Metallized film for secondary battery positive electrode

Abstract

The purpose of the present invention is to obtain a method for producing a film collector foil in which a conductive thin film layer is formed on the surface of a resin having weaker rigidity than conventional aluminum foils, said method being capable of uniformly applying an active material during roll conveyance without causing wrinkles or folds due to heat treatment or dimensional shrinkage during roll conveyance. An aluminum metal film is formed on at least one surface of a resin film, and the rate of dimensional change in the MD direction after heat treatment at 150 DEG C for 30 minutes is-0.10% or less and the rate of dimensional change in the TD direction is-0.02% or more.

Description

Technical Field

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

[0002] In recent years, due to the miniaturization of electrical and electronic equipment and environmental issues, secondary batteries, capacitors and other storage batteries for gasoline-free vehicles (hybrid vehicles, electric vehicles) are required to be smaller and lighter, while having high output density that can instantly charge and discharge large currents.

[0003] In general, in order to improve the weight energy density, the battery mounted on the vehicle has the following structure: the positive electrode and the negative electrode are formed in a sheet shape, and the sheet-shaped positive electrode and the negative electrode are stored in a casing in a wound or stacked state via a separator also formed in a sheet shape. 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 serving as a collector.

[0004] In addition, as one of the methods for obtaining high output density, there is a method of reducing the resistance of various materials constituting the battery (internal resistance of the battery). It is said that in the battery, the current collector is mostly made of aluminum foil, but the current collector made of ordinary aluminum foil has an oxide film, and the internal resistance increases due to the oxide film formed on the surface of aluminum. If the internal resistance increases, the voltage will drop when charging and discharging with a large current, and as a result, the output of the battery will decrease. Generally speaking, a natural oxide film of a strong insulator with a thickness of usually 5 to 10 nm is formed on aluminum, but as an aluminum surface, it has the characteristic of maintaining good conductivity. As a reason for this, there is a saying that current flows through the defective part of the oxide film, and from the tunneling phenomenon in the field of quantum mechanics that particles pass through the area that cannot be normally surmounted in energy with a certain probability, there is a saying that if the electron conductor sandwiches the electrical insulator and approaches about 10 nm or less, a tunneling effect of good electron conduction will be produced, etc. Although it is not clear, it is believed that the aluminum oxide film itself has a strong influence on the internal resistance.

[0005] As a method of suppressing the increase in internal resistance caused by the oxide film and reducing the contact resistance between the electrode and the active material, there is a method of making the surface of the metal foil used in the electrode uneven (for example, Patent Document 1). Although it is unclear whether the number of defects is increased by roughening the aluminum surface or the tunnel effect is easily exhibited by forming more protrusions, it is effective as a method of reducing contact resistance.

[0006] As a method of increasing high output density while achieving miniaturization and lightness, the thin filmization of electrode substrates has been promoted for the purpose of increasing volume energy density and increasing weight energy density. However, if the metal foil used in the corresponding electrode is simply thin-filmed, the problem of insufficient strength will arise. In addition, if the surface unevenness of the thin-filmed metal foil is increased for the purpose of reducing contact resistance, it will become a cause of further reduction in the strength of the metal foil, which is not preferred. Therefore, as a new raw material to replace metal, a raw material having a structure of a conductive film layer such as a metal is provided on the surface of a biaxially stretched polyester film having excellent mechanical properties and heat-resistant dimensional stability, so that it has a collector function and is used as an electrode substrate (for example, Patent Document 2).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2008-160053

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 10-40919 Summary of the invention

[0011] Problems to be solved by the invention

[0012] However, in the case where a conductive thin film layer such as a metal is provided on the surface of a resin film such as a polyester film, the rigidity is weaker than that of conventional aluminum foil, and dimensional shrinkage occurs due to heat treatment, thereby causing wrinkles and folds (Japanese: folding) during roll conveyance, making it difficult to evenly apply the active material during roll conveyance.

[0013] In addition, the total resistance value will increase in accordance with the portion where the metal thickness is thinner than the metal foil used in the past. Moreover, even if the metal surface is roughened for the purpose of reducing the contact resistance of the aluminum metal surface, since the conductive thin film layer such as metal is usually a vapor-deposited metal film formed on the surface of the resin film by vacuum evaporation method, it is a thin film metal and is difficult to be roughened by etching or the like. If the surface of the polyester film itself is roughened, it is easy to break, and the transportation in the manufacturing process becomes difficult.

[0014] In view of the above circumstances, an object of the present invention is to provide a metallized film which does not increase contact resistance even when a conductive thin film layer is formed on a resin surface and can be transported without causing breakage or wrinkles.

