Current collector, electrode for power storage device, and lithium ion secondary battery

Abstract

This current collector comprises a resin layer, a conductive layer, a first intermediate layer positioned between the resin layer and the conductive layer, and a second intermediate layer positioned between the first intermediate layer and the resin layer, wherein the first intermediate layer includes a metal as a main constituent, and the second intermediate layer includes a metal oxide as a main constituent.

Description

[Technical Field]

[0001] The present disclosure relates to a current collector, an electrode for an electricity storage device, and a lithium ion secondary battery. [Background technology]

[0002] It has been proposed to use a composite material in which a conductive layer is formed on one or both sides of a resin film as a current collector for a secondary battery. Patent Document 1 discloses a current collector for a secondary battery in which such a composite material is used as the current collector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-102429 Summary of the Invention [Problem to be solved by the invention]

[0004] In electricity storage devices such as lithium ion secondary batteries that include a non-aqueous electrolyte, it is known that decomposition products of the non-aqueous electrolyte cause deterioration of the current collector. Even when using the current collector of the above-described composite material in an electricity storage device that includes a non-aqueous electrolyte such as a lithium ion secondary battery, it is preferable to consider the effects of decomposition products of the non-aqueous electrolyte. One embodiment of the present disclosure provides a current collector, an electrode for an electricity storage device, and a lithium ion secondary battery that are inhibited from decomposing due to electrolyte decomposition products. [Means for solving the problem]

[0005] A current collector according to one embodiment of the present disclosure comprises a resin layer, a conductive layer, a first intermediate layer located between the resin layer and the conductive layer, and a second intermediate layer located between the first intermediate layer and the resin layer, wherein the first intermediate layer contains a metal as a main component, and the second intermediate layer contains a metal oxide as a main component. [Effects of the Invention]

[0006] According to one embodiment of the present disclosure, a current collector is provided that is inhibited from being deteriorated by decomposition products of the electrolyte. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the current collector of the first embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the relationship between the surface energy of the metal of the underlayer and the (111) plane orientation index of the Cu layer formed on the underlayer. [Figure 3] FIG. 3 is a schematic cross-sectional view showing an example of the current collector of the second embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view showing another example of the current collector of the second embodiment. [Figure 5] FIG. 5 is a schematic exploded perspective view showing an example of an electrode for an electricity storage device according to the third embodiment. [Figure 6] FIG. 6 is a schematic, partially cutaway perspective view showing an example of a lithium ion secondary battery according to the fourth embodiment. [Figure 7] FIG. 7 is a schematic exploded perspective view showing an example of a cell of the lithium ion secondary battery shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] The current collector, which has a conductive layer formed on a resin film, differs from conventional metal foils used alone as current collectors in terms of structure and thickness. In particular, the current collector is a composite of a resin film and a conductive layer, and the conductive layer is thinner than the metal foils used in conventional current collectors.

[0009] Lithium ion secondary batteries generally contain anions containing fluorine atoms as an electrolyte. When such lithium ion secondary batteries are charged and discharged in a high-temperature environment, the anions containing fluorine atoms decompose, producing fluorine ions, i.e., hydrofluoric acid, as a decomposition product. The present inventors have conceived of a current collector having a conductive layer formed on a resin film, which can maintain its charge-discharge characteristics by suppressing deterioration caused by decomposition products of the nonaqueous electrolyte, specifically by suppressing at least one of dissolution or loss of the conductive layer and peeling of the conductive layer from the resin film, and have conceived of a current collector, an electrode for a power storage device, and a lithium ion secondary battery.

[0010] Hereinafter, embodiments of the current collector, electrode for an electricity storage device, and lithium-ion secondary battery of the present disclosure will be described with reference to the drawings. The numerical values, shapes, materials, steps, and the order of steps presented in the following description are merely examples, and various modifications are possible as long as no technical contradictions occur. Furthermore, each embodiment described below is merely an example, and various combinations are possible as long as no technical contradictions occur.

[0011] The thickness, dimensions, shapes, etc. of components depicted in the drawings of this disclosure may be exaggerated for convenience of explanation. Furthermore, in the drawings of this disclosure, some components may be isolated or omitted to avoid excessive complexity. Therefore, the dimensions and relative positions of components depicted in the drawings of this disclosure may not reflect the dimensions and relative positions of components in an actual device. In this disclosure, "perpendicular" and "orthogonal" do not necessarily mean that two lines, sides, surfaces, etc. form an angle of exactly 90°, but also include cases where the angle is within a range of approximately 90° to ±5°. Furthermore, "parallel" includes cases where two lines, sides, surfaces, etc. form an angle of approximately 0° to ±5°.

[0012] In this specification, the term "cell" refers to a structure in which at least one pair of positive and negative electrodes are integrally assembled. In this specification, the term "battery" is used to encompass various forms, such as a battery module and a battery pack, which have one or more "cells" electrically connected to each other.

[0013] (First embodiment) 1 is a schematic cross-sectional view showing an example of a current collector according to this embodiment. The current collector according to this embodiment can be used as a current collector for either the positive or negative electrode of an electricity storage device such as a lithium-ion secondary battery. The current collector 101 includes a resin layer 10, a conductive layer 20, and a first intermediate layer 31 located between the resin layer and the conductive layer 20.

