Metallized film for secondary battery positive electrode

Abstract

To acquire a production method which is capable of uniformly applying an active material to a film collector foil by roll conveyance without the occurrence of wrinkles or folds caused by heating or dimensional shrinkage during the roll conveyance even if the film collector foil is obtained by forming a conductive thin film layer on a resin surface and has a lower stiffness in comparison to conventional aluminum foils.SOLUTION: There is provided a metallized film for secondary battery positive electrodes, which is obtained by forming an aluminum metal film on at least one surface of a resin film. The metallized film has a dimensional change rate in the MD direction of -0.10% or less and a dimensional change rate in the TD direction of -0.4% or more and less than -0.02% after a heat treatment at 150°C for 30 minutes.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a metallized film for a positive electrode of a secondary battery. [Background technology]

[0002] In recent years, due to the miniaturization of electrical and electronic devices and environmental concerns, storage batteries such as secondary batteries and capacitors for non-gasoline vehicles (hybrid vehicles, electric vehicles) are required to be smaller and lighter, while at the same time having a high power density that allows them to charge and discharge large currents instantaneously.

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

[0004] Another way to achieve high power density is to reduce the resistance of the various materials that make up a battery (the battery's internal resistance). Aluminum foil is often used as the current collector in batteries, but conventional aluminum foil current collectors have an oxide film on their surface, which is thought to increase internal resistance. Increased internal resistance leads to voltage drops during high-current charging and discharging, resulting in reduced battery output. Aluminum typically forms a strong, insulating, native oxide film, typically 5–10 nm thick, but its surface exhibits good electrical conductivity. Theories about the reason for this include current flow through defects in the oxide film, and the quantum mechanical tunneling effect, in which particles pass through a region that is normally inaccessible due to energy constraints. When an electronic conductor approaches an electrical insulator within a distance of approximately 10 nm, good electrical conductivity is achieved. While the theory is not entirely clear, it is believed that the aluminum oxide film itself has a significant impact on internal resistance.

[0005] One method for reducing the contact resistance between an electrode that suppresses the increase in internal resistance due to an oxide film and an active material is to roughen the surface of the metal foil used in the electrode (for example, Patent Document 1). It is not clear whether roughening the aluminum surface increases the number of defects or whether forming many protrusions makes it easier for the tunnel effect to occur, but this is an effective method for reducing contact resistance.

[0006] As a method for improving power density while reducing size and weight, efforts have been made to thin electrode substrates with the aim of improving volumetric energy density and weight energy density. However, simply thinning the metal foil used in the electrode to address this issue results in a lack of strength. Furthermore, increasing the surface roughness of the thinned metal foil in order to reduce contact resistance is undesirable as it further reduces the strength of the metal foil. Therefore, as a new material to replace metal, a current collector function has been proposed for use as an electrode substrate (e.g., Patent Document 2). The material is composed of a biaxially oriented polyester thin film, which has excellent mechanical properties and heat-resistant dimensional stability, and a conductive thin film layer of metal or the like provided on the surface. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-160053 [Patent Document 2] Japanese Patent Application Publication No. 10-40919 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the case of a structure in which a conductive thin film layer of metal or the like is provided on the surface of a resin film such as a polyester thin film film, the rigidity is weaker than that of conventional aluminum foil, and dimensional shrinkage occurs due to heat treatment, which causes wrinkles and folds during roll transport, making it very difficult to uniformly apply the active material during roll transport.

[0009] Furthermore, the metal thickness is thinner than the metal foils used previously, resulting in an increase in the total electrical resistance. Even if the metal surface is roughened to reduce the contact resistance of the aluminum metal surface, the conductive thin film layer of metal or the like on the surface of the resin film is typically a vapor-deposited metal film formed by a vacuum deposition method or the like, and since it is a thin metal film, it is very difficult to roughen it by etching or the like. Roughening the surface of the polyester thin film film itself makes it more susceptible to breakage, making it difficult to transport during the manufacturing process.

[0010] In view of the above, an object of the present invention is to provide a metallized film that can be transported without increasing contact resistance and without breaking or wrinkling over time, even when a conductive thin film layer is formed on the resin surface. [Means for solving the problem]

[0011] As a result of intensive research in light of the above-mentioned problems, the inventors have succeeded in developing a metallized film that has low contact resistance and does not break during roll transport or develop wrinkles over time, by controlling the processing temperature and tension as well as the surface shape of the vapor-deposited metal film when or immediately after forming the vapor-deposited metal film using a vacuum vapor deposition method, and have been able to produce such a film, as well as a method for producing the same.

