum deposit an aluminum metal film to a thickness of 1.00 μm, and the results were evaluated. The results are shown in Table 1.

[0092] (Comparative Example 1)

[0093] A biaxially oriented polyethylene terephthalate film (manufactured by SKC, Type: SC42) with a thickness of 11.5 μm was used as the resin film. The surface roughness of this resin film was 1.6 nm. The resin film was placed inside a batch vacuum deposition apparatus (Alvac EBH-800), and aluminum was deposited by sputtering to a thickness of 5 nm by applying a pulsed power source. As a condition, a sputtering output of 2.0 kW was adopted using a pulsed power source. Subsequently, an aluminum metal film was vacuum deposited to a thickness of 1.44 μm by resistance heating deposition, which heats the deposition boat.

[0094] For the metallized film produced in this way, the ratio of the peak intensity of the X-ray diffraction of the 111th plane of aluminum I

[0111] to the peak intensity of the X-ray diffraction of the 200th plane I

[0200] / I

[0111] was 0.3, the specular reflectance at a wavelength of 555 nm of the surface of the aluminum metal film not in contact with the resin film was 71.1%, and the surface roughness was 1.6 nm.

[0095] The surface resistance of the aluminum metal film surface not in contact with the resin film of this metal film was 0.038Ω / □, the contact resistance was 15.38mΩ, and the ratio of the contact resistance to the surface resistance [contact resistance / surface resistance] was 0.41.

[0096] The contact resistance value was greater than 15 mΩ, and the contact resistance was high relative to the surface resistance, and the judgment was passed ×.

[0097] (Comparative Examples 2–5)

[0098] Metallized films were prepared and evaluated in the same manner as Comparative Example 1, except that the thickness of the aluminum metal film was as specified in Table 1. The results are shown in Table 1.

[0099] Explanation of the symbols

[0100] 1 Resin film 2 Anchor Layer 3 aluminum metal film 4 Metallized film

Claims

Claim 1 A metallized film for a positive electrode of a secondary battery, wherein an aluminum metal film is formed on at least one surface of a resin film, the specular reflectance at a wavelength of 555 nm on the surface of the metal film not in contact with the resin film is 30% or less, and the surface roughness (Ra) of the metal film is 2.3 nm or more and 10.0 nm or less. Claim 2 A metallized film for a positive electrode of a secondary battery according to claim 1, wherein the ratio I[200] / I[111] of the peak intensity of the X-ray diffraction of the 111 plane and the peak intensity of the X-ray diffraction of the 200 plane of the aluminum of the metal film is 1.0 or greater. Claim 3 A metallized film for a positive electrode of a secondary battery according to claim 1 or 2, wherein the surface resistance of the metal film is 0.15Ω / □ or less. Claim 4 A metallized film for a positive electrode of a secondary battery according to claim 1 or 2, wherein the surface roughness (Ra) of the resin film is 0.6 nm or more and 2.0 nm or less. Claim 5 delete Claim 6 A method for manufacturing a metallized film for a positive electrode of a secondary battery as described in claim 1 or 2, comprising a process of forming a film by depositing the vaporized aluminum onto a resin film by a vacuum deposition method in which argon gas is introduced when aluminum, which is a deposition source, is heated and vaporized by at least one selected from the group consisting of resistance heating, induction heating, and an electron beam. Claim 7 A method for manufacturing a metallized film for a positive electrode of a secondary battery, wherein, in claim 6, after forming a film of aluminum on a resin film by sputtering, the aluminum is deposited by at least one selected from the group consisting of resistance heating, induction heating, and an electron beam without opening to the atmosphere.

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