Current collectors, electrodes for energy storage devices, and lithium-ion secondary batteries

Abstract

A current collector according to the present invention includes a resin layer 10 having a first surface, and a first metal layer 20 located at the first surface. The first metal layer contains aluminum as a main component, the thickness d of the first metal layer is 0.5-3 μm, and d and r satisfy the following formula (1), where r is the peak intensity ratio B / A, A being the intensity of the highest X-ray diffraction peak at a diffraction angle (2θ) in the range of 36-41° and B being the intensity of the highest X-ray diffraction peak at a diffraction angle (2θ) in the range of 43-48° in the measurement of the first metal layer by the X-ray diffraction method.

Description

[Technical Field]

[0001] This disclosure relates to current collectors, electrodes for energy storage devices, and lithium-ion secondary batteries. [Background technology]

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

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0373584 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] When the composite current collector described above is used in an energy storage device equipped with a non-aqueous electrolyte, such as a lithium-ion secondary battery, it is preferable that the current collector has resistance to the non-aqueous electrolyte. One embodiment of the present disclosure provides a current collector, an electrode for an energy storage device, and a lithium-ion secondary battery with excellent resistance to a non-aqueous electrolyte. [Means for solving the problem]

[0005] A current collector according to one embodiment of the present disclosure comprises a resin layer having a first surface and a second surface located opposite to the first surface, and a first metal layer located on the first surface, wherein the first metal layer mainly contains aluminum, the thickness d of the first metal layer is 0.5 μm or more and 3 μm or less, and when the peak intensity B / A of the highest X-ray diffraction peak intensity A in the diffraction angle (2θ) range of 36° or more and 41° or less is measured by X-ray diffraction of the first metal layer, d and r are given by the following equation (1):

number

[0006] According to one embodiment of the present disclosure, a current collector, an electrode for an energy storage device, and a lithium-ion secondary battery are provided that have excellent resistance to non-aqueous electrolytes. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a current collector according to the first embodiment. [Figure 2] Figure 2 shows an example of an X-ray diffraction chart of an aluminum thin film. [Figure 3] Figure 3 is a schematic cross-sectional view showing an example of a current collector according to the second embodiment. [Figure 4] Figure 4 is a schematic exploded perspective view showing an example of an electrode for a third embodiment of an energy storage device. [Figure 5] Figure 5 is a schematic partial cross-sectional perspective view showing an example of a lithium-ion secondary battery according to the fourth embodiment. [Figure 6] Figure 6 is a schematic exploded perspective view showing an example of a lithium-ion secondary battery cell as shown in Figure 5. [Figure 7]FIG. 7 shows the range of diffraction angle (2θ) from 43° to 48° where the peak of Al(200) can be seen in the X-ray diffraction charts obtained from the samples of Examples 2, 5, and 7.

BEST MODE FOR CARRYING OUT THE INVENTION

[0008] The current collector with the conductive layer formed on the resin film is different from the metal foil conventionally used as a single current collector in terms of structure and thickness. In particular, the fact that the conductive layer is supported by the resin film and is thinner than the metal foil used for conventional current collectors is different from conventional current collectors.

[0009] A lithium-ion secondary battery generally includes a non-aqueous electrolyte containing an anion containing a fluorine atom as an electrolyte. When the above-described current collector is used in a lithium-ion secondary battery, the current collector needs to have appropriate resistance to the non-aqueous electrolyte. For example, when such a lithium-ion secondary battery is charged and discharged in a high-temperature environment, the anion containing a fluorine atom decomposes, and fluorine ions, that is, hydrofluoric acid, are generated as decomposition products. The inventor of the present application has conceived a current collector, an electrode for a power storage device, and a lithium-ion secondary battery that can suppress the deterioration of the current collector with the conductive layer formed on the resin film due to the decomposition products of the non-aqueous electrolyte, specifically, suppress the peeling of the conductive layer from the resin film, thereby suppressing the deterioration of the current collector and maintaining the charge-discharge characteristics.

