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

Abstract

Provided is a current collector comprising: a resin layer having a first surface and a second surface on the opposite side of the first surface; and a metal layer containing copper, wherein the metal layer includes a first metal layer positioned on the first surface side of the resin layer, the yield stress σY1 of the current collector is smaller than the tensile breaking stress σB2 of the resin layer, the yield stress σY1 [MPa] of the current collector is a value obtained by the following equations (1) and (2) from the yield stress σY2 [MPa] of the resin layer, the thickness D2 [μm] of the resin layer, the yield stress σY3 [MPa] of the metal layer, and the thickness D3 [μm] of the metal layer, and the yield stress σY3 [MPa] of the metal layer is a value obtained by the following equation (3) from the half width β [°] of the X-ray diffraction peak showing the highest intensity in the X-ray diffraction pattern of the metal layer.

Description

[Technical Field]

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

[0002] It has been proposed to use a composite material in which metal layers are formed on both sides of a resin film as a current collector for a secondary battery (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-75191 Summary of the Invention [Problem to be solved by the invention]

[0004] A current collector using a composite material including a resin film and a metal layer is required to have appropriate mechanical properties. Embodiments of the present disclosure provide a current collector that can have appropriate mechanical properties, an electrode for an electricity storage device, and a lithium-ion secondary battery that use such a current collector. [Means for solving the problem]

[0005] A current collector according to one embodiment of the present disclosure includes a resin layer having a first surface and a second surface located opposite to the first surface, and a metal layer containing copper, wherein the metal layer includes a first metal layer located on the first surface side of the resin layer, and the yield stress σY1 [MPa] of the current collector is calculated from the yield stress σY2 [MPa] of the resin layer, the thickness D2 [μm] of the resin layer, the yield stress σY3 [MPa] of the metal layer, and the thickness D3 [μm] of the metal layer, using the following formulas (1) and (2): JPEG0007810723000001.jpg13156JPEG0007810723000002.jpg12153, The yield stress σY3 [MPa] of the metal layer is calculated from the half-width β [°] of the most intense X-ray diffraction peak in the X-ray diffraction pattern of the metal layer by the following formula (3): This is the value obtained from JPEG0007810723000003.jpg13157. [Effects of the Invention]

[0006] According to the embodiments of the present disclosure, there are provided a current collector that can have suitable mechanical properties, an electrode for an electricity storage device that uses such a current collector, and a lithium-ion secondary battery. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic cross-sectional view of a current collector according to an embodiment of the present disclosure. [Figure 2] FIG. 4 is a schematic cross-sectional view of another current collector according to an embodiment. [Figure 3] FIG. 10 is a diagram showing the relationship between the half-value width β of the X-ray diffraction peak of a copper film and the yield stress σY3. [Figure 4A] FIG. 10 is a schematic cross-sectional view showing a state in which a tensile load is applied to the current collector of the reference example. [Figure 4B] FIG. 10 is a schematic cross-sectional view showing a state in which a tensile load is applied to the current collector of the reference example. [Figure 4C] FIG. 10 is a schematic cross-sectional view showing a state in which a tensile load is applied to the current collector of the reference example. [Figure 5A] FIG. 2 is a schematic cross-sectional view showing a state in which a tensile load is applied to the current collector of the embodiment. [Figure 5B] FIG. 2 is a schematic cross-sectional view showing a state in which a tensile load is applied to the current collector of the embodiment. [Figure 5C] FIG. 2 is a schematic cross-sectional view showing a state in which a tensile load is applied to the current collector of the embodiment. [Figure 6] FIG. 10 is a schematic cross-sectional view of a current collector according to a modified example. [Figure 7] FIG. 10 is a schematic cross-sectional view of another current collector according to a modified example. [Figure 8]FIG. 2 is a diagram showing an example of a stress-strain curve of a resin layer used in the current collectors of Examples and Comparative Examples. [Figure 9] FIG. 1 is a graph showing the relationship between the thickness ratio A and the half-value width β of the metal layer and the ratio B in the current collectors of Examples and Comparative Examples. [Figure 10A] FIG. 2 is a diagram showing an example of a stress-strain curve of the current collector of Example 1. [Figure 10B] FIG. 1 is a diagram showing an example of a stress-strain curve of the current collector of Comparative Example 1. [Figure 11A] 1 is an exploded perspective view of an electrode for an electricity storage device according to an embodiment of the present disclosure. [Figure 11B] 11B is a cross-sectional view showing a part of the electricity storage device electrode shown in FIG. 11A. FIG. [Figure 12] FIG. 10 is a cross-sectional view showing a part of another electrode for an electricity storage device. [Figure 13] 1 is a schematic external view of a lithium-ion secondary battery according to an embodiment of the present disclosure. [Figure 14] 14 is an exploded perspective view showing a cell taken out from the lithium ion secondary battery shown in FIG. 13. FIG. [Figure 15] FIG. 10 is a schematic external view of another lithium ion secondary battery. [Figure 16] 16 is an exploded perspective view showing a cell taken out from the lithium ion secondary battery shown in FIG. 15. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The current collector, electrode for an electricity storage device, and lithium-ion secondary battery described below are intended to embody the technical concept of the present invention, and unless otherwise specified, the present invention is not limited to the following. Furthermore, the content described in one embodiment can also be applied to other embodiments and modified examples. Furthermore, the size and positional relationship of components shown in the drawings may be exaggerated for clarity of explanation.

[0009] In the following description, components having substantially the same functions are denoted by common reference symbols, and their descriptions may be omitted. Alternatively, components not referred to in the description may not be assigned reference symbols. In this disclosure, "parallel" includes cases where two lines, sides, surfaces, etc. are in the range of approximately 0° to ±5°, unless otherwise specified. Furthermore, in this disclosure, "perpendicular" or "orthogonal" includes cases where two lines, sides, surfaces, etc. are in the range of approximately 90° to ±5°, unless otherwise specified.

[0010] 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 arise. Furthermore, the embodiments described below are also merely examples, and various combinations are possible as long as no technical contradictions arise.

[0011] The dimensions, shapes, etc. of each component shown in the drawings of this disclosure may be exaggerated for the sake of clarity. Furthermore, in the drawings of this disclosure, some components may be isolated or omitted to avoid excessive complexity. Therefore, the dimensions and relative arrangement of each component shown in the drawings of this disclosure may not reflect the dimensions and relative arrangement of each component in an actual device. Terms including "upper" or "lower," such as "upper surface," "lower surface," "upper layer," and "lower layer," may be used in this specification. However, these terms are used merely to facilitate understanding of relative orientations or positions in the referenced drawings. As long as the relative orientations or positions indicated by terms such as "upper" and "lower" in the referenced drawings are the same, the same arrangements as in the referenced drawings may not be used in drawings other than the present disclosure, actual products, manufacturing apparatuses, etc.

[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) When manufacturing secondary batteries, processes that involve volume changes of the current collector, such as a conveying process and a calendering process, are usually performed. If these processes cause cracks or breaks in the current collector, this can lead to an increase in the process defect rate. Furthermore, during operation of the secondary battery, the current collector is subjected to stress from the active material, which expands and contracts with charge and discharge. Therefore, the current collector is required to have appropriate mechanical properties.

[0014] As a result of various investigations, the present inventors have found that in a current collector using a composite material including a resin layer and a metal layer, increasing the elongation (breaking elongation) of the current collector can suppress breakage of the current collector during production or battery operation. Based on this finding, they have investigated a novel current collector structure that can increase the breaking elongation, and have conceived of an embodiment of the present disclosure.

[0015] FIG. 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. For ease of explanation, arrows indicating three mutually orthogonal directions, namely, the X direction, the Y direction, and the Z direction, are shown in FIG. 1. FIG. 1 shows a cross section perpendicular to the Y direction.

