Laminated resin film, current collector and secondary battery

Abstract

This layered resin film comprises a resin layer, and a Cu film provided on one surface side or on each of the two surface sides of the resin layer, wherein the Cu film has an orientation index of 0.15 or greater for the (111) plane according to the Lotgering method and a half-width of 0.3° or less for the X-ray diffraction peak of the (111) plane obtained by X-ray diffraction measurements, and satisfies the following formula (1). Formula (1): Y ≥ 3.75x - 0.675 (In Formula (1), Y represents the orientation index for the (111) plane in the Cu film according to the Lotgering method, and x represents the half-width for the X-ray diffraction peak of the (111) plane in the Cu film, obtained by X-ray diffraction measurements.)

Description

[Technical Field]

[0001] The present disclosure relates to a laminated resin film, a current collector, and a secondary battery. [Background technology]

[0002] Lithium secondary batteries are widely used as power sources for laptops, mobile phones, electric vehicles, and other devices. As a current collector for a lithium secondary battery, there is a laminated resin film in which a metal layer is formed on the surface of a resin layer.

[0003] Patent Document 1 describes a current collector having an insulating layer and a conductive layer, the insulating layer carrying the conductive layer, the conductive layer carrying an electrode active material layer, the conductive layer being located on at least one surface of the insulating layer, and a metal protective layer being provided on at least one surface of the conductive layer. Patent Document 1 also describes that the material of the conductive layer is at least one selected from a metal conductive material and a carbon-based conductive material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-102429 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a laminated resin film in which a metal layer is formed on the surface of a resin layer is used as a current collector for a lithium secondary battery, the following concerns (1) to (3) arise. (1) High electrical resistance. (2) Fracture of the metal layer. (3) Peeling of the metal layer from the resin layer.

[0006] The present disclosure has been made in view of the above problems, and an object thereof is to provide a laminated resin film having low electrical resistance and being difficult to break or peel the metal layer. Another object of the present disclosure is to provide a current collector made of the above laminated resin film and a secondary battery having the current collector and being lightweight and excellent in safety.

Means for Solving the Problems

[0007] In order to solve the above problems, a Cu film was formed as a metal layer on the surface of the resin layer, and intensive studies were repeated focusing on its crystallinity and orientation. As a result, it has been found that a Cu film having an orientation index (factor) by the Lotgering method of the (111) plane and a half-value width of the (111) plane in X-ray diffraction measurement within a specific range may be formed on the surface of the resin layer. That is, the present disclosure relates to the following.

[0008] [1] A laminated resin film having a resin layer and a Cu film provided on one or both sides of the resin layer, wherein the Cu film has an orientation index by the Lotgering method of the (111) plane of 0.15 or more, a half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane of 0.3° or less, and satisfies the following formula (1). Y≧3.75x - 0.675 Formula (1) (In Formula (1), Y is the orientation index by the Lotgering method of the (111) plane in the Cu film, and x is the half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane in the Cu film.)

[0009] [2] The laminated resin film according to [1], wherein the Cu film has an orientation index of 0.3 to 0.98. [3] The laminated resin film according to [1] or [2], wherein the Cu film has a half-value width of the X-ray diffraction peak of 0.08 to 0.26°.

[0010] [4] The laminated resin film according to any one of [1] to [3], wherein the thickness of the Cu film is 0.3 μm to 2.0 μm. [5] The laminated resin film according to any one of [1] to [4], wherein an underlayer is provided between the resin layer and the Cu film in contact with the resin layer and the Cu film.

[0011] [6] A current collector comprising the laminated resin film according to any one of [1] to [5].

[0012] [7] A secondary battery having a negative electrode, a positive electrode facing the negative electrode, and a separator positioned between the negative electrode and the positive electrode, wherein one or both of the negative electrode and the positive electrode include the current collector according to [6].

Advantages of the Invention

[0013] The laminated resin film of the present disclosure has a resin layer and a Cu film provided on one or both sides of the resin layer, and the Cu film has an orientation index of 0.15 or more by the Lotgering method of the (111) plane, a half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane of 0.3° or less, and satisfies formula (1). Therefore, the laminated resin film of the present disclosure has low electrical resistance and can prevent breakage of the Cu film and peeling of the Cu film from the resin layer.

[0014] The current collector of the present disclosure is made of the laminated resin film of the present disclosure. Therefore, the current collector of the present disclosure has low electrical resistance and can prevent breakage of the Cu film and peeling of the Cu film from the resin layer. In addition, in the secondary battery of the present disclosure, one or both of the negative electrode and the positive electrode include the current collector of the present disclosure. Therefore, the secondary battery of the present disclosure is lightweight and has excellent safety.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0016] Hereinafter, the present embodiment will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show the characteristic parts enlarged for the sake of clarity of the features of the present disclosure, and the dimensional ratios of each component may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present disclosure is not limited thereto, and it can be implemented by appropriately changing within the range not changing the gist thereof.