[0015] Means for solving problems

[0016] The inventors of the present application have conducted in-depth research in view of the above-mentioned problems, and as a result, by controlling the processing temperature and tension when forming the evaporated metal film by vacuum evaporation or just after the evaporated metal film is formed, and the surface shape of the evaporated film, a metallized film that does not break or wrinkle during roll transportation and has a low contact resistance, and a method for manufacturing the same.

[0017] That is, the present invention relates to a metallized film for a secondary battery positive electrode, which is a metallized film for a secondary battery positive electrode formed with an aluminum metal film on at least one surface of a resin film and wound into a roll, characterized in that the dimensional change rate of the metallized film for a secondary battery positive electrode after heat treatment at 150° C. for 30 minutes is less than -0.10% in the MD direction and more than -0.02% in the TD direction,

[0018] The metallized film for a secondary battery positive electrode, wherein the ratio of the peak intensity I

[200] of the X-ray diffraction of aluminum of the metal film at the 200 plane to the peak intensity I

[111] of the X-ray diffraction of aluminum at the 111 plane is 1.0 or more, and the specular reflectivity of the surface of the metal film not in contact with the resin film at a wavelength of 555 nm is 30% or less,

[0019] The metallized film for the secondary battery positive electrode, wherein the surface resistance of the metal film is 0.15Ω / □ or less,

[0020] The metallized film for the secondary battery positive electrode, wherein the surface roughness Ra of the resin film is 0.6 nm or more and 2.0 nm or less,

[0021] In the above-mentioned metallized film for a secondary battery positive electrode, the surface roughness Ra of the metal film is not less than 2.3 nm and not more than 10.0 nm.

[0022] Effects of the Invention

[0023] According to the present invention, it is possible to obtain a metallized film which does not increase contact resistance even when a conductive thin film layer is formed on a resin surface and can be conveyed in a roll without causing breakage or wrinkles, and a method for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] [ Figure 1 ] is a schematic cross-sectional view of the metallized film of the present invention.

[0025] [ Figure 2 ] is a schematic cross-sectional view of the metallized film of the present invention.

[0026] [ Figure 3 ] is a schematic cross-sectional view of the metallized film of the present invention.

[0027] [ Figure 4] is an electron microscope (SEM) photograph of the surface of an aluminum metal film (film thickness 1.48 μm) when the grains were enlarged and grown densely using an induction heating evaporation source using a graphite crucible.

[0028] [ Figure 5 ] is a SEM photograph of the surface of an aluminum metal film (film thickness: 0.53 μm) when the grains were enlarged and grown densely using an induction heating evaporation source using a graphite crucible.

[0029] [ Figure 6 ] is a SEM photograph of a cross section of an aluminum metal film (film thickness 1.48 μm) when the grains are enlarged and densely grown using an induction heating evaporation source using a graphite crucible. (with Figure 4 Same, but looking in a different direction.) DETAILED DESCRIPTION

[0030] The present invention is described in detail below.

[0031] <Metalized Film>

[0032] The metallized film 4 of the present invention has an aluminum metal film 3 ( Figure 1 , Figure 2 , Figure 3 ).

[0033] The metallized film 4 of the present invention is a film wound into a roll. When the active material is applied to the metallized film, it can also be pulled out from the roll, and can be wound into a roll after the surface coating and drying process. When processed in a roll, the metallized film is easy to operate, the processing speed can also be accelerated, and the space of the processing device can be easily saved. However, the metallized film 4 is less rigid and has a larger thermal shrinkage than the previous aluminum foil. Therefore, if the roll is transported during the process of applying the heat treatment, it is easy to cause the metallized film to fold or deform into a strip shape and cannot be processed well. In particular, when the heat shrinkage of the metallized film in the direction perpendicular to the roll conveying direction (sometimes referred to as the MD direction), that is, the film width direction (sometimes referred to as the TD direction) is large, the heat shrinkage in the TD direction is used as the starting point, and wrinkles and folds will be generated during the roll conveying. Therefore, the heat shrinkage of the metallized film in the TD direction is preferably small, and the dimensional change rate (shrinkage is a negative value) in the TD direction after the heat treatment at 150°C for 30 minutes is preferably -0.02% or more, and more preferably 0.00% or more.

[0034] As a method for reducing the heat shrinkage in the TD direction, there is usually a method of further heat shrinking the resin of the metallized film by heating. However, if the heat shrinkage in the TD direction of the metallized film is reduced in the same manner as the heat shrinkage in the MD direction, the deformation and flexibility caused by the uneven shrinkage in the MD direction and the TD direction will be impaired, and the flatness of the film during transportation cannot be maintained, which may cause deformation such as wrinkles. Therefore, the heat shrinkage in the MD direction is preferably a value above a certain level. Specifically, the dimensional change rate in the MD direction after heat treatment at 150°C for 30 minutes is preferably less than -0.10%, and more preferably less than -0.20%.

