Current collector, electrode for energy storage device, lithium-ion secondary battery, and method for manufacturing a current collector

Abstract

To provide a current collector having excellent resistance to a non-aqueous electrolyte, an electrode for a power storage device, a lithium ion secondary battery, and a method for manufacturing such a current collector.SOLUTION: A current collector includes a resin layer, a conductive layer, and an intermediate layer positioned between the resin layer and the conductive layer, the conductive layer includes Al or Cu as a main component, and the intermediate layer includes Mo as the main component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a current collector, an electrode for an energy storage device, a lithium-ion secondary battery, and a method for manufacturing a current collector. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-102429 [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 high resistance to the non-aqueous electrolyte. One embodiment of the present disclosure provides a current collector with excellent resistance to a non-aqueous electrolyte, an electrode for an energy storage device, a lithium-ion secondary battery, and a method for manufacturing such a current collector. [Means for solving the problem]

[0005] A current collector according to one embodiment of the present disclosure comprises a resin layer, a conductive layer, and an intermediate layer located between the resin layer and the conductive layer, wherein the conductive layer mainly contains Al or Cu, and the intermediate layer mainly contains Mo.

[0006] Furthermore, a method for manufacturing a current collector according to one embodiment of the present disclosure comprises the steps of: preparing a resin layer; forming an intermediate layer mainly composed of Mo on the resin layer; and forming a conductive layer mainly composed of Al or Cu on the intermediate layer. [Effects of the Invention]

[0007] 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]

[0008] [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 a schematic profile illustrating the distribution of constituent elements in the thickness direction of the cross-section of an intermediate layer when the intermediate layer contains molybdenum oxide. [Figure 3] Figure 3 is a flowchart showing the method for manufacturing a current collector according to the first embodiment. [Figure 4] Figure 4 is a schematic cross-sectional view showing an example of a current collector according to the second embodiment. [Figure 5] Figure 5 shows an example of a schematic profile illustrating the distribution of constituent elements in the thickness direction of the cross-section of the intermediate layer. [Figure 6] Figure 6 is a schematic cross-sectional view showing another example of the current collector of the second embodiment. [Figure 7] Figure 7 is a schematic exploded perspective view showing an example of an electrode for a third embodiment of an energy storage device. [Figure 8] Figure 8 is a schematic partial cross-sectional perspective view showing an example of a lithium-ion secondary battery according to the fourth embodiment. [Figure 9] Figure 9 is a schematic exploded perspective view showing an example of a lithium-ion secondary battery cell as shown in Figure 8. [Modes for carrying out the invention]

[0009] Current collectors with a conductive layer formed on a resin film differ from conventional metal foils used as current collectors in terms of structure and thickness. In particular, the conductive layer is supported by a resin film and is thinner than the metal foil used in conventional current collectors, which distinguishes them from conventional current collectors.

[0010] Lithium-ion secondary batteries generally contain a non-aqueous electrolyte containing an anion with a fluorine atom as the electrolyte. When the current collector described above is used in a lithium-ion secondary battery, it 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 with a fluorine atom decomposes, and fluorine ions, i.e., hydrofluoric acid, are produced as decomposition products. The inventors of this application have conceived of a current collector, an electrode for an energy storage device, and a lithium-ion secondary battery that can suppress the deterioration of the current collector and maintain its charge-discharge characteristics by suppressing the deterioration of the current collector, specifically by suppressing the peeling of the conductive layer from the resin film, due to the decomposition products of the non-aqueous electrolyte.

[0011] Embodiments of the current collector, electrode for energy storage device, and lithium-ion secondary battery of this disclosure will be described below with reference to the drawings. The numerical values, shapes, materials, steps, and the order of those steps presented in the following description are merely examples, and various modifications are possible as long as they do not create a technical inconsistency. Furthermore, each embodiment described below is merely illustrative, and various combinations are possible as long as they do not create a technical inconsistency.

[0012] 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°.

[0013] 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 encompassing various forms such as battery modules and battery packs having one or more "cells" electrically connected to each other.

[0014] (First Embodiment) FIG. 1 is a schematic cross-sectional view showing an example of the 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 includes a resin layer 10, a conductive layer 20, and an intermediate layer 30 located between the resin layer 10 and the conductive layer 20.

[0015] The resin layer 10 functions as a support for the conductive layer 20 in the current collector 101. Also, since the resin layer 10 has a lower density than the conductive layer 20, it can contribute to increasing the charge capacity per unit weight when a power storage device is configured.

[0016] The resin layer 10 is electrically insulating and contains resin. The resin layer 10 may also be thermoplastic. Specifically, the resin layer 10 may contain at least one selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), polyimide (PI), polyethylene (PE), polystyrene (PS), phenolic resin (PF), and epoxy resin (EP). The resin layer 10 may be a single layer or may be 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.

[0017] 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 the overall thickness of the current collector 101 to be reduced. Therefore, when a stacked lithium-ion secondary battery is constructed by stacking multiple electrode pairs, the proportion occupied by the current collector, which does not contribute to energy storage, can be reduced, and the energy density can be increased. If the thickness of the resin layer 10 is 6 μm or less, the overall thickness of the current collector 101 can be reduced even further, and the energy density of the stacked lithium-ion secondary battery can be increased.