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

[0011] The thickness, dimensions, shape, etc. of the members shown in the drawings of the present disclosure may be exaggerated for the sake of convenience of explanation. Also, in the drawings of the present disclosure, in order to avoid excessive complexity, some members may be taken out and illustrated, or the illustration of some elements may be omitted. Therefore, the respective dimensions of the members shown in the drawings of the present disclosure and the arrangement between the members may not reflect the respective dimensions of the members in the actual device and the arrangement between the members. In the present disclosure, "vertical" and "orthogonal" are not limited to the case where two straight lines, sides, surfaces, etc. form a strictly 90° angle, but include the case where they are in the range of about ±5° from 90°. Also, "parallel" includes the case where two straight lines, sides, surfaces, etc. are in the range of about ±5° from 0°.

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

[0013] (First Embodiment) FIG. 1 is a schematic cross-sectional view showing an example of a current collector of the present embodiment. The current collector of the present embodiment can be used as a current collector for either the positive electrode or the negative electrode of a power storage device such as a lithium-ion secondary battery. The current collector 101 shown in FIG. 1 includes a resin layer 10 having a first surface 10a and a second surface 10b located on the side opposite to the first surface 10a, and a first metal layer 20.

[0014] The resin layer 10 functions as a support for the first metal layer 20 in the current collector 101. By having a density smaller than that of the first metal layer 20, the resin layer 10 can contribute to increasing the charge capacity per unit weight when the current collector 101 is applied to a power storage device.

[0015] The resin layer 10 is electrically insulating and contains resin. The resin layer 10 may also be thermoplastic. 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 composed of two or more layers laminated together. In this case, at least one of the layers may contain a different resin than the other layers.

[0016] The thickness of the resin layer 10 is, for example, 3 μm to 12 μm. The thickness of the resin layer 10 may also be 3 μm to 6 μm. A thickness of 3 μm or more for the resin layer 10 provides sufficient strength as a support. Furthermore, a thickness of 12 μm or less for the resin layer 10 allows for a reduction in the overall thickness of the current collector 101. Therefore, in a stacked lithium-ion secondary battery in which multiple electrode pairs are stacked, the proportion occupied by the current collector, which does not contribute to energy storage, can be reduced, thereby increasing the energy density. If the thickness of the resin layer 10 is 6 μm or less, the overall thickness of the current collector 101 can be further reduced, thereby increasing the energy density of the stacked lithium-ion secondary battery.

[0017] The current collector 101 may further include an undercoat layer located between the resin layer 10 and the first metal layer 20. The undercoat layer may be provided to increase the bonding strength between the resin layer 10 and the first metal layer 20, or to suppress the formation of pinholes in the first metal layer 20. The undercoat layer may be a layer formed from an organic material such as acrylic resin or polyolefin resin, or a layer containing metal formed by sputtering.

[0018] The first metal layer 20 mainly contains Al (aluminum). Here, the main component refers to the element that accounts for the largest proportion of the constituent elements when the component contains one or more constituent elements, expressed as a mole percentage. As long as Al is the main component, the first metal layer 20 may further contain other metals.

[0019] The thickness d of the first metal layer 20 is, for example, 0.5 μm or more and 3 μm or less. By having a thickness d of 0.5 μm or more of the first metal layer 20, the electrical resistance of the first metal layer 20 can be reduced. For example, when a power storage device is manufactured, energy loss due to resistance in the current collector can be reduced. Also, by having a thickness of 3 μm or less of the first metal layer 20, the proportion of the first metal layer 20 to the entire current collector 101 becomes small, making it easier to obtain the advantage of reducing the weight of the current collector by using the resin layer 10. The thickness d of the first metal layer 20 may also be 0.7 μm or more and 2 μm or less.

[0020] The first metal layer 20 exhibits strong peaks in the diffraction angle (2θ) range of 36° to 41° and in the diffraction angle (2θ) range of 43° to 48°, respectively, as measured by X-ray diffraction. Here, the highest X-ray diffraction peak in the diffraction angle (2θ) range of 36° to 41° is the Al(111) peak, and the highest X-ray diffraction peak in the diffraction angle (2θ) range of 43° to 48° is the Al(200) peak. The X-ray diffraction measurement is performed using the out-of-plane method. That is, X-rays are incident on the surface of the first metal layer 20, and the intensity of the scattered X-rays is measured.