[0012] That is, the present invention provides a metallized film for a secondary battery positive electrode, which comprises a resin film having an aluminum metal film formed on at least one surface thereof and wound into a roll, the metallized film for a secondary battery positive electrode being characterized in that, after heat treatment at 150°C for 30 minutes, the dimensional change rate in the MD direction is -0.10% or less and the dimensional change rate in the TD direction is -0.4% or more but less than -0.02%. the ratio I

[0111] / I

[0111] of the peak intensity I

[0111] of the X-ray diffraction of the aluminum of the metal film in the 111 plane to the peak intensity I

[0200] of the X-ray diffraction of the aluminum of the 200 plane is 1.0 or more, and the specular reflectance at a wavelength of 555 nm of the metal film surface not in contact with the resin film is 30% or less; the metallized film for a secondary battery positive electrode, wherein the surface resistance of the metal film is 0.15 Ω / □ or less; the metallized film for a secondary battery positive electrode, wherein the resin film has a surface roughness Ra of 0.6 nm or more and 2.0 nm or less; The present invention relates to the above metallized film for a secondary battery positive electrode, wherein the surface roughness Ra of the metal film is 2.3 nm or more and 10.0 nm or less. [Effects of the Invention]

[0013] According to the present invention, it is possible to obtain a metallized film that can be transported by rolls without increasing contact resistance and without breaking or wrinkling over time, even when a conductive thin film layer is formed on the resin surface, and a method for producing the same. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional schematic view of a metallized film of the present invention. [Figure 2] 1 is a cross-sectional schematic view of a metallized film of the present invention. [Figure 3] 1 is a cross-sectional schematic view of a metallized film of the present invention. [Figure 4] This is an electron microscope (SEM) photograph of the surface of an aluminum metal film (film thickness 1.48 μm) when large, dense crystal grains were grown using an induction heating evaporation source with a carbon crucible. [Figure 5] This is an SEM photograph of the surface of an aluminum metal film (film thickness 0.53 μm) when large, dense crystal grains were grown using an induction heating evaporation source with a carbon crucible. [Figure 6]This is an SEM photograph of the cross section of an aluminum metal film (thickness 1.48 μm) grown with large, dense crystal grains using an induction heating evaporation source with a carbon crucible (same as Figure 4, but viewed from a different angle). DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below.

[0016] <Metallized film> Metallized film 4 of the present invention has aluminum metal film 3 on one or both surfaces of resin film 1 (FIGS. 1, 2, and 3).

[0017] The metallized film 4 of the present invention is flexible, allowing it to be unwound from a roll when coating an active material onto the metallized film, and then wound into a roll after passing through the surface coating and drying processes. Processing in roll form makes the metallized film easier to handle, allows for faster processing, and reduces the space required for processing equipment. However, compared to conventional aluminum foil, the metallized film 4 has lower rigidity and greater thermal shrinkage. Therefore, when conveyed by rolls during processing that involves heat treatment, the metallized film is prone to breakage or streaking, resulting in poor processing. In particular, if the metallized film experiences significant thermal shrinkage in the film width direction (sometimes referred to as the TD direction), which is perpendicular to the roll conveyance direction (sometimes referred to as the MD direction), thermal shrinkage in the TD direction can initiate and cause wrinkles and folds during roll conveyance. Therefore, it is preferable for the metallized film to have minimal thermal shrinkage in the TD direction. Tensile stress is generated in the aluminum metal film as crystal grains grow in the film after deposition. If this tensile stress and the shrinkage amount in the TD direction of the film are far apart, the film will change over time after deposition, resulting in wrinkles in the MD direction and a decrease in the quality of the deposited film. Specifically, the dimensional change rate in the TD direction (negative shrinkage) after heat treatment at 150°C for 30 minutes is preferably -0.4% or more and less than -0.02%, and more preferably -0.3% or more and less than -0.02%.

[0018] A common method for reducing thermal shrinkage in the TD direction is to accelerate the thermal shrinkage of the resin in the metallized film by heating. However, if the thermal shrinkage of the metallized film in both the TD and MD directions is reduced equally, deformation and flexibility will be lost due to uneven shrinkage in the MD and TD directions, which may cause the film to lose flatness during transport and lead to deformation such as wrinkles. Therefore, it is preferable that the thermal shrinkage in the MD direction be a certain value or higher. Specifically, the dimensional change in the MD direction after heat treatment at 150°C for 30 minutes is preferably -0.10% or less, and more preferably -0.20% or less.

[0019] To achieve a dimensional change of -0.10% or less in the MD and a dimensional change of -0.4% or more but less than -0.02% in the TD after heat treatment at 150°C for 30 minutes, a heat treatment can be performed while applying tension to the resin film or metallized film in the MD. The tension and heating conditions vary greatly depending on the type of resin in the resin film, the thickness of the resin film, the film width, the vapor-deposited metal film, and the diameter and pitch of the transport rolls during heat treatment. By adjusting and optimizing the tension and heating conditions, it is possible to adjust the dimensional change of the metallized film after heat treatment at 150°C for 30 minutes so that the dimensional change in the MD is -0.10% or less and the dimensional change in the TD is -0.4% or more but less than -0.02%.