[0018] The current collector 101 may further include an undercoat layer located between the resin layer 10 and the intermediate layer 30. The undercoat layer may be provided to increase the bonding strength between the resin layer 10 and the intermediate layer 30, or to suppress the formation of pinholes in the intermediate layer 30. For example, the undercoat layer may be a layer formed from an organic material such as acrylic resin or polyolefin, or a metal-containing layer formed by sputtering.

[0019] The intermediate layer 30 has the function of improving the adhesion between the resin layer 10 and the conductive layer 20 in a non-aqueous electrolyte and suppressing the delamination of the conductive layer 20 from the resin layer 10. The intermediate layer 30 mainly contains Mo. Here, the main component refers to the element that has the highest content when the member contains one or more constituent elements, expressed as a mole percentage. However, if oxygen (O) has the highest content, oxygen is excluded and the next most abundant element is referred to. The content ratio of the constituent elements can be determined, for example, by performing line analysis of the constituent elements on a cross-section parallel to the thickness direction of the intermediate layer 30 using a scanning transmission electron microscope (STEM). Preferably, the intermediate layer 30 contains only Mo as a metallic element, excluding unavoidable impurity elements.

[0020] Although the detailed reasons are not clear, the inclusion of Mo in the intermediate layer 30 suppresses the delamination of the conductive layer 20 from the resin layer 10 when the current collector is held in a non-aqueous electrolyte. In particular, even when fluoride ions, which are thought to be generated when lithium-ion secondary batteries are charged and discharged at high temperatures, are present in the non-aqueous electrolyte, the delamination of the conductive layer 20 from the resin layer 10 is suppressed.

[0021] In the intermediate layer 30, the Mo contained as the main component may be oxidized. In other words, the intermediate layer 30 may contain molybdenum oxide. Because molybdenum oxide is polar, the inclusion of molybdenum oxide in the intermediate layer 30 strengthens the interaction between the intermediate layer 30 and the resin layer 10, which is prone to polarity due to its molecular structure, at the interface between the intermediate layer 30 and the resin layer 10, thereby improving adhesion. The oxidation state of Mo in the molybdenum oxide may be +4, +6, or other oxidation states. It may also contain Mo with different oxidation states. Furthermore, the intermediate layer 30 may be a single layer of molybdenum oxide, consisting entirely of molybdenum oxide.

[0022] For the reasons stated above, when the intermediate layer 30 contains molybdenum oxide, it is preferable that the molybdenum oxide is more abundant on the resin layer 10 side in the thickness direction of the intermediate layer 30. More preferably, the molybdenum oxide is located on the lower surface 30b of the intermediate layer 30 that is in contact with the resin layer 10.

[0023] Figure 2 is an example of a schematic profile showing the distribution of constituent elements in the thickness direction of the cross-section of the intermediate layer 30 when the intermediate layer 30 contains molybdenum oxide. In Figure 2, the horizontal axis represents distance, and the origin is located at the interface between the intermediate layer 30 and the conductive layer 20, i.e., the upper surface 30a of the intermediate layer 30. The vertical axis in Figure 2 represents the amount of constituent elements. Such a distribution of constituent elements in the thickness direction of the cross-section of the intermediate layer 30 can be obtained, for example, by energy-dispersive X-ray spectroscopy (STEM-EDX) using a scanning transmission electron microscope. In this case, the vertical axis represents the X-ray count or intensity.

[0024] As shown in Figure 2, when the intermediate layer 30 contains molybdenum oxide, for example, in the profile of the constituent elements in the thickness direction of the cross-section of the intermediate layer 30, the O peak position P1 is located closer to the resin layer 10 than the Mo peak position P2. Having such a profile allows for improved adhesion between the intermediate layer 30 and the resin layer 10 on the lower surface 30b, as described above. On the other hand, on the conductive layer 20 side of the intermediate layer 30, the high concentration of Mo enhances the metallic properties of the intermediate layer 30 on the conductive layer 20 side, improving its adhesion to the conductive layer 20.

[0025] The distribution profile of the constituent elements shown in Figure 2 is just one example, and O and Mo may be distributed in other profiles. For example, in the intermediate layer 30, the concentration or abundance of O (counts or intensity in the STEM-EDX profile) may increase stepwise or continuously from the upper surface 30a to the lower surface 30b. In this case, the concentration or abundance of Mo may decrease stepwise or continuously from the upper surface 30a to the lower surface 30b. Even if the intermediate layer 30 has such a profile, the adhesion between the upper surface 30a and the conductive layer 20 and the adhesion between the lower surface 30b and the resin layer 10 can be improved.

[0026] Furthermore, if the conductive layer 20 is formed in a different deposition apparatus than the one used to form the intermediate layer 30 after the intermediate layer 30 has been formed, the surface of the intermediate layer 30 may be exposed to the atmosphere before the conductive layer 20 is formed. In this case, the upper surface 30a of the intermediate layer 30 may be oxidized by oxygen in the atmosphere. Even in this case, it is preferable that the molybdenum oxide is more abundant on the resin layer 10 side in the thickness direction of the intermediate layer 30.