[0016] 1 includes a resin layer 20 and at least one metal layer 30 containing copper. The resin layer 20 and the at least one metal layer 30 are laminated in the thickness direction of the resin layer 20 (here, the Z direction).

[0017] The resin layer 20 functions as a support for the metal layer 30 in the current collector 101. The resin layer 20 has a first surface 20a and a second surface 20b located opposite the first surface 20a. The resin layer 20 has a thickness D2. In this specification, the thickness of each layer refers to the average distance in the Z direction between the upper and lower surfaces of that layer. In other words, the thickness D2 of the resin layer 20 is the average distance between the first surface 20a and the second surface 20b.

[0018] At least one metal layer 30 includes a first metal layer 31 located on the first surface 20a side of the resin layer 20. The first metal layer 31 has a first surface 31a located on the resin layer 20 side and a second surface 31b located on the opposite side to the first surface 31a. The first metal layer 31 has a thickness D31.

[0019] In the illustrated example, the upper surface of the current collector 101 is the second surface 31b of the first metal layer 31, and the lower surface of the current collector 101 is the second surface 20b of the resin layer 20. Note that the current collector 101 may further include layers other than the first metal layer 31 and the resin layer 20.

[0020] The current collector 101 of this embodiment is configured so that the yield stress σY1 of the current collector 101 is smaller than the tensile breaking stress σB2 of the resin layer 20. The tensile breaking stress σB2 is measured in accordance with the provisions of JIS K7127:1999.

[0021] The yield stress σY1 of the current collector 101 is a value calculated by the following formula (1) from the yield stress σY2 of the resin layer 20, the yield stress σY3 of the metal layer 30, and the thickness ratio A of the metal layer 30. In this specification, "×" represents multiplication. JPEG0007810723000004.jpg13156σY1 [MPa]: Yield stress of current collector 101 σY2 [MPa]: Yield stress of the resin layer 20 σY3 [MPa]: Yield stress of the metal layer 30 A[-]: Thickness ratio of the metal layer 30

[0022] The yield stress σY2 of the resin layer 20 in formula (1) is a tensile yield stress measured in accordance with the provisions of JIS K7127:1999.

[0023] The thickness ratio A of the metal layer 30 in formula (1) is the ratio of the thickness D3 of the metal layer 30 to the total thickness of the resin layer 20 and the metal layer 30, and is a value calculated by the following formula (2). JPEG0007810723000005.jpg12153In the example of FIG. 1, the value of the thickness ratio A is calculated as D31 / (D2+D31).

[0024] The yield stress σY3 [MPa] of the metal layer 30 in formula (1) is a value calculated by the following formula (3) from the half width (hereinafter abbreviated as "half width") β [°] of the most intense X-ray diffraction peak in the X-ray diffraction pattern of the metal layer 30. When the metal layer 30 is a copper layer, the most intense X-ray diffraction peak is, for example, the X-ray diffraction peak of the (111) plane. JPEG0007810723000006.jpg13157

[0025] Equation (3) was derived by the inventors by focusing on the crystallinity of the metal layer and measuring the relationship between the crystallinity of the metal layer and the yield stress. Using equation (3), it is possible to calculate the yield stress σY3 of the metal layer 30 by performing X-ray diffraction on the metal layer 30. The method for deriving equation (3) will be described later.

[0026] 1 has only the first metal layer 31 as the metal layer 30, and therefore in the above formulas (1) to (3), the yield stress σY3 of the metal layer 30 is the yield stress of the first metal layer 31, and the "thickness D3 of the metal layer 30" is the thickness D31 of the first metal layer 31 (D3 = D31). The current collector of this embodiment may have two or more metal layers, each containing copper. In that case, the thickness D3 in the above formula (2) is the total thickness of those metal layers.

[0027] Fig. 2 is a schematic cross-sectional view showing another example of a current collector according to the present embodiment. The current collector 102 shown in Fig. 2 differs from the current collector 101 shown in Fig. 1 in that it further includes a second metal layer 32 located on the second surface 20b side of the resin layer 20. Such a current collector 102 can be used, for example, in a stacked cell.

[0028] In the current collector 102, the first metal layer 31, the resin layer 20, and the second metal layer 32 are stacked in the Z direction. The second metal layer 32 contains copper. The material of the second metal layer 32 is, for example, the same as the material of the first metal layer 31. Note that the material of the second metal layer 32 may be different from the material of the first metal layer 31 as long as it contains copper. The second metal layer 32 has a thickness D32. The thickness D32 may be the same as or different from the thickness D31 of the first metal layer 31.

[0029] The current collector 102 is also configured so that the yield stress σY1 calculated from the above formulas (1) to (3) is smaller than the tensile fracture stress σB2 of the resin layer 20. The thickness D3 of the metal layer 30 in formula (2) is the sum of the thickness D31 of the first metal layer 31 and the thickness D32 of the second metal layer 32 (D3 = D31 + D32). Furthermore, if the second metal layer 32 is formed using the same material under the same conditions as the first metal layer 31 and the second metal layer 32 have substantially the same crystallinity (i.e., the half-width β is substantially the same), the half-width β of the metal layer 30 in formula (3) may be calculated by X-ray diffraction of the first metal layer 31 or the second metal layer 32.

[0030] <Relationship between yield stress and half-width of metal layer> The method by which the inventors derived the above formula (3) will be explained.

[0031] Metals such as copper are typically polycrystalline, consisting of multiple crystal grains. It is known that the grain size has a significant effect on the yield strength of polycrystalline materials, and that the smaller the grain size (i.e., the greater the proportion of grain boundaries), the higher the yield strength. The relationship between yield stress and grain size is expressed by the Hall-Petch relationship below. JPEG0007810723000007.jpg12154where σ y is the yield stress, σ0 is the friction stress, k is a constant indicating the resistance to grain boundary sliding, and d is the grain size. The relationship between the yield stress and grain size of copper or copper alloys is also known to follow the Hall-Petch equation.

[0032] The present inventors have found that in a current collector including a resin layer and a metal layer, the yield stress σY3 of the metal layer (the yield stress σ of the Hall-Petch equation) y The relational expression between the peak width at half maximum β of the most intense X-ray diffraction peak in the X-ray diffraction pattern of the metal layer and the peak width at half maximum β of the most intense X-ray diffraction peak in the X-ray diffraction pattern of the metal layer was derived from the experimental results shown below. It is known that the peak width at half maximum β of the metal layer is inversely proportional to the crystal grain size (crystallite size) of the metal layer (Scherrer equation).

[0033] The experimental methods and results conducted by the inventors will be described below.

[0034] First, several current collector samples were fabricated using copper films with different crystallinity, for example, with the structure shown in Figure 2. Each current collector sample was fabricated by forming a copper film on both sides of a resin layer by electrolytic plating. A polyethylene terephthalate (PET) film with a thickness of 4.5 μm was used as the resin layer. The thickness of each copper film was 1.0 μm.

[0035] Next, X-ray diffraction measurements were performed on the copper film of each current collector sample, and the half-width β of the most intense X-ray diffraction peak was determined. Furthermore, a tensile test was performed on each current collector sample in accordance with JIS K7127:1999 to obtain a stress-strain curve. The portion dependent on the PET film was then subtracted from the stress-strain curve of the current collector sample to obtain the stress-strain curve of the copper film alone, and the yield stress σY3 of the copper film was calculated.

[0036] Figure 3 plots the relationship between the half-width β and the yield stress σ for the copper film of each current collector sample. The horizontal axis represents the positive square root of the half-width β [°], and the vertical axis represents the yield stress σ [MPa]. The results shown in Figure 3 confirm that the larger the half-width β, i.e., the smaller the crystallite size, the greater the yield stress σ. Furthermore, the measured value of the yield stress σ is roughly proportional to the square root (√β) of the half-width β. This trend is similar to the Hall-Petch equation mentioned above.

