Laminated resin film, current collector and secondary battery

Abstract

Provided is a laminated resin film having a resin layer and a Cu film provided on one or both surfaces of the resin layer, the Cu film being such that the peak intensity y of a (200) plane is 2-30, where 100 designates the peak intensity of a (111) plane in X-ray diffraction measurement, and the Cu film satisfying formula (1). Formula (1): y≥2.5x−7.5 (In formula (1), y is the peak intensity of the (200) plane, where 100 designates the peak intensity of the (111) plane in X-ray diffraction measurement, and x is the peak intensity of a (220) plane, where 100 designates the peak intensity of the (111) plane in X-ray diffraction measurement.)

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 having a metal layer formed on the surface of a resin layer is used as a current collector for a lithium secondary battery, there is a concern that the current collector may deteriorate.

[0006] The present disclosure has been made in view of the above problems, and has an object to provide a laminated resin film that is resistant to deterioration. Another object of the present disclosure is to provide a current collector made of the above-mentioned laminated resin film, and a secondary battery that includes the current collector and is lightweight and has excellent safety. [Means for solving the problem]

[0007] In order to solve the above problems, a Cu film was formed as a metal layer on the surface of a resin layer, and extensive research was conducted, focusing on the orientation of the Cu film. As a result, we found that it is sufficient to form a Cu film on the surface of the resin layer, in which the peak intensity of the (200) and (220) planes falls within a specific range when the peak intensity of the (111) plane in X-ray diffraction measurement is taken as 100. That is, the present disclosure relates to the following:

[0008] [1] A resin layer and a Cu film provided on one or both surfaces of the resin layer, The Cu film is a laminated resin film in which the peak intensity y of the (200) plane in X-ray diffraction measurement is 2 to 30 when the peak intensity of the (111) plane is taken as 100, and the following formula (1) is satisfied: y≧2.5x-7.5 Equation (1) (In formula (1), y is the peak intensity of the (200) plane when the peak intensity of the (111) plane in X-ray diffraction measurement is taken as 100, and x is the peak intensity of the (220) plane when the peak intensity of the (111) plane in X-ray diffraction measurement is taken as 100.)

[0009] [2] The laminated resin film according to [1], wherein the peak intensity x of the (220) plane is 5 or less. [3] The laminated resin film according to [1] or [2], wherein an underlayer is provided between the resin layer and the Cu film and in contact with the resin layer and the Cu film.

[0010] [4] A current collector comprising the laminated resin film according to any one of [1] to [3].

[0011] [5] A battery comprising: a negative electrode; a positive electrode facing the negative electrode; and a separator positioned between the negative electrode and the positive electrode; A secondary battery in which either or both of the negative electrode and the positive electrode are provided with the current collector according to [4]. [Effects of the Invention]

[0012] 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, wherein the Cu film has a peak intensity y of 2 to 30 for the (200) plane in X-ray diffraction measurement when the peak intensity for the (111) plane is taken as 100, and satisfies formula (1). Therefore, the laminated resin film of the present disclosure is less susceptible to deterioration.

[0013] The current collector of the present disclosure is made of the laminated resin film of the present disclosure, and therefore is less susceptible to deterioration. In addition, in the secondary battery of the present disclosure, either or both of the negative electrode and the positive electrode include the current collector of the present disclosure, and therefore the secondary battery of the present disclosure is lightweight and has excellent safety. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a lithium secondary battery according to the present disclosure. [Figure 2] 1 is a schematic cross-sectional view showing an example of a laminated resin film of the present disclosure. [Figure 3] FIG. 2 is a schematic cross-sectional view showing another example of the laminated resin film of the present disclosure. [Figure 4] FIG. 2 is a schematic cross-sectional view showing another example of the laminated resin film of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present disclosure is not limited thereto. Appropriate modifications may be made within the scope of the present disclosure.

[0016] [Lithium secondary battery] Fig. 1 is a cross-sectional schematic diagram showing an example of a lithium secondary battery according to 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 electrolyte is housed within the exterior body 50 along with the power generation unit 40.