[0035] In order to make the dimensional change rate of the metallized film wound into a roll below -0.10% in the MD direction and above -0.02% in the TD direction after heat treatment at 150°C for 30 minutes, it can be achieved by applying tension to the resin film or metallized film in the MD direction while performing heat treatment. Since the tension and heating conditions vary greatly due to the influence of the resin type of the resin film, the thickness of the resin film, the film width, the vapor-deposited metal film, the diameter of the conveying roller during heat treatment, and the distance between the conveying rollers, the tension and heating conditions are adjusted and optimized, so that the dimensional change rate in the MD direction after heat treatment at 150°C for 30 minutes can be adjusted to below -0.10% and above -0.02% in the TD direction in the state of the metallized film.

[0036] The heat treatment may be performed before, during or after vapor deposition, but is more preferably performed during vacuum vapor deposition without separately adding a heat treatment step.

[0037] <Aluminum Metal Film>

[0038] The aluminum metal film 3 in the present invention is an aggregate of aluminum metals in which one or more layers containing aluminum as the main component are stacked. The main component means that the main component accounts for more than 80 atomic % when the entire layer is taken as 100 atomic %.

[0039] The thickness of the aluminum metal film 3 in the present invention is preferably 0.7 μm to 3.0 μm, and more preferably 1.0 μm to 2.5 μm.

[0040] In electrode applications, the lower the resistance, the better. In surface resistance, the metal film surface resistance is preferably 0.15Ω / □ or less, and more preferably 0.05Ω / □ or less. On the other hand, in order to increase the energy density, thin filming is required, so it is not preferred to simply thicken the metal film. Considering the resistance of the electrode, the thickness of the aluminum metal film is preferably 0.7μm or more. If it is 1.0μm or more, it becomes a lower resistance, which can reduce the increase in internal resistance. On the other hand, for the purpose of increasing the volume energy density, it is necessary to thin the electrode substrate, preferably 3.0μm or less, and more preferably 2.5μm or less.

[0041] The aluminum metal film 3 in the present invention has the following characteristics: when the film is formed by vacuum deposition, the crystal growth of the metal film is controlled so that the surface irregularities become larger, thereby being able to reduce the contact resistance.

[0042] The aluminum metal film 3 of the metallized film 4 is placed upward on a 10mm thick NR sponge rubber, and two 25mm×25mm gold-plated copper plates are separated by 1mm intervals, and a 500g weight is placed on each copper plate. When the resistance value between the two copper plates is set as the contact resistance value, in order to reduce the internal resistance rise, the contact resistance value is preferably less than 15mΩ, and more preferably less than 10mΩ. The contact resistance value here is a value including 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 a small influence of the surface resistance, and the ratio of the surface resistance value [contact resistance value] / [surface resistance value] is preferably less than 0.35, and more preferably less than 0.25.

[0043] As a feature of the surface of the aluminum metal film 3 that controls the crystal growth of the metal film and reduces the contact resistance, the specular reflectivity at a wavelength of 555 nm of the surface that is not in contact with the resin film of the aluminum metal film 3 is preferably 30% or less, and more preferably 20% or less. This is because the surface of the aluminum metal film is finely roughened, so the specular reflectivity at a wavelength of 555 nm of visible light is reduced, which is effective in reducing the contact resistance.

[0044] As a feature of the surface of the aluminum metal film 3 that controls the crystal growth of the metal film and reduces the contact resistance, the surface roughness Ra of the aluminum metal film 3 that is not in contact with the resin film 1 is preferably 2.3 nm to 10.0 nm, and more preferably 5.0 nm to 10.0 nm. When the aluminum surface is sufficiently roughened and the height of the convex and concave portions is ensured to be a certain size, there is a tendency for the contact resistance to be reduced, and the larger the surface roughness Ra, the more preferred it is. However, if the surface roughness Ra is too large, it will cause the thin aluminum metal film 3 to break during transportation and bending, so it is preferably less than 10.0 nm.

[0045] As a characteristic of the surface of the aluminum metal film 3 for controlling the crystal growth of the metal film and reducing the contact resistance, the ratio I

[200] / I

[111] of the peak intensity I

[200] of the X-ray diffraction of aluminum at the 200 plane to the peak intensity I

[111] of the X-ray diffraction of aluminum at the 111 plane of the aluminum metal film 3 is preferably greater than 1.0, and more preferably greater than 2.0.