[0037] Based on the results shown in Figure 3, the relationship between the square root of the half-width β (√β) and the yield stress σY3 was calculated by linear regression, resulting in the following equation (3): Note that although a copper film was used in the above experiment, the yield stress σY3 can be calculated using this equation for any metal film containing copper. JPEG0007810723000008.jpg13157

[0038] <Effects> The current collectors 101 and 102 of this embodiment are configured so that the yield stress σY1 calculated by the above formulas (1) to (3) is smaller than the tensile stress at break σB2 of the resin layer 20. By satisfying the relationship σY1<σB2, the elongation (breaking elongation) of the current collectors 101 and 102 can be increased, as will be described later. For example, the breaking elongation of the current collectors 101 and 102 can be increased up to the same level as the breaking elongation of the resin layer 20. This can prevent breakage of the current collectors 101 and 102 during the current collector transport step and calendering step in manufacturing an electrode for an electricity storage device, thereby improving the process defect rate. Furthermore, in a secondary battery using the current collectors 101 and 102, even if a large force is locally applied to the current collectors 101 and 102 due to the expansion and contraction of the active material during charging and discharging, it is possible to suppress battery deformation, deterioration of battery characteristics (increased resistance), and / or characteristic variations caused by breakage or tearing of the current collectors 101 and 102. In this specification, the term "a break occurs in the current collector" refers to a state in which a break or tear occurs throughout the entire thickness of the current collector, including the metal layer and the resin layer, and does not include, for example, a state in which a break occurs only in the metal layer. Furthermore, the term "a break occurs in the current collector" refers to a state in which a break or tear occurs in a part of the current collector across the thickness of the current collector, but does not necessarily mean that the current collector (e.g., a current collector constituting a battery) is completely separated into two or more parts. Among breaks in the current collector, a break that extends linearly in a plan view may be referred to as a "crack."

[0039] The breaking elongation of the current collectors 101, 102 is not particularly limited, but may be greater than the breaking elongation of the metal layer 30 (for example, about 3 to 5%) and equal to or less than the breaking elongation of the resin layer 20. The breaking elongation of the current collectors 101, 102 is preferably greater than 6%, for example, and may be, for example, 20% or more.

[0040] <Relationship between yield stress σY1, tensile breaking stress σB2 and breaking elongation of current collector> With reference to the drawings, the reason why the elongation percentage (breaking elongation) of the current collector can be increased by making the yield stress σY1 of the current collector smaller than the tensile breaking stress σB2 of the resin layer will be explained.

[0041] 4A to 4C are enlarged cross-sectional views that schematically illustrate the state of the metal layer 930 and the resin layer 920 when a tensile load is applied to a reference example current collector 900 in which the yield stress σY1 is greater than the tensile fracture stress σB2 of the resin layer 920 (σY1>σB2).

[0042] As shown in FIG. 4A, a tensile load F is applied to current collector 900 in the X-axis direction shown in the figure. As the tensile load F is increased, metal layer 930 is partially thinned, forming constricted portion 131. This phenomenon is called "necking" or "necking phenomenon." Necking can occur, for example, in areas where adhesion between metal layer 930 and resin layer 920 is low. Furthermore, in areas where necking occurs, cracks can occur on the upper surface of metal layer 930, extending in a direction intersecting the X-axis direction (for example, a direction substantially parallel to the Y-axis direction).

[0043] If the tensile load F is then further increased, necking progresses as shown in FIG. 4B , and when the stress applied to current collector 900 reaches the yield stress σ of current collector 900, fracture occurs in constricted portion 131 of metal layer 930 (that is, the point at which fracture occurs is the yield point of current collector 900). Immediately after fracture occurs in metal layer 930, the entire load applied to constricted portion 131 is applied to portion 21 of resin layer 920 located below fractured portion 132. In current collector 900, the yield stress σ is greater than the tensile fracture stress σ of resin layer 920, and therefore, immediately after metal layer 930 fractures, portion 21 of resin layer 920 is subjected to a stress that exceeds the tensile fracture stress σ. As a result, as shown in FIG. 4C, portion 21 of resin layer 920 may also break, causing breakage in current collector 900 (see the stress-strain curve in FIG. 10B).

[0044] Thus, in the reference example current collector 900, when a fracture 132 occurs in the metal layer 930 (i.e., when the current collector 900 yields), the current collector 900 fractures without stretching, and therefore the fracture elongation of the current collector 900 is considered to be small.

[0045] 5A to 5C are enlarged cross-sectional views schematically illustrating the state of the metal layer 30 and the resin layer 20 when a tensile load is applied to the current collector 101, which is set so that the yield stress σY1 is smaller than the tensile breaking stress σB2 of the resin layer 20.

[0046] As shown in FIGS. 5A and 5B, when a tensile load F is applied to the current collector 101, as in the current collector 900 of the reference example, a constricted portion 131 first forms in the metal layer 30. When the stress applied to the current collector 101 by the tensile load F reaches the yield stress σY1, a fracture may occur in the constricted portion 131. In the current collector 101, the stress applied to the portion 21 of the resin layer 20 immediately after the fractured portion 132 occurs is smaller than the tensile fracture stress σB2 of the resin layer 20, so no fracture occurs in the resin layer 20 at this point. As shown in FIG. 5C, as the tensile load F increases, the resin layer 20 further elongates in the X-axis direction. Therefore, the current collector 101 has a higher fracture elongation than the current collector 900 of the reference example shown in FIGS. 4A to 4C.

[0047] Resin layer 20 can be stretched without breaking, for example, until the stress applied to portion 21 of resin layer 20 reaches tensile breaking stress σB2 (see the stress-strain curve in FIG. 10A). Therefore, current collector 101 can have a breaking elongation that is approximately equal to the breaking elongation of resin layer 20 at maximum.

[0048] It has been explained above that necking and fracture of the metal layer occur due to a tensile load on the current collector, and that necking can occur at a position where the adhesion between the metal layer and the resin layer is low. This is based on findings obtained by the present inventors by repeatedly conducting tensile tests on current collectors including a resin layer and a metal layer and observing the top surface and cross section of the current collector after the tests.

[0049] In the above, the current collectors 101 and 900 in which the metal layer 30 is disposed on only one side of the resin layer 20 have been described as examples, but the same tendency can be obtained even if the metal layer is disposed on both sides of the resin layer 20.

[0050] In the current collector 900 of the reference example, microfractures may occur in the metal layer 930 and the resin layer 920, which serves as the base material, at approximately the same time. Therefore, for example, during calendaring in the manufacture of a battery, the current collector 900 may tear across its entire thickness, resulting in a process failure. Similarly, during battery operation, stress from the active material may cause fractures in the metal layer 930 and the resin layer 920, potentially resulting in a deterioration in battery characteristics (e.g., increased resistance) or electrode deformation. In contrast, with the current collector 101 of the present embodiment, even if microfractures occur in the metal layer 30 during calendaring, the resin layer 20 does not fracture at the same time, and tearing of the current collector 101 is suppressed, making process failure less likely. Similarly, even if microfractures occur in the metal layer 30 during battery operation, the deterioration in battery characteristics and electrode deformation can be minimized compared to the reference example.

[0051] <Stress and thickness of each layer> In this embodiment, the mechanical properties (yield stress, tensile fracture stress) of the resin layer, the crystallinity of the metal layer, and the thickness ratio A are set so that the yield stress σY1 is smaller than the tensile fracture stress σB2 of the resin layer (σY1<σB2). The current collector of this embodiment can be manufactured by controlling the film structure, material, thickness, and formation method of each layer constituting the laminate structure. These control factors are interrelated. For example, if the thickness of the metal layer is different, the appropriate formation conditions for the metal layer and the appropriate thickness of the resin layer may differ.