[0017] (Power Generation Department) The power generation unit 40 has a positive electrode 20 and a negative electrode 30 arranged opposite each other with a separator 10 sandwiched therebetween. Although Fig. 1 illustrates a case in which one power generation unit 40 is housed in the exterior body 50, a plurality of power generation units 40 may be housed in a stacked configuration.

[0018] <Positive electrode> The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24 . (Cathode active material layer) The positive electrode active material layer 24 includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive additive.

[0019] (Cathode active material) The positive electrode active material is a material that absorbs and releases lithium ions, desorbs and inserts lithium ions (intercalates), or converts lithium ions into counter anions (e.g., PF6 - An electrode active material capable of reversibly doping and dedoping with the electrode active material is used.

[0020] Examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese spinel (LiMn2O4), and lithium manganese oxide (LiMnO4) represented by the general formula: LiNi x Co y Mn z M aA composite metal oxide represented by 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), a 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.

[0021] (Binder for the positive electrode) The binder for the positive electrode binds the positive electrode active materials to each other and also binds the positive electrode active material and the positive electrode current collector 22. As the binder for the positive electrode, for example, 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), polyvinyl fluoride (PVF), etc. can be used.

[0022] 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).

[0023] 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.

[0024] (Conductive additive for positive electrode) The positive electrode conductive additive improves the conductivity of the positive electrode active material layer 24. Known conductive additives can be used as the positive electrode conductive additive. Examples of the positive electrode conductive additive include carbon-based materials such as graphite and carbon black, fine metal powders such as copper, nickel, stainless steel, and iron, and conductive oxides such as ITO (indium tin oxide).

[0025] (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.

[0026] <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 negative electrode binder and / or a negative electrode conductive assistant as necessary.

[0027] (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 carbon materials such as metallic lithium, graphite (natural graphite, artificial graphite), carbon nanotubes, graphitization-resistant carbon, graphitization-easy 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, particles containing lithium titanate (Li4Ti5O 12 ) etc. can be used.

[0028] (Negative electrode binder) As the negative electrode binder, the same materials as those that can be used as the positive electrode binder can be used. In addition to those that can be used as the positive electrode binder, for example, one or more selected from cellulose, carboxymethyl cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, polyamideimide resin, and acrylic resin may be used.

[0029] (Negative electrode conductive assistant) 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.

[0030] (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.

[0031] 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 have different peak intensities for the (200) and / or (220) planes when the peak intensity for the (111) plane in X-ray diffraction measurement is taken as 100.

[0032] 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.

[0033] 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.

[0034] The thickness of the resin layer 3a forming the laminated resin film 3, 33 can be appropriately determined depending on the application of the lithium secondary battery 100. The thickness of the resin layer 3a is, for example, preferably 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 film 3, 33 can be suppressed, and rupture of the Cu film 3b and peeling of the Cu film 3b from the resin layer 3a can be further prevented. Furthermore, when the thickness of the resin layer 3a is 12 μm or less, the laminated resin film 3, 33 does not interfere with miniaturization of the lithium secondary battery 100, and this is preferable.

[0035] The Cu film 3b forming the laminated resin films 3, 33 has a peak intensity y of 2 to 30 for the (200) plane in X-ray diffraction measurement when the peak intensity of the (111) plane is taken as 100, and satisfies the following formula (1). Therefore, the laminated resin films 3, 33 are less susceptible to deterioration for the reasons described below.

[0036] y≧2.5x-7.5 Equation (1) (In formula (1), y is the peak intensity of the (200) plane when the peak intensity of the (111) plane in X-ray diffraction measurement is taken as 100, and x is the peak intensity of the (220) plane when the peak intensity of the (111) plane in X-ray diffraction measurement is taken as 100.)

[0037] As a result of extensive research, the inventors have found that the main cause of deterioration of the laminated resin film 3, 33 is that decomposition products generated by decomposition of the electrolyte during charging and discharging corrode and deteriorate the Cu film 3b. In particular, HF generated by decomposition of electrolytes such as LiPF6 during repeated charging and discharging of the lithium secondary battery 100 in a high-temperature environment accelerates deterioration of the Cu film. Specific examples of deterioration of the Cu film due to decomposition products include cracks and breaks in the Cu film, peeling of the Cu film from the resin layer 3a, and dissolution and loss of the Cu film.

