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

Abstract

This current collector comprises: a resin layer that has a main surface; and a conductive layer that is laminated on the main surface of the resin layer, has at least one pinhole, and is formed using a metal as a main component. In a cross section parallel to the lamination direction, the angle formed by the main surface of the resin layer and a line segment linking the opening edge of a lower end opening of the pinhole to the opening edge of an upper end opening thereof is less than 45°. As a result, the pinhole is narrowed, an electrolyte is unlikely to enter the interface between the resin layer and the conductive layer through the pinhole, and peeling of the conductive layer from the resin layer is suppressed.

Description

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

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

[0002] Lithium secondary batteries are widely used as power sources for notebook computers, mobile phones, electric vehicles, etc. Patent Document 1 listed below discloses a current collector used in the positive and negative electrodes of lithium secondary batteries, which has a configuration in which a conductive layer is laminated on a resin layer.

[0003] Japanese Patent Application Laid-Open No. 2019-102429

[0004] In the current collector of the lithium secondary battery according to the above-mentioned conventional technology, pinholes may occur in the conductive layer formed on the resin layer. If the electrolyte penetrates into the interface between the conductive layer and the resin layer through the pinholes, the conductive layer may peel off from the resin layer.

[0005] An object of one aspect of the present disclosure is to provide a current collector, an electrode for a power storage device, and a lithium-ion secondary battery in which peeling of a conductive layer from a resin layer is suppressed.

[0006] A current collector according to one aspect of the present disclosure comprises: a resin layer having a principal surface; and a conductive layer laminated on the principal surface of the resin layer, the conductive layer having a first principal surface located on the resin layer side and a second principal surface located opposite the first principal surface, the conductive layer having at least one pinhole penetrating along the lamination direction and composed primarily of metal; in a cross section parallel to the lamination direction, an angle formed by a line segment connecting an opening edge of the pinhole on the first principal surface side of the conductive layer and an opening edge of the pinhole on the second principal surface side of the conductive layer is less than 45°.

[0007] An electrode for an electricity storage device according to one aspect of the present disclosure includes the current collector and an active material layer laminated on the second main surface of the conductive layer.

[0008] A lithium ion secondary battery according to one aspect of the present disclosure includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte containing lithium ions, and the above-described power storage device electrode is used in at least one of the positive electrode and the negative electrode.

[0009] In the current collector, the electrode for an electricity storage device, and the lithium-ion secondary battery, in a cross section parallel to the stacking direction, the angle formed by the line segment connecting the opening edge of the pinhole on the first main surface side of the conductive layer and the opening edge on the second main surface side of the conductive layer and the main surface of the resin layer is less than 45°, thereby narrowing the pinhole, making it difficult for the electrolyte to penetrate into the interface between the conductive layer and the resin layer through the pinhole, and preventing peeling of the conductive layer from the resin layer.

[0010] According to various aspects of the present disclosure, there are provided a current collector, an electrode for a power storage device, and a lithium-ion secondary battery in which peeling of a conductive layer from a resin layer is suppressed.

[0011] FIG. 1 is a schematic cross-sectional view showing an example of a current collector according to the first embodiment. FIG. 2 is a flowchart showing a method for manufacturing a current collector according to the first embodiment. FIG. 3 is a cross-sectional view showing a pinhole in a current collector according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing another example of a current collector according to the first embodiment. FIG. 5 is a schematic exploded perspective view showing an example of an electrode for a power storage device according to the second embodiment. FIG. 6 is a schematic partially cut-away perspective view showing an example of a lithium ion secondary battery according to the third embodiment. FIG. 7 is a schematic exploded perspective view showing an example of a lithium ion secondary battery according to the third embodiment. FIG. 8 is a table showing evaluation results according to Examples.

[0012] Hereinafter, embodiments of a current collector, an electrode for an electricity storage device, and a lithium-ion secondary battery according to 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 inconsistency occurs. Furthermore, each embodiment described below is merely an example, and various combinations are possible as long as no technical inconsistency occurs.