[0014] The resin layer 10 functions as a support for the conductive layer 20 in the current collector 101. Furthermore, the resin layer 10 has a smaller density than the conductive layer 20, and thus can contribute to increasing the charge capacity per unit weight when an electricity storage device is constructed.

[0015] The resin layer 10 has electrical insulation properties and contains a resin. The resin layer 10 may have thermoplastic properties. Specifically, the resin layer 10 may contain at least one of polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), polyimide (PI), polyethylene (PE), polystyrene (PS), phenolic resin (PF), and epoxy resin (EP). The resin layer 10 may be a single layer, or may be configured by laminating two or more layers. In this case, at least one layer of the multiple layers may contain a different resin.

[0016] The thickness of the resin layer 10 is, for example, 3 μm or more and 12 μm or less. The thickness of the resin layer 10 may be 3 μm or more and 6 μm or less. When the thickness of the resin layer 10 is 3 μm or more, sufficient strength as a support is obtained. Furthermore, when the thickness of the resin layer 10 is 12 μm or less, the overall thickness of the current collector 101 can be reduced. Therefore, when a stacked lithium ion secondary battery is constructed by stacking multiple electrode pairs, the proportion of parts that do not contribute to energy storage can be reduced, and the energy density can be increased. When the thickness of the resin layer 10 is 6 μm or less, the overall thickness of the current collector 101 can be further reduced, and the energy density of the stacked lithium ion secondary battery can be increased.

[0017] The current collector 101 may further include an undercoat layer located between the resin layer 10 and the first intermediate layer 31. The undercoat layer may be provided to increase the bonding strength between the resin layer 10 and the first intermediate layer 31, or to prevent pinholes from being formed in the first intermediate layer 31. For example, the undercoat layer may be a layer formed from an organic material such as an acrylic resin or a polyolefin resin, or a layer containing a metal formed by sputtering.

[0018] The first intermediate layer 31 controls the crystal orientation of the conductive layer 20. Specifically, the first intermediate layer 31 controls the crystal orientation of the conductive layer 20 so that the conductive layer 20 formed on the first intermediate layer 31 has a denser crystal structure. The first intermediate layer 31 contains a metal as a main component, and the surface energy of the metal contained in the first intermediate layer 31 is greater than the surface energy of the metal contained as a main component in the conductive layer 20. As will be described in detail below, satisfying this relationship makes the conductive layer 20 more likely to have a (111) orientation. The main component refers to the component that is contained in the largest proportion, expressed in mole percent, when a member contains one or more components.

[0019] The thickness D1 of the first intermediate layer 31 is, for example, 1 nm or more and 120 nm or less. If the thickness D1 of the first intermediate layer 31 is 1 nm or more, a continuous film can be formed, making it easier to control the orientation of the entire conductive layer 20 to be formed. If the thickness D1 of the first intermediate layer 31 is 120 nm or less, the time required to form the first intermediate layer 31 is not too long, and the influence of damage caused by the conditions during the formation of the first intermediate layer 31, such as heat or plasma, on the resin layer 10 is reduced, thereby suppressing deterioration of the resin layer 10. The thickness of the first intermediate layer 31 may be 2 nm or more and 100 nm or less.

[0020] The first intermediate layer 31 may contain at least one metal selected from the group consisting of, for example, Ni, Cr, Co, Ti, Zr, Nb, Hf, Ta, and W. Among these metals, a metal that satisfies the above-described surface energy relationship with the metal of the conductive layer 20 can be selected. When the conductive layer 20 is made of Cu, the first intermediate layer 31 may be made of, for example, Ni, Cr, a Ni-Cr alloy, Co, or W. When the conductive layer 20 is made of Al, the first intermediate layer 31 may be made of, for example, Ni or Cr. The first intermediate layer 31 may be formed using a known thin film formation technique used in the manufacture of semiconductor devices, such as vacuum deposition or sputtering.

[0021] The conductive layer 20 is the main current path in the current collector 101, and transfers electrons between the positive electrode active material or the negative electrode active material and a terminal or the like connected to the current collector. The conductive layer 20 contains a metal as a main component, and has a (111) orientation due to the function of the first intermediate layer 31. From the viewpoint of providing the (111) orientation, the conductive layer 20 may be in contact with the first intermediate layer 31.

[0022] Generally, the (111) plane of a metal layer has a higher surface atomic density and therefore superior corrosion resistance compared to the (100), (110), etc. Therefore, the conductive layer 20 has high corrosion resistance against decomposition products of the electrolyte in a non-aqueous electrolyte solution of a lithium ion secondary battery or the like.

[0023] The conductive layer 20 may have a high orientation of the (111) plane. Specifically, the orientation index of the (111) plane of the conductive layer 20 relative to the perpendicular direction of the resin layer 10, as determined by the Lotgering method, may be 0.3 or more. The orientation index may be, for example, 0.7 or more. The orientation index will be described in detail below.

[0024] The thickness of the conductive layer 20 is, for example, 0.3 μm or more and 2 μm or less. When the thickness of the conductive layer 20 is 0.3 μm or more, the resistance of the conductive layer 20 can be reduced. For example, when an electricity storage device is produced, energy loss due to resistance in the current collector can be reduced. Furthermore, when the thickness of the conductive layer 20 is 2 μm or less, the ratio of the conductive layer 20 to the resin layer 10 is relatively small, making it easier to obtain the advantage of reducing the weight of the current collector by using the resin layer 10. The thickness of the conductive layer 20 may be 0.5 μm or more and 1.2 μm or less.