[0046] For reference, since aluminum is a cubic system, when aluminum is a powder, the crystal orientation is random, so the peak intensity of the X-ray diffraction of the 111 plane is the largest, and the intensity ratio I

[200] / I

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

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

[200] / I

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

[200] / I

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

[200] / I

[111] becomes less than 1.0.

[0047] By increasing the surface temperature of the substrate (referring to the resin film. Hereinafter, the resin film may be referred to as the substrate) during vapor deposition, the columnar crystals become larger and denser, so that the crystals are aligned in the 200 direction and the intensity ratio I

[200] / I

[111] becomes greater than 1.0.

[0048] However, when the substrate is a resin film, if the temperature of the substrate is increased, it will melt and break. Therefore, the substrate temperature cannot be increased unless it is specially made. The metal particles of the aluminum metal film produced by vacuum evaporation will become a columnar crystal film with large gaps, and the strength ratio I

[200] / I

[111] will become less than 1.0.

[0049] In the present invention, even if the substrate is a resin film, the columnar crystals of the aluminum metal film are successfully grown large and dense, and the grains are enlarged, thereby successfully forming appropriate concavities and convexities on the surface of the aluminum metal film. The resin film is forcedly cooled from the back side while the heat generation of the evaporation source is increased, and the vacuum degree is controlled to 9.0×10 -3 Pa or more, 1×10 -2 The vacuum deposition method at a pressure of Pa or less can increase the temperature of only the vicinity of the surface of the resin film exposed to the deposition source, thereby making the columnar crystals large and dense.

[0050] The vacuum deposition method uses a deposition source with a large heat generation, such as an induction heating method using a graphite crucible or a method using an electron beam, or even in the case of a heating boat method, the distance between the deposition 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 the vacuum is controlled to 9.0×10 -3 Pa or more, 1×10 -2 The vacuum evaporation method with a pressure below 100 Pa makes the crystal grains grow large and dense. However, since the resin film will melt due to heat in this state, it is preferred to forcefully cool the resin film from the back to a temperature just before melting to make the columnar crystals of the aluminum metal film grow large and dense, and form appropriate concavities and convexities on the surface of the aluminum metal film.

[0051] Figure 4 and Figure 5 This is a SEM photograph of the surface of an aluminum metal film when the grains are grown large and densely on the basis of a resin film (polyethylene terephthalate (PET) film) with a surface roughness Ra of 1.6 nm using an induction heating evaporation source using a graphite crucible with high heat generation. Figure 4 This is a surface SEM photo of a 1.48μm thick aluminum metal film. Figure 5 This is a surface SEM photo of a 0.53 μm thick aluminum metal film. Figure 4 and Figure 5 It can be judged that by increasing the size of the crystal grains, appropriate irregularities can be formed on the surface of the aluminum metal film. Figure 4 is 8.3nm, Figure 5 The thickness of the nanostructured carbon fiber is 2.7nm.

[0052] Figure 6 for Figure 4 From the cross-sectional SEM photo of the aluminum metal film, it can be determined that the aluminum metal film is a columnar crystal, and the convex and concave portion of the aluminum metal film surface is equivalent to a columnar crystal. Therefore, it is inferred that the larger the size of the convex and concave portion of the aluminum metal film surface, the larger and denser the columnar crystal. Figure 4 and Figure 5 In comparison, it is presumed that the deposition time is increased to increase the film thickness and the heat is increased. Figure 4 In the experiment, the growth of columnar crystals was larger.

[0053] In addition, in order to enlarge the grains and form a dense metal film, it is necessary to be exposed to the evaporation source as a heat source for a certain period of time. As a result, the evaporation time needs to be prolonged. The aluminum metal film thickness is preferably greater than 0.7μm, and is further preferably greater than 1.0μm.

[0054] <Method for producing aluminum metal film>

[0055] As a film forming method of the aluminum metal film 3, for the purpose of making a thin electrode, a vacuum evaporation method that can form a metal film on a thin resin film without using an adhesive is preferred. Vacuum evaporation methods include induction heating evaporation method, resistance heating evaporation method, laser beam evaporation method, electron beam evaporation method, etc. Among them, electron beam evaporation method, laser beam evaporation method, and induction heating evaporation method with a large calorific value of the evaporation source can be appropriately used. The calorific value of the evaporation source needs to be increased to a degree that the grains of the aluminum metal film 3 are formed large and densely. Although the surface temperature of the substrate needs to be high enough, it is difficult to actually measure it, so the physical properties of the aluminum metal film 3 after evaporation are confirmed to determine whether it is sufficient heat.