[0013] 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 some elements may be omitted to avoid excessive complexity. Therefore, the dimensions and relative positions of the components depicted in the drawings of this disclosure may not reflect the dimensions and relative positions of the 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°.

[0014] 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.

[0015] 1 is a schematic cross-sectional view showing an example of a current collector according to the present embodiment. The current collector according to the present 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 and a conductive layer 20.

[0016] The resin layer 10 has one main surface 10a and functions as a support that supports the conductive layer 20 on the main surface 10a side of 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.

[0017] The resin layer 10 has electrical insulation properties and contains a resin. The resin layer 10 may also be thermoplastic. Specifically, the resin layer 10 may contain at least one selected from the group consisting 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 formed by laminating two or more layers. In this case, at least one layer of the multiple layers may contain a resin different from that of the other layers.

[0018] 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 thickness of the entire current collector 101 can be reduced. Therefore, when a stacked lithium ion secondary battery is constructed by stacking multiple electrode pairs, the proportion of the current collector, which is a portion that does 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 thickness of the entire current collector 101 can be further reduced, and the energy density of the stacked lithium ion secondary battery can be increased.

[0019] The conductive layer 20 is laminated on the main surface 10a of the resin layer 10 and covers the resin layer 10 directly or indirectly. 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 connected to the current collector. The conductive layer 20 contains a metal as a main component. In this disclosure, "main component" means that the proportion of the metal relative to the entirety is 80 mass% or more. The conductive layer 20 has an upper surface 20a and a lower surface 20b. The lower surface 20b is a first main surface located on the resin layer 10 side, and the upper surface 20a is a second main surface located opposite the first main surface.

[0020] In this embodiment, the conductive layer 20 contains Cu as a main component, but may also contain Al as a main component. As long as it contains Cu or Al as a main component, it may further contain other metals. For example, the conductive layer 20 may contain Cu as a main component and may further contain Ni. 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 Cu or a Ni-Cu alloy.

[0021] The thickness T of the conductive layer 20 is, for example, 0.3 μm or more and 2 μm or less. When the thickness T 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 manufactured, energy loss due to resistance in the current collector can be reduced. Furthermore, when the thickness T 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, and it becomes easier to obtain the advantage of reducing the weight of the current collector by using the resin layer 10.

[0022] The conductive layer 20 according to this embodiment includes a seed layer 21 and a main layer 22. Therefore, the thickness T of the conductive layer 20 is the sum of the thickness of the seed layer 21 and the thickness of the main layer 22. In this embodiment, both the seed layer 21 and the main layer 22 are primarily composed of copper (Cu). The seed layer 21 and the main layer 22 may be primarily composed of the same metal or different metals.

[0023] The seed layer 21 can be formed by, for example, a sputtering method or a vacuum deposition method. The main layer 22 can be formed by a plating method. By forming the entire conductive layer 20 by a sputtering method or a vacuum deposition method, it is possible to avoid a longer formation time, a decrease in productivity, and increased damage to the resin layer 10 during the formation of the conductive layer 20.

[0024] In this embodiment, the substrate further includes an intermediate layer 30 located between the resin layer 10 and the conductive layer 20. The intermediate layer 30 directly covers the main surface 10a of the resin layer 10. The intermediate layer 30 functions to enhance adhesion between the resin layer 10 and the conductive layer 20. The intermediate layer 30 is composed of a material different from the material constituting the conductive layer 20. The intermediate layer 30 may contain, for example, at least one metal selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Hf, Ta, and W. In this embodiment, the intermediate layer 30 is composed of a metal material containing Cr. The thickness of the intermediate layer 30 may be 1 nm or more but less than 200 nm, or 1 nm or more but 20 nm or less. The intermediate layer 30 may be formed, for example, by a sputtering method.

[0025] In this embodiment, a protective layer 40 is laminated on the conductive layer 20, covering the upper surface 20a of the conductive layer. The protective layer 40 can be made of an organic material, for example, benzotriazoles such as methylbenzotriazole, aminobenzotriazole, and carboxylbenzotriazole, or imidazoles. The protective layer 40 is designed to have a surface energy of 40 mN / m or more. By covering the upper surface 20a of the conductive layer 20 with the protective layer 40, it is possible to control the wettability with the electrolyte and to prevent the electrolyte from penetrating into the current collector 101 through pinholes 50, which will be described later.