[0025] The conductive layer 20 may contain, for example, one metal selected from the group consisting of Al, Ag, Cu, Ni, and a Ni-Cu alloy. When the current collector 101 is used for a positive electrode, the conductive layer 20 may contain Al. When the current collector 101 is used for a negative electrode, the conductive layer 20 may contain one metal selected from the group consisting of Ag, Cu, Ni, and a Ni-Cu alloy.

[0026] In this embodiment, the conductive layer 20 includes a seed layer 21 and a main layer 22. The seed layer 21 and the main layer 22 each contain a metal as a main component, and may be made of the same metal.

[0027] The seed layer 21 is formed by, for example, sputtering or vacuum deposition, and the main layer 22 is formed by plating. This is because, if the conductive layer 20 is relatively thick and the entire conductive layer 20 is formed by sputtering or vacuum deposition, the formation time would be long, reducing productivity and increasing damage to the resin layer 10 during the formation of the conductive layer 20. However, the conductive layer 20 does not necessarily have to include the seed layer 21. For example, the first intermediate layer 31 may be used as a conductive layer for plating.

[0028] When the conductive layer 20 includes the seed layer 21 and the main layer 22, the seed layer 21 in contact with the first intermediate layer 31 has a (111) orientation due to the function of the first intermediate layer 31. The main layer 22 has a (111) orientation in accordance with the orientation of the seed layer 21.

[0029] Next, we will explain how the first intermediate layer 31 controls the orientation of the conductive layer 20. As mentioned above, in order to suppress corrosion caused by decomposition products of the electrolyte contained in the nonaqueous electrolyte, it is considered to use a conductive layer with a high orientation of the (111) plane, which is a densely oriented plane, as a current collector. The inventors formed underlayers made of various metals and investigated the orientation of the Cu layer formed thereon. Figure 2 shows the relationship between the surface energy of the metals constituting the underlayer and the (111) plane orientation index of the Cu layer when the Cu layer is formed on the underlayer. For the sample, an underlayer made of Al, Ag-Pd-Cu, Cu, Ni-Cr, or Ti is formed on a substrate, and a Cu layer is formed thereon. The underlayer has a thickness of 10 nm, and the Cu layer has a thickness of 50 nm to 60 nm, and they are formed by sputtering.

[0030] The (111) plane orientation index is the orientation index F by the Lotgering method. The maximum value of the orientation index by the Lotgering method is 1. An orientation index of 1 indicates perfect orientation, and an orientation index of 0 indicates no orientation. The orientation index F can be calculated using the intensity of the X-ray diffraction peak obtained by X-ray diffraction measurement of the layer (film) to be evaluated, using the following formula: F=(ρ-ρ0) / (1-ρ0) ρ0=ΣI0(111) / ΣI0(hkl) ρ=ΣI(111) / ΣI(hkl)

[0031] I0(111) indicates 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) indicates the intensity of all diffraction peaks obtained by X-ray diffraction measurement of non-oriented Cu film. Furthermore, a non-oriented Cu film is a Cu film whose X-ray diffraction peak intensity pattern is similar to that of the X-ray diffraction peak intensity pattern of a copper standard sample listed in the JCPDS (Joint Committee on Powder Diffraction Standards).

[0032] I(111) indicates the intensity of the (111) plane X-ray diffraction peak obtained by X-ray diffraction measurement of the layer (film) to be evaluated. I(hkl) indicates the intensity of all diffraction peaks obtained by X-ray diffraction measurement of the layer (film) to be evaluated.

[0033] The surface energy of metals was measured using the values ​​described in the non-patent literature: L. Vitos, AV Ruban, H.L. Skriver, J. Kollar, "The surface energy of metals," Surface Science, Elsevier, 1998, Vol. 411, Pages 186-202. Table 1 shows the literature values ​​for the surface energy of various metals. For alloys, calculations were performed from the values ​​in Table 1 based on the content ratio. It is difficult to measure the surface energy of metals accurately, and the surface energy values ​​of metals vary by about 10% depending on the literature. The values ​​shown in Table 1 are examples of the surface energy of metals.

[0034] As shown in Figure 2, the (111) orientation index of the Cu layer formed on the underlayer varies depending on the type of metal in the underlayer, and it is thought that there is a correlation between the surface energy of the metal that makes up the underlayer and the (111) orientation index of the Cu layer. The higher the surface energy of the metal that makes up the underlayer, the larger the (111) orientation index of the Cu layer.

[0035] On the other hand, it is known that the surface energy of metals depends on the plane orientation, and in metals with an FCC structure, the surface energy has the relationship (110)>(100)>(111).

[0036] From these facts, it is thought that when the surface energy of the metal of the first intermediate layer 31 is greater than the surface energy of the metal of the conductive layer 20, the formation of the conductive layer 20 on the first intermediate layer 31 is an energetically advantageous state transformation, and therefore the metal atoms of the first intermediate layer 31 are selectively arranged from the state in which the first intermediate layer 31 is exposed to the state in which the energy difference is greatest, i.e., the state in which the (111) plane of the conductive layer 20 is formed.

