Electrode for power storage device, power storage device, method for manufacturing electrode of power storage device, and method for manufacturing power storage device

Abstract

The present invention provides: an electrode for a power storage device that makes it possible to achieve high charge / discharge performance, that has a simple configuration, and that is easily manufactured; and a power storage device that includes said electrode. The electrode is used in a chargeable / dischargeable power storage device which includes a first electrode and a second electrode and in which metal atoms that have been ionized in the second electrode is deposited on the first electrode during charging. The electrode constitutes the first electrode and includes a metal substrate such that: a two-dimensional Debye ring diffraction image by a two-dimensional X-ray detector is obtained as a discontinuous arc-shaped image in which points or line segments are arranged; and the metal atoms are deposited on the surface of the metal substrate during charging of the power storage device.

Description

Electrode for power storage device, power storage device, method for manufacturing electrode for power storage device, and method for manufacturing power storage device

[0001] The present application relates to an electrode for an electricity storage device, an electricity storage device, a method for manufacturing an electrode for an electricity storage device, and a method for manufacturing an electricity storage device.

[0002] A known example of a chargeable and dischargeable electricity storage device is a secondary battery. Typically, an active material layer made of a material involved in the battery reaction of the secondary battery is formed on the surface of a current collector in the electrode of the secondary battery. For example, in the lithium ion secondary batteries disclosed in Patent Documents 1 and 2 below, an active material layer containing lithium (Li) is provided on the positive electrode, and an active material layer made of carbon (C) is provided on the negative electrode. Japanese Patent No. 2668678 and Japanese Patent Laid-Open No. 2010-9980

[0003] In the technical field of electricity storage devices, it has been common technical knowledge that the active material layer of an electrode has a significant impact on charge / discharge performance such as charge capacity, and extensive research has been conducted on various active material layers in order to improve the charge / discharge performance of electricity storage devices.

[0004] For example, in Patent Document 1, the active material layer of the negative electrode of a lithium ion secondary battery is prepared by firing graphite powder, and in Patent Document 2, it is disclosed that by preparing the active material layer of the negative electrode of a lithium ion secondary battery by firing fine graphite of carbon nanowalls, charge / discharge performance is improved compared to when graphite is used in the active material layer.

[0005] However, the lithium-ion secondary battery of Patent Document 1, which uses graphite powder in the active material layer, cannot be said to fully achieve the charge / discharge performance required for an energy storage device. Furthermore, the lithium-ion secondary battery of Patent Document 2 requires that, after the carbon nanowalls are produced, they be further micrographitized and fired, and it is difficult to say that the improvement in charge / discharge performance is sufficient to justify the manufacturing cost. Thus, in the case of lithium-ion secondary batteries, there has yet to be sufficient ingenuity to address the issues of improving their charge / discharge performance while providing a simpler, more easily manufactured configuration, reducing manufacturing costs, and facilitating mass production.

[0006] The above-described problems are not limited to lithium-ion secondary batteries, but are common to various secondary batteries other than lithium-ion secondary batteries and other power storage devices. The present application aims to provide an electrode for a power storage device that can achieve high charge / discharge performance, has a simple configuration, and is easy to manufacture, and a technology that enables the manufacture of a power storage device including the electrode.

[0007] Through extensive research into electrodes for electricity storage devices, the inventors of the present invention have made a discovery that overturns conventional technical wisdom regarding electricity storage devices: that high charge / discharge performance can be achieved without using an active material layer. Based on this discovery, the inventors of the present invention have succeeded in developing an electrode for electricity storage devices that has a simpler configuration than conventional ones, is easier to manufacture, and is capable of achieving high charge / discharge performance. The present invention can be realized, for example, in the following forms.

[0008] One aspect of the present invention provides an electrode for an electricity storage device. The electricity storage device to which the electrode of this aspect is applied is capable of charging and discharging, and includes a first electrode and a second electrode, and during charging, metal atoms ionized at the second electrode are precipitated at the first electrode. The electrode of this aspect also includes a metal substrate that constitutes a current collector for the first electrode, and on whose surface the metal atoms are precipitated during charging of the electricity storage device, a two-dimensional diffraction image of Debye rings obtained by a two-dimensional X-ray detector is a discontinuous arc-shaped image with an array of points or line segments.

[0009] Through extensive research into energy storage devices, the inventors of the present invention discovered that by using a metal substrate heat-treated under atmospheric gas as an electrode of an energy storage device, high charge / discharge performance can be achieved in the device without providing an active material layer on the electrode. The metal substrate constituting this type of electrode exhibits a two-dimensional diffraction pattern of Debye rings obtained by a two-dimensional X-ray detector, which is a discontinuous arc-shaped image of an array of points or line segments, indicating the heat treatment history of the metal substrate. Therefore, by using this type of electrode, an energy storage device with high charge / discharge performance can be obtained without providing an active material layer on the first electrode.

[0010] The present invention can be realized in various forms other than an electrode for an electricity storage device, an electricity storage device using the same, a method for manufacturing an electrode, and a method for manufacturing an electricity storage device. The present invention can be realized in the form of, for example, an apparatus for manufacturing an electrode for an electricity storage device, an apparatus for manufacturing an electricity storage device, a power generation apparatus or power generation system including an electricity storage device, or other apparatus or system including an electricity storage device.

[0011] 1 is a schematic diagram showing the configuration of an electricity storage device. A process flow diagram showing a manufacturing process for an electricity storage device. An explanatory diagram showing photographed images of a comparative example and an example of a metal substrate. An explanatory diagram showing changes in X-ray diffraction patterns before and after heat treatment. An explanatory diagram showing two-dimensional diffraction images obtained by a two-dimensional X-ray detector before and after heat treatment. An explanatory diagram showing an SEM-EDX mapping image of a comparative example. An explanatory diagram showing an SEM-EDX mapping image of an example. An explanatory diagram showing a graph showing analysis results by EDS of an example. An explanatory diagram showing evaluation test results for charge and discharge performance of an electricity storage device of an example. An explanatory diagram showing evaluation test results for charge and discharge performance of an electricity storage device of an example. An explanatory diagram showing evaluation test results for charge and discharge performance of an electricity storage device of an example. An explanatory diagram showing evaluation test results for charge and discharge performance of an electricity storage device of a comparative example.