[0038] A Cu film 3b having the peak intensity y of the (200) plane satisfying the formula (1) exhibits good adhesion to the resin layer 3a. Therefore, decomposition products generated by electrolyte decomposition are less likely to penetrate between the Cu film 3b and the resin layer 3a, and the Cu film 3b is less likely to peel off from the resin layer 3a. Furthermore, a Cu film 3b having a peak intensity y of 2 or more exhibits excellent ductility. A Cu film 3b with excellent ductility is less likely to crack. Furthermore, a Cu film 3b having a peak intensity y of 30 or less is less likely to be corroded by decomposition products generated by electrolyte decomposition. In the laminated resin film 3, 33, these synergistic effects suppress the progression of deterioration of the Cu film 3b. Therefore, the laminated resin film 3, 33 is less likely to deteriorate.

[0039] In order to make the Cu film 3b less susceptible to cracking, it is preferable that the peak intensity y of the (200) plane be 2.5 or more when the peak intensity of the (111) plane is taken as 100 in X-ray diffraction measurement. In order to make the Cu film 3b even more resistant to corrosion, it is preferable that the peak intensity y of the (200) plane be 15 or less when the peak intensity of the (111) plane is taken as 100 in X-ray diffraction measurement.

[0040] In the Cu film 3b, the peak intensity x of the (220) plane in X-ray diffraction measurement, where the peak intensity of the (111) plane is taken as 100, is preferably 5 or less, and more preferably 2 or less. The Cu film 3b having the peak intensity x of the (220) plane of 5 or less has better adhesion to the resin layer 3a. This makes the Cu film 3b even less likely to peel off from the resin layer 3a.

[0041] 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.

[0042] "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.

[0043] Next, a Cu film 3b is formed on one or both surfaces of the resin layer 3a in contact with the resin layer 3a. In an X-ray diffraction measurement of the Cu film 3b, the peak intensity of the (200) and (220) planes can be controlled by the method for forming the Cu film 3b, assuming that the peak intensity of the (111) plane is 100. 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.

[0044] Examples of the step of forming the Cu seed layer include 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). Among the above film formation methods, it is preferable to form the Cu seed layer using a method selected from electroless plating, sputtering, and vapor deposition, and sputtering is particularly preferable. This is because forming a Cu plating layer on the Cu seed layer makes it easier to form a Cu film 3b whose peak intensities for the (200) and (220) planes satisfy specific conditions when the peak intensity for the (111) plane is set to 100 in X-ray diffraction measurement.

[0045] 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 easily forms a Cu film 3b, in which the peak intensities of the (200) and (220) planes satisfy specific conditions when the peak intensity of the (111) plane is set to 100 in X-ray diffraction measurement.

[0046] 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, performing the step of forming the Cu plating layer makes it easier to obtain a Cu film 3b in which the peak intensities of the (200) and (220) planes satisfy specific conditions when the peak intensity of the (111) plane in X-ray diffraction measurement is set to 100, 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) that reach 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.

[0047] The step of forming the Cu plating layer may involve forming a Cu film 3b having a thickness of, for example, 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 having a 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.

[0048] The current density in the electrolytic plating method is, for example, 2.5 to 4.8 A / dm 2 By changing the current density in the electrolytic plating method, it is possible to control the peak intensity of the (200) plane when the peak intensity of the (111) plane in X-ray diffraction measurement of the Cu film 3b is set to 100. Specifically, when the current density is lowered, a Cu film 3b with a strong peak intensity of the (200) plane is obtained, and when the current density is increased, a Cu film 3b with a weak peak intensity of the (200) plane is obtained.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] As shown in Fig. 4, the underlayer 3c is provided between the resin layer 3a and the Cu film 3b and in contact with the resin layer 3a and the Cu film 3b. The presence of the underlayer 3c can improve adhesion between the resin layer 3a and the Cu film 3b. When the Cu films 3b are provided on both sides of the resin layer 3a, the underlayer 3c may be provided on both sides of the resin layer 3a as shown in Fig. 4, or may be provided on only one side of the resin layer 3a.