[0052] Typically, when designing a current collector, a relatively thick metal layer is used or the thickness ratio A of the metal layer to the overall thickness of the current collector is increased to ensure sufficient electrical properties. In this case, the thickness ratio A of the metal layer in Equation (2) increases. This increases the "A × σ" term in Equation (1), making it difficult to make the yield stress σ of the current collector smaller than the tensile fracture stress σ of the resin layer. In contrast, in this embodiment, the current collector is designed to satisfy the relationship σ<σ by focusing on the crystallinity of the metal layer 30. For example, by forming a metal layer 30 with a relatively large crystallite size (i.e., a small half-width β) without increasing the thickness of the metal layer 30, the "A × σ" term in Equation (1) can be reduced. This satisfies the relationship σ<σ, resulting in high fracture elongation. Furthermore, a metal layer 30 with a small half-width β has excellent crystallinity and can have low electrical resistance (sheet resistance). Therefore, even if the thickness of the current collectors 101 and 102 is reduced in order to increase the breaking elongation, sufficient electrical properties can be ensured.

[0053] 1 and 2 again, examples of the stress and thickness of each layer constituting current collectors 101 and 102 will be described in more detail below.

[0054] In this embodiment, the yield stress σY2, tensile breaking stress σB2, thickness D2, thickness ratio A of metal layer 30, thickness D3 of metal layer 30, etc. of resin layer 20 of current collectors 101 and 102 are not particularly limited as long as they are set to satisfy σY1<σB2.

[0055] For example, the thickness D2 of the resin layer 20 may be, for example, 3 μm or more, preferably 4 μm or more. This more reliably ensures the strength of the current collectors 101, 102. Furthermore, by making the resin layer 20 thicker, it becomes easier to adjust the thickness ratio A of the metal layer 30 to fall within a desired range. On the other hand, from the viewpoint of improving energy density, the thickness of the resin layer 20 may be, for example, 12 μm or less, preferably 6 μm or less.

[0056] The resin layer 20 may have a yield stress σY2 of, for example, 120 MPa or less, and a tensile breaking stress σB2 of, for example, 150 MPa or more.

[0057] The thickness (total thickness) D3 of the metal layer 30 may be, for example, 0.1 μm or more. This allows for a lower sheet resistance. On the other hand, the thickness D3 of the metal layer 30 may be, for example, 6 μm or less, preferably 3 μm or less. This allows for a suppressed increase in the weight of the current collector 101. This also makes it easier to adjust the thickness ratio A of the metal layer 30 within a desired range. The thickness D3 of the metal layer 30 may be smaller than the thickness D2 of the resin layer 20. When the metal layer 30 includes a first metal layer 31 and a second metal layer 32 provided on both sides of the resin layer 20, the thicknesses of the first metal layer 31 and the second metal layer 32 may each be, for example, 0.05 μm or more and 1.5 μm or less.

[0058] The half-width β of the most intense X-ray diffraction peak in the X-ray diffraction pattern of the metal layer 30 may be, for example, 0.33° or less, more preferably 0.25° or less. The larger the crystal grain size (crystallite size) of the metal layer 30, the smaller the half-width β (Scherrer equation). The yield stress of the metal layer 30 is believed to follow the Hall-Petch equation. Therefore, the larger the crystallite size in the metal layer 30, i.e., the smaller the half-width β, the smaller the yield stress σY3 of the metal layer 30. Therefore, by setting the half-width β to 0.33° or less, preferably 0.25° or less, the yield stress σY1 of the current collector calculated from Equation (1) can be easily set smaller than the tensile fracture stress σB2 of the resin layer. On the other hand, the half-width β may be, for example, 0.08° or more. This can suppress a decrease in sheet resistance due to deformation (plastic deformation) or cracking of the metal layer 30.

[0059] The thickness ratio A of the metal layer 30 may be, for example, 0.44 or less. This reduces the yield stress σY1 of the current collectors 101 and 102, making it easier to increase the breaking elongation. Also, an increase in the weight of the current collectors 101 and 102 can be suppressed. On the other hand, the thickness ratio A of the metal layer 30 may be, for example, 0.02 or more. If it is 0.02 or more, the sheet resistance of the metal layer 30 can be reduced.

[0060] <Resin layer 20> The resin layer 20 is, for example, a sheet made of a thermoplastic resin as a base material. As the base material of the resin layer, polyester resins, polyamide resins, polyethylene resins, polypropylene resins, polyolefin resins, polystyrene resins, phenol resins, polyurethane resins, acetal resins, cellophane, and ethylene-vinyl alcohol copolymers (EVOH), polyethylene terephthalate, polystyrene (PS), polyimide, polyvinyl chloride, etc. can be used. Examples of polyolefin resins are polyethylene (PE) and polypropylene (PP), etc. The polyolefin resin may be an acid-modified polyolefin resin. Examples of polyester resins are polybutylene terephthalate (PBT) and polyethylene naphthalate, etc. Examples of polyamide resins are nylon 6, nylon 66, and polymetaxylylene adipamide (MXD6), etc. For example, a uniaxially stretched sheet or biaxially stretched sheet of polyethylene terephthalate, or a biaxially stretched sheet of polypropylene can be suitably used for the resin layer.

[0061] In the present embodiment, the resin layer 20 preferably contains at least one of, for example, polyethylene terephthalate, polyimide, polypropylene, polycarbonate, polyamide, and polyvinyl chloride.

[0062] The resin layer 20 is not limited to a single-layer film. The resin layer 20 may have a laminated structure including a plurality of resin films. When having a laminated structure, as the tensile fracture stress σB2 and yield stress σY2 of the resin layer 20, the tensile fracture stress and yield stress of the thickest main layer in the laminated structure can be used. Or, as the yield stress σY2 (or tensile fracture stress σB2) of the resin layer 20, the yield stress (or tensile stress) of each layer constituting the resin layer 20 may be weighted by the ratio of the thickness, and the value obtained by adding them may be used. For example, the yield stress of the entire resin layer 20 can be obtained as the sum of "(ratio to the total thickness of the resin layer 20) × yield stress" of each layer constituting the resin layer 20.

[0063] <Metal layer 30> The metal layer 30 preferably contains copper as a main component. "Containing copper as a main component" includes a metal layer having a copper content of more than 50% by weight. The copper content of the metal layer 30 may be 80% by weight or more. The metal layer 30 may contain an alloy containing copper as a main component. Examples of the metal layer 30 include a copper layer and a copper alloy layer such as Cu-Sn or Cu-Ni.

[0064] The metal layer 30 preferably has a low sheet resistance, for example, 60 mΩ / □ or less, and preferably 30 mΩ / □ or less.

[0065] The metal layer 30 may include multiple metal films that are different from each other in terms of material, composition ratio, formation method, etc. When the metal layer 30 includes multiple metal films that have different crystallinity, the yield stress of the metal layer 30 may be calculated by weighting the yield stress of each metal film included in the metal layer 30 by the ratio of their thicknesses and adding them together.

[0066] For example, the first metal layer 31 and the second metal layer 32 may be formed of different materials. In that case, the yield stress σY3 of the metal layer 30 can be calculated, for example, from the following formulas (4) and (5) using the yield stress σY31 of the first metal layer 31 calculated from the half-value width β of the first metal layer 31 and the yield stress σY32 of the second metal layer 32 calculated from the half-value width β of the second metal layer 32. JPEG0007810723000009.jpg13166JPEG0007810723000010.jpg12168

[0067] The first metal layer 31 and / or the second metal layer 32 may be a single-layer film or a laminated film. When the first metal layer 31 and the second metal layer 32 have a laminated structure, the yield stress of the thickest main layer in the laminated structure of the metal layers 31 and 32 may be used as the yield stresses σY31 and σY32 in the above formula (4).