[0037] From FIG. 2, when the conductive layer 20 contains Cu as a main component, the surface energy of the first intermediate layer 31 is 1.5 J / m 2 If this is the case, the conductive layer 20 is expected to exhibit a (111) plane orientation index of about 0.7 or more.

[0038] [Table 1]

[0039] As described above, according to the current collector of the present embodiment, the first intermediate layer 31 contains a metal as a main component, and the surface energy of the metal contained in the first intermediate layer 31 is greater than the surface energy of the metal contained as a main component in the conductive layer 20, which facilitates the formation of the conductive layer 20 with a high (111) orientation. Therefore, the conductive layer 20 has high corrosion resistance to decomposition products of the electrolyte in a lithium-ion secondary battery or the like.

[0040] (Second embodiment) 3 is a schematic cross-sectional view showing an example of a current collector of this embodiment. A current collector 102 of this embodiment includes a resin layer 10, a conductive layer 20, a first intermediate layer 31, and a second intermediate layer 32. The first intermediate layer 31 is located between the resin layer 10 and the conductive layer 20. The second intermediate layer 32 is located between the first intermediate layer 31 and the resin layer 10. The current collector 102 differs from the current collector 101 of the first embodiment in that it further includes the second intermediate layer 32. The materials and thicknesses of the resin layer 10, the conductive layer 20, and the first intermediate layer 31, as well as the functions of these layers, are as described in the first embodiment.

[0041] The second intermediate layer 32 improves adhesion between the resin layer 10 and a layer formed on the resin layer 10. For this purpose, the second intermediate layer 32 contains a metal oxide as a main component. The second intermediate layer 32 may be in contact with the resin layer 10. When the second intermediate layer 32 contains a metal oxide as a main component, adhesion with the resin layer 10 is improved compared to when the conductive layer 20 or the first intermediate layer 31, which contains a metal as a main component, is in contact with the resin layer 10.

[0042] The thickness D2 of the second intermediate layer 32 is, for example, 0.5 nm or more and 20 nm or less. When the thickness D2 of the second intermediate layer 32 is 0.5 nm or more, a continuous second intermediate layer 32 is formed, which makes it easier to achieve improved adhesion. When the thickness of the second intermediate layer 32 is 20 nm or less, the time required to form the second intermediate layer 32 can be shortened, and the influence of damage caused by the conditions during the formation of the second intermediate layer 32, such as heat or plasma, on the resin layer 10 can be reduced, thereby suppressing deterioration of the resin layer 10. The thickness of the second intermediate layer 32 may be 1 nm or more, or may be 2 nm or more. Alternatively, the thickness of the second intermediate layer 32 may be 10 nm or less.

[0043] The thickness D1 of the first intermediate layer 31 and the thickness D2 of the second intermediate layer 32 may satisfy the relationship D1 / D2≦10. By satisfying D1 / D2≦10, it is believed that a decrease in adhesion between the second intermediate layer 32 and the resin layer 10 due to a large stress being applied to the second intermediate layer 32 caused by the first intermediate layer 31 becoming too thick is suppressed. D1 / D2 may satisfy the relationship 2≦D1 / D2≦10.

[0044] The second intermediate layer 32 may contain an oxide of at least one metal selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Hf, Ta, and W. These metal oxides are passive and inhibit oxidation from progressing to the interior. In other words, the second intermediate layer 32 itself is poorly soluble in the decomposition products of the electrolyte in the nonaqueous electrolyte. This prevents dissolution of the second intermediate layer 32 at the interface with the resin layer 10, thereby maintaining high adhesion for a long period of time. The second intermediate layer 32 can be formed, for example, by sputtering using a metal oxide as a target or by sputtering using a metal as a target in an oxygen-containing atmosphere.

[0045] The ratio of oxygen in the metal oxide contained in the second intermediate layer 32 may be 0.3 or more in molar ratio to the metal element 1. That is, the metal oxide may be represented by the following composition formula. MOx (x≧0.3)

[0046] Here, M is at least one element selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Hf, Ta and W.

[0047] When x is 0.3 or more, polarity is generated in the second intermediate layer 32, and intermolecular forces act more easily between the second intermediate layer 32 and the resin layer 10, thereby improving adhesion. x is not limited to an integer. The upper limit of x depends on the largest valence of the stable oxidation states that the metal can assume.

[0048] The second intermediate layer 32 may further contain a metal carbide. By containing a carbide of at least one metal selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Hf, Ta, and W, the adhesion to the resin layer 10 can be further improved.

[0049] Furthermore, the element constituting the metal oxide contained in the second intermediate layer 32 may be the same element as the metal contained in the first intermediate layer 31. In this case, for example, the second intermediate layer 32 and the first intermediate layer 31 can be formed successively by a sputtering method using targets of the same metal, and the adhesion between the second intermediate layer 32 and the first intermediate layer 31 can also be improved.