[0021] Figure 2 shows an example of X-ray diffraction peaks for an aluminum thin film. As shown in Figure 2, a peak in the (111) plane is observed in the range of 36° to 41°, and a peak in the (200) plane is observed in the range of 43° to 48°. Since aluminum metal has an fcc structure, according to the extinction rule, peaks are observed only when the values ​​of h, k, and l, when expressed as (h, k, l) in Miller indices, are all even or all odd.

[0022] When r is the ratio B / A of the peak intensities using the intensity A of the highest X-ray diffraction peak in the diffraction angle (2θ) range of 36° to 41° and the intensity B of the highest X-ray diffraction peak in the diffraction angle (2θ) range of 43° to 48°, d and r of the first metal layer 20 are given by the following equation (1)

number

[0023] More preferably, d and r of the first metal layer 20 are given by the following formula (2)

number

[0024] In equations (1) and (2), d is the value when the thickness of the first metal layer is expressed in units of μm. The value of the thickness d of the first metal layer 20 can be obtained, for example, by cross-sectional observation using a SEM.

[0025] r is given by the following equation (3) r<1 (3) It is preferable that the following conditions are met. When r satisfies equation (3), the (111) orientation of the first metal layer 20 is increased, and a denser metal layer is obtained. Therefore, the resistance of the first metal layer 20 to non-aqueous electrolytes is also improved.

[0026] It is more preferable that the Al(200) peak is hardly observed. In other words, it is preferable that the peak intensity B of Al(200) is comparable to the baseline intensity in the X-ray diffraction measurement. Comparability means that it is substantially indistinguishable from the noise-induced intensity variation of the baseline in the X-ray diffraction measurement. If the peak intensity B of Al(200) is comparable to the baseline intensity in the X-ray diffraction measurement, it can be substantially considered as B=0. Therefore, in this case, √r / d 2 The value of is said to be equal to 0. Conversely, if the peak intensity B of Al(200) is large enough to be distinguishable from the baseline noise in the X-ray diffraction measurement, then √r / d 2 It takes a value greater than 0.

[0027] It is preferable that the orientation index of the (111) plane of aluminum in the first metal layer, measured by the Rotgering method with respect to the direction perpendicular to the first surface 10a of the resin layer 10, is 0.8 or higher. This increases the (111) orientation of the first metal layer 20, resulting in a denser metal layer.

[0028] Here, the orientation index of the (111) plane refers to the orientation index F obtained by the Rottgering method. The maximum value of the orientation index by the Rottgering method is 1. An orientation index of 1 indicates that the surface is perfectly oriented, and an orientation index of 0 indicates that the surface is not oriented. The orientation index F is determined using the intensity of the X-ray diffraction peak obtained by X-ray diffraction measurement of the layer (film) to be evaluated, by the following formula.

number

[0029] I0(111) represents the intensity of the X-ray diffraction peak of the (111) plane obtained by X-ray diffraction measurement of an unoriented Al film. I0(hkl) represents the intensity of the total diffraction peak obtained by X-ray diffraction measurement of an unoriented Al film. Furthermore, an unoriented Al film means an Al film whose X-ray diffraction peak intensity pattern is similar to the intensity pattern of the X-ray diffraction peak of a standard aluminum sample listed in JCPDS (Joint Committee on Powder Diffraction Standards).

[0030] I(111) represents the intensity of the X-ray diffraction peak of the (111) plane obtained by X-ray diffraction measurement of the layer (film) to be evaluated. I(hkl) represents the intensity of the total diffraction peak obtained by X-ray diffraction measurement of the layer (film) to be evaluated.

[0031] Note that the orientation index F obtained by the Rottgering method may be a negative value. This can occur when the intensity of the X-ray diffraction peak at the orientation plane from which the orientation index F is obtained from the layer (film) to be evaluated is lower than the intensity obtained from an unoriented film. If the orientation index F obtained by the above formula is a negative value, for example, the layer to be evaluated may be strongly oriented in an orientation direction other than the orientation plane from which the orientation index F is obtained.