[0017] [Lithium Secondary Battery] FIG. 1 is a schematic cross-sectional view showing an example of the lithium secondary battery of the present disclosure. The lithium secondary battery 100 shown in FIG. 1 includes a power generation unit 40, an exterior body 50, and leads 60 and 62. The exterior body 50 houses the power generation unit 40 in a sealed state. One end of each of the pair of leads 60 and 62 is connected to the power generation unit 40, and the other end extends to the outside of the exterior body 50. Although not shown, an electrolytic solution is housed in the exterior body 50 together with the power generation unit 40.

[0018] (Power Generation Unit) In the power generation unit 40, a positive electrode 20 and a negative electrode 30 are disposed opposite to each other with a separator 10 interposed therebetween. In FIG. 1, the case where one power generation unit 40 is housed in the exterior body 50 is illustrated, but a plurality of power generation units 40 may be stacked and housed.

[0019] (Positive Electrode) The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24. (Positive Electrode Active Material Layer) The positive electrode active material layer 24 contains a positive electrode active material, a binder for the positive electrode, and a conductive assistant for the positive electrode.

[0020] (Positive electrode active material) As the positive electrode active material, an electrode active material capable of reversibly proceeding with the occlusion and release of lithium ions, the desorption and insertion (intercalation) of lithium ions, or the doping and dedoping of lithium ions and a counter anion of lithium ions (for example, PF6 - ) is used.

[0021] Examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese spinel (LiMn2O4), and the general formula: LiNi x Co y Mn z M a O2 (x + y + z + a = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium vanadium compound (LiV2O5), olivine-type LiMPO4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr or VO), lithium titanate (Li4Ti5O 12 ), LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1), and the like.

[0022] (Binder for positive electrode) The binder for the positive electrode binds the positive electrode active materials to each other and binds the positive electrode active material and the positive electrode current collector 22. Examples of binders that can be used for the positive electrode include polyvinylidene fluoride (PVDF), polyethersulfone (PESU), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

[0023] Examples of the binder for the positive electrode that can be used include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFPTFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber).

[0024] The positive electrode binder may be an electron-conductive conductive polymer and / or an ion-conductive conductive polymer. Examples of electron-conductive conductive polymers include polyacetylene. In this case, the positive electrode binder also functions as a positive electrode conductive additive. Therefore, the positive electrode active material layer 24 does not need to contain a positive electrode conductive additive. Examples of ion-conductive conductive polymers include a composite of a polymer compound such as polyethylene oxide or polypropylene oxide with a lithium salt or a lithium-based alkali metal salt.

[0025] (Conductive aid for the positive electrode) The conductive aid for the positive electrode improves the conductivity of the positive electrode active material layer 24. As the conductive aid for the positive electrode, known conductive aids can be used. Examples of the conductive aid for the positive electrode include carbon-based materials such as graphite and carbon black, metal fine powders such as copper, nickel, stainless steel, and iron, and conductive oxides such as ITO (indium tin oxide).

[0026] (Positive electrode current collector) As the positive electrode current collector 22, for example, a metal foil or a thin metal plate made of a metal such as aluminum, copper, or nickel can be used. The positive electrode current collector 22 may be a laminated resin film provided with a resin layer (not shown) and a metal layer made of a metal such as aluminum, copper, or nickel on one or both sides of the resin layer.

[0027] (Negative electrode) The negative electrode 30 includes a negative electrode current collector 32 and a negative electrode active material layer 34. (Negative electrode active material layer) The negative electrode active material layer 34 contains a negative electrode active material and may further contain a binder for the negative electrode and / or a conductive aid for the negative electrode as required.

[0028] (Negative electrode active material) The negative electrode active material is a compound capable of occluding and releasing lithium ions, and known negative electrode active materials for lithium secondary batteries can be used. Examples of the negative electrode active material include metallic lithium, carbon materials such as graphite (natural graphite, artificial graphite), carbon nanotubes, graphitizable carbon, non-graphitizable carbon, and low-temperature fired carbon, metals capable of combining with lithium such as aluminum, silicon, and tin, SiO x (0 < x < 2), amorphous compounds mainly composed of oxides such as tin dioxide, and particles containing lithium titanate (Li4Ti5O 12 ) etc. can be used.

[0029] (Binder for the negative electrode) The binder for the negative electrode may be the same as that for the positive electrode. In addition to the binders that can be used for the positive electrode, the binder for the negative electrode may also be one or more selected from the group consisting of cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, polyamide-imide resin, and acrylic resin.

[0030] (Conductive additive for negative electrode) Examples of the conductive additive for the negative electrode that can be used include carbon powders such as carbon black, carbon materials such as carbon nanotubes, metal fine powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal fine powders, and conductive oxides such as ITO.