[0012] Hereinafter, embodiments and examples of an electrode for an electricity storage device, an electricity storage device, a method for manufacturing an electrode for an electricity storage device, and a method for manufacturing an electricity storage device according to the present invention will be described with reference to the drawings.

[0013] 1. Embodiments: 1-1. Configuration of the power storage device: Fig. 1 is a schematic diagram showing the configuration of a power storage device 10 of this embodiment. In this embodiment, the power storage device 10 is configured as a lithium ion secondary battery in which lithium (Li) ions are involved in charging and discharging.

[0014] The electricity storage device 10 includes a container 11, an electrolyte solution 12, a separator 15, a first electrode 20, and a second electrode 30. For convenience, in Fig. 1, the container 11 is illustrated by a dashed line and the separator 15 is illustrated by a dashed double-dashed line.

[0015] The container 11 has an internal space filled with the electrolyte solution 12. The container 11 is made of a material that is unlikely to react with the electrolyte solution 12 and is liquid-tight.

[0016] The electrolyte solution 12 has a property of being able to transfer metal ions involved in charging and discharging between the first electrode 20 and the second electrode 30. In this embodiment, the electrolyte solution 12 is made of a solution in which a lithium salt is dissolved in an organic solvent, and is able to transfer lithium ions.

[0017] The lithium salt of the electrolyte solution 12 is, for example, lithium hexafluorophosphate (LiPF ６ As the organic solvent, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be used.

[0018] The separator 15 divides the internal space of the container 11 into a first electrode chamber 16 and a second electrode chamber 17. The first electrode chamber 16 houses a first electrode 20, and the second electrode chamber 17 houses a second electrode 30.

[0019] The separator 15 is made of a thin film, such as a porous resin film or nonwoven fabric, and has electrical insulation and ion conductivity. The separator 15 electrically insulates the first electrode 20 from the second electrode 30 and allows metal ions transferred via the electrolyte solution 12 to pass through.

[0020] The first electrode 20 corresponds to an electrode for the power storage device. In this embodiment, the first electrode 20 also serves as an electrode for the secondary battery. In the following description, the first electrode 20 will also be simply referred to as "electrode 20." In the power storage device 10 of this embodiment, the electrode 20 constitutes a negative electrode. When the power storage device 10 is charged, metal atoms ionized at the second electrode 30 are deposited on the electrode 20.

[0021] The electrode 20 includes a metal substrate 21 that functions as a current collector. The metal substrate 21 is placed in the first electrode chamber 16 with the first surface 21a and the second surface 21b in direct contact with the electrolyte solution 12. Before being assembled into the electricity storage device 10, the metal substrate 21 is subjected to a heat treatment in which it is heated in an atmospheric gas at a predetermined temperature for a predetermined time. The conditions for the heat treatment will be described in detail below.

[0022] In the electricity storage device 10, high charge / discharge performance is achieved by configuring the current collector of the electrode 20 using a heat-treated metal substrate 21. "Charge / discharge performance" refers to performance expressed by indices related to charge / discharge, such as chargeable capacity, output density, charge time, and charge rate. As shown in the examples described later, the electricity storage device 10 of this embodiment has a specific capacity of 8 mAh / cm ２ The charge / discharge performance is as described above.

[0023] In conventional energy storage devices such as secondary batteries, an active material layer composed of materials involved in charge and discharge is typically provided on the surface of the current collector. In contrast, no such active material layer is formed on the first surface 21a or the second surface 21b of the metal substrate 21 of this embodiment. Through extensive research into energy storage devices, the inventors of the present invention discovered that using a metal substrate that has undergone a specific heat treatment as a current collector can promote the deposition of metal ions involved in charge and discharge onto the current collector without the need for an active material layer, thereby achieving high charge and discharge performance. The improvement in charge and discharge performance of an energy storage device using a heat-treated metal substrate is presumably due to changes in the crystalline structure of the metal substrate and the reduction of metal oxides in the metal substrate caused by the heat treatment. The following examples will explain experimental results demonstrating the improvement in charge and discharge performance of an energy storage device using a heat-treated metal substrate.

[0024] In the case of a metal substrate 21 that has been subjected to heat treatment, a two-dimensional diffraction image of the Debye rings obtained by a two-dimensional X-ray detector is not a continuous solid arc-shaped image, but rather a discontinuous arc-shaped image consisting of an array of points or line segments. An example of this image is shown as an image after heat treatment in Figure 5, which will be referred to in the Examples described later.

[0025] Furthermore, in the metal substrate 21, the heat treatment causes the metal particles to coarsen, changing the crystalline structure of the metal from before the heat treatment. The average particle size of the metal particles enlarged by the heat treatment may be greater than 10 μm and less than 30 mm. In this specification, the particle size of the metal particles is, for example, a value measured in a photographed image, and is the maximum diameter of the metal particles in all directions. In the examples described below, experimental results showing the change in the crystalline structure of the metal substrate 21 due to the heat treatment will also be described.

[0026] The metal substrate 21 is preferably in a state in which the content of oxygen (O) atoms is reduced compared to before the heat treatment due to the reduction of the metal oxide by the heat treatment. If the content of O is reduced, the amount of metal oxide in the surface layer of the metal substrate 21 is reduced, and therefore, the deposition of Li on the surfaces 21 a and 21 b of the metal substrate 21 during charging of the electricity storage device 10 is promoted.