[0027] The thickness d2 of the intermediate layer 30 is, for example, 1 nm or more and less than 200 nm. If the thickness d2 of the intermediate layer 30 is 1 nm or more, a continuous film can be formed, and adhesion can be improved throughout the entire region between the conductive layer 20 and the resin layer 10. By having a thickness d2 of the intermediate layer 30 of less than 200 nm, the time required to form the intermediate layer 30 does not become too long, and the damage caused by the conditions during the formation of the intermediate layer 30, such as the influence of heat or plasma on the resin layer 10, is reduced, thereby suppressing the degradation of the resin layer 10.

[0028] Damage to the resin layer 10 caused by heat or plasma includes, for example, wrinkles that form on the surface of the resin layer 10. When such wrinkles form on the resin layer 10, the unevenness of the wrinkles is reflected in the intermediate layer 30 and the conductive layer 20. As a result, when forming the active material layer on the conductive layer 20 by coating, the thickness of the active material layer becomes uneven. In other words, by having a thickness d2 of the intermediate layer 30 of less than 200 nm, the formation of wrinkles in the intermediate layer 30 is suppressed, making it easier to form an active material layer of uniform thickness on the current collector.

[0029] The thickness d2 of the intermediate layer 30 may be between 6 nm and 100 nm. If the thickness d2 of the intermediate layer 30 is 6 nm or more, the adhesion between the conductive layer 20 and the resin layer 10 can be more reliably improved. Also, if the thickness d2 of the intermediate layer 30 is 100 nm or less, the damage to the intermediate layer 30 described above can be further suppressed.

[0030] The intermediate layer 30 may contain other metals as long as it contains Mo as its main component. The intermediate layer 30 can be formed using known thin-film formation techniques used in the manufacture of semiconductor devices, such as vacuum deposition and sputtering.

[0031] The conductive layer 20 is the main current path in the current collector 101 and facilitates the exchange of electrons between the positive electrode active material or negative electrode active material and terminals connected to the current collector. The conductive layer 20 mainly contains metal as its component.

[0032] The conductive layer 20 mainly contains Al or Cu. It may also contain other metals as long as it mainly contains Al or Cu. For example, the conductive layer 20 may mainly contain Cu and also contain Ni. When the current collector 101 is used as the positive electrode, the conductive layer 20 may contain Al. When the current collector 101 is used as the negative electrode, the conductive layer 20 may contain Cu or a Ni-Cu alloy.

[0033] The thickness d1 of the conductive layer 20 is, for example, 0.3 μm or more and 3 μm or less. By making the thickness d1 of the conductive layer 20 0.3 μm or more, the resistance of the conductive layer 20 can be reduced. For example, when fabricating an energy storage device, energy loss due to resistance in the current collector can be reduced. Also, by making the thickness of the conductive layer 20 3 μm or less, the relative ratio of the conductive layer 20 to the resin layer 10 becomes smaller, making it easier to obtain the advantage of reducing the weight of the current collector by using the resin layer 10. The thickness of the conductive layer 20 may also be 0.5 μm or more and 1.2 μm or less.

[0034] If the conductive layer 20 is relatively thick, it may include, for example, a seed layer 21 and a main layer 22. The seed layer 21 and the main layer 22 each have metal as their main component and may be made of the same metal.

[0035] The seed layer 21 is formed, for example, by sputtering or vacuum deposition, and the main layer 22 is formed by plating. This avoids the increased formation time and reduced productivity that would result from forming the entire conductive layer 20 by sputtering or vacuum deposition, and also avoids the increased damage to the resin layer 10 during the formation of the conductive layer 20. When the conductive layer 20 includes a seed layer 21 and a main layer 22, it is preferable that the combined thickness of the seed layer 21 and the main layer 22 satisfies the above-mentioned preferred conductive layer thickness d1.

[0036] On the other hand, if the conductive layer 20 is relatively thin, the entire layer may be a single layer film formed by the same method. For example, the entire conductive layer 20 may be formed by sputtering or vacuum deposition. Alternatively, the intermediate layer 30 may be used as a base layer for plating, and the entire conductive layer 20 may be formed by plating.

[0037] As described above, in the current collector of this embodiment, the placement of an intermediate layer 30 mainly composed of Mo between the resin layer 10 and the conductive layer 20 enhances the adhesion between the conductive layer 20 and the resin layer 10. Therefore, even when fluoride ions, which are thought to be generated when lithium-ion secondary batteries are charged and discharged at high temperatures, are present in the non-aqueous electrolyte, the delamination of the conductive layer 20 from the resin layer 10 in the current collector is suppressed.

[0038] Next, the manufacturing method of the current collector according to this embodiment will be described. Figure 3 is a flowchart showing the manufacturing method of the current collector according to this embodiment. The manufacturing method of the current collector according to this embodiment includes a step S1 of preparing a resin layer, a step S2 of forming an intermediate layer, and a step S3 of forming a conductive layer. Each step will be described in detail below.

