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

Abstract

To provide an electrode for a power storage device that can achieve high charge / discharge performance, that has a simple configuration, and that is easily manufactured; and a power storage device including the electrode.SOLUTION: An electrode is used in a chargeable / dischargeable power storage device which includes a first electrode and a second electrode, and in which metal atoms ionized in the second electrode are 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.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[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. [Background technology]

[0002] A known example of a chargeable and dischargeable electricity storage device is a secondary battery. Typically, an electrode of a secondary battery has an active material layer formed on the surface of a current collector, the active material layer being made of a material involved in the battery reaction of the secondary battery. For example, in the lithium-ion secondary batteries disclosed in Patent Documents 1 and 2 listed 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.

[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 effect on charge / discharge performance such as charge capacity, and various active material layers have been studied to improve the charge / discharge performance of electricity storage devices. For example, Patent Document 1 discloses that the active material layer of the negative electrode of a lithium ion secondary battery is prepared by sintering graphite powder. Furthermore, Patent Document 2 discloses that by preparing the active material layer of the negative electrode of a lithium ion secondary battery by sintering carbon nanowall graphite, charge / discharge performance is improved compared to when graphite is used in the active material layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2668678 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-9980 Summary of the Invention [Problem to be solved by the invention]

[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 electricity 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 sintered, 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 challenges 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. [Means for solving the problem]

[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 is 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 on 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. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of an electricity storage device. [Figure 2] FIG. 3 is a process flow diagram showing a manufacturing process of an electricity storage device. [Figure 3] 10A and 10B are explanatory views showing photographed images of a comparative example and an example of a metal substrate. [Figure 4]FIG. 2 is an explanatory diagram showing the change in X-ray diffraction pattern before and after heat treatment. [Figure 5] FIG. 2 is an explanatory diagram showing two-dimensional diffraction images obtained by a two-dimensional X-ray detector before and after heat treatment. [Figure 6] FIG. 10 is an explanatory diagram showing a SEM-EDX mapping image of a comparative example. [Figure 7A] FIG. 1 is an explanatory diagram showing a mapping image of an SEM-EDX in an embodiment. [Figure 7B] FIG. 1 is an explanatory diagram showing a graph illustrating the analysis results by EDS in an example. [Figure 8] FIG. 4 is an explanatory diagram showing the results of an evaluation test of the charge / discharge performance of the electricity storage device of the example. [Figure 9] FIG. 4 is an explanatory diagram showing the results of an evaluation test of the charge / discharge performance of the electricity storage device of the example. [Figure 10] FIG. 4 is an explanatory diagram showing the results of an evaluation test of the charge / discharge performance of the electricity storage device of the example. [Figure 11] FIG. 10 is an explanatory diagram showing the results of an evaluation test of the charge / discharge performance of an electricity storage device according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[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. Embodiment: 1-1. Configuration of the energy storage device: 1 is a schematic diagram showing the configuration of an electricity storage device 10 of this embodiment. In this embodiment, the electricity 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 shown by a dashed line, and the separator 15 is shown by a broken 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 the property of being able to transfer metal ions involved in charge and discharge 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] For example, lithium hexafluorophosphate (LiPF6) can be used as the lithium salt of the electrolyte solution 12. Furthermore, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be used as the organic solvent.

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

[0020] The first electrode 20 corresponds to an electrode for the electricity 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 electricity storage device 10 of this embodiment, the electrode 20 constitutes a negative electrode. When the electricity 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 later.

[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 either 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, even 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, which occur as a result of the heat treatment. The following examples will describe experimental results demonstrating the improvement in charge and discharge performance of an energy storage device using a heat-treated metal substrate.

[0024] In 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 where the content of oxygen (O) atoms is reduced compared to before the heat treatment due to 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, deposition of Li on the surfaces 21a and 21b 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 for the electricity storage device 10. Furthermore, Cu is easy to process, which facilitates processing of the metal substrate 21, facilitating the manufacture of the electricity storage device 10 and increasing 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 made 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 21a, 21b of the metal substrate 21 are configured to be flat. In another embodiment, instead of configuring the surfaces 21a, 21b 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 when the electricity storage device 10 is being charged, 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 other metals 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 corrugated shape.

[0033] The positive electrode active material layer 32 is formed on each of the first surface 31a and the second surface 31b 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 such as lithium cobalt oxide (LiCoO), lithium manganese oxide (LMO), or lithium nickel oxide (NCA) can be used. As the conductive additive of 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 the electrodes during charging and discharging: The chemical reactions occurring during charging and discharging at the electrodes 20, 30 of the electricity storage device 10 configured as a lithium ion secondary battery can be expressed by the following reaction formula, for example.