[0031] (Negative electrode current collector) In the lithium secondary battery 100 of this embodiment, the negative electrode current collector 32 is made of a laminated resin film 3 shown in Fig. 2. As shown in Fig. 2, the laminated resin film 3 has a resin layer 3a and Cu films 3b provided on both sides of the resin layer 3a in contact with the resin layer 3a. 2 as the negative electrode current collector 32, the weight of the lithium secondary battery 100 can be reduced compared to when a current collector made of a metal plate is used. Furthermore, by using the laminated resin film 3 as the negative electrode current collector 32, it is possible to prevent conductive parts in the lithium secondary battery 100 from shorting out via the negative electrode current collector 32, which would cause the lithium secondary battery 100 to reach a high temperature state.

[0032] In the laminated resin film 3 shown in FIG. 2, the Cu films 3b provided on both sides of the resin layer 3a may be the same or may differ in one or more of the following properties selected from the orientation index of the (111) plane determined by the Lotgering method, the half-width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane, and the thickness.

[0033] As shown in Fig. 2, the laminated resin film 3 has a resin layer 3a and Cu films 3b provided on both sides of the resin layer 3a. In the lithium secondary battery 100 of this embodiment, only one power generation unit 40 is housed in the exterior package 50. Therefore, instead of the laminated resin film 3 shown in Fig. 2, a laminated resin film 33 may be used in which a Cu film 5b is provided in contact with the resin layer 3a only on one side of the resin layer 3a (the side facing the negative electrode active material layer 34 in the lithium secondary battery 100 of this embodiment), as shown in Fig. 3. When a plurality of power generating units 40 are housed in a stacked state within the exterior packaging 50, it is preferable to use a laminated resin film 3 in which Cu films 3b are provided on both sides of a resin layer 3a as the negative electrode current collector 32. In this case, by providing negative electrode active material layers 34 on both sides of the laminated resin film 3, one laminated resin film 3 can also serve as the negative electrode current collectors 32 for two negative electrodes 30.

[0034] Examples of the resin layer 3a forming the laminated resin film 3, 33 include films made of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyamide, polyimide, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly-p-phenylene terephthalamide, polypropylene ethylene, polyformaldehyde, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, etc. Among these, it is preferable to use a film made of PET because it has excellent chemical resistance, stretchability, and tensile strength.

[0035] The thickness of the resin layer 3a forming the laminated resin films 3 and 33 can be appropriately determined according to the application of the lithium secondary battery 100. The thickness of the resin layer 3a is preferably, for example, 3 μm to 12 μm, and more preferably 3 μm to 6 μm. When the thickness of the resin layer 3a is 3 μm or more, deformation of the laminated resin films 3 and 33 can be suppressed, and furthermore, breakage of the Cu film 3b and peeling of the Cu film 3b from the resin layer 3a can be prevented. Also, when the thickness of the resin layer 3a is 12 μm or less, it is preferable because the laminated resin films 3 and 33 do not hinder the miniaturization of the lithium secondary battery 100.

[0036] The Cu film 3b forming the laminated resin films 3 and 33 has an orientation index of 0.15 or more by the Lotgering method for the (111) plane, a half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane of 0.3° or less, and satisfies the following formula (1).

[0037] Y≧3.75x - 0.675 Formula (1) (In Formula (1), Y is the orientation index by the Lotgering method for the (111) plane in the Cu film 3b, and x is the half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane in the Cu film 3b.)

[0038] The orientation index (factor) by the Lotgering method for the (111) plane of the Cu film 3b is a numerical value that indicates the orientation of the Cu film 3b. The maximum value of the orientation index by the Lotgering method is 1. When the orientation index is 1, it indicates complete orientation, and when the orientation index is 0, it indicates non-orientation. The orientation index by the Lotgering method can be calculated by the method shown below.

[0039] The orientation index (factor (F)) by the Lotgering method for the (111) plane of the Cu film 3b is calculated by the following formula (2) using the intensity of the X-ray diffraction peak obtained by X-ray diffraction measurement of the Cu film. F = (ρ - ρ0) / (1 - ρ0) Formula (2) (In formula (2), ρ0 is a value calculated by formula (3) below, and ρ is a value calculated by formula (4) below.)

[0040] ρ0=ΣI0(111) / ΣI0(hkl) Equation (3) (In equation (3), I0(111) represents the intensity of the X-ray diffraction peak of the (111) plane obtained by X-ray diffraction measurement of non-oriented Cu powder. I0(hkl) represents the intensity of all diffraction peaks obtained by X-ray diffraction measurement of non-oriented Cu film.) In this embodiment, a non-oriented Cu film means that the intensity pattern of the X-ray diffraction peak is close to the intensity pattern of the X-ray diffraction peak of a copper standard sample listed in the JCPDS (Joint Committee on Powder Diffraction Standards).