[0039] (1) Step S1 of preparing the resin layer First, a resin layer 10 is prepared, consisting of the materials described above and having the thickness described above. The resin layer 10 may, for example, be sized to correspond to a current collector 101 used in a single lithium-ion secondary battery, or it may be a resin roll in which a sheet-like resin layer, long in one direction, is wound into a roll. If the current collector is to be manufactured using the resin roll without cutting it, manufacturing equipment capable of manufacturing using a roll-to-roll method is provided.

[0040] (2) Step S2 to form the intermediate layer An intermediate layer 30 is formed by sputtering. A target containing Mo is prepared, and the intermediate layer 30 is formed on the resin layer 10 using a sputtering apparatus. The thickness of the intermediate layer 30 can be adjusted by the deposition rate and deposition time. To form an intermediate layer 30 that is substantially free of molybdenum oxide, for example, a Mo target of 3N or higher is used, and the intermediate layer 30 is formed in an argon atmosphere.

[0041] When forming the intermediate layer 30 containing molybdenum oxide, sputtering may be performed using a target containing molybdenum oxide, or sputtering may be performed using a Mo target in an atmosphere containing oxygen gas. Furthermore, the oxygen (O) content in the thickness direction of the intermediate layer 30 can be changed by changing the oxygen gas concentration in the atmosphere during the formation of the intermediate layer 30. For example, by starting sputtering in an atmosphere containing oxygen gas at a first concentration and gradually or continuously decreasing the oxygen gas concentration from the first concentration, an intermediate layer can be formed in which the O content is high on the resin layer 10 side and low on the conductive layer 20 side.

[0042] (3) Step S3 to form a conductive layer A conductive layer 20 is formed on the intermediate layer 30. For example, a conductive layer 20 containing Cu as the main component is formed. First, a seed layer 21 is formed on the intermediate layer 30 by, for example, a sputtering method. Subsequently, a main layer 22 is formed on the seed layer 21 by electroplating with the seed layer 21 as the cathode. This makes it possible to form a conductive layer 20 including the seed layer 21 and the main layer 22.

[0043] When forming a conductive layer 20 mainly composed of Al, the conductive layer 20 containing only the main layer 22 may be formed by sputtering or vacuum deposition.

[0044] (Second embodiment) Figure 4 is a schematic cross-sectional view showing an example of a current collector of this embodiment. The current collector 102 of this embodiment comprises a resin layer 10, a conductive layer 20, and an intermediate layer 33, and differs from the current collector 101 of the first embodiment in that the intermediate layer 33 has a first sub-intermediate layer 31 and a second sub-intermediate layer 32. As shown in Figure 4, the first sub-intermediate layer 31 is closer to the resin layer 10 than the second sub-intermediate layer 32, and the second sub-intermediate layer 32 is closer to the conductive layer 20 than the first sub-intermediate layer 31.

[0045] The first sub-intermediate layer 31 and the second sub-intermediate layer 32 are made of the same material as the intermediate layer 30 described in the first embodiment. However, the oxygen content in the first sub-intermediate layer 31 is greater than the oxygen content in the second sub-intermediate layer 32. When comparing the oxygen content in the first sub-intermediate layer 31 and the second sub-intermediate layer 32, the average value of the oxygen content in the thickness direction in each layer is used.

[0046] Figure 5 is an example of a schematic profile showing the distribution of constituent elements in the thickness direction of the cross-section of the intermediate layer 33. Similar to the first embodiment, in Figure 5, the horizontal axis represents distance, and the origin is located at the interface between the intermediate layer 33 and the conductive layer 20. The vertical axis represents the amount of constituent elements. Even in the profile of constituent elements obtained by STEM-EDX line analysis, the X-ray count or intensity shows a similar change with distance.

[0047] As shown in Fig. 5, in the profile of the constituent elements in the thickness direction of the cross-section of the intermediate layer 33, the O peak position P3 is located closer to the resin layer 10 side than the Mo peak position P4. Preferably, the O peak position P3 is located within the first sub-intermediate layer 31, and the Mo peak position P4 is located within the second sub-intermediate layer 32. By having such a profile, the adhesion between the lower surface 33b of the intermediate layer 33, that is, the first sub-intermediate layer 31 and the resin layer 10, can be further enhanced. On the other hand, the adhesion between the upper surface 33a of the intermediate layer 33, that is, the second sub-intermediate layer 32 and the conductive layer 20, is improved.

[0048] The thickness d3 of the first sub-intermediate layer 31 is, for example, 1 nm or more and 100 nm or less. Also, the thickness d4 of the second sub-intermediate layer 32 is, for example, 1 nm or more and 100 nm or less. The total thickness of the thickness d3 of the first sub-intermediate layer 31 and the thickness d4 of the second sub-intermediate layer 32 is preferably less than 200 nm. Since the thicknesses d3 and d4 of the first sub-intermediate layer 31 and the second sub-intermediate layer 32 are each 1 nm or more, it becomes easier for each layer to be formed as a continuous film. For this reason, the effect of improving the adhesion between the resin layer 10 and the first sub-intermediate layer 31 and between the conductive layer 20 and the second sub-intermediate layer 32 can be easily obtained. Also, since the thicknesses d3 and d4 of the first sub-intermediate layer 31 and the second sub-intermediate layer 32 are each 100 nm or less, damage to the resin layer 10 due to heat or the like can be further suppressed. The thickness d4 of the second sub-intermediate layer 32 is preferably greater than the thickness d3 of the first sub-intermediate layer 31 (d3 < d4). By making the second sub-intermediate layer 32, which has higher metallic properties, thicker than the first sub-intermediate layer 31, the strength of the entire intermediate layer 33 can be increased.