[0037] When the positive electrode material is LiCoO2, the reaction formula at the second electrode 30, which is the positive electrode, is expressed by the following formula (1): x represents the proportion of reacting atoms and is a real number greater than 0 and less than 1. Li 1-x CoO2+ xLi + + xe- ⇔ LiCoO2…(1)

[0038] In contrast, the reaction formula at the negative electrode 20 is expressed by the following formula (2): As shown in formula (2), when the electricity storage device 10 is charged, Li is deposited on the surface of the electrode 20, and a Li layer 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 deposited on the electrode 20. Note that Li is deposited 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 a 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 accordingly, and the materials used in manufacturing the electricity storage device 10 can be reduced.

[0041] Additionally, 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 because 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 nucleate heterogeneously and be regularly arranged with the same crystal orientation. If the metal substrate is not heat-treated, there are no nuclei that act as seed crystals like those in the heat-treated metal substrate 21, and Li nucleates irregularly and uniformly, 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 damaging and deteriorating 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, problems such as deterioration or fall-off of the active material layer do not occur. Therefore, the electrode 20 of the present embodiment is easy to handle, facilitating mass production of the electrode 20.

[0044] 1-3. Manufacturing method of electricity storage device: 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 configured 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. For example, hydrogen (H2) can be used as the reducing gas. Instead of H2, for example, carbon monoxide (CO), ammonia (NH3), hydrocarbon gas, etc. can be used as the reducing gas. For example, methane (CH4), ethane (C2H5), propane (C3H8), butane (C4H 10), ethylene (C2H4), acetylene (C2H2), etc. may be used. The reducing gas is not limited to the examples given above. 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 having dangling bonds of these.

[0048] In other embodiments, an inert gas such as argon (Ar), helium (He), xenon (Xe), or nitrogen (N) may be used as the atmospheric gas instead of the reducing gas.

[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 less 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, when the inert gas is Ar or N2, the oxygen partial pressure in the atmospheric gas is set to 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 perspective 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 step P3, the second electrode 30, which will be the positive electrode, is produced. The method for producing the second electrode 30 is well known, and therefore a detailed description thereof will be omitted.

[0053] In step P4, as shown in Fig. 1, first electrode 20 and second electrode 30 are assembled into container 11 filled with electrolytic solution 12. Metal substrate 21 constituting the current collector of first electrode 20 is housed in container 11 in a state where it is immersed in electrolytic solution 12 so that its surface is in direct contact with electrolytic solution 12. Through the above steps, 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, the electricity storage device 10 can be easily manufactured. 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 mass productivity of the electrode 20 and facilitates the manufacture of electricity storage devices 10 using the electrode 20.

[0056] 1-4. Summary of embodiments: As described above, according to the electrode 20 of this embodiment, the energy storage device 10 using the electrode 20, and the manufacturing method thereof, high charge / discharge performance in the energy storage device 10 can be achieved by the heat-treated metal substrate 21, even without providing an active material layer on the electrode 20. [Example]

[0057] 2. Examples and Comparative Examples of Electrodes for Electricity Storage Devices: 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] [Table 1]

[0060] In all of Examples E1, E2, E3, and E4, a reducing gas, H2, was used as the atmospheric gas in the heat treatment. During the heat treatment, H2 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, which was heat-treated at 400°C, it was observed that the metal structure of the surface was finer and more regular than that of Comparative Example C1. Furthermore, the uneven portions DP observed in Comparative Example C1 were hardly observed.

[0064] In the photographed image of Example E2, which was heat-treated at 700°C, it was observed that the metal structure of the surface was finer and more uniform than that of Example E1, and that the smoothness was even higher. In the photographed image of Example E3, which was heat-treated at 800°C, it was observed that the metal structure of the surface 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 uneven portion DP was observed.

[0065] In the image of Example E4, which was heat-treated at 850 ° C., it was observed that the surface metal structure was finer and more uniform 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 of more 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, the SEM images of Comparative Example C1 and Examples E1, E2, E3, and E4 in Figure 3 confirm that the heat treatment refines the metal structure of the metal substrate and improves the surface smoothness. Furthermore, it was confirmed that when the heat treatment temperature is high, for example, 800°C or higher, the metal particles become enlarged.

[0067] 2-3.X-ray diffraction analysis: Changes in X-ray diffraction (XRD) of metal substrates due to heat treatment will be described 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.