[0041] ρ=ΣI(111) / ΣI(hkl) Equation (4) (In formula (4), I(111) represents the intensity of the X-ray diffraction peak of the (111) plane obtained by X-ray diffraction measurement of the Cu film forming the laminate resin film of this embodiment. I(hkl) represents the intensity of all diffraction peaks obtained by X-ray diffraction measurement of the Cu film forming the laminate resin film of this embodiment.)

[0042] In the laminate resin films 3 and 33 of this embodiment, the higher the orientation index of the (111) plane in the Cu film 3b as determined by the Lotgering method, the more improved the ductility of the Cu film and the less likely the Cu film 3b is to peel off from the resin layer 3a, which is preferable. The orientation index of the Cu film 3b is 0.15 or more, preferably 0.3 or more, and more preferably 0.35 or more. The orientation index of the Cu film 3b is preferably 0.98 or less, and more preferably 0.75 or less. When the orientation index of the Cu film 3b is 0.98 or less, the Cu film 3b is less susceptible to oxidation, thereby suppressing an increase in the electrical resistance of the Cu film 3b.

[0043] In the laminated resin films 3 and 33 of the present embodiment, the full width at half maximum of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane in the Cu film 3b is a numerical value serving as an index of the crystallite size of the Cu film 3b. Specifically, the smaller the full width at half maximum of the above X-ray diffraction peak, the larger the crystallite size of the Cu film 3b. In the laminated resin film 3 of the present embodiment, the smaller the full width at half maximum of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane in the Cu film 3b, the larger the elongation at break of the Cu film 3b, the less likely it is to break, and the lower the electrical resistance, which is preferable. The full width at half maximum of the X-ray diffraction peak of the (111) plane in the Cu film 3b is 0.3° or less, preferably 0.26° or less, and more preferably 0.22° or less. Further, the full width at half maximum of the X-ray diffraction peak of the (111) plane in the Cu film 3b is preferably 0.08° or more. When the full width at half maximum of the X-ray diffraction peak of the (111) plane in the Cu film 3b is 0.08° or more, the Cu film 3b can be formed efficiently and easily.

[0044] The Cu film 3b in the laminated resin films 3 and 33 of the present embodiment satisfies formula (1). For this reason, the laminated resin film 3 of the present embodiment has low electrical resistance and can prevent breakage of the Cu film 3b and peeling of the Cu film 3b from the resin layer 3a. When the Cu film 3b does not satisfy formula (1), even if the orientation index by the Lotgering method of the (111) plane is 0.15 or more and the full width at half maximum of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane is 0.3° or less, the above effects cannot be sufficiently obtained.

[0045] The Cu film 3b in the laminated resin film 3, 33 of this embodiment preferably has a thickness of 0.3 μm to 2.0 μm, and more preferably 0.5 μm to 1.0 μm. When the thickness of the Cu film 3b is 0.3 μm or more, the laminated resin film 3, 33 has even lower electrical resistance. Furthermore, when the thickness of the Cu film 3b is 0.5 μm or more, breakage of the Cu film 3b and peeling of the Cu film 3b from the resin layer 3a can be even more effectively prevented. Furthermore, when the thickness of the Cu film 3b is 2.0 μm or less, by using the laminated resin film 3, 33 as the negative electrode current collector 32, the weight of the lithium secondary battery 100 can be even more effectively reduced.

[0046] "Method of manufacturing laminated resin film" Next, a method for producing the laminated resin films 3 and 33 will be described using an example. First, a resin layer 3a having a predetermined thickness is formed using a predetermined resin by a known method. A commercially available resin film may be used as the resin layer 3a.

[0047] Next, a Cu film 3b is formed on one or both surfaces of the resin layer 3a in contact with the resin layer 3a. The orientation index of the (111) plane of the Cu film 3b as determined by the Lotgering method and the half-width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane can be controlled by the film formation method and thickness of the Cu film 3b. In this embodiment, the Cu film 3b is preferably formed by performing, in this order, a step of forming a Cu seed layer on one or both sides of the resin layer 3a, and a step of forming a Cu plating layer on the Cu seed layer by electroplating.

[0048] Examples of the step of forming a Cu seed layer include a method of forming a Cu seed layer made of a Cu film on one or both surfaces of the resin layer 3a by a film formation method such as electroless plating, sputtering, vapor deposition, or chemical vapor deposition (CVD). In the step of forming a Cu seed layer, it is preferable to form the Cu seed layer using any of the above film formation methods selected from electroless plating, sputtering, and vapor deposition, and sputtering is particularly preferable. By performing the step of forming a Cu plating layer, a Cu seed layer can be obtained that is likely to produce a Cu film 3b having a (111) plane orientation index of 0.15 or more according to the Lotgering method and an X-ray diffraction peak half-width of 0.3° or less obtained by X-ray diffraction measurement of the (111) plane.