[0053] The base 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 base 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, and is preferably a metal layer containing Ni, and more preferably a metal layer made of an alloy of Ni and Cr, as this improves corrosion resistance to HF.

[0054] The laminate resin film 35 shown in FIG. 4 can be produced, for example, by the following method. A resin layer 3a is formed in the same manner as when producing the laminate resin film 3 shown in FIG. 2. Next, base layers 3c are formed on both sides of the resin layer 3a in contact with the resin layer 3a by a film formation method such as sputtering or vapor deposition. Thereafter, Cu films 3b are formed on the base layers 3c provided on both sides of the resin layer 3a in the same manner as when forming the Cu films 3b of the laminate resin film 3 shown in FIG. 2. Through the above steps, the laminate resin film 35 shown in FIG. 4 is obtained.

[0055] <separator> Known separators, such as those having an electrically insulating porous structure, can be used as separator 10. Specific examples include a monolayer or laminate of a film made of a polyolefin resin such as polyethylene or polypropylene, a stretched membrane of a mixture of multiple polyolefin resins, and a fibrous nonwoven fabric made of at least one constituent material selected from the group consisting of cellulose, polyester, and polypropylene.

[0056] (electrolyte) The electrolytic solution is impregnated in the power generation unit 40. An electrolytic solution or a non-aqueous electrolytic solution can be used as the electrolytic solution. When a non-aqueous electrolytic solution is used as the electrolytic solution, the withstand voltage during charging can be increased, which is preferable compared to when an electrolytic aqueous solution is used.

[0057] The non-aqueous electrolyte solution is a solution in which an electrolyte is dissolved in a non-aqueous solvent, such as a cyclic carbonate or a chain carbonate. The cyclic carbonate used is one that can solvate the electrolyte, and examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, and butylene carbonate. The chain carbonate used is one that reduces the viscosity of the cyclic carbonate, and examples of the chain carbonate include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0058] 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 be used.

[0059] Examples of the electrolyte contained in the non-aqueous electrolyte solution include lithium salts such as LiPF, LiClO, LiBF, LiCF, SO, LiCF, CF, SO, LiC(CF), LiN(CF, SO), LiN(CF, CF, SO), LiN(CF, SO)(CF, SO), LiN(CF, CF, CO), and LiBOB. These lithium salts may be used alone or in combination of two or more. From the viewpoint of ionization degree, the electrolyte preferably contains LiPF.

[0060] For example, an ionic liquid may be used as the non-aqueous electrolyte solution. Ionic liquids are salts (room-temperature molten salts) that are made up of a combination of cations and anions and remain liquid even at low temperatures, such as temperatures below 100°C. Ionic liquids have strong electrostatic interactions and are non-volatile and non-flammable. Therefore, a lithium secondary battery 100 that uses an ionic liquid as the non-aqueous electrolyte solution is highly safe. Known cation components and anion components of the ionic liquid can be used.

[0061] (Lead) The leads 60 and 62 are made 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.

[0062] (exterior body) The exterior body 50 seals the power generation unit 40 and the electrolyte inside. The exterior body 50 is not particularly limited as long as it can prevent the electrolyte from leaking to the outside and the intrusion of moisture and the like from the outside into the inside.

[0063] The exterior body 50 may be made of a metal laminate film in which both sides of a metal foil 52 are coated with a polymer film 54, as shown in FIG. For example, aluminum foil can be used as the metal foil 52. For the outer polymer film 54, it is preferable to use a film made of a polymer with a high melting point, such as polyethylene terephthalate (PET), polyamide, etc. For the inner polymer film 54, it is possible to use a film made of polyethylene (PE), polypropylene (PP), etc.