[0049] The current collector 102 can also be manufactured by the same method as the current collector 101 of the first embodiment. When manufacturing the current collector 102, an intermediate layer 33 is formed instead of the intermediate layer 30. That is, in the step S2 described above for forming the intermediate layer, a first sub-intermediate layer 31 and a second sub-intermediate layer 32 are formed. For example, using a Mo target, the first sub-intermediate layer 31 is formed in an atmosphere containing oxygen at a first concentration, and the second sub-intermediate layer 32 is formed in an atmosphere containing oxygen at a second concentration lower than the first concentration. As a result, an intermediate layer 33 is formed that includes the first sub-intermediate layer 31 and the second sub-intermediate layer 32.

[0050] According to the current collector 101 of this embodiment, the adhesion between the conductive layer 20 and the resin layer 10 is enhanced by arranging an intermediate layer 33 mainly composed of Mo between the resin layer 10 and the conductive layer 20. In particular, by including a first sub-intermediate layer 31 and a second sub-intermediate layer 32 in the intermediate layer 33, the adhesion between the intermediate layer 33 and the resin layer 10, and between the intermediate layer 33 and the conductive layer 20 can be further improved. Therefore, even when fluoride ions, which are thought to be generated when a lithium-ion secondary battery is charged and discharged at high temperatures, are present in the non-aqueous electrolyte, the delamination of the conductive layer 20 from the resin layer 10 in the current collector is further suppressed.

[0051] In addition, while the current collector 101 described with reference to Figure 1 and the current collector 102 described with reference to Figure 4 had a conductive layer 20 on only one side of the resin layer 10, the conductive layer 20 may be provided on both sides. For example, Figure 6 shows a current collector 103 having conductive layers on both sides of the resin layer. The current collector 103 has a resin layer 10 having a first surface 10a and a second surface 10b located on the opposite side of the first surface 10a. The first surface 10a of the resin layer 10 has the same structure as the current collector 102 described above.

[0052] On the other hand, a structure similar to that of the current collector 102 is formed on the second surface 10b of the resin layer 10. Specifically, the current collector 103 further comprises a conductive layer 20' and an intermediate layer 33' including a first sub-intermediate layer 31' and a second sub-intermediate layer 32'. The first sub-intermediate layer 31' is located between the resin layer 10 and the second sub-intermediate layer 32'. The second sub-intermediate layer 32' is located between the first sub-intermediate layer 31' and the conductive layer 20'. The materials and thicknesses constituting the conductive layer 20', the first sub-intermediate layer 31', and the second sub-intermediate layer 32', as well as the functions of these layers, are the same as those of the corresponding conductive layer 20, the first sub-intermediate layer 31, and the second sub-intermediate layer 32. From the viewpoint of stress, the materials and thicknesses constituting the first sub-intermediate layer 31' and the second sub-intermediate layer 32' may be the same as those constituting the corresponding first sub-intermediate layer 31 and the second sub-intermediate layer 32. The material constituting the conductive layer 20' is the same as the material constituting the corresponding conductive layer 20. From a stress standpoint, the thickness of the conductive layer 20' may be the same as the thickness of the conductive layer 20.

[0053] According to the current collector 103, conductive layers 20 and 20' are provided on both sides of the resin layer 10, allowing electrodes to be formed on both sides. Therefore, the proportion of the resin layer in the energy storage device can be reduced, thereby increasing the battery capacity per unit area.

[0054] (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 both the positive and negative electrodes of an energy storage device. Figure 7 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 second portion 210t does not have an active material layer 220 and functions as a tab for electrical connection to the outside. The active material layer 220 contains an active material that is oxidized and reduced during 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.

[0055] The current collector 210 is any one of the current collectors 101, 102, and 103 described in the first embodiment or the second embodiment. When using the current collector 103, other active material layers not shown in FIG. 7 are disposed in the first portion 210s on the back side of the current collector 210 (the side where the active material layer 220 is not disposed).

[0056] The active material layer 220 contains a positive electrode active material or a negative electrode active material that occludes and releases lithium ions. The positive electrode active material includes, for example, a composite metal oxide containing lithium. Examples of the composite metal oxide containing lithium include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMnO2), lithium manganese spinel (LiMn2O4), lithium vanadium compound (LiV2O5), olivine-type LiMPO4 (where M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr or vanadium oxide), lithium titanate (Li4Ti5O 12 ), general formula: LiNi x Co y Mn z M a O2 (x + y + z + a = 1, 0 ≦ x < 1, 0 ≦ y < 1, 0 ≦ z < 1, 0 ≦ a < 1, M in the above general formula is one or more elements selected from the group consisting of Al, Mg, Nb, Ti, Cu, Zn, Cr), and a composite metal oxide represented by the general formula: LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1), etc. can be mentioned. The positive electrode active material may contain polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc. as a material capable of occluding and releasing lithium ions.