[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 locations showing significant 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 220However, in Comparative Example C1, it was 1, whereas in Example E2, it 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 FIG. 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 FIG. 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 arc-shaped points or line segments. This 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 FIG. 5 for Example E2 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 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 FIG. 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] 7A shows a Cu mapping image MId of the surface layer of Example E1. FIG. 7B shows a graph illustrating the EDS analysis results of Example E1. 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 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 energy storage device: 8 to 11, the results of evaluation tests on the charge / discharge performance of electricity storage devices using the electrodes of Examples E1, E3, E4 and Comparative Example C1 will be described.

[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] [Table 2]

[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 charging capacity was approximately 12.75 mAh, and the charging time from 0% to full charge 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 charging capacity was approximately 13.29 mAh, and the charging time was approximately 26 hours.

[0081] 10, the specific capacity of the electricity storage device using the electrode of Example E4 was approximately 10.06 [mAh / cm2], the charge capacity was approximately 13.29 [mAh], and the charge time was approximately 26 hours.

[0082] 11, the electricity storage device using the electrode of Comparative Example C1 was unable to charge and 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 electricity storage device using the electrode of Comparative Example C1 was almost unable to charge and discharge, whereas the electricity 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 with a current collector formed from a heat-treated metal substrate could produce an electricity storage device with high charge / discharge performance without the need for an active material layer. Furthermore, the heat-treated metal substrate exhibited changes in the metal's crystalline structure, such as enlargement of metal particles, compared to the state before heat treatment. The two-dimensional diffraction image of the Debye rings obtained by a two-dimensional X-ray detector was a discontinuous arc-shaped image with an array of points or line segments. Furthermore, EDS analysis of the heat-treated metal substrate showed almost no O, indicating a significantly reduced oxygen content compared to before 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. Other embodiment 1: The metal substrate 21 may be made of a metal other than Cu or a Cu alloy, and 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. For example, the power storage device 10 may be configured as a secondary battery that uses metal ions other than lithium ions, such as sodium (Na) ions, potassium (K) ions, magnesium (Mg) ions, etc., in charge and discharge. Alternatively, the power storage device 10 may be configured as, for example, a condenser or capacitor.

[0088] 3-3. Other 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. Furthermore, a fine uneven structure may be formed on the surface of the metal substrate 21 by electrolytic treatment or the like.

[0089] 4. Example of morphology: The present invention can be realized in the following forms.

[0090] [First Form] The first form 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, and during charging, metal atoms ionized at the second electrode are precipitated on the first electrode. The electrode of the first form constitutes a current collector for the first electrode, and includes a metal substrate on whose surface the metal atoms are precipitated 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 array of points or line segments. Through extensive research into electricity 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 electricity 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 the first 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 with an array of points or line segments, indicating the heat treatment history of the metal substrate. Therefore, by using this type of electrode, an electricity storage device with high charge / discharge performance can be obtained without providing an active material layer on the first electrode.

[0091] [Second Mode] In the electrode of the first mode, the content of oxygen atoms in the metal substrate may be less than 1 atomic %. The electrode of the second embodiment reduces metal oxide on the surface of the metal substrate, which promotes the deposition of metal atoms on the surface of the metal substrate when the electricity storage device is charged, thereby further improving 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 structure in which metal particles having an average particle size of more than 50 μm and 20 mm or less are densely packed together. The electrode of the third embodiment promotes the deposition of metal atoms on the surface of the metal substrate when the electricity storage device is being charged, 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 embodiment can more reliably improve the charge / discharge performance of the electricity storage device. In addition, the improved workability of the metal substrate can improve the degree of freedom in designing the electricity storage device.

[0094] [Fifth Aspect] The fifth aspect is provided as an electricity storage device. The electricity storage device of the fifth aspect includes a container filled with an electrolyte, 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 that constitutes 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 disposed 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 in which points or line segments are arranged, and the surface of the metal substrate is in direct contact with the electrolyte, and the metal atoms precipitate on the surface during charging. In the fifth embodiment of the electricity storage device, the first electrode is formed from a metal substrate that has been heat-treated by heating under atmospheric gas, so that high charge / discharge performance can be achieved even if an active material layer is not provided on the first electrode.

[0095] [Sixth Mode] In the electricity storage device of the fifth mode, the content of oxygen atoms in the metal substrate may be less than 1 atomic %. According to the electricity storage device of the sixth 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, thereby further improving the charge / discharge performance.