[0068] An undercoat layer or the like may be interposed between the first metal layer 31, the second metal layer 32 and the resin layer 20. Also, a protective layer or the like may be provided on the surface of the first metal layer 31 and the second metal layer 32.

[0069] (Variation) The current collector of this embodiment may further include another solid layer located between the resin layer and the metal layer. Such a solid layer is called an "intervening layer."

[0070] 6 and 7 are schematic cross-sectional views showing other examples of the current collector of this embodiment.

[0071] Current collector 103 shown in FIG. 6 differs from current collector 101 shown in FIG. 1 in that it further includes first intermediate layer 41 between first surface 20a of resin layer 20 and first metal layer 31.

[0072] The first intermediate layer 41 contains a metal other than copper as a main component. The intermediate layer 41 may be a single-layer film or a laminated film. The intermediate layer 41 may be, for example, an undercoat layer or an anchor coat layer for strengthening the bond between the resin layer 20 and the metal material. The undercoat layer or anchor coat layer may be an organic layer such as an acrylic resin or a polyolefin resin, or may be a metal layer formed by a sputtering method or the like. The provision of the undercoat layer strengthens the bond between the first metal layer 31 and the resin layer 20, thereby improving adhesion and / or suppressing the formation of pinholes in the first metal layer 31.

[0073] The current collector 104 shown in Figure 7 differs from the current collector 102 shown in Figure 2 in that it further includes a first intermediate layer 41 located between the first surface 20a of the resin layer 20 and the first metal layer 31, and a second intermediate layer 42 located between the second surface 20b of the resin layer 20 and the second metal layer 32.

[0074] The first intermediate layer 41 and the second intermediate layer 42 contain a metal other than copper as a main component. The material and function of the first intermediate layer 41 and the second intermediate layer 42 may be similar to that of the first intermediate layer 41 of the current collector 103 shown in FIG. 6. The materials of the first intermediate layer 41 and the second intermediate layer 42 may be the same or different from each other.

[0075] The thicknesses of the first intermediate layer 41 and the second intermediate layer 42 in the current collectors 103 and 104 are not particularly limited and may be selected appropriately depending on the function of the intermediate layer, etc. The first intermediate layer 41 is preferably thinner than the resin layer 20 and the first metal layer 31. Similarly, the second intermediate layer 42 is preferably thinner than the resin layer 20 and the second metal layer 32. The thicknesses of the first intermediate layer 41 and the second intermediate layer 42 may be the same or different from each other.

[0076] The current collector of this modified example only needs to have at least one intervening layer located between the resin layer 20 and the metal layer 30. For example, the current collector of this modified example may have an intervening layer between only one of the first metal layer 31 and the second metal layer 32 and the resin layer 20.

[0077] In this modification, the thickness (total thickness) D4 of the intermediate layers in the current collector may satisfy, for example, the following formula. JPEG0007810723000011.jpg13157In the above formula, thickness D4 is the total thickness of the intermediate layers in the current collector. That is, thickness D4 is the thickness of first intermediate layer 41 in current collector 103, and is the total thickness of first intermediate layer 41 and second intermediate layer 42 in current collector 104. Satisfying the above formula reduces the effect of the intermediate layers on the yield stress of current collectors 103 and 104, so that design using the above formulas (1) and (2) can more reliably improve the breaking elongation of current collectors 103 and 104.

[0078] (Manufacturing method of current collector) The method for producing a current collector according to this embodiment will be described in more detail below, taking the current collector 102 shown in FIG. 2 as an example.

[0079] <Preparation of current collector> First, prepare the resin layer 20. The resin layer 20 is, for example, a polyethylene terephthalate film.

[0080] Next, a metal layer 30 is formed on the surface of the resin layer 20. The metal layer 30 can be formed by a known semiconductor process. For example, vapor deposition, sputtering, electrolytic plating, electroless plating, etc. may be used. For example, the metal layer 30 may be formed by forming a seed layer on the surface of the resin layer and then forming a copper film on the seed layer by electrolytic plating. Alternatively, the metal layer 30 may be formed by attaching a metal foil containing copper, such as copper foil, to the surface of the resin layer 20.

[0081] Here, a first metal layer 31 is formed on a first surface 20a of the resin layer 20, and a second metal layer 32 is formed on a second surface 20b of the resin layer 20. For example, a copper film is formed as the first metal layer 31 and the second metal layer 32. After a nickel chromium (NiCr) or copper seed layer is formed on both sides of the resin layer 20 by, for example, sputtering, a copper film may be formed on the seed layer by electrolytic plating.

[0082] The formation conditions and thicknesses of the metal films that become the first metal layer 31 and the second metal layer 32 can be adjusted so that the yield stress σY1 obtained from equations (1) to (3) is smaller than the tensile fracture stress σB2 of the resin layer 20. In the case of vapor deposition, the formation conditions of the metal film include the substrate temperature during vapor deposition, the purity of the vapor deposition raw material, the vapor deposition rate, and the vapor deposition time. In the case of plating, the formation conditions include the current density, growth rate, plating time, the material of the underlying seed layer, the formation conditions of the seed layer, and the type and amount of additives. In the case of sputtering, the formation conditions include the purity of the target, the ultimate vacuum level in the chamber, the sputtering atmosphere, the sputtering pressure, the sputtering power, the film formation rate, the substrate temperature, and the film formation time.

[0083] As an example, the full width at half maximum β of the metal film can be reduced (the crystal grain size can be increased) by increasing the plating current density when forming the metal film and / or by increasing the sputtering power when forming the seed layer by sputtering. Increasing the plating current density first grows a metal film with high internal stress. This internal stress acts as a driving force to promote recrystallization of the metal film, thereby increasing the crystallinity and forming a metal film with a large crystal grain size. Furthermore, when the seed layer is deposited using high sputtering power, the seed layer heats up, promoting recrystallization of the seed layer and increasing the crystallinity. Forming a highly crystalline seed layer makes it possible to form a highly crystalline metal film, i.e., a large crystal grain size, on the seed layer.

[0084] <Current collector design> In this embodiment, it is preferable to include a step of designing the yield stress and thickness of each layer constituting the laminated structure of the current collector so that the yield stress σY1 of the current collector is smaller than the tensile fracture stress σB2 of the resin layer.

[0085] The yield stress σY1 of the current collector may be calculated by adding up the "thickness ratio a × yield stress σY" of each layer constituting the current collector. The "thickness ratio a" is the ratio of the thickness of that layer to the total thickness of the multiple layers constituting the current collector (including the metal layer 30 and resin layer 20 shown in Figures 1 and 2, etc.). Note that in the design process, layers that are thinner than the other layers (layers with a small thickness ratio a) among the layers constituting the current collector may be ignored.

[0086] The value of the tensile breaking stress σB2 of the resin layer may be a value measured by, for example, a tensile test. In this case, the design step may include a step of measuring the tensile breaking stress σB2 of the resin layer.

[0087] The designing step may include a step of designing the yield stress σ of the metal layer based on the half-width β of the most intense X-ray diffraction peak in the X-ray diffraction pattern of the metal layer. In this case, the designing step may include a step of deriving a relational expression between the yield stress σ and the half-width β of the metal layer. The method of deriving the relational expression is the same as the method described above with reference to FIG. 3.

[0088] Alternatively, the crystal grain size (or crystallite size) of the metal layer 30 may be measured by a method other than X-ray diffraction, and the yield stress σY3 of the metal layer may be designed based on the measured crystal grain size.

[0089] Examples and Comparative Examples Current collectors of the examples and the comparative examples were produced, and the breaking elongation of the current collectors was evaluated.