[0056] For the aluminum metal film 3, the specular reflectivity of the metal film surface not in contact with the resin film at a wavelength of 555nm is preferably 30% or less, the ratio of the peak intensity I

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

[111] of the X-ray diffraction of the 111 plane I

[200] / I

[111] is preferably 1.0 or more and 10 or less, and the surface roughness Ra of the surface of the metal film is preferably 2.3nm or more and 10.0nm or less. However, when the heat generated by the evaporation source is increased to the required heat, the temperature of the resin film may rise and melt under the management of the cooling function of the usual vacuum evaporation method. Therefore, in order to prevent the temperature from rising excessively during evaporation, it is necessary to manage the cooling function in a manner that can uniformly cool the film while performing evaporation. Specifically, it is necessary to uniformly cool from the back of the evaporation surface by a cooling mechanism formed by a metal plate or a metal roller that is fully cooled by a refrigerant. In order to perform uniform cooling, the resin film and the cooling mechanism must be tightly fitted without a gap.

[0057] For example, if there is damage on the metal roller of the cooling mechanism, the damaged part becomes a gap, and the resin film cannot be cooled and melts at the damaged part. For example, if foreign matter enters the resin film and the metal roller of the cooling mechanism, the resin film cannot be cooled and melts due to the foreign matter. If the calorific value of the evaporation source is increased to the required heat, the damage to the metal roller and the mixing of foreign matter allowed in the usual vacuum evaporation method become a problem, so the management of the damage to the metal roller and the mixing of foreign matter needs to be more stringent. By increasing the heat generation of these evaporation sources and strengthening the management of the cooling function, the grains of the aluminum metal film 3 can be grown larger and densely formed, resulting in a reduction in internal resistance including contact resistance. In particular, in the case of electron beam evaporation and laser beam evaporation, by using an alumina crucible with better heat preservation than a graphite crucible as an evaporation crucible, the calorific value of the evaporation source can be made larger, so it is further preferred.

[0058] <Resin film>

[0059] The resin film 1 used in the present invention is preferably formed into a thin film by molding a polymer such as a synthetic resin. As the resin film suitable for use in the present invention, for example, a polyester film can be exemplified, and among the polyester films, polyethylene terephthalate film, polyethylene naphthalate film, or polyimide film, polyphenylene sulfide film, and polypropylene film can be exemplified. Among them, polyethylene terephthalate film is more preferably used. These resin films can be used alone or in combination. In addition, a film coated with a resin, an adhesive, etc. on the surface of the resin film can also be used.

[0060] The thickness of the resin film 1 is preferably 1 μm to 20 μm, more preferably 3 μm to 10 μm. In order to thin the electrode substrate, the thickness of the resin film is preferably thin, preferably 20 μm or less, more preferably 10 μm or less. However, if it is too thin, the yield may be reduced due to breakage in the manufacturing process, and it is preferably 1 μm or more, more preferably 3 μm or more.

[0061] The surface roughness Ra of the resin film is preferably 0.6 nm or more and 2.0 nm or less. When the surface roughness of the resin film is 0.6 nm or less, sometimes when the resin film is wound into a roll, it may stick and make it difficult to carry. 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, it is preferred that the surface of the aluminum metal film has large concavities and convexities, but if the surface roughness Ra of the resin film is increased for this purpose, it becomes easy to break when the resin film is carried, so it is not preferred. As a resin film, in order to carry it, it is preferred to form the minimum concavities and convexities required, and it 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.

[0062] <Anchoring layer>

[0063] 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 preferred to form a metal layer on the resin film by sputtering. The sputtering method can reduce the thickness of the anchor layer, and is most suitable for storage battery applications that require further thin film.

[0064] As the anchoring layer 2, it is preferred that a metal layer containing any one or more selected from the group consisting of aluminum, nickel, titanium, nickel-chromium alloy, and chromium is included. At this time, it should be noted that it is important to form an aluminum metal film thereon while maintaining a state in which the surface of the metal such as aluminum, nickel, titanium, chromium, nickel-chromium alloy, etc. selected as the anchoring layer 2 is not oxidized. Specifically, it is important that after the metal layer is formed as the anchoring layer 2 by sputtering, the aluminum metal film 3 is formed while maintaining a vacuum state without being exposed to the atmosphere. If the surface of the metal such as aluminum, nickel, titanium, chromium, nickel-chromium alloy, etc. selected as the anchoring layer 2 is oxidized, a stable metal oxide film will be formed, and the metal bonding at the interface with the aluminum metal film 3 formed thereon will become difficult, and sometimes the adhesion cannot be ensured, resulting in the aluminum metal film 3 being peeled off from the anchoring layer 2. Therefore, it is important not to oxidize the aluminum, nickel, titanium, chromium, nickel-chromium alloy, etc. selected as the anchoring layer 2.