[0057] 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. As the binder in the active material layer 220 used in 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.

[0058] 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 a binder to the active material layer 220 used as the positive electrode.

[0059] 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 used in the positive electrode include metal powders such as nickel, stainless steel, and iron, and conductive oxide powders such as ITO. Two or more of the above materials may be mixed and included in the active material layer 220.

[0060] The negative electrode active material contains a carbon material. Examples of the carbon material include, for example, natural or artificial graphite, carbon nanotubes, non-graphitizable carbon, graphitizable carbon (soft carbon), low-temperature calcined carbon, and the like. The negative electrode active material may contain materials other than the carbon material. For example, alkali metals and alkaline earth metals such as metallic lithium, metals such as tin or silicon that can form compounds with metals such as lithium, silicon-carbon composites, amorphous compounds mainly composed of oxides (SiO x (0 < x < 2), tin dioxide, etc.), and may contain particles such as lithium titanate (Li4Ti5O 12 ).

[0061] For the binder and conductive assistant of the active material layer 220 used for the negative electrode, the above-mentioned binder and conductive assistant can be used in the same manner. Also, as the binder for the negative electrode, cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide, polyamideimide, acrylic resin, etc. may be used.

[0062] The electrodes for the power storage device for the positive electrode and the negative electrode can be manufactured by known manufacturing methods.

[0063] 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, in a lithium-ion secondary battery including the electrode for the power storage device of this embodiment, even when the lithium-ion secondary battery is used under conditions where the electrolyte is likely to decompose, for example, at high temperature, the peeling of the conductive layer from the resin layer is more suppressed, and the deterioration of the current collector due to the deterioration of the current collector is suppressed.

[0064] (Fourth Embodiment) An embodiment of a lithium-ion secondary battery will be described.

[0065] Figure 8 is a schematic external view showing an example of a lithium-ion secondary battery 301, and Figure 9 is an exploded perspective view showing a cell removed from the lithium-ion secondary battery shown in Figure 8. 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 example shown, the positive electrode, separator, and negative electrode that constitute the cell are stacked along the Z direction in the figure.

[0066] The lithium-ion secondary battery 301 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.

[0067] Cell 310 includes an electrode 201 for the energy storage device, an electrode 201' for the energy storage device, and a separator 320 positioned between them. In the illustrated example, cell 310 is a single-layer cell containing a pair of electrodes.

[0068] The electrode 201 for the energy storage device and the electrode 201' for the energy storage device are the same as the electrode 201 for the energy storage device described in the third embodiment, with one being configured as a positive electrode containing a positive electrode active material and the other as a negative electrode containing a negative electrode active material.

[0069] 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 used.

[0070] 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, 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 8) is placed between the outer casing 313 and the lead 311 to prevent leakage of the non-aqueous electrolyte.

[0071] 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 mixed.

[0072] For the solvent of electrolyte 314, for example, cyclic carbonates and linear carbonates can be used. Specifically, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, and the like can be used.

[0073] 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 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.

[0074] 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.

[0075] (Examples) Current collectors for the embodiment and reference example were fabricated and their characteristics were evaluated.

[0076] [Sample preparation] The current collectors for Examples 1 to 36 and Reference Examples 1 to 4 were manufactured by the following method.

[0077] Examples 1 to 26 In a current collector 103 having the structure shown in Figure 6, a current collector was fabricated in which the intermediate layer 33 and intermediate layer 33' were single layers. A polyethylene terephthalate resin with a thickness of 6 μm was used for the resin layer 10. Intermediate layers were formed on both sides of the resin layer by sputtering using the materials shown in Table 1 as targets. A molybdenum oxide target with an oxygen (O) content of 70 atomic percent was used. The thickness of the intermediate layer was adjusted according to the deposition time and power output as shown in Table 1. The intermediate layer thicknesses shown in Table 1 indicate the thickness of the intermediate layer formed on one side.

[0078] The Al conductive layers 20 and 20' were formed on the intermediate layer of each face of the resin layer 10 by vacuum deposition. The Cu conductive layers 20 and 20' were formed in two parts: seed layers 21 and 21' and main layers 22 and 22'. After forming the 50 nm thick seed layer 21 on the intermediate layer of each face of the resin layer 10 by sputtering, the main layers 22 and 22' were formed simultaneously by electroplating. The thickness of the main layers 22 and 22' was adjusted by the plating time and current density during electroplating so that the sum of the thicknesses of the seed layers 21 and 21' and the main layers 22 and 22' equals the value in Table 1. The conductive layer thicknesses shown in Table 1 represent the thickness of the conductive layer formed on one side.

[0079] Reference example 1~Reference example 4 The current collector in Reference Example 1 was manufactured using the same procedure as in Example 1, except that Ni was used as the intermediate layer. The current collector in Reference Example 3 was manufactured using the same procedure as in Example 14, except that Ni was used as the intermediate layer. The Ni intermediate layer was formed by sputtering. The current collector in Reference Example 2 was manufactured using the same procedure as in Example 1, except that an intermediate layer was not formed. The current collector in Reference Example 4 was manufactured using the same procedure as in Example 14, except that an intermediate layer was not formed.