[0027] The O content in the metal substrate 21 is preferably less than 1 atomic %, and more preferably 0.5 atomic % or less. Here, "atomic %" is also written as "at %" and indicates the ratio of the number of target atoms to the total number of atoms. It is more preferable that the metal substrate 21 is in a state where almost no O is detected in EDS analysis.

[0028] In this embodiment, the metal substrate 21 is made of a metal foil of copper (Cu). As will be shown in the examples described later, Cu can more reliably obtain high charge / discharge performance of the electricity storage device 10. Furthermore, because Cu is easy to process, the processing of the metal substrate 21 is facilitated, which facilitates the manufacture of the electricity storage device 10 and increases the degree of freedom in design. Furthermore, Cu is easy to obtain, which is effective for mass production of the electrode 20 and the electricity storage device 10. In other embodiments, the metal substrate 21 may be made of a Cu alloy.

[0029] The metal substrate 21 does not have to be made of metal foil. The metal substrate 21 may be made of, for example, a thin metal plate. The metal substrate 21 does not have to be configured in a flat plate shape, and may be bent into various shapes, such as a cylindrical shape or a corrugated shape.

[0030] In this embodiment, the pair of surfaces 21 a, 21 b of the metal substrate 21 are configured to be flat. In another embodiment, instead of configuring the surfaces 21 a, 21 b of the metal substrate 21 to be flat, a fine uneven structure may be formed on at least one of the surfaces. With this configuration, it is possible to promote the deposition of metal atoms during charging of the electricity storage device 10, starting from the protrusions of the uneven structure.

[0031] The second electrode 30 constitutes the positive electrode of the electricity storage device 10. The second electrode 30 has a positive electrode current collector 31 and a positive electrode active material layer 32. The positive electrode current collector 31 is made of, for example, a metal foil such as aluminum (Al) or titanium (Ti).

[0032] In other embodiments, the positive electrode current collector 31 may be made of another metal or may have a form other than a metal foil. The positive electrode current collector 31 does not have to be configured in a flat shape, and may be bent into various shapes such as a cylindrical shape or a wavy shape.

[0033] The positive electrode active material layer 32 is formed on each of the first surface 31 a and the second surface 31 b of the positive electrode current collector 31. The positive electrode active material layer 32 contains a positive electrode active material containing Li atoms, a conductive additive, and a binder. The positive electrode active material layer 32 may also contain a thickener.

[0034] As the positive electrode active material of the positive electrode active material layer 32, for example, a ternary material can be used, and lithium cobalt oxide (LiCoO ２ ), lithium manganese oxide (LMO), and lithium nickel oxide (NCA) can be used. As the conductive additive for the positive electrode active material layer 32, for example, acetylene black or carbon black can be used.

[0035] For example, polyvinylidene fluoride (PVDF) or styrene butadiene rubber (SBR) can be used as the binder for the positive electrode active material layer 32. For example, carboxymethyl cellulose (CMC) can be used as the thickener for the positive electrode active material layer 32.

[0036] 1-2. Chemical Reactions at Electrodes During Charging and Discharging: The chemical reactions at the electrodes 20, 30 of the electricity storage device 10 configured as a lithium ion secondary battery during charging and discharging can be expressed by the following reaction formulas, for example.

[0037] The positive electrode material is LiCoO ２ In this case, the reaction formula at the second electrode 30, which is the positive electrode, is expressed by the following formula (1): x represents the ratio of reacting atoms and is a real number greater than 0 and less than 1. １－ｘ CoO ２ + xLi ＋ + xe － ⇔ LiCoO ２ …(1)

[0038] In contrast, the reaction formula at the electrode 20, which is the negative electrode, is expressed by the following formula (2). As shown in formula (2), when the electricity storage device 10 is charged, Li is precipitated on the surface of the electrode 20, and a layer of Li is formed. Li ＋ + e － ⇔ Li … (2)

[0039] As shown in the above formula (2), the electricity storage device 10 of this embodiment is theoretically capable of charging and obtaining a high charge capacity as long as Li can be precipitated on the electrode 20. Note that Li precipitates on the surface of the electrode 20 that does not have an active material layer because the metal substrate 21 that constitutes the electrode 20 has been subjected to heat treatment.

[0040] Thus, according to the electricity storage device 10 of this embodiment, even if the electrode 20 does not have an active material layer, by applying a voltage, Li can be ionized at the second electrode 30 and the Li ions can be deposited on the surface of the metal substrate 21. Therefore, a high charge capacity can be achieved in the electricity storage device 10. According to the electricity storage device 10 of this embodiment, the active material layer on the surface of the electrode 20 can be omitted, and therefore the configuration can be simplified to the extent that the active material layer on the surface of the electrode 20 can be omitted, and the materials used in manufacturing the electricity storage device 10 can be reduced.

[0041] In addition, according to the electricity storage device 10 of this embodiment, during charging, Li can be uniformly precipitated on the surface of the metal substrate 21. This makes it possible to suppress the generation of dendrites (branched crystals) in the electrode 20, and to suppress damage and deterioration of the electricity storage device 10 due to dendrites.

[0042] The reason why dendrite formation is suppressed in the heat-treated metal substrate 21 is thought to be that the crystal grains of the metal substrate 21, which have enlarged and have a specific crystal orientation, act as seed crystals, causing the precipitated Li to undergo heterogeneous nucleation and be regularly arranged with the same crystal orientation. If the metal substrate is not heat-treated, there are no nuclei acting as seed crystals like those in the heat-treated metal substrate 21, and therefore Li undergoes irregular homogeneous nucleation, resulting in the formation of fine polycrystalline dendrites like snowflakes. The formation of dendrites hinders the practical application of secondary batteries because the tips of the dendrites break through the separator and come into contact with the positive electrode, causing an electrical short circuit and causing damage and deterioration to the secondary battery.