[0020] The heat treatment may be carried out before, during or after deposition, but is more preferably carried out during vacuum deposition, which does not require an additional heat treatment step.

[0021] <Aluminum metal film> The aluminum metal film 3 in the present invention is an aggregate of aluminum metal, consisting of one or more laminated layers each containing aluminum as the main component. The term "main component" refers to a component that accounts for more than 80 atomic % of the entire layer, taken as 100 atomic %.

[0022] The thickness of the aluminum metal film 3 in the present invention 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.

[0023] For electrode applications, lower electrical resistance is preferable, and in terms of surface resistance, the metal film surface resistance is preferably 0.15 Ω / □ or less, and more preferably 0.05 Ω / □ or less. On the other hand, since thinning is necessary to improve energy density, simply increasing the thickness of the metal film is not preferable. 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 will be lower and the increase in internal resistance can be reduced. On the other hand, to improve volumetric energy density, it is necessary to further reduce the thickness of the electrode substrate, and a thickness of 3.0 μm or less is preferable, and a thickness of 2.5 μm or less is more preferable.

[0024] The aluminum metal film 3 in the present invention has the feature that contact resistance can be reduced by controlling the crystal growth of the metal film so that the surface roughness becomes large when the film is formed by vacuum deposition.

[0025] The aluminum metal film 3 of the metallized film 4 is placed on a 10 mm thick piece of NR sponge rubber with the aluminum metal layer 3 facing upward. Two 25 mm x 25 mm gold-plated copper plates are placed 1 mm apart, with a 500 g weight placed on each copper plate. The resistance between the two copper plates is taken as the contact resistance. To minimize the increase in internal resistance, the contact resistance is preferably 15 mΩ or less, and more preferably 10 mΩ or less. The contact resistance here includes the contact resistance of the two 25 mm x 25 mm electrode surfaces and the film resistance (surface resistance) between the two electrodes. Therefore, the ratio of the contact resistance to the surface resistance [contact resistance] / [surface resistance] indicates a value that is minimally affected by surface resistance. The ratio of the surface resistance [contact resistance] / [surface resistance] is preferably 0.35 or less, and more preferably 0.25 or less.

[0026] As a feature of the surface of the aluminum metal film 3 that controls the crystal growth of the metal film and reduces contact resistance, the specular reflectance of the surface of the aluminum metal film 3 that is not in contact with the resin film at a wavelength of 555 nm is preferably 30% or less, and more preferably 20% or less. This is because the surface of the aluminum metal film is finely roughened, which reduces the specular reflectance of visible light at 555 nm, and is effective in reducing contact resistance.

[0027] As a feature of the surface of the aluminum metal film 3 that controls the crystal growth of the metal film and reduces contact resistance, the surface roughness Ra of the surface of the aluminum metal film 3 that is not in contact with the resin film 1 is preferably 2.3 nm or more and 10.0 nm or less, and more preferably 5.0 nm or more and 10.0 nm or less. When the aluminum surface is sufficiently roughened and a certain degree of height is ensured between the convex and concave portions, contact resistance tends to be low, and the larger the surface roughness Ra, the more preferable it tends to be. However, if the surface roughness Ra is too large, the thin aluminum metal film 3 may break during transportation or bending, so a surface roughness of 10.0 nm or less is preferable.

[0028] As a feature of the surface of the aluminum metal film 3 that controls the crystal growth of the metal film and reduces contact resistance, the ratio I

[0111] / I

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

[0111] of the aluminum 111 plane of the aluminum metal film 3 to the X-ray diffraction peak intensity I

[0200] of the aluminum 200 plane is preferably 1.0 or more, and more preferably 2.0 or more.

[0029] For reference, because aluminum has a cubic crystal system, when aluminum is in powder form, the crystal orientation is random, resulting in the largest peak intensity of X-ray diffraction from the 111 plane, and the intensity ratio I

[0200] / I

[0111] being less than 1.0. On the other hand, rolled aluminum foil becomes denser through the rolling process, and the crystal orientation is aligned, so the peak intensity I

[0111] of X-ray diffraction from the oblique 111 plane is weaker, and the intensity ratio I

[0200] / I

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

[0200] / I

[0111] , the more densely aligned the crystal orientation of the aluminum metal film 3 is, resulting in a smaller film resistance (surface resistance) and a lower contact resistance at the contact surface. The metal particles in aluminum metallized films produced by conventional vacuum deposition methods are columnar crystal films with large gaps, and the X-ray diffraction peak intensity of the 111 plane is the strongest, with the intensity ratio I

[0200] / I

[0111] being less than 1.0.