[0080] Examples 27-36 A current collector 103 having the structure shown in Figure 6 was fabricated. The first sub-intermediate layers 31, 31' and the second sub-intermediate layers 32, 32' were formed by sputtering using the materials shown in Table 2 as targets. A molybdenum oxide target with an oxygen (O) content of 70 atomic% was used. The thickness of the first sub-intermediate layers 31, 31' and the second sub-intermediate layers 32, 32' was adjusted by the deposition time and power. The resin layer 10 and the conductive layers 20, 20' were formed by the same procedure as in Examples 1 to 26. In Example 36, conductive layers 20, 20' made of an alloy with a ratio of Cu:90 atomic%-Ni:10 atomic% were formed by vapor deposition.

[0081] [evaluation] (1) Visual evaluation The surfaces of the current collectors fabricated in Examples 1 to 36 and Reference Examples 1 to 4 were observed using an optical microscope, and the number of wrinkles per unit area (300 mm wide x 200 mm long) was counted. The quality was evaluated as follows: no wrinkles = Excellent, 1-2 wrinkles = Good, 3 or more wrinkles = Poor.

[0082] (2) Electrolyte resistance The current collectors of Examples 1 to 36 and Reference Examples 1 to 4 were held in an environment similar to that of a lithium-ion secondary battery, and the peeling of the conductive layer was evaluated. Specifically, a non-aqueous electrolyte of dimethyl curlbone containing LiPF6 at a concentration of 1 mol% was prepared, and water was added to the non-aqueous electrolyte at a rate of 1000 ppm by mass.

[0083] A non-aqueous electrolyte was placed in a container, the prepared current collector was immersed in the non-aqueous electrolyte inside the container, the entire assembly was sealed with a laminate film, and stored in a constant temperature bath at 85°C for 72 hours. After that, the current collector was removed from the laminate film and washed with an organic solvent.

[0084] The electrolyte resistance of the obtained current collectors after high-temperature storage was evaluated.

[0085] Electrolyte resistance was evaluated using two methods. After high-temperature storage, the surface of the conductive layer of the current collector 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. In addition, an adhesive tape with an adhesion strength of 4 N / cm was applied to the surface of the conductive layer of the current collector after high-temperature storage, and it was checked whether the conductive layer adhered. If no peeling was observed with the cotton swab but adhesion was observed with the adhesive tape, the result was judged as GOOD. If neither peeling with the cotton swab nor adhesion with the adhesive tape was observed, the result was judged as EXCELLENT.

[0086] Tables 1 and 2 show the evaluation results.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Results and Discussion] As shown in Tables 1 and 2, in the current collectors of Reference Examples 2 and 4, which do not have an intermediate layer, electrolyte resistance is not possible, regardless of whether the conductive layer is made of Al or Cu. Furthermore, as can be seen from Reference Examples 1 and 3, electrolyte resistance is not possible even when a Ni intermediate layer is used.

[0090] In contrast, when the intermediate layer contains Mo, good or excellent electrolyte resistance is obtained whether the intermediate layer is composed of molybdenum metal or molybdenum oxide (Example 13). Furthermore, it can be seen that there are conditions under which excellent electrolyte resistance can be obtained regardless of whether the structure is that of the first or second embodiment.

[0091] These results suggest that, when a current collector does not have an intermediate layer, the adhesion between the conductive layer and the resin layer decreases, at least after storage in a non-aqueous electrolyte at high temperatures. Furthermore, the presence of an intermediate layer between the conductive layer and the resin layer does not necessarily mean that adhesion is sufficiently improved; the main elemental component of the intermediate layer is considered important. From the results in Tables 1 and 2, it is considered that when the intermediate layer contains Mo, the adhesion between the conductive layer and the resin layer improves, whether it is molybdenum oxide or metallic molybdenum. In addition, since the effect of improving adhesion was obtained with Cu conductive layers, Cu-Ni conductive layers, and Al conductive layers, it can be seen that the present invention is applicable to both positive electrode current collectors and negative electrode current collectors.

[0092] Based on the results of Examples 1 and 14, it is considered that a good improvement in adhesion can be obtained if the thickness of the intermediate layer is 2 nm or more. Furthermore, based on the results of Examples 1-3, 14-16, and 27, it is considered that the improvement in adhesion can be further enhanced if the thickness of the intermediate layer is 6 nm or more.

[0093] In the examples, samples with an intermediate layer thickness of 1 nm were not prepared. However, in film formation using general thin-film deposition techniques such as sputtering and vacuum deposition, films with a thickness of 1 nm can be formed as continuous films. Therefore, if the intermediate layer contains Mo and the thickness of the intermediate layer is 1 nm or more, it is thought that the effect of improving adhesion can be obtained as discussed above.