[0032] The first metal layer 20 may be formed by any method as long as it possesses the characteristics described above. The first metal layer 20 can be formed on the resin layer 10 by, for example, a thin-film formation technique such as sputtering or vacuum deposition. In this case, the thickness of the first metal layer 20, the peak intensity of Al(111) and Al(200) in the first metal layer 20 can be adjusted by changing conditions such as the film formation time, the vacuum level achieved during film formation, the film formation rate, the heating temperature of the substrate, and the bias voltage.

[0033] According to this embodiment, the current collector 101 exhibits excellent electrolyte resistance because the first metal layer 20 satisfies formula (1) above. Therefore, the lithium-ion secondary battery equipped with the current collector 101 of this embodiment has suppressed degradation of battery characteristics and excellent reliability.

[0034] (Second embodiment) Figure 3 is a schematic cross-sectional view showing an example of the current collector of this embodiment. The current collector 102 of this embodiment differs from the current collector 101 of the first embodiment in that conductive layers are provided on both sides of the resin layer 10.

[0035] The current collector 102 comprises a resin layer 10 and a first metal layer 20 and a second metal layer 20'. The first metal layer 20 is arranged on the first surface 10a, as described in the first embodiment. On the other hand, the second metal layer 20' is arranged on the second surface 10b of the resin layer 10.

[0036] Similar to the first metal layer 20, the second metal layer 20' also contains aluminum as its main component. The thickness d' of the second metal layer 20' is preferably 0.5 μm or more and 3 μm or less. In the measurement of the second metal layer 20' by X-ray diffraction, when r' is the ratio B' / A' of the peak intensities of the highest X-ray diffraction peak A' in the diffraction angle (2θ) range of 36° to 41° and the highest X-ray diffraction peak B' in the diffraction angle (2θ) range of 43° to 48°, d' and r' are given by the following equation (4).

number

[0037] More preferably, d' and r' of the second metal layer 20' are given by the following formula (5)

number

[0038] r' is given by the following equation (6) r'<1 (6) It is preferable that the following conditions are met. By satisfying formula (6), the (111) orientation of the second metal layer 20' is increased, and a denser metal layer can be obtained.

[0039] It is preferable that the orientation index of the (111) plane of aluminum in the second metal layer 20', measured by the Rotgering method with respect to the second surface 10b of the resin layer 10, is 0.8 or higher. This increases the (111) orientation of the second metal layer 20', resulting in a denser metal layer.

[0040] According to the current collector 102, the first surface 10a of the resin layer 10 is provided with a first metal layer 20, and the second surface 10b is provided with a second metal layer 20', so electrodes can be formed on both sides of the current collector 102. Therefore, the proportion of the resin layer in the energy storage device can be reduced, and the battery capacity per unit area can be increased.

[0041] (Third embodiment) An embodiment of an electrode for an energy storage device will be described. The electrode for an energy storage device of this embodiment can be used as either the positive or negative electrode of an energy storage device. Figure 4 is an exploded perspective view of the electrode 201 for an energy storage device. The electrode 201 for an energy storage device comprises 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 located in the first portion 210s. The active material layer 220 is not provided in the second portion 210t, and the second portion 210t functions as a tab for electrical connection to the outside. The active material layer 220 may contain an active material that is oxidized and reduced in conjunction with charging (or energy 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.

[0042] For the current collector 210, the current collector 101 or the current collector 102 described in the first embodiment or the second embodiment can be used. When using the current collector 102, other active material layers not shown in FIG. 4 are arranged in the first portion 210s on the back side of the current collector 210 (the side where the active material layer 220 is not arranged).

[0043] The active material layer 220 may contain a positive electrode active material or a negative electrode active material that occludes and releases lithium ions. The positive electrode active material includes, for example, a composite metal oxide containing lithium. Examples of the composite metal oxide containing lithium include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMnO2), lithium manganese spinel (LiMn2O4), lithium vanadium compound (LiV2O5), olivine-type LiMPO4 (where M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr or vanadium oxide), lithium titanate (Li4Ti5O 12 ), general formula: LiNi x Co y Mn z M a O2 (x + y + z + a = 1, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 ≤ a < 1, M in the above general formula is one or more elements selected from the group consisting of Al, Mg, Nb, Ti, Cu, Zn, Cr), and a composite metal oxide represented by the general formula: LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1), etc. can be mentioned. The positive electrode active material may contain polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc. as a material capable of occluding and releasing lithium ions.