[0049] When sputtering is used in the step of forming the Cu seed layer, it is preferable to form the Cu seed layer in an atmosphere containing argon. The argon-containing atmosphere may be an atmosphere consisting of argon gas alone or a mixed gas atmosphere of argon gas and hydrogen gas, but an atmosphere consisting of argon gas alone is preferable. This is because a Cu seed layer can be obtained that is likely to form a Cu film 3b having a (111) plane orientation index of 0.15 or more as determined by the Lotgering method.

[0050] In the step of forming the Cu seed layer, it is preferable to form a Cu seed layer consisting of a Cu film with a thickness of 10 to 300 nm. When the thickness of the Cu seed layer is 300 nm or less, the step of forming the Cu plating layer more easily obtains a Cu film 3b having a (111) plane orientation index of 0.15 or more as determined by the Lotgering method and an X-ray diffraction peak half-width of 0.3° or less obtained by X-ray diffraction measurement of the (111) plane, which is preferable. When the thickness of the Cu seed layer is 10 nm or more, it is preferable to prevent the Cu seed layer from dissolving in the plating solution in the step of forming the Cu plating layer, thereby preventing the formation of holes (pinholes) reaching the resin layer 3a. By performing the step of forming the Cu plating layer, the Cu seed layer is integrated with the Cu plating layer and becomes part of the Cu film.

[0051] The step of forming the Cu plating layer may involve forming a Cu film 3b having a thickness of 0.3 μm to 2.0 μm by electroplating on a Cu seed layer formed on one or both sides of the resin layer 3a. A plating solution of known composition can be used in the electroplating method. The plating conditions, such as the plating temperature and plating time, in the electroplating method can be appropriately determined depending on the thickness of the Cu film 3b of the laminated resin film 3, 33.

[0052] The current density in the electrolytic plating method is, for example, 1.5 to 5.0 A / dm 2 By changing the current density in the electrolytic plating method, the orientation index of the (111) plane as determined by the Lotgering method can be controlled.

[0053] The method for forming the Cu film 3b on one or both surfaces of the resin layer 3a is not limited to a method that involves a step of forming a Cu seed layer and a step of forming a Cu plating layer by electrolytic plating. For example, the Cu film 3b may be formed on one or both surfaces of the resin layer 3a using only one film formation method selected from electroless plating, sputtering, vapor deposition, chemical vapor deposition (CVD), etc. In this case, the resin layer 3a can be formed efficiently with fewer manufacturing steps than when a step of forming a Cu seed layer and a step of forming a Cu plating layer are performed.

[0054] When forming the Cu film 3b on both sides of the resin layer 3a, the Cu film 3b may be formed on both sides of the resin layer 3a simultaneously, or the Cu film 3b may be formed on one side and then on the other side. When forming the Cu film 3b on both sides of the resin layer 3a, it is preferable to form the Cu film 3b on both sides of the resin layer 3a simultaneously, as this allows the laminated resin film 3 to be produced efficiently.

[0055] In the lithium secondary battery 100 of this embodiment, instead of the laminated resin film 3, a laminated resin film 35 may be used in which an underlayer 3c and a Cu film 3b are provided in this order on both sides of a resin layer 3a, as shown in FIG.

[0056] As shown in FIG. 4, the underlying layer 3c is provided in contact with the resin layer 3a and the Cu film 3b between the resin layer 3a and the Cu film 3b. By having the underlying layer 3c, the adhesion between the resin layer 3a and the Cu film 3b can be enhanced. When the Cu films 3b are provided on both sides of the resin layer 3a, the underlying layer 3c may be provided on both sides of the resin layer 3a respectively as shown in FIG. 4, or may be provided only on one side of the resin layer 3a.

[0057] The underlying layer 3c is preferably a metal layer containing at least one element selected from the group consisting of Cr, Ti, and Ni. When the laminated resin film 35 is used as the negative electrode current collector 32, the underlying layer 3c may be a metal layer containing at least one element selected from the group consisting of Cr, Ti, Ni, Ta, Zn, Nb, and Cu, preferably a metal layer containing Ni, and more preferably a metal layer composed of an alloy of Ni and Cr.

[0058] The laminated resin film 35 shown in FIG. 4 can be manufactured, for example, by the following method. In the same manner as when manufacturing the laminated resin film 3 shown in FIG. 2, the resin layer 3a is formed. Next, an underlying layer 3c is formed in contact with the resin layer 3a on both sides of the resin layer 3a by a film forming method such as sputtering or vapor deposition. Then, a Cu film 3b is formed on the underlying layer 3c provided on both sides of the resin layer 3a in the same manner as when forming the Cu film 3b of the laminated resin film 3 shown in FIG. 2. Through the above steps, the laminated resin film 35 shown in FIG. 4 is obtained.

[0059] <Separator> As the separator 10, a known separator such as one having a porous structure with electrical insulation can be used. Specifically, for example, a single layer or laminate of a film made of a polyolefin resin such as polyethylene or polypropylene, a stretched film of a mixture of multiple types of polyolefin resins, or a fibrous non-woven fabric made of at least one constituent material selected from the group consisting of cellulose, polyester, and polypropylene can be mentioned.