[0030] By raising the surface temperature of the substrate (resin film; hereafter, the resin film will be referred to as the substrate) during vapor deposition, the columnar crystals become larger and denser, the crystals align in the 200-plane direction, and the intensity ratio I

[0200] / I

[0111] becomes greater than 1.0.

[0031] However, if the substrate is a resin film, increasing the substrate temperature will cause it to melt and break, so if it is produced without any ingenuity, the substrate temperature cannot be raised and the metal particles in the aluminum metallized film produced by vacuum deposition will become a columnar crystal film with large gaps, and the intensity ratio I

[0200] / I

[0111] will be less than 1.0.

[0032] In the present invention, even if the substrate is a resin film, by growing the columnar crystals of the aluminum metal film large and densely, and by increasing the size of the crystal grains, we succeeded in forming an appropriate unevenness on the surface of the aluminum metal film. While forcibly cooling the resin film from the back side, the heat generation of the evaporation source was increased, and a vacuum of 9.0 × 10 -3 Pa or more, 1×10 -2 By using a vacuum deposition method controlled at a pressure below 1 Pa, it is possible to increase the temperature only near the surface of the resin film where the deposition source is exposed, thereby making it possible to produce large, dense columnar crystals.

[0033] The evaporation source used is an induction heating method using a carbon crucible or an electron beam heating method, which generates a large amount of heat. Alternatively, even if the evaporation source is a heating boat method, the distance between the evaporation source and the resin film is shortened to increase the amount of heat transferred to the resin film surface. An inert gas such as argon is introduced, and a vacuum of 9.0 x 10 is created. -3 Pa or more, 1×10 -2 The crystal grains are grown large and dense by a vacuum deposition method controlled at a pressure of 100 Pa or less. However, since the resin film will melt due to heat if left as is, it is preferable to forcibly cool the resin film from the back side to a temperature just below the melting point, thereby growing the columnar crystals of the aluminum metal film large and dense and forming appropriate irregularities on the surface of the aluminum metal film.

[0034] Figures 4 and 5 are SEM photographs of the surface of an aluminum metal film when large, dense crystal grains were grown on a resin film (polyethylene terephthalate (PET) film) with a surface roughness Ra of 1.6 nm using an induction heating evaporation source with a carbon crucible that generates a large amount of heat. Figure 4 is an SEM photograph of the surface of an aluminum metal film with a thickness of 1.48 μm, and Figure 5 is an SEM photograph of the surface of an aluminum metal film with a thickness of 0.53 μm. It can be seen from Figures 4 and 5 that by increasing the crystal grain size, it is possible to form appropriate irregularities on the aluminum metal film surface. The surface roughness Ra in this case was 8.3 nm in Figure 4 and 2.7 nm in Figure 5.

[0035] Figure 6 is a cross-sectional SEM photograph of the aluminum metal film in Figure 4, from which it can be seen that the aluminum metal film is columnar crystals, and that each convex part of the unevenness on the aluminum metal film surface corresponds to a single columnar crystal. From this, it can be inferred that the larger the convex part of the unevenness on the aluminum metal film surface, the larger and denser the columnar crystals. Comparing Figure 4 and Figure 5, it can be inferred that the growth of columnar crystals is greater in Figure 4, where the deposition time is longer and the heat amount is greater to increase the film thickness.

[0036] Furthermore, to produce a dense metal film with large crystal grains, it is necessary to expose the film to the evaporation source, which is a heat source, for a certain period of time, which results in a longer evaporation time. The aluminum metal film thickness is preferably 0.7 μm or more, and more preferably 1.0 μm or more.

[0037] <Method for producing aluminum metal film> The preferred method for forming the aluminum metal film 3 is vacuum deposition, which can form a metal film on a thin resin film without using an adhesive, for the purpose of producing thin electrodes. Vacuum deposition methods include induction heating deposition, resistance heating deposition, laser beam deposition, and electron beam deposition. Among these, electron beam deposition, laser beam deposition, and induction heating deposition, which generate large amounts of heat from the deposition source, are preferred. The heat generation rate of the deposition source must be large enough to form large, dense crystal grains in the aluminum metal film 3, and the substrate surface temperature must be sufficiently high. However, this is difficult to measure, so whether the heat generation rate is sufficient is determined by checking that the aluminum metal film 3 after deposition has the required physical properties.