[0026] In this embodiment, the conductive layer 20 has at least one pinhole 50. The pinhole 50 penetrates the conductive layer 20 along the stacking direction of the resin layer 10 and the conductive layer 20, as shown in the cross-sectional view of FIG. 3 parallel to the stacking direction of the resin layer 10 and the conductive layer 20. When viewed from the stacking direction of the resin layer 10 and the conductive layer 20, the pinhole 50 has a planar shape such as a substantially circular, substantially elliptical, or substantially polygonal shape. The pinhole 50 is believed to be caused by defects (voids) that occur during the deposition of the seed layer 21, and the seed layer 21 is not present at the location of the pinhole 50. The main layer 22 of the conductive layer 20 near the pinhole 50 is in direct contact with the resin layer 10 exposed from the intermediate layer 30, forming the lower surface 20b of the conductive layer 20 and defining the lower opening 51 of the pinhole 50. Meanwhile, the main layer 22 of the conductive layer 20 near the pinhole 50 defines the upper opening 52 of the pinhole 50 on the upper surface 20a. Although the protective layer 40 is omitted in FIG. 3, the protective layer 40 covering the upper surface 20 a of the conductive layer may also cover the main surface 10 a of the resin layer 10 exposed through the pinhole 50 .

[0027] The opening width of the upper end opening 52 of the pinhole 50 is W ２ and the opening width of the lower end opening 51 of the conductive layer 20 is W １ When this is the case, the opening width W of the upper end opening 52 is ２ is the opening width W of the lower end opening 51 １ It is wider (i.e., W ２ >W １ The opening width W of the upper opening 52 ２ The opening width W of the lower end opening 51 can be calculated as the distance between the opening edges P2-P2 where the upper surface 20a starts to descend. １ The opening width W of the upper opening 52 can be calculated as the distance between the opening edges P1-P1 where the upper surface 20a contacts the resin layer 10. ２ The opening width W of the lower end opening 51 may be greater than the thickness T of the conductive layer 20 or may be equal to or less than the thickness T of the conductive layer 20. １ may be greater than the thickness T of the conductive layer 20 or may be equal to or less than the thickness T of the conductive layer 20 .

[0028] In this embodiment, the taper ratio of the pinhole 50 is higher than 200%.２ -W １ ) / T×100%. When the pinhole 50 is axisymmetric (more specifically, bilaterally symmetric) in the cross section shown in FIG. 3 , the taper ratio correlates with the angle θ formed between the line segment connecting the opening edge P1 of the lower opening 51 and the opening edge P2 of the upper opening 52 and the main surface 10a of the resin layer 10. That is, when the taper ratio is 200%, the angle θ is 45°. Therefore, when the pinhole 50 is axisymmetric in the cross section shown in FIG. 3 , if the taper ratio of the conductive layer 20 in the pinhole 50 is higher than 200%, the angle θ becomes narrower than 45° (θ<45°). When the angle θ is narrower than 45°, the portion of the conductive layer 20 defining the lower opening 51 has a sharp cross-sectional shape and extends elongatedly toward the inside of the pinhole 50, as shown in FIG. 3 . The taper ratio can be adjusted, for example, by adjusting the composition of the plating solution used to plate the conductive layer 20. The plating solution may contain, for example, copper sulfate pentahydrate, sulfuric acid, chloride ions, a sulfur-based organic compound, a nonionic surfactant, and a leveler. Examples of the sulfur-based organic compound include thiourea, disodium 3,3'-dithiobis(1-propanesulfonate) (SPS), and sodium 3-mercapto-1-propanesulfonate (MPS). Examples of the nonionic surfactant include polyoxyethylene surfactants such as polyoxyethylene propylene glycol, polyethylene glycol, and polyoxyethylene alkyl ether. The leveler may be a compound containing a nitrogen atom, such as a quaternary ammonium compound or an amine compound. In this embodiment, a plating solution containing the above components is used to achieve a taper ratio of more than 200%.