[0060] (Electrolyte solution) The electrolyte solution is impregnated in the power generation unit 40. As the electrolyte solution, an electrolyte solution or a non-aqueous electrolyte solution can be used. When using a non-aqueous electrolyte solution as the electrolyte solution, it is preferable because the withstand voltage during charging can be increased compared to the case of using an aqueous electrolyte solution.

[0061] The non-aqueous electrolyte solution is one in which an electrolyte is dissolved in a non-aqueous solvent. As the non-aqueous solvent, for example, cyclic carbonates and chain carbonates can be used. As the cyclic carbonate, one that can solvate the electrolyte is used. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, and butylene carbonate. As the chain carbonate, one that reduces the viscosity of the cyclic carbonate is used. Examples of the chain carbonate include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0062] As the non-aqueous solvent, in addition to cyclic carbonates and chain carbonates, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, etc. may also be used.

[0063] Examples of the electrolyte contained in the non-aqueous electrolyte solution include lithium salts such as LiPF6, LiClO4, LiBF4, LiCF3SO3, LiCF3CF2SO3, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(CF3CF2CO)2, and LiBOB. These lithium salts may be used alone or in combination of two or more. From the viewpoint of ionization degree, it is preferable that the electrolyte contains LiPF6.

[0064] As the non-aqueous electrolyte solution, for example, an ionic liquid may be used. An ionic liquid is a salt (room temperature molten salt) that remains liquid even at a low temperature of, for example, less than 100°C, which is formed by a combination of a cation and an anion. Ionic liquids have strong electrostatic interactions, are non-volatile, and non-flammable. Therefore, the lithium secondary battery 100 using an ionic liquid as the non-aqueous electrolyte solution is excellent in safety. As the cation component and anion component of the ionic liquid, known ones can be used.

[0065] (Lead) The leads 60 and 62 are formed of a conductive material such as aluminum. As shown in FIG. 1, the lead 60 is electrically connected to the negative electrode current collector 32 of the negative electrode 30. The lead 62 is electrically connected to the positive electrode current collector 22 of the positive electrode 20.

[0066] (Outer package) The outer package 50 seals the power generation unit 40 and the electrolytic solution inside. The outer package 50 is not particularly limited as long as it can prevent the leakage of the electrolytic solution to the outside and the intrusion of moisture and the like from the outside to the inside.

[0067] As the outer package 50, for example, as shown in FIG. 1, a metal laminate film obtained by coating both sides of a metal foil 52 with a polymer film 54 can be used. As the metal foil 52, for example, an aluminum foil can be used. As the outer polymer film 54, it is preferable to use a polymer having a high melting point, and for example, a film made of polyethylene terephthalate (PET), polyamide, or the like can be used. As the inner polymer film 54, for example, a film made of polyethylene (PE), polypropylene (PP), or the like can be used.

[0068] [Manufacturing method of lithium secondary battery] Next, the manufacturing method of the lithium secondary battery 100 shown in FIG. 1 will be described in detail with examples. To manufacture the lithium secondary battery 100 of the present embodiment, first, the positive electrode 20 and the negative electrode 30 are manufactured.

[0069] The positive electrode 20 can be manufactured, for example, by applying a coating material containing a positive electrode active material onto the positive electrode current collector 22 and drying it. The paint containing the positive electrode active material may contain a positive electrode active material, a positive electrode binder, a positive electrode conductive additive, and a solvent. Examples of the solvent that can be used include water and N-methyl-2-pyrrolidone. The paint containing the positive electrode active material can be produced by mixing the components used in the paint containing the positive electrode active material by a known method. The method for mixing the components used in the paint containing the positive electrode active material is not particularly limited, and the mixing order is also not particularly limited.

[0070] There are no particular limitations on the method for applying the paint containing the positive electrode active material to the positive electrode current collector 22, and it is possible to use a method that is usually employed when producing the positive electrode 20. Examples of methods for applying the paint containing the positive electrode active material include a slit die coating method and a doctor blade method.

[0071] After applying the paint containing the positive electrode active material to form a coating film, the method for removing the solvent in the coating film and drying it is not particularly limited. For example, a method can be used in which the positive electrode current collector 22 coated with the paint containing the positive electrode active material is dried in an atmosphere at 80°C to 150°C. This results in a positive electrode 20 in which a positive electrode active material layer 24 is formed on the positive electrode current collector 22.

[0072] To manufacture the negative electrode 30, first, a laminated resin film 3 shown in FIG. 2 is prepared as a negative electrode current collector 32. Then, a paint containing a negative electrode active material is applied to the laminated resin film 3 and dried. The negative electrode active material layer 34 can be formed in the same manner as the positive electrode active material layer 24, except that a paint containing a negative electrode active material is used instead of the paint containing a positive electrode active material.