[0038] The aluminum metal film 3 preferably has a specular reflectance of 30% or less at a wavelength of 555 nm on the surface of the metal film not in contact with the resin film. The ratio of the X-ray diffraction peak intensity I

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

[0200] of the aluminum 200 plane, I

[0111] , is preferably 1.0 or more and 10 or less. Furthermore, the surface roughness Ra of the metal film is preferably 2.3 nm or more and 10.0 nm or less. However, if the heat output of the evaporation source is increased to the required heat output, the resin film may rise in temperature and melt if the cooling function of a conventional vacuum evaporation method is not controlled. Therefore, during evaporation, the cooling function must be controlled to ensure uniform cooling of the film and prevent excessive temperature rise. Specifically, uniform cooling is required from the backside of the evaporation surface using a cooling mechanism consisting of a metal plate or metal roll sufficiently cooled by a refrigerant. Uniform cooling requires close contact between the resin film and the cooling mechanism without any gaps.

[0039] For example, scratches on the metal rolls of the cooling mechanism create gaps, preventing the resin film from cooling and resulting in melting. For example, if foreign matter gets into the resin film and the metal rolls of the cooling mechanism, the foreign matter prevents the resin film from cooling and melts. Increasing the heat output of the evaporation source to the required level can cause scratches and foreign matter in the metal rolls, which are acceptable in conventional vacuum evaporation processes, to become a problem. Therefore, stricter control of scratches and foreign matter in the metal rolls is required. Increasing the heat output of the evaporation source and strengthening control of the cooling function can result in larger and denser crystal grains in the aluminum metal film 3, leading to reduced internal resistance, including contact resistance. In particular, for electron beam evaporation and laser beam evaporation, using an alumina crucible, which has better heat retention than a carbon crucible, is even more preferable because it allows for greater heat output from the evaporation source.

[0040] <Resin film> The resin film 1 used in the present invention is preferably a thin film formed from a polymer such as a synthetic resin. Examples of resin films suitable for use in the present invention include polyester films, and among polyester films, polyethylene terephthalate films and polyethylene naphthalate films, as well as polyimide films, polyphenylene sulfide films, and polypropylene films. Of these, polyethylene terephthalate films are more preferred. These resin films may be used alone or in combination. Furthermore, resin films whose surfaces are coated with resins, adhesives, or the like may also be used.

[0041] The thickness of the resin film 1 is preferably 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 10 μm or less. To reduce the thickness of the electrode substrate, a thinner resin film is more preferable, preferably 20 μm or less, and more preferably 10 μm or less. However, if the resin film is too thin, breakage during the manufacturing process may occur, reducing the yield. Therefore, the thickness is preferably 1 μm or more, and more preferably 3 μm or more.

[0042] The surface roughness Ra of the resin film is preferably 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, when the resin film is wound into a roll, it may stick to the surface, making it difficult to transport. The surface roughness of the resin film is preferably 0.6 nm or more, and more preferably 1.0 nm or more. On the other hand, since it is preferable that the surface roughness of the aluminum metal film is large, if the surface roughness Ra of the resin film is large, the resin film is likely to break during transport, which is not preferable. It is preferable that the resin film has the minimum amount of roughness necessary for transport and is as smooth as possible, so the surface roughness Ra is preferably 2.0 nm or less, and more preferably 1.5 nm or less.

[0043] <Anchor layer> The metallized film 4 of the present invention may have an anchor layer 2 between the resin film and the aluminum metal film 3. By providing the anchor layer 2, it is expected that the adhesion between the resin film and the aluminum metal film will be improved. As the anchor layer 2, it is preferable to form a metal layer on the resin film by a sputtering method. The sputtering method makes it possible to reduce the thickness of the anchor layer, which is ideal for storage battery applications where thinner layers are required.

[0044] The anchor layer 2 is preferably a metal layer containing at least one selected from the group consisting of aluminum, nickel, titanium, nichrome, and chromium. It is important to prevent oxidation of the surface of the metal selected for the anchor layer 2, such as aluminum, nickel, titanium, chromium, or nichrome, while forming the aluminum metal film on the metal. 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 exposing the metal layer to the atmosphere. If the surface of the metal selected for the anchor layer 2, such as aluminum, nickel, titanium, chromium, or nichrome, is oxidized, a stable metal oxide film is formed, which makes it difficult to form a metal bond with the interface with the aluminum metal film 3 formed thereon. This can lead to insufficient adhesion and the aluminum metal film 3 peeling off from the anchor layer 2. Therefore, it is important to prevent oxidation of the metal selected for the anchor layer 2, such as aluminum, nickel, titanium, chromium, or nichrome.

[0045] The thickness of the anchor layer 2 is preferably 3 nm to 40 nm, and more preferably 5 nm to 20 nm. If the thickness is less than 3 nm, sufficient adhesion may not be obtained. On the other hand, even if the anchor layer is made thicker than 40 nm, the effect of improving adhesion is not great, so it is preferably 40 nm or less. When the anchor layer is made by a sputtering method, which has a slow film formation rate, it is even more preferable to make the anchor layer 20 nm or less to improve productivity.