[0029] In this embodiment, the main layer 22 of the conductive layer 20 is formed by plating growth from the seed layer 21. Therefore, the upper surface 20a of the conductive layer 20 that constitutes the inner side surface 50a of the pinhole 50 is curved so as to protrude inward of the pinhole 50. In this case, in the cross section shown in FIG. 3 , the upper surface 20a of the conductive layer 20 that constitutes the inner side surface 50a of the pinhole 50 protrudes inward of the pinhole 50 beyond the line segment connecting the opening edge P1 of the lower end opening 51 and the opening edge P2 of the upper end opening 52. Therefore, the angle θ' formed between the upper surface 20a of the conductive layer 20 and the main surface 10a of the resin layer 10 can be wider than the angle θ (θ' > θ).

[0030] Next, a method for manufacturing the current collector of this embodiment will be described. Fig. 3 is a flowchart showing the method for manufacturing the current collector of this embodiment. The method for manufacturing the current collector of this embodiment includes step S1 of preparing a resin layer, step S2 of forming an intermediate layer, and step S3 of forming a conductive layer. Each step will be described in detail below.

[0031] (1) Step S1 of Preparing a Resin Layer First, a resin layer 10 made of the above-described material and having the above-described thickness is prepared. The resin layer 10 may have a size corresponding to the current collector 101 used in one lithium-ion secondary battery, for example, or may be a resin roll in which a sheet-like resin layer elongated in one direction is wound into a roll. When a current collector is to be produced from the resin roll as is without cutting it, manufacturing equipment capable of production by a roll-to-roll method is prepared.

[0032] (2) Step S2 of Forming Intermediate Layer: The intermediate layer 30 is formed by sputtering. A target containing Cr is prepared, and the intermediate layer 30 is formed on the resin layer 10 using a sputtering device. The thickness of the intermediate layer 30 can be adjusted by the deposition rate and deposition time. The intermediate layer 30 is formed, for example, in an argon atmosphere.

[0033] (3) Step S3 of forming a conductive layer: The conductive layer 20 is formed on the intermediate layer 30. For example, the conductive layer 20 containing Cu as a main component is formed. First, the seed layer 21 is formed on the intermediate layer 30 by, for example, sputtering. Next, the main layer 22 is formed on the seed layer 21 by electrolytic plating using the seed layer 21 as a cathode. In this way, the conductive layer 20 including the seed layer 21 and the main layer 22 can be formed.

[0034] According to the current collector 101 of this embodiment, in a cross section parallel to the stacking direction, the angle θ formed between the line segment connecting the opening edge P1 of the lower opening 51 of the pinhole 50 and the opening edge P2 of the upper opening 52 and the main surface 10a of the resin layer 10 is less than 45°, and the portion of the conductive layer 20 defining the lower opening 51 of the pinhole 50 extends long toward the inside of the pinhole 50. This narrows the pinhole 50, and a relatively narrow pinhole 50 having a width approximately equal to the thickness of the conductive layer 20 is filled with the conductive layer 20. In this case, the electrolyte is less likely to penetrate into the interface between the resin layer 10 and the conductive layer 20 through the pinhole 50, and peeling of the conductive layer 20 from the resin layer 10 is suppressed. For example, even when fluorine ions, which are thought to be generated when a lithium-ion secondary battery described below is charged and discharged at high temperatures, are present in the nonaqueous electrolyte, peeling of the conductive layer 20 from the resin layer 10 is suppressed.

[0035] While the current collector 101 described with reference to Fig. 1 has the conductive layer 20 on only one side of the resin layer 10, the conductive layer 20 may be provided on both sides. For example, Fig. 4 shows a current collector 102 having conductive layers on both sides of a resin layer. The current collector 102 has a resin layer 10 having a first main surface 10a and a second main surface 10b located opposite the first main surface 10a. The first main surface 10a of the resin layer 10 has a structure similar to that of the current collector 101 described above.