[0065] The thickness of the anchor layer 2 is preferably 3 nm to 40 nm, 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 larger than 40 nm, the effect of improving adhesion will not increase, so it is preferably 40 nm or less. In the case of preparing the anchor layer by sputtering method with slow film formation speed, it is further preferred to make the anchor layer 20 nm or less to improve productivity.

[0066] <Battery>

[0067] The storage battery referred to in the present invention comprises an electrode assembly and a battery case for housing 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.

[0068] Examples of such storage batteries include primary batteries, secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors. In the present invention, the storage batteries refer to secondary batteries.

[0069] Examples of the secondary battery include lithium secondary batteries, lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-iron storage batteries, silver oxide-zinc storage batteries, manganese dioxide-lithium secondary batteries, lithium cobaltate-carbonate secondary batteries, and vanadium-lithium secondary batteries.

[0070] Among these, secondary batteries are preferred from the viewpoint of long-term use, and lithium secondary batteries that achieve high energy density by using an organic solvent are more preferred.

[0071] The positive electrode is formed by laminating a positive electrode material composed 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.

[0072] Examples of active materials include layered lithium-containing transition metal oxides such as LiCoO2, LiNiO2, and Li(NiCoMn)O2, spinel manganese oxides such as LiMn2O4, and iron-based compounds such as LiFePO4.

[0073] As the binder resin, a resin having high oxidation resistance may be used, and specific examples thereof include fluorine-containing resins, acrylic resins, and styrene-butadiene resins.

[0074] Examples of the conductive auxiliary agent include carbon materials such as carbon black and graphite.

[0075] Examples of the electrolyte include LiPF6, LiBF4, and LiClO4. From the viewpoint of solubility in organic solvents and ion conductivity, LiPF6 is preferably used.

[0076] Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Two or more of these organic solvents may be used in combination.

[0077] Hereinafter, a method for producing a lithium secondary battery which is preferably used as a storage battery will be described.

[0078] As a method for making a lithium secondary battery, an active material and a conductive aid are first dispersed in a binder resin solution to prepare an electrode coating liquid, the coating liquid is applied to a collector, and the solvent is dried to obtain a positive electrode and a negative electrode, respectively. The film thickness of the dried coating film is preferably 50 μm to 500 μm. Furthermore, it is preferred to apply pressure to the active material layer formed on the collector by a method such as a roller pressing method to densify the collector to make it thin film.

[0079] The separator for lithium secondary battery is arranged between the obtained positive electrode and negative electrode in a manner that is in contact with the active material layer of each electrode, and is sealed in an outer packaging material such as an aluminum laminate film. After injecting the electrolyte, the negative electrode tab and safety valve are set, and the outer packaging material is sealed.

[0080] The lithium secondary battery obtained in this manner has high adhesion to the electrode and excellent battery characteristics, and can be manufactured at low cost.

[0081] Example

[0082] Hereinafter, the present invention will be described based on examples. It should be noted that the present invention is not limited to these examples, and these examples can be modified and altered based on the gist of the present invention, and these are not excluded from the scope of the invention.

[0083] (Magnetron Sputtering)

[0084] The resin film was placed in a roll vacuum deposition apparatus (ULVAC EWC-060) using a target material of 70 mm × 550 mm in size, and the vacuum was adjusted to 1 × 10 -2 Pa or less, a pulse power supply is applied to form a metal layer.

[0085] It should be noted that, unless otherwise specified, sputtering and vacuum deposition were performed continuously so that there was no contact between the anchor layer and the aluminum metal film with the air.

[0086] (Vacuum deposition)

[0087] A resin film was placed in a roll vacuum deposition apparatus (EWC-060 manufactured by ULVAC) and evacuated until the vacuum reached a degree of 9.0 × 10 -3 Pa or less, and then the vapor deposition boat is heated using a conveying speed, output conditions, and a conveying speed for sending the aluminum wire to the vapor deposition boat so that the aluminum film thickness becomes a specified value, thereby heating the sent aluminum wire, thereby performing vacuum vapor deposition to form an aluminum metal film.

[0088] Alternatively, a resin film is set in a roller vacuum deposition device (EWC-060 manufactured by ULVAC), and under the conveying speed and output conditions where the aluminum film thickness reaches a specified value, the aluminum ingot is heated by an induction heating deposition method using a graphite crucible, thereby performing vacuum deposition to form an aluminum metal film.