[0064] [Method of manufacturing lithium secondary batteries] Next, a method for manufacturing the lithium secondary battery 100 shown in FIG. 1 will be described in detail using an example. To manufacture the lithium secondary battery 100 of this embodiment, first, the positive electrode 20 and the negative electrode 30 are prepared.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] The paint containing the negative electrode active material may contain a negative electrode active material, a negative electrode binder, a negative 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 negative electrode active material can be produced by mixing the components used in the paint containing the negative electrode active material by a known method. The method for mixing the components used in the paint containing the negative electrode active material is not particularly limited, and the mixing order is also not particularly limited.

[0070] Next, as shown in Fig. 1, the positive electrode 20 and the negative electrode 30 are laminated with the separator 10 interposed therebetween to form the power generation unit 40. Thereafter, the power generation unit 40, together with the electrolyte solution, is placed in a bag-shaped exterior body 50 that has been prepared in advance, and the inlet of the exterior body 50 is sealed. Through the above steps, the lithium secondary battery 100 shown in Fig. 1 is obtained.

[0071] 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 sides of the resin layer 3a. The Cu film 3b has a peak intensity y of 5 to 30 in the (200) plane when the peak intensity of the (111) plane is defined as 100 in X-ray diffraction measurement, and satisfies formula (1). Therefore, the negative electrode current collector 32 made of the laminated resin film 3 shown in FIG. 2 is less susceptible to cracking or breaking of the Cu film 3b, peeling of the Cu film 3b from the resin layer 3a, and dissolution or loss of the Cu film 3b, and is less susceptible to deterioration. Therefore, the lithium secondary battery 100 of this embodiment is lightweight and has excellent safety.

[0072] The above describes the embodiments of the present disclosure in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and addition, omission, substitution, and other modifications of the configuration are possible within the scope that does not deviate from the spirit of the present disclosure. 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. [Example]

[0073] (Experimental Examples 1 to 31) A 4.5 μm-thick resin layer 3a (product name: Diafoil, manufactured by Mitsubishi Chemical Corporation) made of polyethylene terephthalate (PET) was prepared. Next, a 50 nm-thick Cu seed layer was formed using a sputtering method in the atmosphere shown in Table 1. Then, a Cu plating layer was formed on the Cu seed layer by electroplating at the current density shown in Table 1. By performing the above steps, a 0.5 μm-thick Cu film 3b was simultaneously formed on both sides of the resin layer 3a, and a laminated resin film 3 shown in FIG. 2 was obtained.

[0074] [Table 1]

[0075] "Ar+O2" listed in the sputtering deposition atmosphere in Table 1 is a mixed gas containing argon gas and oxygen gas in a volume ratio of 9999:1. "Ar+H2" is a mixed gas containing argon gas and hydrogen gas in a volume ratio of 999:1.

[0076] 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) to obtain the peak intensities of the (111) plane, (200) plane, and (200) plane. From the results, the peak intensities of the (200) plane and (220) plane were calculated, assuming that the peak intensity of the (111) plane in the X-ray diffraction measurement was 100. The results are shown in Table 1.

[0077] Furthermore, the peak intensities of the (200) and (220) planes shown in Table 1 were substituted into the above formula (1) to examine whether the Cu film 3b satisfied formula (1). The results are shown in Table 1. In Table 1, cases where formula (1) was satisfied are marked with "○", and cases where formula (1) was not satisfied are marked with "×".

[0078] The laminated resin film 3 thus obtained was used as a negative electrode current collector to obtain a lithium secondary battery by the method described below. First, a coating material containing a negative electrode active material was applied to a negative electrode current collector made of the laminated resin film 3 of Experimental Examples 1 to 31 so that the film thickness after drying would be 70 μm, and then dried to produce a negative electrode. The paint containing the negative electrode active material consisted of 95 parts by mass of graphite (negative electrode active material), 1 part by mass of carbon black (conductive additive), 1.5 parts by mass of styrene-butadiene rubber (binder), 2.5 parts by mass of carboxymethyl cellulose (binder), and a solvent.