[0044] 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. When the electrode 201 for the energy storage device is used as the positive electrode, 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) can be used as the binder in the active material layer 220.

[0045] A vinylidene fluoride-based fluororubber may be used as a binder. For example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP type fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE type fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP type fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE type fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE type fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE type fluororubber), etc., may be applied as the binder for the active material layer 220.

[0046] Examples of conductive additives include carbon materials such as carbon powder and carbon nanotubes. Carbon black can be used as the carbon powder. Other examples of conductive additives for the active material layer 220 when the electrode 201 for the energy storage device is used as 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 materials may be mixed and included in the active material layer 220.

[0047] The negative electrode active material may contain a carbon material. Examples of the carbon material include, for example, natural or artificial graphite, carbon nanotubes, non-graphitizable carbon, graphitizable carbon (soft carbon), low-temperature calcined carbon, and the like. The negative electrode active material may contain materials other than the carbon material. For example, alkali metals and alkaline earth metals such as metallic lithium, metals such as tin or silicon that can form compounds with metals such as lithium, silicon-carbon composites, amorphous compounds mainly composed of oxides (SiO x (0 < x < 2), tin dioxide, etc.), and may contain particles such as lithium titanate (Li4Ti5O 12 ).

[0048] When applying the electrode 201 for a power storage device to the negative electrode, the same binders and conductive aids as described above can be used for the binder and conductive aid of the active material layer 220. Also, as the binder for the negative electrode, cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide, polyamideimide, acrylic resin, or the like may be used.

[0049] The electrodes for the power storage device for the positive electrode and the negative electrode can be manufactured by known manufacturing methods. In the electrode for the power storage device of this embodiment, the adhesion between the resin layer and the conductive layer of the current collector is enhanced. Therefore, even when the lithium-ion secondary battery including the electrode for the power storage device of this embodiment is used under conditions where the electrolyte is likely to decompose, for example, at high temperatures, the peeling of the conductive layer from the resin layer can be suppressed, and a decrease in battery characteristics due to deterioration of the current collector can be suppressed.

[0050] (Fourth Embodiment) Embodiments of a lithium-ion secondary battery will be described. Figure 5 is a schematic external view showing an example of a lithium-ion secondary battery, and Figure 6 is an exploded perspective view showing a cell removed from the lithium-ion secondary battery shown in Figure 5. Here, a lithium-ion secondary battery called a pouch type or laminate type is given as an example. The lithium-ion secondary battery shown is a single-layer type, but it may also 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.

[0051] The lithium-ion secondary battery 301 shown in Figure 5 comprises a cell 310, a pair of leads 311 connected to the cell 310, an outer casing 313 covering the cell 310, and an electrolyte 314.

[0052] As schematically shown in Figure 6, cell 310 includes an electrode 201 for the energy storage device, an electrode 201' for the energy storage device, and a separator 320 placed between them. In the illustrated example, cell 310 is a single-layer cell containing a pair of electrodes.

[0053] The same structure as that described in the third embodiment can be applied to each of the electrodes 201 and 201' for the energy storage device. In this example, one of the electrodes 201 and 201' for the energy storage device 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.

[0054] The separator 320 is an insulating porous material. For example, a single-layer or laminated film of polyolefin such as polyethylene or polypropylene, or a nonwoven fabric or porous film of at least one fiber selected from the group consisting of cellulose, polyester, polyacrylonitrile, polyimide, polyamide (e.g., aromatic polyamide), polyethylene, and polypropylene can be applied to the separator 320.

[0055] An electrolyte 314 is further arranged in the space inside the outer casing 313. The electrolyte 314 is a non-aqueous electrolyte containing lithium ions, and may be, for example, a non-aqueous electrolyte containing lithium ions. When a non-aqueous electrolyte is applied to the electrolyte 314, typically a sealing material (for example, a resin film such as polypropylene, not shown in Figure 5) is placed between the outer casing 313 and the lead 311 to prevent leakage of the non-aqueous electrolyte.