[0089] (XRD (X-ray diffraction) measurement method)

[0090] The measurement was performed using X-ray diffraction (RIGAKU SmartLab9kW). The measurement conditions were: voltage and current of the X-ray tube: 45kV-200mA, scanning speed: 2° / min, incident slit: 1.0mm, and receiving slit: 1.0mm. The peak intensity I

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

[200] of the X-ray diffraction of the 200 plane that appeared in the measurement results were determined, and the ratio I

[200] / I

[111] was calculated and compared.

[0091] (Spectrophotometer Absolute Reflectance)

[0092] The absolute reflectance measuring device ASR-3105 (incident angle 5°) was installed on the spectrophotometer UV-3600iPlus manufactured by Shimadzu Corporation with the large sample chamber unit MPC-603A, and the reflectance of the sample was measured using the aluminum mirror attached to the absolute reflectance measuring device as a reference. The reflectance data of visible light 555nm was used as a representative value.

[0093] (Contact resistance measurement)

[0094] The metallized film was placed on a 10 mm thick NR sponge rubber (NRS-06 manufactured by Waki ​​Sangyo Co., Ltd.) with the metal film facing upward, and two 25 mm × 25 mm gold-plated copper plates were separated by 1 mm, and a 500 g weight was placed on each copper plate. The resistance value between the two copper plates was measured using a resistance meter RM3544 manufactured by Hioki Electric Co., Ltd. as the contact resistance.

[0095] (Surface resistance measurement)

[0096] The metallized film was cut into a size of about 300 mm x about 80 mm, and the surface resistance was measured at three locations by a four-terminal method using a simple low resistivity meter ("Loresta (registered trademark)" EP MCP-T360 manufactured by Mitsubishi Chemical Analytech Co., Ltd.), and the average value was used as the surface resistance value.

[0097] (Aluminum metal film thickness)

[0098] The metallized film is cut into a size of about 30 mm x about 30 mm, and 10 sheets are overlapped. The thickness is measured with a micrometer to calculate the thickness of each metallized film. Then, the thickness of the metallized film is calculated in the same way from the thickness of 10 overlapping undeposited resin films measured with a micrometer. The thickness of the aluminum metal film is calculated based on the difference between the thickness of the metallized film and the thickness of the aluminum metal film.

[0099] (Surface roughness)

[0100] The surface roughness Ra was measured using a scanning white interference microscope manufactured by Hitachi High-Tech Corporation. The measurement conditions were: measurement mode was "wave", light source was 530White, objective lens was 50 times, and the attached analysis software was used to calculate under the conditions of surface correction of 4 times, complementation of "complete", and Gaussing filter of "cutoff 2μm", and the obtained value was used.

[0101] (Dimensional change rate measurement)

[0102] Prepare a metallized film of approximately 300 mm x 300 mm and drill a hole in the center. With the hole in the center as the starting point, one hole is opened at a distance of 75 mm in front and behind the roll conveying direction (MD direction) of the metallized film. Then, for these 3 holes, one hole was opened at the position of 50 mm before and after the film width direction (TD direction), and a total of 9 holes were opened.

[0103] First, the distances between adjacent holes among 9 holes were measured using a manual two-dimensional image measuring instrument "EXLON-Y" manufactured by Nakamura Manufacturing Co., Ltd. Then, the metallized film was heat-treated at 150° C. in an oven for 30 minutes, and the distances between adjacent holes among the same 9 holes were measured using a manual two-dimensional image measuring instrument "EXLON-Y" manufactured by Nakamura Manufacturing Co., Ltd.

[0104] The average values ​​of the dimensional change rates in the MD direction and the TD direction when the distances of the nine adjacent holes are set to 100% are calculated. Dimensional shrinkage is expressed as negative, and expansion is expressed as positive.

[0105] (Evaluation of transportability)

[0106] On both sides of the metallized film or on one side of the aluminum metal film that is not in contact with the resin film, the positive electrode active material is continuously coated by the method described in the embodiment, and after heating and drying, the positive electrode current collector is processed by rolling and pressing. During this processing, carefully observe whether wrinkles and folds occur during the transportation or winding process. If these defects do not occur, it is judged as "○" for transportation suitability, and if these defects occur, it is judged as "×" for transportation suitability.