[0043] For example, in the manufacturing process of a conventional secondary battery having an active material layer, when an electrode on which the active material layer is formed is rolled up for transportation, storage, or the like, there are cases where a portion of the active material layer is damaged or falls off. In contrast, with the electrode 20 of the present embodiment, even if the electrode is rolled up and transported or stored in a rolled state in the manufacturing process of the electricity storage device 10, the problem of deterioration or fall-off of the active material layer does not occur. Therefore, the electrode 20 of the present embodiment is easy to handle, which facilitates mass production of the electrode 20.

[0044] 2 is a process flow diagram showing the manufacturing process of the electricity storage device 10. Processes P1 and P2 are processes for manufacturing the electrode 20.

[0045] In step P1, a base material of the metal substrate 21 is prepared. The base material is, for example, a metal foil or a metal thin plate. As described above, in this embodiment, the base material of the metal substrate 21 is copper foil and has a flat surface.

[0046] In step P2, a heat treatment is performed on the base material of the metal substrate 21. In this heat treatment, the base material of the metal substrate 21 is heated in an atmospheric gas at a predetermined temperature for a predetermined time. In the electricity storage device 10, the electrode 20 is formed by the metal substrate 21 that has undergone the heat treatment in step P2.

[0047] In this embodiment, a reducing gas is used as the atmospheric gas. The reducing gas may be, for example, hydrogen (H ２ The reducing gas may be H ２ Instead of carbon monoxide (CO) or ammonia (NH ３ ), hydrocarbon gas, etc. may be used. Examples of hydrocarbon gases include methane (CH ４ ) and ethane (C ２ H ５ ), propane (C ３ H ８ ), butane (C ４ H １０ ), ethylene (C ２ H ４ ), acetylene (C ２ H ２) or the like may be used. The reducing gas is not limited to the above-mentioned examples. The reducing gas may be any gas that can cause a reduction reaction of the base material of the metal substrate 21 during heat treatment, and may be a hydrogen compound containing at least H, N, or C, an oxygen compound, or a compound of these having dangling bonds.

[0048] In another embodiment, an inert gas may be used as the atmospheric gas instead of the reducing gas. Examples of the inert gas include argon (Ar), helium (He), xenon (Xe), and nitrogen (N ２ ) can be used.

[0049] In the heat treatment of step P2, the atmospheric gas is preferably adjusted to a predetermined oxygen partial pressure at the treatment temperature of the heat treatment so as not to oxidize the metal substrate 21. The oxygen partial pressure of this atmospheric gas may be set to a value equal to or lower than the thermal equilibrium oxygen partial pressure derived from a graph showing the relationship between the standard free energy of oxide formation and temperature, which is obtained by thermodynamic calculation. For example, the inert gas may be Ar or N ２ In this case, the oxygen partial pressure in the atmospheric gas is 10 －６ If the oxygen partial pressure in the atmospheric gas is higher than the thermal equilibrium oxygen partial pressure, the oxygen partial pressure may be reduced by purifying the atmospheric gas using a purification device.

[0050] In the heat treatment of this embodiment, the base material of the metal substrate 21 is heated at a treatment temperature of, for example, 400° C. or higher and 1000° C. or lower. The treatment temperature at which the base material of the metal substrate 21 is heated in the heat treatment is preferably 500° C. or higher, and more preferably 600° C. or higher. The treatment temperature for the heat treatment is further preferably 700° C. or higher, and more preferably 800° C. or higher.

[0051] The heat treatment time may be determined as appropriate depending on the type of metal constituting the metal substrate 21, the heat treatment temperature, and the like. The heat treatment time may be determined as the time required for the metal structure of the metal substrate 21 to undergo a predetermined change or the time required for most of the metal oxide in the metal substrate 21 to be reduced. The heat treatment time may be set to a time longer than the time required for the metal oxide to be reduced, but from the viewpoint of suppressing increases in manufacturing costs due to longer process times, the heat treatment time is preferably, for example, 5 minutes or more and 60 minutes or less. The heat treatment time is preferably 7 minutes or more and 30 minutes or less. The heat treatment time is more preferably 8 minutes or more and 20 minutes or less.

[0052] In process P3, the second electrode 30, which will be the positive electrode, is manufactured. The method for manufacturing the second electrode 30 is known, and therefore a detailed description thereof will be omitted.

[0053] 1 , the first electrode 20 and the second electrode 30 are assembled into a container 11 filled with an electrolytic solution 12. The metal substrate 21 constituting the current collector of the first electrode 20 is housed in the container 11 in a state where it is immersed in the electrolytic solution 12 so that its surface is in direct contact with the electrolytic solution 12. Through the above steps, the electricity storage device 10 is completed.

[0054] According to the manufacturing method of this embodiment, it is possible to easily manufacture an electrode 20 for an electricity storage device 10 that can achieve high charge / discharge performance in the electricity storage device 10 by heat treating the base material of the metal substrate 21. Therefore, it is possible to easily manufacture the electricity storage device 10. Furthermore, according to the manufacturing method of this embodiment, it is not necessary to provide an active material layer on the metal substrate 21 that constitutes the electrode 20, and therefore the number of steps for manufacturing the electrode 20 and the electricity storage device 10 can be reduced accordingly. Furthermore, it is possible to reduce the manufacturing costs of the electrode 20 and the electricity storage device 10.

[0055] Furthermore, as described above, the electrode 20 prepared in steps P1 and P2 is easy to handle because the active material layer is not damaged or removed even when rolled up and transported, which improves the mass productivity of the electrode 20 and facilitates the production of the electricity storage device 10 using the electrode 20.

[0056] 1-4. Summary of the embodiment As described above, according to the electrode 20 of the present embodiment, the electricity storage device 10 using the same, and the manufacturing method thereof, it is possible to achieve high charge / discharge performance in the electricity storage device 10 by using the heat-treated metal substrate 21, even without providing an active material layer on the electrode 20.