[0050] According to the current collector 102 of this embodiment, by providing the second intermediate layer 32 containing a metal oxide, the adhesion between the conductive layer and the resin layer can be improved compared to when the conductive layer and the resin layer are in direct contact. Furthermore, by including the first intermediate layer 31 containing a metal, the conductive layer 20 comes into contact with the first intermediate layer 31, which is mainly composed of a metal rather than a metal oxide, unlike when only the second intermediate layer 32 is provided. Therefore, the crystallinity of the conductive layer 20 can be improved when the conductive layer 20 is formed, and the corrosion resistance of the conductive layer 20 to electrolyte decomposition products in the non-aqueous electrolyte can be improved.

[0051] Furthermore, the surface energy of the metal contained in first intermediate layer 31 is greater than the surface energy of the metal contained as a main component in conductive layer 20, thereby enhancing the (111) orientation of conductive layer 20. Therefore, conductive layer 20 has high corrosion resistance against electrolyte decomposition products that may be generated in nonaqueous electrolyte solutions such as those used in lithium-ion secondary batteries.

[0052] While the current collector 102 described with reference to FIG. 3 has the conductive layer 20 on only one side of the resin layer 10, the conductive layer 20 may be provided on both sides. FIG. 4 shows a current collector 103 having a conductive layer on both sides of the resin layer. The current collector 103 has a resin layer 10 having a first surface 10a and a second surface 10b located opposite the first surface 10a. The first surface 10a of the resin layer 10 has a structure similar to that of the current collector 102 described above.

[0053] Meanwhile, a structure similar to that of the current collector 102 is also formed on the second surface 10b of the resin layer 10. Specifically, the current collector 103 further includes a conductive layer 20′, a first intermediate layer 31′, and a second intermediate layer 32′. The first intermediate layer 31′ is located between the resin layer 10 and the conductive layer 20′. The second intermediate layer 32′ is located between the first intermediate layer 31′ and the resin layer 10. The materials and thicknesses of the conductive layer 20′, the first intermediate layer 31′, and the second intermediate layer 32′, as well as the functions of these layers, are the same as those of the corresponding conductive layer 20, the first intermediate layer 31, and the second intermediate layer 32. In terms of stress, the materials and thicknesses of the conductive layer 20′, the first intermediate layer 31′, and the second intermediate layer 32′ may be the same as those of the corresponding conductive layer 20, the first intermediate layer 31, and the second intermediate layer 32.

[0054] According to the current collector 103, since the conductive layers 20, 20' are provided on both sides of the resin layer 10, electrodes can be formed on both sides. This reduces the proportion of the resin layer in the electricity storage device, and increases the battery capacity per unit area.

[0055] (Third embodiment) An embodiment of an electrode for an electricity storage device will be described. The electrode for an electricity storage device of this embodiment can be used as either a positive electrode or a negative electrode of an electricity storage device. FIG. 5 is an exploded perspective view of an electrode for an electricity storage device 201. The electrode for an electricity storage device 201 includes a current collector 210 and an active material layer 220. The current collector 210 includes a first portion 210s and a second portion 210t, and the active material layer 220 is disposed in the first portion 210s. The second portion 210t is not provided with the active material layer 220 and functions as a tab for electrical connection to the outside. The active material layer 220 contains an active material that is oxidized and reduced in association with charging (or electricity storage) and discharging. The current collector 210 supports the active material layer 220, supplies electrons to the active material layer 220, and receives electrons from the active material layer 220.

[0056] Electric collector 210 is the electric collectors 101, 102, and 103 described in the first or second embodiment. When using the electric collector 103, another active material layer not shown in FIG. 5 is disposed on the first portion 210s on the back surface side of the electric collector (on the side where the active material layer 220 is not disposed).

[0057] The active material layer 220 contains a positive electrode active material or a negative electrode active material that occludes and releases lithium ions. The positive electrode active material includes, for example, a composite metal oxide containing lithium. Examples of the composite metal oxide containing lithium include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMnO2), lithium manganese spinel (LiMn2O4), lithium vanadium compound (LiV2O5), olivine-type LiMPO4 (where M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr or vanadium oxide), lithium titanate (Li4Ti5O 12 )), 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 in the above general formula is one or more elements selected from the group consisting of Al, Mg, Nb, Ti, Cu, Zn, Cr), and a composite metal oxide represented by the general formula: LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1), etc. can be mentioned. The positive electrode active material may contain polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc. as a material capable of occluding and releasing lithium ions.

[0058] The active material layer 220 may further contain at least one of a binder and a conductive additive. Various known materials can be used as the binder. Examples of binders that can be used in the active material layer 220 for the positive electrode include fluororesins such as polyvinylidene fluoride (PVDF), 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).

[0059] A vinylidene fluoride-based fluororubber may be used as the binder. For example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), or the like may be used as the binder for the active material layer 220 used in the positive electrode.

[0060] Examples of the conductive additive include carbon materials such as carbon powder and carbon nanotubes. Carbon powder can be carbon black or the like. Other examples of the conductive additive for the active material layer 220 used in the positive electrode include metal powder such as nickel, stainless steel, and iron, and conductive oxide powder such as ITO. Two or more of the above-mentioned materials may be mixed and contained in the active material layer 220.

[0061] The negative electrode active material contains a carbon material. Examples of the carbon material include, for example, natural or artificial graphite, carbon nanotubes, non-graphitizable carbon, graphitizable carbon (soft carbon), low-temperature calcined carbon, and the like. The negative electrode active material may contain materials other than the carbon material. For example, alkali metals and alkaline earth metals such as metallic lithium, metals such as tin or silicon that can form compounds with metals such as lithium, silicon-carbon composites, amorphous compounds mainly composed of oxides (SiO x (0 < x < 2), tin dioxide, etc.), and may contain particles such as lithium titanate (Li4Ti5O 12 ).