[0046] <Storage battery> The storage battery according to the present invention includes an electrode assembly and a battery case that houses the electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0047] Such storage batteries include, for example, primary batteries, secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors, but in the present invention, they refer to secondary batteries.

[0048] Examples of secondary batteries include lithium secondary batteries, lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-iron batteries, silver oxide-zinc batteries, manganese dioxide-lithium secondary batteries, lithium cobalt oxide-carbonate secondary batteries, and vanadium-lithium secondary batteries.

[0049] Among these, secondary batteries are preferred because they can be used for a long period of time, and lithium secondary batteries are more preferred because they achieve high energy density by using organic solvents.

[0050] The positive electrode is formed by laminating a positive electrode material, which is made of an active material, a binder resin, and a conductive additive, on a current collector. It is preferable to use the metallized film 4 of the present invention as the current collector.

[0051] Examples of active materials include layered lithium-containing transition metal oxides such as LiCoO2, LiNiO2, and Li(NiCoMn)O2, spinel-type manganese oxides such as LiMn2O4, and olivine-type iron-based compounds such as LiFePO4.

[0052] The binder resin may be a resin with high oxidation resistance, such as a fluorine-containing resin, an acrylic resin, or a styrene-butadiene resin.

[0053] Examples of the conductive additive include carbon materials such as carbon black and graphite.

[0054] Examples of the electrolyte include LiPF6, LiBF4, and LiClO4, but LiPF6 is preferably used from the viewpoints of solubility in organic solvents and ionic conductivity.

[0055] Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and two or more of these organic solvents may be mixed and used.

[0056] A method for producing a lithium secondary battery, which is preferably used among storage batteries, will be described below.

[0057] The method for producing a lithium secondary battery involves first dispersing an active material and a conductive additive in a binder resin solution to prepare an electrode coating solution, then coating the coating solution on a current collector and drying the solvent to obtain a positive electrode and a negative electrode. The thickness of the coating film after drying is preferably 50 μm to 500 μm. Furthermore, it is preferable to apply pressure to the active material layer formed on the current collector, preferably by a roll press method, to densify it and thin the current collector.

[0058] A lithium secondary battery separator is placed between the obtained positive electrode and negative electrode so as to be in contact with the active material layer of each electrode, and the resulting battery is enclosed in an exterior material such as an aluminum laminate film. After injecting an electrolyte, a negative electrode lead and a safety valve are installed, and the exterior material is sealed.

[0059] The lithium secondary battery obtained in this manner has high adhesion to the electrode, has excellent battery characteristics, and can be produced at low cost. [Example]

[0060] The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples can be modified or changed based on the spirit of the present invention, and such modifications are not excluded from the scope of the invention.

[0061] (Magnetron sputtering) A resin film was placed in a roll-type vacuum deposition device (ULVAC EWC-060), and a target of 70 mm x 550 mm was used, and the vacuum reached was 1 x 10 in an argon gas atmosphere. -2 The pressure was adjusted to 0.1 Pa or less, and a pulsed power supply was applied to form a metal layer.

[0062] Unless otherwise specified, sputtering and vacuum deposition were carried out successively to prevent contact between the anchor layer and the aluminum metal film with the air.

[0063] (Vacuum deposition) A resin film was placed in a roll-type vacuum deposition device (ULVAC EWC-060) and the vacuum reached was 9.0 x 10 -3 After drawing a vacuum until the pressure reached a value below 1 Pa, vacuum deposition was performed by heating the deposition boat and heating the aluminum wire being fed out, using a transport speed, output conditions, and feed rate that would result in a predetermined aluminum film thickness, thereby forming an aluminum metal film.

[0064] Alternatively, a resin film was placed in a roll-type vacuum deposition device (ULVAC EWC-060), and vacuum deposition was performed by heating an aluminum ingot using induction heating deposition with a carbon crucible under conveying speed and output conditions that would result in a specified aluminum film thickness, thereby forming an aluminum metal film.

[0065] (XRD (X-ray diffraction) measurement method) Measurements were taken using an X-ray diffractometer (RIGAKU SmartLab 9kW). Measurement conditions were: X-ray tube voltage and current: 45kV-200mA, scanning speed: 2° / min, entrance slit: 1.0mm, receiving slit: 1.0mm. The peak intensity I

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

[0200] of the X-ray diffraction from the 200 plane were determined, and the ratio I

[0200] / I

[0111] was calculated and compared.

[0066] (Spectrophotometer absolute reflectance) The absolute reflectance measurement device ASR-3105 (incident angle 5°) was attached to a Shimadzu Corporation UV-3600i Plus spectrophotometer with a large sample chamber unit MPC-603A, and the reflectance of the measurement sample was measured using the aluminum mirror attached to the absolute reflectance measurement device as the reference. The reflectance data for visible light of 555 nm was used as the representative value.