[0107] (Example 1)

[0108] As the resin film, a biaxially oriented polyethylene terephthalate film with a thickness of 5.7 μm ("Lumirror (registered trademark)" manufactured by Toray Industries, Inc., type: F53) was used. The surface roughness of the resin film was 1.6 nm. For the coiled material of the resin film, the resin film was set in a roller vacuum deposition device (EWC-060 manufactured by ULVAC), a pulse power supply was applied, and aluminum was deposited to a thickness of 5 nm by sputtering. As a condition, a pulse power supply was used and the sputtering output was 2.0 kW. Then, the aluminum metal film was vacuum deposited to a thickness of 1.06 μm by a vacuum deposition method in which the deposition boat was heated immediately after sputtering to heat the aluminum wire fed out.

[0109] At this time, argon was introduced and the vacuum degree during evaporation was controlled at 9.0×10 -3 Pa or more, 1×10 -2At this time, the output of the vapor deposition source, the conveying speed and the tension during vapor deposition were adjusted so that the dimensional change rate before and after 150°C × 30 minutes was -0.10% or less in the MD direction and -0.02% or more in the TD direction.

[0110] Regarding the metallized film produced in this way, the dimensional change rate before and after 150℃×30 minutes is -0.28% in the MD direction and 0.06% in the TD direction, the ratio of the peak intensity I

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

[111] of the X-ray diffraction of the 111 plane is 3.1, the mirror reflectivity of the surface of the aluminum metal film not in contact with the resin film at a wavelength of 555nm is 7.1%, and the surface roughness is 6.1nm.

[0111] The surface resistance value of the aluminum metal film surface not in contact with the resin film of the metal film was 0.051Ω / □, the contact resistance value was 10.12mΩ, and the ratio of the contact resistance value to the surface resistance value [contact resistance / surface resistance] was 0.20.

[0112] The contact resistance was sufficiently small, and the contact resistance was judged as acceptable, i.e., 0, and the evaluation of the transportability was 0.

[0113] (Example 2)

[0114] Argon was not introduced during the deposition, and the vacuum degree during the deposition was set to 9.0×10 -3 Pa or more, and the thickness of the aluminum metal film was as described in Table 1. A metallized film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0115] (Comparative Example 1)

[0116] The output of the evaporation source, the conveying speed, and the tension during evaporation were not adjusted so that the dimensional change rate before and after 150°C × 30 minutes would be -0.10% or less in the MD direction and -0.02% or more in the TD direction, and the output of the induction heating evaporation method using a graphite crucible as the evaporation source was reduced to perform vacuum evaporation in order to minimize thermal 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.

[0117] (Comparative Example 2)

[0118] Argon was not introduced during the deposition, and the vacuum degree during the deposition was set to 9.0×10 -3Pa or more, and the output of the vapor deposition source, the conveying speed, and the tension during vapor deposition were not adjusted so that the dimensional change rate before and after 150°C × 30 minutes would be -0.10% or less in the MD direction and -0.02% or more in the TD direction, and vacuum vapor deposition was performed under the conditions of reducing the tension on the resin film as much as possible. A metallized film was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0119] (Comparative Example 3)

[0120] Argon was not introduced during the deposition, and the vacuum degree during the deposition was set to 9.0×10 -3 Pa or more, the output of the vapor deposition source during vapor deposition, the conveying speed and the tension were not adjusted so that the dimensional change rate before and after 150°C × 30 minutes was -0.10% or less in the MD direction and -0.02% or more in the TD direction, the tension on the resin film was reduced as much as possible, and the aluminum wire was vacuum-deposited under the condition of not increasing the output of the vapor deposition boat, and a metallized film was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0121] [Table 1]

[0122]

[0123] Description of Reference Numerals

[0124] 1. Resin film

[0125] 2 Anchoring layer

[0126] 3 Aluminum metal film

[0127] 4 Metallized film

Claims

1. A metallized film for a secondary battery positive electrode, wherein an aluminum metal film is formed on at least one surface of a resin film and the film is wound into a roll, wherein: The metallized film for a secondary battery positive electrode has a dimensional change rate of -0.10% or less in the MD direction and a dimensional change rate of -0.02% or more in the TD direction after heat treatment at 150° C. for 30 minutes.

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[200] of X-ray diffraction at the 200 plane of aluminum of the metal film, to the peak intensity I[111] of X-ray diffraction at the 111 plane, is greater than 1.0, and the mirror reflectivity of the metal film surface not in contact with the resin film at a wavelength of 555 nm is less than 30%.

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

4. The metallized film for a secondary battery positive electrode according to claim 1, wherein The surface roughness Ra of the resin film is not less than 0.6 nm and not more than 2.0 nm.

5. The metallized film for a secondary battery positive electrode according to claim 1, wherein The surface roughness Ra of the metal film is greater than or equal to 2.3 nm and less than or equal to 10.0 nm.

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

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

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

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