[0062] For the binder and conductive assistant of the active material layer 220 used for the negative electrode, the above-described binder and conductive assistant can be used in the same manner. Also, as the binder for the negative electrode, cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide, polyamideimide, acrylic resin, etc. may be used.

[0063] The electrodes for the power storage device for the positive electrode and the negative electrode can be manufactured by known manufacturing methods.

[0064] The electrode for the power storage device of the present embodiment has high corrosion resistance against the decomposition products of the electrolyte in the non-aqueous electrolyte. Therefore, in a lithium-ion secondary battery including the electrode for the power storage device of the present embodiment, even when the lithium-ion secondary battery is used under conditions where the electrolyte is likely to decompose, for example, at high temperature, a decrease in battery characteristics due to deterioration of the current collector is suppressed.

[0065] (Fourth Embodiment) An embodiment of a lithium-ion secondary battery will be described.

[0066] FIG. 6 is a schematic external view showing an example of a lithium-ion secondary battery 301, and FIG. 7 is an exploded perspective view showing a cell removed from the lithium-ion secondary battery shown in FIG. 6. Here, a pouch-type or laminate-type lithium-ion secondary battery is shown as an example of the lithium-ion secondary battery. The lithium-ion secondary battery shown in the figure is a single-layer type, but it may also be a laminate type. In the example shown in the figure, the positive electrode, separator, and negative electrode that constitute the cell are stacked along the Z direction in the figure.

[0067] The lithium ion secondary battery 301 includes a cell 310 , a pair of leads 311 connected to the cell 310 , an exterior body 313 that covers the cell 310 , and an electrolyte 314 .

[0068] The cell 310 includes an electricity storage device electrode 201, an electricity storage device electrode 201′, and a separator 320 disposed therebetween. In the illustrated example, the cell 310 is a single-layer cell including a pair of electrodes.

[0069] The electrode 201 for the electricity storage device and the electrode 201' for the electricity storage device are the electrodes 201 for the electricity storage device described in the third embodiment, one being configured as a positive electrode containing a positive electrode active material and the other being a negative electrode containing a negative electrode active material.

[0070] Separator 320 is an insulating porous material. For example, a monolayer film or laminated film of polyolefin such as polyethylene or polypropylene, or a nonwoven fabric or porous film made of at least one type of fiber selected from the group consisting of cellulose, polyester, polyacrylonitrile, polyimide, polyamide (e.g., aromatic polyamide), polyethylene, and polypropylene can be used.

[0071] An electrolyte 314 is further disposed in the space inside the exterior body 313. The electrolyte 314 is a non-aqueous electrolyte containing lithium ions, for example, a non-aqueous electrolyte solution containing lithium ions. When a non-aqueous electrolyte solution is used as the electrolyte 314, a sealant (for example, a resin film such as polypropylene, not shown in FIG. 6) is typically disposed between the exterior body 313 and the lead 311 to prevent leakage of the non-aqueous electrolyte solution.

[0072] For example, a non-aqueous electrolyte solution containing a metal salt such as a lithium salt and an organic solvent can be used as the electrolyte 314. Examples of the lithium salt that can be used include LiPF6, LiClO4, LiBF4, LiCF3SO3, LiCF3CF2SO3, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(CF3CF2CO)2, and LiBOB. One of these lithium salts may be used alone, or two or more may be mixed.

[0073] For example, cyclic carbonates and chain carbonates can be used as the solvent for the electrolyte 314. Specifically, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, etc. can be used.

[0074] The lithium ion secondary battery 301 can be manufactured, for example, by the following method. First, the electrodes 201 and 201' are fabricated as described in the above embodiment. Then, the electrode 201 and the electrode 201' are held with the separator 320 interposed between them so that the active material layers face each other, and are inserted into the space in the exterior body 313. The electrolyte 314 is placed in the space in the exterior body 313, and the exterior body 313 is sealed, thereby completing the lithium ion secondary battery 301.

[0075] The lithium ion secondary battery 301 has high corrosion resistance against decomposition products of the electrolyte in the non-aqueous electrolyte solution, and therefore, even when the lithium ion secondary battery is used at high temperatures, deterioration of the battery characteristics due to deterioration of the current collector is suppressed.

[0076] (Example) Current collectors of Examples and Reference Examples were produced and their properties were evaluated.

[0077] [Sample preparation] The current collectors of Examples 1 to 24 and Reference Examples 1 to 4 were prepared by the following method.

[0078] A current collector 102 having the structure shown in FIG. 3 was fabricated. The resin layer 10 was made of polyethylene terephthalate resin with a thickness of 5 μm. The first intermediate layer 31 and the second intermediate layer 32 were formed by sputtering using the metal or metal oxide targets shown in Tables 3 to 6. The thicknesses of the first intermediate layer 31 and the second intermediate layer 32 were adjusted by adjusting the deposition time and output. The Cu conductive layer 20 was formed in two parts: a seed layer 21 and a main layer 22. After forming the 50 nm thick seed layer 21, the main layer 22 was formed by electroplating to the thicknesses shown in Tables 3 to 6. The Al and Cu-Ni conductive layers were formed by sputtering to the thicknesses shown in Tables 3 to 6.