[0090] <Sample preparation> As the current collectors of Examples 1 to 9 and Comparative Examples 1 to 4, current collectors 102 having the structure shown in FIG. 2 were produced by the following method.

[0091] First, a resin layer 20 (width: 500 mm, length: 100 m) was prepared. In Examples 1 to 8 and Comparative Examples 1 to 3, a polyethylene terephthalate (PET) film (Diafoil K880, manufactured by Mitsubishi Chemical Polyester Film Corporation) was used as the resin layer 20, and in Example 9 and Comparative Example 4, a polypropylene (PP) film (4X-2172, manufactured by Toray Industries, Inc.) was used. The thickness D2 of the resin layer 20 in each Example and Comparative Example is shown in Table 1.

[0092] Next, a 50 nm-thick copper layer was formed as a seed layer on the first surface 20a and the second surface 20b of the resin layer 20 by sputtering. Here, the temperature of the substrate (resin layer 20) during sputtering was set to room temperature if the substrate was a PET film, and to -20°C if the substrate was a PP film. Thereafter, copper layers were formed as the first metal layer 31 and the second metal layer 32 on the seed layer on the first surface 20a side and the second surface 20b side of the resin layer 20 by electrolytic plating, respectively. Here, the plating temperature was set to 40°C. In this way, the current collectors of Examples 1 to 9 and Comparative Examples 1 to 4 were obtained.

[0093] The sputtering power (film formation power) when forming the seed layer, the plating current density when forming the first metal layer 31 and the second metal layer 32, and the total thickness D3 of the first metal layer 31 and the second metal layer 32 for each example and comparative example are shown in Table 1. In each current collector, the thicknesses of the first metal layer 31 and the second metal layer 32 were each set to 1 / 2 of the total thickness D3.

[0094] [Table 1]

[0095] <Measurement of Yield Stress σY2 and Tensile Breaking Stress σB2 of Resin Layer 20> The PET film and the PP film used as the resin layer 20 in the examples and comparative examples were subjected to a tensile test in accordance with the above-mentioned JIS standard to determine the yield stress σY2 and the tensile breaking stress σB2 of each film. The yield stress σY2 and the tensile breaking stress σB2 of each resin layer 20 are shown in Table 1.

[0096] Fig. 8 shows an example of the stress-strain curve of the PET film used in the current collectors of Examples 1 to 8 and Comparative Examples 1 to 3. Fig. 8 shows that the yield stress σY2 of the PET film is approximately 110 MPa, and the tensile breaking stress σB2 is approximately 225 MPa. In the example shown in Fig. 8, the breaking elongation is approximately 35%, but the breaking elongation of the PET film varies for each measured sample, falling within the range of approximately 25 to 35%.

[0097] <Measurement of half-width β> The half-value width β of the metal layer 30 of each current collector was determined by X-ray diffraction. The results are shown in Table 1.

[0098] The measurement results show that the higher the plating current density and the higher the sputtering power during seed layer formation, the smaller the full width at half maximum β, and that these conditions can control the crystallinity of the metal layer 30. This is thought to be because, as mentioned above, setting the plating current density high causes a metal film (here, a copper film) with high internal stress to grow, and the internal stress acts as a driving force to promote recrystallization of the metal film, thereby increasing the crystallinity and resulting in a metal film with a small full width at half maximum β. It is also thought that setting the sputtering power during seed layer formation high promotes thermal recrystallization in the deposited seed layer, resulting in a seed layer with a large crystal grain size. By increasing the crystal grain size of the seed layer, a metal film with a large crystal grain size can be grown on the seed layer.

[0099] <Calculation of the yield stress σY1 of the current collector> The yield stress σY3 of the metal layer 30 of each current collector was calculated from the half-width β obtained by X-ray diffraction and the above-mentioned formula (3). Next, the yield stress σY1 of each current collector was determined from the yield stress σY3 of the metal layer 30, the yield stress σY2 of the resin layer 20, the thickness ratio A of the metal layer 30, and the above-mentioned formulas (1) and (2). The obtained values ​​of yield stress σY3 and σY1 are also shown in Table 1.

[0100] As shown in Table 1, in Examples 1 to 9, the yield stress σY1 of the current collector was smaller than the tensile breaking stress σB2 (225 MPa) of the resin layer 20, and in Comparative Examples 1 to 4, the yield stress σY1 of the current collector was larger than the tensile breaking stress σB2 of the resin layer 20.

[0101] <Method for evaluating breaking elongation of current collector> The breaking elongation of each current collector was evaluated by a tensile test.

[0102] First, 40 test samples were cut out from the current collector of Example 1. Here, in order to reduce thickness variations among the test samples, sampling was performed from a portion of the current collector having a width of 500 mm, excluding a region within 50 mm from the edge (edge ​​region). Note that the edge region is usually removed when manufacturing a battery.

[0103] Next, a tensile test was performed on each test sample to determine the breaking elongation. The tensile test was performed in accordance with the provisions of JIS K7127:1999. Next, the percentage B of test samples with a breaking elongation of 6% or less out of the 40 test samples was determined. B = {(number of test samples with breaking elongation of 6% or less) / 40} × 100

[0104] Similarly, for each of the current collectors of the other examples and comparative examples, 40 test samples were subjected to a tensile test, and the proportion B of test samples with a breaking elongation of 6% or less was determined.

[0105] The reason for using 6% as the standard is that if resin layer 20 barely elongates after metal layer 30 breaks (see FIG. 4C), the breaking elongation of the current collector will be approximately 3 to 5%, which is the breaking elongation of the metal layer, and will be 6% or less. If resin layer 20 continues to elongate after metal layer 30 breaks (see FIG. 5C), the breaking elongation of the current collector will be sufficiently larger than the breaking elongation of the metal layer, and ideally will be close to the breaking elongation of resin layer 20, exceeding 6%.

[0106] <Evaluation results> Percentage B Table 1 shows the percentage B obtained by the tensile test for each current collector test sample.

[0107] The results shown in Table 1 confirm that the current collectors of Examples 1 to 9 had a ratio B of 20% or less, regardless of the thickness D3 of the metal layer or the material of the resin layer. In current collectors with a ratio B of 20% or less, the current collector as a whole has a predetermined elongation (breaking elongation), but it is believed that (relatively small) regions with low elongation exist discretely due to material factors and other factors. In other words, each small region with low elongation is surrounded by a region with a predetermined elongation. Since stress applied to the current collector during calendering and other processes is dispersed to the surrounding regions of the low elongation regions, if the ratio B is 20% or less, breakage of the current collector is unlikely to occur, and the process defect rate is believed to be reduced. For the same reason, breakage of the current collector during battery operation is also believed to be suppressed. Therefore, when batteries are manufactured using the current collectors of Examples 1 to 9, the process defect rate during, for example, transporting the current collector or calendering can be significantly reduced.

[0108] As for the material factors mentioned above, it is possible that, for example, there are areas in the resin layer 20 where the filler aggregates, or there are areas in the metal layer 30 where recrystallization is inhibited due to the segregation of impurities, resulting in localized areas of low elongation in the current collector.

[0109] On the other hand, in Comparative Examples 1 to 4, in which the tensile fracture stress σB2 of the resin layer 20 was greater than the yield stress σY1 of the current collector, the proportion B exceeded 45%, which was significantly higher than the proportion B in the Examples. That is, in nearly half or more of the test samples of the current collectors of Comparative Examples 1 to 4, after the metal layer 30 broke, the resin layer 20 broke with almost no elongation. In such current collectors, the proportion of regions with low elongation within the current collector surface is high, and it is thought that stress applied to the current collector during calendering or the like can cause the current collector to break, increasing the possibility of process defects.

[0110] Therefore, it was confirmed that the breaking elongation of the current collector can be controlled by the relationship between the yield stress σY1 of the current collector calculated by the formulas (1) to (3) and the tensile breaking stress σB2 of the resin layer 20.