[0036] Meanwhile, the second main surface 10b of the resin layer 10 also has a structure similar to that of the current collector 101. Specifically, the current collector 102 further includes a conductive layer 20', an intermediate layer 30', and a protective layer 40'. The materials and thicknesses of the conductive layer 20', intermediate layer 30', and protective layer 40', as well as the functions of these layers, are the same as those of the corresponding conductive layer 20, intermediate layer 30, and protective layer 40. In terms of stress, the material and thickness of the intermediate layer 30' may be the same as those of the corresponding intermediate layer 30. The material of the conductive layer 20' is the same as those of the corresponding conductive layer 20. In terms of stress, the thickness of the conductive layer 20' may be the same as those of the conductive layer 20. In terms of stress, the material and thickness of the protective layer 40' may be the same as those of the corresponding protective layer 40.

[0037] According to the current collector 102, 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, thereby increasing the battery capacity per unit area.

[0038] Second 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, with the active material layer 220 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 includes an active material that is oxidized and reduced upon 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.

[0039] The current collector 210 is either the current collector 101 or 102 described in the first embodiment. When the current collector 102 is used, another active material layer not shown in Fig. 6 is disposed on a first portion 210s on the back surface side of the current collector 210 (the side on which the active material layer 220 is not disposed).

[0040] The active material layer 220 includes a positive electrode active material or a negative electrode active material that absorbs 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 (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese oxide (LiMnO ２ ), lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compounds (LiV ２ O ５ ), olivine-type LiMPO ４ (wherein M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr, or vanadium oxide), lithium titanate (Li ４ Ti ５ O １２ ), general formula: LiNi ｘ Co ｙ Mn ｚ MaO ２ (x+y+z+a=1, 0≦x<1, 0≦y<1, 0≦z<1, 0≦a<1, and M in the general formula is one or more elements selected from the group consisting of Al, Mg, Nb, Ti, Cu, Zn, and Cr), and a composite metal oxide represented by the general formula: LiNi ｘ Co ｙ Al ｚ O ２ (x+y+z<1.1) The positive electrode active material may contain polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, or the like as a material capable of absorbing and releasing lithium ions.

[0041] 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).

[0042] 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-perfluoromethylvinyl ether-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.

[0043] 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 powders such as nickel, stainless steel, and iron, and conductive oxide powders such as ITO. Two or more of the above-mentioned materials may be mixed and contained in the active material layer 220.

[0044] The negative electrode active material includes a carbon material. Examples of the carbon material include natural or artificial graphite, carbon nanotubes, non-graphitizable carbon, graphitizable carbon (soft carbon), and low-temperature fired carbon. The negative electrode active material may include a material other than a 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, and amorphous compounds mainly composed of oxides (SiO ｘ (0<x<2), tin dioxide, etc.), lithium titanate (Li ４ Ti ５ O １２ ) or other particles.

[0045] The binder and conductive additive for the negative electrode active material layer 220 may be the same as those described above. Alternatively, cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide, polyamide-imide, acrylic resin, or the like may be used as the binder for the negative electrode.

[0046] The positive and negative electrodes for an electricity storage device can be produced by a known production method.

[0047] In the electricity storage device electrode 201 of this embodiment, peeling of the conductive layer 20 of the current collector 101 from the resin layer 10 is suppressed. Therefore, even when a lithium ion secondary battery including the electricity storage device electrode of this embodiment is used under conditions where the electrolyte is likely to decompose, for example, at high temperatures, peeling of the conductive layer 20 from the resin layer 10 is further suppressed, and deterioration of battery characteristics due to deterioration of the current collector is suppressed. (Third Embodiment) An embodiment of a lithium ion secondary battery will be described.

[0048] 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.

[0049] 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 .

[0050] The cell 310 includes an electric storage device electrode 201, an electric 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.

[0051] The electrode 201 for the power storage device and the electrode 201′ for the power storage device are the electrodes 201 for the power storage device described in the second embodiment, one being configured as a positive electrode containing a positive electrode active material and the other being configured as a negative electrode containing a negative electrode active material.

[0052] The separator 320 is an insulating porous material, and may be, 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.

[0053] 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.