[0079] In Examples 14 to 20 and Examples 21 and 23, the molar ratio of metal to oxygen in the second intermediate layer was controlled to be 1:1. In Examples 22 and 24, a metal carbide was also used as a target. The composition ratio in the metal oxide was confirmed by composition analysis using X-ray photoelectron spectroscopy (XPS).

[0080] As shown in Table 3, the current collectors of Reference Examples 1 to 4 were produced without forming at least one of the first intermediate layer and the second intermediate layer.

[0081] [evaluation] The (111) plane orientation index of the conductive layer was measured by X-ray diffraction and determined as the orientation index F by the Lotgering method described above. The apparatus and conditions used for the measurement are as follows: Equipment name: PANalytical XPert PRO Radiation source: CuKα radiation Accelerating voltage: 40 kV Current: 45mA Scan speed: 6deg. / min. Sampling width: 0.02 deg. Measurement method: Out-of-plane

[0082] The current collectors of Examples 1 to 24 and Reference Examples 1 to 4 were maintained in an environment similar to that of a lithium-ion secondary battery, and the peeling and corrosion of the conductive layer were evaluated. Specifically, an electrolyte solution of dimethyl carbonate containing LiPF6 at a concentration of 1 mol% was prepared. Furthermore, water was added to the electrolyte solution at a ratio of 1000 ppm by mass to prepare electrolyte solution 1. Similarly, electrolyte solution 2 was prepared by adding 3000 ppm by mass of water, and electrolyte solution 3 was prepared by adding 5000 ppm by mass of water.

[0083] One of the electrolyte solutions 1 to 3 was placed in a container, and the prepared current collector was immersed in the electrolyte solution in the container. The whole was sealed with a laminate film and stored in a thermostatic chamber at 85°C for 72 hours. The current collector was then removed from the laminate film and washed with an organic solvent.

[0084] The resulting current collectors after high-temperature storage were evaluated for corrosion resistance and peel resistance. Corrosion resistance was evaluated by measuring the surface resistance of the conductive layer and observing it with an optical microscope. The surface resistance of the conductive layer was measured using a low-resistance resistivity meter (trade name: Loresta GX MCP-T700, manufactured by Nitto Seiko Analytech Co., Ltd.). Observation with an optical microscope was performed at a magnification of 100 to 200 times. Three observation areas were arbitrarily selected and evaluated based on whether holes had formed within the selected areas. If the surface resistance of the conductive layer increased by 20% or more compared to before high-temperature storage or if holes were found in the conductive layer upon observation, the current collector was evaluated as poor. If the resistance increase was less than 20% and no holes were found in the conductive layer, the current collector was evaluated as good.

[0085] Peel resistance was evaluated using two methods. The surface of the conductive layer of the current collector after high-temperature storage was rubbed with a cotton swab. If part of the conductive layer adhered to the cotton swab, it was determined that the conductive layer had peeled off from the resin layer, and the product was rated as poor. In addition, adhesive tape with an adhesive strength of 4 N / cm was applied to the surface of the conductive layer of the current collector after high-temperature storage to check whether the conductive layer adhered. If no peeling was observed with the cotton swab but adhesion was observed with the adhesive tape, the product was rated as good. If neither peeling with the cotton swab nor adhesion with the adhesive tape was observed, the product was rated as excellent.

[0086] The produced current collectors, the electrolyte used for storage, and the evaluations performed are summarized in Table 2. The evaluation results are shown in Tables 3 to 6.

[0087] [Table 2]

[0088] [Results and Discussion] As shown in Table 3, the current collectors of Reference Examples 1 to 4, which do not have a second intermediate layer, all obtained poor results in the peel resistance test, whereas the current collectors of Examples 1 to 6 obtained good or excellent results. The current collectors of Reference Examples 2 and 4 have a first intermediate layer, but because it is not a metal oxide layer, it is thought that the effect of improving peel resistance is small. It can be seen that good peel resistance can be obtained when the thickness of the second intermediate layer is 0.5 nm or more and 20 nm or less. In particular, excellent peel resistance can be obtained when the thickness of the second intermediate layer is 2 nm or more and 10 nm or less.

[0089] [Table 3]

[0090] As shown in Table 4, when the thickness of the first intermediate layer is 1 nm or more and 120 nm or less, the conductive layer exhibits good corrosion resistance and peeling resistance. In particular, when the thickness of the first intermediate layer is 2 nm or more and 100 nm or less, the conductive layer exhibits excellent corrosion resistance and peeling resistance. Furthermore, Tables 3 and 4 show that when the ratio D1 / D2 of the first intermediate layer to the second intermediate layer satisfies D1 / D2≦10, a current collector with excellent peeling resistance and corrosion resistance can be obtained. Furthermore, when D1 / D2 satisfies 2≦D1 / D2≦10, the current collector exhibits even better peeling resistance and corrosion resistance.