[0056] As the electrolyte 314, for example, a non-aqueous electrolyte containing a metal salt such as a lithium salt and an organic solvent can be used. Examples of lithium salts 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, LiBOB, etc. One of these lithium salts may be used alone, or two or more may be used in mixture form.

[0057] For example, cyclic carbonates and linear carbonates can be used as solvents for electrolyte 314. Examples of solvents for electrolyte 314 include ethylene carbonate, propylene carbonate, butylene carbonate, and dimethyl carbonate.

[0058] The lithium-ion secondary battery 301 can be manufactured, for example, by the following method. First, the electrodes 201 and 201' for the energy storage device are fabricated as described in the above embodiment. Then, the electrodes 201 and 201' for the energy storage device are held together with the active material layers facing each other via a separator 320, and these components are inserted into the space of the outer casing 313. The electrolyte 314 is placed in the space of the outer casing 313, and the outer casing 313 is sealed to complete the lithium-ion secondary battery 301.

[0059] According to the lithium-ion secondary battery 301, the adhesion between the resin layer and the conductive layer of the current collector is improved. As a result, even when the lithium-ion secondary battery is used at high temperatures, the delamination of the conductive layer from the resin layer is further suppressed, and the deterioration of battery characteristics due to the degradation of the current collector is suppressed.

[0060] (Examples) Current collectors for the embodiment and reference example were fabricated, and their characteristics were evaluated.

[0061] [Sample preparation] The current collectors of Examples 1 to 15 and Reference Examples 1 to 8 were manufactured by the following method. Table 1 shows the conditions for forming the first metal layer of the current collectors of Reference Examples 1 to 8 and Examples 1 to 15.

[0062] Examples 1 to 15 A current collector 102 having the structure shown in Figure 3 was fabricated. A polyethylene terephthalate resin with a thickness of 6 μm was used for the resin layer 10. The first metal layer 20 and the second metal layer 20' were formed by vacuum deposition of Al. The thickness of the first metal layer 20 and the second metal layer 20' were adjusted by the deposition time. In order to produce samples with various crystalline states, the achievable vacuum and deposition rate during the formation of these metal layers were varied among the current collectors, as shown in Table 1. Table 1 shows the achievable true pressure and deposition rate when the first metal layer 20 of the current collectors of Examples 1 to 15 was formed. The classification of the achievable pressure and deposition rate shown in Table 1 is as shown in Tables 2 and 3.

[0063] Reference example 1~Reference example 8 The current collectors of Reference Examples 1 to 8 were manufactured using the same procedure as in Examples 1 to 15. Table 1 shows the achievable pressure and deposition rate when the first metal layer 20 of the current collectors of Reference Examples 1 to 8 was formed. The classification of achievable pressure and deposition rate shown in Table 1 is as shown in Tables 2 and 3.

[0064] [evaluation] (1) Thickness of the first metal layer The thickness d of the first metal layer 20 in Examples 1 to 15 and Reference Examples 1 to 8 was determined by SEM observation of the cross-section of each current collector.

[0065] (2) Measurement by X-ray diffraction The crystallinity of the first metal layer 20 in each current collector of Examples 1 to 15 and Reference Examples 1 to 8 was evaluated using X-ray diffraction.

[0066] The equipment and measurement conditions used for the measurement are as follows: Device name: PANalytical X'Pert PRO, manufactured by Malvern Panalytical Ltd. Acceleration voltage: 45kV Current: 40mA Scan speed: 7 degrees / min. Sampling width: 0.008 degrees. From the obtained X-ray diffraction charts, the peak intensity A for Al(111) and the peak intensity B for Al(200) were determined for each sample, and the value of r = B / A was calculated. Furthermore, √r / d 2 The value of was determined. In addition, the Lotgering factor of Al(111) was determined from the peak intensity A of Al(111).

[0067] (3) Surface resistance The surface resistance of the first metal layer 20 in each current collector of Examples 1 to 15 and Reference Examples 1 to 8 was measured using a four-terminal measuring device (Loresta AX MCP-T370, manufactured by Nitto Seiko Analytech Co., Ltd.). The volume resistivity of the first metal layer 20 for each sample was determined from the surface resistance value and thickness d of the first metal layer 20.