[0111] Furthermore, the results in Table 1 show that, for example, when the thickness D2 of the resin layer 20 is in the range of 4 μm to 6 μm, if the thickness D3 of the metal layer 30 exceeds 3.0 μm or the half-width β exceeds 0.25°, the ratio B tends to increase. For this reason, it is preferable that the thickness D3 is, for example, 3.0 μm or less and / or the half-width β is, for example, 0.25° or less. On the other hand, from the viewpoint of reducing the sheet resistance of the current collector, it is preferable that the thickness D3 of the metal layer 30 is, for example, 0.1 μm or more. For example, in the current collectors of Examples 1 and 2, which satisfy all of the following conditions: the thickness D2 of the resin layer 20 is 4 μm or more and 6 μm or less, the thickness D3 of the metal layer 30 is 0.1 μm or more and 3.0 μm or less, and the half-width β is 0.25° or less, the ratio B is 5% or less, and it can be seen that the fracture elongation is more reliably improved. Furthermore, even if the thickness of the resin layer 20 is outside the range of 4 μm to 6 μm (for example, Example 3), it can be confirmed that by appropriately setting the thickness D2 and half-width β of the metal layer 30, the yield stress σY1 can be made lower than the tensile fracture stress σB2, and high fracture elongation can be achieved.

[0112] FIG. 9 is a plot of the thickness ratio A of the metal layer and the half-width β for the current collectors of Examples 1 to 8 and Comparative Examples 1 to 3, which used a polyethylene terephthalate film as the resin layer 20. A ratio B of less than 15% is represented by a black circle, a ratio B of 15% to 20% is represented by a triangle, and a ratio B of more than 20% is represented by an x. Curve f2 in FIG. 9 indicates the set of half-width β and thickness ratio A when the yield stress σY1 is equal to 225 MPa, which is the tensile stress of the polyethylene terephthalate film. The region above curve f2 is the region where σY1>σB2, and the region below curve f2 is the region where σY1<σB2.

[0113] 9, it can be seen that a current collector with excellent fracture elongation can be realized by controlling the half-value width β and the thickness ratio A so that they are positioned in the region below the curve f2, i.e., so that σY1<σB2 is satisfied. Although not shown, if a resin film with a tensile fracture stress σB2 of less than 225 MPa is used as the resin layer, the curve f2 shifts downward (towards -y), and the region where σY1<σB2 is satisfied becomes narrower.

[0114] Stress-strain curve The stress-strain curves of the current collectors of the examples and comparative examples will be explained using the current collectors of Example 1 and Comparative Example 1 as examples.

[0115] 10A and 10B are diagrams showing examples of the measurement results of the stress-strain curves of the current collectors of Example 1 and Comparative Example 1. As can be seen from Table 1, the current collector of Example 6 and the current collector of Comparative Example 1 have substantially the same thickness D2 of the resin layer (PET film) and thickness D3 of the metal layer.

[0116] As shown in FIG. 10A, in the current collector of Example 1, fracture occurs in the metal layer at a yield stress σY1 that is lower than the tensile fracture stress σB2 (225 MPa in this example). Even after fracture occurs in the metal layer, the resin layer continues to deform (stretch) in response to the stress, increasing the strain of the current collector (see FIG. 5C). When the stress applied to the current collector reaches the tensile fracture stress σB2 (225 MPa), the resin layer also fractures. In this example, the fracture elongation of the current collector is approximately the same as that of the resin layer, at approximately 35%.

[0117] On the other hand, as shown in FIG. 10B, in the current collector of Comparative Example 1, a fracture occurs in the metal layer at a yield stress σY1 that is higher than the tensile fracture stress σB2 (225 MPa in this example). Immediately after this point (yield point), a stress of 225 MPa or more is applied to the portion of the resin layer located below the fracture in the metal layer, causing the resin layer to fracture without stretching (see FIG. 4C). As a result, the fracture elongation of the current collector is significantly smaller than that of the current collector of Example 1 shown in FIG. 10A. In this example, the fracture elongation of the current collector is approximately 3 to 5%.

[0118] 10A and 10B are merely examples, and may vary depending on, for example, the rupture elongation of the PET film. The rupture elongation of the current collector in the examples may be smaller than that of the resin layer. Even in such cases, the rupture elongation of the current collector is greater (6% or more) than that of the metal layer (copper layer) and is therefore believed to be effective in suppressing breakage of the current collector.

[0119] (Second embodiment) An embodiment of an electrode for an electricity storage device will be described below. The electrode for an electricity storage device (hereinafter simply referred to as "electrode") of this embodiment is preferably used as the negative electrode of an electricity storage device, but may also be used as the positive electrode.

[0120] 11A is an exploded perspective view of electrode 110, and FIG. 11B is a cross-sectional view showing a portion of electrode 110. Electrode 110 includes a current collector 201 and an active material layer 210. Active material layer 210 contains an active material that is oxidized and reduced as charging (or storing) and discharging occur. Current collector 201 supports active material layer 210, and supplies electrons to and receives electrons from active material layer 210.

[0121] The current collector 201 is any one of the current collectors 101 to 104 described in the first embodiment. That is, the current collector 201 includes a resin layer 20 and a first metal layer 31 located on the first surface 20a side of the resin layer 20. The current collector 201 may further include a second metal layer 32 located on the second surface 20b side of the resin layer 20.

[0122] The current collector 201 includes a first portion 201s and a second portion 201t, and an active material layer 210 is disposed in the first portion 201s. The active material layer 210 is not provided in the second portion 201t, and the second portion 201t functions as a tab for electrical connection to the outside.

[0123] The active material layer 210 is located on the opposite side of the first metal layer 31 to the resin layer 20. The active material layer 210 contains a positive electrode active material or a negative electrode active material that absorbs and releases lithium ions.

[0124] The electrode 110 of this embodiment has the desired electrical characteristics and includes the current collector 201 with high breaking elongation. This can prevent the current collector from being torn by a calendering process or the like when forming the active material layer 210, thereby improving the process defect rate. Furthermore, even when large localized stresses are applied to the current collector 201 due to the expansion and contraction of the active material layer 210 during battery operation, deformation of the battery and deterioration of its characteristics caused by breakage of the current collector 201 can be prevented.

[0125] The electrodes 110 for the positive electrode and the negative electrode can be manufactured by known manufacturing methods.

[0126] The structure of the electrode for the power storage device of the present embodiment is not limited to the structures shown in FIGS. 11A and 11B. For example, as shown in FIG. 12, the active material layer 210 may also be disposed on the side opposite to the resin layer 20 of the second metal layer 32.

[0127] <active material layer 210> When the electrode 110 is used as the positive electrode of the power storage device, the active material layer 210 contains a positive electrode active material.

[0128] 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 )), a composite metal oxide represented by the general formula: LiNi x Co y Mn z M a O2 (x + y + z + a = 1, 0 ≦ x < 1, 0 ≦ y < 1, 0 ≦ z < 1, 0 ≦ a < 1, M 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[[ID=第28]] x Co y Al z O2 (0.9 < x + y + z < 1.1), etc. The positive electrode active material may contain polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc. as a material capable of occluding and releasing lithium ions.

[0129] ]> The active material layer 210 used in the positive electrode 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 210 used in 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).

[0130] 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 210 used in the positive electrode.

[0131] 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 210 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 210.

[0132] When the electrode 110 is used as the negative electrode of the power storage device, the active material layer 210 used for the negative electrode contains a negative electrode active material.

[0133] 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, 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 ).

[0134] For the binder and conductive assistant of the active material layer 210 used for the negative electrode, the above-described binder and conductive assistant can be used in the same manner. Further, as the binder for the negative electrode, cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide, polyamideimide, acrylic resin, or the like may be used.