[0091] [Table 4]

[0092] In Table 5, in the current collector of Example 16, the surface energy of Ag, the metal of the first intermediate layer, is smaller than the energy of Cu, the metal of the conductive layer (Table 1). Furthermore, in current collectors other than Example 16, the surface energy of the metal of the first intermediate layer is larger than the energy of the metal of the conductive layer. The (111) plane orientation index is small, at 0.25, in the current collector of Example 16, but large values ​​of 0.65 or greater are observed in the current collectors of Examples 14, 15, and 17 to 20 other than Example 16. This is thought to indicate that, as described above, the relationship in the magnitude of the metal surface energy between the first intermediate layer and the conductive layer affects the ease of (111) plane orientation.

[0093] Furthermore, in the current collectors of Examples 14, 15, and 17 to 20, the metals constituting the first intermediate layer were various, including Cr, Mo, Co, Ni-Cr, and W, but the (111) plane orientation index was large in all current collectors. This is thought to indicate that the lattice constant of the crystal of the metal constituting the first intermediate layer and the crystallinity of the first intermediate layer do not have much effect on the (111) plane orientation index.

[0094] Furthermore, the corrosion resistance of the conductive layer is improved in the current collectors of Examples 14, 15, and 17 to 20 compared to the current collector of Example 16. This is thought to indicate that there is a correlation between the (111) plane orientation index of the conductive layer and corrosion resistance.

[0095] From these facts, as explained in detail in the first embodiment, it is believed that the surface energy of the metal contained in the first intermediate layer is greater than the surface energy of the metal contained in the conductive layer, which effectively increases the orientation of the (111) plane of the conductive layer and improves corrosion resistance.

[0096] [Table 5]

[0097] As shown in Table 6, it can be seen that the second intermediate layer has improved peeling resistance by further including a metal carbide compared to when it includes only a metal oxide.

[0098] [Table 6]

[0099] These examples and reference examples demonstrate that the current collector of this embodiment, by being provided with a first intermediate layer and a second intermediate layer, can improve corrosion resistance and peeling resistance against electrolyte decomposition products in a non-aqueous electrolyte solution. [Industrial Applicability]

[0100] An electrode for an electricity storage device according to an embodiment of the present disclosure is useful as a power source for various electronic devices, electric motors, etc. An electricity storage device according to an embodiment of the present disclosure is applicable, for example, to power sources for vehicles such as bicycles and automobiles, power sources for communication devices such as smartphones, power sources for various sensors, and power sources for unmanned eXtended Vehicles (UxVs). [Explanation of symbols]

[0101] 10, 10' resin layer 10a 1st page 10b 2nd side 20, 20' conductive layer 21 Seed layer 22 Main layer 31, 31' First middle class 32, 32' Second middle layer 101, 102, 103 Current collector 201, 201' Electrodes for electricity storage devices 210 Current collector 210s Part 1 210t 2nd part 220 Active material layer 300 exterior body 301 Lithium-ion secondary battery 310 cells 311 leads 313 Exterior body 314 Electrolyte 320 Separator

Claims

1. A resin layer; a conductive layer; a first intermediate layer located between the resin layer and the conductive layer; a second intermediate layer located between the first intermediate layer and the resin layer; Equipped with the first intermediate layer contains a metal as a main component, the second intermediate layer contains a metal oxide as a main component, the orientation index of the (111) plane of the conductive layer according to the Lotgering method in the direction perpendicular to the resin layer is 0.3 or more; Current collector.

2. The thickness D2 of the second intermediate layer is 0.5 nm≦D2≦20 nm The current collector according to claim 1 , which satisfies the following:

3. The thickness D1 of the first intermediate layer is 1 nm≦D1≦120 nm The current collector according to claim 1 or 2, which satisfies the following:

4. the conductive layer contains a metal as a main component, The current collector according to claim 1 , wherein the surface energy of the metal of the first intermediate layer is greater than the surface energy of the metal of the conductive layer.

5. 5. The current collector according to claim 1, wherein the first intermediate layer contains at least one metal selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Hf, Ta, and W.

6. 6. The current collector according to claim 1, wherein the second intermediate layer contains an oxide of at least one metal selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Hf, Ta, and W.

7. The current collector of claim 1 , wherein the first intermediate layer and the second intermediate layer comprise the same metal.

8. The current collector according to claim 1 , wherein the second intermediate layer further contains a metal carbide.

9. 9. The current collector according to claim 1, wherein the conductive layer contains one metal selected from the group consisting of Al, Ag, Cu, Ni, and Ni--Cu alloys.

10. The thickness D3 of the conductive layer is 0.3 μm≦D3≦2 μm The current collector according to claim 1 , which satisfies the following:

11. The thickness D1 of the first intermediate layer and the thickness D2 of the second intermediate layer are D1 / D2≦10 The current collector according to claim 3 , which satisfies the following:

12. The current collector according to claim 1 , wherein the resin layer contains at least one of polyethylene terephthalate, polypropylene, polyamide, polyimide, polyethylene, polystyrene, a phenolic resin, and an epoxy resin.

13. The current collector according to any one of claims 1 to 12; an active material layer located on the conductive layer of the current collector; An electrode for an electricity storage device comprising:

14. A positive electrode and a negative electrode; a separator disposed between the negative electrode and the positive electrode; a non-aqueous electrolyte containing lithium ions; Equipped with A lithium ion secondary battery, wherein at least one of the positive electrode and the negative electrode is the electrode for a power storage device according to claim 13 .

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