[0068] (4) Electrolyte resistance The current collectors of Examples 1 to 15 and Reference Examples 1 to 8 were kept in an environment similar to that of a lithium-ion secondary battery, and the presence or absence of delamination of the conductive layer was evaluated. Specifically, a non-aqueous electrolyte of dimethyl curbonate containing 1 mol% LiPF6 was prepared, and water was added to the non-aqueous electrolyte at a rate of 1000 ppm by mass before being placed in a container. The prepared current collectors were immersed in the non-aqueous electrolyte in the container, the entire assembly was sealed with a laminate film, and stored in a constant temperature bath at 85°C for 72 hours (high-temperature storage). After that, the current collectors were removed from the laminate film and washed with an organic solvent.

[0069] The electrolyte resistance of the current collectors obtained after high-temperature storage was evaluated. The electrolyte resistance was evaluated using the following method: 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 off from the resin layer, and the result was judged as poor (POOR). If no peeling of the conductive layer was observed due to friction with a cotton swab, the result was judged as good (GOOD).

[0070] Table 1 shows the evaluation results.

[0071] [Table 1]

[0072] [Table 2] [Table 3]

[0073] [Results and Discussion] As shown in Table 1, in the current collectors of Examples 1 to 15 and Reference Examples 1 to 8, d, r, √r / d 2 The ranges are 0.33≦d≦2.00, 0.01≦r≦21.4, and 0.03≦√r / d 2 The result was ≤2.1. This is when r and d satisfy the relationship in equation (1), i.e., √r / d 2If the value of is 2.1 or less, the electrolyte resistance is good for all current collectors of the samples, except for Reference Example 2. On the other hand, √r / d 2 If the value is greater than 2.1, the electrolyte resistance is poor. The reason why the current collector in Reference Example 2 has poor electrolyte resistance is thought to be because the thickness d of the first metal layer 20 is less than 0.5 μm.

[0074] In Examples 1 to 15, the volume resistivity of the first metal layer 20 is in the range of 3.6 to 5.2 μΩ·cm, while when r and d satisfy the relationship in equation (2), i.e., √r / d 2 When the value of is 1 or less, the volume resistivity of the first metal layer 20 is in the range of 3.6 to 4.52 μΩ·cm, indicating that a first metal layer 20 with lower resistance can be obtained.

[0075] In samples where the Lotgering factor for Al(111) is negative, the intensity of the Al(200) peak B is greater than the intensity of the Al(111) peak A, except for Example 11. Furthermore, it is considered that there is a trade-off relationship between the Al(111) peak intensity A and the Al(200) peak intensity B. Figure 7 shows the diffraction angle (2θ) range of 43° to 48° in the X-ray diffraction charts obtained from samples of Examples 2, 5, and 7, in which the Al(200) peak is observed. The Al(111) peak intensity A decreases in the order of Example 2, Example 7, and Example 5, while the Al(200) peak intensity B increases in the order of Example 2, Example 7, and Example 5. In Example 2, no Al(200) peak is observed in the range from 43° to 48°, and the intensity of the Al(200) peak is about the same as the baseline intensity of the X-ray diffraction chart. In other words, in the data for Example 2, the peak intensity B can be said to be virtually zero.

[0076] Comparing the results of the current collectors from Examples 5 and 6, and from Examples 11 and 12, where the thickness of the first metal layer 20 is approximately the same, the sample in which the peak intensity A of Al(111) is greater than the peak intensity B of Al(200) has a smaller volume resistivity. This is thought to be because the increased orientation of Al(111) reduces voids in the first metal layer 20, increasing density and thus reducing volume resistivity. It is also thought that a larger peak intensity B of Al(200), i.e., increased orientation of Al(200), reduces voids in the first metal layer 20. However, according to the examples, the peak intensity A of Al(111) tends to be larger than that of Al(200), meaning that it is easier to obtain an Al film with high crystalline (111) orientation and thus easier to reduce the volume resistivity of the first metal layer 20. According to the examples, if the Rotgering factor of Al(111) is 0.8 or higher, the volume resistivity of the first metal layer 20 can be reduced to 4 μΩ·cm or less, and it is considered that a current collector with lower resistance can be realized.