[0057] 2. Examples and Comparative Examples of Electrode for Electricity Storage Device: Examples E1, E2, E3, and E4 of the electrode 20 described in the above embodiment, and a comparative example C1 thereof will be described below.

[0058] 2-1. Manufacturing conditions: In Examples E1, E2, E3, and E4 and Comparative Example C1, Cu foils of the same size and mass were used as the metal substrates constituting the electrodes. Table 1 below summarizes the conditions for the heat treatments applied to the metal substrates of Examples E1, E2, E3, and E4. Note that, as shown in Table 1, the metal substrate of Comparative Example C1 was not subjected to heat treatment.

[0059]

[0060] In all of Examples E1, E2, E3, and E4, the reducing gas H was used as the atmospheric gas during the heat treatment. ２ In the heat treatment, H ２ was supplied to the processing chamber at a flow rate of 50 sccm, and the pressure in the processing chamber was maintained at 2 Pa. Here, 1 sccm may be converted to 1 mL / min. In Examples E1, E2, E3, and E4, the metal substrates were heated in the processing chamber at processing temperatures of 400°C, 700°C, 800°C, and 850°C, respectively, for 10 minutes.

[0061] 2-2. SEM Images: Figure 3 shows images of the surfaces of the metal substrates of Comparative Example C1 and Examples E1, E2, E3, and E4 taken with a scanning electron microscope (SEM). Images of Comparative Example C1 and Examples E1, E2, E3, and E4 were taken at an electron beam acceleration voltage of 10 kV. The magnification of the images of Comparative Example C1 and Examples E1, E2, and E3 is 1000x. For Example E4, two images taken at magnifications of 1000x and 4000x are shown.

[0062] In the SEM image of the untreated comparative example C1, which had not been subjected to heat treatment, crack-like uneven areas DP were observed in the metal structure on the surface, and it was observed that the metal structure was rougher than in Examples E1, E2, E3, and E4.

[0063] In the photographed image of Example E1 heat-treated at 400°C, it was observed that the metal structure of the surface was finer and more uniform than that of Comparative Example C1. Furthermore, the uneven portion DP observed in Comparative Example C1 was hardly observed.

[0064] In the photographed image of Example E2, which was heat-treated at 700 ° C., it was observed that the surface metal structure was finer and more uniform than that of Example E1, and that the smoothness was even higher. In addition, in the photographed image of Example E3, which was heat-treated at 800 ° C., it was observed that the surface metal structure was finer and more uniform than that of Example E2, and that the smoothness was even higher. In the photographed images of Examples E2 and E3, almost no unevenness DP was observed.

[0065] In the photographed image of Example E4, which was heat-treated at 850 ° C., it was observed that the surface metal structure was more finely ordered than that of Example E3, and that the enlarged metal particles MP were densely packed. The metal particles MP of the metal substrate of Example E4 had an average particle size greater than 10 μm and less than 30 mm. The particle size of the metal particles MP was measured as the maximum diameter in all directions for each metal particle MP in the SEM image.

[0066] As described above, it was confirmed from the SEM images of Comparative Example C1 and Examples E1, E2, E3, and E4 in Fig. 3 that the heat treatment refined the metal structure of the metal substrate and improved the surface smoothness. It was also confirmed that when the treatment temperature in the heat treatment was high, for example, 800°C or higher, the metal particles became enlarged.

[0067] 2-3. X-ray Diffraction Analysis: The change in X-ray diffraction (XRD) of the metal substrate due to heat treatment will be explained with reference to Figures 4 and 5. Figure 4 shows the X-ray diffraction patterns of Comparative Example C1, which corresponds to the metal substrate before heat treatment, and Example E2, which corresponds to the metal substrate after heat treatment. In Figure 4, the numbers in parentheses after Cu represent Miller indices. Figure 5 shows two-dimensional diffraction images of the Debye rings obtained by a two-dimensional X-ray detector for Comparative Example C1 and Example E2, respectively.

[0068] As shown in Figure 4, in the X-ray diffraction pattern of the metal substrate, Example E2, which was heat-treated at 700°C, had fewer prominent peaks than Comparative Example C1, which was not heat-treated. For example, in Example E2, the Cu(220) peak was reduced to an almost negligible level compared to Comparative Example C1. This resulted in the ratio of the Cu(200) peak to the Cu(220) peak, I ２００ / I ２２０ However, in Comparative Example C1, the value was 1, whereas in Example E2, the value increased to 2000. Furthermore, in Example E2, the Cu(200) peak and the Cu(400) peak were significantly smaller than in Comparative Example C1. Such a change in the X-ray diffraction pattern indicates that the metal particles constituting the metal substrate were coarsened by the heat treatment.

[0069] Furthermore, as shown in Figure 5, in the two-dimensional diffraction image of Comparative Example C1, which was not subjected to heat treatment, the Debye rings corresponding to the peaks shown in Figure 4 were confirmed as clear, continuous solid line images. In contrast, in the two-dimensional diffraction image of Example E2, which was subjected to heat treatment, the two-dimensional diffraction image of the Debye rings was obtained as a discontinuous arc-shaped image composed of points or line segments arranged in an arc. Such a change in the two-dimensional diffraction image indicates that the metal crystal structure in the metal substrate was recrystallized into a preferred orientation crystal structure by the heat treatment. The blurred two-dimensional diffraction image shown in Example E2 in Figure 5 can be said to indicate the history of the metal substrate undergoing heat treatment.

[0070] As described above, the changes in X-ray diffraction before and after the heat treatment shown in Figures 4 and 5 indicate that the heat treatment causes changes in the crystal structure of the metal substrate, such as enlargement of metal particles.

[0071] 2-4. SEM-EDX Analysis Results: The results of elemental analysis of the surface layer by energy dispersive X-ray spectroscopy (SEM-EDX) will be described with reference to Figures 6, 7A, and 7B. SEM-EDX is an elemental analysis technique performed by combining an SEM with an energy dispersive X-ray spectroscopy (EDS).