[0094] In the current collectors of Examples 9, 10, 23, and 24, the results of the visual evaluation were either good or bad. However, since the electrolyte resistance results for these current collectors were excellent, it is considered that even when wrinkles occur in the conductive layer, the adhesion between the conductive layer and the resin layer does not decrease. In other words, from the viewpoint of improving the adhesion between the conductive layer and the resin layer, there is no upper limit to the thickness of the intermediate layer, and it is considered that the effect of improving adhesion can be obtained even if the intermediate layer is thick.

[0095] The wrinkles observed through visual inspection are thought to be caused by damage to the resin layer due to the conditions during intermediate layer formation. As mentioned above, from the viewpoint of ensuring uniform thickness of the active material layer formed on the current collector, the thickness of the intermediate layer is preferably less than 200 nm, and more preferably 100 nm or less.

[0096] From these examples and reference examples, it was found that the current collector of this embodiment has an intermediate layer mainly composed of Mo placed between the resin layer and the conductive layer, thereby improving the adhesion between the conductive layer and the resin layer. [Industrial applicability]

[0097] 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]

[0098] 10 resin layer 10a 1st page 10b 2nd side 20, 20' conductive layer 21, 21' Seed layer 22, 22' main layer 30, 33, 33' Intermediate layer 30a, 33a top surface 30b, 33b bottom surface 31, 31' First sub-intermediate layer 32, 32' Second sub-intermediate layer 101, 102, 103, 210 Current collectors 201, 201' Electrodes for energy storage devices 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. resin layer, A conductive layer, An intermediate layer located between the resin layer and the conductive layer, Equipped with, The conductive layer mainly contains Al or Cu, The aforementioned intermediate layer contains Mo as its main component. Current collector.

2. The thickness d1 of the conductive layer is 0.3 μm ≤ d1 ≤ 3 μm A current collector according to claim 1 that satisfies the following conditions.

3. The thickness d2 of the intermediate layer is 1nm≦d2<200nm A current collector according to claim 1 or 2 that satisfies the following conditions.

4. The thickness d2 of the intermediate layer is 6 nm ≤ d² ≤ 100 nm A current collector according to claim 1 or 2 that satisfies the following conditions.

5. The current collector according to any one of claims 1 to 4, wherein the intermediate layer contains molybdenum oxide.

6. The aforementioned intermediate layer includes a first sub-intermediate layer and a second sub-intermediate layer, each of which is mainly composed of Mo. The first sub-intermediate layer is closer to the resin layer than the second sub-intermediate layer. The current collector according to claim 5, wherein the oxygen content in the first sub-intermediate layer is greater than the oxygen content in the second sub-intermediate layer.

7. The current collector according to claim 5 or 6, wherein, in the profile of constituent elements by STEM-EDX line analysis in the thickness direction of the cross-section of the intermediate layer, the peak position of O is located closer to the resin layer than the peak position of Mo.

8. The thickness d3 of the first sub-intermediate layer and the thickness d4 of the second sub-intermediate layer are, 1 nm ≤ d3 ≤ 100 nm 1 nm ≤ d4 ≤ 100 nm A current collector according to claim 6 that satisfies the following conditions.

9. The current collector according to claim 8, satisfying the relationship d3 < d4.

10. The current collector according to any one of claims 1 to 9, 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.

11. A current collector according to any one of claims 1 to 10, The active material layer located on the conductive layer of the current collector, An electrode for an energy storage device equipped with the following features.

12. Positive electrode and, The negative electrode and, A separator is disposed between the negative electrode and the positive electrode, A non-aqueous electrolyte containing lithium ions, Equipped with, A lithium-ion secondary battery wherein at least one of the positive electrode or the negative electrode is an electrode for an energy storage device as described in claim 11.

13. The process of preparing the resin layer, A step of forming an intermediate layer containing Mo as the main component on the resin layer, A step of forming a conductive layer mainly composed of Al or Cu on the intermediate layer. A method for manufacturing a current collector, comprising the features described above.

14. The method for manufacturing a current collector according to claim 13, wherein the intermediate layer is formed by sputtering using a target containing Mo.

15. The aforementioned intermediate layer contains molybdenum oxide, The method for manufacturing a current collector according to claim 14, wherein the target comprises molybdenum oxide.

16. The aforementioned intermediate layer contains molybdenum oxide, The aforementioned target is a Mo target, The method for manufacturing a current collector according to claim 14, wherein the intermediate layer is formed in an atmosphere containing oxygen gas during the process of forming the intermediate layer.

17. The aforementioned target is a Mo target, The aforementioned intermediate layer includes a first sub-intermediate layer and a second sub-intermediate layer, each of which is mainly composed of Mo. In the process of forming the intermediate layer, A step of forming the first subintermediate layer in an atmosphere containing oxygen gas at a first concentration, A step of forming the second sub-intermediate layer in an atmosphere containing oxygen gas at a second concentration lower than the first concentration, A method for manufacturing a current collector according to claim 14, including the method described in claim 14.

18. A method for manufacturing a current collector according to any one of claims 13 to 17, wherein the conductive layer contains Al, and at least a portion of the conductive layer is formed by a vapor deposition method.

19. A method for manufacturing a current collector according to any one of claims 13 to 18, wherein the conductive layer contains Cu, and at least a portion of the conductive layer is formed by a plating method.

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