[0054] The electrolyte 314 may be, for example, a non-aqueous electrolyte solution containing a metal salt such as a lithium salt and an organic solvent. ６ , LiClO ４ , LiBF ４ , LiCF ３ SO ３ , LiCF ３ CF ２ SO ３ , LiC(CF ３ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(CF ３ CF ２ SO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(CF ３ CF ２ CO) ２ , LiBOB, etc. These lithium salts may be used alone or in combination of two or more.

[0055] 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.

[0056] The lithium ion secondary battery 301 can be manufactured, for example, by the following method. First, the power storage device electrodes 201, 201' are fabricated as described in the above embodiment. Then, the power storage device electrode 201 and the power storage device 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. An 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.

[0057] In the lithium ion secondary battery 301, the resin layer and the conductive layer of the current collector have improved adhesion, which further prevents the conductive layer from peeling off from the resin layer even when the lithium ion secondary battery is used at high temperatures, thereby preventing a decrease in battery characteristics due to deterioration of the current collector.

[0058] Examples 1 to 14 and Comparative Example 1, each having the current collector 101 structure shown in FIG. 1 , were maintained in an environment similar to that of a lithium-ion secondary battery to evaluate the peel resistance of the conductive layer. A 5 μm-thick polyethylene terephthalate resin was used for the resin layer 10 of the current collector 101. The conductive layer 20 of the current collector 101 was formed by forming a 50 nm-thick seed layer 21 and then forming a main layer 22 by electrolytic plating. The protective layer 40 was formed on the upper surface 20 a of the conductive layer 20 by immersing the current collector for 30 seconds in a 10% by mass imidazole aqueous solution prepared by dissolving imidazole in water and heating it to 35°C.

[0059] LiPF ６ An electrolyte solution of dimethyl carbonate containing 1 mol% of dimethyl carbonate was prepared. Furthermore, water was added to the electrolyte solution at a rate 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.

[0060] 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 entire assembly 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. The peel resistance of the resulting current collector after high-temperature storage was evaluated.

[0061] 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 a portion of the conductive layer adhered to the cotton swab, it was determined that the conductive layer had peeled from the resin layer, and the result was judged as unacceptable (POOR). In addition, adhesive tape with an adhesion 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 with the adhesive tape was observed, the result was judged as acceptable (GOOD). If no peeling was observed with the cotton swab but slight adhesion with the adhesive tape was observed, the result was judged as good (GREAT). If neither peeling with the cotton swab nor adhesion with the adhesive tape was observed, the result was judged as excellent (EXCELLENT).

[0062] The evaluation results are shown in the table of Figure 8. As shown in the table of Figure 8, in Comparative Example 1, in which the angle θ formed between the line segment connecting the opening edge P1 of the lower end opening 51 of the pinhole 50 and the opening edge P2 of the upper end opening 52 and the main surface 10a of the resin layer 10 was 45° or more, the peel resistance was poor, while in Examples 1 to 14, in which the angle θ was less than 45°, the peel resistance was good (i.e., either fair, good, or excellent). Furthermore, a comparison between Example 1 and Example 2 confirmed that a smaller angle θ resulted in better peel resistance.

[0063] From Examples 3 to 6, it was confirmed that the protective layer 40 has better peel resistance when its surface energy is relatively high, and in the present Examples, peel resistance was further improved when the surface energy of the protective layer 40 was 40 mN / m or more. The surface energy of the protective layer 40 can be adjusted by the material constituting the protective layer 40. Furthermore, if the protective layer 40 is so thin that its continuity is not maintained, the surface energy decreases, and therefore, in order to achieve a high surface energy, the protective layer 40 needs to have a certain thickness.

[0064] From Examples 7 to 10, it was confirmed that a certain thickness of the intermediate layer 30 results in better peel resistance, and in these examples, peel resistance was further improved when the thickness of the intermediate layer 30 was 1 nm or more. Furthermore, from the viewpoint of peel resistance, there is no particular upper limit to the thickness of the intermediate layer 30, but from the viewpoint of productivity, such as sputtering deposition time, the thickness of the intermediate layer 30 can be designed to be 20 nm or less.