[0072] Images MIa, MIb, and MIc in Figure 6 are element mapping images of the surface layer of Comparative Example C1 by SEM-EDX. Image MIa is a mapping image of Cu and O, image MIb is a mapping image of Cu, and image MIc is a mapping image of O. As shown in the mapping images MIa, MIb, and MIc, it was confirmed that a large amount of copper oxide (CuO) was distributed in the surface layer of Comparative Example C1, which corresponds to the metal substrate before heat treatment. In Comparative Example C1, the Cu content was approximately 98 atomic %, and the O content was approximately 2 atomic %.

[0073] Fig. 7A shows a mapping image MId of Cu in the surface layer of Example E1. Fig. 7B shows a graph showing the analysis results of Example E1 by EDS. In Example E1, heat treatment was performed at a treatment temperature of 400°C as shown in Table 1 above. As shown in Figs. 7A and 7B, in Example E1, which corresponds to the metal substrate after the heat treatment, CuO was reduced by the heat treatment, and almost no O was detected in the EDS analysis.

[0074] As described above, from the results shown in FIGS. 6, 7A, and 7B, it was confirmed that the metal oxide in the metal substrate was reduced by the heat treatment, and the O content in the metal substrate was reduced.

[0075] 2-5. Evaluation Results of Charge / Discharge Performance of Electricity Storage Devices: The results of evaluation tests of the charge / discharge performance of electricity storage devices using the electrodes of Examples E1, E3, E4 and Comparative Example C1 will be described with reference to FIGS.

[0076] 8, 9, and 10 show graphs obtained for the electricity storage devices having the electrodes of Examples E1, E3, and E4, respectively. Also, Fig. 11 shows a graph obtained for the electricity storage device having the electrode of Comparative Example C1. In Figs. 8 to 11, the relationship between the voltage and specific capacity of the electricity storage device during charging is shown by a solid line, and during discharging by a dashed-dotted line.

[0077] The power storage device was a lithium ion secondary battery having the same configuration as that described in the above embodiment, and the electrodes of Examples E1, E3, and E4 and Comparative Example C1 were used as the negative electrode. Other configurations of the power storage device are shown in Table 2 below.

[0078]

[0079] As shown in FIG. 8, in the electricity storage device using the electrode of Example E1, the specific capacity was approximately 9.65 [mAh / cm ２ The charge capacity was approximately 12.75 mAh, and the charging time required to fully charge the battery from a remaining charge of 0% was approximately 25 hours.

[0080] As shown in FIG. 9, in the electricity storage device using the electrode of Example E3, the specific capacity was approximately 10.06 [mAh / cm ２ The charge capacity was about 13.29 [mAh], and the charge time was about 26 hours.

[0081] As shown in FIG. 10, in the electricity storage device using the electrode of Example E4, the specific capacity was approximately 10.06 [mAh / cm ２ The charge capacity was about 13.29 [mAh], and the charge time was about 26 hours.

[0082] 11, the electricity storage device using the electrode of Comparative Example C1 was unable to charge or discharge. This result shows that a metal substrate that has not been subjected to heat treatment does not function as an electrode for an electricity storage device.

[0083] As described above, the energy storage device using the electrode of Comparative Example C1 was almost unable to charge and discharge, whereas the energy storage devices using the electrodes of Examples E1, E3, and E4 all showed high charge and discharge performance.

[0084] 2-6. Summary of Examples: As shown by the results of the above examples and comparative examples, an electrode in which the current collector is formed from a heat-treated metal substrate can produce an electricity storage device with high charge / discharge performance without providing an active material layer. Furthermore, in the heat-treated metal substrate, changes in the metal crystal structure, such as enlargement of metal particles, occur from the state before the heat treatment, and the two-dimensional diffraction image of the Debye rings obtained by a two-dimensional X-ray detector is a discontinuous arc-shaped image with an arrangement of points or line segments. Furthermore, in the heat-treated metal substrate, almost no O was detected in EDS analysis, indicating that the oxygen content was significantly reduced compared to before the heat treatment.

[0085] 3. Other Embodiments: The present invention is not limited to the configurations of the above-described embodiments and examples, and can also be realized in the following forms, for example. Any configurations described below as other embodiments are positioned as examples of forms for implementing the present invention, similar to the above-described embodiments and the configurations and examples described as other embodiments within the above-described embodiments.

[0086] 3-1. Alternative embodiment 1: The metal substrate 21 may be made of a metal other than Cu or a Cu alloy. The metal substrate 21 may be made of, for example, Al or an Al alloy.

[0087] 3-2. Alternative Embodiment 2: The power storage device 10 may be configured as a power storage device other than a lithium ion secondary battery. The power storage device 10 may be configured as, for example, a secondary battery in which metal ions other than lithium ions, such as sodium (Na) ions, potassium (K) ions, or magnesium (Mg) ions, are involved in charging and discharging. Alternatively, the power storage device 10 may be configured as, for example, a condenser or capacitor.

[0088] 3-3. Alternative Embodiment 3: In the electricity storage device 10, an active material layer may be provided on the surface of the metal substrate 21. In this case, the active material may be, for example, graphite or a carbon nanostructure such as a carbon nanowall or a carbon nanotube. In addition, a fine uneven structure may be formed on the surface of the metal substrate 21 by electrolytic treatment or the like.

[0089] 4. Examples of embodiments: The present invention can be realized in the following embodiments.