[0135] (Third Embodiment) An embodiment of a lithium-ion secondary battery will be described.

[0136] FIG. 13 is a schematic external view showing an example of a lithium-ion secondary battery 301, and FIG. 14 is an exploded perspective view showing the cell in the lithium-ion secondary battery shown in FIG. 13 taken out. Here, as the lithium-ion secondary battery, a lithium-ion secondary battery called a pouch type or a laminate type is exemplified. The illustrated lithium-ion secondary battery is a single-layer type, but may be a stacked type. In the illustrated example, the positive electrode, separator, and negative electrode constituting the cell are stacked along the Z direction in the figure.

[0137] 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 .

[0138] The cell 310 includes an electrode 110, an electrode 120, and a separator 330 disposed therebetween. In the illustrated example, the cell 310 is a single-layer cell including a pair of electrodes.

[0139] One of the electrodes 110 and 120 is configured as a positive electrode containing a positive electrode active material, and the other is configured as a negative electrode containing a negative electrode active material. The electrode 110 is the electrode 110 described in the third embodiment and is configured as, for example, a negative electrode.

[0140] The electrode 120 includes a current collector 202 and an active material layer 220 disposed on one surface of the current collector 202. The active material layer 220 is a layer containing the negative electrode active material or positive electrode active material described in the second embodiment. The current collector 202 may have a laminated structure including a resin layer and a metal layer disposed on one or both surfaces of the resin layer, similar to the current collectors 101 to 104 described in the first embodiment, for example. The material and thickness of the resin layer and / or metal layer in the current collector 202 may be different from those in the electrode 110. Alternatively, the current collector 202 may be a metal current collector made of metal foil.

[0141] Separator 330 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.

[0142] The electrolyte 314 is 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. 13 ) is typically disposed between the exterior body 313 and the lead 311 to prevent leakage of the non-aqueous electrolyte solution.

[0143] 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.

[0144] 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.

[0145] The lithium ion secondary battery 301 can be manufactured, for example, by the following method. After producing the electrodes 110 and 120, the electrodes 110 and 120 are held together with the active material layers 210 and 220 facing each other via the separator 330, thereby forming a cell 310. The obtained cell 310 is 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.

[0146] Fig. 15 is a schematic external view showing another lithium ion secondary battery 302 of this embodiment, and Fig. 16 is an exploded perspective view showing cells extracted from the lithium ion secondary battery shown in Fig. 15. The lithium ion secondary battery 302 differs from the lithium ion secondary battery 301 shown in Fig. 13 in that it has a stacked cell 320.

[0147] The cell 320 includes a plurality of electrodes 110, a plurality of electrodes 120, and a plurality of separators 330. The cell 320 has a structure in which the electrodes 110 and the electrodes 120 are alternately stacked with the separators 330 interposed therebetween. One of the electrodes 110 and the electrodes 120 is a positive electrode, and the other is a negative electrode. In this example, the electrode 110 is the electrode 110 described in the second embodiment, and is preferably configured as a negative electrode.

[0148] Each electrode 110 may have the structure described above with reference to Figure 12. Each electrode 120 includes a current collector 202 and active material layers 220 disposed on the upper and lower surfaces of the current collector 202. As described with reference to Figure 14, the current collector 202 may have a laminated structure including a resin layer and metal layers disposed on both sides of the resin layer, or may be a metal current collector made of metal foil.

[0149] The power storage device to which the electrode of the present embodiment can be applied is not limited to a lithium ion secondary battery, and the electrode of the present embodiment can also be suitably used in, for example, an electric double layer capacitor. [Industrial Applicability]

[0150] 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 a power source for vehicles such as bicycles and automobiles, a power source for communication devices such as smartphones, a power source for various sensors, and a power source for an unmanned eXtended Vehicle (UxV). [Explanation of symbols]

[0151] 20: Resin layer 20a: First surface of resin layer 20b: Second surface of the resin layer 21: Resin layer 30: Metal layer 31: 1st metal layer 31a: First surface of first metal layer 31b: second surface of the first metal layer 32: 2nd metal layer 32a: First surface of second metal layer 32b: second surface of second metal layer 41: 1st intervening layer 42: 2nd intervening layer 101, 102, 103, 104: current collectors 110, 120: Electrodes for electricity storage devices 131: Neck 132: Breaking part 201, 202: current collectors 201s: First part of the current collector 201t: Second part of current collector 202: Current collector 210, 220: Active material layer 301, 302: Lithium-ion secondary battery 310, 320: Cell 311: Lead 313: Exterior body 314: Electrolyte 330: Separator

Claims

1. a resin layer having a first surface and a second surface located opposite the first surface; a metal layer containing copper, the metal layer includes a first metal layer located on the first surface side of the resin layer, the yield stress σY1 of the current collector is smaller than the tensile breaking stress σB2 of the resin layer, The yield stress σY1 [MPa] of the current collector is calculated from the yield stress σY2 [MPa] of the resin layer, the thickness D2 [μm] of the resin layer, the yield stress σY3 [MPa] of the metal layer, and the thickness D3 [μm] of the metal layer, using the following formulas (1) and (2): [Equation 1] [Equation 2] is the value calculated by The yield stress σY3 [MPa] of the metal layer is calculated from the half-width β [°] of the most intense X-ray diffraction peak in the X-ray diffraction pattern of the metal layer by the following formula (3): [Equation 3] is the value calculated by the half-value width β is 0.25° or less, The thickness D3 of the metal layer is 1.0 μm or more, A current collector, wherein the thickness ratio A of the metal layer calculated by the formula (2) is 1 / 5.5 or more.

2. The current collector according to claim 1 , wherein the metal layer further includes a second metal layer located on the second surface side of the resin layer.

3. The current collector according to claim 1 or 2, wherein the metal layer contains copper as a main component.

4. The current collector according to claim 1 , wherein the resin layer has a thickness D2 of 4 μm or more and 6 μm or less.

5. The current collector according to claim 1 , wherein the thickness D3 of the metal layer is 3 μm or less.

6. A collector described in any one of claims 1 to 5, wherein the thickness ratio A of the metal layer is 0.44 or less.

7. 7. The current collector according to claim 1, further comprising an intervening layer between the first surface of the resin layer and the first metal layer, the intervening layer containing a metal other than copper as a main component.

8. The current collector according to claim 1 , wherein the resin layer contains at least one of polyethylene terephthalate, polyimide, polypropylene, polycarbonate, polyamide, and polyvinyl chloride.

9. The current collector according to any one of claims 1 to 8, an active material layer located on the opposite side of the metal layer from the resin layer; An electrode for an electricity storage device comprising:

10. 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, A lithium ion secondary battery, wherein the negative electrode is the electrode for an electricity storage device according to claim 9 .

11. A method for producing a current collector having a laminated structure including a resin layer and a metal layer containing copper, comprising: a step of designing the yield stress and thickness of each layer constituting the laminated structure so that the yield stress σY1 of the current collector is smaller than the tensile fracture stress σB2 of the resin layer.

12. 12. The method for producing a current collector according to claim 11, wherein the designing step includes a step of designing a yield stress σY3 of the metal layer based on a crystal grain size of the metal layer or a half-value width β of a most intense X-ray diffraction peak in an X-ray diffraction pattern of the metal layer.

13. The method for producing a current collector according to claim 12 , wherein the step of designing the yield stress σY3 of the metal layer includes a step of deriving a relational expression between the yield stress σY3 of the metal layer and the half-value width β.

14. In the step of designing the yield stress σY3 of the metal layer, the yield stress σY3 [MPa] of the metal layer is calculated using the half-value width β [°] and the following formula: [Equation 4] The method for producing a current collector according to claim 12, wherein the current collector is designed based on the following formula:

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