[0065] From Examples 11 to 14, even if the angle θ is the same (40°) and the conductive layer has the same thickness (1.0 μm), the opening width W of the lower end opening 51 of the pinhole 50 １ and the opening width W of the upper end opening 52 ２ It was confirmed that the peel resistance differed when the opening width W of the upper end opening 52 was different. ２ is 60 μm or less, and the opening width W of the lower end opening 51 １ In Examples 11 to 14, the opening width W of the upper end opening 52 is 58 μm or less. ２ is 30 μm or less, and the opening width W of the lower end opening 51 １ It was confirmed that better peeling resistance was obtained in Examples 11 to 13, in which the width W of the upper end opening 52 was 28 μm or less. ２ is 3 μm or less, and the opening width W of the lower end opening 51 １ It was confirmed that even better peel resistance was obtained in Example 11, where the thickness was 1.00 μm or less.

[0066] As can be understood from the above description, the present specification discloses the following. [Appendix 1] A current collector comprising: a resin layer having a main surface; and a conductive layer laminated on the main surface of the resin layer, having a first main surface located on the resin layer side and a second main surface located opposite to the first main surface, and having at least one pinhole penetrating along the lamination direction, the conductive layer being composed mainly of metal, wherein, in a cross section parallel to the lamination direction, an angle formed by a line segment connecting an opening edge of the pinhole on the second main surface side of the conductive layer and an opening edge of the pinhole on the first main surface side of the conductive layer and the main surface of the resin layer is less than 45°. [Appendix 2] A current collector comprising: a resin layer having a main surface; and a conductive layer laminated on the main surface of the resin layer, the conductive layer having a first main surface side of the pinhole and a second main surface side of the pinhole, the conductive layer having a first main surface side of the pinhole and a first ... ２ and the width of the opening edge of the pinhole on the first main surface side of the conductive layer is W １ and the thickness of the conductive layer in the stacking direction is T, W ２ >W １ holds, and (W ２ -W １) / T×100% is greater than 200%. [Appendix 3] The current collector according to Appendix 2, wherein the width of the opening edge of the pinhole on the second main surface side of the conductive layer is greater than the thickness of the conductive layer in the stacking direction. [Appendix 4] The current collector according to Appendix 2, wherein the width of the opening edge of the pinhole on the second main surface side of the conductive layer is equal to or less than the thickness of the conductive layer in the stacking direction. [Appendix 5] The current collector according to any one of Appendices 2 to 4, wherein the width of the opening edge of the pinhole on the first main surface side of the conductive layer is greater than the thickness of the conductive layer in the stacking direction. [Appendix 6] The current collector according to any one of Appendices 2 to 4, wherein the width of the opening edge of the pinhole on the first main surface side of the conductive layer is equal to or less than the thickness of the conductive layer in the stacking direction. [Appendix 7] The current collector according to any one of Appendices 2 to 6, wherein the width of the opening edge of the pinhole on the second main surface side of the conductive layer is 60 μm or less and the width of the opening edge of the pinhole on the first main surface side of the conductive layer is 58 μm or less. [Appendix 8] The current collector according to any one of Appendices 1 to 7, wherein the inner side surface of the pinhole is curved so as to protrude toward the inside of the pinhole. [Appendix 9] The current collector according to any one of Appendices 1 to 8, further comprising a protective layer stacked on the second main surface of the conductive layer. [Appendix 10] The current collector according to Appendices 9, wherein the surface energy of the protective layer is 40 mN / m or more. [Appendix 11] The current collector according to any one of Appendices 1 to 10, wherein the metal that is the main component of the conductive layer is copper. [Appendix 12] The current collector according to any one of Appendices 1 to 11, wherein the thickness of the conductive layer in the stacking direction is 0.3 μm or more and 2 μm or less. [Appendix 13] The current collector according to any one of Appendices 1 to 12, further comprising an intermediate layer interposed between the main surface of the resin layer and the first main surface of the conductive layer. [Appendix 14] The current collector according to Appendices 13, wherein the intermediate layer contains, as a main component, a metal different from a metal that is a main component of the conductive layer. [Appendix 15] The current collector according to Appendices 13 or 14, wherein a thickness of the intermediate layer in the stacking direction is 1 nm or more and 20 nm or less. [Appendix 16] An electrode for an electricity storage device, comprising the current collector according to any one of Appendices 1 to 15, and an active material layer stacked on the second main surface of the conductive layer.[Supplementary Note 17] A lithium ion secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte containing lithium ions, wherein the power storage device electrode according to Supplementary Note 16 is used for at least one of the positive electrode and the negative electrode.