[0090] [First embodiment] The first embodiment is provided as an electrode for an electricity storage device. The electricity storage device is capable of charging and discharging and includes a first electrode and a second electrode. During charging, metal atoms ionized at the second electrode precipitate on the first electrode. The electrode of the first embodiment comprises a metal substrate that constitutes a current collector for the first electrode and that exhibits a two-dimensional diffraction pattern of Debye rings obtained by a two-dimensional X-ray detector as a discontinuous arc-shaped image with an array of points or line segments, and on whose surface the metal atoms precipitate during charging of the electricity storage device. Through extensive research into electricity storage devices, the inventors of the present invention discovered that by using a metal substrate heat-treated under an atmospheric gas as an electrode for an electricity storage device, high charge / discharge performance can be achieved in the electricity storage device without providing an active material layer on the electrode. The metal substrate constituting the electrode of the first embodiment exhibits a two-dimensional diffraction pattern of Debye rings obtained by a two-dimensional X-ray detector as a discontinuous arc-shaped image with an array of points or line segments, indicating the heat treatment history of the metal substrate. Therefore, by using an electrode of this type, it is possible to obtain an electricity storage device having high charge / discharge performance without providing an active material layer on the first electrode.

[0091] [Second embodiment] In the electrode of the first embodiment, the oxygen atom content of the metal substrate may be less than 1 atomic %. According to the electrode of the second embodiment, the metal oxide on the surface of the metal substrate is reduced, which promotes the deposition of metal atoms on the surface of the metal substrate during charging of the electricity storage device. This further improves the charge / discharge performance of the electricity storage device.

[0092] [Third Mode] In the electrode according to the first or second mode, the metal substrate may have a configuration in which metal particles having an average particle size of more than 50 μm and not more than 20 mm are densely packed together. The electrode of the third mode promotes deposition of metal atoms onto the surface of the metal substrate during charging of the electricity storage device, thereby further improving the charge / discharge performance of the electricity storage device.

[0093] [Fourth Mode] In the electrode according to any one of the first, second, and third modes, the metal substrate may be made of copper or a copper alloy. The electrode of the fourth mode can more reliably improve the charge / discharge performance of the electricity storage device. Furthermore, the improved workability of the metal substrate can increase the design freedom of the electricity storage device.

[0094] [Fifth Aspect] The fifth aspect is provided as an electric storage device. The electric storage device of the fifth aspect includes a container filled with an electrolyte solution, an electrically insulating and ionically conductive separator that divides the interior space of the container into a first electrode chamber and a second electrode chamber, a metal substrate forming a current collector, a first electrode housed in the first electrode chamber, and a second electrode housed in the second electrode chamber and containing metal atoms that ionize and migrate to the first electrode. The metal substrate is positioned in the first electrode chamber so that a two-dimensional diffraction image of the Debye rings obtained by a two-dimensional X-ray detector is a discontinuous arc-shaped image with an array of points or line segments. The metal substrate is positioned so that its surface is in direct contact with the electrolyte solution in the first electrode chamber, and the metal atoms precipitate on the surface during charging. In the electric storage device of the fifth aspect, the first electrode is formed of a metal substrate that has been heat-treated by heating under an atmospheric gas, thereby achieving high charge / discharge performance even if the first electrode does not have an active material layer.

[0095] [Sixth Aspect] In the electricity storage device of the fifth aspect, the oxygen atom content of the metal substrate may be less than 1 atomic %. In the electricity storage device of the sixth aspect, the metal oxide on the surface of the metal substrate is reduced, which promotes the deposition of metal atoms on the surface of the metal substrate during charging. Therefore, the charge / discharge performance can be further improved.

[0096] [Seventh Mode] In the electricity storage device according to the fifth or sixth mode, the metal substrate may have a configuration in which metal particles having an average particle size of more than 10 μm and not more than 30 mm are densely packed together. According to the electricity storage device of the seventh mode, deposition of metal atoms onto the surface of the metal substrate during charging is promoted, thereby further improving charge / discharge performance.

[0097] [Eighth aspect] The electricity storage device according to any one of the fifth, sixth, and seventh aspects, wherein the specific capacity is 8 mAh / cm ２ The electricity storage device of the eighth embodiment can achieve higher charge / discharge performance.

[0098] [Ninth Mode] In the electricity storage device according to any one of the fifth, sixth, seventh, and eighth modes, the metal substrate may be made of copper or a copper alloy. According to the electricity storage device of the ninth mode, by using a metal substrate containing copper as a main component for the first electrode, higher charge / discharge performance can be achieved. In addition, since the metal substrate is easier to process, the degree of freedom in designing the electricity storage device can be increased.

[0099] [Tenth Aspect] The tenth aspect provides a method for manufacturing an electrode for an electricity storage device. The electricity storage device is chargeable and dischargeable and includes a first electrode and a second electrode. During charging, metal atoms ionized at the second electrode precipitate on the first electrode. The manufacturing method of the tenth aspect includes the steps of preparing a base material for a metal substrate constituting the first electrode and subjecting the base material to a heat treatment in an atmospheric gas at a temperature of 400°C or higher for a predetermined time. According to the manufacturing method of the tenth aspect, by using a heat-treated metal substrate, high charge and discharge performance can be achieved in the electricity storage device, even without providing an active material layer on the first electrode.

[0100] [Eleventh Aspect] The eleventh aspect provides a method for manufacturing a chargeable / dischargeable electricity storage device including a first electrode and a second electrode, wherein, during charging, metal atoms ionized at the second electrode precipitate at the first electrode. The manufacturing method of the eleventh aspect includes the steps of: performing a heat treatment on a metal substrate base material by heating it at a temperature of 400°C or higher under an atmospheric gas for a predetermined time; and assembling the heat-treated metal substrate as the first electrode by immersing the metal substrate in a container filled with an electrolyte solution with the surface in contact with the electrolyte solution. According to the manufacturing method of the eleventh aspect, a power storage device with high charge / discharge performance can be obtained by using a heat-treated metal substrate without providing an active material layer on the first electrode.

[0101] [Twelfth Mode] In the manufacturing method according to the tenth or eleventh mode, the metal substrate may be made of copper or a copper alloy. According to the manufacturing method of the twelfth mode, the charge / discharge performance of the electricity storage device can be more reliably improved. Furthermore, since the metal substrate is easy to process, the degree of freedom in designing the electricity storage device can be increased.