[0073] As the paint containing the negative electrode active material, those containing a negative electrode active material, a binder for the negative electrode, a conductive assistant for the negative electrode, and a solvent can be used. As the solvent, for example, water, N-methyl-2-pyrrolidone, etc. can be used. The paint containing the negative electrode active material can be produced by mixing each component used in the paint containing the negative electrode active material by a known method. The method of mixing each component used in the paint containing the negative electrode active material is not particularly limited, and the mixing order is also not particularly limited.

[0074] Next, as shown in FIG. 1, the positive electrode 20 and the negative electrode 30 are laminated via the separator 10 to form the power generation unit 40. Then, the power generation unit 40 together with the electrolytic solution is placed in a previously prepared bag-shaped exterior body 50, and the entrance of the exterior body 50 is sealed. Through the above steps, the lithium secondary battery 100 shown in FIG. 1 is obtained.

[0075] In the lithium secondary battery 100 of this embodiment, the negative electrode current collector 32 is made of the laminated resin film 3 shown in FIG. 2. The laminated resin film 3 shown in FIG. 2 has a resin layer 3a and Cu films 3b provided on both surfaces of the resin layer 3a. The Cu film 3b has an orientation index of 0.15 or more by the Lotgering method for the (111) plane, and the half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane is 0.3° or less, and satisfies formula (1). Therefore, the negative electrode current collector 32 made of the laminated resin film 3 shown in FIG. 2 has low electrical resistance and can prevent breakage of the Cu film 3b of the laminated resin film 3 and peeling of the Cu film 3b from the resin layer 3a. Therefore, the lithium secondary battery 100 of this embodiment is lightweight and has excellent safety.

[0076] As described above, the embodiments of the present disclosure have been described in detail with reference to the drawings. However, each configuration and their combinations in each embodiment are examples, and additions, omissions, substitutions, and other changes of the configuration are possible without departing from the spirit of the present disclosure.

[0077] For example, in the lithium secondary battery 100 of the above-described embodiment, the laminate resin film 3 shown in Fig. 2 is provided as the negative electrode current collector 32, but in the lithium secondary battery of the present disclosure, either one or both of the negative electrode and positive electrode may include a current collector made of the laminate resin film of the present disclosure. That is, in the lithium secondary battery of the present disclosure, the positive electrode current collector may include the laminate resin film of the present disclosure, and the positive electrode current collector and the negative electrode current collector may include the laminate resin film of the present disclosure. When the positive electrode current collector 22 includes the laminated resin film 35 shown in FIG. 4, the underlayer 3c may be a metal layer containing at least one element selected from the group consisting of Cr, Ti, Ni, Ta, Zn, Nb, Cu, and Al. [Example]

[0078] ( Experimental Examples 1 to 21 , Comparative Examples 1 to 2) A resin layer 3a (trade name: Diafoil, manufactured by Mitsubishi Chemical Corporation) made of polyethylene terephthalate (PET) with a thickness of 4.5 μm was prepared. Next, Cu films 3b with thicknesses shown in Table 2 were simultaneously formed on both sides of the resin layer 3a using the Cu film formation method shown in Table 1, thereby obtaining a laminated resin film 3 shown in FIG.

[0079] [Table 1]

[0080] [Table 2]

[0081] The "1st" in the Cu film formation method shown in Table 1 is the film formation method in the step of forming a Cu seed layer. Table 1 shows the thickness of the Cu seed layer and the film formation atmosphere when the Cu seed layer is formed. The "2nd" step in the Cu film formation method shown in Table 1 is a film formation method in the step of forming a Cu plating layer that was performed after the "1st" step. The plating current density in the step of forming the Cu plating layer is shown in Table 1.

[0082] For the laminated resin film 3 thus obtained, X-ray diffraction measurement of the Cu film 3b was performed using an X-ray diffraction (XRD) device (trade name: X'Pert PRO MRD, manufactured by PANalytical). From the results, the orientation index of the (111) plane of the Cu film 3b by the Lotgering method and the half-width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane were calculated using the above-mentioned method. The results are shown in Table 2. Furthermore, using the calculated orientation index of the (111) plane by the Lotgering method and the half-width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane, it was investigated whether the Cu film 3b satisfied the above formula (1). The results are shown in Table 2. In Table 2, cases where the above formula (1) was satisfied are marked with "○", and cases where the above formula (1) was not satisfied are marked with "×".

[0083] Furthermore, the breaking elongation and resistance of the laminated resin film 3 were measured by the methods described below, and the resistance to calendering was evaluated. "Breaking elongation" A tensile test was carried out using a tabletop load tester (product name: FTN1-13A, manufactured by Aiko Engineering Co., Ltd.), and the elongation at the time when the sample broke was measured. The breaking elongation was calculated by the following formula. Breaking elongation (%) = {(ΔL / L)-1} × 100 (In the formula, L is the sample length before the tensile test. △L is the sample length at the time of break.)