[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 30 mm or less are densely packed together. According to the electricity storage device of the seventh embodiment, deposition of metal atoms onto the surface of the metal substrate during charging is promoted, thereby further improving the 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 That's all. According to the electricity storage device of the eighth embodiment, higher charge / discharge performance can be achieved.

[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 embodiment, by using a metal substrate mainly composed of copper for the first electrode, higher charge / discharge performance can be achieved. In addition, since the metal substrate is easy to process, the degree of freedom in designing the electricity storage device can be increased.

[0099] [Tenth Mode] The tenth mode is provided as a method for manufacturing an electrode for an electricity storage device. This electricity storage device is chargeable and dischargeable 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 manufacturing method of the tenth mode includes the steps of preparing a base material for a metal substrate that constitutes the first electrode, and subjecting the base material to a heat treatment in which the base material is heated at a temperature of 400°C or higher in an atmospheric gas for a predetermined time. According to the manufacturing method of the tenth embodiment, by using a heat-treated metal substrate on the first electrode, high charge / discharge performance can be achieved in the electricity storage device, even if an active material layer is not provided.

[0100] [Eleventh embodiment] The eleventh embodiment is provided as 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 manufacturing method of the eleventh embodiment comprises the steps of: subjecting a base material of a metal substrate to a heat treatment by heating it at a temperature of 400°C or higher in 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 embodiment, by using a heat-treated metal substrate, it is possible to obtain an electricity storage device that achieves high charge / discharge performance, even if an active material layer is not provided on the first electrode.

[0101] [12th feature] In the manufacturing method according to the 10th or 11th feature, the metal substrate may be made of copper or a copper alloy. According to the manufacturing method of the twelfth embodiment, the charge / discharge performance of the electricity storage device can be more reliably improved. In addition, since the metal substrate is easy to process, the degree of freedom in designing the electricity storage device can be increased.

[0102] [13th feature] In the manufacturing method according to any one of the 10th, 11th and 12th features, the atmospheric gas may be a reducing gas. According to the manufacturing method of the thirteenth embodiment, the reducing gas can promote the reduction of the metal oxide on the surface of the metal substrate during the heat treatment, thereby reducing the metal oxide on the surface of the metal substrate and achieving higher charge / discharge performance in the electricity storage device.

[0103] [14th feature] In the production method according to the 13th feature, 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 fourteenth embodiment, the metal oxide on the surface of the metal substrate can be more reliably reduced by the action of the reducing gas during the heat treatment, thereby achieving higher charge / discharge performance in the electricity storage device.

[0104] [15th feature] In the manufacturing method according to any one of the 10th, 11th and 12th features, the atmospheric gas may be an inert gas. According to the manufacturing method of the fifteenth embodiment, the metal oxide on the surface of the metal substrate can be reduced by heat treatment, thereby realizing high charge / discharge performance 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 It may be below atmospheric pressure. 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. [Explanation of symbols]

[0106] 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, during charging, metal atoms ionized at the second electrode are precipitated at the first electrode, An electrode comprising a metal substrate that constitutes a current collector of 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 on whose surface the metal atoms precipitate when the energy storage device is charged.

2. 10. The electrode of claim 1, The metal substrate has an oxygen atom content of less than 1 atomic %.

3. 10. The electrode of claim 1, 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 gathered together.

4. 4. The electrode according to claim 1, wherein: The metal substrate is made of copper or a copper alloy.

5. An electricity storage device, a container filled with an electrolyte; a separator having electrical insulation and ion conductivity, which 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 accommodated in the first electrode chamber; a second electrode accommodated in the second electrode chamber and including metal atoms that ionize and migrate to the first electrode; Equipped with The metal substrate is arranged 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 of an array of points or line segments, and the surface is in direct contact with the electrolyte, and the metal atoms precipitate on the surface during charging.

6. The electricity storage device according to claim 5, The metal substrate has an oxygen atom content of less than 1 atomic %.

7. The electricity storage device according to claim 5, The metal substrate has a structure in which metal particles having an average particle size of more than 10 μm and not more than 30 mm are densely gathered together.

8. The electricity storage device according to claim 5, Specific capacity is 8mAh / cm ２ That's it for the energy storage device.

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

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

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

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

13. The manufacturing method according to claim 10 or claim 11, The manufacturing method, wherein the atmospheric gas is a reducing gas.

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

15. The manufacturing method according to claim 10 or claim 11, The manufacturing method, wherein the atmospheric gas is an inert gas.

16. The method of claim 15, 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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