[0077] When forming the first metal layer 20 by vacuum deposition, the lower the target pressure, the more likely the first metal layer 20 is to be oriented in the (111) plane. From these examples and reference examples, it was found that the current collector of this embodiment has excellent electrolyte resistance by satisfying the relationship in equation (1). [Industrial applicability]

[0078] The electrodes for energy storage devices according to the embodiments of this disclosure are useful as power sources for various electronic devices, electric motors, etc. The energy storage devices according to the embodiments of this disclosure can be applied, for example, to power sources for vehicles such as bicycles and passenger cars, power sources for communication devices such as smartphones, power sources for various sensors, and power sources for unmanned eXtended vehicles (UxV). [Explanation of Symbols]

[0079] 10 resin layer 10a 1st page 10b 2nd side 20 1st metal layer 20' second metal layer 101, 102, 210 Current collectors 201, 201' Electrodes for energy storage devices 210 Current collector 210s Part 1 210t 2nd part 220 Active material layer 301 Lithium-ion rechargeable battery 310 cells 311 Reed 313 Exterior 314 Electrolyte 320 Separator

Claims

1. A resin layer having a first surface and a second surface located opposite to the first surface, The first metal layer located on the first surface and Equipped with, The first metal layer contains aluminum as its main component, The thickness d of the first metal layer is 0.5 μm or more and 3 μm or less. In the measurement of the first metal layer by X-ray diffraction, when the ratio of the peak intensities B / A between the intensity A of the highest X-ray diffraction peak in the diffraction angle (2θ) range of 36° to 41° and the intensity B of the highest X-ray diffraction peak in the diffraction angle (2θ) range of 43° to 48° is denoted as r, then d and r are given by the following equation (1): [Math 1] Satisfying the conditions, A current collector in which the aforementioned r is 1.3 or more and 21.4 or less.

2. The above d is 0.7 μm or more and 2 μm or less. The above d and the above r are given by the following equation (2) [Math 2] A current collector according to claim 1, satisfying the requirements.

3. The highest X-ray diffraction peak in the diffraction angle (2θ) range of 36° to 41° is the peak of the (111) plane of aluminum. The current collector according to claim 1 or 2, wherein the orientation index of the (111) plane of aluminum in the first metal layer by the Rotgering method with respect to the direction perpendicular to the first surface of the resin layer is 0.8 or more.

4. The current collector according to any one of claims 1 to 3, wherein the intensity B of the highest X-ray diffraction peak in the range of diffraction angle (2θ) of 43° to 48° is approximately the same as the baseline intensity measured by the X-ray diffraction method.

5. The second surface further comprises a second metal layer located on the second surface, The second metal layer contains aluminum as its main component, The thickness d' of the second metal layer is 0.5 μm or more and 3 μm or less. In the X-ray diffraction measurement of the second metal layer, when r' is the ratio B' / A' of the peak intensities of the highest X-ray diffraction peak A' in the diffraction angle (2θ) range of 36° to 41° and the highest X-ray diffraction peak B' in the diffraction angle (2θ) range of 43° to 48°, d' and r' are given by the following equation (4): [Math 3] A current collector according to any one of claims 1 to 4, which satisfies the requirements.

6. The current collector according to any one of claims 1 to 5, wherein the resin layer comprises at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polyamide, polyimide, polyethylene, polystyrene, phenolic resin, and epoxy resin.

7. A current collector according to any one of claims 1 to 4, The active material layer located on the first metal layer of the current collector, An electrode for an energy storage device, comprising the above features.

8. The current collector according to claim 5, The first active material layer located on the first metal layer of the current collector, A second active material layer located on the second metal layer of the current collector, An electrode for an energy storage device, comprising the above features.

9. A positive electrode including an electrode for an energy storage device according to claim 7 or 8, A negative electrode including a negative electrode active material layer and a negative electrode current collector, A separator is placed between the negative electrode and the positive electrode, Non-aqueous electrolytes containing lithium ions and A lithium-ion secondary battery equipped with these features.

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