[0084] "resistance" A low resistance resistivity meter (product name: Loresta GX MCP-T700, manufactured by Nitto Seiko Analytech Co., Ltd.) was used to measure the surface resistance of the laminate resin film 3. The volume resistance of the laminate resin film 3 was calculated by multiplying the obtained surface resistance of the laminate resin film 3 by the film thickness of the Cu film, and this was used as the resistance.

[0085] "Calendar-resistant treatment" A primer paint composed of carbon black, carboxymethyl cellulose, styrene butadiene rubber and water was applied onto the Cu film 3b of the laminated resin film 3 to form a primer layer. Also, an active material paint composed of graphite, carboxymethyl cellulose, styrene butadiene rubber and water was applied onto the primer layer of the laminated resin film 3 and dried at 60 °C for 3 hours to form an active material layer.

[0086] Thereafter, a calendering process was performed in which the laminated resin film 3 having the active material layer formed thereon was passed between rotating rolls at a line pressure of 600 kg / cm². Regarding the laminated resin film 3 after passing between the rolls, the presence or absence of peeling of the Cu films 3b on both sides from the resin layer 3a was observed under the following conditions using a scanning electron microscope (Hitachi High-Tech S-4800) and evaluated according to the following criteria.

[0087] (Observation conditions) Microscope observation magnification: 5000 times Number of observation fields: 30 fields (Evaluation criteria) "No peeling": No peeling at a line pressure of 1.0 times (600 kg / cm²) (no peeling points were observed in 30 fields of observation) "Extremely good": No peeling at a line pressure of 1.5 times (900 kg / cm²) (no peeling points were observed in 30 fields of observation) "NG": Peeling was observed at a line pressure of 1.0 times (600 kg / cm²) (one or more peeling points were observed in 30 fields of observation)

[0088] As shown in Table 2, Experimental Examples 1 to 21 the laminated resin film had a low electrical resistance of 3 μΩ·cm or less. Also, Experimental Examples 1 to 21 the laminated resin film had a sufficient elongation at break of 4.5% or more. Also, Experimental Examples 1 to 21 the laminated resin film had an evaluation of "no peeling" or "extremely good" for the calendering resistance, and the Cu film 3b was difficult to peel from the resin layer 3a.

[0089] In contrast, as shown in Table 2, the laminated resin films of Comparative Examples 1 and 2, in which the orientation index of the (111) plane of the Cu film 3b measured by the Lotgering method was less than 0.15, were evaluated as "NG" in terms of resistance to calendering. [Explanation of symbols]

[0090] 3,33,35 Laminated resin film 3a Resin layer 3b Cu film 3c Base layer 10 Separator 20 positive electrode 22 Positive electrode current collector 24 Cathode active material layer 30 negative electrode 32 Negative electrode current collector 34 Negative electrode active material layer 40 Power Generation Department 50 Exterior body 60,62 leads 100 Lithium secondary battery

Claims

1. A laminated resin film having a resin layer and a Cu film provided on one or both surfaces of the resin layer, wherein the Cu film is composed of a Cu seed layer formed on the resin layer side and a Cu plating layer formed on the Cu seed layer, has a thickness of 1.0 μm or less, an orientation index by the Lotgering method of the (111) plane of 0.15 or more, and a half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane of 0.18° or less, and satisfies the following formula (1). y ≧ 3.75x - 0.675 Formula (1) (In Formula (1), y is the orientation index by the Lotgering method of the (111) plane in the Cu film, and x is the half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane in the Cu film.)

2. The laminated resin film according to Claim 1, wherein the Cu film has an orientation index of 0.3 to 0.

98.

3. The laminated resin film according to Claim 1 or Claim 2, wherein the Cu film has a half-value width of the X-ray diffraction peak of 0.08° or more.

4. The laminated resin film according to any one of Claims 1 to 3, wherein the thickness of the Cu film is 0.3 μm or more.

5. The laminated resin film according to any one of Claims 1 to 4, wherein an underlayer is provided between the resin layer and the Cu film in contact with the resin layer and the Cu film.

6. A current collector composed of the laminated resin film according to any one of Claims 1 to 5.

7. A secondary battery having a negative electrode, a positive electrode facing the negative electrode, and a separator positioned between the negative electrode and the positive electrode, wherein either one or both of the negative electrode and the positive electrode include the current collector according to Claim 6.

8. A laminated resin film having a resin layer and a Cu film provided on one surface side or both surface sides of the resin layer, wherein the Cu film is formed using only the sputtering method, has an orientation index by the Lotgering method of the (111) plane of 0.15 or more and 0.40 or less, a half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane of 0.22° or more and 0.3° or less, and satisfies the following formula (1). Y ≧ 3.75x - 0.675 Formula (1) (In Formula (1), Y is the orientation index by the Lotgering method of the (111) plane in the Cu film, and x is the half-value width of the X-ray diffraction peak obtained by X-ray diffraction measurement of the (111) plane in the Cu film.)

Images