[0067] (Contact resistance measurement) A metallized film was placed on a 10 mm thick NR sponge rubber (NRS-06 manufactured by Wake Sangyo Co., Ltd.) with the metal film facing upward, and two 25 mm x 25 mm gold-plated copper plates were placed 1 mm apart, with a 500 g weight on each copper plate. The resistance between the two copper plates was measured using a Hioki EE RM3544 resistance meter, and this was taken as the contact resistance.

[0068] (surface resistance measurement) The metallized film was cut to a size of approximately 300 mm x approximately 80 mm, and the surface resistance was measured at three locations using a simple low resistivity meter (Loresta (registered trademark) EP MCP-T360 manufactured by Mitsubishi Chemical Analytech Corporation) using the four-terminal method, and the average value was used as the surface resistance value.

[0069] (Aluminum metal film thickness) The metallized film was cut into pieces approximately 30 mm x 30 mm in size, 10 sheets were stacked, and the thickness was measured with a micrometer to calculate the thickness of each metallized film.The thickness of each metallized film was then calculated from the difference between this and the metallized film thickness calculated from the thickness of an undeposited resin film, which was similarly measured with a micrometer after 10 sheets were stacked.The aluminum metal film thickness was calculated from the difference between this and the metallized film thickness calculated from the thickness of each undeposited resin film.

[0070] (surface roughness) Surface roughness Ra was measured using a scanning white light interference microscope manufactured by Hitachi High-Tech Science Co., Ltd. Measurement conditions were measurement mode "wave," light source 530 White, objective lens 50x, and values ​​calculated using the attached analysis software under the following conditions: surface correction was set to fourth order, interpolation was set to "full," and Gaussing filter "cutoff 2μm" were used.

[0071] (Dimensional change rate measurement) A metallized film measuring approximately 300 mm x 300 mm is prepared, and a φ1 mm hole is drilled approximately in the center. Starting from the central hole, three φ1 mm holes are drilled, one at each end 75 mm apart in the direction of roll transport (MD) of the metallized film. Then, one hole is drilled 50 mm in front of and 50 mm behind each of the three holes in the direction of film width (TD), for a total of nine holes.

[0072] First, the distance between adjacent holes was measured using a manual two-dimensional image measuring instrument "EXLON-Y" manufactured by Nakamura Mfg. Co., Ltd. for nine holes. The metallized film was then heated in an oven at 150°C for 30 minutes, and the distance between adjacent holes was measured using the same nine holes using a manual two-dimensional image measuring instrument "EXLON-Y" manufactured by Nakamura Mfg. Co., Ltd.

[0073] For nine adjacent holes, the average dimensional change rate in the MD and TD directions was calculated, with each distance taken as 100%. Shrinkage is shown as a negative value, and expansion is shown as a positive value.

[0074] (Evaluation of wrinkles over time) After vapor deposition of the metallized film, the film was left rolled up for two weeks, and then the state of wrinkles on the film was checked. Those with good wrinkles were rated as "Good", and those with wrinkles to the extent that they could not be used were rated as "Poor".

[0075] Example 1 A 5.7 μm thick biaxially oriented polyethylene terephthalate film ("Lumirror (registered trademark)", Type: F53, manufactured by Toray Industries, Inc.) was used as the resin film. The surface roughness of this resin film was 1.6 nm. A roll of this resin film was placed in a roll-type vacuum deposition apparatus (EWC-060 manufactured by ULVAC), and a pulsed power supply was applied to deposit aluminum to a thickness of 5 nm by sputtering. The sputtering output was 2.0 kW using a pulsed power supply. An aluminum metal film was then vacuum-deposited to a thickness of 1.05 μm using a vacuum deposition method in which the deposition boat was heated immediately after sputtering to heat the aluminum wire being fed out.

[0076] At this time, argon was introduced, and the vacuum level during deposition was 9.0 × 10 -3 Pa or more, 1×10 -2 The pressure was controlled to be equal to or less than Pa. At this time, the output of the evaporation source, the conveying speed, and the tension during evaporation were adjusted so that the dimensional change rate at 150°C for about 30 minutes was -0.10% or less in the MD direction and -0.4% or more and less than -0.02% in the TD direction.

[0077] For the metallized film produced in this manner, the dimensional change rate at 150°C for approximately 30 minutes was -0.21% in the MD direction and -0.11% in the TD direction. The ratio I

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

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

[0200] of the aluminum 200 plane was 2.0. The specular reflectance of the aluminum metal film surface not in contact with the resin film at a wavelength of 555 nm was 9.8%, and the surface roughness was 8.3 nm.

[0078] The surface resistance of the aluminum metal film surface not in contact with the resin film of this metal film was 0.048 Ω / □, the contact resistance was 9.23 mΩ, and the ratio of the contact resistance to the surface resistance [contact resistance / surface resistance] was 0.19.