[0102] [13th Aspect] In the manufacturing method according to any one of the 10th, 11th, and 12th aspects, the atmospheric gas may be a reducing gas. According to the manufacturing method of the 13th aspect, the reducing gas can promote the reduction of metal oxide on the surface of the metal substrate during heat treatment. Therefore, the metal oxide on the surface of the metal substrate can be reduced, and higher charge / discharge performance can be achieved in the electricity storage device.

[0103] [14th Aspect] In the manufacturing method described in the 13th aspect, the reducing gas may be any one of hydrogen, carbon monoxide, ammonia, methane, ethane, propane, butane, ethylene, and acetylene. According to the manufacturing method of the 14th aspect, the action of the reducing gas during heat treatment can more reliably reduce metal oxide on the surface of the metal substrate. Therefore, higher charge / discharge performance can be achieved in the electricity storage device.

[0104] [15th Mode] In the manufacturing method according to any one of the 10th, 11th, and 12th modes, the atmospheric gas may be an inert gas. According to the manufacturing method of the 15th mode, the metal oxide on the surface of the metal substrate can be reduced by heat treatment. Therefore, high charge / discharge performance can be achieved in the electricity storage device.

[0105] [16th feature] In the manufacturing method according to the 15th feature, the inert gas is argon or nitrogen, and the oxygen partial pressure during the heat treatment is 10 －６ According to the manufacturing method of the sixteenth embodiment, the metal oxide on the surface of the metal substrate can be more reliably reduced during the heat treatment, thereby achieving higher charge / discharge performance in the electricity storage device.

[0106] DESCRIPTION OF SYMBOLS 10...electricity storage device, 11...container, 12...electrolyte, 15...separator, 16...first electrode chamber, 17...second electrode chamber, 20...first electrode, 21...metal substrate, 21a...first surface, 21b...second surface, 30...second electrode, 31...positive electrode current collector, 31a...first surface, 31b...second surface, 32...positive electrode active material layer, DP...uneven portion, MP...metal particle, MIa, MIb, MIc, MId...mapping image

Claims

1. An electrode for a chargeable and dischargeable electricity storage device, comprising a first electrode and a second electrode, wherein metal atoms ionized at the second electrode precipitate on the first electrode during charging; the electrode comprising a metal substrate that constitutes a current collector for the first electrode, and on whose surface the metal atoms precipitate during charging of the electricity storage device, a two-dimensional diffraction image of the Debye rings obtained by a two-dimensional X-ray detector is a discontinuous arc-shaped image with an arrangement of points or line segments.

2. The electrode according to claim 1, wherein the oxygen atom content of said metal substrate is less than 1 atomic %.

3. An electrode according to claim 1 or 2, wherein the metal substrate has a structure in which metal particles having an average particle size of more than 50 μm and not more than 20 mm are densely packed together.

4. An electrode according to any one of claims 1 to 3, wherein the metal substrate is made of copper or a copper alloy.

5. An electricity storage device comprising: a container filled with an electrolyte; an electrically insulating and ionically conductive separator that divides the internal space of the container into a first electrode chamber and a second electrode chamber; a first electrode having a metal substrate that constitutes a current collector and is housed in the first electrode chamber; and a second electrode that is housed in the second electrode chamber and contains metal atoms that are ionized and migrate to the first electrode, wherein a two-dimensional diffraction image of the Debye rings obtained by a two-dimensional X-ray detector is obtained as a discontinuous arc-shaped image in which points or line segments are arranged, and the metal substrate is positioned in the first electrode chamber so that its surface is in direct contact with the electrolyte, and the metal atoms precipitate on the surface during charging.

6. An electric storage device according to claim 5, wherein the content of oxygen atoms in the metal substrate is less than 1 atomic %.

7. An electric storage device according to claim 5 or 6, wherein the metal substrate has a structure in which metal particles having an average particle size of more than 10 μm and 30 mm or less are densely packed together.

8. The electricity storage device according to any one of claims 5 to 7, wherein the specific capacity is 8 mAh / cm ２ That's it for the energy storage device.

9. An electricity storage device according to any one of claims 5 to 8, wherein the metal substrate is made of copper or a copper alloy.

10. A method for manufacturing an electrode for a chargeable and dischargeable electricity storage device, which comprises a first electrode and a second electrode, and in which metal atoms ionized at the second electrode precipitate at the first electrode during charging, the method comprising the steps of: preparing a base material for a metal substrate that constitutes a current collector for the first electrode; and subjecting the base material for the metal substrate to a heat treatment in an atmospheric gas at a temperature of 400°C or higher for a predetermined period of time.

11. A method for manufacturing a chargeable and dischargeable electricity storage device comprising a first electrode and a second electrode, wherein metal atoms ionized at the second electrode are precipitated at the first electrode during charging, the method comprising the steps of: subjecting a metal substrate base material to heat treatment in an atmospheric gas at a temperature of 400°C or higher for a predetermined time; and assembling the heat-treated metal substrate as the first electrode by immersing the metal substrate in a container filled with an electrolyte solution with the surface in contact with the electrolyte solution.

12. A manufacturing method according to claim 10 or 11, wherein the metal substrate is made of copper or a copper alloy.

13. A manufacturing method according to any one of claims 10 to 12, wherein the atmospheric gas is a reducing gas.

14. The manufacturing method according to claim 13, wherein the reducing gas is any one of hydrogen, carbon monoxide, ammonia, methane, ethane, propane, butane, ethylene, and acetylene.

15. A manufacturing method according to any one of claims 10 to 12, wherein the atmospheric gas is an inert gas.

16. The manufacturing method according to claim 15, wherein the inert gas is argon or nitrogen, and the oxygen partial pressure during the heat treatment is 10 －６ The manufacturing method is below atmospheric pressure.

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