[0079] Next, the paint containing the positive electrode active material was applied onto a positive electrode current collector made of aluminum foil with a thickness of 8 μm so that the film thickness after drying would be 70 μm, and then dried to produce a positive electrode. The paint containing the positive electrode active material was composed of 94 parts by mass of lithium cobalt oxide (LiCoO2) (positive electrode active material), 2 parts by mass of carbon black (conductive additive), 4 parts by mass of polyvinylidene fluoride (binder), and a solvent.

[0080] The positive and negative electrodes were then stacked with a polyethylene separator 10 between them to form a power generation unit. The power generation unit and the electrolyte were then placed in a bag-shaped exterior made of aluminum laminate film, and the entrance to the exterior was sealed. The electrolyte used was dimethyl carbonate to which 1 mol / L of LiPF6 had been added. Through the above steps, the lithium secondary batteries of Experimental Examples 1 to 31 were obtained.

[0081] The lithium secondary battery thus obtained was placed in a thermostatic chamber at 60°C and subjected to 100 charge / discharge cycles. The power generating section of the lithium secondary battery was then cut off, and the negative electrode current collector (laminated resin film) was observed at 5000x magnification using a scanning electron microscope (SEM) (Hitachi High-Tech S-4800), and the "breakage resistance" and "peeling resistance" were evaluated according to the following criteria.

[0082] "Break resistance" (OK) Not a single crack was found in 30 fields of view. (NG) One or more cracks are found in 30 fields of view. "Peeling resistance" (EXCELLENT) No peeling was observed in 30 fields of view. (GOOD) Three or fewer peeling sites were observed in 30 visual fields. (NG) Four or more detached areas were observed in 30 fields of view.

[0083] As shown in Table 1, in Experimental Examples 2 to 6, 9 to 12, 14, 15, 17, 18, 21, 30, and 31, which used laminated resin films having a Cu film in which the peak intensity y of the (200) plane in X-ray diffraction measurement was 2 to 30 when the peak intensity of the (111) plane was 100 and which satisfied formula (1), the fracture resistance was evaluated as (OK) and the peel resistance was evaluated as (EXCELLENT) or (GOOD). In particular, in experimental examples 2 to 6, 9, 10, 12, 30, and 31, which used laminated resin films having a Cu film in which the peak intensity x of the (220) plane was 5 or less when the peak intensity of the (111) plane in X-ray diffraction measurement was taken as 100, the peel resistance was evaluated as (EXCELLENT), indicating good peel resistance.

[0084] In contrast, as shown in Table 1, in Experimental Examples 1, 7, 8, 13, 16, 19, 20, 22 to 29, which used laminated resin films having a Cu film in which the peak intensity y of the (200) plane was not between 2 and 30 when the peak intensity of the (111) plane in X-ray diffraction measurement was taken as 100, and / or which did not satisfy formula (1), the fracture resistance and peel resistance were evaluated as (NG). [Explanation of symbols]

[0085] 3,33 Laminated resin film 3a Resin layer 3b Cu film 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 resin layer and a Cu film provided on one or both surfaces of the resin layer; The Cu film comprises a Cu seed layer formed on the resin layer side and a Cu plating layer formed on the Cu seed layer, and the peak intensity y of the (200) plane in X-ray diffraction measurement is 2 to 18 when the peak intensity of the (111) plane is taken as 100, and the laminated resin film satisfies the following formula (1): y≧2.5x−7.5 Formula (1) (In formula (1), y is the peak intensity of the (200) plane when the peak intensity of the (111) plane in X-ray diffraction measurement is taken as 100, and x is the peak intensity of the (220) plane when the peak intensity of the (111) plane in X-ray diffraction measurement is taken as 100, and is 5 or less.)

2. 2. The laminated resin film according to claim 1, further comprising an underlayer provided between the resin layer and the Cu film in contact with the resin layer and the Cu film.

3. A current collector comprising the laminated resin film according to claim 1 or 2.

4. a negative electrode, a positive electrode facing the negative electrode, and a separator positioned between the negative electrode and the positive electrode; A device in which either or both of the negative electrode and the positive electrode are provided with the current collector according to claim 3. Next battery.

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