[0079] The contact resistance was sufficiently small and the evaluation of the contact resistance was good, and the evaluation of wrinkles over time was good.

[0080] Example 2 A 5.9 μm thick biaxially oriented polyethylene terephthalate film ("Lumirror (registered trademark)" manufactured by Toray Industries, Inc., type: XR40H) was used as the resin film. A metallized film was produced and evaluated in the same manner as in Example 1, except that the thickness of the aluminum metal film was as shown in Table 1. The results are shown in Table 1.

[0081] Example 3 The output of the evaporation source, the conveying speed, and the tension during evaporation were adjusted so that the dimensional change rate after 30 minutes at 150°C was -0.10% or less in the MD and -0.4% or more and less than -0.02% in the TD, and the output of the induction heating method using a carbon crucible as the evaporation source was reduced to minimize heat damage to the resin film. A metallized film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0082] (Comparative Example 1) A metallized film was produced and evaluated in the same manner as in Example 1, except that the output of the evaporation source, the conveying speed, and the tension during evaporation were not adjusted so that the dimensional change rate after 30 minutes at 150°C was −0.10% or less in the MD and −0.4% or more and less than −0.02% in the TD, and the output of the evaporation boat was reduced to minimize heat damage to the resin film. The results are shown in Table 1.

[0083] (Comparative Example 2) No argon was introduced during deposition, and the vacuum level during deposition was 9.0 x 10 -3 A metallized film was prepared and evaluated in the same manner as in Example 1, except that vacuum deposition was performed under conditions in which the tension on the resin film was as low as possible, without adjusting the output, conveying speed, and tension of the deposition source during deposition so that the dimensional change rate after 150°C x 30 minutes was -0.10% or less in the MD and -0.4% or more and less than -0.02% in the TD. The results are shown in Table 1.

[0084] [Table 1] [Explanation of symbols]

[0085] 1 Resin film 2 Anchor layer 3. Aluminum metal film 4 Metallized Film

Claims

1. A metallized film for a secondary battery positive electrode, comprising a resin film and an aluminum metal film formed on at least one surface thereof, characterized in that after heat treatment at 150°C for 30 minutes, the dimensional change rate in the MD direction is -0.10% or less, and the dimensional change rate in the TD direction is -0.4% or more but less than -0.02%.

2. 2. The metallized film for a secondary battery positive electrode according to claim 1, wherein the ratio I[200] / I[111] of the peak intensity I[111] of X-ray diffraction of the aluminum of the metal film in the 111 plane to the peak intensity I[200] of X-ray diffraction of the aluminum of the 200 plane is 1.0 or more, and the specular reflectance at a wavelength of 555 nm of the metal film surface not in contact with the resin film is 30% or less.

3. 2. The metallized film for a secondary battery positive electrode in accordance with claim 1, wherein the surface resistance of the metal film is 0.15 Ω / □ or less.

4. 2. The metallized film for a secondary battery positive electrode in accordance with claim 1, wherein the resin film has a surface roughness Ra of 0.6 nm or more and 2.0 nm or less.

5. 2. The metallized film for a secondary battery positive electrode in accordance with claim 1, wherein the metal film has a surface roughness Ra of 2.3 nm or more and 10.0 nm or less.

6. 2. The metallized film for a secondary battery positive electrode according to claim 1, wherein the surface resistance of the metal film is 0.15 Ω / □ or less, the ratio I[200] / I[111] of the peak intensity I[111] of the X-ray diffraction of the aluminum of the metal film in the 111 plane to the peak intensity I[200] of the X-ray diffraction of the aluminum of the metal film in the 200 plane is 1.0 or more, and the specular reflectance at a wavelength of 555 nm of the metal film surface not in contact with the resin film is 30% or less.

7. 2. The metallized film for a secondary battery positive electrode according to claim 1, wherein the resin film has a surface roughness Ra of 0.6 nm or more and 2.0 nm or less, the ratio I[200] / I[111] of the peak intensity I[111] of X-ray diffraction of the aluminum 111 plane to the peak intensity I[200] of X-ray diffraction of the aluminum 200 plane, I[200], is 1.0 or more, and the specular reflectance at a wavelength of 555 nm of the metal film surface not in contact with the resin film is 30% or less.

8. 2. The metallized film for a secondary battery positive electrode according to claim 1, wherein the metal film has a surface roughness Ra of 2.3 nm or more and 10.0 nm or less, a ratio I[200] / I[111] of the peak intensity I[111] of X-ray diffraction of the aluminum 111 plane to the peak intensity I[200] of X-ray diffraction of the aluminum 200 plane, that is, I[200] / I[111], of 1.0 or more, and a specular reflectance at a wavelength of 555 nm of the metal film surface not in contact with the resin film is 30% or less.

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