[0067] 10...resin layer, 20, 20'...conductive layer, 20a...second main surface, 20b...first main surface, 30, 30'...intermediate layer, 40, 40'...protective layer, 50...pinhole, 51...lower end opening, 52...upper end opening, 101, 102, 210...current collector, 201, 201'...electrode for electricity storage device, 220...active material layer, 301...lithium ion secondary battery, 320...separator.

Claims

1. A current collector comprising: a resin layer having a principal surface; and a conductive layer laminated on the principal surface of the resin layer, the conductive layer having a first principal surface located on the resin layer side and a second principal surface located opposite the first principal surface, the conductive layer having at least one pinhole penetrating along the lamination direction, the conductive layer being composed primarily of metal, wherein in a cross section parallel to the lamination direction, an angle formed by a line segment connecting an opening edge of the pinhole on the second principal surface side of the conductive layer and an opening edge of the pinhole on the first principal surface side of the conductive layer, and the principal surface of the resin layer is less than 45°.

2. In a cross section parallel to the lamination direction, the width of the opening edge of the pinhole on the second main surface side of the conductive layer is W ２ The width of the opening edge of the pinhole on the first main surface side of the conductive layer is W １ and the thickness of the conductive layer in the stacking direction is T, W ２ >W １ is satisfied, and (W ２ -W １ 2. The current collector of claim 1, wherein the taper ratio, expressed as 1 / T×100%, is greater than 200%.

3. The current collector according to claim 2, wherein the width of the opening edge of the pinhole on the second main surface side of the conductive layer is greater than the thickness of the conductive layer in the stacking direction.

4. The current collector according to claim 2, wherein the width of the opening edge of the pinhole on the second main surface side of the conductive layer is equal to or less than the thickness of the conductive layer in the stacking direction.

5. The current collector according to claim 2, wherein the width of the opening edge of the pinhole on the first main surface side of the conductive layer is greater than the thickness of the conductive layer in the stacking direction.

6. The current collector according to claim 2, wherein the width of the opening edge of the pinhole on the first main surface side of the conductive layer is equal to or less than the thickness of the conductive layer in the stacking direction.

7. The current collector according to claim 2, wherein the width of the opening edge of the pinhole on the second main surface side of the conductive layer is 60 μm or less, and the width of the opening edge of the pinhole on the first main surface side of the conductive layer is 58 μm or less.

8. The current collector according to claim 1, wherein the inner surface of the pinhole is curved so as to protrude inwardly of the pinhole.

9. The current collector of claim 1, further comprising a protective layer laminated on the second major surface of the conductive layer.

10. The current collector according to claim 9, wherein the surface energy of the protective layer is 40 mN / m or more.

11. The current collector according to claim 1, wherein the metal that is the main component of the conductive layer is copper.

12. The current collector according to claim 2, wherein the thickness of the conductive layer in the stacking direction is 0.3 μm or more and 2 μm or less.

13. The current collector according to claim 1, further comprising an intermediate layer interposed between the main surface of the resin layer and the first main surface of the conductive layer.

14. The current collector according to claim 13, wherein the intermediate layer contains, as a main component, a metal different from the main component metal of the conductive layer.

15. The current collector according to claim 13, wherein the thickness of the intermediate layer in the stacking direction is 1 nm or more and 20 nm or less.

16. An electrode for an electricity storage device, comprising the current collector according to claim 1 and an active material layer laminated on the second main surface of the conductive layer.

17. A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte containing lithium ions, wherein the electrode for an electric storage device according to claim 16 is used for at least one of the positive electrode and the negative electrode.

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